Battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery which comprises a positive plate, a negative plate and a diaphragm located between the positive plate and the negative plate, the diaphragm comprises a base material layer and a ceramic layer located on the surface of one side of the base material layer, a first polymer glue layer is arranged on the surface of the side, away from the base material layer, of the ceramic layer, and a second polymer glue layer is arranged on the surface of the side, away from the ceramic layer, of the base material layer. The diaphragm in the battery can provide certain binding force for the expansion of the silicon negative electrode, the contact resistance at an interface is reduced, the stress acting on the positive plate during the expansion of the silicon negative electrode is reduced, and the transmission rate of lithium ions in the battery is improved, so that the cycle performance and the safety performance of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a battery. Background Art

[0002] Due to many advantages, lithium-ion batteries have become the main power source for consumer electronics and electric vehicles. At present, the diaphragms of lithium-ion batteries adopt gravure roll coating and gravure dip coating. During the dip coating and gravure coating processes, the entire surface of the diaphragm is coated with an adhesive layer. The adhesive layer itself has high adhesiveness. During high-temperature formation hot pressing, the adhesive layer will bond with the electrode sheet, and the adhesion force between the diaphragm and the electrode sheet is too large, resulting in difficult displacement at the junction of the single and double sides of the positive electrode sheet. When the positive electrode sheet is cycled, the electrode sheet is prone to break at the junction of the single and double sides. Especially for batteries containing silicon-based materials, the silicon negative electrode expands in the later stage of cycling, further increasing the risk of positive electrode sheet fragmentation, seriously affecting the safety performance of the battery; moreover, the expansion of the silicon negative electrode prolongs the lithium-ion diffusion distance, increases the contact impedance at the electrode interface, hinders the diffusion and migration of lithium ions on the electrode surface, increases the risk of lithium deposition, and also significantly reduces the cycling performance of lithium-ion batteries. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above problems existing in the prior art and provide a battery. The diaphragm in the battery of the present invention can provide a certain binding force for the expansion of the silicon negative electrode, reduce the contact resistance at the interface and reduce the stress acting on the positive electrode sheet when the silicon negative electrode expands, thereby reducing the risk of electrode sheet fragmentation and the risk of lithium deposition; and can simultaneously improve the transmission rate of lithium ions in the battery, thereby simultaneously improving the cycling performance and safety performance of the battery.

[0004] The present invention provides a battery, which includes a positive electrode sheet, a negative electrode sheet, and a diaphragm located between the positive electrode sheet and the negative electrode sheet. The diaphragm includes a substrate layer and a ceramic layer on one surface of the substrate layer. A first polymer adhesive layer is provided on the surface of the ceramic layer facing away from the substrate layer, and a second polymer adhesive layer is provided on the surface of the substrate layer facing away from the ceramic layer;

[0005] The first polymer adhesive layer is close to the positive electrode sheet, the second polymer adhesive layer is close to the negative electrode sheet, the coverage rate of the first polymer adhesive layer relative to the substrate layer is A, the coverage rate of the second polymer adhesive layer relative to the substrate layer is B, and the coverage rate B of the second polymer adhesive layer relative to the substrate layer is greater than the coverage rate A of the first polymer adhesive layer relative to the substrate layer;

[0006] The negative electrode sheet includes a negative electrode active material, the negative electrode active material includes a silicon-based material, the particle size Dv50 of the silicon-based material is S, and A, B, and S satisfy 1 ≤ 100*|A - B| / S ≤ 9.

[0007] Through the above technical solution, the present invention has at least the following advantages compared with the prior art: The separator in the battery of the present invention can provide a certain binding force for the expansion of the silicon negative electrode by designing the coverage difference of the polymer glue layers on both sides of the separator and the particle size of the silicon particles in the silicon negative electrode, reduce the contact resistance at the interface and reduce the stress acting on the positive electrode sheet when the silicon negative electrode expands, thereby reducing the risk of pole piece fragmentation and the risk of lithium plating on the pole piece, improving the cycling performance and safety performance of the lithium-ion battery; and can simultaneously improve the transmission rate of lithium ions in the battery, reduce side reactions during the charge and discharge process of the battery, improve the chemical stability of the battery, and thus extend the cycle life of the battery.

[0008] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Schematic diagram of the separator structure in an example provided by the present invention;

[0010] Figure 2 SEM image of the surface of the ceramic layer in an example provided by the present invention;

[0011] Figure 3 SEM image of the side surface of the first polymer glue layer of the separator in an example provided by the present invention;

[0012] Figure 4 SEM image of the side surface of the second polymer glue layer of the separator in an example provided by the present invention.

[0013] Reference numerals:

[0014] Substrate layer - 100, ceramic layer - 110, first polymer glue layer 111, second polymer glue layer - 120. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0016] The present invention provides a battery, which includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet. The separator includes a base material layer and a ceramic layer located on one surface of the base material layer. A first polymer adhesive layer is provided on the surface of the ceramic layer facing away from the base material layer, and a second polymer adhesive layer is provided on the surface of the base material layer facing away from the ceramic layer;

[0017] The first polymer adhesive layer is close to the positive electrode sheet, the second polymer adhesive layer is close to the negative electrode sheet. The coverage rate of the first polymer adhesive layer relative to the base material layer is A, and the coverage rate of the second polymer adhesive layer relative to the base material layer is B. The coverage rate B of the second polymer adhesive layer relative to the base material layer is greater than the coverage rate A of the first polymer adhesive layer relative to the base material layer;

[0018] The negative electrode sheet includes a negative electrode active material, the negative electrode active material includes a silicon-based material, and the particle size Dv50 of the silicon-based material is S. A, B, and S satisfy 1 ≤ 100 * |A - B| / S ≤ 9.

[0019] The battery of the present invention includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet. Among them, the separator is as Figure 1 shown Figure 1 is a schematic diagram of the separator structure in an example provided by the present invention. The separator includes a base material layer 100 and a ceramic layer 110 located on one surface of the base material layer 100. A first polymer adhesive layer 111 is provided on the surface of the ceramic layer 110 facing away from the base material layer 100, and a second polymer adhesive layer 120 is provided on the surface of the base material layer 100 facing away from the ceramic layer 110.

[0020] Furthermore, in the present invention, the first polymer adhesive layer is close to the positive electrode sheet, the second polymer adhesive layer is close to the negative electrode sheet. The coverage rate of the first polymer adhesive layer relative to the base material layer is A, and the coverage rate of the second polymer adhesive layer relative to the base material layer is B. The coverage rate B of the second polymer adhesive layer relative to the base material layer is greater than the coverage rate A of the first polymer adhesive layer relative to the base material layer.

[0021] By controlling the coverage rate of the polymer adhesive layer on the side of the separator close to the positive electrode sheet relative to the substrate layer to be less than that of the polymer adhesive layer on the side close to the negative electrode sheet, the adhesive force between the separator and the positive electrode sheet can be reduced, making it smaller than the adhesive force between the separator and the negative electrode sheet. The decrease in the adhesive force between the separator and the positive electrode sheet can, on the one hand, prevent the active material of the positive electrode sheet from peeling off from the current collector or the structure of the active substance from changing, thereby preventing internal short circuit of the battery and capacity drop of the electrode sheet during cycling, and avoiding affecting the safety performance and cycle life of the battery; on the other hand, by relatively reducing the coverage area of the polymer adhesive layer on the positive electrode sheet side relative to the substrate layer so that its adhesive layer coverage rate is less than that of the negative electrode sheet side, expansion space can be provided for the expansion of the negative electrode active material during cycling, reducing the expansion stress generated by the negative electrode expansion. Moreover, because the adhesion between the separator and the positive electrode side is weak, a certain degree of displacement can occur between the separator and the positive electrode sheet during negative electrode expansion, avoiding the stacking of expansion stress on vulnerable positions of the positive electrode sheet (for example, at the junction of the single side and double side of the positive electrode sheet, because the transition extrusion of the positive electrode active layer on the positive electrode current collector may cause damage at the junction of the single side and double side), or forming a region with high stress on the positive electrode sheet (for example, the outermost or the second outermost circular arc region of the positive electrode sheet, because due to the characteristics of the winding structure, the closer to the outer circle of the wound battery cell, the more uneven the force on the circular arc region, the greater the expansion force from the inside to the outside, and the smaller the binding force from the outside to the inside, resulting in an increased risk of fracture in the outermost or the second outermost circular arc region of the positive electrode sheet), thus avoiding the breakage of the positive electrode tab caused by the expansion of the silicon negative electrode, reducing the risk of electrode sheet breakage, and further improving the safety performance of the battery.

[0022] Among them, the test method for the coverage rates of the first polymer adhesive layer and the second polymer adhesive layer relative to the substrate layer respectively is as follows: After disassembling the separator in the battery and cleaning it, take a small piece of the separator and cut it into several small separator samples of 10 mm×10 mm (for example, take 5 small separator samples of 10 mm×10 mm), then place several small separator samples under a scanning electron microscope (SEM) and take pictures at a magnification of 5000 times. Test the adhesive layer area of these small separator samples and the area of the entire separator through the SEM, count the coverage rate of each small separator sample, and then take the average value to obtain the coverage rate of the first polymer adhesive layer or the second polymer adhesive layer on the observation surface (that is, relative to the substrate layer), that is, the coverage rate A of the first polymer adhesive layer relative to the substrate layer, or the coverage rate B of the second polymer adhesive layer relative to the substrate layer.

[0023] Further, the surface of the polymer adhesive layer on the side of the separator of the present invention with the ceramic layer faces the positive electrode sheet, and the polymer adhesive layer on the other side faces the negative electrode sheet, and the coverage rate B of the second polymer adhesive layer facing the negative electrode sheet is greater than the coverage rate A of the first polymer adhesive layer facing the positive electrode sheet. Through such a structural design, the second polymer adhesive layer with a higher coverage rate can effectively form a buffer layer on the negative electrode sheet side, and since the polymer adhesive layer has good flexibility and adhesiveness, it can well absorb the expansion stress of the silicon negative electrode, thereby reducing the extrusion of the separator caused by the expansion of the negative electrode silicon, avoiding the problem of internal short circuit caused by the local area of the separator becoming thinner and thermally shrinking, and further improving the safety performance of the battery; in addition, the positive electrode active material is prone to generate more heat when working at a high voltage. At this time, the separator adhesive with a low coverage rate on the positive electrode sheet side can make the positive electrode sheet have a large-area contact with the ceramic coating with high thermal stability, effectively preventing the problem of shrinkage or melting of the separator at high temperature, thereby further improving the thermal safety of the battery.

[0024] Furthermore, in the present invention, the negative electrode sheet includes a negative electrode active material, the negative electrode active material includes a silicon-based material, the particle size Dv50 of the silicon-based material is S, and A, B, and S satisfy 1 ≤ 100 * |A - B| / S ≤ 9, for example, 1, 2, 3, 4, 5, 6, 7, 8, or 9. Among them, the particle size Dv50 is also called the median particle size, which refers to the particle size value corresponding to the cumulative volume distribution percentage reaching 50%.

[0025] When 100*|A - B| / S is less than 1, it will cause the coverage rate difference between the first polymer adhesive layer and the second polymer adhesive layer to be too small or the particle size Dv50 of the silicon-based material of the negative electrode active material to be too large. If the coverage rate difference between the first polymer adhesive layer and the second polymer adhesive layer is too small, the adhesion force difference on both sides of the separator will be small, weakening the effect of reducing the expansion stress generated by the negative electrode swelling. And if the particle size of the silicon particles is also large at the same time, it will further exacerbate the adverse effects caused by the swelling of the silicon negative electrode. When the particle size Dv50 of the silicon-based material of the negative electrode active material is too large, the large-particle silicon-based material is likely to pierce the separator after swelling and powdering, resulting in lithium plating or short circuit of the battery, seriously affecting the safety of the battery. When 100*|A - B| / S is greater than 9, the coverage rate difference between the first polymer adhesive layer and the second polymer adhesive layer is too large or the particle size Dv50 of the silicon-based material of the negative electrode active material is too small. If the coverage rate difference between the first polymer adhesive layer and the second polymer adhesive layer is too large, the adhesion force between the polymer adhesive layer on one side of the separator and the electrode sheet will be too low, which may lead to insufficient tightness between the separator and the electrode sheet, making the separator unable to provide a good binding force for the swelling of the silicon negative electrode. During the charge and discharge process of the battery, the separator may shift or wrinkle, affecting the stability of the internal structure of the battery and thus triggering safety problems. Moreover, the too-low adhesion force between the separator and the electrode sheet will also increase the contact resistance at the interface, accelerating the aging and attenuation of the battery active material, shortening the cycle life of the battery. And the increase in the contact resistance at the interface will also hinder the diffusion and migration of lithium ions on the electrode surface, resulting in the inability of lithium ions to be uniformly deintercalated and deposited to form lithium dendrites, easily causing the problem of lithium plating on the electrode sheet. If the particle size Dv50 of the silicon-based material is too small, it will lead to an increase in side reactions of the negative electrode active material, limited diffusion of lithium ions, and an increase in irreversible capacity due to particle crushing after the volume expansion of the silicon-based material, seriously affecting the capacity of the negative electrode active material and the safety and cycle performance of the battery.Therefore, by controlling the ratio range of 100*|A - B| / S within 1 to 9, that is, designing the ratio relationship between the difference in the coverage rate of the polymer adhesive layers on both sides of the separator and the particle size of the silicon particles of the silicon negative electrode, and making it satisfy 1 ≤ 100*|A - B| / S ≤ 9, the adhesive force on both sides of the separator can be balanced, as well as the relationship between the size of the compressible space and the size of the silicon-based material that actually generates cyclic volume expansion, so that the adhesive force on the positive electrode side of the separator is less than that on the negative electrode side of the separator, while maintaining a certain difference in adhesive force on both sides of the separator and avoiding too large a difference. This ensures that the separator provides a certain binding force for the expansion of the silicon negative electrode to a certain extent, reduces the contact resistance at the interface, and reduces the stress acting on the positive electrode sheet when the silicon negative electrode expands, thereby further reducing the risk of pole piece fragmentation and simultaneously improving the lithium deposition problem at the pole piece interface, enhancing the cycling performance and safety performance of the lithium-ion battery; moreover, by simultaneously adjusting the relationship between the coverage rate of the separator adhesive layer and the particle size of the silicon-based material of the negative active material, it is possible to avoid the silicon-based material from expanding and piercing the separator due to too large a particle size or the aggravation of side reactions caused by too large a contact area with the electrolyte, further enhancing the safety performance and cycling performance of the battery; in addition, the present invention can effectively improve the lithium-ion transmission rate between the separator and the negative electrode sheet. This is because the separator of the present invention can provide a certain binding force for the expansion of the silicon negative electrode, so that the increase in the thickness of the negative active layer caused by the expansion of the silicon-based material of the negative electrode is not particularly obvious, which helps to improve the lithium-ion transmission rate between the separator and the negative active layer, and the appropriate particle size of the silicon-based material can promote the effective diffusion of lithium ions between the separator and the negative electrode sheet, thereby effectively improving the lithium-ion transmission rate between the separator and the negative electrode sheet, and further making the battery more stable during long-term cyclic use and extending the cycle life of the battery.

[0026] In one example, 1 ≤ 100*|A - B| / S ≤ 5.

[0027] In one example, the positive electrode sheet includes a positive electrode current collector, and the tensile strength of the positive electrode current collector in the length direction is T. The A, B, and T satisfy 0.01 ≤ 100*|A - B| / T ≤ 0.2, such as 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.2.

[0028] In one example, 0.04 ≤ 100*|A - B| / T ≤ 0.1.

[0029] In one example, the tensile strength T of the positive current collector in the length direction is 200 MPa - 1000 MPa, such as 200 MPa, 210 MPa, 220 MPa, 230 MPa, 240 MPa, 250 MPa, 260 MPa, 270 MPa, 280 MPa, 290 MPa, 300 MPa, 400 MPa, 500 MPa, 600 MPa, 700 MPa, 800 MPa, 900 MPa or 1000 MPa.

[0030] Test method for the tensile strength of the positive current collector in the length direction: Place the positive current collector sample on the tensile test fixture of a universal testing machine and vertically fix the fixture; The universal testing machine applies stress to stretch the sample at a constant rate (10 m / min), causing the sample to elongate along the length direction of the positive current collector to produce tensile deformation until the sample ruptures or breaks; Read the maximum load stress value P max (in N), and calculate the tensile strength T of the positive current collector sample through the following formula, T = P max / S 正 , where S 正 is the initial cross-sectional area of the positive current collector.

[0031] By controlling the ratio range of |A - B| / T, the present invention can balance the relationship between the adhesion force between the separator and the positive electrode or the negative electrode and the ability of the positive electrode to resist expansion and stretching. The difference in the adhesion force between the separator and the positive electrode or the negative electrode can ensure that when the silicon negative electrode expands in volume during the later stage of the battery cycle, there is sufficient adhesion force between the negative electrode and the separator, inhibiting the expansion of the negative electrode while reducing the risk of the positive electrode strip breakage caused by the expansion of the negative electrode. Further, by controlling the relationship between the ability of the positive electrode to resist expansion and stretching and the difference in the coverage rates on both sides of the separator, it can be ensured that the difference in the adhesion force between the separator and the positive and negative electrodes is not too large, effectively preventing the distance between the positive and negative electrodes and the separator from becoming larger after the negative electrode expands, avoiding situations such as the lengthening of the lithium-ion transmission path between the silicon negative electrode and the separator and the hindrance of lithium-ion insertion and extraction, reducing the internal resistance of the battery, lowering the risk of lithium deposition, and improving the cycle performance of the battery, as well as avoiding problems such as lithium deposition on the negative electrode or short circuit and fire caused by the positive and negative electrodes, balancing the problem of positive electrode strip breakage while ensuring the electrical performance of the battery. Specifically, when 100*|A - B| / T is greater than 0.2, the tensile strength T of the positive electrode current collector is too small or the difference in the coverage rates of the first polymer adhesive layer and the second polymer adhesive layer is too large. The too small tensile strength T of the positive electrode current collector will result in poor ability of the positive electrode to resist expansion and stretching, increasing the risk of positive electrode strip breakage. The too large difference in the coverage rates of the first polymer adhesive layer and the second polymer adhesive layer will lead to too large a difference in the adhesion force between the positive and negative electrodes and the separator, easily causing the distance between the positive and negative electrodes and the separator to become larger after the negative electrode expands, resulting in a lengthened lithium-ion transmission path, increased internal resistance, and hindrance of lithium-ion insertion and extraction, deteriorating the cycle performance of the battery and even causing risks such as lithium deposition or short circuit and fire. When 100*|A - B| / T is less than 0.01, the tensile strength T of the positive electrode current collector is too large or the difference in the coverage rates of the first polymer adhesive layer and the second polymer adhesive layer is too small. The too large tensile strength T of the positive electrode current collector will lead to a decrease in the contact tightness between the positive electrode current collector and the positive electrode active layer, increasing the interfacial resistance of the positive electrode, affecting electron conduction, and easily causing the problem of lithium deposition on the electrode. The too small difference in the coverage rates of the first polymer adhesive layer and the second polymer adhesive layer, that is, the coverage rates of the two-sided adhesive layers are similar, may result in insufficient adhesion force between the negative electrode and the separator, unable to effectively inhibit the expansion of the negative electrode, easily increasing the risk of positive electrode strip breakage and affecting the safety of the battery. Therefore, by further controlling the ratio range of 100*|A - B| / T, the risk of positive electrode strip breakage can be further reduced, and the cycle performance and safety performance of the battery can be improved.

[0032] In one example, the air permeability of the separator is D, and A, B, and D satisfy 0.03 ≤ 100 * |A - B| / D ≤ 0.25, such as 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, or 0.25. The unit of the air permeability D of the separator is "s / 100cc", which represents the time (seconds, s) required for 100 cubic centimeters (cc) of gas to pass through the separator. The larger the value of the air permeability D of the separator, the poorer the air permeability performance of the separator; the smaller the value of the air permeability D of the separator, the better the air permeability performance of the separator.

[0033] The amount of the polymer adhesive layer coated on the separator will affect the air permeability of the separator. When the amount of the polymer adhesive layer coated on the separator is larger, the coverage rate is higher and the coating is denser, the value of the air permeability of the separator will be larger, that is, the time for gas to pass through the separator is longer, indicating that the overall structure of the separator is denser, and the air permeability performance of the separator is poorer. However, at this time, the mechanical strength of the separator is higher, the puncture resistance performance is better, and the safety of the separator can be improved; but if the polymer adhesive layer is too dense, the transmission of lithium ions between the positive and negative electrode plates through the separator will be blocked, which is likely to cause uneven local current density and trigger the precipitation of lithium metal (lithium dendrites), and the air permeability of the separator is too small, which may cause the separator to rupture due to stress concentration during thermal expansion, exacerbating the risk of thermal runaway; when the amount of the polymer adhesive layer coated on the separator is smaller, the air permeability of the separator will be smaller, indicating that the time for gas to pass through the separator becomes shorter, the overall structure of the separator is relatively loose, and the air permeability of the separator is better. However, when the amount of the polymer adhesive layer coated on the separator is too small, it will cause the mechanical strength of the separator to deteriorate accordingly, the pores of the separator are too open, the electrolyte is easily over-consumed, especially when the silicon-based negative electrode expands, the interface dries up faster, resulting in an accelerated decline in battery capacity and seriously affecting the cycle life of the battery. Therefore, by controlling the relationship between the coverage rate difference of the polymer adhesive layers on both sides of the separator and the air permeability of the separator, when |A - B| / D satisfies a certain range, it can ensure that the separator has a certain mechanical strength while ensuring that the expansion of the negative electrode will not damage the separator, and can also ensure the transmission efficiency of lithium ions, ensuring that the battery has a high capacity and good cycle performance. The test method for the air permeability D of the separator is as follows: Take a separator of a certain size (5x5 cm), place the separator on the test platform of a Gurley air permeability tester to measure the air permeability D of the separator, and the unit is s / 100cc.

[0034] In one example, 0.03 ≤ 100 * |A - B| / D ≤ 0.1.

[0035] Further, the air permeability D of the separator is 100 s / 100 cc - 400 s / 100 cc, for example, 100 s / 100 cc, 110 s / 100 cc, 120 s / 100 cc, 130 s / 100 cc, 140 s / 100 cc, 150 s / 100 cc, 200 s / 100 cc, 250 s / 100 cc, 300 s / 100 cc, 350 s / 100 cc or 400 s / 100 cc. When the air permeability of the separator is within this range, the mechanical strength and ionic impedance of the separator can be further balanced, the puncture resistance of the separator can be improved, and it has excellent safety performance. At the same time, the transfer impedance of lithium ions between the positive and negative electrodes through the separator and the electrodes can be reduced, avoiding the precipitation of lithium metal, reducing the risk of lithium precipitation on the electrodes, and preventing the separator from cracking due to stress concentration during thermal expansion, improving the thermal safety performance of the battery. In addition, a suitable air permeability D of the separator can avoid the accelerated attenuation of the battery capacity caused by excessive consumption of the electrolyte, and improve the cycle performance of the battery.

[0036] In one example, the coverage area of the first polymer adhesive layer relative to the substrate layer and the coverage area of the second polymer adhesive layer relative to the substrate layer are both smaller than the area of the substrate layer. When the coverage areas of the polymer adhesive layers on both sides of the separator are smaller than the area of the substrate layer, more expansion space can be provided for the expansion of the negative electrode active material during the cycling process, which can better relieve the expansion stress caused by the negative electrode expansion, thus avoiding the breakage of the positive electrode tab caused by the expansion of the silicon negative electrode, reducing the risk of tab breakage of the electrode, and further improving the safety performance of the battery.

[0037] In one example, the coverage rate A of the first polymer adhesive layer relative to the substrate layer is 20% - 70%, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%. The test method for the coverage rate A of the first polymer adhesive layer relative to the substrate layer is as shown above, which refers to the projected area of the first polymer adhesive layer in the thickness direction of the separator / the projected area of the substrate layer in the thickness direction of the separator × 100%.

[0038] In one example, the coverage rate B of the second polymer adhesive layer relative to the substrate layer is 30% - 80%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%. The test method for the coverage rate A of the second polymer adhesive layer relative to the substrate layer is as shown above, which refers to the projected area of the second polymer adhesive layer in the thickness direction of the separator / the projected area of the substrate layer in the thickness direction of the separator × 100%.

[0039] In one example, 0 < |A - B| ≤ 60%, such as 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%.

[0040] In the present invention, the adhesion force on the side of the separator in contact with the positive electrode sheet is F1, and the adhesion force on the side of the separator in contact with the negative electrode sheet is F2. The F1 and F2 satisfy F1 < F2.

[0041] In one example, the F1 is 4N - 25N, such as 4N, 5N, 6N, 7N, 8N, 9N, 10N, 11N, 12N, 13N, 14N, 15N, 16N, 17N, 18N, 19N or 20N, and the F2 is 5N - 30N, such as 5N, 6N, 7N, 8N, 9N, 10N, 15N, 11N, 12N, 13N, 14N, 15N, 16N, 17N, 18N, 19N, 20N, 21N, 22N, 23N, 24N, 25N or 30N.

[0042] In one example, the F1 is 8N - 12N.

[0043] In one example, the F2 is 15N - 20N.

[0044] By controlling the adhesion force F1 on the side of the separator in contact with the positive electrode sheet to be less than the adhesion force F2 on the side of the separator in contact with the negative electrode sheet, the present invention can make the adhesion force between the separator and the positive electrode sheet less than the adhesion force between the separator and the negative electrode sheet, thereby reducing the risk of deformation that is likely to occur in the later stage of the charge and discharge cycle of the electrochemical device. A slightly lower adhesion force F1 on the side of the separator in contact with the positive electrode sheet can also reduce the risk of ceramic layer peeling.

[0045] Test method for the adhesion force of the electrode sheet in contact with the separator: Fully charge and disassemble the lithium-ion battery to obtain the part where the separator is combined with the positive and negative electrodes. Cut the combined part into strip-shaped samples of 15mm x 54.2mm, and test the adhesion force between the first polymer adhesive layer or the second polymer adhesive layer of the separator and the positive and negative electrode sheets according to the national standard GB / T2792 - 1998 (Test Method for 180° Peel Strength of Pressure-Sensitive Adhesive Tapes).

[0046] In one example, the adhesion force between the separator and the positive electrode sheet is less than the adhesion force between the separator and the negative electrode sheet.

[0047] In the present invention, the ratio between the coverage rate A of the first polymer adhesive layer relative to the substrate layer and the adhesion force F1 on the side of the separator in contact with the positive electrode sheet is 0.025 - 0.045, such as 0.025, 0.026, 0.027, 0.028, 0.029, 0.03, 0.031, 0.032, 0.033, 0.034, 0.035, 0.036, 0.037, 0.038, 0.039, 0.04, 0.041, 0.042, 0.043, 0.044 or 0.045.

[0048] In the present invention, the ratio between the coverage rate B of the second polymer adhesive layer relative to the substrate layer and the adhesion force F2 on the side of the separator in contact with the negative electrode sheet is 0.025 - 0.04, such as 0.025, 0.026, 0.027, 0.028, 0.029, 0.03, 0.031, 0.032, 0.033, 0.034, 0.035, 0.036, 0.037, 0.038, 0.039 or 0.04.

[0049] Since the elongation of the positive electrode sheet is less than that of the negative electrode sheet, preferably the adhesion force between the separator and the negative electrode sheet is greater than the adhesion force between the separator and the positive electrode sheet. In this way, the bonding strength can be ensured through the coverage rate, and while ensuring that the adhesion force meets the usage requirements, the bonding strength between the separator and the electrode sheet can be minimized as much as possible. This is because if the bonding strength between the separator and the positive and negative electrode sheets is too high, it may lead to a reduction in the contact area between the electrolyte and the electrode sheet, affecting the infiltration effect of the electrolyte, thereby causing a decline in the electrochemical performance of the battery; in addition, too high a bonding strength between the separator and the electrode sheet may also cause the electrode sheet and the separator to be overly adhered during the hot pressing process, affecting the heat dissipation performance inside the battery and increasing the risk of thermal runaway of the battery. Therefore, by controlling the coverage rate of each adhesive layer and the ratio range of the adhesion force between the separator and the corresponding electrode sheet, the present invention can further optimize the bonding strength between the separator and the electrode sheet, thereby further improving the safety performance and electrochemical performance of the battery.

[0050] In the present invention, the thickness of the first polymer adhesive layer is 0.1 μm - 2 μm, such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2 μm; the thickness of the second polymer adhesive layer is 0.1 μm - 4 μm, such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm or 4 μm. The method for testing the thickness of the first polymer adhesive layer or the second polymer adhesive layer: First, take a substrate of a certain size (5x5 cm) and use a micrometer to measure the sum of the thicknesses of the separator substrate layer and the ceramic layer H1. Then, disassemble the separator in the battery and clean it. Take a separator of a certain size (5x5 cm) and use a micrometer to measure the thickness of the separator after coating the polymer adhesive layer H2. Then, the sum of the thicknesses of the first polymer adhesive layer and the second polymer adhesive layer H3 can be obtained by calculation: H3 = H2 - H1. Then, through the thickness ratio when coating the first polymer adhesive layer and the second polymer adhesive layer during the preparation of the separator, the individual thickness of the first polymer adhesive layer or the second polymer adhesive layer of the separator disassembled from the battery can be calculated.

[0051] The first polymer adhesive layer on the side of the ceramic layer corresponds to the positive electrode sheet, and its thickness range can be 0.1 μm - 2 μm; the second polymer adhesive layer on the other side corresponds to the negative electrode sheet, and its thickness range can be 0.1 μm - 4 μm; the thickness difference between the two side adhesive layers can not only ensure high bonding force on both sides of the separator, which is more conducive to the transmission of the electrolyte, but also can improve the wettability of the separator to the electrolyte as much as possible, improving the cycle performance of the electrochemical device; moreover, it can further ensure the thickness of the separator, avoid its excessive thickness, and thus improve the energy density of the battery cell.

[0052] In one example, the thickness of the first polymer adhesive layer is 0.5 μm - 1 μm.

[0053] In one example, the thickness of the second polymer adhesive layer is 1 μm - 2 μm.

[0054] In one example, the silicon-based material includes at least one of silicon-carbon composite material and silicon-oxygen composite material.

[0055] In one example, the material of the ceramic layer includes at least one of silicon dioxide, aluminum oxide, zirconium dioxide, magnesium hydroxide, boehmite, barium sulfate, fluorophlogopite, fluorapatite, mullite, cordierite, aluminum titanate, titanium dioxide, copper oxide, zinc oxide, boron nitride, aluminum nitride, magnesium nitride, attapulgite or PI piezoelectric ceramic.

[0056] In one example, each of the first polymer adhesive layer and the second polymer adhesive layer independently comprises at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene tetrafluoride, polyvinylidene fluoride - hexafluoropropylene modification and its copolymer, polyacrylonitrile, polymethyl methacrylate, polyacrylic acid, styrene - butadiene rubber (SBR), polyvinyl alcohol and its copolymer - modified polyvinyl alcohol, polyvinyl acetate, polyacrylamide, phenolic resin, epoxy resin, waterborne polyurethane, ethylene - vinyl acetate copolymer, polyacrylic copolymer, lithium polystyrenesulfonate, pure benzene latex, polyvinylidene fluoride - trichloroethylene, polyvinylidene fluoride - chlorotrifluoroethylene, polyvinylpyrrolidone, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylated amylose, cyanoethylated polyvinyl alcohol, cyanoethylated cellulose, cyanoethylated sucrose.

[0057] In one example, the material of the substrate layer comprises at least one of polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), polyimide (PI), polyamide (nylon), polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), polyethylene terephthalate (PET), cellulose or poly - p - phenylene terephthalamide (aramid) or polyurethane (spandex).

[0058] In one example, the particle size Dv50 of the silicon - based material is 5 μm - 15 μm.

[0059] In another example, the particle size Dv50 of the silicon - based material is 6 μm - 12 μm.

[0060] In the present invention, the test method for the particle size Dv50 of the silicon - based material: Measure using a Malvern particle size analyzer. The test steps are as follows: Disperse the silicon - based material particles in deionized water containing a dispersant (such as nonylphenol polyoxyethylene ether, with a content of 0.02 wt% - 0.03 wt%) to form a mixture. Ultrasonic the mixture for about 2 minutes, and then put it into the Malvern particle size analyzer for testing to obtain the particle size Dv50 of the silicon - based material particles.

[0061] In one example, the mass content of element C on the surface of the separator facing the positive electrode sheet is 10% - 35% (for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%), the mass content of element O is 30% - 55% (for example, 30%, 35%, 40%, 41%, 42%, 43%, 44%, 45%, 50% or 55%), the mass content of element Al is 30% - 55% (for example, 30%, 31%, 32%, 33%, 34%, 35%, 40%, 45%, 50% or 55%), and the mass content of element F is 1% - 5% (for example, 1%, 2%, 3%, 4% or 5%). The test method for the mass content of each element on the surface of the separator facing the positive electrode sheet is as follows: After disassembling the separator in the battery, cut it into several samples of 10 mm × 10 mm, then place the surface of the sample separator facing the positive electrode sheet under SEM and take a picture at a magnification of 500 times, and then use EDS for area scanning to test the content of each element on the surface of the separator facing the positive electrode sheet. Then, take the average value of the results of several small samples to obtain the mass content of each element on the surface of the separator facing the positive electrode sheet.

[0062] In one example, the mass content of element C on the surface of the separator facing the positive electrode sheet is 20% - 25%, the mass content of element O is 40% - 45%, the mass content of element Al is 32% - 34%, and the mass content of element F is 2% - 4%.

[0063] In one example, the mass content of element C on the surface of the separator facing the negative electrode sheet is 70% - 98% (for example, 70%, 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97% or 98%), the mass content of element O is 0% - 3% (for example, 0%, 1%, 2% or 3%), and the mass content of element F is 1% - 10% (for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%). The test method for the mass content of each element on the surface of the separator facing the negative electrode sheet is as follows: After disassembling the separator in the battery, cut it into several samples of 10 mm × 10 mm, then place the surface of the sample separator facing the negative electrode sheet under SEM and take a picture at a magnification of 500 times, and then use EDS for area scanning to test the content of each element on the surface of the separator facing the negative electrode sheet. Then, take the average value of the results of several small samples to obtain the mass content of each element on the surface of the separator facing the negative electrode sheet.

[0064] In addition, it should be noted that since the first polymer adhesive layer covers the ceramic layer, when the elemental types and contents on the surface of the separator facing the positive electrode plate are tested by EDS surface scanning, the components in the ceramic layer not covered by the first polymer adhesive layer will be detected. Therefore, the Al element in the ceramic layer is contained on the surface of the separator facing the positive electrode plate, while the second polymer adhesive layer covers the other side of the substrate layer, and the substrate layer does not contain Al element. Therefore, the detection result of the surface of the separator facing the negative electrode plate does not contain Al element.

[0065] In one example, the mass content of C element on the surface of the separator facing the negative electrode plate is 95%-98%, the mass content of O element is 0.3%-0.6%, and the mass content of F element is 2%-4%.

[0066] The main component of the adhesive solution used for the first polymer adhesive layer and the second polymer adhesive layer is generally a fluorine-containing adhesive, such as PVDF, etc. Therefore, the content of the fluorine-containing adhesive in the first polymer adhesive layer and the second polymer adhesive layer can be controlled by controlling the mass content of F element on the surface of the separator facing the positive electrode plate and the surface of the separator facing the negative electrode plate, which further helps to regulate the adhesion force between the positive and negative electrode plates and the separator, thereby reducing the risk of pole piece fragmentation and preventing the pole piece from diving during the cycling process, and further improving the safety performance of the battery.

[0067] It should be noted that the numerical representation methods such as "first" and "second" in the present invention are only used to distinguish different substances or usage methods, and do not represent the difference in order.

[0068] The present invention will be described in detail below through embodiments. The embodiments described in the present invention are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0069] In the following examples, unless otherwise specified, the materials used are commercially available analytical pure.

[0070] The following examples are used to illustrate the battery of the present invention.

[0071] Example 1

[0072] Preparation of separator:

[0073] (1) Preparation of ceramic adhesive solution:

[0074] Mix 2 g of aluminum oxide ceramic particles with an average particle size of 20 nm, 0.6 g of polyacrylic acid binder, and 15 g of N-methylpyrrolidone evenly and perform shear stirring using a stirrer to obtain a ceramic adhesive solution. The stirring time is 4 h and the stirring speed is 800 r / min;

[0075] (2) Preparation of the ceramic layer:

[0076] Coat the ceramic glue solution obtained in step (1) on one side of the slit separator substrate (polyethylene) and dry it in vacuum. The vacuum degree is 0.01 Mpa, the drying temperature is 80 °C, and the drying time is 8 h to obtain a separator substrate with a single-sided coated ceramic layer. Among them, the thickness of the ceramic layer is 1 μm, and the thickness of the separator substrate layer is 5 μm.

[0077] (3) Preparation of the first polymer glue layer / second polymer glue layer: Using the atomized spraying method, spray the PVDF glue solution (the content of PVDF is 5%, and the solvent is acetone) on the surface of the ceramic layer in step (2) (to form the first polymer glue layer) and the other side of the separator substrate layer that is not coated with the ceramic layer on the outside (to form the second polymer glue layer), and then put it into an oven and bake it at a temperature of 40 °C - 85 °C to obtain the separator of this embodiment.

[0078] Among them, the thickness of the first polymer glue layer is 0.5 μm, the thickness of the second polymer glue layer is 1 μm, and the air permeability value of the tested separator is about 350 s / 100 cc; observe the two side surfaces of the separator through a scanning electron microscope, and calculate that the coverage rate A of the first polymer glue layer on the surface of the ceramic layer is 50%, and the coverage rate B of the second polymer glue layer on the surface of the substrate layer is 70%;

[0079] In addition, Figure 2 is the SEM image on the surface of the ceramic layer in Example 1, Figure 3 is the SEM image on the surface of the first polymer glue layer sprayed and formed on the surface of the ceramic layer in Example 1. It can be seen from the figure that the first polymer glue layer 111 covers a part of the surface of the ceramic layer 110, Figure 4 is the SEM image on the surface of the second polymer glue layer sprayed and formed on the other side of the separator substrate layer that is not coated with the ceramic layer on the outside in Example 1. The surface of the substrate layer is also partially covered.

[0080] Preparation of lithium-ion battery:

[0081] (1) Preparation of the positive electrode sheet

[0082] Mix lithium cobaltate (LCO), polyvinylidene fluoride (PVDF), acetylene black, and carbon nanotubes (CNTs) according to a mass ratio of 96:2:1.5:0.5, add N-methylpyrrolidone, and stir under the action of a vacuum mixer until a uniform positive electrode paste is formed. Coat the positive electrode paste uniformly on an aluminum foil with a thickness of 12 μm (the positive electrode current collector aluminum foil, and its tensile strength T in the length direction is 230 MPa). Bake the above-coated aluminum foil in an oven, then transfer it to an oven at 120 °C and dry it for 8 h, and then roll and slit it to obtain the required positive electrode sheet.

[0083] (2) Preparation of the negative electrode sheet

[0084] Mix the silicon-carbon composite material (particle size Dv50 S = 9 μm), artificial graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber, SuperP, and single-walled carbon nanotubes (SWCNTs) in a ratio of 10:86.5:1.6:1.6:0.2:0.1, add deionized water, and obtain the negative electrode slurry under the action of a vacuum mixer. Uniformly coat the negative electrode slurry on both surfaces of the negative electrode current collector with a thickness of, and the surface density of the negative electrode slurry coated on the surface of the negative electrode current collector is 11.0 mg / cm 2 . Transfer the negative electrode current collector coated with the negative electrode slurry to an 80 °C oven and dry for 12 h, and then roll press (control the compaction density within the range of 1.4 - 1.8 g / cm 3 ), and slit to obtain the negative electrode sheet.

[0085] (3) Separator

[0086] Select the above-mentioned separator.

[0087] (4) Electrolyte

[0088] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), mix EC / PC / PP / PA evenly according to a mass ratio of 10 / 15 / 55 / 20, and then quickly add lithium hexafluorophosphate (LiPF6) with a content of 14.38% based on the total mass of the electrolyte as the lithium salt. After dissolution, add fluoroethylene carbonate with a content of 5% based on the total mass of the electrolyte, as well as 4% of 1,3-propane sultone (PS), 2% of 1,3,6-hexanetricarbonitrile (HTCN), 2% of adiponitrile (ADN), and 1% of succinonitrile (SN), stir evenly, and after passing the moisture and free acid tests, obtain the required electrolyte.

[0089] (5) Preparation of the lithium-ion battery

[0090] Stack the positive electrode sheet in step (1), the separator in step (3), and the negative electrode sheet in step (2) in sequence, ensure that the first polymer adhesive layer is close to the positive electrode sheet, the second polymer adhesive layer is close to the negative electrode sheet, and ensure that the separator is between the positive and negative electrode sheets to play an isolation role, and then obtain a bare battery core by winding. Place the bare battery core in an aluminum-plastic film shell, inject the electrolyte in step (4) into the dried bare battery core, and after processes such as vacuum packaging, standing, formation, shaping, and sorting, obtain the required lithium-ion battery.

[0091] Among them, the adhesion force F1 on the side of the separator in contact with the positive electrode sheet measured is 15 N, and the adhesion force F2 on the side of the separator in contact with the negative electrode sheet is 24 N.

[0092] For the specific situation of Example 1, please refer to Table 1 and Table 2.

[0093] Example 2 group

[0094] The preparation method of the separator in this group of examples is the same as that of the separator in Example 1. The only difference is that by changing the spraying flow rate and spraying time on the surface of the ceramic layer in step (2), the coverage rate of the first polymer adhesive layer on the surface of the ceramic layer, that is, the coverage rate A of the first polymer adhesive layer relative to the substrate layer, is changed. For the specific situation, please refer to Table 1 and Table 2.

[0095] Example 3 group

[0096] The preparation method of the separator in this group of examples is the same as that of the separator in Example 1. The only difference is that by changing the spraying flow rate and spraying time on the surface of the ceramic layer in step (2), and the spraying flow rate and spraying time on the other side of the separator substrate layer that is not coated with the ceramic layer, the coverage rate A of the first polymer adhesive layer relative to the substrate layer is 40%, and the coverage rate B of the second polymer adhesive layer relative to the substrate layer is changed. For the specific situation, please refer to Table 1 and Table 2.

[0097] Example 4 group

[0098] The preparation method of the separator in this group of examples is the same as that of the separator in Example 1. The only difference is that by changing the spraying flow rate and spraying time on the surface of the ceramic layer in step (2), and the spraying flow rate and spraying time on the other side of the separator substrate layer that is not coated with the ceramic layer, the coverage rate A of the first polymer adhesive layer relative to the substrate layer and the coverage rate B of the second polymer adhesive layer relative to the substrate layer are changed simultaneously. For the specific situation, please refer to Table 1 and Table 2.

[0099] Example 5 group

[0100] The preparation method of the separator in this group of examples is the same as that of the separator in Example 1. The only difference is that during the preparation of the negative electrode sheet, the particle size Dv50 S of the silicon-carbon composite material is changed. For the specific situation, please refer to Table 1 and Table 2.

[0101] Example 6 group

[0102] The preparation method of the separator in this group of examples is the same as that of the separator in Example 1. The only difference is that the tensile strength T of the positive current collector aluminum foil in the length direction is changed. For the specific situation, please refer to Table 1 and Table 2.

[0103] Comparative Example 1

[0104] The preparation method of the separator in this comparative example is the same as that of the separator in Example 1, except that the coating method is changed. Specifically: (3) Preparation of the first polymer adhesive layer / second polymer adhesive layer: Using the gravure coating method, apply the PVDF adhesive solution on the surface of the ceramic layer in step (2) and the other side of the separator substrate layer that is not coated with the ceramic layer, and then place it in an oven and bake at a temperature of 40°C - 85°C to obtain the separator of this comparative example. Among them, the thicknesses of the first polymer adhesive layer and the second polymer adhesive layer remain unchanged, the coverage rate A of the first polymer adhesive layer on the surface of the ceramic layer becomes 99%, and the coverage rate B of the second polymer adhesive layer on the surface of the substrate layer becomes 98%.

[0105] Comparative Example 2 group

[0106] The preparation method of the separator in this group of comparative examples is the same as that of the separator in Example 1. The only difference is that by changing the spraying flow rate and spraying time of the ceramic layer surface in step (2), and the spraying flow rate and spraying time of the other side of the separator substrate layer that is not coated with the ceramic layer, the coverage rate A of the first polymer adhesive layer relative to the substrate layer and / or the coverage rate B of the second polymer adhesive layer relative to the substrate layer are changed. For specific situations, please refer to Table 1 and Table 2.

[0107] Table 1

[0108]

[0109]

[0110] Record the separators prepared in the above examples and comparative examples and other parameters of the lithium-ion battery in Table 2.

[0111] Table 2

[0112]

[0113]

[0114] Then, after disassembling the separators in the batteries prepared in the above Example 1, Example 2 group, Example 3 group, Example 4 group and comparative examples, cut them into 5 samples of 10mm×10mm, and then place the surfaces of the 5 samples facing the positive electrode sheet under the SEM and take pictures at a magnification of 500 times, and then use EDS for surface scanning to test the element contents on the surfaces of the separators facing the positive electrode sheet. Then take the average value of the results of the 5 small samples and record it in Table 3. The element contents of the Example 5 group and the Example 6 group hardly change, so they will not be elaborated; the testing method for the element contents on the surfaces of the separators facing the negative electrode sheet is the same as above.

[0115] Table 3

[0116]

[0117]

[0118] Lithium-ion battery test example

[0119] (1) Cycle performance: In an environment of 45°C ± 2°C, the lithium-ion battery prepared in the above steps is charged at a constant current and constant voltage of 0.7C to 4.53V, cut off at 0.05C, and the initial thickness P0 is recorded. Then, it is discharged at a constant current of 0.2C to 3.0V, and the initial discharge capacity is denoted as C0. After standing for 10 minutes, the cycle mode is: charged at a constant current and constant voltage of 3C to 4.25V, cut off at 2C, then switched to a constant current and constant voltage of 2C to 4.48V, cut off at 1.5C, then switched to a constant current and constant voltage of 1.5C to 4.53V, cut off at 0.18C, stand for 5 minutes, and discharge at 0.7C to 3.0V. After 600 cycles, it is charged at a constant current and constant voltage of 0.7C to 4.53V, cut off at 0.05C, and the final thickness P1 is recorded. Then, it is discharged at a constant current of 0.2C to 3.0V, and the initial discharge capacity is denoted as C1. Capacity retention rate: C = C1 / C0 * 100%, and the test results are recorded in Table 4.

[0120] (2) Lithium plating test: The lithium-ion battery prepared in the above steps is left standing at the specified temperature for 2.5 hours, charged at 1, 2C to the upper cut-off voltage, left standing for 30 minutes, discharged at 3, 5C to the lower voltage, left standing for 30 minutes, 4, 2 - 3 cycles of 20T, charged at 2C to the upper cut-off voltage, left standing for 30 minutes to test the state of the next stage, then the battery cell is disassembled to observe whether there is lithium plating. For each group of prepared batteries in the examples and comparative examples, 50 batteries are taken, and then 50 batteries are tested under the above conditions. Record the proportion of the number of batteries with lithium plating to the total number of tested batteries. The test results are shown in Table 4.

[0121] (3) Positive electrode strip breakage test: For each group of prepared batteries in the examples and comparative examples, 50 batteries are taken, and then the lithium-ion batteries prepared in the above examples and comparative examples are disassembled to actually confirm whether there is a situation of positive electrode strip breakage. If there is a crack on the positive electrode sheet, it is determined as strip breakage. Record the proportion of the number of batteries with strip breakage to the total number of tested batteries. The test results are shown in Table 4.

[0122] Table 4

[0123]

[0124]

[0125] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A battery, characterized in that: The battery comprises a positive electrode sheet, a negative electrode sheet and a separator located between the positive electrode sheet and the negative electrode sheet, wherein the separator comprises a substrate layer and a ceramic layer located on one side of the substrate layer, a first polymer adhesive layer is arranged on the side of the ceramic layer away from the substrate layer, and a second polymer adhesive layer is arranged on the side of the substrate layer away from the ceramic layer; The first polymer glue layer is close to the positive electrode sheet, the second polymer glue layer is close to the negative electrode sheet, the coverage rate of the first polymer glue layer relative to the substrate layer is A, the coverage rate of the second polymer glue layer relative to the substrate layer is B, and the coverage rate B of the second polymer glue layer relative to the substrate layer is greater than the coverage rate A of the first polymer glue layer relative to the substrate layer; The negative electrode sheet includes a negative electrode active material, the negative electrode active material includes a silicon-based material, the particle size Dv50 of the silicon-based material is S, and A, B and S satisfy 1≤100*|AB| / S≤9.

2. The battery according to claim 1, wherein The positive electrode sheet includes a positive electrode current collector, the tensile strength of the positive electrode current collector in the length direction is T, and A, B and T satisfy 0.01≤100*|AB| / T≤0.2; Preferably, the tensile strength T of the positive electrode current collector in the length direction is 200 MPa-1000 MPa.

3. The battery according to claim 1, wherein The air permeability of the separator is D, and A, B and D satisfy 0.03≤100*|AB| / D≤0.25; Preferably, the air permeability D of the diaphragm is 100s / 100cc-400s / 100cc.

4. The battery according to claim 1, wherein The coverage area of ​​the first polymer adhesive layer relative to the substrate layer and the coverage area of ​​the second polymer adhesive layer relative to the substrate layer are both smaller than the area of ​​the substrate layer; And / or, the coverage A of the first polymer adhesive layer relative to the substrate layer is 20%-70%; And / or, the coverage B of the second polymer adhesive layer relative to the substrate layer is 30%-80%; And / or, 0<|AB|≤60%.

5. The battery according to claim 1, wherein The adhesive force of the side of the diaphragm contacted by the positive electrode sheet is F1, and the adhesive force of the side of the diaphragm contacted by the negative electrode sheet is F2, and F1 and F2 satisfy F1<F2; preferably, F1 is 4N-25N, and F2 is 5N-30N; And / or, the bonding force between the separator and the positive electrode sheet is smaller than the bonding force between the separator and the negative electrode sheet.

6. The battery according to claim 1, wherein The ratio of the coverage A of the first polymer glue layer relative to the substrate layer to the adhesion force F1 of the side of the separator in contact with the positive electrode sheet is 0.025-0.045; And / or, the ratio between the coverage B of the second polymer glue layer relative to the substrate layer and the adhesion force F2 of the side of the separator in contact with the negative electrode sheet is 0.025-0.

04.

7. The battery according to claim 1, wherein The thickness of the first polymer adhesive layer is 0.1 μm-2 μm; And / or, the thickness of the second polymer adhesive layer is 0.1 μm-4 μm; And / or, the silicon-based material includes at least one of a silicon-carbon composite material and a silicon-oxygen composite material.

8. The battery according to claim 1, wherein The material of the ceramic layer includes at least one of silicon dioxide, aluminum oxide, zirconium dioxide, magnesium hydroxide, boehmite, barium sulfate, fluorphlogopite, fluoroapatite, mullite, cordierite, aluminum titanate, titanium dioxide, copper oxide, zinc oxide, boron nitride, aluminum nitride, magnesium nitride, attapulgite or PI piezoelectric ceramics; And / or, the first polymer adhesive layer and the second polymer adhesive layer each independently contain at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene tetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene modified and its copolymer, polyacrylonitrile, polymethyl methacrylate, polyacrylic acid, styrene-butadiene rubber (SBR), polyvinyl alcohol and its copolymer modified polyvinyl alcohol, polyvinyl acetate, polyacrylamide, phenolic resin, epoxy resin, water-based polyurethane, ethylene-vinyl acetate copolymer, multi-acrylic copolymer, lithium polystyrene sulfonate, pure benzene latex, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polyvinyl pyrrolidone, polyethylene oxide, cellulose acetate, butyl cellulose, propyl cellulose, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, and cyanoethyl sucrose.

9. The battery according to claim 1, wherein The particle size Dv50 of the silicon-based material is 5 μm-15 μm, preferably 6 μm-12 μm.

10. The battery according to claim 1, wherein The mass content of the C element on the surface of the side of the separator facing the positive electrode sheet is 10%-35%, the mass content of the O element is 30%-55%, the mass content of the Al element is 30%-55%, and the mass content of the F element is 1%-5%; And / or, the mass content of C element on the surface of one side of the separator facing the negative electrode sheet is 70%-98%, the mass content of O element is 0%-3%, and the mass content of F element is 1%-10%.

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