Discover how silicon anodes degrade in a lithium battery

The performance and life of lithium-ion batteries are affected by the changes that occur in the electrode materials during the charging and discharging processes. However, it is difficult monitor such changes during this operation because the main battery materials, electrodes and electrolytes, are instantly contaminated when exposed to air. In an article published in the magazine ACS Energy Lettersthe research team of Korea Institute of Science and Technology (KIST) has managed to observe how the material inside lithium-ion batteries degrades.

In a battery, lithium ions move toward the anode during charging and toward the cathode during discharge. The KIST team was able to observe in real time the process that occurs in an anode made up of silicon and graphite, one of the options that currently arouses the most interest for its commercialization due to the high capacity that can be achieved with this combination. In theory, the energy capacity of silicon is 10 times greater than that of graphite, which is the material conventionally used in the anode. However, the volume of silicon nanopowders it quadruples during the charging process, making it difficult to ensure performance and security.

It has been hypothesized that these nanopores formed during the mixing of the silicon and graphite composite components can accommodate the volume expansion of silicon during battery charging, thus changing its volume. However, the role of these nanopores has never been confirmed by direct observation using electrochemical voltage curves.

silicon anode degradation lithium-interior batteries
3D reconstructed single particle of Si-C composite using SEM images obtained from the FIB milling process. (Image from ACS Energy Letters).

Using a self-designed battery analysis platform, Korean researchers directly observed migration of lithium ions towards the silicon-graphite composite anode during charging and identified the practical role of nanopores. Lithium ions were found to migrate sequentially towards carbon, nanopores and silicon in the silicon-graphite composite.

Furthermore, they found that nano-sized pores tend to store lithium ions (pre-fill lithiation) before lithium-silicon particles (S lithiation), whereas, as previously believed, micro-sized pores accommodate the volume expansion of silicon. This investigation allows the research team tosuggest more suitable anode materials for high capacity lithium batteries.

“The KIST battery analysis platform opens up new horizons in materials research by enabling the observation of structural changes in electric batteries,” says Jae-Pyoung Ahn, head of KIST’s Research Resources Division. The team plans to continue research “to drive innovations in battery material design by observing structural changes in battery materials that are not affected by atmospheric exposure,” Ahn adds.

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