Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries

Advanced Powder Technology xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt

Invited review paper

Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries Dae Soo Jung a, You Na Ko a, Yun Chan Kang b, Seung Bin Park a,⇑ a b

Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejon 305-701, Republic of Korea Department of Chemical Engineering, Konkuk University, 1 Hwayang-dong, Gwangjin-gu, Seoul 143-701, Republic of Korea

a r t i c l e

i n f o

Article history: Received 18 October 2013 Received in revised form 16 January 2014 Accepted 21 January 2014 Available online xxxx Keywords: Spray pyrolysis Lithium ion battery Composite materials Nano-structure Electrode design

a b s t r a c t We review the effect that various structures and composites synthesized by spray pyrolysis have on the electrochemical performance of next-generation electrodes for medium and large lithium ion batteries. The morphologies of electrode particles in particular have a strong influence on the capacity, power, safety, and cycle life. Recent progress in improving the electrochemical performance of electrodes is provided with a particular focus on electrodes composed of nanoparticles, core–shell or yolk–shell structures, and carbon-based composites. Finally, we propose a direction for future research for highperformance lithium ion batteries incorporating fabrication by spray pyrolysis. Ó 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Contents 1. 2. 3.

4.

5.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design of particles by spray pyrolysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nanostructured electrode materials prepared by spray pyrolysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Nano-sized electrode materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Electrode materials with a yolk–shell structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Electrode materials with a core–shell structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Composite electrode materials prepared by spray pyrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Carbon composite electrode materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Graphene composite electrode materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. CNT composite electrode materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary and outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction The development of sustainable energy resources and green technology is an imperative and global issue due to the exhaustion of current fossil fuel supplies, rising oil prices, environmental degradation and climate change. A national agenda has been established to develop new energy systems for the next generation ⇑ Corresponding author. Tel.: +82 42 350 3928; fax: +82 42 350 3910. E-mail address: [email protected] (S.B. Park).

00 00 00 00 00 00 00 00 00 00 00 00

and to allocate sizable resources to research and development of energy generation and storage. R & D in the energy sector is also justified by increased energy security and the need for effective market response to steep changes in energy prices [1]. Many renewable energy sources such as solar, tidal, and wind energy are subject to variations in output with changing weather conditions. Consequently, a continuous supply of energy from such sources is problematic, resulting in a discrepancy between supply and demand. A technology that can store energy and convert it into a usable form when required is therefore imperative. The most

http://dx.doi.org/10.1016/j.apt.2014.01.012 0921-8831/Ó 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

2

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx

well-known and commercialized lithium ion batteries (LIBs) are already used in portable electronic devices, but it is estimated that their future use will be extended to encompass electric vehicles (EV) or energy storage systems (ESS). Accordingly, the battery industry is expected to expand to $78 billion USD by the end of 2020. In 1991, Sony was able to develop and commercialize a LIB utilizing a LiCoO2 cathode and graphite anode. Based on these same electrode materials, a LIB with a 3200 mA h capacity has been recently developed; however, the performance level of LIBs sold currently still falls short of the levels required for next generation EVs and ESS. In fact, batteries for such applications require approximately five times the currently available energy and power densities, along with also requiring a high stability [2–5]. Consequently, many research institutes have strived to develop various highcapacity electrode materials in order to meet these requirements. Unfortunately, none have yet been able to successfully commercialize such materials owing to problems such as volume expansion, side reactions, and low electrical conductivity generated during charge and discharge processes. In order to improve the performance of high-capacity electrode materials, several groups are currently attempting to achieve a breakthrough by applying nanostructures and composites [6–9], along with research into the development of new processes to allow for cost minimization and mass production. Spray pyrolysis is a process for preparing particles or films by forming droplets from a precursor solution, then evaporating and decomposing them in a reactor. This process has proven to be quite useful for the preparation of multi-functional particles, with many reports into the effect of the main variables on particle formation [10–15]. In recent studies, various structures and composites for electrode materials have been reported that are aimed at enhancing the electrochemical performance in LIBs by means of spray pyrolysis. In this review, we introduce spray pyrolysis as a process for synthesizing ‘designer particles’, and discuss suitable methods for achieving various structures and composites for LIB electrodes based on recent research studies. In addition, we discuss how each structure and composite may affect particular properties of electrodes and provide an insight into future research directions with regards to the structure and composition of electrode materials.

2. Design of particles by spray pyrolysis Spray pyrolysis involves the atomization of a precursor solution in a droplet generating apparatus, followed by evaporation in a heated reactor, and decomposition into particles and films. Fig. 1 shows a schematic diagram of a typical high capacity spray pyrolysis process; consisting of a droplet generator, a quartz reactor 2000 mm long and 100 mm in diameter, and a powder collector. A 1.7 MHz ultrasonic spray generator with twenty vibrators was used to generate a large quantity of droplets. The process of

particle formation by spray pyrolysis can be described as follows: A combination of solutes such as inorganic compounds, metal– organic compounds, organometallic compounds, and colloids [16–21]; are dissolved in a solvent, atomized into droplets, and then transported by a carrier gas to a reactor furnace. Solid particles are then formed through drying, decomposition, and crystallization. The reactant gas is in the form of a pure gas or a dilute mixture, while the heat source is an ohmic resistive heater, flame, microwave, plasma, or laser [22–25]. During particle formation, droplets that enter the reactor furnace are dried and reacted with the reactant gas. The particle formation reaction is confined within the space of a single droplet, and so each droplet effectively acts as a micro-reactor. Thus, the particle maintains the shape of the droplet, resulting in spherical particles with no agglomeration. Furthermore, particles that are difficult to synthesize with existing methods can be easily prepared using spray pyrolysis, as it is governed by metastable phase formation and thermodynamics do not play a major role. Another advantage of spray pyrolysis originates from the fact that the precursor material precipitated from micro-scale droplets is well distributed at a nanoscale level. This makes it possible to synthesize at low temperatures, as well as reducing the possibility of contamination during the milling that is required for conventional particle production processes. In addition, by ensuring continuous supply of precursor solutions the process can be easily scaled up. Industrial implementation of spray pyrolysis is already used in the commercial production of iron oxide (Fe2O3) particles from acid waste generated by pickling the surface of heated steel sheets with hydrochloric acid. Also, Scimarec (Japan), Merck (Germany), and SCC (U.S.) have been producing high quality ceramic powders by spray pyrolysis. As shown in Fig. 2, the key elements of spray pyrolysis are the precursor, solvent, droplet generator, and heat source. A mix and match strategy for these components enables production of a wide range of particles of varying morphology and features on the surface of particles for a range of potential applications [15,26–31]. Conventional methods for synthesizing high performance composites and nanostructured particles typically require delicate control of the surrounding conditions, thus making it difficult and time-consuming to incorporate small changes in composition or morphology one may wish to apply to certain materials. Spray pyrolysis, however, is not limited to a specific powder material or set of process conditions. It is therefore a widely applicable method, that allows for the fabrications of various ‘designer particles’.

3. Nanostructured electrode materials prepared by spray pyrolysis Nano-structured LIB electrode materials offer the following advantages: [8,32,33] (1) Owing to the reduced dimensions, the

Fig. 1. Schematic diagram of the spray pyrolysis process.

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx

3

Fig. 2. Key elements of spray pyrolysis and its applications.

diffusion distance becomes shorter. Diffusion time is also reduced; being proportional to the square of the diffusion distance, which improves the rate capability of LIBs. (2) A high specific surface area provides more active sites, making it possible to increase the gravimetric capacity of the electrode to accept more lithium ions. (3) Electron transport is improved, which subsequently improves the overall reaction kinetics during charging and discharging. (4) In the case of anode materials with large capacities, such as Si, Sn, and SnO2, a large volume expansion is encountered during charging and discharging. Cycle stability can be improved as the structure is more stable with nanostructured anode materials, which can accommodate, to some extent, the strain caused by the insertion of lithium. On the basis of these advantages, there have been significant achievements in improving the electrochemical properties of LIB electrode materials by synthesizing structures such as: nanoparticles, porous structures, nanowires, yolk–shells, and core–shell nanostructures. However, despite these advantages, most complex composite nanostructures are prohibitively expensive to produce at a commercial scale. In Section 3, we discuss the various structural features of electrode materials prepared by spray pyrolysis and their effect on electrochemical performance. 3.1. Nano-sized electrode materials As part of the research effort to enhance the rate capability of LIBs, electrode materials have been synthesized in the form of nanometer-size particles. However, even if LIBs have a high energy density, the speed of lithiation and delithiation from the anode and cathode limits the effective power of a battery as the solid state diffusivity of lithium ion is intrinsically low. High power density is

one of the key characteristics required for successful commercialization of high-power electric cars, and energy storage systems (ESS) for renewable energy. If battery electrodes are made of nanosized materials, the diffusion distance of the lithium ions is subsequently reduced and a relatively high output performance can be expected. In addition, lithium ions can also diffuse along the surface of particles, as the nanoparticles provide a high surface area in contact with the electrolyte per unit of mass. A wide variety of solid and liquid processes have been reported for the synthesis of LIB electrode materials; however, few produce aggregation-free particles of uniform chemical composition in large quantities. Spray pyrolysis is one of the few versatile processes for producing multicomponent nanosized particles with a homogeneous and narrow particle size distribution. Taniguchi’s group reported a unique process combining spray pyrolysis and wet ball-milling, which resulted in a variety of nanosized cathode materials such as: LiFePO4, LiCoPO4, LiMnPO4, and Li2FexMn1 xSiO4. The growth of fine and uniform carbon composite nanoparticles was demonstrated by preventing the growth of particles in the sintering stage, through the addition of acetylene black in the ball-milling stage. The synthesized LiFePO4–C composite nanoparticle exhibited a high capacity of 158 mA h/g at 0.1 C, and 96% retention of the initial capacity (114 mA h/g) during the first 100 cycles at 5 C [34]. Kang’s group proposed a similar combination of spray pyrolysis and milling, adding organics such as citric acid or ethylenediaminetetraacetic acid (EDTA) to the precursor solution, as shown in Fig. 3. In this process, the key idea is to make the precursor particles with a more hollow structure. The organic materials used as additive generate a large amount of gas inside the droplet by decomposition, passing through the hot zone of a reactor, which

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

4

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx

Fig. 3. General formation mechanism of nanoparticles by spray pyrolysis.

makes the precursor particles more hollow. After calcination process, the precursor particles are recrystallized and turned into slightly aggregated morphology of primary particles with a nanometer size. Then, the aggregated particles are easily disintegrated to nanosized particles by simple milling process [35]. As shown in Fig. 4, the Li3V2(PO4)3/C composite with a nanometer size were prepared by the organic assisted spray pyrolysis. Although the composite particles is not monodispersed in size and shape, the uniformity could be improved through an optimization of preparation condition. The detailed information technically is described in elsewhere [11]. Table 1 provides a summary of the typical anode and cathode nanoparticle materials prepared by spray pyrolysis, along with their electrochemical properties under various testing conditions. This data provides a rough comparison of the different electrode materials, but further testing is still required for a comprehensive comparison of performance. 3.2. Electrode materials with a yolk–shell structure Various studies are currently being conducted to improve the performance of LIBs by controlling the shape and structure of the electrode materials. Hollow structures have been a particular focus, with an expectation of improved structural stability and enhanced rate capability [45–49]. Employing a hollow structure provides a large surface area for the diffusion of lithium ions and extra space to accommodate the volume expansion of the electrodes during cycling. These advantages contribute to stability and a high rate capability, both of which are required for electric vehicle applications [32,50–52]. However, a low energy density and tap density makes hollow structures difficult to apply to practical applications such as electrode materials. To solve this contradictory problem of low energy and tap density, a yolk–shell structure in which a core particle is encapsulated inside a hollow structure was proposed. This yolk–shell structure has attracted much attention as an electrode material for LIBs, especially after the Oh’s group reported the synthesis of Sn-encapsulated spherical hollow carbon and its application as

an anode material [53]. The advantages of this yolk–shell structure are two-fold: (1) the carbon shell prevents small Sn particles from growing in size during charging and discharging and (2) the space between Sn and carbon acts to buffer the volume change of electrode materials during charging and discharging. This buffering space enhances the structural stability of the electrode and maintains an effective surface area for electrochemical reaction. The synthesis of a yolk–shell structure has predominantly been studied using solution methods by various groups [54–59]; however, it has become increasingly important to develop a more efficient process for the simple and fast production of yolk–shell structured electrode materials. In recent years, several research groups have reported the preparation of yolk–shell structured materials by spray pyrolysis and their application as electrode materials for LIBs. The Tang’s group reported the use of spray pyrolysis to produce rattle-type Sn nanoparticles encapsulated inside a hollow carbon shell from SnCl4
5H2O and sodium citrate, which acted as both a carbon source and an inert matrix [60]. As the precursor droplets pass through a high temperature spray reactor, SnCl4
5H2O is decomposed and grows into Sn nanoparticles uniformly dispersed in sodium citrate. Since the heated sodium citrate is lighter than Sn, it moves rapidly towards the outer part of the droplet by capillary action. With increasing temperature, the sodium citrate is carbonized to form a carbon shell. The result is particles with a 3 layered-structure of Sn nanoparticles, sodium citrate, and a carbon shell. After collection of particles at the exit of the spray reactor, removal of the sodium citrate by washing results in a 2-layered yolk–shell structure, which is denoted as Sn@C. This process is a variation of salt-assisted spray pyrolysis, which was originally proposed to produce nanoparticles or porous particles through the removal of residual salt by washing [61–67]. The as-prepared Sn@C yolk–shell structure maintained a high capacity of 460 mA h/g after 95 cycles at a current density of 0.55 mA/cm2, despite a high carbon content of 54%. The following three methods for the synthesis of yolk–shell structures by spray pyrolysis were reported by the Kang’s group. The first is a one-step method in which a solution of metal

Fig. 4. TEM images of the Li3V2(PO4)3/C powders before (a) and after (b) milling process.

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

5

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx Table 1 Summary of nano-sized electrode materials prepared by spray pyrolysis. Materials used as electrode in LIB

Morphology

Electrochemical performance

Ref.

LiFePO4 (cathode)

Carbon-coated LiFePO4

[34]

LiFePO4 (cathode)

LiFePO4 nanoparticles

LiFePO4 (cathode) LiCoPO4 (cathode)

Carbon-coated LiFePO4 nanoparticles LiCoPO4/C nanocomposites

LiMnPO4 (cathode)

LiMnPO4/C nanocomposites

Li2FexMn1 xSiO4 (cathode) Li2FeSiO4 (cathode) Li3V2(PO4)3 (cathode)

Li2FexMn1 xSiO4/C nanocomposites Li2FeSiO4/C nanocomposites Li3V2(PO4)3–carbon composite nanoparticles Nano-sized SnO2 powders Fine-sized LiCoO2 powders Nanosized LiCrO2–Li2MnO3 composite powders

Initial capacity (158 mA h/g at 0.1 C, and 114 mA h/g at 5 C), 97% after 100th cycles at 0.1 C and 96% 100 mA h/g at 5 C Initial capacity (163 mA h/g at 0.1 C, 154 mA h/g at 1 C, and 97 mA h/g at 10 C), 100 and 97% after 100th cycles at 1 C and 10 C Initial capacity (165 mA h/g at 0.1 C, 130 mA h/g at 5 C, 105 mA h/g at 20 C and 75 mA h/g at 60 C), 100% after 100th cycles Initial capacity (134 mA h/g at 0.05 C, 133 mA h/g at 0.1 C, 131 mA h/g at 0.5 C, 128 mA h/g at 1 C, 88 mA h/g at 10 C, and 52 mA h/g at 20 C) Initial capacity (147 mA h/g at 0.05 C, 145 mA h/g at 0.1 C, 123 mA h/g at 1 C, and 65 mA h/g at 10 C), 80% and 92% after 100th cycles at 0.2 C and 0.5 C Initial capacity (197, 195, 195, and 178 mA h/g at 0.05 C at x = 0, 0.2, 0.5, and 0.8), 34, 31, 48, and 85% after 50th cycles at 1 C at x = 0, 0.2, 0.5, and 0.8 Initial capacity (149 mA h/g), 144 mA h/g after 70th cycles at 0.1 C Initial capacity (147 mA h/g), 119 mA h/g after 50th cycles at 1 C

[41] [35]

Initial capacity (781 mA h/g) at 0.1 C Initial capacity (151 mA h/g), 135 mA h/g after 50th cycles at 0.1 C Initial capacity (233 mA h/g), 95% after 50th cycles at 18 mA/g

[42] [43] [44]

SnO2 (anode) LiCoO2 (cathode) LiCrO2–Li2MnO3 (cathode)

precursor and sucrose is atomized and decomposed in air, with the formation mechanism briefly shown in Fig. 5 [68–74]. In a hot spray reactor, the metal and sucrose precursors are decomposed to produce a metal oxide and carbon composite. However, the surface of this composite is preferentially combusted under an air carrier gas, subsequently resulting in a metal oxide–carbon composite enclosed in metal oxide. However, it should be emphasized that this is a core–shell structure and not yet a true yolk–shell structure. Only through further shrinking of the core and combustion of carbon does the core–shell structure eventually transition into a yolk–shell structure of metal oxide in metal oxide. This method has been successfully applied to prepare multi-component yolk– shell structures as shown in Fig. 6. The second variant of yolk–shell particle production is a twostep process involving spray pyrolysis and subsequent combustion. During spray pyrolysis, a solution of metal precursor and sucrose is atomized and decomposed in a N2 atmosphere. This prevents the combustion of carbon, resulting in the production of metal oxide–carbon composites at the exit of reactor. The subsequent controlled combustion of the composite particles produces a yolk–shell structure, although only metal oxides with a low meting point exhibited a dense structure. Vanadium oxide is a good example of a low melting point oxide suitable for preparation by this method [75,76]. Using by this strategy, the synthesis of V2O5 and LiV3O8 with yolk–shell structures was reported, as shown in Fig. 7. Finally, metal sulfide yolk–shell structures were also obtained after post-treatment sulfidation of particles obtained by either the first or the second method (Fig. 8) [77,78]. For example, yolk–shell structured SnO2 prepared by spray pyrolysis was transformed into yolk–shell structured SnS by sulfidation using hydrogen sulfide gas. These synthesized SnS@SnS powders demonstrated good cycling performance with a high capacity of

[36] [37] [38] [39] [40]

672 mA h/g at 1 A/g after 150 cycles. A summary of the performance of 10 different yolk–shell structures reported for lithium batteries is shown in Table 2. 3.3. Electrode materials with a core–shell structure Most electrode materials known suffer from dissolution when they are in contact with an electrolyte. Side reactions on the electrode surface are also a problem that shortens battery life, with both resulting in a degradation of structural stability and electrochemical characteristics during charge and discharge cycles [79,80]. To overcome these problems, eluted metal ions can be partially substituted with other transition metals [81–83]. It may also be possible to reduce the contact between the electrode and the electrolyte by coating stable materials on the surface of the electrode [4,84–86]. Of particular note is a core–shell structure consisting of a key active component coated with a stable material, denoted as ‘‘electrode material@stable coating layer.’’ Depending on the type of coating material, the structural and thermal stability, as well as electrochemical characteristics such as cycle and rate capability can all be simultaneously improved. Most core–shell structures reported thus far are generally synthesized through a multi-step process of preparation and coating. More recent studies, however, have begun to report improved characteristics with core–shell structures used as electrode materials as synthesized by a one-step spray pyrolysis process. It is therefore becoming increasingly important to develop a more simplified process for the production of electrode materials with a core–shell structure. Manganese spinel materials such as LiMn2O4 (LMO) are one of the more suitable alternatives to LiCoO2 in high power applications

Fig. 5. Formation mechanism of yolk–shell structure by spray pyrolysis.

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

6

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx

Fig. 6. TEM images of the multi-component electrode materials with yolk–shell structures prepared by spray pyrolysis: (a) LiNi0.5Mn1.5O4 and (b) ZnCo2O4.

Fig. 7. TEM images of the multi-component electrode materials with yolk–shell structures prepared by spray pyrolysis: (a) V2O5 and (b) LiV3O8.

Fig. 8. TEM images of the metal sulfides with yolk–shell structures prepared by spray pyrolysis: (a) SnS@SnS and (b) Co9S8@Co9S8.

because of their abundance and non-toxicity [87–90]. However, this material is difficult to commercialize owing to a drastic drop in capacity caused by the dissolution of Mn during cycling [91,92]. In order to solve this problem, a LMO core coated with lithium boron oxide glass, denoted as LMO@LBO, was synthesized by spray pyrolysis, as shown in Fig. 9 [93]. To achieve this, precursors of lithium, manganese and boron were first dissolved and atomized into droplets. As the droplets were exposed to a high temperature in a reactor, the evaporation of solvent and reaction between lithium and manganese resulted in the formation of LMO. Simultaneously, a reaction between lithium and boron produced LBO glass. The driving force of preparing a core–shell structure using

one-step spray pyrolysis is phase segregation by difference of physical properties. The substance with high melting point tends to bond together due to strong bond energy between molecules, which forms the core, while the substance with relatively low melting point is being pushed outwardly and forms the coating layer (Fig. 10). The LMO had capacity retention of 80% after 100 cycles at 1 C, but improved capacity retention of 86% was achieved by using core–shelled LMO@LBO. Furthermore, owing to high lithium ionic conductivity of LBO glass, LMO@LBO demonstrated a higher capacity compared to bare LMO. By using a one-step in situ spray pyrolysis method, core–shell structures of various compositions were synthesized by the Kang’s

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

7

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx Table 2 Summary of electrode materials with a yolk–shell structure prepared by spray pyrolysis. Materials used as electrode in LIB

Morphology

Electrochemical performance

Ref.

Sn (anode)

LiNi0.5Mn1.5O4 (cathode) WO3 (anode) Co3O4 (anode)

LiNi0.5Mn1.5O4 yolk–shell powders WO3 yolk–shell particles Co3O4 yolk–shell powders

[69] [70] [71]

CoMn2O4 (anode)

Yolk–shell CoMn2O4 powders

SnO2 (anode)

Double-shelled SnO2 yolk–shellstructured powders Yolk–shell-structured ZnCo2O4 powders Yolk–shell V2O5 powders Yolk–shell-structured metal sulfide powders

High capacity and good cycles performance (460 mA h/g after 95th cycles at 0.55 mA/ cm2) Initial capacity (132, 123, and 116 mA h/g at 3, 5, and 10 C), 127, 120, and 115 mA h/g after 200th cycles at 3, 5, and 10 C Initial capacity (112 mA h/g), 108 mA h/g after 1000th cycles at 10 C Initial capacity (1067 mA h/g), 523 mA h/g after 120th cycles at 0.3 A/g Initial capacity (998, 855, and 548 mA h/g), 77, 75, and 72% after 100th cycles at 1.4, 7, and 10 A/g Initial capacity (1029, 1036, and 753 mA h/g), 579, 530, and 443 mA h/g after 40th cycles at 1.6, 2.4, and 3.2 A/g Initial capacity (678 mA h/g), 91% after 40th cycles at 625 mA/g

[60]

LiMn2O4 (cathode)

Rattle-type hollow carbon spheres (Sn@C) LiMn2O4 yolk–shell powders

Initial capacity (753 mA h/g), 99% after 200th cycles at 3 A/g

[74]

Initial capacity (264 mA h/g), 201 mA h/g after 100th cycles at 1 A/g Initial capacity (733 mA h/g), 89% after 150th cycles at 1 A/g

[75] [77]

ZnCo2O4 (anode) V2O5 (cathode) SnS (anode)

[68]

[72] [73]

Fig. 9. SEM images of the LiMn2O4 powders prepared by spray pyrolysis: (a) without Li2O–2B2O3 glass and with Li2O–2B2O3 glass.

group in order to verify their potential [94]. Core–shell particles of LMO@TiO2 were successfully synthesized by the direct injection of titanium tetraisopropoxide (TTIP) vapor into the reactor. A stable TiO2 coating on the surface of LMO particles prevents contact between electrolyte ions and LMO particles, and thereby reduces Mn dissolution. The synthesized core–shell structure contributed significantly to enhancing the high rate cycle characteristics. Table 3 contains a summary of various core–shell electrode materials synthesized through spray pyrolysis.

4. Composite electrode materials prepared by spray pyrolysis A variety of carbon forms such as amorphous carbon, carbon nanotube (CNT), and graphene are used as electrode materials in LIBs [100–102]. These same carbon materials have also been used as additives to produce advanced, high capacity, composite electrodes with improved electrochemical performance [96,103–107]. In Section 4, we review synthesis methods and electrochemical

performance of composite electrode materials prepared by spray pyrolysis, based on recent publications.

4.1. Carbon composite electrode materials Carbon materials such as carbon black, or acetylene black, are commonly used to improve the electrical conductivity of electrode materials. However, the inhomogeneous mixing between carbon and active electrode materials, especially when low conductive materials are used, generally results in poor battery performance in terms of cycle stability and rate capability. To solve this problem, the application of carbon composite electrode materials has been proposed. The fast transportation of Li ions and electrons through the carbon network is expected to contribute to improved battery performance due to the unique chemical and physical properties of carbon. However, previous methods of preparing carbon composite electrodes have involved a series of complex steps

Fig. 10. Formation mechanism of core–shell structure by spray pyrolysis.

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

8

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx

Table 3 Summary of electrode materials with a core–shell structure prepared by spray pyrolysis. Materials used as electrode in LIB

Morphology

Electrochemical performance

Ref.

LiMn2O4 (cathode) LiMn2O4 (cathode) LiMnPO4 (cathode) Si (anode)

Li2O–2B2O3 glass-modified LiMn2O4 powders TiO2-coated LiMn2O4 powders Carbon-coated LiMnPO4 powders Carbon-coated Si nanocomposites

(131 mA h/g), 86% after 100th cycles at 1 C (126 mA h/g), 86% after 170th cycles at 1 C (118 mA h/g), 97.3% after 15th cycles at 0.05 C (1857 mA h/g), 1489 mA h/g after 20th cycles at

[93] [94] [95] [96]

Si (anode)

Silicon-disordered carbon nanocomposites

(2045 mA h/g), 43.1% after 100th cycles at

[97]

Si (anode)

Amorphous carbon-coated silicon nanocomposites

(2045 mA h/g), 1120 mA h/g after 100th cycles at

[98]

Ni (anode)

Hollow carbon cage with nanocapsules of graphtic shell/ nickel core

Initial capacity Initial capacity Initial capacity Initial capacity 100 mA/g Initial capacity 100 mA/g Initial capacity 100 mA/g Initial capacity 500 mA/g

(590 mA h/g), 619 mA h/g after 100th cycles at

[99]

including polymerization, carbonization, washing process, etc., which are unsuitable for industrial scale application [107,108]. Preparation using spray pyrolysis is far more amenable to large scale fabrication of carbon based composite particles with a controlled composition and morphology. Generally, carbon composites have been synthesized by a spray pyrolysis process shown schematically in Fig. 11. In this, an aqueous precursor including an electrode and carbon source is sprayed into a heated reactor, where the fast evaporation of the solvent and decomposition of the electrode precursors produces nanocrystalline electrode particles. The simultaneous decomposition and carbonization of the carbon precursor forms a 3D-conductive carbon network within the nanocrystalline electrode particles, improving the electrochemical performance of electrode by a number of means. Recent publications on carbon composites synthesized by spray pyrolysis are summarized in Table 4. Zachariah’s group synthesized amorphous MnOx–carbon nanocomposites by spray pyrolysis [109]. Since transition metal oxides with high capacity were first proposed as an anode material for LIBs in 2000 by Poizot et al. [110], various efforts were made to replace the commercialized graphite anode material [111]. However, performance did not prove satisfactory for commercial application owing to structural instability, low electronic conductivity, and development of high stress and strain in crystalline metal oxides during charging and discharging [112,113]. Over time metallic grains gradually migrated, destabilizing the entire electrode structure. However, a solution for these problems was proposed by Zachariah’s group. They reported that the electrochemical performance was improved when amorphous MnOx–carbon nanocomposites were prepared by spray pyrolysis, in which carbon was contained inside amorphous MnOx. The following structural advantages were listed as reasons for the improved performance: (1) Penetration of liquid electrolyte into MnOx is prevented by the porous carbon. As a result, the formation of a solid electrolyte interphase (SEI) layer is reduced and a relatively high reversible capacity is achieved. (2) Rate capability is improved by the high

electrical conductivity of carbon networks. (3) An inter-dispersed carbon network serves as a barrier structure in preventing the aggregation and growth of manganese grains. (4) Since the amorphous structure of MnOx can reduce the stress/strain of the conversion reaction (MnOx + 2xLi M Mn + xLi2O), the lithiation/ delithiation overpotential is lowered. Kang’s group synthesized spherical ZnS–C composites through a direct sulfidation of a metal oxide–carbon intermediate phase formed by spray pyrolysis [114]. Richardson’s group reported hollow spherical particles of 10 lm, composed of carbon-coated LiCoPO4 primary particles of 70 nm. The composite electrode exhibited an excellent rate capability, with over 80 mA h/g delivered at 5 C, and 123 mA h/g at 0.1 C [115]. Significant research progress into carbon composite electrodes has been made in the effort to solve the problems associated with metal alloy-based anode materials with a high capacity. Ever since the commercialization of LIBs, graphite has been mainly used as the anode material; however, the theoretical capacity of graphite is insufficient for medium to large size applications such as EVs, and EES. Metal alloy-based anode materials have been the focus for a viable alternative to graphite for LIB anodes. Anode materials such as Sn, Si, and Ge-based alloys have capacities 2–10 times greater than that of conventional graphite [116]. However, during lithiation, they are also subjected to a volume change that is 2–4 times greater. Since this severe change in volume causes pulverization, delamination, and structural instability of the interface, a successful alternative for graphite is yet to be claimed for commercial scale production. As part of an effort to solve this volume change issue during charging and discharging, the adaptation of metallic nanostructures, alloy formation of non-reactive metals with lithium, and carbon composites have all been proposed and tested [96,117,118]. Among these, carbon composites have been demonstrated to be the most successful alternative. The flexible structure of carbon accommodates the volume change and improves conductivity of electrode, thereby facilitating the charge transfer reaction [119]. However, it is challenging to produce these sophisticated composites rapidly while still

Fig. 11. Formation mechanism of carbon composite by spray pyrolysis.

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

9

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx Table 4 Summary of carbon composite electrode materials prepared by spray pyrolysis. Materials used as electrode in LIB

Morphological characteristics

Electrochemical performance

Ref.

MnOx (anode) Zinc sulfide (anode) LiCoPO4 (cathode) Sn (anode) Silicon (anode) Tin (anode) NiO (anode) LiFePO4 (cathode) Fe3O4 (anode) ZnO (anode) Graphite/silicon (anode) Silicon (anode)

Amorphous MnOx–carbon nanocomposites Zinc sulfide–carbon nanocomposites Nanoporous LiCoPO4/C composite Uniform Nano-Sn–C composite Si NPs embedded in porous carbon particles Hierarchical tin–carbon composite NIO–C nanocomposites LiFePO4–C nanocomposites Fe3O4–carbon microspheres ZnO/C nanocomposites Graphite/silicon/carbon spherical composite Amorphous silicon–carbon nanocomposites

Initial capacity (650 mA h/g), 93% after 130th cycles at 0.2 A/g 100% after 2nd-300th cycles at 1 A/g Initial capacity (123 mA h/g), 95% after 20th cycles at C/10 Initial capacity (710 mA h/g), 100% after 130th cycles at 0.25 A/g Initial capacity (1956 mA h/g at 0.1A/g), 91% after 150th cycles at 4 A/g Initial capacity (640 mA h/g), 98% after 200th cycles at 0.5 A/g (1 C) Initial capacity (1155 mA h/g), 382 mA h/g after 50th cycles at 700 mA/g Initial capacity (147 mA h/g at 0.1 C), 98% after 100th cycles at 1 C Initial capacity (147 mA h/g at 0.1 C), 98% after 100th cycles at 1 C Initial capacity (915 mA h/g), 100% after 100th cycles at 1 C Initial capacity (602.7 mA h/g), 92% after 20th cycles Initial capacity (1150 mA h/g), 1000 mA h/g after 160th cycles at 1 A/g

[109] [114] [115] [120] [121] [122] [123] [124] [125] [126] [127] [128]

maintaining a uniform distribution of Sn, Si, and Ge inside the carbon pore. Compared to other synthetic processes, spray pyrolysis can produce an ideal structure of nanosized metal particles uniformly dispersed in a spherical conductive carbon matrix. Zachariah’s group synthesized Sn–C composites by spray pyrolysis, in which nanosized Sn particles were uniformly distributed [120]. A precursor solution of SnCl2 and polyvinlypyrrolidone (PVP) was atomized and pyrolyzed in a heated reactor. The Sn precursor is decomposed within one second in the hot reactor; forming nanosized particles that serve as a catalyst promoting the decomposition of PVP, and help to form a networked carbon structure that hinders the growth of Sn particles. The Sn–C composite exhibited an exceptional rate performance and cycling stability with 710 mA h/g at an initial capacity at 0.25 C for 130 cycles, and 600 mA h/g capacity at a high rate of 20 C. Choi’s group adopted a spray process to enable scalable synthesis of Si–C composite particles, in which silicon nanoparticles are embedded in a spherical porous carbon matrix [121], as shown in Fig. 12. Locating entire nanosized Si particles within pores with enough spaces may not be a trivial matter though, especially in high speed synthetic processes. Previously reported Si–C composites lacked well-defined pore structures, which resulted in limited capacity retention even after several tens of cycles. However, the porous Si–C composite prepared by silica-assisted spray pyrolysis possesses sufficient empty space to accommodate the volume change of Si during charging and discharging, and thus addresses the chronic fading of Si anodes. The composite had a capacity of 1956 mA h/g at a rate of 0.5 C, and remained at 95% of the initial capacity even after 150 cycles at 2 C. 4.2. Graphene composite electrode materials Graphene is a 2-D sheet with a sp2 bond structure possessing excellent physical and chemical properties such as a large specific surface area, and high electrical conductivity. It has been

extensively studied and applied to nanoelectronics, nanosensors, and energy storage devices [129]. The possibility of replacing conventional graphite anodes with graphene has previously been proposed and investigated [130–132]. The justification for using graphene as an anode in LIBs lies in the unique hexagonal carbon ring surface structure, which provides more lithium ion storage sites than conventional graphite. This implies that the lithium insertion capacity of graphene is possibly higher than that of bulk graphite anode material. However, this improvement can only be achieved when each layer of graphene is dispersed without agglomeration caused by van der Waals force [133]. It is therefore essential to develop a process to prepare electrode materials with a uniform dispersion of graphene. Recently, Jang’s group reported on a spray pyrolysis method to prepare a crumpled paper ball graphene structure [134]. As shown in Fig. 13, a droplet generator produced a stream in which graphene oxide particles were uniformly dispersed. As soon as these droplets were exposed to a high temperature environment, the solvent was rapidly evaporated and crumpled graphene oxide sheets were formed due to isotropic capillary compression. The crumpled paper ball graphene was demonstrated to be an excellent super capacitor, with a high specific capacitance and excellent output characteristics. Restacking of graphene was not observed even if when the mass loading was increased, which not the case with other supercapacitors synthesized with a flat or a wrinkled sheet structure. The crumpled graphene particles produced by spray pyrolysis are immune to agglomeration and maintain a high accessible surface for electrochemical reactions. Jang’s group also synthesized crumpled particles of graphene into which silicon nanoparticles were embedded [135]. These graphene-encapsulated silicon nanoparticles were applied in improving the performance of silicon anodes in LIBs, which typically have about 10 times the storage capacity of a conventional graphite anode (370 mA h/g). The development of a high capacity Si anode is expected to accelerate the popularity of EVs, and EES. However, despite the promising electrochemical performance, Si

Fig. 12. SEM images of (a) spherical porous carbon particle and (b) Si NPs embedded in porous carbon sphere prepared by spray process.

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

10

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx

Fig. 13. Formation mechanism of crumpled paper ball graphene particles by spray pyrolysis.

typically suffers from capacity fade during the charge/discharge process, which is attributed to a large volume change of 300%. This volume change results in pulverization of the electrode materials, loss of electric contact, and unstable SEI formation. To overcome this problem, as mentioned in Section 4.1, Si–C composites and nanostructured Si are proposed. However, these methods exhibit a limit in electrochemical performance that cannot completely prevent excessive deposition of an insulating SEI layer after repeated cycling. The cumulative volume change of the Si anode also causes continuous fracture of the Si particles, with the new surface generated being exposed to the electrolyte solvent and forming a thick SEI layer. The end result is a dramatic reduction in the capacity and cycling stability of Si anodes [110,136,137]. When crumpled graphene-encapsulated Si nanoparticles are synthesized by spray pyrolysis, substantial voids are created between the Si particles and the graphene shell. These empty spaces are sufficient to accommodate the high volume expansion of silicon, and prevent additional SEI layer formation by blocking the penetration of electrolyte. The Si composite exhibits a greatly improved performance over LIB anodes in terms of capacity, cycle stability, and coulombic efficiency.

Similar approaches to the preparation of graphene-based composite electrode materials by spray pyrolysis are summarized in Table 5, with graphene sheet-wrapped nano-Fe2O3 [138], MoO3 [139], LiFePO4 [140], Li4Ti5O12 [141], etc. all prepared by spray pyrolysis (Fig. 14). In this process, the nanoparticles/graphene oxide-suspended precursor solution is nebulized to form micro-sized droplet through a droplet generator. The droplets are subsequently dried in the reactor in which the graphene oxide sheets enable to assemble in the surface of the droplets due to their amphiphilicity and shrink by solvent evaporation. Thus, the nanoparticles can be wrapped in the graphene sheets. The wrapped structure significantly enhanced the electrode performance in terms of rate capability and cycle stability. The spray process is gradually being accepted as a suitable method for the large-scale production of various 3D graphene sheet-wrapped composite electrode materials. 4.3. CNT composite electrode materials The excellent electrical conductivity, mechanical strength and chemical stability of carbon nanotubes have prompted investigation into the possibility of their use in place of carbon anodes in

Table 5 Summary of graphene composite electrode materials prepared by spray pyrolysis. Materials used as electrode in LIB

Morphological characteristics

Electrochemical performance

Ref.

Silicon (anode) Fe2O3 (anode)

Crumpled graphene-encapsulated Si NPs 3D graphene-encapsulated Fe2O3 nanoparticles LiFePO4 NPs embedded in micro-sized secondary particles LTO primary particles wrapped with RGO network Li3V2(PO4)3 primary particles wrapped with RGO network Spitball-like structured graphene powder

Excellent coulombic efficiency, 83% after 250th cycles at 1 A/g Initial capacity (936 mA h/g at 0.1A/g), 94% after 50th cycles at 0.8 A/g

[135] [138]

70 mA h/g at the rate of 60 C, reaching 47% of the initial capacity (148 mA h/g) at 0.1 C.

[140]

Initial capacity (168, 157, 135, 106 mA h/g at 2, 5, 10, 20 C), 100 mA h/g after 300 cycles at 20 C Initial capacity (131.4 and 181.5 mA h/g in the voltage range 3.0–4.3 V and 3.0–4.8 V at 0.1 C), stable after 100 cycles at 0.1 C 180 mA h/g at ultrahigh C rate of 40 C, 95.4% after 100th cycles at 40 C

[141]

LiFePO4 (cathode) Li4Ti5O12 (LTO) (anode) Li3V2(PO4)3 (cathode) Graphene

[142] [143]

Fig. 14. FE-SEM (a) and TEM (b) images of the crumpled granphene–MoO3 composite powders.

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx

Fig. 15. Various nano-structure and composite particles prepared by spray pyrolysis. In this review, nano-particles, yolk–shell, core–shell, carbon composite, graphene composite, and CNT composite are mainly covered.

LIBs [31,144–149]. As it turns out, no advantage over conventional carbon electrode has been reported owing to the low bulk density and large irreversible capacity of carbon materials. To overcome this problem, composites of carbon nanotubes and transition metal oxides have been subsequently proposed as LIB electrodes in which carbon nanotubes serve as an electron pathway [149,150]. The enhanced high electrical conductivity could be applicable to hybrid electric vehicles. The key in the preparation of carbon nanotubes and metal oxides is to maintain phase uniformity. Chou and Wang’s group prepared a Fe2O3–CNT composite in which hollow Fe2O3 nanospheres were dispersed in the middle of a carbon nanotube network [151]. As a precursor for spray pyrolysis, iron (II) lactate hydrate dissolved in a solution of carbon nanotubes (CNT) was used. Fe2O3 nanospheres of 20 nm were formed on the surface of the CNTs as droplets of the precursor solution were passed through a hot reactor zone, the super hydrophobicity of CNT playing a role in the nanoparticle formation. The synthesized Fe2O3–CNT composite demonstrated a high storage capacity of 700 mA h/g at a rate of 40 mA/g, and remained at 360 mA h/g even at the high rate of 6.4 A/g. This research confirms the possibility of synthesizing CNT composite electrode materials by spray pyrolysis, which can promote electron transport and maintain mechanical integrity by accommodating volume changes of metal oxide particles. This in turn should result in an improvement in the rate capability and cycle stability.

5. Summary and outlook The remarkable development of digital devices has been always accompanied by a corresponding improvement in powder materials. Control of the morphology and structure of such materials is essential to make devices thinner, smaller, lighter, and with high and multi-functionality. This trend is equally applicable to the search for new and improved electrode materials in future lithium batteries. In particular, in order to produce high-capacity and high performance LIBs, electrode materials should be dramatically improved. However, technical issues still need to resolved and matched with regards to viable commercial application. Spray pyrolysis is a process in which a precursor solution is atomized in a droplet generating apparatus, evaporated in a heated reactor, and then decomposed into particles and films. This process

11

has numerous intrinsic advantages over conventional solid state mixing methods due to its inherent uniqueness. For example, a wide range of precursors are available that are soluble in either water or organic liquids; allowing for a variety of multicomponent particles to be produced and easily modified by doping. The chemical reaction is also physically confined within a small droplet, and so nanoscale mixing of multicomponent precursors is intrinsically guaranteed. Since the reactivity of fine particles is high, the synthesis of various particles is possible even at quite low temperatures. In addition, since spherical particles are normally produced it is not essential to go through a milling process, thereby allowing for a higher purity powder. Scale up of the device is also relatively easily achieved by increasing the reactor diameter and ensuring continuous injection of the precursor solution. The key elements in spray pyrolysis are the precursor, solvent, droplet generator, carrier gas, reaction vessel for evaporation and decomposition, and the heat source. A mix and match strategy with these components allows production of a wide range of particles of various morphologies and features on the surface of particles. In this review, we focus specifically on spray pyrolysis due to its versatility in the detailed design of LIB electrode materials, with an intention towards large scale production. Fig. 15 shows the topics covered in this review in terms of the various morphologies and structures of the electrode materials produced that could potentially improve the performance of LIBs. In particular, the relationship between specific particle structures and battery performance was reviewed and summarized. (1) Nano-sized electrode materials prepared by spray pyrolysis are beneficial in preventing agglomeration, and possessing a homogeneous chemical composition. Nanoparticles also enhance the rate capability through a short Li ion diffusion distance that could not be obtained from any bulk material. (2) Spray pyrolysis is useful for the synthesis of yolk–shell structured electrode materials, which have the advantage of a short Li-ion diffusion length, large surface area, and a buffer space capable of accommodating volume changes, all of which results in improved electrochemical properties and structural stability. (3) Stable layer-coated electrode materials (core–shell structure) enhance the structural stability by preventing the dissolution of active material during cycling. (4) Carbon composite electrode materials prepared by spray pyrolysis are particularly desirable for constructing 3D-conductive carbon networks on nanocrystalline electrode particles. This 3D network prevents aggregation and growth of the nanocrystalline particles, as well as improving the electrical conductivity of the electrode. (5) The rapid evaporation of solvent in spray pyrolysis can form crumpled paper ball graphene due to isotropic capillary compression, thereby preventing the agglomeration of graphene sheets caused by van der Waals force. This ball structure accommodates the volume expansion of electrode materials such as Si, Sn, and Ge, resulting in an improved rate capability and cycle stability. (6) CNT composites promote electron transport, and maintain mechanical integrity, by accommodating volume changes in metal oxide particles. This results in an improvement in the rate capability and cycling stability. The current review suggests that the spray pyrolysis method will become increasingly viable for the large-scale production of next generation LIB electrode materials requiring sophisticated nanostructures, or multi-composite materials. However, it is not yet fully understood how particles are formed in the droplet after the decomposition of precursors under

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

12

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx

extremely rapid changes in temperature. It is also vital to understand the detailed general mechanism of yolk–shell formation and carbon network structures. Thus, future research should concentrate on these aspects, and the effect of key operating variables in spray pyrolysis. In addition, progress also needs to be made towards the development of new electrode architecture for excellent electrochemical performance, which would make the spray pyrolysis process more attractive for the commercial scale production of electrode materials in the next generation of lithium ion batteries.

References [1] M.Z. Jacobson, Review of solutions to global warming, air pollution, and energy security, Energy Environ. Sci. 2 (2009) 148–173. [2] B.L. Ellis, K.T. Lee, L.F. Nazar, Positive electrode materials for Li-ion and Libatteries, Chem. Mater. 22 (2010) 691–714. [3] Y. Wang, G. Cao, Developments in nanostructured cathode materials for highperformance lithium-ion batteries, Adv. Mater. 20 (2008) 2251–2269. [4] H. Li, Z. Wang, L. Chen, X. Huang, Research on advanced materials for Li-ion batteries, Adv. Mater. 21 (2009) 4593–4607. [5] J. Chen, F. Cheng, Combination of lightweight elements and nanostructured materials for batteries, Acc. Chem. Res. 42 (2009) 713–723. [6] S.W. Lee, B.M. Gallant, H.R. Byon, P.T. Hammond, Y. Shao-Horn, Nanostructured carbon-based electrodes: bridging the gap between thinfilm lithium-ion batteries and electrochemical capacitors, Energy Environ. Sci. 4 (2011) 1972–1985. [7] N.A. Kaskhedikar, J. Maier, Lithium storage in carbon nanostructures, Adv. Mater. 21 (2009) 2664–2680. [8] P.G. Bruce, B. Scrosati, J.M. Tarascon, Nanomaterials for rechargeable lithium batteries, Angew. Chem. Int. Ed. 47 (2008) 2930–2946. [9] Y. Wang, H. Li, P. He, E. Hosono, H. Zhou, Nano active materials for lithium-ion batteries, Nanoscale 2 (2010) 1294–1305. [10] J.H. Bang, K.S. Suslick, Applications of ultrasound to the synthesis of nanostructured materials, Adv. Mater. 22 (2010) 1039–1059. [11] D.S. Jung, S.B. Park, Y.C. Kang, Design of particles by spray pyrolysis and recent progress in its application, Korean J. Chem. Eng. 27 (2010) 1621– 1645. [12] W.Y. Teoh, R. Amal, L. Mädler, Flame spray pyrolysis: an enabling technology for nanoparticles design and fabrication, Nanoscale 2 (2010) 1324–1347. [13] P.S. Patil, Versatility of chemical spray pyrolysis technique, Mater. Chem. Phys. 59 (1999) 185–198. [14] R. Strobel, S.E. Pratsinis, Flame aerosol synthesis of smart nanostructured materials, J. Mater. Chem. 17 (2007) 4743–4756. [15] A.B.D. Nandiyanto, K. Okuyama, Progress in developing spray-drying methods for the production of controlled morphology particles: From the nanometer to submicrometer size ranges, Adv. Powder Technol. 22 (2011) 1–19. [16] Y.S. Chung, Y.C. Kang, S.B. Park, Luminescence and CL saturation characteristics of Eu doped Y–Al–O multicomposition phosphor prepared by spray pyrolysis, J. Electrochem. Soc. 151 (2004) H180–H183. [17] M.E. Fortunato, M. Rostam-Abadi, K.S. Suslick, Nanostructured carbons prepared by ultrasonic spray pyrolysis, Chem. Mater. 22 (2010) 1610– 1612. [18] B. Lokhande, P. Patil, M. Uplane, Studies on cadmium oxide sprayed thin films deposited through non-aqueous medium, Mater. Chem. Phys. 84 (2004) 238– 242. [19] M. Nyman, J. Caruso, M.J. Hampden-Smith, T.T. Kodas, Comparison of solidstate and spray-pyrolysis synthesis of yttrium aluminate powders, J. Am. Ceram. Soc. 80 (1997) 1231–1238. [20] S.E. Skrabalak, K.S. Suslick, Porous MoS2 synthesized by ultrasonic spray pyrolysis, J. Am. Chem. Soc. 127 (2005) 9990–9991. [21] S.A. Song, K.Y. Jung, S.B. Park, Preparation of Y2O3 particles by flame spray pyrolysis with emulsion, Langmuir 25 (2009) 3402–3406. [22] Y.C. Kang, H.S. Roh, S.B. Park, H.D. Park, Use of LiCl flux in the preparation of Y2O3: Eu phosphor particles by spray pyrolysis, J. Eur. Ceram. Soc. 22 (2002) 1661–1665. [23] D.S. Jung, S.K. Hong, J.S. Cho, Y.C. Kang, Morphologies and crystal structures of nano-sized Ba1 xSrxTiO3 primary particles prepared by flame spray pyrolysis, Mater. Res. Bull. 43 (2008) 1789–1799. [24] E.K. Nyutu, W.C. Conner, S.M. Auerbach, C.-H. Chen, S.L. Suib, Ultrasonic nozzle spray in situ mixing and microwave-assisted preparation of nanocrystalline spinel metal oxides: nickel ferrite and zinc aluminate, J. Phys. Chem. C 112 (2008) 1407–1414. [25] N. Kambe, Highly-uniform nano-structured building blocks of metal–(O, C, N, S) and their complex compounds, Scripta Mater. 44 (2001) 1671–1675. [26] J. Walter, M. Nishioka, S. Hara, Ultrathin platinum nanoparticles encapsulated in a graphite lattice prepared by a sonochemical approach, Chem. Mater. 13 (2001) 1828–1833. [27] J.H. Bang, R.J. Helmich, K.S. Suslick, Nanostructured ZnS: Ni2+ photocatalysts prepared by ultrasonic spray pyrolysis, Adv. Mater. 20 (2008) 2599–2603. [28] W.H. Suh, A.R. Jang, Y.H. Suh, K.S. Suslick, Porous, hollow, and ball-in-ball metal oxide microspheres: preparation, endocytosis, and cytotoxicity, Adv. Mater. 18 (2006) 1832–1837.

[29] Y. Itoh, M. Abdullah, K. Okuyama, Direct preparation of nonagglomerated indium tin oxide nanoparticles using various spray pyrolysis methods, J. Mater. Res. 19 (2004) 1077–1086. [30] J.H. Kim, H.Y. Koo, S.K. Hong, J.M. Han, H.C. Jang, Y.N. Ko, Y.J. Hong, Y.C. Kang, S.H. Kang, S.B. Cho, Combustion characteristics of the heat pellet prepared from the Fe powders obtained by spray pyrolysis, Adv. Powder Technol. 23 (2012) 387–392. [31] F. Iskandar, S.-G. Kim, A.B.D. Nandiyanto, Y. Kaihatsu, T. Ogi, K. Okuyama, Direct synthesis of hBN/MWCNT composite particles using spray pyrolysis, J. Alloy. Compd. 471 (2009) 166–171. [32] H.B. Wu, J.S. Chen, H.H. Hng, X.W. Lou, Nanostructured metal oxide-based materials as advanced anodes for lithium-ion batteries, Nanoscale 4 (2012) 2526–2542. [33] H.K. Song, K.T. Lee, G. Kim, L.F. Nazar, J. Cho, Recent progress in nanostructured cathode materials for lithium secondary batteries, Adv. Funct. Mater. 20 (2010) 3818–3834. [34] M. Konarova, I. Taniguchi, Preparation of carbon coated LiFePO4 by a combination of spray pyrolysis with planetary ball-milling followed by heat treatment and their electrochemical properties, Powder Technol. 191 (2009) 111–116. [35] Y.N. Ko, J.H. Kim, Y.J. Hong, Y.C. Kang, Electrochemical properties of nanosized Li3V2(PO4)3/C composite powders prepared by spray pyrolysis from spray solution with chelating agent, Mater. Chem. Phys. 131 (2011) 292–296. [36] M. Konarova, I. Taniguchi, Physical and electrochemical properties of LiFePO4 nanoparticles synthesized by a combination of spray pyrolysis with wet ballmilling, J. Power Sources 194 (2009) 1029–1035. [37] M. Konarova, I. Taniguchi, Synthesis of carbon-coated LiFePO4 nanoparticles with high rate performance in lithium secondary batteries, J. Power Sources 195 (2010) 3661–3667. [38] B. Shao, I. Taniguchi, Synthesis of Li2FeSiO4/C nanocomposite cathodes for lithium batteries by a novel synthesis route and their electrochemical properties, J. Power Sources 199 (2012) 278–286. [39] I. Taniguchi, Effect of spray pyrolysis temperature on physical and electrochemical properties of LiCoPO4/C nanocomposites, Powder Technol. 217 (2012) 574–580. [40] I. Taniguchi, Cathode performance of LiMnPO4/C nanocomposites prepared by a combination of spray pyrolysis and wet ball-milling followed by heat treatment, J. Power Sources 196 (2011) 1399–1408. [41] B. Shao, Y. Abe, I. Taniguchi, Synthesis and electrochemical characterization of Li2FexMn1 xSiO4/C (0 6 x 6 0.8) nanocomposite cathode for lithium-ion batteries, Powder Technol. 235 (2013) 1–8. [42] S.H. Ju, H.C. Jang, Y.C. Kang, Characteristics of nano-sized tin dioxide powders prepared by spray pyrolysis, J. Ceram. Soc. Jpn. 117 (2009) 922–925. [43] S.H. Ju, Y.C. Kang, Fine-sized LiCoO2 cathode powders prepared from the nano-sized cobalt oxide powders obtained by gas phase reaction method, J. Ceram. Soc. Jpn. 115 (2007) 767–771. [44] Y.N. Ko, J.H. Kim, J.-K. Lee, Y.C. Kang, J.-H. Lee, Electrochemical properties of nanosized LiCrO2 Li2MnO3 composite powders prepared by a new concept spray pyrolysis, Electrochim. Acta 69 (2012) 345–350. [45] Y. Yao, M.T. McDowell, I. Ryu, H. Wu, N. Liu, L. Hu, W.D. Nix, Y. Cui, Interconnected silicon hollow nanospheres for lithium-ion battery anodes with long cycle life, Nano Lett. 11 (2011) 2949–2954. [46] N. Yan, F. Wang, H. Zhong, Y. Li, Y. Wang, L. Hu, Q. Chen, Hollow porous SiO2 nanocubes towards high-performance anodes for lithium-ion batteries, Scientific Reports 3 (2013) 1568. [47] Y. Xia, Z. Xiao, X. Dou, H. Huang, X. Lu, R. Yan, Y. Gan, W. Zhu, J. Tu, W. Zhang, Green and facile fabrication of hollow porous MnO/C microspheres from microalgaes for lithium-ion batteries, ACS Nano 7 (2013) 7083–7092. [48] A.M. Cao, J.S. Hu, H.P. Liang, L.J. Wan, Self-assembled vanadium pentoxide (V2O5) hollow microspheres from nanorods and their application in lithiumion batteries, Angew. Chem. Int. Ed. 44 (2005) 4391–4395. [49] X.W. Lou, Y. Wang, C. Yuan, J.Y. Lee, L.A. Archer, Template-free synthesis of SnO2 hollow nanostructures with high lithium storage capacity, Adv. Mater. 18 (2006) 2325–2329. [50] Z. Wang, L. Zhou, Metal oxide hollow nanostructures for lithium-ion batteries, Adv. Mater. 24 (2012) 1903–1911. [51] X.W. Lou, L.A. Archer, Z. Yang, Hollow micro-/nanostructures: synthesis and applications, Adv. Mater. 20 (2008) 3987–4019. [52] S. Han, B. Jang, T. Kim, S.M. Oh, T. Hyeon, Simple synthesis of hollow tin dioxide microspheres and their application to lithium-ion battery anodes, Adv. Funct. Mater. 15 (2005) 1845–1850. [53] K.T. Lee, Y.S. Jung, S.M. Oh, Synthesis of tin-encapsulated spherical hollow carbon for anode material in lithium secondary batteries, J. Am. Chem. Soc. 125 (2003) 5652–5653. [54] X. Wang, X.L. Wu, Y.G. Guo, Y. Zhong, X. Cao, Y. Ma, J. Yao, Synthesis and lithium storage properties of Co3O4 nanosheet-assembled multishelled hollow spheres, Adv. Funct. Mater. 20 (2010) 1680–1686. [55] Y. Qiao, S.-R. Li, Y. Yu, C.-H. Chen, Synthesis and electrochemical properties of high performance yolk-structured LiMn2O4 microspheres for lithium ion batteries, J. Mater. Chem. A 1 (2013) 860–867. [56] L. Zhou, D. Zhao, X.W. Lou, Double-shelled CoMn2O4 hollow microcubes as high-capacity anodes for lithium-ion batteries, Adv. Mater. 24 (2012) 745– 748. [57] Y. Zhao, J. Li, C. Wu, Y. Ding, L. Guan, A yolk–shell Fe3O4@C composite as an anode material for high-rate lithium batteries, ChemPlusChem 77 (2012) 748–751.

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx [58] N. Liu, H. Wu, M.T. McDowell, Y. Yao, C. Wang, Y. Cui, A yolk-shell design for stabilized and scalable Li-ion battery alloy anodes, Nano Lett. 12 (2012) 3315–3321. [59] J. Liu, H. Xia, D. Xue, L. Lu, Double-shelled nanocapsules of V2O5-based composites as high-performance anode and cathode materials for Li ion batteries, J. Am. Chem. Soc. 131 (2009) 12086–12087. [60] R. Zheng, X. Meng, F. Tang, L. Zhang, J. Ren, A general, one-step and templatefree route to rattle-type hollow carbon spheres and their application in lithium battery anodes, J. Phys. Chem. C 113 (2009) 13065–13069. [61] H. Xu, J. Guo, K.S. Suslick, Porous carbon spheres from energetic carbon precursors using ultrasonic spray pyrolysis, Adv. Mater. 24 (2012) 6028– 6033. [62] J.H. Bang, K. Han, S.E. Skrabalak, H. Kim, K.S. Suslick, Porous carbon supports prepared by ultrasonic spray pyrolysis for direct methanol fuel cell electrodes, J. Phys. Chem. C 111 (2007) 10959–10964. [63] A.K. Peterson, D.G. Morgan, S.E. Skrabalak, Aerosol synthesis of porous particles using simple salts as a pore template, Langmuir 26 (2010) 8804– 8809. [64] S. Kim, B. Liu, M. Zachariah, Synthesis of nanoporous metal oxide particles by a new inorganic matrix spray pyrolysis method, Chem. Mater. 14 (2002) 2889–2899. [65] T. Ogi, Y. Kaihatsu, F. Iskandar, E. Tanabe, K. Okuyama, Synthesis of nanocrystalline GaN from Ga2O3 nanoparticles derived from salt-assisted spray pyrolysis, Adv. Powder Technol. 20 (2009) 29–34. [66] B. Xia, I. Lenggoro, K. Okuyama, Synthesis of CeO2 nanoparticles by saltassisted ultrasonic aerosol decomposition, J. Mater. Chem. 11 (2001) 2925– 2927. [67] A.K. Mann, S. Wicker, S.E. Skrabalak, Aerosol-assisted molten salt synthesis of NaInS2 nanoplates for use as a new photoanode material, Adv. Mater. 24 (2012) 6186–6191. [68] C.M. Sim, S.H. Choi, Y.C. Kang, Superior electrochemical properties of LiMn2O4 yolk–shell powders prepared by a simple spray pyrolysis process, Chem. Commun. 49 (2013) 5978–5980. [69] S.H. Choi, Y.J. Hong, Y.C. Kang, Yolk-shelled cathode materials with extremely high electrochemical performances prepared by spray pyrolysis, Nanoscale 5 (2013) 7867–7871. [70] C.M. Sim, Y.J. Hong, Y.C. Kang, Electrochemical properties of yolk–shell, hollow, and dense WO3 particles prepared by using spray pyrolysis, ChemSusChem 6 (2013) 1320–1325. [71] M.Y. Son, Y.J. Hong, Y.C. Kang, Superior electrochemical properties of Co3O4 yolk–shell powders with filled core and multishells prepared by a one-pot spray pyrolysis, Chem. Commun. 49 (2013) 5678–5680. [72] M.H. Kim, Y.J. Hong, Y.C. Kang, Electrochemical properties of yolk–shell and hollow CoMn2O4 powders directly prepared by continuous spray pyrolysis process as negative electrode materials for lithium ion batteries, RSC Adv. 3 (2013) 13110–13114. [73] Y.J. Hong, M.Y. Son, Y.C. Kang, One-pot facile synthesis of double-shelled SnO2 yolk–shell-structured powders by continuous process as anode materials for Li-ion batteries, Adv. Mater. 25 (2013) 2279–2283. [74] S.H. Choi, Y.C. Kang, Yolk–shell, hollow, and single-crystalline ZnCo2O4 powders: preparation using a simple one-pot process and application in lithium-ion batteries, ChemSusChem 6 (2013) 20111–20116. [75] Y.N. Ko, Y.C. Kang, S.B. Park, New strategy for synthesizing yolk–shell V2O5 powders with low melting temperature for high performance Li-ion batteries, Nanoscale 5 (2013) 8899–8903. [76] S.H. Choi, Y.C. Kang, Excellent electrochemical properties of yolk–shell LiV3O8 powder and its potential as cathodic material for Lithium-ion batteries, Chem. – A Eur. J. 19 (2013) 17305–17309. [77] S.H. Choi, Y.C. Kang, Synthesis for yolk–shell-structured metal sulfide powders with excellent electrochemical performances for lithium-ion batteries, Small (2013), http://dx.doi.org/10.1002/smll.201301483. [78] Y.N. Ko, S.H. Choi, S.B. Park, Y.C. Kang, Preparation of yolk–shell and filled Co9S8 microspheres and comparison of their electrochemical properties, Chem. Asian J. 8 (2013) 572–576. [79] D. Aurbach, B. Markovsky, G. Salitra, E. Markevich, Y. Talyossef, M. Koltypin, L. Nazar, B. Ellis, D. Kovacheva, Review on electrode–electrolyte solution interactions, related to cathode materials for Li-ion batteries, J. Power Sources 165 (2007) 491–499. [80] P. Arora, R.E. White, M. Doyle, Capacity fade mechanisms and side reactions in lithium-ion batteries, J. Electrochem. Soc. 145 (1998) 3647–3667. [81] J.W. Fergus, Recent developments in cathode materials for lithium ion batteries, J. Power Sources 195 (2010) 939–954. [82] Y. Ma, C. Fang, B. Ding, G. Ji, J.Y. Lee, Fe-doped MnxOy with hierarchical porosity as a high-performance lithium-ion battery anode, Adv. Mater. 25 (2013). [83] L. Xiong, Y. Xu, T. Tao, J.B. Goodenough, Synthesis and electrochemical characterization of multi-cations doped spinel LiMn2O4 used for lithium ion batteries, J. Power Sources 199 (2012) 214–219. [84] Z. Chen, Y. Qin, K. Amine, Y.-K. Sun, Role of surface coating on cathode materials for lithium-ion batteries, J. Mater. Chem. 20 (2010) 7606–7612. [85] S.-T. Myung, K. Amine, Y.-K. Sun, Surface modification of cathode materials from nano-to microscale for rechargeable lithium-ion batteries, J. Mater. Chem. 20 (2010) 7074–7095. [86] T.-F. Yi, Y.-R. Zhu, X.-D. Zhu, J. Shu, C.-B. Yue, A.-N. Zhou, A review of recent developments in the surface modification of LiMn2O4 as cathode material of power lithium-ion battery, Ionics 15 (2009) 779–784.

13

[87] D.K. Kim, P. Muralidharan, H.-W. Lee, R. Ruffo, Y. Yang, C.K. Chan, H. Peng, R.A. Huggins, Y. Cui, Spinel LiMn2O4 nanorods as lithium ion battery cathodes, Nano Lett. 8 (2008) 3948–3952. [88] J.-Y. Luo, H.-M. Xiong, Y.-Y. Xia, LiMn2O4 nanorods, nanothorn microspheres, and hollow nanospheres as enhanced cathode materials of lithium ion battery, J. Phys. Chem. C 112 (2008) 12051–12057. [89] T. Ogihara, H. Aikiyo, N. Ogata, K. Katayama, Y. Azuma, H. Okabe, T. Okawa, Particle morphology and battery properties of lithium manganate synthesized by ultrasonic spray pyrolysis, Adv. Powder Technol. 13 (2002) 437–445. [90] K. Myojin, T. Ogihara, N. Ogata, N. Aoyagi, H. Aikiyo, T. Ookawa, S. Omura, M. Yanagimoto, M. Uede, T. Oohara, Synthesis of non-stoichiometric lithium manganate fine powders by internal combustion-type spray pyrolysis using gas burner, Adv. Powder Technol. 15 (2004) 397–403. [91] L. Yang, M. Takahashi, B. Wang, A study on capacity fading of lithium-ion battery with manganese spinel positive electrode during cycling, Electrochim. Acta 51 (2006) 3228–3234. [92] F. Cheng, H. Wang, Z. Zhu, Y. Wang, T. Zhang, Z. Tao, J. Chen, Porous LiMn2O4 nanorods with durable high-rate capability for rechargeable Li-ion batteries, Energy Environ. Sci. 4 (2011) 3668–3675. [93] S.H. Choi, J.H. Kim, Y.N. Ko, Y.J. Hong, Y.C. Kang, Electrochemical properties of Li2O–2B2O3 glass-modified LiMn2O4 powders prepared by spray pyrolysis process, J. Power Sources 210 (2012) 110–115. [94] Y.J. Hong, M.Y. Son, J.-K. Lee, H.B. Lee, S.H. Lee, Y.C. Kang, Characteristics of stabilized spinel cathode powders obtained by in-situ coating method, J. Power Sources 244 (2013) 625–630. [95] S.-M. Oh, S.W. Oh, S.-T. Myung, S.-M. Lee, Y.-K. Sun, The effects of calcination temperature on the electrochemical performance of LiMnPO4 prepared by ultrasonic spray pyrolysis, J. Alloy. Compd. 506 (2010) 372–376. [96] S.H. Ng, J. Wang, D. Wexler, K. Konstantinov, Z.P. Guo, H.K. Liu, Highly reversible lithium storage in spheroidal carbon-coated silicon nanocomposites as anodes for lithium-ion batteries, Angew. Chem. Int. Ed. 45 (2006) 6896–6899. [97] S. Ng, J. Wang, K. Konstantinov, D. Wexler, S. Chew, Z. Guo, H. Liu, Spraypyrolyzed silicon/disordered carbon nanocomposites for lithium-ion battery anodes, J. Power Sources 174 (2007) 823–827. [98] S.H. Ng, J. Wang, D. Wexler, S.Y. Chew, H.K. Liu, Amorphous carbon-coated silicon nanocomposites: a low-temperature synthesis via spray pyrolysis and their application as high-capacity anodes for lithium-ion batteries, J. Phys. Chem. C 111 (2007) 11131–11138. [99] G. Zhou, D.-W. Wang, X. Shan, N. Li, F. Li, H.-M. Cheng, Hollow carbon cage with nanocapsules of graphitic shell/nickel core as an anode material for high rate lithium ion batteries, J. Mater. Chem. 22 (2012) 11252–11256. [100] Z.-H. Yang, H.-Q. Wu, Electrochemical intercalation of lithium into raw carbon nanotubes, Mater. Chem. Phys. 71 (2001) 7–11. [101] E. Yoo, J. Kim, E. Hosono, H.S. Zhou, T. Kudo, I. Honma, Large reversible Li storage of graphene nanosheet families for use in rechargeable lithium ion batteries, Nano Lett. 8 (2008) 2277–2282. [102] H. Zhou, S. Zhu, M. Hibino, I. Honma, M. Ichihara, Lithium storage in ordered mesoporous carbon (CMK-3) with high reversible specific energy capacity and good cycling performance, Adv. Mater. 15 (2003) 2107–2111. [103] W.X. Chen, J.Y. Lee, Z. Liu, The nanocomposites of carbon nanotube with Sb and SnSb0.5 as Li-ion battery anodes, Carbon 41 (2003) 959–966. [104] Z. Guo, Z. Zhao, H. Liu, S. Dou, Electrochemical lithiation and de-lithiation of MWNT–Sn/SnNi nanocomposites, Carbon 43 (2005) 1392–1399. [105] J. Eom, J. Park, H. Kwon, S. Rajendran, Electrochemical insertion of lithium into multiwalled carbon nanotube/silicon composites produced by ballmilling, J. Electrochem. Soc. 153 (2006) A1678–A1684. [106] Z.-S. Wu, W. Ren, L. Wen, L. Gao, J. Zhao, Z. Chen, G. Zhou, F. Li, H.-M. Cheng, Graphene anchored with Co3O4 nanoparticles as anode of lithium ion batteries with enhanced reversible capacity and cyclic performance, ACS Nano 4 (2010) 3187–3194. [107] X. Zhu, Y. Zhu, S. Murali, M.D. Stoller, R.S. Ruoff, Nanostructured reduced graphene oxide/Fe2O3 composite as a high-performance anode material for lithium ion batteries, ACS Nano 5 (2011) 3333–3338. [108] W.M. Zhang, X.L. Wu, J.S. Hu, Y.G. Guo, L.J. Wan, Carbon coated Fe3O4 nanospindles as a superior anode material for lithium-ion batteries, Adv. Funct. Mater. 18 (2008) 3941–3946. [109] J. Guo, Q. Liu, C. Wang, M.R. Zachariah, Interdispersed amorphous MnOx– carbon nanocomposites with superior electrochemical performance as lithium-storage material, Adv. Funct. Mater. 22 (2012) 803–811. [110] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J. Tarascon, Nano-sized transition-metal oxides as negative-electrode materials for lithium-ion batteries, Nature 407 (2000) 496–499. [111] X. Huang, J. Tu, C. Zhang, X. Chen, Y. Yuan, H. Wu, Spherical NiO–C composite for anode material of lithium ion batteries, Electrochim. Acta 52 (2007) 4177–4181. [112] J. Fan, T. Wang, C. Yu, B. Tu, Z. Jiang, D. Zhao, Ordered, nanostructured tinbased oxides/carbon composite as the negative-electrode material for lithium-ion batteries, Adv. Mater. 16 (2004) 1432–1436. [113] F. Cheng, Z. Tao, J. Liang, J. Chen, Template-directed materials for rechargeable lithium-ion batteries, Chem. Mater. 20 (2007) 667–681. [114] Y.S. Jang, Y.C. Kang, Facile one-pot synthesis of spherical zinc sulfide–carbon nanocomposite powders with superior electrochemical properties as anode materials for Li-ion batteries, Phys. Chem. Chem. Phys. 15 (2013) 16437– 16441.

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012

14

D.S. Jung et al. / Advanced Powder Technology xxx (2014) xxx–xxx

[115] J. Liu, T.E. Conry, X. Song, L. Yang, M.M. Doeff, T.J. Richardson, Spherical nanoporous LiCoPO4/C composites as high performance cathode materials for rechargeable lithium-ion batteries, J. Mater. Chem. 21 (2011) 9984–9987. [116] X.L. Wu, Y.G. Guo, L.J. Wan, Rational design of anode materials based on group IVA elements (Si, Ge, and Sn) for lithium-ion batteries, Chem. – Asian J. 8 (2013) 1948–1958. [117] C.K. Chan, H. Peng, G. Liu, K. McIlwrath, X.F. Zhang, R.A. Huggins, Y. Cui, Highperformance lithium battery anodes using silicon nanowires, Nat. Nanotechnol. 3 (2007) 31–35. [118] Y. Yu, L. Gu, C. Zhu, S. Tsukimoto, P.A. van Aken, J. Maier, Reversible storage of lithium in silver-coated three-dimensional macroporous silicon, Adv. Mater. 22 (2010) 2247–2250. [119] J. Guo, X. Chen, C. Wang, Carbon scaffold structured silicon anodes for lithium-ion batteries, J. Mater. Chem. 20 (2010) 5035–5040. [120] Y. Xu, Q. Liu, Y. Zhu, Y. Liu, A. Langrock, M.R. Zachariah, C. Wang, Uniform nano-Sn/C composite anodes for lithium ion batteries, Nano Lett. 13 (2013) 470–474. [121] D.S. Jung, T.H. Hwang, S.B. Park, J.W. Choi, Spray drying method for largescale and high-performance silicon negative electrodes in Li-ion batteries, Nano Lett. 13 (2013) 2092–2097. [122] L. Archer, Z. Yang, J. Guo, Aerosol assisted synthesis of hierarchical tin–carbon composites and their application as lithium battery anode materials, J. Mater. Chem. A 1 (2013) 8710–8715. [123] M. Rahman, S.-L. Chou, C. Zhong, J.-Z. Wang, D. Wexler, H.-K. Liu, Spray pyrolyzed NiO–C nanocomposite as an anode material for the lithium-ion battery with enhanced capacity retention, Solid State Ionics 180 (2010) 1646–1651. [124] I. Taniguchi, R. Tussupbayev, Synthesis of LiFePO4/C nanocomposites by a novel process and their electrochemical properties, Chem. Eng. J. 192 (2012) 334–342. [125] X. Jia, Z. Chen, X. Cui, Y. Peng, X. Wang, G. Wang, F. Wei, Y. Lu, Building robust architectures of carbon and metal oxide nanocrystals toward highperformance anodes for lithium-ion batteries, ACS Nano 6 (2012) 9911–9919. [126] G. Yang, H. Song, H. Cui, Y. Liu, C. Wang, Ultrafast Li-ion battery anode with superlong life and excellent cycling stability from strongly coupled ZnO nanoparticle/conductive nanocarbon skeleton hybrid materials, Nano Energy 2 (2013) 579–585. [127] J. Lai, H. Guo, Z. Wang, X. Li, X. Zhang, F. Wu, P. Yue, Preparation and characterization of flake graphite/silicon/carbon spherical composite as anode materials for lithium-ion batteries, J. Alloy. Compd. 530 (2012) 30–35. [128] Z. Yang, J. Guo, S. Xu, Y. Yu, H.D. Abruña, L.A. Archer, Interdispersed siliconcarbon nanocomposites and their application as anode materials for lithiumion batteries, Electrochem. Commun. 28 (2012) 40–43. [129] I. Lahiri, W. Choi, Carbon nanostructures in lithium ion batteries: past, present, and future, Crit. Rev. Solid State Mater. Sci. 38 (2013) 128–166. [130] T. Bhardwaj, A. Antic, B. Pavan, V. Barone, B.D. Fahlman, Enhanced electrochemical lithium storage by graphene nanoribbons, J. Am. Chem. Soc. 132 (2010) 12556–12558. [131] Z.-S. Wu, W. Ren, L. Xu, F. Li, H.-M. Cheng, Doped graphene sheets as anode materials with superhigh rate and large capacity for lithium ion batteries, ACS Nano 5 (2011) 5463–5471. [132] L. Tang, Y. Wang, Y. Li, H. Feng, J. Lu, J. Li, Preparation, structure, and electrochemical properties of reduced graphene sheet films, Adv. Funct. Mater. 19 (2009) 2782–2789. [133] R.O. Brennan, The interlayer binding in graphite, J. Chem. Phys. 20 (1952) 40.

[134] J. Luo, H.D. Jang, J. Huang, Effect of sheet morphology on the scalability of graphene-based ultracapacitors, ACS Nano 7 (2013) 1464–1471. [135] J. Luo, X. Zhao, J. Wu, H.D. Jang, H.H. Kung, J. Huang, Crumpled grapheneencapsulated Si nanoparticles for lithium ion battery anodes, J. Phys. Chem. Lett. 3 (2012) 1824–1829. [136] H. Li, X. Huang, L. Chen, Z. Wu, Y. Liang, A high capacity nano Si composite anode material for lithium rechargeable batteries, Electrochem. Solid-State Lett. 2 (1999) 547–549. [137] J.-M. Tarascon, M. Armand, Issues and challenges facing rechargeable lithium batteries, Nature 414 (2001) 359–367. [138] G.-W. Zhou, J. Wang, P. Gao, X. Yang, Y.-S. He, X.-Z. Liao, J. Yang, Z.-F. Ma, Facile spray drying route for the three-dimensional graphene-encapsulated Fe2O3 nanoparticles for lithium ion battery anodes, Ind. Eng. Chem. Res. 52 (2012) 1197–1204. [139] S.H. Choi, Y.C. Kang, Crumpled graphene–molybdenum oxide composite powders: preparation and application in lithium-ion batteries, ChemSusChem 7 (2014) 523–528. [140] X. Zhou, F. Wang, Y. Zhu, Z. Liu, Graphene modified LiFePO4 cathode materials for high power lithium ion batteries, J. Mater. Chem. 21 (2011) 3353–3358. [141] Q. Zhang, W. Peng, Z. Wang, X. Li, X. Xiong, H. Guo, Z. Wang, F. Wu, Li4Ti5O12/ reduced graphene oxide composite as a high rate capability material for lithium ion batteries, Solid State Ionics 236 (2013) 30–36. [142] Y. Jiang, W. Xu, D. Chen, Z. Jiao, H. Zhang, Q. Ma, X. Cai, B. Zhao, Y. Chu, Graphene modified Li3V2(PO4)3 as a high-performance cathode material for lithium ion batteries, Electrochim. Acta 85 (2012) 377–383. [143] J. Yang, Q. Liao, X. Zhou, X. Liu, J. Tang, Efficient synthesis of graphene-based powder via in-situ spray pyrolysis and its application in lithium ion batteries, RSC Adv. 3 (2013) 16449–16455. [144] H.-X. Zhang, C. Feng, Y.-C. Zhai, K.-L. Jiang, Q.-Q. Li, S.-S. Fan, Cross-stacked carbon nanotube sheets uniformly loaded with SnO2 nanoparticles: a novel binder-free and high-capacity anode material for lithium-ion batteries, Adv. Mater. 21 (2009) 2299–2304. [145] R. Kamalakaran, M. Terrones, T. Seeger, P. Kohler-Redlich, M. Rühle, Y.A. Kim, T. Hayashi, M. Endo, Synthesis of thick and crystalline nanotube arrays by spray pyrolysis, Appl. Phys. Lett. 77 (2000) 3385. [146] A.B.D. Nandiyanto, Y. Kaihatsu, F. Iskandar, K. Okuyama, Rapid synthesis of a BN/CNT composite particle via spray routes using ferrocene/ethanol as a catalyst/carbon source, Mater. Lett. 63 (2009) 1847–1850. [147] I. Khatri, T. Soga, T. Jimbo, S. Adhikari, H.R. Aryal, M. Umeno, Synthesis of single walled carbon nanotubes by ultrasonic spray pyrolysis method, Diam. Relat. Mater. 18 (2009) 319–323. [148] M. Ono-Ogasawara, T. Myojo, Characteristics of multi-walled carbon nanotubes and background aerosols by carbon analysis; particle size and oxidation temperature, Adv. Powder Technol. 24 (2013) 263–269. [149] S.-F. Zheng, J.-S. Hu, L.-S. Zhong, W.-G. Song, L.-J. Wan, Y.-G. Guo, Introducing dual functional CNT networks into CuO nanomicrospheres toward superior electrode materials for lithium-ion batteries, Chem. Mater. 20 (2008) 3617– 3622. [150] J. Shu, H. Li, R. Yang, Y. Shi, X. Huang, Cage-like carbon nanotubes/Si composite as anode material for lithium ion batteries, Electrochem. Commun. 8 (2006) 51–54. [151] S.-L. Chou, J.-Z. Wang, Z.-X. Chen, H.-K. Liu, S.-X. Dou, Hollow hematite nanosphere/carbon nanotube composite: mass production and its high-rate lithium storage properties, Nanotechnology 22 (2011) 265401.

Please cite this article in press as: D.S. Jung et al., Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries, Advanced Powder Technology (2014), http://dx.doi.org/10.1016/j.apt.2014.01.012