Research On The Preparation And Application Of High-performance Solid-state Electrolytes For All-solid-state Batteries

Solid-state lithium batteries are potential battery systems because of their higher energy density and safety than liquid lithium ion batteries.Solid electrolyte is the key component of solid-state batteries,while composite electrolytes are one of the most promising system of them due to the combination of advantages of both the organic and inorganic electrolytes.The design and optimization of interfaces in composite electrolytes have important influence on the performance of electrolytes.Besides,in addition to the interface inside the composite electrolyte,the interface inside the cathode electrode of solid-state battery is also particularly important,and there are few reports on the research of lithium ion transport in the cathode electrode of solid-state batteries.Therefore,the preparation of efficient and stable solid-state cathode and corresponding all-solid-state battery is another important research direction of solid-state battery.In this paper,the preparation and properties of several different solid-state electrolytes are studied,and their applications as well as mechanism in solid-state batteries are explored.To improve the processing ability and air stability of sulfide electrolyte-?-Li₃PS₄,a hybrid solid-state electrolyte composed of ?-Li₃PS₄ and glycidyl methacrylate is prepared through a controlled interfacial reaction between the polymer and the Li₃PS₄.The resulting hybrid electrolyte can be processed through simple slurry coating method,which also can be coated directly on the electrode for in-situ thermal polymerization to ensure good contact of the electrolyte/electrode interface.Furthermore,it exhibits improved air stability and decreased interfacial resistance with metallic lithium as compared with pure Li₃PS₄ electrolyte.This hybrid electrolyte exhibits wide electrochemical window of nearly 5 V and high ionic conductivity of 1.8×10-4 S cm^-1 at room temperature,which is even slightly higher than the ionic conductivity of the pure ?-Li₃PS₄.On the basis of organic porous crystal molecular cage,a new kind of solid electrolyte is designed and developed through structure construction and lithium salt recombination.It composed by cation amine of cage skeleton andClO₄-counter ions.The molecular cage can completely separate the anion-cation ions in the added LiClO₄ salt.Besides,the-NH2+-on the molecular cage can restrain theClO₄-anions of the LiClO₄ salt,thus obtaining a high concentration of free lithium ions.A pure solid electrolyte based on the novel molecular cage without adding any liquid electrolytes and plasticizers is prepared for the first time.The new electrolyte has good thermal stability and high ion transference number?0.7?,with ionic conductivity of 5.13×10-5 S cm^-1 and 1.2×10-4 S cm^-1 at 25 ? and 60 ?,respectively.To improve the internal lithium ion transport network and build good electrode/electrolyte interface in the solid cathode,a series of advantages of the molecular cage electrolyte-good ionic conductance,three-dimensional skeleton structure,large specific surface area and good solubility were taken into consideration,which was added by the traditional liquid-phase mixing method to construct continuous and uniform ion conduction paths in the solid cathode.As a result,the all solid-state LFP?Li batteries employ this cage electrolyte as ionic conductive additive at much lower mass percentage of 20 wt% than common all-solid-state batteries with inorganic solid-state electrolyte or polymer electrolyte additives.The morphology of solid-state cathode was directly expressed through a series of characterization methods,and the performance of the battery are optimized.The all-solid-state batteries show excellent electrochemical properties at room temperature,delivering a specific discharge capacity of ?147 m Ah g^-1 at 0.1 C and exhibiting stable long-term cycling performance with a capacity retention rate of 90% at 0.5 C during 300 cycles.In order to enhance the ion conduction between the molecular cage electrolyte particles and improve the processability of the molecular cage electrolyte,composite electrolyte based on PEO and the molecular cage was prepared by combining it with PEO polymer electrolyte.Uniform morphology can be obtained by in situ precipitation due to the good solubility of the molecular cage electrolyte which can be dissolved in the PEO pecursor solution.In addition,the molecular cage with ion splitting ability can increase the concentration of free lithium ions in the composite system.As a result,the conductivity of the composite electrolyte increased to 6.1×10-5 S cm^-1 at roomtemperature,the transference number and electrochemical window is as high as 0.66 and 5.5 V,respectively.In addition,the solid-state battery composed of the composite electrolyte and the LFP positive electrode and the lithium anode has excellent cycling performance at 70 ?.Besides,the battery with LFP areal density of 3 mg cm^-2 has a discharge capacity of more than 150 m Ah g^-1 under 0.1 C.