Composite current collector, pole piece, battery cell and lithium battery

Abstract

The utility model discloses a composite current collector, which includes: a polymer matrix, including two first surfaces spaced opposite to each other; two conductive layers, respectively bonded to the two first surfaces of the polymer matrix; the conductive layer has a second surface facing the polymer matrix and a third surface facing away from the polymer matrix, the second surface is bonded to the first surface, and the roughness of the second surface is greater than the roughness of the third surface. The utility model uses a conductive layer to replace the metal layer electroplated or evaporated in the prior art, thereby reducing the probability of problems such as uneven coating thickness and large internal stress in the coating that may occur in the electroplating or evaporation process, and directly presses the side of the conductive layer with higher roughness to the polymer matrix, which is simple in process, easy to process, and makes the connection between the conductive layer and the polymer matrix tighter, resulting in higher production efficiency. In addition, the utility model also discloses a pole piece, a battery cell and a lithium battery.

Description

Technical Field

[0001] The utility model relates to the technical field of lithium ion batteries, and in particular to a composite current collector, a pole piece, a battery core and a lithium battery. Background Art

[0002] With the strategic measures to address climate change and promote green development, lithium batteries have been widely studied as important energy storage devices. It has always been the goal of the industry to achieve high capacity, lightweight and thin lithium batteries while ensuring their safety.

[0003] The traditional negative electrode current collector uses copper foil, which has good conductivity. In order to comply with the development direction of lithium batteries, its thickness is getting lower and lower. However, this is accompanied by a decrease in mechanical properties. During the coating and rolling process of the battery, it is easy to produce protrusions, holes and even fractures, which not only affects the safety performance of the battery, but also has a high manufacturing cost. This has led to the development of composite current collectors, which use polymer materials with good insulation, low density and low cost as the base material.

[0004] Generally, the metal layer of a composite current collector is connected to the polymer layer by electroplating or evaporation process, which is complicated, difficult and time-consuming to process. In addition, the thickness of the produced coating is prone to unevenness, resulting in unstable performance of the battery cell. Utility Model Content

[0005] The main purpose of the utility model is to provide a composite current collector, aiming to solve the problem that the thickness of the metal layer is easily uneven in the existing composite current collector.

[0006] In order to achieve the above object, the utility model provides a composite current collector, which comprises:

[0007] A polymer matrix includes two first surfaces that are spaced apart and opposite to each other;

[0008] Two conductive layers are respectively bonded to the two first surfaces of the polymer matrix; the conductive layer has a second surface facing the polymer matrix and a third surface facing away from the polymer matrix, the second surface is bonded to the first surface, and the roughness of the second surface is greater than the roughness of the third surface.

[0009] In some embodiments, the roughness Ra of the second surface is 0.1 μm to 4 μm.

[0010] In some embodiments, the conductive layer is bonded to the first surface by an adhesive.

[0011] In some embodiments, the first surface is a flat surface or a surface having at least one groove and / or at least one protrusion.

[0012] In some embodiments, the conductive layer is a metal sheet.

[0013] In some embodiments, the thickness of the conductive layer is 1 μm to 5 μm.

[0014] In some embodiments, the polymer matrix has a thickness of 2 μm to 7 μm.

[0015] The utility model also discloses a pole piece, comprising an active material layer and the composite current collector described in any one of the aforementioned embodiments, wherein the active material layer is arranged on the third surface of at least one of the conductive layers.

[0016] The utility model also discloses a battery cell including a positive electrode sheet, a negative electrode sheet and a diaphragm, wherein the diaphragm is arranged between the positive electrode sheet and the negative electrode sheet, and at least one of the positive electrode sheet and the negative electrode sheet adopts the electrode sheet described in the above embodiment.

[0017] The utility model also discloses a lithium battery, comprising a shell and the battery core described in the above embodiment, wherein the battery core is arranged in the shell.

[0018] The composite current collector of the utility model comprises a polymer matrix and a conductive layer arranged on two first surfaces of the polymer matrix. By replacing the metal layer electroplated or evaporated in the prior art with the conductive layer, the probability of problems such as uneven coating thickness and large internal stress in the coating that may be generated in the electroplating or evaporation process is reduced. The side of the conductive layer with higher roughness is directly pressed against the polymer matrix, the process is simple, the processing difficulty is small, the connection between the conductive layer and the polymer matrix is ​​tighter, and the production efficiency is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic structural diagram of an embodiment of the composite current collector of the utility model;

[0020] Figure 2 This is a schematic structural diagram of an embodiment of a polymer matrix in a composite current collector of the utility model;

[0021] Figure 3 This is a schematic structural diagram of another embodiment of the polymer matrix in the composite current collector of the utility model.

[0022] Reference numerals:

[0023] 100, polymer matrix; 110, first surface; 200, conductive layer; 210, second surface; 220, third surface. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the scheme in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0025] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back...) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0026] It should also be noted that when an element is referred to as being "fixed on" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element at the same time. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element at the same time.

[0027] In addition, the descriptions of "first", "second", etc. in the present utility model are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present utility model.

[0028] The utility model proposes a composite current collector, referring to Figure 1 ,include:

[0029] The polymer matrix 100 includes two first surfaces 110 spaced apart and facing each other;

[0030] The two conductive layers 200 are respectively bonded to the two first surfaces 110 of the polymer matrix 100; the conductive layer 200 has a second surface 210 facing the polymer matrix 100 and a third surface 220 facing away from the polymer matrix 100, the second surface 210 is bonded to the first surface 110, and the roughness of the second surface 210 is greater than the roughness of the third surface 220.

[0031] In this embodiment, the composite current collector is composed of two conductive layers 200 and a polymer matrix 100 sandwiched between the two conductive layers 200, and the size thereof can be selected as required, and this embodiment does not limit this. The conductive layer 200 has good electrical conductivity and plays a role in ensuring the effective transmission of the internal current of the battery. For example, a carbon-based conductive material, such as at least one of graphite, acetylene black, graphene, and carbon nanotubes, can be used as the material of the conductive layer.

[0032] The polymer matrix 100 can be selected from polymer materials used in conventional composite current collectors, and the material of the polymer layer is selected from at least one of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetheretherketone, polyimide, polyamide, polyethylene glycol, polyamideimide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, polyvinylidene fluoride-hexafluoropropylene, poly(vinylidene fluoride-co-chlorotrifluoroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester and polysulfone and their derivatives.

[0033] It should be noted that there are multiple bonding methods for the conductive layer 200 and the polymer matrix 100 in this embodiment. For example, the two conductive layers 200 and the polymer matrix 100 can be stacked together in a "sandwich" structure, and then directly pressed into a composite current collector at a certain molding pressure and temperature, and the conductive layer 200 and the polymer matrix 100 are tightly connected by the van der Waals force between molecules. It is also possible to use plasma treatment to activate the surface of the conductive layer 200 or the polymer matrix 100 using plasma in a vacuum or low-pressure environment, thereby improving the surface energy and adhesion.

[0034] Furthermore, in this embodiment, the second surface 210 of the conductive layer 200 is controlled to increase the roughness, so that the second surface 210 of the conductive layer 200 can produce more microscopic concave-convex structures. When the polymer material is solidified or condensed thereon, these concave-convex structures can be embedded in the polymer matrix 100, thereby generating a mechanical interlocking effect to increase the strength of the bonding interface, so that the bonding between the conductive layer 200 and the polymer matrix 100 is more solid. In addition, the rough surface has a larger effective contact area, and the increased contact area provides more adhesion points, so that the polymer material can be better attached to the metal surface, thereby improving the bonding force.

[0035] Specifically, the roughness of the second surface 210 can be increased by sandblasting, etching or machining, and then the second surfaces 210 of the two conductive layers 200 are stacked toward the polymer matrix 100, and they are directly pressed into a composite current collector at a certain molding pressure and temperature, so that the bonding between the conductive layer 200 and the polymer matrix 100 is tighter, reducing the probability of the conductive layer 200 falling off, and facilitating the subsequent welding of the pole ears.

[0036] Compared with the electroplating and evaporation processes, in this embodiment, the conductive layer 200 with a rough surface is used to replace the metal layer electroplated or evaporated in the prior art. The process is simple, the preparation efficiency can be greatly improved, and the probability of problems such as uneven coating thickness and large internal stress in the coating that may occur in the electroplating or evaporation process is reduced. In addition, in the utility model, the rougher side of the conductive layer 200 is pressed with the polymer matrix 100, the process is simple, the processing difficulty is small, and the connection between the conductive layer 200 and the polymer matrix 100 is tighter, and the production efficiency is higher.

[0037] like Figure 1 As shown, in some embodiments, the roughness Ra of the second surface 210 is 0.1 μm to 4 μm; and / or,

[0038] The third surface 220 is a flat surface.

[0039] Among them, Ra can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.7μm, 0.9μm, 1.0μm, 1.5μm, 2.0μm, 2.5μm, 3.0μm, 3.5μm, or 4.0μm. Preferably, Ra of the second surface 210 is set to 1.0μm, which can not only ensure the connection strength between the conductive layer 200 and the polymer matrix 100, but also avoid the structural strength of the conductive layer 200 being too low, which may lead to damage.

[0040] In some embodiments, the conductive layer 200 is bonded to the first surface 110 by an adhesive.

[0041] The binder is usually polyvinylidene fluoride (PVDF), which is applied to the polymer matrix 100 by roller coating or spraying to increase the connection strength between the conductive layer 200 and the polymer matrix 100. Exemplarily, the binder can cover all the connection areas between the conductive layer 200 and the polymer matrix 100, or can be spread on the polymer matrix 100 in a dispersed manner by point coating, which is not limited in this embodiment. It can be understood that the binder can also be at least one of carboxymethyl cellulose, styrene butadiene rubber (SBR) emulsion, polyacrylic acid (PAA), polyimide, polyurethane, polyvinyl alcohol, and polyvinyl pyrrolidone.

[0042] like Figure 2 and Figure 3 As shown, in some embodiments, the first surface 110 is a flat surface or a surface having at least one groove and / or at least one protrusion.

[0043] When the first surface 110 is a flat surface, that is, a flat type, the processing difficulty of the polymer matrix 100 is relatively small, and the structural strength of the composite current collector is also relatively high; when at least one groove or protrusion is provided on the first surface 110, the bonding between the polymer matrix 100 and the conductive layer 200 is closer, which can reduce the probability of separation of the conductive layer 200 and facilitate the subsequent welding of the pole ears.

[0044] For example, refer to Figure 2 The first surface 110 may be concave-convex, that is, crenel-shaped, similar to a defensive architectural design on the top of an ancient city wall, consisting of a series of alternating protrusions and depressions; Figure 3 , it may also be a wavy, sawtooth, or other irregular rough surface, which is not limited in this embodiment.

[0045] In some embodiments, the conductive layer 200 is a metal sheet. That is, the conductive layer is made of a metal conductive material, and the metal conductive material used in the metal sheet can be at least one of aluminum, copper, nickel, titanium, silver, nickel-copper alloy, and aluminum-zirconium alloy, which can be selected according to actual needs, and the utility model does not limit this.

[0046] In some embodiments, the thickness of the conductive layer 200 is 1 μm to 5 μm.

[0047] Specifically, the thickness of the conductive layer 200 can be 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm, and can be selected according to actual needs. Preferably, in this embodiment, a conductive layer 200 with a thickness of 2 μm is selected to ensure effective transmission of the internal current of the battery while avoiding excessively thick conductive layer 200 that is too heavy and occupies a large amount of space, resulting in a lower volume energy density and mass energy density of the final manufactured battery.

[0048] In some embodiments, the polymer matrix 100 has a thickness of 2 μm to 7 μm.

[0049] Specifically, the thickness of the polymer matrix 100 can be 2μm, 2.2μm, 2.4μm, 2.6μm, 2.8μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, which can be selected according to actual needs. Preferably, in this embodiment, the polymer matrix 100 with a thickness of 3μm is selected, which can provide sufficient structural strength and avoid occupying too much space, thereby improving the energy density of the battery.

[0050] The utility model further proposes a pole piece including an active material layer and a composite current collector. The specific structure of the composite current collector refers to the above embodiment. Since the pole piece adopts all the technical solutions of all the above embodiments, it at least has all the technical effects brought by the technical solutions of the above embodiments, which will not be repeated here. Among them, the active material layer is arranged on the third surface 220 of at least one conductive layer 200. Specifically, the active material layer can be arranged on only one conductive layer 200, or it can be arranged on two conductive layers 200 at the same time, and this embodiment does not limit this.

[0051] The utility model further proposes a battery cell, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet, and at least one of the positive electrode sheet and the negative electrode sheet adopts the electrode sheet in the above-mentioned embodiment.

[0052] Since the battery cell adopts all the technical solutions of all the above embodiments, it has at least all the technical effects brought by the technical solutions of the above embodiments, which will not be described one by one here. It is worth mentioning that the battery cell in this embodiment can be a rolled core or a laminated battery cell.

[0053] The utility model further proposes a lithium battery, which includes a housing and the battery cell in the above embodiment, and the battery cell is arranged in the housing. The specific structure of the lithium battery refers to the above embodiment. Since all the technical solutions of all the above embodiments are adopted, it has at least all the technical effects brought by the technical solutions of the above embodiments, which will not be described one by one here. Refer to the following embodiments:

[0054] Embodiment 1:

[0055] The PET without conductive agent doping and with a flat surface is used as the polymer matrix, and the copper foil with a rough surface near the inner layer is directly pressed into a composite current collector in a "sandwich" structure at a certain molding pressure and temperature.

[0056] The active material LiCoO2, the conductive agent acetylene black, the conductive carbon nanotubes and PVDF are fully dispersed and evenly coated on the aluminum current collector in an N-methylpyrrolidone solvent system in a weight ratio of 97.6:0.7:0.5:1.2, and then cold-pressed and sliced ​​to obtain the positive electrode sheets.

[0057] Active material graphite, Super P, sodium carboxymethyl cellulose, and SBR emulsion are mixed in deionized water in a weight ratio of 96.8:0.5:1.1:1.6, fully dispersed and evenly coated on the composite current collector, and then cold pressed and stripped to obtain the negative electrode sheet;

[0058] The positive electrode sheet, negative electrode sheet and isolation film are wound or stacked to produce a bare cell, which is then packaged and injected with electrolyte to produce a finished lithium-ion battery.

[0059] Example 2: Using SBR as a binder and PET without doping with a conductive agent and with a flat surface as the polymer matrix, the rest is the same as Example 1.

[0060] Example 3: Using SBR as a binder and PET without doping with a conductive agent and with a flat surface as the polymer matrix, the rest is the same as Example 1.

[0061] Example 4: Using binder PAA and PET without doping with a conductive agent and with a flat surface as the polymer matrix, the rest is the same as Example 1.

[0062] Example 5: Using binder PAA and PET without doping with conductive agent and with flat surface as the polymer matrix, the rest is the same as Example 1.

[0063] Example 6: Using binder PAA and PET without doping with conductive agent and with wavy surface shape as the polymer matrix, the rest is the same as Example 1.

[0064] Example 7: Using binder PAA and PET without doping with a conductive agent and with a concave-convex surface shape as the polymer matrix, the rest is the same as Example 1.

[0065] Example 8: Using PVDF as a binder and PET doped with 5% CNT conductive agent and having a flat surface as the main polymer matrix, the rest is the same as Example 1.

[0066] Example 9: Using PVDF as a binder and PET doped with 5% CuO conductive agent and having a flat surface as the main polymer matrix, the rest is the same as Example 1.

[0067] Example 10: Using PVDF as a binder and PET doped with 5% PAn conductive agent and having a flat surface as the main polymer matrix, the rest is the same as Example 1.

[0068] Example 11: Using PVDF as a binder and PET doped with 10% PAn conductive agent and having a flat surface as the main polymer matrix, the rest is the same as Example 1.

[0069] Example 12: Using PVDF as a binder and PET doped with 15% PAn conductive agent and having a flat surface as the main polymer matrix, the rest is the same as Example 1.

[0070] Example 13: Using PVDF as a binder and PET doped with 10% CNT conductive agent and having a wavy surface shape as the polymer matrix, the rest is the same as Example 1.

[0071] Example 14: Using PVDF as a binder and PET doped with 15% CNT conductive agent and having a wavy surface shape as the main polymer matrix, the rest is the same as Example 1.

[0072] Comparative Example 1:

[0073] The active material LiCoO2, the conductive agent acetylene black, the conductive carbon nanotubes and PVDF are fully dispersed and evenly coated on the aluminum current collector in an N-methylpyrrolidone solvent system in a weight ratio of 97.6:0.7:0.5:1.2, and then cold-pressed and sliced ​​to obtain the positive electrode sheets.

[0074] The active materials graphite, Super P, sodium carboxymethyl cellulose and SBR emulsion are mixed in deionized water in a weight ratio of 96.8:0.5:1.1:1.6, fully dispersed and evenly coated on a general composite current collector with the same thickness and a flat surface, and then cold pressed and stripped to obtain the negative electrode sheet.

[0075] The positive electrode sheet, negative electrode sheet and isolation film are wound or stacked to produce a bare cell, which is then packaged and injected with electrolyte to produce a finished lithium-ion battery.

[0076] Comparative Example 2: The composite current collector in Comparative Example 1 was replaced with a copper current collector, and other conditions were the same as those in Comparative Example 1.

[0077] Testing process:

[0078] The current collectors prepared in the above embodiments and comparative examples were tested using a resistance tester. The resistance values ​​of three different positions of the test sample were measured, and the arithmetic average of the three resistance values ​​was taken as the resistance value of the sample.

[0079] The lithium ion batteries prepared in the above embodiments and comparative examples were cycled in the steps of 2C CC to 4.5V, CV0.05C; 1CDC to 3.0V to obtain the number of cycles when the retention rate was 80%.

[0080] The battery cells prepared in the above embodiments and comparative examples are placed on a plane after being fully charged, and a steel column with a diameter of 15.8±0.2mm is placed in the center of the battery cell with the longitudinal axis of the steel column parallel to the plane. A weight with a mass of 9.1±0.1kg is allowed to fall freely from a height of 610±25mm onto the steel column above the center of the battery. The test is considered passed if there is no fire or explosion after observing for 6 hours after the test is completed.

[0081] The battery cells prepared in the above embodiments and comparative examples were tested at 1.0C-5.0C with an increment of 0.1C, an upper limit voltage of 4.5V, a cut-off current of 0.05C, and a discharge of 1C DC to 3.0V for 20 cycles to obtain battery lithium deposition window data.

[0082] The data is as follows:

[0083]

[0084]

[0085] From the above data, it can be seen that in Example 1, the composite current collector is formed by setting one side of the conductive layer to a rough surface and adopting hot pressing molding, and the lithium-ion battery prepared therefrom has better performance than the conventional composite current collector in Comparative Example 1, including smaller internal resistance, more cycle times, higher heavy object impact pass rate, and larger lithium precipitation window (that is, lithium deposition will not occur in a wider potential range, and charging efficiency is higher).

[0086] On the basis of Example 1, the surface shape of the polymer matrix is ​​changed from flat to wavy or concave-convex, and the obtained lithium-ion battery has better performance in all aspects; PVDF has better adhesion than SBR and PAA, and the obtained lithium-ion battery has a higher heavy object impact passing rate, and the lithium-ion battery with CNT as a conductive agent has better conductivity and a smaller internal resistance. The lithium-ion battery obtained in Example 13 has the best comprehensive performance.

[0087] The above description is only a partial or preferred embodiment of the present invention. Neither the text nor the drawings can limit the scope of protection of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the overall concept of the present invention, or direct / indirect application in other related technical fields are included in the scope of protection of the present invention.

Claims

1. A composite current collector, characterized in that: include: A polymer matrix includes two first surfaces that are spaced apart and opposite to each other; Two conductive layers are respectively bonded to the two first surfaces of the polymer matrix; the conductive layer has a second surface facing the polymer matrix and a third surface facing away from the polymer matrix, the second surface is bonded to the first surface, and the roughness of the second surface is greater than the roughness of the third surface.

2. The composite current collector according to claim 1, characterized in that: The roughness Ra of the second surface is 0.1 μm to 4 μm.

3. The composite current collector according to claim 2, characterized in that: The conductive layer is bonded to the first surface of the polymer matrix through a bonding agent.

4. The composite current collector according to claim 3, characterized in that: The first surface is a flat surface or a surface having at least one groove and / or at least one protrusion.

5. The composite current collector according to claim 1, characterized in that: The conductive layer is a metal sheet.

6. The composite current collector according to claim 1, characterized in that: The thickness of the conductive layer is 1 μm to 5 μm.

7. The composite current collector according to claim 1, characterized in that: The thickness of the polymer matrix is ​​2 μm to 7 μm.

8. A pole piece, characterized in that: The invention comprises an active material layer and the composite current collector according to any one of claims 1 to 7, wherein the active material layer is arranged on the third surface of at least one of the conductive layers.

9. A battery cell, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet, and at least one of the positive electrode sheet and the negative electrode sheet adopts the electrode sheet described in claim 8.

10. A lithium battery, characterized in that: The invention comprises a housing and the battery core as claimed in claim 9, wherein the battery core is arranged in the housing.

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