Interfacial Design And Electrochemical Behavior Of Lithium Metal Batteries

High energy density lithium metal batteries are expected to replace traditional lithium-ion batteries as the next generation energy storage system,further promoting the rapid development of electric vehicles and other fields.However,the problems of lithium dendrite growth,low Coulombic efficiency and poor cycling stability in lithium metal batteries have seriously hindered their commercial application.Therefore,the development of dendrite-free and highly stable lithium metal batteries is of great significance to the development of the new energy industry.In this work,a series of methods that can optimize the interfacial properties and lithium deposition behavior are developed from the interface design perspective,and the intrinsic mechanisms are investigated in depth.The specific works are as follows:（1）The structure and interface of the anode can significantly affect the lithium metal deposition behavior,and this chapter designs a Li/Mo composite anode that can regulate the decentralized lithium deposition behavior.The Li/Mo composite anode was prepared by the molten lithium infusion method with a three-dimensional metallic Mo mesh as the skeleton.Combined with density functional theory（DFT）calculations and experimental results,the Mo-modified interface contributes to the promotion of decentralized lithium metal deposition and inhibition of lithium dendrite growth,while reducing the loss of inactive lithium during the stripping process,ultimately reducing the internal resistance and voltage polarization of the battery during cycling,and improving the cycling stability of the lithium metal batteries.The Li/Mo composite anode can maintain a stable cycle time of 1200 h at 1 m A cm^-2 and 1 m Ah cm^-2,and the capacity retention ratio is more than 90%after 200 cycles at 1 C in commercial carbonate and ether electrolytes.（2）In addition to the anode structure,the lithium metal deposition behavior is largely influenced by the solid electrolyte interface（SEI）film on the anode side.In this chapter,a low concentration mixed ether electrolyte was designed to regulate the composition of the SEI film and induce homogeneous lithium deposition.The 0.3 M lithium bis（fluorosulfonyl）imide（Li FSI）salt was dissolved in a mixed ether system of the active solvent of 1,2-dimethoxyethane（DME）and the inert solvent of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether（HFE）.The high proportion of inert solvent（94%by volume）in the electrolyte can effectively increase the localized concentration of lithium salt relative to the active solvent region and promote the interaction between Li⁺and FSI^-in the active region and the decomposition of anions on the lithium metal anode surface,forming a stable inorganic-rich SEI film which is favorable for Li⁺transport and regulating the uniform dense lithium deposition behavior.Under this electrolyte system,the average Coulombic efficiency of the Li||Cu cell can reach over 99.3%for 250 cycles at 2 m A cm^-2 and 1m Ah cm^-2,and the Li||Li₄Ti₅O₁₂ and Li||S full cells also exhibit excellent cycling and rate performance.（3）In addition to the stability of the anode side,an excellent electrolyte for lithium metal batteries should possess both anode and cathode stability.In this chapter,a weakly solvating electrolyte was designed to simultaneously regulate the compositions of SEI film and cathode electrolyte interface（CEI）film to enhance the deposition uniformity of lithium metal anode and the high voltage resistance of cathode.From the perspective of molecular design,tetrahydropyran（THP）with a large-sized cyclic structure was used as a solvent to construct the weakly solvating electrolyte.Compared with linear ether of DME and small-sized cyclic ether of tetrahydrofuran（THF）,THP has weaker coordination binding ability with Li⁺,which can effectively reduce the dissociation of lithium salt in the electrolyte and promote the interaction between Li⁺and anions.The formed anion agglomerated solvation structure facilitates the construction of inorganic-rich SEI film and promotes uniform dense lithium deposition,while reducing the side decomposition on the cathode side and forming a stable CEI film to enhance the high voltage resistance of the electrolyte.The Li||NCM523 full cells based on THP-based weakly solvating electrolyte exhibit stable cycling performance at charge cut-off voltages of 4.3 and 4.5 V.（4）In addition to liquid electrolytes,solid-state electrolytes have received much attention due to their high safety and other advantages.In this chapter,a salt-rich polymer/inorganic composite solid-state electrolyte was designed to achieve high room-temperature ionic conductivity(1.67×10^-3 S cm^-1)and construct stable electrode/electrolyte interfaces.Poly（vinylidene fluoride-co-hexafluoropropylene）（PVDF-HFP）was used as the polymer matrix,a high proportion of Li FSI salt to build a Li⁺hopping transport network,a small amount of solvent to promote Li⁺migration in the electrolyte,and Li_6.4La₃Zr_1.4Ta_0.6O₁₂（LLZTO）inorganic electrolyte as a filler to enhance the interfacial stability of the electrolyte.It is shown that the salt-rich system can significantly enhance the ionic conductivity and reduce the voltage polarization of the electrolyte,and the LLZTO stabilizer can reduce the interfacial side decomposition reaction of the solvent in the electrolyte.Based on the above design,the Li||Li Fe PO₄full cell with the salt-rich PVDF-HFP/Li FSI/LLZTO composite electrolyte can maintain the cycling stability for 300 cycles at 0.5 C.