Improved Electrochemical Performance of Li1.2Mn0.54Ni0.13Co0.13O2 By Surface Modification with Li-Ion-Conductive Li2TiO3

Abstract

With the development of electric vehicles, hybrid electric vehicles, and electric power tools, lithium-rich oxide electrodes with layered structures have attracted considerable interest, due to their high specific capacity of about 250 mA·h/g between 2.0 V and 4.8 V. However, it suffers from intrinsic poor rate capability, voltage decay and cycle stability. In this paper, Li2TiO3 coated Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials were fabricated via a combined method of wet chemical processes and high temperature solid state method. The precursor Mn0.54Ni0.13Co0.13(OH)1.6, obtained by a co-precipitation method as reported by Y.Chen[1], and an appropriate amount of concentrated ammonia were dispersed in absolute ethanol. Afterword a mixed solution of Ti(OC4H9)4 and absolute ethanol (10 mL) was added drop-wise for 10 min. Finally, the obtained TiO2@Mn0.53Ni0.13Co0.13(OH)1.6 were thoroughly mixed with an appropriate amount of LiOH·H2O, and then calcined at 900 ℃ for 12 h in air. The Li1.2Mn0.54Ni0.13Co0.13O2 samples coated with 3 wt% and 5 wt% Li2TiO3 were denoted as LNCM-T3 and LNCM-T5 respectively. The SEM image and EDS area mapping analysis of LNCM-T3 composite material presented in Fig.1 were performed to further identify the distribution of the LTO coating layer on the surface of coated LNCM. It is seen from Fig. 1 b–f that the Ti, O, Ni, Co and Mn elements uniformly distribute in the selected region of the nanoparticles, indicating that LTO were uniformly coated on the LNCM surface. Fig.1 g shows the improved electrochemical performance of the coated samples, especially, the LNCM-T3 electrode delivers a discharge capacity of 164 mA·h/g even at a high rate of 5C, whereas only 136 mA·h/g specific capacities can be obtained for the LNCM electrode at the same rate. In addition, when the current rate is reversed back to 0.1 C, a 96% of the initial capacity (252 mA·h/g at 0.1C) was recovered for the LNCM-T3 electrode compared to 91% of the LNCM electrode, which means that 3% LTO coating sample has a better structure stability. According, LTO serve as a surface protecting layer, not only protect the active materials from the erosion of HF, which produced during the high potential charging process and long-term cycling, but also improves the velocity of Li+ migration on electrode surface, particularly, when LTO was doped with aliovalent ions[2]. Fig.1 SEM plot (a) and the corresponding EDS area mapping of Ti(b), O (c), Ni (d), Co (e) and Mn (f) for LNCM-T3. And（g）Rate capability of pristine and coated LNCM under variable current rate. Acknowledgements This work is financially supported by the National Natural Science Foundation of China (no.5157020571). Reference [1] Chen Y, Xu G, Li J, et al. High capacity 0.5Li2MnO3·0.5LiNi0.33Co0.33Mn0.33O2 cathode material via a fast co-precipitation method[J]. Electrochimica Acta, 2013,87:686-692. [2] Lu J, Peng Q, Wang W, et al. Nanoscale Coating of LiMO2 (M = Ni, Co, Mn) Nanobelts with Li+-Conductive Li2TiO3: Toward Better Rate Capabilities for Li-Ion Batteries[J]. Journal of the American Chemical Society, 2013,135(5):1649-1652. Figure 1