Synthesis And Performance Research Of Anti-Perovskite Li-ion Solid Electrolyte And Cathode

Traditional lithium-ion batteries have been widely applied in energy storage,electric vehicles,portable electronic equipment and other areas because of their high energy density,long cycle life and environmental friendliness.However,the liquid organic electrolytes of traditional lithium-ion batteries are generally flammable,volatile and poor thermostability.So,traditional lithium-ion batteries may suffer from serious safety concerns.All-solid-state lithium-ion batteries(ASS-LIBs)are one of the most promising next generation energy storage devices in the future because of their larger energy density and higher security.However,low ionic conductivities and poor compatibilities with cathode of solid electrolytes in ASS-LIBs make it can't be practical used yet.Therefore,at present,most researchers focus on designing and synthesizing new solid electrolytes with different structure that have high ionic conductivities.But there are little systematic studies on enhancing ionic transport performance of ionic conductor,the structure-activity relationship in ionic conductor is not clear.Hence,it's difficult to develop and design appropriate solid electrolytes,and it's a key to study and build the structure-activity relationship of ionic transport property with crystal structure for developing new materials and improving ionic transport performance of solid electrolytes.Meanwhile,except for solid electrolytes,cathode materials also play an important role in ASS-LIBs.Because of interface problem between electrodes and solid electrolytes,the transport efficiency of Li-ion is usually low.So,it's required to develop larger capacity,higher stability and cheap cathode materials.In this thesis,basing on anti-perovskite structure materials,structure-activity relationship of ionic transport property with crystal structure in solid electrolytes and the performance optimization of cathode materials are investigated.New idea is derived for developing new solid electrolytes and cathode materials.The detail research are as follows:(1)The anti-perovskite solid electrolyte material Li2OHCl was prepared by melting method and its structure and electrochemical properties were characterized.The results show that the synthesized Li2OHCl is an anti-perovskite structure with a space group of Pm3m and the lattice parameter a=3.9109(1)A.The room temperature ionic conductivity of Li2OHCl is 8.85×10-6 S cm-1,and the activation energy is 0.7043 eV.The material has a good electrochemical stability to metallic lithium that the electrochemical stability window is up to 10 V from CV test,and constant current charge and discharge profile shows great cycle stability.All-solid-state battery assembled with LiFePO4 positive electrode and lithium metal negative electrode can work normally.However,cycle performance is poor due to interface compatibility problems.In order to improve the interface compatibility between electrolyte and electrode,Li2OHCl is compounded with PEO.The electrochemical window of the PEO-20%Li2OHCl composite electrolyte measured by CV reaches 5.4 V,and the cycle stability of metallic lithium is also great.LiFePO4/PEO-20%Li2OHCl/Li solid state battery can work normally at 60?,and the cycle performance is better than in LiFePO4 Li2OHCl/Li all-solid-state batteries.The above results fully demonstrate that Li2OHCl can be used as a solid electrolyte material for all-solid-state lithium ion battery,and at the same time,electrochemical performance of solid-state battery can be improved by compounding with the organic polymer.(2)The gradient material Li20HX(X=Cl,Br)is synthesized,and crystal structure,lattice dynamics and ions transport performance of which are characterized,meanwhile,the influence mechanism of lattice dynamics on ionic transport performance is analyzed.The results show that,with the increase of Br content in Li2OHX,there is no large structure changes except the increasing unit cell dimensions in the static structure.In the lattice dynamics,lattice polarization and distortion can be observed.With the increase of Br content in Li2OHX5 lattice polarizability gradually increases,and the lattice distortion becomes larger due to the decrease of structural symmetry,which leads to the activation barrier of ion migration Ea and Arrhenius pre-factor ?0 gradually decrease.When Cl is completely replaced by Br,although the lattice polarizability is further enhanced,the structural symmetry of Li2OHBr increases,the lattice distortion decreases,and the activation barrier Ea and Arrhenius pre-factors ?0 increase.Based on experimental results and theoretical analysis,it is shown that lattice dynamics plays an important role in ion transport performance in electrolyte materials.(3)The anti-perovskite cathode material Li2Fe1-xMnxSO are obtained by vacuum solid-phase sintering and quenching cooling.The crystal structure and electrochemical properties are investigated.The effect of Mn on its structure and electrochemical properties was discussed.The results show that,in Li2Fe1-xMnxSO cathode materials,as the Mn content increases,the unit cell parameters increase gradually,Li2TM gradually deviates from the lattice site,the distortion of Li2TM-O octahedron increases,Li+migration barrier decreases,and deintercalation Li+is easier to remove and embed from the material,which improves the rate performance and cycle performance of the material.However,since the low electrochemical activity of the Mn2+/Mn3+redox pair and poor electronic conductivity of Mn,when the Mn content is further increased,the capacity is lowered,and the stability of the charge and discharge cycle is deteriorated.Among them,Li2Fe0.8Mn0.2SO is the optimal component,the capacity reaches 220 mAh g-1 at 0.05 C rate,130 mAh g-1 at 1 C rate,and the capacity retention rate reaches 70%at 0.5 C rate.