China University of Science and Technology researches and develops a mother-of-pearl membrane to effectively improve the impact resistance of lithium batteries

The reporter learned from the University of Science and Technology of China that the research team of Yao Hongbin, Ni Yong and Yu Shuhong used bionics principles to construct a mother-of-pearl membrane, which can effectively protect lithium batteries and reduce potential safety hazards. The research results were published online recently in the "Advanced Materials", a top journal in the field of international materials.

Porous polyolefins are widely used as lithium ion battery separators due to their excellent electrochemical stability. As an insulating layer to prevent short circuit between the positive and negative electrodes of the battery, the porous structure inside the polyolefin is conducive to the passage of lithium ions during the charging and discharging of the battery, but it also results in poor mechanical properties of the separator. Especially when the separator is subjected to local external impact, its internal pore structure will inevitably cause distortion and cause cracking and partial pore closure, thereby affecting the performance and safety of the lithium battery. At present, ceramic nanoparticle coatings are widely used in the industry to improve the thermal stability of polyolefin separators and the wettability of electrolytes, but nanoparticle coatings are difficult to effectively resist the localized impact of external forces, which will inevitably lead to internal charging and discharging of batteries The process has an uneven lithium ion flow, which causes uneven lithium deposition on the electrode and even leads to the formation of lithium dendrites.

In order to solve this problem, researchers built an ordered structure of "brick and mud" imitating nacre on the surface of polyolefin membrane. The mother-of-pearl coating effectively expands the force-bearing area through the effect of sheet slip to dissipate the impact stress, thereby effectively protecting the internal pore structure of the separator and maintaining a uniform lithium ion flow inside the battery. Compared with a soft-pack battery using a commercial ceramic separator, a soft-pack battery using an imitation nacre membrane shows a smaller open-circuit voltage change and better cycle stability and high safety when faced with an impact. The research team conducted an impact test on the soft-pack batteries assembled with two types of separators. The results show that the mother-of-pearl-like separator has a good protective effect on the battery and can effectively reduce potential safety hazards.

The research results proposed a strategy to build a nacre-like toughened separator, and proved its ability to improve the impact resistance of lithium batteries from theoretical simulations and experimental tests, which will open up new ways for improving the safety of lithium batteries in the future.

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