One-step synthesis and effect of heat-treatment on the structure and electrochemical properties of LiNi_(0.5)Mn_(1.5)O_4 cathode material for lithium-ion batteries

摘要

Spinel LiNi_(0.5)Mn_(1.5)O_4 (Fd-3 m) powders are synthesized by a facile one-step sol-gel approach with a resorcinol formaldehyde (RF) resin as a chelating agent. The cross-linked metal-containing RF xerogel particles are sintered at different high temperatures from 750 to 950℃ to produce several micronsized LiNi_(0.5)Mn_(1.5)O_4 powders. Electrochemical measurements suggest that the 850℃-sintered (in air) sample (Fd-3m phase) performs the best with a discharge capacity of 141 mAh g~(-1) at 0.1 C and 110 mAh g~(-1) at 10C, and capacity-retention of 96.3% after 60 cycles at 0.25 C and 89% after 200 cycles at 1 C. For comparison, the LiNi_(0.5)Mn_(1.5)O_4 sample sintered at 850℃ in O_2 (P4_332 phase) presents limited rate performance (45 mAh g~(-1) at 10 C) and higher values in both AC impedance and DC-method derived resistance. A characteristic double "w"-shape curve of DC resistance against cell potential can be possibly considered as an indicator to probe the material structure transition during the charge/discharge process of the cell.