Interface Modification And Engineering For Dendrite-free Li-Metal Anode

The energy density of conventional Li-ion battery will be hard to catch up with the booming electronics and EV industries,because of the theoretical limitation of the cathode/anode materials used in conventional Li-ion battery.Li-metal battery is considered as the promising next-generation energy storage device for its super high specific energy density.Developing a well-performed lithium anode is the key to improve the reliability and practicability of Li-metal battery.Currently,almost all the safety designs about lithium anode are actually to obtain uniform SEI on the deposition surface.The ideal SEI can not only hinder the formation of dendritic lithium but also stop the side reaction between lithium and electrolytes.In order to get such an ideal SEI,a normal way is to put additive in the formation process of the SEI.It is not sustainable because of the consuming of the additive during cycling.however,one possible way to obtain a stable SEI is to regulate Li⁺transportation by modifying lithium anode surface with optimized structures.In addition,preparing in-situ or ex-situ artificial SEI on lithium anode is another effective method to obtain a stable SEI.So,this research is focus on stabilizing the surface of lithium anode through structure modification and surface protection.Regarding to the structure modification,spatial dimension-optimized ZnO nanosheets are constructed on the 3D Ni foam.ZnO can greatly reduce the nucleation barrier of metallic lithium deposition and achieve regular deposition on the surface of the anode.About the surface protection,ex-situ artificial SEI protective film is prepared with an in-situ reaction on the surface of lithium.The protected lithium anode can deliver a super stable electrochemical performance for the good mechanical strength and Li⁺conductivity of the protective film.Finally,structure modified and surface protected Li-meal anodes are obtained as high-capacity/log-life metal lithium anodes and the research includes the following contents:（1）Using Zn-MOFs as the self-sacrificing templates to construct grain-like ZnO（GZNF）and vertical ZnO nanosheets（LZNF）on the Ni foam.Different lithium deposition behaviors are compared to analysis the structural influence on lithium plating.The results show that ZnO nanosheets arrays with higher structure and larger specific surface area provide more nucleation sites for lithium to deposit regularly.Then,3D composite Li-metal anodes are constructed by infusing molten Li into the LZNF and GZNF,respectively.The symmetric cells and LFP full cells assembled with LZNF@Li or GZNF@Li electrodes are compared with different current density.LZNF@Li shows smaller overpotential and better cycling performance than GZNF@Li.The SEM analysis show that GZNF@Li can’t maintain stable Li plating morphology,while LZNF@Li electrodes can keep regulated Li deposition behavior and exhibit more stable long-life cycling performance than GZNF@Li.（2）Preparing Li₅Sn₂/PVDF-HFP（PSI）composite protective film with gradient structure by in-situ reaction on lithium anode.Cross-sectional EDX and surface etching XPS verify the gradient distribution of Li₅Sn_2.In-situ optical observation shows that PSI protective film can effectively prevent the side reaction between electrolyte and lithium.In addition,PSI with a gradient distribution of Li₅Sn₂ can not only improve the dynamic performance of Li⁺transportation,but also stop the dendrite growth for its high mechanical strength.As a result,the symmetric cells with PSI-Li electrodes deliver more stable cycling performance than pure PVDF-HFP protected Li-metal electrodes,and even at a super high current density of 20 mA cm^-2,the symmetric cell with PSI-Li electrodes can still maintain stable for more than 100 cycles,reflecting extremely electrochemical stability during cycling.