Lithium ion battery pole piece, preparation method thereof and lithium ion battery

Abstract

The invention relates to a lithium ion battery pole piece, a preparation method thereof and a lithium ion battery. The lithium ion battery pole piece comprises a foil material, a first layer of slurry and a second layer of slurry, the bottom of the first layer of slurry is adhered to the foil material, the bottom of the second layer of slurry is adhered to the top of the first layer of slurry, and the lithium ion battery pole piece is characterized in that a plurality of grooves are distributed in the top of the first layer of slurry; a plurality of raised lines corresponding to the grooves in the top of the first layer of slurry are distributed at the bottom of the second layer of slurry, and the raised lines at the bottom of the second layer of slurry are bonded in the corresponding grooves in the top of the first layer of slurry. The cohesiveness between the two layers of slurry can be enhanced, and electrolyte permeation in the bottom layer of the thick electrode is improved.

Description

Technical Field

[0001] This invention relates to a lithium-ion battery electrode, its preparation method, and a lithium-ion battery, belonging to the field of lithium-ion batteries. Background Technology

[0002] With the vigorous development of new energy technologies, the demand for power batteries is gradually increasing, leading to a shift in battery technology towards higher energy density and faster charging. However, high energy density and fast charging requirements often conflict. Increasing battery energy density typically requires increasing the loading of active materials, but a thick electrode structure with a high loading can lead to increased battery polarization, thus affecting the fast charging performance of the cell.

[0003] To balance the fast charging performance and high energy density requirements of batteries, the main methods to improve the poor wettability and high tortuosity of electrolytes in thick electrodes, which lead to large battery polarization, are as follows: adding pore-forming agents, creating pores on the electrode surface, and improving the porosity of the upper and lower layers through double-layer coating.

[0004] Improving the transport efficiency of lithium ions and electrons in the electrode can be achieved by adding pore-forming agents (such as Chinese patents with publication numbers CN113422005A and CN111490225A). However, the addition of pore-forming agents brings the risk of residue and the energy consumption cost of removing pore-forming agents. It may also affect the adhesion performance of the electrode and make it easy for the active material to fall off.

[0005] In addition, mechanical pore formation on the electrode surface and template-based pore formation (such as Chinese patent publication number CN106531961A) are also methods to enhance the lithium-ion transport speed of thick electrodes. However, pore formation has limited improvement on the wettability of the underlying electrode, and excessively deep pore formation can affect the stability of the electrode structure.

[0006] Dual-layer coating technology has become a mainstream solution for ensuring both fast charging and energy density. However, there are two types of dual-layer coating. One type uses a dual-layer coating die for dual-layer coating, but this requires production line modifications, incurs costs, and the process still has some unresolved issues. For example, the mixing of the two slurries can lead to coating instability, and differences in viscosity and surface tension can affect coating quality, making it unsuitable for large-scale application. The other type uses a traditional coating machine for secondary coating, which can achieve its purpose with minimal changeover and process costs.

[0007] The main steps for secondary coating using a traditional coating machine are: homogenization, primary coating, drying, rolling, secondary coating, drying, and rolling (e.g., Chinese patents with publication numbers CN115528205A and CN114156437A); or homogenization, primary coating, drying, secondary coating, drying, and rolling (e.g., Chinese patent with publication number CN111490225A). If the electrode is not rolled after the primary coating, the solvent in the secondary coating slurry will quickly penetrate to the lower layer due to the high porosity of the electrode after direct drying, resulting in insufficient time for leveling. Therefore, rolling before coating may be a preferred method, but it also presents some other problems. A significant issue is that after rolling, the surface of the first slurry layer is smooth, leading to poor adhesion between the two slurry layers. Therefore, a new method is needed to address the adhesion problem between the two slurry layers. The main reason is that the adhesion between the adhesive and the foil is due to the hydrogen bonds formed by the groups of the adhesive and the groups on the surface of the copper foil, which undergo a condensation reaction to form chemical bonds. After the first coating and rolling, the bonding points of the second layer of slurry are mainly on the relatively smooth and shiny surface of the active material, and the main force is the intermolecular force. Therefore, the adhesion is relatively poor compared to that between the adhesive and the foil. Summary of the Invention

[0008] The purpose of this invention is to overcome the above-mentioned deficiencies in the prior art and to provide a lithium-ion battery electrode sheet that can enhance the adhesion between two slurry layers and improve the electrolyte penetration in the thick electrode bottom layer, as well as the preparation method and the lithium-ion battery thereof.

[0009] The technical solution adopted by the present invention to solve the above problems is as follows: the lithium-ion battery electrode includes a foil, a first slurry layer and a second slurry layer. The bottom of the first slurry layer is bonded to the foil, and the bottom of the second slurry layer is bonded to the top of the first slurry layer. Its structural feature is that: the top of the first slurry layer has several grooves, and the bottom of the second slurry layer has several protrusions corresponding to the grooves on the top of the first slurry layer. The protrusions on the bottom of the second slurry layer are bonded to the corresponding grooves on the top of the first slurry layer to form a mechanical interlocking structure.

[0010] Preferably, the cross-section of the groove in the first layer of slurry is one or more of the following: wedge-shaped, semi-circular, and square.

[0011] Preferably, the width of the grooves in the first layer of slurry is 50 μm to 1 cm, and the depth is 5 μm to 100 μm; the spacing between two adjacent grooves is 50 μm to 1 cm.

[0012] A method for preparing a lithium-ion battery electrode sheet includes the following steps in sequence: homogenization, first layer coating, drying, first rolling, second coating, drying, and second rolling, characterized in that: the first rolling is performed using a shaped roller, the surface of which is uniformly distributed with strip-shaped protrusions, the protrusions being distributed along the axial or radial direction; after the shaped roller rolls the first layer of slurry after the first layer of coating and drying, the protrusions on the shaped roller form uniformly distributed grooves on the first layer of slurry.

[0013] Preferably, the shape of the convex strips on the shaped roller is one or more of wedge, semi-circular and square, the width of the convex strips on the shaped roller is 50μm to 1cm, the height of the convex strips on the shaped roller is 5μm to 100μm, and the circumference interval between two adjacent convex strips on the shaped roller is 50μm to 1cm.

[0014] A lithium-ion battery includes: a positive electrode, a negative electrode, a separator, a casing, and an electrolyte, characterized in that: both the positive electrode and the negative electrode adopt the structure of the lithium-ion battery electrode described above.

[0015] Preferably, the negative electrode active material is one or more of graphite, hard carbon, soft carbon, lithium titanate, silicon-oxygen materials, and silicon-carbon materials; the positive electrode active material is one or more of nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate materials, lithium cobalt oxide, lithium manganese iron oxide, lithium titanate layered oxide sodium-ion battery positive electrode materials, and Prussian blue sodium-ion battery positive electrode materials.

[0016] Preferably, the thickness of both the positive and negative electrode sheets is between 100 μm and 400 μm. The ratio of the thickness of the first slurry layer to the thickness of the second slurry layer can be 1:1, 2:1, 1:2, etc., but is not limited to the ratios given in the examples.

[0017] Preferably, the positive electrode sheet contains the following mass percentages: 95%–97.5% positive active material, 1.5%–3% conductive agent, and 1%–2% binder; the negative electrode sheet contains the following mass percentages: 94%–97% negative active material, 1%–3% conductive agent, and 1%–3% binder.

[0018] Preferably, the binder is one or more of polyvinylidene fluoride, sodium cellulose, PAA, CMC, and SBR.

[0019] Preferably, the conductive agent is one or more of conductive graphite, conductive carbon black, carbon nanotubes, and carbon nanofibers.

[0020] Preferably, the foil material of the positive electrode is aluminum foil with a thickness of 8μm to 15μm; the foil material of the negative electrode is copper foil with a thickness of 5μm to 10μm.

[0021] Compared with the prior art, the present invention has the following advantages and effects: based on changing the kinetic properties of the active materials in the upper and lower slurries or on the porosity gradient distribution of the upper and lower layers, double-layer coating is carried out. By rolling the first layer of slurry with a special-shaped roller, the adhesion between the two layers of slurry is greatly increased. It also facilitates the longitudinal penetration of the electrolyte and reduces the polarization inside the electrode.

[0022] The solution in this application can be operated on the basis of existing production lines without the need for modification of new double-layer coating equipment. It is simple, easy to implement, and has low manufacturing costs, making it suitable for large-scale production on existing production lines. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention and / or the prior art, the drawings used in the description of the embodiments and / or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the irregular roller in this invention. The irregular roller has strip-shaped protrusions arranged in the radial direction of the roller. The white strips in the figure are the protrusions, and the yellow area between two adjacent protrusions is the groove.

[0025] Figure 2 This is a schematic diagram of another irregularly shaped roller in the present invention. The irregularly shaped roller has strip-shaped protrusions arranged in the axial direction of the roller. The white strips in the figure are the protrusions, and the yellow area between two adjacent protrusions is the groove.

[0026] Figure 3 This is a cross-sectional schematic diagram of the lithium-ion battery electrode sheet of the present invention. The bottom layer, represented by black, is a foil material. The middle layer, represented by yellow, is the first slurry layer. The top layer, represented by green, is the second slurry layer. The top of the first slurry layer has several grooves. The bottom of the second slurry layer has several raised strips corresponding to the grooves on the top of the first slurry layer. The raised strips at the bottom of the second slurry layer are bonded to the corresponding grooves on the top of the first slurry layer. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are explanations of the present invention, but the present invention is not limited to the following embodiments. Example

[0028] See Figures 1 to 3In this embodiment, the lithium-ion battery electrode includes a foil, a first slurry layer, and a second slurry layer. The bottom of the first slurry layer is bonded to the foil, and the bottom of the second slurry layer is bonded to the top of the first slurry layer. The top of the first slurry layer has several grooves, and the bottom of the second slurry layer has several raised strips corresponding to the grooves on the top of the first slurry layer. The raised strips on the bottom of the second slurry layer are bonded to the corresponding grooves on the top of the first slurry layer to form a mechanical interlocking structure.

[0029] The cross-section of the grooves in the first layer of slurry can be one or more of the following: wedge-shaped, semi-circular, and square. The width of the grooves in the first layer of slurry is typically 50 μm to 1 cm, and the depth is typically 5 μm to 100 μm; the spacing between two adjacent grooves is typically 50 μm to 1 cm.

[0030] The method for preparing lithium-ion battery electrode sheets in this embodiment includes the following steps in sequence: homogenization, first layer coating, drying, first rolling, second coating, drying and second rolling. The first rolling is performed using a shaped roller. The surface of the shaped roller is uniformly distributed with strip-shaped protrusions. The protrusions are distributed along the axial or radial direction. After the shaped roller rolls the first layer of slurry after the first layer of coating and drying, the protrusions on the shaped roller form uniformly distributed grooves on the first layer of slurry.

[0031] The shape of the convex strips on the shaped roller is one or more of wedge, semi-circular and square. The width of the convex strips on the shaped roller is 50μm to 1cm, the height of the convex strips on the shaped roller is 5μm to 100μm, and the circumference interval between two adjacent convex strips on the shaped roller is 50μm to 1cm.

[0032] The lithium-ion battery in this embodiment includes a positive electrode, a negative electrode, a separator, a casing, and an electrolyte. Both the positive and negative electrodes employ the structure described above for lithium-ion battery electrodes. The thickness of both the positive and negative electrodes is 100 μm to 400 μm. The foil material of the positive electrode is aluminum foil with a thickness of 8 μm to 15 μm; the foil material of the negative electrode is copper foil with a thickness of 5 μm to 10 μm.

[0033] In this embodiment, the negative electrode active material is one or more of graphite, hard carbon, soft carbon, lithium titanate, silicon-oxygen materials, and silicon-carbon materials; the positive electrode active material is one or more of nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate materials, lithium cobalt oxide, lithium manganese iron oxide, lithium titanate layered oxide sodium-ion battery positive electrode materials, and Prussian blue sodium-ion battery positive electrode materials.

[0034] In this embodiment, the mass percentage of the positive electrode sheet is: 95%–97.5% positive active material, 1.5%–3% conductive agent, and 1%–2% binder; the mass percentage of the negative electrode sheet is: 94%–97% negative active material, 1%–3% conductive agent, and 1%–3% binder; the binder is one or more of polyvinylidene fluoride, sodium cellulose, PAA, CMC, and SBR; the conductive agent is one or more of conductive graphite, conductive carbon black, carbon nanotubes, and carbon nanofibers. Example

[0035] The following is a comparative experiment using the technical solution in this application as Example 2, compared with Comparative Example 1.

[0036] In the negative electrode sheet of this embodiment, the formulation ratio (mass ratio) of the first layer slurry is artificial graphite: conductive carbon black: multi-walled carbon nanotubes: sodium carboxymethyl cellulose: styrene-butadiene rubber = 96.2:1:0.3:1.2:1.3; the formulation ratio (mass ratio) of the second layer slurry is artificial graphite: hard carbon: conductive carbon black: multi-walled carbon nanotubes: sodium carboxymethyl cellulose: styrene-butadiene rubber = 86.58:9.62:1:0.3:1.2:1.3, wherein the D of artificial graphite is... 50 =13μm, hard carbon (D) was added to the second layer of active material. 50 =5μm), which is beneficial to improve the fast charging performance of high areal density negative electrodes.

[0037] (1) Mix 0.3 parts of multi-walled carbon nanotubes, 1 part of conductive carbon black and 1.2 parts of sodium carboxymethyl cellulose solution at 1500 rpm for 30 min, add 1 / 2 of the active material (i.e. 48.1 parts of artificial graphite), mix at 2500 rpm for 30 min, add the remaining 1 / 2 of the active material (i.e. 48.1 parts of artificial graphite), mix at 2500 rpm for 30 min, add appropriate deionized water and 3 parts of N-methylpyrrolidone, mix at 1200 rpm for 20 min, finally add 1.3 parts of styrene-butadiene rubber, mix at 800 rpm for 30 min, the final slurry has a solid content of 52%, after vacuum defoaming treatment, pass through a 150 mesh sieve twice to obtain the first layer of slurry.

[0038] (2) Mix 0.3 parts of multi-walled carbon nanotubes, 1 part of conductive carbon black and 1.2 parts of sodium carboxymethyl cellulose solution at 1500 rpm for 30 min, add 1 / 2 of the active material (i.e. 43.29 parts of artificial graphite and 4.81 parts of hard carbon), mix at 2500 rpm for 30 min, add the remaining 1 / 2 of the active material (i.e. 43.29 parts of artificial graphite and 4.81 parts of hard carbon), mix at 2500 rpm for 30 min, add appropriate deionized water and 3 parts of N-methylpyrrolidone, mix at 1200 rpm for 20 min, finally add 1.3 parts of styrene-butadiene rubber, mix at 800 rpm for 30 min, the final slurry has a solid content of 52%, after vacuum defoaming treatment, pass through a 150 mesh sieve twice to obtain the second layer of slurry.

[0039] (3) The first coating is performed using a first layer of slurry. The foil material is 6μm copper foil, and the coating density on both sides is 15 mg / cm². 2 The maximum temperature of the oven shall not exceed 100℃.

[0040] (4) Rolling is performed using the shaped roller of this application. The strip-shaped convex strips are arranged along the axial direction. The groove depth between two convex strips is 5μm, the groove width is 100μm, the interval between two adjacent grooves is 100μm, and the rolling thickness of the first layer of slurry coated on the metal copper foil is 109μm (the thickness of the first layer of slurry in the groove is 104μm).

[0041] (5) Apply a second layer of slurry for the second coating. After coating, the surface density on both sides is 30 mg / cm³. 2 The maximum temperature of the oven shall not exceed 100℃.

[0042] (6) Roll pressing was performed using conventional rollers. The thickness of the second layer of slurry after rolling was 190 μm, and the total compaction of the negative electrode sheet was 1.63 mg / cm. 3 .

[0043] The negative electrode of the lithium-ion battery in this embodiment uses the aforementioned negative electrode sheet, and the positive electrode uses existing lithium iron phosphate technology. The formula ratio (mass ratio) of the positive electrode is lithium iron phosphate: single-walled carbon nanotubes: conductive carbon black: polyvinylidene fluoride = 97:0.5:1:1.5, and the bifacial density is 65 mg / cm³. 2 The compaction density is 2.6 g / cm³. 3 The separator is a 12+4 ceramic separator, which is then subjected to slitting, die-cutting, baking, stacking, welding, encapsulation, baking, electrolyte injection, formation, and capacity testing to obtain a high-energy-density lithium iron phosphate experimental cell with a discharge NP ratio of 1.13 and an energy density of 26.7Ah. (The energy density of the 55Ah 143155194 model can reach 206Wh / kg; 445Wh / L).

[0044] Comparative Example 1.

[0045] Comparative Example 1 uses the same materials and proportions as the negative electrode sheet in Example 2 above. The difference is that the first rolling is performed using a conventional roller, and the positive electrode sheet is from the same batch as in Example 2.

[0046] To conduct electrolyte diffusion tests (electrode liquid absorption performance) and rate performance tests (1C=26.7A) on the electrodes of Example 2 and Comparative Example 1, the test methods are as follows: (1) Electrode absorption test: At room temperature of 25±2℃, 5μL of dimethyl carbonate was dropped onto the negative electrode using a microsyringe. The time for the droplet to disappear was recorded. The average of 5 tests was taken as the absorption time of the negative electrode. The results are shown in Table 1 below.

[0047] Table 1

[0048] (2) Peeling force test of negative electrode sheet: Under the condition of room temperature 25±2℃, a 20mm wide and 100mm long test tape is bonded to the electrode sheet to be tested. After pressing it ten times with a roller with a rolling force of 4 kg, it is placed on the Lloyd universal material tester. The peeling test speed is 100mm / min, the machine extension length is 200mm, and the output value is the average value of 20% to 80% of the machine extension. The results are shown in Table 2 below.

[0049] Table 2

[0050] (3) Rate performance test: At room temperature of 25±2℃, the battery was discharged to 2V at 1 / 2C, left to stand for 30min, and then charged to 3.75V at currents of 1 / 2C, 1C, 1.5C, and 2C respectively. Then, it was switched to constant voltage charging until the cutoff current was 0.05C, and then left to stand for 30min. The charging capacity of the battery at different rates was obtained, as shown in Table 3 below.

[0051] Table 3: Battery Rate Charging Capacity Table

[0052] Table 1 shows that the negative electrode sheet of Example 2 has better electrolyte diffusion performance. Table 2 also shows that the negative electrode sheet of Example 2 has greater peel force, indicating that the grooves formed by the first layer of slurry after being rolled by the shaped roller can increase the peel force of the double coating, which is beneficial to the safety of the battery cell. In Comparative Example 1, the first and second coating layers separated after being peeled off by adhesive tape, indicating poor adhesion between the two layers. In contrast, the electrode sheet of Example 2 exposed the foil after bonding, indicating better adhesion between the two layers. Furthermore, Table 3 shows that the lithium-ion battery assembled in Example 2 also has higher rate performance, which can improve the fast-charging performance of high-energy-density battery cells.

[0053] The solution proposed in this application is simple and easy to operate, has low manufacturing costs, and is conducive to large-scale production.

[0054] Furthermore, it should be noted that the specific embodiments described in this specification may differ in the shape and name of their components, etc. The above description is merely illustrative of the structure of the present invention. All equivalent or simple variations made based on the structure, features, and principles described in this patent concept are included within the protection scope of this patent. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to substitute them, as long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, all of which should fall within the protection scope of this invention.

Claims

1. A lithium-ion battery electrode, comprising a foil, a first slurry layer, and a second slurry layer, wherein the bottom of the first slurry layer is bonded to the foil, and the bottom of the second slurry layer is bonded to the top of the first slurry layer, characterized in that: The top of the first layer of slurry has several grooves. The cross-section of the grooves in the first layer of slurry is one or more of wedge-shaped, semi-circular, and square. The width of the grooves in the first layer of slurry is 50μm to 1cm, and the depth is 5μm to 100μm. The distance between two adjacent grooves is 50μm to 1cm. The bottom of the second layer of slurry has several raised strips corresponding to the grooves on the top of the first layer of slurry. The raised strips at the bottom of the second layer of slurry are bonded to the corresponding grooves on the top of the first layer of slurry to form a mechanical interlocking structure.

2. A method for preparing a lithium-ion battery electrode as described in claim 1, comprising the following steps in sequence: homogenization, first layer coating, drying, first rolling, second coating, drying, and second rolling, characterized in that: The first rolling is performed using a shaped roller. The surface of the shaped roller is evenly distributed with strip-shaped protrusions. The protrusions are distributed along the axial or radial direction. After the shaped roller rolls the first layer of slurry after the first layer is coated and dried, the protrusions on the shaped roller form evenly distributed grooves on the first layer of slurry.

3. The method for preparing lithium-ion battery electrodes according to claim 2, characterized in that: The shape of the convex strips on the shaped roller is one or more of wedge, semi-circular and square. The width of the convex strips on the shaped roller is 50μm to 1cm, the height of the convex strips on the shaped roller is 5μm to 100μm, and the circumference interval between two adjacent convex strips on the shaped roller is 50μm to 1cm.

4. A lithium-ion battery, comprising: The positive electrode, negative electrode, separator, shell and electrolyte are characterized in that: the positive electrode and negative electrode both adopt the structure of the lithium-ion battery electrode as described in claim 1.

5. The lithium-ion battery according to claim 4, characterized in that: The negative electrode active material is one or more of graphite, hard carbon, soft carbon, lithium titanate, silicon-oxygen materials, and silicon-carbon materials; the positive electrode active material is one or more of nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate materials, lithium cobalt oxide, lithium manganese iron oxide, lithium titanate layered oxide sodium-ion battery positive electrode materials, and Prussian blue sodium-ion battery positive electrode materials.

6. The lithium-ion battery according to claim 4, characterized in that: The thickness of both the positive and negative electrode sheets ranges from 100 μm to 400 μm.

7. The lithium-ion battery according to claim 4, characterized in that: The positive electrode sheet contains the following mass percentages: 95%–97.5% positive active material, 1.5%–3% conductive agent, and 1%–2% binder; the negative electrode sheet contains the following mass percentages: 94%–97% negative active material, 1%–3% conductive agent, and 1%–3% binder; the binder is one or more of polyvinylidene fluoride, sodium cellulose, PAA, CMC, and SBR; the conductive agent is one or more of conductive graphite, conductive carbon black, carbon nanotubes, and carbon nanofibers.

8. The lithium-ion battery according to claim 4, characterized in that: The foil material of the positive electrode is aluminum foil with a thickness of 8μm to 15μm; the foil material of the negative electrode is copper foil with a thickness of 5μm to 10μm.

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