The Structure Design Of Li Metal Anodes And Their Electorchemical Performance

The ever-increasing dependency and demands on consumable electronics,electric vehicles（EVs）,and smart grid storages have stimulated the rising demands for high-energy-density rechargeable batteries.Although lithium-ion batteries dominate the current consumer markets,the capacities of cathodes and graphitic anodes have both reached bottlenecks.Li metal anode has been regarded as the“Holy Grail”due to its high specific capacity(3860 m Ah g^-1),low redox potential（-3.04 V vs.SHE）and low density(0.534 g cm^-3).More importantly,the utilization of Li metal anode broadens the range of applicable cathode materials（sulfur and air）,for the realization of differing types of lithium batteries with higher energy densities.However,the large-scale commercialization of Li metal anodes is still plagued by numerous technical and industrial challenges,as follows:high reactivity of lithium metal anodes,manifested in repeated interaction with electrolyte constituents to form discontinuous solid electrolyte interphase（SEI）layers,exhausting the limited amount of electrolyte;formation of Li dendrites and the subsequent partial cracking of these fragile Li from the root,forming isolated“dead Li”and diminishing Li utilization;the large volume change may lead to safety risks.To solve these problems,we design a variety of 2D and 3D structures to construct stable Li metal anode based on the research of Li dendrite growth and the formation principle of SEI film.The main works are as follows:（1）A metal organic framework（MOF）material of Li₂Sn₂（bdc）₃（H₂O）_xwas fabricated by a simple hydrothermal reaction.Then,the MOF particles were uniformly casted onto the Cu foil via a doctor blade method to guide the uniform Li deposition and inhibit the generation of lithium dendrites.Abundant polar bonds including O-H and M-O formed by metal and coordinating atoms serve as lithiophilic functional groups,facilitating the transport of lithium ions through the MOF channels.MOF particles also present excellent affinity with organic electrolyte due to presence of polar ligands.During cycling,enhanced adhesive interaction between electrolyte and MOF facilitates homogeneous Li ions flux,thus alleviating uncontrolled Li dendrite growth and subsequently improving cycle life.Symmetric cells with MOF modifed current collector can be stably cycled for over 2000 h at a current density of 0.5 m A cm^-2 with a cycle capacity of 1.0 m A h cm^-2.（2）A modifiedγ-aminopropyltrimethoxysilane（γ-APS）thin film with nanopores fabricated by self-assembly is developed to construct functional Cu current collector.The lithiophilic property of Si-O-Si backbones and NHx groups can reduce the Li nucleation barrier and the nanopores of the thin film allow Li⁺to pass through.These factors contribute to uniform lithium ion flux and deposition,thereby suppressing the lithium dendrite formation.The combination of strong Cu-N bonds and Si-O-Cu covalent bonds ensure the polymer film attached to the Cu foil tightly during repeated Li charging/discharging process.The Si-O-Si network and Cu-N bonds exhibit high chemical/electrochemical stability,contributing to excellent corrosion resistance.Based on the above advantages,theγ-APS-Cu electrode demonstrates enhanced electrochemical performance.The symmetric cell ofγ-APS-Cu@Li shows an improved lifespan of 1400 h with small voltage hysteresis of 12 m V at 0.5 m A cm^-2.（3）A facile electrochemical method was developed for the direct growth of Cu O nanoneedle arrays onto Ni foam.Cu O nanoneedle arrays were fabricated by electrochemical oxidation and annealing strategies.The needle-like Cu O arrays improve the lithiophilicity and large specific surface area of Ni foam,which make the thermal infusion easy and greatly reduce the local current density.Meanwhile,Cu O nanoneedle arrays can overcome the nucleation barrier,which is favorable for steady Li deposition even at high areal capacity.Thus,the gaps between the Cu O nanoneedle arrays supply sufficient void spaces to endure large-volume fluctuation during Li plating/stripping,and accommodate more deposited Li in comparison with nanoparticle coating.Based on the above advantages,the NCNF@Li electrode demonstrates stable Li metal anodes in both symmetric cells and full cells.The symmetric cells delivered a long cycling life over 1100 h at 1 m A cm^-2 with a capacity of 1 m Ah cm^-2.（4）Carbon cloth（CC）decorated by highly-ordered CoO nanorod arrays was applied as a three-dimension（3D）framework（noted as CoO@CC）for lithium metal anode.CC is a feasible candidate framework in consideration of its excellent electrical conductivity,surface area,and large interstice for metallic Li infusion.Then a thermal infusion route to prestore Li was utilized to obtain CoO@CC-Li composite anode with suppressed Li dendrite.The contact area of composites can be increased effectively due to the CoO nanorod arrays on the surface of CC.The local current homogeneity of the anode can be improved simultaneously.The unique structure of CC and the 3D hierarchical architecture between CoO nanorod arrays with CC contributes to the excellent electrochemical performance of the CoO@CC-Li anode.