A current collector, its preparation method and application

Abstract

The application provides a current collector and a preparation method and application thereof. The current collector comprises a current collector substrate and a primer layer on the surface of the current collector substrate, and the primer layer comprises a polymer lithium salt which can be ionized in a solution to obtain lithium ions and polymer anions. The application adds the polymer lithium salt which can be ionized in a solution to obtain lithium ions in the primer layer of the current collector. When the polymer lithium salt is used in an electrode tab, the local lithium salt concentration is improved, thereby solving the lithium ion diffusion problem in a thick-coated electrode and improving the rate performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a current collector, its preparation method and application. Background Technology

[0002] Lithium-ion batteries boast advantages such as high energy density and long lifespan, leading to their widespread application in electric vehicles and energy storage. To enhance energy density, lithium-ion batteries are often designed with a greater amount of active material coated on the current collector surface. This increases the coating thickness, lengthening the diffusion path of lithium ions within the battery. This hinders the performance of materials near the current collector, ultimately impacting the battery's kinetic performance. This contradicts consumer demand for fast charging and high power output.

[0003] CN113745463A provides a negative electrode sheet, including a current collector and a coating disposed on the surface of the current collector. The coating includes at least two active layers and a porous diffusion layer disposed between two adjacent active layers. The porosity of the porous diffusion layer is greater than the porosity of the adjacent active layers, and the thickness of the porous diffusion layer is less than the thickness of the adjacent active layers. In this document, the active coating is excessively thick, which to some extent lengthens the diffusion path of lithium ions in the battery, hindering the performance of materials near the current collector.

[0004] Compared to comprehensively increasing the lithium-ion concentration in the electrolyte, selectively increasing the lithium-ion concentration near the current collector is a more economical and effective approach.

[0005] Therefore, how to effectively utilize the electrochemical performance of the active layer near the current collector is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide a current collector, its preparation method, and its application. This invention achieves a localized increase in lithium salt concentration when the current collector is used as an electrode by adding a polymer lithium salt that can be electrolyzed to produce lithium ions in solution to the bottom coating of the current collector. This solves the problem of lithium ion diffusion in thickly coated electrodes and improves the rate performance of the battery.

[0007] To achieve this objective, the present invention employs the following technical solution:

[0008] In a first aspect, the present invention provides a current collector comprising a current collector substrate and a base coating layer located on the surface of the current collector substrate, the base coating layer comprising a polymer lithium salt, the polymer lithium salt being ionizable in solution to yield lithium ions and polymer anions.

[0009] In the present invention, a polymeric lithium salt capable of electrolyzing to obtain lithium ions and polymeric anions in a solution is added to the bottom coating of the current collector. When it is used in an electrode sheet, the electrolyte penetrates deep into the coating, and the lithium ions in the polymeric lithium salt are released into the electrolyte, increasing the lithium ion concentration at this position. At the same time, due to the presence of organic anions in the polymeric lithium salt, the attractive force between positive and negative charges prevents the lithium ions from diffusing reversely to positions far from the coating, thereby achieving an increase in the local lithium salt concentration, solving the problem of lithium ion diffusion in thick-coated electrodes, and improving the rate performance of the battery.

[0010] The polymeric lithium salt in the present invention can ionize lithium ions in a solution and can re-adsorb lithium ions after drying. The organic anions therein, such as acid radical ions, will ionize to generate lithium ions after the electrode sheet electrolyte is injected and infiltrates the electrode sheet, increasing the lithium ion concentration in the active layer near the current collector position. However, due to the presence of acid radical ions, there is still an attractive force between positive and negative charges, thus preventing the lithium ions from diffusing reversely, that is, achieving a fixed-point increase in the lithium ion concentration and broadening the lithium ion diffusion path.

[0011] In the polymeric lithium salt of the present invention, the polymer itself does not migrate after the lithium ions are ionized and solvated, and still remains near the current collector in the electrode sheet. While traditional polymeric solid electrolytes are mostly inorganic or organic lithium salts wrapped by a polymer network. When the electrolyte is sufficient, these lithium salt molecules will dissolve and ionize simultaneously and will be finally uniformly dispersed into the whole electrolyte due to the diffusion caused by concentration difference, so the effects of the present invention cannot be achieved.

[0012] Preferably, the polymeric lithium salt includes any one or a combination of at least two of lithium carboxymethylcellulose, lithium polystyrenesulfonate, lithium polyacrylate or lithium polylactate.

[0013] Preferably, the molecular weight M of the polymeric lithium salt satisfies 200000 < M < 700000, such as 200000, 300000, 400000, 500000, 600000 or 700000, etc.

[0014] Preferably, the current collector substrate includes aluminum foil and / or copper foil.

[0015] Preferably, the bottom coating further includes a conductive agent and a binder.

[0016] In the present invention, a conductive agent and a binder can be added to the bottom coating. The addition of the conductive agent can improve the electronic conductivity between the coating and the current collector, thereby improving the kinetic performance of the battery. After adding the binder to the bottom coating, the surface of the current collector substrate can be completely covered, and there will be no phenomenon that the peeling force of the active layer on the surface of the bottom coating is insufficient and it is easy to fall off.

[0017] Preferably, the mass ratio of the binder in the bottom coating is 1-25%, such as 1%, 3%, 5%, 8%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%, etc.

[0018] In the present invention, if the proportion of the binder is too high, it will affect the proportion of the conductive carbon and the polymer lithium salt, thereby reducing the electronic conductivity and the local lithium ion concentration, which is not conducive to the kinetic performance of the battery. If too little binder is added, it cannot play the role of maintaining the peel strength of the active material coating, which has a negative impact on the cycle life of the battery.

[0019] Preferably, the mass ratio of the conductive agent in the bottom coating is 5-25%, such as 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23% or 25%, etc.

[0020] Preferably, when the bottom coating includes a binder, the thickness of the bottom coating is 1-5 μm, such as 1 μm, 2 μm, 3 μm, 4 μm or 5 μm, etc.

[0021] Preferably, the bottom coating includes a conductive agent and does not include a binder.

[0022] Preferably, when the bottom coating does not include a binder, the bottom coating does not completely cover the surface of the current collector substrate.

[0023] In the present invention, when no binder is added to the bottom coating, it is necessary for the bottom coating not to completely cover the surface. If it completely covers, it is very easy to have insufficient adhesion between the active material coating and the current collector, and then there will be a problem of coating peeling. The design of incomplete coverage plays a key role in improving the peel strength of the electrode and extending the service life of the battery. At the same time, while the bottom coating is incompletely covering, it should be spread as evenly as possible on the surface of the current collector substrate material, that is, its distribution should be extensive and not concentrated in a single area.

[0024] Preferably, when the bottom coating does not include a binder, the thickness of the bottom coating is 1-100 μm, such as 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm, etc.

[0025] Preferably, when the bottom coating does not include a binder, the coverage rate r of the bottom coating on the surface of the current collector substrate is 1% < r < 90%, such as 1.5%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 88% or 89%, etc.

[0026] Preferably, when the primer layer does not include a binder, the conductive agent accounts for 5% to 50% of the mass of the primer layer, such as 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%.

[0027] In this invention, adding too much conductive agent will affect the adhesion of the base coating. This is because conductive agents generally have a large specific surface area, making them prone to adsorbing the binder and affecting its adhesion effect. Conversely, adding too little conductive agent will result in low electronic conductivity, affecting the base coating's optimization effect on battery performance.

[0028] In this invention, the conductive agents are all conventionally selected, including but not limited to activated carbon, carbon nanotubes, conductive carbon black, carbon nanofibers, graphite particles, soft carbon or hard carbon, etc., and the binders are also conventionally selected, including but not limited to polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, polyamide, polyacrylic acid or polyacrylonitrile, etc.

[0029] In a second aspect, the present invention provides a method for preparing a current collector as described in the first aspect, the method comprising the following steps:

[0030] The base coating slurry is applied to the surface of the current collector substrate and dried to obtain the current collector.

[0031] The base coating slurry includes a polymer lithium salt, which can be ionized in solution to produce lithium ions.

[0032] Preferably, the primer coating slurry further includes a conductive agent and a binder, or the primer coating slurry includes a conductive agent but does not include a binder.

[0033] In this invention, when the base coating slurry does not contain a binder, it can be coated using a textured coating roller or by simply applying it by dot coating or spraying. When the base coating slurry contains a binder, it can be coated directly over the entire area using a conventional coating method.

[0034] Thirdly, the present invention provides an electrode sheet comprising a current collector as described in the first aspect and an active material layer located on the surface of the current collector, the active material layer being located on the side of the current collector having an undercoat layer.

[0035] The electrode plates in this invention include positive electrode plates and / or negative electrode plates, which can be selected adaptively according to actual conditions.

[0036] Fourthly, the present invention also provides a lithium-ion battery, the lithium-ion battery comprising the electrode plates as described in the third aspect.

[0037] When the above-mentioned electrode is used in the battery provided by this invention, after the electrolyte in the battery wets the electrode, the electrolyte penetrates deep into the electrode coating. Lithium ions in the polymer lithium salt in the current collector are released into the electrolyte, increasing the lithium ion concentration at that location. At the same time, due to the presence of organic anions in the polymer lithium salt, the attraction between positive and negative charges prevents lithium ions from diffusing backward to locations far from the coating, thereby achieving a local increase in lithium salt concentration. This solves the problem of lithium ion diffusion in thick-coated electrodes and improves the rate performance of the battery.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] This invention adds a polymer lithium salt, which can be electrolyzed to produce lithium ions in solution, to the bottom coating of a current collector. When used as an electrode, the electrolyte penetrates deep into the coating, releasing lithium ions from the polymer lithium salt into the electrolyte and increasing the lithium ion concentration at that location. Simultaneously, the presence of organic anions in the polymer lithium salt and the attraction between positive and negative charges prevent lithium ions from diffusing further away from the coating, thus achieving a localized increase in lithium salt concentration. This solves the problem of lithium ion diffusion in thickly coated electrodes and improves the rate performance of the battery. When the current collector provided by this invention is used in lithium-ion batteries, the 2C / 0.33C rate performance is above 82.6%. Attached Figure Description

[0040] Figure 1 This is a top view of the bottom coating side of the current collector provided in Example 1.

[0041] Figure 2 This is a top view of the bottom coating side of the current collector provided in Example 1.

[0042] Figure 3 This is a top view of the bottom coating side of the current collector provided in Example 1. Detailed Implementation

[0043] 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.

[0044] Example 1

[0045] This embodiment provides a current collector, which consists of an aluminum foil with a thickness of 10 μm and a base coating (20 μm thick) located on one side of the aluminum foil. The base coating consists of 5% carbon nanotubes and 95% lithium carboxymethyl cellulose (molecular weight 500,000) by mass. The base coating has a 50% coverage of the aluminum foil surface and appears as uniformly spaced stripes on the aluminum foil surface. Figure 1 ).

[0046] The method for preparing the current collector is as follows:

[0047] Carbon nanotubes and lithium carboxymethyl cellulose were dispersed in water at a mass ratio of 5:95 to form a base coating slurry. The slurry was then coated onto the surface of aluminum foil using a textured coating roller and dried at 80°C to obtain the current collector.

[0048] Example 2

[0049] This embodiment provides a current collector, which consists of an aluminum foil with a thickness of 10 μm and a base coating (thickness of 65 μm) located on one side of the aluminum foil. The base coating consists of 50% conductive carbon black and 50% lithium polystyrene sulfonate (molecular weight of 200,000) by mass. The base coating has a coverage of 10% on the aluminum foil surface and is distributed in a grid pattern on the aluminum foil surface. Figure 2 ).

[0050] The method for preparing the current collector is as follows:

[0051] Carbon nanotubes and lithium polystyrene sulfonate were dispersed in water at a mass ratio of 35:65 to form a base coating slurry. The slurry was then sprayed onto the surface of an aluminum foil and dried at 80°C to obtain the current collector.

[0052] Example 3

[0053] This embodiment provides a current collector, which consists of an aluminum foil with a thickness of 10 μm and a base coating (45 μm thick) located on one side of the aluminum foil. The base coating consists of 25% conductive carbon black and 65% lithium polystyrene sulfonate (molecular weight 200,000) by mass. The base coating has a coverage of 25% on the aluminum foil surface and appears as evenly spaced dot-shaped circular spots on the aluminum foil surface. Figure 3 ).

[0054] The method for preparing the current collector is as follows:

[0055] Carbon nanotubes and lithium polystyrene sulfonate were dispersed in water at a mass ratio of 35:65 to form a base coating slurry. The slurry was then applied to the surface of an aluminum foil by dot coating and dried at 80°C to obtain the current collector.

[0056] Example 4

[0057] The difference between this embodiment and Embodiment 1 is that carbon nanotubes are not added to the base coating in this embodiment.

[0058] The remaining preparation methods are consistent with those in Example 1.

[0059] Example 5

[0060] The difference between this embodiment and Embodiment 1 is that the mass percentage of carbon nanotubes in this embodiment is 55%.

[0061] The remaining preparation methods are consistent with those in Example 1.

[0062] Example 6

[0063] This embodiment provides a current collector, which consists of an aluminum foil with a thickness of 10 μm and a base coating (thickness of 5 μm) located on one side of the aluminum foil. The base coating consists of carbon nanotubes with a mass percentage of 25%, polyvinylidene fluoride with a mass percentage of 20%, and lithium carboxymethyl cellulose (molecular weight of 650,000) with a mass percentage of 55%. The base coating completely covers the surface of the aluminum foil.

[0064] The method for preparing the current collector is as follows:

[0065] Carbon nanotubes, polyvinylidene fluoride, and lithium carboxymethyl cellulose were dispersed in water at a mass ratio of 25:20:55 to form a base coating slurry. The slurry was then coated onto the surface of aluminum foil using a textured coating roller and dried at 80°C to obtain the current collector.

[0066] Example 7

[0067] The difference between this embodiment and Embodiment 1 is that in this embodiment, the current collector substrate is a copper foil with a thickness of 6μm, and the conductive agent is hard carbon.

[0068] The remaining preparation methods and parameters are consistent with those in Example 1.

[0069] Example 8

[0070] The difference between this embodiment and Embodiment 6 is that in this embodiment, the current collector substrate is a copper foil with a thickness of 6μm, and the conductive agent is artificial graphite.

[0071] The remaining preparation methods and parameters are consistent with those in Example 6.

[0072] Comparative Example 1

[0073] The difference between this comparative example and Example 6 is that the polymer lithium salt carboxymethyl cellulose lithium is not added to the base coating of this comparative example, and the mass ratio of carbon nanotubes to polyvinylidene fluoride is 75:25.

[0074] The remaining preparation methods are consistent with those in Example 6.

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 1 is that this comparative example directly uses the aluminum foil from Example 1 as the current collector.

[0077] Comparative Example 3

[0078] The difference between this comparative example and Example 1 is that lithium carboxymethyl cellulose is replaced with a polymer electrolyte in this comparative example. The specific method is as follows: PEO with a molecular weight of 500,000 and LiFSI are mixed and ground at a mass ratio of 20:1. Then, carbon nanotubes and the mixture are dispersed in water at a mass ratio of 5:95 to form a base coating slurry. The slurry is coated on the surface of aluminum foil using a textured coating roller and dried at 80°C to obtain the current collector.

[0079] Preparation of the positive electrode sheet: The positive electrode active material NCM523 was mixed with conductive agent carbon black and binder PVDF in a ratio of 97:1.7:1.3 and added to the organic solvent NMP. The mixture was stirred at high speed to form a uniform dispersion. After high-speed stirring, negative pressure defoaming was performed in a mixing tank to obtain a positive electrode slurry suitable for coating. The obtained positive electrode slurry was coated onto the current collectors described in Examples 1-6 and Comparative Examples 1-3, or onto aluminum foil with a thickness of 10 μm, using a transfer coating machine. After drying, cold pressing, and slitting, the resulting positive electrode sheets were formed into the desired shapes. During cold pressing, the compaction density of the positive electrode active material coating area was controlled at 3.45 g / cm³. 3 .

[0080] Preparation of the negative electrode sheet: Graphite (negative electrode active material), carbon black (conductive agent), SBR (binder), and CMC (binder) were mixed in a ratio of 96.8:1.2:1.2:0.8 and added to deionized water. The mixture was stirred at high speed to form a uniform dispersion. After high-speed stirring, the mixture was defoamed under negative pressure in a mixing tank to obtain a negative electrode slurry suitable for coating. The obtained negative electrode slurry was coated onto a 6 μm thick copper foil or the current collector described in Examples 7-8 using a transfer coating machine. After drying, cold pressing, and slitting, the resulting negative electrode sheets were formed into the desired shapes. During cold pressing, the compaction density of the negative electrode active material coating area was controlled at 1.6 g / cm³. 3 .

[0081] Battery fabrication: Positive and negative electrode sheets are placed on both sides of the separator and wound together to form a core. The uncoated area is retained and connected to the nickel electrode tab by ultrasonic welding. The core is then wrapped with aluminum-plastic film and heat-sealed, leaving one side reserved for electrolyte injection.

[0082] An electrolyte was prepared by adding 13 wt% LiPF6, 1 wt% vinylene carbonate, and 2 wt% DTD as lithium salts and additives to a mixed solvent of EC:EMC:DEC = 3:5:2. This electrolyte was then injected into an aluminum-plastic film wrapped with a core. The resulting lithium-ion battery underwent vacuum sealing, settling, and formation processes.

[0083] Rate testing: Using a charge / discharge device, the battery's SOC was adjusted to 100% at a rate of 0.33C (i.e., 0.33 times the battery's rated capacity in ampere-hours). After resting for 30 minutes, the battery was discharged at a constant current of 0.33C A at 25°C, and the capacity C1 at the end of the discharge was recorded. The process was repeated: charging to 100% SOC at 0.33C, resting for 30 minutes, and then discharging the battery at a constant current of 2C A, recording the capacity C2 at the end of the discharge. The ratio of C2 to C1 was used as a comparison indicator of rate performance. The test results are shown in Table 1.

[0084] Table 1

[0085]

[0086]

[0087] The data results from Examples 1-3 and Example 6 show that rate performance can be improved regardless of whether a binder is added to the bottom coating, indicating that the polymer lithium salt placed near the current collector has a significant effect on improving the kinetic performance of the battery.

[0088] The data results from Examples 1 and 4 show that if no conductive agent is added to the base coating, the overall rate performance of the battery will be dragged down due to insufficient electronic conductivity.

[0089] The data from Examples 1 and 5 show that when too much conductive agent is added to the undercoat, the electronic conductivity is excessive and is no longer a bottleneck in the high-rate discharge process. However, the excessive conductive carbon, at the same undercoat thickness, crowds out the proportion of polymer lithium salt, resulting in a lower local lithium-ion concentration, which is detrimental to the battery's kinetic performance.

[0090] The data results from Examples 1-3 and Examples 6-7 show that the current collector provided by the present invention is suitable for both positive and negative electrode sheets.

[0091] The data from Example 6 and Comparative Example 1 show that without adding polymer lithium salt to the base coating, it is impossible to achieve the effect of increasing the local lithium-ion concentration near the current collector, which does not help the rate performance of the battery.

[0092] The data from Example 1 and Comparative Example 2 show that without an undercoating, the current collector exhibits low electronic conductivity and significant ion migration resistance. The overall kinetic performance of the battery is low, resulting in poor rate performance.

[0093] The data from Example 1 and Comparative Example 3 show that when lithium ions obtained from the ionization of lithium salt in solution cannot be bound near the current collector, the effect of increasing the local lithium ion concentration cannot be achieved. Although the presence of carbon nanotubes enhances the electronic conductivity to some extent, the overall kinetic performance is still similar to that of traditional carbon-coated foil.

[0094] In summary, this invention, by adding a polymer lithium salt capable of electrolyzing to produce lithium ions in solution to the bottom coating of the current collector, allows the electrolyte to penetrate deep into the coating when used as an electrode. This releases lithium ions from the polymer lithium salt into the electrolyte, increasing the lithium ion concentration at that location. Simultaneously, the presence of organic anions in the polymer lithium salt and the attraction between positive and negative charges prevent lithium ions from diffusing further away from the coating, thus achieving a localized increase in lithium salt concentration. This solves the problem of lithium ion diffusion in thickly coated electrodes and improves the rate performance of the battery. When the current collector provided by this invention is used in lithium-ion batteries, the 2C / 0.33C rate performance is above 82.6%.

[0095] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A current collector characterized by comprising: The current collector comprises a current collector substrate and a primer layer on the surface of the current collector substrate, the primer layer comprising a polymer lithium salt, the polymer lithium salt ionizing in solution to produce lithium ions and polymer anions; The primer layer comprises a conductive agent but no binder, the mass ratio of the conductive agent in the primer layer being 5-50%; the coverage ratio r of the primer layer on the surface of the current collector substrate being 10%≤r≤50%; the coverage shape of the primer layer on the surface of the current collector substrate being any one of regularly spaced stripes, regularly spaced dot-shaped circular spots or a checkered pattern; the thickness of the primer layer being 20-65 μm; The polymer lithium salt comprises any one of lithium carboxymethyl cellulose, lithium polystyrene sulfonate, lithium polyacrylate or lithium polylactate or a combination of at least two thereof.

2. A method of making a current collector as claimed in claim 1, characterized in that, The preparation method comprises the following steps: coating a primer layer slurry on the surface of the current collector substrate, drying to obtain the current collector; The primer layer slurry comprises a polymer lithium salt, the polymer lithium salt ionizing in solution to produce lithium ions; The primer layer slurry comprises a conductive agent but no binder.

3. An electrode tab, characterized by The electrode tab comprises the current collector according to claim 1 and an active material layer on the surface of the current collector, the active material layer being on the side of the current collector having the primer layer.

4. A lithium-ion battery, characterized by, The lithium ion battery comprises the electrode tab according to claim 3.

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