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Shape preserving metal particles in advanced graphene: Materials

wallpapers News 2020-08-27

has the lowest electrochemical potential the highest theoretical specific capacity. Lithium metal is the best choice for the anode of high-energy lithium-ion batteries. However when Li is in contact with electrolyte the side reaction occurs. The SEI passivation layer formed at the interface is not deformable fragile which leads to the continuous occurrence of cracks uneven Li deposition dendrite growth eventually leads to fire accidents even explosions. In addition the repeated deposition / dissolution of dendrite consumes electrolyte Li metal resulting in low coulomb efficiency (CE) short cycle life high overpotential electrode volume change. Therefore the protection of lithium anode is an important issue in the commercialization of lithium metal batteries. It is found that the change of planar interface morphology can avoid the problems of Li dendrite crushing the following conditions need to be met: 1) the surface of Li metal anode is smooth the charge distribution is uniform; 2) SEI has uniform morphology chemical composition; 3) the original uneven Li ion flux in electrolyte needs to be redistributed. However it is difficult to form super conformal contact between the film the surface of Li metal by conventional methods the mechanical properties are limited by the wavy structure. Therefore it is still a challenge to construct practical extensible shape preserving SEI.

Professor Yu Guihua's team at the University of Texas at Austin USA aims at this problem by using mechanical shear force to peel the graphite on the Li surface into graphene arrange it in parallel in the Li metal block. After electrochemical lithium extraction a few layers of graphene nanosheets are stacked on the lithium metal surface as a super conformal protective layer which has the characteristics of shape adaptation good mechanical properties The mechanical properties lead to the change of the planar morphology of the interface effectively inhibit the side reaction between the electrolyte Li metal.

the research team proposed a simple effective method to construct a flexible protective film of super conformal shape by stacking a few layers of defect free graphene nanosheets on the surface of Li metal in situ. The two-dimensional protective film can exp / contract conformally with the deposition / dissolution of micron sized Li metal particles which can prevent the direct contact between electrolyte Li metal for a long time tightly wrap the lower Li anode. Due to the interlaminar sliding of the two-dimensional material the film can adapt to the volume change of Li metal without cracks due to its excellent tensile property. In addition the defect free graphene with few layers contributes to the rapid transfer of Li ions promotes the re uniform distribution of Li ion flux at the interface. The Li metal anode with this protective film can work stably for 1000 h at 5 Ma cm-2 in symmetrical batteries which is longer than the life of graphene film stabilized Li metal anode. Therefore it provides an efficient practical strategy for the commercialization of lithium metal batteries provides a new idea for solving the stability problems of other metal metal alloy anode materials.

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