Negative pole piece and lithium ion battery

Abstract

The utility model relates to the technical field of lithium ion batteries, in particular to a negative pole piece which comprises a current collector, a bottom coating and an active layer which are sequentially stacked from bottom to top, the bottom coating comprises a current collector bonding bottom coating and a water-resistant bottom coating which are arranged from bottom to top. According to the negative pole piece provided by the utility model, the double-layer composite bottom coating is adopted, and the water resistance of the bottom coating is improved while the bonding force between the bottom coating and the current collector and the bonding force between the active layer and the bottom coating are improved, so that the high stripping force of the negative pole piece is realized, the phenomenon of negative pole stripping during high-speed charging is avoided, and the service life of the negative pole piece is prolonged. And the thermal runaway risk during high-power charging and discharging is reduced.

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 are rechargeable batteries that primarily function by the movement of lithium ions between the positive and negative electrodes. During charging and discharging, lithium ions repeatedly insert and extract between the two electrodes; during charging, lithium ions extract from the positive electrode, pass through the electrolyte, and insert into the negative electrode, leaving the negative electrode in a lithium-rich state; the reverse occurs during discharging. Due to their advantages such as small size, large capacity, and long lifespan, lithium-ion batteries are widely used in digital products, energy storage systems, power batteries, commercial vehicles, two-wheeled vehicles, power tools, and medical devices.

[0003] Lithium-ion batteries consist of a casing, and internal components such as coiled / stacked cores and electrolyte; the coiled / stacked cores are composed of positive electrode sheets, negative electrode sheets, and separators. With increasingly stringent fast-charging requirements for power batteries and digital batteries, the negative electrode in existing technologies is prone to delamination during high-speed charging, leading to a high risk of battery thermal runaway and limiting the development of lithium-ion batteries. Utility Model Content

[0004] To address the problem of negative electrode detachment during high-speed charging in existing technologies, this invention provides a negative electrode that employs a composite undercoating. This undercoating increases the adhesion between the active layer and the current collector while improving the water resistance of the undercoating and increasing the adhesion of the electrode, thereby solving the problem of negative electrode detachment during high-speed charging in existing technologies.

[0005] The technical solution adopted by this utility model to solve its technical problem is:

[0006] A negative electrode sheet includes a current collector, a base coating layer, and an active layer stacked sequentially from bottom to top; the base coating layer includes a current collector bonding base coating layer and a water-resistant base coating layer stacked sequentially from bottom to top.

[0007] Optionally, the thickness of the current collector adhesive primer is greater than the thickness of the water-resistant primer.

[0008] Optionally, the total thickness of the base coating is 0.5-3 μm.

[0009] Optionally, the active layer includes a first active layer and a second active layer disposed from bottom to top; the lithium ion insertion rate in the second active layer is greater than the insertion rate in the first active layer.

[0010] Optionally, the specific capacity of the first active layer is greater than the specific capacity of the second active layer.

[0011] Optionally, the thickness of both the first active layer and the second active layer is in the range of 20-200 μm.

[0012] Optionally, the current collector is a copper foil with a thickness of 2-15 μm.

[0013] Optionally, it further includes an edge coating layer; the edge coating layer is disposed on the current collector and is located on both sides of the base coating layer and the active layer.

[0014] Optionally, the thickness of the edge coating is less than the thickness of the active layer.

[0015] Another objective of this invention is to provide a lithium-ion battery, including the negative electrode sheet as described above.

[0016] The beneficial effects of this utility model are:

[0017] The negative electrode sheet provided by this utility model adopts a double-layer composite base coating. While improving the adhesion between the base coating and the current collector and between the active layer and the base coating, it also improves the water resistance of the base coating, thereby achieving high peel force of the negative electrode sheet, avoiding the phenomenon of negative electrode delamination during high-speed charging, and reducing the risk of thermal runaway during high-power charging and discharging. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Figure 1 This is a cross-sectional schematic diagram of the negative electrode sheet in this utility model;

[0020] Figure 2 This is a cross-sectional schematic diagram of the negative electrode sheet in Comparative Example 1 of this utility model;

[0021] Figure 3 This is a cross-sectional schematic diagram of the negative electrode sheet in Comparative Example 2 of this utility model;

[0022] Figure 4 This is a cross-sectional schematic diagram of the negative electrode sheet in Comparative Example 3 of this utility model.

[0023] In the figure: 1-current collector; 2-base coat; 21-current collector bonding base coat; 22-water resistant base coat; 3-active layer; 31-first active layer; 32-second active layer; 4-edge coat. Detailed Implementation

[0024] The present invention will now be described in further detail. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0025] In the description of this utility model, it should be understood that the terms "first" and "second" are used only for simplification and should not be construed as indicating or implying relative importance, or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0026] In this utility model, unless otherwise explicitly specified and limited, "above" or "below" the first feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "on top of," and "over" the first feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the first feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0027] To address the problem of negative electrode delamination during high-speed charging in existing technologies, this invention provides a negative electrode sheet, see [link to relevant documentation]. Figure 1As shown, the negative electrode includes a current collector 1, a base coating 2, and an active layer 3 stacked sequentially from bottom to top. Preferably, the coating area of ​​the base coating 2 and the active layer 3 are the same size. The current collector 1 is made of copper foil. The base coating 2 is applied to the current collector 1 to increase the adhesion between the active layer 3 and the current collector 1. Preferably, the base coating 2 includes a current collector bonding base coating 21 and a water-resistant base coating 22 arranged from bottom to top. The current collector bonding base coating 21 is a coating that can bond well with the current collector 1. The current collector bonding base coating 21 is applied to the current collector 1. The current collector bonding base layer 21 is in contact with the current collector 1 to ensure the adhesion between the base layer 2 and the current collector 1. The water-resistant base layer 22 is a coating with good hydrophobicity after curing. The water-resistant base layer 22 is applied to the current collector bonding base layer 21 and is in contact with the active layer 3 to increase the adhesion between the active layer 3 and the base layer 2. At the same time, it can reduce the risk of the base layer 2 being eroded by water during the preparation of the active layer 3, thereby ensuring the reliability of the adhesion between the base layer 2 and the current collector 1, as well as between the active layer 3 and the base layer 2, and avoiding the phenomenon of negative electrode delamination during high-speed charging.

[0028] Both the current collector bonding primer 21 and the water-resistant primer 22 are selected from existing coatings. Specifically, electrode sheets designed using traditional processes are mostly without a primer coating, or use a single-layer primer to increase the adhesion between the foil and the active coating. However, traditional single-layer primers use PAA or SBR as the primer adhesive. When using PAA as the primer adhesive, it can bond well with the foil, but PAA is not water-resistant and is easily dissolved by water in the active coating slurry during the active coating process. SBR primer adhesive, on the other hand, is very effective on bright copper foil. While effective adhesion is difficult to achieve with SBR, its adhesion is relatively weaker compared to the PAA system. However, as a type of rubber, SBR has excellent hydrophobicity after curing. The SBR primer system can reduce the risk of water erosion during the preparation of the active coating. For the technical solution provided by this utility model, the current collector adhesive primer 21 can use PAA as an adhesive to enhance the adhesion between the primer 2 and the current collector 1. The water-resistant primer 22 can use SBR as an adhesive to improve the adhesion between the primer 2 and the active layer 3 and improve its water resistance.

[0029] The negative electrode sheet provided by this utility model adopts a double-layer composite base coating. While improving the adhesion between the base coating 2 and the current collector 1 and between the active layer 3 and the base coating 2, it also improves the water resistance of the base coating 2, thereby achieving high peel force of the negative electrode sheet, avoiding the phenomenon of negative electrode delamination during high-speed charging, and reducing the risk of thermal runaway during high-power charging and discharging.

[0030] To balance adhesion and water resistance, the present invention preferably has a thickness of the current collector adhesive base layer 21 that is greater than the thickness of the water-resistant base layer 22, and preferably has a total thickness of 0.5-3μm, that is, the sum of the thicknesses of the current collector adhesive base layer 21 and the water-resistant base layer 22 is 0.5-3μm.

[0031] The active layer 3 in this invention can be selected from existing active coatings suitable for lithium-ion battery anode sheets; preferably, the active layer 3 includes a first active layer 31 and a second active layer 32 arranged from bottom to top; the first active layer 31 is coated on and in contact with the water-resistant bottom coating 22; the second active layer 32 is coated on and in contact with the first active layer 31; the main materials of the first active layer 31 and the second active layer 32 can both be graphite anode material, silicon-carbon anode material, silicon-oxygen anode material, or hard carbon anode material. Materials, soft carbon anode materials, etc.; the binder in the formulation of the first active layer 31 and the second active layer 32 can be CMC, PAA, SBR, styrene-acrylic, pure acrylic, etc.; to improve kinetic performance and cycle life, the main material of the first active layer 31 and the second active layer 32 of the electrode sheet is preferably one or a combination of graphite anode, silicon anode, hard carbon, etc.; specifically, the main material of the second active layer 32 is preferably fast-charging type; further, to improve energy density, the first active layer 31 is preferably energy-type main material.

[0032] Specifically, to ensure kinetic performance and energy density, this invention preferably has a lithium ion insertion rate in the second active layer 32 that is greater than that in the first active layer 31; and a specific capacity in the first active layer 31 that is greater than that in the second active layer 32.

[0033] The present invention preferably uses energy-type graphite as the main material, SBR (DA-231) as the water-based binder, SP as the conductive agent, and carboxymethyl cellulose (CMC) as the dispersant in the first active layer 31; the second active layer 32 uses fast-charging graphite as the main material, SBR (DA-231) as the water-based binder, SP as the conductive agent, and carboxymethyl cellulose (CMC) as the dispersant.

[0034] Furthermore, the present invention preferably has the thickness range of 20-200μm for both the first active layer 31 and the second active layer 32, and even more preferably has the thickness range of 30-100μm for both the first active layer 31 and the second active layer 32.

[0035] To further reduce the risk of short-circuit thermal runaway of the battery during high-power charging and discharging, the present invention preferably includes an edge coating 4 for the negative electrode sheet; the edge coating 4 is an insulating layer, disposed on the edge of the electrode tab, that is, on the current collector 1, and the edge coating 4 is located on both sides of the bottom coating 2 and the active layer 3.

[0036] The edge coating 4 serves to provide insulation and reduce burrs, thereby lowering the risk of thermal runaway during high-power charging and discharging. More preferably, the edge coating 48 overlaps with the edge of the base coating / active layer on at least one side, providing insulation, reducing burrs during laser cutting / die cutting, and lowering the risk of subsequent self-discharge. The edge coating 4 can be made using existing technologies. Preferably, the adhesive for the edge coating 4 can be PAA, SBR, CMC, or similar materials. Preferably, the thickness of the edge coating 4 is less than the thickness of the active layer 2.

[0037] This invention increases the adhesion between the foil and the active layer 3 through the composite base coating 2, improving the water resistance of the base coating 2; in conjunction with the double-layer negative electrode active layer 3, by changing the stacking method of the base coating 2 and the active layer 3, the adhesion of the electrode sheet is increased, which can effectively improve the negative electrode detachment phenomenon caused by charging and discharging, achieving high peel force, high kinetics, and high energy density; in addition, the insulating coating on the edge of the electrode tab can reduce burrs and provide insulation, greatly reducing the risk of short circuit thermal runaway of the battery during high-power charging and discharging.

[0038] Another objective of this invention is to provide a lithium-ion battery comprising the negative electrode sheet as described above.

[0039] Specifically, the lithium-ion battery structure provided by this utility model includes stacked and wound types; the corresponding positive electrode of the lithium-ion battery can be lithium iron phosphate, ternary lithium, lithium cobalt oxide, and other materials.

[0040] The lithium-ion battery provided by this utility model adopts a double-layer composite bottom coating for the negative electrode sheet. While improving the adhesion between the bottom coating 2 and the current collector 1 and between the active layer 3 and the bottom coating 2, it also improves the water resistance of the bottom coating 2, thereby achieving high peel force of the negative electrode sheet, avoiding the phenomenon of negative electrode delamination during high-speed charging, and reducing the risk of thermal runaway during high-power charging and discharging.

[0041] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the specific embodiments of this utility model will be described in detail below with reference to the accompanying drawings.

[0042] Example 1

[0043] This embodiment provides a negative electrode sheet, the structure of which is described in [reference needed]. Figure 1 As shown, the negative electrode sheet can be prepared according to the following method:

[0044] S1, the base coating 2 is prepared on the foil by gravure coating method;

[0045] The current collector adhesive base coating 21, applied to the foil, is prepared using 50% polyacrylic acid (PAA) as a water-based binder and 50% SP as a filler. The water-resistant base coating 22 is prepared using 30% styrene-butadiene latex (SBR) as a water-based binder, 65% SP as a filler, and 5% carboxymethyl cellulose (CMC) as a dispersant. The current collector adhesive base coating 21 and the water-resistant base coating 22 are then coated using a gravure coating machine.

[0046] S2, an active layer 3 is prepared on a foil with a base coating 2 using a double-layer coating method;

[0047] The first active layer 31, coated on the water-resistant base coating 22, is prepared using 95.5% by mass energy-type graphite as the main material, 2% by mass SBR (DA-231) as the water-based binder, 1% by mass SP as the conductive agent, and 1.5% by mass carboxymethyl cellulose (CMC) as the dispersant. The second active layer 32, coated on the first active layer 31, is prepared using 95.5% by mass fast-charging graphite as the main material, 2% by mass SBR (DA-231) as the water-based binder, 1% by mass SP as the conductive agent, and 1.5% by mass carboxymethyl cellulose (CMC) as the dispersant. Then, the first active layer 31 and the second active layer 32 are coated onto the base coating foil prepared in S1 using an extrusion coating machine.

[0048] S3, edge coating 4 is prepared on the tab of the electrode using an extrusion coating method;

[0049] The insulating coating applied to the edge tabs of the electrode sheet is prepared using 80% by mass nano-alumina as filler, 15% by mass SBR (DA-1014) as water-based binder, and 5% by mass carboxymethyl cellulose (CMC) as dispersant; then the edge coating is applied to the edge of the tab using an extrusion coating machine.

[0050] S4. Roll the coated electrode sheet and slice it to obtain the negative electrode sheet.

[0051] The electrode obtained in step S4 is soaked in electrolyte for 24 hours. The active layer is not easy to fall off the foil, and the tab part is not easy to have burrs.

[0052] Comparative Example 1

[0053] This comparative example provides a negative electrode sheet, the structure of which is shown below. Figure 2 As shown, the negative electrode sheet can be prepared according to the following method:

[0054] S1, The electrode is prepared by double-layer coating on the foil;

[0055] The first active coating 31, applied to the foil, is prepared using 95.5% by mass energy-type graphite as the main material, 2% by mass SBR (DA-231) as the water-based binder, 1% by mass SP as the conductive agent, and 1.5% by mass carboxymethyl cellulose (CMC) as the dispersant. The second active layer 32, applied to the first active layer 31, is prepared using 95.5% by mass fast-charging graphite as the main material, 2% by mass SBR (DA-231) as the water-based binder, 1% by mass SP as the conductive agent, and 1.5% by mass carboxymethyl cellulose (CMC) as the dispersant. Then, the first active coating 31 and the second active layer 32 are coated using an extrusion coating machine.

[0056] S2, edge coating 4 is prepared on the tab of the electrode using an extrusion coating method;

[0057] The insulating coating applied to the edge tabs of the electrode sheet is prepared using 80% by mass nano-alumina as filler, 15% by mass SBR (DA-1014) as water-based binder, and 5% by mass carboxymethyl cellulose (CMC) as dispersant; then the edge coating is applied to the edge of the tab using an extrusion coating machine.

[0058] S3, roll and slice the coated electrode sheet to obtain the negative electrode sheet.

[0059] When the electrode sheet prepared in step S3 is soaked in electrolyte for 24 hours, the active layer is easily detached from the foil, and burrs are also easily formed on the tab part.

[0060] Comparative Example 2

[0061] This comparative example provides a negative electrode sheet, the structure of which is shown below. Figure 3 As shown, the negative electrode sheet can be prepared according to the following method:

[0062] S1, The base coating is prepared on the foil by gravure coating method;

[0063] The base coating applied to the foil uses 50% polyacrylic acid (PAA) as a water-based binder and 50% SP as a filler to prepare the slurry.

[0064] S2, an active coating is prepared on a foil with a base coating by means of a double-layer coating method;

[0065] The first active layer 31, coated on the base coating, is prepared using 95.5% by mass energy-type graphite as the main material, 2% by mass SBR (DA-231) as the water-based binder, 1% by mass SP as the conductive agent, and 1.5% by mass carboxymethyl cellulose (CMC) as the dispersant. The second active layer 32, coated on the first active layer 31, is prepared using 95.5% by mass fast-charging graphite as the main material, 2% by mass SBR (DA-231) as the water-based binder, 1% by mass SP as the conductive agent, and 1.5% by mass carboxymethyl cellulose (CMC) as the dispersant. Then, the first active layer 31 and the second active layer 32 are coated onto the base coating foil prepared in S1 using an extrusion coating machine.

[0066] S3, edge coating 4 is prepared on the tab of the electrode using an extrusion coating method;

[0067] The insulating coating applied to the edge tabs of the electrode sheet is prepared using 80% by mass nano-alumina as filler, 15% by mass SBR (DA-1014) as water-based binder, and 5% by mass carboxymethyl cellulose (CMC) as dispersant; then the edge coating is applied to the edge of the tab using an extrusion coating machine.

[0068] S4, the coated electrode sheet is rolled and sliced ​​to obtain the negative electrode sheet.

[0069] When the electrode obtained in step S4 is soaked in electrolyte for 24 hours, the active layer is easily detached, and burrs are easily found on the tab part.

[0070] Comparative Example 3

[0071] This comparative example provides a negative electrode sheet, the structure of which is shown below. Figure 4 As shown, the negative electrode sheet can be prepared according to the following method:

[0072] S1, The base coating is prepared on the foil by gravure coating method;

[0073] The base coating applied to the foil uses 30% by mass of styrene-butadiene latex (SBR) as a water-based binder, 65% by mass of SP as a filler, and 5% by mass of carboxymethyl cellulose (CMC) as a dispersant to prepare the slurry.

[0074] S2, an active coating is prepared on a foil with a base coating by means of a double-layer coating method;

[0075] The first active layer 31, coated on the base coating, is prepared using 95.5% by mass energy-type graphite as the main material, 2% by mass SBR (DA-231) as the water-based binder, 1% by mass SP as the conductive agent, and 1.5% by mass carboxymethyl cellulose (CMC) as the dispersant. The second active layer 32, coated on the first active layer 31, is prepared using 95.5% by mass fast-charging graphite as the main material, 2% by mass SBR (DA-231) as the water-based binder, 1% by mass SP as the conductive agent, and 1.5% by mass carboxymethyl cellulose (CMC) as the dispersant. Then, the first active layer 31 and the first active layer 32 are coated onto the base coating foil prepared in S1 using an extrusion coating machine.

[0076] S3, edge coating 4 is prepared on the tab of the electrode using an extrusion coating method;

[0077] The insulating coating applied to the edge tabs of the electrode sheet is prepared using 80% by mass nano-alumina as filler, 15% by mass SBR (DA-1014) as water-based binder, and 5% by mass carboxymethyl cellulose (CMC) as dispersant; then the edge coating is applied to the edge of the tab using an extrusion coating machine.

[0078] S4, the coated electrode sheet is rolled and sliced ​​to obtain the negative electrode sheet.

[0079] When the electrode obtained in step S4 is soaked in electrolyte for 24 hours, the active layer is easily detached, and burrs are easily found on the tab part.

[0080] Based on the above-described preferred embodiments of this utility model, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the technical concept of this utility model. The technical scope of this utility model is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A negative electrode sheet, characterized in that, It includes a current collector (1), a base layer (2) and an active layer (3) stacked sequentially from bottom to top; the base layer (2) includes a current collector adhesive base layer (21) and a water-resistant base layer (22) stacked sequentially from bottom to top.

2. The negative electrode sheet as described in claim 1, characterized in that, The thickness of the current collector adhesive undercoating (21) is greater than the thickness of the water-resistant undercoating (22).

3. The negative electrode sheet as described in claim 1, characterized in that, The total thickness of the base coating (2) is 0.5-3 μm.

4. The negative electrode sheet as described in claim 1, characterized in that, The active layer (3) includes a first active layer (31) and a second active layer (32) disposed from bottom to top; the lithium ion insertion rate in the second active layer (32) is greater than the insertion rate in the first active layer (31).

5. The negative electrode sheet as described in claim 4, characterized in that, The specific capacity of the first active layer (31) is greater than that of the second active layer (32).

6. The negative electrode sheet as described in claim 5, characterized in that, The thickness of both the first active layer (31) and the second active layer (32) is 20-200 μm.

7. The negative electrode sheet as described in claim 1, characterized in that, The current collector is a copper foil with a thickness of 2-15 μm.

8. The negative electrode sheet according to any one of claims 1-6, characterized in that, It also includes an edge coating layer (4); the edge coating layer (4) is disposed on the current collector (1), and the edge coating layer (4) is located on both sides of the base coating layer (2) and the active layer (3).

9. The negative electrode sheet as described in claim 8, characterized in that, The thickness of the edge coating (4) is less than the thickness of the active layer (3).

10. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-9.

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