How it works: Solid-state batteries

There’s a race happening in automotive. Firms are chasing the next generation of battery technology that will boost electric vehicles (EVs), allowing them to travel further and charge faster. And the finish line? Solid-state batteries.

A large number of firms are in the race, including Toyota, Nissan, NIO and Samsung SDI, and they are all getting closer to bringing the technology to market, with Toyota and Nissan aiming to commercialise solid-state batteries by 2027-28.  But how much better is solid-state technology than the liquid lithium-ion batteries that are currently used in electric vehicles?

The benefits of solid-state

Toyota’s solid-state lithium-ion batteries feature a solid electrolyte that enables the faster movement of ions and offers a greater tolerance of high voltages and temperatures. This make the batteries suitable for rapid charging and discharging, as well as delivering power in a smaller form.

In numbers, that equates to a 20% increase in driving range compared to the firm’s performance battery, resulting in a 621-mile range on a single charge and fast-charging times of 10 minutes or less to go from a 10% to an 80% state of charge.

Nissan also highlights the lower cost of solid-state batteries thanks to their use of cheaper materials. With these benefits, the company expects to use solid-state batteries in a wide range of vehicle segments, making its EVs more competitive.

Here comes the science bit 

Current lithium-ion batteries use a liquid organic solvent as the electrolyte. While a liquid electrolyte can easily penetrate inside the cathode/anode and conduct lithium, high temperatures accelerate the chemical deterioration of the electrolyte, while  the flammability of organic solvents can cause accidents such as ignition in the event of a malfunction. You may have seen videos of EVs suffering thermal runaway and be aware of how difficult they are to extinguish – although it’s worth noting that EVs suffer less fires than combustion engine vehicles. In a solid-state battery, the electrolyte is not volatile or flammable and is said to be highly safe, stable in high temperatures and resistant to deterioration.

Since liquid electrolytes use organic solvents, which have low boiling points and high volatility, there are narrow operating temperature limits for charging and driving. However, as solid-state batteries don’t use liquid electrolytes, they have high operating temperature limits and excellent fast-charging performance.

With liquid electrolytes, there are also restrictions on the materials that can be selected due to side reactions with the cathode and anode materials. However, there’s less risk of side reactions with solid electrolytes thanks to their solid nature, enabling more combinations of materials. This makes it possible to select cathode materials with lower costs and anode materials with higher energy density.

Who will win the race to get solid-state batteries on the market and widely adopted is yet to be decided, but we’re getting closer to the finish line. And when solid-state batteries finally hit the market, the change in perception of EVs could be dramatic.

This is an edited extract from IMI's new MotorPro magazine, received free as part of IMI membership