Exploring New Metal Halide Solid State Electrolytes For All Solid State Lithium Battery

All-solid-state lithium battery(ASSLB)based on inorganic solid-state electrolyte(SE)with improved energy density,long cycle life,and enhanced safety is one of the competitive candidates for the next-generation energy storage system.The key to fabricating high-performance ASSLB is the design and synthesis of inorganic SEs with superionic conductivity,wide electrochemical windows,and interfacial compatibility.The current inorganic SEs mainly include three types:oxides,sulfides,and chlorides.Oxide-based SEs display wide electrochemical windows,but the solid lattice results in poor contact at the electrode-electrolyte interface,accompanied by low ionic conductivity and undesired grain boundary,which are not suitable for achieving the high-power ASSLBs.Sulfide-based SEs exhibit superionic conductivity comparable to or even exceeding that of liquid electrolytes.However,the limited oxidation stability and thermodynamic instability hinder their applications.Chloride-based SEs combining the antioxidation capability of oxides with the good ductility of sulfides can be obtained by a simple preparation process without a harsh environment and extremely high sintering temperature,which is suitable for next-generation high-performance ASSLBs.Unfortunately,there are several challenges to the practical application of chloride SEs and corresponding ASSLBs,including low intrinsic Li-ion conductivity,limited Li-ion percolating of the composite cathode,and thermodynamic instability with Limetal.Therefore,we take the realization of ASSLBs with high energy density as the research goal,aiming to explore high-performance novel chloride SEs.Besides,the discussion of the mechanism of Li-ion conduction and the application of chloride SEs in ASSLBs are also performed.The thesis mainly includes the following four aspects:1.We report a class of amorphous Li-Ta-Cl-based chloride SEs possessing high Li-ion conductivity(up to 7.16 mS cm-1)and low Young’s modulus(approximately 3 GPa)to enable excellent Li-ion conduction and intact physical contact among rigid components in ASSLBs.We reveal that the amorphous Li-Ta-Cl matrix is composed of LiCl43-,LiCl54-,LiCl65-polyhedron,and TaCl6-octahedral via machine learning simulation,solid 7Li nuclear magnetic resonance,and X-ray absorption analysis.Attractively,this new type of amorphous chloride SE exhibits excellent compatibility with high-nickel cathodes.We demonstrate that ASSLBs comprising amorphous chloride SEs and high nickel single-crystal cathodes(LiNi0.88Co0.07Mn0.05O2)exhibit 99%capacity retention after 800 cycles at～3 C under 1 mAh cm-2 and～80%capacity retention after 75 cycles at 0.2 C under a high areal capacity of 5 mAh cm-2.Most importantly,a stable operation of up to 3000 cycles with a capacity retention of 76%at a high rate of 3.4 C can be achieved in a freezing environment of-10℃.Our amorphous chloride SEs will pave the way to realize high-performance high nickel cathodes in high energy density ASSLBs.2.We employ neural network potential to simulate materials composed of Li,Zr/Hf,and Cl using the stochastic surface walking method,identifying two potential unique layered halide SEs,named Li2ZrCl6 and Li2HfCl6,for stable ASSLBs.The predicted halide SEs possess high Li+conductivity and compatibility with Li metal anodes.We synthesize these SEs and demonstrate their superior stability against Li metal anodes with a record performance of 4000 hours of steady lithium plating/stripping.We further fabricate the prototype stable ASSLBs using these halide SEs without any interfacial modifications,showing small internal cathode/SE resistance(19.48Ωcm2),high average coulombic efficiency(～99.48%),good rate capability(63 mAh g-1 at 1.5 C),and unprecedented cycling stability(87%capacity retention for 70 cycles at 0.5 C).3.We report a metal halide perovskite-type chloride ion conductor,Cs2LiYCl6,which crystallizes in a double perovskite structure.In this structure,Cs+ ions are situated within the cuboctahedral spaces formed by the interconnected frameworks of LiCl65-and YCl63-octahedra.We have discovered that this metal halide fast chlorideion conductor features a unique octahedral X-site vacancy pathway for chloride ion migration,exhibiting an ionic conductivity of 0.015 mS cm-1 and a low ionic migration energy barrier of approximately 0.40 eV.CS2LiYCl6 as a chloride-ion conductor represents a novel instance of a metal halide perovskite-type solid electrolyte,highlighting the proposed X-site vacancy migration mechanism within this double perovskite structure.Additionally,the potential for lithium ion conduction at the B-site within the perovskite lattice framework is further explored at a theoretical level through first-principles calculations.These findings promise to open new avenues for the exploration of metal halide perovskite-type ionic conductors.4.We propose an in-situ chemical modification strategy to construct a uniform fluorinated alloy type interfacial layer(LiF-LiZn)on the surface of the Li metal anode by using highly dispersed metal fluoride nanoparticles(ZnF2).Based on the transport and regulation synergistic effect of the alloy site and lithium fluoride,the uncontrolled growth of lithium dendrite can be effectively suppressed.Lithium symmetrical battery can achieve a stable operation of more than 500 h at high current density(1 mA cm-2),which greatly improves the cycling stability and capacity retention of the Li|LiNi0.8Co0.15Al0.05O2 battery.In addition,the strategy is generally universal,and the selection of fluoride nanoparticles can be extended to MgF2 and AlF3,which can realize the construction of a similar functional interfacial layer(LiF-LiMg,LiF-LiAl).Furthermore,the strategy can be further applied to stabilizing the Li/electrolytes interface of all-solid-state lithium metal batteries based on metal halide solid electrolytes.