Method for preparing electrode by wet coating of porous current collector

Abstract

The invention provides a method for preparing an electrode by wet coating of a porous current collector. The method comprises a slurry mixing stage and a coating stage, wherein in the slurry mixing stage, electrode slurry containing sodium alginate is formed, and in the coating stage, a porous current collector is coated with a calcium salt solution, and then the electrode slurry is coated, so that the calcium salt solution can be crosslinked with the sodium alginate in the electrode slurry.

Description

Technical Field

[0001] The present application belongs to the field of electrode preparation, and in particular relates to a method for preparing an electrode by wet coating of a porous current collector. Background Art

[0002] Lithium-ion capacitors are electrochemical energy storage devices with both high energy density and high power density, which make up for the unilateral shortcomings of supercapacitors and lithium-ion batteries. Pre-embedding lithium in the negative electrode is a major problem in the production process of lithium-ion capacitors. The current solution to pre-embedding lithium is mainly to use porous current collectors to make positive and negative electrodes to ensure the uniformity of lithium embedding in the negative electrode. There are two main preparation processes for electrodes using porous current collectors: dry method and wet method. Among them, the production of dry electrodes is to knead the active material and the binder, press them into an electrode film, and then hot-press them together with the current collector to prepare the electrode. The dry electrode mixing and production process are complicated, and the consistency of the prepared electrode is worse than that of the wet preparation method. The main difficulty in the preparation of wet electrodes is the problem of leakage during the coating process. The current common solutions are coating with a porous current collector coated with a PET film and vertical coating (coating rate 2m / min). The coating rate is slow, the production cycle is long, and the production efficiency is low. In addition, the use of a microporous current collector is one of the current wet coating solutions, but the electrodes prepared using a microporous current collector are more difficult to pre-embed lithium than electrodes prepared using a macroporous current collector (pore size ≥ 20um), and the lithium embedding cycle is longer. Summary of the invention

[0003] In view of some deficiencies in the prior art, the present application provides a method for preparing electrodes by wet coating of a porous current collector, which can solve the problem of material leakage during the coating process.

[0004] The first aspect of the present application provides a method for preparing an electrode by wet coating of a porous current collector (hereinafter referred to as a method for preparing an electrode), comprising a slurry mixing stage and a coating stage; wherein the slurry mixing stage forms an electrode slurry containing sodium alginate; wherein the coating stage first coats a calcium salt solution on the porous current collector, and then coats the electrode slurry, so that the calcium salt solution can cross-link with the sodium alginate in the electrode slurry.

[0005] In one embodiment, the method for preparing an electrode more specifically comprises the following steps:

[0006] Preparation of glue solution: Sodium alginate and thickener are fully stirred and mixed in water to prepare glue solution;

[0007] Preparing electrode slurry: dry-mixing the conductive agent and the active material as electrode materials, then adding the glue, the binder and the solvent, mixing and dispersing, and forming a uniform electrode slurry;

[0008] Preparation of calcium salt aqueous solution: Prepare calcium salt aqueous solution as a cross-linking agent for standby use;

[0009] First coating: firstly, the porous current collector is infiltrated with the prepared calcium salt aqueous solution to form a calcium salt liquid film in the pores of the porous current collector; then, the prepared electrode slurry is coated on the first surface of the porous current collector and dried;

[0010] Second coating: coating the prepared electrode slurry on the second surface of the porous current collector which is arranged opposite to the first surface, and drying it; obtaining the electrode.

[0011] In one embodiment, in the adhesive solution, the mass ratio of sodium alginate to thickener is 1:0.5-5; preferably 1:1-2.

[0012] In one embodiment, the thickener is selected from at least one of the following groups: CMC and PVA.

[0013] In one embodiment, the viscosity of the formed electrode slurry is 4000-9000 mPa.s.

[0014] In one embodiment, in the electrode material, the mass ratio of the conductive agent to the active material is 1:15-200, preferably 1:15-50.

[0015] In one embodiment, the mass percentages of the electrode material (including the conductive agent and the active substance), the glue (dry weight) and the binder are 80-96%, 2-15%, and 2-5%; preferably, the mass percentages are 85-96%, 2-10%, and 2-5%.

[0016] In one embodiment, the conductive agent is selected from at least one of the following groups: conductive carbon black, acetylene black, Ketjen black, furnace black, carbon nanofiber, graphene, and carbon nanotube.

[0017] In one embodiment, the active material is selected from at least one of the following groups: activated carbon, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium titanate, natural flake graphite, artificial graphite, expanded graphite, mesophase carbon microspheres, hard carbon, and soft carbon.

[0018] In one embodiment, the binder is selected from one of the following groups: SBR, a mixture of SBR and PTFE, and a mixture of SBR and PAN.

[0019] In one embodiment, the solvent is water, preferably deionized water.

[0020] In one embodiment, the calcium salt is a water-soluble calcium salt.

[0021] In one embodiment, the calcium salt is calcium nitrate or calcium chloride, and its mass concentration is 1-10%.

[0022] In one embodiment, the pore size of the porous current collector is no more than 200 um, preferably, the pore size is 30-200 um; the porosity is less than 50%, preferably, the porosity is 15-30%.

[0023] A second aspect of the present application provides an electrode, which is prepared using the method for preparing an electrode described in any of the above embodiments.

[0024] The third aspect of the present application provides a battery cell, which has an electrode prepared by the method for preparing an electrode described in any of the preceding embodiments; during the winding or stacking process of the battery cell, a lithium metal sheet is inserted at a portion of the negative electrode side so that the negative electrode and the lithium metal sheet are in a short-circuit state after injection, and lithium ions can shuttle through the pores of the porous current collector to achieve uniform pre-embedding of lithium at the negative electrode.

[0025] The method for preparing electrodes by wet coating of porous current collectors provided in at least one embodiment of the present application is a simpler way to solve the problem of leakage in wet coating, and can improve the production efficiency of existing wet electrode preparation of porous current collectors; the present application can use current collectors with larger pore sizes for electrode preparation, which is more conducive to the pre-lithium embedding and energy density improvement of energy storage batteries / capacitors.

[0026] The method for preparing an electrode by wet coating of a porous current collector provided in at least one embodiment of the present application has a fast coating speed and high working efficiency.

[0027] At least one embodiment of the present application provides a method for preparing electrodes by wet coating of a porous current collector. Using an electrode prepared with a porous current collector, a small amount of lithium metal is added at a suitable position to short-circuit the negative electrode during the winding / stacking process to prepare a battery cell. A simple short-circuit lithium insertion process is used to achieve pre-lithium insertion of lithium-ion batteries / capacitors, thereby solving the lithium loss caused by the irreversible reaction of the first charge and discharge of the battery cell monomer and improving the overall capacity of the battery cell monomer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of preparing electrodes by wet coating of porous current collectors;

[0029] In the figure: 1 coater, 2 roller, 3 nozzle, 4 porous current collector, 5 first surface of the porous current collector. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] In the description of the present application, it should be understood that the terms "center", "lateral", "longitudinal", "up", "down", "front", "back", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0032] The terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Thus, a feature defined as "first", "second", and "third" may explicitly or implicitly include one or more of the features.

[0033] The first aspect of the present application provides a method for preparing an electrode by wet coating of a porous current collector (hereinafter referred to as a method for preparing an electrode), comprising a slurry mixing stage and a coating stage; wherein the slurry mixing stage forms an electrode slurry containing sodium alginate; in the coating stage, a calcium salt solution is first coated on the porous current collector, and then the electrode slurry is coated, so that the calcium salt solution as a cross-linking agent can quickly cross-link with the sodium alginate in the electrode slurry, forming a roughly gel state at the pores of the porous current collector, which can effectively block the pores and prevent leakage.

[0034] The method for preparing the electrode, more specifically, comprises the following steps:

[0035] (1) Preparation of glue solution: Sodium alginate and thickener are thoroughly stirred and mixed in water to form glue solution.

[0036] Specifically, sodium alginate and thickener are dissolved in deionized water, and stirred for about 2 hours, with the stirrer revolving at 15-30 rpm and rotating at 200-1200 rpm; the viscosity of the glue is controlled to be 2000-30000 mPa.s.

[0037] The sodium alginate is latex-like and viscous, and can react with calcium ions, mainly playing a cross-linking role with calcium salts. The thickener mainly plays a thickening role; a water-soluble thickener can be selected, such as sodium carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), or a mixture thereof.

[0038] The mass ratio of sodium alginate to thickener is 1:0.5-5, for example, 1:1, 1:2, 1:3, 1:4, 1:5, etc.; more specifically, it is 1:1-2, for example, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, etc.

[0039] (2) Preparing electrode slurry: After dry mixing the conductive agent and active material as electrode materials, the glue, binder and solvent are added, and mixed and dispersed to form a uniform electrode slurry.

[0040] The dry mixing time of the electrode material is about 0.5h, the stirrer revolution is 10-30rpm, and the rotation is 100-300rpm. The electrode material is mixed and dispersed with the glue, binder and solvent, and the stirrer revolution is 15-30rpm and the rotation is 600-1500rpm. The viscosity of the formed electrode slurry is 4000-9000mpa.s, for example, 5000mpa.s, 6000mpa.s, 7000mpa.s, 8000mpa.s, etc.

[0041] In the electrode material, the mass ratio of the conductive agent to the active material is 1:15-200, for example, 1:25, 1:30, 1:50, 1:100, 1:120, 1:150, 1:180, etc.; more specifically, it is 1:15-50, for example, 1:16, 1:30, 1:35, 1:40, 1:45, etc.

[0042] The mass percentages of the electrode material (including conductive agent and active substance), glue (dry weight, only containing sodium alginate and thickener) and binder are 80-96%, 2-15% and 2-5%; more specifically, the mass percentages are 85-95%, 2-10% and 2-5%.

[0043] The solvent is water, such as deionized water, which can be added according to actual needs, such as increasing the amount of solvent according to the viscosity of the electrode slurry to be controlled.

[0044] In one embodiment, the conductive agent is selected from one of conductive carbon black, acetylene black, Ketjen black, furnace black, carbon nanofiber, graphene, carbon nanotube or a combination thereof.

[0045] The active material is selected from one of activated carbon, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium titanate, natural flake graphite, artificial graphite, expanded graphite, mesophase carbon microspheres, hard carbon, and soft carbon, or a combination thereof.

[0046] The binder is selected from styrene-butadiene rubber emulsion (SBR), or a mixture of SBR, polytetrafluoroethylene emulsion (PTFE) and polyacrylonitrile emulsion (PAN).

[0047] (3) Preparation of calcium salt aqueous solution: Prepare a calcium salt aqueous solution of a certain concentration as a cross-linking agent for later use.

[0048] The calcium salt can be selected from water-soluble calcium salts such as calcium nitrate and calcium chloride; its mass concentration is 1-10%, such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% and the like.

[0049] (4) First coating: first, the porous current collector is infiltrated with the calcium salt aqueous solution prepared in step (3) to form a layer of calcium salt liquid film in the pores of the porous current collector; then the electrode slurry prepared in step (2) is coated on the first surface of the porous current collector.

[0050] Specifically, you can Figure 1 As shown, the porous current collector 4 first passes through the nozzle 3, then reaches the roller 2, and then enters between the roller 2 and the coater 1. The nozzle 3 can spray out a calcium salt solution for soaking the porous current collector 4, and the coater 1 can spray out the electrode slurry at the coating head facing the roller 2, covering the first surface 5 of the porous current collector. Then enter the oven for drying.

[0051] The nozzle 3 can directly spray the calcium salt solution onto the porous current collector 4, or spray the calcium salt solution onto the roller 2. When the roller 2 rotates clockwise, the calcium salt solution is automatically introduced onto the porous current collector.

[0052] The nozzle 3 is a nozzle of a spray device, which can continuously spray calcium salt mist on the roller 2. By adjusting the nozzle and pressure of the spray device, the droplet size is controlled to be less than 30 um.

[0053] The porous current collector is selected from copper foil, aluminum foil, nickel foam, etc., with a pore size of no more than 200um, optionally, a pore size of 30-200um, such as 50um, 100um, 150um, etc.; a porosity of less than 50%, optionally, a porosity of 15-30%, such as 20%, 22%, 25%, 28%, etc.; a thickness of the porous current collector of 5-30um. The method of the present application is particularly effective in preventing leakage for large pores with a pore size of more than 30um.

[0054] (2) Second coating: coating the electrode slurry prepared in step (2) on the second surface of the porous current collector, wherein the second surface is arranged opposite to the first surface, that is, the electrode slurry is coated on both sides of the porous current collector.

[0055] After the first surface of the porous current collector is coated and dried, the second surface is coated and dried, so that an electrode is prepared. Similarly, when the second surface is coated, the porous current collector can be placed in a second set of rollers and coaters that are arranged opposite to each other, and the coating head of the coater facing the roller can spray the electrode slurry to cover the second surface of the porous current collector, and then enter the second set of ovens for drying.

[0056] During the first and second coating, the gap between the coating head and the roller and the pump speed need to be adjusted for coating; the gap is 5-150um, the pump speed is 20-60rpm, and the coating speed is 5-50m / min; during the two dryings, the oven temperature is 60-120℃.

[0057] A second aspect of the present application provides an electrode, which is prepared using the method described in any of the above embodiments.

[0058] The third aspect of the present application provides a battery cell having an electrode prepared by the method described in any of the above embodiments. During the winding or lamination process of the battery cell, a lithium metal sheet can be inserted into a part of the negative electrode side, and contacted with the negative electrode by welding or direct bonding, so that the negative electrode and the lithium metal sheet are in a short-circuit state after injection, and lithium ions can shuttle through the pores of the porous current collector to achieve uniform pre-embedded lithium in the negative electrode, reduce the negative electrode potential and solve the consumption of lithium by the initial charge and discharge irreversible reaction, thereby improving the performance of the battery cell.

[0059] The capacity of existing electrode materials is close to the bottleneck of theoretical capacity. It is difficult to achieve the improvement of energy density of a single battery cell by simply relying on electrode materials. The weight proportion of the current collector of existing battery cells is about 8%-10%. The electrode obtained by this application can reduce the weight proportion of the porous current collector of lithium-ion batteries / capacitor monomers to about 6%-8%, reduce the overall weight of the battery cell, and increase the energy density of lithium batteries / capacitor monomers by about 2% without changing the positive and negative electrode materials.

[0060] Finally, it should be noted that: the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0061] The present application is described in detail below in conjunction with embodiments. It is worth noting that these embodiments are merely some preferred embodiments of the present application and are not to be construed as limiting the scope of protection of the present application.

[0062] Example 1

[0063] (1) Preparation of glue solution: Sodium alginate and CMC were dissolved in deionized water and stirred for 2 h. The stirrer was rotated at 20 rpm and 800 rpm. The viscosity of the glue solution was controlled to be 10000 mPa.s. The mass ratio of sodium alginate to CMC was 1:1.

[0064] (2) Preparation of electrode slurry: dry-mix the conductive agent and active material for 0.5 h, with the stirrer rotating at 20 rpm and 200 rpm. Add the glue, binder and deionized water, mix and disperse, and stir at 20 rpm and 1000 rpm to form a uniform electrode slurry with a viscosity of 5000 mPa.s. Load the slurry into the first coater and the second coater respectively.

[0065] Among them, in the electrode slurry, the conductive agent is 3 parts by weight, and conductive carbon black is selected; the active material is 92 parts by weight, and hard carbon is selected; the glue is 3 parts by weight, and the binder is 2 parts by weight, and SBR is selected.

[0066] (3) Preparation of calcium salt aqueous solution: A calcium salt aqueous solution with a mass concentration of 5% is prepared using calcium nitrate and poured into a spray device.

[0067] (4) First coating: The porous current collector first passes through the nozzle of the spray device, then reaches the roller, and then enters between the first roller and the first coater. The nozzle sprays a calcium salt solution for soaking the porous current collector toward the roller, and the coater sprays the electrode slurry toward the coating head of the roller, covering the first surface of the porous current collector. Then it enters the first oven for drying. The gap between the porous current collector and the first coater is 50um, the pump speed is 40rpm, the coating speed is 20m / min; the drying temperature of the oven is 100℃.

[0068] In addition, the porous current collector is selected from copper foil, with a pore size of 100um, a porosity of 25%, and a thickness of 15um.

[0069] (5) Second coating: After the first side of the porous current collector is dried, it enters between the second roller and the second coater. The coater sprays the electrode slurry from the coating head toward the roller, covering the uncoated second side of the porous current collector. Then it enters the second oven for drying. The gap between the porous current collector and the second coater is 50um, the pump speed is 40rpm, the coating speed is 20m / min; the drying temperature of the oven is 100°C. After the second side is dried, it is rolled up for subsequent preparation of battery cells.

[0070] Example 2

[0071] (1) Preparation of glue solution: Sodium alginate and CMC were dissolved in deionized water and stirred for 2 h. The stirrer was rotated at 20 rpm and 800 rpm. The viscosity of the glue solution was controlled to be 10000 mPa.s. The mass ratio of sodium alginate to CMC was 1:1.5.

[0072] (2) Preparation of electrode slurry: dry mix the conductive agent and active material for 0.5 h, with the stirrer rotating at 20 rpm and 200 rpm. Add the glue, binder and deionized water, mix and disperse, and stir at 20 rpm and 1000 rpm to form a uniform electrode slurry with a viscosity of 6000 mPa.s. Load it into the first coater and the second coater respectively.

[0073] Among them, in the electrode slurry, the conductive agent is 5 parts by weight, and carbon nanofiber is selected; the active material is 80 parts by weight, and graphite is selected; the glue is 10 parts by weight, and the binder is 5 parts by weight, and a mixture of SBR and PTFE is selected.

[0074] (3) Preparation of calcium salt aqueous solution: A calcium salt aqueous solution with a mass concentration of 5% is prepared using calcium nitrate and poured into a spray device.

[0075] (4) First coating: The porous current collector first passes through the nozzle of the spray device, then reaches the roller, and then enters between the first roller and the first coater. The nozzle sprays a calcium salt solution for soaking the porous current collector toward the roller, and the coater sprays the electrode slurry toward the coating head of the roller, covering the first surface of the porous current collector. Then it enters the first oven for drying. The gap between the porous current collector and the first coater is 50um, the pump speed is 40rpm, the coating speed is 20m / min; the drying temperature of the oven is 100℃.

[0076] In addition, the porous current collector is selected from copper foil, with a pore size of 50um, a porosity of 30%, and a thickness of 15um.

[0077] (5) Second coating: After the first side of the porous current collector is dried, it enters between the second roller and the second coater. The coater sprays the electrode slurry from the coating head toward the roller, covering the uncoated second side of the porous current collector. Then it enters the second oven for drying. The gap between the porous current collector and the second coater is 50um, the pump speed is 40rpm, the coating speed is 20m / min; the drying temperature of the oven is 100°C. After the second side is dried, it is rolled up for subsequent preparation of battery cells.

[0078] Example 3

[0079] (1) Preparation of glue solution: Sodium alginate and PVA were dissolved in deionized water and stirred for 2 h. The stirrer was rotated at 20 rpm and 800 rpm. The viscosity of the glue solution was controlled to be 10000 mPa.s. The mass ratio of sodium alginate to PVA was 1:1.

[0080] (2) Preparation of electrode slurry: dry mix the conductive agent and active material for 0.5 h, with the stirrer rotating at 20 rpm and 200 rpm. Add the glue, binder and deionized water, mix and disperse, and stir at 20 rpm and 1000 rpm to form a uniform electrode slurry with a viscosity of 7000 mPa.s. Load it into the first coater and the second coater respectively.

[0081] Among them, in the electrode slurry, the conductive agent is 5 parts by weight, and carbon nanotubes are selected; the active material is 85 parts by weight, and artificial graphite is selected; the glue is 5 parts by weight, and the binder is 5 parts by weight, and a mixture of SBR and PAN is selected.

[0082] (3) Preparation of calcium salt aqueous solution: Calcium nitrate is used to prepare a calcium salt aqueous solution with a mass concentration of 8%, and the solution is poured into a spray device.

[0083] (4) First coating: The porous current collector first passes through the nozzle of the spray device, then reaches the roller, and then enters between the first roller and the first coater. The nozzle sprays a calcium salt solution for soaking the porous current collector toward the roller, and the coater sprays the electrode slurry toward the coating head of the roller, covering the first surface of the porous current collector. Then it enters the first oven for drying. The gap between the porous current collector and the first coater is 50um, the pump speed is 40rpm, the coating speed is 20m / min; the drying temperature of the oven is 100℃.

[0084] In addition, the porous current collector is selected from copper foil, with a pore size of 150um, a porosity of 20%, and a thickness of 15um.

[0085] (5) Second coating: After the first side of the porous current collector is dried, it enters between the second roller and the second coater. The coater sprays the electrode slurry from the coating head toward the roller, covering the uncoated second side of the porous current collector. Then it enters the second oven for drying. The gap between the porous current collector and the second coater is 50um, the pump speed is 40rpm, the coating speed is 20m / min; the drying temperature of the oven is 100°C. After the second side is dried, it is rolled up for subsequent preparation of battery cells.

[0086] Example 4

[0087] (1) Preparation of glue solution: Sodium alginate, CMC and PVA were dissolved in deionized water and stirred for 2 h. The stirrer was rotated at 20 rpm and 800 rpm. The viscosity of the glue solution was controlled to be 10000 mPa.s. The mass ratio of sodium alginate, CMC and PVA was 1:1:1.

[0088] (2) Preparation of electrode slurry: dry mix the conductive agent and active material for 0.5 h, with the stirrer rotating at 20 rpm and 200 rpm. Add the glue, binder and deionized water, mix and disperse, and stir at 20 rpm and 1000 rpm to form a uniform electrode slurry with a viscosity of 8000 mPa.s. Load it into the first coater and the second coater respectively.

[0089] Among them, in the electrode slurry, the conductive agent is 2 parts by weight, and carbon nanotubes are selected; the active material is 92 parts by weight, and artificial graphite is selected; the glue is 3 parts by weight, and the binder is 3 parts by weight, and a mixture of SBR and PAN is selected.

[0090] (3) Preparation of calcium salt aqueous solution: A calcium salt aqueous solution with a mass concentration of 5% is prepared using calcium nitrate and poured into a spray device.

[0091] (4) First coating: The porous current collector first passes through the nozzle of the spray device, then reaches the roller, and then enters between the first roller and the first coater. The nozzle sprays a calcium salt solution for soaking the porous current collector toward the roller, and the coater sprays the electrode slurry toward the coating head of the roller, covering the first surface of the porous current collector. Then it enters the first oven for drying. The gap between the porous current collector and the first coater is 50um, the pump speed is 40rpm, the coating speed is 20m / min; the drying temperature of the oven is 100℃.

[0092] In addition, the porous current collector is selected from copper foil, with a pore size of 35um, a porosity of 25%, and a thickness of 15um.

[0093] (5) Second coating: After the first side of the porous current collector is dried, it enters between the second roller and the second coater. The coater sprays the electrode slurry from the coating head toward the roller, covering the uncoated second side of the porous current collector. Then it enters the second oven for drying. The gap between the porous current collector and the second coater is 50um, the pump speed is 40rpm, the coating speed is 20m / min; the drying temperature of the oven is 100°C. After the second side is dried, it is rolled up for subsequent preparation of battery cells.

[0094] Comparative Example 1:

[0095] The ingredients and parameters of this comparative example are the same as those of Example 1, except that CMC is used to replace sodium alginate, and deionized water is used to replace the calcium salt aqueous solution, that is, this comparative example does not contain sodium alginate and calcium salt.

[0096] Comparative Example 2:

[0097] The components and parameters of this comparative example are the same as those of Example 1, except that a microporous current collector is used instead, that is, the microporous etched copper foil used in this comparative example has a pore size of 5-20 um and a porosity of about 5%.

[0098] Comparative Example 3:

[0099] The components and parameters of this comparative example are the same as those of Example 1, except that a conventional current collector is used instead, that is, the copper foil used in this comparative example has no pores.

[0100] The parameters of each embodiment are compared as follows:

[0101]

[0102] As can be seen from the above table, the method for preparing electrodes provided in the present application (Examples 1-4) has a good effect on the leakage prevention of porous current collectors, especially for current collectors with larger pore sizes. The porous current collector can significantly reduce the surface density of the current collector. In the process of pre-lithium insertion by short-circuit lithium insertion, a large-pore and high-porosity current collector is used for pre-lithium insertion operation, and the lithium dissolution and lithium insertion effects are better. It is almost impossible to pre-insert lithium by short-circuit lithium insertion using micropores (Comparative Example 2) and conventional current collectors (Comparative Example 3). In the lithium-ion capacitor assembled with electrodes made by the method for preparing electrodes provided in the present application, the monomers assembled with large-pore current collectors can work normally, and the current collectors prepared using micropores (Comparative Example 2) and conventional foils (Comparative Example 3) cannot work normally. In summary, the method for preparing electrodes provided in the present application is an effective leakage prevention process for preparing electrodes with porous current collectors, which has good results in reducing the weight proportion of current collectors and pre-inserting lithium using short-circuit lithium insertion processes.

[0103] The above embodiments are only used to illustrate the technical solution of the present application rather than to limit it. Although the present application has been described in detail with reference to the preferred embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present application can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present application, which should be included in the scope of the technical solution requested for protection in the present application.

Claims

1. A method for preparing an electrode by wet coating of a porous current collector, comprising a slurry mixing stage and a coating stage; wherein: The slurry mixing stage forms an electrode slurry containing sodium alginate; the coating stage first coats the porous current collector with a calcium salt solution, and then coats the electrode slurry, so that the calcium salt solution can cross-link with the sodium alginate in the electrode slurry.

2. The method for preparing an electrode according to claim 1, characterized in that: More specifically, the following steps are included: Preparation of glue solution: Sodium alginate and thickener are fully stirred and mixed in water to prepare glue solution; Preparing electrode slurry: dry-mixing the conductive agent and the active material as electrode materials, then adding the glue, the binder and the solvent, mixing and dispersing, and forming a uniform electrode slurry; Preparation of calcium salt aqueous solution: Prepare calcium salt aqueous solution as a cross-linking agent for standby use; First coating: firstly, the porous current collector is infiltrated with the prepared calcium salt aqueous solution to form a calcium salt liquid film in the pores of the porous current collector; then, the prepared electrode slurry is coated on the first surface of the porous current collector and dried; Second coating: coating the prepared electrode slurry on the second surface of the porous current collector opposite to the first surface, and drying; Thus, the electrode is prepared.

3. The method for preparing an electrode according to claim 2, characterized in that: In the glue, the mass ratio of sodium alginate to thickener is 1:0.5-5; the thickener is selected from at least one of the following groups: CMC and PVA.

4. The method for preparing an electrode according to claim 2, characterized in that: In the electrode material, the mass ratio of the conductive agent to the active material is 1:15-200; the mass percentages of the electrode material, the glue (dry weight) and the binder are 80-96%, 2-15% and 2-5%; the viscosity of the formed electrode slurry is 4000-9000mpa.s.

5. The method for preparing an electrode according to any one of claims 2 to 4, characterized in that: The conductive agent is selected from at least one of the following groups: conductive carbon black, acetylene black, Ketjen black, furnace black, carbon nanofiber, graphene, carbon nanotube; the active substance is selected from at least one of the following groups: activated carbon, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium titanate, natural flake graphite, artificial graphite, expanded graphite, mesophase carbon microspheres, hard carbon, soft carbon; the binder is selected from one of the following groups: SBR, a mixture of SBR and PTFE, a mixture of SBR and PAN; the solvent is water.

6. The method for preparing an electrode according to claim 2, characterized in that: The solvent is deionized water; the calcium salt is a water-soluble calcium salt.

7. The method for preparing an electrode according to claim 2, characterized in that: The calcium salt is calcium nitrate or calcium chloride, and its mass concentration is 1-10%.

8. The method for preparing an electrode according to any one of claims 1 to 4, characterized in that: The pore size of the porous current collector is 30-200 um; the porosity is 15-30%.

9. An electrode prepared by the method for preparing an electrode according to any one of claims 1 to 8.

10. A battery cell, comprising an electrode prepared by the method for preparing an electrode according to any one of claims 1 to 8; during the winding or stacking process of the battery cell, a lithium metal sheet is inserted at a portion of the negative electrode side so that the negative electrode and the lithium metal sheet are in a short-circuit state after injection, and lithium ions can shuttle through the pores of the porous current collector to achieve uniform pre-embedding of lithium at the negative electrode.

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