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

Effects of SmPO_(4) Coating on Electrochemical Performance of High-voltage LiNi_(0.5)Mn_(1.5)O_(4) Cathode Materials

尖晶石型镍锰酸锂(LiNi_(0.5)Mn_(1.5)O_(4))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_(0.5)Mn_(1.5)O_(4)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(SmPO_(4))表面包覆改性LiNi_(0.5)Mn_(1.5)O_(4)正极材料,研究了SmPO_(4)包覆量对LiNi_(0.5)Mn_(1.5)O_(4)材料电化学性能的影响.结果表明,当SmPO_(4)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SmPO_(4)包覆能够有效缓解LiNi_(0.5)Mn_(1.5)O_(4)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.

Spinel-type LiNi_(0.5)Mn_(1.5)O_(4) 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_(0.5)Mn_(1.5)O_(4) 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_(0.5)Mn_(1.5)O_(4) cathode material was successfully coated with a thin layer of SmPO_(4) via a hydrothermal process.The influence of the coating amount of SmPO_(4) on the electrochemical performance of LiNi_(0.5)Mn_(1.5)O_(4) material was systematically studied.The results indicate that the as-prepared LiNi_(0.5)Mn_(1.5)O_(4) coated with 0.5%(mass fraction)SmPO_(4)(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 129.2and 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 SmPO_(4) coating can effectively alleviate the side reaction between LiNi_(0.5)Mn_(1.5)O_(4) material and electrolyte,and reduce the polarization degree and charge transfer resistance of the electrode,and increase the diffusion coefficient of Li+.