The Research On High Conductivity Organic-Inorganic Composite Solid Electrolyte

Solid-state batteries（SSBs）are considered to be one of the most promising directions for lithium-ion batteries,because of their remarkable energy density and safety properties.However,limited by ionic conductivity of solid-state electrolytes（SSEs）and interfacial problems between SSEs and electrodes,SSBs are still far from stable operation.The combination of ceramic particles with polymer electrolytes to form solid composite electrolytes（SCEs）has been considered as an effective strategy of designing high-performance solid electrolytes.SCEs with high concentration of ceramic particles have continuous ion-conducting phase since the mechanical integrity and rigidity of the system is assured by the ceramic phase.In this paper,the factors affecting the electrochemical and mechanical performance of SCEs are studied.We developed SCEs with good electrochemical and mechanical properties,and demonstrated that high ceramic concentration SCEs can suppress lithium dendrites effectively.（1）Li₇La₃Zr_1.4Ta_0.6O₁₂（LLZTO） porous microspheres with both specific surface area and larger particle size were prepared by spray drying.The LLZTO microspheres and polyethylene oxide（PEO）composite electrolyte was prepared by solvent evaporation method（called SD LLZTO-PEO）.The electrolyte prepared in this way can effectively prevent ionic conductivity decrease from the agglomeration of LLZTO nanoparticles.Compared with the SCE composed of nano-LLZTO and PEO,the SD LLZTO-PEO SCE has batter ionic conductivity.Furthermore,when the content of LLZTO microspheres up to 60 wt%,the ionic conductivity of SD LLZTO-PEO SCE can reach 1.99×10^-4 S cm^-1 at 60℃.The Li|60 wt%SD LLZTO-PEO SCE|Li Febattery displays a reversible capacity of 132.2 m Ah g^-1 at 60℃with a coulomb efficiency of 97.54%,and retain 84.9%after 50 cycles.（2）LLZTO and polyvinylidene fluoride（PVDF）composite electrolytes（LPCE）with a high ceramic content up to 80 wt%have been developed.Compared to PEO,PVDF possesses stronger adhesivity and higher strength,which ensures the better flexibility of LPCE even with a content of LLZTO up to 80 wt%.The influence of hot pressing on the conductivity of LPCEs was also investigated.Hot pressing can significantly reduce the porosity of LPCEs and increase the conductivity to 1.08×10^-4S cm^-1 at 60℃.The LPCE membrane shows excellent Li dendrite suppression property and sustain Li plating/stripping cycling for over 1500 h.Moreover,the solid Li Fe|LPCE|Li cells displayed long cycling stability with a capacity retention of 86%in 200cycles.（3）Adding a trace amount of high lithium salt concentration electrolyte to the composite electrolyte can reduce the energy barrier between the polymer and the ceramic.The quasi-solid electrolyte was prepared by screening the high lithium salt concentration electrolyte on to the PVDF-Li_1.5Al_0.5Ge_1.5P₃O₁₂ composite electrolyte.The ionic conductivity and electrochemical window of the quasi-solid electrolyte at room temperature can reach 1.62×10^-4S cm^-1,4.9V respectively.The symmetric battery using the quasi-solid electrolyte has tiny interfacial impedance and good stability to lithium at room temperature.It and can have a polarization voltage of 0.2V at a current density of 0.1C cm^-2,and sustain Li plating/stripping cycling for over 100 h.