Synthesis and Electrochemical performance of layered Li[Li(1-2x)/3NixMn(2-x)/3]O2 for lithium secondary batteries

초록

Due to high cost of LiCoO2, a commonly used cathode material in commercial rechargeable lithium batteries, much effort has been made to develop cheaper cathode materials than LiCoO2. To this end, LiNiO2 and LiMnO2 have been studied extensively as possible alternatives to LiCoO2. But both materials still possess various problems for practical applications. Recently, many research groups have studied to stabilize layered structure by using solid solution between Li2MnO3 and LiMO2 (M=Cr, Ni, Co) such as Li[Li(1-2x)/3MxMn(2-x)/3]O2 (M=Cr, Ni, Co). Li2MnO3 has a layered structure similar to LiCoO2 but electrochemically inactive material. It is reported that Li2MnO3 contribute to the stabilization of LiMO2 (M=Cr, Ni, Co) structure. In this study, sol-gel method was employed to prepare layered Li[Li(1-2x)/3NixMn(2-x)/3]O2 (x=0.425, 0.35, 0.275, 0.2, and 0.125) materials using glycolic acid as a chelating agent. Li[Li(1-2x)/3NixMn(2-x)/3]O2 (x=0.275) materials exhibited discharge capacity over 200 mAh/g with excellent cycleability at 30 ℃ in the voltage range of 2.5-4.6 V. Effect of calcination temperature on electrochemical properties of Li[Li0.1Ni0.35Mn0.55]O2 was also studied at the temperature range of 900 ℃∼1000 ℃. Li[Li0.1Ni0.35Mn0.55]O2 material calcined at 1000 ℃ exhibited excellent voltage profiles during galvanostatic charge/discharge test.