Insight Into Modification And Design For Li Metal Anodes In Rechareable Li Batteries

Nowadays Lithium-ion batteries（LIBs）play an important role on our daily life,but inherent limitations make it difficult to meet the ever-increasing demands in portable electronics,electric vehicles,and grid-scale energy storage.Replacing graphite anode in conventional LIBs with Li metal anode is considered as one of the most favored choices for next-generation electrochemical energy-storage systems since metallic Li has a high theoretical specific capacity(3860 m Ah g^-1)and lowest electrochemical potential（-3.04V vs.standard hydrogen electrode）.Although appealing properties,its commercialization is hampered by some formidable challenges,which include the growth of Li dendrites resulting in safety hazards,severe side reactions causing a rapid performance decline,the infinite volume fluctuations and so on.Targeted at these problems of Li metal anode,we have conducted three parts of our work as follows:（1）In situ artificial solid electrolyte interphase fabricated by photopolymerization for stable Li metal anodeLi metal spontaneously reacts with electrolytes owing to its high reactivity,which would consume active materials continuously,giving rise to rapid decay of performance.Herein,an in situ solid electrolyte interphase（SEI）is constructed by photopolymerization of hexafluorobutyl acrylate for stabilizing Li metal anode.The artificial SEI comprised flexible polymer matrix and inorganic Li F filler not only adapts volume fluctuations during cycling but also regulates Li deposition behavior,enabling it to suppress the dendrite growth and block side reactions between the electrolyte and Li metal.Accordingly,Li metal anode with artificial SEI presents superior stable cycling performance over 500 h at 1 m A·cm^-2 for 1 m A·h·cm^-2 without dendrites growth in carbonate electrolyte.（2）PEO-based polymers serving as protective layer to improve the cycling performance of Li metal anodeDespite the native SEI generated by Li metal anode reacting spontaneously with electrolytes is non-uniform and unstable,among all the products,PEO is believed to passivate Li metal anode and reduce side reactions.However,the uneven distribution and low content of PEO greatly limits its effect.Here,a variety of PEO-based protective layer are prepared on the surface of Li metal anodes by dipping method,such as Poly（ethylene glycol）,Poly（ethylene glycol）bis（carboxymethyl）ether,Poly（ethylene glycol）dimethyl ether.Symmetric batteries testing at 2 m A cm^-2 for 1 m Ah cm^-2 show that PEO-based protective layers enable to reduce overpotential and improve cycling performance.（3）Accommodating Li into 3D Cu@Ag composite matrix towards long-life Li metal anodeOwing to the‘host-less’nature of Li metal anode,the relative volume contraction/expansion during Li stripping/plating process is virtually infinite.Such inherent huge volume fluctuations degrade the electrode stability and dramatically shorten the lifespan of Li metal batteries.In this study,a three-dimensional copper（3D Cu）with a submicron-sized skeleton and porous structure was prepared by ammonia etching,then 3D Cu@Ag is obtained after 3D Cu was decorated with a lithiophilic layer of Ag by magnetron sputtering.3D Cu@Ag is a stable HOST material for storing Li and reducing the nucleation barrier during Li plating.The cycling results demonstrated that Li metal anode using 3D Cu@Ag HOST exhibits uniform deposition morphology,low voltage hysteresis,and superior lifespan.