固相燃烧法制备LiMg_(0.02)Mn_(1.98)O_(4)正极材料及电化学性能

Synthesis and electrochemical properties of LiMg_(0.02)Mn_(1.98)O_(4) cathode materials by solid-state combustion method

采用固相燃烧法制备出包含{111},{110}和{100}晶面且呈单晶截角八面体形貌的LiMg_(0.02)Mn_(1.98)O_(4)(LMMO)正极材料.结果表明,联合Mg掺杂和截角八面体单晶形貌调控所制备的尖晶石型LiMn_(2)O_(4)材料,既能有效抑制Jahn-Teller效应,又能减缓Mn溶解及增加部分Li+迁移通道,这对其晶体结构起稳定作用.与纯LiMn_(2)O_(4)(LMO)样品相比,Mg掺杂促进了尖晶石型LiMn_(2)O_(4)材料的结晶性和单晶截角八面体颗粒的形成.在1 C倍率下,LiMg_(0.02)Mn_(1.98)O_(4)材料的初始放电比容量为116.8 mAh/g, 200次循环后保持率为78.3%;在5 C和10 C高倍率下,LiMg_(0.02)Mn_(1.98)O_(4)样品经1 000次循环后,其容量保持率分别为64.2%和56.3%,而未掺杂Mg的LiMn_(2)O_(4)样品的容量保持率分别为52.7%和38.7%.单晶截角八面体形貌的LiMg_(0.02)Mn_(1.98)O_(4)材料有较大的Li+扩散系数和较低的表观活化能,这证明其有较好的倍率性能和长循环寿命.

A single-crystal truncated octahedral LiMg_(0.02)Mn_(1.98)O_(4)(LMMO)cathode material with{111},{100},and{110}crystal faces is synthesized via a solid-state combustion method.The results exhibit that the spinel LiMn_(2)O_(4) prepared by Mg doping and single-crystal truncated octahedral morphology strategy can not only effectively inhibit the Jahn-Teller effect,but also reduce the Mn dissolution and increase the Li+diffusion channel,which could stabilize the crystal structure.Compared with pure LiMn_(2)O_(4)(LMO),Mg doping promotes the crystallization of spinel LiMn_(2)O_(4) and the formation of single-crystal truncated octahedral particles.At 1 C,78.3% of the initial discharge capacity(116.8 mAh/g)can be maintained after 200 cycles.At high rates of 5 C and 10 C,the initial discharge capacity is 102.3 mAh/g and 90.3 mAh/g,whose capacity retention rate is 64.2% and 56.3% after 1000 cycles,respectively,while the capacity retention rates of the LiMn_(2)O_(4) without Mg-doping is 52.7% and 38.7% respectively.The LiMg_(0.02)Mn_(1.98)O_(4) material with a single-crystal truncated octahedral morphology has a larger Li^(+)diffusion coefficient and a lower apparent activation energy,which indicates an excellent rate performance and a long cycle life.