Preparation method of battery pole piece, battery pole piece and battery

Abstract

The invention relates to a preparation method of a battery pole piece, the battery pole piece and a battery, the preparation method of the battery pole piece comprises the following steps: preparing the battery pole piece by using a dry process, the used active substance is graphite, and the binder is PTFE; soaking the battery pole piece in a Lewis acid solution; and drying the battery pole piece soaked in the Lewis acid solution. For the graphite negative pole piece prepared by adopting a dry process, in order to reduce side reaction between PTFE and graphite and improve the first effect of the lithium ion battery, Lewis acid is adopted to treat the pole piece, and the Lewis acid can effectively break C-F bonds at the tail end of a PTFE chain and reduce side reaction between PTFE and graphite through the strong electron acceptor property of the Lewis acid, so that the positive effect of the lithium ion battery is improved. Therefore, the first cycle efficiency of the lithium ion battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a method for preparing a dry-process battery pole piece, a battery pole piece, and a battery. Background Art

[0002] Lithium-ion batteries are high-energy-density batteries widely used in mobile communications, electronic devices, electric vehicles, and other fields, and their performance directly affects the user experience of the product. The dry process is a new battery electrode preparation process that has emerged in recent years. In the dry process, the active material, conductive agent, and binder are mixed and then formed into a membrane by roller pressing. The membrane is then composited with the current collector to produce the battery electrode. The dry process does not use solvents, which can avoid the impact of solvents on the service life of the electrode. PTFE (polytetrafluoroethylene) is a commonly used binder material for dry process preparation of battery negative electrode sheets. The ends of the PTFE molecular chain contain C-F bonds. These C-F bonds easily react with the active sites of graphite, the negative electrode active material, during the charge and discharge process of lithium-ion batteries, leading to side reactions. These side reactions not only consume lithium ions and reduce the battery's capacity, but also significantly reduce the initial efficiency of the lithium-ion battery, affecting the battery's first cycle efficiency. Summary of the Invention

[0003] The object of the present invention is to provide a method for preparing a battery pole piece, a battery pole piece and a battery that can reduce the side reaction between PTFE and graphite and improve the initial efficiency of the battery.

[0004] In order to achieve the above objectives, the present invention adopts the following technical solutions:

[0005] A method for preparing a battery electrode comprises the following steps:

[0006] The battery pole pieces are prepared using a dry process, with graphite as the active material and PTFE as the binder;

[0007] soaking the battery electrode in a Lewis acid solution;

[0008] The battery electrodes that have been immersed in the Lewis acid solution are dried.

[0009] Furthermore, the concentration of the Lewis acid solution is 0.1 mol / L to 3 mol / L.

[0010] Furthermore, the temperature of the Lewis acid solution is 20°C to 60°C.

[0011] Furthermore, the battery pole piece is immersed in the Lewis acid solution for 30 minutes to 2 hours.

[0012] Furthermore, when the battery electrode is dried, the drying temperature is 50° C. to 120° C., and the drying time is 1 hour to 2 hours.

[0013] The present invention also provides a battery pole piece, which is prepared using the above-mentioned preparation method. The battery pole piece includes a current collector and a membrane, and the membrane includes an active material, a binder and a conductive agent.

[0014] The present invention also provides a battery comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the negative electrode sheet is the aforementioned battery sheet.

[0015] It can be seen from the above technical solution that for the graphite negative electrode plate prepared by the dry process, the present invention uses Lewis acid to treat the plate in order to reduce the side reaction between PTFE and graphite and improve the first efficiency of the lithium-ion battery. Lewis acid can effectively break the CF bond at the end of the PTFE chain through its strong electron acceptor properties, reduce the side reaction between PTFE and graphite, and thus improve the first cycle efficiency of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 Schematic diagram of the equipment used in the method for preparing a battery electrode according to an embodiment of the present invention.

[0018] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings. DETAILED DESCRIPTION

[0019] The present invention is described in detail below in conjunction with the accompanying drawings. When describing the embodiments of the present invention in detail, for the convenience of explanation, the drawings showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. It should be noted that the drawings are simplified and all use non-precise scales, which are only used to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features; the terms "front", "back", "bottom", "upper", "lower", "front", "back", "left", "right", etc. indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0020] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, it can mean a fixed connection, a detachable connection, or an integral connection; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean internal communication between two components; it can mean a wireless connection or a wired connection. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0021] The dry process is a novel process for preparing battery electrodes. It uses a calendaring process to form a membrane, which is then composited with a current collector to form the electrode. Compared to the traditional wet process, the dry process does not use solvents or coating, thus reducing the impact of solvents on battery life.

[0022] The dry process for preparing electrode sheets mainly includes the following steps: 1. Material mixing: Active materials, conductive agents, binders, and other electrode materials are mixed together and stirred evenly; 2. Material crushing to obtain a powder, such as fiberizing the materials through a crushing device to obtain a powdered material; 3. Rolling the powder into a film to produce a dry-process membrane, that is, rolling the powder into a membrane by rolling; 4. Hot pressing and laminating: The dry-process membrane and current collector are hot-pressed together to produce a battery electrode. For a more detailed description of the dry process, please refer to the Chinese invention patent application with publication number CN 117096265 A.

[0023] The dry process has the advantages of simple preparation process and greater mechanical strength of the electrode. It can avoid the hygroscopicity problem of sodium ferric pyrophosphate, achieve a higher active material content, and improve the compaction density and thickness of the electrode. The dry process mainly relies on the fiberization of polytetrafluoroethylene adhesive to form a network structure to connect the active material, which can greatly avoid the short circuit caused by electrode powder falling during battery manufacturing.

[0024] Polytetrafluoroethylene (PTFE) is a very common binder in dry-process sheeting, while graphite is a very common negative electrode active material in the preparation of lithium-ion battery negative electrodes. When these two materials are used to prepare battery negative electrode sheets through a dry process, because the PTFE molecular chain ends contain C-F bonds, these C-F bonds easily react with the active sites of graphite during the charge and discharge process of the lithium-ion battery, resulting in side reactions. These side reactions consume lithium ions, reduce battery capacity, and reduce the first cycle efficiency (referred to as the first efficiency) of the lithium-ion battery.

[0025] In order to solve the problem that the CF bond at the end of the PTFE binder easily undergoes side reactions with graphite, resulting in a decrease in the initial efficiency of the battery, the inventors proposed a new dry-process battery electrode preparation method. After the dry-process membrane and the current collector are hot-pressed and composited, the composite electrode is further treated with Lewis acid.

[0026] Lewis acids (such as AlCl3 and BF3) are substances that can accept electron pairs. In the present invention, the battery pole piece produced by the dry process is immersed in a Lewis acid. The Lewis acid acts as an electron pair acceptor, forming a coordination bond with the lone electron pair on the F atom, causing the electron cloud distribution of the C-F bond to shift and reduce the bond energy. This electron pair coordination can further polarize the C-F bond at the end of the PTFE, thereby weakening the bond strength and breaking the C-F bond. Simultaneously, the Lewis acid may promote the reaction by stabilizing the reaction intermediates (e.g., generating F- or fluoride complexes).

[0027] The specific reaction pathway during the Lewis acid treatment process is: after the Lewis acid coordinates with the terminal F atom, it may trigger the heterolytic cleavage of the C-F bond to form a carbon cation intermediate and a fluorine-Lewis acid complex (such as generating F- or fluoride complex), such as: C-F+AlCl3→C++[F-AlCl3]-C-F+AlCl3→C++[F-AlCl3]-.

[0028] The present invention utilizes the electron acceptor properties of Lewis acid to effectively break the C-F bond at the end of the PTFE molecular chain, prevents the C-F bond from reacting with the active site of graphite, reduces side reactions between PTFE and graphite, reduces unnecessary lithium ion consumption during the charge and discharge process of the lithium ion battery, and improves the initial efficiency of the lithium ion battery.

[0029] The steps of the method for preparing the battery electrode of the present invention are as follows:

[0030] The battery negative electrode is produced by a dry process;

[0031] Immerse the negative electrode of the battery in the Lewis acid solution for a certain period of time;

[0032] The battery electrode piece soaked in the Lewis acid solution is dried to remove the residual solvent (Lewis acid) to obtain the final battery negative electrode piece.

[0033] The Lewis acid of the present invention includes boron trifluoride (BF3), aluminum chloride (AlCl3), aluminum fluoride (AlF3), etc. The concentration of the Lewis acid solution used is 0.1 mol / L to 3 mol / L.

[0034] The battery negative electrode plate can be immersed in the Lewis acid solution for 30 minutes to 2 hours, and the temperature of the Lewis acid solution during the immersion can be 20°C to 60°C. By immersing the battery plate in the Lewis acid solution of a specific temperature and concentration for a certain period of time, the C-F bond at the end of the PTFE chain is effectively broken while avoiding excessive degradation of the PTFE.

[0035] When drying the battery pole pieces, the drying temperature can be 50°C to 120°C, and the drying time is 1 hour to 2 hours.

[0036] The present invention is further described below by way of specific examples. Unless otherwise specified, the reagents, materials, and instruments used in the following description are all conventional reagents, materials, and instruments, which are commercially available. The reagents involved can also be synthesized by conventional synthesis methods.

[0037] Example 1

[0038] Figure 1 Schematic diagram of the Lewis acid electrode processing equipment of this embodiment. Figure 1 As shown, the device includes a pole piece unwinding mechanism 1, a first pole piece pulling mechanism 2, a solvent tank 3, a baking machine 4, a second pole piece pulling mechanism 5 and a pole piece winding mechanism 6 which are arranged in sequence.

[0039] A roll of battery negative electrode sheets prepared using a dry process is placed on a sheet unwinding mechanism 1, where it is unwound. A first traction mechanism 2 is used to pull the negative electrode sheets unwound by the unwinding mechanism 1. The negative electrode sheets are immersed in a solvent tank 3, which contains a Lewis acid solution maintained at a set temperature. A drying machine 4 is used to dry the immersed negative electrode sheets. A second traction mechanism 5 is used to pull the dried negative electrode sheets, which are then rewound by a sheet rewinding mechanism 6.

[0040] The battery electrode preparation method of this embodiment includes the following steps:

[0041] The battery negative electrode sheet is prepared by a dry process, wherein the negative electrode active material used in the battery negative electrode sheet is graphite and the binder used is PTFE;

[0042] Soak the negative electrode of the battery in a 1 mol / L aluminum chloride solution at 40°C for 1 hour.

[0043] The battery negative electrode sheet that has been soaked in Lewis acid is dried.

[0044] The battery negative electrode prepared in this example was assembled with a conventional positive electrode and separator into a battery, and the battery cycle performance test was performed. The cycle performance test was conducted at 25°C for charge and discharge. The battery prepared in this example achieved an initial efficiency of 91% and a coulombic efficiency of 99.8% during the first charge and discharge. In the cycle performance test, the battery capacity retention rate was 90% after 300 cycles.

[0045] Example 2

[0046] The difference between this embodiment and embodiment 1 is that the Lewis acid solution in this embodiment is a boron trifluoride solution.

[0047] The battery electrode preparation method of this embodiment includes the following steps:

[0048] The battery negative electrode sheet is prepared by a dry process, wherein the negative electrode active material used in the battery negative electrode sheet is graphite and the binder used is PTFE;

[0049] Soak the negative electrode of the battery in a 2 mol / L boron trifluoride solution at 50°C for 1.5 hours.

[0050] The battery negative electrode sheet that has been soaked in Lewis acid is dried.

[0051] The battery negative electrode sheet produced in this example was assembled with a conventional positive electrode sheet and separator into a battery, and the battery cycle performance test was conducted. The battery achieved an initial efficiency of 93% during the first charge and discharge cycle. In the cycle performance test, the battery capacity retention rate was 91% after 300 cycles.

[0052] Example 3

[0053] The difference between this embodiment and embodiment 1 is that the Lewis acid solution in this embodiment is an aluminum fluoride solution.

[0054] The battery electrode preparation method of this embodiment includes the following steps:

[0055] The battery negative electrode sheet is prepared by a dry process, wherein the negative electrode active material used in the battery negative electrode sheet is graphite and the binder used is PTFE;

[0056] Soak the negative electrode of the battery in a 0.5 mol / L aluminum fluoride solution at 60°C for 2 hours.

[0057] The battery negative electrode sheet that has been soaked in Lewis acid is dried.

[0058] The battery negative electrode sheet prepared in this embodiment was assembled with a conventional battery positive electrode sheet and a separator to form a battery, and the battery cycle performance test was conducted. The battery's initial efficiency during the first charge and discharge was 94%.

[0059] The thermal stability test of the negative electrode of the battery of Example 3 was performed. The thermal stability test was performed using thermogravimetric analysis (TGA). The test steps are as follows:

[0060] Sample preparation: Dry the battery negative electrode to remove moisture, grind into uniform powder or flakes (particle size ≤ 200 mesh recommended), and weigh the sample (usually 5-20 mg);

[0061] Instrument settings: Set the starting temperature (e.g., 30°C), ending temperature (800–1000°C), and heating rate (e.g., 10–20°C / min); select the carrier gas type (e.g., N2 for thermal decomposition, air for oxidation) and control the flow rate (e.g., 150 mL / min);

[0062] Test and data collection: Place the sample flat in a crucible (materials can be platinum, ceramics, etc.), record the TG curve (mass change) and DTG curve (mass change rate), and mark the weight loss starting temperature (T i ) and final temperature (T).

[0063] Thermal stability tests showed that the mass loss rate of the PTFE binder treated with Lewis acid at 300°C was reduced by 6%.

[0064] Comparative Example

[0065] The difference between the comparative example and the aforementioned embodiment is that the negative electrode plate of the battery has not been treated with Lewis acid, and the rest are the same. The negative electrode plate of the battery that has not been treated with Lewis acid solution and the conventional positive electrode plate and diaphragm are assembled into a battery, and the battery cycle performance test is carried out. The first efficiency of the battery of the comparative example in the first charge and discharge is 78%, and the coulomb efficiency is 98%. In the cycle performance test, the battery capacity retention rate is 85% after 300 cycles. The first efficiency of the battery prepared in Examples 1-3 is at least 13% higher than that of the battery of the comparative example. The cycle test results of the comparative example and Example 1 are shown in the following table.

[0066] Serial number Battery cell number Formation charging Capacity-divided charging Discharge by capacity Charging capacity Discharge capacity First effect 1 Comparative Example Battery 01 2.2053 3.3149 4.3155 155.89 121.87 78.18％ 2 Comparative Example Battery 02 2.2056 3.3779 4.27 157.68 120.59 76.48％ 3 Comparative Example Battery 03 2.2047 3.3398 4.3345 156.58 122.41 78.18％ 4 Comparative Example Battery 04 2.2053 3.3231 4.3243 156.13 122.12 78.22％ 5 Comparative Example Battery 05 2.2059 3.358 4.3692 157.13 123.39 78.53％ 6 Example 1 Battery 01 2.1368 3.2554 4.88033 157.30 142.37 90.51％ 7 Example 1 Battery 02 2.1371 3.2473 4.8710 157.07 142.09 90.47％ 8 Example 1 Battery 03 2.1363 3.2672 4.8465 157.63 141.38 89.69％ 9 Example 1 Battery 04 2.1366 3.3762 4.9299 160.82 143.81 89.43％ 10 Example 1 Battery 05 2.1371 3.3125 4.9898 158.97 145.56 91.56％

[0067] The internal resistance of the batteries of the comparative example and Example 2 was tested. The internal resistance of the battery of Example 2 was reduced by 10% compared with the internal resistance of the battery of the comparative example.

[0068] The above test results show that the first efficiency (more than 90%) and battery capacity retention rate of batteries made from battery negative electrode sheets treated with Lewis acid are significantly improved compared to the first efficiency (less than 80%) and battery capacity retention rate of batteries made from battery negative electrode sheets that have not been treated with Lewis acid. By improving the first efficiency, the overall performance and service life of lithium-ion batteries can be improved, and their market competitiveness can be enhanced. Moreover, the processing method of the present invention is simple, efficient, and moderately cost-effective, and can be directly applied in the process of preparing battery sheets, reducing complex operations in the production process.

[0069] The present invention involves soaking the negative electrode of a battery produced using a dry process in a Lewis acid treatment. This Lewis acid breaks the C-F bonds at the ends of the PTFE molecular chains, halting the reaction after the initial break. Internal C-F bonds remain inactive, leading to a stable state and exposing more fluoride or hydride functional groups on the electrode surface. X-ray photoelectron spectroscopy (XPS) analysis reveals the appearance of new nitrogen (N) and hydrogen (H) functional groups on the PTFE surface after Lewis acid treatment. The presence of these new functional groups prevents further C-F bond reactions, preventing side reactions with graphite and improving the initial efficiency of the lithium-ion battery.

[0070] Because Lewis acid breaks C-F bonds and reduces the amount of F, the fluorine content on the PTFE surface is significantly reduced after Lewis acid treatment, from the original 70% to 40%-50%, achieving a surface modification effect. Water contact angle tests show that the hydrophilicity of the electrode surface is enhanced after Lewis acid treatment, with the contact angle dropping from the original 110° to approximately 90°.

[0071] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a battery electrode, characterized in that: The following steps are involved: The battery pole pieces are prepared using a dry process, with graphite as the active material and PTFE as the binder; soaking the battery electrode in a Lewis acid solution; The battery electrodes that have been immersed in the Lewis acid solution are dried.

2. The battery cell winding device according to claim 1, characterized in that: The concentration of the Lewis acid solution is 0.1 mol / L to 3 mol / L.

3. The method for preparing a battery electrode according to claim 1, wherein: The temperature of the Lewis acid solution is 20°C to 60°C.

4. The method for preparing a battery electrode according to claim 1, wherein: The battery pole piece is immersed in the Lewis acid solution for 30 minutes to 2 hours.

5. The method for preparing a battery electrode according to claim 1, wherein: When the battery pole piece is dried, the drying temperature is 50° C. to 120° C., and the drying time is 1 hour to 2 hours.

6. A battery pole piece, characterized in that: The battery electrode is prepared using the preparation method according to any one of claims 1 to 5, wherein the battery electrode comprises a current collector and a membrane, and the membrane comprises an active material, a binder and a conductive agent.

7. A battery comprising a positive electrode sheet, a negative electrode sheet and a separator, characterized in that: The negative electrode plate is the battery plate according to claim 6.

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