Facile template-guided synthesis of conformal Bi2O3-coated LiMn2O4 hollow microspheres for enhanced stability of lithium-ion battery cathodes

Abstract

Manganese-based cathodes have gained significant attention for lithium-ion batteries (LIBs) due to their cost-effectiveness, safety, and environmental compatibility. Among them, LiMn₂O₄ (LMO) is a promising candidate due to its high operating voltage (4.0 V) and three-dimensional lithium-ion transport pathways. However, its practical application is limited by Mn dissolution, induced by the disproportionation of Mn³⁺, leading to capacity fading and structural degradation. Surface coating strategies have been widely investigated to address this issue, with oxide coatings providing enhanced electrochemical stability while maintaining the intrinsic properties of LMO. Here, a Bi₂O₃-coated LiMn₂O₄ hollow microsphere (BiLMOhms) was synthesized via a solution-based templated self-assembly method. This approach enables the formation of an ultrathin (2 nm) conformal Bi₂O₃ coating, ensuring uniform coverage while preserving the LMO hollow structure. The Bi₂O₃ layer improves the electrochemical performance by stabilizing the cathode-electrolyte interface, enhancing lithium-ion transport, and increasing the Mn⁴⁺/Mn³⁺ ratio, thereby reducing Jahn-Teller distortion and suppressing Mn dissolution. Electrochemical characterization reveals that BiLMOhms exhibits superior cycling stability compared to pristine LMO. In half-cell tests, BiLMOhms retains 80.1% of its capacity after 1000 cycles, significantly higher than the 45.8 % retention of pristine LMO. Moreover, in a full-cell configuration with a graphite anode, BiLMOhms achieves a capacity retention of 89.5% after 100 cycles at 1C, compared to 38.4% for pristine LMO. The coating effectively mitigates capacity degradation while facilitating ionic transport at the cathode-electrolyte interface. This study demonstrates a cost-effective and scalable synthesis strategy for stabilizing Mn-based cathodes in next-generation fast-charging LIBs.