Electrochemical behavior of NH₄F-pretreated Li_1.25Ni_0.20Fe_0.13Co_0.33Mn_0.33O₂ cathodes for lithium-ion batteries

We report a novel method to fabricate lithium-ion batteries cathodes with the NH₄F pretreatment. In this study, NH₄F-pretreated Li_1.25Ni_0.20Fe_0.13Co_0.33Mn_0.33O₂ hollow nano-micro hierarchical microspheres were synthesized for use as cathode materials. The X-ray diffraction patterns of NH₄F-pretreated Li_1.25Ni_0.20Co_0.33Fe_0.13Mn_0.33O₂ were analyzed with the RIETAN-FP software program, and the results showed that the samples possess a layered ff-NaFeO2 structure. The effects of pretreatment withNH₄F on the electrochemical performance of the pristine material were evaluated through charge/discharge cycling, the rate performance, and electrochemical impedance spectroscopy (EIS). Pretreatment with NH₄F significantly improved the discharge capacities and coulombic efficiencies of Li_1.25Ni_0.20Co_0.33Fe_0.13Mn_0.33O₂ in the first cycle and during subsequent electrochemical cycling. The sample pretreated with an appropriate amount of NH₄F (NFCM 90) showed the highest discharge capacity (209.1 mA h g^-1) and capacity retention (85.2% for 50 cycles at 0.1 C). The EIS results showed that the resistance of the NFCM 90 sample (76.32 Ω) is lower than that of the pristine one (206.2 Ω).