Electrode plate for alkali metal ion battery, manufacturing method and battery

Abstract

The invention relates to the technical field of batteries, and particularly provides an electrode plate for an alkali metal ion battery, a manufacturing method and the battery. The electrode pole piece for the alkali metal ion battery comprises a current collector, the plurality of coatings are sequentially coated on the side surface of the current collector in a direction far away from the current collector; wherein each coating layer is provided with pores; the raw materials of the coating comprise an electrode material and a pore-forming agent; the pore-forming agents of each coating are at least different from one another in the following aspects: the types of the pore-forming agents, the particle sizes of the pore-forming agents and the volume ratio of the pore-forming agents in the electrode material of the coating where the pore-forming agents are located. According to the invention, the rate and cycle performance of the battery are improved by improving the overall distribution of pores of each coating of the pole piece.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and specifically provides an electrode plate for an alkali metal ion battery, a manufacturing method and a battery. Background Art

[0002] Pole sheet design and manufacturing are key processes in the production of lithium-ion batteries. In traditional pole sheet structure design, the porosity of the pole sheet after roller pressing will show a significant decreasing trend in the vertical direction from the current collector to the surface. As the compaction density of the pole sheet continues to increase, the porosity will gradually decrease. Since the porosity and pore distribution have a decisive influence on the diffusion of lithium ions in the liquid phase, the traditional pole sheet pore structure will largely limit the rate performance and cycle life of the battery. Therefore, in order to break through this bottleneck, effectively increasing the total pore volume of the pole sheet and improving its pore distribution in the vertical direction have become an important research direction for optimizing the pole sheet structure design and improving the overall performance of the battery.

[0003] The existing method has complex process and is not suitable for industrial mass production in terms of efficiency, energy consumption and space. Therefore, it is necessary to develop a method suitable for mass production that can effectively improve the problem of the porosity or total pore volume of the existing electrode gradually decreasing from the current collector to the surface in the vertical direction of the electrode after rolling, so as to improve the battery rate and cycle performance. Summary of the invention

[0004] In order to overcome the above-mentioned defects, the present invention provides an electrode plate for an alkali metal ion battery, a method for manufacturing an electrode plate for an alkali metal ion battery, a method for preparing a battery cell, and a lithium ion battery, which improves the battery's rate and cycle performance by improving the total pore volume distribution of each coating of the electrode plate.

[0005] In a first aspect, the present invention provides an electrode plate for an alkali metal ion battery, comprising: current collector; In a direction away from the current collector, three coatings are sequentially coated on the side of the current collector; wherein each coating contains pores; and the raw materials of the coatings include electrode materials and pore-forming agents; The pore formers between the three coatings differ in at least one of the following: The type of pore former, the particle size of the pore former, and the volume proportion of the pore former in the electrode material of the coating in which it is located.

[0006] Furthermore, after baking and / or drying, the pore-forming agent can be sublimated or pyrolyzed and volatilized to form the pores in the corresponding coating, and the total volume of the pores in the coating gradually increases in a direction away from the current collector.

[0007] Furthermore, the electrode material comprises: Active materials, conductive agents and binders; and / or The types of pore formers include: One or more of ammonium salts, amides, organic peroxides, terpenoids, naphthols and halogen elements.

[0008] Furthermore, in each coating layer, the particle size of the pore former D50 is in the range of 0.1-50 μm.

[0009] Furthermore, when the types of pore formers between the coating layers are different, the average single-pore pore-forming volume of the pore formers of the coating layers gradually increases in a direction away from the current collector.

[0010] Furthermore, in the case where the particle sizes of the pore formers in the respective coating layers are different, the particle sizes of the pore formers in the respective coating layers gradually increase in a direction away from the current collector.

[0011] Furthermore, when the volume proportion of the pore-forming agent between each coating layer in the electrode material of the coating layer is different, the volume proportion in each coating layer gradually increases in the direction away from the current collector.

[0012] In a second aspect, the present invention provides a method for manufacturing an electrode sheet for an alkali metal ion battery, comprising: The electrode material and the pore former are wet mixed respectively to form slurries of three coating layers; wherein the pore former used in each wet mixing is different in at least one of the following aspects: the type of the pore former, the particle size of the pore former, and the volume proportion of the pore former in the electrode material of the coating layer.

[0013] Furthermore, after baking and / or drying, the pore-forming agent can be sublimated or pyrolyzed and volatilized to form the pores in the corresponding coating, and the total volume of the pores in the coating gradually increases in a direction away from the current collector.

[0014] In a third aspect, the present invention provides a method for preparing a battery cell, comprising: An electrode sheet according to the first aspect or an electrode sheet prepared by the preparation method according to the second aspect; Winding or stacking the pole pieces to obtain a battery cell; Baking and / or drying the battery cell to complete pore formation; The battery cell with completed holes is pressure-formed.

[0015] Further, the baking and / or drying comprises: Vacuum baking and / or vacuum drying is performed at 60-120°C for a preset time.

[0016] Furthermore, the preset duration is 1-48 hours.

[0017] In a fourth aspect, the present invention provides a lithium-ion battery, comprising a battery cell prepared by the method of the third aspect.

[0018] The above one or more technical solutions of the present invention have at least one or more of the following beneficial effects: In the technical solution of the present invention, pore formers of different types, different particle sizes or proportions are mixed in each coating to form multiple coatings with different pore state distributions. Specifically, the total pore volume of the coating gradually increases as the pole piece moves away from the current collector. This unique multi-coating structure can effectively adjust the pore distribution of the pole piece in the vertical direction, thereby significantly improving the liquid phase transmission speed of lithium ions in the pole piece. In this way, the rate performance and cycle performance of the battery are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The disclosure of the present invention will become more easily understood with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present invention. In addition, similar numbers in the figures are used to represent similar components, among which: Figure 1 It is a schematic flow chart of main steps of a method for manufacturing an electrode sheet according to an embodiment of the present invention; Figure 2 is a schematic diagram of mixing electrode materials and pore-forming agent dry powder according to one embodiment of the present invention; Figure 3 is a schematic cross-sectional view of a pole piece before the pore-forming agent is removed after the pole piece is rolled according to an embodiment of the present invention; Figure 4 is a schematic cross-sectional view of a pole piece after removing a pore-forming agent according to an embodiment of the present invention; Figure 5 It is the test result of 0.5P cycle energy retention rate according to the present invention; Figure 6 is the CP-SEM characterization result of the reference positive electrode according to Comparative Example 2 of the present invention; Figure 7 This is the CP-SEM characterization result of the positive electrode sheet according to Example 1 of the present invention.

[0020] List of reference numerals: 1. Active material powder; 2. Binder; 3. Conductive agent; 4. Solvent; 5. Pore-forming agent; 6. Electrode material; 7. Pores formed by non-pore-forming agent; 8. Pores formed after the pore-forming agent is removed. DETAILED DESCRIPTION

[0021] Some embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0022] The present invention provides an electrode plate for an alkali metal ion battery, comprising: current collector; In a direction away from the current collector, three coatings are sequentially coated on the side of the current collector; wherein each coating contains pores; and the raw materials of the coatings include electrode materials and pore-forming agents; The pore formers between the three coatings differ in at least one of the following: The type of pore former, the particle size of the pore former, and the volume proportion of the pore former in the electrode material of the coating in which it is located.

[0023] The present invention relates to a pole piece manufactured by a multi-layer coating technology, which forms multiple coatings with different pore distributions by mixing pore formers of different types, different particle sizes or proportions in each coating. This unique coating structure can effectively adjust the pore distribution of the pole piece in the vertical direction, thereby significantly improving the liquid phase transmission speed of lithium ions in the pole piece. In this way, the rate performance and cycle performance of the battery are significantly improved.

[0024] Specifically, the manufacturing process of the present invention follows the traditional electrode production process, and only an appropriate amount of pore-forming agent needs to be added to the electrode material. Subsequently, a pole piece with multiple coatings is formed through multi-layer coating technology. In the battery manufacturing process, when heating or baking steps are required, these pore-forming agents are removed by heating. The entire production process makes full use of the existing battery manufacturing process without introducing additional complex processes, thereby achieving a significant improvement in battery performance without increasing additional manpower and equipment costs.

[0025] In addition, the electrode sheet of the present invention has a particularly significant effect on improving the battery rate performance and cycle performance when the thickness is large or the compaction degree is high. This is because thicker electrode sheets or higher compaction degrees usually lead to longer lithium ion transmission paths and lower porosity, thereby affecting battery performance. However, through the use of multi-layer coating and pore-forming agents of the present invention, these problems can be effectively solved and the overall performance of the battery can be further optimized.

[0026] In one embodiment, after baking and / or drying, the pore former can be sublimated or pyrolyzed and volatilized to form the pores in the corresponding coating, and the total volume of the pores in the coating gradually increases in a direction away from the current collector.

[0027] Since the total pore volume of each coating is different, it is necessary to adjust and differentiate the addition of pore formers in each coating. By differentiating any one or more of the above characteristics, coatings with different total pore volumes can be successfully formed. For example, different types of pore formers can be selected, or the same pore formers with different particle sizes can be selected to form different pore size distributions in the coating. In addition, the volume proportion of the pore former in the electrode material can be adjusted to control the total pore volume of the coating. Through these methods, electrode coatings with specific pore structures can be flexibly designed and prepared to meet the needs of different application scenarios.

[0028] A method for regulating the pore structure by adjusting parameters such as the type of pore formers (ammonium bicarbonate, urea, dibenzoyl peroxide, azobisisobutyronitrile, natural camphor, naphthol, iodine, sulfur, etc.), particle size (D50: 0.1-50μm), and quantity (1-20% by volume) in multi-layer coating, wherein each layer of coating can be composed of a single or multiple pore formers, and the parameters and types of the pore formers in different layers of coating are different (using the different decomposition temperatures, decomposition rates, size morphology and other properties of different pore formers to match each other, so as to form a design in which the total pore volume of the pole piece gradually increases from the inside to the outside in the vertical direction, and the total pore volume of the overall coating of the pole piece gradually increases.

[0029] In one embodiment, the electrode material comprises: Active materials, conductive agents and binders; and / or The types of pore formers include: One or more of ammonium salts, amides, organic peroxides, terpenoids, naphthols and halogen elements.

[0030] In one embodiment, the ammonium salts include ammonium bicarbonate and the like.

[0031] The amides include urea and the like.

[0032] The organic peroxide includes dibenzoyl peroxide and the like.

[0033] The terpenoid compounds include natural camphor and the like.

[0034] The naphthols include 1-naphthol and the like.

[0035] The halogen element includes iodine, sulfur and the like.

[0036] These pore formers play a place-occupying role after being mixed with the electrode material, and are removed after heating or baking, thereby leaving place-occupying pores in the electrode material.

[0037] In the traditional battery manufacturing process, the pore former usually needs to have the property of being insoluble in the solvent used in the slurry mixing process. This means that the pore former used in the organic solvent system of the positive electrode is often not suitable for the aqueous solvent system of the negative electrode. However, the present invention breaks this conventional limitation and proposes a new idea. Even if the pore former has a certain solubility in the solvent, as long as this solubility does not cause other substances in the slurry mixing system to react, then this pore former can be used in both the positive and negative electrodes.

[0038] Therefore, the method for controlling the total pore volume ratio of each coating layer of the pole piece proposed in the present invention has wide applicability and can meet the requirements of both the positive electrode and the negative electrode. This innovation not only simplifies the process flow of battery manufacturing, but also improves production efficiency and the stability of battery performance.

[0039] In one embodiment, in each coating layer, the pore former has a D50 particle size in the range of 0.1-50 μm.

[0040] The pore former has a particle size distribution of 0.1 μm≤D50≤50 μm.

[0041] D50 is the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%.

[0042] Its physical meaning is that particles with a diameter larger than it account for 50%, and particles with a diameter smaller than it also account for 50%. D50 is also called the median diameter or median particle size. D50 is often used to indicate the average particle size of powders.

[0043] In one embodiment, the electrode material includes an active substance, a conductive agent and a binder, and the volume ratio of the pore-forming agent to the active substance is 1:(1-25).

[0044] The active material in the positive electrode sheet is the positive electrode active material.

[0045] The active material in the negative electrode sheet is the negative electrode active material.

[0046] In one embodiment, when the volume proportion of the pore-forming agent in the electrode material is different in each coating, the volume proportion of the electrode sheet gradually increases in a direction away from the current collector.

[0047] In one embodiment, when the types of pore formers in the various coating layers are different, the average single-pore pore-forming volume of the pore formers in the various coating layers gradually increases in a direction away from the current collector.

[0048] In one embodiment, when the particle sizes of the pore formers in each coating layer are different, the particle sizes of the pore formers in each coating layer gradually increase in a direction away from the current collector.

[0049] In one embodiment, when the volume proportion of the pore former between each coating layer in the electrode material of the coating layer is different, the volume proportion in each coating layer gradually increases in the direction away from the current collector.

[0050] The present invention provides a method for manufacturing an electrode sheet for an alkali metal ion battery, referring to Figure 1 ,include: S1, wet-mixing the electrode material and the pore-forming agent respectively to form slurries of three coatings; wherein the pore-forming agent used in each wet-mixing is different in at least one of the following aspects: the type of pore-forming agent, the particle size of the pore-forming agent, and the volume proportion of the pore-forming agent in the electrode material of the coating in which it is located; the pore-forming agent can be sublimated or pyrolyzed and volatilized to form the pores in the corresponding coating after baking and / or drying, and the total volume of the pores in the coating gradually increases along the direction away from the current collector.

[0051] In one embodiment, in step S1, the step of wet-mixing the electrode material and the pore-forming agent to form three coating slurries comprises: S11, mixing the active material, the conductive agent, the binder and the pore-forming agent to obtain a dry powder mixture.

[0052] Slurry mixing process reference Figure 2 .

[0053] S12, still refer to Figure 2 , adding a solvent to the dry powder mixture for wet mixing.

[0054] S13, coating the wet mixed slurry on the current collector through a coating process.

[0055] The solvent for the positive electrode is usually water, and the solvent for the negative electrode is usually NMP.

[0056] The present invention provides a method for preparing a battery core, comprising: S2, using the electrode sheet or the electrode sheet prepared by the preparation method; S3, winding or stacking the electrode sheets to obtain a battery cell; S4, baking and / or drying the battery cell to complete pore formation; S5, pressure shaping is performed on the battery cell after the hole is formed.

[0057] It should be noted that the hot pressing process is not used in the manufacturing process of the battery cell of the present invention. This is because the hot pressing process is carried out under high temperature conditions, and high temperature will cause thermal decomposition of the pore former mixed in the pole piece. Once the pore former decomposes at high temperature, the originally constructed pore structure will be compressed during the subsequent rolling process, and may even collapse completely. The destruction of this pore structure is extremely unfavorable for the construction of the pore structure and the specific distribution of the pore volume. Therefore, the present invention adopts the method of cold pressing first and then pressure shaping to ensure the integrity of the pore structure and the performance of the battery cell.

[0058] In one embodiment, in step S3, the baking and / or drying comprises: Vacuum baking and / or vacuum drying is performed at 60-120°C for a preset time.

[0059] In one embodiment, the preset duration is 1-48 hours.

[0060] The present invention provides a lithium ion battery, characterized in that it comprises the battery core prepared as above.

[0061] The present invention optimizes the pore structure method by precisely controlling the key parameters in the baking process. Specifically, by adjusting the temperature range for removing the pore former during the baking process, that is, selecting between 60°C and 120°C, and the length of the baking time, that is, adjusting between 1 hour and 48 hours, the pore structure of the material can be effectively regulated and optimized. This method allows the key characteristics of the material, such as the total pore volume, pore size and its distribution, to be finely regulated according to actual application requirements, thereby meeting the specific requirements of pore structure in different fields.

[0062] Figure 3 The cross-sectional schematic diagram of the electrode sheet after step S3 is completed and before step S4 is started, that is, before the pore-forming agent is removed. The pores in the figure are the pores originally present in the electrode sheet, and then after winding or lamination, a battery cell is obtained.

[0063] Figure 4 After the pores are formed in step S4, the pore-forming agent is separated from the electrode sheet to form new pores. Figure 4 .

[0064] The present invention introduces a pore former during the slurrying process of the positive electrode and / or the negative electrode, that is, during the dry mixing and high-speed dispersion stage. This process ensures that the pore former can be evenly dispersed in the slurry. After the rolling process is completed, it must be ensured that the pore former is still present in the electrode piece, and the volatilization amount of the pore former should be as small as possible during coating or other subsequent processes, that is, not more than 50% of its total amount. In order to achieve this, the present invention adjusts the vacuum baking step in the conventional process. Specifically, the vacuum baking step is adjusted from the process before liquid injection to after winding. The temperature range of this baking process is set at 60-120°C, and the time is 1-48 hours. In this way, the pore former is effectively removed, thereby ensuring that the weight loss rate of the electrode piece does not exceed 0.3%. In this way, there is no need for an additional vacuum baking step before the subsequent liquid injection process.

[0065] In addition, the present invention also provides a flexible adjustment mechanism. By changing the type, amount, vacuum baking parameters, etc. of the pore former in the multi-layer coating, the pore distribution in the vertical direction of the pole piece and the total pore volume of each coating layer of the pole piece can be adjusted within a certain range. This adjustment mechanism enables the battery to exhibit different rate performance and cycle performance. Therefore, according to the specific needs of product development, pole pieces with different vertical pore distributions and pore volumes can be quickly matched and designed to meet diverse application needs.

[0066] After step S5, the method further includes: S6, injecting electrolyte into the battery cell.

[0067] The present invention also provides a lithium ion battery, including a battery cell prepared by the preparation method. The present invention performs the steps of slurry mixing, coating, winding or lamination, heating / baking, pressure shaping, and liquid injection through S1-S6 to obtain a battery cell, and then undergoes conventional high-temperature standing, formation, and capacity separation to obtain a lithium ion battery.

[0068] The following examples and comparative examples are used to prepare electrode sheets and then make batteries.

[0069] In the following description, the layer closest to the current collector is the first layer, and the layers away from the current collector are the second and third layers. The positive electrode material includes active material lithium iron phosphate, conductive agent SP and binder PVDF. The negative electrode material includes active material graphite, binder CMC, binder SBR, binder PAA and conductive agent SP.

[0070] Example 1 ①Weigh the materials used for the positive electrode The first layer of slurry solid matter mass ratio: Lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (ammonium bicarbonate) to lithium iron phosphate is 1:20, and the solid content of slurry is 62%; The second layer slurry solid matter mass ratio is: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (ammonium bicarbonate: urea = 1:1, volume ratio) to lithium iron phosphate is 1:20, and the slurry solid content is 62%; The third layer slurry solid matter mass ratio is: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (urea) to lithium iron phosphate is 1:20, and the slurry solid content is 62%; Since the pore volume of urea is larger than that of ammonium bicarbonate, this design can achieve that the total pore volume of each coating gradually increases from the inside to the outside of the electrode along the vertical direction, and the overall porosity of the electrode will also increase.

[0071] Negative electrode: Use conventional electrode ② The particle size of the pore-forming agent is D50: 30±5μm; ③ Dry-mix the electrode material solid material and pore-forming agent weighed in step ① according to a certain proportion, add NMP solvent after mixing evenly, wherein the slurry solid content is 62%; ④ Then apply the slurry to the roller in the conventional way until it is wound or stacked, but do not heat press it. The unheat pressed battery cell is vacuum baked at 105℃ for 24h, during which time the air is ventilated to remove the pore-forming agent.

[0072] ⑤ The battery cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0073] Example 2 The layer closest to the current collector is the first layer, and the layer farthest from the current collector is the second layer, with a thickness ratio of 1:1.

[0074] ①Weigh the negative electrode material The mass ratio of solid matter in the first layer of slurry is: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%, the volume ratio of pore-forming agent (natural camphor D50: 15±5μm) to graphite is 1:20, and the solid content of slurry is 55%.

[0075] The second layer slurry solid matter mass ratio is: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%. The volume ratio of pore-forming agent (natural camphor D50: 30±5μm) to graphite is 1:20, and the slurry solid content is 55%.

[0076] This design can realize that the total pore volume of each coating gradually increases from the inside to the outside of the pole piece along the vertical direction, and the overall porosity of the pole piece will also increase.

[0077] Positive electrode: conventional electrode ② Dry-mix the electrode material solid material and pore-forming agent weighed in step ① according to a certain proportion, add NMP solvent after mixing evenly, wherein the slurry solid content is 62%; ③ Then, the slurry is coated and rolled in a conventional manner until it is wound or laminated, but not hot-pressed. The un-hot-pressed battery cell is vacuum-baked at 105°C for 24 hours, during which time the air is ventilated to remove the pore-forming agent. ④ The battery cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0078] Example 3 ①Weigh the materials used for the positive electrode The first layer of slurry solid matter mass ratio: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (ammonium bicarbonate) to lithium iron phosphate is 1:25, and the slurry solid content is 62%; The second layer slurry solid matter mass ratio is: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (ammonium bicarbonate) to lithium iron phosphate is 1:15, and the slurry solid content is 62%; This design can realize that the total pore volume of each coating gradually increases from the inside to the outside of the pole piece along the vertical direction, and the overall porosity of the pole piece will also increase.

[0079] Negative electrode: conventional electrode ②Pore-forming agent particle size D50: 30±5μm; ③ Dry-mix the electrode material solid material and pore-forming agent weighed in step ① according to a certain proportion, add NMP solvent after mixing evenly, wherein the slurry solid content is 62%; ④ Then, the slurry is coated and rolled in a conventional manner until it is wound or laminated, but not hot-pressed. The un-hot-pressed battery cell is vacuum-baked at 95°C for 30 hours, during which time the air is ventilated to remove the pore-forming agent; ⑤ The battery cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0080] Example 4 ①Weigh the materials used for the positive electrode The first layer of slurry solid matter mass ratio: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (ammonium bicarbonate) to lithium iron phosphate is 1:5, and the slurry solid content is 62%; The second layer slurry solid matter mass ratio: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (ammonium bicarbonate) to lithium iron phosphate is 1:1, and the slurry solid content is 62%; This design can realize that the total pore volume of each coating gradually increases from the inside to the outside of the pole piece along the vertical direction, and the overall porosity of the pole piece will also increase.

[0081] Negative electrode: conventional electrode ②Pore-forming agent particle size D50: 40±5μm; ③ Dry-mix the electrode material solid material and pore-forming agent weighed in step ① according to a certain proportion, add NMP solvent after mixing evenly, wherein the slurry solid content is 62%; ④ Then, the slurry is coated and rolled in a conventional manner until it is wound or laminated, but not hot-pressed. The un-hot-pressed battery cell is vacuum-baked at 60°C for 48 hours, during which time the air is ventilated to remove the pore-forming agent; ⑤ The battery cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0082] Example 5 ①Weigh the materials used for the positive electrode The first layer of slurry solid matter mass ratio: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (ammonium bicarbonate) to lithium iron phosphate is 1:25, and the slurry solid content is 62%; The second layer slurry solid matter mass ratio: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, the volume ratio of pore former (ammonium bicarbonate) to lithium iron phosphate is 1:20, and the slurry solid content is 62%; This design can realize that the total pore volume of each coating gradually increases from the inside to the outside of the pole piece along the vertical direction, and the overall porosity of the pole piece will also increase.

[0083] Negative electrode: conventional electrode ②Pore-forming agent particle size D50: 30±5μm; ③ Dry-mix the electrode material solid material and pore-forming agent weighed in step ① according to a certain proportion, add NMP solvent after mixing evenly, wherein the slurry solid content is 62%; ④ Then apply the slurry to the roll in a conventional manner until it is wound or laminated, but do not heat press it. The unheat pressed battery cell is vacuum baked at 100°C for 20 hours, during which time the air is ventilated to remove the pore-forming agent. ⑤ The battery cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0084] Example 6 The layer closest to the current collector is the first layer, and the layer farthest from the current collector is the second layer, with a thickness ratio of 1:1.

[0085] ①Weigh the negative electrode material The mass ratio of solid matter in the first layer of slurry is: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%; the volume ratio of pore-forming agent (natural camphor D50: 0.1±5μm) to graphite is 1:20, and the solid content of the slurry is 55%.

[0086] The second layer slurry solid matter mass ratio: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%, the volume ratio of pore former (natural camphor D50: 10±5μm) to graphite is 1:20, and the slurry solid content is 55%; This design can realize that the total pore volume of each coating gradually increases from the inside to the outside of the pole piece along the vertical direction, and the overall porosity of the pole piece will also increase.

[0087] Positive electrode: conventional electrode ② Dry-mix the electrode material solid material and pore-forming agent weighed in step ① according to a certain proportion, add NMP solvent after mixing evenly, wherein the slurry solid content is 62%; ③ Then, the slurry is coated and rolled in a conventional manner until it is wound or laminated, but not hot-pressed. The un-hot-pressed battery cell is vacuum-baked at 105°C for 24 hours, during which time the air is ventilated to remove the pore-forming agent. ④ The battery cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0088] Example 7 The layer closest to the current collector is the first layer, and the layer farthest from the current collector is the second layer, with a thickness ratio of 1:1.

[0089] ①Weigh the negative electrode material The mass ratio of solid matter in the first layer of slurry is: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%, the volume ratio of pore-forming agent (natural camphor D50: 30±5μm) to graphite is 1:20, and the solid content of slurry is 55%.

[0090] The second layer slurry solid matter mass ratio: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%; The volume ratio of pore-forming agent (natural camphor D50: 50±5μm) to graphite is 1:20, and the solid content of the slurry is 55%.

[0091] This design can achieve a gradual increase in the total pore volume of each coating layer along the vertical direction of the pole piece from the inside to the outside, and the overall porosity of the pole piece will also increase.

[0092] Positive electrode: conventional electrode ② Dry-mix the electrode material solid material and pore-forming agent weighed in step ① according to a certain proportion, add NMP solvent after mixing evenly, wherein the slurry solid content is 62%; ③ Then, the slurry is coated and rolled in a conventional manner until it is wound or laminated, but not hot-pressed. The un-hot-pressed battery cell is vacuum-baked at 120°C for 1 hour, during which time the air is ventilated to remove the pore-forming agent; ④ The battery cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0093] Comparative Example 1 ① Negative electrode: solid material mass ratio: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%, the volume ratio of pore-forming agent (ammonium bicarbonate: a pore-forming agent conventionally used for positive electrodes) to graphite is 1:20, and the solid content of the slurry is 55%; Positive electrode: conventional electrode ②Pore-forming agent particle size D50: 25 μm; ③ Dry-mix the electrode material and pore-forming agent weighed in step ① according to the proportion, add water solvent after mixing evenly, wherein the solid content of the slurry is 55%; ④ Then, the slurry is coated and rolled in a conventional manner until it is wound or laminated, but not hot-pressed. The un-hot-pressed battery cell is vacuum-baked at 105°C for 24 hours, during which time the air is ventilated to remove the pore-forming agent; ⑤ The battery cell with the pore-forming agent removed is transferred to the subsequent process in a conventional manner to be made into a battery.

[0094] Comparative Example 2-Reference ① Negative electrode: conventional electrode, solid material mass ratio: graphite: CMC: PAA: SP: SBR = 96.2%: 0.6%: 0.8%: 1.2%: 1.2%, slurry solid content 55%; ② Positive electrode: conventional electrode, slurry solid material mass ratio: lithium iron phosphate: PVDF: SP = 97.2%: 1.6%: 1.2%, slurry solid content 62%; ③ Transfer to the subsequent process in the conventional manner to make batteries.

[0095] Electrochemical performance test The batteries prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to electrochemical tests. The test results of the total pore volume ratio and rate performance of the batteries are shown in Table 1. At 25°C, the 0.5P cycle energy retention rate Figure 5 .

[0096] Table 1 Test results of the batteries of the embodiments and comparative examples

[0097] From Table 1 and Figure 5The data provided show that, for the pore formation of the positive electrode, the three-layer positive electrode sheet structure formed in Example 1 has better performance than the two-layer positive electrode sheet structure formed in Example 3, and the battery performance prepared by the positive electrode sheet obtained by the multi-layer pore formation method of the present invention is better than that of the conventional battery (Comparative Example 2). For the pore formation of the negative electrode, the battery performance of the negative electrode sheet structure formed in Example 2 is better than that of the conventional battery (Comparative Example 2).

[0098] The multi-layer coating technology is used to construct a multi-layer pore structure, which can significantly improve the rate performance of the battery. The pore distribution and structural stability constructed by this specific preparation method are good, which makes the battery perform well during long-term use and ensures its excellent performance in stability and reliability.

[0099] Microstructure characterization tests Comparative Example 2 is a reference positive electrode. The present invention conducts microstructural characterization tests on the reference positive electrode of Comparative Example 2 and the positive electrode sheet coated with three layers of slurry in Example 1 to obtain the microscopic morphology of the material cross section on the positive electrode current collector. Through the observation of this microscopic morphology, various microscopic geometric shape information of the cross section of the positive electrode material can be understood. This information is one of the important parameters for studying the performance of battery positive electrode materials and the electrochemical reaction mechanism. In order to obtain more accurate microscopic morphology data, the present invention adopts argon ion polishing technology, also known as CP cross-section polishing technology. This technology bombards the cross section of the material sample to obtain a flat polished cross section. Subsequently, the observation and analysis of the microscopic characteristics of the internal structure of the sample were completed by using a scanning electron microscope (SEM).

[0100] In the CP-SEM characterization results of the reference positive electrode of Comparative Example 2, it can be seen that Figure 6 The CP-SEM characterization results of the positive electrode sheet of Example 1 are Figure 7 Through careful observation of these cross-sectional morphologies, it can be found that the number of pores in the pole piece constructed by the present invention is significantly increased. When the total volume of the upper pores in the vertical direction of the pole piece is greater than that of the lower layer, the liquid phase diffusion of the pore-forming agent pole piece is first fast and then slow. When the pore distribution in the vertical direction of the pole piece is consistent or the total volume of the upper pores is smaller than that of the lower layer, the liquid phase diffusion rate of the pole piece is stable or first slow and then fast. The higher total pore volume of the upper layer allows the electrolyte to quickly infiltrate and penetrate into the pole piece, and multiple layers of coatings with different pore volumes form a gradient pore volume, which reduces the difference in pore volume of the coating in the vertical direction of the pole piece, which is beneficial to improving the overall performance of the battery.

[0101] Disassemble and observe the battery after it is fully charged The batteries of Examples 1-3, Comparative Examples 1 and 2 were disassembled after being fully charged after cycling for 400 cls.

[0102] Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 reference electrodes, after 400 cycles of charge and discharge, these batteries were fully charged and then disassembled and analyzed. The interface state of the pole piece corresponds to the total pore volume, cycle, and rate performance of each coating. The present invention effectively improves the pore distribution of the pole piece in the vertical direction by constructing a plurality of coatings with different pore-forming states on the pole piece. This improvement not only significantly improves the performance of the battery under high-rate discharge conditions, but also makes the battery have cycle stability. Specifically, the structure of the present invention starts from the surface layer of the current collector and is constructed layer by layer to form a layered structure with high stability. Although more pores are introduced in this process, the stability of the overall structure is ensured by the gradient pore structure. This gradient pore structure not only optimizes the penetration of the electrolyte and the ion transmission path, but also effectively alleviates the volume change and stress concentration generated during the charge and discharge cycle, thereby further improving the cycle life and overall performance of the battery.

[0103] The pole piece pore structure proposed in the present invention is significantly different from the traditional design. It introduces an innovative design concept for the pore distribution in the vertical direction of the pole piece and its corresponding preparation method. Specifically, the present invention adopts a multilayer coating technology, and adds a specific pore-forming agent in the process of preparing the slurry. When performing the rolling process, the present invention adopts a secondary rolling method, which can more finely control the pore structure of the pole piece. After the winding or lamination is completed, the present invention also adopts a vacuum baking or vacuum heating method to effectively remove the pore-forming agent added to the slurry. These pore-forming agents can be materials of different types, different particle sizes and different contents. In this way, the present invention achieves the design goal that the total volume of pores in the upper coating of the pole piece is greater than the total volume of pores in the lower coating, thereby significantly improving the pore distribution in the vertical direction of the pole piece.

[0104] This innovative pore distribution design can effectively improve the liquid phase transmission speed of lithium ions in the pole piece. Due to the optimization of pore distribution, the diffusion path of lithium ions in the pole piece is optimized, thereby reducing the resistance during the transmission process. This improvement not only improves the rate performance of the battery, that is, the charge and discharge capacity of the battery at high current density, but also significantly improves the cycle performance of the battery, that is, the capacity retention rate and stability of the battery after multiple charge and discharge cycles. Therefore, the present invention has important application value and market potential in improving battery performance.

[0105] It should be pointed out that although the various steps in the above embodiments are described in a specific order, those skilled in the art can understand that in order to achieve the effects of the present invention, different steps do not have to be performed in such an order. They can be performed simultaneously (in parallel) or in other orders. These changes are within the scope of protection of the present invention.

[0106] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. An electrode plate for an alkali metal ion battery, characterized in that: include: current collector; In a direction away from the current collector, three coatings are sequentially coated on the side of the current collector; wherein each coating contains pores; and the raw materials of the coatings include electrode materials and pore-forming agents; The pore formers between the three coatings differ in at least one of the following: The type of pore former, the particle size of the pore former, and the volume percentage of the pore former in the electrode material of the coating in which the pore former is located; After baking and / or drying, the pore-forming agent can be sublimated or pyrolyzed and volatilized to form the pores in the corresponding coating, and the total volume of the pores in the coating gradually increases in a direction away from the current collector.

2. The pole piece according to claim 1, characterized in that: The electrode material comprises: Active materials, conductive agents and binders; and / or The types of pore formers include: One or more of ammonium salts, amides, organic peroxides, terpenoids, naphthols and halogen elements.

3. The pole piece according to claim 1, characterized in that: In each coating layer, the particle size D50 of the pore former is in the range of 0.1-50 μm.

4. The pole piece according to claim 1, characterized in that: In the case where the types of pore formers are different between the coating layers, the average single-pore pore-forming volume of the pore formers of the coating layers gradually increases in a direction away from the current collector.

5. The pole piece according to claim 1, characterized in that: In the case where the particle sizes of the pore formers in the respective coating layers are different, the particle sizes of the pore formers in the respective coating layers gradually increase in a direction away from the current collector.

6. The pole piece according to claim 1, characterized in that: When the volume proportion of the pore former between each coating layer in the electrode material of the coating layer is different, the volume proportion in each coating layer gradually increases in the direction away from the current collector.

7. A method for manufacturing an electrode sheet for an alkali metal ion battery, characterized in that: include: Wet-mixing the electrode material and the pore-forming agent respectively to form slurries of three coating layers; wherein the pore-forming agent in each wet-mixing is different in at least one of the following: the type of the pore-forming agent, the particle size of the pore-forming agent, and the volume proportion of the pore-forming agent in the electrode material of the coating layer in which the pore-forming agent is located; After baking and / or drying, the pore-forming agent can be sublimated or pyrolyzed and volatilized to form the pores in the corresponding coating, and the total volume of the pores in the coating gradually increases in a direction away from the current collector.

8. A method for preparing a battery cell, characterized in that: include: A pole piece according to any one of claims 1 to 6 or a pole piece prepared by the preparation method according to claim 7; Winding or stacking the pole pieces to obtain a battery cell; Baking and / or drying the battery cell to complete pore formation; The battery cell with completed holes is pressure-formed.

9. The method according to claim 8, characterized in that The baking and / or drying comprises: Vacuum baking and / or vacuum drying is performed at 60-120°C for a preset time.

10. The method according to claim 9, characterized in that The preset duration is 1-48 hours.

11. A lithium ion battery, characterized in that: The invention comprises a battery cell prepared by the method according to any one of claims 8 to 10.

Images