Multiple Strategies For Alkali Metal Anodes Protection

With the increasingly acute problem of fossil fuels and the growing demand for green energy,it is imperative to develop a green,safe and efficient high-energy-density battery.Recently,the actual specific capacity of graphite anode in commercial lithiumion battery has gradually approached its theoretical specific capacity value.However,it still cannot meet the market requirements for higher energy density energy storage.Therefore,alkali metal anodes with high specific theoretical capacity(Li:3860 mAh g1,Na:1165 mAh g-1,K:687 mAh g-1)have been attracted widely attention.However,the practical application of alkali metal anodes still faces many problems and challenges,such as:unstable solid electrolyte interface(SEI),infinite volume change,continue side reactions and dendrite growth.To address the above issues,we design threedimensional(3D)structure to achieve the uniform deposition of alkali metal ions,relieve the infinite volume change,and enhance the cycle lifespan.In addition,we also construct an artificial interface layer to reduce the side reaction between lithium metal and electrolyte and accelerate the rapid transport of Li+ ions,achieving uniform Li+plating/stripping.Finally,we develop a bifunctional electrolyte.The electrolyte can not only inhibit the growth of potassium dendrites,but also relieve the shuttle effect of potassium polysulfides.Therefore,the cycle stability of potassium-sulfur batteries has been significantly improved.In this dissertation,the action mechanism of the materials was deeply analyzed by combining in situ/ex-situ characterization and theoretical computational simulation.In chapter 1,the working principle,existing scientific issues and existing modification strategies of alkali metal anodes are systematically concluded.In chapter 2,we introduce the chemicals,testing instruments and characterization methods involved in the experiments of this dissertation.In chapter 3,we prepare RuO2 nanoparticle-modified carbon cloth framework(RuO2@CC)by a simple soaking method.RuO2 nanoparticles improves the affinity between the carbon cloth and molten Li.Furthermore,the 3D framework effectively confines the volume change of Li metal.Density functional theory(DFT)calculation proves that Ru has higher adsorption energy for Li+,provides nucleation sites for Li+,and realizes uniform deposition of Li metal.As a result,symmetric batteries with Li composite electrode show long cycle lifespan for 570 h at 1 mA cm-2 and 10 mAh cm2.And LiFePO4-based full battery with Li composite electrode show a capacity retention rate of 90%after 650 cycles.When the method is extended to the protection of Na metal anode,the Na composite anode also has excellent electrochemical performance.At 1 mA cm-2 and 1 mAh cm-2.symmetric batteries with Na composite electrode show long cycle lifespan for 250 h.In chapter 4.based on the previous chapter,the effects of physical morphology confinement and chemical adsorption/diffusion regulation on Li metal plating/stripping are systematically discussed by taking nickel-based lithiophilic compounds as examples through computation and experiment.Finite element simulations reveal that the design of two-dimensional nanosheets has the best physical morphology confinement effect.DFT calculations confirm that Li3N with high Li+adsorption energy and high Li+conductivity can promote Li+diffusion and control uniform Li+nucleation.The composite electrode(Li-Ni/Li3N-NS@CC)was obtained by combining the Ni3N-modified carbon cloth with molten lithium by a simple melting method.The Li-Ni/Li3N-NS@CC electrode can achieve a long cycle life(1000 h)at 60 mA cm-2/60 mAh cm-2.In chapter 5,we introduce the preparation of ionically/electronically conductive 3D bismuth-based(Na3Bi/K3Bi)alloy frameworks by a simple high-temperature melting method.DFT calculations indicate that Na3Bi has high Na+ conductivity,electron conductivity and sodiophilicity.Therefore,the Na3Bi alloy skeleton can provide a smooth electron/ion diffusion path,effectively relieve volume expansion,reduce side reactions,and inhibit the growth of dendrites.At 1 mA cm-2 and 1 mAh cm2,symmetric batteries with the Na composite electrode show long cycle lifespan for 700 h.And Na3V2(PO4)3-based full battery with Na composite electrode shows sustainable cycle performance over for 400 cycles at a current density of 1 A g-1.When the method was extended to the protection of K metal anode,the K composite electrode also achieved excellent electrochemical performance.At 0.5 mA cm-2 and 1 mAh cm-2,symmetric batteries with the K composite electrode show long cycle lifespan for 450 h.In chapter 6,the in-situ construction of an organic/inorganic composite artificial interface layer by a high-temperature redox method is introduced,which achieves uniform deposition of Li+and suppresses the growth of Li dendrites.DFT calculations reveal that organic components(nitrogen-containing functional groups)have strong adsorption energy for Li+,which can guide the uniform distribution of Li+on the electrode surface and provide sufficient Li+nucleation sites.In addition,the inorganic component Li3N has high ion conductivity,which can promote the migration of Li+in interface layer.Therefore,symmetric battery with the Li composite electrode exhibits long cycle lifespan for 1100 h at 1 mA cm-2 and 2 mAh cm-2.And LiNi0.6Co0.2Mn0.2O2based full battery with Li composite anode shows stable cycle for 100 cycles at 1 C.In chapter 7,the effects of four different single-solvent carbonate electrolytes on the performance of K-S batteries are systematically introduced.Among them,3 M KTFSI EC electrolyte can greatly improve the reversible specific capacity and cycling stability of K-S batteries.DFT calculations confirmed that the organic groups in the cathode solid electrolyte interfacial layer(CEI)have strong binding energy with potassium polysulfide,which can prevent the shuttle effect of potassium polysulfide.The high-concentration electrolyte(3 M KTFSI EC)can not only reduce the dissolution of potassium polysulfide,but also stabilize the potassium anode.At 0.1 mA cm-2 and 0.1 mAh cm-2,the K metal symmetric battery based on the electrolyte can be cycled stably for 3000 hours.The potassium-sulfur battery based on the electrolyte can still display a specific capacity of 646 mAh g-1 after 850 cycles at a current density of 0.5 A g-1.In chapter 8,the innovations and shortcomings of the works in this dissertation are systematically summarized,and the content and direction of future work are prospected.