Achieving Ultrahigh Cycling Stability of LiMn _0.5 Fe _0.5 PO ₄ Through Oxygen Vacancy with Jahn‐Teller Distortion Accommodation Induced by B‐Doping at P‐site

The development of lithium manganese iron phosphate (LiMn_0.5Fe_0.5PO₄) as a high-energy-density cathode material offers significant advantages over LiFePO₄, but its practical application is hindered by the Jahn-Teller distortion induced by Mn during charge-discharge cycles, leading to reduced cycling stability. In this study, B-doping at the P-site through a solvothermal method is introduced, which induces the formation of oxygen vacancies. These vacancies result in the partial removal of oxygen from MnO₆ octahedra, creating structural flexibility to accommodate Jahn-Teller distortion, thereby enhancing the cycling stability of LiMn_0.5Fe_0.5PO₄. The B-doped sample, LiMn_0.5Fe_0.5P_0.97B_0.03O_4-δ/C (LMFP-B3/C), exhibited superior electrochemical performance, retaining 98.09% of its capacity after 1000 cycles at a 1C rate, with a final capacity of 121.43 mAh g^-1. In contrast, the undoped sample retained only 74.28% of its capacity under the same conditions, with a final capacity of 86.17 mAh g^-1. Density functional theory (DFT) calculations confirmed that the presence of oxygen vacancies not only mitigates lattice volume changes during cycling but also reduces Li⁺ migration barriers. This work provides critical insights into the role of B-doping and oxygen vacancies in stabilizing the structure and improving the electrochemical performance of phosphate-based cathode materials, paving the way for more durable and efficient lithium-ion batteries.