Negative pole piece and lithium ion battery
By adding a hydrophilic coating between the two active material layers of the negative electrode, the problem of poor electrolyte wettability was solved, thereby optimizing the current density distribution and improving the performance of the lithium-ion battery.
Patent Information
- Application Number
- CN202520071048.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-13
- Publication Date
- 2026-02-03
- Estimated Expiration
- 2035-01-13
AI Technical Summary
Existing technologies struggle to improve electrode capacity utilization and electrolyte wettability in lithium-ion batteries, leading to uneven current density distribution and safety issues.
Adding a hydrophilic coating layer between the two active material layers of the negative electrode plate optimizes the diffusion direction of the electrolyte and improves the wetting uniformity and current density distribution.
The multi-layer structure design improves the uniformity of electrolyte wetting in the Z-axis direction of the thick electrode sheet, reduces pore impedance, and enhances the overall performance of the lithium-ion battery.
Smart Images
Figure CN223871451U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of lithium-ion battery technology, and in particular to a negative electrode sheet and a lithium-ion battery. Background Technology
[0002] Lithium-ion batteries (LIBs) are widely used in electronic devices and are entering the electric vehicle (EV) and grid energy storage markets, with a growing demand for higher energy density LIBs and improved performance. One of the challenging technical hurdles in developing high-energy-density lithium-ion batteries is improving electrode capacity utilization and reducing poor electrolyte wetting caused by high electrode compaction density or excessive electrode thickness. Therefore, improving the electrolyte wettability of the electrode sheets is considered key to solving this problem. Uneven wetting leads to uneven current density distribution and unstable solid electrolyte interphase (SEI) formation; furthermore, incomplete wetting affects battery performance and causes lithium plating on the negative electrode, resulting in safety issues.
[0003] Related technologies can improve the wettability of negative electrode sheets by adding additives. Introducing short fibers into the active material layer of the electrode sheet as a wetting modifier improves the wetting speed and efficiency of the electrolyte. However, this involves directly adjusting the material type of the active material layer of the electrode sheet. This process inevitably causes some damage to the original active layer or alters it, thus adversely affecting the overall performance of the lithium-ion battery. Summary of the Invention
[0004] Based on the existing technology, this invention provides an innovative multi-layer electrode design, starting from the structure of the negative electrode sheet. By adding a hydrophilic coating layer between the two active material layers, the immersion rate is increased, the electrolyte distribution concentration gradient is reduced, the wetting uniformity of the electrolyte in the Z-axis direction of the thick electrode sheet is improved, the current density distribution is optimized, and the pore impedance of the negative electrode sheet is reduced, thereby improving the overall performance of the lithium-ion battery.
[0005] To achieve the objective of this utility model, the following technical solution is adopted:
[0006] This utility model provides a negative electrode sheet, the negative electrode sheet including a current collector 101 and an active material coating formed on at least one side of the current collector, the active material coating including: a first active material coating 102, a second active material coating 104 and a hydrophilic coating 103 disposed between the first active material coating 102 and the second active material coating 104.
[0007] Figure 1This is a schematic diagram of the negative electrode sheet in a specific embodiment of this utility model. In the figure, 101 is the current collector, 102 is the first active material coating, 103 is the hydrophilic coating, and 104 is the second active material coating. The hydrophilic coating 103 is distributed between the first active material coating 102 and the second active material coating 104.
[0008] Preferably, the material of the hydrophilic coating 103 includes one of polymethyl methacrylate powder, polystyrene-acrylate powder, polyurethane powder, and silica powder, and the hydrophilic coating 103 further includes a conductive agent and a binder.
[0009] More preferably, the material of the hydrophilic coating 103 includes silica powder, a conductive agent, and a binder.
[0010] The conductive agent is carbon nanotubes.
[0011] The adhesive is styrene-butadiene rubber.
[0012] The particle size D50 of the polymethyl methacrylate powder is 400-1200 nm, the particle size D50 of the polystyrene-acrylate powder is 300-1200 nm, the particle size D50 of the polyurethane powder is 300-1200 nm, and the particle size D50 of the silica powder is 300-800 nm.
[0013] Preferably, the thickness of the hydrophilic coating 103 is 2-8 micrometers.
[0014] Preferably, the thickness of the first active material coating 102 and the second active material coating 104 is 30-80 micrometers, for example 40-60 micrometers.
[0015] The thickness of the current collector 101 is generally conventional in the art, for example, 6-20 micrometers, preferably 8-10 micrometers.
[0016] Preferably, both the first active material coating 102 and the second active material coating 104 include graphite and / or silicon, conductive agent, and binder.
[0017] The conductive agent is generally selected from one of conductive carbon black (SP), acetylene black, Ketjen black, carbon nanotubes, and graphene.
[0018] The adhesive is generally selected from one of polyacrylic acid, polyvinyl alcohol, hydroxymethyl cellulose, sodium hydroxymethyl cellulose, polyethylene glycol, styrene-butadiene rubber, and polyvinylidene fluoride.
[0019] Preferably, the current collector comprises copper foil.
[0020] This utility model also provides a lithium-ion battery, which includes a negative electrode, a positive electrode, a separator 105, and an electrolyte as described above.
[0021] The method for preparing the negative electrode sheet described in this utility model generally adopts the following steps:
[0022] S1. Mix graphite and / or silicon, conductive agent, binder and solvent to obtain a slurry;
[0023] S2. The slurry is coated on at least one surface of the current collector, the material of the hydrophilic coating is coated on the surface of the slurry, and then another layer of slurry is coated on the surface of the hydrophilic coating to obtain a layered negative electrode sheet.
[0024] Preferably, the mass ratio of graphite and / or silicon, conductive agent, and binder is (48-52):(0.4-1):(0.5-1.5).
[0025] Preferably, in step S2, a drying step is included after the coating step.
[0026] The drying temperature can be 60-90℃, for example 80℃.
[0027] The drying equipment typically employs conventional heating equipment in this field, such as an oven.
[0028] Preferably, the solvent is selected from one of N-methylpyrrolidone, deionized water, dimethyl sulfoxide, and tetrahydrofuran.
[0029] Compared with the prior art, the present invention has the following advantages:
[0030] This invention proposes a novel multilayer negative electrode sheet. By adding a hydrophilic coating layer between the two active material coatings, the electrolyte diffusion direction changes from unidirectional to bidirectional diffusion, increasing the immersion rate and improving the uniformity of electrolyte wetting in the Z-axis direction of the thick electrode sheet. At the same time, it optimizes the current density distribution and reduces the pore impedance of the negative electrode sheet, thereby improving the overall performance of the lithium-ion battery. Attached Figure Description
[0031] To more clearly illustrate the technical solution of this utility model, the accompanying drawings used in the description of this utility model will be briefly introduced below.
[0032] Figure 1 This is a schematic diagram of the negative electrode sheet and the separator in a specific embodiment of this utility model.
[0033] Figure 2 This is a schematic diagram of the negative electrode sheet and the diaphragm in Comparative Example 2 of this utility model.
[0034] The labels in the attached figures include: 101 - current collector; 102 - first active material coating; 103 - hydrophilic coating; 104 - second active material coating; 105 - diaphragm.
[0035] 201 - Current collector; 202 - First active material coating; 204 - Second active material coating; 205 - Separator. Detailed Implementation
[0036] The embodiments of this implementation are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this implementation, and should not be construed as limiting this implementation.
[0037] In the description of this embodiment, the use of "first" and "second" is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of technical features indicated, or implicitly indicating the order of the technical features indicated.
[0038] In this article, "and / or" means either one of two options or both.
[0039] All reagents and raw materials used in this invention are commercially available. Among them, polymethyl methacrylate (CAS No. 9011-14-7), polystyrene-butyl acrylate (CAS No. 25586-20-3), polyurethane (CAS No. 51852-81-4), and silica (CAS No. 10279-57-9).
[0040] Figure 1 and Figure 2 The color intensity indicates the wetting of the electrode by the electrolyte. Figure 1 The negative electrode sheet exhibits a multi-layered structure with consistent grayscale, indicating uniform wetting of the electrode sheet by the electrolyte; while Figure 2 The grayscale levels vary, with the electrolyte concentration being highest at the separator 205 and lowest at the interface between the current collector copper foil 201 and the first active material coating 202. This is because the electrolyte permeates faster at the separator than at the electrodes. The electrolyte first wets the separator and then slowly diffuses to the electrodes, especially thicker electrodes, where the diffusion path is longer and the speed is slower, potentially leading to insufficient wetting of the electrodes and uneven electrolyte distribution.
[0041] visible, Figure 1The electrolyte provides uniform and thorough wetting of the electrode due to the addition of a hydrophilic coating 103 between the first active material coating 102 and the second active material coating 104, which changes the electrolyte diffusion direction from a single direction to bidirectional diffusion, resulting in more thorough wetting.
[0042] This invention addresses the challenge of improving electrolyte wettability without altering the original active material layer in existing technologies. It proposes a multi-layer electrode design, where the inventors discovered that forming a hydrophilic coating between two active material layers can effectively accelerate electrolyte diffusion and improve the wettability of thick electrodes.
[0043] In this invention, the hydrophilic coating 103 has the characteristic of strong affinity with electrolyte. At the same time, the polarity of the material itself is similar to that of carbonate solvents in conventional electrolytes. The two have a very small contact angle, allowing the electrolyte to quickly wet the body.
[0044] In some embodiments, the material of the hydrophilic coating 103 includes one of polymethyl methacrylate powder, polystyrene-acrylate powder, polyurethane powder, and silica powder, preferably silica powder. The hydrophilic coating 103 also includes a conductive agent and a binder.
[0045] In some embodiments, the conductive agent is carbon nanotubes.
[0046] In some embodiments, the adhesive is styrene-butadiene rubber.
[0047] In some embodiments, the thickness of the hydrophilic coating 103 can be 2-8 micrometers, preferably 3-7 micrometers, and more preferably 5 micrometers.
[0048] In some embodiments, the thickness of the first active material coating 102 and the thickness of the second active coating 104 may be the same or different, and the thickness is generally any thickness in the range of 30-80 micrometers, for example 40-60 micrometers.
[0049] In some embodiments, the thickness of the current collector 101 is conventional in the art, generally 6-20 micrometers, for example any thickness between 8-10 micrometers, preferably 8 micrometers.
[0050] In some embodiments, the raw materials for the first active material coating 102 and the second active material coating 104 are generally conventional electrode active materials in the art.
[0051] In some embodiments, the first active material coating 102 and the second active material coating 104 generally include graphite and / or silicon, conductive agents, and binders.
[0052] The conductive agent and the binder are generally conventional choices in the art. In some embodiments, the conductive agent may be one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes and graphene; the binder may be one of polyacrylic acid, polyvinyl alcohol, hydroxymethyl cellulose, sodium hydroxymethyl cellulose, styrene-butadiene rubber, polyethylene glycol and polyvinylidene fluoride.
[0053] In this invention, the lithium-ion battery includes the aforementioned negative electrode, positive electrode, separator 105, and electrolyte.
[0054] The electrolyte and electrolyte solvent can be conventional electrolytes and electrolyte solvents used in lithium-ion batteries, such as EC:DMC mixed solvent with a mass ratio of 1:1, and electrolyte containing 1.0M LiPF6 in the mixed solvent.
[0055] The present invention will be further explained and illustrated below with reference to embodiments. Example 1
[0056] In this embodiment, the negative electrode sheet includes a current collector 101 and an active material coating formed on at least one side of the current collector. The active material coating includes a first active material coating 102, a hydrophilic coating 103, and a second active material coating 104. The hydrophilic coating 103 is disposed between the first active material coating 102 and the second active material coating 104.
[0057] In this embodiment, the current collector 101 is a copper foil with a thickness of 8 micrometers, the first active material coating 102 and the second active material coating 104 are both 50 micrometers thick, and the active material coating contains graphite, conductive carbon black, sodium hydroxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 50:0.5:0.5:0.4; the hydrophilic coating includes silica powder with a particle size D50=400nm, conductive carbon nanotubes and binder styrene-butadiene rubber, and has a thickness of 5 micrometers. Example 2
[0058] The difference between this embodiment and Embodiment 1 is that the silica powder in the hydrophilic coating 103 is replaced with polymethyl methacrylate powder with a particle size D50=400nm. Example 3
[0059] The difference between this embodiment and Embodiment 1 is that the silica powder in the hydrophilic coating 103 is replaced with polystyrene-acrylate powder with a particle size D50=400nm. Example 4
[0060] The difference between this embodiment and Embodiment 1 is that the silica powder in the hydrophilic coating 103 is replaced with polyurethane powder with a particle size D50=400nm. Example 5
[0061] The difference between this embodiment and Embodiment 1 is that the thickness of the hydrophilic coating is 2 micrometers. Example 6
[0062] The difference between this embodiment and Embodiment 1 is that the thickness of the hydrophilic coating is 8 micrometers. Comparative Example 1
[0063] The difference between this comparative example and Example 1 is that no hydrophilic coating is provided, and at least one surface of the current collector has an active material coating with a thickness of 100 micrometers. Comparative Example 2
[0064] The difference between this comparative example and Example 1 is that no hydrophilic coating is provided, and at least one surface of the current collector has a first active material coating 202 and a second active material coating 204, both of which have a thickness of 50 micrometers.
[0065] Table 1 shows a comparison of the parameters of the above embodiments and comparative examples.
[0066] Table 1
[0067]
[0068] Performance Evaluation
[0069] Test 1: Liquid Absorption Rate Test Method
[0070] Cut the negative electrode sheet into 15cm*4cm pieces, weigh them and record the weight as m1 (g). Place the electrode sheet on the inner wall of a 200mL beaker containing 50mL of electrolyte (EC:DMC mixed solvent with a mass ratio of 1:1 containing 1.0M LiPF6). Keep the electrode sheet vertical and slowly lower it to immerse it in the liquid surface for 1cm, and start timing. Stop timing when the liquid rises to the 12cm mark and record it as t (min). The weight is m2 (g). The liquid absorption rate is calculated using the formula: (m2-m1) / t (g / min). Take the average value of 3 tests.
[0071] Test 2: Electrode Hole Impedance Test Method
[0072] The electrode sheets were cut into six small sheets of 6cm*5cm using a mold. The coating on the tab area was scraped off and cleaned, and then the tabs were welded on. A separator (12 micrometers thick) was added between every two small electrodes, and then they were encapsulated in an aluminum-plastic film. Each sheet was injected with 0.3g of electrolyte (1.0M LiPF6 in a 1:1 EC:DMC mixed solvent) to assemble three symmetrical cells. The EIS pore impedance spectra of the symmetrical cells at 25±2℃ were measured using an electrochemical workstation, and the 45 Hz high-frequency region was detected. oThe aperture impedance of the electrode was measured in mW / cm along the angled line. 2 ), take the average value of 3 symmetrical cells.
[0073] The results of tests one and two are shown in Table 2.
[0074] Table 2
[0075]
[0076] As can be seen from Table 2, the liquid absorption rate of Examples 1-6 is higher than that of Comparative Examples 1 and 2, and the electrode pore resistance is lower than that of Comparative Examples 1 and 2. This is because a hydrophilic coating is added between the negative electrode sheets of the double-layer structure, which allows the electrolyte accumulated at the bottom to penetrate into both the hydrophilic layer and the separator at the same rate. This makes the electrolyte diffusion direction change from unidirectional to bidirectional, resulting in a more uniform concentration distribution, improved electrolyte wettability of the thick electrode, optimized current density distribution, reduced pore resistance of the negative electrode sheet, and improved overall performance of the lithium battery.
[0077] By comparing Examples 1 and 2-4, it can be seen that when silica powder is selected as the hydrophilic coating material, the electrode absorbs liquid faster and the electrode pore resistance is lower, indicating that the electrolyte diffusion is more uniform and the wetting performance of the thick electrode is stronger.
[0078] Furthermore, in Example 1, the thickness of the hydrophilic coating was changed compared to Examples 5-6. At this time, the liquid absorption rate of the negative electrode was the highest and the pore resistance of the electrode was the lowest, indicating that the optimal solution is to add a layer of silica powder with a thickness of 5 micrometers between the two active material coatings.
[0079] Although embodiments of this implementation have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this implementation, the scope of which is defined by the claims and their equivalents.
Claims
1. A negative electrode sheet, comprising a current collector (101) and an active material coating formed on at least one side of the current collector, characterized in that, The active material coating includes: a first active material coating (102), a second active material coating (104), and a hydrophilic coating (103) disposed between the first active material coating (102) and the second active material coating (104).
2. The negative electrode sheet according to claim 1, characterized in that, The hydrophilic coating (103) material includes one of polymethyl methacrylate powder, polystyrene-acrylate powder, polyurethane powder and silica powder, and the hydrophilic coating (103) material also includes a conductive agent and a binder.
3. The negative electrode sheet according to claim 2, characterized in that, The hydrophilic coating (103) material includes silica powder, a conductive agent, and a binder.
4. The negative electrode sheet according to any one of claims 1-3, characterized in that, The thickness of the hydrophilic coating (103) is 2-8 micrometers.
5. The negative electrode sheet according to any one of claims 1-3, characterized in that, The thickness of the first active material coating (102) is 30-80 micrometers.
6. The negative electrode sheet according to any one of claims 1-3, characterized in that, The thickness of the second active material coating (104) is 30-80 micrometers.
7. The negative electrode sheet according to any one of claims 1-3, characterized in that, Both the first active material coating (102) and the second active material coating (104) include graphite and / or silicon, conductive agent, and binder.
8. The negative electrode sheet according to any one of claims 2-3, characterized in that, At least one of the following conditions must be met: a. The current collector (101) comprises copper foil; b. The particle size D50 of the polymethyl methacrylate powder is 400-1200nm, the particle size D50 of the polystyrene-acrylate powder is 300-1200nm, the particle size D50 of the polyurethane powder is 300-1200nm, and the particle size D50 of the silica powder is 300-800nm. c. The conductive agent is carbon nanotubes; d. The adhesive is styrene-butadiene rubber.
9. The negative electrode sheet according to claim 7, characterized in that, The conductive agent is selected from one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene. And / or, the adhesive is selected from one of polyacrylic acid, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyethylene glycol, styrene-butadiene rubber, and polyvinylidene fluoride.
10. A lithium-ion battery, characterized in that, The lithium-ion battery comprises a negative electrode, a positive electrode, a separator (105), and an electrolyte as described in any one of claims 1-9.