One-step synthesis and effect of heat-treatment on the structure and electrochemical properties of LiNi0.5Mn1.5O4 cathode material for lithium-ion batteries

• A one-step sol-gel route with resorcinol-formaldehyde resin is designed to synthesis LiNi0.5Mn1.5O4.
• Fd-3 m phase delivers an excellent high rate performance and stable cycling retention.
• A double “w”-shape R-V curve is a potential tool to indicate structure transition.

Spinel LiNi0.5Mn1.5O4 (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 °C to produce several micron-sized LiNi0.5Mn1.5O4 powders. Electrochemical measurements suggest that the 850 °C-sintered (in air) sample (Fd-3 m phase) performs the best with a discharge capacity of 141 mAh g−1 at 0.1 C and 110 mAh g−1 at 10 C, and capacity-retention of 96.3% after 60 cycles at 0.25 C and 89% after 200 cycles at 1 C. For comparison, the LiNi0.5Mn1.5O4 sample sintered at 850 °C in O2 (P4332 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.