KAIST Identifies Cause of Degradation in Solid-State Batteries

A domestic research team has identified the cause of degradation in an anode-free battery. This battery, expected to be installed in electric vehicles, can travel 800 km on a single charge and be recharged more than 1,000 times, making it known as a dream technology.

(Front row from left) Lee Jeong-ah, Doctoral Program; Kang Ha-neul, Master's Program; (Back row from left) Kim Se-hoon, Doctoral Program; Choi Nam-soon, Professor. Provided by KAIST

On the 5th, KAIST announced that Professor Namsoon Choi's research team from the Department of Bio and Chemical Engineering analyzed the irreversibility of reactions occurring at the electrode interface and changes in the interfacial film structure to identify the cause of degradation in the anode-free battery.

Immediately after battery manufacturing, the solvent adsorbs onto the surface of the copper current collector, forming an initial interfacial film. During charging, lithium ions migrating from the cathode to the copper current collector receive electrons on the copper surface and are deposited as lithium metal. At this time, electrolyte anions decompose on the surface of the deposited lithium metal, forming an interfacial film on the lithium metal surface.

However, the research team confirmed that during the first charge of the anode-free battery, undesirable electrolyte decomposition reactions occur on the copper current collector surface and the deposited lithium surface, causing the interfacial film components to become unstable.

Immediately after battery manufacturing, the solvent decomposes on the current collector surface to form the interfacial film, and through galvanic and chemical corrosion of the electrolyte, the interfacial film components become unstable, reducing the reversibility of lithium metal deposition and stripping reactions.

Galvanic corrosion refers to the process where two different metals are electrically connected and immersed in an electrolyte, causing one side to corrode due to their inherent potential difference. Chemical corrosion occurs when electrons transferred to the deposited lithium metal surface layer interact with electrolyte components, causing reductive decomposition of the electrolyte.

In particular, the FSI- anion, which has high reactivity with lithium metal, repeatedly decomposes during charge and discharge cycles, thickening the lithium metal interfacial film and reducing lithium salt concentration. This results in an increase in free solvent that does not interact with lithium ions.

Free solvent has the characteristic of not participating in the dissolution process that breaks ionic bonds of ionic compounds and ionizes them. Additionally, it decomposes easily, and the decomposition products accumulate on the cathode surface, increasing resistance and causing a chain reaction of cathode structural degradation, which the research team explained is the cause of performance degradation in anode-free batteries.

They also emphasized that to prevent degradation of anode-free batteries, it is essential to create a stable initial electrode interfacial film to reduce galvanic and chemical corrosion of the electrolyte.

Professor Choi said, “The research team confirmed that undesirable electrolyte decomposition reactions occur on the lithium metal surface deposited on the current collector, and when the interfacial film components formed during this process are not stably maintained, performance degradation (degradation) of the anode-free battery occurs. This achievement will provide an important clue for developing next-generation battery systems based on anode-free technology in the future.”

This content was produced with the assistance of AI translation services.