Rational design of magnetron sputtering modification strategies to unlock the cycle reversibility and rate capability of LiMn0.8Fe0.2PO4 cathodes

Abstract

Compared to commercial LiFePO₄ (LFP) cathode materials, manganese-based olivine material LiMn_0.8Fe_0.2PO₄ (LMFP) has garnered greater attention due to its comprehensive enhancement of battery performance, particularly achieving significant breakthroughs in energy density. However, its rate performance and cycle life are limited by low charge conduction and Jahn-Teller distortion of Mn³⁺. To address these issues, this study employed radio-frequency magnetron sputtering to deposit LiPON, ZnO, and Li₃PO₄ films on LMFP electrodes for comparison. The results demonstrate that the cross-linked network structure formed by nitrogen bidentate and tridentate bonds in LiPON enhances ionic conductivity and interfacial stability. Increasing the LiPON coating layer to 2.4 nm resulted in optimal electrochemical performance of the LiMn_0.8Fe_0.2PO₄ cathodes. The initial discharge capacity was 156.9 mAh g^-1 at a rate of 0.1C. The capacities measured during multi-rate charge-discharge experiments at rates ranging from 0.1C to 5C were 147.8 mAh g^-1, 141.2 mAh g^-1, and 122.7 mAh g^-1 at 1C, 2C, and 5C, respectively. There was very little capacity loss when the rate was brought back to 0.1C. Capacity retention rose from 88.0% to 95.7% after 100 cycles at 0.5C. LMFP-LiPON materials have better transition metal states close to the Fermi level and lower band gaps, according to density functional theory (DFT) simulations. In addition to increasing electronic conductivity, accelerating lithium-ion transport, and improving corrosion resistance, these changes significantly reduce the Li migration barrier. The approach offers a strong and adaptable lever for designing lithium-ion batteries of the future.