Abstract: Methods of improving the performance of an energy storage device are described. The method can include providing an energy storage device, which may be a lithium ion battery. The provided energy storage device may include an electrode and a room temperature ionic liquid electrolyte. The room temperature ionic liquid electrolyte may include a lithium salt, wherein the concentration of the lithium salt in the room temperature ionic liquid is greater than 1.2M, such as from 2.4M to 3.0M. The method may further include charging and discharging the provided energy storage device. Other methods described include providing an energy storage device comprising an electrode and a room temperature ionic liquid electrolyte, heating the energy storage device to a temperature above ambient temperature (e.g., 45° C.) and charging and discharging the energy storage device.