A thick electrode, its preparation method and application

Abstract

The application discloses a thick electrode and a preparation method and application thereof, and relates to the technical field of secondary batteries. The thick electrode comprises a three-dimensional network structure formed by a binder long fiber, and active material particles and conductive agent particles filled in the three-dimensional network structure; the thickness of the thick electrode is greater than or equal to 300 micrometers; the electrode loading of the thick electrode is greater than or equal to 20 mg / cm 2 ; and the mass percentage of the active material particles is greater than or equal to 85%. The thick electrode is prepared by simultaneously performing electrostatic spinning and electrostatic spraying. The thick electrode is prepared by combining electrostatic spinning and electrostatic spraying technologies, the thickness of the prepared thick electrode is significantly improved compared with the thick electrode prepared by a conventional film coating method, and the thick electrode is not cracked. Meanwhile, the rate performance of the electrode can be improved on the basis of no cracking.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a thick electrode, its preparation method, and its application. Background Technology

[0002] To improve the energy density of secondary batteries, fabricating thick electrodes is a common and effective strategy. This is achieved by increasing the loading of active materials (e.g., >10 mg / cm³). 2 Reducing the proportion of inert components is an effective way to improve battery energy density. Thick electrode technology can also significantly reduce battery production costs, thus becoming a research hotspot in the industry. However, there are certain difficulties in preparing thick electrodes using traditional casting methods. For example, electrodes using polyvinylidene fluoride (PVDF) as a binder are prone to cracking due to capillary forces during drying, with a maximum crack-free thickness of approximately 127 μm. Electrodes exceeding this thickness are extremely prone to cracking, and PVDF tends to migrate and aggregate after dissolution, damaging the conductive network. In current commercial lithium-ion batteries, the electrode thickness, including both the cathode and anode, is limited to between 50-100 μm. Therefore, there is an urgent need to develop new thick electrode preparation technologies. In addition, increasing electrode thickness leads to a significant decrease in the rate performance of thick electrodes, which poses an obstacle to their commercial application. Therefore, it is necessary to develop thick electrodes that ensure ion / electron transport and new preparation technologies. Summary of the Invention

[0003] The purpose of this invention is to provide a thick electrode, its preparation method, and its application to solve the problems existing in the prior art. Specifically, the traditional casting method for preparing thick electrodes mainly has the following two problems: (1) poor mechanical stability of the electrode: during the drying process, the conductive agent and binder diffuse to the electrode surface under the action of capillary stress, forming agglomerates, which damages the mechanical properties, and the electrode is prone to cracking as the thickness increases; (2) poor electrochemical performance of the electrode: high loading electrodes increase the thickness of the electrode film, thereby increasing the diffusion distance of the charge in the electrode. In the electrochemical process, the longer the charge diffusion distance, the lower the mass transfer efficiency, resulting in poor electrochemical performance. Based on the above problems, the main purpose of this invention is to: (1) improve the mechanical stability of the electrode: increase the thickness of the electrode while ensuring that the electrode does not crack; (2) enhance the electrochemical performance of the electrode: improve the rate performance of the electrode without cracks.

[0004] To achieve the above objectives, the present invention provides the following solution:

[0005] One of the technical solutions of the present invention is a thick electrode, comprising a three-dimensional network structure formed by binder long fibers (continuous filaments with high continuity), and active material particles and conductive agent particles filled in the three-dimensional network structure (see schematic diagram of the thick electrode structure as shown). Figure 1 (as shown)

[0006] The thickness of the thick electrode is ≥300μm;

[0007] The electrode loading (i.e., the mass of active material loaded on a unit area electrode) of the thick electrode is ≥20 mg / cm². 2 ;

[0008] The mass percentage of the active material particles is ≥85% (i.e., the mass of active material particles / (mass of binder long fibers + mass of active material particles + mass of conductive agent particles) × 100% ≥ 85%, which is also the mass of active material in the raw material / (mass of binder + mass of active material particles + mass of conductive agent) × 100% ≥ 85%).

[0009] The binder fibers form a three-dimensional network structure, with active material particles and conductive agent particles uniformly filling (i.e., uniformly distributed) within this network, much like plant roots tightly gripping the soil. This unique structure effectively enhances the mechanical strength of thick electrodes and prevents them from cracking. Simultaneously, this structure ensures point / line contact between the active material and conductive agent and the binder fibers, preventing blockage of ion transport pores and contributing to improved rate performance.

[0010] Preferably, the thickness of the thick electrode is 300–1000 μm.

[0011] Preferably, the electrode loading of the thick electrode is 20–100 mg / cm³. 2 .

[0012] Furthermore, the diameter of the adhesive long fibers is 50–1000 nm.

[0013] Furthermore, the average length of the binder long fibers is >100μm; the ratio of the average length of the binder long fibers to the average particle size of the active material particles is >100, preferably >500, more preferably >1000.

[0014] The second technical solution of the present invention: a method for preparing the above-mentioned thick electrode, comprising the following steps:

[0015] Long fibers of binder are deposited on the current collector by electrospinning, and active material particles and conductive agent particles are deposited on the current collector by electrostatic spraying during electrospinning.

[0016] Alternatively, binder long fibers and conductive agent particles can be deposited on the current collector by electrospinning, and active material particles can be deposited on the current collector by electrostatic spraying during electrospinning.

[0017] The above method combines electrospinning and electrospraying techniques to prepare thick electrodes (see schematic diagram of the operation of preparing thick electrodes using the combined electrospinning and electrospraying technique). Figure 2 (As shown). Specifically, binder long fibers are prepared using electrospinning technology, while active material particles are sprayed onto the binder long fibers using electrostatic spraying technology. Conductive agent particles can be sprayed using either electrospinning or electrostatic spraying technology. Electrospinning and electrostatic spraying are performed simultaneously, depositing the binder, conductive agent, and active material onto the current collector in a specific ratio. The combined use of electrospinning and electrostatic spraying technologies significantly increases the active material loading compared to electrospinning alone, while maintaining stable and continuous spinning.

[0018] Further, the deposition of binder long fibers on the current collector by electrospinning, and the deposition of active material particles and conductive agent particles on the current collector by electrostatic spraying simultaneously with electrospinning, includes: dispersing the active material and conductive agent in solvent 1 to obtain a spray solution; dissolving the binder in solvent 2 to obtain a spinning solution; placing the current collector on a collecting drum, and simultaneously performing electrospinning and electrostatic spraying to deposit binder long fibers, active material particles and conductive agent particles on the current collector at the same time; drying after deposition to obtain the thick electrode.

[0019] Furthermore, the deposition of binder long fibers and conductive agent particles on the current collector by electrospinning, and the deposition of active material particles on the current collector by electrostatic spraying during electrospinning, includes: dispersing the active material in solvent 1 to obtain a spray solution; dissolving the binder and conductive agent in solvent 2 to obtain a spinning solution; placing the current collector on a collecting drum, and simultaneously performing electrospinning and electrostatic spraying to simultaneously deposit binder long fibers, active material particles, and conductive agent particles on the current collector; drying after deposition to obtain the thick electrode.

[0020] Optionally, the adhesive includes, but is not limited to, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polystyrene, polyurethane, or cellulose acetate.

[0021] Optionally, the active material includes, but is not limited to, LiFePO4 (LFP), LiCoO2 (LCO), ternary cathode material, silicon anode material, or sodium electrode material.

[0022] Optionally, the conductive agent includes, but is not limited to, carbon nanotubes (CNTs), Ketjen black, acetylene black, graphene, or Mxene.

[0023] Furthermore, the solvent 1 is a solvent that does not dissolve the binder but can disperse the active material and the conductive agent.

[0024] Optionally, the solvent 1 includes, but is not limited to, ethanol or isopropanol.

[0025] Furthermore, the solvent 2 is a solvent capable of dissolving the adhesive.

[0026] Optionally, the solvent 2 includes, but is not limited to, one or more of methylpyrrolidone (NMP), acetone, and N,N-dimethylformamide (DMF).

[0027] Optionally, after dispersing the active substance or active substance + conductive agent in solvent 1, the process further includes sonication for 1 to 3 hours and stirring for 6 to 15 hours.

[0028] Optionally, after dissolving the adhesive or adhesive + conductive agent in solvent 2, the process further includes sonicating at 60°C for 1–3 hours and stirring for 6–15 hours.

[0029] Optionally, the concentration of the binder in the spinning solution is 2 to 20 wt%.

[0030] When the concentration of binder in the spinning solution is within the above range, smooth and continuous spinning can be ensured, resulting in continuous filaments with high continuity.

[0031] Furthermore, the parameters of the electrospinning include: negative voltage of -1 to -2 kV and positive voltage of 10 to 20 kV.

[0032] Furthermore, the rotational speed of the collecting drum is 100–140 rpm.

[0033] Optionally, the current collector may include, but is not limited to, aluminum foil, copper foil, titanium foil, or nickel foil.

[0034] Furthermore, during the electrospinning and electrospraying processes, the mass ratio of binder long fibers, active material particles, and conductive agent particles deposited on the current collector is controlled by adjusting the injection speed of electrospinning and electrospraying, as well as the mass ratio of active material to conductive agent in the spray solution or the mass ratio of binder to conductive agent in the spinning solution. This ensures that the mass percentage of active material particles in the binder long fibers, active material particles, and conductive agent particles deposited on the current collector is ≥85%.

[0035] Preferably, during the electrospinning and electrospraying processes, by controlling the injection speed of electrospinning and electrospraying, as well as the mass ratio of active material to conductive agent in the spray solution or the mass ratio of binder to conductive agent in the spinning solution, at a mass ratio of 85-97:1-5:2-10, long fibers of binder, particles of active material, and particles of conductive agent are deposited on the current collector (i.e., based on a total mass of 100, the mass ratio of active material, conductive agent, and binder is 85-97:1-5:2-10).

[0036] The preparation method of this invention can be used to prepare both thin-film electrodes and thick electrodes, and is particularly effective for the preparation of thick electrodes. The prepared thick electrodes have good mechanical strength, with a typical thickness ≥300μm and an electrode loading ≥20mg / cm³. 2 The mass percentage of active material in thick electrodes is ≥85%.

[0037] The second technical solution of the present invention: an application of the above-mentioned thick electrode in the preparation of secondary batteries.

[0038] The third technical solution of the present invention: a secondary battery, wherein the above-mentioned thick electrode is used as the working electrode.

[0039] The present invention discloses the following technical effects:

[0040] In the thick electrode of this invention, the binder long fibers form a three-dimensional network structure. Active material particles and conductive agent particles are uniformly filled within this three-dimensional network structure, similar to plant roots tightly gripping the soil. This unique structure effectively enhances the mechanical strength of the thick electrode and prevents cracking. Simultaneously, this structure ensures point / line contact between the active material and conductive agent and the binder long fibers, preventing blockage of ion transport pores and contributing to improved rate performance.

[0041] This invention uses a combination of electrospinning and electrospraying techniques to prepare thick electrodes. The resulting thick electrodes have a significantly higher thickness than those prepared by conventional coating methods and do not crack.

[0042] The preparation method of the present invention can prepare thick electrodes using various electrode materials as raw materials, such as LFP, LCO, ternary cathode, silicon anode material, sodium electrode material, etc., and has high versatility. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the structure of the thick electrode of the present invention.

[0045] Figure 2 This is a schematic diagram illustrating the operation of preparing thick electrodes using a combination of electrospinning and electrospraying in this invention.

[0046] Figure 3The images are SEM images of the thick electrode prepared in Example 1 at different magnifications, where the scale bar of (a) is 10 μm, the scale bar of (b) is 1 μm, and the scale bar of (c) is 50 μm.

[0047] Figure 4 This is a photograph of the thick electrode prepared in Example 1.

[0048] Figure 5 The electrochemical performance test results of the thick electrode prepared in Example 1 are shown, where (a) is the charge-discharge curve at 0.1C and (b) is the rate performance. Detailed Implementation

[0049] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0050] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0051] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0052] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0053] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0054] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0055] In the following embodiments and comparative examples of the present invention, if room temperature or normal temperature is mentioned, it specifically refers to 20-30 ℃.

[0056] Unless otherwise specified, all raw materials used in the following embodiments and comparative examples of this invention are commercially available products.

[0057] Example 1

[0058] A method for preparing a thick electrode, comprising the following steps:

[0059] 4g of the active ingredient LFP was dispersed in 76g of ethanol, sonicated at room temperature for 1 hour, and then stirred for 12 hours to obtain a spray solution; 1.2g of PVDF binder and 0.12g of conductive agent Ketjen Black were dissolved in DMF. A mixture of 11.28 g of aluminum foil and 7.52 g of acetone was ultrasonicated at 60°C for 1 hour, followed by stirring for 12 hours to obtain a spinning solution. Aluminum foil was placed on a collecting drum rotating at 120 rpm as a current collector. Simultaneously, electrospinning and electrospraying equipment were activated (spinning nozzle inner diameter 0.33 mm, outer diameter 0.63 mm; spray nozzle inner diameter 0.6 mm, outer diameter 0.9 mm). By controlling the injection rates of electrospinning and electrospraying (electrospinning injection rate 0.0225 mL / min, electrospraying injection rate 0.45 mL / min), the active material, conductive agent, and binder were deposited on the current collector at a mass ratio of 89:1:10. The negative pressure for electrospinning was -1.5 kV, and the positive pressure was 10 kV. After reaching the expected load, the electrospinning and electrospraying equipment were simultaneously turned off. The current collector was then removed and vacuum-dried at 120°C for 12 hours to obtain a thick electrode.

[0060] SEM images of the thick electrode prepared in this embodiment at different magnifications are shown below. Figure 3 As shown, (a) has a scale bar of 10 μm, (b) has a scale bar of 1 μm, and (c) has a scale bar of 50 μm. It can be seen that the binder in the thick electrode is electrospun into long fibers, which form a three-dimensional network structure. The active material and conductive agent are uniformly filled in the three-dimensional network structure of the binder in particulate form. The diameter of the binder long fibers is 500–1000 nm. It can also be seen that the binder long fibers are very long (average length > 100 μm), and their length scale is more than 100 times the diameter of the active material particles (i.e., the ratio of the average length of the binder long fibers to the average particle size of the active material particles is > 100).

[0061] The average thickness of the thick electrode prepared in this embodiment is 350 μm, and the electrode loading is 26.75 mg / cm². 2 The active material content in the thick electrode is 89 wt%.

[0062] A physical image of the thick electrode prepared in this embodiment is shown below. Figure 4As shown, the electrode sheet is free of cracks.

[0063] Example 2

[0064] A method for preparing a thick electrode, comprising the following steps:

[0065] 4g of active material LFP and 0.045g of conductive agent Ketjen black were dispersed in 76g of ethanol, sonicated at room temperature for 1 hour, and then stirred for 12 hours to obtain a spray solution; 1.2g of PVDF binder was dissolved in DMF A mixture of 11.28 g of aluminum foil and 7.52 g of acetone was ultrasonicated at 60°C for 1 hour, followed by stirring for 12 hours to obtain a spinning solution. Aluminum foil was placed on a collecting drum rotating at 120 rpm, and electrospinning and electrospraying equipment were simultaneously turned on (spinning nozzle inner diameter 0.33 mm, outer diameter 0.63 mm; spray nozzle inner diameter 0.6 mm, outer diameter 0.9 mm). By controlling the injection speed of electrospinning and electrospraying (electrospinning speed 0.0225 mL / min, electrospraying speed 0.45 mL / min), the active material, conductive agent, and binder were deposited on the current collector at a mass ratio of 89:1:10. The negative pressure of electrospinning was -1.0 kV, and the positive pressure was 15 kV. After reaching the expected load, the electrospinning and electrospraying equipment were simultaneously turned off, and the current collector was removed and vacuum dried at 120°C for 12 hours to obtain a thick electrode.

[0066] In this embodiment, the binder in the thick electrode is electrospun into long fibers, which form a three-dimensional network structure. The active material and conductive agent are uniformly filled in the three-dimensional network structure of the binder in particulate form (the SEM image is similar to that of Example 1 and is not provided here). The diameter of the binder long fibers is 500-1000 nm, and the length of the binder long fibers is very long (average length > 100 μm), with a length scale more than 100 times the diameter of the active material particles.

[0067] The average thickness of the thick electrode prepared in this embodiment is 320 μm, and the electrode loading is 24 mg / cm². 2 The active material content in the thick electrode is 89 wt%. Furthermore, the electrode sheet shows no cracking.

[0068] Example 3

[0069] A method for preparing a thick electrode, comprising the following steps:

[0070] 4g of the active ingredient LFP was dispersed in 76g of ethanol, sonicated at room temperature for 1 hour, and then stirred for 12 hours to obtain a spray solution; 1.2g of PVDF binder and 0.24g of conductive agent Ketjen Black were dissolved in DMF. A mixture of 11.28 g of aluminum foil and 7.52 g of acetone was ultrasonicated at 60°C for 3 hours, followed by stirring for 15 hours to obtain a spinning solution. Aluminum foil was placed on a collecting drum rotating at 100 rpm, and electrospinning and electrospraying equipment were simultaneously turned on (spinning nozzle inner diameter 0.33 mm, outer diameter 0.63 mm; spray nozzle inner diameter 0.6 mm, outer diameter 0.9 mm). By controlling the injection speed of electrospinning and electrospraying (electrospinning speed 0.0225 mL / min, electrospraying speed 0.43 mL / min), the active material, conductive agent, and binder were deposited on the current collector at a mass ratio of 88:2:10. The negative pressure of electrospinning was -1.5 kV, and the positive pressure was 15 kV. After reaching the expected load, the electrospinning and electrospraying equipment were simultaneously turned off, and the current collector was removed and vacuum dried at 120°C for 12 hours to obtain a thick electrode.

[0071] In this embodiment, the binder in the thick electrode is electrospun into long fibers, which form a three-dimensional network structure. The active material and conductive agent are uniformly filled in the three-dimensional network structure of the binder in particulate form (the SEM image is similar to that of Example 1 and is not provided here). The diameter of the binder long fibers is 500-1000 nm, and the length of the binder long fibers is very long (average length > 100 μm), with a length scale more than 100 times the diameter of the active material particles.

[0072] The average thickness of the thick electrode prepared in this embodiment is 320 μm, and the electrode loading is 24 mg / cm². 2 The active material content in the thick electrode is 88 wt%. Furthermore, the electrode sheet shows no cracking.

[0073] Example 4

[0074] A method for preparing a thick electrode, comprising the following steps:

[0075] 4g of the active ingredient LFP was dispersed in 76g of ethanol, sonicated at room temperature for 3 hours, and then stirred for 15 hours to obtain a spray solution; 1.2g of PVDF binder and 0.12g of conductive agent CNT were dissolved in DMF. A mixture of 11.28 g of aluminum foil and 7.52 g of acetone was ultrasonicated at 60°C for 1 hour, followed by stirring for 12 hours to obtain a spinning solution. Aluminum foil was placed on a collecting drum rotating at 100 rpm, and electrospinning and electrospraying equipment were simultaneously turned on (spinning nozzle inner diameter 0.33 mm, outer diameter 0.63 mm; spray nozzle inner diameter 0.6 mm, outer diameter 0.9 mm). By controlling the injection speed of electrospinning and electrospraying (electrospinning speed 0.0225 mL / min, electrospraying speed 0.45 mL / min), the active material, conductive agent, and binder were deposited on the current collector at a mass ratio of 89:1:10. The negative pressure of electrospinning was -1.5 kV, and the positive pressure was 18 kV. After reaching the expected load, the electrospinning and electrospraying equipment were simultaneously turned off, and the current collector was removed and vacuum dried at 100°C for 15 hours to obtain a thick electrode.

[0076] In this embodiment, the binder in the thick electrode is electrospun into long fibers, which form a three-dimensional network structure. The active material and conductive agent are uniformly filled in the three-dimensional network structure of the binder in particulate form (the SEM image is similar to that of Example 1 and is not provided here). The diameter of the binder long fibers is 500-1000 nm, and the length of the binder long fibers is very long (average length > 100 μm), with a length scale more than 100 times the diameter of the active material particles.

[0077] The average thickness of the thick electrode prepared in this embodiment is 300 μm, and the electrode loading is 22 mg / cm². 2 The active material content in the thick electrode is 89 wt%. Furthermore, the electrode sheet shows no cracking.

[0078] Example 5

[0079] A method for preparing a thick electrode, comprising the following steps:

[0080] 4g of active material LCO and 0.235g of conductive agent Ketjen black were dispersed in 76g of ethanol, sonicated at room temperature for 3 hours, and then stirred for 10 hours to obtain a spray solution; 1.2g of PVDF binder was dissolved in DMF A mixture of 11.28 g of aluminum foil and 7.52 g of acetone was ultrasonicated at 60°C for 1 hour, followed by stirring for 10 hours to obtain a spinning solution. Aluminum foil was placed on a collecting drum rotating at 120 rpm, and electrospinning and electrospraying equipment were simultaneously turned on (spinning nozzle inner diameter 0.33 mm, outer diameter 0.63 mm; spray nozzle inner diameter 0.6 mm, outer diameter 0.9 mm). By controlling the injection speed of electrospinning and electrospraying (electrospinning speed 0.0225 mL / min, electrospraying speed 0.41 mL / min), the active material, conductive agent, and binder were deposited on the current collector at a mass ratio of 85:5:10. The negative pressure of electrospinning was -1.0 kV, and the positive pressure was 15 kV. After reaching the expected load, the electrospinning and electrospraying equipment were simultaneously turned off, and the current collector was removed and vacuum dried at 100°C for 15 hours to obtain a thick electrode.

[0081] In this embodiment, the binder in the thick electrode is electrospun into long fibers, which form a three-dimensional network structure. The active material and conductive agent are uniformly filled in the three-dimensional network structure of the binder in particulate form (the SEM image is similar to that of Example 1 and is not provided here). The diameter of the binder long fibers is 500-1000 nm, and the length of the binder long fibers is very long (average length > 100 μm), with a length scale more than 100 times the diameter of the active material particles.

[0082] The average thickness of the thick electrode prepared in this embodiment is 300 μm, and the electrode loading is 20 mg / cm³. 2 The active material content in the thick electrode is 85 wt%. Furthermore, the electrode sheet is free of cracks.

[0083] Comparative Example 1

[0084] The conventional coating method for preparing thin electrodes involves the following steps:

[0085] 0.32 g of the active material LFP and 0.04 g of the conductive agent Ketjen black were mixed, and 0.8 g of a PVDF NMP solution (PVDF concentration 5 wt%) was added and stirred for 6 hours. The stirred slurry was then directly coated onto aluminum foil and vacuum dried at 120 °C for 12 hours. This method is a common technique for preparing thin electrodes. By controlling the coating amount of the slurry, a thickness of 30 μm and an electrode loading of 1.89 mg / cm³ were obtained. 2 The thin electrode contains 80 wt% active material, with a ratio of active material: conductive agent: binder of 80:10:10 (this ratio is the most commonly used ratio in the coating method for preparing electrode sheets in the prior art).

[0086] The electrode prepared in this comparative example did not crack.

[0087] Comparative Example 2

[0088] The conventional coating method for preparing thicker electrodes involves the following steps:

[0089] 0.32 g of active material LFP and 0.04 g of conductive agent Ketjen Black were mixed, and 0.8 g of PVDF NMP solution (PVDF concentration 5 wt%) was added and stirred for 6 hours. The ratio of active material: conductive agent: binder was 80:10:10. The stirred slurry was directly coated onto aluminum foil and then vacuum dried at 120°C for 12 hours. If this method is used to prepare thicker electrodes (e.g., >10 mg / cm²),... 2 The electrode is highly susceptible to cracking. To compare the electrochemical performance of the thick electrode prepared in Example 1 using a combination of electrospinning and electrospraying, this comparative example prepared an electrode with a thickness of 98 μm and an electrode loading of 10.75 mg / cm² by controlling the coating amount of the slurry. 2 The electrode is relatively thick, but cracks are visible to the naked eye.

[0090] Comparative Example 3

[0091] 5.34 g of active material LFP, 0.6 g of PVDF binder, and 0.06 g of conductive agent Ketjenblack were dissolved in a mixture of 11.28 g of DMF and 7.52 g of acetone (mass ratio of active material, conductive agent, and binder: 89:1:10). The mixture was sonicated at 60°C for 1 hour, followed by stirring for 12 hours to obtain a spinning solution. Aluminum foil was placed on a collecting roller rotating at 120 rpm as a current collector. An electrospinning apparatus (spinning nozzle inner diameter 0.33 mm, outer diameter 0.63 mm) was turned on, and electrode material was deposited on the current collector solely through electrospinning. The negative voltage for electrospinning was -1.5 kV, and the positive voltage was 10 kV. The experiment failed because the content of active material in the spinning solution was too high, preventing stable spinning. This further demonstrates the superiority of the synergistic method of electrospinning and electrospraying in preparing thick electrodes.

[0092] Test Example 1

[0093] Electrochemical performance tests were conducted on the electrodes prepared in each embodiment and comparative example. Specifically, the electrode sheets were cut into positive electrode sheets with a diameter of 10 mm. In an argon-filled glove box, they were assembled into CR2032 button cells in the order of negative electrode sheet, separator, electrolyte, and positive electrode sheet. A 1 M LiPF6 solution was used as the electrolyte, with ethyl carbonate (EC) and dimethyl carbonate (DMC) as the solvents (EC:DMC = 1:1, v / v). 150 μL of electrolyte was added to each cell. A GF / D glass fiber separator was used as the separator, and a lithium sheet was used as the negative electrode. The assembled button cells were connected to the Xinwei Battery Testing System, and the electrochemical performance of the electrode materials was tested in the range of 2.5-4.2 V.

[0094] Figure 5 The electrochemical performance test results of the thick electrode prepared in Example 1 are shown, where (a) is the charge-discharge curve at 0.1C and (b) is the rate performance.

[0095] Table 1 shows a comparison of the specific electrochemical performance data of the electrodes prepared in Example 1 and Comparative Examples 1-2.

[0096] Table 1

[0097]

[0098] As shown in Table 1, the thick electrode sheet (with a loading greater than 20 mg / cm²) obtained by the preparation method of the present invention 2 While significantly increasing the thickness, its rate performance remains excellent. Compared to conventional coating methods, regardless of whether the conventional coating method yields a thin electrode (with a loading of 1.89 mg / cm²), it achieves superior performance. 2 ), or a relatively thick electrode (loading of 10.75 mg / cm²). 2 Furthermore, when the content of the conductive agent is 10 times that of the thick electrode of the present invention, the thick electrode of the present invention has significant advantages in terms of capacity and rate capability.

[0099] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A thick electrode, characterized in that, It consists of a three-dimensional network structure formed by long fibers of binder, and active material particles and conductive agent particles filled in the three-dimensional network structure; The thickness of the thick electrode is ≥300μm; The electrode loading of the thick electrode is ≥20 mg / cm³. 2 ; The active substance particles account for ≥85% of the total mass. The average length of the long fibers in the adhesive is >100 μm; The preparation steps of the thick electrode include: Long binder fibers are deposited on the current collector by electrospinning, and active material particles and conductive agent particles are deposited on the current collector by electrostatic spraying during electrospinning; or, long binder fibers and conductive agent particles are deposited on the current collector by electrospinning, and active material particles are deposited on the current collector by electrostatic spraying during electrospinning. The process of depositing binder long fibers on the current collector by electrospinning, and simultaneously depositing active material particles and conductive agent particles on the current collector by electrostatic spraying, includes: dispersing the active material and conductive agent in solvent 1 to obtain a spray solution; dissolving the binder in solvent 2 to obtain a spinning solution; placing the current collector on a collecting drum, and simultaneously performing electrospinning and electrostatic spraying to deposit binder long fibers, active material particles, and conductive agent particles on the current collector; drying after deposition to obtain the thick electrode. The process of depositing binder long fibers and conductive agent particles on the current collector by electrospinning, and simultaneously depositing active material particles on the current collector by electrostatic spraying, includes: dispersing the active material in solvent 1 to obtain a spray solution; dissolving the binder and conductive agent in solvent 2 to obtain a spinning solution; placing the current collector on a collecting drum, and simultaneously performing electrospinning and electrostatic spraying to deposit binder long fibers, active material particles, and conductive agent particles on the current collector; drying after deposition to obtain the thick electrode. The adhesive includes polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polystyrene, polyurethane, or cellulose acetate; Solvent 1 is a solvent that does not dissolve the binder but can disperse the active material and the conductive agent; solvent 2 is a solvent that can dissolve the binder.

2. The thick electrode as described in claim 1, characterized in that, The diameter of the long fibers in the adhesive is 50–1000 nm.

3. The thick electrode as described in claim 1, characterized in that, The ratio of the average length of the binder long fibers to the average particle size of the active material particles is >100.

4. The application of a thick electrode as described in any one of claims 1-3 in the preparation of a secondary battery.

5. A secondary battery, characterized in that, The thick electrode described in any one of claims 1-3 is used as the working electrode.

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