Study On Constructing A Solid-State Electrolyte System And On Their Electrochemical Performance In Lithium-ion Battery

Compared with the traditional liquid lithium-ion battery（LMB）,solid lithium metal battery has become a promising battery system due to its higher energy density and safety,and is considered as one of the candidates for the next generation energy storage system.As one of the key components of solid-state batteries,solid-state electrolytes cannot be mass-produced due to large interface impedance and high preparation costs.At present,organic-inorganic solid composite electrolytes can complement the advantages of organic matrix and inorganic materials,which is expected to overcome the existing shortcomings of solid electrolytes and has become one of the focuses of scientific researchers.In this paper,a novel solid electrolyte system which can be prepared in air was constructed,the preparation of the solid electrolyte under different technological conditions and its influence on the electrochemical performance of LMB were studied,and the related mechanism of action has been studied in depth.The research is as follows:（1）Lithium trifluoromethanesulfonate（Li CF₃SO₃）,Li_6.4La₃Zr_1.4Ta_0.6O₁₂（LLZTO）and polyvinylidene fluoride/polyvinyl acetate（PVDF/PVAC）were used as raw materials,the electrolyte precursor solution was coated on a smooth substrate by simple solution gel method,then successfully Solid composite electrolyte（SCE）membrane was synthesized.In the preparation process,the material ratio in the electrolyte membrane was continuously optimized and the thickness of the electrolyte film was adjusted.On the other hand,the compatibility of SCE films with different cathode materials was also explored.Finally,this chapter explored the effects of different current-collecting and film-forming interfaces on the electrochemical performance of LMB.The results show that when PVAC accounts for 20%,PVDF accounts for 47.5%,Li CF₃SO₃accounts for 22.5%,LLZTO accounts for 10%and the coating thickness of the electrolyte film is 140μm,the SCE film has the best performance.Also,the compatibility of SCE film with lithium ferrous phosphate（LFP）cathode is better.（2）Based on the previously optimized process conditions,the interface reaction mechanism between the solid composite electrolyte（a SCE）film prepared in air and the LFP cathode was further studied,and the solid-state lithium battery based on PVDF-PVAC-LLZTO-Li CF₃SO₃electrolyte system was prepared and its electrochemical performance was studied,compared with the solid electrolyte composite film（i SCE）prepared under inert atmosphere protection.The results show that under the air atmosphere,H₂O molecules form hydrogen bonds with PVDF in the a SCE film,which hinders the aggregation between the molecular chains of PVDF itself,thereby reducing the crystallinity of PVDF,increasing the amorphous area provides more jump nodes for Li⁺and enhances the conductivity of Li⁺.At the same time,the H₂O molecules formed hydrogen bonds with the lithium salt Li CF₃SO₃in the a SCE membrane and PVDF in the LFP electrode,respectively,so that Li CF₃SO₃was evenly distributed in the electrolyte membrane.Due to the hydrogen bonding of H₂O molecules,more Li CF₃SO₃entered the LFP electrode,which played a pre-lithium effect to a certain extent.At room temperature,the ionic conductivity of a SCE membrane is about 5.09×10^-4S cm^-1,which is an order of magnitude higher than that of i SCE membrane(1.93×10^-4S cm^-1).The solid-state lithium battery assembled by LFP-a SCE composite sheet and lithium metal sheet still had a stable capacity of 137m Ah g^-1after 180 cycles at 0.2 C rate and the capacity retention rate is 96%.The first coulombic efficiency was 93.2%and the high specific capacity of 143.7 m Ah g^-1remained after 150 cycles at 0.5 C.At a high temperature of 50°C,the first discharge specific capacity was 148 m Ah g^-1and the capacity retention rate was 96%after 200cycles at 0.2 C,which had good electrochemical and thermal stability.The capacity retention rate of a solid-state button full battery assembled with LFP-a SCE and graphite anode was 48%after 500 cycles at 0.2 C.In conclusion,the solid electrolyte prepared in this paper can be prepared in air and has good electrochemical performance and thermal stability.The process is simple and the production cost is greatly reduced under non-inert environment,which has certain significance for industrial production of solid-state lithium battery.