High rate performance of LiMn2O4 cathodes for lithium ion batteries synthesized by low temperature oxygen plasma assisted sol–gel process

• A low temperature process has been used to synthesize LiMn2O4 thin films.
• Plasma treatment can reduce the interface charge transfer resistances for LiMn2O4.
• LiMn2O4 cathodes treated by plasma treatment can deliver high rate capability.

Nano-crystalline LiMn2O4 thin films have been synthesized by the sol–gel process at low temperature (623 K). The low temperature prepared films are treated by a direct current pulsed oxygen plasma, and tested as cathodes for lithium batteries. The plasma treated films are able to sustain charge–discharge cycles under significant high current density of up to 5.4 A/g corresponding to 45 C for battery operation. The capacity ratio for discharging at 1.2 A/g and 0.024 A/g is over 65%, indicating low internal resistance, which meets the requirement of fast charge and discharge for electric vehicles. The stable high current density performances can be attributed to the formation of a dense surface morphology that is induced by the plasma irradiation. The formation of the surface morphology results in the more uniform current distribution on the film surface, which decreases the interface charge transfer resistances as measured by the electrochemical impedance spectra.