Solid-State Lithium-Ion Batteries in EVs: A Tech Revolution in the Process

Transition to electric mobility is now undeniable with every auto-maker around the world having stated their plans from partial to fully electric within the next decade. And China leads the game with more than 70% of demand for the lithium-ion cells being catered by chinese battery manufacturers. Asian, European and American governments are trying to catch-up but the difference in investment to growth with the existing li-ion battery technology between China and other countries is phenomenal. Also, the need for safe battery technologies is by default the most important search for all the automakers around the world, as the existing semi-liquid electrolyte based LiB’s are prone to short-circuit causing runaway events due to multiple reasons. With the motivation to develop safe LiB’s and bring in parity across the world through new technology development, the Solid-state Lithium-ion batteries came into existence.

What makes solid-state lithium batteries better than liquid-state lithium batteries?
Lithium batteries have four main components: electrolyte, separator, anode, and cathode. A lithium-ion battery, which is presently used in smartphones and EVs, has a liquid-state electrolyte solution. While solid-state lithium batteries have a solid electrolyte, which also functions as a separator between the cathode and anode..

In the present LiB’s, the lithium ion’s travel from cathode to anode while charging and move back to cathode while discharging through the liquid electrolyte. During the initial cycling process, a SEI layer forms at the interface that also acts as a protection layer and as a separator. However, the continuous cycling of LiB’s leads to dendrite formations on the electrodes, which could possibly pierce through the electrolyte causing internal short-circuit leading to catastrophic events. With Solid electrolytes in place, the dendrites cannot go past the electrolyte and hence the situation is completely avoided in theory. The LiB’s are breathing during charging and discharging of the packs, i.e. they expand and contract in volume majorly attributed to the change in volume of liquid electrolyte due to the electro-chemical reactions. This is minimized in Solid electrolytes as they are more resistant to such changes. The Solid electrolytes are also stable compared to liquid electrolytes in both lower and higher temperatures. Solid-State LiB’s can also have higher energy density compared to liquid electrolyte based LiB’s.

Benefits for the e-mobility sector
Solid-state lithium-ion batteries can bring promising changes to the current EV technology. The solid-state batteries will ensure better performance, be much smaller and less expensive, and allow for fast charging. It can be estimated that the batteries get charged about 80% in 15 minutes, which will increase battery optimization and be faster than the current charging rate for liquid-state lithium batteries. With affordability, these batteries also have a longer lifeline, and these batteries will also occupy less space. It also lowers the risk of catching fire in extreme temperatures, as it is non-flammable and much safer. Solid-state lithium batteries are far more ideal for EVs than liquid-state ones, as they can store 50% more energy than the liquid-lithium battery.
 

 

Challenges with the technology
Liquid electrolyte based LiB’s evolved over a time period of 20+ years. The research on Solid state LiB’s are done only for the past 5 to 6 years. There are a lot of challenges yet to be solved Some of them are

• The manufacturing of true-solid electrolytes without any porosity that would allow Li-ions to pass through.
• The expansion and contraction of the solid electrolytes might exert enormous pressure on the electrodes.
• The increase in charge transfer resistance that indicates the resistance to the flow of ions through the electrolyte might lead to higher internal temperatures
• Initial investments for research in this area is an expensive affair

If these challenges can be worked out, then it will be a turning point for the EV industry. Many companies are working to make this happen. The Japanese company Toyota has been researching and monitoring the developments of solid-state lithium batteries, and by 2030, they are aiming to invest 13.5 billion dollars in developing the next generation of solid-state lithium batteries. Samsung is also making groundbreaking discoveries in the solid-lithium battery sector; their prototype battery for EVs can drive 800 km on a single charge.

- Ganesh Moorthi, Chief Technology Officer, Renon India Private Limited