The role and electrochemical behavior of high-valence Mo cations doped in LiNi0.8Co0.15Al0.05O2

Abstract

NCA (LiNi_xCo_yAl_1−x−yO₂, x ≥ 0.8) cathode materials have become some of the leading candidates for lithium-ion batteries due to their superior specific discharge capacity and more cost-effective production. Yet, NCA materials are facing significant challenges such as surface reconstruction and micro-cracks, which adversely impact their electrochemical performance and practical application. Herein, a simple doping modification strategy using high-valence Mo⁶⁺ cations is proposed to address these issues. The experimental analysis results demonstrate the following: (1) the high-valence Mo⁶⁺ cations provide additional positive charge and reduce the migration barrier for Li⁺, thereby improving the Li⁺ transport kinetics of NCA; (2) Mo⁶⁺ doping not only refines the primary particle size, which compacts the stacking of particles, but also optimizes the microstructure of NCA, which prevents the development of micro-cracks and thus enhances the interfacial and bulk-phase stability of NCA; (3) acting as lattice pillars in the TM layers, the high-valence Mo⁶⁺ cations increase the thermodynamic barrier for Ni²⁺ migration from TM sites to lithium sites as well as strengthen the binding with oxygen atoms, thereby suppressing surface reconstruction and oxygen release. Based on the results of electrochemical testing, the prepared Li(Ni_0.80Co_0.15Al_0.05)_0.995Mo_0.005O₂ (NCAM-1) demonstrates a remarkable capacity retention rate of 89.3% after 100 cycles within the voltage range of 3.0–4.3 V and at a rate of 1C, which is significantly higher than the 79.1% retention observed for Li(Ni_0.80Co_0.15Al_0.05)O₂ (NCA). Additionally, NCAM-1 delivers a specific discharge capacity of 153.5 mA h g⁻¹ at a high rate of 10C, which is substantially elevated compared to that of NCA (113.5 mA h g⁻¹).