Broadening the Mn2+/Mn3+ redox plateau in LiMn0.6Fe0.4PO4 cathodes for high-power and long-life Li-ion batteries

Abstract

LiMn_xFe_1−xPO₄ (LMFP, 0 < x < 1) cathodes exhibit 20% higher energy density compared to LiFePO₄ cathodes owing to the higher voltage plateau of the Mn²⁺/Mn³⁺ redox couple (4.1 V vs. Li/Li⁺). However, the sluggish reaction kinetics of this redox couple lead to a serious phase transition, shortening the voltage plateau and reducing the electrochemical performance. Here, we report a novel LMFP cathode with a broadened Mn²⁺/Mn³⁺ redox plateau via in situ Mg²⁺ and Ti⁴⁺ dual-doping. Mg²⁺, with its smaller ionic radius (0.65 Å), expands the Li⁺ transfer channel by elongating the Li–O bond, while the Ti⁴⁺ further accelerates Li⁺ diffusion rates by inducing (101) crystal-facet exposure. The accelerated Li⁺ diffusion effectively enhances reaction kinetics to mitigate the phase transition, resulting in a wider redox plateau with increased reversible capacity, especially at high power. The as-obtained LMFP-Mg/Ti delivers a capacity of 117 mA h g ⁻¹ at 5 C, which represents a significant increase compared to the pristine LMFP (79 mA h g ⁻¹). Additionally, this cathode retains 94.6% of its initial capacity over 1000 cycles at 3 C, highlighting its strong potential for high-power and long-life LIBs.