Research On Lignocellulose-based Gel Polymer Electrolyte

Gel polymer electrolyte(GPE)has been getting attention for the higher ionic conductivity than solid polymer electrolyte(SPE)and zero safety problem caused by leakage of liquid electrolyte(LE).GPEs are made up of polymer,plasticizer,lithium salt and organic liquid.The polymer matrixes have been widely studied including polyethylene oxide(PEO),polyacrylonitrile(PAN),polymethyl methacrylate(PMMA)and polyvinylidene fluoride(PVDF).These polymers are mainly deriving from the petroleum industry and nondegradable.When LIBs are total loss and discarded,these polymers will cause serious environmental problems.Therefore,renewable and biocompatible natural polymers are ideal materials for GPEs.However,the natural polymers based GPE,such as cellulose,chitosan,rubber,protein et al,indeed do not show satisfactory electrochemical properties:low ionic conductivity,lithium ion transference number and poor battery capacity.In order to solve this problem,the lignocelluloses(LC)are used as main material to prepare polymer electrolyte membrane,and then soak and swell in luquid electrolyte to form gel with biodegradability and high comprehensive performances.This kind of membranes possess three-dimensional structure and prepare via a simple solution casting,different additives and process parameters are adopted in three systems in the preparation process.1.GPE based on polyethylene glycol(PEG)composite LC with compact structure for application in lithium ion batteries(LIBs)is prepared.The composite membrane dramatically enhances mechanical properties,and displays as high as 3-4 times than that of pure LC when adopting 30%PEG-1000.Meanwhile,the increased liquid electrolyte uptake is obtained(267 wt.%),and caused high ionic conductivity(3.22×10-3 S cm-1)at room temperature.Moreover,the lithium ion transference number is as high as 0.81,much higher than most of reported separators,and shows good thermal and electrochemical stability.The rate and cycling performances further confirm that the GPE possess excellent performances for LIBs.2.GPE based on natural composite polymers matrix of LC and potato starch(PS)with higher comprehensive performance is prepared.When the content of potato starch is 5%,the composite membrane presents 6 times tensile strength of pure LC membrane and high electrolyte uptake of 194 wt.%.Meantime,ionic conductivity of 1.27×10-3 S cm-1,lithium ion transference number of 0.79,wide electrochemical window and good affinity with electrodes for the as-prepared GPEs can be obtained.In addition,the Li/GPE/LiFePO4 cells display excellent initial discharge capacity,rate and cycling performances.3.For the first time LC with different fiber length are exploited as the matrix of GPE in lithium-sulfur(Li-S)batteries.The prepared GPE based on LC fiber length range(150-300?m)presents extremely excellent comprehensive performances:high enough liquid electrolyte uptake of 428 wt.%,satisfying tensile strength of 3.89 MPa,outstanding ionic conductivity of 4.52×10-3 S cm-1 at room temperatureC excellent lithium ion transference number of 0.79,electrochemical stability window of 5.3 V,good compatibility with lithium electrode and thermal stability.The assembled lithium sulfur cell using obtained GPE shows excellent rate and cycling performance compared to corresponding cell with commercial liquid electrolyte with separator,which is attributed to the successfully suppressed "shuttle effect" in the cell with GPE.