A thick electrode, its preparation method and use

Abstract

This invention provides a thick electrode, its preparation method, and its applications. The thick electrode includes a current collector and at least two electrode layers located on the surface of the current collector. An electrospun layer is disposed between the electrode layers. The active material in the electrode layer closer to the current collector surface is a large-particle-size active material, while the active material in the electrode layer farther from the current collector surface is a small-particle-size active material. This invention improves the electrode loading and thickness by designing at least two electrode layers and optimizing the particle size distribution of the main active material in each layer, thereby increasing the specific capacity and energy density of the battery. Simultaneously, the electrospun layer connects the electrode layers, creating a porosity gradient distribution along the direction perpendicular to the electrode, constructing efficient ion diffusion and conduction channels and electron transport channels. This results in good ion diffusion and conduction, reduces polarization during charging and discharging, and ensures high energy density and power performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a thick electrode, its preparation method and application, and particularly to a thick positive electrode, its preparation method and application. Background Technology

[0002] According to "Made in China 2025," the development plan for power batteries is clearly defined: by 2020, battery energy density will reach 300Wh / kg; by 2025, it will reach 400Wh / kg; and by 2030, it will reach 500Wh / kg. Traditional lithium-ion battery manufacturing methods are no longer sufficient to meet future energy density requirements. Therefore, improving battery energy density is a crucial direction for future development. Based on the working principle and structural composition of lithium-ion batteries, increasing the loading and thickness of active materials on the current collector and reducing the content of inactive materials in the electrodes is the most convenient and effective way to improve lithium battery energy density.

[0003] However, high-load electrodes cause uneven current distribution along the thickness direction, and the lithium-ion concentration varies significantly between the upper and lower surfaces, leading to severe polarization, reduced utilization of active materials, and problems such as lithium plating on the negative electrode surface and damage to the positive electrode structure during charging. Furthermore, as energy density increases, the diffusion and conduction kinetics of lithium ions are severely restricted, making it impossible to maintain the electrode's power performance. The key to high-load electrode design is to ensure increased battery energy density while addressing the conduction kinetics of ions and electrons within the electrode, thus guaranteeing the electrode's power performance.

[0004] CN102324493A discloses a thick electrode with good electrochemical performance. It employs a slurry coating method to composite an electrode film with a current collector, followed by drying and rolling. A second slurry coating is then applied to the dried electrode film surface, and the film is dried and rolled again to prepare the thick electrode. By controlling the rolling pressure of the two processes, different conductivity and porosity of the electrode film at different locations are ensured, solving the problem of difficult electron and ion transport in thick electrodes. However, this invention uses a slurry coating method to composite the electrode film with the current collector and the electrode film. Because wet slurry is applied to the dried electrode film surface, the dried material inevitably dissolves again, affecting the electrode's electronic conductivity and porosity distribution. Furthermore, this method involves two coating, drying, and rolling processes, making it cumbersome and energy-intensive.

[0005] CN110010900A discloses a thick electrode with good electrochemical performance. This patent uses two electrode films with different porosities pressed together, and then the composite electrode film is pressed onto a carbon-coated aluminum foil to form a composite electrode film. However, this invention uses two electrode films with different porosities pressed together, and then the composite electrode film is pressed onto a carbon-coated aluminum foil. Because it is made by pressing two dry electrode films together, there must be an interface between the two electrode films inside the electrode film. This interface is easily delaminated and detached during the charging and discharging process of the battery due to changes in internal electrode stress, affecting the battery's cycle performance and also increasing the cost.

[0006] CN112670443A discloses a method for preparing thick electrodes. This document describes a method of preparing active layers of different thicknesses by adding different concentrations of pore-forming agents to a slurry, and then using high-temperature drying to decompose the pore-forming agents and generate gas to adjust the porosity. However, this method of preparing electrodes by adding pore-forming agents and then decomposing them at high temperatures can easily leave non-conductive pore-forming agents in the coating, increasing the battery's internal resistance. Furthermore, the high-temperature decomposition process can easily create closed pores, reducing the electrode's porosity, and the pore size cannot be controlled, making it easier to increase the tortuosity of the pores, which is detrimental to improving the battery's energy density.

[0007] Therefore, how to simultaneously ensure high energy density and dynamic performance of thick electrode batteries is a technical problem that urgently needs to be solved. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a thick electrode, its preparation method, and its applications. The present invention improves the electrode loading and thickness by designing at least two electrode layers and optimizing the particle size distribution of the main active material in each layer, thereby increasing the specific capacity and energy density of the battery. Simultaneously, electrospinning layers connect the electrode layers, creating a porosity gradient distribution along the direction perpendicular to the electrode, constructing efficient ion diffusion and conduction channels as well as electron transport channels. This results in excellent ion diffusion and conduction, reduces polarization during charging and discharging, and ensures high energy density and power performance of the battery.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a thick electrode, the thick electrode comprising a current collector and at least two electrode layers located on the surface of the current collector, wherein an electrospinning layer is further disposed between the electrode layers, the active material in the electrode layer near the surface of the current collector is a large-particle-size active material, and the active material in the electrode layer away from the surface of the current collector is a small-particle-size active material.

[0011] In this invention, at least two electrode layers are located on the same side of the current collector. The current collector may have at least two electrode layers on both sides, or it may have at least two electrode layers on only one side.

[0012] This invention improves the electrode loading and thickness by designing at least two electrode layers and optimizing the particle size distribution of the main active material in each layer, thereby increasing the specific capacity and energy density of the battery. At the same time, the connection between the electrode layers is achieved through electrospinning, which creates a porosity gradient distribution along the direction perpendicular to the electrode, constructing an efficient ion diffusion and conduction channel as well as an electron transport channel. This results in good ion diffusion and conduction, reduces polarization during charging and discharging, and ensures the high energy density and power performance of the battery.

[0013] In this invention, a continuous ion channel is formed between the electrode layer and the electrospinning layer, which can greatly improve the redox reaction kinetics and form a gradient pore structure perpendicular to the electrode direction, ensuring rapid electrolyte wetting and lithium ion deintercalation / intercalation during rapid charging and discharging.

[0014] In this invention, the electrospinning layer plays a role in improving the electronic conductivity between electrode layers. If the electrospinning layer is not provided between the electrode layers, the transfer of electrons between the electrode layers will be seriously affected.

[0015] In this invention, the design of gradient electrodes is achieved by matching large and small particle sizes, which improves the rate charging performance of the electrode and the capacity utilization at high rates. If the particle size of the active material in different electrode layers is consistent, the performance at high rates will deteriorate. However, if the active material with small particle size is close to the current collector and the active material with large particle size is far away from the current collector, the rapid insertion and extraction of lithium ions cannot be achieved.

[0016] Preferably, the electrospun layer comprises nanofibers and a binder.

[0017] Preferably, the electrospun layer further includes a conductive agent.

[0018] In this invention, adding a conductive agent to the electrospun layer can further enhance the electronic conductivity of the electrospun layer.

[0019] Preferably, the nanofibers include any one or a combination of at least two of polyacrylonitrile, polymethyl methacrylate, or carbon fiber.

[0020] Preferably, the nanofibers are carbon fibers.

[0021] In this invention, when the electrospun layer is made of carbon fiber, it can form a 3D continuous electronic network / ion channel with the electrode layer. Furthermore, the active particles embedded in the 3D framework can greatly improve the redox reaction kinetics and form a gradient pore structure perpendicular to the electrode direction, ensuring rapid wetting of the electrolyte and the deintercalation and intercalation of lithium ions during rapid charging and discharging.

[0022] Preferably, the electrode layer near the current collector surface includes a conductive agent and a binder.

[0023] Preferably, the electrode layer near the current collector surface further includes a polymer electrolyte.

[0024] In this invention, by adding a polymer electrolyte, the active material particles can be coated by a cross-linked network formed by the conductive agent and the organic polymer electrolyte, providing a rapid ion / electron channel. It can also help fill the gaps between the active materials to form dense particles. Furthermore, due to its good wettability and solubility, the compound electrolyte can also promote the penetration of the electrolyte, thereby improving the electrochemical performance of the electrode.

[0025] Preferably, with the electrode layer near the current collector surface as 100%, the mass percentage of the polymer electrolyte is 0.3% to 1%, for example, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%.

[0026] Preferably, the polymer electrolyte comprises any one or a combination of at least two of polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polypropylene oxide, or polyvinylidene chloride.

[0027] Preferably, the electrode layer away from the current collector surface includes a conductive agent and a binder.

[0028] The conductive agent and binder in this invention are both conventional technical choices, that is, commonly used substances in the electrode preparation process. This invention is applicable to both. For example, the conductive agent can be selected from one or a mixture of several of carbon black, conductive graphite, carbon fiber, graphene, and carbon nanotubes, and the binder can be selected from one or a mixture of two of PVDF and PAA.

[0029] Preferably, the large-particle-size active material and the small-particle-size active material each independently include any one or a combination of at least two of lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium nickel manganese oxide.

[0030] The thick electrode in this invention is suitable for positive electrodes.

[0031] Preferably, the D50 of the large-particle-size active material is 7.5 to 30 μm, such as 7.5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 23 μm, 25 μm, 28 μm or 30 μm.

[0032] Preferably, the D50 of the small-particle-size active material is 0.5 to 10 μm, such as 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0033] In a second aspect, the present invention provides a method for preparing a thick electrode as described in the first aspect, the method comprising the following steps:

[0034] (1) The first electrode layer slurry is coated onto the surface of the current collector to obtain an electrode layer close to the surface of the current collector;

[0035] (2) Electrospinning slurry is electrospinned into an electrode layer near the surface of the current collector by electrospinning.

[0036] (3) The second electrode layer slurry is coated onto the surface of the electrospinning layer to obtain the thick electrode;

[0037] The active material in the electrode layer near the current collector surface is a large-particle active material, while the active material in the electrode layer far from the current collector surface is a small-particle active material.

[0038] This invention improves the electrode loading and thickness by using different processes to prepare at least two electrode layers, and optimizes the particle size distribution of the main active material in each layer to increase the specific capacity and energy density of the battery. At the same time, an electrospun layer is obtained between the electrode layers through electrospinning technology, and a porosity gradient distribution along the direction perpendicular to the electrode is formed to construct an efficient ion diffusion and conduction channel and an electron transport channel, thereby obtaining good ion diffusion and conduction, reducing polarization during charging and discharging, and ensuring the high energy density and power performance of the battery.

[0039] Preferably, the first electrode layer slurry in step (1) includes large-particle-size active material, binder, conductive agent and organic solvent.

[0040] Preferably, the first electrode layer slurry in step (1) further includes a polymer electrolyte.

[0041] Preferably, after coating in step (1), the product is dried.

[0042] In this invention, drying brings the sizing material to a semi-dry state. The purpose of this is to achieve better integration with the electrospinning layer, resulting in a large interfacial contact area and low resistance.

[0043] In this invention, by adding polymer electrolyte and organic solvent to the slurry of the first electrode layer, the active material particles can be coated by the cross-linked network formed by the conductive agent and the organic polymer electrolyte during the drying process as the organic solvent evaporates. This provides a fast ion / electron channel and also helps to fill the gaps between the active materials to form dense particles. Furthermore, the organic compound electrolyte promotes the penetration of the electrolyte due to its good wettability and solubility, thereby improving the electrochemical performance of the electrode.

[0044] Preferably, the electrospinning slurry in step (2) includes nanofibers, organic solvents, and binders.

[0045] Preferably, the electrospinning slurry in step (2) further includes a conductive agent.

[0046] Preferably, after electrospinning in step (2), the fibers are dried.

[0047] In this invention, the electrospun layer is also dried to a semi-dry state.

[0048] Preferably, the coating method in step (3) is electrostatic spraying.

[0049] This invention utilizes electrospinning and electrospraying technologies to form a continuous electron network / ion channel. Furthermore, the embedding of active particles into the framework structure greatly enhances the redox reaction kinetics and creates a gradient pore structure perpendicular to the electrode direction, ensuring rapid electrolyte wetting and lithium ion deintercalation / intercalation during rapid charging and discharging.

[0050] Furthermore, different coatings using different preparation methods can effectively increase the utilization rate of active materials, reduce internal polarization of the battery, and improve the energy density and rate performance of the battery.

[0051] Preferably, the second electrode slurry in step (3) includes small-particle-size active material, conductive agent, binder and organic solvent.

[0052] In this invention, the organic solvent includes one or a mixture of several of N-methylpyrrolidone (NMP), propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC).

[0053] Preferably, after the coating process in step (3) is completed, drying and rolling are performed sequentially.

[0054] Thirdly, the present invention also provides a lithium-ion battery, the lithium-ion battery comprising the thick electrode as described in the first aspect.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] (1) This invention improves the electrode loading and thickness by designing at least two electrode layers and optimizing the particle size distribution of the main active material in each layer, thereby increasing the specific capacity and energy density of the battery. Simultaneously, the electrospinning layer connects the electrode layers, creating a porosity gradient distribution perpendicular to the electrode direction, constructing efficient ion diffusion and conduction channels and electron transport pathways. This achieves good ion diffusion and conduction, reduces polarization during charging and discharging, and ensures high energy density and power performance of the battery. When the battery uses the thick electrode provided by this invention, a polymer electrolyte is added to the electrode layer near the current collector, and a conductive agent is added to the electrospinning layer. Simultaneously, when the second electrode layer is prepared by spraying, the energy density can reach over 230 Wh / kg, the first-cycle efficiency at 0.2C can reach over 93%, the rate performance at 5C / 0.2C can reach over 85%, and the capacity retention rate after 1000 cycles at 1C can reach over 90%. When lithium iron phosphate cathode material is selected, the capacity retention rate after 1000 cycles at 1C can reach over 95%.

[0057] (2) In the preparation process of this invention, different coatings are prepared by different methods, which can effectively increase the utilization rate of active materials, reduce the internal polarization of the battery, and improve the energy density and rate performance of the battery. Furthermore, the combination of electrospinning and electrospraying technology can form a continuous electronic network / ion channel. Moreover, the active particles embedded in the skeleton structure can greatly improve the redox reaction kinetics and form a gradient pore structure perpendicular to the electrode direction, ensuring rapid wetting of the electrolyte and the de-intercalation / intercalation of lithium ions during rapid charging and discharging. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the structure of the thick electrode provided in Example 1.

[0059] Wherein, 1-current collector, 2-first electrode layer, 3-electrospinning layer, 4-second electrode layer. Detailed Implementation

[0060] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0061] Example 1

[0062] This embodiment provides a thick electrode, such as Figure 1As shown, the thick electrode includes a current collector 1 and two electrode layers located on the surface (double-sided) of the current collector 1. An electrospinning layer 3 is also disposed between the electrode layers. The active material in the electrode layer (first electrode layer 2) close to the surface of the current collector 1 is large-particle lithium iron phosphate (D50 is 7.5μm), and the active material in the electrode layer (second electrode layer 4) far from the surface of the current collector 1 is small-particle lithium iron phosphate (D50 is 0.6μm).

[0063] The first electrode layer is composed of polyethylene oxide, large-particle-size lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride (mass ratio of 0.5:96.5:1.5:1.5), the electrospinning layer is composed of carbon fiber, conductive carbon black, and polyvinylidene fluoride (mass ratio of 40:40:20), and the second electrode layer is composed of small-particle-size lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride.

[0064] The method for preparing the thick electrode is as follows:

[0065] (1) Prepare the first electrode layer slurry, the electrospinning slurry, and the second electrode layer slurry respectively;

[0066] The preparation method of the first electrode layer slurry is as follows: polyethylene oxide, large particle size lithium iron phosphate, conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 0.5:96.5:1.5:1.5, NMP is added, and the mixture is mixed to obtain the first electrode layer slurry.

[0067] The preparation method of electrospinning slurry is as follows: carbon fiber, conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 40:40:20, NMP is added, and the mixture is mixed to obtain electrospinning slurry;

[0068] The preparation method of the second electrode layer slurry is as follows: small particle size lithium iron phosphate, conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 97.0:1.5:1.5, NMP is added, and the mixture is mixed to obtain the second electrode layer slurry.

[0069] (2) The first electrode layer slurry is coated (brushed) onto the surface of the aluminum foil and baked at low temperature to keep the electrode sheet in a semi-dry state, thus obtaining the first electrode sheet;

[0070] (3) The electrospinning slurry is sprayed out by electrospinning and uniformly coated on the electrode layer surface of the first electrode prepared in (2), and then dried at low temperature to keep it in a semi-dry state to obtain the second electrode.

[0071] (4) The second electrode layer slurry is sprayed onto the electrospinning layer surface of the second electrode sheet prepared in (3) by electrostatic spraying, dried, rolled and die-cut to obtain the thick electrode.

[0072] Example 2

[0073] This embodiment provides a thick electrode, which includes a current collector and two electrode layers located on the surface (double-sided) of the current collector. An electrospinning layer is also disposed between the electrode layers. The active material in the electrode layer (first electrode layer) closer to the surface of the current collector is large-particle-size NCM811 (D50 is 11.0 μm), and the active material in the electrode layer (second electrode layer) farther from the surface of the current collector is small-particle-size NCM811 (D50 is 4.0 μm).

[0074] The first electrode layer is composed of polyvinylidene chloride, large-particle-size NCM811, conductive graphite, and polyvinylidene fluoride (mass ratio of 0.8:96.5:1.2:1.5), the electrospinning layer is composed of polyacrylonitrile, conductive graphite, and polyvinylidene fluoride (mass ratio of 38:38:24), and the second electrode layer is composed of small-particle-size NCM811, conductive graphite, and polyvinylidene fluoride.

[0075] The method for preparing the thick electrode is as follows:

[0076] (1) Prepare the first electrode layer slurry, the electrospinning slurry, and the second electrode layer slurry respectively;

[0077] The preparation method of the first electrode layer slurry is as follows: polyvinylidene chloride, large particle size NCM811, conductive graphite and polyvinylidene fluoride are mixed in a mass ratio of 0.8:96.5:1.2:1.5, NMP is added, and the mixture is mixed to obtain the first electrode layer slurry.

[0078] The preparation method of electrospinning slurry is as follows: polyacrylonitrile, conductive graphite and polyvinylidene fluoride are mixed in a mass ratio of 38:38:24, NMP is added, and the mixture is mixed to obtain electrospinning slurry;

[0079] The preparation method of the second electrode layer slurry is as follows: small particle size NCM811, conductive graphite and polyvinylidene fluoride are mixed in a mass ratio of 96.5:1.5:1.5, NMP is added, and the mixture is mixed to obtain the second electrode layer slurry.

[0080] (2) The first electrode layer slurry is coated (brushed) onto the surface of the aluminum foil and baked at low temperature to keep the electrode sheet in a semi-dry state, thus obtaining the first electrode sheet;

[0081] (3) The electrospinning slurry is sprayed out by electrospinning and uniformly coated on the electrode layer surface of the first electrode prepared in (2), and then dried at low temperature to keep it in a semi-dry state to obtain the second electrode.

[0082] (4) The second electrode layer slurry is sprayed onto the electrospinning layer surface of the second electrode sheet prepared in (3) by electrostatic spraying, dried, rolled and die-cut to obtain the thick electrode.

[0083] Example 3

[0084] The difference between this embodiment and Embodiment 1 is that in this embodiment, polyethylene oxide is not added to the first electrode layer, and the mass ratio in the first electrode layer is adjusted to 97:1.5:1.5.

[0085] The remaining preparation methods and parameters are consistent with those in Example 1.

[0086] Example 4

[0087] The difference between this embodiment and Embodiment 1 is that conductive carbon black is not added to the electrospinning layer in this embodiment, and the mass ratio is adjusted to 1.0:97.0:2.0.

[0088] The remaining preparation methods and parameters are consistent with those in Example 1.

[0089] Example 5

[0090] The difference between this embodiment and embodiment 1 is that the coating method in step (4) of this embodiment is brush coating.

[0091] The remaining preparation methods and parameters are consistent with those in Example 1.

[0092] Comparative Example 1

[0093] The difference between this comparative example and Example 1 is that the thick electrode in this comparative example does not have an electrospinning layer, and the preparation method does not involve the preparation and treatment of electrospinning slurry.

[0094] The remaining preparation methods and parameters are consistent with those in Example 1.

[0095] Comparative Example 2

[0096] The difference between this comparative example and Example 1 is that the active material in both the first and second electrode layers of this comparative example is large-particle-size lithium iron phosphate.

[0097] The remaining preparation methods and parameters are consistent with those in Example 1.

[0098] Comparative Example 3

[0099] The difference between this comparative example and Example 1 is that the active material in both the first and second electrode layers of this comparative example is small-particle-size lithium iron phosphate.

[0100] The remaining preparation methods and parameters are consistent with those in Example 1.

[0101] Comparative Example 4

[0102] The difference between this comparative example and Example 1 is that the first electrode layer in this comparative example is made of small-particle-size lithium iron phosphate, and the second electrode layer is made of large-particle-size lithium iron phosphate.

[0103] The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] Using the electrodes provided in Examples 1-5 and Comparative Examples 1-4 as positive electrodes and artificial graphite as negative electrodes, batteries were assembled and their electrochemical performance was tested. The test conditions were: the first charge-discharge cycle at 0.2C, and the rate performance test at 5.0C. The cycle consisted of 1000 charge-discharge cycles at 1.0C / 1.0C, and the capacity retention rate was tested. The results are shown in Table 1.

[0105]

[0106]

[0107] The data from Examples 1 and 3 show that the addition of polymer electrolyte can further enhance the diffusion ability of lithium ions, thereby improving the rate performance and cycle performance of the battery.

[0108] The data results from Examples 1 and 4 show that adding a conductive agent to electrospinning facilitates the conduction of electrons between different electrode layers, thereby improving rate performance and cycle performance.

[0109] The data results from Examples 1 and 5 show that different coating methods can better achieve the design of high energy density.

[0110] The data from Example 1 and Comparative Example 1 show that without the addition of an electrospinning layer, it is impossible to achieve high-speed passage of electrons and lithium ions between different electrode layers, resulting in poor rate performance and deteriorated cycle performance.

[0111] The data from Example 1 and Comparative Examples 2 and 3 show that the combination of active materials with the same particle size in the electrode layer leads to a decrease in battery rate performance.

[0112] The data from Example 1 and Comparative Example 4 show that the electrode layer near the current collector has small particle size, while the layer further away has large particle size, which affects the rate performance of the battery.

[0113] In summary, this invention improves the electrode loading and thickness by designing at least two electrode layers and optimizing the particle size distribution of the main active material in each layer, thereby increasing the battery's specific capacity and energy density. Simultaneously, electrospinning layers connect the electrode layers, creating a porosity gradient distribution perpendicular to the electrode direction. This constructs efficient ion diffusion and conduction channels and electron transport pathways, resulting in excellent ion diffusion and conduction, reducing polarization during charge and discharge, and ensuring high energy density and power performance of the battery. Furthermore, different preparation methods are used for different coatings during the fabrication process, effectively increasing the utilization rate of active materials, reducing internal polarization, and improving the battery's energy density and rate performance. The combination of electrospinning and electrospraying technologies forms a continuous electron network / ion channel, and the embedding of active particles into the framework greatly enhances the redox reaction kinetics and forms a gradient pore structure perpendicular to the electrode direction, ensuring rapid electrolyte wetting and lithium ion deintercalation / intercalation during rapid charge and discharge. When the battery uses the thick electrode provided by this invention, a polymer electrolyte is added to the electrode layer near the current collector, a conductive agent is added to the electrospun layer, and the second electrode layer is prepared by spraying. At the same time, the energy density can reach more than 230wh / kg, the first efficiency at 0.2C can reach more than 93%, the rate performance at 5C / 0.2C can reach more than 85%, and the capacity retention rate after 1000 cycles at 1C can reach more than 90%.

[0114] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A thick electrode, characterized in that, The thick electrode includes a current collector and at least two electrode layers located on the surface of the current collector. An electrospinning layer is also provided between the electrode layers. The active material in the electrode layer close to the surface of the current collector is a large-particle active material, and the active material in the electrode layer far from the surface of the current collector is a small-particle active material. The electrospun layer comprises nanofibers and a binder, wherein the nanofibers include carbon fibers; The electrode layer near the current collector surface includes a conductive agent, a binder, and a polymer electrolyte; The thick electrode is prepared using the following method: (1) The first electrode layer slurry is coated on the surface of the current collector and dried to a semi-dry state to obtain an electrode layer close to the surface of the current collector. (2) The electrospinning slurry is electrospinned to form an electrospinning layer on the electrode layer near the surface of the current collector by electrospinning. After electrospinning, the slurry is dried to reach a semi-dry state. (3) The second electrode layer slurry is coated onto the surface of the electrospinning layer by electrostatic spraying to obtain the thick electrode; Among them, the active material in the electrode layer close to the surface of the current collector is a large-particle active material, and the active material in the electrode layer far from the surface of the current collector is a small-particle active material. Step (1) The first electrode layer slurry includes large-particle-size active material, polymer electrolyte, binder, conductive agent and organic solvent; The electrospinning slurry in step (2) includes nanofibers, organic solvents and binders, wherein the nanofibers include carbon fibers.

2. The thick electrode according to claim 1, characterized in that, The electrospun layer also includes a conductive agent.

3. The thick electrode according to claim 1, characterized in that, With the electrode layer near the current collector surface as 100%, the polymer electrolyte accounts for 0.3% to 1% of the total mass.

4. The thick electrode according to claim 1, characterized in that, The polymer electrolyte includes any one or a combination of at least two of polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polypropylene oxide, or polyvinylidene chloride.

5. The thick electrode according to claim 1, characterized in that, The electrode layer, located away from the current collector surface, includes a conductive agent and a binder.

6. The thick electrode according to claim 1, characterized in that, The large-particle-size active material and the small-particle-size active material each independently include any one or a combination of at least two of lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium nickel manganese oxide.

7. The thick electrode according to claim 1, characterized in that, The D50 of the large-particle-size active material is 7.5~30.0 μm.

8. The thick electrode according to claim 1, characterized in that, The D50 of the small-particle-size active material is 0.5~10.0 μm.

9. A method for preparing a thick electrode as described in any one of claims 1-8, characterized in that, The preparation method includes the following steps: (1) The first electrode layer slurry is coated on the surface of the current collector and dried to a semi-dry state to obtain an electrode layer close to the surface of the current collector. (2) The electrospinning slurry is electrospinned to form an electrospinning layer on the electrode layer near the surface of the current collector by electrospinning. After electrospinning, the slurry is dried to reach a semi-dry state. (3) The second electrode layer slurry is coated onto the surface of the electrospinning layer by electrostatic spraying to obtain the thick electrode; Among them, the active material in the electrode layer close to the surface of the current collector is a large-particle active material, and the active material in the electrode layer far from the surface of the current collector is a small-particle active material. Step (1) The first electrode layer slurry includes large-particle-size active material, polymer electrolyte, binder, conductive agent and organic solvent; The electrospinning slurry in step (2) includes nanofibers, organic solvents and binders, wherein the nanofibers include carbon fibers.

10. The method for preparing a thick electrode according to claim 9, characterized in that, The electrospinning slurry in step (2) also includes a conductive agent.

11. The method for preparing a thick electrode according to claim 9, characterized in that, Step (3) The second electrode layer slurry includes small-particle-size active material, conductive agent, binder and organic solvent.

12. The method for preparing a thick electrode according to claim 9, characterized in that, After the coating process in step (3) is completed, drying and rolling are performed in sequence.

13. A lithium-ion battery, characterized in that, The lithium-ion battery includes a thick electrode as described in any one of claims 1-8.

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