A damage-free way to assess the health of next-generation batteries for electric vehicles

Tokyo, Japan – Researchers at Tokyo Metropolitan University have demonstrated that electrochemical impedance spectroscopy (EIS) can be a powerful non-destructive tool for studying the degradation mechanisms of solid-state lithium metal batteries. They studied ceramic-based, all-solid-state Li-metal batteries prepared by aerosol deposition and heating, identifying the specific interface responsible for the performance drop. Their work accurately highlights the technical hurdles that must be overcome to bring these high-end batteries to market.

Electric vehicles (EVs) are a crucial part of efforts around the world to reduce carbon emissions. And at the heart of every electric vehicle is its battery. Battery design remains a major bottleneck when it comes to maximizing range and improving vehicle safety. One of the proposed solutions, solid-state lithium metal batteries, has the potential to provide higher energy density, safety and lower complexity, but technical issues continue to impede their transition to vehicles. daily.

A major problem is the large interfacial resistance between the electrodes and the solid electrolytes. In many battery designs, the cathode and electrolyte materials are brittle ceramics; it is therefore difficult to have good contact between them. There is also the challenge of diagnosing which interface is actually causing problems. Studying the degradation of all-solid-state lithium metal batteries usually requires opening them up: this makes it impossible to know what is happening during battery operation.

A team led by Professor Kiyoshi Kanamura of Tokyo Metropolitan University has developed solid-state Li-metal batteries with lower interfacial resistance using a technique called aerosol deposition. Microscopic pieces of cathode material are accelerated towards a layer of ceramic electrolyte material where they collide and form 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. Their latest solid-state Li/LisevenThe3Zr2O12/LiCoO2 the cell offers a high initial discharge capacity of 128 mAh g-1 at 0.2 and 60°C and maintains a high capacity retention of 87% after 30 charge/discharge cycles. This is the best-in-class result for solid-state Li-metal batteries with ceramic oxide electrolytes, making it all the more important to fully understand how they might degrade.

Here, the team used electrochemical impedance spectroscopy (EIS), a widely used diagnostic tool in electrochemistry. By interpreting how the cell responds to electrical signals of different frequency, they could separate the range resistors from the different interfaces of their battery. In the case of their new cell, they found that an increase in resistance between the cathode material and the solder was the main reason for the cell’s capacitance degradation. Above all, they achieved this without tearing the cell. They were also able to confirm this using in situ electron microscopy, clearly identifying interface cracking during cycling.

The team’s innovations not only achieved state-of-the-art battery design, but highlighted next steps for further improvements using a damage-free and widely available method. Their new paradigm promises exciting new advances for next-generation electric vehicle batteries.

This work was supported by the Advanced Low-Carbon Technologies (ALCA) Research and Development Program – Specially Promoted Research for Innovative Next-Generation Batteries (SPRING) (Grant No. JPMJAL1301) of the Japan Agency for science and technology (JST).

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