Discover the secrets of material degradation in a lithium-ion battery


Block diagram of the KIST battery analysis platform. Credit: Korea Institute of Science and Technology (KIST)

As part of global efforts towards carbon neutrality, automakers around the world are actively engaged in research and development to convert internal combustion engine vehicles into electric vehicles. As a result, the competition to improve battery performance, which is at the heart of electric vehicles, is intensifying. Since their commercialization in 1991, lithium-ion batteries have held a dominant market share in most market segments, from small household appliances to electric vehicles, thanks to continuous improvements in energy density and efficiency. However, some phenomena occurring within such batteries are still poorly understood, such as expansion and deterioration of the anode material.

The Korea Institute of Science and Technology announced that its team led by Dr. Jae-Pyoung Ahn (Research Resources Division) and Dr. Hong-Kyu Kim (Advanced Analysis and Data Center) successfully observed real-time l expansion and deterioration of the anode material in batteries due to the movement of lithium ions. The team’s research is published in ACS Energy Letters.

The performance and lifespan of lithium-ion batteries are generally known to be affected by various changes that occur in the internal electrode materials during charging and discharging processes. However, it is difficult to monitor these changes during operation because key battery materials, such as electrodes and electrolytes, are instantly contaminated when exposed to air. Therefore, the accurate observation and analysis of the structural changes of the electrode material during the migration of lithium ions is the most important factor for improving performance and safety.

In a lithium-ion battery, lithium ions move to the anode during charging and to the cathode during discharge. The KIST research team succeeded in real-time observation of a silicon-graphite composite anode, which is being studied for its commercial use as a high-capacity battery. Theoretically, the load capacity of silicon is 10 times greater than that of graphite, a classic anode material. However, the volume of silicon nanopowders quadruples during the charging process, making it difficult to guarantee performance and safety. It has been hypothesized that the nanopores formed during the mixing of the constituents of silicon-graphite composites can adapt to the volume expansion of silicon during battery charging, thereby changing the volume of the battery. However, the role of these nanopores has never been confirmed by direct observation with electrochemical voltage curves.

Discover the secrets of material degradation in lithium-ion batteries

Scanning electron microscopy (SEM) images of lithium migration in silicon-graphite composites. Credit: Korea Institute of Science and Technology (KIST)

Using a self-designed battery analysis platform, the KIST research team directly observed the migration of lithium ions into the silicon-graphite composite anode during charging and identified the role practice of nanopores. It was found that lithium ions migrate sequentially into carbon, nanopores and silicon in the silicon-graphite composite. Additionally, the research team noted that nano-sized pores tend to store lithium ions (pre-fill lithiation) before lithium-silicon particles (Si lithiation), while micro-sized pores adapt to the volume expansion of silicon as previously believed. Therefore, the research team suggests that a new approach that appropriately distributes micro and nano sized pores to mitigate the volume expansion of silicon, thereby improving material safety, is needed for the design of silicon materials. capacity anode for lithium-ion batteries.

“Just as the James Webb Space Telescope heralds a new era in space exploration, the KIST Battery Analysis Platform opens new horizons in materials research by enabling the observation of structural changes in electric batteries. “, said Dr. Ahn, head of KIST’s research resources division. . “We plan to continue the additional research needed to drive innovations in battery material design, observing structural changes in battery materials that are unaffected by atmospheric exposure,” he said.

Prevention of lithium loss for high capacity lithium-ion batteries

More information:
Hyun-Jeong Lee et al, Lithiation pathway mechanism of Si-C composite anode revealed by the role of nanopores using in situ lithiation, ACS Energy Letters (2022). DOI: 10.1021/acsenergylett.2c01022

Provided by the National Science and Technology Research Council

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