Positive electrode sheet, secondary battery, and electric device

Abstract

Provided in the present application are a positive electrode sheet, a secondary battery, and an electric device. The positive electrode sheet of the present application facilitates the preparation of low-cost secondary batteries. The secondary battery has a relatively low Hi-pot defect rate and relatively low direct-current internal resistance, and also has an excellent high-temperature capacity retention rate and high-temperature capacity recovery rate.

Description

Positive electrode plate, secondary battery and electrical device

[0001] Cross-referencing

[0002] This application incorporates Chinese Patent Application No. 202410968894.7, filed on July 18, 2024, entitled "Positive Electrode, Secondary Battery and Electrical Device", which is incorporated herein by reference in its entirety. Technical Field

[0003] This application relates to the field of secondary battery technology and secondary battery recycling technology, and in particular to a positive electrode sheet, a secondary battery, and an electrical device. Background Technology

[0004] Energy and the environment have become increasingly important issues. Since China's new energy vehicle production began to ramp up in 2015, sales have continued to climb, reaching 6.887 million units in 2022. This rapid growth in new energy vehicles has led to a wave of retired power batteries, creating an urgent need for battery recycling. Furthermore, constrained by upstream raw material resources, rising raw material prices have driven up recycling costs, making battery recycling even more pressing.

[0005] Currently, there are two main types of recycling technologies for spent lithium-ion batteries: chemical recycling and physical recycling. Chemical recycling involves solvent extraction and high-temperature smelting to recover the cathode material. However, chemical recycling technology is relatively complex, requires significant capital expenditure, and involves the addition of strong acids, strong alkalis, and large amounts of ammonia during the production process. Improper handling can pollute the air, water, and soil. Physical recycling primarily utilizes magnetic separation and sieving technologies to separate and purify the cathode material. It allows for fully automated, pollution-free dismantling and is economically viable, especially when lithium carbonate prices are low, making the recycling of lithium iron phosphate materials less economical. However, the cathode material recovered using this method has a high impurity content, such as Al, Cu, Zn, and Cr.

[0006] Therefore, it is urgent to develop new technologies for the reuse of low-cost secondary batteries. Summary of the Invention

[0007] This application addresses the aforementioned issues and aims to resolve at least one of the technical problems existing in the prior art. To this end, this application provides a positive electrode, a secondary battery, and an electrical device. The positive electrode of this application facilitates the fabrication of low-cost secondary batteries, which exhibit a low Hi-pot defect rate and DC internal resistance, while also demonstrating good high-temperature capacity retention and recovery rates. The positive electrode and secondary battery of this application open new avenues for developing low-cost secondary battery reuse technologies.

[0008] The first aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a first positive electrode active material and a second positive electrode active material. The difference between the first positive electrode active material and the second positive electrode active material is that the first positive electrode active material includes current collector particles containing a metal component suitable for the positive current collector. The content of the current collector particles is less than or equal to 5000 ppm and greater than 0 ppm based on the total mass of the first positive electrode active material. The mass ratio of the first positive electrode active material to the second positive electrode active material is (1-10):1.

[0009] One of the key limiting factors preventing the use of physically recovered positive electrode active materials in new battery fabrication is that the recycled material often contains current collector debris. This debris is similar in size to the active particles and is difficult to remove completely through particle size screening. Therefore, it remains in the recycled active material, affecting the performance of the electrode sheets prepared after reuse. For example, aluminum particles in the current collector can puncture the separator between the two electrodes, causing a short circuit, poor high-pot performance, and severely impacting battery performance. The current collector may also contain metallic impurities such as copper and zinc. When the voltage during battery formation reaches the redox potential of these impurities, these metals will first oxidize at the positive electrode and then reduce at the negative electrode. When the metal elemental deposits accumulate to a certain level at the negative electrode, the hard edges of the deposited metal can puncture the separator, fatally impacting the lithium-ion battery and even causing an explosion.

[0010] The positive electrode sheet of this application mixes a first positive electrode material containing current collector particles and a second positive electrode active material that does not contain current collector particles. Furthermore, the content of current collector particles in the first positive electrode active material and the mass ratio of the first to second positive electrode active materials are controlled. This reasonable combination dilutes the content of current collector particles in the positive electrode active material, significantly reducing the risk of the separator being punctured. The secondary battery prepared from this positive electrode sheet not only minimizes manufacturing costs but also exhibits good electrical performance. Specifically, the resulting low-cost secondary battery combines a low Hi-pot defect rate and DC internal resistance with good high-temperature capacity retention and high-temperature capacity recovery.

[0011] In any embodiment, the content of current collector particles is less than or equal to 3000 ppm based on the total mass of the first positive electrode active material.

[0012] In the recycling process of the positive electrode sheet, the recycled positive electrode active material, namely the first positive electrode active material of this application, inevitably contains current collector particles. When the content of residual current collector particles in the recycled positive electrode active material is reduced, it helps to further reduce the risk of current collector particles puncturing the separator, thereby helping to further reduce the DC internal resistance of the secondary battery.

[0013] In any embodiment, the mass ratio of the first positive electrode active material to the second positive electrode active material is (1-5):1.

[0014] Further controlling the mass ratio of the first positive electrode active material to the second positive electrode active material helps to further balance the manufacturing cost and electrical performance of the secondary battery.

[0015] In any implementation, the maximum side length of the current collector particles is ≤50μm.

[0016] In any implementation, the maximum side length of the current collector particles is ≤30μm.

[0017] Reasonably controlling the maximum side length of the current collector particles helps reduce the risk of them puncturing the separator membrane. Furthermore, when the maximum side length of the current collector particles is less than or equal to 30 μm, it helps to further reduce the risk of puncturing the separator membrane, thereby further reducing the DC internal resistance of the secondary battery.

[0018] In any embodiment, the metal component suitable for the positive electrode current collector refers to a metal component that will not be oxidized at the positive electrode when the potential is >2.0V, and the temperature conditions include at least one temperature between 20°C and 30°C.

[0019] In any embodiment, the metal component suitable for the positive electrode current collector includes at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0020] In the recycling process of the positive electrode sheet, the recycled positive electrode active material, namely the first positive electrode active material of this application, will inevitably be mixed with current collector particles. These current collector particles will inevitably contain metal components suitable for positive electrode current collectors. These metal components may originate from the current collectors or positive electrode active material recycled from the positive electrode sheet. They are suitable for positive electrode current collectors and will not be oxidized at the positive electrode when the potential is >2.0V, which is beneficial for further maintaining the electrical performance of the secondary battery.

[0021] In any embodiment, the first positive electrode active material includes at least one of lithium phosphate, lithium transition metal oxide, a modified form of lithium phosphate, and a modified form of lithium transition metal oxide. Optionally, the first positive electrode active material includes a material with the molecular formula Li. m1 B1 a1 Fe x1 D1d1 P y1 E1 e1 O z1 G1 g1 The material, B1 includes at least one of Al, Na, K or Mg; D1 includes at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti or V; E1 includes at least one element of B, S, Si or N; G1 includes at least one element of S, F, Cl or Br; 0.5≤m1≤1.15, 0≤a1≤0.1, 0.95≤x1≤1, 0≤d1≤0.1, 0.95≤y1≤1, 0≤e1≤0.1, 3.5≤z1≤4, 0≤g1≤0.1; and / or,

[0022] The second positive electrode active material includes at least one of lithium phosphate, lithium transition metal oxide, modified form of lithium phosphate, and modified form of lithium transition metal oxide. Optionally, the second positive electrode active material includes a material with the molecular formula Li. m2 B2 a2 Fe x D2 d2 P y E2 e2 O z G2 g2 The material, B2 includes at least one of Al, Na, K or Mg, D2 includes at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti or V, E2 includes at least one of B, S, Si or N, G2 includes at least one of S, F, Cl or Br, 0.5≤m2≤1.15, 0≤a2≤0.1, 0.95≤x2≤1, 0≤d2≤0.1, 0.95≤y2≤1, 0≤e2≤0.1, 3.5≤z2≤4, 0≤g2≤0.1.

[0023] A second aspect of this application provides a secondary battery, which includes a negative electrode, a separator, and a positive electrode as described in this application.

[0024] The secondary battery of this application has a low Hi-pot defect rate and DC internal resistance, while also exhibiting good high-temperature capacity retention and high-temperature capacity recovery, opening up new avenues for the development of low-cost secondary battery reuse technology.

[0025] In any embodiment, the separator includes a porous substrate and a coating disposed on at least one surface of the porous substrate, the coating including fillers, elastic particles and binders.

[0026] Adding fillers and elastic particles to the coating of the separator can improve the separator's ability to block current collector particles, thereby further reducing the risk of them puncturing the separator. This is beneficial for further reducing the high-pot defect rate and DC internal resistance of the secondary battery, and further improving the high-temperature capacity retention rate and high-temperature capacity recovery rate of the secondary battery.

[0027] In any embodiment, the separator includes a porous substrate and a coating disposed on at least one surface of the porous substrate, the coating including fillers, linear flocculants and binders.

[0028] Adding fillers and linear flocculants to the coating of the separator can provide support for the coating. Simultaneously, the mechanical strength of the fillers and linear flocculants, along with the linear flocculent morphology, helps improve the separator's ability to block current collector particles, thereby further reducing the risk of current collector puncture and contributing to a further reduction in the high-pot defect rate of the secondary battery.

[0029] In any embodiment, the mass ratio of filler, elastic particles, linear flocculants and binder is (86-40):(30-8):(20-4):(10-2).

[0030] In any embodiment, the mass ratio of filler, elastic particles, linear flocculants and binder is (75-65):(20-10):(15-10):(8-2).

[0031] Reasonable control of the mass ratio of each component in the separator helps to improve the separator's compressive elastic modulus, mechanical strength, and DC resistance, further enhancing the separator's ability to block current collector particles, thereby reducing the risk of current collector puncture. This, in turn, helps to further reduce the high-pot defect rate and DC internal resistance of the secondary battery, and improve the secondary battery's specific capacity, high-temperature capacity retention rate, and high-temperature capacity recovery rate.

[0032] In any embodiment, the compressive elastic modulus of the elastic particles is 150-1200 MPa.

[0033] In any embodiment, the compressive elastic modulus of the elastic particles is 200-400 MPa.

[0034] Controlling the compressive elastic modulus of the elastic particles within a suitable range helps to further control the compressive elastic modulus of the separator within a suitable range, thereby helping to further improve the separator's blocking effect on the current collector particles, reduce the high-pot defect rate and DC internal resistance of the secondary battery, and improve its high-temperature capacity retention rate and high-temperature capacity recovery rate.

[0035] In any implementation, the Dv50 value of the elastic particles is greater than or equal to 7.5 μm and less than or equal to 15 μm.

[0036] In any implementation, the Dv50 value of the elastic particles is greater than or equal to 8 μm and less than or equal to 12 μm.

[0037] The Dv50 value of the elastic particles is greater than or equal to 7.5μm, and further greater than or equal to 8μm. This is beneficial for the elastic particles to better exert their physical barrier function, reduce the risk of current collector particles puncturing the separator, thereby helping to reduce the DC internal resistance of the secondary battery and improve the high-temperature capacity retention rate and high-temperature capacity recovery rate of the secondary battery.

[0038] In any implementation, the elastic particles are soft secondary aggregates.

[0039] When the elastic particles are soft secondary aggregates, they can better block the current collector particles and reduce the risk of them puncturing the separator membrane.

[0040] In any embodiment, the elastic particle comprises at least one of the following: copolymers of acrylate monomer units and styrene monomer units; copolymers of acrylate monomer units and styrene monomer units; copolymers of acrylate monomer units, acrylate monomer units, styrene monomer units, styrene monomer units, unsaturated nitrile monomer units; copolymers of styrene monomer units, olefin monomer units, and unsaturated nitrile monomer units; copolymers of acrylate monomer units, styrene monomer units, and unsaturated nitrile monomer units; copolymers of styrene monomer units, acetate monomer units; copolymers of styrene monomer units, acetate monomer units, and pyrrolidone monomer units; copolymers of fluorinated olefin monomer units; copolymers of fluorinated olefin monomer units, acrylate monomer units, diamine monomer units, dianhydride monomer units; copolymers of polyol monomer units, polyacid monomer units; and modified compounds of copolymers.

[0041] In any embodiment, the elastic particles include butyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate copolymer, isooctyl methacrylate-styrene copolymer, methacrylate-methacrylate-styrene copolymer, methyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, styrene-acrylonitrile copolymer, etc. Polymers, styrene-butadiene-acrylonitrile copolymers, methyl acrylate-styrene-acrylonitrile copolymers, isooctyl methacrylate-styrene-acrylonitrile copolymers, styrene-vinyl acetate copolymers, styrene-vinyl acetate-pyrrolidone copolymers, vinylidene fluoride-trifluoroethylene copolymers, vinylidene fluoride-hexafluoropropylene copolymers, vinylidene fluoride-trifluoroethylene-hexafluoropropylene copolymers, vinylidene fluoride-trifluoroethylene-acrylic acid copolymers, vinylidene fluoride-trifluoroethylene-acrylate copolymers, polyimide, polyethylene terephthalate, and at least one of the copolymer-modifying compounds.

[0042] The copolymers described above have suitable compressive modulus and Dv50, which can better enhance the barrier function of the separator against current collector particles, reduce the risk of them puncturing the separator, reduce the high-pot failure rate and DC internal resistance of the secondary battery, and improve its high-temperature capacity retention rate and high-temperature capacity recovery rate.

[0043] In any embodiment, the linear flocculent includes at least one of cellulose nanofibers, silver nanowires, boron carbide nanowires, copper hydroxide nanowires, aramid nanofibers, silica nanowires, or hydroxyapatite nanowires.

[0044] Nanocellulose, silver nanowires, boron carbide nanowires, copper hydroxide nanowires, aramid nanofibers, silica nanowires, or hydroxyapatite nanowires possess good toughness and mechanical strength, enabling them to better support the coating and thus better fulfill the barrier function of the separator membrane against current collector particles, reducing the risk of them puncturing the separator membrane.

[0045] In any embodiment, the filler includes at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, polystyrene, polyacrylic wax, or a modified thereof.

[0046] The above-mentioned fillers have good heat resistance, wetting properties, and CV oxidation resistance, which are beneficial to improving the thermal safety performance of the battery and reducing the high-pot defect rate of the battery.

[0047] In any embodiment, the separator membrane satisfies at least one of the following conditions (1) to (2):

[0048] (1) The thickness of the isolation membrane is greater than or equal to 4 μm;

[0049] (2) The puncture strength of the isolation membrane is greater than or equal to 400gf.

[0050] When the separator meets one of the above conditions, it can better block the current collector particles, reduce the risk of being punctured by the current collector particles, and thus improve the electrical performance of low-cost secondary batteries.

[0051] A third aspect of this application provides an electrical device, which includes a positive electrode as described in this application or a secondary battery as described in this application.

[0052] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0053] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0054] Figure 1 is a schematic diagram of the structure of the positive electrode sheet according to an embodiment of this application.

[0055] Figure 2 is a schematic diagram of the structure of the isolation membrane according to an embodiment of this application.

[0056] Figure 3 is a schematic diagram of a secondary battery according to an embodiment of this application.

[0057] Figure 4 is an exploded view of the secondary battery according to one embodiment of this application, as shown in Figure 3.

[0058] Figure 5 is a schematic diagram of a battery module according to one embodiment of this application.

[0059] Figure 6 is a schematic diagram of a battery pack according to one embodiment of this application.

[0060] Figure 7 is an exploded view of the battery pack of one embodiment of this application shown in Figure 6.

[0061] Figure 8 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0062] Explanation of reference numerals in the attached drawings: 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover; 61 Positive current collector; 62 Positive electrode film; 63 Current collector particles; 64 Positive electrode active material; 71 Elastic particles; 72 Filler; 73 Linear flocculent material; 74 Porous substrate; 75 Current collector particles. Detailed Implementation

[0063] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack, and electrical device of this application. 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 for the purpose of enabling 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 method may also include step (c), indicating 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] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0069] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0070] Currently, the rapid growth of new energy vehicles is leading to a wave of retired power batteries, creating an urgent need for power battery recycling. Furthermore, constrained by upstream raw material resources, the continuous rise in raw material prices is driving up recycling prices, making battery recycling even more pressing.

[0071] Currently, there are two main technologies for recycling spent lithium-ion batteries: chemical recycling and physical recycling. Chemical recycling involves solvent extraction and high-temperature melting to recover the cathode material. However, chemical recycling technology is relatively complex, requires significant capital expenditure, and involves the addition of strong acids, strong alkalis, and large amounts of ammonia during the production process. Improper handling can pollute the air, water, and soil. Physical recycling primarily utilizes magnetic separation and sieving techniques to separate and purify the cathode material. It allows for fully automated, pollution-free dismantling and is economically viable, especially when lithium carbonate prices are low, making the recycling of lithium iron phosphate materials less economical. However, the cathode material recovered using this method has a high impurity content, and the cathode sheets produced from it cannot meet the normal operating requirements of lithium-ion batteries. Specifically, the cathode active material recovered using physical methods often contains current collector particles that are similar in size to the cathode active material and are difficult to completely remove through particle size screening. The positive electrode sheet prepared using the recycled positive electrode active material contains current collector particles and debris, which can easily puncture the separator, thus affecting the electrical and safety performance of the battery. For example, it can easily cause problems such as poor Hi-pot performance, increased DC internal resistance, reduced high-temperature capacity retention rate, reduced high-temperature capacity recovery rate, and reduced specific capacity.

[0072] [Positive electrode plate]

[0073] The first aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a first positive electrode active material and a second positive electrode active material. The difference between the first positive electrode active material and the second positive electrode active material is that the first positive electrode active material includes current collector particles containing a metal component suitable for the positive current collector. The content of the current collector particles is less than or equal to 5000 ppm and greater than 0 ppm based on the total mass of the first positive electrode active material. The mass ratio of the first positive electrode active material to the second positive electrode active material is (1-10):1.

[0074] In this paper, the term "current collector particles" refers to current collector particles containing a metal composition suitable for positive electrode current collectors.

[0075] The content of current collector particles in the first positive electrode active material can be measured using methods and equipment known in the art. For example, the first positive electrode active material can be digested with aqua regia, and the content of current collector particles in the first positive electrode active material can be tested using an inductively coupled plasma optical emission spectrometer (ICAP7400). Specific measurements can be performed according to YS / T1028.5-2015 and the instrument's instruction manual. The current collector particles are composed of metallic elements.

[0076] In some implementations, the current collector particles are positive electrode current collector particles.

[0077] In some embodiments, the first positive electrode active material is prepared by recycling from a secondary battery, specifically by recycling the positive electrode sheet.

[0078] In some embodiments, the first positive electrode active material is obtained by physically recovering the positive electrode sheet. Specifically, the recycled secondary battery cell is heat-treated to remove the electrolyte, and the positive and negative electrode sheets of the secondary battery are separated to obtain the positive electrode sheet. The recovered positive electrode sheet is crushed to obtain positive electrode recovery particles, which are then sieved for the first time. The sieved positive electrode recovery particles are then calcined to remove volatiles, crushed, demagnetized, and sieved a second time. Solids of the target particle size are collected to obtain the first positive electrode active material. The first positive electrode active material contains positive electrode current collector particles.

[0079] In some implementations, the second positive electrode active material does not contain current collector particles.

[0080] In some embodiments, the first positive electrode active material and the second positive electrode active material are formed in the form of a mixture to form the positive electrode active material.

[0081] In some embodiments, as shown in Figure 1, the positive electrode of this application includes a positive current collector 61 and a positive electrode film layer 62 located on at least one side of the positive current collector 61. The positive electrode film layer 62 includes a positive active material 64 and current collector particles 63.

[0082] One of the key limiting factors preventing the use of physically recovered positive electrode active materials in new battery fabrication is that the recovered materials inevitably contain current collector debris. This debris is similar in size to the active particles and is difficult to remove completely through particle size analysis. Therefore, it remains in the recovered active material, affecting the performance of the electrode sheets prepared after reuse. For example, aluminum particles in the current collector can puncture the separator between the two electrodes, causing a short circuit, poor high-pot performance, and severely impacting battery performance. The current collector may also contain metallic impurities such as copper and zinc. When the voltage during battery formation reaches the redox potential of these impurities, they will first oxidize at the positive electrode and then reduce at the negative electrode. When the metal elemental deposits accumulate to a certain level at the negative electrode, the hard edges of the deposited metal can puncture the separator, fatally impacting the lithium-ion battery and even causing an explosion.

[0083] The positive electrode sheet of this application mixes a first positive electrode material containing current collector particles obtained from recycling with a second positive electrode active material that does not contain current collector particles. Furthermore, the content of current collector particles in the first positive electrode active material and the mass ratio of the first to second positive electrode active materials are controlled. This reasonable combination dilutes the content of current collector particles in the positive electrode active material, significantly reducing the risk of the separator being punctured. The secondary battery prepared from this positive electrode sheet not only minimizes manufacturing costs but also exhibits good electrical performance. Specifically, the resulting low-cost secondary battery combines a low Hi-pot defect rate and DC internal resistance with good high-temperature capacity retention and high-temperature capacity recovery.

[0084] In some embodiments, the content of current collector particles is less than or equal to 3000 ppm based on the total mass of the first positive electrode active material.

[0085] In some embodiments, the content of current collector particles, based on the total mass of the first positive electrode active material, is less than or equal to 4700 ppm, less than or equal to 4500 ppm, less than or equal to 4300 ppm, less than or equal to 4000 ppm, less than or equal to 3700 ppm, less than or equal to 3500 ppm, less than or equal to 3000 ppm, less than or equal to 2700 ppm, less than or equal to 2500 ppm, less than or equal to 2000 ppm, less than or equal to 1500 ppm, or less than or equal to any two of the above-mentioned current collector particle contents.

[0086] In the recycling process of the positive electrode sheet, the recycled positive electrode active material, namely the first positive electrode active material of this application, inevitably contains current collector particles. When the content of residual current collector particles in the recycled positive electrode active material is reduced, it helps to further reduce the risk of current collector particles puncturing the separator, thereby helping to further reduce the DC internal resistance of the secondary battery.

[0087] In some embodiments, the mass ratio of the first positive electrode active material to the second positive electrode active material is (1-5):1.

[0088] In some embodiments, the mass ratio of the first positive electrode active material to the second positive electrode active material is 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, or a value within the range of any two of the above mass ratios.

[0089] Further controlling the mass ratio of the first positive electrode active material to the second positive electrode active material helps to further balance the manufacturing cost and electrical performance of the secondary battery.

[0090] In some implementations, the maximum side length of the current collector particles is ≤50μm.

[0091] In some implementations, the maximum side length of the current collector particles is ≤30μm.

[0092] The maximum side length of the current collector particles can be measured using methods and equipment known in the art. For example, a battery can be disassembled to obtain the positive electrode sheet. An argon ion beam can be used to cut the positive electrode sheet perpendicularly to expose the cross-section. The cross-section can be photographed using a scanning electron microscope. The longest diameter of the current collector particles can be statistically analyzed using the length-diameter statistical method to obtain the longest side length of the current collector particles.

[0093] In some embodiments, the maximum side length of the current collector particle is less than or equal to 48 μm, less than or equal to 46 μm, less than or equal to 44 μm, less than or equal to 42 μm, less than or equal to 40 μm, less than or equal to 38 μm, less than or equal to 36 μm, less than or equal to 34 μm, less than or equal to 32 μm, less than or equal to 30 μm, less than or equal to 28 μm, less than or equal to 26 μm, less than or equal to 24 μm, less than or equal to 22 μm, less than or equal to 20 μm, or less than or equal to a value within the range of any two of the above maximum side lengths.

[0094] Reasonably controlling the maximum side length of the current collector particles helps reduce the risk of them puncturing the separator membrane. Furthermore, when the maximum side length of the current collector particles is less than or equal to 30 μm, it helps to further reduce the risk of puncturing the separator membrane, thereby further reducing the DC internal resistance of the secondary battery.

[0095] In some embodiments, the metal composition suitable for the positive current collector refers to a metal composition that will not be oxidized at the positive electrode when the potential is >2.0V, and the temperature conditions include at least one temperature between 20°C and 30°C.

[0096] In some implementations, determining whether a metal component is "suitable for the positive electrode current collector" can be done as follows: a metal component whose intercalation potential of the active ion is higher than that of the negative electrode active material is considered "suitable for the positive electrode current collector". Taking lithium ions as the active ion and graphite as the negative electrode active material as an example, the lithium intercalation potential of graphite negative electrode material is typically 0.01V to 0.2V.

[0097] In some embodiments, the temperature conditions include 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, or values ​​within a range of any two of the above temperatures.

[0098] In some implementations, the current collector particles are composed of a metallic component suitable for positive electrode current collectors.

[0099] In some embodiments, the metal composition suitable for the positive current collector includes at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0100] In some embodiments, the metal composition suitable for the positive current collector includes at least one of aluminum and aluminum alloys.

[0101] In some embodiments, the aluminum contained in the current collector particles may originate from the aluminum foil current collector of the positive electrode sheet to be recycled. During the recycling process, the surface of the aluminum foil may undergo an oxidation reaction to form aluminum oxide compounds.

[0102] In the recycling process of the positive electrode sheet, the recycled positive electrode active material, namely the first positive electrode active material of this application, will inevitably be mixed with current collector particles. These current collector particles will inevitably contain metal components suitable for positive electrode current collectors. These metal components may originate from the current collectors or positive electrode active material recycled from the positive electrode sheet. They are suitable for positive electrode current collectors and will not be oxidized at the positive electrode when the potential is >2.0V, which is beneficial for further maintaining the electrical performance of the secondary battery.

[0103] In some embodiments, the first positive electrode active material includes at least one of lithium phosphate, lithium transition metal oxide, modified form of lithium phosphate, and modified form of lithium transition metal oxide.

[0104] In some embodiments, the first positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium nickel phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt manganese aluminum oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, and modified forms of any of the foregoing substances.

[0105] In some implementations, the first positive electrode active material includes lithium iron phosphate.

[0106] In some embodiments, the modification includes one or more of doping modification and coating modification. Both doping modification and coating modification can be carried out using or refer to existing modification methods in the art, including but not limited to the selection of element types and doping amounts.

[0107] In some embodiments, the first positive electrode active material includes Li m1 B1 a1 Fe x1 D1 d1 P y1 E1 e1 O z1 G1 g1The material, B1 includes at least one of Al, Na, K or Mg, D1 includes at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti or V, E1 includes at least one element of B, S, Si or N, G1 includes at least one element of S, F, Cl or Br, 0.95≤m1≤1.15, 0≤a1≤0.1, 0.95≤x1≤1, 0≤d1≤0.1, 0.95≤y1≤1, 0≤e1≤0.1, 3.5≤z1≤4, 0≤g1≤0.1.

[0108] In some implementations, m1 can be 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.97, 1.02, 1.04, 1.06, 1.08, 1.1, 1.12, 1.14, or any value within the range of any two of the above m1 values.

[0109] In some implementations, a1 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a value within the range of any two values ​​of a1 mentioned above.

[0110] In some implementations, x1 can be 0.95, 0.96, 0.97, 0.98, 0.99, 1, or any value within the range of any two of the above x1 values.

[0111] In some implementations, d1 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a value within the range of any two of the above d1 values.

[0112] In some implementations, y1 can be 0.95, 0.96, 0.97, 0.98, 0.99, 1, or any value within the range of any two of the above y1 values.

[0113] In some implementations, e1 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a value within the range of any two of the above e1 values.

[0114] In some implementations, z1 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, or any value within the range of any two z1 values ​​mentioned above.

[0115] In some implementations, g1 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a value within any two of the above-mentioned ranges of g1.

[0116] In some embodiments, the second positive electrode active material includes at least one of lithium phosphate, lithium transition metal oxide, modified form of lithium phosphate, and modified form of lithium transition metal oxide.

[0117] In some embodiments, the second positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium nickel phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt manganese aluminum oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, and modified forms of any of the foregoing substances.

[0118] In some implementations, the second positive electrode active material includes lithium iron phosphate.

[0119] In some embodiments, the second positive electrode active material includes Li m2 B2 a2 Fe x D2 d2 P y E2 e2 O z G2 g2 The material, B2 includes at least one of Al, Na, K or Mg, D2 includes at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti or V, E2 includes at least one of B, S, Si or N, G2 includes at least one of S, F, Cl or Br, 0.5≤m2≤1.15, 0≤a2≤0.1, 0.95≤x2≤1, 0≤d2≤0.1, 0.95≤y2≤1, 0≤e2≤0.1, 3.5≤z2≤4, 0≤g2≤0.1.

[0120] In some implementations, m2 can be 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.97, 1.02, 1.04, 1.06, 1.08, 1.1, 1.12, 1.14, or any value within the range of any two of the above m2 values.

[0121] In some implementations, a2 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a value within the range of any two of the above a2 values.

[0122] In some implementations, x2 can be 0.95, 0.96, 0.97, 0.98, 0.99, 1, or any value within the range of any two x2 values ​​mentioned above.

[0123] In some implementations, d2 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a value within the range of any two of the above d2 values.

[0124] In some implementations, y2 can be 0.95, 0.96, 0.97, 0.98, 0.99, 1, or any value within the range of any two of the above y2 values.

[0125] In some implementations, e2 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value within the range of any two of the above e2 values.

[0126] In some implementations, z2 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, or any value within the range of any two z2 values ​​mentioned above.

[0127] In some implementations, g2 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value within the range of any two values ​​of g2 mentioned above.

[0128] In some embodiments, the positive electrode sheet of this application includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, a binder, and a conductive agent. The positive electrode active material is the positive electrode active material of this application or the positive electrode active material prepared by the preparation method of this application.

[0129] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0130] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0131] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0132] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0133] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0134] In some embodiments, the method for preparing the positive electrode sheet of this application includes the following steps:

[0135] The first positive electrode active material of this application is obtained by recycling secondary batteries;

[0136] The positive electrode active material of this application is obtained by mixing the first positive active material and the second positive electrode active material of this application;

[0137] The positive electrode active material, conductive agent, binder and any other components of this application are dispersed in a solvent to form a positive electrode slurry;

[0138] The positive electrode slurry of this application is coated onto the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet of this application can be obtained.

[0139] [Rechargeable Battery]

[0140] A second aspect of this application provides a secondary battery, which includes a negative electrode, a separator, and a positive electrode as described in this application.

[0141] The secondary battery of this application has a low Hi-pot defect rate and DC internal resistance, while also exhibiting good high-temperature capacity retention and high-temperature capacity recovery, opening up new avenues for the development of low-cost secondary battery reuse technology.

[0142] In some embodiments, as shown in Figure 2, the isolation membrane of this application includes a porous substrate 74 and a coating disposed on at least one surface of the porous substrate 74, the coating including filler 72, elastic particles 71, current collector particles 75 and adhesive.

[0143] In some embodiments, the porous substrate includes a substrate with good chemical and mechanical stability.

[0144] In some embodiments, the porous substrate includes, but is not limited to, at least one of porous glass fiber, porous nonwoven fabric, or porous polyolefin-based resin membrane. In some embodiments, the porous polyolefin-based resin membrane includes at least one of polyethylene, polypropylene, or polyvinylidene fluoride.

[0145] In some embodiments, the porous substrate can be a single-layer film or a multi-layer composite film. When the porous substrate is a multi-layer composite film, the materials of each layer can be the same or different.

[0146] In some embodiments, the binder includes at least one of allyl polyether sulfate monomer polymer, acrylic monomer polymer, methacrylic monomer polymer, acrylamide monomer polymer, methyl acrylate monomer polymer, butyl acrylate monomer polymer, ethyl acrylate monomer polymer, glycidyl methacrylate monomer polymer, polyvinyl alcohol monomer polymer, acrylonitrile monomer polymer, hydroxyethyl acrylate monomer polymer, styrene monomer polymer, acetoxyethyl methacrylate monomer polymer, vinyltrimethoxysilane monomer polymer, lithium acrylate monomer polymer, and lithium methacrylate monomer polymer.

[0147] In some embodiments, the polymer includes at least one of homopolymers and copolymers.

[0148] In this text, the term "copolymer" refers to a polymer formed by the polymerization reaction of two or more monomers.

[0149] In this article, the term "homogeneous polymer" refers to a polymer formed by the polymerization of a single monomer.

[0150] In some embodiments, the binder comprises a copolymer of at least two monomers selected from allyl polyether sulfate monomer, acrylic monomer, methacrylic monomer, acrylamide monomer, methyl acrylate monomer, butyl acrylate monomer, ethyl acrylate monomer, glycidyl methacrylate monomer, polyvinyl alcohol monomer, acrylonitrile monomer, hydroxyethyl acrylate monomer, styrene monomer, acetoxyethyl methacrylate monomer, vinyltrimethoxysilane monomer, lithium acrylate monomer, and lithium methacrylate monomer.

[0151] In some embodiments, the binder includes at least one of polyacrylate, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene co-vinyl acetate, polystyrene-co-methyl methacrylate, polystyrene-co-butyl acrylate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile-styrene-butadiene copolymer, or polyimide.

[0152] In some embodiments, the adhesive includes polyacrylate.

[0153] In some embodiments, the separator includes a porous substrate and coatings disposed on two surfaces of the porous substrate.

[0154] Adding fillers and elastic particles to the coating of the separator can improve the separator's ability to block current collector particles, thereby further reducing the risk of them puncturing the separator. This is beneficial for further reducing the high-pot defect rate and DC internal resistance of the secondary battery, and further improving the high-temperature capacity retention rate and high-temperature capacity recovery rate of the secondary battery.

[0155] In some embodiments, as shown in Figure 2, the isolation membrane of this application includes a porous substrate 74 and a coating disposed on at least one surface of the porous substrate 74. The coating includes filler 72, linear flocculents 73, current collector particles 75, and binder.

[0156] In this paper, the term "linear flocculent" refers to materials with an aspect ratio greater than 5.

[0157] Adding fillers and linear flocculants to the coating of the separator can provide support for the coating. Simultaneously, the mechanical strength of the fillers and linear flocculants, along with the linear flocculent morphology, helps improve the separator's ability to block current collector particles, thereby further reducing the risk of current collector puncture and contributing to a further reduction in the high-pot defect rate of the secondary battery.

[0158] In some embodiments, the mass ratio of filler, elastic particles, linear flocculants and binder is (86-40):(30-8):(20-4):(10-2).

[0159] In some embodiments, the mass ratio of filler, elastic particles, linear flocculants and binder is (75-65):(20-10):(15-10):(8-2).

[0160] In some embodiments, the mass ratio of filler, elastic particles, linear flocculants and binder is (75-65):(20-10):(18-11):(5-1).

[0161] In some embodiments, the mass ratio of filler, elastic particles, linear flocculants and binder can be (86, 85, 80, 75, 70, 65, 60, 55, 50, 45 or 40): (30, 28, 26, 24, 22, 20, 18, 16, 14, 12, 10 or 8): (20, 18, 16, 14, 12, 10, 8, 6 or 4): (10, 9, 8, 7, 6, 5, 4, 3, 2, 1).

[0162] In some embodiments, the mass ratio of filler, elastic particles, linear flocculants and binder can be 70:15:10:5, 86:8:4:2 or 40:30:20:10.

[0163] Reasonable control of the mass ratio of each component in the separator helps to improve the separator's compressive elastic modulus, mechanical strength, and DC resistance, further enhancing the separator's ability to block current collector particles, thereby reducing the risk of current collector puncture. This, in turn, helps to further reduce the high-pot defect rate and DC internal resistance of the secondary battery, and improve the secondary battery's specific capacity, high-temperature capacity retention rate, and high-temperature capacity recovery rate.

[0164] In some implementations, the compressive elastic modulus of the elastic particles is 150-1200 MPa.

[0165] In some implementations, the compressive elastic modulus of the elastic particles is 200-400 MPa.

[0166] In this document, the term "compressive modulus" is a physical quantity that describes the elasticity of a material. In some embodiments, the compressive modulus is expressed as the bulk modulus, and where it is unlikely to cause confusion, the compressive modulus in this application may also refer to Young's modulus.

[0167] The compressive modulus of elastic particles can be measured using methods and equipment known in the art. For example, sample pretreatment: elastic particles are coated onto a substrate to form a release liner; the release liner is then punched with a die in the following order: die / white paper / release liner / white paper / pressing block, 5 layers punched at a time, 100 layers per group, 3 parallel groups made, sample size 60*70mm; aluminum-plastic film is punched with a guillotine cutter to a size of 90*200mm; the aluminum-plastic film is folded in half along its length; the punched release liner sample is fixed to the center of its four sides with green adhesive and placed in a Pocket bag; a top-side sealing machine is used to seal the two long sides of the sample, then the top is vacuum-sealed, with the sealing machine heated to 185℃; a pad is placed at the center of the sealed sample, and a frame is marked; the thickness of the release liner within the marked positions is measured with a micrometer, 4 points on the long side and 3 points on the short side; sample testing: the in-situ expansion testing system IEST is activated. SWE2110, open the MISS operating software, pressure calibration; select compression test (transient), thickness calibration; place the sample in the upper and lower clamps, move the upper clamp to ensure it is in the position marked on the sample frame; click MISS software to start the experiment. After the test, measure the sample thickness M1; mark the clamp indentation positions on the upper and lower sides of the sample with a marker; repeat steps 2-3 and test again; data processing: stress = pressure * 10 / clamp area; deformation = initial thickness (M1) - real-time thickness; strain = deformation / initial thickness; plot the stress-strain curve with strain as the abscissa and stress as the ordinate; linearly fit the stress / strain curve at 3-5 MPa to obtain the compressive elastic modulus of the elastic particles.

[0168] In some embodiments, the compressive elastic modulus of the elastic particles can be 150 MPa, 210 MPa, 200 MPa, 250 MPa, 270 MPa, 300 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, 550 MPa, 600 MPa, 650 MPa, 700 MPa, 750 MPa, 800 MPa, 850 MPa, 900 MPa, 950 MPa, 1000 MPa, 1050 MPa, 1100 MPa, 1150 MPa, or 12000 MPa, or a range of any two of the above compressive elastic moduli, or a value within such a range.

[0169] Controlling the compressive elastic modulus of the elastic particles within a suitable range helps to further control the compressive elastic modulus of the separator within a suitable range, thereby helping to further improve the separator's blocking effect on the current collector particles, reduce the high-pot defect rate and DC internal resistance of the secondary battery, and improve its high-temperature capacity retention rate and high-temperature capacity recovery rate.

[0170] In some implementations, the Dv50 value of the elastic particles is greater than or equal to 7.5 μm and less than or equal to 15 μm.

[0171] In some implementations, the Dv50 value of the elastic particles is greater than or equal to 8 μm and less than or equal to 12 μm.

[0172] In this paper, the term "Dv50" refers to the particle size at which the cumulative volumetric particle size distribution percentage in an elastic particle reaches 50%.

[0173] The Dv50 of elastic particles can be measured using methods and equipment known in the art. For example, the Dv50 value of elastic particles can be determined using a laser particle size analyzer (Malvern Master Size 3000) with reference to GB / T19077.1-2016.

[0174] In some embodiments, the Dv50 value of the elastic particles can be 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, or a value within the range of any two of the above Dv50 values.

[0175] The Dv50 value of the elastic particles is greater than or equal to 7.5μm, and further greater than or equal to 8μm. This is beneficial for the elastic particles to better exert their physical barrier function, reduce the risk of current collector particles puncturing the separator, thereby helping to reduce the DC internal resistance of the secondary battery and improve the high-temperature capacity retention rate and high-temperature capacity recovery rate of the secondary battery.

[0176] In some implementations, the elastic particles are soft secondary aggregates.

[0177] In some implementations, the elastic particles can be soft primary particles.

[0178] In this paper, the term "soft secondary agglomerate" refers to an agglomerate formed by the stacking of primary particles.

[0179] In this paper, the term "soft primary particle" refers to a single particle unit.

[0180] The morphology of elastic particles can be measured using methods and equipment known in the art. For example, scanning electron microscopy (SEM) can be used to test the morphology of elastic particles.

[0181] When the elastic particles are soft secondary aggregates, they can better block the current collector particles and reduce the risk of them puncturing the separator membrane.

[0182] In some embodiments, the elastic particles include at least one of the following: copolymers of acrylate monomer units and styrene monomer units; copolymers of acrylate monomer units and styrene monomer units; copolymers of acrylate monomer units, acrylate monomer units, and styrene monomer units; copolymers of styrene monomer units and unsaturated nitrile monomer units; copolymers of styrene monomer units and olefin monomer units and unsaturated nitrile monomer units; copolymers of acrylate monomer units and styrene monomer units and unsaturated nitrile monomer units; copolymers of styrene monomer units and acetate monomer units; copolymers of styrene monomer units and acetate monomer units and pyrrolidone monomer units; copolymers of fluorinated olefin monomer units; copolymers of fluorinated olefin monomer units and acrylate monomer units; copolymers of fluorinated olefin monomer units and acrylate monomer units; copolymers of diamine monomer units and dianhydride monomer units; copolymers of polyol monomer units and polyacid monomer units; and modified compounds of said copolymers.

[0183] In this article, the term "modified compound" refers to a substance formed by further modifying the original molecule through various means, such as physical or chemical means, to change a certain physical or chemical property.

[0184] In some embodiments, the copolymerization molar ratio of acrylate monomers to styrene monomers in the copolymerization unit is (9-1):(1-3). In some embodiments, the copolymerization molar ratio of acrylate monomers to styrene monomers in the copolymerization unit can be 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:2.5, 1:3, or a range of any two of the above copolymerization molar ratios, or a value within that range.

[0185] In some embodiments, the copolymer of acrylic monomer units and styrene monomer units has a copolymer molar ratio of acrylic monomer units to styrene monomer units of (9-3):1. In some embodiments, the copolymer molar ratio of acrylic monomer units and styrene monomer units in the copolymer of acrylic monomer units and styrene monomer units can be 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, or a range of any two of the above copolymer molar ratios, or a value within that range.

[0186] In some embodiments, the copolymer of acrylic monomer units, acrylate monomer units, and styrene monomer units has a copolymer molar ratio of acrylic monomer units to acrylate monomer units of (5-15):(0.5-5):(1-10). In some embodiments, the copolymer molar ratio of acrylic monomer units to acrylate monomer units in the copolymer of acrylic monomer units, acrylate monomer units, and styrene monomer units can be 5:1:2, 10:3:7, 13:4:8, or a range of any two of the above copolymer molar ratios, or a value within that range.

[0187] In some embodiments, the copolymerization molar ratio of styrene monomer units to unsaturated nitrile monomer units in the copolymerization of styrene monomer units and unsaturated nitrile monomer units is (1-5):(5-1). In some embodiments, the copolymerization molar ratio of styrene monomer units to unsaturated nitrile monomer units in the copolymerization of styrene monomer units and unsaturated nitrile monomer units can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:5, 2:4, 2:3, 2:2, 2:1, 3:5, 3:4, 3:2, 3:1, 4:5, 4:3, 4:1, 5:4, 5:3, 5:2, 5:1, or a range of any two of the above copolymerization molar ratios, or a value within that range.

[0188] In some embodiments, the copolymer of styrene-olefin-unsaturated nitrile monomer units has a copolymer molar ratio of styrene monomer units, olefin monomer units, and unsaturated nitrile monomer units of (20-30):(60-80):(3:7). In some embodiments, the copolymer molar ratio of styrene monomer units, olefin monomer units, and unsaturated nitrile monomer units can be 25:70:5, 22:67:4, 28:75:6, or a range of any two of the above copolymer molar ratios, or a value within that range.

[0189] In some embodiments, the copolymer of acrylate monomer units, styrene monomer units, and unsaturated nitrile monomer units has a copolymer molar ratio of acrylate monomer units, styrene monomer units, and unsaturated nitrile monomer units of (25-50):(57-77):(4-12). In some embodiments, the copolymer molar ratio of acrylate monomer units, styrene monomer units, and unsaturated nitrile monomer units can be 35:67:8, 30:63:6, 45:72:10, or a range of any two of the above copolymer molar ratios, or a value within that range.

[0190] In some embodiments, the copolymerization molar ratio of styrene monomer units to acetate monomer units in the styrene monomer unit-acetate monomer unit copolymer is (10-30):(60-100). In some embodiments, the copolymerization molar ratio of styrene monomer units to acetate monomer units in the styrene monomer unit-acetate monomer unit copolymer can be 20:80, 15:75, 25:90, or a range of any two of the above copolymerization molar ratios, or a value within that range.

[0191] In some embodiments, the copolymerization molar ratio of styrene monomer units, acetate monomer units, and pyrrolidone monomer units in the styrene monomer unit-acetate monomer unit-pyrrolidone monomer unit copolymer is (10-30):(65-85):(2-7). In some embodiments, the copolymerization molar ratio of styrene monomer units, acetate monomer units, and pyrrolidone monomer units in the styrene monomer unit-acetate monomer unit-pyrrolidone monomer unit copolymer can be 20:75:5, 15:70:3, 25:80:6, or a range of any two of the above copolymerization molar ratios, or a value within that range.

[0192] In some embodiments, the copolymer molar ratio of the fluorinated olefin monomer unit to the acrylic monomer unit in the fluorinated olefin monomer unit-acrylic monomer unit copolymer is (99.9-95):(0.1-5). In some embodiments, the copolymer molar ratio of the fluorinated olefin monomer unit to the acrylic monomer unit in the fluorinated olefin monomer unit-acrylic monomer unit copolymer can be 99.9:0.1, 98.5:1.5, 95:5, or a range of any two of the above copolymer molar ratios, or a value within that range.

[0193] In some embodiments, the copolymer molar ratio of fluorinated olefin monomer units to acrylate monomer units in the fluorinated olefin monomer unit-acrylate monomer unit copolymer is (99.9-95):(0.1-5). In some embodiments, the copolymer molar ratio of fluorinated olefin monomer units to acrylate monomer units in the fluorinated olefin monomer unit-acrylate monomer unit copolymer can be 99.9:0.1, 98.5:1.5, 95:5, or a range of any two of the above copolymer molar ratios, or a value within that range.

[0194] In some embodiments, the copolymer molar ratio of diamine monomer units to dianhydride monomer units in the diamine monomer unit-dianhydride monomer unit copolymer is (20-80):(80-20). In some embodiments, the copolymer molar ratio of diamine monomer units to dianhydride monomer units in the diamine monomer unit-dianhydride monomer unit copolymer can be 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, or a range of any two of the above copolymer molar ratios, or a value within that range.

[0195] In some embodiments, the copolymer molar ratio of polyol monomer units to polyacid monomer units in the polyol monomer unit-polyacid monomer unit copolymer is (10-90):(90-10). In some embodiments, the copolymer molar ratio of polyol monomer units to polyacid monomer units in the polyol monomer unit-polyacid monomer unit copolymer can be 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, or a range of any two of the above copolymer molar ratios, or a value within that range.

[0196] In some embodiments, the elastic particles include butyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate copolymer, isooctyl methacrylate-styrene copolymer, methacrylate-methacrylate-styrene copolymer, methyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, and styrene-acrylonitrile copolymer. The copolymers include styrene-butadiene-acrylonitrile copolymers, methyl acrylate-styrene-acrylonitrile copolymers, isooctyl methacrylate-styrene-acrylonitrile copolymers, styrene-vinyl acetate copolymers, styrene-vinyl acetate-pyrrolidone copolymers, vinylidene fluoride-trifluoroethylene copolymers, vinylidene fluoride-hexafluoropropylene copolymers, vinylidene fluoride-trifluoroethylene-hexafluoropropylene copolymers, vinylidene fluoride-trifluoroethylene-acrylic acid copolymers, vinylidene fluoride-trifluoroethylene-acrylate copolymers, polyimide, polyethylene terephthalate, and at least one of the following modified compounds of the copolymers.

[0197] The copolymers described above have suitable compressive modulus and Dv50, which can better enhance the barrier function of the separator against current collector particles, reduce the risk of them puncturing the separator, reduce the high-pot failure rate and DC internal resistance of the secondary battery, and improve its high-temperature capacity retention rate and high-temperature capacity recovery rate.

[0198] In some embodiments, the linear flocculent includes at least one of cellulose nanofibers, silver nanowires, boron carbide nanowires, copper hydroxide nanowires, aramid nanofibers, silica nanowires, or hydroxyapatite nanowires.

[0199] In some embodiments, the linear flocculents include nanocellulose.

[0200] Nanocellulose, silver nanowires, boron carbide nanowires, copper hydroxide nanowires, aramid nanofibers, silica nanowires, or hydroxyapatite nanowires possess good toughness and mechanical strength, enabling them to better support the coating and thus better fulfill the barrier function of the separator membrane against current collector particles, reducing the risk of them puncturing the separator membrane.

[0201] In some embodiments, the filler includes at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, polystyrene, polyacrylic wax, or a modified thereof.

[0202] In some embodiments, the filler includes at least one of boehmite, alumina, barium sulfate, magnesium oxide, silicon oxide, titanium oxide, zinc oxide, cerium oxide, barium titanate, or a modified thereof.

[0203] In some embodiments, the modifiers of the filler include chemical and / or physical modifications.

[0204] In some embodiments, chemical modification of the filler includes coupling agent modification (e.g., using silane coupling agents, titanate coupling agents, etc.), surfactant modification, or polymer grafting modification.

[0205] In some implementations, physical modification of the filler includes mechanical dispersion, ultrasonic dispersion, high-energy treatment, etc.

[0206] The above-mentioned fillers have good heat resistance, wetting properties, and CV oxidation resistance, which are beneficial to improving the thermal safety performance of the battery and reducing the high-pot defect rate of the battery.

[0207] In some embodiments, the separator membrane satisfies at least one of the following conditions (1) to (2):

[0208] (1) The thickness of the isolation membrane is greater than or equal to 4 μm;

[0209] (2) The puncture strength of the isolation membrane is greater than or equal to 400gf.

[0210] In some embodiments, the separator membrane satisfies at least one of the following conditions (a) to (g):

[0211] (a) The thickness of the isolation membrane is greater than or equal to 4 μm;

[0212] (b) The puncture strength of the separating membrane is greater than or equal to 400 gf;

[0213] (c) In the coating, the areal density of the filler on one side is greater than or equal to 1.0 g / m². 2 ;

[0214] (d) The elastic recovery rate of the porous substrate is greater than or equal to 30%;

[0215] (e) The specific surface area (BET) of the filler is less than or equal to 15 m². 2 / g;

[0216] (f) The voltage breakdown capability of the separator is greater than 1000V;

[0217] (g) The DC resistance of the isolation membrane is greater than 2 GΩ, and the test humidity is 45%.

[0218] In some implementations, the thickness of the separator is less than 16 μm.

[0219] In some embodiments, the thickness of the separator can be 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, or a range of any two of the above separator thicknesses, or a value within that range.

[0220] In some implementations, the BET of the filler can be 5m. 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g, or a value within the range of any two BET values ​​mentioned above.

[0221] In this application, the thickness of the separator can be measured using methods and equipment known in the art. For example, it can be measured using a micrometer.

[0222] In this application, the puncture strength of the release liner can be measured using methods and equipment known in the art. For example, it can be measured using a universal tensile testing machine. A specific example is as follows: Take a flat section of release liner as a sample, with dimensions greater than 80mm*80mm; install the testing instrument, adjust the distance between the upper and lower clamps, fix the instrument holding the release liner in the lower clamp, ensure the clamping directions of the two testing fixtures are the same, tighten the fixing screws, lay the sample flat on the testing fixture, and screw on the cap. After setting the parameters, click the testing interface, first click zeroing, and then click test; record the puncture strength data based on the test results.

[0223] When the separator meets one of the above conditions, it can better block the current collector particles, reduce the risk of being punctured by the current collector particles, and thus improve the electrical performance of low-cost secondary batteries.

[0224] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0225] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0226] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0227] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 shows a square-structured secondary battery 5 as an example.

[0228] In some embodiments, referring to FIG4, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0229] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0230] Figure 5 shows a battery module 4 as an example. Referring to Figure 5, in the battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, the multiple secondary batteries 5 can be fixed in place using fasteners.

[0231] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0232] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0233] Figures 6 and 7 illustrate a battery pack 1 as an example. Referring to Figures 6 and 7, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0234] [Negative electrode plate]

[0235] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0236] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0237] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0238] In some embodiments, the negative electrode active material may be a 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. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials 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.

[0239] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0240] In some embodiments, 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.

[0241] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0242] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0243] [Electrolytes]

[0244] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0245] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0246] In some embodiments, the electrolyte salt may be selected from 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.

[0247] In some embodiments, the solvent may be selected from 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.

[0248] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0249] [Electrical appliances]

[0250] A third aspect of this application provides an electrical device, which includes a positive electrode as described in this application or a secondary battery as described in this application.

[0251] In some embodiments, the electrical device of this application may further include at least one of a battery module or a battery pack. A secondary battery, battery module, or battery pack can be used as the power source for the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0252] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0253] Figure 8 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0254] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0255] Example

[0256] 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.

[0257] I. Preparation Method

[0258] Example 1

[0259] 1) Preparation of positive electrode active materials

[0260] Obtaining the positive electrode recovery sheet (using known types of positive electrode active materials (Li)) 1.02 Ti 0.01 Fe 0.99 (PO4) positive electrode sheet as recycling sheet): Disassemble the waste battery cell that has not been filled with liquid, separate the positive electrode sheet, negative electrode sheet and separator to obtain the positive electrode recycling sheet.

[0261] Preparation method of the first positive electrode active material (recycled positive electrode active material): The positive electrode sheet is crushed, and the sieved positive electrode recycled particles are calcined at 500-750℃ to remove volatiles. The calcined positive electrode recycled particles are then crushed (with an induced draft frequency of 50Hz). Z ), sieve (using a 150-mesh sieve) and demagnetize to obtain D v 50 is the first positive electrode active material with a thickness of 0.6μm-2.0μm.

[0262] The recovered first positive electrode active material was characterized, and the content of current collector particles and the maximum side length of current collector particles are shown in Table 1 below.

[0263] The first positive electrode active material and the second positive electrode active material (Li) are combined. 1.015 Ti 0.02 Fe 0.98 PO4) was mixed evenly according to the mass ratio in Table 1 to obtain the positive electrode active material.

[0264] 2) Preparation of positive electrode sheet

[0265] The above-mentioned positive electrode active material, conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) binder were mixed evenly at a mass ratio of 96:1.5:2.5. This mixture was then added to the solvent N-methylpyrrolidone and stirred until homogeneous. After stirring, the slurry viscosity was adjusted to 8000-20000 mPa·s to obtain the positive electrode slurry.

[0266] The positive electrode slurry is coated onto aluminum foil in one pass using a double-sided, double-cavity coating equipment. After double-sided coating, the foil undergoes drying, cold pressing, pre-slitting, die-cutting, slitting, and winding to obtain the positive electrode sheet. The coating surface density is 25.0 mg / cm³. 2 The compaction density of the positive electrode sheet is 2.35 g / cm³. 3 .

[0267] 3) Preparation of negative electrode sheet

[0268] Artificial graphite (anode active material), carbon black (conductive agent), carboxymethyl cellulose (thickener), and styrene-butadiene rubber (binder) were added to deionized water in a mass ratio of 95.5:1.0:1.5:2 and stirred evenly to obtain the anode slurry.

[0269] Then, the negative electrode slurry is coated onto the copper foil using a double-sided coating equipment. After double-sided coating, the copper foil undergoes drying, cold pressing, pre-slitting, die-cutting, slitting, and winding to obtain the negative electrode sheet, wherein the coating surface density is 11.0 mg / cm³. 2 The compaction density of the negative electrode sheet is 1.65 g / cm³. 3 .

[0270] 4) Preparation of the separating membrane

[0271] A porous substrate (polyethylene) was prepared, and linear flocculent nanocellulose was incorporated into the porous substrate. A layer of boehmite and alumina fillers was coated on the upper and lower surfaces of the porous substrate, followed by a layer of elastic particles (butyl acrylate-isooctyl acrylate-styrene copolymer), with a copolymer molar ratio of butyl acrylate, isooctyl acrylate, and styrene of 55:35:10. Polyacrylate was added as a binder. The various components of the coated intervertebral disc were fixed through surface adsorption and pore permeation. The mass ratios of the fillers, elastic particles, linear flocculents, and binder are shown in Table 1; the mass ratio of boehmite to alumina in the fillers was 1:1; the elastic particles were soft secondary aggregates; and the thickness of the separating membrane was 5 μm.

[0272] 5) Preparation of electrolyte

[0273] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and dimethyl carbonate (DMC) organic solvents were mixed evenly at a volume ratio of 1 / 1. Lithium salt LiPF6 was added and dissolved in the organic solvent. The concentration of LiPF6 in the solution was 1 mol / L. The mixture was stirred evenly to obtain the electrolyte.

[0274] 6) Battery manufacturing

[0275] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. Tabs are welded onto the bare cell, and the cell is placed in an aluminum casing and baked in a vacuum oven at 100°C for 8 hours. Electrolyte is then injected and the casing is sealed to obtain a non-charged battery. The non-charged battery is then subjected to a series of processes, including settling, hot and cold pressing, formation, shaping, and capacity testing, to obtain the lithium-ion battery of Example 1.

[0276] 7) Preparation of button cells

[0277] In a clean container, add 159g of N-methyl-2-pyrrolidone (NMP). Place the container containing the solvent on a mechanical stirrer and stir at 800 rpm. Weigh out 6g of polyvinylidene fluoride (PVDF) and 6g of SP. First, slowly add PVDF to the container and adjust the speed to 2000 rpm. After the PVDF is completely dissolved, reduce the speed to 800 rpm, add SP, and stir at 2000 rpm until the slurry is free of particles and smooth and bright. Remove the container, weigh it, and place it in a degassing machine for 16 minutes to obtain a spare solution. Weigh out 5.7g of the above solution, add 3.6g of positive electrode active material, cover the container, and place it in a stirrer. Set the stirring process: stir at 850 rpm for 60 seconds, then stir at 2000 rpm for 10-15 minutes to obtain the positive electrode slurry. Place the slurry in a clean and flat container. Ethanol was sprayed onto a glass plate, and a wrinkle-free aluminum foil (10μm thick) was attached to the surface. The glass plate was then placed on an automatic coating machine, clamped, and the name was written in the blank area. The positive electrode slurry was evenly spread on the front end of the aluminum foil. A doctor blade was placed at the front end of the positive electrode slurry and coated at 3cm / s, ensuring no air bubbles and a smooth surface to obtain the positive electrode membrane. The positive electrode membrane was allowed to air dry naturally for 1-2 minutes. Then, the coated positive electrode membrane, along with the glass plate, was placed in a 100℃ oven and dried for 2 hours. After drying, the positive electrode membrane was rolled into a positive electrode sheet, with the compaction controlled at 2.0-2.2g / cm³. 3 The positive electrode sheet is punched into 14mm small round pieces, at least 6 pieces, and then each piece is weighed and the weight is recorded. Four pieces are used for each sample. The weighed positive electrode sheets are placed in a -90kPa, 105℃ vacuum oven and baked for 6 hours. After baking, the positive electrode sheets are transferred to a glove box and then assembled in the order of lithium sheet, separator, and positive electrode sheet, while adding 10-15 drops of electrolyte. The assembly is then sealed at a pressure of 650kg / cm². 2 After assembling the button cell, let it stand for 3 hours to obtain the button cell of Example 1.

[0278] The battery in Example 2 is prepared in a similar way to that in Example 1, but the content of current collector particles and the maximum side length are different. The main difference is that the sieve used in the recovery process of the first positive electrode active material in Example 1 is changed from a 150-mesh sieve to a 100-mesh sieve, and the induced draft frequency of the crushing process is adjusted to 44Hz.

[0279] The batteries in Examples 3-4 were prepared using a similar method to those in Example 1, but the mass ratio of the first positive electrode active material to the second positive electrode active material was different, as shown in Table 1.

[0280] The battery in Example 5 was prepared in a similar manner to that in Example 1, but the type of separator used was different. The separator used in Example 5 was a conventional polypropylene microporous membrane, as shown in Table 1.

[0281] The batteries in Examples 6-9 were prepared using a method similar to that in Example 1, but the composition of the separator was different. Specifically, the separator in Example 6 did not include linear flocculents, and the mass of other components added was the same as in Example 1; the separator in Example 7 did not include elastic particles, and the mass of other components added was the same as in Example 1; the elastic particles in Example 8 were acrylic acid-styrene copolymers (the molar ratio of acrylic acid to styrene was 5:1), and the linear flocculents were silica nanowires; the elastic particles in Example 9 were methacrylate-methacrylate-styrene copolymers (the molar ratio of methacrylate, methacrylate, and styrene was 5:1:2), and the linear flocculents were boron carbide nanowires. Other specific conditions are shown in Table 1.

[0282] The batteries in Examples 10-11 were prepared using a similar method to those in Example 1, but the Dv50 values ​​of the elastic particles were different, as shown in Table 1.

[0283] The batteries in Examples 12-13 were prepared using a method similar to that in Example 1, but the proportions of the components in the separator were different, as shown in Table 1.

[0284] The battery of Comparative Example 1 is prepared in a similar manner to that of Example 1, but the positive electrode active material is entirely composed of the first positive electrode active material, and the separator is a polypropylene microporous membrane, as shown in Table 1.

[0285] The battery of Comparative Example 2 was prepared in a similar manner to that of Example 1, but the mass ratio of the first positive electrode active material to the second positive electrode active material was 12:1, as shown in Table 1.

[0286] The battery of Comparative Example 3 was prepared in a similar manner to that of Example 1, but the content of current collector particles and the maximum side length were different, as were the mass ratios of the first positive electrode active material and the second positive electrode active material, as shown in Table 1.

[0287] II. Testing of the first positive electrode active material, separator, and battery performance.

[0288] 1. Parameter testing of the first positive electrode active material

[0289] 1) Test of the content of current collector particles

[0290] The first positive electrode active material was digested with aqua regia. The content of current collector particles in the first positive electrode active material was tested by inductively coupled plasma atomic emission spectrometry (ICAP7400). For details, please refer to YS / T1028.5-2015 and measure according to the instrument manual. The current collector particles are composed of metal elements.

[0291] 2) Test of the longest side length of the current collector particle

[0292] The battery was disassembled to obtain the positive electrode plate. The positive electrode plate was cut open perpendicularly to the positive electrode plate using an argon ion beam to expose the cross-section. The cross-section was photographed using a scanning electron microscope. The longest diameter of the current collector particles was statistically analyzed using the length-diameter statistical method to obtain the longest side length of the current collector particles.

[0293] 2. Parameter testing of the separator membrane

[0294] 1) Dv50 value test of the first positive electrode active material and elastic particles

[0295] You can refer to GB / T19077.1-2016 and use a laser particle size analyzer (Malvern Master Size 3000) to test the Dv50 value of the first positive electrode active material and elastic particles.

[0296] 2) Test of compressive elastic modulus of elastic particles

[0297] Sample pretreatment:

[0298] The release liner is prepared by coating elastic particles onto a substrate. The release liner is then die-cut using a die, stacked in the following order: die / white paper / release liner / white paper / pressing block, with 5 layers cut at a time. 100 layers are considered a group, and 3 parallel samples are made, each 60*70mm in size. An aluminum-plastic film is then die-cut to a size of 90*200mm. The aluminum-plastic film is folded in half lengthwise. The die-cut release liner sample is fixed to the center of its four sides with green adhesive and placed in a Pocket bag. A top-side sealing machine is used to seal the two long sides of the sample, followed by vacuum sealing of the top. The sealing machine is heated to 185℃. A pad is placed at the center of the sealed sample, and a frame is marked. The thickness of the release liner within the marked positions is measured with a micrometer at 4 points on the long side and 3 points on the short side.

[0299] Sample testing:

[0300] 1. Turn on the IEST SWE2110 in-situ expansion testing system, open the MISS operating software, and perform pressure calibration; select compression test (transient), and thickness calibration; 2. Place the sample in the upper and lower clamps, and move the upper clamp to ensure it is in the position marked on the sample frame; 3. Click the MISS software to start the experiment. After the test is completed, measure the sample thickness M1; mark the clamp indentation positions on both sides of the sample with a marker; repeat steps 2-3 to test again.

[0301] Data processing:

[0302] Stress = Pressure * 10 / Fixture area; Deformation = Initial thickness (M1) - Real-time thickness; Strain = Deformation / Initial thickness; Plot a stress-strain curve with strain as the abscissa and stress as the ordinate; Linearly fit the stress / strain curve at 3-5 MPa to obtain the compressive modulus.

[0303] 3) Morphology determination of elastic particles

[0304] The morphology of the elastic particles was determined using scanning electron microscopy (SEM).

[0305] 4) Thickness test of the separator membrane

[0306] The thickness of the separator was tested using a 1 / 20,000 inch ruler.

[0307] 5) Puncture strength test of the isolation membrane

[0308] Sample preparation: Take a flat section of the isolation membrane as the sample, and the sample size should be greater than 80mm*80mm;

[0309] Test: Install the universal tensile testing instrument (Instron 34TM-5), adjust the distance between the upper and lower clamps, fix the instrument with the release diaphragm in the lower clamp, ensure that the clamping directions of the two testing fixtures are the same, tighten the fixing screws, lay the sample flat on the testing fixture, and screw on the cover.

[0310] Parameter settings: After setting the parameters, click on the test interface, first click "zero", and then click "test": Record the needle puncture intensity data according to the test results.

[0311] 3. Battery performance testing

[0312] 1) Capacity retention and capacity recovery rate tests

[0313] After the batteries of the examples and comparative examples were charged and discharged at 1C, the initial discharge capacity was recorded as C0. After being fully charged at 1C, they were placed in a constant temperature environment of 60°C for 60 days. The capacity after being discharged at 1C rate to the cutoff voltage of 2.0V was recorded as C1. Then, after being charged and discharged once at the cutoff voltage of 2.0V, the discharge capacity was recorded as C2. The capacity retention rate A1 = C1 / C0 × 100%, and the capacity recovery rate A2 = C2 / C0 × 100%.

[0314] 2) Hi-pot test

[0315] The batteries of the examples and comparative examples were subjected to 120V for 2 seconds. If the resistance was ≥20MΩ, the battery was considered to have a Hi-pot that met the requirements; otherwise, the Hi-pot was considered to be defective. 298 sets of parallel experiments were conducted for each set of examples and comparative examples.

[0316] 3) Gram capacity test

[0317] The coin cell was charged at a constant current of 0.1C for 9 hours, followed by constant voltage (3.75V) charging for 15 minutes. After resting for 5 minutes, it was discharged at a constant current of 0.1C for 9 hours. This cycle was repeated twice to obtain the cell's test capacity C. Specific capacity = capacity C / mass M of positive electrode active material.

[0318] 4) DCR test

[0319] The examples and comparative examples were discharged at 3C constant current to 90% SOC, and the OCV value at 90% SOC was recorded. Then, an HPPC-type pulse test regime was performed to obtain the charge / discharge DCR and power capability at 90% SOC. Next, they were discharged at 3C constant current to 50% SOC, and then an HPPC-type pulse test regime was performed to obtain the charge / discharge DCR and power capability at 50% SOC. Next, they were discharged at 3C constant current to 10% SOC, and then an HPPC-type pulse test regime was performed to obtain the charge / discharge DCR and power capability at 10% SOC. The DCR of the examples and comparative examples at 90%, 50%, and 10% SOC were obtained using the above method.

[0320] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0321] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The secondary battery parameters are shown in Table 1, and the performance test results are shown in Table 2.

[0322] Table 2 Performance Test Results

[0323] According to the results in the table above, it can be seen from Example 5 and Comparative Example 3 that, in the positive electrode sheet, controlling the content of current collector particles in the first positive electrode active material to be less than or equal to 5000 ppm is beneficial to reducing the Hi-pot defect rate and DC internal resistance of the secondary battery, and also improves the high-temperature capacity retention rate, high-temperature capacity recovery rate and specific capacity. It can also be seen from Example 5 and Comparative Examples 1-2 that, in the positive electrode sheet, controlling the mass ratio of the first positive electrode active material to the second positive electrode active material to be (1-10):1 is beneficial to reducing the Hi-pot defect rate and DC internal resistance of the secondary battery, and improving its specific capacity, high-temperature capacity retention rate and high-temperature capacity recovery rate.

[0324] As can be seen from Examples 1-2, further controlling the content and maximum side length of the current collector particles in the first positive electrode active material, for example, with a content of less than or equal to 3000 ppm and a maximum side length of less than or equal to 30 μm, is beneficial to further reduce the DC internal resistance of the secondary battery.

[0325] As can be seen from Examples 1 and 3-4, further controlling the mass ratio of the first positive electrode active material to the second positive electrode active material, for example, controlling it to (1-5):1, is beneficial to further improve the specific capacity, high-temperature capacity retention rate and high-temperature capacity recovery rate of the secondary battery, as well as reduce its DC internal resistance.

[0326] As can be seen from the comparison between Examples 1-4 and Examples 5, and Comparative Examples 1-3, the use of the separator of this application in the secondary battery is beneficial to further reduce the Hi-pot defect rate and DC internal resistance of the secondary battery, and improve the specific capacity, high-temperature capacity retention rate and high-temperature capacity recovery rate of the secondary battery.

[0327] As can be seen from Examples 3 and 7, adding elastic particles to the separator is beneficial to further reduce the Hi-pot defect rate and DC internal resistance of the secondary battery, and improve the high-temperature capacity retention rate and high-temperature capacity recovery rate of the secondary battery.

[0328] As can be seen from Examples 3 and 6, adding linear flocculents to the separator is beneficial to further reduce the Hi-pot defect rate of the secondary battery.

[0329] As can be seen from Examples 3 and 8-9, the separator of this application is suitable for different kinds of elastic particles and linear flocculents.

[0330] As shown in Examples 3 and 10-11, controlling the Dv50 value of the elastic particles to be greater than or equal to 7.5 μm is beneficial for further reducing the Hi-pot defect rate and DC internal resistance of the secondary battery, and improving the high-temperature capacity retention rate and high-temperature capacity recovery rate of the secondary battery. Further controlling the Dv50 value of the elastic particles to be greater than or equal to 8 μm is beneficial for further reducing the DC internal resistance of the secondary battery, and improving the high-temperature capacity retention rate and high-temperature capacity recovery rate of the secondary battery.

[0331] As can be seen from Examples 3 and 12-13, controlling the quality of fillers, elastic particles, linear flocculants and binders in the separator helps to further reduce the Hi-pot defect rate and DC internal resistance of the secondary battery.

[0332] It should be noted that this application is not limited to the above-described embodiments. 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, without departing from the spirit of this application, are also included in the scope of this application.

Claims

A positive electrode sheet, characterized in that, The positive electrode tab comprises a positive electrode current collector and a positive electrode film layer located on at least one side of the current collector, the positive electrode film layer comprising a positive electrode active material, the positive electrode active material comprising a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material is distinguished from the second positive electrode active material in that the first positive electrode active material comprises current collector particles containing a metal component suitable for a positive electrode current collector, the content of the current collector particles being less than or equal to 5000 ppm, greater than 0 ppm, based on the total mass of the first positive electrode active material, and the mass ratio of the first positive electrode active material to the second positive electrode active material is (1-10):

1. The positive electrode plate according to claim 1, wherein The content of the current collector particles is less than or equal to 3000 ppm, based on the total mass of the first positive electrode active material. The positive electrode plate according to claim 1 or 2, characterized by The mass ratio of the first positive electrode active material to the second positive electrode active material is (1-5):

1. The positive electrode plate according to any one of claims 1-3, characterized in that, The maximum side length of the current collector particles is ≤50 μm. The maximum side length of the current collector particles is ≤30 μm, according to any one of claims 1-4. The positive electrode plate according to any one of claims 1-5, characterized in that, The metal component suitable for a positive electrode current collector refers to a metal component that can not be oxidized at a positive electrode at an electric potential >2.0 V under a temperature condition comprising at least one temperature of 20-30 °C. The positive electrode plate according to any one of claims 1-6, characterized in that, The metal component suitable for a positive electrode current collector comprises at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. The positive electrode plate according to any one of claims 1-7, characterized in that, The first positive electrode active material includes at least one of lithium phosphates, lithium transition metal oxides, modified forms of the lithium phosphates, modified forms of the lithium transition metal oxides, and optionally, the first positive electrode active material includes a material of a molecular formula of Li m1 B1 a1 Fe x1 D1 d1 P y1 E1 e1 O z1 G1 g1 , B1 includes at least one of Al, Na, K, or Mg, D1 includes at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, or V, E1 includes at least one of B, S, Si, or N, G1 includes at least one of S, F, Cl, or Br, 0.5≤m1≤1.15, 0≤a1≤0.1, 0.95≤x1≤1, 0≤d1≤0.1, 0.95≤y1≤1, 0≤e1≤0.1, 3.5≤z1≤4, 0≤g1≤0.1; and / or, The second positive electrode active material includes at least one of lithium phosphates, lithium transition metal oxides, modified forms of the lithium phosphates, modified forms of the lithium transition metal oxides, and optionally, the second positive electrode active material includes a material of a molecular formula of Li m2 B2 a2 Fe x D2 d2 P y E2 e2 O z G2 g2 , B2 includes at least one of Al, Na, K, or Mg, D2 includes at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, or V, E2 includes at least one element of B, S, Si, or N, G2 includes at least one element of S, F, Cl, or Br, 0.5≤m2≤1.15, 0≤a2≤0.1, 0.95≤x2≤1, 0≤d2≤0.1, 0.95≤y2≤1, 0≤e2≤0.1, 3.5≤z2≤4, 0≤g2≤0.

1. A secondary battery characterized by The secondary battery comprises a negative electrode tab, a separator film, and the positive electrode tab according to any one of claims 1-8. The secondary battery according to claim 9, characterized by The separator film comprises a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprising a filler, an elastic particle, and a binder. The secondary battery according to claim 9 or 10, characterized in that The separator film comprises a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprising a filler, a linear flocculate, and a binder. The secondary battery according to claim 11, characterized in that The mass ratio of the filler, the elastic particle, the linear flocculate, and the binder is (86-40):(30-8):(20-4):(10-2). The secondary battery according to claim 11 or 12, characterized in that, The mass ratio of the filler, the elastic particle, the linear flocculate, and the binder is (75-65):(20-10):(15-10):(8-2). The secondary battery according to any one of claims 10 to 13, characterized in that, The compression elastic modulus of the elastic particle is 150-1200 MPa. The secondary battery according to any one of claims 10 to 14, characterized in that The compression elastic modulus of the elastic particle is 200-400 MPa. The secondary battery according to any one of claims 10 to 15, characterized in that, The Dv50 value of the elastic particle is greater than or equal to 7.5 μm and less than or equal to 15 μm. The secondary battery according to any one of claims 10 to 16, characterized in that The Dv50 value of the elastic particle is greater than or equal to 8 μm and less than or equal to 12 μm. The secondary battery according to any one of claims 10 to 17, characterized in that The elastic particle is a soft secondary agglomerate. The secondary battery according to any one of claims 10 to 18, characterized in that The elastic particles include at least one of an acrylate monomer unit-styrene monomer unit copolymer, an acrylic monomer unit-styrene monomer unit copolymer, an acrylate monomer unit copolymer, an acrylic monomer unit-acrylate monomer unit-styrene monomer unit copolymer, a styrene monomer unit-unsaturated nitrile monomer unit copolymer, a styrene monomer unit-olefin monomer unit-unsaturated nitrile monomer unit copolymer, an acrylate monomer unit-styrene monomer-unsaturated nitrile monomer unit copolymer, a styrene monomer unit-acetate monomer unit copolymer, a styrene monomer unit-acetate monomer unit-pyrrolidone monomer unit copolymer, a fluorine-containing olefin monomer unit copolymer, a fluorine-containing olefin monomer unit-acrylic monomer unit copolymer, a fluorine-containing olefin monomer unit-acrylate monomer unit copolymer, a diamine monomer unit-dianhydride monomer unit copolymer, a polyol monomer unit-polyacid monomer unit copolymer, and a modified compound of the copolymers. The secondary battery according to any one of claims 10 to 19, characterized in that The elastic particles include at least one of a butyl acrylate-styrene copolymer, a butyl methacrylate-isooctyl methacrylate copolymer, an isooctyl methacrylate-styrene copolymer, a methacrylate-methacrylic acid-styrene copolymer, a methyl acrylate-isooctyl methacrylate-styrene copolymer, a butyl acrylate-isooctyl acrylate-styrene copolymer, a butyl acrylate-isooctyl methacrylate-styrene copolymer, a butyl methacrylate-isooctyl methacrylate-styrene copolymer, a butyl methacrylate-isooctyl acrylate-styrene copolymer, a styrene-acrylonitrile copolymer, a styrene-butadiene-acrylonitrile copolymer, a methyl acrylate-styrene-acrylonitrile copolymer, an isooctyl methacrylate-styrene-acrylonitrile copolymer, a styrene-vinyl acetate copolymer, a styrene-vinyl acetate-pyrrolidone copolymer, a vinylidene fluoride-trifluoroethylene copolymer, a vinylidene fluoride-hexafluoropropylene copolymer, a vinylidene fluoride-trifluoroethylene-hexafluoropropylene copolymer, a vinylidene fluoride-trifluoroethylene-acrylic acid copolymer, a vinylidene fluoride-trifluoroethylene-acrylate copolymer, a polyimide, a polyethylene terephthalate, and a modified compound of the copolymers. The secondary battery according to any one of claims 11 to 20, characterized in that The linear flocculus includes at least one of nanocellulose, nanosilver wire, boron carbide nanowire, copper hydroxide nanowire, aramid nanofiber, silicon monoxide nanowire, or hydroxyapatite nanowire. The secondary battery according to any one of claims 10 to 21, characterized in that, The filler includes at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxide compound, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, polystyrene, polyacrylic acid wax, or a modified product thereof. The secondary battery according to any one of claims 9 to 22, characterized in that, The release film satisfies at least one of the following conditions (1) to (2): (1) The thickness of the release film is equal to or greater than 4 µm; (2) The puncture strength of the release film is equal to or greater than 400 gf. An electric power utilization device characterized by comprising: The power-using device includes the positive electrode plate according to any one of claims 1-8 or the secondary battery according to any one of claims 9-23.

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