Molecular engineering of residual lithium compounds for stable LiNi0.92Co0.05Mn0.03O2 cathodes

Abstract

Residual lithium compounds (RLCs) on the surface of high-nickel layered oxides aggravate battery capacity decay, irreversible phase transformation and safety hazards, hindering the development of high-energy density lithium-ion batteries (LIBs). Conventional physical and chemical methods not only increase the steps required to address RLCs but also fail to fully resolve the issues. Herein, we use the alkaline characteristics of RLCs to convert harmful RLCs into functional molecular layers during the slurry preparation process, facilitating the formation of a stable cathode electrolyte interfacial (CEI) layer. As a proof of concept, 2,5-thiophenediylbisboronic acid (TDBA) is selected for surface molecular engineering of a single-crystal LiNi_0.92Co_0.05Mn_0.03O₂ cathode through neutralization with RLCs. After in situ electrochemical reaction, the uniform and stable CEI forms and provides high Li⁺ diffusivity and mechanical strength, effectively suppressing cathode particle cracking and electrolyte decomposition. As a result, the cell with the modified LiNi_0.92Co_0.05Mn_0.03O₂ cathode achieves a high retention of 83.23% over 600 cycles at 1C and excellent capacity at 10C (169.9 mAh g⁻¹) and a charge cutoff voltage of 4.3 V. Even at high voltages (4.4 V, 4.5, and 4.6 V) or 60 °C, it still contributes to much better cycling stability and longevity. The fabricated modified LiNi_0.92Co_0.05Mn_0.03O₂‖graphite pouch cell stably cycles over 450 times (>92% capacity retention) at 1C. Our work presents a novel molecular engineering method that effectively re-decouples RLCs and CEI films in high-nickel layered oxides, emphasizing the significance of interface design for advancing batteries and great potential for strategy applications.