Study On The Protection Of Metal Anode By Gel Polymer Electrolyte

With the popularization and development of new generation electronic devices,the energy density of commercial lithium-ion batteries have nearly reached their theoretical limits,prompting people to explore energy storage devices with higher energy density.In recent years,metal anodes such as lithium,sodium,potassium,and zinc have attracted widespread attention due to their high energy density and low reduction voltage.At present,metal anodes are used in various energy storage devices to achieve a wider voltage window and a higher energy density.However,the metal anodes undergo irreversible dendrite growth and volume expansion during cycling,which greatly shortens its cycle life and may cause potential safety hazards such as short circuit,leakage and explosions.To solve this problem,lots of strategies have been proposed to protect the metal anode,including structured anode,electrolyte additive,superconcentrated electrolyte,gel polymer electrolyte and so on.Among them,gel polymer electrolytes with high ionic conductivity and certain mechanical strength can effectively inhibit dendrite growth and electrode volume expansion,improving the cycling stability of metal anodes,which is an effective method for the protection of metal anodes.Based on the research background above,the main research contents of this article are as follows:（1）The protective effect of the in situ gel polymer electrolyte（GPE）based on pentaerythritol tetraacrylate（PETEA）on the lithium anode was explored.The in situ GPE was prepared by a simple thermal gelling method,which had high ionic conductivity(5.75 m S cm^-1)and good electrochemical stability.Combining it with a lithium metal anode and a three-dimensional porous activated carbon cathode,a flexible lithium metal capacitor was assembled.The assembled flexible lithium metal capacitor exhibited a wide voltage window（1.5-4.3 V vs Li/Li⁺）,high specific capacity(210 F g^-1at 1 A g^-1)and high energy density(under the power density of290 W kg^-1,the maximum energy density was 474 Wh kg^-1;under the maximum output power density of 29 k W kg^-1,the energy density was 192 Wh kg^-1).Compared with the commercial liquid electrolyte,the cycle stability of the assembled quasi-solid lithium metal capacitor was greatly improved(after 5000 cycles at 1 A g^-1,the capacitance retention rate was 68%).SEM results indicate that the dendrite growth on the lithium metal anode was effectively suppressed,proving the protective effect of the in situ GPE on lithium metal anode.Besides,the assembled flexible lithium metal capacitor could work normally under abuse tests such as bending,puncturation and cutting,proving that the in situ GPE enhances the safety of lithium metal anode.（2）The protective effect of the polyvinyl alcohol（PVA）hydrogel electrolyte doped with hectorite on the zinc metal anode was explored.The PVA hydrogel electrolyte was doped with different contents of hectorite to study its influence on the ionic conductivity of PVA hydrogel electrolyte.The results show that the ionic conductivity of PVA hydrogel electrolyte firstly increased and then decreased with the increase of hectorite content.When the hectorite doping concentration was 8%,the doped PVA hydrogel electrolyte exhibited the highest ionic conductivity(13.25 m S cm^-1).Besides,the doping of hectorite improved the mechanical properties（the maximum deformation was 240%,the maximum stress was 1.05 MPa）and the thermal stability of PVA hydrogel electrolyte.Zn-Zn symmetric batteries were assembled with hectorite doped PVA hydrogel electrolyte to study its effect on the cycling stability of zinc metal anode.After doping PVA hydrogel electrolyte with hectorite,the assembled Zn-Zn symmetrical battery exhibited lower overvoltage and longer cycle life at various current densities(for example,at 0.5 m A cm^-2,the Zn-Zn symmetric battery had a cycling life over 2000 h,and its overvoltage was below 50m V).SEM images show that there were almost no dendrite on the surface of the zinc electrode after different number of cycles in the PVA hydrogel electrolyte doped with hectorite,indicating that the doping of hectorite inhibited the growth of zinc dendrite.In addition,Zn-Mn O₂batteries was assembled with the preparedα-Mn O₂anode,zinc metal anode and hydrogel electrolytes.Compared with PVA hydrogel electrolyte,the Zn-Mn O₂battery with hectorite doped PVA hydrogel electrolyte showed higher capacity and improved cycling stability(at 0.5 A g^-1,the Zn-Mn O₂battery exhibited an initial capacity of 152 m Ah g^-1and remained 80%of it after 300 cycles),proving its noteworthy improvement on the cycling stability of zinc metal anode.