| Garnet-type solid state electrolytes have become one of the most promising solid-state electrolytes due to their excellent electrochemical properties and excellent stability.However,there are some problems in the application of pure garnet-type electrolyte pellet,such as poor interface contact with electrodes and fragility.The design strategy of organic/inorganic composite solid-state electrolytes provides possibility for the application of garnet-type electrolyte.Therefore,the application of Ga-doped LLZO-based composite solid-state electrolytes in lithium-ion batteries was studied by preparing Ga-doped LLZO electrolytes and compounding them with PEO-based solid-state electrolytes and PVDF-based solid-state electrolytes,respectively.The main research contents and conclusions are as follows:The Li6.4Ga0.2La3Zr2O12（LGLZO）electrolyte with stable cubic structure and high ionic conductivity was obtained by doping Ga.Sub-micron LGLZO powder was prepared by high-temperature solid-state reaction followed with ball-milling process,and the optimum conditions of powder preparation were determined:after calcination at 1050℃for 10hours,ball-milling was carried out at 250 r/min for 10 hours in a ball milling system with the mass ratio of 10 mm,5 mm and 2 mm balls of2:3:5.A high-performance LGLZO ceramic sintered pellet with ion conductivity of 8.29×10-4 S/cm at room temperature was prepared by sintering the pellet in LLZO powder.In addition,the electrochemical stability of LGLZO electrolyte was also explored by cyclic voltammetry with composite electrode,and it was found that there was a weak oxidation reaction in LGLZO electrolyte at about 4.2 V.The PEO-Li TFSI-LGLZO composite electrolyte membrane with PEO as the main phase was prepared by solution casting.It was determined that the optimum content of LGLZO was 40 wt%,with which the ionic conductivity of the composite electrolyte was 1.38×10-5 S/cm at room temperature and 1.88×10-4 S/cm at 60℃.After modification,the thermal stability,mechanical stability,and stability to lithium of the electrolyte were significantly improved,and the oxidation voltage was increased to4.67 V.At 60℃,the discharge specific capacities of the assembled all-solid-state Li Co O2/Li battery and Li Fe PO4/Li battery under constant current of 0.2C were 117.1 m Ah/g and 141.5 m Ah/g,respectively,and the coulombic efficiency were all stable above 99.0%.After the addition of a constant voltage step in the charging process,the discharge specific capacities of the batteries were further increased to 131.3 m Ah/g and 157.4m Ah/g.The“polymer in ceramic”composite solid electrolyte with LGLZO as the main phase was prepared by coating the slurry on a glass plate with a doctor blade.The electrolyte with the ratio of PVDF:Li TFSI:LGLZO=0.34:0.66:2 has the best ionic conductivity,and the room temperature ionic conductivity was 1.21×10-5 S/cm.The all-solid-state lithium symmetric battery can stably cycle at 0.1 m A/cm2 for more than 350 h after cycling 15 times at current densities of 0.1,0.2,and0.3 m A/cm2 in turn at 60℃.The all-solid-state Li Fe PO4/LGLZO-SE/Li battery exhibited a specific discharge capacity of 123.5 m Ah/g,and the capacity retention rate reached 93.4%after 30 cycles at 0.2C.In addition,the Li Fe PO4/L-PP/Li battery and the Li Co O2/L-PP/Li battery with PP separator modified by LGLZO obtained discharge specific capacities of156.3 m Ah/g and 165.0 m Ah/g under constant current of 0.2C at the electrolyte dosage of 9μL/cm2,and their cycle performance was better than that of batteries with traditional PP separator,providing research experience for constructing lean liquid electrolyte battery system and improving the safety of lithium ion battery. |
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