Constructing Li Metal Anode Based On The Interface Control Of Electrolyte Additives

The increasing demand for portable appliances,electric vehicles and power storage devices is driving the development of Lithium（Li）-ion batteries with longer cycle life and higher energy density.Li metal anode has the lowest redox potential（-3.04 V,relative to the standard hydrogen electrode）,ultra-high theoretical specific capacity(3860 m Ah g^-1),low mass density(0.53 g cm^-3)and can match with high energy density of Li-sulfur and Li-air batteries,so it is considered to be the ultimate anode material for high-energy density batteries.Although these advantages of lithium metal anode,its commercial application still exists many obstacles.Especially,uncontrolled growth of Li dendrites will lead to direct contact between anode and cathode of the cell,thus causing safety accidents.In addition,as a“host-less”material,Li dendrite will separate from the main Li metal anode due to the huge volume changes during charge/discharge processes,resulting in the formation of electrochemical inactive“dead Li”,which seriously reduces the utilization rate of Li.In order to solve the above problems,this paper constructed a stable Li metal/electrolyte interface to regulate the uniform deposition of Li⁺on the Li metal anode and inhibit the growth of Li dendrites,thus improving the electrochemical performances of Li metal anode.The main research contents are as follows:1.In order to improve the stability and Coulombic efficiency（CE）of Li metal anode,the optimal amount of（2%）sulfonyl chloride（SO₂Cl₂）was introduced into the ester-electrolyte as a functional additive electrolyte for Li metal secondary battery to regulate the uniform deposition of Li and achieve dendrite-free Li anode.The SO₂Cl₂ additive enhances the strength of intrinsic solid electrolyte interface（SEI）film by spontaneously reacting with Li metal to in-situ form a stable inorganic protective layer riched in Li chloride（Li Cl）.Li Cl with low surface diffusion barrier is conducive to Li⁺ions migration and uniform nucleation,and inhibits the growth of Li dendrite.As a result,a greatly enhanced CE of 95%after 150 cycles in a Li||Cu cell and a long-term cycling life of over 1200 h with a low and stable overpotential of 40 m V in a Li||Li symmetric cell have been achieved.In addition,the electrochemical performances of Li||Li Fe PO₄ full cell with a higher capacity retention,also has been significantly improved.2.In order to inhibit the growth of dendritic Li and reduce the side reaction of Li/electrolyte interface,an optimal amount（1%）of Li Cl O₄ additive is introduced into the ether-based electrolyte.The Li Cl O₄ additive could react with Li metal to in-situ form a uniform and dense composite SEI layer with rich-Li Cl and Li₂O on the surface of lithium anode.The Li Cl in the SEI layer with a lower interfacial diffusion energy barrier,which is conducive to the rapid migration of Li⁺ions.Besides,Li₂O with a higher ionic conductivity not only facilitates the migration of Li⁺ions,but also renders more homogenous electric field strength distribution on Li surface,thus significantly enhancing uniform deposition of Li at anode and suppress the growth of Li dendrite.Therefore,the electrochemical performances of Li metal anode containing the optimal amount of Li Cl O₄ additive were significantly improved,The Li||Li symmetric cell can be implemented at a relatively low overpotential（～60 m V）over1500 h at a current density of 1 m A cm^-2 under a deposition capacity of 1 m Ah cm^-2.Even under the high current density of 3 m A cm^-2,Li||Li symmetric battery can still maintain long cycle stability for 600 h.The Li||Cu half battery maintains a stable cycle more than 200 cycles with high CE of 96%at a current density of 0.5 m A cm^-2.Moreover,Li||Li Fe PO₄ battery exhibits a higher discharge specific capacity and more stable cycle performance.