Study On Hydroxypropyl Methylcellulose Matrix Gel Polymer Electrolyt

Gel polymer electrolyte(GPE)combines the advantages of liquid electrolyte(LE)and solid polymer electrolyte(SPE),which has good safety and excellent electrochemical performance.GPE is mainly composed of polymer matrices,plasticizers and Li salts,and the commonly employed polymer matrices for GPE are mainly chemical synthetic polymer such as poly(ethylene oxide),poly(methyl methacrylate),poly(acrylonitrile)and poly(vinylidene fluoride)and their derivatives.However,when the battery scrap,these polymers can cause"white pollution" to the environment.Therefore,in the context of widespread use of secondary batteries and the urgent need of environment protection,higher requirements are put forward for the development of electrolytes,which should not only have good electrochemical performance and safety,but also reduce environmental pollution as much as possible after scrap.The environmentally friendly natural polymer matrix therefore has attracted extensive attention,but most of these currently developed natural polymer materials exist some weakness that these GPEs have the limited liquid electrolyte uptake and poor electrochemical properties.In order to modify these weaknesses,in this paper,the high-performance gel polymer electrolyte with high absorbability and degradability was prepared from hydroxypropyl methylcellulose(HPMC),and applied in sodium ion battery(SIB)and lithium ion battery(LIB)for the first time.(1)The HPMC membrane prepared by the phase transfer method possesses dense structure,low porosity(48.6%)and good tensile strength(4.27 MPa),and GPE with excellent performance was obtained after absorbing 1130 wt.%LE and applied in SIBs.HPMC-GPE possess high ionic conductivity(3.3×10-3 S cm-1,25℃),stable electrochemical window(4.72 V,vs.Na/Na+)and good electrode compatibility,which can provide a guarantee for the battery charging-discharging performance.The(SnS/rGO)/HPMC-GPE/Na battery assembled from the cathode SnS/rGO prepared by hydrothermal method can provide good rate performance and long cycle performance and deliver the discharge specific capacity retention rate of 79.4%after 100 cycles at 0.1 A g-1.(2)The HPMC membrane can absorb 1706 wt.%of LE in LIBs,and physical characterization shows that it is impossible to obtain a high liquid electrolyte uptake by physical adsorption.However,FTIR test shows that there is a chemical reaction between HPMC and LE,and the structure of the reaction product is characterized by 13C NMR.Therefore,the mechanism of HPMC membrane high liquid electrolyte uptake is closely related to this chemical reaction.Meanwhile,the prepared HPMC-GPE shows outstanding ionic conductivity(6.74×10-3 S cm-1,25℃),remarkable electrochemical stability window(4.9 V,vs.Li/Li+),excellent interfacial compatibility and good regulation ability for lithium deposition/dissolution.In addition,the assembled Li/HPMC-GPE/LiFePO4 cell shows the initial discharge capacity of 157 mAh g-1 at 0.2 C.After 200 cycles,the capacity remains 144 mAh g-1 and the corresponding capacity retention is 91.7%.(3)The significantly increased volume of HPMC-GPE provides a rich path and an increased area for ion conduction,but it also weakens the interaction force between the polymer matrix and the anion(PF6-),resulting in the lithium ion transference number of HPMC-GPE just 0.47.Therefore,adding cage-type inorganic-organic hybrid nanoparticle polyhedral oligomeric silsesquioxane(POSS)to the HPMC membrane can save this problem.On one hand,the larger steric hindrance of POSS can hinder the migration of PF6-,on the other hand,its cage structure does not affect the conduction of Li+.This not only improves the lithium ion migration number,but also significantly improves other electrochemical performance.The composite GPE with 10 wt.%HPMC achieved the best electrochemical performance,including high lithium ion transference number(0.78),remarkable ionic conductivity(9.05×10-3 S cm-1,25℃)and electrochemical stability window(4.74 V,vs.Li/Li+).In addition,this system has the special ability to regulate lithium deposition/dissolution and exhibits overpotential stability for more than 460 h.