Tin-based Halide Modification Of Solid State Electrolytes And Application For All Solid State Batteries

Traditional lithium-ion batteries based on liquid electrolytes with low energy density and poor safety performance have been unable to meet the requirements of the current consumer market for battery products.All solid state Li-ion batteries with high energy density and good safety performance are expected to solve the current problems of energy shortage,poor electrochemical performance and low safety,and become the best candidate to break the constraints of lithium-ion batteries based on liquid electrolyes.Solid-state electrolytes have attracted extensive attention as the most critical component of solid-state lithium metal batteries.Among them,polymer solid electrolytes are easily applied in the fabrication of safe,ultra-thin and ultra-flexible electrochemical devices,especially portable electronic products,due to their unlimited shape and size.However,the low ionic conductivity,narrow electrochemical window,and difficulty in resisting lithium dendrite puncture restrict the commercial application of polymer solid-state batteries.Compared with polymer solid state electrolytes,inorganic solid state electrolytes exhibit efficient ion transport mechanisms,wide electrochemical windows,and absolute safety with ultra-high melting points.However,insufficient interfacial contact between inorganic solid electrolytes and lithium anodes has always limited the development of inorganic solid state batteries.In this paper,we will explore the effect mechanism of tin-based halide materials on the electrochemical performance of polymer PEO-based solid electrolytes and inorganic LLZTO-based solid electrolytes,and apply them in all solid state batteries.The specific research contents are as follows:(1)CsSnI3 with pure crystal phase was prepared by vacuum thermal evaporation and annealing,and then combined with PEO-LiTFSI matrix by means of solid phase pressure to obtain a uniform PEO-LiTFSI-CsSnI3 polymer solid state electrolyte.The introduction of CsSnI3 increases the proportion of amorphous regions in the PEO-LiTFSI matrix,providing more segments for transporting Li+,and the interaction of TFSI-groups with CsSnI3 will restrict the anion movement of LiTFSI,thereby dissociating more Li+to increase the ion transport number of the electrolyte.Meanwhile,the LixSn and LiI alloys generated at the interface help to construct a uniform interfacial electric field,isolate electrons,achieve uniform deposition/stripping of Li+,reduce the nucleation and growth of dendrites,and improve the cycling stability of the battery.After CsSnI3 modified,the ionic conductivity of the electrolyte membrane at 60℃ could reach 6.1 × 10-4 S cm-1,and the critical current density is increased by 33%.The Li/PEO-LiTFSI-CsSnI3/Li symmetric cell could be stably cycled for more than 500 hours at a current density of 0.1 mA cm-2,and the full cell can still maintain a coulombic efficiency of over 96%after 200 hours of stable cycling.(2)The SnI2 layer was prepared on the surface of LLZTO by vacuum thermal evaporation,and the thickness of SnI2 was adjusted to obtain the best interface modification effect.While SnI2 improves the surface roughness of LLZTO,the LixSn alloy layer and a LiI insulating layer are in situ formed at the interface between the Li anode and the electrolyte.The LixSn alloy layer effectively improves the wettability of the electrolyte to Li metal,reduces the migration barrier of Li+,and inhibits the formation of Li dendrites.The LiI layer promotes Li+conduction while insulating electrons,ensuring the lithium ion migration number of the electrolyte,and constructing an interface with uniformed Li+-flux.After modification,the interfacial impedance of the symmetric cell at room temperature is only 537Ω,the critical current density increased to 0.7 mA cm-2,and the full cell can be stably cycled for 100 cycles at a charge cut-off voltage as high as 4.2 V,and the capacity is still above 140 mAh g-1.This experiment promotes all solid-state power batteries from basic research to practical applications by overcoming the biggest obstacle between inorganic solid electrolytes and Li anodes.