A kinetic study on cobalt-free high-nickel layered oxide cathode materials for practical lithium-ion batteries

The battery industry is accelerating the reduction of cobalt, which is a major component of cathode materials, because its high price is considered to be the main reason for the increased cost of lithium-ion batteries (LIBs). Recently, cobalt-free, high-nickel layered oxide cathodes have been extensively studied in both industry and academia. However, the low initial Coulombic efficiency (ICE) and high residual lithium content in them hinder the commercialization of cobalt-free, high-nickel layered oxides in LIBs. Here, we systematically investigate the ICE of cobalt-free LiNiO2 (LNO), considering the kinetic factors that control this phenomenon in terms of primary particle size, cell operating temperature, and current density. The kinetic hindrance of the H1-H1' phase transition is even more conspicuous with large primary particle size as evidenced by in-depth electrochemical analyses, including differential capacity (dQ/dV) and galvanostatic intermittent titration technique (GITT) experiments. Finally, a correlation between Li+ diffusion kinetics and residual lithium content is discussed, which is useful for practical cells.