Study On The Optimization Of Lithium-Metal Anode And Its Interface For Lithium-metal Batteries

The theoretical capacity of traditional graphite anode materials is only 372 m Ah g^–1,so it is difficult to meet the needs of the development of high-energy-density batteries.Lithium?Li?metal has drawn wide attentions because of its lowest redox potential?–3.040 V vs.standard hydrogen electrodes?,high theoretical specific capacity(?3860 m Ah g^–1),and low density(?0.59 g cm^–3).With Li metal as a negative electrode material,high-energy-density Li-metal batteries can be obtained by matching it with ideal positive electrode materials?such as a ternary material,sulfur or oxygen?.However,Li-metal anode will undergo uneven deposition upon charging and discharging,which will cause dendrite growth and volume expansion.In addition,the exposed fresh Li can react with the electrolyte to form an unstable SEI again,leading to the continuous decomposition of electrolyte.For Li-S battery systems,Li-metal anode also suffers from serious corrosion problems due to the"shuttle effect"of lithium polysulfide.Therefore,Li-metal batteries generally have the disadvantages of poor cycle performance and low safety.In this regard,this study optimizes Li-metal anode from the aspects of surface protection and construction of three-dimensional current collectors,which can achieve the purpose of inhibiting dendrite growth and stabilizing the Li-electrolyte interface.The research that has been carried out is as follows:1.A Li-ion conductive organic/inorganic composite protective layer is used to protect the Li-metal anode in Li-S batteries.Li_1.5Al_0.5Ge_1.5?PO₄?₃ powder with good Li-ion conductivity is compounded with polyvinylidene fluoride binder to form a composite protective layer?CPL?on the surface of the Li-metal anode.The introduction of Li_1.5Al_0.5Ge_1.5?PO₄?₃ powder as an active filler can alleviate the effect of CPL on Li-ion transport,thereby effectively reducing interfacial polarization.At the same time,CPL can not only siginificantly inhibit the growth of Li dendrites,but also block the corrosion of the Li-metal by soluble lithium polysulfide.CPL-protected Li-metal anode greatly improves the electrochemical performance of Li-S batteries.In the electrolyte without a Li NO₃ additive,the Li-S batteries assembled with the protected Li-metal anode can deliver a specific capacity of 832.1 m Ah g^–1 and an average coulomb efficiency of 92%after 100 cycles at 0.5 C.2.The flexible carbon microtube framework is used to guide uniform Li deposition behavior.Carbonization treatment of pure cotton cloth under high temperature conditions can produce lightweight flexible hollow carbon microtube framework?FCMS?.With the FCMS as a three-dimensional current collector of Li-metal anode,the local current density can be effectively reduced,and the volume effect during cycling can be alleviated.In addition,the stable Li-ion intercalation behavior that occurs on FCMS can effectively reduce the nucleation barrier during Li deposition,and improve the Coulomb efficiency of Li deposition/dissolution.More importantly,because the conduction of electrons is faster than the transport of Li ions,the deposition/dissolution reaction of metallic Li occurs mainly in the upper of the FCMS.Therefore,the FCMS in the lower layer can act as a soft conductive"air cushion"during cycling,and dynamically release the internal stress generated during the Li deposition process,thereby achieving the purpose of dendrite suppression.A high-performance composite Li-metal anode?Li@FCMS?can be obtained by loading metallic Li into the FCMS by electrodeposition.The full battery using Li@FCMS composite Li-metal anode and Li Fe PO₄ cathode can operate stably over 250 cycles at 0.5 C.3.The Zn O nanoarray-modified nickel foam is used as a three-dimensional current collector for Li-metal anode.A seed-assisted growth method is used to construct a Zn O nanoarray on the surface of nickel foam to form a lithiophilic three-dimensional current collector?ZMNF?.The introduction of Zn O nanoarray can effectively reduce the overpotential of Li deposition and induce uniform Li deposition behavior.In addition,through Li-Zn alloying and capillary action,ZMNF shows good wetting with molten Li.Thus,a composite Li-metal anode?Li@LZMNF?containing an intermediate layer of Li-Zn alloy can be obtained.The formed Li-Zn alloy layer possesses good affinity with metallic Li,which can significantly reduce the Li nucleation barrier and induce the uniform Li deposition along the three-dimensional conductive framework.By preferentially depositing on such a three-dimensional lithiophilic framework,the formation of Li dendrites on the bulk Li can be effectively reduced.The Li@LZMNF composite Li-metal anode and Li Fe PO₄ cathode are assembled into a full battery,which can maintain a specific discharge capacity of up to 147 m Ah g^–1 after 450 cycles at 1 C.4.In situ preparation of mixed ion/electron-conductive skeleton?MIECS?and its composite Li-metal anode.Cu₃P nanowires supported by copper foil?Cu₃P@Cu?are prepared by facile chemical method and used as a three-dimensional current collector for Li-metal anode.The in-situ optical microscope proves that the formation of mixed conductive discharge products?Cu and Li₃P?can induce non-dendritic Li deposition on the lithiated Cu₃P@Cu foil.At the same time,after evaluating the Gibbs free energy of the reaction between Cu₃P and metallic Li at high temperature,a composite Li-metal anode?Li@MIECS?containing the MIECS is in situ prepared by utilizing the chemical reaction of Cu₃P and molten Li.The formed Li₃P and Cu-Li alloy as the MIECS exhibit good affinity with metallic Li,which can adjust the charge/ion distribution on the three-dimensional current collector and thereby induce uniform Li dissolution/deposition behavior.When Li@MIECS composite Li-metal anode is coupled with Li Fe PO₄cathode,the obtained full batteries can stably work over 700 cycles at 1 C and retain a discharge specific capacity of 146 m Ah g^-1.