Zn-Al共掺杂和形貌调控制备LiMn_(2)O_(4)正极材料及其电化学性能

Preparation and electrochemical properties of LiMn_(2)O_(4) cathode by Zn-Al co-doping and morphology control

采用固相燃烧法在不同焙烧温度(600、650、700和750℃)下制备了LiZn_(0.05)Al_(0.03)Mn_(1.92)O_(4)正极材料,采用XRD、SEM、XPS对其进行了表征,通过循环伏安(CV)和电化学阻抗(EIS)测试了其电化学性能。结果表明,Zn-Al共掺杂和焙烧温度未改变LiMn_(2)O_(4)的晶体结构,正极材料的结晶性随焙烧温度(<750℃)的升高而增加,650℃及以上时形成了较多包含高暴露(111)晶面、小面积(110)、(100)晶面的截断八面体形貌晶粒,但750℃时正极材料发生部分分解。焙烧温度650℃的样品(LZAMO-650)表现出最佳的电化学性能,在5 C和10 C倍率下,初始放电比容量分别为101.3、99.9 mA·h/g,循环1000圈后容量保持率分别为81.5%、74.3%;LZAMO-650样品极化作用较小,有较好的循环可逆性,具有较低的电荷转移阻抗(R_(ct)=132.14Ω)和较大的锂离子扩散系数(DLi^(+)=3.65×10^(–16)cm^(2)/s)。Zn-Al共掺杂和形貌调控改性LiMn_(2)O_(4)正极材料有效抑制了Jahn-Teller效应,形成的截断八面体颗粒形貌降低了Mn的溶解,同时提供了更多的Li^(+)迁移三维通道,从而改善了材料的电化学性能。

LiZn_(0.05)Al_(0.03)Mn_(1.92)O_(4)cathode material,synthesized from solid-state combustion at different calcination temperatures(600,650,700 and 750℃),was characterized by XRD,SEM and XPS,and tested by cyclic voltammetry(CV)and electrochemical impedance(EIS)for evaluation on its electrochemical performance.The results showed that Zn-Al co-doping and calcination temperature did not change the crystal structure of LiMn_(2)O_(4),while the crystallinity increased with the increase of calcination temperature.More truncated octahedral grains containing high exposure(111),small area(110)and(100)crystal faces were formed at 650℃and higher but partial decomposition occured at 750℃.The sample prepared at 650℃(LZAMO-650)exhibited the best electrochemical performance,with the initial discharge specific capacity of 101.3 and 99.9 mA·h/g and the capacity retention after 1000 cycles of 81.5%and 74.3%at 5 C and 10 C respectively.The LZAMO-650 sample had a relatively small polarization effect and good cyclic reversibility,with a lower charge transfer impedance(R_(ct)=132.14Ω)and a larger lithium ion diffusion coefficient(DLi^(+)=3.65×10^(-16)cm^(2)/s).The Zn-Al co-doping and morphology control modified LiMn_(2)O_(4)cathode material could effectively inhibit Jahn-Teller effect,resulting in truncated octahedral particle morphology,which reduced Mn dissolution and provided more Li^(+)migration three-dimensional channels,thus improving the electrochemical performance of the material.