Exploring the distinct effects of ionic and electronic conductivities of cathodes on the electrochemical performance of lithium-ion batteries

Lithium-ion batteries (LIBs) are crucial for advancing modern electronics and achieving widespread electrification in transportation and other sectors. Ni-rich layered oxides, particularly LiNi_xCo_yMn_1−x−yO₂ (x > 0.8), have shown promise as high-energy-density cathode materials because of their relatively high theoretical capacity and favorable rate performance. However, their relatively low ionic and electronic conductivity is the primary obstacle to achieving excellent electrochemical performance at commercial energy densities. Ionic and electronic conductivities of LIB electrodes exhibit a trade-off relationship, making it challenging to distinguish their individual effects on electrochemical behavior, leading to difficulties in electrode design. To analyze the individual effects of these conductivities, we kept one type of conductivity constant while changing the other. Specifically, we prepared three electrodes with similar electronic conductivities to assess the effect of ionic conductivity and another group of three electrodes with similar ionic conductivities to examine the effect of electronic conductivity. In the rate capability tests, electrodes with similar ionic conductivities exhibited comparable behaviors, confirming that ionic conductivity critically affects performance at high C-rates. Conversely, in the cycle life tests at low C-rates, electrodes with similar electronic conductivities showed similar capacity retention after 300 charge–discharge cycles, confirming that electronic conductivity determines performance at low C-rates. Insights from this study are expected to inform the optimized design of cells with Ni-rich electrodes, contributing to the development of high-performance LIBs with excellent rate capabilities and cycle life.