“High-temperature calendar aging mechanism of graphite/SiO composite electrode” was investigated.
Professor Yu Seung-ho’s group focused on the lithium depletion due to the thermal instability of Si).

The research results published in Nature Communications.

▲ (From left) Professor Yu Seung-ho of KU; Lee Ban Seok (master graduate from KU); Oh Sang-Hwan (integrated master-doctoral degree program in KU); and Choi Yoon Jeong (integrated master-doctoral degree program in KU).

Professor Yu Seung-ho’s group of the Department of Chemical and Biological Engineering in the College of Engineering (co-first author: Lee Ban Seok, master course in KU; Oh Sang-Hwan, integrated master-doctoral degree programs in KU; and Choi Yoon Jeong, integrated master-doctoral degree programs in KU) investigated the causes of high-temperature calendar aging that occurs in the graphite/SiO anode materials of lithium secondary batteries. Their research presented a new mechanism of the aging of lithium secondary batteries using a composite anode.

- Title of article : SiO-induced thermal instability and interplay between graphite and SiO in graphtie/SiO composite anode
- Authors : Ban Seok Lee, Sang-Hwan Oh, Yoon Jeong Choi, Min-Jeong Yi, So Hee Kim, Shin-Yeong Kim, Yung-Eun Sung, Sun Young Shin, Yongju Lee and Seung-Ho Yu

With the emergence of the electric vehicle market, there is a need for next-generation anode materials to replace graphite that has been used to increase the energy density of lithium-ion secondary batteries. Silicon anode materials, which have a far higher theoretical capacity than that of graphite, are considered as a replacement candidate, but using silicon alone as an anode has limitations for long-term cycle performance due to the severe volumetric change that occurs during the charge/discharge process. A graphite/SiO composite electrode, manufactured by mixing SiO with graphite, is considered a highly promising strategy for overcoming the limitations, and obtaining higher energy densities.

The aging of batteries involves two processes: one is cycle aging caused by the charge/discharge of batteries, and the other is calendar aging, which refers to spontaneous lifetime deterioration over time even without charge/discharge cycling. Previous studies have shown that the aging that occurs in graphite-based lithium-ion secondary batteries is caused by the parasitic reaction between an electrolyte and an anode. However, most of the previous studies on silicon-based lithium-ion secondary batteries have focused on cycle aging, and the mechanism of calendar aging, which occurs separately from the charge/discharge cycles, has not been clearly investigated. Since batteries are exposed to varied temperature conditions during real-life use, investigating their calendar aging mechanism is necessary for the application of the graphite/SiO composite electrode with the associated high energy densities to commercial battery products.

▲ A schematic diagram of the change in electron energy that occurs in a graphite/SiO composite anode exposed to elevated temperature.

Professor Yu’s group confirmed the capacity reduction of graphite/SiO composite material stored under high temperature conditions through an electrochemical analysis, and found that the capacity reduction is caused by the loss of lithium. In addition, through visual light and X-ray based operando imaging, the researchers observed that the de-intercalation of lithium from graphite by SiO is accelerated during storage under high temperature conditions. They performed other analyses and confirmed that, during storage under high-temperature conditions, unlike a graphite electrode, the graphite/SiO composite electrode forms an additional solid-electrolyte-interphase (SEI) film by the parasitic reaction of the SiO surface with the electrolyte. Based on the experimental results, Professor Yu’s group introduced a calendar aging mechanism of lithium ion batteries including graphite/SiO composite electrodes involving lithium depletion through a parasitic reaction of the SiO surface of the graphite/SiO composite anode exposed to elevated temperature. To equilibrate the energy imbalance between graphite and SiO, graphite, having a higher electron energy, provides its electrons to SiO, resulting in the de-intercalation of lithium from graphite.

This study was supported by the Young Scientist Grants through the National Research Foundation of Korea funded by the Ministry of Science and ICT, and by LG Energy Solution. The results of the study were published in Nature Communications (IF=17.694), a globally renowned journal, on January 11, 2023.

Professor Yu said that “The high-temperature calendar mechanism suggested in our study can help us to find a way to overcome the anodic aging of lithium-ion secondary batteries. We hope that our results can make important contributions to the design and commercialization of a graphite/SiO composite anode of high energy density.”