Directions in secondary lithium battery research and development

The diverse directions in which research and development on ambient temperature secondary lithium batteries is proceeding are discussed. The state-of-the-art in liquid electrolyte-based systems containing Li metal as the anode can be described in terms of the various AA-size cells developed; they are capable of 250–300 full depth of discharge cycles, specific energies of 100–130 Wh kg−1 and energy densities of 250–300 Wh l−1. The commercialization of these batteries has been deterred by concerns of safety hazards. Approaches being pursued to resolve the safety issue include the identification of new or improved electrolytes, the use of alternative anodes, such as lithiated carbon with lower Li activity, and improved microporous separators having smaller pore size, higher porosity and “shut down” capability. The emergence of the carbon anode-based “Li ion” batteries as potentially safe systems makes it necessary to identify organic electrolytes with oxidative stability to potentials of up to 5 V vs. Li+/Li. Solid-polymer electrolyte-based solid-state batteries are being developed for a variety of military and consumer applications including electric vehicle propulsion. Solid-state batteries with performance reminiscent of their liquid electrolyte counterparts can be fabricated with the use of non-conventional polymer electrolytes. These are composed of low volatility organic liquid electrolytes embedded in organic polymer networks and have conductivities of > 10−3 ohm−1 cm−1 at 20°C. A C/LiMn2O4 cell utilizing such an electrolyte exceeded four hundred discharge/charge cycles.