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

Abstract

LiMnxFe1-xPO4 (LMFP, 0 < x < 1) cathodes exhibit a 20% higher energy density when compared to LiFePO4 cathodes owing to a higher voltage platform of Mn2+/Mn3+ redox (4.1V vs Li/Li+). However, the sluggish reaction kinetics of this redox leads to the serious phase transition, shortening the voltage platform with deteriorative electrochemical performance. Herein, we report a novel LMFP cathode with broadening Mn2+/Mn3+ redox platform via in-situ Mg2+ and Ti4+ dual-doping. The Mg2+ with smaller ion radius (0.65 Å) expands Li+ transfer channel by elongating the Li-O bond, while the Ti4+ further accelerates Li+ diffusion rates by inducing the (101) crystal-facet exposure. The accelerated Li+ diffusion effectively enhances reaction kinetics to mitigate the phase transition, resulting in a wider redox platform with increased reversible capacity, especially at high power. The as-obtained LMFP-Mg/Ti delivers a capacity of 117 mAh g -1 at 5 C, significantly increasing compared to the pristine LMFP (79 mAh g -1). Besides, this cathode retains 94.6% of the initial capacity over 1000 cycles at 3 C, highlighting its strong potential for high-power and long-life LIBs.