Novel Sulfide-Based Secondary Batteries With Li-Dendrite-Free Anode

Lithium metal has the lowest electrochemical potential（-3.04 V vs SHE）and ultra-high energy density（3861 m Ah/g）,and has always been an ideal anode material in electrochemical energy storage batteries.Compared with conventional commercial lithium-ion batteries（energy density of 240 Wh/kg）,the theoretical energy density of lithium-sulfur batteries with lithium metal as the anode and S as the cathode material is as high as 2600 Wh/kg.And the theoretical energy density of lithium-oxygen battery with O₂ as cathode material is 3505 Wh/kg.However,the lithium metal anode faces great challenges such as poor thermodynamic stability with liquid organic electrolytes and nucleation/growth of lithium dendrites during the continuous plating/stripping cycle of batteries.These unsolved problems have brought a series of serious consequences,such as serious side reactions,low lithium anode utilization,internal short circuit,thermal runaway,fire and explosion,etc.Therefore,without solving the problem of lithium dendrites,it is impossible to truly use lithium metal batteries safely.Aiming at the problem of dendrite growth of lithium metal anode,we propose a new battery system based on sulfide solid electrolyte and lithium dendrite-free anode"liquid lithium metal",which can fundamentally suppress excessive dendrites growth on the surface of lithium metal anode.This dissertation is divided into three parts,the first part is the research of Li-Biphenyl-Ether（Li-BP-DME/TEGDME）liquid lithium metal anode,the second part is the research of new sulfide solid electrolyte secondary battery with Li-Biphenyl-Ether liquid lithium metal anode,the third part is the research of the interfacial compatibility between Li-Biphenyl-Ether liquid lithium metal anode and sulfide solid electrolyte.In the first part of this dissertation,Li-Biphenyl-Ether liquid lithium metal anode was studied.The solubility measuring of lithium metal in BP-DME solutions and electrochemical properties of liquid lithium metal have been comprehensively studied,and the effects of different variables such as composition ratio and temperature of liquid lithium metal on solubility,conductivity,and viscosity have been studied.The total conductivity of the liquid lithium metal Li-BP-DME（DME-1,2-Dimethoxyethane）solution can reach up to 22.5 m S/cm at 60°C,and the total conductivity is as high as12 m S/cm at room temperature（the electronic conductivity is 8 m S/cm and the ionic conductivity is 4 m S/cm）.The most suitable liquid metal lithium anode solution Li_1.5BP₃DME₁₀ with the highest conductivity（12.2 m S/cm）at room temperature was found after a comprehensive study of the physical and chemical properties of liquid metal lithium.Li_1.5BP₃DME₁₀ combined with sulfide solid electrolyte assembled symmetric batteries.This new battery structure combines liquid lithium metal anode（which can dissolve lithium and fundamentally prevent lithium dendrite nucleation and growth）and sulfide solid electrolyte（the highest room temperature ionic conductivity of all solid electrolytes,a fully compact sulfide SE layer without porosity can be achieved simply by room-temperature cold pressing and ideal mechanical ductility）,resulting in a record high current density（17.78 m A/cm²）and long cycle life（nearly3000 hours）.In the second part of this dissertation,a novel battery structure is developed using Li-BP-（TEG）DME（DME-1,2-Dimethoxyethane/TEGDME-Tetraethylene glycol dimethyl ether）as the anode,combined with sulfide solid electrolyte and lithium cobalt oxide Li Co O₂ cathode.This battery configuration combines the advantages of these materials to operate under negligible external pressure（3 k Pa）and a wide temperature range（-20 to 50°C）.The results show that the battery system has high reversible discharge capacity（140.4 m Ah/g）and high efficiency（99.7%Coulombic efficiency and 96%energy efficiency after 100 cycles）.In addition,the battery exhibits the best cycling stability and highest efficiency among all the liquid lithium anode battery systems with high-voltage cathodes reported so far.In the third part of this dissertation,the interfacial reaction mechanism of sulfide solid electrolyte and liquid lithium anode,and the interfacial layer material compatible with both sulfide solid electrolyte and liquid lithium anode were studied.Among all solid electrolytes at room temperature,sulfide solid electrolytes have the highest ionic conductivity,and with good mechanical ductility and good interfacial contact with electrodes.Sulfide solid electrolytes are considered as one of the most promising solid electrolytes for commercialization.The ohmic resistance of solid-state batteries assembled based on sulfide solid electrolytes is significantly reduced,but the poor chemical and electrochemical stability of the interface between the sulfide solid electrolyte and the electrode leads to a serious problem of high interfacial impedance.Therefore,the formation and evolution of the electrode/sulfide solid electrolyte interface during battery assembly and cycling has a crucial impact on battery performance and is one of the key issues to be addressed in sulfide solid electrolytes battery commercialization.Herein,we broke through the long-standing problem of solid-liquid interface compatibility between sulfide solid electrolytes and organic liquid electrodes,and obtained a variety of interface protective layer materials to match the sulfide solid electrolytes and ether-based organic liquid anodes（i.e.,liquid metal lithium Li-BP-DME）),including PEO-Li TFSI polymer interface layer and theβ-Li₃PS₄/S interface layer,and the symmetric cells assembled with these two interfacial layer materials achieved long time and stable cycles of more than 3000 h and 1000 h,respectively.This technical method of stabilizing the solid-liquid interface of sulfide solid electrolyte and organic liquid electrode successfully solves the key problem of the interfacial side reaction of sulfide solid electrolyte-liquid lithium metal battery system,making the battery system safe and stable cycle for a long time.This technical method provides a valuable method for solving the problem of solid-liquid interface compatibility between sulfide solid electrolytes and organic liquid electrodes,and has important practical significance for further improving the cycle life and safety of lithium batteries.