(Invited) Resolution of the 1st Capacity Loss of Layered Oxide Cathodes

Abstract

Layered transition-metal oxides are the dominant cathodes in present commercial Li-ion batteries, and are also the leading choice for electric vehicles, because much higher capacity can be obtained with high Ni content, which has the potential to achieve the cell-level energy density above 300 Wh/kg for NMC 811. However, the large 1st capacity loss (~ 15% of the charging capacity) limits the achievable capacity for this attractive cathode materials. If this capacity loss can be eliminated, the energy density could 400 Wh/kg. Our initial studies have found that ~ 80% of the 1st capacity loss of NMC 811 can be attributed to slow lithium diffusion at high lithium concentrations; this may be due to the divacancy diffusion mechanism for Li ions in the layers of the structure. The dramatic drop of the Li divacancy concentration can cause the sharp decrease on Li ion diffusion. However, the layered oxide cathode, LiCoO2, has a much smaller 1st capacity loss, 5 mAh/g vs. 27 mAh/g for 811 for the same Li extraction of 120 mAh/g; there appears to be little kinetics limitation (Figure 1). A systematic study is underway to understand the reasons for this difference. The results of this study will be described, and strategies to mitigate the 1st capacity loss in NMC will be discussed. This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy, through the Advanced Battery Materials Research Program (Battery500 Consortium). Figure 1