Near-surface reconstruction in cobalt-free spinel positive electrodes for high-performance lithium-ion batteries

Spinel lithium manganate (LiMn₂O₄) is considered a highly promising cobalt-free cathode material for lithium-ion batteries (LIBs) owing to its three-dimensional Li-ion diffusion channels and the abundance of manganese. However, its practical applications are limited due to the substantial capacity deterioration induced by the Jahn-Teller effect and interfacial instability with the organic electrolyte. In this work, we propose a polyanion-based surface engineering strategy that enables simultaneous doping and the formation of a protective coating on the LiMn₂O₄ cathode. Boric acid surface modification can selectively stabilize the MnO₆ octahedron, while effectively suppressing manganese dissolution and interfacial side reactions. Additionally, the partial surface boron component reacts with PF₆^- in the electrolyte to form thermodynamically stable BF₄^-, which reduces the generation of HF in the electrolyte and stabilizes the cathode electrolyte interphase (CEI). Therefore, the modified BO3-LMO exhibits remarkable cycling stability, with a capacity retention rate of 80.6 % after 900 cycles at 1C, which is significantly superior to that of the unmodified LMO (61.1 %). Additionally, the BO3-LMO demonstrates excellent rate capability and thermal stability, retaining high performance even at elevated temperatures (55 °C) and under high-rate operation (5C). Through a combination of advanced characterization techniques-such as XRD refinement, XPS, HR-TEM and density functional theory calculations, we uncover the origins of the improved electrochemical stability after surface modification. The BO3-LMO demonstrates a higher density of states at the Fermi level, stronger MnO electron bonding, and a lower lithium-ion diffusion energy barrier. This integrated strategy not only solves the interfacial instability and structural degradation challenges but also establishes a scalable strategy for designing high-performance, cobalt-free spinel manganese-based lithium-ion batteries (LIBs).