https://www.samsungsdi.com/column/technology/detail/56462.html?listType=gallery
https://www.jdpower.com/cars/shopping-guides/what-is-a-solid-state-battery-for-an-electric-car
Solid State vs Li-ion:
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If you look at the image above, the Li-ion battery, which is commercially used, has a separator that keeps cathode and anode apart, with liquid electrolyte solution. On the other hand, the solid-state battery uses solid electrolyte, not liquid electrolyte solution, and the solid electrolyte plays a role of a separator as well.
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A solid-state battery can increase energy density per unit area since only a small number of batteries are needed. For that reason, a solid-state battery is perfect to make an EV battery system of module and pack, which needs high capacity.
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Future
For all its benefits, scaling up production to the level needed for usage in EVs remains an expensive endeavor. Remember, solid-state batteries’ claim to fame is a smartwatch and a heartbeat regulator.
Development costs and manufacturing difficulties are key disadvantages in producing solid-state batteries for mass-market EVs. But just as lithium-ion batteries became more affordable, the idea is that the solid-state version will be, too. And automakers are making huge investments into the technology, especially with zero-emissions brand strategies and EV-only lineups being proposed.