去顶角八面体LiFe_(0.12)Mn_(1.88)O_(4)正极材料制备及电化学性能

Preparation and Electrochemical Properties of Truncated Octahedral LiFe_(0.12)Mn_(1.88)O_(4) Cathode Materials

尖晶石型LiMn_(2)MnO_(4)正极材料由于Jahn–Teller效应和Mn溶解,在充放电过程中容量衰减严重,循环稳定性差。联合元素掺杂和单晶形貌调控策略,采用固相燃烧法制备了具有{111}、{100}和{110}晶面的去顶角八面体单晶LiFe_(0.12)Mn_(1.88)O_(4)正极材料。研究结果表明,Fe掺杂没有改变尖晶石型LiMn_(2)MnO_(4)的晶体结构,有效抑制了Jahn–Teller效应,促进了材料的结晶性及{400}和{440}衍射峰晶面的择优生长,表现出良好的倍率性能和容量保持率。在25℃,1 C和5 C倍率下LiFe_(0.12)Mn_(1.88)O_(4)的首次放电比容量分别为105.2 mA·h/g和92.4 mA·h/g,1 000次循环后容量保持率分别为71.1%和75.2%;在高倍率10 C下,经1 000次循环后,其容量保持率可达到88.4%。在55℃和1 C条件下,首次放电比容量为108.6 mA·h/g,经150次循环后,容量保持率为79.1%。通过循环伏安和电化学阻抗分析,Fe掺杂材料具有较好的循环可逆性和较大的Li^(+)扩散系数。Fe掺杂去顶角八面体LiMn_(2)MnO_(4)材料既抑制了Jahn–Teller效应,又减缓了Mn的溶解,稳定晶体结构,同时增加Li^(+)迁移通道,提高电化学倍率性能及长循环寿命。

Spinel LiMnOcathode materials suffer a serious capacity decay and a poor cycle stability during the charge–discharge process due to the Jahn–Teller effect and Mn dissolution.A cathode material of truncated octahedral single crystal LiFe_(0.12)Mn_(1.88)O_(4)with{111},{100}and{110}surfaces was prepared by a solid-state combustion method and element doping and single crystal morphology controlling strategies.The results show that the crystal structure of spinel LiMnOis not changed by Fe doping,the Jahn–Teller effect is effectively inhibited,the crystallinity and the selective growth of{400}and{440}diffraction peak crystal planes are promoted,and the material has superior rate performance and capacity retention.The initial discharge specific capacities at 1 C and 5 C at 25℃are 105.2 m A·h/g and 92.4 m A·h/g,and the capacity retentions after 1 000 cycles are 71.1%and 75.2%,respectively.Moreover,the capacity retention reaches 88.4%after 1 000 cycles at 10 C.The initial discharge capacity of the material is 108.6 mA·h/g at 55℃and 1 C,and the capacity retention rate is 79.1%after 150 cycles,and the capacity retention rate is 79.1%after 150 cycles.By using cyclic voltammetry and electrochemical impedance spectroscopy,we found that the Fe-doped sample has superior circulation reversibility and large Lidiffusion coefficient.The Fe-doped material of truncated octahedral LiMnOinhibits the Jahn–Teller effect,and slows down the Mn dissolution,thus stabilizing the crystal structure,increasing the Limigration channel,and improving the electrochemical rate performance and long cycle life.