| Solid-state batteries are regarded as one of the the most promising next-generation energy storage devices to balance properties of high energy density,high power density and high safety.Although solid-state batteries are widely considered to potentially provide the superior energy density than that of lithium-ion batteries with liquid electrolytes,evaluating the energy density of practical solid-state batteries is necessary to provide in-depth understanding of the development and application of solid-state batteries,requiring consideration of all active materials as well as inactive materials.In order to maximize the energy density of solid-state batteries,thinning the thickness of solid-state electrolyte membranes is one of the feasible strategies.The practical application of solid electrolyte membranes in solid-state batteries still has overwhelming issues,such as the air instability of sulfide electrolyte membranes and the interfacial incompatibility between solid electrolyte membranes and metal lithium.Firstly,systematic,detailed and practical calculations of energy densities of all-solid-state batteries（ASSBs）are proceeded to provide in-depth understanding and guidelines for the potential of ASSBs.The gravimetric/volumetric energy densities of sulfide-based ASSBs with 8 common cathode/anode systems are evaluated,respectively,with practical parameters in a commercialized pouch cell.The typical spacial distribution modes of solid electrolyte in electrodes are all considered to further precisely evaluate their effects on energy densities.Results show that for a Li Co O2/sulfide solid electrolyte（50μm）/Li ASSB,its gravimetric（volumetric）energy density ranges in 410–280Wh kg-1(820–560 Wh L-1),as active material content varies from 96.5 to 67.5 wt%.By providing calculation paradigms of energy densities with practical conditions and reasonable assumptions,this study aims to present an unambiguous understanding in energy density predictions of sulfide ASSBs with real-world conditions.On this basis,the fabrication of thin sulfide electrolyte membranes is preliminary studied.Based on wet coating technologies,the binder-solvent systems compatible with sulfide solid electrolytes are explored.Besides,the negative effect of binder-solvent on the ionic conductivity of sulfide electrolyte membranes is preliminarily investigated.In the second part of this thesis,to solve the air instability problem of sulfide solid electrolytes,a universal method applicable to all types of sulfide SEs is developed to realize water-stable sulfide SE membranes,by spray coating a Li+-conductive superhydrophobic protection layer with Li1.4Al0.4Ti1.6（PO4）3（LATP）nanoparticles and fluorinated polysiloxane（F-POS）via hydrolysis and condensation of tetraethyl orthosilicate and 1H,1H,2H,2H-perfluorodecyltriethoxysilane molecules.LATP nanoparticles provide Li+transport channel and microscale roughness.F-POS binds LATP nanoparticles together on sulfide SE membranes,forming nanoscale roughness and low surface energy.The F-POS@LATP coating layer exhibits excellent superhydrophobicity（water static contact angles>160°）to resist extreme exposure（direct water jetting）,because of its micro-/nanoscale roughness and low surface energy.Moreover,ASSBs using the extreme-condition-exposed modified Li6PS5Cl membrane exhibit a reversible capacity of 147.3 m Ah g-1,comparable with the ASSBs using pristine sulfide membranes.The superhydrophobic Li+-conducting layer is demonstrated to be an effective protection method for sulfide membranes so that they remain stable and functionable in extreme water exposure conditions,providing a new approach to protect all types of sulfide SEs and other air/moisture/water-sensitive materials without sacrificing electrochemical performance.In the third part of this thesis,to overcome overwhelming issues in Li-metal-anode ASSBs in terms of serious interfacial reactions,Li dendrite growth and large interfacial resistance,etc..,an ultrastable and kinetically favorable interface is constructed between sulfide-poly（ethylene oxide）（PEO）composite solid electrolytes（CSE）and lithium metal,via in-situ formation of solid electrolyte interphase（SEI）layer containing Li3PS4.A specially-designed sulfide,lithium polysulfidophosphate（LPS）can distribute uniformly in PEO matrix via simple stirring process because of its complete solubility in acetonitrile solvent,which is advantageous for creating a homogenous SEI layer.The CSE/Li interface with high Li+transportation capability is stabilized quickly through in-situ formation of Li3PS4/Li2S/Li F layer via the reaction between LPS and lithium metal to inhibit lithium dendrite growth.Li/Li symmetric cell with the LPS-integrated CSE exhibits constant and small CSE/Li resistance of 10Ωcm2 during cycling,delivering stable cycling for 3475 h at a current density of 0.2 m A cm-2 and a high critical current density of 0.9 m A cm-2 at 60℃.Impressive electrochemical performance is also demonstrated for Li Fe PO4/CSE/Li all-solid-state batteries with capacity of 127.6 m Ah g-1 after 1000 cycles at 1 C.Besides,the double-layer solid electrolyte membrane Li6PS5Cl/CSE with relatively higher chemical/electrochemical stability and dense CSE attached to lithium may provide an effective strategy for Li protection and long cycle life in Li Co O2/Li ASSBs. |
