A dry electrode pole piece, and a preparation method and application thereof

Abstract

The present application belongs to the technical field of electrode sheet, and particularly relates to a dry electrode sheet and a preparation method and application thereof. The preparation method provided by the present application comprises the following steps: mixing a liquid binder, an active material and a conductive agent to obtain a block-shaped solid; crushing plant fibers into plant fiber filaments with an equal length of 3-10 mm, and then high-speed mixing the plant fiber filaments with the block-shaped solid to obtain a black solid; drying the black solid to obtain a dry electrode raw material; and coating the dry electrode raw material on a current collector and rolling to obtain a dry electrode sheet. The present application retains the uniformity of wet mixing to a large extent, and also retains the advantages of dry electrode sheets, without the need to use toxic solvent NMP and without the need to use expensive coating machines. The present application uses plant fibers as a material for supporting a dry electrode film, and uses a binder as an electrode binder, and the two raw materials are green, healthy, environmentally friendly and low in cost.

Description

Technical Field

[0001] This invention belongs to the field of electrode technology, specifically relating to a dry electrode, its preparation method, and its application. Background Technology

[0002] Traditional wet electrode fabrication requires the use of the toxic solvent NMP, which can significantly impact the environment. Furthermore, compared to dry electrodes, wet electrodes require coating, increasing costs. Dry electrode technology, on the other hand, is solvent-free, eliminating the need for toxic NMP, simplifying the manufacturing process, and eliminating the need for coating, thus reducing electrode production costs to some extent.

[0003] Currently, the most mature dry electrode technology is PTFE technology, which mainly utilizes the fibrous properties of PTFE to prepare dry electrode films. For example, patent document CN115036462A discloses a pure dry-process sodium-ion battery anode, its preparation method, and the battery thereof. The preparation method of the pure dry-process sodium-ion battery anode includes the following steps: adding hard carbon powder to a planetary mixer, then adding carbon black to artificial graphite powder and stirring, then adding modified PTFE powder and stirring, then fibrillating the mixed powder, feeding it into an open mill, extruding a continuous basic anode sheet from two rollers, then extending the basic anode sheet through a multi-stage calender, and finally placing the extended electrode sheet on both sides of aluminum foil for thermal bonding, slitting, and die-cutting. Patent document CN114725320A discloses a method for preparing dry electrode sheets, comprising the following steps: preparing a first mixture containing an electrode active material and a conductive agent at a first temperature; preparing a second mixture containing the first mixture and a non-fibrillated binder at a second temperature; applying shear force to the second mixture to fibrousize it, thereby obtaining a third mixture; preheating the third mixture; applying preforming pressure in multiple directions to the preheated third mixture to prepare a preformed self-supporting electrode film; subjecting the preformed self-supporting electrode film to hot rolling thinning to prepare a self-supporting electrode film; and feeding the prepared self-supporting electrode film and carbon-coated foil into a roller mill to obtain a dry electrode sheet.

[0004] However, PTFE technology needs to be carried out in a high-temperature and high-pressure tank, which is a relatively complex process. Summary of the Invention

[0005] This invention provides a dry electrode sheet, its preparation method, and its application. The purpose is to solve the problem that in the prior art, the dry electrode technology using PTFE technology needs to be carried out in a high-temperature and high-pressure tank, which is a relatively complex process.

[0006] In view of the above-mentioned technical defects, one objective of the present invention is to provide a method for preparing a dry electrode sheet, a second objective of the present invention is to provide a dry electrode sheet obtained by the preparation method, and a third objective of the present invention is to provide an application of the dry electrode sheet.

[0007] In a first aspect, the present invention provides a method for preparing a dry electrode sheet, comprising the following steps:

[0008] S1: Mix the liquid binder, active material, and conductive agent to obtain a block solid;

[0009] S2: Break the plant fiber into plant fiber filaments with a uniform length of 3-10mm, and then mix them with the block solid to obtain a black solid;

[0010] S3: Dry the black solid to obtain dry electrode raw material;

[0011] S4: Coat the dry electrode material onto the current collector and roll it to obtain the dry electrode sheet.

[0012] In this invention, plant fiber serves as the primary material supporting the dry electrode membrane, while the binder is a secondary material. Plant fiber has a high cellulose content, excellent mechanical properties, and high elongation at break, thus providing some support. Plant fiber is extracted from plants, making it an environmentally friendly and pollution-free raw material that poses no harm to the environment. The mechanical properties of plant fiber are similar to those of synthetic fibers, but at a lower cost. The binder primarily functions as a binder in the dry electrode membrane, bonding the plant fiber, active material, and current collector together to form a stable structure.

[0013] In the preparation process, liquid binder, active material, and conductive agent are first mixed at high speed. Then, plant fibers crushed using a crusher are added, and the mixture is mixed at high speed again. The resulting sample is a black, blocky sample with fibrous filaments. The sample is then dried, crushed, and ground, coated onto a current collector, and rolled using a roller press to obtain a dry electrode sheet with good flexibility and adhesion. This manufacturing process is simple and low-cost. The coating process described in this invention refers to placing or laying the dry electrode material onto the current collector.

[0014] The mechanism of this invention involves the combination of plant fibers and a liquid binder, allowing the active material to adhere to a current collector such as copper or aluminum foil in a relatively flexible membrane form. Plant fibers have a high cellulose content and good mechanical properties, supporting the active material, but they lack adhesive properties; therefore, a binder is introduced. The liquid binder bonds the plant fibers and the active material together, and rolling can form a complete support membrane. Simultaneously, the adhesive properties of the binder bond the membrane to the current collector, forming a dry electrode sheet.

[0015] The liquid binder described in this invention can be a solution formed by dissolving a solid binder in a solvent, or it can be a binder that is itself liquid. When mixing the materials initially, the binder is added in liquid form, especially as an aqueous solution, which constitutes wet mixing. This mixing method allows for more thorough and uniform mixing of the sample. Afterward, the prepared sample is dried to remove excess moisture. Therefore, the electrode sheet prepared subsequently retains the characteristics of a dry electrode and also possesses the advantages of a dry electrode, namely, like other dry electrodes, it can improve battery life and energy density.

[0016] In this invention, plant fibers need to be broken into plant fiber filaments with an average length of 3-10 mm. When the average length of the plant fiber filaments is greater than 10 mm, it is difficult for the plant fiber filaments to mix evenly with the active material. When the average length of the plant fiber filaments is less than 3 mm, it is difficult for the plant fiber filaments to interweave with each other to play a connecting role and to support the active material to prepare the electrode sheet.

[0017] In the above preparation method, as a preferred embodiment, the plant fiber includes one or more of coconut shell fiber, flax fiber, bamboo fiber, and cotton fiber, with coconut shell fiber being preferred;

[0018] In this invention, the planting area of ​​flax fiber, bamboo fiber, cotton fiber, etc. is limited, and coconut shell fiber is an agricultural and forestry waste, which is beneficial to environmental protection.

[0019] In the above preparation method, as a preferred embodiment, in S1, the liquid binder includes one or both of sodium alginate aqueous solution and epoxy resin binder.

[0020] Furthermore, the sodium alginate aqueous solution has a mass fraction of 8-15% (e.g., 9%, 11%, 13%).

[0021] In the above preparation method, as a preferred embodiment, in S1 and S2, when the liquid binder is an aqueous solution of sodium alginate, based on the total mass of the plant fiber, the solute of the liquid binder, the active substance and the conductive agent, the amount of the plant fiber is 1-5% (e.g., 2%, 3%, 4%), the amount of the solute of the liquid binder is 1-5% (e.g., 2%, 3%, 4%), the amount of the active substance is 87-97% (e.g., 88%, 92%, 95%), and the amount of the conductive agent is 1-3% (e.g., 1.5%, 2.5%). Alternatively, when the liquid adhesive is an epoxy resin adhesive, based on the total mass of the plant fiber, liquid adhesive, active material, and conductive agent, the amount of plant fiber is 1-5% by weight, the amount of liquid adhesive is 1-5%, the amount of active material is 87-97%, and the amount of conductive agent is 1-3%.

[0022] In the above preparation method, as a preferred embodiment, the active material includes one of a positive electrode active material and a negative electrode active material;

[0023] And / or, the current collector includes one of copper foil and aluminum foil.

[0024] In this invention, there are no particular limitations on the positive electrode active material, negative electrode active material, conductive agent, etc., used, and they can be commonly used materials in the field.

[0025] Furthermore, the positive electrode active materials include, but are not limited to, lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate;

[0026] Furthermore, the negative electrode active materials include, but are not limited to, natural graphite, artificial graphite, soft carbon, hard carbon, etc.

[0027] Furthermore, conductive agents include, but are not limited to, conductive carbon black, conductive graphite, carbon fiber, carbon nanotubes, and graphene.

[0028] In the above preparation method, as a preferred embodiment, in S1, the mixing time is 10-50 min (e.g., 15 min, 20 min, 25 min, 35 min, 45 min), and the rotation speed is 1000-3000 rpm (e.g., 1100 rpm, 1500 min, 1800 min, 2000 min, 2200 min, 2500 rpm, 2800 rpm, 2900 rpm);

[0029] In S2, the mixing time is 10-45 min (e.g., 15 min, 20 min, 25 min, 35 min, 40 min), and the rotation speed is 1000-3000 rpm (e.g., 1100 rpm, 1500 min, 1800 min, 2000 min, 2200 min, 2500 rpm, 2800 rpm, 2900 rpm).

[0030] In the above preparation method, as a preferred embodiment, in S3, the drying temperature is 40-120℃ (e.g., 50℃, 60℃, 80℃, 100℃, 110℃);

[0031] And / or, in S4, the temperature of the rolling is 40-120°C (e.g., 50°C, 60°C, 80°C, 100°C, 110°C).

[0032] In the above preparation method, as a preferred embodiment, in step S3, after drying, the material is further ground and crushed to obtain dry electrode raw material; before step S4, the dry electrode raw material is dried; the drying method includes at least one of heating drying, vacuum drying, and natural air drying. More preferably, the heating drying temperature is 60-90℃ (e.g., 65℃, 70℃, 75℃, 85℃).

[0033] In the above preparation method, as a preferred embodiment, in S3, after drying, the material is ground and crushed;

[0034] The material obtained after grinding and crushing is passed through a 150-mesh sieve, and the material passing through the sieve is used as raw material for dry electrodes.

[0035] Secondly, the present invention also provides a dry electrode sheet, which is obtained by the above-described preparation method.

[0036] Thirdly, the present invention also provides an electrochemical energy storage device, characterized in that the electrochemical energy storage device includes the dry electrode sheet as described in claim 9;

[0037] Preferably, the electrochemical energy storage device includes any one of a lithium-ion battery, a sodium-ion battery, a supercapacitor, a fuel cell, a rechargeable zinc-air battery, or a solar cell, with a lithium-ion battery being more preferred.

[0038] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0039] 1. The process of this invention involves wet mixing, drying, and dry pressing, which largely preserves the uniformity of wet mixing while retaining the advantages of dry electrode sheets. It eliminates the need for the toxic solvent NMP and expensive coating machines. This invention uses plant fibers as the material supporting the dry electrode film and a binder as the electrode binder; both raw materials are green, healthy, environmentally friendly, and low-cost. In summary, this invention is a green, environmentally friendly, simple-to-manufacture, and low-cost dry electrode material.

[0040] 2. The material blending method of the present invention is simple, requiring only high-speed mixing, without the need for high temperature and high pressure conditions, and has low cost. The performance of the dry electrode sheet obtained by the present invention can reach the performance of the dry electrode sheet prepared by PTFE technology. Attached Figure Description

[0041] Figure 1 This is a SEM image of the dry electrode material from Example 1. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0043] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0044] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0045] In this invention, unless otherwise specified and / or stated, all numerical values ​​relating to component amounts are "parts by weight or mass percentage". Process parameters in the following examples that do not specify particular conditions are generally performed under conventional conditions.

[0046] The following detailed description of a method for preparing a dry electrode sheet according to the present invention is provided through embodiments. These embodiments are merely illustrative and not intended to limit the scope of the invention. The embodiments provided below can serve as a basis for further improvements or applications by those skilled in the art, and do not constitute any specific limitation on the present invention.

[0047] Example 1

[0048] This embodiment provides a method for preparing a dry electrode sheet, including the following steps:

[0049] Add 100 mL of deionized water and 10 g of sodium alginate powder to a 2 L beaker, and mechanically stir at 500 rpm for 20 min to obtain a sodium alginate solution.

[0050] Take 33.3g of sodium alginate solution, 94g of active material graphite, and 1g of conductive agent sp and mix them by wet method. Mix them for 20 minutes at 2000rpm using a high-speed defoamer to obtain sodium alginate-active material sample.

[0051] Coconut shell fiber was broken into plant fiber filaments with a length of 3-5 mm. 2 g of natural coconut shell fiber was added to the prepared sodium alginate-active substance sample. The mixture was then mixed at 2000 rpm for 15 min using a high-speed defoamer. The mixture was then dried, ground, and crushed at 60℃. The material passing through a 150-mesh sieve was used to obtain the dry electrode raw material.

[0052] The dry electrode raw material was dried at 70°C to remove moisture, then coated onto copper foil, and rolled at 80°C to form a dry electrode negative sheet with a compaction density of 1.6 g / cm³. 3 The dry electrode negative electrode sheet includes a copper foil current collector and a coating attached to the current collector, wherein the thickness of the current collector is 0.011 mm and the thickness of the coating is approximately 0.09 mm.

[0053] Figure 1 This is a SEM image of the dry electrode material prepared in this embodiment. Figure 1 A distinct fibrous structure can be clearly observed on the graphite.

[0054] Example 2

[0055] This embodiment provides a method for preparing a dry electrode sheet, including the following steps:

[0056] The difference between this embodiment and Embodiment 1 is that the coconut shell fiber is broken into filaments with a length of 5-7 mm, while the other steps are the same as in Embodiment 1.

[0057] Example 3

[0058] This embodiment provides a method for preparing a dry electrode sheet, including the following steps:

[0059] The difference between this embodiment and Embodiment 1 is that the coconut shell fiber is broken into filaments with a length of 7-10 mm, while the other steps are the same as in Embodiment 1.

[0060] Example 4

[0061] The difference between this embodiment and Embodiment 1 is that the amount of natural coconut shell fiber added is 5g, while the rest of the steps are the same as in Embodiment 1.

[0062] Example 5

[0063] The difference between this embodiment and Embodiment 1 is that the amount of natural coconut shell fiber added is 1g, while the rest of the steps are the same as in Embodiment 1.

[0064] Example 6

[0065] The difference between this embodiment and Embodiment 1 is that the amount of sodium alginate solution added is 55g, while the rest of the steps are the same as in Embodiment 1.

[0066] Example 7

[0067] The difference between this embodiment and Embodiment 1 is that 11g of sodium alginate solution was added, while the rest of the steps are the same as in Embodiment 1.

[0068] Example 8

[0069] The difference between this embodiment and Embodiment 1 is that the amount of graphite added is 87g, while the rest of the steps are the same as in Embodiment 1.

[0070] Example 9

[0071] The difference between this embodiment and Embodiment 1 is that the amount of graphite added is 97g, while the rest of the steps are the same as in Embodiment 1.

[0072] Example 10

[0073] The difference between this embodiment and Embodiment 1 is that the plant fiber used is flax fiber, while the other steps are the same as in Embodiment 1.

[0074] Example 11

[0075] The difference between this embodiment and Embodiment 1 is that the adhesive used is 3g of epoxy resin adhesive, while the other steps are the same as in Embodiment 1.

[0076] Comparative Example 1

[0077] This comparative example provides a method for preparing a dry electrode sheet, including the following steps:

[0078] The difference between this comparative example and Example 1 is that the coconut shell fibers are broken into fibers with a length of 0.5-2 mm, while the rest of the steps are the same as in Example 1.

[0079] Comparative Example 2

[0080] This comparative example provides a method for preparing a dry electrode sheet, including the following steps:

[0081] The difference between this comparative example and Example 1 is that the coconut shell fibers are broken into fibers with a length of 11-13 mm, while the other steps are the same as in Example 1.

[0082] Test case

[0083] To facilitate testing the tensile properties of the dry electrode film attached to the copper foil, the dried dry electrode raw materials of Examples 1-11 and Comparative Examples 1-2 were directly rolled into dry electrode films with a thickness of 0.12 mm. Tensile tests were then performed on them. The specific method of the tensile test included: clamping both ends of the film with a tensile testing machine, starting the instrument to stretch the film, and ending the test after the film broke. The maximum tensile force and tensile strength of the film were obtained.

[0084] The specific test results are shown in Table 1:

[0085] Table 1

[0086]

[0087]

[0088] As can be seen from Table 1, the tensile strength is better when the fiber length is 3-10 mm, while the tensile strength of the electrode decreases significantly when the fiber length is less than 3 or greater than 10 mm.

[0089] Battery fabrication:

[0090] The dry electrode negative plates prepared in the above embodiments were assembled with lithium metal electrodes to form lithium-ion coin cells (radius 16 mm). LiPF6 was dissolved at a concentration of 1 mol / L in an electrolyte of ethylene carbonate (EC) / diethyl carbonate (DEC) / ethyl methyl carbonate (EMC) = 2:3:1 (volume ratio). After the coin cell assembly was completed, capacity and initial coulombic efficiency tests were performed according to the following steps: stand for 2 h; constant current discharge: 0.1C to 0.005V; 0.08C to 0.001V; 0.05C to 0.001V; 0.02C to 0.001V; stand for 10 min; constant current charge: 0.1C to 1.5V.

[0091] The test results are shown in Table 2.

[0092] Table 2

[0093]

[0094]

[0095] As can be seen from Table 2, the battery of the present invention has a charging specific capacity of over 321 mAh / g, a discharging specific capacity of over 357 mAh / g, and an initial efficiency of over 89%.

[0096] Compared to the embodiments, in Comparative Example 1, the short length of the broken coconut shell fibers makes it difficult to support the graphite to form a stable film. This results in a smaller maximum tensile force and tensile strength in the dry electrode film, making the dry electrode film more fragile and unstable. It is also prone to material shedding during battery manufacturing, affecting battery performance and thus reducing the initial efficiency.

[0097] Compared to the examples, Comparative Example 2, due to its excessively long fiber length, was difficult to distribute evenly during the mixing process, resulting in unstable membrane quality, reduced physical properties, and impacted battery performance, with a significant decrease in its initial battery efficiency.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for preparing a dry electrode sheet, characterized in that, Includes the following steps: S1: Mix the liquid binder, active material, and conductive agent to obtain a block solid; S2: Break the plant fiber into plant fiber filaments with a uniform length of 3-10mm, and then mix them with the block solid to obtain a black solid; S3: Dry the black solid to obtain dry electrode raw material; S4: Coat the dry electrode material onto the current collector and roll it to obtain the dry electrode sheet; In S1, the liquid adhesive includes one or both of sodium alginate aqueous solution and epoxy resin adhesive.

2. The method for preparing the dry electrode sheet according to claim 1, characterized in that, The plant fibers include one or more of coconut fiber, flax fiber, bamboo fiber, and cotton fiber.

3. The method for preparing the dry electrode sheet according to claim 1, characterized in that, The sodium alginate aqueous solution has a mass fraction of 8-15%.

4. The method for preparing the dry electrode sheet according to any one of claims 1-3, characterized in that, In S1 and S2, when the liquid binder is an aqueous solution of sodium alginate, based on the total mass of the plant fiber, the solute of the liquid binder, the active substance, and the conductive agent, the amount of plant fiber is 1-5% by weight percentage, the amount of solute of the liquid binder is 1-5%, the amount of active substance is 87-97%, and the amount of conductive agent is 1-3%. Alternatively, when the liquid adhesive is an epoxy resin adhesive, based on the total mass of the plant fiber, liquid adhesive, active material, and conductive agent, the amount of plant fiber is 1-5% by weight percentage, the amount of liquid adhesive is 1-5%, the amount of active material is 87-97%, and the amount of conductive agent is 1-3%.

5. The method for preparing the dry electrode sheet according to any one of claims 1-3, characterized in that, The active material includes one of the positive electrode active material and the negative electrode active material; And / or, the current collector includes one of copper foil and aluminum foil.

6. The method for preparing the dry electrode sheet according to any one of claims 1-3, characterized in that, In S1, the mixing time is 10-50 min and the rotation speed is 1000-3000 rpm; And / or, in S2, the mixing time is 10-45 min and the rotation speed is 1000-3000 rpm.

7. The method for preparing the dry electrode sheet according to any one of claims 1-3, characterized in that, In S3, the drying temperature is 40-120°C; And / or, in S4, the temperature of the rolling press is 40-120°C.

8. The method for preparing the dry electrode sheet according to any one of claims 1-3, characterized in that, In step S3, after drying, the material is further ground and crushed to obtain dry electrode raw material; Before S4, the dry electrode material is dried. The drying process includes at least one of heating drying, vacuum drying, and natural air drying.

9. A dry electrode sheet, wherein the dry electrode sheet is obtained by the preparation method according to any one of claims 1-8.

10. An electrochemical energy storage device, characterized in that, The electrochemical energy storage device includes the dry electrode sheet as described in claim 9.

11. The electrochemical energy storage device according to claim 10, characterized in that, The electrochemical energy storage device includes any one of lithium-ion batteries, sodium-ion batteries, supercapacitors, fuel cells, rechargeable zinc-air batteries, or solar cells.

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