Electrode sheet, battery cell and preparation method therefor, and electric device

Abstract

An electrode sheet (1), a battery cell (3) and a preparation method therefor, and an electric device (6), belonging to the technical field of batteries. The battery cell (3) comprises an electrode sheet (1), which comprises: a current collector (10), an active material layer (20) and a first film layer (11), wherein the current collector (10) comprises a main body portion (101) and a tab (102) protruding from the main body portion (101), the main body portion (101) comprising a coated area (1011) and a transition area (1012), the transition area (1012) being arranged between the coated area (1011) and the tab (102); the active material layer (20) is arranged on the surface of at least one side of the coated area (1011); and the first film layer (11) is at least arranged on the surface of at least one side of the transition area (1012), the film layer (11) comprising a thermoplastic polymer and a light-absorbing material. The production efficiency of the electrode sheet (1) and the reliability of the battery cell (3) can be improved.

Description

Pole piece, battery monomer, preparation method thereof, and electric device

[0001] Cross-reference to Related Applications

[0002] This application claims priority to Chinese Patent Application No. 202410864919.9, filed on June 28, 2024, entitled “Pole piece, battery monomer, preparation method thereof, and electric device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application relates to the technical field of batteries, and more particularly, to a pole piece, a battery monomer, a preparation method thereof, and an electric device. BACKGROUND

[0004] With the increasing environmental pollution, new energy industry is attracting more and more attention. In the new energy industry, battery technology is an important factor for its development.

[0005] In addition to considering the performance of the battery, the production efficiency also needs to be considered in the development of the battery technology. The design of the pole piece in the battery monomer is crucial to the reliability of the battery monomer and the production efficiency of the pole piece. Therefore, how to provide a battery monomer including a pole piece to balance the production efficiency of the pole piece and the reliability of the battery monomer is an urgent technical problem to be solved.

[0006] SUMMARY

[0007] The present application is made in view of the above-mentioned problems, and aims to provide a battery monomer including a pole piece to balance the production efficiency of the pole piece and the reliability of the battery monomer.

[0008] To achieve the above-mentioned purpose, the present application provides a pole piece, a battery monomer, a preparation method thereof, and an electric device.

[0009] In a first aspect, a battery monomer is provided, comprising: a pole piece, the pole piece comprising: a current collector, an active material layer, and a first film layer, the current collector comprising a main body portion and a tab, the main body portion comprising a coating area and a transition area, the transition area being provided between the coating area and the tab; the active material layer being provided on at least one side surface of the coating area; the first film layer being provided on at least one side surface of the transition area, the first film layer comprising a thermoplastic polymer and a light-absorbing material.

[0010] In the embodiments of the present application, the pole piece in the battery monomer includes a current collector, an active material layer arranged on at least one side surface of a coating area of the current collector, and a first film layer arranged on at least one side surface of a transition area of the current collector, wherein the current collector includes a main body part and a tab, and the main body part includes the coating area and the transition area. The first film layer includes a thermoplastic polymer and a light-absorbing material, and the light-absorbing material can assist the first film layer and the thermoplastic polymer in the first film layer in absorbing heat, thereby helping to cut the current collector provided with the first film layer at a faster cutting speed and helping to form a film layer covering burrs and exposed end surfaces generated by cutting, reducing the risk of self-discharge and internal short circuit of the battery monomer, and thereby improving the reliability of the battery monomer. Therefore, the pole piece in the battery monomer of the embodiments of the present application can be prepared at a faster cutting speed, and the battery monomer has higher reliability.

[0011] In a possible implementation, the battery monomer further includes a second film layer arranged on at least an end surface of the main body part at the first end, the second film layer including a thermoplastic polymer, and the first end being one end of the main body part in a first direction in which the tab protrudes from the main body part.

[0012] In the above technical solution, the second film layer includes a thermoplastic polymer, and the second film layer can cover the end surface at the first end, reducing the risk of short circuit caused by the burrs and exposed end surfaces of the opposite polarity electrode lapping, and being beneficial to further improving the reliability of the battery monomer.

[0013] In a possible implementation, based on the total mass of the first film layer, the mass percentage A of the light-absorbing material satisfies 5wt%≤A≤25wt%.

[0014] In the case where the mass content A of the light-absorbing material is greater than or equal to 5wt%, the light-absorbing material included in the first film layer can absorb more heat, thereby being beneficial to cutting the current collector provided with the first film layer at a faster cutting speed, and the second film layer can uniformly and densely cover the burrs and exposed end surfaces; in the case where the mass content A of the light-absorbing material is less than or equal to 25wt%, the risk of ablation of the first film layer caused by too much absorbed heat can be reduced.

[0015] In a possible implementation, 5wt%≤A≤15wt%. In this way, the light-absorbing material in the first film layer has a more appropriate mass content, and the production efficiency and the reliability of the battery monomer can be improved while the risk of ablation of the first film layer is reduced.

[0016] In a possible implementation, the volume average particle size Dv50 of the light absorbing material satisfies: 10nm≤Dv50≤5μm. Through the above setting, the first film layer can absorb more heat.

[0017] In a possible implementation, 10nm≤Dv50≤50nm. In this way, the surface of the first film layer is relatively smooth, and the light absorbing material has a more appropriate particle size, which is conducive to the light absorbing material absorbing heat more uniformly.

[0018] In a possible implementation, 0.1μm≤Dv50≤5μm. In this way, the light absorbing material forms protrusions in the first film layer, and the surface of the first film layer is relatively rough, which is conducive to the first film layer absorbing more heat.

[0019] In a possible implementation, the wavelength of the light absorbed by the first film layer includes 0.3μm-10μm. In this way, the first film layer can absorb more light of different wavelengths, so that the first film layer can absorb more heat.

[0020] In a possible implementation, the light absorbing material includes at least one of an organic light absorbing material or an inorganic light absorbing material, the organic light absorbing material includes at least one of resin, polyester, polyurethane or diaryl yellow, and the inorganic light absorbing material includes at least one of cadmium sulfide, cadmium selenide, iron dioxide, carbon powder, boehmite, titanium dioxide or aluminum oxide.

[0021] In a possible implementation, the organic light absorbing material includes at least one of polymethyl methacrylate or polyamide, and / or the inorganic light absorbing material includes carbon powder.

[0022] The above light absorbing material can effectively absorb the heat of the laser, so as to facilitate absorbing more heat in the cutting process, and improve the reliability and production efficiency of the battery cell.

[0023] In a possible implementation, the surface roughness of the first film layer is greater than or equal to 1μm.

[0024] In a possible implementation, the surface roughness of the first film layer is 1μm-15μm.

[0025] In the above technical solution, the first film layer has a relatively rough surface, which is conducive to the first film layer absorbing more heat.

[0026] In a possible implementation, the light absorbing material includes at least one of phthalocyanine blue or white mica. In this way, it is conducive to improving the roughness of the first film layer, so as to facilitate the first film layer absorbing more heat.

[0027] In a possible implementation, the tab includes a first part and a second part, the second part is located between the first part and the main body part, and the first part is at least partially exposed; and the first film layer is arranged on the surface of at least one side of the transition area and the second part.

[0028] In the technical solution, the first part of the tab is at least partially exposed, thereby facilitating the export of the electric energy in the battery monomer through the first part of the tab; and the first film layer is arranged on the surface of at least one side of the transition area and the second part, thereby reducing the risk of short circuit caused by the lapping of the second part and the transition area with the electrode of opposite polarity.

[0029] In a possible implementation, the end surface of the second part is provided with the second film layer in a second direction, and the second direction is perpendicular to the first direction, and the first direction is the direction in which the tab protrudes from the main body part. In this way, the second film layer can cover the end surface of the tab exposed due to cutting, and the risk of lapping with the electrode of opposite polarity can be reduced.

[0030] In a possible implementation, the thickness d1 of the first film layer satisfies 20 μm≤d1≤50 μm.

[0031] In the case where the thickness d1 of the first film layer is greater than or equal to 20 μm, the burr generated by cutting and the exposed end surface have a good protection effect, and the risk of internal short circuit of the battery monomer can be reduced; and in the case where the thickness d1 of the first film layer is less than or equal to 50 μm, the space occupied by the first film layer can be reduced, thereby facilitating the improvement of the energy density of the battery monomer.

[0032] In a possible implementation, 20 μm≤d1≤30 μm. In this way, the exposed end surface and the burr have a good covering effect, and the battery monomer has a high energy density.

[0033] In a possible implementation, the thickness d2 of the second film layer satisfies 200 nm≤d2≤2000 nm.

[0034] In the case where the thickness d2 of the second film layer is greater than or equal to 200 nm, the second film layer can cover the burr generated by cutting and the exposed end surface; and in the case where the thickness d2 of the second film layer is less than or equal to 2000 nm, the space occupied by the second film layer can be reduced, and the thickness of the first film layer and the space occupied by the first film layer can also be reduced, thereby facilitating the improvement of the energy density of the battery monomer.

[0035] In a possible implementation, 200 nm≤d2≤500 nm. In this way, the covering effect of the second film layer on the exposed end surface and the burr and the energy density of the battery monomer can be further considered.

[0036] In a possible implementation, the melting point of the thermoplastic polymer is 80-120 DEG C.

[0037] In a possible implementation, the thermoplastic polymer includes one or more of polyethylene, polypropylene, polyamide, microcrystalline wax, polystyrene, or polymethyl methacrylate.

[0038] By using the thermoplastic polymer described above, it is beneficial to form a uniform and dense coating on the exposed end surface of the current collector after cutting and on burrs.

[0039] In a possible implementation, the first film layer further includes a binder; the mass ratio B of the thermoplastic polymer and the mass ratio C of the binder satisfy 50:25≤B:C≤70:15 based on the total mass of the first film layer. By arranging the binder, the thermoplastic polymer and the light-absorbing material in the first film layer can be bonded to the surface of the current collector, thereby reducing the risk of the light-absorbing material and the thermoplastic polymer falling off the current collector. By arranging 50:25≤B:C≤70:15, the thermoplastic polymer and the binder both have a suitable mass content, which is beneficial to reduce the risk of the first film layer falling off and the second film layer being more uniform and dense, thereby improving the reliability of the battery cell.

[0040] In a possible implementation, 50:45≤B:C≤50:35. In this way, the thermoplastic polymer and the binder have a more suitable mass content, which is beneficial to further improve the reliability of the battery cell.

[0041] In a possible implementation, the tab is a positive tab. In this way, it is beneficial to reduce the risk of internal short circuit caused by the positive tab being overlapped with the negative electrode.

[0042] In a possible implementation, in the positive tab, the active material layer includes a positive active material, and the positive active material includes one or more of a lithium-containing transition metal oxide, an olivine-structured lithium-containing phosphate, or a spinel-structured material. In the positive tab, the risk of short circuit caused by the exposed end surface being overlapped with the negative electrode is greater, and the probability of fire and other phenomena occurring is greater. By arranging the positive tab to have the above structure, it is beneficial to improve the reliability of the battery cell.

[0043] In a possible implementation, the positive active material includes a lithium-containing transition metal oxide.

[0044] In a second aspect, a method for manufacturing a battery cell is provided, including: providing a pole piece to manufacture the battery cell; wherein the providing the pole piece includes: disposing an active material layer on at least one side surface of a transition region of a current collector; disposing a first film layer on at least one side surface of the transition region of the current collector, the first film layer including a thermoplastic polymer and a light-absorbing material; and cutting the current collector along a cutting line to manufacture the pole piece, the cutting line passing through the transition region. In this way, in the process of cutting the current collector provided with the active material layer and the first film layer, the light-absorbing material can assist the first film layer to absorb more heat, so that the thermoplastic polymer in the first film layer can be melted and flow to the end face at a faster cutting speed, and then solidify at the end face to form a second film layer, and the current collector provided with the first film layer can be cut off at a faster speed. Therefore, this embodiment is conducive to manufacturing the pole piece at a faster cutting speed, and can reduce burrs of the pole piece and the risk of short circuit caused by the exposed end face being connected to an electrode with opposite polarity in the battery cell, thereby being conducive to improving the production efficiency of the pole piece and the reliability of the battery cell.

[0045] In a possible implementation, the cutting speed is greater than or equal to 70 m / min. In this way, the current collector provided with the first film layer can be cut off and the second film layer can be manufactured at a faster cutting speed, which is conducive to balancing the production efficiency of the pole piece and the reliability of the battery cell.

[0046] In a third aspect, a power-using device is provided, including the battery cell in the first aspect and any possible implementation thereof, and / or the battery cell manufactured by the method in the second aspect and any possible implementation thereof.

[0047] In a fourth aspect, a pole piece is provided, including: a current collector, an active material layer, and a first film layer, the current collector including a main body portion and a tab protruding from the main body portion, the main body portion including a coated region and a transition region, the transition region being disposed between the coated region and the tab; the active material layer being disposed on at least one side surface of the coated region; and the first film layer being disposed on at least one side surface of the transition region, the first film layer including a thermoplastic polymer and a light-absorbing material. BRIEF DESCRIPTION OF DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of the drawings.

[0049] FIG. 1 is a schematic view of a pole piece according to an embodiment of the present application;

[0050] Figure 2 is a cross-sectional view along the AA direction in Figure 1;

[0051] Figure 3 is a cross-sectional view along the BB direction in Figure 1;

[0052] Figure 4 is a schematic diagram of the electrode sheet before the electrode tab in an embodiment of this application;

[0053] Figure 5 is a schematic diagram of a battery cell according to an embodiment of this application;

[0054] Figure 6 is a schematic diagram of a method for preparing a battery cell according to an embodiment of this application;

[0055] Figure 7 is a schematic diagram of the current collector before coating according to an embodiment of this application;

[0056] Figure 8 is a schematic diagram of a current collector coated with an active material layer according to an embodiment of this application;

[0057] Figure 9 is a schematic diagram of a current collector coated with a first film layer according to an embodiment of this application;

[0058] Figure 10 is a schematic diagram of a cutting current collector according to an embodiment of this application;

[0059] Figure 11 is a schematic diagram of a battery according to an embodiment of this application;

[0060] Figure 12 is a schematic diagram of an electrical device according to an embodiment of this application.

[0061] Figure label:

[0062] 1: Electrode; 124: Cutting line; 10: Current collector; 20: Active material layer; 11: First film layer; 12: Second film layer; 101: Main body; 1011: Coating area; 1012: Transition area; 102: Tab; 1021: First part; 1022: Second part; 1011a: End face at the first end; 1022a: End face of the second part; 3: Battery cell; 31: Housing; 32: End cap assembly; 33: Electrode assembly; 322: Electrode terminal; 331: Tab; 34: Current collector; 5: Battery; 6: Electrical device. Detailed Implementation

[0063] The electrode sheets, battery cells, their preparation methods, and embodiments of the electrical devices described in this application have been appropriately detailed with reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0064] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0065] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0066] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0067] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0068] The development of battery technology requires consideration of both battery performance and production efficiency. Among these, the design and production efficiency of the electrode sheets are crucial to the reliability and overall production efficiency of individual battery cells. With increasing demands for production efficiency, electrode sheets need to be cut at speeds of 70 m / min or higher. At cutting speeds of 70 m / min or higher, the risk of difficulty in cutting the electrode sheets increases. Furthermore, the burrs and exposed end faces generated during cutting pose risks such as self-discharge and internal short circuits due to electrode overlap with opposite polarities.

[0069] In view of this, this application provides a battery cell including an electrode sheet. The electrode sheet includes a current collector, an active material layer, and a first film layer. The current collector includes a main body and a tab protruding from the main body. The main body includes a coating area and a transition area, with the transition area disposed between the coating area and the tab. The active material layer is disposed on at least one surface of the coating area. The first film layer is disposed on at least one surface of the transition area, and the first film layer includes a thermoplastic polymer and a light-absorbing material. The light-absorbing material in the first film layer can help the first film layer absorb more heat, thereby enabling the electrode sheet to be cut at a faster cutting speed. It can also help form a film layer covering burrs and exposing the end face at the end face, which helps reduce the short-circuit risk of the battery cell and improve the reliability of the battery cell.

[0070] [Battery cell]

[0071] This application provides a battery cell, which includes electrodes.

[0072] Figure 1 is a schematic diagram of an electrode according to an embodiment of this application, Figure 2 is a cross-sectional view along the AA direction in Figure 1, and Figure 3 is a cross-sectional view along the BB direction in Figure 1. As an example, referring to Figures 1 to 3, the electrode 1 of this embodiment includes a current collector 10, an active material layer 20, and a first film layer 11.

[0073] The current collector 10 includes a main body 101 and a tab 102 protruding from the main body 101.

[0074] The main body 101 includes a coating area 1011 and a transition area 1012, with the transition area 1012 disposed between the coating area 1011 and the tab 102. The active material layer 20 is disposed on at least one side of the surface of the coating area 1011. In this way, during the cutting of the tab 102, the cutting tool (e.g., a laser) can maintain a certain distance from the active material layer 20, which can reduce the shedding of the active material layer 20.

[0075] The current collector 10 has two opposing surfaces along its thickness direction, and the active material layer 20 can be disposed on at least one of the two opposing surfaces along the thickness direction of the current collector 10. For example, as shown in Figures 2 and 3, the active material layer 20 is disposed on both opposing surfaces along the thickness direction of the current collector 10.

[0076] The thickness direction of the current collector 10 can be the z-direction as shown in Figures 2 and 3.

[0077] The first film layer 11 is disposed on at least one side of the surface of the transition region 1012, and the first film layer 11 includes a thermoplastic polymer and a light-absorbing material.

[0078] The first film layer 11 may be disposed only on at least one side of the surface of the transition region 1012, or it may be disposed on at least one side of the surface of the transition region 1012 and at least one side of the surface of the tab 102 near the main body 101.

[0079] As one example, the first film layer 11 is disposed on the surfaces of both sides of the transition region 1012. As another example, as shown in Figures 2 and 3, the first film layer 11 is disposed on the surfaces of both sides of the transition region 1012 and on both sides of the portion of the tab 102 near the main body 101.

[0080] Thermoplastic polymers can refer to polymers that soften when heated, solidify when cooled, and can soften again. For example, when heated to a certain temperature, a thermoplastic polymer changes from a solid state to a flowable state, and when cooled, it can become solid again.

[0081] Light-absorbing materials can refer to materials that convert light into heat energy. When irradiated by light (such as laser), light-absorbing materials can absorb the energy of at least a portion of the wavelength of light, thereby helping the first film layer 11 absorb more heat, which in turn makes it easier to cut the current collector 10 on which the first film layer 11 is disposed.

[0082] As one example, the light-absorbing material has a darker color, which helps the first film layer 11 absorb more heat. As another example, the light-absorbing material helps increase the surface roughness of the first film layer 11. A rougher surface of the first film layer 11 facilitates multiple reflections and absorption of light, thereby helping the first film layer 11 absorb more heat. The light-absorbing materials in the embodiments of this application include, but are not limited to, these examples.

[0083] In this embodiment of the application, the electrode 1 includes a current collector 10, an active material layer 20 disposed on at least one side surface of the coating area 1011 of the current collector 10, and a first film layer 11 disposed on at least one side surface of the transition area 1012 of the current collector 10. The current collector 10 includes a main body 101 and an electrode tab 102. The main body 101 includes the coating area 1011 and the transition area 1012. The tab 102 needs to be formed by laser cutting of the current collector 10 with a first film layer 11 during the preparation of the electrode 1. The first film layer 11 includes a thermoplastic polymer and a light-absorbing material. The light-absorbing material can help the first film layer 11 absorb the heat of the laser, so that at least part of the thermoplastic polymer in the first film layer 11 can change from solid to fluid state and flow to the end face 1011a at the first end at a relatively fast cutting speed to cover burrs and exposed end faces. It can also cut the current collector 10 with the first film layer 11 at a relatively fast cutting speed, thereby helping to reduce the risk of short circuit caused by burrs generated during cutting and exposed end faces overlapping with electrodes of opposite polarity, and helping to improve the reliability of the battery cell. Therefore, the electrode 1 of this embodiment can be prepared at a relatively fast cutting speed, with high production efficiency, and the battery cell including the electrode 1 has high reliability.

[0084] In some embodiments, the electrode 1 further includes a second film layer 12, which is at least disposed on the end face 1011a of the main body 101 at the first end. The second film layer 12 includes a thermoplastic polymer, the first end is one end of the main body 101 along a first direction, and the first direction is the direction in which the tab 102 protrudes from the main body 101.

[0085] The first direction is parallel to the plane where the current collector 10 is located, and the first direction is the direction in which the tab 102 protrudes relative to the main body 101. For example, the first direction is the y-direction in FIG1.

[0086] The end face 1011a of the main body 101 at the first end is a surface parallel to the thickness direction of the current collector 10. For example, as shown in Figures 1 to 3, the end face 1011a is a surface parallel to the x-direction and the z-direction.

[0087] Figure 4 is a schematic diagram of the electrode sheet before the tabs are cut according to an embodiment of this application. Referring to Figure 4, the end surface 1011a of the main body 101 at the first end and the tab 102 can be formed through the following process: the electrode sheet 1 with the first film layer 11 is cut along the cutting line 124 (the black dashed line in the figure) using a laser. The end surface 1011a is the exposed end surface of the transition region 1012 after cutting. After cutting, the end surface 1011a is exposed and may be accompanied by burrs. During the cutting process, the first film layer 11 can absorb the heat of the laser, causing the thermoplastic polymer in the first film layer 11 to change from solid to liquid and flow to the end surface 1011a at the first end, where it solidifies to form the second film layer 12.

[0088] When the cutting speed is fast, the laser acts on the first film layer 1 for a short time, and the heat absorbed by the first film layer 11 and the current collector 10 is limited. The first film layer 11 includes a light-absorbing material, which can help the first film layer 11 absorb more heat, thereby making it easier to cut the current collector 10 with the first film layer 11 in a shorter time, and also making it easier for the second film layer 12 to uniformly and completely cover the end surface 1011a.

[0089] The second film layer 12 can cover the burrs generated during the cutting process, reducing the risk of burrs overlapping with electrodes of opposite polarity and reducing the risk of burrs puncturing the isolation membrane; the second film layer 12 can also cover the exposed end surface 1011a, reducing the risk of short circuit caused by the end surface 1011a overlapping with electrodes of opposite polarity.

[0090] In the above embodiments, the second film layer 12 includes a thermoplastic polymer. The second film layer 12 can cover the end face 1011a at the first end, reducing the risk of short circuit caused by burrs generated during cutting and the contact between the exposed end face 1011a and the electrode with opposite polarity, which is beneficial to further improve the reliability of the battery cell.

[0091] In some embodiments, based on the total mass of the first film layer 11, the mass percentage A of the light-absorbing material satisfies: 5wt% ≤ A ≤ 25wt%.

[0092] A can be 5wt%, 8wt%, 10wt%, 15wt%, 20wt%, 25wt%, or any value within the above range.

[0093] When the mass content A of the light-absorbing material is greater than or equal to 5 wt%, the light-absorbing material included in the first film layer 11 can absorb more heat, which is beneficial for cutting the current collector 10 with the first film layer 11 at a faster cutting speed, and the second film layer 12 can uniformly and densely cover the burrs and exposed end faces; when the mass content A of the light-absorbing material is less than or equal to 25 wt%, the risk of excessive heat absorption leading to the ablation of the first film layer 11 can be reduced.

[0094] In this embodiment, by setting 5wt%≤A≤25wt%, it is beneficial to cut the electrode 1 with high production efficiency and to reduce the risk of the first film layer 11 being burned due to excessive heat.

[0095] As an example, if A is less than or equal to 20 wt%, then when the light-absorbing material is a darker material, such as carbon black, by setting A to be less than or equal to 20 wt%, the color of the first film layer 11 can be more clearly distinguished from the color of the active material layer 20, thereby facilitating the identification of the coating width of the active material layer 20 and the first film layer 11 by a charge-coupled device (CCD) camera; in addition, it also helps to reduce the risk of ablation caused by excessive heat absorption of the first film layer 11 due to excessive carbon black content.

[0096] As an example, A is less than or equal to 20 wt%. In this case, when the light-absorbing material is a conductive material, such as carbon black, by setting A to be less than or equal to 20 wt%, the first film layer 11 can have a larger resistance. It is also beneficial to reduce the risk of short circuit caused by the connection between the positive electrode and the negative electrode when the electrode is a positive electrode and there is an overhang problem.

[0097] As an example, A is greater than or equal to 20 wt%, for example, A can be 20 wt% to 25 wt% or 20 wt% to 30 wt%. Accordingly, the light-absorbing material can be a white or light-colored material, such as muscovite, which can reduce the risk of ablation of the first film layer 11.

[0098] In some embodiments, 5wt% ≤ A ≤ 15wt%. In this way, the light-absorbing material in the first film layer 11 has a more suitable mass content, which can further reduce the risk of ablation of the first film layer 11 while taking into account both high production efficiency and high reliability of the battery cell.

[0099] In some embodiments, the volume average particle size Dv50 of the light-absorbing material satisfies: 10nm≤Dv50≤5μm.

[0100] The volume average particle size Dv50 can refer to the particle size corresponding to a sample when the cumulative volume distribution percentage reaches 50%.

[0101] The volume average particle size Dv50 of the light-absorbing material can be 10nm, 15nm, 20nm, 30nm, 35nm, 40nm, 50nm, 500nm, 0.1μm, 1μm, 2μm, 3μm, 4μm, 5μm or any value within the above range.

[0102] When the volume average particle size of the light-absorbing material is greater than or equal to 10 nm, the risk of agglomeration of the light-absorbing material can be reduced, which is conducive to the uniform dispersion of the light-absorbing material in the first film layer 11, thereby facilitating the uniform absorption of laser heat by the first film layer 11. When the volume average particle size of the light-absorbing material is less than or equal to 50 nm, it is also conducive to the uniform distribution of the light-absorbing material in the first film layer 11, which is conducive to the uniform absorption of laser heat.

[0103] In this embodiment, by setting 10nm≤Dv50≤5μm, it is beneficial for the light-absorbing material to absorb the heat of the laser more uniformly, thereby making it easier to obtain an electrode with more regular cut boundaries and an electrode with a more uniform thickness of the second film layer 12.

[0104] In some embodiments, 10nm ≤ Dv50 ≤ 50nm. In this way, the surface of the first film layer 11 is relatively smooth, and the light-absorbing material has a more suitable particle size, which is beneficial for the light-absorbing material to absorb heat more uniformly.

[0105] As an example, 8nm≤Dv50≤12nm, in this way, the distribution of light-absorbing material in the first film layer 11 is more uniform, and the heat absorbed by the first film layer 11 is also more uniform, which is conducive to the formation of a uniform and dense second film layer 12.

[0106] In some embodiments, 0.1 μm ≤ Dv50 ≤ 5 μm. This results in a relatively rough surface for the first film layer 11, which helps the first film layer 11 absorb more heat.

[0107] As an example, the volume average particle size of the light-absorbing material is larger than the volume average particle size of other materials (such as binders or thermoplastic polymers) in the first film layer 11. This is beneficial for the first film layer 11 to form a rougher surface, which helps the first film layer 11 absorb more heat.

[0108] In some embodiments, the wavelength of light absorbed by the light-absorbing material is different from the wavelength of light absorbed by the current collector 10 and the wavelength of light absorbed by the thermoplastic polymer.

[0109] As an example, the current collector 10 is aluminum foil, the thermoplastic polymer is microcrystalline wax, and the light-absorbing material is carbon black. Carbon black can absorb infrared light, microcrystalline wax can absorb ultraviolet light, and aluminum foil can absorb red light. In this way, the first film layer 11 contains multiple materials that can absorb light of different wavelengths, thereby making full use of the heat of the laser, which is beneficial to further increase the temperature of the current collector 10 and the first film layer 11, facilitating the rapid cutting of the current collector 10 and the first film layer 11 and the formation of the second film layer 12.

[0110] In this embodiment, the wavelength of light absorbed by the light-absorbing material is different from the wavelength of light absorbed by the current collector 10 and the wavelength of light absorbed by the thermoplastic polymer. This is beneficial for the first film layer 11 to fully absorb the heat of the laser, and is more conducive to improving production efficiency and the uniform and dense coating of the second film layer 12. Thus, both production efficiency and the reliability of the battery cell can be taken into account.

[0111] In some embodiments, the wavelength of light absorbed by the first film layer 11 includes 0.3 μm to 10 μm. In this way, the first film layer 11 can absorb a wider range of light wavelengths, and the first film layer 11 can absorb more light, thereby absorbing more heat.

[0112] In some embodiments, the light-absorbing material includes at least one of organic light-absorbing materials or inorganic light-absorbing materials. The organic light-absorbing material includes at least one of resin, polyester, polyurethane or diaryl yellow. The inorganic light-absorbing material includes at least one of cadmium sulfide, cadmium selenide, iron oxide, toner, boehmite, titanium dioxide or aluminum oxide.

[0113] The aforementioned light-absorbing material can effectively absorb the heat of the laser, thus facilitating the absorption of more heat during the cutting process, which is beneficial to improving the reliability of the battery cell and production efficiency.

[0114] In addition, the light-absorbing materials mentioned above are basically non-toxic and do not contain elements such as Fe, Ni, Cr, Zn, and Cu that affect electrical performance, thus reducing the impact on the electrical performance of individual battery cells.

[0115] In some embodiments, the organic light-absorbing material includes at least one of polymethyl methacrylate or polyamide, and / or, the inorganic light-absorbing material includes toner. The toner may be carbon black, acetylene black, graphite, etc.

[0116] In some embodiments, the light-absorbing material includes carbon black. This allows for more efficient absorption of the heat from the laser.

[0117] Carbon black can absorb almost all the energy of infrared lasers, thus greatly improving the thermal absorption effect of the first film layer 11. Furthermore, due to the large specific surface area of ​​carbon black, light is reflected multiple times on its surface, resulting in multiple absorptions and further enhancing the heat absorption effect of the first film layer 11. The numerous pores and uneven structure on the carbon black surface can effectively scatter and capture photons, increasing light absorption. When carbon black particles are densely packed together, the resulting morphology significantly affects laser absorption. During absorption, carbon black particles of different shapes undergo multiple scattering and absorption processes, effectively improving absorption efficiency, allowing the first film layer 11 to absorb more heat.

[0118] In some embodiments, the light-absorbing material is an inorganic material. For example, the light-absorbing material is titanium dioxide, aluminum oxide, etc. These materials essentially do not participate in the electrochemical reactions in the battery and have a low risk of swelling in the electrolyte.

[0119] In some embodiments, the surface roughness of the first film layer 11 is greater than or equal to 1 μm. For example, the surface roughness of the first film layer 11 is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 18 or any value within the above range.

[0120] In some embodiments, the surface roughness of the first film layer 11 is 1 μm to 15 μm.

[0121] The surface roughness of the first film layer can be represented by Ra, where Ra is the average surface roughness of the first film layer.

[0122] In the above embodiments, the first film layer 11 has a relatively rough surface, which helps the first film layer 11 absorb more heat.

[0123] In some embodiments, the light-absorbing material includes at least one of phthalocyanine blue or muscovite. Thus, the aforementioned material has a large particle size, which contributes to a greater surface roughness of the first film layer.

[0124] As an example, the light-absorbing material is insoluble in the organic solvent NMP. This is beneficial for improving the surface roughness of the first film layer 11.

[0125] In some embodiments, the tab 102 includes a first portion 1021 and a second portion 1022, the second portion 1022 being located between the first portion 1021 and the main body 101, and the first portion 1021 being at least partially exposed; a first film layer 11 is disposed on the surface of at least one side of the transition region 1012 and the second portion 1022.

[0126] The tab 102 includes a first part 1021 and a second part 1022, which are connected. The first part 1021 can be considered as the area on the tab 102 where no film layer is provided.

[0127] As an example, when the current collector 10 is aluminum foil, the first part 1021 being exposed can mean that the first part 1021 is bare aluminum foil and the first part 1021 is not coated with any other coating.

[0128] The at least partial exposure of the second part 1022 can refer to the fact that, in the battery cell, the portion of the second part 1022 connected to the current collector has an area that overlaps with the current collector, and the portion of the second part 1022 not connected to the current collector is exposed.

[0129] The first film layer 11 can be disposed on one side of the transition region 1012 and the second part 1022, or it can be disposed on both sides of the transition region 1012 and the second part 1022.

[0130] In the above technical solution, the first part 1021 of the tab 102 is at least partially exposed, which facilitates the discharge of electrical energy in the battery cell through the first part of the tab 102; a first film layer 11 is provided on at least one side of the transition region 1012 and the second part 1022 of the tab 102, which helps to reduce the risk of short circuit caused by the second part 1022 and the transition region 1012 being connected to an electrode with opposite polarity.

[0131] In some embodiments, a second film layer 12 is provided on the end face 1011a of the second portion 1022 along a second direction, the second direction being perpendicular to the first direction.

[0132] The second direction can be approximately perpendicular to the first direction, but it is not necessarily perfectly perpendicular. When the electrode 1 includes multiple tabs 102, the second direction can be the arrangement direction of the multiple tabs 102. For example, referring to Figures 1 to 3, the second direction is the x-direction.

[0133] During the process of cutting the current collector 10 along the cutting line 124 to prepare the tab 102, the cutting tool passes through the area of ​​the second part 1022. Since the surface of the second part 1022 is provided with a first film layer 11, which includes a thermoplastic polymer, after cutting, a second film layer 12 is formed at the end face 1022a of this area along the second direction, which can reduce the risk of the end face 1022a overlapping with an electrode of opposite polarity.

[0134] In this embodiment, the second film layer 12 can cover the end face 1011a of the tab 102 exposed due to cutting, which can reduce the risk of the end face 1011a overlapping with an electrode of opposite polarity.

[0135] In some embodiments, the thickness d1 of the first film layer 11 satisfies: 20μm≤d1≤50μm.

[0136] The thickness d1 of the first film layer 11 refers to the thickness of one side surface of the current collector 10 along the thickness direction of the electrode; d1 can be 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm or any value within the above range.

[0137] The thickness d1 of the first film layer 11 is the average thickness of the first film layer 11 along the thickness direction of the electrode (e.g., the z-direction in the figure). For example, the thickness d1 is the average of the maximum and minimum dimensions along the thickness direction of the electrode.

[0138] The total thickness of the first film layer 11 can be 2d1, which is 40μm to 100μm.

[0139] As an example, the thickness of the first film layer 11 is less than the thickness of the active material layer 20.

[0140] When the thickness d1 of the first film layer 11 is greater than or equal to 20 μm, during the cutting process of the current collector 10 on which the first film layer 11 is provided, there is more thermoplastic polymer in the first film layer 11. As a result, more thermoplastic polymer can flow to the burrs and the exposed end face 1011a of the current collector 10 after being heated, which is beneficial to uniformly and densely covering the exposed end face 1011a and the burrs. When the thickness d1 of the first film layer 11 is less than or equal to 50 μm, it is beneficial to reduce the energy consumed in the cutting process and to reduce the burrs generated in the cutting process.

[0141] In some embodiments, 20μm≤d1≤30μm. This allows for better coverage of the exposed end face 1011a and burrs while reducing the energy consumed in cutting and the burrs generated during cutting.

[0142] In some embodiments, the thickness d2 of the second film layer 12 satisfies: 200nm ≤ d2 ≤ 2000nm.

[0143] The thickness d2 of the second film layer 12 can be the average thickness of the second film layer 12 along the first direction, and the average thickness can be the average of the maximum thickness and the minimum thickness. For example, the first direction can be the y direction in Figures 1 to 3.

[0144] The thickness d2 of the second film layer 12 can be 200nm, 300nm, 400nm, 500nm, 800nm, 1000nm, 1500nm, 2000nm or any value within the above range.

[0145] When the thickness d2 of the second film layer 12 is greater than or equal to 200 nm, the second film layer 12 can cover the burrs generated by the coating and cutting and the exposed end face 1011a; when the thickness d2 of the second film layer 12 is less than or equal to 2000 nm, the space occupied by the second film layer 12 can be reduced, and the requirements for the thickness of the first film layer 11 and the space occupied by the first film layer 11 can also be reduced, which is beneficial to improving the energy density of the battery cell.

[0146] In some embodiments, 200nm ≤ d2 ≤ 500nm. This further balances the coating effect of the second film layer 12 on the exposed end face 1011a and burrs, as well as the energy density of the battery cell.

[0147] In some embodiments, the melting point of the thermoplastic polymer is less than or equal to 200°C.

[0148] The melting point of a thermoplastic polymer can be defined as the temperature at which the thermoplastic polymer changes from a solid or semi-solid state to a liquid state.

[0149] The melting point of a thermoplastic polymer can be 80°C, 100°C, 150°C, 200°C or any value within the above range.

[0150] In this embodiment, the melting point of the thermoplastic polymer is less than or equal to 200°C. Thus, during the cutting process of the current collector with the second insulating layer 13, the thermoplastic polymer can change from a solid state to a fluid state under the action of the heat generated by the cutting. The fluid thermoplastic polymer can flow to the end surface of the exposed current collector after cutting and the burrs generated by cutting, thereby facilitating the preparation of the insulating layer 13.

[0151] In some embodiments, the melting point of the thermoplastic polymer is 80°C to 200°C.

[0152] The thermoplastic polymer has a dropping melting point of not less than 80°C, which reduces the risk of the thermoplastic polymer melting or flowing due to heating of electrode 1 during other processing.

[0153] By setting the melting point of the thermoplastic polymer to 80℃~200℃, the thermoplastic polymer in the second film layer 12 can be made to flow to the end surface to form the insulating layer 13 during the cutting process. At the same time, the risk of the thermoplastic polymer becoming fluid due to other factors during the uncut current collector process can be reduced.

[0154] In some embodiments, the thermoplastic polymer includes one or more of polyethylene, polypropylene, polyamide, microcrystalline wax, polystyrene, or polymethyl methacrylate. Using the above-mentioned thermoplastic polymer facilitates the formation of a uniform and dense coating on the exposed end surface of the current collector after cutting, as well as at the burrs. Furthermore, the above-mentioned thermoplastic polymer has high insulation and voltage resistance; when the electrode 1 is immersed in the electrolyte, the thermoplastic polymer will not undergo an electrochemical reaction with the electrolyte.

[0155] In some embodiments, the first film layer 11 further includes an adhesive. By using the adhesive, the thermoplastic polymer and the light-absorbing material in the first film layer 11 can be bonded to the surface of the current collector 10, thereby reducing the risk of the light-absorbing material and the thermoplastic polymer falling off the current collector 10.

[0156] As an example, the adhesive may be one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0157] Based on the total mass of the first film layer 11, the mass ratio of thermoplastic polymer B and the mass ratio of binder C satisfy: 50:25≤B:C≤70:15.

[0158] B:C can be 50:25, 50:35, 50:45, 50:25, 55:25, 70:15, or any value within the above range.

[0159] When B:C is greater than or equal to 50:25, the thermoplastic polymer in the first film layer 11 has a suitable mass ratio, and the second film layer 12 is relatively uniform and dense; when B:C is less than or equal to 70:15, the binder in the first film layer 11 has a suitable mass ratio, which can reduce the risk of the first film layer 11 falling off.

[0160] In this embodiment, by setting 50:25≤B:C≤70:15, both the thermoplastic polymer and the binder have suitable mass content, which helps to reduce the risk of the first film layer falling off, and the second film layer 12 is relatively uniform and dense, which helps to improve the reliability of the battery cell.

[0161] In some embodiments, 50:45 ≤ B:C ≤ 50:35. This allows for a more suitable mass ratio of thermoplastic polymer and binder, which is beneficial for further improving the reliability of the battery cells.

[0162] In some embodiments, electrode 1 is a positive electrode. This helps to reduce the risk of internal short circuits caused by the positive electrode and the negative electrode coming into contact.

[0163] In some embodiments, in the positive electrode sheet, the active material layer 20 includes a positive electrode active material, which includes one or more of lithium-containing transition metal oxides, lithium-containing phosphates with an olivine structure, or materials with a spinel structure.

[0164] Lithium-containing transition metal oxides include: LiNi 0.8 Co 0.1 Mn 0.1 O2. In this way, the battery cells prepared from this electrode can have a high capacity.

[0165] Lithium-containing transition metal oxides can also include other ternary materials, such as LiNi. 0.6 Co 0.2 Mn 0.2 O2. Lithium-containing transition metal oxides may also include lithium-rich manganese-based materials, etc.

[0166] Spinel-structured materials can include lithium manganese oxide, etc.

[0167] The general formula for lithium phosphates with an olivine structure can be LiaAxMn1-yByP1-zCzO4-nDn, where 0<a≤1.1, 0.001≤x≤0.1, 0.001≤y<0.5, 0.001≤z≤0.1, 0.001≤n≤0.1, A includes one or more of Zn, Al, Na, K, Mg, Nb, Mo and W, B includes one or more of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, C includes one or more of B, S, Si and N, and D includes one or more of S, F, Cl and Br.

[0168] The lithium phosphate with the olivine structure may also include at least one of lithium manganese phosphate and lithium iron manganese phosphate.

[0169] In the positive electrode, the exposed end surface is more likely to cause a short circuit when it comes into contact with the negative electrode, and the probability of fire is also greater. By setting the positive electrode to have the above structure, it is beneficial to improve the reliability of the battery cell.

[0170] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption. The molar content of Li varies depending on the battery's discharge state. The definition of 'a' above includes the molar content of Li under different charge / discharge states (typically, the battery voltage is between 2-5V). In the examples of cathode materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar content of Li changes after charge / discharge cycles. In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Lattice oxygen release causes changes in the molar content of oxygen, resulting in fluctuations in the actual molar content of O.

[0171] In some embodiments, the positive electrode active material may also be a sodium salt, such as a layered sodium transition metal oxide.

[0172] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. The battery cell can be a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery, a magnesium-ion battery, etc.

[0173] Figure 5 is a schematic diagram of a battery cell according to an embodiment of this application. For example, as shown in Figure 5, the battery cell 3 is a square battery cell. The battery cell 3 includes a housing 31, an end cap assembly 32, and an electrode assembly 33 disposed in the housing 31.

[0174] The electrode assembly 33 can be manufactured by a winding process or a stacking process from a positive electrode sheet, a negative electrode sheet, and a separator. In some embodiments, the positive electrode sheet is electrode sheet 1 in the embodiments of this application.

[0175] The end cap assembly 32 includes electrode terminals 322, as shown in FIG5. The end cap assembly 32 includes two electrode terminals 322, one of which is a positive electrode terminal and the other is a negative electrode terminal.

[0176] The battery cell 3 also includes a current collector 34, which is used to connect the tab 331 of the electrode assembly 33 and the electrode terminal 322. For example, in the case where the electrode 1 in this embodiment is a positive electrode, one current collector 34 is used to connect the tab of the positive electrode and the positive electrode terminal, and another current collector 34 is used to connect the tab of the negative electrode and the negative electrode terminal.

[0177] In some embodiments, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0178] [Preparation methods for electrode sheets]

[0179] Figure 6 is a schematic diagram of a method for preparing a battery cell according to an embodiment of this application. The method 100 for preparing a battery cell may include the following steps.

[0180] Step 110: Provide electrode sheets to prepare battery cells.

[0181] The electrode is provided by: providing an active material layer 20 on at least one side of the coating area 1011 of the current collector 10; providing a first film layer 11 on at least one side of the transition area 1012 of the current collector 10, the first film layer 11 comprising a thermoplastic polymer and a light-absorbing material; and cutting the current collector 10 along a cutting line 124 using a laser to prepare the electrode, the cutting line 124 passing through the transition area 1012.

[0182] As an example, an active material layer 20 is provided on both sides of the coating area 1011. Specifically, the active material can be mixed with solvent, binder, conductive agent, etc. to prepare an active material slurry, and then the active material slurry is coated on the coating area 1011 to prepare the active material layer 20.

[0183] Figure 7 is a schematic diagram of the current collector before coating according to an embodiment of this application. For example, Figure 7 shows a schematic diagram of the current collector 10 before coating and cutting. Before coating the film layer and cutting the tabs, a current collector 10 is provided, for example, the current collector 10 is a square aluminum foil.

[0184] Figure 8 is a schematic diagram of a current collector coated with an active material layer according to an embodiment of this application. For example, Figure 8 shows a current collector 10 with an active material layer 20 disposed in the coated area.

[0185] Figure 9 is a schematic diagram of a current collector coated with a first film layer according to an embodiment of this application. As an example, as shown in Figure 9, a slurry comprising a thermoplastic polymer and a light-absorbing material is coated on the transition region 1012 and the portion of the current collector reserved for setting the tabs to prepare the first film layer 11.

[0186] Figure 10 is a schematic diagram of a current collector being cut according to an embodiment of this application. For example, as shown in Figure 10, the cutting line 124 passes through the transition region 1012. During the cutting process, the laser can cut to the first film layer 11 and there is a certain gap between it and the active material layer 20.

[0187] During the process of cutting the current collector 10 with the active material layer 20 and the first film layer 11, the light-absorbing material can help the first film layer 11 absorb more heat, thereby melting the thermoplastic polymer in the first film layer 11 and flowing to the end face 1011a at a faster cutting speed, and then solidifying at the end face 1011a to form the second film layer 12. The current collector 10 with the first film layer 11 can also be cut at a faster speed.

[0188] This embodiment is advantageous for preparing the electrode 1 with the first film layer 11 and the second film layer 12 at a faster cutting speed, thereby improving the production efficiency of the electrode 1 and the reliability of the battery cell.

[0189] In some embodiments, the cutting speed is greater than or equal to 70 m / min. This allows the current collector 10 with the first film layer 11 to be cut and the second film layer 12 to be prepared at a relatively fast cutting speed, which is beneficial to balancing the production efficiency of the electrode 1 and the reliability of the battery cell.

[0190] The cutting speed can be 70 m / min, 80 m / min, or a higher value. For example, the cutting speed is 80 m / min.

[0191] [Positive electrode plate]

[0192] In this embodiment, the electrode 1 can be a positive electrode. The positive electrode includes a positive current collector and a positive electrode film layer disposed on the positive current collector.

[0193] The positive electrode current collector can be a metal foil or a composite current collector. For example, the positive electrode current collector can be an aluminum foil.

[0194] Composite current collectors may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. Composite current collectors can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0195] The positive electrode film includes a positive electrode active material. This positive electrode active material can be any known battery-grade positive electrode active material. For example, it could be lithium iron phosphate, ternary materials, or lithium-rich manganese-based materials.

[0196] The positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0197] The positive electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0198] [Negative electrode plate]

[0199] In this embodiment, the electrode 1 can be a negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on the negative current collector.

[0200] The negative electrode current collector can be a metal foil or a composite current collector. The negative electrode current collector can be copper foil. Composite current collectors can be formed by depositing metallic materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) onto a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0201] The negative electrode film layer includes a negative electrode active material. The negative electrode active material can be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0202] The negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0203] [Electrolytes]

[0204] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0205] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0206] The electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0207] Solvents may include at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0208] The electrolyte may also optionally include negative electrode film-forming additives, positive electrode film-forming additives, and performance additives that can improve certain battery performance, such as performance additives that improve battery overcharge performance, battery high temperature or low temperature performance, etc.

[0209] [Isolation membrane]

[0210] The separator is used to separate the positive electrode and the negative electrode. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0211] The material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film; there are no particular restrictions. When the separator is a multi-layer composite film, the materials of each layer can be the same or different; there are no particular restrictions.

[0212] Positive electrode, negative electrode and separator can be made into electrode assembly by winding process or stacking process.

[0213] [Battery]

[0214] This application provides a battery, including the battery cells described in the above embodiments. Figure 11 is a schematic diagram of a battery according to an embodiment of this application. As shown in Figure 11, the battery 5 may include multiple battery cells (not shown in the figure).

[0215] Battery cells 3 can be directly assembled into battery 5, or they can be first assembled into battery modules, and then multiple battery modules can be assembled into battery 5.

[0216] [Electrical appliances]

[0217] This application provides an electrical device, including the battery described in the above embodiments.

[0218] Figure 12 is a schematic diagram of an electrical device according to an embodiment of this application. As shown in Figure 12, this application provides an electrical device 6, which includes the battery in the above embodiment.

[0219] Alternatively, the electrical device may also be an energy storage device, a lighting device, a spacecraft, etc., as is the case in the embodiments of this application.

[0220] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0221] [Example]

[0222] Example 1

[0223] In Example 1, the electrode has the structure shown in Figures 1-3. An active material layer 20 is disposed on both sides of the coating area 1011 of the main body 101. A first film layer 11 is disposed on both sides of the transition area 1012 and the second portion 1022 of the tab 102. A second film layer 12 is disposed on the end surface 1011a of the first end and the end faces 1022a of the second portion 1022 along the second direction. The thermoplastic polymer in the first film layer 11 is microcrystalline wax, the light-absorbing material is carbon black, and the binder is polyvinylidene fluoride. Based on the total mass of the first film layer 11, the mass content A of the light-absorbing material is 5 wt%, the mass content B of the thermoplastic polymer is 50 wt%, the mass content C of the binder is 45 wt%, the volume average particle size Dv50 of the light-absorbing material is 10 nm, and the thickness d1 of the first film layer 11 is 50 μm. The thermoplastic polymer in the second film layer 12 is microcrystalline wax, and the thickness d2 of the second film layer 12 is 850 nm.

[0224] Examples 2-4

[0225] The difference between Examples 2-4 and Example 1 is that the mass content A of the light-absorbing material is different.

[0226] Examples 5-7

[0227] The difference between Examples 5-7 and Example 1 is that the volume average particle size Dv50 of the light-absorbing material is different.

[0228] Examples 8-10

[0229] The difference between Examples 8-10 and Example 1 is that the mass ratio B:C of the thermoplastic polymer and the binder in the first film layer is different.

[0230] Examples 11-13

[0231] The difference between Examples 11-13 and Example 1 is that the light-absorbing materials are different; the volume average particle size of the different light-absorbing materials and the mass ratio of the light-absorbing materials in the first film layer are different.

[0232] Examples 14-15

[0233] The difference between Examples 14-15 and Example 1 is that the thermoplastic polymers are different.

[0234] Examples 16-17

[0235] The difference between Examples 16-17 and Example 1 is that the thickness of the first film layer is different, and correspondingly, the thickness of the second film layer is different.

[0236] Comparative Example 1

[0237] The difference between Comparative Example 1 and Example 1 is that the first film layer includes a thermoplastic polymer and a binder, but no light-absorbing material is provided.

[0238] Table 1. Parameters of the Examples and Comparative Examples

[0239] Table 2 Test results of the examples and comparative examples

[0240] [Preparation of battery cells]

[0241] (1) Prepare the slurry for the first membrane layer

[0242] The light-absorbing material, thermoplastic polymer, and binder were mixed in a certain proportion, and a solvent was added and stirred until homogeneous. The viscosity of the slurry was approximately 3000 mPa·s. The binder was polyvinylidene fluoride (PVDF), and the solvent was N-methylpyrrolidone. The specific mass ratios of the light-absorbing material, thermoplastic polymer, binder, and these substances are shown in Table 1.

[0243] (2) Coating and drying

[0244] In the positive electrode active slurry (positive electrode active material is LiNi) 0.8 Co 0.1 Mn 0.1 When O2 is coated onto aluminum foil, an active material layer is prepared; the slurry of the first film layer is coated on the edge of the aluminum foil with a coating width of 9 mm; and then dried in an oven at a drying temperature of 120°C.

[0245] (3) Laser cutting

[0246] The product obtained in step (2) is cut using a laser to obtain an electrode with a second film layer. The cutting speed is 80 m / min.

[0247] (4) Manufacturing battery cells

[0248] The above-mentioned positive electrode sheet is assembled together with other battery components: negative electrode sheet, separator, and electrolyte to form a lithium battery cell.

[0249] [First membrane layer confirmed]

[0250] The surface of the electrode was observed using a scanning electron microscope to check for the presence of a first film layer. The electrode was then cut open, and the cross-section was photographed using a scanning electron microscope. The thickness of the first film layer was then observed based on the photographs.

[0251] [Confirmation of the second membrane layer]

[0252] The end surface was observed using a scanning electron microscope (SEM) to check whether a second film layer was present at the end surface; in addition, the thickness of the second film layer could be observed through images taken by the scanning electron microscope.

[0253] [Testing the resistance of the first film layer]

[0254] The resistance of the first film layer can be measured using an AC impedance meter.

[0255] For example, one end of the AC impedance meter is connected to the first film layer of the positive electrode in the embodiment, and the other end is connected to the tab of the negative electrode, with the end faces of the negative electrode overlapping the positive electrode.

[0256] [Testing the resistance of the second film layer]

[0257] The resistance of the second film layer can be measured using an AC impedance meter.

[0258] For example, one end of the AC impedance meter is connected to the tab of the positive electrode in the embodiment (specifically, the first part of the tab), and the other end is connected to the tab of the negative electrode, with the end faces of the negative electrode overlapping the positive electrode.

[0259] [Surface roughness test of the first film layer]

[0260] The surface roughness of a coating can be measured using the stylus method. A diamond stylus with a tip curvature radius of about 2 micrometers is slowly slid along the surface being measured. The vertical displacement of the diamond stylus is converted into an electrical signal by an electrical length sensor. After amplification, filtering, and calculation, the surface roughness value is indicated by a display instrument.

[0261] [Test of volume average particle size]

[0262] The volume average particle size (Dv50) can be determined using a particle size analyzer-laser diffraction method. Specifically, refer to standard GB / T19077-2016, using a laser diffraction scattering particle size analyzer, and measure according to the manufacturer's instructions. For example, before preparing the slurry, take an appropriate amount of thermoplastic polymer and test the average volume particle size of the material using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer. Take an appropriate amount of the sample to be tested (the sample concentration should be 8-12% opacity), add 20 ml of deionized water, and simultaneously incubate for 5 minutes (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, measure the sample according to GB / T19077-2016 / ISO 13320:2009.

[0263] For example, a scanning electron microscope can be used to test the electrode to obtain an image of the region of the first film layer of the electrode. The average particle size of the thermoplastic polymer can then be measured and calculated based on the image.

[0264] [Confirmation of the melting point of thermoplastic polymers]

[0265] The melting point of thermoplastic polymers can be determined using a differential scanning calorimeter (DSC) device. Specifically, as an example, an 8 mg sample is placed in a DSC device, heated in an N2 atmosphere at a flow rate of 50 ml / min, at a heating rate of 10 °C / min, and with a cutoff temperature of 400 °C, thereby testing the melting point of the thermoplastic polymer.

[0266] For example, the melting point of a thermoplastic polymer can be determined based on the specific type of thermoplastic polymer. As an example, for crystalline thermoplastic polymers, the melting point refers to the melting point of the crystalline thermoplastic polymer; for amorphous thermoplastic polymers, the melting point refers to the glass transition temperature of the amorphous thermoplastic polymer.

[0267] [Mass ratio of thermoplastic polymer, light-absorbing material, and binder]

[0268] The above mass ratio can be obtained based on the mass of the thermoplastic polymer, the mass of the light-absorbing material, and the mass of the binder added during the preparation process.

[0269] In addition, the thermoplastic polymers, binders, and light-absorbing materials in the electrode can be identified in the following ways.

[0270] The first film layer is scraped off with a knife to form powder or lumps. Approximately 1g of the film sample is placed in a mold and heated to the melting point of the thermoplastic polymer to form a thin film. For Fourier Transmission Infrared (FTIR) testing, characteristic peaks are used to determine the type of polymer, light-absorbing material, and binder. Alternatively, thermogravimetric-FTIR (TG-FTIR) can be used to heat the film sample from room temperature to 600°C. The thermal decomposition temperature, weight loss ratio, and product composition are then used to determine the composition and mass percentage of the first film layer.

[0271] [Testing whether the laser cuts the electrode]

[0272] During the process of using laser cutting to prepare electrode tabs, observe whether the current collector or the first film layer is not cut.

[0273] As shown in Examples 1-17 and Comparative Example 1, adding a light-absorbing material to the first film layer can help the first film layer absorb more heat during the process of laser-cutting the current collector with the first film layer to prepare the electrode tab. This allows the current collector with the first film layer to be cut off at a faster cutting speed, and a second film layer is generated at the cut end, reducing the risk that the current collector with the first film layer cannot be cut off. Therefore, the electrode sheet provided in the embodiments of this application is beneficial to improving the production efficiency of the electrode sheet. Furthermore, since the electrode sheet has both a first film layer and a second film layer, applying the electrode sheet to a battery cell helps reduce the risk of internal short circuits in the battery cell, thereby improving the reliability of the battery cell.

[0274] As shown in Comparative Example 1, since the first film layer only contains thermoplastic polymer and binder and no additional light-absorbing material, when the cutting speed is 80 m / min, the cutting speed is relatively fast and the laser dwell time is short. As a result, the first film layer and the current collector absorb less heat, making it difficult to cut the current collector and the first film layer at some locations, and it is also difficult to generate a second film layer at the uncut end face.

[0275] As shown in Examples 1-17, at a cutting speed of 80 m / min, the light-absorbing material allows the first film layer to absorb more heat, thus enabling the tab to be prepared in a shorter time. Furthermore, a second film layer is also provided at the cut end face. The resistance at the end face with the second film layer is greater than 3000 Ω, which can be approximated as an insulating layer. Therefore, the risk of fire is very low when the end face with the second film layer is in contact with the negative electrode of a fully charged battery. Similarly, the resistance at the location where the first film layer is located is greater than 3000 Ω, further reducing the risk of fire when the location with the first film layer is in contact with the negative electrode of a fully charged battery.

[0276] As shown in Examples 1-4 and 11-13, based on the total mass of the first film layer, when the mass content A of the light-absorbing material is 5wt% to 25wt%, the light-absorbing material in the first film layer has a suitable mass content. This is beneficial for cutting the current collector and the first film layer at a relatively fast cutting speed to prepare a second film layer of corresponding thickness, and it can also reduce the risk of the first film layer being ablated due to excessive mass content of the light-absorbing material. When the mass content A of the light-absorbing material is 5wt% to 20wt%, the first film layer can have a relatively obvious color difference from the active material layer, which is convenient for identifying the first film layer and the active material layer, as well as the coating width of the first film layer and the active material layer, through a CCD camera. In addition, when the light-absorbing material is carbon black, setting A to 5wt% to 20wt%, and further setting A to 5wt% to 15wt%, the first film layer has a large resistance, which can reduce the risk of short circuits and fires caused by the first film layer overlapping with electrodes of opposite polarity, and the risk of ablation of the first film layer during the cutting process is low.

[0277] As shown in Examples 5-7, the volume average particle size Dv50 of the light-absorbing material is set to 10nm to 50nm. The first film layer is relatively smooth, which is conducive to the uniform mixing of the light-absorbing material in the slurry of the first film layer and its uniform distribution in the first film layer. This allows the heat absorbed by the first film layer to be more uniform, which is convenient for the cutting of the tabs.

[0278] As shown in Examples 11-12, setting the volume average particle size Dv50 of the light-absorbing material to 0.1 μm to 5 μm helps to form protrusions in the first film layer. The surface roughness of the first film layer is relatively large, which helps the first film layer absorb more heat. At a faster cutting speed, the current collector and the first film layer can be cut to prepare a second film layer of corresponding thickness.

[0279] As shown in Examples 1-4 and 8-10, setting the ratio of the mass content B of the thermoplastic polymer to the mass content C of the binder to be 50:25 to 70:15 can make the first film layer adhere to the current collector and is also conducive to the formation of a second film layer with a suitable thickness.

[0280] Referring to Examples 1 and 11-13, the embodiments of this application are applicable to various light-absorbing materials. Depending on the type of light-absorbing material, the light-absorbing material can be configured with different volume average particle sizes and mass contents in the first film layer. For example, when the light-absorbing material is muscovite, a mass content A of 25 wt% can be set, which not only facilitates the absorption of more heat by the first film layer but also reduces the risk of ablation due to excessive heat absorption. As another example, when the light-absorbing material is muscovite, a volume average particle size of 5 μm can be set to facilitate the formation of a relatively rough first film layer, which helps to further absorb heat.

[0281] In conjunction with Examples 1 and 14-15, the embodiments of this application are applicable to a variety of thermoplastic polymers.

[0282] As shown in Examples 16-17, the embodiments of this application are applicable to first film layers of various thicknesses. By setting the thickness of the first film layer to 20μm to 50μm, a second film layer of suitable thickness can be obtained, which can balance the reliability and energy density of the battery cell.

[0283] It should be noted that this application is not limited to the above-described embodiments. Although the embodiments use a positive electrode as an example, the design of the electrode described above can also be applied to a negative electrode. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this application without departing from the spirit of this application.

Claims

1. A battery cell, characterized in that, include: Electrode; The electrode comprises: a current collector, an active material layer, and a first film layer; The current collector includes a main body and an electrode tab protruding from the main body. The main body includes a coating area and a transition area, and the transition area is disposed between the coating area and the electrode tab. The active material layer is disposed on at least one side of the surface of the coating area; The first film layer is disposed on at least one side of the surface of the transition region, and the first film layer comprises a thermoplastic polymer and a light-absorbing material.

2. The battery cell according to claim 1, characterized in that, The electrode further includes a second film layer, which is disposed at least on the end face of the main body at the first end. The second film layer includes the thermoplastic polymer. The first end is an end along the main body in a first direction, which is the direction in which the electrode tab protrudes from the main body.

3. The battery cell according to claim 1 or 2, characterized in that, Based on the total mass of the first film layer, the mass percentage A of the light-absorbing material satisfies: 5wt% ≤ A ≤ 25wt%.

4. The battery cell according to claim 3, characterized in that, 5wt% ≤ A ≤ 15wt%.

5. The battery cell according to any one of claims 1-4, characterized in that, The volume average particle size Dv50 of the light-absorbing material satisfies: 10nm≤Dv50≤5μm.

6. The battery cell according to claim 5, characterized in that, 10nm≤Dv50≤50nm.

7. The battery cell according to claim 5, characterized in that, 0.1μm≤Dv50≤5μm.

8. The battery cell according to any one of claims 1-7, characterized in that, The wavelengths of light absorbed by the first film layer range from 0.3 μm to 10 μm.

9. The battery cell according to claim 8, characterized in that, The light-absorbing material includes at least one of organic light-absorbing materials or inorganic light-absorbing materials. The organic light-absorbing material includes at least one of resin, polyester, polyurethane or diaryl yellow. The inorganic light-absorbing material includes at least one of cadmium sulfide, cadmium selenide, iron oxide, toner, boehmite, titanium dioxide or aluminum oxide.

10. The battery cell according to claim 9, characterized in that, The organic light-absorbing material includes at least one of polymethyl methacrylate or polyamide, and / or the inorganic light-absorbing material includes toner.

11. The battery cell according to any one of claims 1-10, characterized in that, The surface roughness of the first film layer is greater than or equal to 1 μm.

12. The battery cell according to claim 11, characterized in that, The surface roughness of the first film layer is 1 μm to 15 μm.

13. The battery cell according to claim 11 or 12, characterized in that, The light-absorbing material includes at least one of phthalocyanine blue or muscovite.

14. The battery cell according to any one of claims 1-13, characterized in that, The electrode includes a first part and a second part, the second part being located between the first part and the main body, and the first part being at least partially exposed. The first film layer is disposed on at least one side of the transition region and the second portion.

15. The battery cell according to claim 14, characterized in that, Along the second direction, the end face of the second part is provided with the second film layer, the second direction is perpendicular to the first direction, and the first direction is the direction in which the tab protrudes from the main body.

16. The battery cell according to any one of claims 1-15, characterized in that, The thickness d1 of the first film layer satisfies: 20μm≤d1≤50μm.

17. The battery cell according to claim 16, characterized in that, 20μm≤d1≤30μm.

18. The battery cell according to any one of claims 1-17, characterized in that, The thickness d2 of the second film layer satisfies: 200nm≤d2≤2000nm.

19. The battery cell according to claim 18, characterized in that, 200nm≤d2≤500nm.

20. The battery cell according to any one of claims 1-19, characterized in that, The melting point of the thermoplastic polymer is 80℃~120℃.

21. The battery cell according to claim 20, characterized in that, The thermoplastic polymer includes at least one of polyethylene, polypropylene, polyamide, microcrystalline wax, polystyrene, or polymethyl methacrylate.

22. The battery cell according to any one of claims 1-21, characterized in that, The first film layer also includes an adhesive. Based on the total mass of the first film layer, the mass ratio B of the thermoplastic polymer and the mass ratio C of the adhesive satisfy the following: 50:25 ≤ B:C ≤ 70:

15.

23. The battery cell according to claim 22, characterized in that, 50:45≤B:C≤50:

35.

24. The battery cell according to any one of claims 1-23, characterized in that, The electrode is a positive electrode.

25. The battery cell according to claim 24, characterized in that, In the positive electrode sheet, the active material layer includes a positive electrode active material, which includes one or more of the following: lithium-containing transition metal oxides, lithium-containing phosphates with an olivine structure, or materials with a spinel structure.

26. The battery cell according to claim 25, characterized in that, The positive electrode active material includes lithium-containing transition metal oxides.

27. A method for preparing a single battery cell, characterized in that, include: An electrode is provided to prepare the battery cell; wherein the provision of the electrode comprises: An active material layer is disposed on at least one side of the surface of the coating area of ​​the current collector; A first film layer is provided on at least one side of the transition region of the current collector, the first film layer comprising a thermoplastic polymer and a light-absorbing material; The current collector is cut along a cutting line using a laser to prepare the electrode, the cutting line passing through the transition region.

28. The preparation method according to claim 27, characterized in that, The cutting speed is greater than or equal to 70 m / min.

29. An electrical appliance, characterized in that, Includes the battery cell according to any one of claims 1-26, and / or the battery cell obtained by the preparation method according to claim 27 or 28.

30. An electrode sheet, characterized in that, include: Current collector, active material layer, and first membrane layer; The current collector includes a main body and an electrode tab protruding from the main body. The main body includes a coating area and a transition area, and the transition area is disposed between the coating area and the electrode tab. The active material layer is disposed on at least one side of the surface of the coating area; The first film layer is disposed on at least one side of the surface of the transition region, and the first film layer comprises a thermoplastic polymer and a light-absorbing material.

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