Slurry, pole piece, battery cell, lithium ion battery and preparation method

Abstract

The present application provides a kind of slurry, pole piece, battery cell, lithium ion battery and preparation method.The present application slurry includes active material, conductive agent, binder, pore-forming agent and solvent, pore-forming agent accounts for 0.01-0.1% of the total mass of solid in slurry, and the pore-forming agent includes one or more of lithium chloride, ammonium bicarbonate, iodine, ferric chloride and methacrylic ester.By adding a small amount of pore-forming agent that is easy to sublimate when mixing slurry, the pore-forming agent sublimates and leaves pores when the pole piece is coated and dried, without increasing the process, simple operation, low cost, can greatly improve the pole piece's ability to absorb electrolyte and infiltration performance, improve the quality and density of the formation film and the energy density and power density of the battery.At the same time, the pores on the pole piece can provide more reaction sites, reduce electrode non-uniform polarization, and the pole piece will not deform when it swells during the battery charging and discharging process, so as not to damage the structure of the battery cell, improve the cycle life, rate performance and stability of the battery.

Description

Technical Field

[0001] This invention belongs to the field of new energy battery technology, specifically relating to a slurry, electrode, cell, lithium-ion battery, and preparation method. Background Technology

[0002] With the development of the new energy industry, the demand for lithium-ion batteries is increasing, and the performance requirements for lithium batteries are becoming increasingly stringent. Therefore, the fabrication of lithium-ion batteries with high energy density, high rate performance, and low impedance has become a hot topic. To improve the performance of lithium-ion batteries, researchers have mainly focused on material modification, the development of new materials, and the optimization of battery structure.

[0003] Significant progress has been made in the research of material modification and the development of new materials, which has improved the specific capacity of materials. However, the cost is high and the practical application is limited. In particular, the development of new materials and their large-scale application in service lithium-ion batteries is time-consuming and difficult. Optimizing battery structure is also costly and time-consuming.

[0004] Patent application number 202211629192.3 discloses a porous negative electrode sheet, its preparation method, and a lithium-ion battery. The porous negative electrode sheet comprises: a binder, a conductive agent, a first active material, and a second active material; the second active material comprises a core and a coating layer, the core comprising a third active material; the coating layer coats the surface of the core and comprises a functional active material and an artificial SEI film. The porous negative electrode sheet is prepared by the following method: preparing a slurry; adding the first active material and the conductive agent to the slurry to obtain a first slurry; adding a precursor to the first slurry to obtain a lithium-ion battery negative electrode slurry; sequentially coating, drying, and rolling the lithium-ion battery negative electrode slurry to obtain the porous negative electrode sheet; the precursor comprises a pore-forming agent, polyacrylic acid, and the third active material; wherein the functional active material is nano-silicon; the pore-forming agent is a mixture obtained by ball milling lithium fluoride and the functional active material. After creating pores, this invention can effectively construct an artificial SEI film at the micro-interface of the negative electrode material, achieving a long cycle life of the battery cell. However, its electrode structure and composition are relatively complex, mainly consisting of a composite structure formed by the second active material forming the core and the coating layer, in order to improve the rate performance of the battery cell, maximize its capacity, and increase its energy density.

[0005] Patent application number 201811058338.7 discloses a method for preparing a porous lithium-ion electrode with high energy density and a lithium-ion battery. The preparation method includes the following steps: S1, dissolving a binder with N-methylpyrrolidone to obtain a slurry; adding an active material and a conductive agent to the slurry and mixing thoroughly to obtain a paste; S2, coating the mixed slurry onto a current collector to obtain an electrode; S3, cold-pressing the coated electrode, then brushing a pore-forming agent onto the surface of the cold-pressed electrode, uniformly coating the pore-forming agent onto the surface of the cold-pressed electrode using a coating machine, and drying while coating, with the drying temperature set higher than the decomposition temperature of the pore-forming agent, to obtain a porous lithium-ion electrode with high energy density. This invention improves the porosity of thick electrode sheets and enhances electrical performance by brushing a pore-forming agent onto the electrode surface after cold pressing. However, the added step of brushing the pore-forming agent makes the preparation complex and inefficient, which is not conducive to mass production.

[0006] Therefore, how to efficiently prepare lithium-ion batteries with high energy density, high rate performance, and low impedance still needs further exploration and research. Summary of the Invention

[0007] To address the shortcomings and defects of existing technologies, this invention aims to provide a slurry, electrode, battery cell, lithium-ion battery, and its preparation method. This invention adds a small amount of easily sublimable pore-forming agent during slurry preparation. During electrode coating and drying, the pore-forming agent vaporizes and decomposes, leaving pore spaces (voids). This eliminates the need for additional processes, simplifying the operation and reducing costs. It significantly improves the electrode's electrolyte absorption capacity, wettability, and the density and quality of the formed film. Simultaneously, the pre-reserved pore spaces on the electrode provide more reaction sites, reducing uneven electrode polarization. During battery charging and discharging, the electrode does not deform during expansion, thus preserving the battery cell structure and improving cycle life, rate performance, and stability. This invention increases the porosity of the electrode, greatly improving its wettability. It allows for increased electrode areal density and group margin while maintaining good electrolyte absorption and wettability without increasing cell impedance, thereby improving the battery's energy density and power density.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a slurry comprising an active substance, a conductive agent, a binder, a pore-forming agent, and a solvent. The pore-forming agent comprises 0.01-0.1% (specifically, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, or 0.09%) of the total solids in the slurry. The pore-forming agent includes one or more of lithium chloride, ammonium bicarbonate, elemental iodine, ferric chloride, and methacrylate. The total solids in the slurry refer to the total mass of the active substance, conductive agent, binder, and pore-forming agent.

[0010] In the synthesis of lithium-ion battery slurry according to this invention, a pore-forming agent that readily sublimates is added and volatilizes during coating and baking, leaving micro- and nano-pores on the positive and negative electrode sheets. The pore-forming agent used in this invention has the following advantages: firstly, it readily sublimates and volatilizes at relatively low temperatures, meaning it can be removed within the drying oven of the coating machine; secondly, it is easily dispersed, directly or indirectly and uniformly dispersed in the solvent or slurry, and after subsequent drying and volatilization, the pores are evenly distributed; thirdly, in addition to pore formation, its polarity helps the conductive agent disperse better, reducing particle agglomeration and improving coating uniformity. The pore-forming agent used in this invention is present in very small amounts, is uniformly dispersed, and has no adverse effects on the slurry. Furthermore, the pores left after volatilization are at the micro- and nano-scale. Using the slurry of this invention to prepare porous electrode sheets requires no additional steps, is simple to operate, and has low cost. It can greatly improve the electrolyte absorption capacity of the electrode sheets, improve wetting performance, and enhance the density and quality of the formed film. Meanwhile, the pre-reserved pore spaces on the electrode sheet of this invention provide more reaction sites, reduce uneven electrode polarization, and prevent deformation during battery charging and discharging when the electrode sheet expands, thus avoiding damage to the cell structure and improving the battery's cycle life, rate performance, and stability. This invention can increase the porosity of the electrode sheet, greatly improving its wettability. It allows for increased electrode areal density and group margin while maintaining good liquid absorption and wetting without increasing the cell impedance, thereby improving the battery's energy density and power density.

[0011] Further, the slurry is a positive electrode slurry, the active material is a positive electrode active material, the conductive agent is a positive electrode conductive agent, and the binder is a positive electrode binder. The mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is 95-97 (specifically, 95.2, 95.5, 95.7, 96, 96.2, 96.5, 96.7): 0.5-3 (specifically, 0.55, 0.7, 0.85, 1, 1.15, 1.3, 1.5, 1.7, 1.9, 2.1, 2.3, 2.5, 2.7, 2.9): 1.5-4 (specifically, 1.55, 1.7, 1.9, 2.1, 2.3, 2.5, 2.7, 2.9, 3.1, 3.3, 3.5, 3.7, 3.9).

[0012] Furthermore, the solvent can be any known solvent for positive electrode slurries, such as N-methylpyrrolidone (NMP).

[0013] Furthermore, the positive electrode active material can be one or more of all known positive electrode materials, such as nickel-cobalt-manganese ternary materials, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and lithium manganese iron phosphate. Among them, the chemical formula of the nickel-cobalt-manganese ternary material is LiNi. x Co y Mn zO2, x+y+z=1.

[0014] Furthermore, the positive electrode conductive agent can be one or more of all known positive electrode conductive materials, such as Super-P (SP), carbon nanotubes (CNT), and acetylene black.

[0015] Furthermore, the positive electrode binder can be one or more of all known positive electrode binders, such as polyvinylidene fluoride (PVDF), polyvinyl alcohol, polytetrafluoroethylene, and sodium carboxymethyl cellulose. PVDF is preferred.

[0016] Further, the slurry is a negative electrode slurry, the active material is a negative electrode active material, the conductive agent is a negative electrode conductive agent, and the binder is a negative electrode binder. The mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder is 94-97 (specifically, 94, 94.5, 95, 95.5, 96, 96.5, 96.7, 96.9): 0.5-3 (specifically, 0.55, 0.7, 0.85, 1, 1.15, 1.3, 1.5, 1.7, 1.9, 2.1, 2.3, 2.5, 2.7, 2.9): 1.5-3.5 (specifically, 1.55, 1.7, 1.9, 2.1, 2.3, 2.5, 2.7, 2.9, 3.1, 3.3, 3.45).

[0017] Furthermore, the solvent can be any known solvent for negative electrode slurries, such as pure water.

[0018] Furthermore, the negative electrode active material can be one or more of all known negative electrode materials, such as artificial graphite, natural graphite, silicon-oxygen or silicon-carbon materials.

[0019] Furthermore, the negative electrode binder can be one or more of all known negative electrode bonding materials, such as styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyvinyl alcohol, and polytetrafluoroethylene. Preferably, it is a CMC and SBR in a mass ratio of 1 to 2 (specifically 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9): 0.5 to 1.5 (specifically 0.55, 0.7, 0.85, 1, 1.15, 1.3, 1.45).

[0020] Furthermore, the negative electrode conductive agent can be one or more of all known negative electrode conductive materials, such as Super-P (SP), carbon nanotubes (CNT), and acetylene black.

[0021] Secondly, the present invention provides a method for preparing the above-mentioned slurry, wherein the method for preparing the slurry is as follows: mixing and dispersing the raw materials to obtain the slurry.

[0022] Specifically, the slurry can be prepared using conventional methods in lithium-ion battery slurry preparation, such as dry slurry preparation or wet slurry preparation. Dry slurry preparation involves mixing active materials, conductive agents, binders, and pore-forming agents into a mixture, and then dispersing this mixture with a solvent. In other words, all solid materials are mixed before being mixed with a liquid solvent. The solvent can be added to the mixture or slurry in multiple portions.

[0023] The wet slurry mixing process specifically involves adding active materials, conductive agents, binders, and pore-forming agents to a solvent for mixing and dispersion. This means that at least a portion of the solid materials are first mixed with the liquid solvent. The active materials, conductive agents, and other solid materials can be added to the solvent or slurry in multiple portions.

[0024] Furthermore, the pore-forming agent is directly dissolved and dispersed in a solvent or slurry.

[0025] Furthermore, the pore-forming agent is dispersed in the solvent or slurry in the form of a suspension via a binder.

[0026] Thirdly, the present invention provides an electrode sheet prepared using the above-mentioned slurry.

[0027] Fourthly, the present invention provides a method for preparing the above-mentioned electrode sheet. The method for preparing the electrode sheet includes: coating the slurry on at least one surface of the current collector, and simultaneously performing forced air drying during the coating process to sublimate the pore-forming agent, thereby leaving pores on the active material layer of the electrode sheet, and then subjecting the electrode sheet with pores to rolling, die cutting and slitting to obtain the electrode sheet.

[0028] Furthermore, the coating includes front coating and back coating on opposite sides of the current collector, and both the front coating and the back coating are dried by forced air during the coating process.

[0029] This invention uses a forced-air drying method, which allows for rapid and uniform temperature diffusion, ensuring that the electrode is heated evenly and dries easily, and also allows for the rapid removal of evaporated solvents and other substances.

[0030] Furthermore, the size of the pores is at the micro-nano scale.

[0031] Furthermore, the air frequency control of the blower drying is divided into multiple segments, with each segment having the same or different air frequency control, and the temperature control of the blower drying is divided into multiple segments, with each segment having the same or different temperature control.

[0032] Furthermore, the electrode is a positive electrode. When the positive electrode is coated on the front side, the air frequency of the blower drying is controlled at 10-35Hz (specifically, 11Hz, 13Hz, 15Hz, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz), and the temperature is controlled at 85-125℃ (specifically, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃, 106℃, 108℃, 110℃, 112℃, 114℃, 116℃, 118℃, 120℃, 122℃, 124℃).

[0033] Preferably, the wind frequency control is in the following order: 10-30Hz (specifically, 11Hz, 13Hz, 15Hz, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz), 15-35Hz (specifically, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz), and 15-35Hz (specifically, 17Hz, 19Hz). 15-35Hz (specifically 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz), 10-30Hz (specifically 11Hz, 13Hz, 15Hz, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz);

[0034] The corresponding temperature controls, from highest to lowest, are: 85–105℃ (specifically 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃), 95–115℃ (specifically 96℃, 98℃, 100℃, 102℃, 104℃, 106℃, 108℃, 110℃, 112℃, 114℃), and 104–124℃ (specifically 106℃, 108℃, 114℃). 0℃, 112℃, 114℃, 116℃, 118℃, 120℃, 122℃), 105~125℃ (specifically 106℃, 108℃, 110℃, 112℃, 114℃, 116℃, 118℃, 120℃, 122℃, 124℃), 85~105℃ (specifically 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃);

[0035] During reverse coating, the air frequency of the blower drying is controlled at 15-40Hz (specifically, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz, 35Hz, 37Hz, 39Hz), and the temperature is controlled at 85-135℃ (specifically, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 132℃, 134℃).

[0036] Preferably, the wind frequency control is configured in the following order: 15-35Hz (specifically, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz), 20-40Hz (specifically, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz, 35Hz, 37Hz, 39Hz), 20-40Hz (specifically, 21Hz, 23 ...5Hz, 37Hz, 39Hz), 20-40Hz (specifically, 21Hz, 23Hz, 29Hz, 31Hz, 35Hz, 37Hz, 39Hz), 20-40Hz (specifically, 21Hz, 23Hz, 29Hz, 29Hz, 31 5Hz, 27Hz, 29Hz, 31Hz, 33Hz, 35Hz, 37Hz, 39Hz), 20-40Hz (specifically 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz, 35Hz, 37Hz, 39Hz), 15-35Hz (specifically 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz);

[0037] The corresponding temperature controls, from highest to lowest, are: 85–105℃ (specifically 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃), 96–116℃ (specifically 98℃, 100℃, 102℃, 104℃, 106℃, 108℃, 110℃, 112℃, 114℃), and 95–135℃ (specifically 96℃, 98℃, 100℃, 105℃). 106-126℃ (specifically 108℃, 110℃, 112℃, 114℃, 116℃, 118℃, 120℃, 122℃, 124℃), 85-105℃ (specifically 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃);

[0038] The current collector can be any known current collector for positive electrodes, such as aluminum foil.

[0039] Furthermore, the electrode is a negative electrode. When the negative electrode is coated on the front side, the air frequency of the blower drying is controlled at 10-35Hz (specifically, 11Hz, 13Hz, 15Hz, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz), and the temperature is controlled at 80-115℃ (specifically, 82℃, 84℃, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃, 106℃, 108℃, 110℃, 112℃, 114℃).

[0040] Preferably, the wind frequency control is in the following order: 10-30Hz (specifically, 11Hz, 13Hz, 15Hz, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz), 15-35Hz (specifically, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz), and 15-35Hz (specifically, 17Hz, 19Hz). 15-35Hz (specifically 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz), 10-30Hz (specifically 11Hz, 13Hz, 15Hz, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz);

[0041] The corresponding temperature controls, from highest to lowest, are: 80–100℃ (specifically 81℃, 83℃, 85℃, 87℃, 89℃, 91℃, 93℃, 95℃, 97℃, 99℃), 90–110℃ (specifically 91℃, 93℃, 95℃, 97℃, 99℃, 101℃, 103℃, 105℃, 107℃, 109℃), and 95–115℃ (specifically 96℃, 98℃, 100℃). 102℃, 104℃, 106℃, 108℃, 110℃, 112℃, 114℃), 90~110℃ (specifically 91℃, 93℃, 95℃, 97℃, 99℃, 101℃, 103℃, 105℃, 107℃, 109℃), 80~100℃ (specifically 81℃, 83℃, 85℃, 87℃, 89℃, 91℃, 93℃, 95℃, 97℃, 99℃);

[0042] During reverse coating, the air frequency of the blower drying is controlled at 10-40Hz (specifically, 11Hz, 13Hz, 15Hz, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz, 35Hz, 37Hz, 39Hz), and the temperature is controlled at 80-117℃ (specifically, 82℃, 84℃, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃, 106℃, 108℃, 110℃, 112℃, 114℃, 116℃).

[0043] Preferably, the wind frequency control is configured in the following order: 10–30Hz (specifically, 11Hz, 13Hz, 15Hz, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz), 15–35Hz (specifically, 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz), and 20–40Hz (specifically, 21Hz, 23Hz, 29 ... 5Hz, 27Hz, 29Hz, 31Hz, 33Hz, 35Hz, 37Hz, 39Hz), 20-40Hz (specifically 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz, 35Hz, 37Hz, 39Hz), 15-35Hz (specifically 17Hz, 19Hz, 21Hz, 23Hz, 25Hz, 27Hz, 29Hz, 31Hz, 33Hz);

[0044] The corresponding temperature controls, from highest to lowest, are: 80–100℃ (specifically 81℃, 83℃, 85℃, 87℃, 89℃, 91℃, 93℃, 95℃, 97℃, 99℃), 90–110℃ (specifically 91℃, 93℃, 95℃, 97℃, 99℃, 101℃, 103℃, 105℃, 107℃, 109℃), and 97–117℃ (specifically 98℃, 100℃, 109℃). 2℃, 104℃, 106℃, 108℃, 110℃, 112℃, 114℃, 116℃), 92~112℃ (specifically 94℃, 96℃, 98℃, 100℃, 102℃, 104℃, 106℃, 108℃, 110℃), 80~100℃ (specifically 81℃, 83℃, 85℃, 87℃, 89℃, 91℃, 93℃, 95℃, 97℃, 99℃);

[0045] The current collector can be any known current collector for negative electrodes, such as copper foil.

[0046] During the forced-air drying process of this invention, both airflow and temperature control are flexibly adjusted based on the actual effects of the slurry and coating. Multiple temperature settings are available for easy adjustment, especially multi-stage temperature control, which ensures uniform heating of the electrode sheet from the outside in, preventing excessive temperature differences, rapid heating or cooling that could cause cracking. Furthermore, the temperature in each stage must not be too high or too low. Excessive temperature can easily cause the electrode sheet to crack, and if the negative electrode sheet contains SBR, it can easily cause the SBR to float. Insufficient temperature results in poor drying effect and low drying efficiency. Similarly, excessively high airflow can also cause electrode sheet cracking, while excessively low airflow will also result in poor drying effect. By controlling the airflow and temperature within the range specified in this invention, electrode sheets with both good drying quality and pore formation quality can be obtained.

[0047] Fifthly, the present invention provides a battery cell containing the aforementioned electrode sheets.

[0048] In a sixth aspect, the present invention provides a method for preparing the above-mentioned battery cell, wherein the electrode sheets are wound or stacked to obtain the battery cell.

[0049] In a seventh aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the above-mentioned electrode or comprising the above-mentioned cell.

[0050] Furthermore, the lithium-ion battery is a pouch lithium-ion battery or a hard-shell lithium-ion battery.

[0051] Eighthly, the present invention provides a method for preparing the above-mentioned lithium-ion battery, wherein the battery cell is baked, injected with electrolyte, formed, aged, and capacity tested to obtain a lithium-ion battery.

[0052] Compared with the prior art, the present invention has the following advantages:

[0053] 1. This invention significantly improves the electrolyte absorption capacity of the electrode, enhances wetting performance, and increases the density and quality of the formed film by adding a small amount of easily sublimable pore-forming agent during the slurry mixing process, without adding any additional steps. This is a simple and low-cost method. Simultaneously, the pre-reserved pore spaces on the electrode provide more reaction sites, reduce uneven electrode polarization, and prevent deformation during battery charging and discharging, thus avoiding damage to the cell structure and improving the battery's cycle life, rate performance, and stability.

[0054] 2. This invention can increase the porosity of the electrode and greatly improve its wettability. While increasing the areal density and group margin of the electrode, the electrode still has good liquid absorption and wetting without increasing the impedance of the cell. Therefore, it can improve the energy density and power density of the battery. Attached Figure Description

[0055] Figure 1 This is a SEM image of the positive electrode sheet in Embodiment 1 of the present invention;

[0056] Figure 2 This is a low-magnification SEM image of the negative electrode sheet in Embodiment 1 of the present invention;

[0057] Figure 3 This is a high-magnification SEM image of the negative electrode sheet in Embodiment 1 of the present invention;

[0058] Figure 4 This is an interface diagram of the negative electrode sheet after formation in Embodiment 1 of the present invention;

[0059] Figure 5 This is an interface diagram of the negative electrode sheet after formation in Comparative Example 4 of the present invention.

[0060] Figure 6 These are battery cycle performance test graphs for Embodiment 1 and Comparative Example 4 of the present invention;

[0061] Figure 7 The figures show the battery impedance performance test results of Embodiment 1 and Comparative Example 4 of the present invention. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this invention clearer, the following embodiments are provided to further illustrate the invention. The embodiments of this invention are implemented based on the technical solutions of this invention, and detailed implementation methods and processes are given. Those skilled in the art should understand that the embodiments are merely illustrative of the invention and should not be considered as specific limitations on the invention. Furthermore, the scope of protection of this invention is not limited to the following embodiments. 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.

[0063] In the embodiments of this invention, process parameters not specifically specified are generally performed under conventional conditions. Unless otherwise specified and / or stated, all numerical values ​​relating to component amounts are "values ​​or ratios by weight or mass" throughout. Unless otherwise stated, all raw materials used in this invention are available from commercially available products.

[0064] In this invention, the endpoints and any values ​​of the disclosed ranges 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.

[0065] The present invention will now be described in further detail with reference to specific embodiments.

[0066] Example 1

[0067] (1) Preparation of positive electrode sheet

[0068] A mixture was prepared by mixing lithium iron phosphate (LFP), SP, PVDF, and methacrylate (SPF) in a mass ratio of 96.59:1.4:2:0.01. This mixture was then dispersed with NMP, thus synthesizing the positive electrode slurry via a dry process. The positive electrode slurry was coated onto aluminum foil, and the coating process involved front (single-sided) coating and drying, back (double-sided) coating and drying, rolling, die-cutting, and slitting to obtain the positive electrode sheet. The surface morphology of this sheet is as follows: Figure 1 As shown in the SEM image, the surface of the positive electrode sheet has a porous structure with uniformly dispersed pores at the micro-nano scale; the thickness of the positive electrode sheet is 158 μm, and the areal density is 357 g / m³. 2 The process parameters for coating and drying the positive electrode sheet are shown in Table 1.

[0069] Table 1. Parameters for Coating and Drying of Positive Electrode Sheets

[0070]

[0071] (2) Preparation of negative electrode sheet

[0072] A mixture was prepared by mixing graphite, SP, CMC, SBR, and methacrylate in a ratio of 96.49:0.5:1.6:1.4:0.01. This mixture was then dispersed with pure water, thus synthesizing the negative electrode slurry via a dry process. The negative electrode slurry was coated onto copper foil, and the coating process involved first-side (single-sided) coating and drying, second-side (double-sided) coating and drying, rolling, die-cutting, and slitting to obtain the negative electrode sheet. The surface morphology of this sheet is as follows: Figure 2 , 3 As shown in the SEM image, the surface of the negative electrode sheet has a porous structure with uniformly dispersed pores at the micro-nano scale; the thickness of the negative electrode sheet is 123 μm, and the areal density is 175 g / m³. 2 The process parameters for coating and drying the negative electrode sheet are shown in Table 2.

[0073] Table 2. Parameters for Coating and Drying of Negative Electrode Sheets

[0074]

[0075]

[0076] (3) Cell fabrication

[0077] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain the battery cell. The separator can be any known lithium-ion battery separator, such as polypropylene film, polyethylene film, polytetrafluoroethylene film, glass fiber film, or non-woven ceramic particle composite film. In this embodiment, polypropylene film is used as the separator.

[0078] (4) Preparation of lithium-ion secondary batteries

[0079] The battery cells are welded to the top cover via tabs, placed in the outer packaging shell, and then baked, injected with electrolyte, formed, aged, and tested to obtain a lithium-ion secondary battery with an energy density of 174Wh / kg.

[0080] Examples 2-12 and Comparative Examples 1-5

[0081] The difference between Examples 2-12 and Comparative Examples 1-5 and Example 1 lies in the fact that, during the preparation of the electrode sheet, different electrode sheets and lithium-ion secondary batteries were obtained by adjusting the type and amount of pore-forming agent during the preparation of the slurry. The specific types and amounts of pore-forming agents adjusted are shown in Table 3.

[0082] Table 3

[0083]

[0084]

[0085] Detection example

[0086] The batteries prepared in Examples 1-12 and Comparative Examples 1-5 were tested for liquid absorption performance, cycle performance, and rate performance. The methods were as follows:

[0087] Liquid absorption performance test: After the battery cell is dissolved and weighed after being classified and compatibility determined, the weight of the free electrolyte is measured.

[0088] Cyclic performance testing: Calculate the capacity retention rate after 1000 cycles at 25°C and 1C.

[0089] Rate performance test: Calculate the ratio of the capacity of 1C charging and 2.5C discharging to the capacity of 1C charging and 1C discharging;

[0090] The test results are shown in Table 4.

[0091] Table 4

[0092]

[0093]

[0094] As can be seen from the data in Table 4, the battery in the embodiments of the present invention has less free electrolyte compared to the comparative examples. This indicates that the battery in the embodiments of the present invention has better electrolyte absorption capacity and wetting performance. Table 4 also shows that the battery in the embodiments of the present invention has better cycle performance and rate performance. A comparison of Examples 1-12 with Comparative Examples 1 and 5 shows that when there is more pore-forming agent and more pores left on the electrode, the free electrolyte of the battery does not decrease due to the increased electrode pores. This is because more pores reduce the amount of active material, thus reducing the electrolyte absorption capacity and increasing the amount of free electrolyte. A comparison of Examples 1-12 with Comparative Examples 2-4 shows that when there is very little pore-forming agent and very few or no pores left on the electrode, the free electrolyte of the battery increases due to the reduction or even absence of pores on the positive and / or negative electrode plates. This demonstrates that the appropriate amount of pores on the positive and / or negative electrode plates can greatly improve the battery's electrolyte absorption capacity and wetting performance.

[0095] in addition, Figure 4 The diagram shows the interface of the negative electrode sheet after formation in Example 1. It can be seen from the diagram that after the electrode sheet absorbs liquid, the amount of liquid absorbed is relatively large, the liquid is completely dispersed, and the wetting is uniform. Figure 5 The diagram shows the interface of the negative electrode sheet after formation in Comparative Example 4. It can be seen from the diagram that after the electrode sheet absorbs liquid, the amount of liquid absorbed is small, the liquid cannot be dispersed, and the wetting is very uneven.

[0096] Figure 6 The graph shows the cycle performance test results. As can be seen, Example 1 retains 95.4% of its capacity after 1000 cycles at 25°C using 1C / 1C, and the capacity retention is still above 80% after 7000 cycles. In contrast, Comparative Example 4 retains only 88.1% of its capacity after 1000 cycles at 25°C using 1C / 1C, and it takes less than 5000 cycles to achieve 80% capacity retention. Therefore, the battery of this invention exhibits higher cycle life and stability.

[0097] Figure 7 The impedance performance test diagram shows that the internal resistance of Comparative Example 4 is greater than that of Example 1. Based on the fact that power density is approximately equal to energy density divided by internal resistance, the energy density of Comparative Example 4 is 165Wh / kg, which is less than the energy density of 174Wh / kg tested in Example 1. Therefore, the power density of Comparative Example 4 is less than that of Example 1. It can be seen that the battery of the present invention has higher energy density and power density, and lower impedance.

[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 battery cell, characterized in that, The battery cell includes an electrode sheet, which is prepared by a slurry, the slurry including an active material, a conductive agent, a binder, a pore-forming agent and a solvent; When the slurry is a positive electrode slurry, the active material is a positive electrode active material, the conductive agent is a positive electrode conductive agent, the binder is a positive electrode binder, the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is 95~97:0.5~3:1.5~4, the pore-forming agent is methacrylate, and the pore-forming agent accounts for 0.01% of the total solid mass in the slurry; When the slurry is a negative electrode slurry, the active material is a negative electrode active material, the conductive agent is a negative electrode conductive agent, the binder is a negative electrode binder, the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder is 94~97:0.5~3:1.5~3.5, the pore-forming agent is methacrylate, the pore-forming agent accounts for 0.05% of the total solid mass in the slurry, and the negative electrode binder is carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1~2:1; The preparation method of the slurry is as follows: the raw materials are mixed and dispersed to obtain the slurry. The mixing and dispersion of the raw materials is to first mix the active material, conductive agent, binder and pore-forming agent into a mixture, and then mix and disperse the mixture with a solvent. The preparation method of the electrode sheet includes the following steps: coating the slurry on the surface of the current collector, and simultaneously drying it with forced air during the coating process to sublimate the pore-forming agent, thereby leaving pores on the active material layer of the electrode sheet. Then, the electrode sheet with pores is rolled, die-cut and slit to obtain the electrode sheet. The size of the pores is in the micro-nano scale; The coating includes a front coating and a back coating on opposite sides of the current collector, and both the front coating and the back coating are dried by forced air during the coating process. The electrode is a positive electrode. When the positive electrode is coated on the front side, the wind frequency is controlled from first to last as follows: 10~30 Hz, 15~35 Hz, 15~35 Hz, 15~35 Hz, 10~30 Hz; the corresponding temperature is controlled from first to last as follows: 85~105 ℃, 95~115 ℃, 104~124 ℃, 105~125 ℃, 85~105 ℃. During reverse coating, the air frequency is controlled in the following order: 15~35 Hz, 20~40 Hz, 20~40 Hz, 20~40 Hz, 15~35 Hz; the corresponding temperature is controlled in the following order: 85~105 ℃, 96~116 ℃, 95~135 ℃, 106~126 ℃, 85~105 ℃. The electrode is a negative electrode. When the negative electrode is coated on the front side, the wind frequency is controlled in the following order: 10~30 Hz, 15~35 Hz, 15~35 Hz, 15~35 Hz, 10~30 Hz; the corresponding temperature is controlled in the following order: 80~100 ℃, 90~110 ℃, 95~115 ℃, 90~110 ℃, 80~100 ℃. During reverse coating, the air frequency is controlled in the following order: 10~30 Hz, 15~35 Hz, 20~40 Hz, 20~40 Hz, 15~35 Hz; the corresponding temperature is controlled in the following order: 80~100 ℃, 90~110 ℃, 97~117 ℃, 92~112 ℃, 80~100 ℃.

2. A lithium-ion battery, characterized in that, The lithium-ion battery contains the cell described in claim 1.

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