Research And Design Of Solid State Electrolyte Based On Lepidolite Type Two-dimensional Materials

Rechargeable lithium-ion batteries have been regarded as the most promising energy storage device for future large-scale applications including portable electronics,electric vehicles and power grid.However,conventional LIBs using flammable liquid electrolytes may cause severe safety issues,such as electrolyte leakage,thermal runaway,combustion and explosion.Solid-state batteries are supposed to be one of the best candidates to solve these problems,eliminating the possible electrolyte leakage and enhancing the safe reliability.Moreover,higher energy density can be expected by using solid-state electrolytes（SSEs）,especially if Li metal is adopted as the anode which possesses the highest theoretical capacity(3861 m Ah g^-1)and lowest electrode potential（3.04 V vs.SHE）.The SSEs enable the usage of Li metal as anodes because it can inhibit the formation of Li dendrites and thereby mitigate the possible short circuit,thermal runaway,combustion and explosion.Two-dimensional（2D）layered materials have showed their superiority in ionic transport,not only as electrode materials but also as solid-state electrolytes in lithium-ion batteries（LIBs）.Silicates are one kind of natural ore with 2D layered structures which have been reported as additives in composite polymeric electrolytes（CPEs）for inhibiting the crystallization of the polymer electrolyte（e.g.poly（ethylene oxide）（PEO））,facilitating the dissociation of Li⁺and thereby enhancing the ionic conductivity.However,the possibility of silicates as electrolytes has not been investigated.In this paper,we report that 2D natural ore can be used as SSEs by using lepidolite as a proof-of-concept.Both pure lepidolite and composite lepidolite（only mixed with PEO）showed moderate ionic conductivity,proving the intrinsic ionic conductibility of lepidolite.After adding a certain amount of LiClO₄ to improve the ionic conductivity of the polymer,the composite electrolyte system of lepidolite-PEO-LiClO₄ showed excellent ionic conductivity.When the mass ratio of lepidolite came to 43%,the ionic conductivity reached 1.6×10^-4S cm^-1 at 60℃.Moreover,the ion transference number was increased to 0.72.These results will enrich the materials for SSEs and arouse growing interest of 2D layered silicates for potential application of all-solid-state lithium-ion batteries and lithium-metal batteries.PEO is the most popular polymer for SPEs,which,however,cannot be used for high voltage output batteries because of the oxidization of PEO at high voltages.PVDF can be considered as a potential matrix for SPEs with wide electrochemical window,flame retardance and high thermal stability,which,however,always showed low ionic conductivity.Herein,we reported the PVDF-based CPEs,showing high ionic conductivity of 0.105 m S cm^-1 at RT and 1 m S cm^-1 at 120°C,wide electrochemical window and marvelous fire resistance.The high ionic conductivity can be attributed to the synergistic effect of DMF plasticizer and 2D lepidolite filler.The PVDF-based CPEs therefore showed great potential in all-solid Li-metal batteries with great stability and rate capability.