A composite current collector, electrode sheet and lithium-ion battery

Abstract

This invention proposes a composite current collector, electrode sheet, and lithium-ion battery, comprising: a separator base film; a first PET film layer disposed on one side of the separator base film; a second PET film layer disposed on the side of the separator base film away from the first PET film layer; a first conductive layer disposed on the side of the first PET film layer away from the separator base film; and a second conductive layer disposed on the side of the second PET film layer away from the separator base film. Both the first and second PET film layers have microporous structures, and the first and second conductive layers are made of different materials. The first and second conductive layers are configured to allow charged particles to pass through. This invention enables lightweight composite current collectors, which is beneficial for increasing the filling amount of positive and negative electrode active materials and reducing the weight of foil materials, thereby achieving the goal of increasing energy density.

Description

Technical Field

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

[0002] With the continuous development of the lithium-ion battery industry, people are increasingly pursuing high energy density and lightweight batteries. Currently, the manufacturing of lithium-ion cells generally involves stacking or winding a separator, positive electrode, and negative electrode. The positive electrode is made by coating positive current collector aluminum foil with positive active material, while the negative electrode is made by coating negative current collector copper foil with negative active material. The mass density of a lithium-ion cell is the total energy per unit mass. Increasing the mass energy density of the active material and reducing the weight of the inactive material can increase the energy of the lithium-ion cell per unit space.

[0003] In lithium-ion battery cells, the main inactive materials are the separator and the current collector. First, the separator functions as an ion conductor and electronic insulator. A 9μm PE / PP separator already has the advantage of low material density. Applying 9μm or 12μm base films to power cells places stringent requirements on the cleanliness of the manufacturing process. Further reducing the separator thickness increases safety risks such as internal short circuits. Second, the current collector, as the carrier of the active materials and the electronic conductor in lithium-ion battery cells, is typically made of metal foil. For example, the positive electrode uses 10–18μm aluminum foil, and the negative electrode uses 4–12μm copper foil. The foil accounts for 9%–15% of the total cell weight. Reducing the foil weight in the entire battery significantly improves the cell's gravimetric energy density. However, currently, aluminum foil below 10μm and foil below 6μm are difficult to manufacture to meet the requirements of electrode fabrication, easily leading to process defects.

[0004] Chinese patent CN114843521A discloses a composite current collector and its preparation method, electrode plates, and a secondary battery. It involves symmetrically placing aluminum plating layers on both sides of a polymer composite layer. Although this can reduce the thickness of the current collector to some extent and achieve weight reduction, the current collector only functions as a positive electrode current collector. The same process is required to symmetrically place aluminum plating layers on both sides of the composite layer to form a positive electrode current collector. However, this cannot be called a composite current collector; it is merely a reduction in the thickness of the positive and negative electrode current collectors. During the cell manufacturing process, a separator still needs to be placed between the positive and negative electrode plates, which undoubtedly increases the weight of inactive materials, making it difficult to improve the energy density of the cell. Summary of the Invention

[0005] In view of this, the present invention proposes a composite current collector, electrode sheet and lithium-ion battery to achieve lightweight current collector and improve the energy density of lithium-ion battery.

[0006] The technical solution of this invention is implemented as follows:

[0007] On one hand, the present invention provides a composite current collector, comprising:

[0008] Diaphragm base membrane;

[0009] The first PET film layer is disposed on one side of the separator base film;

[0010] The second PET film layer is disposed on the side of the separator base film away from the first PET film layer;

[0011] A first conductive layer is disposed on the side of the first PET film layer away from the separator base film;

[0012] The second conductive layer is disposed on the side of the second PET film layer away from the separator base film;

[0013] The first PET film layer and the second PET film layer are both provided with microporous structures. The first conductive layer and the second conductive layer are made of different materials. The first conductive layer and the second conductive layer are configured to allow charged particles to pass through.

[0014] Based on the above technical solution, preferably, a gel polymer coating is applied between the diaphragm base membrane and the first PET film layer and the second PET film layer.

[0015] Further, preferably, the gel polymer of the gel polymer coating is any one or any combination of polyvinylidene fluoride, polytetrafluoroethylene, acrylates, and fluoropolymers.

[0016] Furthermore, preferably, the thickness of the diaphragm base membrane is 5-15 μm, the thickness of the gel polymer coating is 0.5-2 μm, and the thickness of the first PET film layer and the first PET film layer are both 1-5 μm.

[0017] Based on the above technical solution, preferably, the microporous structure provided on the first PET film layer and the second PET film layer is a plurality of straight micropores arranged along their thickness direction, the pore diameter of the straight micropores is less than 2μm, and the porosity is 10% to 90%.

[0018] Based on the above technical solution, preferably, both the first conductive layer and the second conductive layer are made by physical vapor deposition process, wherein the physical vapor deposition process is selected from any one of magnetron sputtering, vacuum evaporation coating, and electron beam evaporation coating.

[0019] Furthermore, preferably, the thickness of the first conductive layer and the second conductive layer is 1µm-5µm, and both the first conductive layer and the second conductive layer have pores for charged particles to pass through, the pore diameter of which is less than 1µm.

[0020] Secondly, the present invention also discloses an electrode sheet, including the aforementioned composite current collector, and further including a first active coating and a second active coating, wherein the first active coating is coated on the side of the first conductive layer away from the first PET film layer, and the second active coating is coated on the side of the second conductive layer away from the second PET film layer.

[0021] Furthermore, preferably, the electrode sheet further includes at least one first tab and at least one second tab, the first tab and the second tab being located at opposite ends of the composite current collector, the first tab being welded to the first conductive layer, and the second tab being welded to the second conductive layer.

[0022] Thirdly, the present invention also discloses a lithium-ion battery, including a housing and one or more of the aforementioned electrode plates disposed within the housing, wherein the multiple electrode plates are arranged in a wound or stacked manner, and adjacent electrode plates are arranged in opposite directions.

[0023] The present invention has the following advantages over the prior art:

[0024] (1) The composite current collector disclosed in this invention is formed by combining a first PET film layer, a separator base film, and a second PET film layer together to form a composite film. A first conductive layer and a second conductive layer are respectively provided on both sides of the composite film. At the same time, microporous structures are provided on both the first PET film layer and the second PET film layer. The first conductive layer and the second conductive layer are configured to allow charged particles to pass through, so that the above film layer and conductive layer constitute the composite current collector for lithium ion migration. The entire composite current collector integrates the performance of positive electrode current collector and negative electrode current collector. By reducing the thickness of the composite film, the first conductive layer and the second conductive layer, the weight of the composite current collector can be reduced, which is beneficial to increasing the filling amount of positive and negative electrode active materials and reducing the weight of foil materials, thereby achieving the purpose of increasing energy density.

[0025] (2) The electrode sheet made by the composite current collector has the performance of both positive electrode sheet and negative electrode sheet. In this way, during the cell manufacturing process, multiple electrode sheets can be arranged in a rolled or stacked manner, and the arrangement direction of two adjacent electrode sheets is opposite. The positive or negative coating layers of two adjacent electrode sheets are connected to each other, which improves the quality of the active coating. At the same time, the electrode sheets do not need to be isolated by the traditional separator, eliminating the separator setting, which increases the space utilization in the thickness direction of the cell, further improving the energy density of the cell, and thus improving the energy density of the lithium-ion battery.

[0026] (3) By laminating a first PET film layer and a second PET film layer on both sides of the separator base film, and then adding a first conductive layer and a second conductive layer on the surfaces of the first PET film layer and the second PET film layer respectively, when the battery cell is pierced by a metal object, the first conductive layer, the second conductive layer and the metal object form an electrical circuit, causing a short circuit at high temperature. Because the first conductive layer and the second conductive layer are relatively thin, they are prone to melting at the short circuit temperature, causing the circuit to break. Secondly, the first PET film layer and the second PET film layer expand at high temperature and are squeezed out from the piercing hole to break the electrical circuit, thereby improving the safety performance of the battery cell.

[0027] (4) By coating the diaphragm base membrane and the first PET membrane layer and the second PET membrane layer with a gel polymer coating, on the one hand, the diaphragm base membrane and the first PET membrane layer and the second PET membrane layer can be tightly bonded, and on the other hand, the static electricity phenomenon is reduced to a certain extent, the ionic conductivity and wettability of the diaphragm base membrane are improved, and the flexibility of the diaphragm base membrane is improved.

[0028] (5) The first and second conductive layers, which are made by vapor deposition and vacuum sputtering processes, can make the thickness of the entire composite current collector thinner and further improve its lightweight properties. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, 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 the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the planar structure of the composite current collector disclosed in this invention;

[0031] Figure 2 This is a schematic diagram of the planar structure of the electrode sheet disclosed in this invention;

[0032] Figure 3 This is a schematic diagram of the electrode plate stacking state disclosed in this invention;

[0033] Figure label:

[0034] S, Composite current collector; P, Electrode sheet; 1, Separator base film; 2, First PET film layer; 3, Second PET film layer; 4, First conductive layer; 5, Second conductive layer; 6, Gel polymer coating; 7, First active coating; 8, Second active coating; 9, First tab; 10, Second tab. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] In existing technologies, current collectors, serving as carriers and electronic conductors for active materials in lithium-ion cells, are typically made of metal foil. For example, the positive electrode uses 10–18 μm aluminum foil, and the negative electrode uses 4–12 μm copper foil. The foil accounts for 9%–15% of the total cell weight. Additionally, the separator's thickness also increases the cell's weight. While these inactive materials are indispensable components of current lithium-ion cells, their significant weight limits the overall energy density of lithium-ion cells. Therefore, reducing the weight of inactive materials is a crucial solution for improving the energy density of lithium-ion cells.

[0037] To this end, the present invention discloses a composite current collector to achieve lightweighting of the current collector, thereby improving the energy density of lithium-ion batteries.

[0038] See attached document Figure 1 As shown, the composite current collector S disclosed in this invention includes a diaphragm base membrane 1, a first PET film layer 2, a second PET film layer 3, a first conductive layer 4, and a second conductive layer 5.

[0039] In this embodiment, the diaphragm base membrane 1 serves as the carrier of the entire composite current collector S, and its thickness is set to 5-15 μm. The diaphragm base membrane 1 is the substrate used to make diaphragms in the prior art, which allows lithium ions to pass through and ensures that lithium ions can migrate bidirectionally.

[0040] A first PET film layer 2 is disposed on one side of the separator base film 1, and a second PET film layer 3 is disposed on the side of the separator base film 1 away from the first PET film layer. In this embodiment, the thickness of both the first PET film layer 2 and the second PET film layer 3 is 1-5 μm. A first conductive layer 4 is disposed on the side of the first PET film layer 2 away from the separator base film 1; a second conductive layer 5 is disposed on the side of the second PET film layer 3 away from the separator base film 1. The thickness of the first conductive layer 4 and the second conductive layer 5 is 1 μm-5 μm.

[0041] In this embodiment, the first conductive layer 4 is defined as the positive conductive layer, and the second conductive layer 5 is defined as the negative conductive layer. Both the first conductive layer 4 and the second conductive layer 5 are metal layers configured to allow charged particles to pass through. At the same time, microporous structures are provided on both the first PET film layer 2 and the second PET film layer 3, which can allow various particles in the electrolyte to pass through.

[0042] In the composite current collector S disclosed in the above embodiments, during the fabrication of the electrode plate P, a positive electrode coating can be coated on the outer surface of the first conductive layer 4, and a negative electrode coating can be coated on the outer surface of the second conductive layer 5. During charging, lithium ions are released from the positive electrode coating, pass through the first conductive layer 4 and the first PET film layer 2 in sequence, then pass through the separator base film 1, and then pass through the second PET film layer 3 and the second conductive layer 5 in sequence to reach the negative electrode coating, completing the charging process. During discharging, the lithium ions migrate in the opposite direction.

[0043] In this embodiment, a composite membrane is formed by combining a first PET film layer 2, a separator base film 1, and a second PET film layer 3. A first conductive layer 4 and a second conductive layer 5 are respectively disposed on both sides of the composite membrane. At the same time, microporous structures are provided on both the first PET film layer 2 and the second PET film layer 3. The first conductive layer 4 and the second conductive layer 5 are configured to allow charged particles to pass through, so that the above-mentioned film layers and conductive layers constitute the composite current collector S, which can be used for lithium ion migration. The entire composite current collector S integrates the performance of positive electrode current collector and negative electrode current collector. By reducing the thickness of the composite membrane, the first conductive layer 4, and the second conductive layer 5, the weight of the composite current collector S can be reduced, which is beneficial to increasing the filling amount of positive and negative electrode active materials and reducing the weight of foil materials, thereby achieving the purpose of increasing energy density.

[0044] Furthermore, when fabricating electrode sheets P using the current collector, the quality of the active material coating can be improved. Simultaneously, the electrode sheets P fabricated using the composite current collector S possess the properties of both positive and negative electrodes. This allows for the arrangement of multiple electrode sheets P in a wound or stacked manner during cell fabrication, with adjacent electrode sheets P arranged in opposite directions. The positive or negative coating layers of adjacent electrode sheets P are interconnected, improving the quality of the active coating. At the same time, the electrode sheets P do not require traditional separators for isolation, eliminating the need for separators and increasing the space utilization in the cell's thickness direction, further improving the cell's energy density and consequently, the energy density of the lithium-ion battery.

[0045] Furthermore, when a metal object pierces the battery cell, the first conductive layer 4, the second conductive layer 5, and the metal object form an electrical circuit, causing a short circuit at high temperatures. Because the first conductive layer 4 and the second conductive layer 5 are relatively thin, they are prone to melting at short circuit temperatures, causing the circuit to break. Additionally, the first PET film layer 2 and the second PET film layer 3 expand at high temperatures and are squeezed out from the piercing opening to interrupt the electrical circuit, thereby improving the safety performance of the battery cell.

[0046] In some preferred embodiments, a gel polymer coating 6 is applied between the separator base membrane 1 and the first PET membrane layer 2 and the second PET membrane layer 3. The gel polymer coating 6 allows the separator base membrane 1 and the first PET membrane layer 2 and the second PET membrane layer 3 to adhere tightly, resulting in more uniform deposition of lithium ions at the negative electrode, suppressing dendrite formation, and improving the thermal stability and mechanical properties of the separator base membrane 1. This, in turn, enhances battery safety and extends battery life. The gel polymer coating 6 between the separator base membrane 1 and the first PET membrane layer 2 and the second PET membrane layer 3 also reduces static electricity, improves the ionic conductivity and wettability of the separator base membrane 1, and enhances the flexibility of the separator base membrane 1.

[0047] In this embodiment, the gel polymer coating 6 uses any one or any combination of polyvinylidene fluoride, polytetrafluoroethylene, acrylates, and fluoropolymers. This embodiment does not limit the use of any of these gel polymers; any material that can function as a gel polymer is acceptable. Furthermore, the thickness of the gel polymer coating 6 in this embodiment is 0.5-2 μm, ensuring that the gel polymer coating 6 allows for tight adhesion between the diaphragm base membrane 1, the first PET film layer 2, and the second PET film layer 3 while reducing the thickness.

[0048] To ensure that particles can pass through the first PET film layer 2 and the second PET film layer 3, the microporous structure provided on the first PET film layer 2 and the second PET film layer 3 in this embodiment consists of multiple straight micropores arranged along their thickness direction. The pore size of the straight micropores is less than 2 μm, and the porosity is 10% to 90%. Through the above structural arrangement, on the one hand, the microporous structure can form a channel for particle migration, and on the other hand, it can improve the wettability and thermal stability of the electrolyte.

[0049] In this embodiment, both the first conductive layer 4 and the second conductive layer 5 are fabricated using physical vapor deposition (PVD), which is selected from magnetron sputtering, vacuum evaporation, and electron beam evaporation. As some preferred embodiments, on one side of the composite film composed of the diaphragm base film 1, the first PET film layer 2, and the second PET film layer 3, aluminum is vapor-deposited onto the surface of the first PET film layer 2 to form a 1-5 μm first conductive layer 4, which is an aluminum plating. On the opposite side of the composite film, copper is deposited onto the surface of the first PET film layer 2 using vacuum magnetron sputtering to form a 1-5 μm second conductive layer 5, which is a copper plating. In this embodiment, the aluminum plating serves as the positive electrode plating, and the copper plating serves as the negative electrode plating.

[0050] The first conductive layer 4 and the second conductive layer 5, fabricated using the aforementioned vapor deposition and vacuum sputtering processes, form pores on these layers that allow charged particles to pass through. The pore size of these pores is less than 1 μm. Therefore, during charging, lithium ions can sequentially pass through the first conductive layer 4, the first PET film layer 2, the separator base film 1, the second PET film layer 3, and the second conductive layer 5, thus migrating from the positive electrode to the negative electrode. During discharging, the migration direction of lithium ions is reversed. By using the first conductive layer 4 and the second conductive layer 5 fabricated through the aforementioned vapor deposition and vacuum sputtering processes, the thickness of the entire composite current collector S can be made thinner, further improving its lightweight properties.

[0051] The present invention also discloses an electrode plate P, as shown in the attached figure. Figure 2 and 3 As shown, the composite current collector S includes a first active coating 7 and a second active coating 8. The first active coating 7 is coated on the side of the first conductive layer 4 away from the first PET film layer 2, and the second active coating 8 is coated on the side of the second conductive layer 5 away from the second PET film layer 3. In this embodiment, the first active coating 7 is a positive electrode active material, and the second active coating 8 is a negative electrode active material. Both are conventional materials in the prior art, and the present invention is not limited to them. Since the overall thickness of the composite current collector S is reduced, it is lighter. At the same time, the composite current collector S integrates the performance of the positive electrode current collector and the negative electrode current collector. Thus, by coating the first active coating 7 and the second active coating 8 on both sides of a composite current collector S, the resulting electrode plate P integrates the performance of the positive electrode plate and the negative electrode plate, thereby combining the positive electrode plate and the negative electrode plate into one. In terms of electrode plate manufacturing process, the manufacturing process is greatly simplified, and the cost is also greatly reduced.

[0052] Since the composite current collector S achieves lightweighting, the mass of the first active coating 7 and the second active coating 8 can be increased during the manufacturing process of the electrode plate P, thereby improving the mass density of the lithium-ion cell.

[0053] The electrode plate P disclosed in this embodiment further includes at least one first tab 9 and at least one second tab 10. The first tab 9 and the second tab 10 are respectively located at both ends of the composite current collector S. The first tab 9 is welded to the first conductive layer 4, and the second tab 10 is welded to the second conductive layer 5. According to the above technical solution, the first tab 9 in this embodiment is defined as the positive tab, and the second tab 10 is defined as the negative tab. In some embodiments of this embodiment, the first tab 9 and the second tab 10 are respectively located at both ends of the electrode plate P, which can be used to manufacture a battery with electrodes at both ends. In this embodiment, when the electrode plate P is made into a cell by a stacking process, the first tab 9 and the second tab 10 are located at both ends of the length direction of the electrode plate P. When the electrode plate P is made into a cell by a winding process, the first tab 9 and the second tab 10 are located at both ends of the width direction of the electrode plate P.

[0054] This invention also discloses a lithium-ion battery, including a casing and one or more electrode plates P disposed within the casing. The electrode plates P are arranged in a wound or stacked manner, with adjacent electrode plates P arranged in opposite directions. This configuration allows the electrode plates P, made using a composite current collector S, to possess the properties of both positive and negative electrodes. During cell manufacturing, multiple electrode plates P can be arranged in a wound or stacked manner, with adjacent electrode plates P arranged in opposite directions. The positive or negative coating layers of adjacent electrode plates P are interconnected, improving the quality of the active coating. Simultaneously, the electrode plates P do not require traditional separators for isolation, eliminating the need for separators and increasing the space utilization in the cell's thickness direction, further improving the cell's energy density. After encapsulation, the energy density of the lithium-ion battery is further enhanced.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, Includes a housing and one or more electrode plates (P) disposed within the housing. Each electrode plate (P) includes a composite current collector, a first active coating (7), and a second active coating (8). The composite current collector includes: Diaphragm base membrane (1); The first PET film layer (2) is disposed on one side of the diaphragm base film (1); The second PET film layer (3) is disposed on the side of the separator base film (1) away from the first PET film layer (2); A first conductive layer (4) is disposed on the side of the first PET film layer (2) away from the diaphragm base film (1); The second conductive layer (5) is disposed on the side of the second PET film layer (3) away from the diaphragm base film (1); The first PET film layer (2) and the second PET film layer (3) are provided with microporous structures. The first conductive layer (4) and the second conductive layer (5) are made of different materials. The first conductive layer (4) and the second conductive layer (5) are configured to allow charged particles to pass through. Both the first conductive layer (4) and the second conductive layer (5) are made by physical vapor deposition, and the physical vapor deposition process is selected from any one of magnetron sputtering, vacuum evaporation coating, and electron beam evaporation coating. The thickness of the first conductive layer (4) and the second conductive layer (5) is 1um-5um, and pores for charged particles to pass through are formed on both the first conductive layer (4) and the second conductive layer (5), and the pore diameter of the pores is less than 1um. The first active coating (7) is applied to the side of the first conductive layer (4) away from the first PET film layer (2), and the second active coating (8) is applied to the side of the second conductive layer (5) away from the second PET film layer (3); Multiple electrode plates (P) are arranged in a spiral or stacked manner, with adjacent electrode plates (P) arranged in opposite directions, and the active coatings of the same polarity on adjacent electrode plates (P) are in contact.

2. The lithium-ion battery as described in claim 1, characterized in that: A gel polymer coating (6) is applied between the diaphragm base membrane (1), the first PET film layer (2), and the second PET film layer (3).

3. The lithium-ion battery as described in claim 2, characterized in that: The gel polymer coating (6) is any one or any combination of polyvinylidene fluoride, polytetrafluoroethylene, acrylates, and fluoropolymers.

4. The lithium-ion battery as described in claim 2, characterized in that: The thickness of the diaphragm base membrane (1) is 5-15 μm, the thickness of the gel polymer coating (6) is 0.5-2 μm, and the thickness of the first PET film layer (2) and the first PET film layer (2) are both 1-5 μm.

5. The lithium-ion battery as described in claim 1, characterized in that: The microporous structure provided on the first PET film layer (2) and the second PET film layer (3) consists of multiple straight micropores arranged along their thickness direction. The diameter of the straight micropores is less than 2 μm and the porosity is 10% to 90%.

6. A lithium-ion battery as described in claim 1, characterized in that: The electrode plate (P) further includes at least one first tab (9) and at least one second tab (10), the first tab (9) and the second tab (10) are respectively located at both ends of the composite current collector, the first tab (9) is welded to the first conductive layer (4), and the second tab (10) is welded to the second conductive layer (5).

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