Battery

Abstract

The invention provides a battery. Comprising a positive plate, a negative plate and a diaphragm, the positive plate and the negative plate are oppositely arranged, and the diaphragm is located between the positive plate and the negative plate; the positive plate comprises a positive current collector, and the negative plate comprises a negative current collector; the tensile strength E1 of the positive electrode current collector, the elongation B1 of the positive electrode current collector, the tensile strength E2 of the negative electrode current collector, the elongation B2 of the negative electrode current collector and the porosity C of the diaphragm meet the formula 1; and the positive electrode current collector and the negative electrode current collector in the battery are not easy to extend and break, so that the battery has excellent safety performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy, in particular to a battery. BACKGROUND

[0002] Since the commercialization of lithium ion batteries, they have been widely used in digital, energy storage, power, military aerospace and communication equipment fields due to their advantages of light weight, high specific energy, no memory effect and good cycle performance. With the wide application of lithium ion batteries, consumers have higher requirements for the energy density, cycle life, high temperature performance and safety performance of lithium ion batteries.

[0003] At present, the energy density of the battery is improved by increasing the compaction density and the area density of the pole piece to obtain more active substances on the current collector per unit volume. However, with the increase of the compaction density and the area density, the positive current collector and / or the negative current collector are prone to elongation, which leads to the corner cracking of the battery shell and is prone to breakage, thereby causing the short circuit of the battery. SUMMARY

[0004] The present application provides a battery which not only has excellent energy density, but also the positive current collector and the negative current collector in the battery are not prone to elongation and breakage, and has excellent safety performance.

[0005] The present application provides a battery, wherein the battery comprises a positive pole piece, a negative pole piece and a separator, the positive pole piece and the negative pole piece are oppositely arranged, and the separator is located between the positive pole piece and the negative pole piece.

[0006] The positive pole piece comprises a positive current collector, and the negative pole piece comprises a negative current collector.

[0007] The tensile strength E1 of the positive current collector, the elongation B1 of the positive current collector, the tensile strength E2 of the negative current collector, the elongation B2 of the negative current collector and the porosity C of the separator satisfy formula 1:

[0008]

[0009] The battery as described above, wherein 1.333≤E2 / E1≤5.833; and / or,

[0010] 0.33≤B2 / B1≤8; and / or,

[0011] and / or,

[0012] and / or,

[0013] 1.609≤ln(1+C)≤2.197.

[0014] The battery as described above, wherein the mass percentage content of Al in the positive current collector is ≥ 99%; and / or, 120 MPa ≤ E1 ≤ 300 MPa; and / or,

[0015] 1% ≤ B1 ≤ 6%.

[0016] The battery as described above, wherein the positive current collector further comprises Fe, Si, Cu, Ti, Mn;

[0017] The sum W of the mass percentage content of Fe in the positive current collector and the mass percentage content of Si in the positive current collector satisfies: 0.4% ≤ W ≤ 0.8%. Fe+Si The sum W of the mass percentage content of Fe in the positive current collector and the mass percentage content of Si in the positive current collector satisfies: 0.4% ≤ W ≤ 0.8%. Fe+Si The sum W of the mass percentage content of Fe in the positive current collector and the mass percentage content of Si in the positive current collector satisfies: 0.4% ≤ W ≤ 0.8%; and / or,

[0018] The mass percentage content of Cu in the positive current collector W satisfies: 0.01% ≤ W ≤ 0.19%. Cu The mass percentage content of Cu in the positive current collector W satisfies: 0.01% ≤ W ≤ 0.19%. Cu The mass percentage content of Cu in the positive current collector W satisfies: 0.01% ≤ W ≤ 0.19%; and / or,

[0019] The mass percentage content of Mn in the positive current collector W satisfies: 0.001% ≤ W ≤ 0.1%. Mn The mass percentage content of Mn in the positive current collector W satisfies: 0.001% ≤ W ≤ 0.1%. Mn The mass percentage content of Mn in the positive current collector W satisfies: 0.001% ≤ W ≤ 0.1%; and / or,

[0020] The mass percentage content of Ti in the positive current collector W satisfies: 0.001% ≤ W ≤ 0.1%. Ti The mass percentage content of Ti in the positive current collector W satisfies: 0.001% ≤ W ≤ 0.1%. Ti The mass percentage content of Ti in the positive current collector W satisfies: 0.001% ≤ W ≤ 0.1%.

[0021] The battery as described above, wherein the mass percentage content of Cu in the negative current collector is ≥ 99%; and / or, 400 MPa ≤ E2 ≤ 700 MPa; and / or,

[0022] 2% ≤ B2 ≤ 8%.

[0023] The battery as described above, wherein 40% ≤ C ≤ 80%.

[0024] The battery as described above, wherein the thickness of the positive current collector is 7-12 μm; and / or,

[0025] The thickness of the negative current collector is 3-8 μm.

[0026] The battery as described above, wherein the separator comprises a substrate layer and a material layer on at least one surface of the substrate layer.

[0027] The battery as described above, wherein the thickness D of the substrate layer, the tensile strength E1 of the positive current collector, the elongation B1 of the positive current collector, the tensile strength E2 of the negative current collector, and the elongation B2 of the negative current collector satisfy formula 2.

[0028]

[0029] The battery as described above, wherein 2 μm ≤ D ≤ 20 μm.

[0030] The present application can reduce the breaking probability of the positive electrode current collector or the negative electrode current collector, and avoid the battery expansion caused by the extension of the positive electrode current collector or the negative electrode current collector during the charging and discharging process, so as to effectively improve the safety performance of the battery while improving the energy density of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the drawings needed to be used in the description of the embodiments of the present application or the related art are briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0032] Figure 1 Structure diagram of the positive electrode sheet in some embodiments of the present application;

[0033] Figure 2 Structure diagram of the negative electrode sheet in some embodiments of the present application;

[0034] Figure 3 Structure diagram of the separator in some embodiments of the present application;

[0035] Figure 4 Structure diagram of the battery in some embodiments of the present application;

[0036] Figure 5 Structure diagram of the battery after being pressed in some embodiments of the present application;

[0037] Figure 6 Cycle performance curve of the battery in Embodiment 2 and Embodiment 4 of the present application.

[0038] Explanation of reference signs:

[0039] 1: base material layer;

[0040] 2: material layer;

[0041] 11: positive electrode current collector;

[0042] 12: positive electrode active layer;

[0043] 21: negative electrode current collector;

[0044] 22: Negative electrode active layer;

[0045] 111: Arc-shaped area;

[0046] 112: Membrane shell. Detailed Implementation

[0047] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Figure 1 This is a schematic diagram of the positive electrode sheet in some embodiments of the present invention; Figure 2 This is a schematic diagram of the negative electrode sheet in some embodiments of the present invention; Figure 3 This is a schematic diagram of the diaphragm structure in some embodiments of the present invention; Figure 4 This is a schematic diagram of the battery structure in some embodiments of the present invention; Figure 5 This is a schematic diagram of the battery structure after being compressed in some embodiments of the present invention. For example... Figures 1-5 As shown, the present invention provides a battery including a positive electrode, a negative electrode, and a separator, wherein the positive electrode and the negative electrode are arranged opposite to each other, and the separator is located between the positive electrode and the negative electrode.

[0049] The positive electrode includes a positive current collector 11, and the negative electrode includes a negative current collector 21;

[0050] The tensile strength E1 of the positive electrode current collector 11, the elongation B1 of the positive electrode current collector 11, the tensile strength E2 of the negative electrode current collector 21, the elongation B2 of the negative electrode current collector 21, and the porosity C of the membrane satisfy Equation 1:

[0051]

[0052] like Figure 1 As shown, the positive electrode also includes a positive electrode active layer 12, which is located on at least one surface of the positive electrode current collector 11; as Figure 2 As shown, the negative electrode sheet also includes a negative electrode active layer 22, which is located on at least one surface of the negative electrode current collector 21.

[0053] The positive electrode active layer 12 of the present invention may include positive electrode active particles, a conductive agent and a binder. The positive electrode active particles may be selected from one or more of lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium manganese oxide, cobalt-free layered materials and lithium-rich manganese-based materials. The conductive agent may be selected from at least one of conductive carbon black and carbon nanotubes. The binder may be selected from at least one of PVDF, HSV, PTFE, SBR and PAA.

[0054] The negative electrode active layer 22 of the present invention may include negative electrode active particles, a conductive agent, and a binder. The negative electrode active particles may be selected from at least one of graphitized carbon, coke, glassy carbon, sintered organic polymer compounds, carbon fibers, activated carbon, artificial graphite, natural graphite, silicon-carbon negative electrode, silicon-oxygen negative electrode, mesophase carbon microspheres, pyrolytic carbon, hard carbon, and soft carbon materials. The conductive agent may be selected from at least one of conductive carbon black, carbon nanotubes, carbon fibers, and Ketjen black. The binder may be selected from at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, and polyvinylidene fluoride.

[0055] The battery of the present invention also includes a membrane housing 112 and an electrolyte. The battery of the present invention can be a stacked structure or a wound structure. When the battery is a stacked structure, the positive electrode, the separator, and the negative electrode are stacked sequentially to form a stacked electrode assembly. Then, the electrode assembly is placed in the membrane housing 112, and electrolyte is injected into the membrane housing 112. After sealing, a stacked battery is formed. When the battery is a wound structure, the positive electrode, the separator, and the negative electrode are stacked sequentially and then wound to form a wound electrode assembly. The electrode assembly is placed in the membrane housing 112, and electrolyte is injected into the membrane housing 112. After sealing, a wound battery is formed.

[0056] The electrolyte comprises an electrolyte salt, an organic solvent, and additives; the lithium electrolyte salt comprises at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2), lithium difluorobis(oxalate) phosphate (LiPF2(C2O4)2), lithium tetrafluorooxalate phosphate (LiPF4C2O4), lithium oxalate phosphate (LiPO2C2O4), lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI); the organic solvent is selected from ethylene carbonate (EC) and propylene carbonate. The additive is selected from at least one of the following: ester (PC), diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl butyrate (EB), and γ-butyrolactone (GBL); the additive is selected from at least one of the following: fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), vinyl sulfate (DTD), methanedisulfonate methylene (MMDS), propenesulfonate lactone (PST), maleic anhydride, diethanolic anhydride, succinic anhydride, succinic anhydride, succinic nitrile (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE), and hexanetrionitrile (HTCN).

[0057] In this invention, the tensile strength and elongation of the positive electrode current collector 11 can be obtained by testing using the following method: after battery cycling >300T, the positive electrode active layer 12 on the positive electrode sheet is removed to obtain the positive electrode current collector 11, and the test is conducted using GB-228-87 test parameters with a gauge length of 50mm and a stretching speed of 10mm / min. The tensile strength and elongation of the negative electrode current collector 21 can be obtained by testing using the following method: after battery cycling >300T, the negative electrode active layer 22 on the negative electrode sheet is removed to obtain the negative electrode current collector 21, and the test is conducted using GB-228-87 test parameters with a gauge length of 50mm and a stretching speed of 50mm / min. The porosity of the separator refers to the proportion of the pore volume in the total volume of the separator.

[0058] When the tensile strength E1 of the positive current collector 11, the elongation B1 of the positive current collector 11, the tensile strength E2 of the negative current collector 21, the elongation B2 of the negative current collector 21, and the porosity C of the separator satisfy Equation 1, the probability of breakage of the positive current collector 11 or the negative current collector 21 can be reduced, and the battery external expansion and cracking caused by the extension of the positive current collector 11 or the negative current collector 21 during charging and discharging can be avoided. This can effectively improve the battery's safety performance while increasing its energy density.

[0059] like Figure 4 as well as Figure 5As illustrated, using a wound battery as an example, when the battery is subjected to planar compression, the positive electrode, negative electrode, separator, and various arc regions 111 are compressed along the Z-direction. When the arc regions 111 are compressed to the point where the arc angle is close to horizontal, the inner positive electrode active layer 12 at the fold line of the arc region is compressed and concentrated, resulting in stress concentration. This generates normal stress on the inner side of the positive electrode current collector 11, leading to safety issues such as breakage of the positive electrode current collector 11 and burrs piercing the separator during planar compression. Therefore, to ensure that the internal structure is not significantly damaged after compression during battery production, the tensile strength E1 of the positive electrode current collector 11 can be increased, and the elongation B1 of some of the positive electrode current collector 11 can be reduced, thereby indirectly improving the ability of the positive electrode current collector 11 to withstand the compressive normal stress of the positive electrode active layer 12.

[0060] Meanwhile, during lithium-ion battery charging, lithium ions are extracted from the positive electrode and embedded in the negative electrode, causing an increase in the spacing between the negative electrode active layers 22. This leads to the negative electrode current collector 21 extending along the X / Y directions. Simultaneously, in the lithium-ion battery, the binder in the positive electrode active layer 12 partially dissolves after being wetted by the electrolyte, increasing the spacing between the positive electrode active particles. When the negative electrode extends, under the influence of interfacial forces between the positive electrode, separator, and negative electrode, the positive electrode active particles have space to extend to a certain extent. When the extension length and width exceed the reserved gap between the cell and the casing 112, cracks will appear in the battery casing 112, leading to leakage and a safety accident. Therefore, it is necessary to increase the tensile strength E2 of the negative electrode current collector 21 and reduce its elongation B2 to resist the extension of the positive electrode current collector 111 and the negative electrode current collector 21 driven by the negative electrode active layer 22. This effectively prevents the battery casing from cracking due to electrode extension, thus avoiding a series of safety problems.

[0061] This invention, by ensuring that the tensile strength and elongation of the positive electrode current collector 11, the tensile strength and elongation of the negative electrode current collector 21, and the porosity of the separator satisfy the aforementioned relationship, can reduce the probability of positive electrode breakage during the manufacturing process, increase the discharge rate, suppress expansion, and improve battery safety and electrical performance. Simultaneously, it improves the elongation of the positive and negative electrodes during charging and discharging, reducing the risk of cracks in the battery casing due to electrode elongation, thereby improving battery safety. It can overcome... When the temperature is too high, the tensile strength of the positive electrode current collector 11 decreases, its resistance to deformation is insufficient, and it will break during rolling or hot pressing, resulting in poor process efficiency and poor battery safety; it can also cause surface defects. If the strength is too low, the relative tensile strength of the negative electrode current collector 21 decreases. On the one hand, this causes the electrode to easily stretch in the X / Y direction during charging and discharging, leading to corner cracks in localized areas of the battery casing due to the stretching of the electrode. On the other hand, the reduced permeability of the separator during charging and discharging prevents the electrolyte inside the battery from flowing freely, reducing the reaction efficiency of the positive and negative electrodes, decreasing the battery discharge rate, and decreasing the battery capacity.

[0062] Furthermore, when 1.333 ≤ E2 / E1 ≤ 5.833; and / or,

[0063] 0.33≤B2 / B1≤8; and / or,

[0064] And / or,

[0065] And / or,

[0066] When 1.609≤ln(1+C)≤2.197, the probability of breakage of the positive current collector 11 or the negative current collector 21 can be further reduced, and the battery external expansion and cracking caused by the extension of the positive current collector 11 or the negative current collector 21 during charging and discharging can be avoided. This can effectively improve the battery's safety performance while increasing its energy density.

[0067] In some embodiments of the present invention, the mass percentage of Al in the positive electrode current collector 11 is ≥99%; and / or, 120MPa≤E1≤300MPa; and / or,

[0068] 1% ≤ B1 ≤ 6%.

[0069] It is understandable that the positive current collector 11 is aluminum foil, that is, the mass percentage of aluminum in the aluminum foil is ≥99%.

[0070] In this invention, when the positive current collector 11 meets the above-mentioned limitations, it is beneficial to further reduce the probability of breakage of the positive current collector 11 under high pressure compaction conditions, suppress the extension of the positive electrode sheet, and reduce the risks caused by the battery.

[0071] Furthermore, the positive electrode current collector 11 also includes Fe, Si, Cu, Ti, and Mn;

[0072] Among them, the sum of the mass percentage of Fe in the positive electrode current collector 11 and the mass percentage of Si in the positive electrode current collector 11 is W. Fe+Si Satisfy: 0.4% ≤ W Fe+Si ≤0.8%; and / or,

[0073] The mass percentage W of Cu in the positive electrode current collector 11 Cu Satisfy: 0.01% ≤ W Cu ≤0.19%; and / or,

[0074] The mass percentage of Mn in the positive electrode current collector 11, W Mn Satisfies: 0.001% ≤ W Mn ≤0.1%; and / or,

[0075] The mass percentage of Ti in the positive electrode current collector 11, W Ti Satisfies: 0.001% ≤ W Ti When the content is ≤0.1%, the toughness of the positive electrode current collector 11 can be further improved, reducing the probability of battery failure.

[0076] In some embodiments of the present invention, when the mass percentage of Cu in the negative electrode current collector 21 is ≥99%; and / or, 400MPa≤E2≤700MPa; and / or,

[0077] When 2% ≤ B2 ≤ 8%, it is beneficial to reduce the stretching of the electrode during charging and discharging, avoid the battery film 112 from cracking, and improve the safety performance of the battery.

[0078] The inventors also discovered that when the thickness D of the positive electrode current collector 11... 正 When the thickness is 7-12 μm, the mechanical properties of the positive electrode current collector 11 can be further improved without sacrificing the battery's energy density, thereby enhancing the battery's safety performance; when the thickness D of the negative electrode current collector 21 is... 负 When the thickness is 3-8μm, the mechanical properties of the negative electrode current collector 21 can be further improved while ensuring the energy density of the battery, thereby improving the safety performance of the battery.

[0079] In some embodiments of the present invention, when 40% ≤ C ≤ 80%, the separator can store more electrolyte while ensuring the service life of the separator, thereby improving the cycle performance of the battery.

[0080] The present invention does not impose any particular limitation on the specific structure of the diaphragm. The diaphragm may include a substrate layer 1 and a material layer 2 located on at least one surface of the substrate layer 1. In some embodiments, the material layer 2 may include a ceramic, a polymer electrolyte layer, or a ceramic-polymer composite electrolyte layer.

[0081] The substrate layer 1 may include at least one of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polynaphthalene system polymers, polyimide, polyamide, aramid, and poly(p-phenylenebenzodioxazole).

[0082] The ceramic particles in the ceramic layer or ceramic-polymer composite electrolyte layer may be selected from at least one of alumina, boehmite, magnesium oxide, magnesium hydroxide, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, and nickel oxide.

[0083] The polymer in the polymer electrolyte layer or ceramic-polymer composite electrolyte layer may be selected from at least one of polyethylene and polypropylene.

[0084] When the separator comprises a substrate layer 1 and a material layer 2, the performance of the separator can be controlled according to the material layer 2, and the positive and negative electrodes can be more effectively isolated. This reduces the risk of contact between the positive and negative electrodes due to the extension of the negative electrode or the breakage of the positive current collector 11, thereby reducing the possibility of battery short circuits and improving battery safety. In particular, when the material layer 2 is a ceramic layer, the heat resistance of the separator can be improved, thus enhancing battery safety.

[0085] In some embodiments of the present invention, the thickness D of the substrate layer 1, the tensile strength E1 of the positive current collector 11, the elongation B1 of the positive current collector 11, the tensile strength E2 of the negative current collector 21, and the elongation B2 of the negative current collector 21 satisfy Equation 2.

[0086]

[0087] When the battery is subjected to planar compression, if the tensile strength E1 of the positive electrode current collector 11 is high and the elongation B1 of the positive electrode current collector 11 is low, and the tensile strength E2 of the negative electrode current collector 21 is high and the elongation B2 of the negative electrode current collector 21 is low, the hardness of the burrs generated by the cutting at the edges of the positive and negative electrode sheets will be high, and there is still a chance to puncture the separator, leading to a short circuit and fire. Therefore, the thickness D of the substrate layer 1 is adjusted to prevent the separator from being punctured by the burrs, thereby effectively avoiding the problem of internal short circuit and fire caused by the compression of the battery.

[0088] Furthermore, when the thickness D of the substrate layer 1 satisfies 2μm≤D≤20μm, it helps to prevent direct contact between the positive and negative electrodes due to the extension of the negative electrode sheet or the breakage of the positive electrode current collector 11, thereby improving the safety of the battery. In some embodiments, 4μm≤D≤12μm.

[0089] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0090] Example 1

[0091] The battery in this embodiment is prepared by a method including the following steps:

[0092] 1) Preparation of positive electrode sheet

[0093] A positive electrode slurry is formed by dispersing positive electrode active particles lithium cobalt oxide, conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder using N-methylpyrrolidone. The positive electrode slurry is then uniformly coated onto an Al foil using a coating method. After baking and rolling processes, a positive electrode sheet including a positive electrode active layer 12 is obtained.

[0094] The mass ratio of the positive electrode active particles, conductive agent, and binder is 98:1.5:0.5.

[0095] 2) Preparation of negative electrode sheet

[0096] A negative electrode slurry is formed by dispersing artificial graphite, conductive carbon black, and sodium carboxymethyl cellulose in deionized water; then, a negative electrode active layer 22 is formed on the surface of the negative electrode current collector 21 by coating, baking, and rolling processes to obtain the negative electrode sheet.

[0097] The mass ratio of the negative electrode active particles, conductive agent, and binder is 97:1:2.

[0098] 3) Preparation of the diaphragm

[0099] A certain mass of polyethylene oxide, propylene carbonate, lithium hexafluorophosphate, sodium carboxymethyl cellulose additive, and benzoyl peroxide were weighed and dissolved in acetonitrile to form a uniform gel-like substance as the first slurry. The first slurry was coated on both surfaces of the substrate layer 1, dried, and then coated with the second slurry. After drying, it was ready for use.

[0100] The substrate layer 1 is a polypropylene layer, and the mass ratio of polyethylene oxide, plasticizer, lithium salt, additives and initiator in the first slurry is 95:2:0.5:1:1.5.

[0101] The second slurry is a perfluorosulfonic acid resin (Nafion) solution with a mass fraction of 5%.

[0102] 4) Lithium-ion battery manufacturing

[0103] The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence after fabrication, and then wound to obtain a bare cell. The bare cell is placed in an aluminum-plastic film shell, and electrolyte is injected into the bare cell. After vacuum sealing, standing, formation (0.1C constant current charging to 4% SOC, and then 0.2C constant current charging to 10% SOC), shaping, and capacity testing, a lithium-ion battery is obtained.

[0104] The electrolyte is prepared by a method including the following steps:

[0105] Ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) solvents were mixed uniformly in a mass ratio of 15:10:30:35. LiPF6 (15 wt% of the total electrolyte mass) was slowly added to the mixed solution, followed by fluoroethylene carbonate (10 wt% of the total electrolyte mass), 1,3-propanesulfonate lactone (5 wt% of the total electrolyte mass), and lithium difluorooxalate borate (1 wt% of the total electrolyte mass). After stirring until homogeneous, the electrolyte was obtained after passing tests for moisture and free acid.

[0106] The specific parameters of the positive current collector 11, the negative current collector 21, and the diaphragm in this embodiment are shown in Table 1.

[0107] Examples 1-27, Comparative Examples 1-3

[0108] The preparation methods of the batteries in Examples 1-27 and Comparative Examples 1-3 are basically the same as those in Example 1, with the differences shown in Table 1.

[0109] Performance testing

[0110] The following performance test results were performed on the positive electrode current collector 11, negative electrode current collector 21, separator, and battery in the examples and comparative examples, respectively, as shown in Table 1 and Table 2;

[0111] 1. Diaphragm porosity test

[0112] First, fold the diaphragm into 6 layers, flatten and press it to remove air. Cut the folded diaphragm according to the template and measure the area S of the sample. Then measure the thickness of the sample 10 times and calculate the average value B. Measure the weight of the diaphragm using an electronic balance 3 times and obtain the average value M. Calculate the porosity of the diaphragm using the following formula:

[0113] Porosity C (%) = [(density of membrane raw material × S × B - M) ÷ (density of membrane raw material × S × B)] × 100%.

[0114] 2. Tensile strength and elongation test of positive electrode current collector

[0115] The tensile strength and elongation of the positive current collector were tested using the GB-228-87 test method, with the test parameters set as gauge length 50 mm and tensile speed 10 mm / min.

[0116] 3. Tensile strength and elongation test of negative electrode current collector

[0117] The tensile strength and elongation of the negative electrode current collector were tested using the GB-228-87 test method, with the test parameters being a gauge length of 50 mm and a tensile speed of 50 mm / min.

[0118] 4. Cyclic performance test

[0119] First, the batteries of the examples and comparative examples were left to stand at 25℃±3℃ for 10 minutes; then, they were discharged at a rate of 0.2C to 3.0V, and left to stand for 10 minutes after reaching the target voltage value; then, they were charged at a constant current of 0.8C, and left to stand for 10 minutes after the current was cut off at 0.05C; then, the batteries were discharged at a rate of 0.2C to 3.0V to perform an initial capacity test.

[0120] After completing the initial capacity test, the battery was left to stand at 45℃ for 2 hours, then fully charged according to the specifications, down to 0.05C, and left to stand for 10 minutes before testing the first full-charge data: voltage, internal resistance, thickness, and DC internal resistance. Then, it was discharged at a constant current of 0.5C to 3.0V and left to stand for 10 minutes; finally, it was fully charged again according to the specifications, down to 0.05C, and left to stand for 10 minutes. This charging and discharging cycle at 45℃ was repeated 500 times to obtain the battery cycle curve.

[0121] Figure 6 These are the cycle performance curves of the batteries in Examples 2 and 4 of this invention. From... Figure 6 It can be seen that the battery in the embodiments of the present invention has excellent cycle performance.

[0122] 5. Cyclic expansion rate test

[0123] First, the lithium-ion battery was fully discharged, then charged to full capacity using a constant current. Afterward, it was disassembled, and the surface area of ​​the electrode plates parallel to the width of the cell was measured. Next, the surface area of ​​the electrode plates parallel to the width of the cell was measured at the 300th cycle. The formula was: XY expansion rate (%) of the lithium battery at the 300th cycle = (Electrode surface area at the 300th cycle ÷ Electrode surface area at the first cycle - 1) × 100%.

[0124] 6. Planar extrusion test

[0125] First, the batteries of the examples and comparative examples were charged at a rate of 0.5C to the upper limit cutoff voltage, and after maintaining a constant voltage at 0.05C, they were left to stand for 10 minutes. Next, the wide side of the fully charged battery was placed between two flat surfaces and pressed, with the pressing force gradually increasing, reaching a speed of approximately 900 mm / min at the first contact point. Pressing continued, monitoring the voltage and temperature of the lithium battery until any of the following conditions were met: the applied force reached 13 ± 0.78 KN, the battery voltage dropped by more than 100 mV, or the lithium battery caught fire or emitted smoke. The test was stopped when any of these conditions were met. Five samples were tested in each group, and the percentage of samples passing the test in each group was recorded.

[0126] 7. Energy density

[0127] The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then charged at a constant current of 0.5C to a voltage of 4.5V, followed by constant voltage charging at 4.5V to a current of 0.05C, and then discharged at 0.5C to a voltage of 3.0V. The discharge capacity was recorded. The gravimetric energy density of the lithium-ion battery was calculated using the formula: Gravimetric energy density = Discharge capacity * 4.5V / (Weight of the lithium-ion battery).

[0128] Table 1

[0129]

[0130]

[0131] Table 2

[0132] Cycles Cycles Flatness Energy Density Example 1 631 0.12 100 488 Example 2 654 0.15 100 510 Example 3 677 0.18 100 502 Example 4 441 0.25 100 413 Example 5 449 0.34 100 447 Example 6 457 0.23 100 398 Example 7 455 0.29 100 454 Example 8 438 0.31 100 406 Example 9 488 0.23 100 417 Example 10 374 0.76 90 365 Example 11 384 0.71 86 344 Example 12 390 0.71 84 343 Example 13 443 0.29 100 440 Example 14 380 0.73 88 341 Example 15 399 0.45 100 350 Example 16 453 0.33 100 444 Example 17 380 0.41 99 345 Example 18 461 0.49 94 453 Example 19 390 0.61 84 343 Example 20 453 0.32 100 433 Example 21 488 0.23 100 417 Example 22 374 0.79 84 345 Example 23 441 0.25 100 412 Example 24 453 0.32 100 413 Example 25 391 0.75 90 365 Example 26 662 0.11 100 497 Example 27 624 0.11 100 538 Comparative Example 1 333 0.81 50 298 Comparative Example 2 333 0.94 50 258 Comparative Example 3 290 1.16 0 244

[0133] As can be seen from Table 2, the battery of the present invention has better cycle performance, planar extrusion pass rate and energy density, and after cycling, the cycle expansion rate is smaller. This indicates that by matching the tensile strength of the positive electrode current collector 11, the elongation of the positive electrode current collector 11, the tensile strength of the negative electrode current collector 21, the elongation of the negative electrode current collector 21 and the porosity of the separator, the present invention can obtain a battery with excellent energy density, safety performance and cycle performance.

[0134] Furthermore, as can be seen from Examples 1-3 and Example 10, by further selecting the elongation of the positive electrode current collector 11, the cycle number of the battery, the planar extrusion yield, the energy density can be further improved, and the cycle expansion rate of the battery can be reduced.

[0135] As can be seen from Examples 1-3 and Example 11, by selecting the tensile strength of the positive electrode current collector 11, the number of battery cycles, the planar extrusion yield, and the energy density can be further improved, while the battery cycle expansion rate can be reduced.

[0136] As can be seen from Examples 1-3 and Example 12, by selecting the tensile strength of the negative electrode current collector 21, the number of battery cycles, the planar extrusion yield, and the energy density can be further improved, while the battery cycle expansion rate can be reduced.

[0137] As can be seen from Examples 1-3 and Example 14, by further selecting the elongation of the negative electrode current collector 21, the number of battery cycles, the planar extrusion yield, and the energy density can be further improved, while the battery cycle expansion rate can be reduced.

[0138] As can be seen from Examples 1-3 and Example 15, when the porosity of the separator meets a specific range, a battery with superior cycle performance, safety performance, and energy density can be obtained.

[0139] As can be seen from Examples 1-3 and Example 17, by selecting the thickness of the positive electrode current collector 11, the cycle performance, safety performance and energy density of the battery can be further improved.

[0140] As can be seen from Examples 1-3 and Example 19, by selecting the thickness of the negative electrode current collector 21, the cycle performance, safety performance and energy density of the battery can be further improved.

[0141] As can be seen from Examples 1-3 and Example 22, by matching the thickness of the substrate layer 1 in the separator, the tensile strength of the positive electrode current collector 11, the elongation of the positive electrode current collector 11, the tensile strength of the negative electrode current collector 21, and the elongation of the negative electrode current collector 21, a battery with superior cycle performance, safety performance, and energy density can be obtained. Furthermore, as can be seen from Examples 1-3 and Example 25, by selecting the thickness of the substrate layer 1 in the separator, the tensile strength of the battery, the elongation of the positive electrode current collector 11, the tensile strength of the negative electrode current collector 21, and the elongation of the negative electrode current collector 21 can be further improved.

[0142] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A battery, characterized in that, The battery includes a positive electrode, a negative electrode, and a separator, wherein the positive electrode and the negative electrode are disposed opposite to each other, and the separator is located between the positive electrode and the negative electrode; The positive electrode includes a positive current collector, and the negative electrode includes a negative current collector; The tensile strength E1 of the positive electrode current collector, the elongation B1 of the positive electrode current collector, the tensile strength E2 of the negative electrode current collector, the elongation B2 of the negative electrode current collector, and the porosity C of the membrane satisfy Equation 1:

2. The battery according to claim 1, characterized in that, 1.333≤E2 / E1≤5.833; and / or, 0.33≤B2 / B1≤8; and / or, And / or, And / or, 1.609≤ln(1+C)≤2.

197.

3. The battery according to claim 1 or 2, characterized in that, The Al mass percentage content of the positive electrode current collector is ≥99%; and / or, 120MPa≤E1≤300MPa; and / or, 1％≤B1≤6％。 4. The battery according to claim 3, characterized in that, The positive electrode current collector also includes Fe, Si, Cu, Ti, and Mn; Wherein, the sum of the mass percentage of Fe in the positive electrode current collector and the mass percentage of Si in the positive electrode current collector is W. Fe+Si Satisfy: 0.4% ≤ W Fe+Si ≤0.8%; and / or, The mass percentage of Cu in the positive electrode current collector is W Cu Satisfy: 0.01% ≤ W Cu ≤0.19%; and / or, The mass percentage of Mn in the positive electrode current collector is W Mn Satisfies: 0.001% ≤ W Mn ≤0.1%; and / or, The mass percentage of Ti in the positive electrode current collector W Ti Satisfies: 0.001% ≤ W Ti ≤0.1%.

5. The battery according to any one of claims 1-4, characterized in that, The negative electrode current collector contains ≥99% Cu by mass; and / or, 400MPa≤E2≤700MPa; and / or, 2％≤B2≤8％。 6. The battery according to any one of claims 1-5, characterized in that, 40％≤C≤80％。 7. The battery according to any one of claims 1-6, characterized in that, The thickness of the positive electrode current collector is 7-12 μm; and / or, The thickness of the negative electrode current collector is 3-8 μm.

8. The battery according to any one of claims 1-7, characterized in that, The diaphragm includes a substrate layer and a material layer located on at least one surface of the substrate layer.

9. The battery according to claim 8, characterized in that, The thickness D of the substrate layer, the tensile strength E1 of the positive current collector, the elongation B1 of the positive current collector, the tensile strength E2 of the negative current collector, and the elongation B2 of the negative current collector satisfy Equation 2.

10. The battery according to claim 9, characterized in that, 2μm≤D≤20μm.

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