Continued from Toyota Sees All-solid Battery in Early 2020s (1)
Major candidate: all-solid Li-S battery
All-solid battery is a general term for batteries made by replacing the liquid electrolyte of existing Li-ion rechargeable batteries with solid electrolyte. However, energy density cannot be improved just by employing solid electrolyte. It is also necessary to use next-generation positive and negative electrode materials.
One of the powerful options for improving energy density by about 200% is "all-solid Li-S battery," which uses sulfur (S) and metal lithium (or lithium alloy) as positive and negative electrode materials, respectively. In this case, the solid electrolyte is highly likely to be a sulfide-based material. The Samsung group, including Samsung SDI, which plans to commercialize an all-solid battery in 2025, seems to consider the all-solid Li-S battery as a promising candidate, judging from the announcement that it made at the Battery Symposium.
However, sulfur- and sulfide-based materials can easily catch fire. If Toyota is aiming to develop an all-solid Li-S rechargeable battery, one of the major challenges is to ensure safety.
On the other hand, Toyota is also developing an all-solid battery that is believe to be safe. It is an all-solid battery that uses an oxide material as a solid electrolyte. But it has problems in terms of energy density, output density, etc.
What Toyota is considering as the most promising all-solid battery at this point will probably have a great impact on future technology development.