Lithium-ion battery

Abstract

A lithium-ion battery, characterized in that the lithium-ion battery comprises a negative electrode plate and a separator, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode active layer arranged on at least one functional surface of the negative electrode current collector, wherein the negative electrode active layer contains a negative electrode active material, wherein the lithium-ion battery satisfies the following equation 1: ( 2 M + 3 ) 2 ( S + 2 ) 2 / W ≥ 20 where in equation 1 M = exp (m1 / d1) + (d1-2) (m1-0.26), where m1 is the tensile strength of a negative electrode current collector in a length direction in GPa and d1 is the thickness of the negative electrode current collector in µm; and where S = exp (m2 / d2) + (d2-2) (m2-0.16), where m2 is the puncture resistance of the separator in kgf and d2 is the thickness of a substrate in the separator in µm; and where W = ((exp (-10q)) / (φ-6) + exp (10q)) (d3-13.5) (ρ-3.5) / 100, where d3 is the thickness of the negative electrode active layer in µm, φ is an OI value of the negative electrode active layer, q is the mass percentage of a silicon-based negative electrode material in the negative electrode active material, and ρ is the areal density of the negative electrode active layer in mg / cm 2 stands.

Description

Technical field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to a lithium-ion battery. State of the art

[0002] Lithium-ion batteries have many advantages, such as high voltage, a wide operating temperature range, fast charging and discharging speed, high charging efficiency, high output power, no memory effect, good environmental performance, and no pollution, and are therefore widely used in new energy vehicles, portable electronic devices, energy storage, and other fields. However, during the charging and discharging process, the crystal lattice spacing in the negative electrode active material of the lithium-ion battery changes with the intercalation of lithium ions, leading to the buildup of microscopic internal stresses, which causes the negative electrode to expand. This manifests itself at the macroscopic level as an increase or decrease in the thickness and / or width of a negative electrode coating.This process is repeated during cyclic charging and discharging, which easily leads to crushing of the battery casing and thus damage to it, which poses a safety hazard and affects the cycle life of the battery. Disclosure of the invention

[0003] In order to eliminate the above-mentioned disadvantages, the present invention provides a lithium ion battery which can effectively overcome the crushing of the battery case caused by the volume expansion of the negative electrode material, thereby effectively improving the cycle life and safety of the battery.

[0004] The present invention provides a lithium-ion battery, the lithium-ion battery comprising a negative electrode plate and a separator, the negative electrode plate comprising a negative electrode current collector and a negative electrode active layer disposed on at least one functional surface of the negative electrode current collector, and the negative electrode active layer containing a negative electrode active material.

[0005] The lithium-ion battery satisfies the following equation 1: (2M+3)2(S+2)2 / W≥20 where in equation 1 M = exp (m1 / d1) + (d1-2) (m1-0.26), where m1 is the tensile strength of a negative electrode current collector in a length direction in GPa and d1 is the thickness of the negative electrode current collector in µm; and where S = exp (m2 / d2) + (d2-2) (m2-0.16), where m2 is the puncture resistance of the separator in kgf and d2 is the thickness of a substrate in the separator in µm; and where W = ((exp (-10q)) / (φ-6) + exp (10q)) (d3-13.5) (ρ-3.5) / 100, where d3 is the thickness of the negative electrode active layer in µm, φ is an OI value of the negative electrode active layer, q is the mass percentage of a silicon-based negative electrode material in the negative electrode active material, and ρ is the areal density of the negative electrode active layer in mg / cm 2 stands.

[0006] Furthermore, it is intended that the lithium-ion battery satisfies the following equation 2: (2M+3)2(S+2)2 / W≥50

[0007] Furthermore, it is intended that m1 is 0.3 GPa to 0.8 GPa and d1 is 3 µm to 9 µm.

[0008] Furthermore, it is planned that M will be between 1.2 and 4.9.

[0009] Furthermore, it is intended that m2 is 0.18 kgf to 0.6 kgf and d2 is 3.5 µm to 7 µm.

[0010] Furthermore, it is intended that S is 1.1 to 3.3.

[0011] Furthermore, it is intended that q 0 to 0.3, d3 50 µm to 80 µm, φ 10 to 30, and ρ 7 mg / cm 2 up to 12 mg / cm 2 amounts.

[0012] Furthermore, it is planned that W will be between 2 and 80.

[0013] Furthermore, it is provided that the separator further comprises an adhesive layer on both sides of the substrate, and the adhesive layer on a single side has a thickness of 0.5 to 3 µm.

[0014] Furthermore, it is provided that the separator further comprises a ceramic layer, wherein the ceramic layer is arranged on at least one surface of the adhesive layer facing away from the substrate, and the ceramic layer has a thickness of 0.5 to 3 µm on a single side.

[0015] In the present invention, the tensile strength and thickness of the negative electrode current collector, the puncture strength of the separator and the thickness of the substrate in the separator, and the thickness, OI value, areal density of the negative electrode active layer, and the mass percentage of the silicon-based negative electrode material in the lithium-ion battery are controlled so that the lithium-ion battery satisfies the above Equation 1, thereby effectively suppressing the crushing of the battery case caused by the volume expansion of the negative electrode material. Thus, battery leakage caused by a damaged corner can be avoided, thus improving the safety and cycle performance of the battery. Detailed embodiments

[0016] In the following, the technical solutions of the invention will be described clearly and completely in conjunction with the embodiments of the invention in order to clarify the objectives, technical solutions, and advantages of the present invention. Of course, the described embodiments do not represent all, but only a part of the embodiments of the invention. All other embodiments obtained by those of ordinary skill in the art from the embodiments of the invention without inventive steps are also within the scope of the invention.

[0017] The present invention provides a lithium-ion battery, the lithium-ion battery comprising a negative electrode plate and a separator, the negative electrode plate comprising a negative electrode current collector and a negative electrode active layer disposed on at least one functional surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material.

[0018] The lithium-ion battery satisfies the following equation 1: (2M+3)2(S+2)2 / W≥20 where In the equation 1 M = exp (m1 / d1) + (d1-2) (m1-0.26), where m1 is the tensile strength of a negative electrode current collector in a length direction in GPa and d1 is the thickness of the negative electrode current collector in µm; where S = exp (m2 / d2) + (d2-2) (m2-0.16), where m2 is the puncture resistance of the separator in kgf and d2 is the thickness of a substrate in the separator in µm; and where W = ((exp (-10q)) / (φ-6) + exp (10q)) (d3-13.5) (ρ-3.5) / 100, where d3 is the thickness of the negative electrode active layer in µm, φ is the OI value of the negative electrode active layer, q is the mass percentage of a silicon-based negative electrode material in the negative electrode active material, and ρ is the areal density of the negative electrode active layer in mg / cm 2 stands.

[0019] In particular, the negative electrode current collector has two functional surfaces in a thickness direction. In one embodiment, the negative electrode active layer is arranged on one functional surface of the negative electrode current collector, while no functional layer is provided on the other functional surface. The thickness d3 of the negative electrode active layer is the total thickness of the negative electrode active layer, and the areal density of the negative electrode active layer is the total areal density of the negative electrode active layer. In another embodiment, the negative electrode active layer is arranged on the two functional surfaces of the negative electrode current collector.The thickness d3 of the active layer for the negative electrode is the one-sided thickness of the active layer for the negative electrode and the areal density of the active layer for the negative electrode is the one-sided areal density of the active layer for the negative electrode.

[0020] The tensile strength m1 of the negative electrode current collector according to the present invention in the length direction is determined by testing according to the following method. The negative electrode current collector is cut into rectangular plate-shaped specimens with a length of 200 mm and a width of 13 mm. The length direction refers to the stretching direction, and the loading area A0 of the rectangular plate-shaped specimen is calculated perpendicular to the stretching direction. The test is then performed using a tensile testing machine at a tensile speed of 50 mm / min, and the loading force at the time of fracture of the rectangular plate-shaped specimen is recorded as F0, so that the tensile strength m1 is equal to F0 / A0 in GPa.

[0021] The thickness d1 of the negative electrode current collector according to the invention is measured in µm using a micrometer.

[0022] The puncture resistance m2 of the separator according to the invention is determined by testing according to GB / T 36363-2018 in kgf.

[0023] The thickness d2 of the substrate in the separator according to the invention is determined by performing an SEM examination on the cross section of the separator while obtaining an SEM cross-sectional image and measuring the thickness value of the substrate in the SEM cross-sectional image in µm.

[0024] The thickness d3 of the negative electrode active layer according to the present invention is measured by the following steps. Before manufacturing the negative electrode plate, the thickness of the negative electrode current collector is measured with a micrometer, then the negative electrode active layer is applied to at least one functional surface of the negative electrode current collector. The negative electrode plate is obtained after drying and compacting, and the thickness of the negative electrode plate is measured with the micrometer. When the negative electrode current collector is provided with the negative electrode active layer on only one functional surface, the thickness d3 of the negative electrode active layer is equal to the thickness of the negative electrode plate minus the thickness of the negative electrode current collector.If the negative electrode active layer is provided on both functional surfaces of the negative electrode current collector, the thickness d3 of the negative electrode active layer is (thickness of the negative electrode plate - thickness of the negative electrode current collector) / 2 in µm.

[0025] The OI value φ in the present invention is obtained by XRD testing of the negative electrode plate. The OI value is the ratio of the intensity of a diffraction peak of the (004) crystal plane to the intensity of a diffraction peak of the (110) crystal plane in the test result, where 2θ of the diffraction peak of the (004) crystal plane is between 53.7° and 55.7°, and 2θ of the diffraction peak of the (110) crystal plane is between 76.4° and 78.4°.

[0026] The areal density of the negative electrode active layer according to the invention is measured through the following steps. Before manufacturing the negative electrode plate, the weight of the negative electrode current collector per unit area is weighed, then the negative electrode active layer is applied to at least one functional surface of the negative electrode current collector. The negative electrode plate is obtained after drying and compacting, and the weight of the negative electrode plate per unit area is weighed. When the negative electrode current collector is provided with the negative electrode active layer on only one functional surface, the areal density ρ of the negative electrode active layer is equal to the weight of the negative electrode plate per unit area minus the weight of the negative electrode current collector per unit area.If the negative electrode active layer is provided on both functional surfaces of the negative electrode current collector, the areal density ρ of the negative electrode active layer is (weight of the negative electrode plate per unit area - weight of the negative electrode current collector per unit area) / 2 in mg / cm. 2 .

[0027] In the present invention, there is no specific limitation on the type of the current collector for the negative electrode, for example, selected from copper current collector, copper-PET composite current collector, copper-polypropylene composite current collector, copper-polyimide composite current collector, preferably copper current collector.

[0028] In the present invention, there is also no specific limitation on the type of substrate, e.g., selected from polyethylene substrate, polypropylene substrate, polyethylene / polypropylene hybrid substrate, multilayer polypropylene / ethylene / propylene coextrusion substrate, nonwoven substrate, polyimide substrate, aramid substrate, preferably polyethylene substrate.

[0029] In the present invention, the origin of the negative electrode current collector and the substrate is not specifically limited as long as a commercially available product known to those skilled in the art or a product manufactured by a conventional manufacturing method is used.

[0030] In the technical solutions according to the present invention, the safety and cycle life of the battery can be effectively improved by making the lithium-ion battery satisfy Equation 1. After analyzing this principle, the inventor concluded that this might be the reason: In this case, the tensile strength of the negative electrode current collector in the length direction, the thickness of the negative electrode current collector, the puncture strength of the separator, the thickness of the substrate in the separator, and the thickness, the OI value of the negative electrode active layer and the mass content of the silicon-based negative electrode material in the negative electrode active material, as well as the areal density of the negative electrode active layer in the lithium-ion battery are controlled so that the above parameters satisfy Equation 1 above.In this way, the initial expansion of the negative electrode active layer in the thickness direction can be effectively reduced. At the same time, it can be ensured that the separator and the negative electrode current collector can withstand the expansion of the negative electrode active layer in the width direction, so that the extrusion force on the case caused by the expansion of the negative electrode material (particularly containing a silicon-based material) can be significantly reduced. Therefore, the lithium-ion battery of the present invention has no problems with leakage caused by a damaged corner and a good cyclic capacity retention rate after 800 cycles at a room temperature of 25°C to 35°C.

[0031] The inventors also found that when the lithium-ion battery satisfies Equation 1, the burrs generated by a copper foil can be effectively reduced and the separator can effectively resist the puncture of a foreign matter, thereby effectively mitigating the physical self-discharge and improving the self-discharge capability of the lithium-ion battery.

[0032] In a detailed embodiment, the lithium-ion battery satisfies the following equation 2: (2M+3)2(S+2)2 / W≥50

[0033] Specifically, by further controlling the tensile strength of the negative electrode current collector in the length direction, the thickness of the negative electrode current collector, the puncture strength of the separator, the thickness of the substrate in the separator, the thickness and OI value of the negative electrode active layer, the mass content of the silicon-based negative electrode material in the negative electrode active material, and the areal density of the negative electrode active layer in the lithium-ion battery, the values ​​of M, S, and W are again controlled so that the lithium-ion battery satisfies Equation 2. When the lithium-ion battery satisfies Equation 2, the expansion of the negative electrode active layer in the thickness direction can be further suppressed, and the supporting effect of the separator and the negative electrode current collector on the negative electrode plate can be improved.As a result, the battery can still have no leakage due to a damaged corner after 500 cycles at a high temperature of 35°C to 45°C and has a good retention rate for the cyclic capacity.

[0034] In a detailed embodiment, it is provided that m1 is 0.3 GPa to 0.8 GPa and d1 is 3 µm to 9 µm. For example, it is provided that m1 is 0.3 GPa, 0.4 GPa, 0.5 GPa, 0.6 GPa, 0.7 GPa, or 0.8 GPa, and d1 is 3 µm, 4 µm, 5 µm, 6 µm, 7 µm, 8 µm, or 9 µm. In this range, it is not only possible to ensure the negative electrode current collector with a high tensile strength to provide sufficient supporting force for the negative electrode active layer, but also to select a more moderate thickness of the negative electrode current collector, thereby reducing the energy density loss to a certain extent.

[0035] In a detailed embodiment, M is provided to be 1.2 to 4.9. For example, M is provided to be 1.2, 1.6, 2.0, 2.4, 2.8, 3.2, 3.6, 4.0, 4.4, or 4.9. In this range, the supporting effect of the negative electrode current collector on the negative electrode active layer can be further improved to prevent the negative electrode active layer from peeling off due to its volume expansion, which would impair the cycling performance of the battery. In addition, crushing of the battery case caused by the volume expansion of the negative electrode material is further reduced to prevent leakage caused by a damaged corner.

[0036] In a detailed embodiment, m2 is configured to be 0.18 kgf to 0.6 kgf, and d2 is configured to be 3.5 µm to 7 µm. For example, m2 is configured to be 0.18 kgf, 0.2 kgf, 0.3 kgf, 0.4 kgf, 0.5 kgf, or 0.6 kgf, and d2 is configured to be 3.5 µm, 4 µm, 4.5 µm, 5 µm, 5.5 µm, 6 µm, 6.5 µm, or 7 µm. Not only can it ensure the separator with high puncture resistance to provide sufficient supporting force for the negative electrode active layer, but it can also select a more moderate substrate thickness in the separator, thereby reducing energy density loss to a certain extent.

[0037] In a detailed embodiment, S is provided to be 1.1 to 3.3. For example, S is provided to be 1.1, 1.3, 1.5, 1.7, 1.9, 2.1, 2.3, 2.5, 2.8, 3.1, or 3.3. In this range, the supporting effect of the separator on the negative electrode active layer can be further improved to prevent the negative electrode plate from peeling off from the separator due to the volume expansion of the negative electrode active material and the separator from cracking, which would impair the cycling performance and safety of the battery. In addition, crushing of the battery case caused by the volume expansion of the negative electrode material is further reduced to prevent leakage caused by a damaged corner.

[0038] In a detailed embodiment, it is provided that q 0 to 0.3, d3 50 µm to 80 µm, φ 10 to 30, and ρ 7 mg / cm 2 up to 12 mg / cm 2For example, it is intended that q is 0, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3, that d3 is 50 µm, 55 µm, 60 µm, 65 µm, 70 µm, 75 µm or 80 µm, that φ is 10, 15, 20, 25 or 30, and that ρ is 7 mg / cm 2 , 8 mg / cm 2 , 9 mg / cm 2 , 10 mg / cm 2 , 11 mg / cm 2 or 12 mg / cm 2 Now, the volume expansion of the negative electrode active layer can be further suppressed, further reducing the initial expansion of the negative electrode active layer in the thickness and width directions, and preventing over-expansion of the negative electrode plate, which leads to crushing of the separator and the casing, and thus to leakage caused by a damaged corner. At the same time, energy density loss can also be reduced, ensuring that the battery has a high energy density.

[0039] In a detailed embodiment, W is provided to be 2 to 80. For example, W is 2, 10, 20, 30, 40, 50, 60, 70, or 80. In this range, it is not only possible to further suppress the volume expansion of the negative electrode active material and thus mitigate the crushing of the battery case by the negative electrode material, so that the battery has a long cycle life, but it can also be ensured that the battery has a high energy density.

[0040] In a detailed embodiment, it is provided that the separator further comprises an adhesive layer on each side of the substrate, wherein the adhesive layer has a thickness of 0.5 µm to 3 µm.

[0041] For example, the thickness of the adhesive layer is 0.5 µm, 1.0 µm, 1.5 µm, 2.0 µm, 2.5 µm or 3.0 µm.

[0042] The thickness of the adhesive layer according to the invention is a thickness of the adhesive layer on a single side.

[0043] In the present invention, there is also no specific limitation on the type of adhesive layer, e.g., selected from at least one of the following: polyvinylidene fluoride, polymethyl methacrylate, polyimide, polyetherimide, polyamideimide.

[0044] When the thickness of the adhesive layer is within the above range, not only can the force of action between the separator and the negative electrode plate be improved to ensure that the separator does not peel off from the negative electrode plate due to the expansion of the negative electrode active material, which contributes to improving the cycle stability of the battery, but also can reduce the energy density loss.

[0045] In a detailed embodiment, it is provided that the separator further comprises a ceramic layer, wherein the ceramic layer is arranged on at least one surface of the adhesive layer facing away from the substrate, and wherein the ceramic layer has a thickness of 0.5 µm to 3 µm.

[0046] For example, the thickness of the ceramic layer is 0.5 µm, 1.0 µm, 1.5 µm, 2.0 µm, 2.5 µm or 3.0 µm.

[0047] In the present invention, there is also no specific limitation on the type of the ceramic layer, e.g., it comprises at least one of alumina, boehmite, magnesium oxide, silicon oxide, aluminum nitride, magnesium hydroxide, barium sulfate.

[0048] When the separator includes a ceramic layer, electrolyte absorption by the separator can be increased and thermal shrinkage of the separator can be reduced, thus improving the cycle performance and safety of the battery. When the thickness of the ceramic layer is within the above range, energy density loss can be reduced.

[0049] The lithium-ion battery according to the invention is explained in more detail below by means of detailed embodiments. Example 1 1) Artificial graphite and silicon carbide (85:15 by mass) as the negative electrode active material, carbon black as the conductive agent, styrene-butadiene rubber as the binder, and sodium carboxymethyl cellulose as the dispersant were dispersed in a suitable amount of deionized water at a mass ratio of 97.2:0.5:1:1.3, and then sufficiently stirred to form a homogeneous negative electrode slurry. The negative electrode slurry was then evenly coated onto the surface of a copper foil with a thickness of 6 μm and a tensile strength of 0.55 GPa in the length direction by a coating machine. A negative electrode plate with a one-sided areal density of 9 mg / cm³ was then prepared. 2 , a one-sided compacted density of 1.73 g / cm 3and an OI value of 20 after the processes of drying, roller pressing, and cutting, etc. The one-sided thickness of the active layer for the negative electrode is 65 µm. 2) Lithium cobalt oxide as the positive electrode active material, carbon black as the conductive agent, and polyvinylidene fluoride as the binder were dispersed in an appropriate amount of N-methylpyrrolidone at a mass ratio of 97.6:1.2:1.2, and then sufficiently stirred to form a homogeneous positive electrode slurry. The positive electrode slurry was then evenly coated onto the surface of a 10 μm-thick aluminum foil by a coating machine. A positive electrode plate with a one-sided areal density of 16.7 mg / cm was then prepared. 2 , a one-sided compacted density of 4.12 g / cm 3 obtained after the processes of drying, roller pressing and cutting, etc. 3) The separator comprised a 5.3 µm thick polyethylene layer and a polyvinylidene fluoride layer deposited on both sides of the polyethylene layer. A ceramic alumina layer was provided on one surface of the polyvinylidene fluoride layer. The thickness of the ceramic alumina layer was 2 µm, the thickness of the polyvinylidene fluoride layer on both sides was 1 µm, and the puncture resistance of the polyethylene layer in the substrate was 0.39 kgf. 4) The negative electrode plate, separator, positive electrode plate, and separator, cut to a fixed size, were stacked sequentially, with the ceramic-coated side of the separator facing the positive electrode plate. A wound core was fabricated by winding, with the casing being an aluminum-plastic foil with a cavity measuring 79.2 mm long and 60.8 mm wide. The wound core was fixed in the cavity of the aluminum-plastic foil, and the wound core was impregnated with an electrolyte, which was a mixed solution containing ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), and 1,3-propanesultone (PS) in a weight ratio of 16:16:48:15:3:2. After formation, secondary packaging and sorting, the battery has a voltage of 3.75 V, an initial thickness of 3.34 mm and a capacity of 3001 mAh. Example 2

[0050] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the thickness of the copper foil was set to 4 µm and its tensile strength to 0.43 GPa, and the one-sided thickness of the negative electrode active layer was set to 76 µm, the OI value to 14.5, and the one-sided areal density to 9.67 mg / cm 2 was discontinued; and that in step 3) the thickness of the polyethylene layer was set to 4.2 µm and the puncture resistance of the polyethylene layer in the substrate was set to 0.22 kgf. Example 3

[0051] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the mass ratio between the artificial graphite and the silicon carbide was set to 92:8, the thickness of the copper foil was set to 4 µm, and its tensile strength was set to 0.43 GPa, and the one-sided thickness of the negative electrode active layer was set to 67 µm, the OI value was set to 12.9, and the one-sided areal density was set to 9.25 mg / cm 2 was discontinued; and that in step 3) the thickness of the polyethylene layer was set to 4.2 µm and the puncture resistance of the polyethylene layer in the substrate was set to 0.22 kgf. Example 4

[0052] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the mass ratio between the artificial graphite and the silicon carbide was set to 96:4, the thickness of the copper foil was set to 5 µm, and its tensile strength was set to 0.48 GPa, and the one-sided thickness of the negative electrode active layer was set to 67 µm, the OI value was set to 12.9, and the one-sided areal density was set to 9.24 mg / cm 2 was discontinued; and that in step 3) the thickness of the polyethylene layer was set to 4.7 µm and the puncture resistance of the polyethylene layer in the substrate was set to 0.28 kgf. Example 5

[0053] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the tensile strength of the copper foil was adjusted to 0.3 GPa. Example 6

[0054] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the tensile strength of the copper foil was adjusted to 0.8 GPa. Example 7

[0055] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the thickness of the copper foil was set to 3 µm. Example 8

[0056] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the thickness of the copper foil was set to 9 µm. Example 9

[0057] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the thickness of the copper foil was set to 4 µm and its tensile strength was set to 0.33 GPa. Example 10

[0058] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the thickness of the copper foil was set to 9 µm and its tensile strength was set to 0.8 GPa. Example 11

[0059] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 3), the puncture strength of the polyethylene layer was set to 0.18 kgf. Example 12

[0060] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 3), the puncture strength of the polyethylene layer was set to 0.6 kgf. Example 13

[0061] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 3) the thickness of the polyethylene layer was set to 3.5 µm. Example 14

[0062] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 3) the thickness of the polyethylene layer was set to 7 µm. Example 15

[0063] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 3), the thickness of the polyethylene layer was set to 3.7 µm and the puncture strength of the polyethylene layer in the substrate was set to 0.18 kgf. Example 16

[0064] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 3), the thickness of the polyethylene layer was set to 7 µm and the puncture strength of the polyethylene layer in the substrate was set to 0.6 kgf. Example 17

[0065] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the negative electrode active material was replaced with pure artificial graphite and no silicon carbide was used. Example 18

[0066] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the one-sided thickness of the negative electrode active layer was set to 50 µm, and the OI value of the negative electrode plate was set to 13. Example 19

[0067] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the one-sided thickness of the negative electrode active layer was set to 80 µm, and the OI value of the negative electrode plate was set to 26. Example 20

[0068] The method for producing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the one-sided areal density of the negative electrode plate was set to 7 mg / cm 2 was discontinued. Example 21

[0069] The method for producing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the one-sided areal density of the negative electrode plate was set to 12 mg / cm 2 was discontinued. Example 22

[0070] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the negative electrode active material was replaced with pure artificial graphite and no silicon carbide was used, and the one-sided thickness of the negative electrode active layer was set to 53 μm, the OI value of the negative electrode plate was set to 23, and the one-sided areal density of the negative electrode plate was set to 8.3 mg / cm 2 was discontinued. Example 23

[0071] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the one-sided thickness of the negative electrode active layer was 75 μm, the OI value was 18, and the mass ratio between the artificial graphite and the silicon carbide of the negative electrode active material was set to 70:30. The thickness of the copper foil was set to 7 μm, its tensile strength was set to 0.6 GPa, and the OI value of the negative electrode plate was set to 18 and its one-sided areal density was set to 9.97 mg / cm 2 was set; and that in step 3) the thickness of the polyethylene layer was set to 7 µm and the puncture resistance of the polyethylene layer in the substrate was set to 0.6 kgf. Example 24

[0072] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the one-sided thickness of the negative electrode active layer was 83 μm, the OI value was 35, and the mass ratio between the artificial graphite and the silicon carbide of the negative electrode active material was set to 64:36, the thickness of the copper foil was set to 10.00 μm, its tensile strength was set to 0.85 GPa, the OI value of the negative electrode plate was set to 35.0, and its one-sided areal density was set to 12.42 mg / cm 2 was discontinued; and that in step 3) the thickness of the polyethylene layer was set to 9.0 µm and the puncture strength of the polyethylene layer in the substrate was set to 0.73 kgf. Comparison example 1

[0073] The method for producing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the mass ratio between the artificial graphite and the silicon carbide was set to 70:30, the one-sided thickness of the negative electrode active layer was set to 75 µm, the OI value of the negative electrode plate was set to 18, and the one-sided areal density of the negative electrode plate was set to 9.97 mg / cm 2 was discontinued. Comparison example 2

[0074] The method for manufacturing the lithium-ion battery in this example is essentially the same as in Example 1, except that in step 1), the mass ratio between the artificial graphite and the silicon carbide was set to 89:11, the thickness of the copper foil was set to 2.8 µm, and its tensile strength was set to 0.21 GPa, and the one-sided thickness of the negative electrode active layer was set to 84 µm, the OI value was set to 35, and the one-sided areal density was set to 13 mg / cm 2 was discontinued; and that in step 3) the thickness of the polyethylene layer was set to 3 µm and the puncture resistance of the polyethylene layer in the substrate was set to 0.15 kgf. Exam example

[0075] 1. The tensile strength of the negative electrode current collector in the length direction, the thickness of the negative electrode current collector, the puncture strength of the separator, the thickness of the substrate in the separator, the thickness and OI value of the negative electrode active layer were tested for the above-mentioned respective examples and comparative examples. (1) Tensile strength of the negative electrode current collector in the length direction

[0076] The negative electrode current collector is cut into rectangular plate-shaped specimens with a length of 200 mm and a width of 13 mm. The length direction refers to the stretching direction, and the loading area A0 of the rectangular plate-shaped specimen is calculated perpendicular to the stretching direction. The test is then performed using a tensile testing machine at a tensile speed of 50 mm / min, and the loading force at the time of fracture of the rectangular plate-shaped specimen is recorded as F0, so the tensile strength m1 is equal to F0 / A0 in GPa. (2) Thickness of the current collector for the negative electrode

[0077] The thickness of the negative electrode current collector was measured in µm using a micrometer. (3) Puncture resistance of the separator

[0078] The puncture resistance of the separator was tested according to GB / T 36363-2018. (4) Thickness of the substrate in the separator

[0079] For the substrate, SEM examination was performed and the cross section of the substrate was observed to obtain the thickness of the substrate in µm. (5) Thickness of the active layer for the negative electrode

[0080] The thickness of the negative electrode current collector was measured with a micrometer, and then the thickness of the negative electrode plate including the negative electrode current collector was measured with the micrometer, so that the thickness of the negative electrode active layer is (thickness of the negative electrode plate - thickness of the negative electrode current collector) / 2 in µm. (6) OI value of the active layer for the negative electrode

[0081] An XRD test is performed on the negative electrode plate. The OI value is the ratio of the intensity of a diffraction peak of the (004) crystal plane to the intensity of a diffraction peak of the (110) crystal plane in the test result, where 2θ of the diffraction peak of the (004) crystal plane is between 53.7° and 55.7°, and 2θ of the diffraction peak of the (110) crystal plane is between 76.4° and 78.4°.

[0082] The test result and the calculation result are shown in Table 1 and Table 2. Table 1 m1 GPa d1 µm m2 kgf d2 µm d3 µm φ q p mg / cm 2 Example 1 0,55 6,00 0,39 5,3 65 20 0,15 9,00 Example 2 0,43 4,00 0,22 4,2 76 14,5 0,15 9,67 Example 3 0,43 4,00 0,22 4,2 67 12,9 0,08 9,25 Example 4 0,48 5,00 0,28 4,7 67 12,9 0,04 9,24 Example 5 0,3 6,00 0,39 5,3 65 20 0,15 9,00 Example 6 0,8 6,00 0,39 5,3 65 20 0,15 9,00 Example 7 0,55 3,00 0,39 5,3 65 20 0,15 9,00 Example 8 0,55 9,00 0,39 5,3 65 20 0,15 9,00 Example 9 0,33 4,00 0,39 5,3 65 20 0,15 9,00 Example 10 0,8 9,00 0,39 5,3 65 20 0,15 9,00 Example 11 0,55 6,00 0,18 5,3 65 20 0,15 9,00 Example 12 0,55 6,00 0,60 5,3 65 20 0,15 9,00 Example 13 0,55 6,00 0,39 3,5 65 20 0,15 9,00 Example 14 0,55 6,00 0,39 7,0 65 20 0,15 9,00 Example 15 0,55 6,00 0,18 3,7 65 20 0,15 9,00 Example 16 0,55 6,00 0,60 7,0 65 20 0,15 9,00 Example 17 0,55 6,00 0,39 5,3 65 20 0 9,00 Example 18 0,55 6,00 0,39 5,3 50 13 0,15 9,00 Example 19 0,55 6,00 0,39 5,3 80 26 0,15 9,00 Example 20 0,55 6,00 0,39 5,3 65 20 0,15 7,00 Example 21 0,55 6,00 0,39 5,3 65 20 0,15 12,00 Example 22 0,55 6,00 0,39 5,3 53 23 0 8,3 Example 23 0,6 7,00 0,60 7,0 75 18 0,3 9,97 Example 24 0,85 10,00 0,73 9,0 83 35,0 0,36 12,42 Comparison example 1 0,55 6,00 0,39 5,3 75 18 0,3 9,97 Comparison example 2 0,21 2,80 0,15 3 84 35 0,11 13,00 Table 2 M S W ((M+50) 2 +S 2 ) / (W 2 ×1000) Example 1 2,3 1,8 12,74 65 Example 2 1,5 1,2 17,38 20 Example 3 1,5 1,2 7,05 50 Example 4 1,8 1,4 4,88 100 Example 5 1,2 1,8 12,74 34 Example 6 3,3 1,8 12,74 107 Example 7 1,5 1,8 12,74 41 Example 8 3,1 1,8 12,74 97 Example 9 1,2 1,8 12,74 34 Example 10 4,9 1,8 12,74 188 Example 11 2,3 1,1 12,74 43 Example 12 2,3 2,6 12,74 93 Example 13 2,3 1,5 12,74 53 Example 14 2,3 2,2 12,74 78 Example 15 2,3 1,1 12,74 42 Example 16 2,3 3,3 12,74 124 Example 17 2,3 1,8 3,03 274 Example 18 2,3 1,8 9,06 92 Example 19 2,3 1,8 16,43 51 Example 20 2,3 1,8 8,11 102 Example 21 2,3 1,8 19,69 42 Example 22 2,3 1,8 2,01 413 Example 23 2,8 3,3 79,94 26 Example 24 5,8 5,1 226,89 47 Comparison example 1 2,3 1,8 79,94 10 Comparison example 2 1,0 1,0 20,20 12

[0083] From Table 1 and Table 2 it can be seen that all lithium ion batteries in Examples 1 to 26 satisfy Equation 1, with Example 1, Example 3, Example 4, Example 6, Example 8, Example 10, Examples 12 to 14, 16 to 20, and Example 22 satisfying Equation 2, while Comparative Example 1 and Comparative Example 2 not satisfying Equation 1.

[0084] 2. The lithium-ion batteries in the above-mentioned respective examples and comparative examples were tested for leakage due to a damaged corner, cycle performance, energy density, rate capacity and self-discharge ability. (1) Cycle performance and leakage due to a damaged corner

[0085] Room temperature cycling performance: Each lithium-ion battery prepared in the above-mentioned respective examples and comparative examples was placed in an environment with a temperature of 25 ± 2°C, charged at a constant current of 1 C to a reverse current of 0.05 C, and after the battery was fully charged, it was left standing for 5 minutes and then discharged at a constant current of 0.5 C to a reverse voltage of 3.0 V. Three cycles were performed according to the above-mentioned charging and discharging mechanism, and the highest discharge capacity during the first three cycles was recorded as the initial capacity Q0, and after 800 cycles, the discharge capacity of the battery was recorded as Q1, so that the capacity retention rate of the battery at high temperature is Q1 / Q0×100%.During this process, the appearance of the battery was also checked every 50 cycles and it was observed and recorded whether any cracks appeared at the four corners of the battery.

[0086] High-temperature cycling performance: Each lithium-ion battery manufactured in the above-mentioned respective examples and comparative examples was placed in an environment with a temperature of 45 ± 2°C and allowed to stand still. When the battery body temperature reached 45 ± 2°C, the battery was charged at a constant current of 1.2C to a voltage of 4.25V, then at a current of 0.7C to an upper limit voltage of 4.53V. Subsequently, the battery was charged at a constant voltage to a current of 0.025C and allowed to stand still for 10 minutes. Then, the battery was discharged at a current of 0.5C to a voltage of 3V and allowed to stand still for 10 minutes.A cyclic test was conducted according to the above-mentioned charging and discharging mechanism, and after 500 cycles, the discharge capacity of the battery was recorded as Q3, so that the battery's capacity retention rate at high temperature is Q2 / Q3×100%. During this process, the battery's appearance was also checked every 50 cycles, and whether any cracks appeared at the corners was observed and recorded. (2) Self-discharge capacity

[0087] The value K is used in the present invention to evaluate the self-discharge capacity of the battery. Specifically, after completing the capacity classification of each cell prepared in the above-mentioned respective examples and comparative examples, the cell was placed in a high-temperature room of 45°C and left to stand for 48 hours. After this standstill period, the cell was further left to stand in an environment with a temperature of 25°C for 36 hours. After this standstill period, the voltage of the cell was recorded as V1 (mV). Then, the cell was further left to stand for T hours (about 72 hours), and after this standstill period, the voltage of the cell was recorded as V2 (mV), so that the value K was (V1-V2) / T in mV / h.

[0088] The test results are shown in Table 3. Table 3 Retention rate of capacity for 800 cycles at room temperature % whether a leak occurred after 800 cycles at room temperature due to a damaged corner the number of cycles at room temperature with a leak due to a damaged corner Capacity retention rate for 500 cycles at high temperature % whether leakage occurred after 500 cycles at high temperature due to a damaged corner the number of cycles at high temperature with a leak due to a damaged corner Value t K mV / h Example 1 81,48 no / 73,12 no / 0,0 220 Example 2 76,15 no / 65,49 Yes 350 cycles 0,0 281 Example 3 82,32 no / 74,32 no / 0,0 248 Example 4 82,92 no / 74,29 no / 0,0 213 Example 5 77,75 no / 66,48 Yes 400 cycles 0,2 790 Example 6 81,18 no / 74,48 no / 0,0 194 Example 7 77,96 no / 67,33 Yes 400 cycles 0,0 275 Example 8 80,83 no / 73,95 no / 0,0 183 Example 9 77,36 no / 65,39 Yes 400 cycles 0,0 288 Example 10 82,49 no / 74,73 no / 0,0 184 Example 11 76,55 no / 67,37 Yes 450 cycles 0,0 277 Example 12 80,38 no / 73,65 no / 0,0 192 Example 13 80,03 no / 73,16 no / 0,0 202 Example 14 81,16 no / 73,46 no / 0,0 195 Example 15 78,12 no / 67,95 Yes 450 cycles 0,0 256 Example 16 82,12 no / 74,65 no / 0,0 173 Example 17 84,18 no / 75,59 no / 0,0 159 Example 18 81,04 no / 74,28 no / 0,0 177 Example 19 79,36 no / 73,19 no / 0,0 203 Example 20 81,55 no / 74,59 no / 0,0 187 Example 21 78,02 no / 67,32 Yes 450 cycles 0,0 255 Example 22 84,33 no / 75,42 no / 0,0 136 Example 23 75,38 no / 56,63 Yes 350 cycles 0,0 315 Example 24 76,12 no / 54,37 Yes 350T 0,0 146 Comparison example 1 38,47 Yes 150 cycles 48,37 Yes 100 cycles 0,0 416 Comparison example 2 45,12 Yes 200 cycles 48,52 Yes 150 cycles 0,0 352

[0089] From Table 1 to Table 3 it can be seen that The lithium-ion batteries in Examples 1 to 24 each exhibit improved cycle performance and a lower probability of corner damage leakage compared to Comparative Examples 1 and 2. The lithium-ion battery in Example 22 exhibits a capacity retention rate of up to 84.33% for 800 cycles at room temperature and up to 75.42% for 500 cycles at high temperature without corner damage leakage, with a K value of 0.0136. In contrast, the lithium-ion battery in the corresponding Comparative Example exhibits a capacity retention rate of only 45.12% for 800 cycles at room temperature and 48.52% for 500 cycles at high temperature. Corner damage leakage occurred at 200 cycles at room temperature and 150 cycles at high temperature.It can be seen that the lithium-ion battery according to the present invention can effectively overcome the crushing of the battery case caused by the volume expansion of the negative electrode material, which can thus effectively improve the cycle life and safety of the battery.

[0090] Finally, it should be noted that the above-mentioned individual embodiments are used only to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention is described in detail with reference to the above individual embodiments, those of ordinary skill in the art should understand that they may modify the technical solutions described in the above embodiments or substitute some or all of the technical features contained therein for equivalents; and that these modifications or substitutions, however, do not cause the essence of the respective technical solutions to deviate from the scope of the technical solutions of the individual embodiments of the present invention.

Claims

[1] Lithium-ion battery, characterized by that the lithium-ion battery comprises a negative electrode plate and a separator, wherein the negative electrode plate comprises a current collector for the negative electrode and an active layer for the negative electrode arranged on at least one functional surface of the current collector for the negative electrode, wherein the active layer for the negative electrode contains an active material for the negative electrode, wherein the lithium-ion battery satisfies the following equation 1: (2M+3)2(S+2)2 / W≥20 where in equation 1 M = exp (m1 / d1) + (d1-2) (m1-0.26), where m1 is the tensile strength of a negative electrode current collector in a length direction in GPa and d1 is the thickness of the negative electrode current collector in µm; and where S = exp (m2 / d2) + (d2-2) (m2-0.16), where m2 is the puncture resistance of the separator in kgf and d2 is the thickness of a substrate in the separator in µm; and where W = ((exp (-10q)) / (φ-6) + exp (10q)) (d3-13.5) (ρ-3.5) / 100, where d3 is the thickness of the negative electrode active layer in µm, φ is an OI value of the negative electrode active layer, q is the mass percentage of a silicon-based negative electrode material in the negative electrode active material, and ρ is the areal density of the negative electrode active layer in mg / cm 2 stands. [2] Lithium ion battery according to claim 1, characterized by that the lithium-ion battery satisfies the following equation 2: (2M+3)2(S+2)2 / W≥50 [3] Lithium ion battery according to claim 1 or 2, characterized by that m1 is 0.3 GPa to 0.8 GPa and d1 is 3 µm to 9 µm. [4] Lithium ion battery according to claim 3, characterized by that M is 1.2 to 4.

9. [5] Lithium ion battery according to one of claims 1 to 4, characterized by that m2 is 0.18 kgf to 0.6 kgf and d2 is 3.5 µm to 7 µm. [6] Lithium ion battery according to claim 5, characterized by that S is 1.1 to 3.

3. [7] Lithium ion battery according to one of claims 1 to 6, characterized by that q 0 to 0.3, d3 50 µm to 80 µm, φ 10 to 30, and ρ 7 mg / cm 2 up to 12 mg / cm 2 amounts. [8] Lithium ion battery according to claim 7, characterized by that W is 2 to 80. [9] Lithium ion battery according to one of claims 1 to 8, characterized by that the separator further comprises an adhesive layer on both sides of the substrate, and the adhesive layer has a thickness of 0.5 to 3 µm. [10] Lithium ion battery according to claim 9, characterized bythat the separator further comprises a ceramic layer, wherein the ceramic layer is arranged on at least one surface of the adhesive layer facing away from the substrate, and the ceramic layer has a thickness of 0.5 to 3 µm on a single side.