MWCNTs composite with a 3D conductive network structure used as a cathode material for lithium-ion batteries

Accepted Manuscript A cylindrical FePO4/MWCNTs composite with a 3D conductive network structure used as a cathode material for lithium-ion batteries Wuxiao Wang, Panyu Gao, Shiming Zhang, Junxi Zhang PII:

S0925-8388(16)32369-6

DOI:

10.1016/j.jallcom.2016.08.002

Reference:

JALCOM 38503

To appear in:

Journal of Alloys and Compounds

Received Date: 10 June 2016 Revised Date:

29 July 2016

Accepted Date: 1 August 2016

Please cite this article as: W. Wang, P. Gao, S. Zhang, J. Zhang, A cylindrical FePO4/MWCNTs composite with a 3D conductive network structure used as a cathode material for lithium-ion batteries, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.08.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

A cylindrical FePO4/MWCNTs composite with a 3D conductive network structure used as a cathode material for lithium-ion batteries

a

RI PT

Wuxiao Wanga∗, Panyu Gaob, Shiming Zhangc∗, Junxi Zhangc School of Materials Science and Engineering, Xi'an University of Technology, Xi'an 710048, China

School of Materials Science and Engineering, Hebei University of Technology,

SC

b

c

M AN U

Tianjin, 300130.China

Electrochemical Research Group, Shanghai University of Electric Power, Shanghai, 200090 China

ABSTRACT

TE D

FePO4/MWCNTs (multi-wall carbon nanotubes) composite with a cylindrical core-shell 3D conductive network structure has been fabricated by a simple micro-emulsion technique. Results indicate that FePO4 nanoparticles with a diameter

EP

of 10–20 nm are loaded onto the surfaces of MWCNTs, forming a cylindrical

AC C

core-shell 3D conductive network structure of FePO4/MWCNTs composite. The micro-emulsion plays two key roles in the synthetic process: firstly, dispersing the MWCNTs uniformly, attributing to the presence of an oil phase in the micro-emulsion system; secondly, synthesizing nanoparticle-sized FePO4 due to the nano-sized water nuclear in the micro-emulsion system, decreasing the aggregation of nano-sized FePO4 particles. The FePO4/MWCNTs composite shows excellent electrochemical ∗ ∗

Corresponding author: Wuxiao Wang; E-mail: [email protected] Corresponding author: Shiming Zhang; E-mail: [email protected] 1

ACCEPTED MANUSCRIPT performance with high discharge capacity, excellent reversibility, and cycling stability.

Keywords: Cylindrical FePO4/MWCNTs composite; 3D conductive network

RI PT

structure; Micro-emulsion technique; Cathode materials; Lithium-ion batteries.

1. Introduction

SC

Lithium-ion batteries (LIBs) have drawn increasing attention due to the large-scale

M AN U

application in predominant power sources for electronics and energy storage devices. However, the energy and power densities of the current LIBs can not meet the requirements of the practical application. Moreover, the high cost also restrains their large-scale application[1-5]. Therefore, developing the high performance and low cost

TE D

electrode material is the best way to solve these problems [6, 7]. Compared with other electrode materials, Fe-based electrode material has several advantages with excellent electrochemical performance and low cost [8-17] and silicon based electrode material

EP

is also a promising candidate [17-26]. However, by contrast, the cathode material

AC C

plays a much more important role in improving the electrochemical performance and lowing the cost of the LIBs [27-34]. LiFePO4 cathode has drawn much attention in the past years [8, 14, 35-38]. The

extraction/insertion mechanism of LiFePO4 demonstrates a two-phase behavior between the LiFePO4 phase and the FePO4 phase [39]. During charge process, the LiFePO4 phase de-intercalates lithium ions and transforms to the FePO4 phase, which maintains nearly the same structure. The FePO4 phase can reversibly transform to the 2

ACCEPTED MANUSCRIPT LiFePO4 phase in following discharge process. Therefore, the FePO4 can also be used as cathode for the LIBs [40-42]. The FePO4 has numerous advantages used as cathode material for the LIBs: firstly,

RI PT

Fe(III) compounds are cheap raw materials; secondly, the synthesis of FePO4 is a binary synthesis system, which is usually rather simple, easy to control, without any need for a protective atmosphere compared with that of the LiFePO4 synthesis; thirdly,

SC

the FePO4 shows a theoretical specific capacity of 178 mAhg–1, which is higher than

M AN U

that of the LiFePO4.

However, the FePO4 cathode also suffers from the difficult diffusion of lithium ions inserting into the crystal structure and low electronic conductivity [43-45]. In order to improve electrochemical performance of the FePO4 cathode, lots of strategies

TE D

have been taken to overcome the above problems.

Much attentions have been focused on the possible structures of the FePO4 [46, 47], such as crystalline and amorphous, in order to enhance the electrochemical

EP

performance of the FePO4 cathode [48-50]. The reported studies show that amorphous

AC C

FePO4 has a high electrochemical activity [51, 52], which benefits the diffusion of lithium ions and the electronic conductivity of the FePO4 cathode materials [43, 53, 54]. Okada et al. [50] developed a low cost preparation method to obtain amorphous and crystalline hydrated FePO4 to reveal amorphous FePO4 demonstrates batter electrochemical capacity and cycling stability than that of crystalline hydrated FePO4. Masquelier et al. [55] also found that amorphous FePO4 showed a superior electrochemical performance. The amorphous structure is benefit for the improving 3

ACCEPTED MANUSCRIPT the electrochemical performance of the electrode materials for lithium-ion batteries.[18, 19, 56] Ion doping is another effective way to improve the electronic conductivity of the

RI PT

FePO4 cathode to improve its electrochemical performance [57]. Furthermore, synthesizing electrode materials/conductive materials (such as CNT and graphene, etc.) composites also are significant measures to enhance the electronic conductivity

SC

[58-63]. Croce et al. [64] added RuO2 to FePO4 to enhance the specific capacity due

M AN U

to higher material inter-particle electronic conductivity. Yin et al. [65] discovered that graphene@amorphous FePO4 hollow nanospheres have high electrochemical activity due to the improvement of electronic conductivity by adding graphene. Fedorková et al. [66] investigated surface modification of FePO4 particles with a conductive layer

TE D

of poly-pyrrole (PPy), and their results showed that coating with PPy significantly decreased the charge transfer resistance of the FePO4 cathode. Carbon materials coating onto the surface of the LiFePO4 cathode material is also a very important

EP

technique to improve its electronic conductivity [67-69]. However, this FePO4

AC C

cathode could not be coated with carbon materials using the above method due to the easy formation of Fe2+ from the reduction of high value Fe3+ during the carbon-heat reduction process.

In this work, we propose that nano-sized FePO4 particles coat onto the surfaces of

MWCNTs, forming a 3D cylindrical core-shell conductive network structure of the FePO4/MWCNTs composite. The FePO4/MWCNTs composite can effectively enhance the electronic conductivity and lithium ions diffusion coefficient of electrode 4

ACCEPTED MANUSCRIPT materials. Fig. 1 shows a schematic diagram of the electronic transfer process and lithium ions diffusion path in the FePO4/MWCNTs composite during the charge/discharge process. For this specific 3D conductive network structure, lithium

RI PT

ions could readily diffuse into the amorphous FePO4 shell out of the MWCNTs due to the nano-sized FePO4 particles; electrons could also be effectively supplied into the low conductivity amorphous FePO4 shell through the MWCNTs core. Therefore, this

SC

composite with the 3D cylindrical core-shell conductive network structure can

AC C

EP

TE D

M AN U

effectively improve the kinetic behavior of the FePO4 cathode.

Fig. 1 Schematic diagram of electrons and Lithium ions transfer processes of the FePO4/MWCNTs composite

2. Experimental 2.1. Synthesis of the pure FePO4 and FePO4/MWCNTs The FePO4 and FePO4/MWCNTs composite were synthesized by a micro-emulsion 5

ACCEPTED MANUSCRIPT method.

Two

H2O

(deionized

water)/cyclohexane

(analysis

reagent)/Triton

x-100(analysis reagent)/n-butyl alcohol (analysis reagent) micro-emulsion systems in a volume ratio of 35:25:15:5, A and B, were prepared, differing only in the aqueous

RI PT

phase. The aqueous phase of micro-emulsion A was the reactant solution, which was a 0.1 mol/L Fe (NO3)3•9H2O (AR) + 20% MWCNTs (mass ratio of FePO4 to MWCNTs) solution. The aqueous phase of micro-emulsion B was the precipitant solution, which

SC

is the 0.1 mol/L NH4H2PO4 (AR) solution. The micro-emulsion A was vigorously

M AN U

stirred for 30 min and ultrasonically dispersed for 1 h, and then transferred into an autoclave. The micro-emulsion B was added dropwise to the micro-emulsion A under constant stirring at 350 r/min for 30 min at room temperature, and then the mixed solution, forming a new micro-emulsion, continued to be stirred, and reacted, thus

TE D

producing FePO4/MWCNTs precursors at 45 °C under pH 2.6 for 3 h. Finally, the powders were obtained by centrifugal separation, and washed with ethanol several times to remove the micro-emulsion. The obtained precipitates were dried at 100 °C

EP

for 12 h, and then sintered under N2 atmosphere at 460 °C for 3 h. The pure FePO4

AC C

nanoparticle was synthesized by the above process, but without adding MWCNTs in the micro-emulsion A.

2.2. Structure characterization The crystal phase was identified by X-ray diffraction (D8 Advance, Bruker,

Germany) with Cu Kα radiation, with 2θ in the range from 20° to 90° at a scan rate of 2°/min at 25 °C. The surface morphology of powder particles was characterized by field emission-scanning electron microscopy (SU70, Japan) and transmission electron 6

ACCEPTED MANUSCRIPT microscopy (JEOL-JEM-2100-LaB6, USA). 2.3. Electrochemical tests The characterization of electrochemical properties of the synthesized pure FePO4

RI PT

and FePO4/MWCNTs composite were accomplished by assembling CR2016 coin cells. For the pure FePO4, the sample was prepared by ball-milling mixed with a conductive agent (acetylene black) in a mass ratio of 72:20 under 500 r/min for 2 h.

SC

The FePO4/MWCNTs sample was also prepared by ball-milling with the same

M AN U

conditions, but the FePO4/MWCNTs samples need not to add acetylene black again, which is due to the 20% MWCNTs have been added in the synthetic process. The slurry was mixed by a magnetic stirrer in the mass ratio of 92:8 ((active materials and conductive agent): binder (polytetra-fluoroethylene, PTFE)) for 4 h and then pasted

TE D

onto a stainless sheet mesh. The mass of composite loading to the electrode was 15 mg/cm2; then the electrode sheet was dried in a vacuum oven at 120 °C for 24 h. Finally, coin-type cells were assembled in a glove box (H2O<0.1%, O2<0.1%), and

EP

used lithium foil as negative and reference electrode, the Celgard 2400 microporous

AC C

polypropylene film as the separator, and 1 M LiPF6 in PC/DEC (1:1) as the electrolyte. Charge/discharge tests were performed between 2.0 V and 4.0 V using the Land Battery test system (Wuhan LAND, China) at 25±1 °C.

3. Results and discussion 3.1 Synthetic principle of the FePO4/MWCNTs composite Fig. 2 shows the synthetic schematic diagram of the FePO4/MWCNTs composite 7

ACCEPTED MANUSCRIPT by micro-emulsion technique. For the micro-emulsion system, depending on the proportion of various components and the hydrophilic-lipophilic balance value of the surfactant used, the formation of microdroplets can be in the form of oil-swollen

RI PT

micelles dispersed in water as oil-in-water (O/W) microemulsion or water swollen micelles dispersed in oil as for water–in-oil (W/O) microemulsion, also called reverse microemulsion (Fig. 2a). These nano-droplets can be used as nano-reactors to carry

SC

out the chemical reactions (Fig. 2a). It was initially assumed that these nano-droplets

M AN U

could be used as templates to control the final size of the particles. The synthetic

AC C

EP

TE D

principle of the FePO4/MWCNTs composite is as follows

8

Fig. 2b : in the first step,

ACCEPTED MANUSCRIPT

RI PT

(a)

EP

TE D

M AN U

SC

(b)

Fig. 2 (a) Structure of micro-emulsion; (b) synthetic schematic diagram of the

AC C

FePO4/MWCNTs composite by a micro-emulsion technique.

the MWCNTs were uniformly dispersed in the micro-emulsion A with Fe (NO3)3•9H2O solution, in which the Fe (NO3)3•9H2O was dissolved in water swollen micelles and the MWCNTs were dispersed in oil phase due to its lipophilicity, and the water swollen micelles with Fe3+ ions were adsorbed onto the surfaces of the MWCNTs by physical interactions. In the second step, the heterogeneous nucleation occurred when the micro-emulsion B, with the NH4H2PO4 solution as precipitator, 9

ACCEPTED MANUSCRIPT was added to the micro-emulsion A. In the third step, the produced FePO4 crystal nucleus grew along the MWCNTs, forming the cylindrical core-shell 3D conductive

RI PT

network structure of FePO4/MWCNTs composite.

3.2. Analysis of microscopy and structure

The transmission electron microscopy (TEM) image (Fig. 3a) indicates that the

SC

pure FePO4 presents in the form of nanoparticles, homogeneously distributed with

M AN U

size range from 10 to 20 nm. Fig. 3b shows the scanning electron microscopy (SEM) image of the carbon nanotube with a diameter of about 78 nm. From Fig. 3c, it can be seen that the FePO4 nanoparticles are loaded onto the surfaces of the MWCNTs, forming a close interaction FePO4/MWCNTs composite with a diameter of about 114

TE D

nm. The FePO4 nanoparticle shell outside the MWCNTs is a single shell. It is can be found that the cylindrical core-shell 3D conductive network structure of the

AC C

EP

FePO4/MWCNTs composite was obtained successfully.

10

ACCEPTED MANUSCRIPT

(a)

(b)

RI PT

7 8 nm

3 0 0 nm

11 4 nm

200nm

5 m

EP

TE D

M AN U

SC

(c)

AC C

Fig. 3 (a) TEM image of the pure FePO4, (b) SEM image of the MWCNTs, (c) SEM image of the FePO4/MWCNTs composite.

Recently, studies on cathode materials/MWCNTs composite have drawn attention

due to their special 3D conductivity network structures. However, the cathode materials/CNTs composite has many classifications according the status of CNTs in composite. Liu et al.obtained porous amorphous FePO4 nanoparticles connected by CNTs, which is only simple physics connection between the FePO4 particles and the 11

ACCEPTED MANUSCRIPT CNTs. Zhou et al. [70] reported porous LiFePO4 and carbon nanotube composite, and the CNTs is only added to the composite acting as conductive agents. The XRD patterns of the pure FePO4 and FePO4/MWCNTs composite are shown

RI PT

in Fig. 4 (a). It can be seen that the FePO4 is an amorphous structure. From the XRD patterns of the MWCNTs and FePO4/MWCNTs composite, they show that there is a broad peak observed at 26.8°, corresponding to a characteristic peak on the (0 0 2)

SC

crystal plane of the MWCNTs, which is in good agreement with the previous reports

M AN U

[71]. The absence of the characteristic peaks of the corresponding crystalline FePO4 indicates that the FePO4 shell coated onto the MWCNTs core is also in an amorphous state. Moreover, the high-resolution transmission electron microscope (HRTEM) image of the FePO4 and corresponding electron diffraction pattern (EDP) also clearly

AC C

EP

TE D

confirms that the FePO4 is amorphous structure (Fig. 4(b, c)).

12

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

EP

Fig. 4 the XRD patterns of the pure FePO4, MWCNTs and FePO4/MWCNTs

AC C

composite, (b) the high-resolution transmission electron microscope (HRTEM) image of the FePO4, (c) Electron diffraction pattern (EDP) corresponding to (b).

3.3. Characteristics of electrochemical performance Fig. 5 displays the charge/discharge curves of the pure FePO4 and FePO4/MWCNTs composite at 0.1 C. The discharge specific capacities of the FePO4 and FePO4/MWCNTs composite were 125 mAhg-1 and 160 mAhg-1, respectively. In 13

ACCEPTED MANUSCRIPT addition, the gap between the potential of the charge and discharge of the FePO4/MWCNTs composite was lower than that of the FePO4, implying that FePO4/MWCNTs have a smaller polarization and higher electronic conductivity. The

RI PT

potential of amorphous FePO4 increases smoothly as a function of the state of charge, which is also an advantage of monitoring the energy situation during the charge and

SC

discharge process of the lithium-ion battery system in practical applications.

4.2 A FePO4 B FePO 4/MCNTs

M AN U

3.6 3.3 3.0 2.7

TE D

Voltag e vs. Li/Li+ (V)

3.9

2.4 2.1

EP

1.8 0

20

40

60

80

B A

100

120

140

160

180

-1

AC C

Specific capacity( mAhg )

Fig. 5 Charge/discharge curves of the pure FePO4 and FePO4/MWCNTs composite at 0.1 C.

As shown in Fig. 6, the discharge specific capacity of the FePO4/MWCNTs

composite is about 160 mAhg-1, 152 mAhg-1, 148 mAhg-1, and 142 mAhg-1, 135 mAhg-1, 130 mAhg-1, 110 mAhg-1 at 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 5 C and 10 C, respectively. However, the discharge specific capacity of the FePO4 is only 124 14

ACCEPTED MANUSCRIPT mAhg-1, 108 mAhg-1, 91 mAhg-1, 79 mAhg-1, 65 mAhg-1, 54 mAhg-1, 30 mAhg-1 at 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 5 C and 10 C, respectively. The results presented above demonstrate that the FePO4/MWCNTs composite delivers higher rate performance

RI PT

than that of the pure FePO4, which can be attributed to the facile transport capability of lithium ions and electrons in this 3D core-shell conductive network structure.

0.1C 160

0.3C

FePO4 FePO4 /MCNTs

0.5C 1 C 2C

5C

M AN U

140

SC

180

120 100 80 60 40 20 0

10

20

EP

0

TE D

Discharge specific capacity (mAh/g)

200

30 40 50 Cycle numbers

60

10C

70

80

AC C

Fig. 6 Rate performance of the pure FePO4 and FePO4/MWCNTs composite at different rate.

We further investigate the cycling stability of the FePO4 and FePO4/MWCNTs

composite, which is essential for future battery applications, such as in electric vehicles requiring a high power density and long life. The cycling performance of the pure FePO4 and FePO4/MWCNTs composite at 1 C is shown in Fig. 7. According to the profiles, the pure FePO4 and FePO4/MWCNTs composite deliver the initial discharge specific capacity of 78 mAhg-1 and 146 mAhg-1 at 1C and with the 15

ACCEPTED MANUSCRIPT coulombic efficiency of 97 % and 98 %, respectively. Furthermore, we also find that the discharge specific capacity increased with the cycle number before the 20th cycle and reached 86 mAhg-1 and 155 mAhg-1 for FePO4 and FePO4/MWCNTs composite,

RI PT

respectively. The increase of capacity is attributed to the electrochemical activation process during the charge and discharge. Yong Yang et al. [72]also found the similar

FePO4 FePO4/MCNTs

1C

M AN U

180

SC

200 160 140 120 100 80 60 40 20 0

20

40

EP

0

TE D

-1 Discharg specific capacity (mAhg )

phenomenon in the FePO4 cathode for lithium-ions batteries.

60

80 100 120 140 160 180 200 Cycle numbers

AC C

Fig. 7 Cycling performance of the pure FePO4 and FePO4/MWCNTs at 1 C.

In addition, the cycling stability of the pure FePO4 and FePO4/MWCNTs

composite is excellent, and their discharge specific capacity obtain 85 mAhg-1 and 155 mAhg-1 over 200 cycles, respectively. The coulombic efficiency approached near 97% for all cycles, indicating an excellent cycling stability and reversibility. From the above results, it is easy to find that FePO4/MWCNTs composite has excellent cycling performance. 16

ACCEPTED MANUSCRIPT Electrode materials/C (common carbon, CNT and graphene) composite are effective ways to enhance the low electron conductivity of electrode materials.[73] However, the effects on the performance of the cathode materials are different due to

RI PT

their different conductivity and structures. For the cathode materials/common carbon composite, the carbon is coated on the surface of particles, forming the core-shell structure, which only acts as a conductive agent; for the cathode materials/ graphene

SC

composite, the particles are loaded onto their surfaces, which only improves a large

M AN U

reaction interface and acts as a conductive agent. For the FePO4/MWCNTs composite in this work, the FePO4 particles were loaded onto the surface of the MWCNTs, forming a conductive network structure of 3D-core-shell. In the 3D-core-shell structure, the MWCNTs not only acts as a conductive agent and proving a larger

TE D

reaction interface, but also proves the fast electron transfer tunnels and lithium ions diffusion paths (shown as in Fig. 1). The FePO4/MWCNTs core-shell structure composite has a better conductivity and lithium ions diffusion coefficient. Okada et

EP

al.[74] reported that carbon-coated amorphous FePO4 via mechanical ball milling

AC C

improved the specific capacity by about 35% with high rate capability. However, compared with the pure FePO4 electrode, the FePO4/MWCNTs electrode improved the specific capacity by over 300% with high rate of 10 C. although the carbon-coated method can effectively enhance the conductivity of the FePO4, this method can not facilitate the ions diffusion in the electrode materials. By contrast, the FePO4/MWCNTs composite not only can effectively enhance the electronic conductivity, but also lithium ions diffusion of the electrode materials. In addition, 17

ACCEPTED MANUSCRIPT this method of carbon-coated amorphous FePO4 via mechanical ball milling is difficult for realizing uniform carbon coating onto the FePO4 particles.

RI PT

4. Conclusions In conclusion, the FePO4/MWCNTs composite with a cylindrical core-shell 3D conductive network structure have been prepared via a facile micro-emulsion

SC

technique. The amorphous FePO4 nanoparticle shell coated onto the surface of the

M AN U

MWCNTs provides fast pathway for the transportation of lithium ions and the core of the MWCNTs facilitates the electronic transfer. Consequently, the FePO4/MWCNTs composite exhibits an excellent dynamic performance with a discharge capacity as high as 110 mAhg-1 at 10 C and along with a superior cycling stability with capacity

Acknowledgements

TE D

retention over 100% after 200 cycles at 1C.

EP

This work has been carried out with the financial support of the Project of

AC C

Shanghai Science & Technology Commission (13NM1401400), the Project of Ability Development of Shanghai Science & Technology Commission (09230501400), and the Research Foundation of the Ministry of Education (No. 2050255).

References [1] G.Z. Ren, G.Q. Ma, N. Cong, Review of electrical energy storage system for vehicular applications, Renew Sust. Energ. Rev. 41 (2015) 225-236. [2] J.B. Goodenough, K.-S. Park, The Li-Ion Rechargeable Battery: A Perspective, J. 18

ACCEPTED MANUSCRIPT Am. Chem. Soc. 135 (2013) 1167-1176. [3] C. Liang, M. Gao, H. Pan, Y. Liu, M. Yan, Lithium alloys and metal oxides as high-capacity anode materials for lithium-ion batteries, J. Alloys Compd. 575 (2013) 246-256.

RI PT

[4] Z.G. Yang, J.L. Zhang, M.C.W. Kintner-Meyer, X.C. Lu, D.W. Choi, J.P. Lemmon, J. Liu, Electrochemical Energy Storage for Green Grid, Chem. Rev. 111 (2011) 3577-3613.

[5] Y.X. Wang, B. Liu, Q.Y. Li, S. Cartmell, S. Ferrara, Z.Q.D. Deng, J. Xiao, Lithium

SC

and lithium ion batteries for applications in microelectronic devices: A review, J. Power Sources 286 (2015) 330-345.

M AN U

[6] S. Balaji, D. Mutharasu, N. Sankara Subramanian, K. Ramanathan, A review on microwave synthesis of electrode materials for lithium-ion batteries, Ionics 15 (2009) 765-777.

[7] A. Barre, B. Deguilhem, S. Grolleau, M. Gerard, F. Suard, D. Riu, A review on lithium-ion battery ageing mechanisms and estimations for automotive applications, J.

TE D

Power Sources 241 (2013) 680-689.

[8] Q. T.Wang, R.R. Li, X. Z. Zhou, J.Li, Z. Q. Lei, Polythiophene-coated nano-silicon composite anodes with enhanced performance for lithium-ion batteries, J.

EP

Alloys Compd. 20 (2016) 1331-1336.

[9] F. Fathollahi, M. Javanbakht, H. Omidvar, M. Ghaemi, Improved electrochemical properties of LiFePO4/graphene cathode nanocomposite prepared by one-step

AC C

hydrothermal method, J. Alloys Compd. 627 (2015) 146-152. [10] J. Zhu, Y.Lu, C.Chen, Y.Ge, S.Jasper, J.D.Leary, Porous one-dimensional carbon/iron oxide composite for rechargeable lithium-ion batteries with high and stable capacity, J. Alloys Compd. 672(2016) 79-85. [11] D.E. Demirocak, B. Bhushan, Probing the aging effects on nanomechanical properties of a LiFePO4 cathode in a large format prismatic cell, J. Power Sources 280 (2015) 256-262. [12] F.Y. Jin, Y. Wang, Topotactical conversion of carbon coated Fe-based electrodes on graphene aerogels for lithium ion storage, J. Mater. Chem. A 3 (2015) 19

ACCEPTED MANUSCRIPT 14741-14749. [13] J.H. Wang, M.X. Gao, H.G. Pan, Y.F. Liu, Z. Zhang, J.X. Li, Q.M. Su, G.H. Du, M. Zhu, L.Z. Ouyang, C.X. Shang, Z.X. Guo, Mesoporous Fe2O3 flakes of high aspect ratio encased within thin carbon skeleton for superior lithium-ion battery

RI PT

anodes, J. Mater. Chem. A 3 (2015) 14178-14187. [14] Y.H. Yin, M.X. Gao, J.L. Ding, Y.F. Liu, L.K. Shen, H.G. Pan, A carbon-free LiFePO4 cathode material of high-rate capability prepared by a mechanical activation method, J. Alloys Compd. 509 (2011) 10161-10166.

SC

[15] P. Wang, M.X. Gao, H.G. Pan, J.L. Zhang, C. Liang, J.H. Wang, P. Zhou, Y.F. Liu, A facile synthesis of Fe3O4/C composite with high cycle stability as anode material

M AN U

for lithium-ion batteries, J. Power Sources 239 (2013) 466-474.

[16] J.H. Wang, M.X. Gao, D.S. Wang, X. Li, Y.B. Dou, Y.F. Liu, H.G. Pan, Chemical vapor deposition prepared bi-morphological carbon-coated Fe3O4 composites as anode materials for lithium-ion batteries, J. Power Sources 282 (2015) 257-264. [17] R.J. Ma, Y.F. Liu, Y.X. Yang, K.C. Pu, M.X. Gao, H.G. Pan, Li-Si-alloy-assisted

TE D

improvement in the intrinsic cyclability of Mg2Si as an anode material for Li-ion batteries, Acta Mater. 98 (2015) 128-134.

[18] D.S. Wang, M.X. Gao, H.G. Pan, J.H. Wang, Y.F. Liu, High performance

EP

amorphous-Si@SiOx/C composite anode materials for Li-ion batteries derived from ball-milling and in situ carbonization, J. Power Sources 256 (2014) 190-199. [19] D.S. Wang, M.X. Gao, H.G. Pan, Y.F. Liu, J.H. Wang, S.Q. Li, H.W. Ge,

AC C

Enhanced cycle stability of micro-sized Si/C anode material with low carbon content fabricated via spray drying and in situ carbonization, J. Alloys Compd. 604 (2014) 130-136.

[20] Y.F. Liu, R.J. Ma, Y.P. He, M.X. Gao, H.G. Pan, Synthesis, Structure Transformation, and Electrochemical Properties of Li2MgSi as a Novel Anode for Li-Ion Batteries, Adv. Funct. Mater. 24 (2014) 3944-3952. [21] R.J. Ma, Y.F. Liu, P. Yan, M.X. Gao, H.G. Pan, A facile method for determining a suitable voltage window for an amorphous Li12Si7 anode, Electrochim. Acta 129 (2014) 373-378. 20

ACCEPTED MANUSCRIPT [22] R.J. Ma, Y.F. Liu, Y.X. Yang, M.X. Gao, H.G. Pan, Mg2Si anode for Li-ion batteries: Linking structural change to fast capacity fading, Appl. Phys. Lett. 105 (2014) 213901 - 213901-4. [23] M.J. Wang, X. Li, M.X. Gao, H.G. Pan, Y.F. Liu, A Novel synthesis of MgS and

RI PT

its application as electrode material for lithium-ion batteries, J. Alloys Compd. 603 (2014) 158-166.

[24] M.X. Gao, D.S. Wang, X.Q. Zhang, H.G. Pan, Y.F. Liu, C. Liang, C.X. Shang, Z.X. Guo, A hybrid Si@FeSiy/SiOx anode structure for high performance lithium-ion

SC

batteries via ammonia-assisted one-pot synthesis, J. Mater. Chem. A 3 (2015) 10767-10776.

M AN U

[25] Y.P. He, Y.F. Liu, R.J. Ma, M.X. Gao, H.G. Pan, Synthesis temperature dependence of the structural and electrochemical properties of Mg2Si anodic materials prepared via a hydrogen-driven chemical reaction, Ionics 21 (2015) 2439-2445. [26] Y.F. Liu, P. Yan, R.J. Ma, M.X. Gao, H.G. Pan, Electrochemical properties of the ternary alloy Li5AlSi2 synthesized by reacting LiH, Al and Si as an anodic material for

TE D

lithium-ion batteries, J. Power Sources 283 (2015) 54-60.

[27] H.Tang, L.Zan, J.Zhu, Y.Ma, N.Zhao, Z.Tang, High rate capacity nanocomposite lanthanum oxide coated lithium zinc titanate anode for rechargeable lithium-ion

EP

battery. J. Alloys Compd. 667(2016) 82-90. [28] J. Liu, C.Q. Du, Y.Q. Lin, Z.Y. Tang, X.H. Zhang, Synthesis and performance of LiVTiO4/C as a new anode material for lithium-ion battery, J. Alloys Compd. 622

AC C

(2015) 250-253.

[29] H. Iddir, B. Key, F. Dogan, J.T. Russell, B.R. Long, J. Bareno, J.R. Croy, R. Benedek,

Pristine-state

structure

of

lithium-ion-battery

cathode

material

Li1.2Mn0.4Co0.4O2 derived from NMR bond pathway analysis, J. Mater. Chem. A 3 (2015) 11471-11477. [30]

R.Yang,

L.Wang,

K.Deng,

M.Lv,

Y.Xu,

A

facile

synthesis

of

Li2Fe1/3Mn1/3Ni1/3SiO4/C, composites as cathode materials for lithium-ion batteries, J. Alloys Compd. 676(2016), 260-264. [31] J.F. Wu, H.G. Liu, X.H. Ye, J.P. Xia, Y. Lu, C.W. Lin, X.W. Yu, Effect of Nb 21

ACCEPTED MANUSCRIPT doping on electrochemical properties of LiNi1/3Co1/3Mn1/3O2 at high cutoff voltage for lithium-ion battery, J. Alloys Compd. 644 (2015) 223-227. [32] C.B. Zhu, X.K. Mu, P.A. van Aken, J. Maier, Y. Yu, Fast Li Storage in MoS2-Graphene-Carbon

Nanotube Nanocomposites:

Advantageous

Functional

RI PT

Integration of 0D, 1D, and 2D Nanostructures, Adv. Energy Mater. 5 (2015) 9-15. [33] Z.Q. Wang, X. Li, H. Xu, Y. Yang, Y.J. Cui, H.G. Pan, Z.Y. Wang, B.L. Chen, G.D. Qian, Porous anatase TiO2 constructed from a metal-organic framework for advanced lithium-ion battery anodes, J. Mater. Chem. A 2 (2014) 12571-12575.

SC

[34] M.S.K. Mutyala, J.Z. Zhao, J.Y. Li, H.G. Pan, C. Yuan, X.C. Li, In-situ temperature measurement in lithium ion battery by transferable flexible thin film

M AN U

thermocouples, J. Power Sources 260 (2014) 43-49.

[35] Y.H. Yin, M.X. Gao, H.G. Pan, L.K. Shen, X. Ye, Y.F. Liu, P.S. Fedkiw, X.W. Zhang, High-rate capability of LiFePO4 cathode materials containing Fe2P and trace carbon, J. Power Sources 199 (2012) 256-262.

[36] W.J. Zhang, Structure and performance of LiFePO4 cathode materials: A review,

TE D

J. Power Sources 196 (2011) 2962-2970.

[37] K.Zhu, Y.Zhang, H.Qiu, Y.Meng, Y.Gao, X.Meng, Hierarchical Fe3O4 microsphere/reduced graphene oxide composites as a capable anode for lithium-ion

EP

batteries with remarkable cycling performance, J. Alloys Compd. 675(2016) 399-406. [38] M.X. Gao, Y. Lin, Y.H. Yin, Y.F. Liu, H.G. Pan, Structure optimization and the structural factors for the discharge rate performance of LiFePO4/C cathode materials,

AC C

Electrochim. Acta 55 (2010) 8043-8050. [39] A. Padhi, K. Nanjundaswamy, C. Masquelier, S. Okada, J. Goodenough, Effect of structure on the Fe3+/Fe2+ redox couple in iron phosphates, J. Electrochem. Soc. 144 (1997) 1609-1613.

[40] Z.C. Shi, Y.X. Li, W.L. Ye, Y. Yang, Mesoporous FePO4 with enhanced electrochemical performance as cathode materials of rechargeable lithium batteries, Electrochem. Solid St. 8 (2005) A396-A399. [41] S.J. Xu, S.M. Zhang, J.X. Zhang, T. Tan, Y. Liu, A maize-like FePO4@MCNT nanowire composite for sodium-ion batteries via a microemulsion technique, J. Mater. 22

ACCEPTED MANUSCRIPT Chem. A 2 (2014) 7221-7228. [42] T. Shiratsuchi, S. Okada, J. Yamaki, T. Nishida, FePO4 cathode properties for Li and Na secondary cells, J. Power Sources 159 (2006) 268-271. [43] S.M. Zhang, J.X. Zhang, S.J. Xu, X.J. Yuan, B.C. He, Li ion diffusivity and

RI PT

electrochemical properties of FePO4 nanoparticles acted directly as cathode materials in lithium ion rechargeable batteries, Electrochim. Acta 88 (2013) 287-293.

[44] S.W. Kim, J. Ryu, C.B. Park, K. Kang, Carbon nanotube-amorphous FePO4 core-shell nanowires as cathode material for Li ion batteries, Chem. Commun. (Camb.)

SC

46 (2010) 7409-7411.

[45] C.L. Li, Z.W. Fu, Kinetics of Li+ ion diffusion into FePO4 and FePON thin films

M AN U

characterized by AC impedance spectroscopy, J. Electrochem. Soc. 154 (2007) A784-A791.

[46] Y. Song, P.Y. Zavalij, M. Suzuki, M.S. Whittingham, New iron (III) phosphate phases: Crystal structure and electrochemical and magnetic properties, Inorg. Chem. 41 (2002) 5778-5786.

TE D

[47] Y. Song, S. Yang, P.Y. Zavalij, M.S. Whittingham, Temperature-dependent properties of FePO4 cathode materials, Mater. Res. Bull. 37 (2002) 1249-1257. [48] Z. Shi, Y. Li, W. Ye, Y. Yang, Mesoporous FePO4 with Enhanced Electrochemical

EP

Performance as Cathode Materials of Rechargeable Lithium Batteries, Electrochem. Solid-State Lett. 8 (2005) A396. [49] Y. Liu, Y. Xu, X. Han, C. Pellegrinelli, Y. Zhu, H. Zhu, J. Wan, A.C. Chung, O.

AC C

Vaaland, C. Wang, L. Hu, Porous Amorphous FePO4 Nanoparticles Connected by Single-Wall Carbon Nanotubes for Sodium Ion Battery Cathodes, Nano Lett. 12 (2012) 5664-5668.

[50] S. Okada, T. Yamamoto, Y. Okazaki, J.-i. Yamaki, M. Tokunaga, T. Nishida, Cathode properties of amorphous and crystalline FePO4, J. Power Sources 146 (2005) 570-574. [51] Y.-S. Hong, K.S. Ryu, Y.J. Park, M.G. Kim, J.M. Lee, S.H. Chang, Amorphous FePO4 as 3 V cathode material for lithium secondary batteries, J. Mater. Chem. 12 (2002) 1870-1874. 23

ACCEPTED MANUSCRIPT [52] B. Abeles, T. Tiedje, Amorphous semiconductor superlattices, Phys. Rev. Lett. 5 (1989) 473-480. [53] V. Meunier, J. Kephart, C. Roland, J. Bernholc, Ab initio investigations of lithium diffusion in carbon nanotube systems, Phys. Rev. Lett. 88 (2002)

RI PT

075506-075506 [54] P. Axmann, C. Stinner, M. Wohlfahrt-Mehrens, A. Mauger, F. Gendron, C. Julien, Nonstoichiometric LiFePO4: defects and related properties, Chem. Mater. 21 (2009) 1636-1644.

SC

[55] C. Gerbaldi, G. Meligrana, S. Bodoardo, A. Tuel, N. Penazzi, FePO4 nanoparticles supported on mesoporous SBA-15: Interesting cathode materials for

M AN U

Li-ion cells, J. Power Sources 174 (2007) 501-507.

[56] Q. Shi, R.Z. Hu, L.Z. Ouyang, M.Q. Zeng, M. Zhu, High-capacity LiV3O8 thin-film cathode with a mixed amorphous-nanocrystalline microstructure prepared by RF magnetron sputtering, Electrochem. Commun. 11 (2009) 2169-2172. [57] J. Hu, J. Xie, X. Zhao, H. Yu, X. Zhou, G. Cao, J. Tu, Doping Effects on

TE D

Electronic Conductivity and Electrochemical Performance of LiFePO4, J. Mater. Sci. Techn. 25 (2009) 405-409.

[58] J. Yang, J. Wang, Y. Tang, D. Wang, B. Xiao, X. Li, R. Li, G. Liang, T.-K. Sham,

EP

X.A. Sun, In-situ Self-catalyzed Formation of Core-shell LiFePO4@ CNTs Nanowire for High Rate Performance Lithium-ion Batteries, J. Mater. Chem. A (2013) 7306-7311.

AC C

[59] Y. Yin, M. Gao, J. Ding, Y. Liu, L. Shen, H. Pan, A carbon-free LiFePO4 cathode material of high-rate capability prepared by a mechanical activation method, J. Alloys Compd. 509 (2011) 10161-10166. [60] L. Ouyang, L. Guo, W. Cai, J. Ye, R. Hu, J. Liu, L. Yang, M. Zhu, Facile synthesis of Ge@FLG composites by plasma assisted ball milling for lithium ion battery anodes, J.Mater.Chem.A 2 (2014) 11280-11285. [61] L.Z. Ouyang, Z.J. Cao, L.L. Li, H. Wang, J.W. Liu, D. Min, Y.W. Chen, F.M. Xiao, R.H. Tang, M. Zhu, Enhanced high-rate discharge properties of La11.3Mg6.0Sm 7.4Ni61.0Co7.2Al7.1

with added graphene synthesized by plasma milling, Int. J. 24

ACCEPTED MANUSCRIPT Hydrogen Energy 39 (2014) 12765-12772. [62] Y. Lin, M.X. Gao, D. Zhu, Y.F. Liu, H.G. Pan, Effects of carbon coating and iron phosphides on the electrochemical properties of LiFePO4/C, J. Power Sources 184 (2008) 444-448.

RI PT

[63] J.L. Fan, H.G. Pan, M.X. Gao, Y. Lin, J.Q. Liu, Synthesis and performance of LiFePO4/C prepared by nonaqueous sol-gel method, J Inorg. Mater. 22 (2007) 1032-1036.

[64] F. Croce, A. D’Epifanio, P. Reale, L. Settimi, B. Scrosati, Ruthenium

SC

oxide-added quartz iron phosphate as a new intercalation electrode in rechargeable lithium cells, J. Electrochem. Soc. 150 (2003) A576-A581.

M AN U

[65] Y. Yin, Y. Hu, P. Wu, H. Zhang, C. Cai, A graphene–amorphous FePO4 hollow nanosphere hybrid as a cathode material for lithium ion batteries, Chem. Commun. 48 (2012) 2137-2139.

[66] A. Fedorková, H.D. Wiemhöfer, R. Oriňáková, A. Oriňák, D. Kaniansky, Surface modification of FePO4 particles with conductive layer of polypyrrole, Solid State Sc.

TE D

12 (2010) 924-928.

[67] Z.Q. Jiang, Z.J. Jiang, Effects of carbon content on the electrochemical performance

of

LiFePO4/C

core/shell

nanocomposites

fabricated

using

EP

FePO4/polyaniline as an iron source, J. Alloys Compd. 537 (2012) 308-317. [68] W.H. Zuo, C. Wang, Y.Y. Li, J.P. Liu, Directly Grown Nanostructured Electrodes for High Volumetric Energy Density Binder-Free Hybrid Supercapacitors: A Case

AC C

Study of CNTs//Li4Ti5O12, Sci. Rep. 5 (2015) 7780-7780. [69] B. Zou, Y. Wang, S. Zhou, Spray drying-assisted synthesis of LiFePO4/C composite microspheres with high performance for lithium-ion batteries, Mater. Lett. 92 (2013) 300-303.

[70] Y. Zhou, J. Wang, Y. Hu, R. O’Hayre, Z. Shao, A porous LiFePO4 and carbon nanotube composite, Chem. Commun. 46 (2010) 7151-7153. [71] A.K. Schaper, M.S. Wang, Z. Xu, Y. Bando, D. Golberg, Comparative Studies on the Electrical and Mechanical Behavior of Catalytically Grown Multiwalled Carbon Nanotubes and Scrolled Graphene, Nano Lett. 11 (2011) 3295-3300. 25

ACCEPTED MANUSCRIPT [72] X.M. Liu, Z.D. Huang, S.W. Oh, B. Zhang, P.C. Ma, M.M.F. Yuen, J.K. Kim, Carbon nanotube (CNT)-based composites as electrode material for rechargeable Li-ion batteries: A review, Compos. Sci. Technol. 72 (2012) 121-144. [73] Y. Wang, L. Yang, R. Hu, W. Sun, J. Liu, L. Ouyang, B. Yuan, H. Wang, M. Zhu,

layered graphene, J. Power Sources 288 (2015) 314-319.

RI PT

A stable and high-capacity anode for lithium-ion battery: Fe2O3 wrapped by few

[74] S. Okada, T. Yamamoto, Y. Okazaki, J.I. Yamaki, M. Tokunaga, T. Nishida, Cathode properties of amorphous and crystalline FePO4, J. Power Sources 146 (2005)

AC C

EP

TE D

M AN U

SC

570-574.

26

ACCEPTED MANUSCRIPT

RI PT

SC M AN U




TE D




EP




The cylindrical FePO4/MCNTs core-shell composite is synthesized by a micro-emulsion method. The micro-emulsion uses to disperse the MCNTs and synthesize nano-sized FePO4. The FePO4/MCNTs composite cathode exhibits high specific capacity and cycling performance. The 3D conductive network enhances the high rate performance of the FePO4/MCNTs cathode.

AC C