Relaxing the Jahn-Teller distortion of LiMnFePO cathodes Mg/Ni dual-doping for high-rate and long-life Li-ion batteries

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2024-10, Vol.12 (38), p.2676-2682
• Main Authors: Yu, Haifeng, Zhang, Erdong, Yu, Jinxun, Yu, Songmin, Fang, Yaoguo, Chen, Ling, Jiang, Hao, Li, Chunzhong
• Format: Article
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d4ta04916k

Olivine-type LiMn x Fe 1− x PO 4 (LMFP, 0 < x < 1) is poised to supplant LiFePO 4 cathode materials with a ∼20% energy-density increase for Li-ion batteries (LIBs). However, its intrinsic low conductivities and MnO 6 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. Ni 2+ 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. Mg 2+ 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. The synergistic doping of divalent Mg 2+ and Ni 2+ ions into a carbon-coated LiMn 0.6 Fe 0.4 PO 4 cathode significantly enhances reaction kinetics and structural stability by mitigating the Jahn-Teller effect and accelerating the Li-ion migration rate.