Design Of SEI And Lithiophilic Copper Current Collector For Lithium Metal Anode

In order to reduce the usage of Li metal and the safety hazards of batteries,the preparation of Li thin-film or even "Li-free" anodes on current collectors has received increasing attention.However,the lithiophobicity of the current collector and the non-uniformity and instability of solid-electrolyte interphase(SEI)can promote the growth of lithium dendrites and cause low Coulomb efficiency,which has become two obstacles restricting the development of lithium thin films/lithium-free negative electrodes.Therefore,in order to solve the above application challenges of lithium metal anodes,the dual interface problems on both sides of the Li metal should be firmly grasped.On the basis of constructing a lithiophilic current collector,a robust SEI with both rigidity and flexibility should be formed to obtain a lithium anode with cycle stability and safety.Based on Cu surface substrate structure and the initial nucleation-growth behavior of Li deposition,this thesis focus on the surface lattice matching consideration between Cu collector and Li deposit and employ two simple and facile electrochemical strategies to construct a lithiophilic copper current collector and stable SEI,which significantly improve the electrochemical performance of "Li-free" anodes.The main content and results are outlined as follow:1.Design and construction of lithiophilic copper current collector based on lattice matching.Based on the surface lattice matching between Li and Cu,we have proved that Cu(100)face serves as the most appropriate orientation for achieving lattice coincidence with the Li(110)plane through density functional theory(DFT)calculation and cyclic voltammetry(CV)characterization.Furthermore,a deposition model of Li on Cu(100)is proposed.Two electrochemical methods,electrochemical oxidation-reduction cycle(ORC)and electropolishing-deposition,were used/developed to facet the Cu current collector for(100)dominated surface orientation.The faceted Cu has significantly lower overpotentials for Li nucleation and growth at different current densities.All types of Cu after faceting exhibit remarkably improved surface lithiophilicity for Li.Thus,it is expected that Li deposition on the faceted Cu collectors would proceed under a much reduced nucleation barrier in favour of uniform nucleation and growth on the entire area of the Cu surface.On a two-dimensional planar substrate,flat Li thin-film anodes can be obtained,while on a three-dimensional structural substrate,Li deposit can uniformly and completely cover the skeleton to form a Cu@Li composite anode(i.e.3D Li thin-film anode).2.Construction of ultra-smooth ultra-thin(USUT)SEI on current collector surfaces.We have developed a strategy for preparing USUT SEI on the surface of current collectors on the basis of Li thin-film and Cu@Li composite anode,which provide feasibility in the development for low-cost stable "Li-free" anodes.The combined advantages of the surface lithiophilicity and the USUT SEI can promote uniform nucleation and smooth growth of Li,thereby a smooth Li thin film of up to 25?m may be prepared;the surface and inner active space of current collector skeleton are used fully.Such Li anodes can make Li deposition/dissolution to proceed under a relatively stable state,thus exhibiting significantly enhanced cycling stability and efficiency.