Research On Halogen Regulation Of Perovskite Type Solid Electrolyte

Lithium-ion batteries are currently widely used chemical energy storage devices and power sources for new energy vehicles.However,the use of organic liquid electrolytes in traditional lithium-ion batteries has flammable and explosive security risks.The use of non-flammable solid electrolytes instead of organic liquid electrolytes is expected to fundamentally solve the safety problems faced by traditional lithium-ion batteries.Among many solid electrolyte materials,perovskite-type solid electrolyte Li_0.33La_0.557Ti O₃（LLTO）has attracted wide attention due to its excellent electrochemical performance and safety performance.The main research contents of this thesis are as follows:1.The optimum process of preparing LLTO solid electrolyte by sol-gel method was studied.The optimum preparation process is that the first sintering temperature is 950℃,the excess of Li NO₃ is 30 wt%,and the tabletting pressure is 12 MPa.The ionic conductivity of the electrolyte obtained after secondary sintering is 5.2×10^-5 S cm^-1,and the electronic conductivity is 4.38×10^-9 S cm^-1.2.F-doped Li_0.33La_0.557Ti O_3-xF_x（0≤x≤0.2）electrolyte materials were prepared by sol-gel method.When the F doping ratio is x=0.1,the prepared Li_0.33La_0.557Ti O_2.9F_0.1(LLTOF_0.1)solid electrolyte has the highest ionic conductivity(6.7×10^-5 S cm^-1)and density（98.69%）.The Li|LLTOF_0.1|Li battery exhibits a polarization voltage of 0.018 V after 900 h at a current density of 0.1 m A cm^-2.The Li|LLTOF_0.1|Li Fe PO₄ quasi-solid-state battery has an initial discharge specific capacity of 124.34 m Ah g^-1 at 0.1 C,a maximum discharge specific capacity of 137.66 m Ah g^-1 at 21 cycles,and a discharge specific capacity of 122.78 m Ah g^-1 after 100 cycles.At the same time,the battery exhibits excellent rate performance.The Li|LLTOF_0.1|NCM battery shows that the LLTOF_0.1 electrolyte has excellent high-pressure applicability.3.Cl-doped Li_0.33La_0.557Ti O_3-xCl_x（0≤x≤0.2）electrolyte materials were prepared by sol-gel method.When the Cl doping ratio was x=0.1,the prepared Li_0.33La_0.557Ti O_2.9Cl_0.1(LLTOCl_0.1)solid electrolyte obtained the highest ionic conductivity(6.1×10^-5 S cm^-1)and density（98.07%）.The Li|LLTOCl_0.1|Li battery exhibits a polarization voltage of 0.027 V after900 h at a current density of 0.1 m A cm^-2.The Li|LLTOCl_0.1|Li Fe PO₄ quasi-solid-state battery has an initial discharge specific capacity of 136.46 m Ah g^-1 at 0.1 C,a capacity retention rate of 73.7%after 100 cycles,and exhibits relatively excellent rate performance.The LLTOCl_0.1electrolyte has poor high-pressure applicability,and the cycle life is only 19 cycles.4.Based on the above research,LLTOF_0.1 electrolyte has excellent electrochemical performance.LLTOF_0.1 nanofibers were prepared by electrospinning,and then combined with PVDF-Li TFSI to prepare composite solid electrolytes（CSEs）.When the filling amount of LLTOF_0.1 nanofibers was 30 wt%（CSEs-30 wt%）,the electrolyte obtained the highest ionic conductivity of 4.72×10^-5 S cm^-1.The lithium-ion migration number of CSEs-30 wt%is 0.58,the electrochemical stability window is 4.9 V and exhibits excellent thermal stability.The Li|CSEs-30 wt%|Li symmetrical battery can cycle stably for 995 h without short circuit.The assembled LFP|CSEs-30 wt%|Li solid-state battery has an initial discharge specific capacity of 103.89 m Ah g^-1at a rate of 0.1 C,a capacity retention rate of 88%after 65 cycles,and excellent rate performance.CSEs-30 wt%also exhibits excellent high-pressure cycle performance.