磷酸钐包覆对高电压镍锰酸锂正极材料电化学性能的影响

尖晶石型镍锰酸锂(LiNi_0.5Mn_1.5O₄)因制备成本低、 放电平台高及循环寿命长等优点, 越来越多地应用于大型储能设备、 能量转换设备、 动力汽车等领域. 然而LiNi_0.5Mn_1.5O₄在高电压(5 V)充电状态下电解液易分解, 从而导致比容量降低以及循环性能衰退. 针对以上问题, 采用水热法制备磷酸钐(SmPO₄)表面包覆改性LiNi_0.5Mn_1.5O₄正极材料, 研究了SmPO₄包覆量对LiNi_0.5Mn_1.5O₄材料电化学性能的影响. 结果表明, 当SmPO₄包覆量为0.5%(质量分数)时, 改性材料(LNMO@SP-0.5)的电化学性能最优, 在0.2C和5C倍率下的放电比容量分别为129.2和90.9 mA?h/g, 而未包覆的材料Pristine LNMO的放电比容量分别仅有114.2和77.7 mA?h/g. 在常温1C倍率下循环200次后, LNMO@SP-0.5的容量保持率为93.4%， 而Pristine LNMO的容量保持率仅为86.6%. 这归因于SmPO₄包覆能够有效缓解LiNi_0.5Mn_1.5O₄材料与电解液之间的副反应, 降低电极的极化程度和电荷转移电阻, 增加了Li⁺的扩散系数.

Effects of SmPO4 Coating on Electrochemical Performance of High-voltage LiNi0.5Mn1.5O4 Cathode Materials

Spinel-type LiNi_0.5Mn_1.5O₄ has been widely used in large-scale energy storage equipment， energy conversion equipment and power vehicle， due to its low preparation cost， high discharge platform and long cycle life. However， the electrolyte of LiNi_0.5Mn_1.5O₄ decomposes easily under high voltage（5 V） charging， which leads to a decrease in specific capacity and a decline in cycling performance. To solve the above problems， the LiNi_0.5Mn_1.5O₄ cathode material was successfully coated with a thin layer of SmPO₄via a hydrothermal process. The influence of the coating amount of SmPO₄ on the electrochemical performance of LiNi_0.5Mn_1.5O₄ material was systematically studied. The results indicate that the as-prepared LiNi_0.5Mn_1.5O₄ coated with 0.5%（mass fraction） SmPO₄（LNMO@SP-0.5） exhibits optimal electrochemical performance. In case of 0.2C and 5C， the discharge specific capacity of LNMO@SP-0.5 was 129.2^{and 90.9 mA?h/g， respectively， while Pristine LNMO only had 114.2 and 77.7 mA?h/g. LNMO@SP-0.5 exhibited a capacity retention of 93.4% after 500 cycles at 5C and 25 ℃， whereas the Pristine LNMO exhibited a poor capacity retention of 86.6%. The improvement was due to SmPO₄ coating can effectively alleviate the side reaction between LiNi_0.5Mn_1.5O₄ material and electrolyte， and reduce the polarization degree and charge transfer resistance of the electrode， and increase the diffusion coefficient of Li+.}