Hanyang University announced on July 18th that the Professor Yoo Won-cheol's research team from the Department of Chemical and Molecular Engineering has developed a silicon-based of Lithium Ion Battery with high energy density. The Silicon (theoretical capacity 4200mAh/g) anode material developed by the research team has 10 times or more of the theoretical capacity than the existing graphite (theoretical capacity 372mAh/g) anode material, getting attention as a next generation Lithium Ion Battery (hereinafter referred to as LIB).

Silicon-based LIBs with high theoretical capacity have weaknesses of high volume expansion (approximately 300%) and low electricity conductivity. For the past 10 years to overcome these weaknesses, researchers around the world have tried to use Nano structure. However, new approach has been needed due to the practical issues in the real industry such as high tap density, small surface area, high loading level, high capacity per area and more.

To overcome these shortages, professor Yoon's team conducted research to improve the weakness of volume expansion and low conductivity, using wrinkled-multilayered-graphene(WMG) and silicone in micron size.

Since graphene is a two dimensional material with high conductivity, it is evaluated to have excellent mechanical properties and be used in various fields. However, it needs improved physical strain to take high volume expansion of silicone during charging and discharging. It also has to chemically be attached with silicon, the active material, to prevent performance degradation during continuous charging and discharging cycles.

In order to do so, Professor Yoo's team succeeded in controlling the density of graphene oxide aqueous solution and synthesizing it by using the wrinkled-multilayered-graphene oxide (WMGO).

Professor Yoon's team found out that high density of graphene oxide aqueous solution is easier to have wrinkled structure than the one with low density, since the number of graphene exide layers through pi-pi stacking is limited compared to the relatively low density.

The WMG with wrinkled and thin multilayers has more improved physical strain than graphene. By using the synthesized WMGO in this way, silicon and compound (silicone-WMGO) were synthesized. As WMGO has chemical functionalization group including various oxygens such as carboxylic acid and phenolic acid, silicon-WMGO with excellent adhesive strength could be synthesized through hydrogen bonding with silica on the surface of silicon. 

As a result, the research team succeeded in compounding graphene with excellent conductivity by combining silicon-WMG through a thermal deoxidation, checking that high volume expansion of silicon is effectively buffered during charging and discharging, thanks to the the wrinkled and thin multilayers.

The silicon-WMG using micron silicon showed a very high initial capacity per area when charging and discharging both in low and high speed. In particular, it was reported that the capacity value per area was high (5.3 mAh/cm2 @2 C for 240 cycles) even in the high-speed charge and discharge cycles, showing that the silicon-WMG composite operated stably under various charge/discharge conditions.

Professor Yoo Won-cheol expressed, “This research can contribute to the material development for the next generation energy storage which is mandatory for reducing global warming reduction through carbon neutrality."

This research was done with the support of LG chemicals, basic research project (mid-sized research) by Ministry of Science and ICT, Gyeonggi-Do regional research center and the result of the research was published on a world-renowned journal on energy storage [Energy Storage Materials, IF: 20.831] (Paper name: High-Areal-Capacity of Micron-Sized Silicon Anodes in Lithium-Ion Batteries by Using Wrinkled-Multilayered-Graphenes).