Design And Properties Of Multilayer Composite Structure Based On Lean-lithium Anode

In the environment of continuous seeking of high energy density and high safety energy storage devices,lithium-ion batteries are hardly meeting the requirements of society due to the limitation of its theoretical capacity.Lithium metal is an ideal anode for new generation high energy density batteries owing to its high capacity and low potential.As a derivative system of lithium metal anode,lean-lithium anode with its limited lithium source can resolve the problem of excess lithium metal at root,thus maximizing the advantages of lithium metal.The lean-lithium status poses a higher challenge for the reversibility of lithium ion plating/stripping on the anode.Therefore,aiming at the protection of lean-lithium anode,a layer-by-layer evaporation strategy is designed in this paper to construct a multilayer protection structures integrating a lithium replenishment layer,a lithiophilic alloy(Li₁₅Au₄)layer,and an artificial SEI（Li F）layer on Cu foil using PVD in a highly controlled process.The synergistic effect of the multilayer enables to induce efficient and reversible homogeneous deposition of lithium ions on the anode,while the Li F layer isolates the electrolyte to avoid the side reactions consuming the limited lithium source.The main research results of this article are as follow:（1）The Li（L）layer,Au（A）layer and Li F（F）layer on the surface of Cu（C）foil are prepared by one-pot PVD deposition,and two structures of lean-lithium anode,CLAF and CALF,are designed according to the different order of the vaporized layers.This design can precisely regulate the components and thickness of each functional layer,so that the thickness of Li F layer is controlled at 200 nm,the Li supplement layer is 2μm,and the Au layer is 80 nm.Also,the Li layer and Au layer can react in situ during the evaporation to form a stable Li₁₅Au₄ lithiophilic alloy,which not only can reduce the nucleation over-potential to induce uniform deposition,but also can modify the surface morphology of Cu foil to make the Li F layer bond more tightly and reduce the stress concentration.The difference in design structure reflects the difference in the degree of alloying reaction,and the structure of CLAF ensures a more complete reaction process,thus acting as a more stable homogenized deposition under lean-lithium conditions.In addition,SEM tests on the lithium deposition behavior of the prepared electrode showed that the CLAF was well-maintained after the cycle,demonstrating the reliability of its structure and function.（2）CLAF exhibites 0.11 m Ah g^-1 of lithium replenishment capacity in the first cycles and maintained an average CE of 98.8%after 160 cycles,as well as a good cycling stability in the symmetric cell.The full cell with CLAF anode matched with Li Fe PO₄ cathode exhibited an initial capacity of 148 m Ah g^-1 and 97.5%capacity retention at a lower N/P ratio of 1.32 after 130 cycles,as well as excellent rate performance.Thereby,the stability and reliability of the CLAF structure are demonstrated,and the cycle life of the lean-lithium anode system is greatly improved.