ZnF2包覆对锂离子电池正极材料LiNi0.5Mn1.5O4的性能影响

本文用溶胶凝胶法制备了LiNi0.5Mn1.5O4正极材料，然后用ZnF2对其进行表面包覆。XRD测试表明，包覆处理没有影响材料的晶体结构，EDS、SEM和TEM测试表明，2wt%ZnF2在LiNi0.5Mn1.5O4表面形成了约7 nm厚的均匀包覆层。对未包覆、1wt%、2wt%、3wt%包覆后的材料进行电化学性能测试对比，发现包覆后都能减弱电解液与基体间的相互作用，较大地稳定电极表面，提高了材料的电化学性能。其中，2wt%ZnF2包覆样品表现出最佳的电化学性能，0.2 C倍率下循环200圈后，其放电比容量维持在109 mAh/g，容量保持率为79.7%；在10 C时，放电比容量依然高达102.1 mAh/g；5 C高倍率下循环500圈后，放电比容量维持在94.2 mAh/g，容量保持率为85.6%。

Effect of ZnF2 Coating on LiNi0.5Mn1.5O4 Cathode Material for Lithium-ion Batteries

:LiNi0.5Mn1.5O4 of a 5 V cathode material was prepared by a sol-gel method, and subsequently coated with ZnF2 as a buffering layer. XRD test showed that ZnF2 coating treatment have no effect on the crystal structure of LiNi0.5Mn1.5O4. EDS,SEM,TEM test indicated that 2wt% ZnF2 formed uniform layer on the surface of LiNi0.5Mn1.5O4 with a thickness of 7 nm.The electrochemical performance of the pristine LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4 with various coating levels of 1wt%, 2wt%, 3wt% ZnF2 were tested and compared in half-cells. The ZnF2 coating layer decreased the interaction between the electrolyte and the cathode material, greatly stabilized the electrode surface,thus improving the electrochemical performances. LiNi0.5Mn1.5O4 with an optimized coating level of 2wt% ZnF2 exhibited the best performances, delivering a discharge capacity of 109 mAh·g-1 and maintaining 79.7% capacity retention at 0.2 C after 200 cycles. After cycled 500 cycles at a high current of 5 C, it still showed a high 85.6% capacity retention of 85.6% with a discharge capacity of 94.2 mAh·g-1.