Composite Gel Electrolyte Based On Surface-modified Ceramic Filler Via Silane Coupling Agent Grafting

Lithium-ion batteries（LIBs）have permeated our lives in miscellaneous consumer electronic equipment,power grids,and other domains for several decades.Driven by the ever-increasing demand for high energy density,however,the theoretical bottleneck of LIBs essentially limits their further development.The lithium metal batteries（LMBs）with high energy density(3860 m Ah g^-1)as the anode have revived attention aiming to boost the next-generation rechargeable batteries which endow electric vehicles with long driving mileage.However,several challenges of LMBs,including the notorious lithium dendrite growth and severe parasitic side reactions between liquid electrolytes and lithium anode,must be solved prior to the implementation of practical applications.To this end,replacing organic liquid electrolytes with solid-state electrolytes（SSEs）has been regarded as a promising method,stimulating extensive interests and investigations of SSEs due to their high safety and superior electrochemical properties,which are expected to adapt to modern energy storage devices.Herein,a comprehensive gel hybrid electrolyte is reported as the research object,and their structural characterization and electrochemical performance testing are carried out as follows:We synthesized the LLTO nanofibers via electrospinning methods and then surface grafted byγ-（2,3-epoxypropoxy）propytrimethoxysilane（KH560）,the modified K-LLTO nanorods were combined with polyvinylidene fluoride（PVDF）/poly（propylene carbonate）（PPC）polymer matrix.The K-LLTO/PVDF/PPC hybrid porous electrolyte was prepared via the phase inversion method.The ideal dispersion of surface-modified K-LLTO nanorods in polymer substrates is mainly due to the numerous bridge-linked structures between the nanorods and polymer molecules,such as Si-O-Ti,-OH,and hydrogen bonding.These connections promote the dissociation of lithium salts in the gel system,the increase of amorphous regions in the polymer base,and the overall electrochemical performances.Incorporating 10%of K-LLTO as the filler（10%GHE）,the enhanced filler dispersity contributes to a high ionic conductivity of 3.01 m S cm^-1 and an ideal Li-ion transference number of 0.55 at room temperature,the latter is expected to be beneficial for alleviating concentration polarization inside the cell.Moreover,excellent flexibility and thermal stability are demonstrated.Furthermore,the 10%GHE obtains higher oxidation resistance,the highest electrolyte uptake ratio,and a high critical current density（CCD）of 0.9 m A cm^-2.As a result,the Li|10%GHE|Li symmetric cells achieve extremely stable cycling performance and the Li Fe PO₄|10%GHE|Li（LFP|10%GHE|Li）full cells achieve a good cycling life.The traditional LiPF₆-based liquid electrolyte is replaced by the Li FSI/Li TFSI dual-salt liquid electrolyte,which is ascribed to its finite chemical/thermal stability.The dual-salt gel electrolyte synthesized a density Li F buffer layer on the lithium metal surface,and the electrochemical performances of the gel LMBs were elevated successfully.Taking it together,it is validated that this surface grafting strategy and the application of the dual-salt electrolyte are promising for fabricating high-performance GHEs,which also exhibit the potential to be adapted to other hybrid gel electrolyte systems.