Study On The Interface Control And Electrochemical Performance Of Lithium Metal Anode

With the rapid development of electric vehicles,the demand for long cycle life,high energy density and safety power battery become more urgent.At present,the commercial graphite anode can’t meet the demand for it’s limited theoretical specific capacity（372 m Ah/g）.Lithium metal anode with high theoretical specific capacity（3860 m Ah/g）and lowest reduction potential（-3.04 V vs.SHE）is considered as the best choice for the next generation rechargeable battery.Despite impressive merits of Li metal anode,some intractable barriers,especially for safety issues caused by the uncontrolled Li dendrite growth,severely hamper its practical application.Moreover,highly reactive lithium metal can spontaneously react with electrolyte to form solid electrolyte interface（SEI）membrane,the unstable SEI will constantly break and construct during cycling.The excessive consumption of lithium metal and electrolyte resulted in low Coulombic efficiency and poor cycle life.In this thesis,the deposition behavior of lithium in deposition/stripping process is regulated by introducing electrolyte additives and designing lithiophilic interface to inhibit the growth of lithium dendrite and improve the cycle life and safety performance.In order to improve the coulombic efficiency and cycle life of lithium metal anode,an optional amount（2 wt.%）of ethylene chlorophosphite（ECP）,which used as an additive,was added into the 1.0 M Li TFSI+DME:DOL=1:1 vol%electrolyte.In the process of electrochemical cycling,the additive can trigger the ring-opening polymerization of DOL solvent and generate a flexible oligomer composite protective film rich in Li Cl/Li₃P on the surface of lithium anode.This SEI can not only isolate the contact between electrolyte and electrode,but also effectively alleviate the volume expansion of lithium and avoid lithium dendrite piercing.The addition of ECP in Li||Li symmetric battery can prolong cycling lifespan（>2700 h）with a hysteresis voltage of～35 m V.In lithium-sulfur full battery,the specific discharge capacity is 1385.5 m Ah/g for the first time and 476.7 m Ah/g after 300 cycles,which significantly improves the cycle life of lithium sulfur battery.In order to regulate the deposition behavior of lithium ion,the metal oxide La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ（LSCF）was selected to modify the surface of copper（Cu）collector.The modified layer with excellent lithiophilicity,electronic insulation,surface oxygen vacancy and skeleton structure can effectively guide the migration of lithium ion,and disperse the concentrated Li ion flow.So that it can be uniformly deposited on the surface of copper foil.The Li-Li symmetric battery assembled by the decorated collector,can maintain extremely low overpotential and stable battery system after 2850h during the continuous plating/stripping process of lithium metal.In Li-Cu half cell,the coulombic efficiency reach 98.51%after 300 cycles.With LSCF-Cu@Li as the anode and NCM as the cathode,the full cell system is stable as it also has higher capacity and capacity retention than that of bare lithium anode.In order to improve the energy density of the battery,we reselect the carbon-based collector promoted lithiophilicity by g-C₃N₄ to instead of Cu collector.With g-C₃N₄/C composite collector served as the electrode assemble the Li-Li symmetrical battery,the overpotential maintained at 170 m V in 500 h cycle.We assemble the Li-Cu half battery,97%coulombic efficiency can be maintained after 70 cycles which evidenced that the g-C₃N₄/C composite collector can effectively extend the cycle life of the battery.