Reading time ( words)
In 2016, Li-ion batteries (LIB) celebrated their silver jubilee, i.e. they have been on the market, virtually unchanged, for the last 25 years. While this anniversary marked and underscores their worldwide success and diffusion in consumer electronics and, more recently, electric vehicles (EV), the underlying technology begins to show its limitations in terms of safety, performance, form factor, and cost. Samsung's Firegate has particularly highlighted the risks that even large companies incur when flammable liquid electrolytes are used.
Solid-state electrolytes have the potential to address all of those points, particularly in the electric vehicle, wearable, and drones market. Their first application was in the 70's as primary batteries for pacemakers, where a sheet of Li metal is placed in contact with solid iodine. The two materials behave like a short-circuited cell and their reaction leads to the formation of a lithium iodide (LiI) layer at their interface. After the LiI layer has formed, a very small, constant current can still flow from the lithium anode to the iodine cathode for several years. Fast forward to 2011, and researchers from Toyota and the Tokyo Institute of Technology have claimed the discovery of a sulphide-base material that has the same ionic conductivity of a liquid electrolyte, something unthinkable up to a decade ago. Five years later, they were able to double that value, thus making solid-state electrolytes appealing also for high power applications and fast charging. This and other innovations have fuelled research and investments into new categories of materials that can triple current Li-ion energy densities.
Solid-state batteries can be made thinner, flexible, and contain more energy per unit weight than conventional Li-ion. In addition, the removal of liquid electrolytes can be an avenue for safer, long-lasting batteries. With a battery market currently dominated by Asian companies, European and US firms are striving to win this arms race that might, in their view, shift added value away from Japan, China, and South Korea.