Research On The Construction And Interface Control Of Lithium Metal Anode

Lithium(Li)metal is the most promising anode material for the next generation of Li-ion batteries,but it must overcome key performance defects before it can be used as commercial anode.The main issues are as follows:(1)Dendrite growth caused by uneven Lideposition/stripping and the formation of“dead Li”;(2)Volume change of Limetal electrode during charging and discharging;(3)Poor structural stability;(4)Low ratio of active Lion the electrode.In view of these prominent problems,this paper carries out research work from two aspects of electrode structure construction and interface regulation.A uniform and stable Liplating/stripping process on the electrode surface is achieved by constructing a three-dimensional collaborative Limetal electrode to control the spatial charge distribution,optimize the interfacial electric field and reduce the Limigration barrier on the electrode surface.By reducing the surface tension between molten Liand fluid collection,a uniform and ultrathin composite Limetal electrode can be generated spontaneously.The artificial SEI with high mechanical strength and high ionic conductivity is prepared to realize the rapid and stable Li⁺conversion and migration process on the electrode surface.The research work of this dissertation is as follows:1.NiLibimetallic composite electrode(NiLi-BC)with ultra-high electrochemical stability was studied.Aim to solve the problem of Lidendrite growth in the process of Lideposition/stripping,a bimetallic composite electrode consisting of three-dimensional nickel foam inside and Limetal layer outside was constructed by simple mechanical rolling method.The Ni framework inside the electrode can optimize the electric field and homogenized Li⁺distribution at the electrode/electrolyte interface,inducing the uniform Lideposition.As a result,the NiLi-BC exhibited a Lidendrite-free feature and stable cycling performance under a low overpotential(<15 m V throughout 2180 h at 1 m A cm^-2 with a deposition capacity of 1 m Ah cm^-2).Moreover,the assembled NiLi-BC||LiFe PO₄coin cell and pouch cell exhibited improved capability and stable cycling performance,a specific capacity of more than 100 m Ah g^-1 can be maintained after 500 cycles.Finally,the in-situ optical microscopy and in-situ Raman spectroscopy were employed to obtain a better understanding of the interfacial structure and chemical component during the Liplating and striping processes.2.The ultrathin and electrochemically stable Cu Lialloy electrode(Cu@LC)was studied.Aim to explore the unstable electrochemical process on the surface of Limetal electrode and the low ratio of active Liof normal Limetal electrode,Cu Lialloying method was adopted in this study to increase the Young's modulus of molten Limetal,which was conducive to the Liplating/stripping process on the electrode surface.The surface tension between molten Liand copper foil was reduced,and the ultrathin composite Limetal electrode was prepared.The uniform thickness of the Limetal layer on the surface of the electrode was?30?m,and the cycling performance was stable for nearly 600 h under the test conditions of 1 m A cm^-2 and 1 m Ah cm^-2.It can be stable cycled for more than 100 h under the condition of the maximum Limetal utilization rate was more than 50%.The Limetal battery assembled with NCM811 also showed better stable cycle performance and Coulombic efficiency.After 100 cycles,Cu@LC21||NCM811 full cell remained a discharge specific capacity of 140 m Ah g^-1 with a capacity retention rate of 78%.3.A multi-dimensional cooperative composite flexible film electrode(MD-HFF)with stable electrochemical process was studied.Based on the problem of serious excess Limetal content and volume change during charging and discharging of the electrode,an effective MD-HFF composed of iodine ion(0 dimension),CNTs(1 dimension)and graphene(2 dimensions)is designed for regulating Lideposition and mitigating volume changes.The multi-dimensional components serve separate roles:(1)iodine ion enhances the conductivity of the electrode and provides lithiophilic sites,(2)CNTs strengthen interlaminar conductance and mechanical strength,acting as a spring in the layered structure to alleviate volume changes during Liplating and stripping and(3)graphene provides mechanical flexibility and enhances electrical conductivity.The results of MD-HFF material shows stable Liplating/stripping and high Coulombic efficiency(99%)over230 cycles at 1 m A cm^-2 with a deposition capacity of 1 m Ah cm^-2.Theoretical calculations indicate that LiI contributes to the lateral growth of Lion the MD-HFF surface,thereby inhibiting the formation of Lidendrites.When paired with a typical NCM811 cathode,the assembled MD-HFF||NCM811 cell exhibit improved capability and stable cycling performance,maintain 90%capacity retention rate after 100 cycles.4.A Limetal electrode(LiF/sulfide enriched Li)containing an artificial SEI layer rich in LiF and sulfide was studied.Aim to solve the problem of poor stability of traditional SEI on the Limetal electrodes,a Limetal electrode was designed to prepare the composite SEI layers rich in LiF and sulfide.The experimental and theoretical simulations demonstrate that the ideal artificial SEI can induce uniform Li⁺distribution at the interface and effectively inhibit dendrite growth.As results,the LiF/sulfide enriched Lisymmetrical cells exhibit excellent cycling stability and low Lideposition overpotential,which maintain a low overpotential of?10 m V for over 1000 h at 1 m A cm^-2 in an ether electrolyte of DME/DOL+LiTFSI and steadily cycles for 350 h in a carbonate electrolyte of EC/EMC+LiPF₆.Furthermore,full cells assembled with NCM811 and sulfur cathode exhibit enhanced cyclability.LiF/sulfide enriched Li||NCM811 full cell can stable cycle for 200 times at 0.2 C,LiF/sulfide enriched Li||S full cell retained?550 m Ah g^-1 discharge capacity at 0.5 C after 300 cycles.