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DOI: 10.1039/C6RA14709G (Communication) RSC Adv., 2016, 6, 76933-76937

Li3V2(PO4)3 as a cathode additive for the over-discharge protection of lithium ion batteries†

Tiantian Gaoa, Bo Wang*a, Haitao Fangb, Chunyu Liub, Lei Wanga, Guijing Liua, Tiefeng Liua and Dianlong Wang*a
aMIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, 150001 Harbin, China. E-mail: wangdianlonghit@163.com; wangbo19880804@163.com; Fax: +86 451 86413721; Tel: +86 451 86413751
bHarbin Institute of Technology, School of Materials Science and Engineering, Xidazhi Street, 150001 Harbin, China. E-mail: htfang@hit.edu.cn

Received 6th June 2016 , Accepted 8th August 2016

First published on 8th August 2016

Abstract

Li3V2(PO4)3 has been used as a cathode additive to make lithium ion batteries (LIBs) retain a good electrochemical performance under over-discharge conditions. Its lower discharge voltage plateau effectively prevents the corrosion of anode collector-copper foil during the over-discharge progress. When 7 wt% Li3V2(PO4)3 is added to LiCoO2 through a “layer to layer” mode, the capacity retention ratio of the LIBs has raised from 49.55% to 95.91%.

As one of the main cathode materials for the lithium-ion batteries (LIBs), LiCoO2 (LCO) has good electrochemical performance and energy-storage characteristics, including long cycle life, no memory effect, and high specific energy.1,2 Thus, LCO batteries are the power supply for many electronic devices, such as laptops, mobile phones, digital cameras and so on.3 To date, the present studies mainly have focused on the batteries' over-charge protection,4–8 however, much less attention has been paid on over-discharge protection.

For a full LIB, during the first charge process, a solid electrolyte interface (SEI) film is formed on the surface of graphite anode. Therefore, a certain number of Li+ will be released from cathode and the actually amount of Li+ participating in charge/discharge process will be reduced. In the process of over-discharge, activated Li sites in the cathode are not fully occupied and the positive potential will remain constant. Therefore, in order to make the battery voltage drop to 0 V, the anode potential will be increased relatively. When the anode potential continue to rise until surpassing 3.5 V (vs. Li+/Li), a series of adverse reactions will occur.9–11 Firstly, during the over-discharge process, SEI film coated on the surface of anode will be damaged. Secondly, the anode collector-copper foil will be oxidized to Cu2+ because of the high potential (>3.5 V). And the original binding force between anode materials and anode collector will be lost. All of these abovementioned damages and side reactions will lead to the anode's electronic insulation, and even the failure of batteries' normal charge–discharge process. Therefore, allowing LCO/graphite batteries over-discharge and preventing its over-discharge failure are urgent problems need to be solved. In order to prevent the over-discharge failure, one effective way is adding cathode materials whose discharge voltage is lower than 3.4 V. Then the end potential of the anode can be controlled at a lower level (<3.4 V). Li et al. found that when 20 wt% Li(Ni1/3Co1/3Mn1/3)O2 was added to LCO during the slurry making process, the cell swelling rate could be greatly reduced, and the specific capacity would be enhanced significantly.11 Analogously, Li2MoO3 has a sloping discharge voltage below 3.4 V (vs. Li+/Li),12 and thus, Park et al. introduced it as a cathode additive to prevent the copper anode current collector from oxidative dissolution at the over-discharge condition.13

Li3V2(PO4)3 (LVP) has also been considered as a promising cathode material, because of its high specific capacity and relatively high operating voltage.14,15 More importantly, two Li+ can be reversibly inserted and extracted in the relatively low voltage range of 3.0–0.0 V. Based on this special characteristic, Rui et al. used LVP as an anode material for LIBs.16 They discovered that LVP exhibits stable reversible capacities of 203 and 102 mA h g−1 in the potential ranges of 3.0–0.0 V and 3.0–1.0 V (vs. Li+/Li), respectively. These voltage windows are very useful for reducing the potential of the graphite anode during the over-discharge process. So, besides of Li(Ni1/3Co1/3Mn1/3)O2 and Li2MoO3, LVP is also a good choice to prevent the copper anode current collector from oxidative dissolution at the over-discharge condition. In this paper, 7 wt% LVP was added to LCO through a “layer to layer” mode to make a composite cathode and to reduce the potential of LCO during the over-discharge process. The LVP active layer consisted of LVP, acetylene black and PVDF binder with the ratio of 8[thin space (1/6-em)]:[thin space (1/6-em)]1[thin space (1/6-em)]:[thin space (1/6-em)]1 wt% was directly coated on the LCO electrode to fabricate the composite cathode. Such a preparation process is facile and easy for practical application. The schematic of composite cathode was shown in Scheme 1. At the same time, pre-lithiated graphite anode was used to supplement the Li source for LVP in the charge and discharge process. The cell composed of composite cathode and pre-lithiated graphite anode is recorded as the LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell. For comparison, the cell composed of LCO and graphite is also fabricated and studied, which is recorded as the LCO/graphite cell.


image file: c6ra14709g-s1.tif
Scheme 1 Schematic of the LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93) composite cathode.

LVP was synthesised by a carbon thermal reduction method.16 The experiment details for synthesis of LVP was shown in the Experimental section of ESI.† XRD pattern and SEM images for LVP were shown in Fig. S1 and S2,† respectively. It can be seen the synthesized LVP has a high crystallinity with particle size ranged from several tens nm to 0.5 μm. The details for preparation of batteries, physical characterization testing, steps of over-discharge process and electrochemical measurements can also be seen in the Experimental section of ESI.†17–21

The cyclic voltammogram curves for LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93) composite cathode, LCO and LVP electrode at a scan rate of 0.2 mV s−1 in the voltage range of 1.4–4.4 V are presented in Fig. 1. The CV curve for LVP (inset of Fig. 1), showing that in addition to three pairs of redox peaks in the voltage range of 3.40–4.27 V, there are two pairs of redox peaks (1.85/1.60 V and 1.97/1.79 V) in the voltage range of 1.6–2.0 V. These two pairs of redox peaks at lower voltage range are very useful for reducing the potential of the cathode in the over-discharge progress. For LCO cathode (black line in Fig. 1), there are only one pair of redox peaks. After the addition of LVP, other two pairs of redox peaks appear in the voltage range of 3.5–4.4 V for LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93) composite cathode. It is obvious that there are two redox peaks in the voltage range of 1.6–2.0 V, which is beneficial to improve the electrochemical performance of LCO/graphite-based cell during the over-discharge process. In order to make the battery voltage drop to 0 V, the anode potential needs to be increased until reached the potential value of the cathode. If one kind of cathode material whose discharge voltage is lower than 3.4 V is added to LCO, the end potential of the anode during the over-discharge process can be controlled at a lower level (<3.4 V).11,13 Then the series of adverse reactions (destruction of SEI film and dissolution of anode collector-copper foil) can be effectively avoided. It can been seen from the CV curves, in order to improve the over-discharge performance of the LCO/graphite cell, LVP should be an appropriate cathode additive due to its unique charge–discharge process in the lower voltage range of 1.6–2.0 V.


image file: c6ra14709g-f1.tif
Fig. 1 CV curves for the LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93) composite cathode and LCO cathode at a scan rate of 0.2 mV s−1, the inset shows the CV curves for LVP.

Fig. 2(a) and (b) exhibit the voltage–time curves for LCO/graphite cell and LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell during the normal charge and over-discharge process. The over-discharge tests are performed by applying a constant current of 0.2 C until the voltage dropped to 2 V, and then 0.013 mA until the voltage dropped to 0 V. At the first charge and discharge process at 0.2 C, both the cells exhibit a normal and similar electrochemical behaviour. However, during the slow 0.013 mA over-discharge period, LCO/graphite cell's voltage initially decreases steadily until a plateau region around 0.25 V is observed. This voltage plateau corresponds to the corrosion of the anode collector-copper foil.18 Compared with LCO/graphite cell, the LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell shows different discharge curves as Fig. 2(b) indicates. The voltage plateau at around 0.2–0.3 V disappeared for the LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell. It could be proved that corrosion of copper foil did not occur in LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell. Charge and discharge curves before and after kept at 0 V for 7 weeks for LCO/graphite cell and LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell are shown in Fig. 2(c) and (d). As Fig. 2(c) presents, when LCO/graphite cell was over-discharged with the cell voltage dropped to 0 V and kept at 0 V state for 7 weeks, its recharge and discharge performance was greatly deteriorated. And the larger voltage gap between the charging and discharging platform means a larger electrochemical polarization. After the LCO/graphite cell was kept at 0 V for 7 weeks, the discharge capacity of the battery has reduced from the original 142 mA h g−1 to 74 mA h g−1 with a capacity retention rate of only 49.55%. Compared with that, as Fig. 2(d) shows, when LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell is over-discharged and kept at 0 V for 7 weeks, no significant changes have occurred in the voltage gap between the charging and discharging platform and the capacity retention is still maintained to 95.91%. The charge and discharge curves indicate that when 7 wt% LVP active layer is added to LCO electrode, the battery electrochemical performance under abnormal discharge condition has been improved obviously.


image file: c6ra14709g-f2.tif
Fig. 2 Voltage–time curves during over-discharge process for (a) LCO/graphite cell; (b) LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell. Charge and discharge curves before and after kept at 0 V for 7 weeks for (c) LCO/graphite cell; (d) LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell.

The influence of the content of LVP on the electrochemical performance of composite electrode has been studied by comparing the charge and discharge curves before and after kept at 0 V for 7 weeks with different mass percent of LVP-5 wt% (LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (5[thin space (1/6-em)]:[thin space (1/6-em)]95)), 7 wt% (LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)) and 9 wt% (LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (9[thin space (1/6-em)]:[thin space (1/6-em)]91)), as shown in Fig. S3.† It can be seen that all the charge/discharge curves of the composite electrode maintain well with the addition of LVP. For details, as listed in the Table S1,† the LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93) has the highest retention rate (95.91%) as well as the largest capacity (130.75 mA h g−1), although the voltage gap between the charging and discharging platform is slightly different with other. Such a voltage gap may be caused from the fact that the substantial differences between the electrochemical potential of LVP and LCO, like the self-discharging phenomenon during long-time storage.22,23 On the other side, based on the relatively low theoretical capacity of LVP (133 mA h g−1, 3.0–4.3 V (vs. Li+/Li))14 compared with LCO (160 mA h g−1, 3.0–4.3 V (vs. Li+/Li)),24 the content of LVP must be controlled in a reasonable ratio to guarantee the capacity of the composite electrode. As listed in Table S1,† both the primary capacity and ending capacity (after kept at 0 V for 7 weeks) of the composite electrode with LVP content raised up to 9 wt% (LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (9[thin space (1/6-em)]:[thin space (1/6-em)]91)) is the smallest one. Therefore, in this present work, LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93) has the best electrochemical performance considering capacity retention ratio and specific capacity, and thus, was chosen as the objective for further study.

The cycling performance of both the cells after kept at 0 V for 7 weeks was then evaluated between 3.0 and 4.2 V, as shown in Fig. 3, it can be seen that, after 40 cycles, the specific capacity of LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell is as high as 106 mA h g−1. Compared with that, the specific capacity of LCO/graphite cell is as low as 43 mA h g−1. In addition to specific capacity, after kept at 0 V for 7 weeks, the coulombic efficiency of the first cycle for LCO/graphite cell is only about 40%. The low coulombic efficiency may be caused by the damage of SEI film during the abnormal over-discharge process. The irreversible Li+ may be used in the reconstruction of the SEI film, or react with Cu2+ to produce some by-products, which may prevent the Li+ insertion and extraction and affect the electrochemical performance of the battery. Compared with that, the coulombic efficiency of all the 40 cycles for LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell is almost close to 100%. It can be concluded that because of the addition of LVP, the battery can retain a good electrochemical stability even under the abnormal over-discharge condition.


image file: c6ra14709g-f3.tif
Fig. 3 Specific discharge capacity and coulombic efficiency vs. cycle number for LCO/graphite cell and LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell after kept at 0 V for 7 weeks.

SEM morphologies and EDS results of graphite anodes for LCO/graphite cell and LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell after kept at 0 V for 7 weeks are shown in Fig. 4. As shown in Fig. 4(a1), when LCO/graphite cell was over-discharged and kept at 0 V for 7 weeks, a large number of small uniform particles could be found on the surface of the graphite anode. EDS results in Fig. 4(a2) show that these particles contain a lot of copper element. It is caused by the corrosion of the Cu anode collector in LCO/graphite cell with the Cu2+ deposited on the surface of the anode. During the over-discharge process, Cu anode collector is oxidized to Cu2+ because of the high potential (>3.4 V).9 During the following 7 weeks (kept at 0 V) and charge–discharge cycle process, Cu2+ may deposit and react with electrolyte to produce some by-products on the surface of the graphite surface. Compared with LCO/graphite cell, when LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell was over-discharged and kept at 0 V for 7 weeks, the graphite surface was still smooth, and no small particles generated on the graphite surface as Fig. 4(b1) shows. EDS results in Fig. 4(b2) show that there is almost no copper element can be found on the graphite surface for the LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell, which indicates that when 7 wt% LVP active layer is added to LCO electrode, the potential of the graphite anode can be reduced and the corrosion of copper foil during the over-discharge process can be prevented.


image file: c6ra14709g-f4.tif
Fig. 4 SEM morphologies and EDS results of graphite anodes for: (a) LCO/graphite cell; (b) LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell after kept at 0 V for 7 weeks.

EDS mappings of graphite electrode for LCO/graphite cell and LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell after kept at 0 V for 7 weeks and 40 charge–discharge cycles are shown in Fig. 5 and 6, respectively. It is obvious that some particles whose size is about 1 μm are on the surface of LCO/graphite cell. In addition to the larger particles, some smaller particles are widely speared on all the surface of the graphite. The EDS mapping for LCO/graphite indicates that a large number of copper elements is distributed on the surface of graphite, especially in the range of larger particles. On the contrary, the EDS mapping for LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell shows that there is almost no copper element exist on the surface of graphite for LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell. The EDS mappings for LCO/graphite cell and LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell can also prove that the addition of LVP to LCO can prevent the corrosion of copper foil during the over-discharge process and improve the electrochemical performance of the battery. In order to further observe the dissolution of Cu2+, LCO/graphite cell and LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell were disassembled and the separators were observed after kept at 0 V for 7 weeks. Some yellow or black substance appeared on the surface of the separator for LCO/graphite cell (Fig. S4†). Compared with that, the separator for LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO/graphite cell is still clean after it is kept at 0 V for 7 weeks.


image file: c6ra14709g-f5.tif
Fig. 5 EDS mapping of graphite electrode for LCO/graphite cell after kept at 0 V for 7 weeks and 40 charge–discharge cycles.

image file: c6ra14709g-f6.tif
Fig. 6 EDS mapping of graphite electrode for LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell after kept at 0 V for 7 weeks and 40 charge–discharge cycles.

The structure information of LiCoO2 with and without LVP after over-discharge process was tested using the XRD technique, as presented in Fig. S5.† It can be seen that the crystal structure of LCO maintains very well no matter with or without LVP after kept at 0 V for 7 weeks, suggesting the LCO component is relatively stable under the over-discharge condition. Previous report has similar research phenomenon.25

Fig. 7(a) and (b) show the EIS results and fitting curves for LCO/graphite and LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell, respectively. The EIS results were fitted by the equivalent circuit given in the inset of Fig. 7.25,26 The fitting values for LCO/graphite cell and LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell are listed in Tables 1 and 2, respectively. RΩ (Ω) is the high-frequency intercepts with the real axis that is related to the total internal ohmic resistance from electrolyte, electrodes, separator and all the internal connections. RSEI (Ω), corresponding to the first semicircle in EIS curves, is related to the ability that Li+ diffuses through the SEI film. Rct (Ω), corresponding to the second semicircle in EIS curves, is related to the charge-transfer resistance at the electrode/electrolyte interface. W (Ω s−1/2) is related to transports limitations in solid and liquid phase. All parts of the impedance include the cathode and anode.25,27–30


image file: c6ra14709g-f7.tif
Fig. 7 EIS results and fitting curves for (a) LCO/graphite cell; (b) LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell.
Table 1 The fitting values for LCO/graphite cell
  Before over-discharge After over-discharge Kept at 0 V for 7 weeks
a Rtotal = RΩ + RSEI + Rct.
RΩ/Ω 3.144 3.445 3.462
RSEI/Ω 44.65 — —
Rct/Ω 53.68 67.29 318.9
Rtotala/Ω 101.474 70.735 322.362

Table 2 The fitting values for LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell
  Before over-discharge After over-discharge Kept at 0 V for 7 weeks
a Rtotal = RΩ + RSEI + Rct.
RΩ/Ω 6.192 7.367 7.006
RSEI/Ω 2.402 — —
Rct/Ω 14.23 1.975 3.631
Rtotala/Ω 22.824 9.342 10.637

It can be observed from Fig. 7(a) and (b) that after over-discharged and kept at 0 V for 7 weeks, the semicircles in LCO/graphite and LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell standing for the resistance of SEI have disappeared. It may be caused by the damage of the SEI film during the over-discharge process.11 According to the fitting values, as listed in Table 1, the charge-transfer resistance (Rct) for LCO/graphite cell has dramatically increased from 53.68 to 318.9 Ω after kept at 0 V for 7 weeks, and the Rtotal has increased from 101.474 to 322.362 Ω. The increase of Rct and Rtotal for LCO/graphite cell may be caused by the dissolution of copper during the over-discharge process. The Cu-based compound deposited on the surface of graphite prevent electron transfer between graphite particles and the charge transfer between the cathode and anode. In comparison to LCO/graphite cell, there is no significant increase in the Rct and Rtotal for LVP[thin space (1/6-em)]:[thin space (1/6-em)]LCO (7[thin space (1/6-em)]:[thin space (1/6-em)]93)/graphite cell as shown in Table 2. On the contrary, Rct and Rtotal values are slightly decreased which may be due to the activation process during the normal charge and discharge cycles. In a word, when 7 wt% LVP is added to LCO, the electrochemical performance of the battery has been improved obviously.

In summary, because of LVP's lower discharge voltage plateaus (1.85/1.60 V and 1.97/1.79 V), the end potential of the anode can be controlled at a lower level (<3.4 V) during over-discharge process. Therefore the dissolution of the anode collector-copper foil can be avoided during the abnormal discharge process. When 7 wt% LVP is added to LCO through a “layer to layer” mode to make a composite cathode, the capacity retention rate of the battery has raised from 49.55% to 95.91% after a series of abnormal discharge processes. Therefore, this work demonstrates that LVP as a cathode additive is very beneficial for the over-discharge performance of LIBs, which is significant for their practical applications with special over-discharge conditions.

Acknowledgements

Financial supports from the National Natural Science Foundation of China (No. 51272051) and the Fundamental Research Funds for the Central Universities (Grant No. HIT.NSRIF.2017024) are gratefully acknowledged. The analysis and testing centre at The Harbin Institute of Technology is acknowledged.

Notes and references

  1. K. Ozawa, Solid State Ionics, 1994, 69, 212 CrossRef CAS.
  2. E. Antolini, Solid State Ionics, 2004, 170, 159 CrossRef CAS.
  3. J. M. Tarascon and M. Armand, Nature, 2001, 414, 359 CrossRef CAS PubMed.
  4. Z. Chen, Y. Qin and K. Amine, Electrochim. Acta, 2009, 54, 5605 CrossRef CAS.
  5. Q. Wang, S. M. Zakeeruddin, I. Exnar and M. Grätzel, Electrochem. Commun., 2008, 10, 651 CrossRef CAS.
  6. B. Wang, Q. Xia, P. Zhang, G. C. Li, Y. P. Wu, H. J. Luo, S. Y. Zhao and T. van Ree, Electrochem. Commun., 2008, 10, 727 CrossRef CAS.
  7. L. Zhang, Z. Zhang, P. C. Redfern, L. A. Curtiss and K. Amine, Energy Environ. Sci., 2012, 5, 8204 CAS.
  8. L. Chen, M. Xu, B. Li, L. Xing, Y. Wang and W. Li, J. Power Sources, 2013, 244, 499 CrossRef CAS.
  9. M. Zhao, S. Kariuki, H. D. Dewald and F. R. Lemke, J. Electrochem. Soc., 2000, 147, 2874 CrossRef CAS.
  10. M. Zhao, H. D. Dewald, F. R. Lemke and R. J. Staniewicz, J. Electrochem. Soc., 2000, 147, 3983 CrossRef CAS.
  11. H. Li, J. Gao and S. Zhang, Chin. J. Chem., 2008, 26, 1585 CrossRef CAS.
  12. A. C. W. P. James and J. B. Goodenough, J. Solid State Chem., 1988, 76, 87 CrossRef CAS.
  13. K.-S. Park, D. Im, A. Benayad, A. Dylla, K. J. Stevenson and J. B. Goodenough, Chem. Mater., 2012, 24, 2673 CrossRef CAS.
  14. X. Rui, Q. Yan, M. Skyllas-Kazacos and T. M. Lim, J. Power Sources, 2014, 258, 19 CrossRef CAS.
  15. C. Wei, W. He, X. Zhang, F. Xu, Q. Liu, C. Sun and X. Song, RSC Adv., 2015, 5, 54225 RSC.
  16. X. H. Rui, N. Yesibolati and C. H. Chen, J. Power Sources, 2011, 196, 2279 CrossRef CAS.
  17. B. Wang, D. Wang, Q. Wang, T. Liu, C. Guo and X. Zhao, J. Mater. Chem. A, 2013, 1, 135 CAS.
  18. Y. S. Kim, S. H. Lee, M. Y. Son, Y. M. Jung, H. K. Song and H. Lee, ACS Appl. Mater. Interfaces, 2014, 6, 2039 CAS.
  19. B. Wang, A. Liu, W. A. Abdulla, D. Wang and X. S. Zhao, Nanoscale, 2015, 7, 8819 RSC.
  20. H. Lee, S. K. Chang, E. Y. Goh, J. Y. Jeong, J. H. Lee, H. J. Kim, J. J. Cho and S. T. Hong, Chem. Mater., 2008, 20, 5 CrossRef CAS.
  21. H. Maleki and J. N. Howard, J. Power Sources, 2006, 160, 1395 CrossRef CAS.
  22. X. Liao, Q. Huang, S. Mai, X. Wang, M. Xu, L. Xing, Y. Liao and W. Li, J. Power Sources, 2015, 286, 551 CrossRef CAS.
  23. S. Kuppan, H. Duncan and G. Chen, Phys. Chem. Chem. Phys., 2015, 17, 26471 RSC.
  24. A. T. Appapillai, A. N. Mansour, J. Cho and Y. Shao-Horn, Chem. Mater., 2007, 19, 5748 CrossRef CAS.
  25. L. Zhang, Y. Ma, X. Cheng, C. Du, T. Guan, Y. Cui, S. Sun, P. Zuo, Y. Gao and G. Yin, J. Power Sources, 2015, 293, 1006 CrossRef CAS.
  26. B. Wang, T. Liu, A. Liu, G. Liu, L. Wang, T. Gao, D. Wang and X. S. Zhao, Adv. Energy Mater., 2016 DOI:10.1002/aenm.201600426.
  27. X. Zheng, T. Huang, Y. Pan, W. Wang, G. Fang, K. Ding and M. Wu, J. Power Sources, 2016, 319, 116 CrossRef CAS.
  28. B. Wang, B. Xu, T. Liu, P. Liu, C. Guo, S. Wang, Q. Wang, Z. Xiong, D. Wang and X. S. Zhao, Nanoscale, 2014, 6, 986 RSC.
  29. D. Y. Wang, N. N. Sinha, R. Petibon, J. C. Burns and J. R. Dahn, J. Power Sources, 2014, 251, 311 CrossRef CAS.
  30. B. Wang, W. A. Abdulla, D. Wang and X. S. Zhao, Energy Environ. Sci., 2015, 8, 869 CAS.

Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ra14709g
This journal is © The Royal Society of Chemistry 2016
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