Adverse to beneficial: upcycling residual lithium compounds on LiNi0.8Mn0.1Co0.1O2 into a stabilizing Li1+xMn2−xO4 interface

Abstract

Ni-rich layered oxide (NRLO) cathodes, though promising for next-generation high-energy Li-ion batteries (LIBs), suffer from both bulk and surface structural instability. The chemical reactivity of NRLO surfaces to moisture (H₂O and CO₂) is an industrial concern, as it leads to the formation of residual lithium compounds (RLCs) such as Li₂CO₃ and LiOH. The alkaline RLCs undergo parasitic reactions with electrolytes, forming a resistive layer on NRLO cathode surfaces and limiting electrochemical performance. This work presents an “adverse to beneficial” approach, converting surface RLCs on LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) into a high-voltage stable Li_1+xMn_2−xO₄-based interface. The chemically inert protective interface, formed by a simple wet-coating method, reduces surface side reactions with electrolytes, enhancing NMC811's cycle life by retaining 75% capacity after 300 cycles at a voltage range of (3.0–4.3) V vs. Li⁺/Li. The protective interface stabilizes the cathode surface, lowering the Li⁺ intercalation barrier and reducing the overpotential for the H2 → H3 phase transition. It also mitigates microcrack development and delays structural collapse. This surface modification enhances NMC811's stability at high voltages (4.5 V and 4.7 V vs. Li⁺/Li), improving its chemical stability and overall electrochemical performance.