Dry-method electrode, preparation method and battery

Abstract

The invention discloses a dry-method electrode, a preparation method and a battery. The preparation method comprises the following steps: S1, uniformly mixing a conductive agent and an active substance; s2, adding a binder into the mixture of the conductive agent and the active substance, and premixing; s3, performing fibrosis treatment on the premixed mixture of the conductive agent, the active substance and the binder; s4, pressing the fiberized material into a diaphragm, and combining the diaphragm with a current collector to form a battery pole piece; wherein the active substance is a positive active material or a negative active material; the conductive agent is a mixed compound conductive agent formed by at least two different types of conductive materials. According to the invention, by premixing the conductive agent and the active substance and using the compound conductive agent, the dry-method electrode process realizes collaborative optimization in the aspects of conductivity, structural stability, process efficiency, cost control and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a dry electrode, a preparation method and a battery. Background Art

[0002] Conductive agent is an important component of lithium-ion batteries. Although it accounts for a small proportion in the battery, it greatly affects the performance of lithium-ion batteries and plays a very important role in improving battery cycle performance, capacity utilization, and rate performance.

[0003] In traditional wet processes, the application of conductive agents is well-established, resulting in excellent initial efficiency and rate performance for lithium batteries. However, in dry electrode preparation, the lack of solvents makes it difficult to evenly disperse the conductive agent, leading to localized agglomeration. This often results in incomplete initial Coulombic efficiency, poor rate performance, and significantly lower electrode conductivity than in wet processes. Therefore, a process formula for compounding conductive agents for dry electrode preparation is urgently needed to address these technical issues. Summary of the Invention

[0004] The purpose of the present invention is to provide a dry electrode, a preparation method and a battery to improve the performance of the battery.

[0005] To achieve the above object, the technical solution provided by the present invention is:

[0006] The first aspect of the present application provides a method for preparing a dry electrode, comprising the following steps:

[0007] S1: Mix the conductive agent and active material evenly;

[0008] S2: adding a binder to the mixture of the conductive agent and the active material for pre-mixing;

[0009] S3: Fiberizing the pre-mixed mixture of the conductive agent, active material and binder;

[0010] S4: pressing the fiberized material into a membrane, and combining the membrane with a current collector to form a battery electrode;

[0011] Wherein, the active material is a positive electrode active material or a negative electrode active material; and the conductive agent is a mixed composite conductive agent formed by at least two different types of conductive materials.

[0012] To optimize the above technical solutions, specific limitations also include:

[0013] The conductive agent is nano-scale mixed particles.

[0014] In the mixture of the conductive agent, the active material and the binder, the mass fraction of the conductive agent accounts for 1 to 5%, and the mass fraction of the binder accounts for 1 to 3%.

[0015] The mixed composite conductive agent formed by at least two different types of conductive materials is selected from one of a composite of vapor-grown carbon fiber and conductive carbon black, a composite of carbon nanotubes and vapor-grown carbon fiber, a composite of carbon nanotubes and conductive carbon black, and a composite of conductive graphite and vapor-grown carbon fiber.

[0016] Furthermore, the mixed composite conductive agent formed by at least two different types of conductive materials is a composite of conductive carbon black and vapor-grown carbon fibers.

[0017] Preferably, the conductive carbon black accounts for 30% to 50% by mass in the compound of conductive carbon black and vapor-grown carbon fiber.

[0018] The pre-mixing in step S2 adopts low shear force and low speed coating: shear linear speed 3-5 m / min, temperature <20° C., time 200-300 s.

[0019] The fiberization treatment in step S3 adopts high-speed coating with high shear force: the initial temperature is set to <14°C, a binder is added, and the shear line speed is set to 10-20 m / min and the time is 300-600 s; after the temperature is raised to ≥40°C, the shear line speed is set to 30 m / min and the time is 600-1000 s, and the shearing is stopped after the temperature reaches 60°C.

[0020] The second aspect of the present application provides a dry electrode prepared by the above method.

[0021] The third aspect of the present application provides a battery comprising the above-mentioned dry electrode.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] In response to the problems of low first coulombic efficiency and poor rate performance of batteries prepared by dry-process electrodes, the present invention redesigns the conductive agent ratio and selects materials from the perspective of compounding multiple conductive agents. Through compounding different groups and adding different proportions, a process scheme is obtained to significantly improve the first efficiency of the dry process and significantly improve battery performance. Among them, the compounding of conductive carbon black and vapor-grown carbon fibers is the preferred scheme. After the conductive carbon black and vapor-grown carbon fibers are compounded, multiple contact modes are formed. The conductive fibers formed can be better coated in the conductive grid and can reduce the polarization problem of lithium batteries. The compounding of the two can reduce the overall resistivity of the electrode and improve the electron transmission efficiency.

[0024] The present invention also optimizes the process of preparing electrodes by a dry process. Before adding the binder, the conductive agent is first mixed, stirred and dispersed with the active material to avoid agglomeration of the conductive agent due to the addition of the binder. After the conductive agent and the active material are stably coated, strong fiberization is started to obtain a better film-forming effect.

[0025] The present invention achieves synergistic optimization of the dry electrode process in terms of conductivity, structural stability, process efficiency and cost control by premixing the conductive agent with the active material and using a compound conductive agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 : Schematic diagram of the steps of the preparation method of the dry electrode of the present invention. DETAILED DESCRIPTION

[0027] The above contents of the present invention are further described in detail below in the form of specific implementation methods, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments. All technologies implemented based on the above contents of the present invention belong to the scope of the present invention.

[0028] The experimental methods used in the following examples are conventional methods unless otherwise specified, and the reagents, methods and equipment used are conventional reagents, methods and equipment in the art unless otherwise specified.

[0029] The present invention provides a method for preparing a dry electrode, such as Figure 1 As shown, the following steps are included:

[0030] S1: Mix the conductive agent and active material evenly;

[0031] S2: adding a binder to the mixture of the conductive agent and the active material for pre-mixing;

[0032] S3: Fiberizing the pre-mixed mixture of the conductive agent, active material and binder;

[0033] S4: Pressing the fiberized material into a membrane, and combining the membrane with a current collector to form a battery electrode;

[0034] Among them, the active material is a positive electrode active material or a negative electrode active material; the conductive agent is a mixed composite conductive agent formed by at least two different types of conductive materials, and the conductive agent is a nano-scale mixed particle.

[0035] In the mixture of the conductive agent, the active material and the binder, the mass fraction of the conductive agent accounts for 1 to 5%, and the mass fraction of the binder accounts for 1 to 3%.

[0036] The primary function of the conductive agent is to improve electronic conductivity. To ensure that the battery has good charge and discharge performance, it collects microcurrents between active materials and between active materials and current collectors to reduce the contact resistance of the electrodes and accelerate the movement rate of electrons. In addition, in the preparation of dry electrodes, the conductive agent is also important for improving the processability of the electrode sheets, promoting the infiltration of the electrolyte into the electrode sheets, and can also effectively increase the migration rate of lithium ions in the electrode material, reduce polarization, and thus improve the charge and discharge efficiency and service life of the lithium battery.

[0037] A single conductive agent can only carry a single conductive structure network and cannot fully exert the conductive performance of the dry electrode. The present invention uses two or more conductive agents in combination to construct an optimal conductive grid between conductive particles of various different structures. It can have a significant optimization effect on the electrodes produced by the dry process, thereby improving battery performance.

[0038] The mixed composite conductive agent of the present invention is formed by at least two different types of conductive materials, wherein the conductive materials can be selected from: two of: conductive carbon black (SP), vapor grown carbon fiber (VGCF), carbon nanotubes (CNT), graphene (GN) or conductive graphite.

[0039] In some preferred embodiments, the mixed composite conductive agent formed by at least two different types of conductive materials is selected from one of a composite of vapor-grown carbon fiber and conductive carbon black, a composite of carbon nanotubes and vapor-grown carbon fiber, a composite of carbon nanotubes and conductive carbon black, and a composite of conductive graphite and vapor-grown carbon fiber. The preferred composite system provided by the present invention is shown in Table 1. Different schemes can be selected according to whether the electrode system is a positive electrode or a negative electrode.

[0040] Table 1

[0041]

[0042]

[0043] The pre-mixing in step S2 adopts low-shear-force, low-speed coating; the fiberization treatment in step S3 adopts high-shear-force, high-speed coating.

[0044] Due to the different types of conductive agents, materials, morphologies and particle sizes, the mixing order of adding conductive agents, the amount of conductive agents added and the composite state of different types of conductive agents all have different effects on lithium-ion batteries. In the present invention, in the process of preparing electrodes using a dry process, the conductive agent is first mixed and stirred with the active material before the binder is added to avoid the addition of the binder causing the conductive agent to agglomerate. At the same time, the linear speed of pre-mixing should not be too large. Compared with the active material and the binder, the particle size of the conductive agent has a smaller molecular weight and the morphology is more easily destroyed. Therefore, after the conductive agent and the active material are stably coated, strong fiberization is started to obtain a better film-forming effect.

[0045] In some particularly preferred embodiments, the mixed composite conductive agent formed by at least two different types of conductive materials is a composite of conductive carbon black and vapor-grown carbon fibers.

[0046] In some embodiments, the conductive carbon black accounts for 30% to 50% by weight in the compound of the conductive carbon black and the vapor-grown carbon fiber.

[0047] Conductive carbon black (SP) has a small particle size and forms a dense conductive network. After compounding with vapor-grown carbon fiber (VGCF), it has multiple contact modes such as line-line contact, point-line contact, and point-point contact. The conductive fibers formed can be better coated in the conductive grid. SP fills the tiny gaps between the active material particles through point contact to form a local conductive network. The fibrous structure of VGCF provides a long-range conductive path, connecting the dispersed active material and carbon black particles to form a continuous three-dimensional conductive network. At the same time, VGCF has high electrical and thermal conductivity, which can reduce the polarization problem of lithium batteries. Its aspect ratio is relatively large. During the cycle of lithium batteries, even if corresponding structural changes occur between the active material particles, the conductive network is not affected and will not affect the performance of the battery. The combination of the two can reduce the overall resistivity of the electrode and improve the efficiency of electron transmission.

[0048] In terms of structural stability, the fibrous structure of VGCF forms a skeleton support in the electrode, enhancing the tensile strength and flexibility of the electrode membrane and reducing cracks caused by shear force or rolling during processing; the stable coating of SP and active substances reduces the interfacial contact resistance and reduces the risk of particle shedding during the fiberization process.

[0049] The present invention also provides a dry electrode prepared by the method.

[0050] The present invention also provides a battery comprising the above-mentioned dry-process electrode.

[0051] The positive electrode active materials involved in the present invention can be exemplarily nickel cobalt manganese (NCM), lithium iron phosphate (LFP), lithium manganese oxide (LMO), lithium cobalt oxide, lithium manganese iron phosphate (LMFP), etc., and the negative electrode active materials can be exemplarily carbon materials, silicon-doped negative electrodes, and carbon materials include artificial graphite, natural graphite or a combination thereof.

[0052] The binder involved in the present invention can be illustratively one or more of polytetrafluoroethylene (PTFE), polytetrafluorovinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA) and polyacrylonitrile (PAN).

[0053] The technical solution of the present invention is further described in detail below with reference to specific embodiments:

[0054] Example 1

[0055] A dry electrode, the preparation method of which comprises the following steps:

[0056] (1): The conductive agent and the active material are mixed uniformly; the conductive agent is a compound of nano-scale mixed particles of conductive carbon black (SP) and vapor-grown carbon fiber (VGCF), and the conductive carbon black (SP) and vapor-grown carbon fiber (VGCF) are compounded in a mass ratio of 5:5; the active material is artificial graphite;

[0057] (2) Adding a binder to the mixture of the conductive agent and the active material for premixing; the binder is polytetrafluoroethylene (PTFE), and the premixing is performed by low shear force and low speed coating, with a shear line speed of 3 to 5 m / min, a temperature of <20°C, and a time of 200 to 300 s;

[0058] (3): The pre-mixed mixture of the conductive agent, active material and binder is subjected to a fiberization treatment. The fiberization treatment adopts a high-speed coating with a high shear force. The initial temperature is less than 14°C. The binder is added and the shear line speed is set to 10-20 m / min and the time is 300-600 s. After the temperature is raised to ≥40°C, the shear line speed is set to 30 m / min and the time is 600-1000 s. After the temperature reaches 60°C, the equipment is turned off and the fiberization step is completed.

[0059] (4): The fiberized material is pressed into a membrane, and the membrane is combined with a current collector to form a battery negative electrode; the current collector is made of copper foil.

[0060] In the mixture of the conductive agent, the active material and the binder, the mass fraction of the conductive agent accounts for 3%, and the mass fraction of the binder accounts for 2%.

[0061] Example 2

[0062] A dry-process electrode is prepared by the same method as in Example 1, except that conductive carbon black (SP) and vapor-grown carbon fiber (VGCF) are compounded in a mass ratio of 3:7.

[0063] Example 3

[0064] A dry-process electrode is prepared by the same method as in Example 1, except that conductive carbon black (SP) and vapor-grown carbon fiber (VGCF) are compounded in a mass ratio of 1:9.

[0065] Example 4

[0066] A dry-process electrode is prepared by the same method as in Example 1, except that conductive carbon black (SP) and vapor-grown carbon fiber (VGCF) are compounded in a mass ratio of 7:3.

[0067] Example 5

[0068] A dry-process electrode, the preparation method of which is basically the same as that of Example 1, except that the conductive agent is a compound of nano-scale mixed particles of conductive graphite and vapor-grown carbon fiber (VGCF), and the conductive graphite and vapor-grown carbon fiber (VGCF) are compounded in a mass ratio of 5:5.

[0069] Comparative Example 1

[0070] A dry-process electrode is prepared by a method substantially similar to that of Example 1, except that only conductive carbon black (SP) is used as the conductive agent.

[0071] Comparative Example 2

[0072] A dry electrode is prepared by the same method as in Example 5, except that the conductive agent is only conductive graphite.

[0073] Battery Assembly Instructions:

[0074] Material preparation

[0075] Positive electrode: lithium sheet (as counter electrode and reference electrode).

[0076] Negative electrode: dry-process negative electrode sheet prepared in Examples 1-5 and Comparative Examples 1-2.

[0077] Electrolyte: 1M LiPF6, EC / DMC (volume ratio 1:1).

[0078] Diaphragm: Celgard 2325 polypropylene / polyethylene composite membrane.

[0079] Assembly steps

[0080] Electrode sheet cutting: Cut the negative electrode sheet into discs with a diameter of 14 mm.

[0081] Battery shell assembly:

[0082] Place the negative electrode shell, lithium sheet, separator (with electrolyte added), negative electrode sheet, gasket, spring sheet and positive electrode shell in the CR2032 button battery shell in sequence.

[0083] Packaging: Use button battery packaging machine to press and package.

[0084] Test conditions

[0085] Charge and discharge test: voltage range 0.01-2.0V, charge and discharge rate 0.1C-2C.

[0086] Rate performance test: gradually increase from 0.1C to 2C, and record the capacity retention rate.

[0087] First Coulombic efficiency test: record the first charge and discharge capacity and calculate ICE.

[0088] The dry-process electrodes prepared in each embodiment and comparative example were made into batteries according to the above battery assembly method, and their performance was tested. The test results are shown in Table 2.

[0089] Table 2

[0090]

[0091]

[0092] The test results show that:

[0093] By comparing Examples 1 to 4, it can be seen that as the proportion of conductive carbon black (SP) increases, the first efficiency is improved. However, since the conductivity of conductive carbon black (SP) is relatively poor compared to vapor grown carbon fiber (VGCF), its surface resistance tends to increase, and when the proportion of conductive carbon black (SP) rises to a certain proportion, the first efficiency will tend to stabilize or even decrease; therefore, the higher the content, the better, so the preferred proportion is 30% to 50% of conductive carbon black (SP).

[0094] By comparing Example 1 and Comparative Example 1, it can be seen that the conductive agent prepared by compounding conductive carbon black (SP) and vapor grown carbon fiber (VGCF) has a better primary effect than the conductive agent prepared by simply using conductive carbon black (SP), has a smaller electrode resistance, and has better rate performance.

[0095] By comparing Example 5 and Comparative Example 2, it can be seen that the conductive agent prepared by compounding conductive graphite and vapor-grown carbon fiber (VGCF) has better electrical properties than the conductive agent prepared by simply using conductive graphite.

[0096] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modification, equivalent replacement and improvement made by any technician familiar with the profession to the above embodiment without departing from the scope of the technical solution of the present invention and based on the technical essence of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a dry electrode, characterized in that: The following steps are involved: S1: Mix the conductive agent and active material evenly; S2: adding a binder to the mixture of the conductive agent and the active material for pre-mixing; S3: Fiberizing the pre-mixed mixture of the conductive agent, active material and binder; S4: pressing the fiberized material into a membrane, and combining the membrane with a current collector to form a battery electrode; Wherein, the active material is a positive electrode active material or a negative electrode active material; and the conductive agent is a mixed composite conductive agent formed by at least two different types of conductive materials.

2. The method for preparing a dry electrode according to claim 1, wherein: The conductive agent is nano-scale mixed particles.

3. The method for preparing a dry electrode according to claim 1, wherein: In the mixture of the conductive agent, the active material and the binder, the mass fraction of the conductive agent accounts for 1 to 5%, and the mass fraction of the binder accounts for 1 to 3%.

4. The method for preparing a dry electrode according to claim 1, wherein: The mixed composite conductive agent formed by at least two different types of conductive materials is selected from one of a composite of vapor-grown carbon fiber and conductive carbon black, a composite of carbon nanotubes and vapor-grown carbon fiber, a composite of carbon nanotubes and conductive carbon black, and a composite of conductive graphite and vapor-grown carbon fiber.

5. The method for preparing a dry electrode according to claim 4, wherein: The mixed composite conductive agent formed by at least two different types of conductive materials is a composite of conductive carbon black and vapor-grown carbon fibers.

6. The method for preparing a dry electrode according to claim 5, wherein: The conductive carbon black accounts for 30% to 50% by mass in the compound of the conductive carbon black and the vapor-grown carbon fiber.

7. The method for preparing a dry electrode according to claim 1, wherein: The pre-mixing in step S2 adopts low shear force and low speed coating: shear linear speed 3-5 m / min, temperature <20° C., time 200-300 s.

8. The method for preparing a dry electrode according to claim 1, wherein: The fiberization treatment in step S3 adopts high-speed coating with high shear force: the initial temperature is set to <14°C, a binder is added, and the shear line speed is set to 10-20 m / min and the time is 300-600 s; after the temperature is raised to ≥40°C, the shear line speed is set to 30 m / min and the time is 600-1000 s, and the shearing is stopped after the temperature reaches 60°C.

9. A dry electrode prepared by the method according to any one of claims 1 to 8.

10. A battery, characterized in that: Containing the dry electrode according to claim 9.

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