Solid-state electrolytes drive the quest for a safer battery
He points to polymer-based electrolytes that are already used in Bolloré’s cars in France, and several companies like SEEO, Solvay, and Solidenergy developing organic ionic conductors for wearables, drones and electric vehicles. Solvay in particular is promoting its research and development on gel polymer electrolytes for low-power applications, he says.
Volkswagen, BMW, Toyota, Hyundai, and many other automotive companies are also looking at the technology for safer batteries. Grande highlights Toyota as the car company doing the most work in this field, demonstrating a golf cart in Japan equipped with a small inorganic solid-state battery, with an energy density that is in the 200-400 Wh/L range. Toyota is using a composite electrolyte made of LLZO particles immersed in a LPS matrix.
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 shift added value away from Japan, China, and South Korea he says.
However, he points out that inorganic solid-state electrolytes are significantly heavier than liquid ones, and interfacial properties are not yet optimised to enable stability to the anode and the cathode. On top of that, solid electrolytes only make sense in terms of performance enhancement if lithium metal is used as anode material.
Next: Challenges and related stories…
The problem with that is twofold: first, lithium is a very reactive material and does not cycle reversibly in most cases; secondly, it has to be made thin enough (20 microns and below) to truly make use of its high specific capacity. Solving both issues comes however at the expense of cost. On top of this, no large-scale manufacturing processes exist yet for inorganic electrolytes.
Grande points to start-up Solid Power that is working on the manufacturing process, but it is still at a pilot stage. Replacing bare lithium metal with a host material like silicon is an attractive solution, and some companies are working on that, but only in combination with standard liquid electrolytes. For example Polyplus in California has developed a new glassy electrolyte, together with Schott in Germany that can be coupled with ultra-thin lithium metal and is inexpensive and easy to process. At the same time Li-ion battery pioneer Prof John Goodenough has says he has found an alternative path to cheap and long-lasting solid-state batteries with three times the energy density of today’s designs.
IDtechX predicts the market will reach over $7 billion by 2027 in its latest report on solid state and polymer technologies at www.idtechex.com/research/reports/solid-state-and-polymer-batteries-2017-2027-technology-markets-forecasts-000498.asp
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