Relaxing the Jahn–Teller distortion of LiMn0.6Fe0.4PO4 cathodes via Mg/Ni dual-doping for high-rate and long-life Li-ion batteries

Abstract

Olivine-type LiMn_xFe_1−xPO₄ (LMFP, 0 < x < 1) is poised to supplant LiFePO₄ cathode materials with a ∼20% energy-density increase for Li-ion batteries (LIBs). However, its intrinsic low conductivities and MnO₆ octahedral unit-cell Jahn–Teller distortion limit its power capability and cycling life. Herein, we report a Mg/Ni dual-doped and carbon-coated LMFP micro-sized secondary sphere with greatly enhanced reaction kinetics and superior structure stability. Ni²⁺ reduces the average valence state of Mn ions to alleviate Jahn–Teller distortion by participating in charge compensation during charging while improving electronic conductivity together with carbon coating. Mg²⁺ with a smaller ion radius (65 pm) significantly widens the Li-ion transfer channel by extending Li–O bonds. The as-obtained LMFP cathodes increase reversible specific capacity by about 2.4 times at 5C compared with a pristine sample, reaching 115 mA h g⁻¹. In a pouch-type full cell, 92% of its initial capacity is still maintained after 2000 cycles at 1C, demonstrating its attractive potential for practical application in high-power and long-life LIBs.