The Preparation And Application Investigation Of Solid-State Electrolytes For Solid-State Lithium-Air Batteries

With the rapid development of microelectronics,information and renewable energies,people have put forward higher and higher requirements for the performance of secondary batteries.The existing battery system has limited room for improvement in energy density.However,there is an urgent need to develop new secondary battery system based on new materials and new technology.Lithium-air battery is composed of metal lithium anode,electrolyte and air cathode.Its theoretical energy density is more than ten times that of lithium-ion battery.It is regarded as a next-generation power source that can improve the specific energy of secondary batteries by leaps and bounds.At present,most of the electrolytes of lithium-air batteries are organic electrolytes,which are volatile and flammable and cannot inhibit dendrites,which makes lithium-air batteries have a greater safety hazard.If the organic electrolyte is replaced with a solid electrolyte,the constructed solid-state lithium-air battery can not only suppress lithium dendrites,but also completely isolate the lithium anode from the air positive electrode,so that the lithium-air battery can run directly in the air,which is expected to achieve the market application.Therefore,the development of solid-state lithium-air batteries is not only a wise move to pursue scientific development,but also an inevitable choice to meet market demands.However,the current development of solid-state lithium-air batteries is still in its infancy,and the lack of high-performance solid-state electrolytes,stable interface contacts,and reasonable solid-state cathode design hinder its development.Based on the above problems,this thesis mainly focuses on the preparation of solid-state electrolytes for solid-state lithium-air batteries,optimization of electrolyte/electrode interface,and design of solid-state cathode,and the research mainly focuses on the following aspects:1.The air stability of the garnet ceramic electrolyte is improved by introducing the Al₂O₃sintering-aid.After optimization,the room temperature ionic conductivity of the garnet ceramic electrolyte is as high as 5.4×10^-4 S cm^-1,and it can be kept in the air for a long time without producing Li₂CO₃.Based on the garnet ceramic electrolyte with enhanced air stability,a composite solid electrolyte with an organic/ceramic/organic electrolyte(OCOE)structure was designed.OCOE can effectively inhibit the corrosion of the lithium anode caused by the degradation of the organic electrolyte and the shuttle of oxygen from the cathode.Compared with the lithium-oxygen battery using organic electrolyte,the cycle life of the semi-solid lithium oxygen battery with OCOE is increased by two times.2.Hybrid solid electrolytes need to meet multiple prerequisites such as high modulus,close contact with lithium metal,and uniform Li⁺distribution to inhibit the growth of lithium dendrites.To this end,we developed a hybrid solid electrolyte with a rigid Li_1.5Al_0.5Ge_1.5(PO₄)₃(LAGP)core@ultra-thin flexible polyvinylidene fluoride-hexafluoropropylene(PVDF-HFP)shell interface.A large number of nano-scale LAGP cores can not only achieve high Young's modulus,but also construct a three-dimensional Li⁺diffusion network to make Li⁺evenly distributed.The ultra-thin and flexible PVDF-HFP shell can establish a soft and stable contact between the rigid core and the lithium metal without affecting the Li⁺distribution,and at the same time avoid the reduction of LAGP caused by direct contact with the lithium metal.The hybrid solid electrolyte has an ultra-high Young's modulus of 25 GPa,and can achieve dendritic-free lithium deposition even with a large deposition capacity of 23.6 m Ah.The semi-solid lithium-oxygen battery assembled with the hybrid solid electrolyte exhibits good flexibility,lower overpotential and long cycle life.In addition,the semi-solid lithium-oxygen battery also exhibits excellent safety.Even if the battery is heated,it will not be short-circuited,deformed,etc.,and can still work normally.3.The limited three-phase interface in the solid-state cathode and the high impedance caused by the solid-state electrolyte make the performance of the all-solid-state lithium-oxygen battery poor.Therefore,we have successfully manufactured a plastic crystal electrolyte with adjustable porosity through thermally induced phase separation technology.By introducing the porous plastic crystal electrolyte in situ on the surface of the cathode active material,the simultaneous transfer of Li⁺and e^-is realized,and the rapid flow of O₂ is ensured,thereby forming a large number of continuous three-phase interfaces inside the solid-state cathode.The dense plastic crystal electrolyte as the electrolyte layer separating the anode and cathode has high ionic conductivity,high flexibility and strong viscosity,which can reduce the impedance of the all-solid-state lithium-oxygen battery to 115?.The all-solid-state lithium-oxygen battery assembled based on the plastic crystal electrolyte with adjustable porosity has excellent electrochemical performance,including large discharge capacity(5963 m Ah g^-1),high-rate performance and long cycle life up to 130 cycles.