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Advanced functional materials: self correcting stable evolution of lithium metal under large cycle capacity with periodic conductive structure

wallpapers News 2020-07-06
Because of its high theoretical capacity low reduction potential

lithium metal anode is considered to be an indispensable part of the next generation of high energy density lithium-based electrochemical batteries. However the application of lithium metal anode is still faced with some important challenges such as uncontrollable dendrite growth unstable SEI film formation large volume change. In the process of repeated deposition / stripping of lithium metal due to the complex non-uniform distribution of multiple physical fields (concentration field electric field stress field temperature field etc.) electrochemical reaction "hot spots" will inevitably appear in the electrode which will induce lithium metal to preferentially deposit at these "hot spots"; during the long-term service the lithium metal with asynchronous deposition will gradually evolve into branches The low coulomb efficiency short cycle life of the battery are caused by the crystal. This problem becomes more serious when the battery is cycled at high current density high capacity. Therefore if the lithium metal anode can repair the growth of lithium dendrite (i.e. "self correction") through its own structure design it is expected to greatly improve the safety electrochemical stability of the battery.

to solve the above problems Professor Yang Cheng of Shenzhen International Graduate School of Tsinghua University proposed a functional negative electrode composed of periodic skeleton lithium metal which is composed of conductive dielectric thin layers alternately. Combining with theoretical simulation of electric field experimental observation it shows that the functional anode has the function of "self-healing". Compared with the pure conductive structure the periodic conductive structure can realize the "bottom-up" growth mode of lithium metal avoid the disorder growth of lithium metal on the surface of the framework under the condition of large capacity cycling; compared with the pure dielectric framework structure the dielectric layer in the periodic structure can provide more electrochemical active sites thus improving the rate characteristics of the electrode. More importantly even in the case of uncontrolled growth of lithium dendrite in the dielectric thin layer (or conductive thin layer) when the dendrite growth contacts the conductive thin layer in the upper periodic layer due to the equipotential characteristics of the conductive layer the electric field (tip) at the top of the dendrite can be reduced Effect) is dispersed homogenized then the further deterioration of growth is automatically restrained which is manifested as "self correction" effect. The composite lithium metal anode based on this periodic framework can stably cycle more than 800 cycles at 5 MAH cm − 2 (50% DoD) 5 Ma cm − 2 the cumulative cycle capacity is up to 4000 MAH cm − 2.

are different from the traditional work of suppressing dendrite growth at the beginning. From the perspective of "correcting" the existing dendrite growth this research puts forward a new understing of the growth management of lithium metal provides a new design idea for the realization of high safety high stability metal negative electrode battery. The related work was recently published in

of advanced functional materials
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