Composite modification layer for negative electrode current collector and preparation method and application of composite modification layer

Abstract

The invention relates to the technical field of negative-electrode-free lithium batteries, in particular to a composite modification layer for a negative electrode current collector and a preparation method and application of the composite modification layer. The composite modification layer for the negative electrode current collector is prepared by the following steps: carrying out pre-lithiation treatment on montmorillonite by utilizing lithium salt and oxalic acid to obtain a first solution; performing pre-lithiation treatment on polystyrolsulfon acid by using lithium hydroxide, and mixing with an alcohol solvent to obtain a second solution; uniformly mixing the first solution and the second solution to obtain a mixed solution; and performing planar two-dimensional spraying on the surface of the negative electrode substrate by using the mixed solution, and after drying, forming a composite modification layer on the surface of the negative electrode substrate. The preparation method solves the problems that solvent molecules of a traditional modification layer are gathered due to polar groups, the desolvation process is hindered, SEI rich in organic matter is formed, and transmission of lithium ions on the surface of the modification layer is hindered.

Description

Technical Field

[0001] This invention relates to the field of negative electrode-free lithium battery technology, specifically to a composite modification layer for negative electrode current collectors, its preparation method, and its application. Background Technology

[0002] With the development of modern energy storage systems, the demand for batteries that combine high energy density and long lifespan has increased significantly. Electrodeless lithium metal batteries have attracted considerable research attention due to their higher energy density, lower cost, and simpler manufacturing process.

[0003] To fully utilize the limited lithium resources in batteries, solvent molecules in the electrolyte typically employ a polar structure to promote the dissolution and dissociation of lithium salts. However, polar solvent molecules readily form strong coordination with lithium ions, leading to a solvent-dominated solvation structure. This increases the desolvation energy barrier, slowing down the lithium-ion desolvation process at the negative electrode. Simultaneously, solvent molecules surrounding lithium ions are reduced at the negative electrode to organic components with low ionic conductivity, ultimately forming a solid electrolyte interface rich in organic matter, exhibiting a high ion diffusion energy barrier. Therefore, negative electrodeless lithium metal batteries exhibit shorter cycle life due to the slow lithium-ion kinetics at the interface. The English name for the solid electrolyte interface is Solid Electrolyte Interface, abbreviated as SEI.

[0004] Currently, traditional modification layers attract lithium ions to the negative electrode through polar groups, effectively accelerating the separation of lithium ions from solvent molecules. However, due to the presence of polar groups, these modification layers often exhibit polarity and a certain affinity for solvent molecules. Therefore, the separated solvent molecules tend to aggregate near the modification layer, leading to an increase in solvent molecules around the lithium ions and hindering the continuous desolvation process. Simultaneously, these solvent molecules may still penetrate into the modification layer, eventually forming an organic-rich SEI, which impedes the rapid transport of lithium ions on the surface of the modification layer. Furthermore, simply reducing the solvent's affinity for the modification layer will prevent the electrolyte from quickly wetting the modification layer, thus affecting the rapid diffusion of lithium ions on the surface of the modification layer. Summary of the Invention

[0005] To address the problems of traditional modified layers where polar groups cause solvent molecules to aggregate, hindering the desolvation process, and where organic-rich SEIs form, hindering lithium ion transport on the modified layer surface, this invention provides a composite modified layer for negative electrode current collectors, its preparation method, and its application.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] The first aspect of this invention provides a method for preparing a composite modification layer for a negative electrode current collector, comprising the following steps: Using montmorillonite and polystyrene sulfonic acid as the main materials, and lithium hydroxide, lithium salt, and oxalic acid as lithiation materials, the montmorillonite is pre-lithiated with lithium salt and oxalic acid to obtain a first solution; the polystyrene sulfonic acid is pre-lithiated with lithium hydroxide and mixed with an alcohol solvent to obtain a second solution; the first and second solutions are mixed evenly to obtain a mixed solution; the mixed solution is used to perform planar two-dimensional spraying on the surface of the negative electrode substrate, and after drying, a composite modification layer is formed on the surface of the negative electrode substrate to obtain a composite modification layer for use as a negative electrode current collector.

[0008] Preferably, the lithium salt is lithium carbonate; and the alcohol solvent is ethanol.

[0009] The purpose of adding an alcohol solvent after pre-lithiation of polystyrene sulfonic acid in this invention is to reduce the surface tension of the solution in the syringe during electrospraying, so that the solution can be sprayed out more easily and evenly. Otherwise, if there is only water, the solution will be difficult to spray out during electrospraying due to surface tension.

[0010] In this invention, lithium carbonate serves to provide lithium ions for cation exchange with montmorillonite, thereby lithiating the montmorillonite.

[0011] This invention uses montmorillonite and polystyrene sulfonic acid as the main materials, and lithium carbonate and oxalic acid as lithiation materials. The montmorillonite is pre-lithiated with lithium carbonate and oxalic acid; the polystyrene sulfonic acid is pre-lithiated with lithium hydroxide; and a composite modification layer is formed on the surface of the negative electrode substrate using a planar two-dimensional spraying method. The purpose of pre-lithiating montmorillonite and polystyrene sulfonic acid is to replenish the modification layer with appropriate lithium ions, thereby reducing lithium consumption during battery cycling and extending battery life.

[0012] Among them, lithium carbonate and oxalic acid are used as lithium lithiation materials for pre-lithiation treatment of montmorillonite, while lithium hydroxide is used for pre-lithiation treatment of polystyrene sulfonic acid. This is mainly because montmorillonite and polystyrene sulfonic acid have different reactivity with different lithium lithiation materials, so it is necessary to select appropriate lithium lithiation materials for pre-lithiation treatment.

[0013] This invention prepares a composite modification layer at the negative electrode of a negative electrodeless lithium metal battery by selecting appropriate materials. This can appropriately reduce the aggregation of solvent molecules and adsorb lithium ions without affecting the wettability of the electrolyte, ultimately achieving rapid desolvation and lithium ion transport, thereby improving battery performance.

[0014] Preferably, the mass ratio of montmorillonite to polystyrene sulfonic acid is 1:0.5 to 1.5; the molecular weight of polystyrene sulfonic acid is 70,000 Mw. Preferably, the mass ratio of montmorillonite to polystyrene sulfonic acid is 1:1.

[0015] This invention, through the selection of main material ratios and the control of lithiation and spraying conditions, enables the preparation of a composite modification layer for negative electrode current collectors, which can improve lithium-ion kinetics, promote desolvation and accelerate lithium-ion transport, resulting in high ionic conductivity SEI, and further optimizes the interfacial mass transfer kinetics of the negative electrode, exhibiting excellent coulombic efficiency and long cycle life. It can provide valuable reference for the research and development of other advanced negative electrode modification layers.

[0016] Preferably, the mass ratio of montmorillonite to lithium salt is 0.25–0.5:0.015; the mass ratio of lithium salt to oxalic acid is 0.8–0.85:1. More preferably, the mass ratio of lithium salt to oxalic acid is 0.82:1.

[0017] Preferably, the reaction conditions for pre-lithiation treatment of montmorillonite using lithium salt and oxalic acid are: pH=8~9, temperature 75℃~85℃, and time 4h.

[0018] Preferably, the specific operation of pre-lithiation treatment of montmorillonite using lithium salt and oxalic acid is as follows: Montoverite, lithium salt and water were mixed and the pH was adjusted to 8-9 with oxalic acid. The mixture was then stirred and reacted at 75-85℃ for 4 hours.

[0019] In this invention, montmorillonite disperses into tiny particles in water, forming a suspension. Under a weakly alkaline environment, the Li in the lithium salt... + It will undergo ion exchange reactions with cations between montmorillonite layers, causing Li + It enters the interlayer structure of montmorillonite, thereby promoting the uniform distribution of lithium ions between the montmorillonite layers.

[0020] Preferably, the mass ratio of lithium hydroxide to polystyrene sulfonic acid is 0.13:1 to 2. More preferably, the mass ratio of lithium hydroxide to polystyrene sulfonic acid is 0.13:1.

[0021] Preferably, the specific steps for pre-lithiation treatment of polystyrene sulfonic acid using lithium hydroxide are as follows: Pre-lithiation treatment is performed by mixing polystyrene sulfonic acid, lithium hydroxide, and water.

[0022] In this invention, polystyrene sulfonic acid is a water-soluble polymer with a molecular weight of 70,000 Mw. After being uniformly dispersed in water, polystyrene sulfonic acid undergoes a pre-lithiation reaction with lithium hydroxide, causing Li... + Grafting onto polystyrene sulfonic acid forms a pre-lithiated substance, PSS-Li. Adding ethanol to the system helps reduce the surface tension of the solution in the syringe during electrospraying, thus allowing the solution to be sprayed more evenly.

[0023] Preferably, the negative electrode substrate is copper foil, nickel foil, or zinc foil.

[0024] Preferably, the planar two-dimensional spraying is performed using electro-spraying. The present invention mainly involves injecting the mixture into the needle of the electro-spraying device, placing the negative electrode substrate on a substrate platform, and performing planar two-dimensional spraying on the negative electrode substrate.

[0025] Preferably, the voltage for planar two-dimensional spraying is 5.0kV to 5.3kV.

[0026] Preferably, the drying temperature is 60℃~65℃ and the time is 12h.

[0027] A second aspect of the present invention provides a composite modification layer for a negative electrode current collector, which is prepared by the method described above for preparing a composite modification layer for a negative electrode current collector.

[0028] A third aspect of the present invention provides the application of a composite modification layer for a negative electrode current collector in the preparation of a negative electrode-free lithium metal battery.

[0029] In the negative electrode-free lithium metal battery of the present invention, the negative electrode uses commercially available copper foil. By selecting appropriate materials to prepare a composite modification layer at the negative electrode of the negative electrode-free lithium metal battery, the aggregation of solvent molecules can be appropriately reduced and lithium ions can be adsorbed without affecting the wettability of the electrolyte. Ultimately, rapid desolvation and lithium ion transport are achieved, thereby improving battery performance.

[0030] Preferably, the negative electrode-free lithium metal battery is a lithium symmetric battery, a half-cell, or a full-cell.

[0031] The beneficial effects of this invention are: 1. This invention uses montmorillonite and polystyrene sulfonic acid as the main materials, pre-lithiating both materials and then forming a composite modification layer on the surface of the negative electrode substrate using a planar two-dimensional spraying method. By selecting suitable materials to prepare the composite modification layer at the negative electrode of a cathode-less lithium metal battery, this invention can appropriately reduce the aggregation of solvent molecules and adsorb lithium ions without affecting the wettability of the electrolyte, ultimately achieving rapid desolvation and lithium-ion transport, thereby improving battery performance and overcoming the current problem of slow lithium-ion desolvation and transport at the negative electrode of cathode-less lithium metal batteries.

[0032] 2. The composite modification layer of the present invention can attract lithium ions while repelling solvent molecules, achieving rapid and continuous desolvation. Low migration energy barrier lithium ion channels are formed between molecules inside the modification layer, accelerating lithium ion transport. The attraction of anions by the modification layer can also allow more anions to reach the negative electrode, forming a SEI with high ionic conductivity, further accelerating lithium ion kinetics.

[0033] 3. The composite modification layer of this invention is ultra-thin and uniform, with a thickness of 35 nm, and the main body is uniform and flat. The negative electrode with the composite modification layer has a lower solvation energy barrier, and the activation energy required for desolvation of the modified battery is reduced.

[0034] 4. This invention effectively improves the cycle life of anode-free lithium metal batteries. The anode with a composite modification layer enables rapid desolvation and transport of lithium ions, forming a high-ionic-conductivity SEI, with the ionic conductivity increased to 8.2 × 10⁻⁶. -5 S·cm -1 It has good application potential.

[0035] 5. The composite modification layer of the present invention improves the operational stability of the battery and enhances the coulombic efficiency and cycle life of the modified battery. Attached Figure Description

[0036] Figure 1 These are physical images of the mixed solution injected into the electrospray device in Example 1 and the composite modification layer sprayed to form a negative electrode current collector. Among them, (a) is a physical image of the mixed solution injected into the electrospray device in Example 1 of the present invention; (b) is a physical image of the composite modification layer sprayed to form a negative electrode current collector in Example 1 of the present invention.

[0037] Figure 2 These are surface microstructure images of the composite modified layer for the negative electrode current collector prepared in Example 1 and the unmodified copper foil. Specifically, a is the surface microstructure image of the composite modified layer for the negative electrode current collector prepared in Example 1; b is the surface microstructure image of the unmodified copper foil.

[0038] Figure 3 The curves show the comparison of the activation energy of desolvation after fitting the impedance values ​​of the symmetric lithium battery with the unmodified CuLi||CuLi system and the MS-CuLi||MS-CuLi system modified with the composite modification layer for the negative electrode current collector in Example 1 at different temperatures.

[0039] Figure 4 The intrinsic impedance and corresponding ionic conductivity are obtained from tests of batteries composed of sheets of the same size and thickness made of a single main material sandwiched between two identical stainless steel sheets in Comparative Examples 1 and 2, and batteries composed of sheets of the same size and thickness made of two different main materials sandwiched between two identical stainless steel sheets in Example 1.

[0040] Figure 5 The data are cycle data of the negative electrode and lithium sheet before and after the composite modification layer for the negative electrode current collector in Example 1 is modified, and then formed into a negative electrode-free lithium half cell.

[0041] Figure 6This is a comparison chart of the long-cycle performance of the negative electrode and the lithium iron phosphate positive electrode assembled in Example 1 before and after the modification of the composite modification layer for the negative electrode current collector. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0043] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] The technical solution of the present invention will be further described below through specific embodiments.

[0045] In the following embodiments, unless otherwise specified, the methods described are conventional methods; and unless otherwise specified, the reagents and materials described are commercially available.

[0046] The full English name for Montmorillonite is Montmorillonite, abbreviated as MMT.

[0047] The full English name of polystyrene sulfonic acid is Polystyrene sulfonic acid, abbreviated as PSS.

[0048] In the following embodiments, montmorillonite and polystyrene sulfonic acid are used as the main materials, and lithium hydroxide, oxalic acid and lithium carbonate are used as lithiation materials.

[0049] Example 1 A method for preparing a composite modification layer for a negative electrode current collector includes the following steps: Step 1: Add 0.25g of MMT and 0.015g of lithium carbonate to 5mL of deionized water, adjust the pH to 7-8 with 0.0183g of oxalic acid, and then stir at 2900r / min at 80℃ for 4h to obtain the first solution.

[0050] Step 2: Add 0.05g of PSS and 0.0065g of LiOH to 5mL of deionized water for pre-lithiation, then add 1mL of ethanol and stir for 5min to obtain the second solution.

[0051] Step 3: Measure 1 mL of the first solution and add it to the container containing the second solution. Stir the mixture ultrasonically for 10 min to obtain a mixed solution. The mass ratio of MMT to PSS in the mixed solution is 1:1.

[0052] Step 4: Inject the mixed solution into the syringe of the electrospray device, place the copper foil on the substrate stage, and perform planar two-dimensional spraying at a voltage of 5.2kV. After spraying, vacuum dry at 60°C for 12 hours to form a composite modification layer for the negative electrode current collector on the surface of the copper foil.

[0053] Example 2 A method for preparing a composite modification layer for a negative electrode current collector differs from Example 1 in that, in step 1, the amount of MMT added is 0.5 g. The specific preparation method includes the following steps:

[0054] Step 1: Add 0.5g of MMT and 0.015g of lithium carbonate to 5mL of deionized water, adjust the pH to 7-8 with 0.0183g of oxalic acid, and then stir at 2900r / min at 80℃ for 4h to obtain the first solution.

[0055] Step 2: Add 0.05g of PSS and 0.0065g of LiOH to 5mL of deionized water for pre-lithiation, then add 1mL of ethanol and stir for 5min to obtain the second solution.

[0056] Step 3: Measure 1 mL of the first solution and add it to the container containing the second solution. Stir the mixture ultrasonically for 10 min to obtain a mixed solution. The mass ratio of MMT to PSS in the mixed solution is 2:1.

[0057] Step 4: Inject the mixed solution into the syringe of the electrospray device, place the copper foil on the substrate stage, and perform planar two-dimensional spraying at a voltage of 5.2kV. After spraying, vacuum dry at 60°C for 12 hours to form a composite modification layer for the negative electrode current collector on the surface of the copper foil.

[0058] Example 3 A method for preparing a composite modification layer for a negative electrode current collector differs from Example 1 in that, in step 2, the amount of PSS added is 0.1 g. The specific preparation method includes the following steps:

[0059] Step 1: Add 0.25g of MMT and 0.015g of lithium carbonate to 5mL of deionized water, adjust the pH to 7-8 with 0.0183g of oxalic acid, and then stir at 2900r / min at 80℃ for 4h to obtain the first solution.

[0060] Step 2: Add 0.1g of PSS and 0.0065g of LiOH to 5mL of deionized water for pre-lithiation, then add 1mL of ethanol and stir for 5min to obtain the second solution.

[0061] Step 3: Measure 1 mL of the first solution and add it to the container containing the second solution. Stir the mixture ultrasonically for 10 min to obtain a mixed solution. The mass ratio of MMT to PSS in the mixed solution is 1:2.

[0062] Step 4: Inject the mixed solution into the syringe of the electrospray device, place the copper foil on the substrate stage, and perform planar two-dimensional spraying at a voltage of 5.2kV. After spraying, vacuum dry at 60°C for 12 hours to form a composite modification layer for the negative electrode current collector on the surface of the copper foil.

[0063] Comparative Example 1 A method for preparing a composite modification layer for a negative electrode current collector, differing from Example 1 in that MMT is not added in step 1. The specific preparation method includes the following steps:

[0064] Step 1: Add 0.015g of lithium carbonate to 5mL of deionized water, adjust the pH to 7-8 with 0.0183g of oxalic acid, and then stir at 2900r / min for 4h at 80℃ to obtain the first solution.

[0065] Step 2: Add 0.05g of PSS and 0.0065g of LiOH to 5mL of deionized water for pre-lithiation, then add 1mL of ethanol and stir for 5min to obtain the second solution.

[0066] Step 3: Measure 1 mL of the first solution and add it to the container containing the second solution. Stir the mixture ultrasonically for 10 min to obtain a mixed solution. The mass ratio of MMT to PSS in the mixed solution is 1:1.

[0067] Step 4: Inject the mixed solution into the syringe of the electrospray device, place the copper foil on the substrate stage, and perform planar two-dimensional spraying at a voltage of 5.2kV. After spraying, vacuum dry at 60°C for 12 hours to form a composite modification layer for the negative electrode current collector on the surface of the copper foil.

[0068] Comparative Example 2 A method for preparing a composite modification layer for a negative electrode current collector, differing from Example 1 in that PSS is not added in step 2. The specific preparation method includes the following steps:

[0069] Step 1: Add 0.25g of MMT and 0.015g of lithium carbonate to 5mL of deionized water, adjust the pH to 7-8 with 0.0183g of oxalic acid, and then stir at 2900r / min at 80℃ for 4h to obtain the first solution.

[0070] Step 2: Add 0.0065g of LiOH to 5mL of deionized water for pre-lithiation, then add 1mL of ethanol and stir for 5min to obtain the second solution.

[0071] Step 3: Measure 1 mL of the first solution and add it to the container containing the second solution. Stir the mixture ultrasonically for 10 min to obtain a mixed solution. The mass ratio of MMT to PSS in the mixed solution is 1:1.

[0072] Step 4: Inject the mixed solution into the syringe of the electrospray device, place the copper foil on the substrate stage, and perform planar two-dimensional spraying at a voltage of 5.2kV. After spraying, vacuum dry at 60°C for 12 hours to form a composite modification layer for the negative electrode current collector on the surface of the copper foil.

[0073] Table 1 Comparison of conditions in Examples 1 to 3 Note: "-" indicates that it was not added or is not present.

[0074] Test 1: Surface micromorphology analysis of the composite modification layer used for negative electrode current collector.

[0075] Figure 1 These are physical images of the mixed solution injected into the electrospray device in Example 1 and the composite modification layer sprayed to form a negative electrode current collector. Among them, (a) is a physical image of the mixed solution injected into the electrospray device in Example 1 of the present invention; (b) is a physical image of the composite modification layer sprayed to form a negative electrode current collector in Example 1 of the present invention.

[0076] Depend on Figure 1 As can be seen, the composite modification layer for the negative electrode current collector in Embodiment 1 of the present invention is ultra-thin and uniform, with a thickness of 35 nm, and the main body is uniform and flat.

[0077] Figure 2 These are surface microstructure images of the composite modified layer for the negative electrode current collector prepared in Example 1 and the unmodified copper foil. Specifically, a is the surface microstructure image of the composite modified layer for the negative electrode current collector prepared in Example 1; b is the surface microstructure image of the unmodified copper foil.

[0078] Depend on Figure 2 As can be seen, the microstructure of the composite modified layer for negative electrode current collector prepared in Example 1 is very uniform compared with the unmodified copper foil.

[0079] Test 2: Battery performance analysis.

[0080] In Examples 1 to 3, a copper-based current collector with a composite modification layer for the negative electrode current collector was obtained after forming a composite modification layer for the negative electrode current collector on the surface of the copper foil. This current collector was denoted as MS-Cu. The copper-based current collector with the composite modification layer for the negative electrode current collector and the positive electrode were assembled into a negative electrode-free lithium battery.

[0081] The preparation methods of different systems of negative electrode-free lithium batteries are explained in detail below.

[0082] For the CuLi||CuLi system: two identical copper foils without special modification are used as two electrodes to form a negative electrode-free lithium symmetric battery in an electrolyte containing lithium salt.

[0083] For the MS-CuLi||MS-CuLi system: two identical copper foils modified with the composite modification layer for negative electrode current collector as described in Example 1 are used as two electrodes to construct a negative electrode-free lithium symmetric battery in an electrolyte containing lithium salt.

[0084] For the Li||Cu system: a half-cell is formed by using copper foil as the positive electrode current collector and lithium foil as the negative electrode current collector.

[0085] For the Li||MS-Cu system: a half cell is formed by using copper foil modified with the composite modification layer of Example 1 as the positive electrode current collector and lithium sheet as the negative electrode current collector.

[0086] For the Cu||LFP system: copper foil is used as the negative electrode current collector, and it is assembled with lithium iron phosphate as the positive electrode to form a negative electrode-free lithium full cell.

[0087] For the MS-Cu||LFP system: the copper foil modified with the composite modification layer of Example 1 for the negative electrode current collector is used as the negative electrode current collector, and it is assembled with the lithium iron phosphate positive electrode to form a negative electrode-free lithium full cell.

[0088] Lithium iron phosphate (LFP) is short for Lithium Iron Phosphate. Super P indicates Super P type conductive carbon black. Polyvinylidene fluoride (PVDF) is short for Polyvinylidene Fluoride.

[0089] The method for preparing lithium iron phosphate cathode is to mix LFP, super P and PVDF in N-methyl-2-pyrrolidone at a weight ratio of 8:1:1, then coat the resulting slurry onto aluminum foil and dry it in a vacuum environment at a temperature of 9°C.

[0090] Figure 3 The curves show the comparison of the activation energy of desolvation after fitting the impedance values ​​of the symmetric lithium battery with the unmodified CuLi||CuLi system and the MS-CuLi||MS-CuLi system modified with the composite modification layer for the negative electrode current collector in Example 1 at different temperatures.

[0091] activation energy E a The calculation is based on the Arrhenius equation: ,in, E aIndicates activation energy. T Where is the absolute temperature, and R is the gas constant. R ct Interface Li + Transfer resistance, A For the pre-exponential factor. The conversion formula uses ln( T / R ct )and R ct By fitting a straight line to the coordinates, we can calculate... E a .

[0092] MS-CuLi impedance test results at different temperatures R ct The values ​​and their corresponding calculated values ​​are shown in Table 2. The Rct values ​​and their corresponding calculated values ​​for the Cu-Li||Cu-Li impedance tests at different temperatures are shown in Table 3.

[0093] Table 2. Corresponding impedance measurements of MS-CuLi||MS-CuLi R ct Values ​​and their corresponding calculated values ​​using formulas Table 3. R corresponding to the impedance test results of Cu Li||Cu Li ct Values ​​and their corresponding calculated values ​​using formulas from Figure 3 As can be seen from Tables 2 and 3, compared with the unmodified CuLi||CuLi system, the desolvation activation energy of the MS-CuLi||MS-CuLi system modified with the composite modification layer for the negative electrode current collector in Example 1 is reduced, indicating that the desolvation process is accelerated.

[0094] Figure 4 The intrinsic impedance and corresponding ionic conductivity are obtained from tests of batteries composed of sheets of the same size and thickness made of a single main material sandwiched between two identical stainless steel sheets in Comparative Examples 1 and 2, and batteries composed of sheets of the same size and thickness made of two different main materials sandwiched between two identical stainless steel sheets in Example 1.

[0095] In the impedance test, all the batteries were composed of a sheet material of the same thickness sandwiched between two stainless-steel sheets. The sheet materials were the sheet-like objects of the same size and thickness made of a single main material for Comparative Example 1 and Comparative Example 2, and the sheet-like objects of the same size and thickness made of two main materials for Example 1. The sheet materials were wetted with the same electrolyte, which was the commercial electrolyte LS-042. Specifically, 1 M LiTFSI was dissolved in a DOL / DME mixture with a volume ratio of 1:1, and 5 wt% LiNO3 was added as an additive. The electrolytes used in Test 2 were all commercial electrolyte LS-042.

[0096] The full English name of LiTFSI is Lithium bis(trifluoromethanesulfonyl)imide, and the Chinese name is lithium bis(trifluoromethanesulfonyl)imide; the full English name of DOL is 1,3-Dioxolane, and the Chinese name is 1,3-dioxolane; the full English name of DME is 1,2-Dimethoxyethane, and the Chinese name is 1,2-dimethoxyethane.

[0097] Among them, -Z" represents the intrinsic impedance value, with the unit ohm. The Chinese name of ohm is ohm.

[0098] Table 4 Performance comparison of lithium-free symmetric lithium batteries with different main materials Note: MS represents two main materials, MMT and PSS.

[0099] From Figure 4 and the data in Table 4, it can be seen that compared with the lithium-free symmetric lithium batteries modified with a composite modification layer using a single main material for Comparative Example 1 and Comparative Example 2 for the negative electrode current collector, the lithium-free symmetric lithium batteries modified with a composite modification layer using two main materials for Example 1 for the negative electrode current collector have significantly improved ionic conductivity, reaching as high as 8.2×10 - 5 S·cm -1 , indicating that a channel conducive to the rapid transport of lithium ions is formed between the two main materials, PSS and MMT.

[0100] Figure 5 are the cycling data of the lithium-free lithium half-cell formed by the negative electrode and the lithium sheet before and after being modified with the composite modification layer for the negative electrode current collector of Example 1.

[0101] All half-cells were assembled in an argon-filled glove box, with environmental parameters controlled within the range of water <1 ppm and O2 <1 ppm. The electrolyte used was commercially available LS-042. The 2400-type polypropylene membrane and electrolyte were used directly without further purification. In the preparation of the half-cells, unmodified copper or MS-Cu current collectors were cut into 12 mm diameter discs as the positive electrode, and lithium sheets of the same size were prepared as the negative electrode. The long-term cycling performance of the half-cells was determined using the galvanostatic method, i.e., at a current density of 1 mA·cm⁻¹. -2 and capacity 1mAh·cm -2 Cyclic lithium plating stripping test was conducted under the specified conditions.

[0102] Table 5 Performance data of the negative electrode-free lithium half-cells in Examples 1 to 3 Depend on Figure 5 As can be seen from the data in Table 5, the coulombic efficiency of the electrodeless lithium half-cell modified with a composite modification layer of two main materials for the negative electrode current collector in Example 1 was increased to 99.2%, and the cycle life was also extended.

[0103] Figure 6 This is a comparison chart of the long-cycle performance of the negative electrode and the lithium iron phosphate positive electrode assembled in Example 1 before and after the modification of the composite modification layer for the negative electrode current collector.

[0104] All cells were assembled in an argon-filled glove box, with environmental parameters controlled within the range of water <1 ppm and O2 <1 ppm. The electrolyte used was commercially available LS-042. The 2400-type polypropylene membrane was used directly with the electrolyte without further purification. When preparing a cathode-free full cell, MS-Cu or Cu current collectors and commercially available LiFePO4 cathodes were used, achieving a mass loading of approximately 17.1 mg·cm⁻¹. -2 .

[0105] Depend on Figure 6 As can be seen, the negative electrode-free lithium full cell modified with a composite modification layer of two main materials for the negative electrode current collector in Example 1 exhibits excellent long-term cycling stability and capacity retention, maintaining 40% capacity retention after 350 cycles.

[0106] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite modification layer for a negative electrode current collector, characterized in that, Includes the following steps: Using montmorillonite and polystyrene sulfonic acid as the main materials, and lithium hydroxide, lithium salt, and oxalic acid as lithiation materials, the montmorillonite is pre-lithiated with lithium salt and oxalic acid to obtain a first solution; the polystyrene sulfonic acid is pre-lithiated with lithium hydroxide and mixed with an alcohol solvent to obtain a second solution; the first and second solutions are mixed evenly to obtain a mixed solution; the mixed solution is used to perform planar two-dimensional spraying on the surface of the negative electrode substrate, and after drying, a composite modification layer is formed on the surface of the negative electrode substrate to obtain a composite modification layer for use as a negative electrode current collector.

2. The method for preparing the composite modification layer for a negative electrode current collector according to claim 1, characterized in that, The mass ratio of montmorillonite to polystyrene sulfonic acid is 1:0.5 to 1.5; the molecular weight of polystyrene sulfonic acid is 70,000 Mw.

3. The method for preparing the composite modified layer for the negative electrode current collector according to claim 1, characterized in that, The mass ratio of montmorillonite to lithium salt is 0.25–0.5:0.015; the mass ratio of lithium salt to oxalic acid is 0.8–0.85:1; and the mass ratio of lithium hydroxide to polystyrene sulfonic acid is 0.13:1–2.

4. The method for preparing the composite modified layer for the negative electrode current collector according to claim 3, characterized in that, The reaction conditions for pre-lithiation of montmorillonite using lithium salt and oxalic acid are: pH = 8-9, temperature = 75℃-85℃, and time = 4h.

5. The method for preparing the composite modified layer for the negative electrode current collector according to claim 1, characterized in that, The lithium salt is lithium carbonate; the alcohol solvent is ethanol.

6. The method for preparing the composite modified layer for a negative electrode current collector according to claim 1, characterized in that, The negative electrode substrate is copper foil, nickel foil, or zinc foil.

7. The method for preparing the composite modified layer for a negative electrode current collector according to claim 1, characterized in that, The planar two-dimensional spraying adopts electro-spraying; the voltage for planar two-dimensional spraying is 5.0kV~5.3kV.

8. A composite modification layer for a negative electrode current collector, characterized in that, The composite modified layer for negative electrode current collector is prepared by any one of claims 1 to 7.

9. The application of a composite modification layer for a negative electrode current collector in the preparation of a negative electrode-free lithium metal battery, characterized in that, The composite modification layer for the negative electrode current collector is the composite modification layer for the negative electrode current collector as described in claim 8.

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