A new high-valence cation pillar within the Li layer of compositionally optimized Ni-rich LiNi0.9Co0.1O2 with improved structural stability for Li-ion battery

Abstract

Elevating the nickel (Ni) content within layered cathodes constitutes a straightforward and effective approach to enhance the energy density of lithium-ion batteries (LIBs). However, the phase transition from H2 to H3 introduces substantial alterations in lattice volume, leading to structural degradation and diminished electrochemical performance. This study employs density functional theory (DFT) calculations to determine that the formation energy for Nb5+ occupied at Li 3b sites is lower compared to that of Ni 3a and Co 3a sites, yet higher than that of Mn 3a sites. This suggests a preference for Nb5+ doping within the Li layer of Mn-free cathodes. Motivated by these DFT results, we show the viability of high-valence Nb5+ as a stable pillar in the compositionally optimized binary oxide LiNi0.9Co0.1O2. The inclusion of this Nb5+ pillar in the Li layer of Ni/Co-based oxide significantly enhances the reversibility of the H2–H3 redox couple and mitigates microcrack formation in polycrystalline cathodes. As a result, the Nb-doped Ni/Co-based cathode exhibits an extended cycling lifespan, elevated rate capability, and increased thermal stability compared to the undoped. This investigation achieves precise control over doping sites by optimizing the chemical composition of Ni-rich cathodes and provides novel insights into advancing their electrochemical performance for high-energy LIBs.