Effect of molybdenum substitution on electrochemical performance of Li[Li0.2Mn0.54Co0.13Ni0.13]O2 cathode material

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Effect of molybdenum substitution on electrochemical performance of Li[Li0.2Mn0.54Co0.13Ni0.13]O2 cathode material ⁎

Wei Pana, Wenjie Penga, , Huajun Guoa, Jiexi Wanga,b, Zhixing Wanga, Hangkong Lib, ⁎ Kaimin Shihb, a b

School of Metallurgy and Environment, Central South University, Changsha 410083, China Department of Civil Engineering, The University of Hong Kong, Hong Kong, China

A R T I C L E I N F O

A BS T RAC T

Keywords: Lithium ion battery Cathode material Li-rich Mo doping

Molybdenum doping is introduced to improve the electrochemical performance of lithium-rich manganesebased cathode material. X-ray diffraction (XRD) results illustrate that the crystallographic parameters a, c and lattice volume V become larger with the increase of Mo content. The scanning electron microscope (SEM) shows that the molybdenum substitution increases the crystallinity of the primary particles. When evaluated as cathode material, the as-prepared Li[Li0.2Mn0.54-x/3Ni0.13-x/3Co0.13-x/3Mox]O2 (x = 0.007) delivers a discharge capacity of 155.5 mA h g−1 at 5 C (1 C = 250 mA g−1) and exhibits the capacity retention of 81.8% at 1 C after 200 cycles. The results of cyclic voltammetry (CV) and electronic impedance spectroscopy (EIS) tests reflect that the molybdenum substitution is able to significantly reduce the electrode polarization and lower the chargetransfer resistance. Within appropriate amount of Mo doping, the lithium ion diffusion coefficient of the material can reach to 8.92 × 10–15 cm2 s−1, which is ~ 30 times higher than that of pristine materials (2.65 × 10– 16 cm2 s−1).

1. Introduction The environmental pollutions and fossil fuel shortage promote the development of clean energy [1–4]. Lithium ion batteries (LIBs) have received worldwide attention as power sources for electric vehicles (EVs), plug-in hybrid vehicle (PHEV) and portable energy storage [5]. With the exigent demands for materials with high energy density and large capacity, traditional cathode materials seem unable to satisfy the need of next generation LIBs. The lithium-rich and manganese-base (LRM) layered structure cathode materials [xLi2MnO3·(1-x)LiMO2, M = Ni, Co, Mn or combinations] have been considered as an excellent alternative because of much higher discharge capacity (> 250 mA h g−1) compared to conventional positive materials like LiCoO2, LiFePO4, etc [6–8]. The crystal structure of lithium-rich and manganese-based (LRM) cathode materials is generally considered to be composed of a rhombohedral LiMO2 component with R-3m structure and a monoclinic Li2MnO3 component with C2/m structure [9]. However, the LRM cathode materials suffer from large initial capacity loss, which is ascribed to the formation of Li2O when the charge cutoff voltage exceeds 4.5 V [10]. In addition, the rate capability is unsatisfactory due to the low lithium ion diffusion coefficient and poor electrical conductivity. Worse still, this kind of materials show the

⁎

limited cycle life and undesirable voltage fade owing to the extensive lithium ion removal and the oxygen extraction at high voltage [11]. The voltages of LRM cathodes exceeding 4.5 V (vs Li+/Li) are often high enough to oxidize the alkyl carbonates and accelerate migration of transition metal (TM) ions from TM sites to neighboring Li vacancies, causing irreversible layered to spinel phase transformation [12,13]. Different strategies, such as improved synthetic method [8,14–19], lattice doping [20–22], surface modification [23–30] and structure designing [31,32], have been proposed to optimize the electrochemical performance of layered cathode materials. Among these, the use of lattice doping has been proved to be one of the most promising methods for inhibiting the TM ions migration to Li-Layer during long-term cycling (or improving its reversibility). This method may alter the electronic structure of the material, enhance the c-lattice parameter to improve rate capabilities and realize the pillar effect to stabilize the crystal structure of the material. Chen et al. reported that zirconium doping could accelerate the diffusion of lithium ions in the bulk LRM cathode materials by stabilizing the layered structure and enlarging the lattice parameters [22]. Zhen et al. proposed that a very small amount of K+ might reduce the formation of trivacancies in Li layers and hamper the migration of TM ions to Li layers [33]. In addition, the substitution of F- for O2- has been validated to be an

Corresponding authors. E-mail addresses: [email protected] (W. Peng), [email protected] (K. Shih).

http://dx.doi.org/10.1016/j.ceramint.2017.07.232 Received 6 July 2017; Received in revised form 28 July 2017; Accepted 31 July 2017 0272-8842/ © 2017 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Please cite this article as: Pan, W., Ceramics International (2017), http://dx.doi.org/10.1016/j.ceramint.2017.07.232

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Fig. 1. XRD patterns and enlarged XRD patterns in selected 2θ range of as-prepared samples.

was used in the 2θ range of 10–80° at a scan rate of 5° min−1. The detailed morphology and composition of the samples were observed via scanning electron microscopy (SEM, JEOL 5612LV) equipped with energy-dispersive X-ray spectrometer (EDAX).

effective way to stabilize the structural stability and mitigate the voltage fade of LRM cathode materials [34]. Substitution of molybdenum has also been widely investigated in anode materials [35–37]. Molybdenum doping is generally considered to increase the stability of the crystal structure during the cycling process. Since Mo6+ radius is larger than TM (Ni2+, Mn4+) ions radius and the bond dissociation energy of Mo-O is stronger than that of M-O (M=Li, Ni, Co and Mn), it is reasonable to use Mo as an ideal dopant for improving the structural stability of LRM cathode materials, hence enhancing its electrochemical performance. Inspired by the Mo-doping idea, a series of Mo doped LRM materials, Li[Li0.2Mn0.54-x/3Ni0.13-x/3Co0.13-x/3Mox]O2 (x = 0, 0.002, 0.005, 0.007, 0.015), are synthesized by a typical co-precipitation and a two-step high temperature calcination. The effects of molybdenum substitution on the lattice structure, morphology, electrochemical performance, and electrode kinetics are systematically investigated within this work.

2.3. Electrochemical measurements The electrochemical properties of the materials were evaluated by a CR2025 coin-type cell with lithium foil as a counter electrode and reference electrode. The working electrode was prepared by coating slurry, a mixture of as-prepared samples (80 wt%) as active materials, acetylene black (10 wt%) as conductive agent and polyvinylidene fluoride (PVDF) (10 wt%) as binder within NMP, onto aluminum foils and dried overnight at 120 °C. A porous polypropylene film was used as separator. The electrolyte was composed of 1 M LiPF6 dissolved in a mixed organic solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (1:1:1 in volume ratio). The coin-type cells were assembled in an Ar-filled glove box. Galvanostatic charge-discharge test of the as-prepared coin cells were conducted between 2.0 and 4.6 V (vs. Li/Li+) using LAND CT2001A battery testing system. The cyclic voltammetry (CV) was recorded by CHI1000c electrochemical work station between 2.0 V and 4.6 V at a scanning rate of 0.1 mV s−1. Electrochemical impedance spectroscopy (EIS) measurement was carried out in the frequency range from 0.01 Hz to 100 kHz with the sinusoidal voltage signal of 5 mV in amplitude as the perturbation by CHI660A electrochemical work station at room temperature. Before ESI tests, the cells were precycled for three times.

2. Experimental 2.1. Sample preparations The pristine Li1.2[Mn0.54Co0.13Ni0.13]O2 powders were prepared by a typical co-precipitation followed by two-step calcination method. For precursor preparation, the transition metal sulfates MnSO4·H2O (Xi long Group, 99%, China), NiSO4·6H2O (Xi long Group, 98%, China) and CoSO4·7H2O (Xi long Group, 99%, China) were dissolved in deionized water with the molar ratio of 4:1:1 to form a 1 M aqueous solution. 1 M solution of Na2CO3 (precipitator), 0.8 M solution of NH4HCO3 (chelating agent) and the solution of transition metal sulfates were separately pumped into a tank reactor in the inert atmosphere. In this reaction process, the temperature and pH value of the mixture were maintained at 55 °C and 8.5, respectively. The obtained carbonate precipitate was centrifuged and vacuum-dried at 120 °C overnight. To prepare the Modoped LRM cathode materials, an appropriate amount of nano MoO3 (Chemical Reagent, 99.6%, China) was mixed and blended thoroughly with Li2CO3 (3% excess), and carbonate precursor in an agate mortar. The mixed powder was calcined at 500 °C for 5 h, followed by 900 °C for 15 h in air at a heating rate of 5 °C min−1. After cooled to room temperature, a series of Li[Li0.2Mn0.54-x/3Ni0.13-x/3Co0.13-x/3Mox]O2 (x = 0, 0.002, 0.005, 0.007, 0.015) samples were obtained and denoted by M0, M1, M2, M3 and M4 in sequence.

3. Results and discussion 3.1. Material characterizations Fig. 1 shows the XRD patterns of as-prepared materials, all of which show high crystallinity degree as we can see sharp characterized peaks. The Bragg diffraction peaks are indexed to the typical hexagonal layered α-NaFeO2 structure (space group: R-3m). The clear split of (006)/(102) and (108)/(110) peaks imply a highly ordered layered structure of the samples [38]. Besides, the broad peaks in the 2θ range of 20–25° are the characteristics of Li2MnO3 structure which belongs to a space group C2/m. There is no obvious evidence for the existence of secondary phase when x < 0.007. Nevertheless, when the doping amount of Mo increase to 0.015, an impurity phase (Li2MoO4 was marked as ♣) can be detected. This result shows that x = 0.015 is an extreme value for Mo substitution to avoid the secondary phase. It has been reported that the layered structure and cation disorder could be measured indirectly by the intensity ratio of (003) to (104) and lattice

2.2. Material characterizations To characterize the crystallographic phase of as-prepared samples, X-ray diffractometer (Rigaku Rint2000) with Cu Kα radiation source 2

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(M1, M2, M3, M4) samples at a current density of 0.1 C (25 mA g−1) between 2.0 and 4.6 V. All cells experience a typical two-step profile during the initial charge process. The first plateau around 4.0 V can be ascribed to extraction process of Li+ from the layered structure accompanied by Ni2+/Co3+ oxidation in the materials. The second plateau above 4.5 V corresponds to the activation of Li2MnO3. The initial charge capacities for M0, M1, M2, M3 and M4 are 330, 318, 314, 324 and 310 mA h g−1, respectively. Accordingly, the discharge capacities are 265, 259, 253, 260 and 252 mA h g−1, hence the initial coulombic efficiency of 80.1%, 81.3%, 80.6%, 80.4% and 81.3%. Compared to the pristine material, the discharge capacity of Mo doped electrodes shows a decrease trend, which can be ascribed to the electrochemical inactive Mo6+. The cycle performance of the cells at 1 C is shown in Fig. 4b. It can be seen that all electrodes have capacity fade in different extent. The M3 retains a high discharge capacity of 181 mA h g−1 after 200 cycles at 1 C, showing outstanding capacity retention of 81.8%, while the pristine sample (M0) only manages to main 144 mA h g−1 with the capacity retention of 75.4%. Although the Mo-doping is beneficial to improve the cycling stability, it is worth to visit the Li diffusion of the as-prepared samples. Fig. 5 shows the rate capability of the samples with and without Modoping. The discharge capacity of both cells decreases with the increasing of current density. It should be noted that the discharge capacity is lower at 0.1 C for Mo-doped samples, while they are able to achieve higher capacity at higher current density compared to the pristine material except M4 sample. These electrochemical data indicate that the Li+ transmission in Mo-doped sample is enhanced. This phenomenon can be attributed to the enlarged interplanar spacing and reduced activation barrier for Li+ diffusion with slight Mo doping, similar phenomena can be seen in other reports [41,42]. Obviously, the M3 exhibits best rate capability than others. In order to investigate the kinetic properties of the prepared samples, the electrochemical impedance spectroscopy (EIS) measurement was conducted [43]. The results are shown in Fig. 6. Before the measurement, electrodes were galvanostatically charged and discharged for three cycles between 2.0 and 4.6 V at low rate of 0.1 C. The Nyquist plots (Fig. 6a) consist of two parts, a depressed semicircle in the high-frequency region and an inclined straight line in the low-

Table 1 The crystallographic parameters of all the samples. Samples

a (Å)

c (Å)

c/a

V (Å3)

I

M0 M1 M2 M3 M4

2.8511 2.8489 2.8528 2.8527 2.8513

14.2148 14.2092 14.2357 14.2375 14.2189

4.9857 4.9877 4.9899 4.9908 4.9889

99.87 100.03 100.07 100.34 100.38

1.7282 1.8564 1.8641 1.9168 1.7934

(003)/I (104)

parameter ratio c to a [39]. Table 1 summarizes the lattice parameters and I(003/104) of pristine and Mo-doped samples. The rate of Ni2+ will increase with the increase of Mo6+, which results in a slight increase of the lattice parameters as the ionic radius of Ni2+(0.69 Å) and Mo6+(0.59 Å) are greater than those of Ni3+(0.56 Å) and Mn4+(0.53 Å). The calculated value of I(003/104) (> 1.2) and c/a (> 4.9) for all samples reflect good crystalline structure [38,40]. In addition, the increased ratio of c/a after Mo doping indicates that the layered structure has been meliorated. Therefore, we can come to a conclusion that the moderate Mo substitution is effective for stabilizing the lattice structure of the LRM cathode material on the basis of structural analysis. Fig. 2 shows the typical morphologies of M0, M1, M2, M3 and M4. The morphology of all samples is spherical, and the surface of particles gradually become smoother as the molybdenum content increases, which indicates that molybdenum doping is conducive to the aggregation of the primary particles. As can be seen from Fig. 3, EDS elements mapping of sample M3 presents that the transition metal elements, especially Mo elements are uniformly distributed in the Mo-doped samples. It is well in accordance with the XRD results, confirming that Mo ions are introduced into LMR structure without forming the secondary phase.

3.2. Electrochemical performance To evaluate the effect of Mo-doping on the electrochemical properties of prepared LRM cathode materials, galvanostatic test was carried out. Fig. 4a shows the first cycle profiles of pristine (M0) and Mo-doped

Fig. 2. SEM images of as-prepared samples.

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Fig. 3. EDS elemental mapping of the M3 sample.

Fig. 4. (a) Initial charge-discharge curves and (b) cyclic performance of as-prepared samples.

frequency region. The semicircle in the high-frequency region could be indexed with the charge-transfer resistance (Rct), which corresponds to the resistance at the interface of electrode/electrolyte. From the inclined line in the low-frequency region, lithium ion diffusivity (DLi+) can be calculated using a certain equation [44,45]. The detailed values of resistance could be obtained from fitting result, which are summarized in Table 2. From the fitting results, Rct of M3 corresponded to 114.4 Ω, which is much smaller than that of M0 (225.7 Ω). This result indicates that lithium ion transfer is much easier inside Modoped LRM electrode. In addition, the lithium ion diffusion coefficient of all samples are calculated from the inclined line in the low-frequency region by the following equation [30].

D = 0.5(

RT 2 ) AF 2δωC

(1) −1

−1

In Eq. (1), R is gas constant (8.3143 J mol K ), T is absolute temperature (298 K), A is the surface area of electrode (1.13 cm2), n is the number of electrons per molecule during oxidation, F is faraday constant (96,485 C mol−1), C is the concentration of lithium ions in the corresponding electrode material, and δω is Warburg coefficient which

Fig. 5. The rate capability of as-prepared samples.

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Fig. 6. (a) AC impedance measurements of as-prepared samples. (b) Plots of Z′ vs. ω−1/2. batteries, Energy Environ. Sci. 5 (2012) 6173–6179. [4] L. Chai, Y. Chen, Z. Yang, Kinetics and thermodynamics of arsenate and arsenite biosorption by pretreated spent grains, Water Environ. Res. 81 (2009) 843–848. [5] J.B. Goodenough, K.-S. Park, The Li-ion rechargeable battery: a perspective, J. Am. Chem. Soc. 135 (2013) 1167–1176. [6] A.R. Armstrong, A.D. Robertson, P.G. Bruce, Overcharging manganese oxides: extracting lithium beyond Mn4+, J. Power Sources 146 (2005) 275–280. [7] J. Zheng, S. Myeong, W. Cho, P. Yan, J. Xiao, C. Wang, J. Cho, J.-G. Zhang, Li- and Mn-rich cathode materials: challenges to commercialization, Adv. Energy Mater. (2016) 1601284. [8] J.-c. Zheng, Y.-d. Han, B. Zhang, C. Shen, L. Ming, J.-f. Zhang, Comparative investigation of phosphate-based composite cathode materials for lithium-ion batteries, ACS Appl. Mater. Interfaces 6 (2014) 13520–13526. [9] Z. Lu, J.R. Dahn, Understanding the anomalous capacity of Li/Li[NixLi1/3−2x/3Mn2/ 3−x/3]O2 cells using in situ X-ray diffraction and electrochemical studies, J. Electrochem. Soc. 149 (2002) A815. [10] A.D. Robertson, P.G. Bruce, Mechanism of electrochemical activity in Li2MnO3, Chem. Mater. 15 (2003) 1984–1992. [11] H. Yu, H. Zhou, High-energy cathode materials (Li2MnO3-LiMO2) for lithium-ion batteries, J. Phys. Chem. Lett. 4 (2013) 1268–1280. [12] S.H. Kang, P. Kempgens, S. Greenbaum, A.J. Kropf, K. Amine, M.M. Thackeray, Interpreting the structural and electrochemical complexity of 0.5Li2MnO3· 0.5LiMO2 electrodes for lithium batteries (M = Mn0.5−xNi0.5−xCo2x, 0 ≤ x ≤ 0.5), J. Mater. Chem. 17 (2007) 2069–2077. [13] M. Gu, A. Genc, I. Belharouak, D. Wang, K. Amine, S. Thevuthasan, D.R. Baer, J.G. Zhang, N.D. Browning, J. Liu, C. Wang, Nanoscale phase separation, cation ordering and surface chemistry in pristine Li1.2Ni0.2Mn0.6O2 for Li-ion batteries, Chem. Mater. 25 (2013) 2319–2326. [14] L. Yu, W. Qiu, F. Lian, J. Huang, X. Kang, Understanding the phenomenon of increasing capacity of layered 0.65Li[Li1/3Mn2/3]O2·0.35Li(Ni1/3Co1/3Mn1/3)O2, J. Alloy. Compd. 471 (2009) 317–321. [15] J.-H. Kim, C. Park, Y.-K. Sun, Synthesis and electrochemical behavior of Li[Li0.1Ni0.35-x/2CoxMn0.55-x/2]O2 cathode materials, Solid State Ion. 164 (2003) 43–49. [16] G.-Y. Kim, S.-B. Yi, Y.J. Park, H.-G. Kim, Electrochemical behaviors of Li[Li(1-x)/ 3Mn(2-x)/3Nix/3Cox/3]O2 cathode series (0 < x < 1) synthesized by sucrose combustion process for high capacity lithium ion batteries, Mater. Res. Bull. 43 (2008) 3543–3552. [17] T. Li, X. Li, Z. Wang, H. Guo, A short process for the efficient utilization of transition-metal chlorides in lithium-ion batteries: a case of Ni0.8Co0.1Mn0.1O1.1 and LiNi0.8Co0.1Mn0.1O2, J. Power Sources 342 (2017) 495–503. [18] A. Ito, D. Li, Y. Ohsawa, Y. Sato, A new approach to improve the high-voltage cyclic performance of Li-rich layered cathode material by electrochemical pre-treatment, J. Power Sources 183 (2008) 344–346. [19] L. Wu, S. Zhong, F. Lv, J. Liu, Improving the electrochemical performance of LiMnPO4/C by liquid nitrogen quenching, Mater. Lett. 110 (2013) 38–41. [20] L. Li, Q. Yao, H. Zhu, Z. Chen, L. Song, J. Duan, Effect of Al substitution sites on Li1−xAlx(Ni0.5Co0.2Mn0.3)1−yAlyO2 cathode materials for lithium ion batteries, J. Alloy. Compd. 686 (2016) 30–37. [21] Z. Huang, X. Li, Y. Liang, Z. He, H. Chen, Z. Wang, H. Guo, Structural and electrochemical characterization of Mg-doped Li1.2[Mn0.54Ni0.13Co0.13]O2 cathode material for lithium ion batteries, Solid State Ion. 282 (2015) 88–94. [22] H. Chen, Q. Hu, Z. Huang, Z. He, Z. Wang, H. Guo, X. Li, Synthesis and electrochemical study of Zr-doped Li[Li0.2Mn0.54Ni0.13Co0.13]O2 as cathode material for Li-ion battery, Ceram. Int. 42 (2016) 263–269. [23] Z. Liu, W. Peng, K. Shih, J. Wang, Z. Wang, H. Guo, G. Yan, X. Li, L. Song, A. MoS2, coating strategy to improve the comprehensive electrochemical performance of LiVPO4F, J. Power Sources 315 (2016) 294–301. [24] Y. Liu, Q. Wang, X. Wang, T. Wang, Y. Gao, M. Su, A. Dou, Improved electrochemical performance of Li1.2Ni0.2Mn0.6O2 cathode material with fast ionic conductor Li3VO4 coating, Ionics 21 (2015) 2725–2733. [25] J. Zheng, M. Gu, J. Xiao, B.J. Polzin, P. Yan, X. Chen, C. Wang, J.-G. Zhang,

Table 2 The impedance parameters of as-prepared samples. Samples

Rct (Ω)

σω (Ω cm2 S0.5)

D (cm2 S−1)

M0 M1 M2 M3 M4

225.7 213.2 189.3 114.4 124.4

213.1 59.7 54.7 36.8 104.8

2.65 3.36 4.03 8.92 1.16

× × × × ×

10–16 10–15 10–15 10–15 10–15

can be calculated from the correlation between the frequency and impedance, according to the following equation [46,47]:

Z re = R s + R ct + δω⋅ω−0.5

(2)

where in Eq. (2), ω represents frequency. Based on the obtained δω value, the lithium ion diffusivity can be calculated. As shown in Table 2, M3 demonstrates higher lithium ion diffusivity than other electrodes, which agree well with the electrochemical results. 4. Conclusions In conclusion, the effects of molybdenum substitution on the lattice structures, particles morphologies and electrochemical performance were comprehensively investigated. Partial molybdenum substitution into the compound gave rise to insignificant change in host structure. The structure stability of the material has been improved after Modoping. The results of EIS indicated that the molybdenum substitution could significantly lower the charge-transfer resistance. The Mo-doped samples with suitable Mo content showed enhanced cycling performance and rate capability. Among those samples, the sample M3 exhibited the best electrochemical performance. Acknowledgements The author would like to appreciate the financial support from the National Natural Science Foundation of China (51674296, 51574287), the National Science and Technology Support Program of China (No. 2015BAB06B00) and T21-711/16R and 17212015 from the Research Grants Council (RGC) of the Government of Hong Kong SAR. References [1] G. Liu, Development of a general sustainability indicator for renewable energy systems: a review, Renew. Sustain. Energy Rev. 31 (2014) 611–621. [2] Z.Q. Liu, A.X. Xu, Y.Y. Lv, X.X. Wang, Promoting the development of distributed concentrated solar thermal technology in China, Renew. Sustain. Energy Rev. 16 (2012) 1174–1179. [3] H. Wang, S. Liu, Y. Ren, W. Wang, A. Tang, Ultrathin Na1.08V3O8 nanosheets—a novel cathode material with superior rate capability and cycling stability for Li-ion

5

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W. Pan et al.

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

[36]

Functioning mechanism of AlF3 coating on the Li- and Mn-rich cathode materials, Chem. Mater. 26 (2014) 6320–6327. F. Zheng, C. Yang, X. Xiong, J. Xiong, R. Hu, Y. Chen, M. Liu, Nanoscale surface modification of lithium-rich layered-oxide composite cathodes for suppressing voltage fade, Angew. Chem. Int. Ed. 54 (2015) 13058–13062. Y. Xu, X. Li, Z. Wang, H. Guo, W. Peng, W. Pan, The enhanced high cut-off voltage electrochemical performances of LiNi0.5Co0.2Mn0.3O2 by the CeO2 modification, Electrochim. Acta 219 (2016) 49–60. L. Li, M. Xu, Q. Yao, Z. Chen, L. Song, Z. Zhang, C. Gao, P. Wang, Z. Yu, Y. Lai, Alleviating surface degradation of nickel-rich layered oxide cathode material by encapsulating with nanoscale Li-ions/electrons superionic conductors hybrid membrane for advanced Li-ion batteries, ACS Appl. Mater. Interfaces 8 (2016) 30879–30889. Y. Liu, Z. Zhang, Y. Fu, Q. Wang, J. Pan, M. Su, V.S. Battaglia, Investigation the electrochemical performance of Li1.2Ni0.2Mn0.6O2 cathode material with ZnAl2O4 coating for lithium ion batteries, J. Alloy. Compd. 685 (2016) 523–532. J. Zhao, Z. Wang, H. Guo, X. Li, Enhanced electrochemical properties of LiNiO2based cathode materials by nanoscale manganese carbonate treatment, Appl. Surf. Sci. 403 (2017) 426–434. Z. He, Z. Wang, H. Chen, Z. Huang, X. Li, H. Guo, R. Wang, Electrochemical performance of zirconium doped lithium rich layered Li1.2Mn0.54Ni0.13Co0.13O2 oxide with porous hollow structure, J. Power Sources 299 (2015) 334–341. J. Ma, Y.-N. Zhou, Y. Gao, X. Yu, Q. Kong, L. Gu, Z. Wang, X.-Q. Yang, L. Chen, Feasibility of using Li2MoO3 in constructing Li-rich high energy density cathode materials, Chem. Mater. 26 (2014) 3256–3262. Z. Zheng, X.-D. Guo, Y.-J. Zhong, W.-B. Hua, C.-H. Shen, S.-L. Chou, X.-S. Yang, Host structural stabilization of Li1.232Mn0.615Ni0.154O2 through K-doping attempt: toward superior electrochemical performances, Electrochim. Acta 188 (2016) 336–343. L. Li, B.H. Song, Y.L. Chang, H. Xia, J.R. Yang, K.S. Lee, L. Lu, Retarded phase transition by fluorine doping in Li-rich layered Li1.2Mn0.54Ni0.13Co0.13O2 cathode material, J. Power Sources 283 (2015) 162–170. T.V. Thi, A.K. Rai, J. Gim, S. Kim, J. Kim, Effect of Mo6+ doping on electrochemical performance of anatase TiO2 as a high performance anode material for secondary lithium-ion batteries, J. Alloy. Compd. 598 (2014) 16–22. J.n. Morales, Improving the electrochemical performance of SnO2 cathodes in

[37]

[38]

[39] [40]

[41]

[42]

[43]

[44]

[45]

[46]

[47]

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lithium secondary batteries by doping with Mo, J. Electrochem. Soc. 146 (1999) 1640. T.-F. Yi, Y. Xie, L.-J. Jiang, J. Shu, C.-B. Yue, A.-N. Zhou, M.-F. Ye, Advanced electrochemical properties of Mo-doped Li4Ti5O12 anode material for power lithium ion battery, RSC Adv. 2 (2012) 3541–3547. Z. Lu, L.Y. Beaulieu, R.A. Donaberger, C.L. Thomas, J.R. Dahn, Synthesis, structure, and electrochemical behavior of Li[NixLi1/3−2x/3Mn2/3−x/3]O2, J. Electrochem. Soc. 149 (2002) A778. J. Cho, LiNi0.74Co0.26−xMgxO2 cathode material for a Li-ion cell, Chem. Mater. 12 (2000) 3089–3094. J. Xiao, N.A. Chernova, M.S. Whittingham, Layered mixed transition metal oxide cathodes with reduced cobalt content for lithium ion batteries, Chem. Mater. 20 (2008) 7454–7464. D. Wang, X. Li, Z. Wang, H. Guo, Y. Xu, Y. Fan, J. Ru, Role of zirconium dopant on the structure and high voltage electrochemical performances of LiNi0.5Co0.2Mn0.3O2 cathode materials for lithium ion batteries, Electrochim. Acta 188 (2016) 48–56. Y. Zhang, Z.-B. Wang, F.-D. Yu, L.-F. Que, M.-J. Wang, Y.-F. Xia, Y. Xue, J. Wu, Studies on stability and capacity for long-life cycle performance of LiNi0.5Co0.2Mn0.3O2 by Mo modification for lithium-ion battery, J. Power Sources 358 (2017) 1–12. X. Wu, Y. Li, Y. Xiang, Z. Liu, Z. He, X. Wu, Y. Li, L. Xiong, C. Li, J. Chen, The electrochemical performance of aqueous rechargeable battery of Zn/Na0.44MnO2 based on hybrid electrolyte, J. Power Sources 336 (2016) 35–39. A.Y. Shenouda, K.R. Murali, Electrochemical properties of doped lithium titanate compounds and their performance in lithium rechargeable batteries, J. Power Sources 176 (2008) 332–339. M. Wang, M. Luo, Y. Chen, Y. Su, L. Chen, R. Zhang, Electrochemical deintercalation kinetics of 0.5Li2MnO3·0.5LiNi1/3Mn1/3Co1/3O2 studied by EIS and PITT, J. Alloy. Compd. 696 (2017) 907–913. T. Yuan, R. Cai, K. Wang, R. Ran, S. Liu, Z. Shao, Combustion synthesis of highperformance Li4Ti5O12 for secondary Li-ion battery, Ceram. Int. 35 (2009) 1757–1768. F. Amalraj, D. Kovacheva, M. Talianker, L. Zeiri, J. Grinblat, N. Leifer, G. Goobes, B. Markovsky, D. Aurbach, Integrated materials xLi2MnO3⋅(1−x)LiMn1/3Ni1/3Co1/ 0.5, 0.7) synthesized, J. Electrochem. Soc. 157 (2010) A1121. 3O2 (x=0.3,