A surface-modified aluminum foil anode and its preparation method, and a lithium-ion battery.

Abstract

This invention provides a method for preparing a surface-modified aluminum foil anode. By using a lithium-containing solution with strong reducing power to carry out an oxidation-reduction reaction with the alumina film on the surface of the aluminum foil anode at high temperature, the Al2O3 in the alumina film is rapidly lithiated into α-LiAlO2, which has a dense structure, can withstand the volume expansion of aluminum, and can freely transport lithium ions. This achieves uniform alloying / dealloying of the aluminum foil anode, causes the volume expansion to occur in a direction perpendicular to the aluminum foil anode, and isolates the electrolyte from the aluminum foil anode, preventing electrolyte decomposition. This effectively suppresses the structural failure of the aluminum foil anode and the capacity decay of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, and relates to a surface-modified aluminum foil anode and its preparation method, as well as a lithium-ion battery. Background Technology

[0002] When aluminum anodes are used in lithium-ion batteries, they have a theoretically high specific capacity (993 mAh g). -1 Aluminum anodes offer several advantages, including high conductivity, abundant reserves, environmental friendliness, and low cost. Currently, the active materials for aluminum anodes mainly exist in the form of aluminum powder or aluminum foil. The former requires mixing with a conductive agent (conductive carbon black) and an oil-based binder (polyvinylidene fluoride) or a water-based binder (carboxymethyl cellulose) and grinding into a uniform slurry, which is then coated onto a copper current collector and dried. The latter can be used directly as a single-material anode in lithium-ion batteries. Therefore, aluminum foil is an ideal anode material, which can further reduce the manufacturing cost of lithium-ion batteries and is a potential candidate for the next generation of high-energy-density rechargeable batteries.

[0003] However, the aluminum foil anode surface has a natural aluminum oxide (Al2O3) layer. This oxide layer undergoes irreversible lithiation during cycling, leading to capacity loss and a large lithiation overpotential. Furthermore, the aluminum foil anode experiences a volume expansion rate as high as 95% during alloying with lithium (Al→β-AlLi alloy). During dealloying, cracking occurs in the reaction zone. When the electrolyte penetrates into these cracks and comes into direct contact with the aluminum active material, side reactions occur, causing the electrode to pulverize and enter a vicious cycle, resulting in gradual capacity decay. Therefore, the aluminum foil anode faces problems of both poor structural stability and poor cycle stability. Summary of the Invention

[0004] To address the above problems, this invention provides a surface-modified aluminum foil negative electrode, its preparation method, and a lithium-ion battery.

[0005] To achieve the above objectives, the present invention proposes the following solution:

[0006] The first objective of this invention is to provide a method for preparing a surface-modified aluminum foil negative electrode, comprising the following steps:

[0007] (1) Prepare an organic lithium salt solution with strong reducing ability;

[0008] (2) Under an inert atmosphere, the aluminum foil negative electrode is placed in the organic lithium salt solution with strong reducing ability and heated to convert the aluminum oxide in the aluminum oxide film on the surface of the aluminum foil negative electrode into lithium aluminum oxide, and the lithium aluminum oxide is mainly α-LiAlO2. After the reaction is completed, the electrode is rinsed with a volatile organic solvent to remove the residual organic solution, and then dried to obtain a clean surface-modified aluminum foil negative electrode.

[0009] Preferably, in step (1), the organolithium salt solution with strong reducing ability is selected from at least one of lithium naphthalene (Li-Naph), lithium biphenyl (Li-Biph), and lithium 9,9-dimethylfluorene (Li-9,9-Dime) solution.

[0010] Preferably, in step (1), the preparation of the organic lithium salt solution with strong reducing ability includes:

[0011] S11. Under an inert atmosphere, organic compounds in which hydrogen in the molecule can be replaced by lithium are dissolved in organic solvent I to prepare a homogeneous solution II.

[0012] S12. Under an inert atmosphere, a substance containing metallic lithium is added to homogeneous solution II and stirred to accelerate the dissolution of lithium, thereby obtaining organic lithium salt solution III.

[0013] Preferably, the organic compounds in which hydrogen in the molecule can be replaced by lithium are one or more of naphthalene (Naph), biphenyl (Biph) and their derivatives, and 9,9-dimethylfluorene (9,9-Dime).

[0014] Preferably, the organic solvent I is one or more of dimethyl ether (DME) and tetrahydrofuran (THF), and the preferred organic solvent is conducive to the substitution of hydrogen in organic compounds by lithium.

[0015] The lithium-containing substance is one or more of lithium metal blocks, lithium metal sheets, and lithium metal powder.

[0016] Preferably, the concentration of organic compounds in the homogeneous solution II where hydrogen molecules can be replaced by lithium is 0.1–2 mol / L. -1 When the concentration is too low, the consumption of solution II is large; when the concentration is too high, the cost is high.

[0017] Preferably, in step (2), the heating temperature is 40-120°C and the heating time is 5-60 minutes.

[0018] Preferably, in step (2), the aluminum foil negative electrode is prepared by the following method: washing commercial aluminum foil with anhydrous ethanol, drying and cutting it;

[0019] The thickness of the commercial aluminum foil is 10–200 μm.

[0020] Preferably, the volatile organic solvent is one or more of ethers, alcohols, and esters.

[0021] The second objective of this invention is to provide an aluminum foil negative electrode, which is prepared by the aforementioned method for preparing a surface-modified aluminum foil negative electrode. The surface of the aluminum foil negative electrode has a dense lithium aluminum oxide film, which is mainly composed of α-LiAlO2.

[0022] A third objective of this invention is to provide a lithium-ion battery comprising a positive electrode, a separator, an electrolyte, and the aforementioned surface-modified aluminum foil negative electrode.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention employs a lithium-containing solution with strong reducing power to conduct a redox reaction with the Al2O3 film on the surface of the aluminum foil anode at high temperature. This rapidly lithiates the Al2O3 film on the surface of the aluminum foil anode into a lithium aluminum oxide film with α-LiAlO2 as its main component. This lithium aluminum oxide film has a dense structure, can withstand the volume expansion of aluminum, and can freely transport lithium ions. It can achieve uniform alloying / dealloying of the aluminum foil anode, allowing the volume expansion to occur in a direction perpendicular to the aluminum foil anode. It also isolates the electrolyte from the aluminum foil anode, preventing electrolyte decomposition, thereby effectively suppressing the failure of the aluminum foil anode structure and the degradation of battery capacity. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart of the preparation method of the surface-modified aluminum foil negative electrode of the present invention.

[0027] Figure 2 SEM image of the untreated aluminum foil negative electrode.

[0028] Figure 3 The images shown are SEM images of the surface-modified aluminum foil negative electrode of Example 1, where (a) is a surface SEM image and (b) is a cross-sectional SEM image.

[0029] Figure 4 The image shows the Al 2p spectrum of the surface-modified aluminum foil negative electrode in Example 1.

[0030] Figure 5 A comparison of the long-cycle performance of full cells assembled with unmodified raw aluminum foil anodes and the modified aluminum foil anodes of Example 1.

[0031] Figure 6The images show SEM images of the unmodified original aluminum foil anode after 200 complete cycles in an NCM811 full cell. (a) and (c) are surface SEM images, and (b) and (d) are cross-sectional SEM images.

[0032] Figure 7 The images are SEM images of the surface-modified aluminum foil negative electrode of Example 1 after 400 complete cycles in an NCM811 full cell. (a) and (b) are surface SEM images, and (c) is a cross-sectional SEM image. Detailed Implementation

[0033] This invention provides a specific embodiment of a method for preparing a surface-modified aluminum foil negative electrode, comprising the following steps:

[0034] (1) Prepare an organolithium salt solution III with strong reducing power;

[0035] (2) The aluminum foil anode is placed in the organic solution containing lithium metal with strong reducing ability and heated to react. After the reaction is completed, it is washed and dried with volatile organic solvent to obtain the surface modified aluminum foil anode.

[0036] In some preferred embodiments, step (1) of preparing the organic lithium salt solution III with strong reducing ability includes:

[0037] S11. Under an inert atmosphere, organic compounds in which hydrogen in the molecule can be replaced by lithium are dissolved in organic solvent I to prepare a homogeneous solution II.

[0038] S12. Add a substance containing metallic lithium to the homogeneous solution II and stir to obtain an organic lithium salt solution III with strong reducing ability.

[0039] In some optional embodiments, steps S11 and S12 are performed under an inert atmosphere, specifically in a glove box filled with argon, or in other inert atmospheres, as long as the atmosphere of the entire system can be protected.

[0040] In some preferred embodiments, the organic compounds in which hydrogen in the molecule can be replaced by lithium are one or more of naphthalene (Naph), biphenyl (Biph) and its derivatives, and 9,9-dimethylfluorene (9,9-Dime). The preferred organic compounds have sufficiently strong reducing properties to rapidly lithiate the Al2O3 on the aluminum foil surface into α-LiAlO2, which has a dense structure, can withstand the volume expansion of aluminum, and can freely transport lithium ions.

[0041] In some preferred embodiments, the organic solvent I is one or more of dimethyl ether (DME) and tetrahydrofuran (THF).

[0042] In some preferred embodiments, the lithium-containing substance is one or more of lithium metal blocks, lithium metal sheets, and lithium metal powder.

[0043] In some preferred embodiments, the concentration of organic compounds in the homogeneous solution II where hydrogen molecules can be replaced by lithium is 0.1–2 mol / L. -1 .

[0044] In some preferred embodiments, step S11 involves preparing a homogeneous solution II under stirring conditions. The preferred stirring time is not less than 5 minutes, and the stirring speed is not less than 400 rpm.

[0045] In some preferred embodiments, in step S12, the stirring time is not less than 20 minutes and the stirring speed is not less than 400 rpm.

[0046] In some preferred embodiments, in step (2), the heating temperature is 40-120°C, including 50, 60, 70, 80, 90, 100, 110°C, etc., and more preferably 60-120°C; the heating time is 5-60 minutes.

[0047] In some preferred embodiments, in step (2), the aluminum foil negative electrode is prepared by rinsing commercial aluminum foil with anhydrous ethanol, drying and cutting it.

[0048] In some preferred embodiments, the thickness of the commercial aluminum foil is 10–200 μm, including 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 μm, etc.

[0049] In some specific embodiments, the volatile organic solvent mentioned in step (2) is one or more of ethers, alcohols and esters.

[0050] The present invention also provides a surface-modified aluminum foil negative electrode prepared using the aforementioned specific embodiments.

[0051] The present invention also provides a lithium-ion battery, comprising a positive electrode, a separator, an electrolyte, and an aluminum foil negative electrode, wherein the aluminum foil negative electrode is a surface-modified aluminum foil negative electrode prepared by the methods of the above specific embodiments.

[0052] In some optional embodiments, the positive electrode is composed of a positive electrode active material, a conductive agent, and a binder.

[0053] In some optional embodiments, the positive electrode active material can be selected from conventional lithium-ion battery positive electrode materials, including but not limited to nickel-cobalt-manganese ternary oxides, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and lithium manganese iron phosphate.

[0054] In some optional embodiments, the electrolyte is composed of lithium salt and organic solvent.

[0055] In some optional embodiments, the lithium salt may be selected from conventional lithium salts such as lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), and lithium tetrafluoroborate (LiBF4).

[0056] In some optional embodiments, the organic solvent may be selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), vinylene carbonate (VC), propylene carbonate (PC), and fluoroethylene carbonate (FEC).

[0057] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0058] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0059] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0060] Example 1

[0061] A method for preparing a surface-modified aluminum foil negative electrode, the steps of which are shown in the flowchart below. Figure 1 As shown, the specific implementation method is as follows:

[0062] S1: In a glove box filled with argon atmosphere, take 1.28174 g of dry Naph compound and place it in a glass bottle. Add 10 ml of DME solvent and stir with a magnetic stirrer at 800 rpm for 10 minutes. Then add 69.47 mg of clean lithium metal and stir with a magnetic stirrer at 800 rpm for 40 minutes to obtain a homogeneous 1 M Li-Naph organolithium salt solution.

[0063] S2: In a glove box filled with argon atmosphere, place a 20 μm thick aluminum foil negative electrode in a glass bottle, add 1 ml of Li-Naph organic lithium salt solution and ensure that the aluminum foil negative electrode is completely submerged, and then place it on a hot plate and heat at 100°C for 10 minutes.

[0064] S3: In a glove box filled with argon atmosphere, take out the treated aluminum foil negative electrode and rinse it three times with DME solvent, then let it air dry.

[0065] Figure 2 This is a morphology image of the raw aluminum foil negative electrode without surface treatment. Figure 3 This is a morphology image of the surface-modified aluminum foil negative electrode of Embodiment 1 of the present invention. (Comparison) Figure 2 and Figure 3 It can be seen that after surface modification, the surface of the aluminum foil negative electrode is uniformly covered by a layer of dense, fine particles.

[0066] Figure 4 The image shows the Al 2p X-ray photoelectron spectroscopy (XPS) spectrum of the surface-modified aluminum foil anode of Example 1. Analysis of the spectrum reveals that the surface layer of the aluminum foil anode comprises α-LiAlO2 and Li. x AlO y The aluminum foil contains Al, Li₂O₃, and Li₄Al₉, with α-LiAlO₂ being the most abundant and the main component. Therefore, the surface modification method provided in Example 1 can convert Al₂O₃ on the surface of the aluminum foil negative electrode into α-LiAlO₂.

[0067] The unmodified original aluminum foil negative electrode and the modified aluminum foil negative electrode prepared in Example 1 were respectively subjected to nickel-cobalt-manganese ternary oxide positive electrode (LiNi). 0.8 Co 0.1 Mn 0.1 A full cell was prepared by matching O2 (NCM811) with 1 M LiPF6-DEC / FEC (volume ratio 1:1) as electrolyte.

[0068] The cycle performance of the prepared full cell is shown in the figure below. Figure 5 As shown, from Figure 5 It can be seen that the unmodified aluminum foil negative electrode-based lithium-ion battery has a specific capacity of 80.6 mAh g⁻¹ during the first positive electrode discharge after activation. -1 After several cycles, the specific capacity rapidly decreased, and after 100 cycles, the remaining specific capacity was 19.8 mAh g. -1 The capacity retention rate was only 24.6%. The modified aluminum foil negative electrode lithium-ion battery provided in Example 1 had a first-cycle positive electrode discharge capacity of 115.7 mAh g after activation. -1 After 400 cycles, the remaining specific capacity is 107 mAh g. -1The capacity retention rate is as high as 92.5%, corresponding to a specific capacity decay of 0.02 mAh g / L per cycle. -1 Therefore, lithium-ion batteries with modified aluminum foil anode bases have higher reversible capacity and longer cycle stability.

[0069] See Figure 6 After undergoing 200 cycles in an NCM811 full cell, the unmodified raw aluminum foil anode exhibited severe pulverization on both the electrode surface and interior. This was primarily because the aluminum alloying process preferentially proceeded along the rolling direction of the aluminum foil (e.g., ...). Figure 6 (As shown by the yellow dashed line in -a), a large horizontal volume expansion occurred. During the dealloying process, due to the stress relaxation, cracks appeared in the reaction area. After the electrolyte penetrated into the cracks, it would react with the freshly exposed aluminum active material, causing the electrolyte to decompose and the cracked area to crack and pulverize further, thus causing the battery capacity to decay rapidly and the aluminum foil negative electrode structure to be destroyed.

[0070] See Figure 7 The modified aluminum foil negative electrode provided in Example 1 showed only minor surface cracking after 400 cycles in an NCM811 full cell, with no pulverization. Figure 7 -a), local region magnification Figure 7 -b indicates that the surface of the modified aluminum foil negative electrode is covered by a dense glassy substance, which is the surface modification layer α-LiAlO2. (From the cross-section...) Figure 7 From the -c perspective, the aluminum foil anode substrate maintains its intact structure, but its thickness increases to 56 μm, indicating that the aluminum foil anode has undergone significant volume expansion in the vertical direction after long cycling. This phenomenon suggests that α-LiAlO2 can stably exist on the surface of the aluminum foil anode during cycling, effectively preventing direct contact between the electrolyte and the aluminum active material, thus reducing the reversible capacity loss caused by electrolyte decomposition. Furthermore, it can induce alloying / dealloying reactions to occur uniformly in the vertical direction on the aluminum foil anode surface, avoiding horizontal volume expansion and effectively mitigating horizontal cracking and pulverization of the aluminum foil anode. This results in high structural stability of the aluminum foil anode after long cycling.

[0071] Examples 2-3

[0072] The only difference between Examples 2 and 3 and Example 1 is the heating conditions during the preparation process, as detailed in Table 1.

[0073] The modified foil anodes prepared in Examples 2 and 3 were assembled into full cells according to the aforementioned full cell assembly method. The electrochemical test results of the full cells assembled from each example and the original aluminum foil anode are shown in Table 1.

[0074] Table 1. Modification conditions for each embodiment, and electrochemical test results of full cells assembled with the modified aluminum foil anode and the original aluminum foil anode in each embodiment.

[0075] sample Heating conditions: temperature-time Initial specific capacity (mAh g⁻¹) Number of cycles Specific capacity (mAh g⁻¹) Capacity retention rate (%) Example 1 100℃ for 10 minutes 115.7 400 107 92.5% Example 2 80℃-60 minutes 156.3 200 125.5 80.3% Example 3 120℃ - 5 minutes - 80℃ - 20 minutes 143.4 250 132.9 92.7% Original aluminum foil negative electrode / 80.6 100 19.8 24.6%

[0076] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a surface-modified aluminum foil negative electrode, characterized in that, Including the following steps: (1) Prepare an organic lithium salt solution with strong reducing ability; (2) Under an inert atmosphere, the aluminum foil negative electrode is placed in the organic lithium salt solution with strong reducing ability and heated to convert the aluminum oxide in the aluminum oxide film on the surface of the aluminum foil negative electrode into lithium aluminum oxide, and the lithium aluminum oxide is mainly α-LiAlO2. After the reaction is completed, the electrode is rinsed with a volatile organic solvent to remove the residual organic solution, and then dried to obtain a clean surface-modified aluminum foil negative electrode.

2. The method for preparing the surface-modified aluminum foil negative electrode as described in claim 1, characterized in that, In step (1), the organolithium salt solution with strong reducing ability is selected from at least one of lithium naphthalene (Li-Naph), lithium biphenyl (Li-Biph), and lithium 9,9-dimethylfluorene (Li-9,9-Dime) solution.

3. The method for preparing the surface-modified aluminum foil negative electrode as described in claim 1 or 2, characterized in that, In step (1), the preparation of the organic lithium salt solution with strong reducing ability includes: S11. Under an inert atmosphere, organic compounds in which hydrogen in the molecule can be replaced by lithium are dissolved in organic solvent I to prepare a homogeneous solution. S12. Add a substance containing metallic lithium to a homogeneous solution under an inert atmosphere and stir to obtain the final product.

4. The method for preparing the surface-modified aluminum foil negative electrode as described in claim 3, characterized in that, Organic compounds in which hydrogen in the molecule can be replaced by lithium are one or more of naphthalene (Naph), biphenyl (Biph) and its derivatives, and 9,9-dimethylfluorene (9,9-Dime); The organic solvent I is one or more of dimethyl ether (DME) and tetrahydrofuran (THF); The lithium-containing substance is one or more of lithium metal blocks, lithium metal sheets, and lithium metal powder.

5. The method for preparing the surface-modified aluminum foil negative electrode as described in claim 3, characterized in that, The concentration of organic compounds in the homogeneous solution in which hydrogen molecules can be replaced by lithium is 0.1–2 mol / L. -1 .

6. The method for preparing the surface-modified aluminum foil negative electrode as described in claim 1, characterized in that, In step (2), the heating temperature is 40-120°C; the heating time is 5-60 minutes.

7. The method for preparing the surface-modified aluminum foil negative electrode as described in claim 1, characterized in that, In step (2), the aluminum foil negative electrode is prepared by the following method: washing commercial aluminum foil with anhydrous ethanol, drying and cutting it; The thickness of the commercial aluminum foil is 10–200 μm.

8. The method for preparing the surface-modified aluminum foil negative electrode as described in claim 1, characterized in that, The volatile organic solvent is one or more of ethers, alcohols, and esters.

9. A surface-modified aluminum foil negative electrode, characterized in that, The aluminum foil anode is prepared by any one of the preparation methods described in claims 1 to 8, wherein the surface of the aluminum foil anode has a dense lithium aluminum oxide film, and the lithium aluminum oxide film is mainly composed of α-LiAlO2.

10. A lithium-ion battery, characterized in that, It includes a positive electrode, a separator, an electrolyte, and an aluminum foil negative electrode as described in claim 9.

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