High-entropy Li-rich layered oxide cathode for Li-ion batteries

Abstract

High-entropy oxides (HEOs) are emerging as promising cathode materials for Li-ion batteries (LIBs) due to their stable solid-state phase and compositional flexibility. Herein, we investigate the structural and electrochemical properties of a novel non-equimolar high-entropy cathode material, termed high-entropy Li-rich layered oxide (HE-LLO, Li_1.15Na_0.05Ni_0.19Mn_0.56Fe_0.02Mg_0.02Al_0.02O_1.97F_0.03), in comparison to a pristine Li-rich layered oxide (PR-LLO, Li_1.2Ni_0.2Mn_0.6O₂). The incorporation of multiple cations (Na⁺, Al³⁺, Mg²⁺, Fe³⁺) and anion (F⁻) into HE-LLO introduces compositional diversity, enhancing structural stability through the entropy stabilization effect. Theoretical calculations confirm a significantly higher configurational entropy in HE-LLO compared to PR-LLO, supporting its high-entropy nature. Electrochemical evaluations demonstrate that HE-LLO exhibits considerable capacity retention, preserving 76.8 % of its discharge capacity at 0.5C after 200 cycles, compared to only 36.2 % for PR-LLO. Even under high-temperature conditions, HE-LLO outperformed PR-LLO, maintaining 76.1 % of its discharge capacity after 100 cycles at 5C, while PR-LLO retained only 12.4 %. These enhancements are attributed to the improved phase reversibility and higher Li⁺ ion diffusion coefficients of HE-LLO, validated by ex-situ characterizations using a synchrotron X-ray technique, along with density functional theory (DFT) calculations. These findings highlight the promise of non-equimolar HEOs as a novel design strategy for high-performance cathode materials.