Tailoring Redox Couples of Li-Rich Mn-Based Cathode Materials by In-Situ Surface Reconstruction for High-Performance Lithium-Ion Batteries

Abstract

Li-rich Mn-based layered oxides (LLOs) are promising cathode materials due to their high capacity derived from the unique cation and anion redox couples. However, the poor cycling stability and drastic voltage decay impede their practical application. Despite the covalency theory is proposed to understand the redox activity of LLOs, comprehensive design guidelines are still lacking. Inspired by the covalency theory of polyanion cathodes, high-performance LLOs are developed through an in-situ surface reconstruction strategy of near-surface doping and surface coating. Density function theory (DFT) calculations show that through the introduction of Ni²⁺ and PO₄^3-, the energy bands of the transition metal (TM) 3d-O 2p and non-bonding O-2p shift to lower energy, resulting in the elevated working potential, reduced activity of lattice oxygen, and enhanced reversibility of redox oxygen. Meanwhile, the Li₃PO₄ coating can prevent electrolyte corrosion and mitigate surface degradation of LLOs upon cycling. As a result, the capacity retention of the modified LLOs is increased from 35.9% to 77%, and the voltage retention is raised from 68.6% to 75.1% after 700 cycles at 1 C. Furthermore, at 55 ^oC the capacity retention of the modified LLOs is also elevated from 32.1% to 85.9%, and the voltage retention is improved from 67.9% to 82.3% after 120 cycles at 1 C. The proposed strategy could advance the application of high-performance LLOs and their high-energy-density Li-ion batteries.