Study On Doping And Compound Modification Of Li_1.7Al_0.3Ti_1.7（PO₄）₃ Solid Electrolyte

The demand for energy in social development continues to grow,the development of safe and reliable high-energy,high-power energy storage devices has become the forefront of energy research.Since inception,lithium-ion batteries（LIBs）have been the main energy storage solution for portable electronics and electric vehicles,and compared with other secondary batteries,LIBs have high energy density and good cycle stability.However,the organic electrolyte used in lithium-ion batteries has many disadvantages,such as flammability,leakage and corrosion.Short circuit and overheating may cause serious safety accidents such as fire.Replacing the organic electrolytes in traditional batteries with solid-state electrolytes is an effective solution to the above problems.Solid-state electrolytes can match lithium metal and high-voltage cathodes,enabling batteries with higher energy density.Among many solid electrolyte candidate materials,Li_1.7Al_0.3Ti_1.7（PO₄）₃（LATP）with NASICON structure has attracted much attention because of its high chemical stability,ionic conductivity and high safety.However,this kind of inorganic solid electrolyte still has problems such as being hard and brittle,and the interface impedance is large,and the ionic conductivity still needs to be further improved for commercial application.In view of the above problems,in this paper,LATP was doped with metal cations and organic-inorganic composite solid electrolytes（CSE）were prepared.The purpose was designed to improve its ionic conductivity,reduce the interface impedance and improve the electrochemical performance.The main research contents of this paper are as follows:（1）LATP electrolyte powder was prepared by hydrothermal method,and the effect of p H value on its phase was investigated.The results showed that the purity of LATP was the highest when p H=7,and no other impurity phase was formed.In this paper,Li_1.7Al_0.3-xBi_xTi_1.7（PO4）₃（x=0.01,0.02,0.03）（LABTP）electrolyte was prepared by doping LATP with Bi as a dopant for the first time.The effects of Bi-doped on the morphology,structure and ionic conductivity of the electrolyte were investigated.The results showed that Bi-doped is beneficial to improve the ionic conductivity and density of LATP.When the Bi-doped x=0.02,the prepared LABTP electrolyte has higher density and the highest ionic conductivity(at room temperature 6.31×10^-4 S cm^-1).（2）In order to improve the interfacial contact between the solid electrolyte and the electrode,the interfacial impedance was reduced.In this paper,the organic polymer polyvinyl butyral（PVB）was combined with LABTP/LATP electrolyte to prepare CSE for the first time,and a solid electrolyte film with a certain thickness was obtained by the tape casting method.We found that the CSE prepared with 85 wt.%Li_1.7Al_0.28Bi_0.02Ti_1.7（PO₄）₃ had higher ionic conductivity(1.03×10^-3 S cm^-1 at 80℃),which was the best preparation condition.The electrochemical properties of CSE under the best preparation conditions were studied.The button battery assembled with lithium iron phosphate（LFP）as cathode and lithium metal（Li）as anode can still maintain the capacity of 146.2 m Ah g^-1 after 200 cycles at room temperature,and the coulomb efficiency is about 94.2%（3）The ionic conductivity of Bi-doped LATP is significantly improved,but the electrochemical performance needs to be further improved for commercial application.In this experiment,the organic polymer PVB and the inorganic filler LATP were added to the ethanol solvent in a certain proportion and mixed uniformly to obtain a slurry,which was made into a film of a certain thickness by electrospinning,and composited with cellulose as a support skeleton.In this paper,ordinary qualitative filter paper（FP）is used as the cellulose source for the first time.The structure of FP is similar to that of electrospinning membrane,and both belong to the fibrous network structure,which saves the step of secondary processing of cellulose and simplifies the experimental process.And FP as skeleton can make CSE have higher mechanical strength.Finally,the prepared framework was compounded with succinonitrile（SN）to prepare LIBS solid electrolyte.SN not only has good flame retardancy,but also improves the cycle stability of solid-state lithium-ion batteries.The results showed that when the mass ratio of LATP to PVB was 2:1,the prepared CSE had the highest conductivity(2.52×10^-3S cm^-1 at 60℃),and the best electrochemical performance.The button battery assembled with Li phosphate as the cathode and lithium metal as the anode still has a capacity of150.7 m Ah g^-1 after 200 cycles,with a coulomb efficiency close to 99.0%...