A composite lithium negative electrode based on borate surface modification and a preparation method thereof

Abstract

The application discloses a borate surface modified composite lithium negative electrode and a preparation method thereof. A piece of lithium foil is laid flat, then inorganic lithium borate salt powder is sprinkled on the surface of the lithium foil, and the lithium foil is repeatedly rubbed with a gloved finger. The inorganic lithium borate salt powder is repeatedly sprinkled on the surface of the lithium foil and the lithium foil is repeatedly rubbed to form a high ion / electron interface layer on the surface of the lithium foil, thereby obtaining the borate surface modified composite lithium negative electrode. The preparation method provided by the application can avoid the use of toxic organic solvents, and the preparation method is simple, and green and large-scale production can be realized. The composite lithium negative electrode provided by the application has excellent cycle stability and rate performance.

Description

Technical Field

[0001] This invention relates to a composite lithium anode based on borate surface modification and its preparation method, belonging to the field of lithium metal battery anode material preparation technology. Background Technology

[0002] Renewable energy sources, such as wind, solar, hydro, and geothermal energy, which are non-fossil fuels, serve as alternatives to traditional energy sources. They can significantly slow the pace of ecological degradation and address the current energy supply shortages. However, while these energy sources are clean and environmentally friendly, they generally face challenges such as large output volatility and difficulties in storage and transmission technologies.

[0003] Lithium metal batteries have a theoretically high specific capacity (3860 mAh g). -1 It has the lowest redox potential (-3.04V, compared to the standard hydrogen electrode) and the lowest density (6.94g mol). -1 With its advantages such as [missing information], lithium metal anodes far surpass graphite anodes, which rely on intercalation chemistry for energy storage, and are considered the most promising battery anode material. However, the dendrite growth and unstable SEI interface layer on lithium anodes seriously hinder the practical application of lithium metal batteries. Commercially available lithium sheets typically have a passivation layer such as Li₂CO₃, Li₂O, or LiOH on their surface. An uneven passivation layer reacts with the electrolyte to form an unstable SEI layer. This results in uneven charge distribution and slow ion transport during electrochemical cycling, leading to excessively high local current density. Lithium ions then concentrate, forming lithium dendrites, which rapidly cause battery failure. Therefore, designing a multifunctional lithium anode with a modified interface is urgently needed. In recent years, domestic and international research on interface design has mainly focused on artificial SEI layers, vapor deposition, and electrolyte additives. Among these approaches, constructing artificial coatings is the simplest, safest, and most efficient modification method. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the first objective of this invention is to provide a method for preparing a composite lithium anode based on borate surface modification. This method involves rubbing an inorganic lithium borate powder onto the surface of lithium metal to promote an in-situ chemical conversion reaction between the lithium borate and lithium metal. This generates a lithium borate layer and a lithium alloy layer or metal layer on the lithium metal surface, thus obtaining a composite lithium anode. This lithium borate layer and lithium alloy layer or metal layer serve as a highly conductive ion / electron interface layer, acting as both a ion-conducting and electron-conducting layer. It regulates the uniform deposition of lithium ions, accelerates charge transfer, rectifyes lithium ions, homogenizes charge distribution, inhibits dendrite growth, enhances the stability of the lithium interface, and reduces side reactions between the lithium metal anode and the electrolyte, thereby improving its cycle stability. The preparation method provided by this invention avoids the use of toxic organic solvents, is simple, and enables green, large-scale production.

[0005] A second objective of this invention is to provide a composite lithium anode based on borate surface modification prepared by the above-described method. The composite lithium anode provided by this invention exhibits excellent cycle stability and rate performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention discloses a method for preparing a composite lithium anode based on borate surface modification. A lithium foil is taken and laid flat. Inorganic lithium borate salt powder is then sprinkled onto the surface of the lithium foil. The foil is rubbed repeatedly with gloved fingers. This process of sprinkling inorganic lithium borate salt powder onto the lithium foil surface and rubbing repeatedly is repeated to form a highly conductive ion / electron interface layer on the lithium foil surface, thus obtaining the composite lithium anode based on borate surface modification.

[0008] The method of this invention promotes an in-situ chemical conversion reaction between lithium borate salt powder and the lithium metal anode by rubbing the lithium metal surface with lithium borate salt powder. This generates a lithium borate layer and a lithium alloy layer or metal layer on the lithium metal surface. The generated lithium borate salt acts as an ion conductor, providing a channel for lithium ion transport, while the lithium alloy layer or metal layer acts as an electronic conductor, accelerating charge transfer. As a highly conductive ion / electron hybrid interface layer of the composite lithium anode, this method regulates the uniform deposition of lithium ions, accelerates charge transfer, rectifyes lithium ions, uniformizes charge distribution, inhibits dendrite growth, enhances the stability of the lithium interface, and reduces side reactions between the lithium metal anode and the electrolyte, thereby improving its cycle stability.

[0009] In this invention, the size of the lithium foil is not limited and can be selected according to the application requirements, such as using 20cm*10cm.

[0010] The preferred method is to first use a brush to evenly remove the oxide layer from the surface of the lithium foil.

[0011] In a preferred embodiment, the inorganic lithium borate salt in the inorganic lithium borate powder is selected from one or more of zinc borate, aluminum borate, magnesium borate, nickel borate, and copper borate.

[0012] Further preferred, the inorganic lithium borate salt in the inorganic lithium borate powder is selected from zinc borate. The inventors discovered that when the inorganic lithium borate salt powder is selected from zinc borate, lithium borate with high ion conductivity and a lithium-zinc alloy with strong lithiophilic properties are formed, resulting in the composite lithium anode with optimal performance, maintaining stable cycling over a long period. Other inorganic lithium borate salts can also form a highly conductive ion / electron interface layer, improving the performance of the composite lithium anode, but they are inferior to zinc borate. For example, the lithium-aluminum alloy formed by aluminum borate has lower lithiophilicity than the lithium-zinc alloy, while the lithium-magnesium solid solution formed by magnesium borate is not stable enough, making the battery prone to short circuits. The metallic nickel and copper formed by nickel borate and copper borate cannot form alloys with lithium and are non-lithiophilic. Although they also have conductivity, the interface layer performance is poor, resulting in lower cycle performance than when the inorganic lithium borate salt is selected from zinc borate.

[0013] In a preferred embodiment, the mass of inorganic lithium borate powder taken in any given batch is 5-20 mg. In this invention, controlling the mass of inorganic lithium borate powder taken in each batch within the above range ensures optimal performance of the resulting composite lithium anode. If too little powder is used, the reaction between the lithium foil and the powder is insufficient, resulting in surface unevenness and unreacted areas. If too much powder is used, only a fixed amount will react with the lithium foil, leading to waste.

[0014] In the preferred embodiment, a constant frictional pressure of 1-2 N / cm is continuously applied during any repeated rubbing of the gloved fingers. -2 Frictional pressure is determined through a test experiment in which lithium foil is placed on a balance and rubbed uniformly. If the frictional pressure is too low, it cannot provide the energy required for the in-situ chemical reaction, which will result in a slow reaction rate between the powder and the lithium foil. If the frictional pressure is too high, there is a risk of wearing the surface of the lithium foil to pieces.

[0015] In a preferred embodiment, the inorganic lithium borate salt powder is repeatedly sprinkled onto the lithium foil surface and rubbed repeatedly 1-3 times, preferably 2 times. The inventors have found that the number of rubbing repetitions needs to be effectively controlled. If too few repetitions are made, the resulting layer with high ion / electron conductivity will be too thin, making it easily damaged during lithium depreciation, thus causing rapid battery failure. If too many repetitions are made, the resulting layer with high ion / electron conductivity will be too thick, hindering ion transport and increasing the polarization voltage of the symmetrical battery, thus affecting cycle life.

[0016] In a preferred embodiment, the thickness of the highly conductive ion / electron interface layer in the borate-based composite lithium anode is 1-2 μm, preferably 1.3-1.8 μm, and more preferably 1.5 μm.

[0017] The present invention also provides a composite lithium anode based on borate surface modification prepared by the above preparation method.

[0018] Features and benefits of the present invention

[0019] The method of this invention promotes an in-situ chemical conversion reaction between lithium borate salt powder and the lithium metal anode by rubbing the lithium metal surface with lithium borate salt powder. This generates a lithium borate layer and a lithium alloy layer or metal layer on the lithium metal surface. The generated lithium borate salt acts as an ion conductor, providing a channel for lithium ion transport, while the lithium alloy layer or metal layer acts as an electronic conductor, accelerating charge transfer. As a highly conductive ion / electron hybrid interface layer of the composite lithium anode, this method regulates the uniform deposition of lithium ions, accelerates charge transfer, rectifyes lithium ions, uniformizes charge distribution, inhibits dendrite growth, enhances the stability of the lithium interface, and reduces side reactions between the lithium metal anode and the electrolyte, thereby improving its cycle stability.

[0020] The method provided by this invention is a solvent-free, dry powder friction method, which involves in-situ lithiation of powder on the surface of lithium foil to form a modified interface layer composed of lithiated particles. This is a promising surface modification strategy that is safe, green, environmentally friendly, and efficient, and can promote the commercialization of lithium metal batteries. Moreover, the powder can serve as a low-cost interface modifier, which can be directly applied to the lithium metal surface, and this is of great significance for the commercialization of lithium metal anodes.

[0021] Compared with the prior art, the preparation method provided by the present invention has at least the following advantages:

[0022] (1) The preparation method of the present invention abandons the use of organic solvent modified lithium metal anode, which is safer and greener.

[0023] (2) The essence of the method of the present invention is the in-situ mechanical chemical reaction of lithium metal, and the resulting mixed interface layer is more uniform and dense.

[0024] (3) The modified lithium metal anode obtained by the method of the present invention has better cycle stability in symmetrical cells and full cells, and higher coulombic efficiency and cycle number in half cells.

[0025] (4) The method of the present invention can induce the planar deposition of lithium by a mixed interface layer, thereby forming a dendrite-free lithium metal battery.

[0026] (5) The highly conductive ion / electron interface layer formed by the method of the present invention can accelerate the transport of lithium ions and the transfer of charge, and greatly improve the performance of lithium metal anode.

[0027] To facilitate understanding of the interface layer of the present invention, a more comprehensive description of the preparation method of a composite lithium anode based on borate surface modification and its application in batteries will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention. Attached Figure Description

[0028] Figure 1 This is a microscopic morphology diagram of the zinc borate powder provided in Example 1.

[0029] Figure 2 An optical photograph of the modified lithium metal electrode prepared in Example 1.

[0030] Figure 3 This is a microscopic morphology diagram of the modified lithium metal electrode prepared in Example 1.

[0031] Figure 4 The image shown is a FIB-SEM image of the modified lithium metal electrode provided in Example 1.

[0032] Figure 5 XRD pattern of the modified lithium metal electrode provided in Example 1

[0033] Figure 6 XPS image of the modified lithium metal electrode provided in Example 1

[0034] Figure 7 The graph shows the cycle performance of the symmetrical battery at 25°C provided in Example 1.

[0035] Figure 8 The graph shows the cycling performance of the Li||Cu half-cell at 25°C, as provided in Example 1.

[0036] Figure 9 The graph shows the cycling performance of the Li||LiFePO4 full cell at 25°C, as provided in Example 1.

[0037] Figure 10 The 5mAh cm-deposited sample provided in Example 1 -2 Scanning electron microscope image of a symmetrical cell.

[0038] Figure 11 The image is a scanning electron microscope image obtained after 100 cycles as provided in Example 1.

[0039] Figure 12 The image shows a FIB-SEM image of the modified lithium metal electrode provided in Example 2.

[0040] Figure 13 The image shown is a FIB-SEM image of the modified lithium metal electrode provided in Example 3.

[0041] Figure 14The cycling performance diagrams are provided for symmetrical cells with electrodes of different thicknesses.

[0042] Figure 15 The graph shows the cycle performance of the symmetrical battery at 25°C provided in Example 4.

[0043] Figure 16 The graph shows the cycle performance of the symmetrical battery at 25°C provided in Example 5.

[0044] Figure 17 An optical photograph of a lithium sheet provided for Comparative Example 1. Detailed Implementation

[0045] Example 1

[0046] A certain mass of zinc borate powder was placed in a vacuum drying oven and dried. Figure 1 It can be seen that the micron-sized powder agglomerates together. After drying, it is placed in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm). First, a 20cm*10cm lithium foil is laid flat on the surface of a dry glass plate, and its four ends are fixed with labels. The oxide layer on the surface of the lithium foil is brushed off. Then, wearing clean and dry disposable nitrile gloves, a measured amount of zinc borate powder (10mg) is evenly sprinkled on the surface of the lithium foil. The surface of the lithium foil is repeatedly rubbed with gloved fingers to ensure uniform powder coating. During this process, a constant frictional pressure (1.5 N cm) is continuously applied. -2 The process continues until the lithium foil turns black, indicating that the zinc borate powder has been lithiated and an in-situ mechanochemical reaction has occurred. Then, the same mass of zinc borate powder is sprinkled on top and rubbed, repeating this process twice. Finally, excess zinc borate powder is removed from the lithium foil surface with a brush, successfully preparing a lithium metal electrode with a modified interface layer thickness of 1.5 μm.

[0047] pass Figure 2 The optical photographs show that the surface of the modified lithium sheet is uniformly black. Figure 3 The electron microscope images show that the surface morphology of the modified lithium sheet is different from that of the modified lithium sheet. Figure 1 The morphology of the powder indicates the successful preparation of the modified interface layer. FIB-SEM analysis revealed that the thickness of the modified interface layer was approximately 1.5 μm. Figure 4 ),pass Figure 5 and Figure 6XRD and XPS analysis revealed that the modified interface layer mainly consisted of a lithium borate phase with high ion conductivity and a lithium zinc alloy phase with high electron conductivity. The obtained negative electrode material was cut into 14mm diameter sheets and assembled into a 2016 model symmetric battery. Celgard 2400 was used as the separator. The electrolyte for the symmetric battery and half-cell was LS-009 (1.0M LiTFSI + DME:DOL = 1:1 Vol% + 2% LiNO3), and the electrolyte for the full cell was LB-515 (1.0M LiPF6, EC:EMC (3:7 v / v) with 10% FEC). Cyclic performance was tested. The symmetric battery cycle performance at 25℃ is as follows: Figure 7 As shown, at 0.5 mAcm -2 0.5mAh cm -2 Under certain conditions, it can cycle stably for over 4200 hours without short circuit, demonstrating the excellent interfacial properties of its modified negative electrode. The cycling performance of the Li||Cu half-cell at 25℃ is as follows: Figure 8 As shown, it can stably cycle for more than 90 cycles. The cycling performance of the Li||LiFePO4 full cell at 25℃ is as follows: Figure 9 As shown, the amount of active substance is 10 mg cm -2 Under conditions of a current density of 2C, it can stably cycle for over 500 cycles, significantly increasing cycle life and validating its commercial value. From Figure 10 5mAh cm -2 Lithium and Figure 11 The SEM images after 100 cycles show that the highly conductive ion / electron hybrid interface layer has the ability to induce a planar deposition mode of lithium, thereby realizing a dendrite-free lithium metal battery.

[0048] Example 2

[0049] A certain mass of zinc borate powder was dried in a vacuum drying oven. After drying, it was placed in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm). First, a 20 cm * 10 cm lithium foil was laid flat on the surface of a dry glass plate, and its four ends were fixed with labels. The oxide layer on the surface of the lithium foil was brushed off. Then, wearing clean and dry disposable nitrile gloves, a measured amount of zinc borate powder (10 mg) was evenly sprinkled on the surface of the lithium foil. The surface of the lithium foil was repeatedly rubbed with gloved fingers to ensure uniform powder coating. During this process, a constant friction pressure (1.5 N cm) was continuously applied. -2 The process continues until the lithium foil turns black, then the same mass of zinc borate powder is sprinkled on top and rubbed, repeated three times. Finally, excess zinc borate powder is removed from the lithium foil surface with a brush, successfully preparing a lithium metal electrode with a modified interface layer thickness of 2 μm. The cycling performance of the lithium anode prepared by repeating this rubbing process three times is as follows: Figure 14As shown, the performance is inferior to that of lithium anodes obtained by rubbing twice. This is because the modified interface layer is thicker, which hinders ion transport, thereby increasing the polarization voltage of the symmetrical cell and affecting cycle life.

[0050] Example 3

[0051] A certain mass of zinc borate powder was dried in a vacuum drying oven. After drying, it was placed in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm). First, a 20 cm * 10 cm lithium foil was laid flat on the surface of a dry glass plate, and its four ends were fixed with labels. The oxide layer on the surface of the lithium foil was brushed off. Then, wearing clean and dry disposable nitrile gloves, a measured amount of zinc borate powder (10 mg) was evenly sprinkled on the surface of the lithium foil. The surface of the lithium foil was repeatedly rubbed with gloved fingers to ensure uniform powder coating. During this process, a constant friction pressure (1.5 N cm) was continuously applied. -2 The process continues until the lithium foil turns black, then the same mass of zinc borate powder is sprinkled on top and rubbed, repeating this process once. Finally, excess zinc borate powder is removed from the lithium foil surface with a brush, successfully preparing a lithium metal electrode with a modified interface layer thickness of 1 μm. The cycling performance of the lithium anode prepared by repeating this rubbing process once is as follows: Figure 14 As shown, the performance is inferior to that of lithium anodes obtained by rubbing twice. This is because the modified interface layer is thinner and is easily damaged during the lithium depreciation process, which leads to rapid battery failure.

[0052] Example 4

[0053] A certain mass of magnesium borate powder was dried in a vacuum drying oven. After drying, it was placed in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm). First, a 20 cm * 10 cm lithium foil was laid flat on the surface of a dry glass plate, and its four ends were fixed with labels. The oxide layer on the surface of the lithium foil was brushed off. Then, wearing clean and dry disposable nitrile gloves, a measured amount of magnesium borate powder (10 mg) was evenly sprinkled on the surface of the lithium foil. The surface of the lithium foil was repeatedly rubbed with gloved fingers to ensure uniform powder coating. During this process, a constant friction pressure (1.5 N cm) was continuously applied. -2 The process was repeated twice, involving rubbing the lithium foil with the same amount of magnesium borate powder until it turned black. Finally, excess magnesium borate powder was removed from the lithium foil surface with a brush, successfully preparing a lithium metal electrode with a modified interface layer thickness of 1.5 μm. The symmetric battery cycle performance at 25°C was as follows: Figure 15 As shown, at 0.5 mAcm -2 0.5mAh cm -2 A short circuit occurred after 2000 hours of cycling under certain conditions.

[0054] Example 5

[0055] A certain mass of nickel borate powder was dried in a vacuum drying oven. After drying, it was placed in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm). First, a 20 cm * 10 cm lithium foil was laid flat on the surface of a dried glass plate, and its four ends were fixed with labels. The oxide layer on the surface of the lithium foil was brushed off. Then, wearing clean and dry disposable nitrile gloves, a measured amount of nickel borate powder (10 mg) was evenly sprinkled on the surface of the lithium foil. The surface of the lithium foil was repeatedly rubbed with gloved fingers to ensure uniform powder coating. During this process, a constant frictional pressure (1.5 N cm) was continuously applied. -2 The process was repeated twice, involving rubbing the lithium foil with the same amount of nickel borate powder until it turned black. Finally, excess nickel borate powder was removed from the lithium foil surface with a brush, successfully preparing a lithium metal electrode with a modified interface layer thickness of 1.5 μm. The symmetric battery cycle performance at 25°C was as follows: Figure 16 As shown, at 0.5 mAcm -2 0.5mAh cm -2 Under these conditions, the polarization increased significantly after 2000 hours of cycling.

[0056] Comparative Example 1

[0057] Untreated Li foil, such as Figure 17 As shown, commercially available lithium foil typically has a passivation layer such as Li₂CO₃, Li₂O, or LiOH on its surface. The obtained Li foil was cut into 14mm diameter sheets and assembled into a 2016 model symmetric battery. Celgard 2400 was used as the separator. The electrolyte for the symmetric and half-cell batteries was LS-009 (1.0M LiTFSI + DME:DOL = 1:1 Vol% + 2% LiNO₃), and the electrolyte for the full cell was LB-515 (1.0M LiPF₆, EC:EMC (3:7 v / v) with 10% FEC). Its cycle performance was tested. Figure 7 , 8 As shown in Figures 9, the performance of lithium metal electrodes in symmetrical cells, half-cells, and full cells is far inferior to that of lithium metal electrodes with highly conductive ion / electron modified interface layers.

[0058] In summary, existing technologies lack a simple method for preparing lithium metal electrodes with modified interface layers, addressing current problems with lithium metal anodes. This invention provides a method for preparing a composite lithium anode based on borate surface modification. This invention uses lithium borate powder to rub the lithium metal surface, promoting an in-situ chemical conversion reaction between the lithium borate and the lithium metal anode. This generates a lithium borate layer and a lithium alloy layer or metal layer on the lithium metal surface. The lithium borate layer possesses lithium-ion transport properties, improving the transport dynamics of lithium ions, while the lithium alloy or metal layer exhibits strong electronic conductivity. The synergistic effect of the two components achieves high ionic / electronic conductivity at the interface, optimizes interface kinetics, and induces planar lithium growth, thus realizing a dendrite-free lithium metal battery. Furthermore, this preparation technology is environmentally friendly, simple, and efficient, meeting commercialization requirements.

[0059] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., 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 lithium negative electrode based on borate surface modification, characterized by: Take a piece of lithium foil, lay it flat, then sprinkle inorganic borate powder on the surface of the lithium foil, and rub it repeatedly with gloved fingers. Repeat the process of sprinkling inorganic borate powder on the surface of the lithium foil and rubbing it repeatedly to form a lithium borate layer and a lithium alloy layer or metal layer on the surface of the lithium foil as a highly conductive ion / electron interface layer, thus obtaining a composite lithium anode based on borate surface modification. The inorganic borates in the inorganic borate powder are selected from one or more of zinc borate, aluminum borate, magnesium borate, nickel borate, and copper borate.

2. The method of claim 1, wherein the method is characterized by: First, use a brush to evenly remove the oxide layer from the surface of the lithium foil.

3. The method for preparing a composite lithium anode based on borate surface modification according to claim 1, characterized in that: The inorganic borate in the inorganic borate powder is selected from zinc borate.

4. The method for preparing a composite lithium anode based on borate surface modification according to claim 1, characterized in that: The mass of any single inorganic borate powder taken is 5-20 mg.

5. The method for preparing a composite lithium anode based on borate surface modification according to claim 1, characterized in that: Any time with gloved fingers repeatedly rubbing, constant friction pressure 1-2 N cm -2 .

6. The method for preparing a composite lithium anode based on borate surface modification according to claim 1, characterized in that: Repeat the process of sprinkling inorganic borate powder onto the lithium foil surface and rubbing it repeatedly 1-3 times.

7. The method for preparing a composite lithium anode based on borate surface modification according to claim 1, characterized in that: In the composite lithium anode based on borate surface modification, the thickness of the highly conductive ion / electron interface layer is 1-2 μm.

8. The composite lithium anode based on borate surface modification prepared by the preparation method according to any one of claims 1-7.

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