Researchers from Tokyo Metropolitan University successfully demonstrated a damage-free method that allows lithium metal batteries to be used in electric vehicles.
They found that electrochemical impedance spectroscopy (EIS) is a powerful, non-destructive tool for studying the degradation processes of solid-state lithium metal batteries. The study precisely identifies the interface responsible for the drop in battery performance.
This new discovery makes it possible to create a new generation of electric vehicles, overcoming previous engineering problems that prevented the use of lithium metal batteries.
The role of metallic LI batteries in electric vehicles
Electric vehicles are a key advance in reducing carbon emissions, with their most crucial component being the battery.
Using lithium metal batteries in electric vehicles would maximize their potential. They may provide higher energy density, safety and less complexity, but technical issues conceal their chances of becoming the most common type of vehicle.
The biggest problem is the large interfacial resistance between the electrodes and the solid electrolytes. Both materials are composed of fragile ceramics, which leads to a lack of good contact between them. Scientists are struggling to identify which interface is causing the problem.
Studying the degradation process of lithium metal batteries is also a challenge. The process requires opening them, making it impossible to know what’s going on while the battery is still in working order.
How does EIS overcome these technical issues?
The team developed solid-state batteries with lower interfacial resistance through a technique called aerosol deposition, where microscopic pieces of cathode material are accelerated toward a layer of ceramic electrolyte material, colliding and forming a dense layer.
To overcome the problem of cracks forming during the collision, the team coated the pieces of cathode material with a “solder” material, i.e. a softer material with a low melting point. which can be heat treated to generate excellent contact between the newly formed cathode and electrolyte.
The results show that the lithium metal batteries retain a high capacity retention of 87% after thirty cycles. The researchers say this is the best result for lithium metal batteries with ceramic oxide electrolytes and is a crucial development in understanding how they might degrade.
The researchers then used EIS to interpret how lithium metal batteries respond to electrical signals of different frequencies. This allowed them to separate the resistance of the different battery interfaces and they discovered that the increase between the cathode material and the solder was the main reason for the cell’s capacity degradation.
Because they were able to identify this without opening the battery, the researchers identified a harmless and widely available method. This promises exciting new advances towards the use of lithium metal batteries in the next generation of electric vehicles.