Research On The Application Of Ionic Liquid In Lithium Metal Battery

Lithium-ion rechargeable batteries have become the primary choice in the field of energy storage due to the high working voltage,low self-discharge rate and no memory effect.With the rapid development of electronic technology,higher energy density and longer battery life are required in rechargeable batteries.Because of its low density(0.534 g·cm^-3),high theoretical specific capacity(up to 3860 m Ah·g^-1)and low reduction potential（-3.04 V vs standard hydrogen electrode）,metal Li can be used as an ideal negative electrode material.Lithium metal battery with extremely high energy density and longer cycle life could better meet practical applications.However,this kind of battery has some fatal problems,such as excessive reactivity of lithium,severe volume expansion,poor SEI stability,and disordered lithium deposition,which could result in worse battery stablility,thereby impeding its commercial development.In response to these problems,people have proposed new electrolytes or designed multi-dimensional collectors to achieve stable lithium plating/lithium stripping behavior and prolong the battery life.Ionic liquids exhibit high ionic conductivity,wide electrochemical window and strong thermal stability.It can not only be introduced into the electrolyte to construct a new type of electrolyte system,but also can be used as a reaction medium in the preparation process of materials.In view of this,this paper chose ionic liquids as the solvent to prepare ionic gel electrolyte and three-dimensional porous carbon current collector for lithium metal batteries.The main research contents and results are as follows:（1）Quaternary Ionogel electrolyte with 3D cross-linked organic/inorganic double network for lithium-ion batteries.A quaternary ionic gel electrolyte（PSIL）with low ion association and more free Li⁺was obtained by the one-step sol-gel method.The in situ cross-linking process of the hybrid solid matrix provides a low crystallinity,which ensures the fast Li⁺transportation.At the same time,the presence of the solid matrix effectively could promote the dissociation of Li（TFSI）₂^-clusters in the ionic liquid electrolyte,increase the amount of free Li+and achieve uniform ion transport.Moreover,due to the presence of a high proportion of ionic liquid,the ionic gel electrolyte retains the electrochemical properties of liquid electrolytes and improves interface compatibility.When assembling Li/Li Fe PO₄and Li/Li Ni_0.8Co_0.1Mn_0.1O₂,PSIL showed excellent electrochemical performance at room temperature.In addition,ex-situ characterization and molecular dynamics simulations have proved that PSIL-containing batteries have good interface stability and can effectively inhibit the growth of lithium dendrites.（2）Preparation of highly conductive reduced graphene oxide and its application in lithium metal batteriesWith the aid of ionic liquid Bmim H₂PO₄,a highly conductive reduced graphene oxide（IL-rGO）was obtained,which was used as a current collector of a lithium metal negative electrode.During the reduction process,the electrostatic interaction between the ionic liquid and the GO can inhibit the agglomeration of the graphene layer,resulting in a loose sheet structure,which is convenient for the rapid transmission of Li⁺.At the same time,this method can also deepen the reduction degree of rGO and improve its electrical conductivities.In addition,the anions in IL create a weakly acidic environment,increasing the proportion of carboxyl（-COOH）and hydroxyl（-OH）on the surface of rGO,thereby improving the overall lithiumphilicity.Therefore,it can be seen from the ex-situ SEM image that small-sized Li deposits are obtained on the IL-rGO substrate.Its assembled half-cells and symmetrical cells both exhibit stable electrochemical performance and have a small overpotential.