Lithium ion battery composite current collector and lithium ion battery

Abstract

The utility model relates to battery technical field especially is a kind of lithium ion battery composite current collector and lithium ion battery, including metal matrix layer and the spacing of metal matrix layer is located at the side of the reinforcing layer of battery winding center away from one side, the metal matrix layer is located in the area of battery corner is corner area, the reinforcing layer is respectively arranged in the corner area surface of the metal matrix layer, the reinforcing layer completely covers the corner area of the metal matrix layer, the coating width of the reinforcing layer along the winding direction of current collector is greater than the length of the corner area of the metal matrix layer.The composite current collector of the utility model has the advantages of high tensile strength and lightweight, and is not prone to breakage.

Description

Technical Field

[0001] This utility model relates to the field of battery technology, and in particular to a lithium-ion battery composite current collector and a lithium-ion battery. Background Technology

[0002] Silicon-carbon based materials, used as anodes in high-capacity lithium-ion batteries, theoretically have a much higher capacity than traditional graphite materials. However, silicon undergoes significant volume expansion during charging and discharging, with an expansion rate of approximately 300%. This causes the anode sheet to be repeatedly subjected to mechanical stress, leading to the fracture of the aluminum foil current collector, commonly known as "fracture." Current technologies improve the strength of the aluminum foil by increasing its thickness or surface roughening, but this sacrifices battery energy density or affects electrolyte wettability. Therefore, a solution is urgently needed that can improve the mechanical properties of the aluminum foil while also maintaining lightweight and conductivity. Utility Model Content

[0003] This invention provides a composite current collector for lithium-ion batteries, which solves the problem that existing current collectors are prone to breakage.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A lithium-ion battery composite current collector includes a metal substrate layer and a plurality of reinforcing layers spaced apart on the side of the metal substrate layer away from the battery winding center. The area of ​​the metal substrate layer at the corner of the battery is called a corner region. The plurality of reinforcing layers are respectively disposed on the surface of the corner region of the metal substrate layer. The reinforcing layers completely cover the corner region of the metal substrate layer. The coating width of the reinforcing layers along the winding direction of the current collector is greater than the length of the corner region of the metal substrate layer.

[0006] Furthermore, the metal substrate layer is located at the outermost end of the battery as the tail of the metal substrate layer. The metal substrate layer includes a tab region for setting the tabs, and a plurality of the reinforcement layers are respectively disposed in the corner region between the tab region of the metal substrate layer and the tail of the metal substrate layer.

[0007] Furthermore, the coating width k of the reinforcing layer along the winding direction of the current collector satisfies the relationship k = (πh / 2) + 6;

[0008] Where h is the thickness of the bare cell after winding.

[0009] Furthermore, the midpoint of each of the reinforcing layers along the winding direction of the metal substrate layer corresponds to the midpoint of the corner region of the metal substrate layer.

[0010] Furthermore, the metal substrate layer is aluminum foil or aluminum alloy foil.

[0011] Furthermore, the thickness of the metal collective layer is 8-15 μm.

[0012] Furthermore, the reinforcing layer is a carbon fiber layer.

[0013] Furthermore, the carbon fibers in the carbon fiber layer are short-cut carbon fibers, with a diameter of 2-5 μm and a length of 50-200 μm.

[0014] Furthermore, the thickness of the composite current collector is 10-18 μm.

[0015] This invention also provides a lithium-ion battery comprising the aforementioned composite current collector.

[0016] The beneficial effects of this invention are as follows: By setting a reinforcing layer at each corner of the metal substrate layer and placing the reinforcing layer on the side away from the battery winding center, the reinforcing layer completely covers the corner area of ​​the metal substrate layer and the coating width is greater than the length of the corner area, effectively improving the tensile strength of the current collector. This effectively solves the problem of the current collector easily breaking during cycling. The composite current collector of this invention is suitable for use as the positive electrode current collector of lithium-ion batteries, especially for batteries with large expansion and high requirements for current collector strength, such as silicon-based or silicon-doped lithium-ion batteries, to suppress aluminum foil breakage during battery cycling while maintaining high conductivity and lightweight characteristics. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the current collector of this utility model;

[0019] Figure 2 This is another schematic diagram of the current collector of this utility model;

[0020] Figure 3 This is a partial schematic diagram of the current collector of this utility model in a battery.

[0021] Explanation of reference numerals in the attached figures: 1. Metal substrate layer; 2. Reinforcing layer; 3. Corner area; 4. Tab area. Detailed Implementation

[0022] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0023] like Figure 1-3 As shown, this utility model provides a lithium-ion battery composite current collector, which includes a metal substrate layer 1 and a plurality of reinforcing layers 2 spaced apart on the side of the metal substrate layer 1 away from the battery winding center. The area of ​​the metal substrate layer 1 at the corner of the battery is called a corner region 3. The plurality of reinforcing layers 2 are respectively disposed on the surface of the corner region 3 of the metal substrate layer 1, and the reinforcing layers 2 completely cover the corner region 3 of the metal substrate layer 1. The coating width of the reinforcing layers 2 along the winding direction of the current collector is greater than the length of the corner region 3 of the metal substrate layer 1. Specifically, after the battery is wound, the wound current collector will form an arc region at the corner of each turn, and the length of the corner region 3 is the arc length of the arc region.

[0024] This invention provides an reinforcing layer 2 at each corner area 3 of the metal substrate layer 1, and places the reinforcing layer 2 on the side away from the battery winding center. The reinforcing layer 2 completely covers the corner area 3 of the metal substrate layer 1 and the coating width is greater than the length of the corner area 3, which effectively improves the tensile strength of the current collector and can effectively solve the problem that the current collector is prone to breakage during the circulation process.

[0025] In another embodiment, the metal substrate layer 1 is located at the outermost end of the battery as the tail of the metal substrate layer 1. The metal substrate layer 1 includes a tab region 4 for setting tabs, and a plurality of the reinforcement layers 2 are respectively disposed in the corner region 3 between the tab region 4 and the tail of the metal substrate layer 1.

[0026] Since the stress on the current collector is mainly concentrated at the corner of the cell, and the corner stress increases sequentially from the inner ring to the outer ring of the cell, that is, the stress at the corner near the outermost end of the electrode is much greater than the stress at the corner near the innermost end of the electrode, this utility model improves the tensile strength of the current collector by placing the reinforcing layer 2 on the surface of the corner area 3 between the tab area 4 and the tail of the metal substrate layer 1, thereby reducing the coating area of ​​the reinforcing layer 2 and reducing the overall weight of the current collector.

[0027] Furthermore, the coating width k of the reinforcing layer 2 along the winding direction of the current collector satisfies the relationship k = (πh / 2) + 6; where h is the thickness of the bare cell after winding.

[0028] When k = (πh / 2) + 6, it can be guaranteed that the reinforcing layer 2 can cover the entire corner, prevent process tolerance fluctuations and better disperse corner stress. If the coating width is at the critical value of (πh / 2), the aluminum foil is still at risk of breakage. If the coating width exceeds (πh / 2) + 6, it will affect the thickness and energy density.

[0029] Furthermore, the midpoint of each reinforcing layer 2 along the winding direction of the metal substrate layer 1 corresponds to the midpoint of the corner region 3 of the metal substrate layer 1. Aligning the midpoints of the reinforcing layers 2 and the corner regions 3 ensures that the reinforcing layers 2 precisely cover the area of ​​maximum stress at the center of the corner region 3. This helps to achieve efficient utilization of the reinforcing material, avoids material waste or insufficient reinforcement, improves the mechanical support effect of the composite current collector in the corner region 3, and enhances tensile strength.

[0030] Specifically, the reinforcement layer 2 is coated on the surface of the metal substrate layer 1 at positions ranging from Pi-k / 2 to Pi+k / 2. The end of the metal substrate layer 1 at the innermost ring of the battery is called the head of the metal substrate layer 1, and the end of the metal substrate layer 1 at the outermost ring of the battery is called the tail of the metal substrate layer 1. Pi refers to the distance from the corner of the cell to the head of the metal substrate layer 1. Counting from the head to the tail of the metal substrate layer 1, P1 refers to the position of the first bend when the cell is wound for the first turn, P2 refers to the position of the second bend, ... Pi to the position of the i-th bend, where Pi is greater than k / 2. Thus, the position of the reinforcement layer 2 in each turn can be calculated.

[0031] Furthermore, the metal substrate layer 1 is an aluminum foil or an aluminum alloy foil.

[0032] Furthermore, the thickness of the metal collective layer is 8-15 μm.

[0033] Furthermore, the reinforcing layer 2 is a carbon fiber layer.

[0034] Furthermore, the carbon fibers in the carbon fiber layer are short-cut carbon fibers with a diameter of 2-5 μm and a length of 50-200 μm. The high tensile strength (≥3 GPa) of the carbon fibers and the aluminum foil form a synergistic reinforcing effect, increasing the tensile strength of the composite aluminum foil by nearly 50%, with no obvious cracks after cycling. The continuous conductive network of carbon fibers reduces interfacial resistance, the composite layer thickness is controllable, and the overall weight increases by only 1-10% compared to pure aluminum foil. Controlling the carbon fiber size within the range of 2-5 μm diameter and 50-200 μm length provides good reinforcement without causing uneven coating or equipment wear due to excessive fiber length. This helps to form a continuous conductive network, improves interfacial conductivity, and enhances mechanical properties.

[0035] Furthermore, the thickness of the composite current collector is 10-18 μm.

[0036] This invention also provides a lithium-ion battery comprising the aforementioned composite current collector.

[0037] Example 1

[0038] Carbon fiber slurry preparation: Short carbon fibers and polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 4:6, and N-methylpyrrolidone is added and ultrasonically dispersed evenly. The diameter of the carbon fibers is 2-5 μm and the length is 100-150 μm to obtain carbon fiber slurry.

[0039] Aluminum foil pretreatment: Take 8μm thick 1060 aluminum foil and clean one side of the aluminum foil with argon plasma;

[0040] Preparation of composite aluminum foil: The aforementioned carbon fiber slurry was coated onto the corner positions of the aluminum foil after several folds following the tabs. The carbon fiber slurry was coated onto one side of the aluminum foil after argon plasma cleaning. The carbon fiber slurry coated on the aluminum foil surface was dried at 120°C to form a reinforcing layer. After drying, it was hot-pressed at a pressure of 8 MPa to obtain a composite aluminum foil with a thickness of 9 μm. The weight of the composite aluminum foil was 34.7 mg.

[0041] Preparation of the positive electrode sheet:

[0042] Lithium cobalt oxide, carbon nanotube conductive agent, and PVDF binder are dispersed in an N-methylpyrrolidone solvent system at a mass ratio of 98:1:1. After thorough mixing, a positive electrode slurry is prepared. The slurry is coated on both surfaces of the above-mentioned composite aluminum foil. After drying, rolling, and slitting, a positive electrode sheet is obtained.

[0043] Negative electrode preparation: The negative electrode active material, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener are dispersed in deionized water at a mass ratio of 97.8:1.1:1.1. After thorough mixing, the negative electrode slurry is coated onto both surfaces of a copper foil. After drying, rolling, and slitting, the negative electrode sheet is obtained. The silicon-to-carbon mass ratio in the negative electrode active material is SiO₂. x :C=10:90.

[0044] Electrolyte preparation:

[0045] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0046] Battery assembly:

[0047] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. This is then wound to form the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. Following vacuum sealing, settling, formation, degassing, and edge trimming, the battery is obtained.

[0048] After 1000 cycles of 1.2C stepped charging and 1.0C discharging, the prepared battery showed no electrode breakage and retained 82% of its capacity.

[0049] Comparative Example 1

[0050] The difference between Comparative Example 1 and Example 1 is that, in Comparative Example 1, the aluminum foil, after being treated with argon plasma cleaning, was continuously coated with carbon fiber slurry, so that the entire surface of the aluminum foil was covered with a carbon fiber reinforcement layer, thus obtaining a composite aluminum foil. The other preparation methods for the composite aluminum foil of Comparative Example 1 and the preparation methods for the battery are the same as in Example 1.

[0051] The composite aluminum foil of Comparative Example 1 has a tensile strength of 220 MPa and a weight of 36.1 mg.

[0052] The battery obtained by using the composite aluminum foil of Comparative Example 1 as the positive electrode current collector showed no breakage of the electrode sheet after 1000 cycles of 1.2C stepped charging and 1.0C discharging. The capacity retention rate was 82%.

[0053] Comparative Example 2

[0054] The difference between Comparative Example 2 and Example 1 is that Comparative Example 1 uses ordinary aluminum foil instead of composite aluminum foil and uses ordinary aluminum foil as the positive electrode current collector to prepare the battery. The battery preparation method is the same as that of Example 1.

[0055] The tensile strength of ordinary aluminum foil is 150MPa and its weight is 34.3mg. After the battery is used for 1000 cycles of 1.2C step charging and 1.0C discharge, the battery electrode breaks into three folds (two folds are single-sided areas and one fold is double-sided areas), and the capacity retention rate is 65%.

[0056] A comparison of Example 1 and Comparative Example 1 shows that the composite aluminum foil prepared by intermittently coating carbon fiber slurry at the corners of the aluminum foil to form a reinforcing layer, and using this composite aluminum foil as the positive electrode current collector in the battery fabrication, exhibited no electrode breakage after 1000 cycles of 1.2C stepped charging and 1.0C discharging. This performance was comparable to that of completely coating the aluminum foil surface with carbon fiber slurry, but with a lighter weight. Therefore, using an intermittent coating method to form a reinforcing layer of carbon fiber slurry at the corners of the aluminum foil as the positive electrode current collector effectively suppresses aluminum foil breakage during battery cycling while maintaining the lightweight characteristics of the aluminum foil.

[0057] Compared with Example 1 and Comparative Example 2, the composite aluminum foil of this invention increases the weight by 1.2% compared with ordinary aluminum foil. The electrode is less prone to breakage during charge and discharge cycles, and the capacity retention rate is higher. Using the composite current collector of this invention as the positive electrode current collector of silicon-based lithium-ion batteries can effectively suppress aluminum foil breakage during battery cycling, while maintaining high conductivity and lightweight characteristics.

[0058] The above embodiments are preferred implementations of this utility model. In addition, this utility model can also be implemented in other ways. Any obvious substitutions without departing from the concept of this technical solution are within the protection scope of this utility model.

Claims

1. A lithium-ion battery composite current collector, characterized in that: The device includes a metal substrate layer and several reinforcing layers spaced apart on the side of the metal substrate layer away from the battery winding center. The area of ​​the metal substrate layer at the corner of the battery is called the corner region. The several reinforcing layers are respectively disposed on the surface of the corner region of the metal substrate layer. The reinforcing layers completely cover the corner region of the metal substrate layer. The coating width of the reinforcing layers along the winding direction of the current collector is greater than the length of the corner region of the metal substrate layer.

2. The lithium-ion battery composite current collector according to claim 1, characterized in that: The metal substrate layer is located at the outermost end of the battery, which is the tail of the metal substrate layer. The metal substrate layer includes a tab area for setting the tabs. Several reinforcement layers are respectively disposed in the corner area between the tab area and the tail of the metal substrate layer.

3. The lithium-ion battery composite current collector according to claim 1, characterized in that: The coating width k of the reinforcing layer along the winding direction of the current collector satisfies the relationship k = (πh / 2) + 6; Where h is the thickness of the bare cell after winding.

4. A lithium-ion battery composite current collector according to claim 3, characterized in that: The midpoint of each of the reinforcing layers along the winding direction of the metal substrate layer corresponds to the midpoint of the corner region of the metal substrate layer.

5. A lithium-ion battery composite current collector according to claim 1, characterized in that: The metal substrate layer is aluminum foil or aluminum alloy foil.

6. A lithium-ion battery composite current collector according to claim 1, characterized in that: The thickness of the metal substrate layer is 8-15 μm.

7. A lithium-ion battery composite current collector according to claim 1, characterized in that: The reinforcing layer is a carbon fiber layer.

8. A lithium-ion battery composite current collector according to claim 7, characterized in that: The carbon fibers in the carbon fiber layer are short-cut carbon fibers with a diameter of 2-5 μm and a length of 50-200 μm.

9. A lithium-ion battery composite current collector according to claim 1, characterized in that: The thickness of the composite current collector is 10-18 μm.

10. A lithium-ion battery, characterized in that: Includes the composite current collector as described in any one of claims 1-9.

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