Solid State Cells

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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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Structure of Li-ion battery(left) and solid-state battery(right) 

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. 

Reasons to develop a solid-state battery

Then, why do we need a solid-state battery? It is to increase capacity of EV batteries and increase safety.  

Safety

What users most worry about a lithium-ion battery is safety. The current Li-ion battery has a risk of battery damage such as swelling caused by temperature change or leakage caused by external force since it uses liquid electrolyte solution. Therefore, we need devices or components that can improve safety. 

However, a solid-state battery with solid electrolyte shows improved stability with a solid structure, and increased safety since it maintains the form even if the electrolyte is damaged. 

Capacity

Market research companies expect that EVs will replace ICEVs(internal combustion engine vehicles), and become the mainstream in the auto industry. And to become the unarguable leader in the industry, EV should have the similar level of mileage as the current ICEV, and it is important to increase the battery capacity of an EV battery to do so.  

There are two ways to increase capacity. First is increasing the number of batteries. But in this case, the battery price goes up and batteries take up so much space in the vehicle. 

A solid-state battery has higher energy density than a Li-ion battery that uses liquid electrolyte solution. It doesn’t have a risk of explosion or fire, so there is no need to have components for safety, thus saving more space. Then we have more space to put more active materials which increase battery capacity in the battery. 

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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A downsized solid-state battery(right) with the same capacity as the Li-ion battery(left)

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.