Current collector, electrode sheet, secondary battery, and power consumption device

Abstract

A power consumption device equipped with a secondary battery. The secondary battery comprises an electrode sheet, the electrode sheet comprising a current collector and a positive electrode active material disposed on the current collector. The current collector is used to support the electrode active material and comprises a foil material and a conductive coating disposed on both sides of the foil material. The conductive coating comprises a high-density conductive material region and a plurality of recessed low-adhesion regions spaced apart within the high-density conductive material region, the high-density conductive material region comprising a conductive material and a binder, the conductive material comprising a granular conductive agent. At least a portion of each recessed low-adhesion region does not contain the binder, and at least a portion of the region does not contain the granular conductive material.

Description

[Technical Field]

[0001] This application claims priority to Chinese Patent Application No. 202310224558.7, filed with the China National Intellectual Property Administration on 28 February 2023, titled "Current Collector, Electrode Sheet, Secondary Battery, and Power Consumption Device," which is incorporated herein by reference in its entirety.

[0002] This application relates to the field of battery technology, and more specifically to current collectors, electrode plates, secondary batteries, and power consumption devices. [Background technology]

[0003] Typically, the surface of current collectors used in lithium-ion batteries has a conductive coating, such as a carbon coating, which usually covers the entire surface of the current collector. However, existing carbon-coated current collectors focus on reducing the contact resistance of the battery. This reduces the apparent internal resistance of the battery and improves the battery's room-temperature performance, but it does not have a clear effect on improving the battery's low-temperature performance. For example, even using carbon-coated aluminum foil does not have a clear effect on improving the low-temperature performance of lithium batteries that use lithium iron phosphate as the positive electrode active material. [Overview of the project] [Problems that the invention aims to solve]

[0004] In view of this, this application provides a current collector of a new type structure to reduce the ohmic resistance of the battery and further reduce the contact resistance, thereby significantly improving the low-temperature performance of the battery. [Means for solving the problem]

[0005] Specifically, a first aspect of this application provides a current collector for supporting an electrode active material. The current collector is Gold leaf and A conductive coating wherein the conductive coating is disposed on both sides of the foil, including, the conductive coating a high-density conductive material region, the high-density conductive material region including a conductive material and a binder, the conductive material including a granular conductive agent, and a plurality of concave low-binder regions, the plurality of concave low-binder regions being arranged at intervals within the high-density conductive material region, at least a part of each of the plurality of concave low-binder regions not including a binder, and at least a part of each of the plurality of concave low-binder regions not including a conductive material; including.

[0006] Since the current collector has a conductive coating including concave low-binder regions, the ohmic resistance and contact resistance of a battery using the current collector can be reduced simultaneously, and as a result, the low-temperature performance of the battery is significantly improved. At the same time, the room-temperature performance, high-temperature performance, etc. of the battery do not deteriorate and are slightly improved.

[0007] In some embodiments, the current collector satisfies one or more of the following conditions. (a) The average area S of the plurality of concave low-binder regions is smaller than the projected area corresponding to the particle size D 50 of the electrode active material. (b) The average particle size d of the granular conductive agent is less than 1 / 2 of the particle size D 10 of the electrode active material, where D 10 and D 50 each represent the particle size corresponding to the case where the cumulative distribution rate of the particle amount of the electrode active material reaches 10% and 50% respectively.

[0008] In some embodiments, the average thickness h1 of the high-density conductive material region satisfies D 50 / 2 ≦ h1 ≦ D 90 / 2, where D 90 represents the particle size corresponding to the case where the cumulative distribution rate of the particle amount of the electrode active material reaches 90%.

[0009] In some embodiments, h1 is in the range of 0.2 μm to 2 μm.

[0010] In some implementation configurations, the diameter d of the granular conductive material is in the range of 20 nm to 100 nm.

[0011] In some mounting configurations, the total coverage of multiple concave low-binder regions on the surface of the foil on one side is in the range of 33% to 70%.

[0012] In some implementations, the work function of the conductive coating lies between the work function of the foil and the work function of the electrode active material.

[0013] In some implementations, the granular conductive material is one or more of the following: carbon black, conductive carbon spheres, and metal carbide particles.

[0014] In some implementations, the conductive material further comprises a sheet-like conductive agent, with at least some concave low-binder regions containing the sheet-like conductive agent, and the thickness of the sheet-like conductive agent being smaller than the diameter of the granular conductive agent.

[0015] In some implementation configurations, when the conductive material includes a sheet-like conductive agent, each of the multiple concave low-binder regions includes the sheet-like conductive agent.

[0016] In some implementation configurations, the mass of the sheet-like conductive material is 0.01 to 0.1 times the mass of the granular conductive material.

[0017] In some implementations, the sheet-like conductive material is one or more of graphene, conductive carbon nitride, maxine nanosheets, and metal carbide nanosheets.

[0018] In some implementation configurations, the mass percentage of sheet-like conductive material within the conductive material ranges from 0.1% to 9%, while the mass percentage of granular conductive material within the conductive material ranges from 91% to 99.9%.

[0019] In some implementations, the binder includes one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin (such as polyethylene, polypropylene, and polystyrene), sodium carboxymethylcellulose (CMC), and sodium alginate.

[0020] According to a second aspect, the present application provides an electrode plate. The electrode plate comprises a current collector according to the first aspect of the present application and an electrode active material layer disposed on the current collector. The electrode plate may be a positive electrode plate or a negative electrode plate.

[0021] Because a current collector is used, the effective contact area between the electrode active material particles on the electrode plate and the conductive material on the current collector is greatly increased, and the amount of unnecessary interface is reduced. This leads to a further reduction in the battery's contact resistance and a decrease in its ohmic resistance, resulting in a significant improvement in the battery's low-temperature performance.

[0022] According to a third aspect, the present application provides a secondary battery. The secondary battery includes electrode plates according to a second aspect of the present application. Since the positive and / or negative electrodes of the secondary battery use electrode plates, the low-temperature performance of the secondary battery is greatly improved.

[0023] According to a fourth aspect, the present application provides a power consumption device, which includes a secondary battery according to a third aspect of the present application. [Brief explanation of the drawing]

[0024] [Figure 1A] This is a schematic cross-sectional view of the structure of a current collector according to one embodiment of this application. [Figure 1B] This document shows a top view of a conductive coating in a current collector and a side view of a conductive coating supporting electrode active material according to one embodiment of this application. [Figure 2]Figure 2 is an electron microscope image of a surface scan of the current collector F1 according to Embodiment 1 of this application, where the scale in Figure 2 represents the particle size D50 of the positive electrode active material. [Figure 3] This is an electron microscope image of the surface scanning of the current collector DF2, according to Comparative Example 2. [Figure 4] This figure summarizes the DC internal resistance analysis results obtained when the battery of Example 1 and the comparative example battery were discharged separately at 25°C (a) and -10°C (b) for 30 seconds with a constant current of 0.1C. [Figure 5] This is a structural diagram of a power consumption device according to one embodiment of the present application. [Modes for carrying out the invention]

[0025] The technical solutions in the embodiments of this application will be described in detail below with reference to the attached drawings.

[0026] See also Figures 1A and 1B. One embodiment of the present application provides a current collector. The current collector 10 includes a foil 1 and a conductive coating 2 disposed on both sides of the foil 1. The conductive coating 2 includes a high-density conductive material region 21 and a plurality of recessed low-binder regions 22 spaced apart within the high-density conductive material region 21. The high-density conductive material region 21 includes a conductive material and a binder. The conductive material includes a granular conductive agent (Figures 1A and 1B show an example where the conductive material is only a granular conductive agent). At least a portion of each recessed low-binder region 22 does not contain a binder, and at least a portion of each recessed low-binder region 22 does not contain a granular conductive agent. The conductive material includes a granular conductive agent (Figures 1A and 1B show an example where the conductive material is only a granular conductive agent).

[0027] Each conductive coating 2 contains conductive material and a binder, but it will be understood that the conductive material and binder do not completely cover the foil 1. As a result, the conductive coating 2 is divided into high-density conductive material regions 21 and recessed low-binder regions 22 arranged at intervals. The conductive material is not evenly distributed on the foil 1, but it may be evenly distributed within the high-density conductive material regions 21. Contact between the granular conductive agent and the foil 1 is a single-point contact, and the granular conductive agent needs to adhere to the foil 1 with the help of the binder. At least a portion of the recessed low-binder regions 22 is controlled to be free of granular conductive agent, and as a result, the amount of binder used can be significantly reduced, or the binder may not be included at all.

[0028] The presence of such a concave low-binder region 22 in the conductive coating 2 ensures that when the electrode active material layer is coated onto the current collector 10, contact sites between some of the electrode active material particles (see number 20 in Figure 1B) and the current collector 10 fall into the concave low-binder region 22. This portion of the region has little to no insulating binder, thereby allowing for the existence of binder-free conductive paths between the foil 1 of the current collector 10 and the electrode active material. This leads to a reduction in the ohmic resistance of the battery, resulting in a significant reduction in the low-temperature internal resistance of the battery and an increased degree of improvement in the battery's low-temperature performance. In addition, the presence of a high-density region of conductive material of a certain thickness causes the sides of the concave low-binder region 22 to have a curved structure, thereby increasing the amount of contact sites between each particle of the electrode active material and the current collector 10 (locations where the electrode active material particles make single-point contact with the conductive coating within the non-concave region). This leads to a further reduction in the battery's contact resistance, resulting in a significant reduction in the battery's low-temperature internal resistance and an even greater improvement in the battery's low-temperature performance.

[0029] Therefore, compared to conventional current collectors whose entire surface is covered with a conductive coating, the current collector provided in this embodiment of the present application can reduce the ohmic resistance of the battery and achieve the effect of further reducing contact resistance. The internal resistance of a battery is typically the ohmic resistance RΩ 、Contact resistance R c 、Electrochemical reaction resistance (SEI mode resistance R SEI and charge transfer resistance R ct ) and includes polarization internal resistance caused by diffusion resistance R d In this application, the ohmic resistance and contact resistance are simultaneously reduced to reduce the electrochemical reaction resistance. As a result, the electric field gradient force of the solid-phase diffusion of active ions is indirectly promoted, the diffusion resistance is reduced, the solid-phase diffusion rate of active ions is increased, and particularly the diffusion rate at low temperatures is significantly increased. This leads to reducing the low-temperature internal resistance of the battery, improving the cycle performance, power performance, etc. at low temperatures, reducing the charging voltage platform at low temperatures, increasing the discharge voltage platform, and improving the specific discharge capacity and energy density of the battery. Furthermore, the use of the current collector does not reduce the room-temperature performance, high-temperature performance, etc. of the battery.

[0030] In this application, the concave low-binder region 22 may not contain a binder or a part of the region may contain a binder. When a part of the region contains a binder, the mass ratio of the binder in the concave low-binder region 22 is much lower than the mass ratio of the binder in the high-density conductive material region 21. In some implementation forms, the concave low-binder region 22 does not contain a binder. This further leads to reducing the ohmic resistance of the battery using the current collector 10. Each concave low-binder region 22 may not contain a granular conductive agent or a part of the region may not contain a granular conductive agent. Certainly, the concave low-binder region 22 may contain another shape of conductive material (such as a sheet-like conductive agent). It will be understood that the thickness h2 of the concave low-binder region 22 is 0 or more and can be less than the thickness of the high-density conductive material region 21. When the thickness of the concave low-binder region 22 is 0, it represents that the concave low-binder region is a blank region without material, that is, it does not contain a binder and a conductive material.

[0031] In one implementation form of this application, the current collector 10 can satisfy one or more of the following conditions.

[0032] (a) Refer to Figure 1B. The average area S of the multiple concave low-binder regions 22 is equal to the particle size D of the electrode active material. 50 The corresponding projected area S 影 It is smaller than that.

[0033] (b) The average particle size d of the granular conductive agent is equal to the particle size D of the electrode active material. 10 It is less than half of that.

[0034] D 10 and D 50 These values ​​represent the particle size corresponding to the point where the cumulative distribution rate of the electrode active material particles reaches 10% and 50%, respectively.

[0035] Condition (a) ensures that when the electrode active material layer is coated onto the current collector 10, the electrode active material particles may settle in the concave low-binder region 22. As a result, the direct contact area between the electrode active material particles and the foil 1 is located in a region with excessively little binder, reducing the electron transmission resistance between the foil and the electrode active material, thereby achieving the effect of reducing the ohmic resistance of the battery. At the same time, condition (a) also ensures that the conductive material in the conductive coating 2 is mainly filled in the gaps between the electrode active material particles, ensuring that the conductive network structure between the electrode active material particles is complete, thereby achieving the effect of reducing the contact resistance of the battery. 影 =π × (0.5D 50 ) 2 .

[0036] Condition (b) can ensure that the particle size of the granular conductive agent is small, and as a result it may come into contact with the electrode active material particles, effectively increasing the amount of conductive material adjacent to the inner wall of the concave low binder region 22, increasing the electron transfer path between the electrode active material particles and the current collector 10, and significantly reducing the contact resistance. In condition (b), d and D 10 When comparing d and D 10 Both need to be converted to the same unit. Similarly, S and S 影 They also need to be converted to the same units for comparison.

[0037] The area of ​​each concave low-binder region 22 may be obtained based on electron microscope images of the conductive coating 2, and the average area S of multiple concave low-binder regions 22 is calculated. The area of ​​the concave low-binder region 22 is the maximum projected area of ​​the concave low-binder region 22 on the foil 1, i.e., the concave aperture area of ​​the concave low-binder region. S is greater than 0, and S 影 It may be smaller than that.

[0038] In this application, on one side of the foil 1, the total coverage of the multiple concave low-binder regions 22 on the surface of the foil 1 is in the range of 33% to 70%. In other words, the sum of the areas of the multiple concave low-binder regions 22 is 33% to 70% of the surface area of ​​the side of the foil 1 where the concave low-binder regions 22 are located. In this way, the coverage of the concave low-binder regions on the foil 1 is appropriate, thereby facilitating a significant reduction in both the ohmic resistance and contact resistance of the battery using the current collector 10. In addition, from the coverage, it can be seen that the total distribution area of ​​the high-density conductive material regions 21 on the foil 1 occupies 30% to 67% of the surface area of ​​the foil 1.

[0039] In some implementations of this application, the average thickness h1 of the high-density conductive material region 21 satisfies the following condition (c).

[0040] (c)D 50 / 2≦h1≦D 90 / 2, here, D 90 This represents the particle size corresponding to the point where the cumulative distribution rate of the electrode active material particles reaches 90%.

[0041] Condition (c) ensures that the surface of the high-density conductive material region 21, which is separated from the foil 1, is essentially coplanar with half the height of the electrode active material particles, and that approximately half the size of a single electrode active material particle fills the concave low-binder region 22, thereby significantly increasing the contact area between the electrode active material particles and the conductive material adjacent to the inner wall of the concave low-binder region 22, thereby significantly reducing the contact resistance of the battery, and subsequently significantly reducing the low-temperature internal resistance of the battery, and further improving the room-temperature internal resistance of the battery. As a result, when the low-temperature performance of the battery is significantly improved, the room-temperature performance of the battery does not decrease, and is even improved to a certain extent. When it is determined whether condition (c) is met, D 50 , D 90 h1 and h1 must be compared using the same units.

[0042] In some implementations of this application, the current collector 10 satisfies one or more of the above conditions (a), (b), and (c). In addition, when the current collector 10 satisfies (a), (b), and (c) simultaneously, the low-temperature internal resistance of the battery prepared using the current collector 10 is lower, and the low-temperature performance is more significantly improved.

[0043] The above parameter D 10 , D 50 , and D 90 This may be obtained from a particle size distribution map of the electrode active material obtained based on laser diffraction, or through a statistical analysis of the particle size of several particles of the electrode active material performed based on electron microscope images of the electrode active material. However, D 10 , D 50 , and D 90 It should be noted that these must be obtained by the same method. Similarly, the average particle size d of the granular conductive material may be obtained from electron microscope images of the granular conductive material or from particle size distribution maps of the granular conductive material obtained based on laser diffraction (in the latter method, d is the median particle size). Parameter h1 may be the average value of the thicknesses of different regions of the high-density conductive material region 21, obtained by directly or indirectly measuring the thickness of different regions of the high-density conductive material region 21.

[0044] Optionally, h1 is in the range of 0.2 μm to 2 μm. This ensures a specific thickness difference between the high-density conductive material region 21 and the concave low-binder region 22, and ensures a large surface area on the sides of the concave low-binder region 22 to increase the contact area between the electrode active material particles and the current collector 10, resulting in reduced contact resistance of the battery and significantly improved low-temperature performance. Optionally, the diameter d of the granular conductive material is in the range of 20 nm to 100 nm. Optionally, the D of the electrode active material 50 This range is from 0.1 μm to 1 μm.

[0045] In this application, the work function of the conductive material in conductive coating 2 is between the work function of foil 1 and the work function of the electrode active material. The term "work function" represents the minimum energy required for electrons with an initial energy equal to the Fermi level to escape from the interior of the metal / semiconductor into the vacuum. The magnitude of the work function value indicates how strongly electrons are coupled within the metal / semiconductor. The direction in which electrons move from the current collector foil through the conductive coating to the electrode active material is opposite between the charging and discharging processes, and the contact potential difference between materials with similar work functions is small. Therefore, by controlling the work function of the conductive material between the work function of foil 1 and the work function of the electrode active material, a small interfacial contact potential difference between both positive and negative electron movement can be ensured, resulting in a reduction of interfacial contact resistance.

[0046] The materials of the conductive material may include, but are not limited to, carbon materials (such as carbon black, graphene, and conductive carbon spheres). The shape of the conductive material may include, but is not limited to, granular, and may be one or more of the following: sheet, tubular, etc. In one implementation embodiment of this application, the granular conductive agent is one or more of carbon black, conductive carbon spheres, and metal carbide particles.

[0047] In some implementations of this application, the conductive material further comprises a sheet-like conductive agent, and at least some concave low-binder regions 22 comprise the sheet-like conductive agent, wherein the thickness of the sheet-like conductive agent is smaller than the diameter of the granular conductive agent.

[0048] The phrase "at least some of the concave low-binder regions 22 contain sheet-like conductive material" ensures that a two-dimensional conductive path exists between the electrode active material falling into some of the concave low-binder regions 22 and the foil 1. As a result, the ohmic resistance of the battery can be further reduced, the low-temperature internal resistance of the battery is further reduced, and the degree of improvement in the low-temperature performance of the battery is further increased. In some mounting configurations, when the conductive material contains sheet-like conductive material, each concave low-binder region 22 contains sheet-like conductive material. In this way, the effect of improving the low-temperature performance of the battery becomes clearer. The phrase "the thickness of the sheet-like conductive material is smaller than the diameter of the granular conductive material" ensures that the thickness of the concave low-binder regions 22 is less than or equal to the thickness of the high-density conductive material regions 21.

[0049] In one implementation embodiment of this application, the sheet-like conductive material is one or more of graphene, conductive carbon nitride, maxine nanosheets, and metal carbide nanosheets. Furthermore, the mass of the sheet-like conductive material is 0.01 to 0.1 times the mass of the granular conductive material. This further contributes to maintaining a good balance between the ohmic resistance and contact resistance of the battery using the current collector 10. Optionally, the mass percentage of the sheet-like conductive material in the conductive material is in the range of 0.1% to 9%, and the mass percentage of the granular conductive material in the conductive material is in the range of 91% to 99.9%. In some embodiments, the conductive material may be carbon black and graphene.

[0050] In this application, the binder may be, but is not limited to, one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin (such as polyethylene, polypropylene, and polystyrene), sodium carboxymethylcellulose (CMC), sodium alginate, etc. The type of binder may be selected depending on whether the current collector 10 is specifically used as a current collector for a positive electrode plate or for a negative electrode plate. For example, when the current collector 10 is specifically used as a current collector for a positive electrode plate, the binder may typically be PVDF, PTFE, etc. When the current collector 10 is specifically used as a current collector for a negative electrode plate, the binder may be SBR, CMC, PAA, sodium alginate, etc. In one implementation embodiment of this application, the mass of the binder in the conductive coating 2 may account for 37% to 67% of the total mass of the binder and the conductive material.

[0051] In this application, when the current collector 10 is specifically used to prepare a positive electrode plate, the foil 1 may be aluminum foil, aluminum alloy foil, etc., or when the current collector 10 is specifically used to prepare a negative electrode plate, the foil 1 may be copper foil, copper alloy foil, nickel foil, nickel alloy foil, etc.

[0052] One embodiment of this application further provides an electrode plate. The electrode plate includes the current collector 10 described above in the embodiment of this application. The electrode plate using the current collector 10 may be a positive electrode plate or a negative electrode plate. In other words, the current collector may be used specifically as a positive electrode current collector or a negative electrode current collector.

[0053] Typically, an electrode plate includes a current collector 10 and an electrode active material layer disposed on the current collector 10. The electrode active material layer may be located on one side of the current collector 10, or it may be located on both sides of the current collector 10. If the electrode plate is a positive electrode plate, the electrode active material layer is specifically a positive electrode active material layer, and if the electrode plate is a negative electrode plate, the electrode active material layer is specifically a negative electrode active material layer.

[0054] In some implementations of this application, the electrode plate is a positive electrode plate comprising a current collector 10 and a positive electrode active material layer disposed on the current collector 10. The conductivity of the positive electrode active material is usually worse than that of the negative electrode active material, and the active ion diffusion coefficient of the positive electrode active material tends to decrease significantly with decreasing temperature. This has a significant impact on the low-temperature performance of the battery. Therefore, using a current collector 10 in the positive electrode plate significantly improves the low-temperature performance of the battery. The particle size of the positive electrode active material is larger than that of the conductive material described above, and it has a high degree of compatibility with the concave low-binder region 22 described above, making it easier to satisfy the aforementioned conditions (a), (b), and (c).

[0055] In the case of lithium batteries, the positive electrode active material may include, but is not limited to, one or more of the following: lithium-containing phosphates (such as lithium iron phosphate (LFP) and lithium iron manganese phosphate (LMFP)); single oxides of lithium (such as lithium cobaltate, lithium nickelate, and lithium manganate); binary oxides of lithium (such as lithium nickel manganese oxide, lithium nickel cobalt oxide, and lithium cobalt manganese oxide); ternary oxides of lithium (such as lithium nickel cobalt manganese oxide ternary material and lithium nickel cobalt aluminum oxide ternary material); and polyelemental oxides of lithium.

[0056] One embodiment of this application further provides a secondary battery. The secondary battery includes the electrode plates described above in the embodiment of this application. The positive electrode and / or negative electrode of the secondary battery may be electrode plates.

[0057] A secondary battery can be a liquid battery, a solid battery, or a semi-solid battery. In the case of a liquid battery, where the electrolyte is liquid, a secondary battery typically includes a positive electrode, a negative electrode, a separator and electrolyte placed between the positive and negative electrodes. The separator is used to separate the positive electrode from the negative electrode in order to maintain insulation between the positive and negative electrodes. The separator, positive electrode plate, and negative electrode plate together form a battery cell of the secondary battery, and the battery cell is housed in a battery housing.

[0058] In this embodiment of the present application, the secondary battery is a lithium secondary battery, a sodium secondary battery, a potassium secondary battery, a zinc secondary battery, etc. In some implementations, the secondary battery is a lithium secondary battery. Furthermore, the positive electrode of the lithium secondary battery is a positive electrode plate prepared using the current collector 10 described above in the embodiment of the present application. In this way, the low-temperature performance of the battery is more significantly improved.

[0059] As shown in Figure 5, one embodiment of the present application further provides a power consumption device, the power consumption device being equipped with a secondary battery according to the embodiment of the present application. The power consumption device may be a means of transport such as a vehicle or ship, or it may be a 3C product, etc.

[0060] The technical solutions of this application are described further below in relation to several specific embodiments.

[0061] Example 1 A method for preparing a current collector used in a positive electrode plate includes the following steps:

[0062] A conductive slurry was obtained by dispersing a conductive material (specifically, nanoconductive carbon black with an average particle size d of 35 nm) and a binder (specifically, a polyacrylic acid aqueous binder) in deionized water at a mass ratio of 1:1.5. The conductive slurry was coated onto both sides of an aluminum foil and fired to form a conductive coating, obtaining a current collector designated F1. The slurry coating area, coating rate, slurry composition, etc., were controlled to adjust the distribution location and area of ​​each concave low-binder region, as well as the thickness of the high-density conductive material region.

[0063] In the current collector F1 prepared in Example 1, the conductive coating includes a high-density conductive material region and a plurality of recessed low-binder regions (see the circular dotted frame in Figure 2) spaced apart within the high-density conductive material region, each recessed low-binder region being free of conductive carbon black and binder. The average area S of the plurality of recessed low-binder regions is equal to the particle size D of the positive electrode active material. 50 The total coverage of the multiple concave low-binder regions on the aluminum foil surface is 58%, which is smaller than the corresponding projected area. In addition, the thickness distribution range of the high-density conductive material region is 1 μm to 2 μm, and the average thickness h1 of the high-density conductive material region is 1.5 μm.

[0064] Preparation methods for lithium-ion batteries include the following:

[0065] (1) Prepare the positive electrode plate: (Specifically, particle size D 10 The particle size is 0.1 μm, and the particle size D 50 The particle size is 0.5 μm, and the particle size D 90A positive electrode active material (which was lithium iron phosphate coated with a 4 μm carbon material), a conductive agent (specifically conductive carbon black with an average particle size d of 40 nm), and a binder (specifically PVDF) were mixed in solvent NMP in a mass ratio of 100:2:3 and uniformly stirred to obtain a positive electrode slurry. The positive electrode slurry was then coated onto the aforementioned current collector F1, and a positive electrode plate was obtained via firing and rolling. A positive electrode active material layer was formed on both sides of the current collector F1, and the relevant particle size parameters of the positive electrode active material matched those of the conductive coating on the current collector F1.

[0066] (2) Preparation of the negative electrode plate: The negative electrode active material (specifically, graphite), the conductive agent (specifically, conductive carbon black), and the binder (specifically, SBR) were dispersed in deionized water in a mass ratio of 100:2:3 and uniformly stirred to obtain a negative electrode slurry. The negative electrode slurry was coated onto both sides of a copper foil, and the negative electrode plate was obtained by firing and rolling.

[0067] (3) Battery assembly: In an argon-filled glove box, the positive electrode plate, separator, and negative electrode plate were stacked to obtain a battery cell. The stacked battery cell was then rolled up and placed in an aluminum-plastic film, and the electrolyte was injected. After formation and degassing, the battery cell was subjected to secondary packaging and capacity grading to obtain a softpack lithium battery with a design capacity of 1600mAh, indicated as C1.

[0068] Example 2 The main difference between Example 2 and Example 1 is that when the current collector used for the positive electrode plate was prepared, the conductive materials used were specifically nanoconductive carbon black (with the same average particle size as in Example 1) and a small number of layers of graphene (with a length of approximately 1 μm and a thickness of less than 10 nm). The mass ratio of graphene to carbon black was 1:40, which corresponds to the particle size D of the positive electrode active material. 10 Particle size D 90The ratio was equal to . When a conductive coating with a concave low-binder region was formed, first a first slurry containing a few layers of graphene and a binder was coated onto aluminum foil, and then a second slurry containing highly conductive carbon black and a binder was coated onto the region. The coating material for the concave region was a few layers of graphene.

[0069] The current collector prepared in Example 2 was designated F2. The current collector F2 of Example 2 was used to prepare the positive electrode plate according to the method described in Example 1, and the soft pack battery C2 was obtained through assembly.

[0070] On the conductive coating of the current collector F2, each concave low-binder region does not contain conductive carbon black, at least a portion of each concave low-binder region does not contain binder, and at least a portion of the concave low-binder regions contains a few layers of graphene. The two-dimensional planar structure of graphene, which has ultra-high conductivity, enables electron transmission without interfaces at the micron level, and as a result, the minimum thickness of the concave low-binder regions and the amount of unnecessary interfaces between aluminum foils are greatly reduced. In addition, on a single-surface conductive coating, the total coverage of multiple concave low-binder regions on the surface of the aluminum foil is in the range of 33% to 70%. The thickness distribution range of the high-density conductive material regions is 0.2 μm to 1.8 μm, and the average thickness h1 of the high-density conductive material regions is 1 μm.

[0071] To highlight the beneficial effects of this application, this application further establishes the following Comparative Examples 1 and 2.

[0072] Comparative Example 1 Pure aluminum foil is used as the current collector DF1 for the positive electrode plate. The positive electrode plate was prepared according to the method described in Example 1, and the soft pack battery D1 was obtained through assembly.

[0073] Comparative Example 2 The main difference between Comparative Example 2 and Example 1 is that when the current collector used for the positive electrode plate was prepared, a conductive slurry containing conductive carbon black and binder was coated over the entire surface of the aluminum foil, and the resulting conductive coating did not have a concave low-binder region (as shown in Figure 3).

[0074] The aluminum foil with the conductive coating prepared in Comparative Example 2 is shown as DF2, and the thickness of the conductive coating on one surface was controlled to 1.5 ± 0.5 μm. The current collector DF2 from Comparative Example 2 was used to prepare the positive electrode plate according to the method described in Example 1, and the soft pack battery D2 was obtained through assembly.

[0075] To strongly support the beneficial effects brought about by the technical solution in the embodiments of this application, the aforementioned softpack battery was subjected to the following performance tests.

[0076] (1) Testing the DC internal resistance (DCIR) of batteries at different temperatures. At room temperature (25°C), the aforementioned softpack battery was discharged to 2.0V with a constant current of 1 / 3C, and then charged to 50% SOC with a constant current of 1 / 3C. The softpack battery was discharged separately for 30 seconds at 25°C and -10°C with a constant current of 1.5C, and the voltages before and after discharge were recorded. The discharge DCIR was calculated, where discharge DCIR(mΩ) = (voltage before discharge - voltage after discharge) / discharge current * 1000. The results are shown in Table 1 below.

[0077] (2) Test of battery discharge capacity at low temperatures The initial discharge capacity of each softpack battery after formation was shown as C0. The softpack batteries were fully charged at 25°C with a constant current and voltage of 1 / 3C0, where the constant voltage cutoff current was 0.05C0. Next, the softpack batteries were discharged to 2.0V at -10°C with a constant current of 1 / 3C, and the discharge capacity was shown as C1. The retention rate of discharge capacity at -10°C and 1 / 3C was calculated as C1 / C0 * 100%. The results are shown in Table 2.

[0078] (3) Test of DC internal resistance analysis of batteries The aforementioned softpack batteries were maintained at 50% SOC, and electrochemical resistance spectroscopy and discharge DCIR tests were performed, involving discharging at a constant current of 0.1C for 30 seconds. Test temperatures were 25°C and -10°C. Ω , R c , R sei , R ct , and R d The time constant of the polarization response was obtained via resistance spectroscopy, and the corresponding value between time and DCIR obtained during a 30-second discharge at a constant current of 0.1C was obtained. Finally, the polarization internal resistance was isolated based on the time constant, and the DC internal resistance analysis results for the batteries were obtained. Figure 4 summarizes the DC internal resistance analysis results obtained when the batteries of Example 1, as well as Comparative Examples 1 and 2, were discharged separately at 25°C (a) and -10°C (b) at a constant current of 0.1C for 30 seconds. Table 3 below lists the resistance values ​​of the batteries at 25°C and -10°C. [Table 1] [Table 2] [Table 3]

[0079] The positive electrode current collector of Comparative Example 1 is aluminum foil without a conductive coating on its surface, while the surface of the positive electrode current collector of Comparative Example 2 is uniformly and completely covered with a conductive coating containing highly conductive nanocarbon black. From Figure 4 and Table 3, the battery of Comparative Example 2 has an ohmic resistance R Ω The contact resistance R is not reduced. c It can be seen that this differs from battery D1 of Comparative Example 1 in that only the ohmic resistance R is reduced. In Example 1, where the conductive coating of the positive electrode current collector has a concave low binder region, the ohmic resistance R of the battery is reduced. Ω The contact resistance R is reduced compared to that of Comparative Example 2. c This is further reduced compared to that of Comparative Example 2, and as a result, RSEI +R ct , especially R at -10℃ SEI +R ct This is significantly reduced. This is because the use of the positive electrode current collector in the embodiments of this application leads to a simultaneous reduction in the ohmic resistance and contact resistance of the battery, resulting in an excessively small sum of the battery's polarization internal resistance at both room temperature and low temperatures. In particular, the low-temperature internal resistance is reduced (see Tables 1 and 3), leading to an improved discharge capacity of the battery at low temperatures (see Table 2).

[0080] The embodiments described above are merely some implementations of the present application, and while their descriptions are specific and detailed, they should not be understood as limitations on the scope of the patent in this application. Those skilled in the art should note that several modifications and improvements can be made without departing from the concepts of this application, and such modifications and improvements will fall within the scope of protection of this application.

Claims

1. Foil (1) and, A conductive coating (2), wherein the conductive coating (2) is disposed on both sides of the foil (1), A current collector (10) for supporting an electrode active material, wherein the conductive coating (2) is A high-density conductive material region (21), wherein the high-density conductive material region (21) includes a conductive material and a binder, and the conductive material includes a granular conductive agent, A plurality of concave low-binder regions (22), wherein the plurality of concave low-binder regions (22) are spaced apart within the high-density conductive material region (21), and at least a portion of each of the plurality of concave low-binder regions (22) does not contain the binder, and at least a portion of each of the plurality of concave low-binder regions (22) does not contain the granular conductive agent, A current collector (10) is provided.

2. The current collector (10) is subject to the following conditions: (a) The average area S of the plurality of concave low binder regions (22) is equal to the particle size D of the electrode active material. ５０ It is smaller than the corresponding projected area, and (b) The average particle size d of the granular conductive agent is equal to the particle size D of the electrode active material. １０ Less than 1 / 2 One or more of the following conditions must be met: D １０ and D ５０ However, these represent the particle sizes corresponding to the point when the cumulative distribution rate of the particle amount of the electrode active material reaches 10% and 50%, respectively. The current collector (10) according to claim 1.

3. The average thickness h of the high-density region of the conductive material １ However, D ５０ / 2 ≤ h １ ≤ D ９０ Satisfying / 2, D ９０ represents the particle size corresponding to the case where the cumulative distribution rate of the amount of the electrode active material particles reaches 90%, The current collector (10) according to claim 1 or 2.

4. h １ The current collector (10) according to claim 3, wherein the diameter is in the range of 0.2 μm to 2 μm.

5. The current collector (10) according to any one of claims 1 to 4, wherein the diameter d of the granular conductive agent is 20 nm to 100 nm.

6. The current collector (10) according to any one of claims 1 to 5, wherein on one side of the foil (1), the total coverage of the plurality of concave low binder regions (22) on the surface of the foil (1) is in the range of 33% to 70%.

7. The current collector (10) according to any one of claims 1 to 6, wherein the work function of the conductive coating (2) is between the work function of the foil (1) and the work function of the electrode active material.

8. The current collector (10) according to any one of claims 1 to 7, wherein the granular conductive agent is one or more of carbon black, conductive carbon spheres, and metal carbide particles.

9. The current collector (10) according to any one of claims 1 to 8, wherein the conductive material further comprises a sheet-like conductive agent, and at least some concave low-binder regions (22) comprise the sheet-like conductive agent, and the thickness of the sheet-like conductive agent is smaller than the diameter of the granular conductive agent.

10. The current collector (10) according to claim 9, wherein when the conductive material includes the sheet-like conductive agent, each of the plurality of concave low-binder regions (22) includes the sheet-like conductive agent.

11. The current collector (10) according to claim 9 or 10, wherein the mass of the sheet-like conductive agent is 0.01 to 0.1 times the mass of the granular conductive agent.

12. The current collector (10) according to any one of claims 9 to 11, wherein the sheet-like conductive agent is one or more of graphene, conductive carbon nitride, maxine nanosheets, and metal carbide nanosheets.

13. The current collector (10) according to any one of claims 9 to 12, wherein the mass ratio of the sheet-like conductive agent in the conductive material is in the range of 0.1% to 9%, and the mass ratio of the granular conductive agent in the conductive material is in the range of 91% to 99.9%.

14. The current collector (10) according to any one of claims 1 to 13, wherein the binder comprises one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin (such as polyethylene, polypropylene, and polystyrene), sodium carboxymethylcellulose (CMC), sodium alginate, etc.

15. An electrode plate comprising a current collector (10) according to any one of claims 1 to 14 and an electrode active material layer disposed on the current collector (10).

16. A secondary battery, wherein the secondary battery comprises the electrode plate described in claim 15.

17. A power consumption device, wherein the power consumption device comprises the secondary battery described in claim 16.

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