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Enhance the safety of lithium batteries

Lithium-ion batteries are a widely used class of rechargeable batteries in today’s world. One of the processes that can hamper the functioning of these batteries is an internal short circuit caused by direct contact between the cathode and anode (the conductors that complete the circuit within a battery). To avoid this, separators composed of polyolefins – a type of polymer – can be employed to maintain separation. However, these separators can melt at higher temperatures, and the inadequate absorption of electrolytes (essential for conveying charges between electrodes) can result in short circuits and diminished efficiency. Several different methods have been proposed to tackle these issues.

One such method is to apply ceramic coatings on the separators to improve the way they handle pressure and heat. However, this can increase the thickness of the separators, reduce their adhesion, and harm battery performance. Another technique is to use polymer coatings, in a process known as graft polymerisation. This involves the attachment of individual units (monomers) to the separators to give them the desired qualities.

Now advancing research, a recent study published in Energy Storage Materials demonstrates successful graft polymerisation on a polypropylene (PP) separator, incorporating a uniform layer of silicon dioxide (SiO₂). The research results of the joint study conducted by a team of researchers, including Assistant Professor Jeongsik Yun from the Department of Energy and Chemical Engineering at Incheon National University, were made available online on 13 December, 2023, and featured in Volume 65 of Energy Storage Materials in February 2024.

Dr Yun was motivated by the need for high-performance battery materials in electric vehicles to achieve longer driving ranges, an area he has been actively working on. Beyond improving battery performance, his goal is to ease consumer concerns about battery explosions, potentially influencing their decisions to embrace electric vehicles. According to him, “Battery explosions are frequently initiated from the melting of a separator. The commercial battery separator is made of polyolefins, a class of polymers which are vulnerable to heat. We therefore aimed to improve the thermal stability of the commercial separators by coating them with thermally robust materials such as SiO₂ particles.”

In this study, a PP separator was modified in several ways. Initially, it was coated with a layer of polyvinylidene fluoride, a chemical chosen to enhance electrolyte affinity and thermal stability, while also introducing grafting reaction sites. Then, the separator underwent grafting with methacrylate molecules, followed by a final coating with SiO₂ particles. These modifications made the separator stronger and more resistant to heat, suppressed the growth of lithium dendrites, and helped improve the cycling performance.

Furthermore, the modifications not only preserved the energy storage of Li-ion batteries per unit volume, but also outperformed other coating methods in cell performance. This technique thus shows promise for creating robust separators and advancing the use of lithium-ion batteries in electric vehicles and energy storage systems.

“We hope that the results of this study can enable the development of high-safety lithium batteries. We believe that the thermal stability of these batteries will greatly benefit the current fire-sensitive electric vehicle field. In the long term, this can motivate people to choose electric vehicles and, in urban areas, reduce the suffering of people from breathing in the polluted air generated by the internal combustion engines,” envisions Dr Yun.

In summary, this study presents a reliable method for creating an innovative and durable separator for lithium-ion batteries, potentially paving the way for a greener future!

References

Title of original paper: Ultra-thin SiO₂ nanoparticle layered separators by a surface multi-functionalization strategy for Li-metal batteries: Highly enhanced Li-dendrite resistance and thermal properties

Journal: Energy Storage Materials

DOI: https://doi.org/10.1016/j.ensm.2023.103135

Authors: Jaewon Park¹, Young Je Kwon¹, Jeongsik Yun², Kaiyun Zhang¹, Min Jeong Lee¹, Gyeong Min Choi¹, Ji woo Bae¹, Se Hun Kim¹, Joon Ha Chang³, Min Wook Pin³, Jin Hong Lee⁴, Hoik Lee⁵, and Kie Yong Cho¹

Affiliations:

¹Department of Industrial Chemistry, Pukyong National University

²Department of Energy and Chemical Engineering, Incheon National University

³Analysis and Assessment Research Center, Research Institute of Industrial Science and Technology (RIST)

⁴School of Chemical Engineering, Pusan National University

⁵Research Institute of Convergence Technology, Korea Institute of Industrial Technology

Corresponding author’s email: kieyongh@pknu.ac.kr

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