Regulation On Ga-Based Liquid Metal/Cellulose Interface For Li-Metal Anodes

Lithium metal has the advantages of high theoretical specific capacity(～3860 m Ah g^-1),low electrochemical potential（-3.04 V vs.standard hydrogen electrode）and light weight,which make it an ideal anode material for the next-generation high-energy-density secondary batteries.However,lithium metal anodes suffer from problems such as interfacial instability and disordered growth of dendrites,which seriously affect their practical application.Gallium（Ga）,a kind of room-temperature liquid metal,has a low energy barrier for Li nucleation.And the reversible solid-liquid phase transition of Ga during the reactions with Li endows Li-metal with the self-healing function.Thus,Ga has the potential of being a stable interface for Li metal anodes,which can promote the uniform deposition of lithium,and alleviate the growth of lithium dendrites.However,the solid-liquid phase transition reaction of Ga occurs along with the plating and stripping process of Li,resulting in poor coverage of Ga on Li metal after several cycles,which means decreased self-healing effect.Therefore,the development of highly stable Ga-based interfaces for Li-metal anodes is of great research significance.Ga-based liquid metal artificial interface is taken as the research object,and the limited self-healing effect of Ga is treated as the main issue.Simple approaches of in situ polymerization,double-interface layer construction and alloying are adopted to prepare high-stability Ga-based interfaces.In addition,the environmentally friendly cellulose is also studied as a Li-metal interface,which is prepared by a cost-effective coating method.The main research contents,results and conclusions are as follows:（1）A dual-interfacial PEGDA Li-Ga protective layer with excellent structural stability was constructed on Li anode via in-situ photopolymerization of PEGDA on Li-Ga layer.The Li-Ga alloy layer can effectively homogenize the Li⁺flux,induce uniform nucleation and deposition of Li⁺,and avoid the generation of Li dendrites.The PEGDA polymer layer can both help Li metal anode form a stable SEI film and maintain the structural stability of the Li-Ga alloy layer during Li plating/stripping.Thus,PEGDA Li-Ga-modified Li metal anode has excellent interfacial stability and high reversibility of Li plating/stripping,which results in stable long-cycle performance and excellent rate performance.Pouch cell with Li Ni_0.6Co_0.2Mn_0.2O₂（NCM622）cathode(1.52 m Ah cm^-2),the dual interface layers ensure a stable performance over60 cycles,with a capacity retention of 82%.（2）Aiming at improving the self-healing capability of Ga-based liquid metal,an in-situ polycarbonate layer is synthesized（AIFP）on Li-Ga surface by electrocatalytic method.The AIFP layer can effectively protect the structural stability of Li-Ga alloy layer during Li deposition and stripping.Under the protection of AIFP layer,the self-repairing Li-Ga layer has high reversibility of solid-liquid phase transition,which can efficiently repair the defects on Li metal surface.And the Li-Ga layer can induce uniform nucleation and deposition of Li⁺and avoid the generation of Li dendrites.Therefore,the AIFP Li-Ga protective layer can effectively enhance the interfacial stability and electrochemical performance of Li metal anodes.AIFP Li-Ga was coupled with LFP(cathode loading of 2 m Ah cm^-2,electrolyte usage=15μL cm^-2,3.8V cut-off voltage)cathode,resulting in capacity retention of 90%after 150 cycles at 0.5 C(discharge capacity of 136.77 m Ah g^-1).（3）A fast ion-conducting Ga-Al alloy layer was prepared on Li metal surface by a simple and facile drop-casting method.The crystal structure of Ga is modulated to enhance the self-healing ability of Ga-based liquid metal and the Li⁺transport rate of the interface.As the uniformly dispersed Al can be regarded as the skeleton of Ga,an inside-out Li⁺deposition process in the Ga-Al alloy is formed,which can effectively improve the self-healing capability of Ga-based liquid metal on Li metal.In addition,the introduction of Al effectively reduces the Li nucleation barrier and improves the Li⁺diffusion rate,which is favorable for uniform Li deposition and stripping,and significantly improves the interfacial stability of the Li metal electrode.（4）A Ga-Sn interface with good adhesion with Li was prepared using drop-casting method to further improve the interfacial stability of Li anode.Sn can effectively improve the adhesion between Ga-based liquid metal and Li metal,helping obtain a stable interface on Li anode during long cycling.This Ga-Sn interface can not only effectively inhibit the occurrence of side reactions,but also improve the interfacial charge transfer rate.Therefore,the good-adhesion Ga-Sn modified Li metal anode has excellent structural and electrochemical stability.（5）An inert cellulose membrane（CM）was covered on Li metal anode as a protective layer using the patch method.The electrically insulating CM layer on the upper layer and the highly conductive Li metal on the lower layer make Li⁺follow a bottom-up deposition process,3D CM can provide sufficient space for Li⁺deposition and its electrical insulation property can effectively inhibit the growth of Li dendrites.CM has good electrolyte wettability,helping to adsorb electrolyte and promote the uniform distribution of electrolyte on Li metal.Thus,the 3D CM-protected Li metal anode shows excellent electrochemical performance and interfacial stability.