Lithium ion batteries have become an indispensable part of our daily lives. However, our energy-scarce society needs longer life, faster charging speed and lighter batteries for various applications from electric vehicles to portable electronic products.
At present, this generation of lithium-ion batteries use graphite as the anode, which has a relatively low capacity and may be replaced by a silicon anode with a higher capacity and less environmental impact. This is a very promising research direction-but it is elusive, because batteries with large-particle silicon anodes tend to have a shorter life, usually less than 50 cycles.
But when researchers tried to use nanoparticles of silicon, aluminum and bismuth, they found that these nano-alloy anodes still have short cycle and high cost problems. However, now a team of researchers from the University of Maryland and the US Army Research Laboratory may have found a new solution to this degradation problem: the electrolyte.
These researchers have created an electrolyte that forms a protective layer on silicon; this layer is stable and resists the swelling that normally occurs in silicon anode particles. The new electrolyte-rationally designed with basic principles-provides anode particle space for silicon to expand within the protective layer. The researchers reported their work in a paper in Nature Energy.
"Our research proves that as long as the electrolyte is properly designed, silicon, aluminum and bismuth particles can be cyclically used as anodes for lithium ion batteries, which was not possible in the past, said Ji Chen of the Department of Chemistry and Biomolecular Engineering at the University of Maryland. , He is the lead author of this paper.
"The energy density of the battery is determined by the electrode, and the performance of the battery is strictly controlled by the electrolyte. The designed electrolyte can use a micro-alloy anode, which will significantly improve the energy density of the battery," Xiulin from the University of Maryland, a professor at Zhejiang University in China Fan said.
Oleg Borodin, a collaborator of the US Army Research Laboratory, said: "At present, the combined efforts of molecular simulation and experiment have opened up a new direction for the rational design of electrolytes that can extend the cycle life of large-capacity silicon anodes."
The purpose of the current silicon anolyte design is to form a uniform polymer layer called a solid electrolyte interface (SEI) on the anode, which is flexible and firmly bonded to silicon. To make matters worse, the strong bond between the polymer SEI and the silicon anode forces the SEI to undergo the same volume change as the anode particles when it expands, causing the particles and SEI to crack simultaneously during battery operation.
Chunsheng Wang, a professor of chemistry and biomolecular engineering at the University of Maryland, said: "After extensive research on silicon electrodes, the battery industry has reached a consensus that micro silicon anodes cannot be used in commercial lithium-ion batteries." We successfully avoided the damage of SEI and formed A ceramic SEI with low affinity for siliconized lithium particles enables siliconized silicon to be repositioned on the interface without changing the volume without damaging the SEI. The electrolyte design principle is universal for all alloy anodes, opening up new opportunities for the development of high-energy batteries. "
Wang said that the commercialization of electrolytes still faces challenges; for example, the 4.2V voltage window still needs to be expanded.