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Amid their thriving business caused by growing popularity of smartphones and electric cars, lithium-ion battery makers have constantly been haunted by the possibility of the self explosion of their batteries, due to the formation of dendrite in lithium, which may penetrate the insulation layer, due to over-charging or after multiple usages. The problem is especially serious in the case of organic lithium-ion battery, a major blockage for its commercialization.
Reza Shahbazian-Yassar, associated professor at UIC Department of Mechanical and Industrial Engineering, explains that although organic electrolytic solution can augment the energy density of lithium-ion battery, heterogeneous lithium, after multiple times of charging and discharging, tend to produce uneven deposition, leading to the formation of dendrite.
Therefore, UIC and Texas A&M University (TAMU) has formed a team to solve the problem, in addition to understanding the chemical and physical principles behind the formation of dendrite, via the assistance of supercomputer. Perla Balbuena, professor at the TAMU Department of Chemical University, points out that the team aims to develop protective coating material for lithium, thereby dampening lithium deposition.
The team has developed a oxidized graphene nanosheet which can be sprayed onto the fiberglass separating layer of the battery, which can facilitate low of lithium-ion, while slowing down and controlling the combination of ions and electrons to form neutral atoms. The coating can help with even deposition of atoms to form a flat surface at the bottom, rather than an uneven one like needles.
Researchers utilize computer model and simulation, plus physical test and use of microscope, to produce images, showing that lithium-ion would form thin film on oxidized graphene layer before passing through interstices between materials and then depositing beneath the oxidized graphene layer.
In addition, oxidized graphene can lengthen the life of batteries to 160 cycles, compared with 120 of other batteries.
Although cost of oxidized graphene coating is low, it is challenging to ascertain the position of the coating, which is very thin. Balbuena, however, notes that the result of tests show there is no need to determine the position of the coating precisely.
Researchers also try to understand, via computer model, whether parallel or vertical coating method for oxidized graphene, relative to current collector, can produce better result. The finding is that both methods are effective, although larger interstices between materials is needed, in the case of parallel coating. Balbuena points out that computer simulation can help the team and collaborators understand how ions are transferred via coating. The finding has been published in "Advanced Functional Materials."
(Written by Daisy Chuang; First photo courtesy of Pixabay)