A synchronous surface flattening and artificial SEI coating process for lithium-containing metal strips, modified lithium-containing metal strips and applications thereof

Abstract

This invention discloses a process for simultaneous surface smoothing and artificial SEI coating of lithium-containing metal strips, modified lithium-containing metal strips, and their applications. During the rolling and thinning process of lithium-containing metal strips, this invention uses an artificial SEI film-forming sacrificial agent that also acts as a lubricant. Through the deformation energy of machining, a large-area, instantaneous, and uniform reaction is stimulated between the active lithium metal surface and the film-forming sacrificial agent (which also acts as a lubricant). The lubrication effect of the film-forming sacrificial agent improves the surface quality of the lithium metal. Ultimately, while smoothing the lithium metal side of the lithium-containing metal strip, a continuous, complete, dense, and uniform artificial SEI layer, mainly composed of inorganic salts, is formed on the lithium metal surface. This simultaneously completes the smoothing of the lithium metal side of the lithium-containing metal strip and the artificial SEI coating. Therefore, it not only reduces the process cost of lithium metal anode forming and improves production efficiency, but also further optimizes the performance of the anode.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage materials, and in particular to a process for simultaneous surface planarization and artificial SEI coating of lithium-containing metal strips, modified lithium-containing metal strips, and the application of the modified lithium-containing metal strips as a negative electrode material in lithium metal primary / secondary batteries. Background Technology

[0002] Currently, commercially available lithium-ion batteries based on graphite anodes are limited by the low capacity density of graphite materials (372 mAh / g), which cannot meet the future demand for high-energy-density energy storage devices (400-500 Wh / kg). Therefore, the core work in developing battery systems with higher energy density is to develop anode materials with low electrode potential and high capacity density.

[0003] Among all the candidate materials, lithium metal anode materials have the lowest electrode potential (-3.04V vs. SHE) and extremely high specific capacity (3860mAh / g). They can also be matched with cathode materials such as sulfur and air to achieve high energy density battery systems with energy densities higher than 600Wh / kg, showing great application potential. Therefore, they have received widespread attention from scientific research and industry and are one of the main directions of high energy density battery research and development.

[0004] However, the practical application of lithium metal anodes faces several challenges:

[0005] First, lithium metal foil has low mechanical properties, with an ultimate tensile strength of only 1.5 MPa and a Young's modulus of only 4.9 GPa. Therefore, lithium metal foil anodes are highly susceptible to structural damage during processing, battery assembly, and application.

[0006] Secondly, the electrochemical reaction process of lithium metal anode is accompanied by unrestricted deposition / dissolution of lithium metal and severe deformation stress, which leads to cracking and pulverization of metal foil, and continuous irreversible reaction between active lithium metal and electrolyte, resulting in loss of battery active material and performance degradation.

[0007] Finally, due to its reactive chemical properties, lithium metal or lithium metal-based composites rapidly undergo side reactions and deteriorate in humid atmospheres, while lithium metal melts are also highly susceptible to oxidation in dry atmospheres. Therefore, using lithium metal / alloy foil as the negative electrode in batteries requires vacuum or inert atmosphere protection, which significantly increases production costs.

[0008] To address the issues of low structural strength and high chemical reactivity of lithium metal, the most common approach in the industry is to combine lithium metal with other high-strength conductive thin film materials (such as copper foil or porous carbon felt) or form alloys during the anode material preparation process. This produces lithium-containing metal strips, which utilize the high-strength composite phase within the metal strips to enhance the overall structure of the metal anode, thus mitigating stress damage to the anode structure during processing and application. Furthermore, a continuous artificial SEI film composed of inorganic or organic solid electrolyte is coated onto the lithium metal side of the lithium-containing metal strip, thereby passivating the metal surface to some extent and improving the stability of lithium metal in environments such as air and liquid electrolytes.

[0009] However, the current technology also has two disadvantages in actual production and application:

[0010] First, the current cold rolling process for lithium-containing metal strips is a lubrication-free process. During rolling, the dead zone of the lithium metal is difficult to maintain stability, resulting in high internal and external friction and uneven distribution of deformation stress on the surface of the lithium-containing metal strip. This leads to severe defects such as indentations, bite marks, and scratches on the lower-strength lithium metal side, damaging the surface smoothness of the lithium metal. When the lithium-containing metal strip is subsequently used as a negative electrode in batteries, the numerous surface defects, poor smoothness, and uneven distribution of residual stress from surface work hardening will induce uneven deposition of lithium metal, severely damaging the uniformity and stability of the negative electrode interface, causing damage to the passivation layer and dendrite proliferation, and accelerating the failure of the negative electrode.

[0011] Secondly, the current industry-standard artificial SEI modification process for lithium-containing metal strips is overly complex and cumbersome. It involves first cold-rolling the lithium-containing metal strip into shape, then removing oxides and other impurities from the surface, and finally coating the lithium-copper composite strip surface with a film-forming sacrificial agent, combined with electrochemical / thermal formation processes, vacuum sputtering, and polymer solid electrolyte membrane coating to form an artificial SEI coating on the lithium metal surface. Because the forming and surface modification steps are performed separately, the production process is significantly more complex, increasing the demands on production equipment, special process environments, and energy consumption. This leads to a substantial increase in production costs and a decrease in yield for artificially SEI-modified metal strips. Furthermore, due to limitations in the film formation mechanism, the uniformity, continuity, and integrity of the artificial SEI coating on the lithium-containing metal strip surface using existing processes are not ideal, thus making the passivation and protection of the lithium-containing metal strip unreliable.

[0012] In summary, in order to achieve a low-cost, high-energy-density lithium metal battery system, there is an urgent need for a method that can rapidly, continuously, cost-effectively, and with low energy consumption prepare a smooth and defect-free lithium metal strip, and coat its lithium metal side with a complete, continuous, and uniform artificial SEI. Summary of the Invention

[0013] This invention addresses the current industry's problem of separating the dry and cold rolling forming steps and the artificial SEI step for lithium-containing metal strips, resulting in cumbersome modification processes and poor product quality. It proposes a scheme to simultaneously perform surface smoothing and artificial SEI modification on lithium-containing metal strips, thereby obtaining lithium-containing metal strips with a smooth and defect-free lithium metal surface and a complete and uniform artificial SEI coating on the lithium metal surface. When used as a negative electrode material for lithium metal batteries, it can achieve a dendrite-free negative electrode with long-term stable charge and discharge.

[0014] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In its first aspect, the present invention provides a process for simultaneous surface planarization and artificial SEI coating of lithium-containing metal strips, comprising the following steps:

[0015] S1. A film-forming sacrificial agent is pre-coated onto the lithium metal surface containing the lithium metal strip to form a liquid film;

[0016] S2: Apply a flat and smooth metal roll to roll the lithium metal surface of the lithium metal strip, simultaneously achieving lithium metal surface smoothing and artificial SEI coating.

[0017] The film-forming sacrificial agent serves both as a rolling lubricant and as a sacrificial precursor required for artificial SEI formation, reacting with lithium metal to generate an artificial SEI film.

[0018] Preferably, the film-forming sacrificial agent is selected from at least one of the following substances: liquid haloalkanes and their derivatives, solutions of inorganic salts, and solutions of sulfurized small organic molecules.

[0019] Preferably, the liquid haloalkane and its derivatives are one or more of haloalkanes, alkenes, benzene-based small organic molecules and their derivatives, such as 1,2-dibromoethane, trichloroethylene, hexafluorobenzene, and pentafluorobromobenzene; the inorganic salt is at least one of nitrates and phosphates (the metal ions of nitrates and phosphates include, but are not limited to, silver, zinc, aluminum, tin, germanium, gallium, indium, niobium, antimony, bismuth, and molybdenum); the sulfide organic small molecules include organic small molecules and inorganic salts, wherein the organic small molecules include sulfides or thiobenzene-based small molecules and their derivatives such as DtbDS, DPDTe, DMDS, DMTS, AMDS, BTB, and ADS; and the inorganic salt includes one or more sulfides or polysulfides of metals such as lithium, silver, zinc, aluminum, tin, germanium, gallium, indium, niobium, antimony, bismuth, and molybdenum.

[0020] Preferably, the lithium-containing metal strip is selected from any one of pure lithium metal strip, binary or multi-element alloy strip of lithium and any other metal, lithium-copper composite strip, and lithium-carbon composite strip.

[0021] Preferably, metallic lithium or lithium alloy is distributed on at least one side of the metal strip, and the thickness of the lithium-containing metal strip is 1~100μm, and the lithium content is 1~100%.

[0022] Preferably, the thickness of the liquid film formed in step S1 is 10~100μm.

[0023] Preferably, in step S2, the rolling process conditions are as follows: the processing stress is 1~100 MPa, the single rolling reduction is 0.01~1 mm, the roll linear speed is 0.1~100 cm / s, the processing is a combination of roughing and finishing rolling, and the number of rolling passes is 2~10.

[0024] Preferably, the simultaneous process of surface leveling and artificial SEI coating of the lithium-containing metal strip includes the following steps:

[0025] S1. 1,2-Dibromoethane is pre-coated on the lithium metal surface of the lithium-copper composite strip as a film-forming sacrificial agent to form a liquid film;

[0026] S2: The lithium metal surface of the lithium metal strip is rolled using smooth metal rolls to simultaneously achieve surface smoothing and artificial SEI coating. The rolling process conditions are as follows:

[0027] The relative humidity of the processing environment is 5~10%, the number of rolling passes is 2~5, the rolling process is 2H roughing followed by 4H finishing rolling, the single reduction of roughing is 1~10μm, the single reduction of finishing is 0.1~2μm, the roll winding speed is 1~30 cm / s, and the relative humidity of the rolling processing environment is 5~10%.

[0028] In a second aspect, the present invention provides a modified lithium-containing metal strip, which is prepared by the method described above.

[0029] A third aspect of the present invention provides the application of the modified lithium-containing metal strip as described above as a negative electrode material in lithium metal primary / secondary batteries.

[0030] The beneficial effects of this invention are:

[0031] (1) This invention provides a process for simultaneous surface planarization and artificial SEI coating of lithium-containing metal strips, modified lithium-containing metal strips, and the application of the modified lithium-containing metal strips as negative electrode materials in primary / secondary lithium metal batteries. Utilizing the various properties of common film-forming sacrificial agents, this invention proposes a method for simultaneously achieving surface planarization and artificial SEI modification of the lithium metal side of a lithium-containing metal strip in a single processing step. This method can improve the surface quality of the lithium metal in the lithium-containing metal strip raw material while forming a continuous, complete, uniform, and dense artificial SEI layer on the lithium metal surface in a short time. This process design avoids the problems of poor lithium metal surface quality, poor uniformity and integrity of the modification layer, and reduced yield and increased cost due to distributed processing in traditional lithium-containing metal strip preparation and modification processes. The process proposed in this invention enables large-scale preparation of flat lithium-containing metal strips with artificial SEI coating through simple procedures, resulting in high product quality and good consistency. Therefore, it is more suitable for the production of commercial battery electrode materials and helps improve the performance consistency of commercial battery cells.

[0032] (2) The process of the present invention adopts a lubricated cold rolling process in the processing of lithium metal strip. The processing stress is uniformly dispersed during the rolling process. Therefore, the lithium metal side of the lithium metal strip can be uniformly deformed, thereby improving the flatness of the metal surface, reducing defects and achieving uniform residual stress dispersion. In addition, the uniform processing stress can induce a uniform film formation reaction between the lithium metal surface and the film-forming sacrificial agent in a large area, thereby forming a continuous, uniform, complete and dense artificial SEI dominated by inorganic lithium salt with high ion conductivity and high strength on the lithium metal surface.

[0033] (3) The lithium-containing metal strip prepared by the process described in this invention, when used as a negative electrode in a lithium metal battery, can induce a relatively uniform lithium metal deposition / pull-out reaction due to its flat, defect-free lithium metal substrate with uniformly dispersed residual stress. Meanwhile, the high-intensity, continuous, complete, and uniform inorganic salt-dominated artificial SEI can improve the surface and interface stability of the negative electrode and promote a uniform lithium-ion mass transfer process, thereby improving the uniformity and stability of the interface reaction. Therefore, under the combined effect of various structural optimizations, the electrochemical stability of the lithium-containing metal strip can be effectively improved and the dendrite problem can be alleviated.

[0034] (3) Taking the bromine-rich SEI-coated lithium-copper composite strip material prepared based on the scheme of the present invention as an example, the half-cell of the lithium-copper composite strip electrode prepared based on the present invention can achieve a speed of 1 mA / cm² in an ester electrolyte system. 2A 2-hour charge-discharge time enables stable charge-discharge for over 350 hours while maintaining a dendrite-free, flat negative electrode surface. In stark contrast, half-cell samples based on ester electrolytes, assembled using existing dry rolling and heat treatment processes to form lithium-copper composite strips coated with artificial SEI, exhibit drastic voltage fluctuations during cycling in less than 200 hours, and show obvious dendrites or pulverization on the negative electrode surface after cycling. Subsequent full-cell tests revealed that the modified lithium-copper composite strip of this invention, paired with lithium iron phosphate (R-LiBr / Li-Cu||LFP), exhibited excellent coulombic efficiency (99.79±0.06%) and low capacity decay rate (2.52%) during over 200 charge-discharge cycles at 1C rate. In contrast, the control group (H-LiBr / Li-Cu||LFP) of the modified lithium-copper composite strip prepared by conventional formation processes showed lower coulombic efficiency and poor stability (99.61±0.76%) during 150 charge-discharge cycles, while exhibiting a higher capacity decay rate (7.61%). These two sets of comparative test results demonstrate the superior design of this invention, which achieves surface optimization and artificial SEI modification of the lithium metal side of the lithium metal strip in a single processing step. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the process for simultaneous surface planarization and artificial SEI coating of lithium-containing metal strips in Example 1;

[0036] Figure 2 Scanning electron microscope images and corresponding energy dispersive spectroscopy analysis of the lubricated cold-rolled lithium bromide artificial SEI-coated lithium-copper composite strip (labeled as R-LiBr / Li-Cu) prepared in Example 1;

[0037] Figure 3 Scanning electron microscope images and corresponding energy dispersive spectroscopy analysis of artificial SEI-coated lithium-copper composite bands (labeled H-LiBr / Li-Cu) formed by thermal treatment;

[0038] Figure 4 The repeated charge-discharge voltage curve of the R-LiBr / Li-Cu half-cell prepared in Example 2;

[0039] Figure 5 The repeated charge-discharge voltage curves of the H-LiBR / Li-Cu half-cell prepared in Example 2;

[0040] Figure 6 Scanning electron microscope (SEM) images of the surface morphology of the R-LiBr / Li-Cu (left) and H-LiBr / Li-Cu (right) electrodes after multiple charge-discharge cycles of the half-cell in Example 3;

[0041] Figure 7The capacity curves and coulombic efficiency curves of the R-LiBr / Li-Cu||LFP full cell experimental group and the H-LiBR / Li-Cu||LFP full cell control group in Example 4 are shown.

[0042] Figure 8 The polarization voltage curves are shown for the R-LiBr / Li-Cu||LFP full cell experimental group and the H-LiBR / Li-Cu||LFP full cell control group in Example 4.

[0043] Figure 9 The figures show the charge-discharge voltage curves for a specific number of cycles in the R-LiBr / Li-Cu||LFP full cell experimental group and the H-LiBR / Li-Cu||LFP full cell control group in Example 4. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0045] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0046] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. For examples where specific conditions are not specified, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments whose manufacturers are not specified, they are all commercially available products.

[0047] This invention provides a process for simultaneous surface planarization and artificial SEI coating of lithium-containing metal strips, comprising the following steps:

[0048] S1. A film-forming sacrificial agent is pre-coated onto the lithium metal surface containing the lithium metal strip to form a liquid film;

[0049] S2: Apply a flat and smooth metal roll to roll the lithium metal surface of the lithium metal strip, simultaneously achieving lithium metal surface smoothing and artificial SEI coating.

[0050] The film-forming sacrificial agent serves both as a rolling lubricant and as a sacrificial precursor required for artificial SEI formation, reacting with lithium metal to generate an artificial SEI film. Through the rolling stress and the lubricating effect of the film-forming sacrificial agent, the lithium metal surface is smoothed, its roughness is improved, and residual processing stress on the lithium metal surface is dispersed. The formation mechanism of the artificial SEI utilizes the intense instantaneous stress and thermal effect during the rolling process to activate a uniform, instantaneous reaction between the film-forming sacrificial agent and lithium atoms on the lithium metal surface over a large area, thereby forming a uniform, continuous, and complete artificial SEI with inorganic lithium salt as its main component on the lithium metal surface.

[0051] The selection criteria for the film-forming sacrificial agent are: appropriate polarity and viscosity; good wettability with lithium metal / lithium alloy; ability to form a stable extreme pressure lubricating layer with sufficient toughness and compressive strength on the lithium metal surface; ability to regulate the internal friction of lithium metal; and ability to react rapidly with lithium under applied stress to form an artificial SEI. In a preferred embodiment, the film-forming sacrificial agent is selected from at least one of the following substances: liquid haloalkanes and their derivatives, solutions of inorganic salts, and solutions of sulfurized small organic molecules.

[0052] In a preferred embodiment, the liquid haloalkane and its derivatives are one or more of halogenated alkanes, alkenes, benzene-based small organic molecules and their derivatives, such as 1,2-dibromoethane, trichloroethylene, hexafluorobenzene, and pentafluorobromobenzene. The inorganic salt is at least one of nitrates and phosphates (the metal ions referred to as nitrates and phosphates include, but are not limited to, silver, zinc, aluminum, tin, germanium, gallium, indium, niobium, antimony, bismuth, and molybdenum). The sulfide organic small molecules include organic small molecules and inorganic salts, wherein the organic small molecules include sulfides or thiobenzene-based small molecules and their derivatives such as DtbDS, DPDTe, DMDS, DMTS, AMDS, BTB, and ADS, and the inorganic salts include one or more sulfides or polysulfides of metals such as lithium, silver, zinc, aluminum, tin, germanium, gallium, indium, niobium, antimony, bismuth, and molybdenum.

[0053] In a preferred embodiment, the lithium-containing metal strip is selected from any one of pure lithium metal strip, binary or multi-element alloy strip of lithium and any other metal, lithium-copper composite strip, and lithium-carbon composite strip.

[0054] In a preferred embodiment, metallic lithium or lithium alloy is distributed on at least one side of the metal strip, and the thickness of the lithium-containing metal strip is 1~100μm, and the lithium content is 1~100%.

[0055] In a preferred embodiment, the lithium-containing metal strip is the lithium-copper composite strip most commonly used in the industry, with a thickness of 50~90μm, of which the copper foil thickness is 5~10μm.

[0056] In a preferred embodiment, the coating method in step S1 is a combination of spraying and scraping, the film-forming sacrificial agent is a small molecule liquid of halogenated hydrocarbons, and the thickness of the formed liquid film is 10~100μm.

[0057] In a preferred embodiment, the rolling process conditions in step S2 are as follows: the processing stress is 1~100 MPa, the single rolling reduction is 0.01~1 mm, the roll linear speed is 0.1~100 cm / s, the processing is a combination of roughing and finishing rolling, and the number of rolling passes is 2~10.

[0058] In a preferred embodiment, the simultaneous process of surface planarization and artificial SEI coating of the lithium-containing metal strip includes the following steps:

[0059] S1. 1,2-Dibromoethane is pre-coated on the lithium metal surface of the lithium-copper composite strip as a film-forming sacrificial agent to form a liquid film;

[0060] S2: The lithium metal surface of the lithium metal strip is rolled using smooth metal rolls to simultaneously achieve surface smoothing and artificial SEI coating. The rolling process conditions are as follows:

[0061] The relative humidity of the processing environment is 5~10%, the number of rolling passes is 2~5, the rolling process is 2H roughing followed by 4H finishing rolling, the single reduction of roughing is 1~10μm, the single reduction of finishing is 0.1~2μm, the roll winding speed is 1~30 cm / s, and the relative humidity of the rolling processing environment is 5~10%.

[0062] The present invention also provides a modified lithium-containing metal strip, which is prepared by the method described above.

[0063] The present invention also provides an application of the modified lithium-containing metal strip as described above as a negative electrode material in lithium metal primary / secondary batteries.

[0064] This invention primarily utilizes the following advantages of polar artificial SEI film-forming sacrificial agents: they can both wet and spread on the lithium metal surface to form a continuous liquid film layer with a certain strength, thereby lubricating the rolling process, and react with the reactive lithium metal under external energy to generate artificial SEI. Thus, when a specific sacrificial agent is pre-coated onto the lithium metal side of a lithium-containing metal strip, the sacrificial agent can wet the rough lithium metal surface, forming a continuous extreme pressure film. Subsequently, during the rolling thinning and leveling process of the lithium-containing metal strip, the leveled metal rolls directly contact the lithium metal side coated with the sacrificial agent and undergo roll pressing. This triggers instantaneous high deformation stress, deformation energy, and thermal effects at the contact point between the rolls and the lithium metal. On the one hand, this induces a rapid and uniform artificial SEI film-forming reaction between the film-forming sacrificial agent and the lithium metal; on the other hand, the processing stress and the lubricating effect of the sacrificial agent further level the lithium metal surface and form a uniform processing stress distribution. Finally, it can also compact the artificial SEI structure, reducing internal structural defects and enhancing the interfacial bonding between the artificial SEI and the lithium metal.

[0065] Through the above steps and special film-forming reaction behavior, a lithium metal side with high flatness, uniform residual stress distribution, and few defects can be achieved. A dense, continuous, complete, uniform, and reliably bonded high-performance artificial SEI is formed on the lithium metal surface. Since the film-forming reaction and rolling processing are carried out simultaneously, surface optimization and artificial SEI modification of the lithium metal side of the lithium metal strip can be achieved in a single process. This not only yields high-performance modified composite strip materials but also effectively improves yield, reduces production costs, and lowers the requirements for processing energy consumption and special production environments.

[0066] The above is the general concept of the present invention. Based on this, detailed embodiments and comparative examples are provided below to further illustrate the present invention.

[0067] Example 1

[0068] A method for simultaneously smoothing the lithium metal surface and coating a lithium-copper composite strip with a bromine-rich artificial SEI includes the following specific steps:

[0069] Using an 80μm thick lithium-copper composite strip as raw material (lithium metal thickness of 70μm), in an environment with a relative humidity of 5%, 1,2-dibromoethane was sprayed onto the lithium metal surface using a blade coating method to form a liquid film with a thickness of 50-1000μm as a sacrificial agent for artificial SEI film formation. The lithium-copper composite strip was then rough-rolled in one pass using smooth 2H stainless steel rolls with an absolute reduction of 8μm. Subsequently, the dibromoethane liquid film was recoated (coating thickness of 50-1000μm), and then finish-rolled in one pass using 4H stainless steel rolls with an absolute reduction of 1μm. This yielded a lithium-copper composite strip with a smooth surface and coated with a bromine-rich artificial SEI, named R-LiBr / Li-Cu. Figure 1 Scanning electron microscopy analysis revealed a smooth lithium metal surface, and energy dispersive spectroscopy further confirmed the continuous and uniform distribution of abundant bromine on the lithium metal surface, demonstrating that the method employed in this invention can effectively optimize the surface quality of the lithium-copper composite band. Figure 2 ).

[0070] As a control, in an environment with 5% humidity, polyethylene was used as a release film to coat the lithium metal surface of the lithium-copper composite strip. An 80μm thick lithium-copper composite strip (70μm lithium metal thickness) was subjected to unlubricated cold rolling using the same rolling process. After rolling, the lithium-copper composite strip was coated with a 200μm thick dibromoethane liquid film using a spray-and-scrape coating method as a film-forming sacrificial agent. Under argon atmosphere protection, it was heat-treated at 45℃ for 24h to achieve artificial SEI film formation, obtaining the control group H-LiBr / Li-Cu lithium-copper composite strip with bromine-rich artificial SEI coating formed by heat treatment. Scanning electron microscopy revealed obvious microcracks in the heat-treated film, proving that the heat treatment process is difficult to achieve continuous artificial SEI coating. Subsequent energy dispersive spectroscopy characterization showed that the bromine distribution on the H-LiBr / Li-Cu surface was uneven, proving that the traditional formation process is difficult to achieve continuous and uniform SEI. Figure 3 ).

[0071] Example 2

[0072] The R-LiBr / Li-Cu and H-LiBr / Li-Cu prepared in Example 1 were respectively stamped and cut into 16 mm diameter discs, and then matched with 80 μL of 1M LiPF6 / EC+DEC ester electrolyte. Symmetric half-cells were assembled using a Celgard 2400PP membrane and CR2032. Subsequently, the experimental group R-LiBr / Li-Cu was subjected to an A / cm² flow rate of 1 mA. 2 Repeated charge-discharge tests were conducted on the H-LiBr / Li-Cu control group using a charge-discharge current density and a charge-discharge time of 2 hours, while the control group used a charge-discharge current density of 1 mA / cm². 2 Repeated charge-discharge tests were conducted using the specified charge-discharge current density and a charge-discharge time of 1 hour. After multiple cycles, the experimental group of R-LiBr / Li-Cu half-cells maintained a flat voltage curve. Figure 4 ), while the control group H-LiBr / Li-Cu could not achieve stable charge-discharge cycles ( Figure 5 ).

[0073] Example 3

[0074] To investigate the reasons for the differences in cycle performance of bromine-rich SEI-coated lithium-copper anodes prepared by different processes, R-LiBr / Li-Cu and H-LiBr / Li-Cu electrode samples from two sets of batteries in Example 2 were taken and their surface morphology was observed using scanning electron microscopy. The surface morphology showed that the R-LiBr / Li-Cu electrode maintained a relatively smooth morphology in the ester electrolyte system, while the H-LiBr / Li-Cu electrode surface was severely cracked and pulverized. This demonstrates the effectiveness of the simultaneous lithium metal surface smoothing and artificial SEI coating scheme of the present invention in optimizing the lithium metal surface quality and artificial SEI. Figure 6 ).

[0075] Example 4

[0076] To further verify the electrochemical performance of the lithium-copper composite belt prepared by the scheme designed in this invention, R-LiBr / Li-Cu and H-LiBr / Li-Cu were used as negative electrode materials, respectively, and commercial lithium iron phosphate (LFP, with an active material surface loading of ~19 mg / cm³) was used. 2 Using 1M LiPF6 / EC+DEC as the positive electrode material and 80 μL of 1M LiPF6 / EC+DEC as the electrolyte, a full cell was assembled using a Celgard 2400PP film and CR2032. After 200 cycles, R-LiBr / Li-Cu||LFP exhibited good coulombic efficiency (99.79±0.06%) and low capacity decay rate (2.52%), with a stable polarization voltage between 80 and 110 mV; while H-LiBr / Li-Cu||LFP showed lower coulombic efficiency and poor stability (99.61±0.76%) and a higher capacity decay rate (7.61%) during 150 charge-discharge cycles, and its polarization voltage rapidly increased from 80 mV to 150 mV with increasing cycle count. Figure 7-9 ).

[0077] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A process for simultaneous surface planarization and artificial SEI coating of lithium-containing metal strips, characterized in that, Includes the following steps: S1. A film-forming sacrificial agent is pre-coated onto the lithium metal surface of a lithium metal strip to form a liquid film; the film-forming sacrificial agent is a liquid halohydrocarbon or its derivative. S2: The lithium metal surface of the lithium-containing metal strip is rolled using smooth metal rolls to simultaneously achieve surface smoothing and artificial SEI coating; the rolling process conditions are as follows: The rolling passes are 2 to 5, the rolling process is roughing followed by finishing, the single reduction in roughing is 1 to 10 μm, the single reduction in finishing is 0.1 to 2 μm, the coiling speed is 1 to 30 cm / s, and the relative humidity of the rolling environment is 5 to 10%. The film-forming sacrificial agent serves both as a rolling lubricant and as a sacrificial precursor required for the formation of artificial SEI, reacting with lithium metal to generate artificial SEI.

2. The simultaneous surface smoothing and artificial SEI coating process for lithium-containing metal strips according to claim 1, characterized in that, in, Liquid haloalkanes and their derivatives are selected from one or more of 1,2-dibromoethane, trichloroethylene, hexafluorobenzene, pentafluorobromobenzene haloalkanes, alkenes, benzene-based small organic molecules and their derivatives.

3. The simultaneous surface smoothing and artificial SEI coating process for lithium-containing metal strips according to claim 1, characterized in that, The lithium-containing metal strip is selected from any one of the following: pure lithium metal strip, binary or multi-element alloy strip of lithium and any other metal, lithium-copper composite strip, and lithium-carbon composite strip.

4. The simultaneous surface smoothing and artificial SEI coating process for lithium-containing metal strips according to claim 3, characterized in that, Lithium metal or lithium alloy is distributed on at least one side of the metal strip, the thickness of the lithium-containing metal strip is 1~100μm, and the lithium content is 1~100%.

5. The simultaneous surface smoothing and artificial SEI coating process for lithium-containing metal strips according to claim 1, characterized in that, The thickness of the liquid film formed in step S1 is 10~100μm.

6. A modified lithium-containing metal strip, characterized in that, It is prepared by the process described in any one of claims 1-5.

7. The application of the modified lithium-containing metal strip as described in claim 6 as a negative electrode material in lithium metal primary / secondary batteries.

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