Effect Of Surface Oxygen Vacancies Of TiO₂ On Properties Of PEO-based Composite Solid Electrolytes For Lithium Batteries

All-solid-state lithium metal battery causes extensive attention due to its high energy density and high safety performance.However,as the key component of the solid-state battery,solid-state electrolyte still faces series of problems,which include low ion conductivity,narrow electrochemical window,unstable lithium anode/electrolytes interfaces and lithium dendrite.Therefore,this paper focus on the PEO-based solid-state electrolyte with double filler（ie,the active filler LLZTO particles and passive filler Ti O₂ nanoparticles）.The effects of nano-Ti O₂ filler on PEO-based composite solid-state electrolyte properties are studied.By constructing double-layer PEO-based composite solid electrolyte,we study the performance of solid-state electrolytes at low temperatures,matching with high loading positive electrode and high voltage cathode materials.The main research contents of this thesis are as follows:1.Firstly,Ti O₂ nanoparticles with different surface oxygen vacuum concentrations are prepared by adjusting the sintering time.Then,the as-prepared Ti O₂ fillers（Ti O₂,Ti O₂-1 h and Ti O₂-8 h）with different proportions are added into the PEO-LTFSI-LLZTO composite solid electrolytes,named as PLLT,PLLT-1 h,and PLLT-8 h,respectively.The results indicate that ion conductivity of PLLT-8 h with rich oxygen vacancy reaches 5×10^-4 S/cm at 25°C and 4×10^-3 S/cm at 70°C.It is attributed to the presence of Ti O₂ surface oxygen vacancies,which help to the dissociation of Li TFSI and the fix of anion.PLLT electrolyte can maintain a high oxidative stability below 5.4V.The Li/PLLT/Li symmetrical cell can run stably over 1000 h at a current density of0.2 m A/cm² with low over-potential of 50 m V.After cycles,surface of the lithium electrode is flat,and there is no significant lithium dendrite.2.Double-layer solid-state electrolytes（D-SSE）are prepared by simple coating method.Cathode is close to PLLT-8 h with high ion conductivity,and anode is close to PLLT with high interface stability.There is no significant layer gap inside the D-SSE.The research indicates ion conductivity of D-SSE achieves 2.8×10^-4 S/cm at 25°C,and ion transference number reaches 0.52.Electrochemical window of D-SSE reaches above 5 V.Li/D-SSE/Li symmetrical cell presents a stable Li deposition without short circuit over 1500 h at 0.2 m A/cm²,and a low overpotential of just 40 m V.LFP/D-SSE/Li can still maintain a high specific capacity of 159.7 m Ah/g and a capacity retention ratio of 97.3%after 200 cycles at 0.1 C.The discharge capacity of cell is 91.2m Ah/g even at 2 C.The cell displays good initial discharge capacity of 134.5 m Ah/g at0°C.After 50th cycles,capacity retention rate is 81.8%.And the cell can run 30 cycles at below zero 20°C.In addition,the cell with high load LFP cathode（10 mg/cm²）can achieve high discharge capacity of 144.6 m Ah/g and keep great cycling stability at 0.1C.NCM811/D-SSE/Li cell can also display a reversible capacity of 185.7 m Ah/g at 0.1C after 100 cycles.