Construction Of Stabilized Lithium Anode Based On Surface Modification Strategy And Its Electrochemical Properties

Under the dual carbon goal of“carbon peak and carbon neutrality”,the transition from traditional fossil energy to new energy has become the choice of the time.Lithium-ion batteries,as a relatively high degree of commercialization,have been widely used in portable electronic equipment,electric vehicles and large-scale energy storage.However,the theoretical energy density of lithium ion batteries based on the“rocking chair”principle is about 400 Wh kg^-1 and the current energy density of commercial Li-ion batteries is close to 300 Wh kg^-1 making it hard to meet the demand for high energy density in downstream applications.Thus,it is necessary to achieve a transition of energy density through the innovation of electrode material system.Lithium metal anode has nearly 10 times higher theoretical specific capacity,low potential and low density compared with traditional graphite materials,so lithium metal anode has been recognized as an ideal anode material for high energy density batteries.For lithium metal anode,the Li deposition mainly occurs on the surface of the electrode,i.e.,at the interface between electrode and the electrolyte.Thus,the surface and interface properties of electrodes,such as lithium ion migration barrier,lithiophilicity and surface energy play a key role in the dense Li deposition.Although many researchers have proposed many strategies for the modification of surface/interface,the uniform and dense Li deposition and the stability of the interface have not been fully realized,and the mechanism needs to be further analyzed.How to improve the electrochemical deposition behavior of Li ion through surface/interface optimization is still an important topic in the research of lithium metal anodes.To address the critical role of the electrode surface/interface for lithium ion deposition,we have conducted corresponding modulation studies on the surface/interface of electrode substrate from the following four levels.The specific researches are as follows:1.The graphitized carbon nanospheres with ultra-small particle size are uniformly attached to the surface of lithium foil by a simple mechanical roller pressing method to generate an in situ Li C₆ heterogeneous microstructure interfacial layer with good lithium ion and electron conductor.The differences in the interfacial layers formed using different carbon materials are investigated,and the type of carbon material significantly affected the physical and chemical properties of the formed heterogeneous layers.The Li C₆ heterogeneous microstructure interfacial layer can homogenize Li⁺flux and the current density on the surface of lithium metal,effectively improve the uniformity and reversibility of Li plating/stripping behavior,and improve the stability of the interface.In the carbonate base electrolyte,a stable cycle over 300h is achieved.2.For any battery system with lithium containing cathode materials,the use of anode-free electrode with only current collector can greatly improve the energy density.Therefore,how to uniformly and controllably deposit lithium on the heterogeneous substrate copper foil is very necessary to improve the energy density.Thus,lithiophilic Li_4.4Sn layer with fully lithiated phases is uniformly constructed on the surface of cooper foil by liquid phase chemical lithiation solution to guide more uniform and reversible lithium deposition.Chronoamperometry is used to compare the nucleation model and nucleation density of lithium ion plating on bare Cu and Li_4.4Sn@Cu.Through the comparative analysis of nucleation thermodynamics and diffusion kinetics,the copper foil with Li_4.4Sn nucleation layer has lower energy barrier for nucleation,faster lithium ion diffusion,and lithium ion presents epitaxial dense growth deposition.In the half-cell efficiency test,the Li_4.4Sn@Cu still maintain 99.6%coulombic efficiency after more than 600 cycles.However,the bare copper foil is lower than 40%due to dead lithium accumulation after 300 cycles.The capacity retention rate of pouch cell using Li_4.4Sn@Cu is increased from 56.3%to 85.5%.3.In order to alleviate the risk of volume expansion and dendrite piercing through the separator,a strategy of constructing a protective layer with a uniform coaxial structure on the surface of three-dimensional current collector（3D SSM@C electrode）is proposed.A homogeneous coaxially structured carbon film（3D SSM@C）is prepared on the surface of 3D stainless steel mesh（SSM）by electropolymerization and high-temperature carbonization to form a non-equipotential body with the SSM substrate.The carbon film acts as a stable interface layer to weaken the contact between the deposited lithium and the electrolyte.At the same time,the reserved space limitation of lithium ion deposition is reserved to avoid the generation of dendritic lithium.The three-dimensional structure also alleviates the huge volume expansion caused by planar deposition.3D SSM@C electrode makes half cell efficiency more than 99%,stable 430cycles in symmetric battery stable cycle 1300 h.4.The nucleation and primary SEI film at the interface between copper foil and electrolyte are optimized by simple high current activation to regulate the lithiophilic/lithiophobic properties of Cu foil,avoiding the introduction of inactive substances and the complex operation of chemical modification.The effect of nucleation at different current densities from 1 m A cm^-2 to 20 m A cm^-2 on the subsequent lithium ion deposition is investigated.From the thermodynamic and kinetic analysis,the uniform coated lithium nuclear layer and Li F-rich SEI formed by the activation of 20 m A cm^-2 facilitates the subsequent uniform electrodeposition of lithium ions.The cycle performance of pouch cell using the high current activation method is increased by nearly three times.