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Sunday, 23 February 2020

New material doubles the battery life of electric vehicles


The anodes currently constituting most energy storage systems are made from graphite. However, this material is not the most optimal for ensuring long-term storage and stability during the many charge / discharge cycles. The alternative is silicon, a much more effective material, but suffering from certain defects preventing its commercialization. Recently, a team of Korean researchers has developed a series of very simple procedures using corn starch, making it possible to correct these defects and opening the way for a massive use of silicon in future batteries.

Hun-Gi Jung and his research team at the Center for Energy Storage Research at the Korean Institute of Science and Technology (KIST) announced the development of silicon anodes that can quadruple the capacity of a battery, compared to graphite anode materials, and which allow rapid charging to over 80% of capacity in just five minutes. When applied to electric vehicle batteries, the new materials are expected to more than double their range.

The batteries currently installed in standard electric vehicles use graphite materials, but their low capacity contributes to the fact that electric vehicles have a shorter range than vehicles with internal combustion engines. Consequently, silicon, with an energy storage capacity 10 times greater than graphite, has attracted attention as a new generation material for the development of long-range electric vehicles.



Improving silicon capabilities with carbon-silicon composites

However, the silicon materials have not yet been marketed because their volume increases rapidly and the storage capacity decreases considerably during the charge and discharge cycles, which limits marketing. A number of methods have been suggested to improve the stability of silicon as an anode material, but the cost and complexity of these methods have prevented silicon from replacing graphite.

To improve the stability of silicon, Jung and his team focused on the use of common materials in our daily lives, such as water, oil and starch. They dissolved starch and silicon in water and oil, respectively, and then mixed and heated them in order to produce carbon-silicon composites. A simple thermal process used for frying food was employed to firmly fix the carbon and silicon, preventing the silicon anode materials from expanding during charge and discharge cycles.

Higher performance than graphite anodes
The composite materials developed by the research team demonstrated a capacity four-times greater than that of graphite anode materials (360mAh/g - 1,530mAh/g) and stable capacity retention over 500 cycles. It was also found that the materials enable batteries to charge to more than 80% capacity in only five minutes.  The results were published in the journal Nano Letters.


Structure and properties of the carbon-silicon hybrid developed by the researchers. Credits: Hyun Jung Kwon et al. 2020

Carbon spheres prevent the usual volume expansion of silicon, thereby enhancing the stability of silicon materials. Also, the use of highly conductive carbon and the rearrangement of the silicon structure resulted in a high output.

"We were able to develop carbon-silicon composite materials using common, everyday materials and simple mixing and thermal processes with no reactors," said Dr. Jung, the lead researcher of the KIST team. He continued, "The simple processes we adopted and the composites with excellent properties that we developed are highly likely to be commercialized and mass-produced. The composites could be applied to lithium-ion batteries for electric vehicles and energy storage systems (ESSs)."





Bibliography:

Nano/Microstructured Silicon–Carbon Hybrid Composite Particles Fabricated with Corn Starch Biowaste as Anode Materials for Li-Ion Batteries

Hyun Jung KwonJang-Yeon HwangHyeon-Ji ShinMin-Gi JeongKyung Yoon ChungYang-Kook Sun, Hun-Gi Jung

Nano Lett. 2020, 20, 1, 625-635
Publication Date:December 11, 2019

https://doi.org/10.1021/acs.nanolett.9b04395

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