Enhanced Electrochemical Performance of LiNi_0.6Co_0.2Mn_0.2O₂ by Expanded Graphite

Abstract

High‐capacity ternary materials are attractive for the development of electric vehicles for long‐distance driving, but they still face some challenges. To improve the performance, expanded graphite (EG) with a unique loose‐layered structure is mixed with (Ni0.6Co0.2Mn0.2)(OH)2 and LiOH·H2O aqueous solution to supply microscale reaction space and limit grain growth via hydrothermal treatment as well as accommodate LiNi0.6Co0.2Mn0.2O2 (NCM622) particles between the graphene layers. The key factors affecting electrochemical performance are investigated using various techniques. The NCM622 sample synthesized by adding 6.6 wt% of EG (PEG6.6%) exhibits the best performance. EG improves the discharge capacity of NCM622 from 156 to 175 mAh g−1 after 50 cycles at 1 C. As the surrounding temperature increases to 60 °C, the sample also shows good cyclability at 1 C, the 50th discharge specific capacity remains 153 mAh g−1 and the capacity retention rate is 82.3%, which is much higher than that of NCM622. Also, the columbic efficiency of NCM622 after 50 cycles improves from 69% to 99% with EG. The possible enhanced mechanism of NCM622 by EG is discussed. The effective way to enhance the performance using the layered structure of EG is promising for other energy materials.