M. Stanley Whittingham1
Binghamton University1
The first solid-state batteries were developed more than 50 years as primary cells for medical applications. With the discovery by Yao and Kummer of the high ionic conductivity of the beta alumina class of material in the late 1960s, rechargeable solid electrolyte based batteries became a reality. Although commercialized, the operational temperature of over 300°C needed for molten sodium and sulfur has severely restricted their application.<br/> Later, Armand and his team developed polyethylene oxide (PEO) as the electrolyte for lithium metal batteries. Initially commercialized in Canada, they proved not to be safe. Blue Solutions in France later successfully commercialized such a battery using LFP as the cathode for the grid and vehicles that operates around 70°C. The safety of these cells will be discussed relative to similar liquid electrollyte cells.<br/> Two other leading classes of solid electrolyte are based on either s soft sulfide lattice or on a inorganic ceramic. Each has its own advantages and disadvantages. Critical questions that still need to be addressed that I will discuss include:<br/>1. Can a solid electrolyte stop dendrites from forning, and if not is thermal runaway less of an issue with a solid than with a solid?<br/>2. Can the interfaces between the electrodes and the electrolyte be married to allow high rates of reaction with only practical pressures being applied, or must another soft phase such as a liquid be used to "grease" the interface?<br/>3. If dual solid electrolytes are used, to ensure thermodynamic stability with both the lithium anode and the cathode, what is the manufacturing and cost penalty?<br/>4. Can thermal management be eliminated for a solid electrolyte battery pack? This would eliminate the 20% round trip efficeincy lost on Li-ion grid systems.<br/>5. Is there a limit on the thickness of ionically poorly conducitng solids such as the NMC?<br/>6. Can a Li/S cell be made to work? This would allow for the highest gravimetric energy denisty and possibly the lowest cost. What would such a cell look like?