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

Abstract The development of lithium manganese iron phosphate (LiMn 0.5 Fe 0.5 PO 4 ) as a high‐energy‐density cathode material offers significant advantages over LiFePO 4 , 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 MnO 6 octahedra, creating structural flexibility to accommodate Jahn‐Teller distortion, thereby enhancing the cycling stability of LiMn 0.5 Fe 0.5 PO 4 . The B‐doped sample, LiMn 0.5 Fe 0.5 P 0.97 B 0.03 O 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.