| All-solid-state batteries have been extensively studied owing to their higher safety performance than liquid batteries,and can use lithium metal with a high theoretical capacity of 3860 mAh g-1 and a lower potential of-3.04 V vs.SHE as a negative electrode.The safer solid electrolyte is used as the lithium ion transmission medium in the all-solid-state battery,and its ion conductivity directly affects the cycle performance of the all-solid-state battery.Therefore,it is very important to design a new solid electrolyte system with high ionic conductivity.However,solid electrolytes with high ionic conductivity often have poor electrochemical stability,and the two contradict each other,and a series of interface problems existing in all solid-state batteries are a direct manifestation of this contradiction.To solve the problem of the interface between the electrode and the electrolyte,it is necessary not only to consider the performance of the solid electrolyte itself,but also to solve the problem from the electrode material.Therefore,the design of the voltage-resistant buffer layer material between the electrode and the electrolyte can lay a foundation for the preparation of an integrated all-solid-state battery.At the same time,exploring the positive electrode materials suitable for solid-state batteries,with zero-volume phase change,voltage plateau matching the oxidation potential of solid electrolytes,high theoretical capacity,and excellent ionic conductivity is also one of the research focuses of solid-state batteries.This article mainly conducts systematic theoretical and experimental research on the above aspects,and the specific content is as follows:(1)The anti-perovskite structure material Li3OCl based on the material genome method,aiming at the problem of poor ionic conductivity,this paper adopts S element to replace O element and the homologous substitution of halogen element positions to design a new double anti-perovskite structure Li6OSI2 solid state electrolyte.In this modified design,the S element with a larger atomic radius is used to broaden the diffusion channel of lithium ions,and at the same time,I replace the Cl element as interstitial atoms to fill the middle of the structure to support the crystal structure and expand the transport channel.Two diffusion mechanisms in Li6OSI2 are proposed:interstitial diffusion and vacancy diffusion,and the diffusion activation energy of the two diffusion mechanisms are theoretically calculated respectively.(2)Based on the theoretical design in work(1),the proposed new type of double anti-perovskite Li6OSI2 solid electrolyte material was synthesized experimentally by solid-phase ball milling-sintering method,and Li6.5O1.5S1.5I2 was obtained through partial stoichiometric ratio of lithiation enrichment component to further improve its ionic conductivity.The ionic conductivity performance test of Li6OSI2,Li6.5O1.5S1.5I2 and Li3OCl prepared in the experiment was carried out.The results show that the overall ionic conductivity of Li6.5O1.5S1.5I2 is 2-3 orders of magnitude higher than that of Li3OCl,but there is still a certain grain boundary impedance problem.Through further theoretical analysis,it is found that both Li3OCl and Li6.5O1.5S1.5I2 have serious interface component segregation,and halogen atoms are easy to overflow the surface of the structure from the gap,resulting in serious grain boundary resistance.Subsequently,the amorphous components Li6.5O1.5S1.5I2 and Li3OCl were synthesized by the liquid phase method,which greatly reduced the overall impedance.(3)Aiming at the narrow voltage window of the argyrodite phase Li6PS5Cl and the incompatibility with metal lithium anode and high-voltage cathode materials,based on the first principle of DFT,the S element is replaced with O element to design a new type of high-voltage resistant and stable buffer layer material Li6PO5Cl.The composition Li6PSO4Cl is obtained by adjusting different O/S ratios.Li6PSO4Cl has the same structural symmetry as Li6PS5Cl,so there is no structural lattice matching problem.This paper predicts the diffusion activation energy of Li6PO5Cl and Li6PSO4Cl,respectively 0.46 eV and 0.33 eV,which are better than other oxide coating materials,and the oxidation potential is increased.Since the ionic conductivity of the oxygen-rich phase compound is equivalent to that of the oxide,it can be used as both an electrolyte material and an excellent buffer layer material on the electrode.Furthermore,an allsolid-state battery system was designed:Li|Li6PO4SCl|Li6PO5Cl|Li0.25MnO2,the theoretical operating voltage platform is 2.47-3.65 V,and the energy density can reach 436.054 mW h g-1.This strategy is to design high performance the integrated all-solidstate battery system provides a theoretical basis.(4)According to the theoretical work in(3),experimental synthesis is carried out for the new material system Li6PS5(1-x)O5xCl(0≤x≤1).In the experiment,the solid-phase ball milling method was further used to synthesize a series of compound compositions with different O/S ratios,and the optimal composition was finally selected as Li6.25PS4O1.25Cl0.75.With the introduction of oxygen,Li6.25PS4O1.25Cl0.75 has the following obvious advantages compared with Li6PS5Cl:(a)the sensitivity to water and oxygen is greatly improved;(b)the oxidation potential is increased by about 0.4 V;(c)the stability of the lithium metal negative electrode has also been greatly improved,and the assembled lithium battery can achieve long-term stable cycling at a higher current;(d)the full battery assembled with the uncoated positive electrode LiCoO2 can achieve stable charge and discharge cycle.In addition,through the disassembly and characterization of the symmetrical battery and all-solid-state battery after cycling,it is found that a thin layer of Li3PO4 is formed in situ on the interface between Li6.25PS4O1.25Cl0.7 and the lithium metal negative electrode and the LiCoO2 positive electrode during the cycle,which can greatly Improved the electrochemical cycling stability of Li6.25PS4O1.25Cl0.7.(5)In view of the compatibility of cathode materials and electrolyte materials,from the perspective of cathode materials,the DFT material genome method is used to integrate the common cathode materials layered LiCoO2,layered LiMnO2,spinel LiMn2O4(LMO)and olivine LiFePO4 in liquid lithium-ion batteries.In this paper,based on DFT calculation,without any fitting parameters,the PBE cross-correlation function is directly used to accurately estimate the voltage platform of several cathode materials,and it is consistent with the experimental values.In addition,the volume change of the positive electrode material in the process of lithium ion deintercalation,the corresponding voltage,electronic conductance and ion conductance of different lithium ion concentrations have been systematically evaluated,and the various properties of several positive electrode materials have been evaluated through the radar chart.The intuitive summary provides a reference for the further design of new cathode materials. |
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