Battery

Abstract

A battery, comprising an electrode assembly of a stacked structure. The electrode assembly comprises: a plurality of electrode plates arranged in a stacked manner, which comprise two surface-layer electrode plates located at the outermost layers and a plurality of intermediate-layer electrode plates located between the two surface-layer electrode plates, the surface-layer electrode plates being single-sided positive plates, and the intermediate-layer electrode plates being double-sided positive plates and double-sided negative plates; surface-layer separators, each of which is located between a single-sided positive plate and a double-sided negative plate; and intermediate-layer separators, each of which is located between a double-sided positive plate and a double-sided negative plate, wherein the adhesive strength between the surface-layer separator and the single-sided positive plate is greater than the adhesive strength between the intermediate-layer separator and the double-sided positive plate. The battery can reduce the purple spot formation and lithium precipitation on the single-sided positive plate, thereby improving the overall rate capability and cycling performance of the stacked battery.

Description

A battery

[0001] The present application claims priority to the Chinese patent application No. 202411374057.8 filed on September 29, 2024, and entitled "A battery", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of lithium batteries, in particular to a battery. BACKGROUND

[0003] Lithium-ion batteries have the advantages of high energy density, long cycle life, small self-discharge, no memory effect, etc. compared with other secondary batteries. Therefore, since the advent of lithium-ion batteries, they have been widely recognized and applied in the market. With the increasing frequency of battery use by consumers, the requirements for the charging and discharging speed and service life of the battery are also increasing.

[0004] The actual charging and discharging performance of the lithium-ion battery cannot meet the requirements of multiple working conditions at the same time. Although the internal resistance of the lithium-ion battery with multiple tab structures is already small and the charging and discharging performance is good, it is difficult to achieve consistency in the charging speed of each region during high-rate charging and discharging. In the prior art, the surface of the laminated battery is prone to lithium precipitation due to structural design, thereby affecting the cycle performance and safety performance of the battery.

[0005] Therefore, it is a technical problem to be solved to develop a battery that solves the surface lithium precipitation during fast charging and meets the optimal rate performance. SUMMARY

[0006] The present application aims to overcome the above-mentioned problems existing in the prior art, and provides a battery with a laminated structure, having a surface layer separator and an intermediate layer separator. By adjusting the adhesion of the surface layer separator and the single-sided positive electrode sheet, the adhesion of the intermediate layer separator and the double-sided positive electrode sheet, and the adhesion of the surface layer separator and the double-sided negative electrode sheet, the adhesion of the intermediate layer separator and the double-sided negative electrode sheet, the generation of purple spots and lithium precipitation in the single-sided positive electrode sheet can be reduced, and the rate performance and cycle performance of the laminated battery as a whole can be improved.

[0007] To achieve the above-mentioned purpose, the present application provides a battery, comprising an electrode assembly with a laminated structure, the electrode assembly comprising a plurality of electrode sheets stacked, the electrode sheets comprising two surface layer electrode sheets located at the outermost layer and a plurality of intermediate layer electrode sheets located between the two surface layer electrode sheets, the surface layer electrode sheets being single-sided positive electrode sheets, and the intermediate layer electrode sheets being double-sided positive electrode sheets and double-sided negative electrode sheets.

[0008] a surface layer separator located between the single-sided positive electrode sheet and the double-sided negative electrode sheet;

[0009] and an intermediate layer separator, the intermediate layer separator is located between the double-sided positive electrode sheet and double-sided negative electrode sheet;

[0010] The adhesion of the surface layer separator to the single-sided positive electrode sheet is greater than the adhesion of the intermediate layer separator to the double-sided positive electrode sheet.

[0011] The technical scheme has the following beneficial effects:

[0012] (1) The battery separator is divided into a surface layer separator and an intermediate layer separator, the adhesion of the surface layer separator to the single-sided positive electrode sheet is greater than the adhesion of the intermediate layer separator to the double-sided positive electrode sheet, which can reduce the occurrence of purple spots and lithium precipitation of the single-sided positive electrode sheet, and improve the rate performance and cycle performance of the overall electrode stack.

[0013] (2) Further, the electrode stack of the application can improve the electrolyte wettability and liquid retention performance of the surface layer separator and the intermediate layer separator corresponding to the electrode sheet, and improve the rate performance and cycle performance of the overall electrode stack.

[0014] (3) Further, the electrode stack of the application can reduce the curling and separation of the single-sided positive electrode sheet, and improve the stability of the battery structure.

[0015] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges are included in the range. Any numerical value, however, can only be approximate. The numerical characteristics disclosed herein can vary by +1%. The endpoints of the ranges and any values are provided as a separate value from but in close proximity to the stated value in the range. The ranges and individual points are combinable to create new ranges and individual points that are not expressly stated herein. In the event of a conflict in meaning or description, the present specification controls. BRIEF DESCRIPTION OF DRAWINGS

[0016] FIG. 1 shows a structure schematic diagram of a battery in an example of the application.

[0017] FIG. 2 shows a structure schematic diagram of a battery in another example of the application.

[0018] Reference signs: 1: battery; 1-1: single-sided positive electrode sheet; 1-2: double-sided negative electrode sheet; 1-3: double-sided positive electrode sheet; 1-4: surface layer separator; 1-5: intermediate layer separator. DETAILED DESCRIPTION

[0019] The specific embodiments of the application are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the application, and are not used to limit the application.

[0020] Unless otherwise defined, all scientific and technical terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0021] In this application, the terms "battery", "lamination battery", "lithium battery", "lithium ion battery", "lithium ion secondary battery" all have the same meaning, all refer to lithium ion secondary batteries, which generally include an electrode assembly (such as a positive electrode sheet, a negative electrode sheet, and a separator), a container (a shell) containing the electrode assembly, and an electrolyte.

[0022] The present application provides a battery, which comprises an electrode assembly in a lamination structure, the electrode assembly comprising a plurality of electrode sheets stacked, the electrode sheets comprising two surface layer electrode sheets located at the outermost layer and a plurality of intermediate layer electrode sheets located between the two surface layer electrode sheets, the surface layer electrode sheets being single-sided positive electrode sheets, and the intermediate layer electrode sheets being double-sided positive electrode sheets and double-sided negative electrode sheets.

[0023] a surface layer separator located between the single-sided positive electrode sheet and the double-sided negative electrode sheet;

[0024] and an intermediate layer separator located between the double-sided positive electrode sheet and the double-sided negative electrode sheet;

[0025] wherein the adhesion of the surface layer separator to the single-sided positive electrode sheet is greater than the adhesion of the intermediate layer separator to the double-sided positive electrode sheet.

[0026] In a lamination battery, the single-sided positive electrode sheet of the surface layer is prone to curling due to internal stress caused by the positive electrode current collector coating only one side with positive electrode material, the curling direction being away from the direction of the lamination core, which is prone to causing the single-sided positive electrode sheet to separate from the lamination core and gradually affecting the adhesion of the adjacent surface layer separator, resulting in poor adhesion and poor kinetics of the surface layer separator and the single-sided positive electrode sheet in the lamination battery, and being prone to causing purple stains and lithium precipitation in the single-sided area.

[0027] In this application, by using the surface layer separator in the single-sided positive electrode compounding process and the intermediate layer separator in the double-sided positive electrode compounding process through the process of the lamination battery, and by adjusting the parameters of the separators to satisfy the condition that the adhesion of the surface layer separator to the single-sided positive electrode sheet is greater than the adhesion of the intermediate layer separator to the double-sided positive electrode sheet, the single-sided positive electrode sheet at the outermost layer of the lamination battery and the surface layer separator can maintain good adhesion, the battery is less prone to voids and / or displacement during the cycling process, the curling and separation of the single-sided positive electrode sheet are reduced, the resistance of lithium ion transport is reduced, the lithium ion transport performance of the single-sided positive electrode sheet is improved, the generation of purple stains and lithium precipitation in the single-sided positive electrode sheet is reduced, and thus the rate performance and the cycling performance of the lamination battery as a whole are improved.

[0028] In the present application, the "surface layer" refers to the top layer and the bottom layer of the electrode assembly of the stack structure in the thickness direction; the "intermediate layer" refers to the part between the top layer and the bottom layer of the electrode assembly of the stack structure in the thickness direction, as shown in Figure 1. The "single-sided positive electrode sheet" refers to the current collector of the positive electrode sheet having an active layer coated on only one side surface, i.e., the single-sided positive electrode sheet comprises a first positive electrode current collector and a first positive electrode active layer located on one side surface of the first positive electrode current collector; the "double-sided positive electrode sheet" refers to the current collector of the positive electrode sheet having an active layer coated on both side surfaces, i.e., the double-sided positive electrode sheet comprises a second positive electrode current collector and a second positive electrode active layer located on both side surfaces of the second positive electrode current collector; the "double-sided negative electrode sheet" refers to the current collector of the negative electrode sheet having an active layer coated on both side surfaces, i.e., the double-sided negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on both side surfaces of the negative electrode current collector.

[0029] In some embodiments, as shown in Figure 2, the battery comprises an electrode assembly of a stack structure, in the thickness direction of the battery, the top layer and the bottom layer of the electrode assembly are single-sided positive electrode sheets 1-1, and the intermediate layer is a stack of double-sided positive electrode sheets 1-3 and double-sided negative electrode sheets 1-2. The surface layer separator 1-4 is located between the single-sided positive electrode sheet 1-1 and the double-sided negative electrode sheet 1-2, and the intermediate layer separator 1-5 is located between the double-sided positive electrode sheet 1-3 and the double-sided negative electrode sheet 1-2. The number of double-sided positive electrode sheets, double-sided negative electrode sheets and intermediate layer separators shown in Figure 2 is 3, and the number of double-sided positive electrode sheets, double-sided negative electrode sheets and intermediate layer separators in the present application is ≥2, and the specific value is not limited, and the specific number can be adjusted according to the volume and energy density requirements of the battery.

[0030] In some embodiments, the single-sided positive electrode sheet comprises a first positive electrode current collector, and the double-sided positive electrode sheet comprises a second positive electrode current collector; the thickness of the first positive electrode current collector > the thickness of the second positive electrode current collector, and the difference is denoted as c μm. The difference c is the difference between the thickness of the first positive electrode current collector and the thickness of the second positive electrode current collector, and c > 0. The thickness of the first positive electrode current collector and the thickness of the second positive electrode current collector are not limited, and the thickness range commonly used in the art of positive electrode current collector can be selected, and the difference c meets the requirements.

[0031] Optionally, the thickness of the first positive electrode current collector and the thickness of the second positive electrode current collector can be measured by a micrometer.

[0032] In some embodiments, the thickness of the first positive electrode current collector can be 8 μm-20 μm; and / or the thickness of the second positive electrode current collector can be 6 μm-12 μm. The first positive electrode current collector and / or the second positive electrode current collector can be a metal foil or a composite material of a metal foil and a polymer film.

[0033] In some embodiments, the first positive electrode current collector and / or the second positive electrode current collector can be an aluminum foil or a composite material of an aluminum foil and a PP film or a composite material of an aluminum foil and a PET film.

[0034] In some embodiments, the adhesion of the surface layer separator to the double-sided negative electrode sheet is greater than the adhesion of the intermediate layer separator to the double-sided negative electrode sheet. Under the condition that the adhesion of the surface layer separator to the single-sided positive electrode sheet is greater than the adhesion of the intermediate layer separator to the double-sided positive electrode sheet, further adjusting the adhesion of the surface layer separator and the intermediate layer separator to the double-sided negative electrode sheet to satisfy the above condition helps to maintain the flatness and stability of the negative electrode sheet, reduces the problem of local lithium precipitation caused by deformation or movement of the negative electrode sheet, and also helps to reduce lithium precipitation of the surface single-sided positive electrode and reduce the risk of internal short circuit of the battery, thereby improving the safety of the battery.

[0035] In some embodiments, the adhesion of the surface layer separator to the single-sided positive electrode sheet is greater than the adhesion of the surface layer separator to the double-sided negative electrode sheet. Under the condition that the adhesion of the surface layer separator to the single-sided positive electrode sheet is greater than the adhesion of the intermediate layer separator to the double-sided positive electrode sheet, further adjusting the adhesion of the surface layer separator to the single-sided positive electrode sheet and the double-sided negative electrode sheet to satisfy the above condition can further reduce the occurrence of gaps and / or displacement of the single-sided positive electrode sheet, improve the lithium ion transmission performance of the single-sided positive electrode sheet, and further reduce the occurrence of purple stains and lithium precipitation of the single-sided positive electrode sheet.

[0036] In some embodiments, the adhesion of the surface layer separator to the single-sided positive electrode sheet is denoted as d1 N / m, the adhesion of the intermediate layer separator to the double-sided positive electrode sheet is denoted as d3 N / m, the difference a = d1 - d3, and the unit is N / m; a / c satisfies: 0.025≤a / c≤19.5, and the ratio of a / c may, for example, be 0.025, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 19.5, or any point value in the range formed by any two of the above point values, preferably 0.5≤a / c≤5.

[0037] Under the condition that the adhesion of the surface layer separator to the single-sided positive electrode sheet is greater than the adhesion of the intermediate layer separator to the double-sided positive electrode sheet, adjusting a / c to satisfy 0.025≤a / c≤19.5, the greater a is, the greater the adhesion d1 of the surface layer separator to the single-sided positive electrode sheet is, and correspondingly c can also be adjusted to increase, i.e., the thickness of the first positive electrode current collector is increased, thereby maintaining good adhesion performance of the single-sided positive electrode sheet of the stacked battery and the surface layer separator, and effectively avoiding the curling of the single-sided positive electrode sheet and reducing purple stains and lithium precipitation of the single-sided positive electrode sheet.

[0038] The present application researches and finds that if a / c < 0.025, a is too small, the adhesion between the single-face positive plate of the laminated battery and the surface layer separator is weak (d1 is too small), and gaps and / or displacements are prone to occur in the battery during the battery cycle process, resulting in increased resistance of lithium ion transmission and prone to lithium precipitation of the single-face positive plate; or c is too large, the thickness of the first positive current collector is too large, affecting the energy density of the battery, and meanwhile causing lithium ion transmission to be blocked, and more prone to purple stain and lithium precipitation of the single-face positive plate, and more prone to lithium precipitation in the corresponding negative region; or the thickness of the second positive current collector is too small, causing c to be too large, and the thickness of the second positive current collector being too small may cause it to be easily damaged in the processing process, form tiny defects, increase the resistance, affect the electron transmission capacity of the current collector, and reduce the rate performance of the battery. If a / c > 19.5, a is too large, the adhesion between the single-face positive plate of the laminated battery and the surface layer separator is too strong (d1 is too large), the electrolyte is difficult to soak, affecting the process capability and electrolyte replenishment after the later cycle, causing insufficient electrolyte and generating liquid deficiency type local lithium precipitation; or c is too small, the thickness of the first positive current collector is small, causing the single-face positive plate to be prone to curling and prone to the single-face positive plate being separated from the laminated core; or the thickness of the second positive current collector is too large, causing large loss of the energy density of the battery.

[0039] In some embodiments, a = d1-d3, a satisfies: 0.5N / m≤a N / m≤19.5N / m, for example, a can be 0.5N / m, 1N / m, 2N / m, 5N / m, 8N / m, 10N / m, 12N / m, 14N / m, 15N / m, 16N / m, 18N / m, 19.5N / m, or any point value in the range formed by any two of the above point values, preferably 0.5N / m≤a≤10.5N / m.

[0040] In some embodiments, the adhesion d1 between the surface layer separator and the single-face positive plate satisfies: 5N / m≤d1N / m≤50N / m, for example, d1 can be 5N / m, 6N / m, 7N / m, 8N / m, 9N / m, 10N / m, 12N / m, 20N / m, 30N / m, 40N / m, 50N / m, preferably 5N / m≤d1N / m≤30N / m.

[0041] In some embodiments, the adhesion d3 between the intermediate layer separator and the double-face positive plate satisfies: 4.5N / m≤d3N / m≤50N / m, for example, d3 can be 4.5N / m, 5N / m, 6N / m, 7N / m, 8N / m, 9N / m, 10N / m, 12N / m, 15N / m, 18N / m, 20N / m, 25N / m, 30N / m, 35N / m, 40N / m, 45N / m, 50N / m, preferably 4.5N / m≤d3N / m≤25N / m.

[0042] When a and c satisfy 0.025≤a / c≤19.5, adjusting a, d1 and d3 within the above range can adjust the adhesion between the surface layer separator and the single-sided positive electrode sheet, and the adhesion between the intermediate layer separator and the double-sided positive electrode sheet within a suitable range, so that the adhesion between the electrode sheet and the separator in the stacked battery is better, further reducing the curling of the single-sided positive electrode sheet, reducing the purple stain and lithium precipitation of the single-sided positive electrode sheet, and taking into account the energy density and cycle performance of the battery.

[0043] In some embodiments, c satisfies: 1 μm≤cμm≤20 μm, for example, c can be 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm, or any point value in the range consisting of any two of the above point values, preferably 5 μm≤c≤15 μm. When a and c satisfy 0.025≤a / c≤19.5, adjusting the value of c within the above range can control the thickness of the first positive current collector and the thickness of the second positive current collector within a suitable range, further reducing the curling of the single-sided positive electrode sheet, improving the structural stability of the battery, and taking into account the energy density and cycle performance of the battery.

[0044] In some embodiments, the adhesion between the surface layer separator and the double-sided negative electrode sheet is denoted as d2 N / m, the adhesion between the intermediate layer separator and the double-sided negative electrode sheet is denoted as d4 N / m, and the difference b = d2-d4, with the unit of N / m;

[0045] a, b and c satisfy: 0.05≤(a+b) / c≤20, for example, the value of (a+b) / c can be 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, preferably 0.1≤(a+b) / c≤6. Under the condition that the adhesion between the surface layer separator and the single-sided positive electrode sheet is greater than the adhesion between the intermediate layer separator and the double-sided positive electrode sheet, adjusting a, b and c to satisfy 0.05≤(a+b) / c≤20, the greater a+b is, the greater the adhesion d1 between the surface layer separator and the single-sided positive electrode sheet and the adhesion d2 between the surface layer separator and the double-sided negative electrode sheet (d1 and d2 are greater), accordingly c can also be adjusted to increase at the same time, i.e. the thickness of the first positive current collector is increased or the thickness of the second positive current collector is reduced, which can improve the energy density of the battery, and the surface layer separator and the double-sided negative electrode sheet can maintain good adhesion performance, which can reduce the resistance of lithium ion transmission, improve the lithium ion transmission performance of the single-sided positive electrode sheet, reduce the purple stain and lithium precipitation of the single-sided positive electrode sheet, thereby improving the rate performance and cycle performance of the overall stacked battery; at the same time, the corresponding electrode sheet has good electrolyte wetting performance and liquid retention performance, which can improve the rate performance and cycle performance of the overall stacked battery.

[0046] The application research found that if (a+b) / c<0.05, a is too small, the adhesion between the single-face positive plate of the laminated battery and the surface layer separator is weak (d1 is too small), which increases the resistance of lithium ion transmission and easily causes lithium precipitation of the single-face positive plate; or the thickness of the first positive current collector is too large, which affects the energy density of the battery and easily causes the single-face positive plate to separate, the single-face positive plate to have purple stains and lithium precipitation, and the corresponding negative region to have lithium precipitation; or the thickness of the second positive current collector is too small, which causes c to be too large, affects the electron transmission capacity of the current collector, and reduces the rate performance of the battery. If (a+b) / c>20, a and b are both too large, or one of a and b is too large, which causes the adhesion difference between the surface layer separator and the intermediate layer separator to be too large, reduces the consistency of the battery, causes the structure of the battery to be unstable; or the thickness difference between the first positive current collector and the second positive current collector is too small, the thickness of the first positive current collector is small, which causes the single-face positive plate to easily curl and the single-face positive plate to easily have purple stains and lithium precipitation; or the thickness of the second positive current collector is too large, which causes too much loss of the energy density of the battery.

[0047] In some embodiments, b satisfies: 0.5N / m≤b N / m≤19.5N / m, for example, b can be 0.5N / m, 1N / m, 2N / m, 5N / m, 8N / m, 10N / m, 12N / m, 15N / m, 16N / m, 18N / m, 19.5N / m, or any point value in the range formed by any two of the above point values, preferably 0.5N / m≤b≤12N / m.

[0048] In some embodiments, the adhesion d2 between the surface layer separator and the double-face negative plate satisfies: 5N / m≤d2N / m≤50N / m, for example, d2 can be 5N / m, 6N / m, 7N / m, 8N / m, 9N / m, 10N / m, 12N / m, 15N / m, 18N / m, 20N / m, 25N / m, 30N / m, 35N / m, 40N / m, 45N / m, 50N / m, preferably 5N / m≤d2N / m≤30N / m.

[0049] In some embodiments, the adhesion d4 between the intermediate layer separator and the double-face negative plate satisfies: 5N / m≤d4N / m≤35N / m, for example, d4 can be 5N / m, 6N / m, 7N / m, 8N / m, 9N / m, 10N / m, 12N / m, 15N / m, 18N / m, 20N / m, 22N / m, 25N / m, 30N / m, 35N / m, preferably 5N / m≤d4N / m≤30N / m.

[0050] When a, b, and c satisfy 0.05≤(a+b) / c≤20, and the values of b, d2, and d4 are adjusted within the above range, the adhesion between the surface layer separator and the double-sided negative electrode sheet and the adhesion between the intermediate layer separator and the double-sided negative electrode sheet can be adjusted within a suitable range, so that the adhesion between the electrode sheet and the separator in the stacked battery is better, and the problem of lithium precipitation of the single-sided positive electrode sheet is further improved, the electrolyte infiltration performance and liquid retention performance of the separator corresponding to the electrode sheet are improved, and the rate performance and cycle performance of the entire stacked battery are improved.

[0051] In some embodiments, the adhesion between the surface layer separator and the single-sided positive electrode sheet is denoted as d1 N / m, the adhesion between the surface layer separator and the double-sided negative electrode sheet is denoted as d2 N / m, d=d1-d2, and d and c satisfy 0.05≤d / c≤10. For example, the ratio d / c can be 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, preferably 0.1≤d / c≤4.

[0052] In some embodiments, d satisfies 1 N / m≤d N / m≤20 N / m, for example, d can be 1 N / m, 2 N / m, 3 N / m, 5 N / m, 8 N / m, 10 N / m, 12 N / m, 15 N / m, 18 N / m, 20 N / m, preferably 1 N / m≤d N / m≤15 N / m.

[0053] Under the condition that the adhesion between the surface layer separator and the single-sided positive electrode sheet is greater than the adhesion between the intermediate layer separator and the double-sided positive electrode sheet, and d and c satisfy 0.05≤d / c≤10, the adhesion between the surface layer separator and the single-sided positive electrode sheet and the negative electrode of the stacked battery is good, the lithium ion transmission distance is short, and the problem of lithium precipitation of the single-sided positive electrode sheet is less likely to occur, thereby reducing the problem of purple stain / lithium precipitation in the single-sided area and improving the cycle performance and rate performance of the battery. At the same time, when d / c<0.05, d is too small, i.e., the adhesion d1 between the surface layer separator and the single-sided positive electrode sheet is too small, the adhesion between the surface layer separator and the single-sided positive electrode sheet is poor, and the single-sided positive electrode sheet is prone to lithium precipitation; or c is too large, i.e., the thickness of the first positive current collector is too large, which affects the energy density of the battery and the lithium ion transmission, causing the corresponding negative electrode area to be more prone to lithium precipitation; or the thickness of the second positive current collector is too small, causing c to be too large, which affects the electron transmission capacity of the current collector and reduces the rate performance of the battery. When d / c>10, the adhesion between the surface layer separator and the single-sided positive electrode sheet is too good, the electrolyte infiltration performance is poor, and lithium precipitation is likely to occur due to insufficient electrolyte in the later stage of the cycle; or the thickness of the first positive current collector is small, causing the single-sided positive electrode sheet to be prone to curling and to be easily separated from the stack core; or the thickness of the second positive current collector is too large, causing a large loss of the energy density of the battery.

[0054] In some embodiments, the surface layer separator has a gas permeability of 80 s / 100 ml to 300 s / 100 ml, for example, the gas permeability can be 80 s / 100 ml, 100 s / 100 ml, 120 s / 100 ml, 140 s / 100 ml, 150 s / 100 ml, 180 s / 100 ml, 200 s / 100 ml, 220 s / 100 ml, 240 s / 100 ml, 250 s / 100 ml, 260 s / 100 ml, 280 s / 100 ml, 300 s / 100 ml. Under the condition that the adhesion of the surface layer separator to the single-sided positive electrode sheet is greater than the adhesion of the intermediate layer separator to the double-sided positive electrode sheet, adjusting the gas permeability of the surface layer separator in the above range can promote the transmission of lithium ions by the surface layer, reduce the ion conduction resistance, and further reduce the situation that the single-sided positive electrode sheet is prone to lithium precipitation.

[0055] In some embodiments, the intermediate layer separator has a gas permeability of 100 s / 100 ml to 350 s / 100 ml, for example, the gas permeability can be 100 s / 100 ml, 120 s / 100 ml, 140 s / 100 ml, 150 s / 100 ml, 180 s / 100 ml, 200 s / 100 ml, 220 s / 100 ml, 240 s / 100 ml, 250 s / 100 ml, 260 s / 100 ml, 280 s / 100 ml, 300 s / 100 ml, 320 s / 100 ml, 350 s / 100 ml. Under the condition that the adhesion of the surface layer separator to the single-sided positive electrode sheet is greater than the adhesion of the intermediate layer separator to the double-sided positive electrode sheet, adjusting the gas permeability of the intermediate layer separator in the above range helps lithium ions pass through the separator quickly during charging and discharging, thereby improving the rate performance and cycle performance of the battery.

[0056] In some embodiments, the absolute value of the difference between the gas permeability of the surface layer separator and the gas permeability of the intermediate layer separator is greater than or equal to 5 s / 100 ml. That is, it can be explained that (1) the gas permeability of the surface layer separator is greater than the gas permeability of the intermediate layer separator, and the difference is greater than or equal to 5 s / 100 ml, or (2) the gas permeability of the intermediate layer separator is greater than the gas permeability of the surface layer separator, and the difference is greater than or equal to 5 s / 100 ml. Preferably, the gas permeability of the intermediate layer separator is greater than the gas permeability of the surface layer separator, the surface layer separator corresponds to a larger positive and negative electrode current density, and a lower gas permeability can better transmit lithium ions, reduce ion conduction resistance, and help improve the problem that the single-sided positive electrode sheet is prone to lithium precipitation.

[0057] In this application, the gas permeability of the separator is defined in accordance with the definition of gas permeability in GB / T 36363-2018. The gas permeability represents that under the test temperature and humidity, normal pressure environment, 100 mL of air passes through an area of 6.45 cm 2The time required for the diaphragm to pass through the 6.45 cm 2 The pressure applied is a constant pressure of 1.21 kPa, and the area passed through is a fixed area of 6.45 cm

[0058] In some embodiments, the surface layer diaphragm comprises a first substrate, and a first polymer layer disposed on at least one surface of the first substrate. That is, the first polymer layer can be disposed on one surface of the first substrate, or on both surfaces of the first substrate. Preferably, the first polymer layer is disposed on both surfaces of the first substrate, so that the surface layer diaphragm has good adhesion to the single-sided positive and negative electrode sheets.

[0059] In some embodiments, the first substrate is a high-molecular polymer base film having pores, for example, the first substrate comprises at least one of polyethylene, polypropylene, polyethylene and polypropylene composite material, polyamide, polyimide, aramid. The porosity of the first substrate is 35% to 60% (for example, 35%, 40%, 50%, 55%, or 60%); and / or, the pore size of the pores in the first substrate is 20 nm to 90 nm (for example, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, or 90 nm); and / or, the thickness of the first substrate is 3 μm to 20 μm (for example, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, or 20 μm). When the porosity and pore size of the first substrate are within the above ranges, it helps to reduce the resistance of lithium ion transmission in the surface layer diaphragm, thereby reducing the purple stain / lithium precipitation problem of the single-sided area positive electrode sheet.

[0060] In some embodiments, the first polymer layer comprises a first polymer; the mass fraction of the first polymer in the total mass of the first polymer layer is 60% to 100%, for example, the mass fraction can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%. The first polymer layer further comprises 0 to 40% of an auxiliary agent, which includes but is not limited to thickening agents, wetting agents, and adhesives, etc., and the type of specific auxiliary agent is not limited, and can be selected as needed in the art.

[0061] In some embodiments, the monomer of the first polymer comprises at least one of styrene, chlorovinyl, perfluoropropylene, trifluorochloroethylene, tetrafluoroethylene, vinylidene chloride, tetrachloroethylene, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, acrylonitrile.

[0062] Exemplarily, the first polymer comprises one or more of polytetrafluoroethylene, polychlorotrifluoroethylene, polyfluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, a copolymer of different fluorine-containing olefin monomer units, a copolymer of fluorine-containing olefin monomer units and olefin monomer units, a copolymer of fluorine-containing olefin monomer units and acrylic monomer units, a copolymer of fluorine-containing olefin monomer units and acrylate monomer units, a butyl acrylate-styrene copolymer, a butyl methacrylate-isooctyl methacrylate copolymer, an isooctyl methacrylate-styrene copolymer, a methacrylate-methacrylic acid-styrene copolymer, a methyl acrylate-isooctyl methacrylate-styrene copolymer, a butyl acrylate-isooctyl acrylate-styrene copolymer, a butyl acrylate-isooctyl methacrylate-styrene copolymer, a butyl methacrylate-isooctyl acrylate-styrene copolymer, a butyl methacrylate-isooctyl methacrylate-styrene copolymer, a methyl acrylate-isooctyl methacrylate-styrene copolymer, a styrene-acrylonitrile copolymer, a styrene-butadiene-acrylonitrile copolymer, a methyl acrylate-styrene-acrylonitrile copolymer, an isooctyl methacrylate-styrene-acrylonitrile copolymer, a styrene-vinyl acetate copolymer, a styrene-vinyl acetate-pyrrolidone copolymer, and a modified compound of the above copolymers.

[0063] In some embodiments, the first polymer has a number average molecular weight of 100,000 to 800,000 (e.g., 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, or 800,000).

[0064] In some embodiments, the first polymer has a softening point of -30°C to 180°C (e.g., -30°C, -10°C, 0°C, 10°C, 30°C, 50°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, or 180°C). When the softening point is too low (e.g., less than 30°C), the first polymer can self-adhere and stick to the roller during use, causing damage to the first polymer layer and affecting the performance of the surface layer separator (e.g., the tensile strength, adhesion performance, etc. decrease). When the softening point is too high (e.g., greater than 180°C), the first polymer requires a high temperature to achieve good adhesion, and the high temperature can damage the uniformity and compactness of the solid electrolyte interface film, increase the interface impedance, reduce the transmission efficiency of lithium ions, and thus affect the performance of the lithium ion battery.

[0065] In some embodiments, the first polymer layer has a thickness of 0.3 μm to 5 μm (e.g., 0.3 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm). And / or, the first polymer layer has an area density of 0.1 g / m 2 to 1 g / m 2 , e.g., 0.1 g / m 2 , 0.2 g / m2 0.3 g / m 2 0.4 g / m 2 0.5 g / m 2 0.6 g / m 2 0.7 g / m 2 0.8 g / m 2 1 g / m 2 , preferably 0.2 g / m 2 ~0.8 g / m 2 When the areal density of the first polymer layer is too low (e.g. less than 0.1 g / m 2 ), the amount of the first polymer is insufficient to provide sufficient adhesion, the battery is soft, and safety accidents are easily triggered; when the areal density is too high (e.g. greater than 1 g / m 2 ), the amount of the first polymer is too high, hindering the transmission channel of the electrolyte, which is not conducive to the rate performance and cycle performance of the lithium ion battery.

[0066] In the present application, by adjusting the type, molecular weight and softening point of the first polymer within the above range, or by adjusting the thickness and areal density of the first polymer layer within the above range, the adhesion of the surface layer separator to the pole piece can be adjusted, and then the adhesion of the surface layer separator to the single-sided positive pole piece is greater than the adhesion of the intermediate layer separator to the double-sided positive pole piece, thereby reducing the resistance of lithium ion transmission, improving the lithium ion transmission performance of the single-sided positive pole piece, reducing the occurrence of purple spots and lithium precipitation of the single-sided positive pole piece, and thereby improving the rate performance and cycle performance of the overall laminated battery.

[0067] In some embodiments, the surface layer separator further comprises at least one first heat-resistant layer disposed on at least one side of the first substrate and / or between the first substrate and the first polymer layer. The first heat-resistant layer comprises first inorganic particles and a first binder. Preferably, the first heat-resistant layer comprises 80wt%-99wt% first inorganic particles and 1wt%-20wt% first binder. The first heat-resistant layer has high chemical stability and thermal stability due to the presence of inorganic particles, which helps to maintain the adhesion performance of the separator more stable during long-term use. Even in harsh working environments (such as high temperature, high pressure, etc.), the heat-resistant layer can maintain the stability of the structure and performance of the separator, thereby ensuring that the adhesion performance of the separator is not affected.

[0068] In some embodiments, the first inorganic particles include, but are not limited to, at least one of alumina, magnesia, boehmite, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, and nickel oxide. The first binder includes, but is not limited to, at least one of methyl methacrylate, sodium polymethylcellulose, polyacrylate, polytetrafluoroethylene, polyvinylidene fluoride, hexafluoropropylene-vinylidene fluoride copolymer (e.g., polyvinylidene fluoride-hexafluoropropylene copolymer), polyimide, polyacrylonitrile, and polymethyl methacrylate. The first heat-resistant layer has a thickness of 0.2 μm to 5 μm, such as 0.2 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm. When the type of the first inorganic particles and the thickness of the first heat-resistant layer are within the above ranges, the function of the first heat-resistant layer can be further improved, and the stability of the structure and performance of the surface layer separator can be better improved.

[0069] In some embodiments, the intermediate layer separator includes a second substrate and a second polymer layer disposed on at least one side surface of the second substrate. That is, the second polymer layer can be disposed on one side surface of the second substrate, or on the surfaces of the opposite sides of the second substrate. Preferably, the second polymer layer is disposed on the surfaces of the opposite sides of the second substrate, so that the intermediate layer separator has good adhesion with the double-sided positive electrode sheet and the double-sided negative electrode sheet.

[0070] In some embodiments, the second substrate is a high polymer-based film having pores, such as a second substrate including at least one of polyethylene, polypropylene, polyethylene and polypropylene composite material, polyimide, and aramid. The second substrate has a porosity of 30% to 50% (such as 30%, 35%, 40%, or 50%); and / or, the second substrate has a pore size of 20 nm to 90 nm (such as 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, or 90 nm); and / or, the second substrate has a thickness of 3 μm to 20 μm (such as 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, or 20 μm). When the porosity and the pore size of the second substrate are within the above ranges, the resistance of lithium ion transmission in the intermediate layer separator can be reduced, thereby reducing the internal resistance of the battery and improving the cycle performance of the battery.

[0071] In some embodiments, the second polymer layer includes a second polymer, and the mass fraction of the second polymer in the total mass of the second polymer layer is 60% to 100%, such as 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%. The second polymer layer further includes 0 to 40% of an auxiliary agent, which includes, but is not limited to, thickening agents, wetting agents, and adhesives, and the type of the auxiliary agent is not limited, and can be selected as needed in the art.

[0072] In some embodiments, the monomer of the second polymer comprises at least one of styrene, vinyl chloride, perfluoropropylene, trifluorochloroethylene, tetrafluoroethylene, vinylidene chloride, tetrachloroethylene, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, acrylonitrile.

[0073] Illustratively, the second polymer comprises one or more of polytetrafluoroethylene, polytrifluorochloroethylene, polyfluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, a copolymer of different fluorine-containing olefin monomer units, a copolymer of fluorine-containing olefin monomer units and olefin monomer units, a copolymer of fluorine-containing olefin monomer units and acrylic monomer units, a copolymer of fluorine-containing olefin monomer units and acrylate monomer units, a butyl acrylate-styrene copolymer, a butyl methacrylate-isooctyl methacrylate copolymer, an isooctyl methacrylate-styrene copolymer, a methacrylate-methacrylic acid-styrene copolymer, a methyl acrylate-isooctyl methacrylate-styrene copolymer, a butyl acrylate-isooctyl acrylate-styrene copolymer, a butyl acrylate-isooctyl methacrylate-styrene copolymer, a butyl methacrylate-isooctyl acrylate-styrene copolymer, a butyl methacrylate-isooctyl methacrylate-styrene copolymer, a styrene-acrylonitrile copolymer, a styrene-butadiene-acrylonitrile copolymer, a methyl acrylate-styrene-acrylonitrile copolymer, an isooctyl methacrylate-styrene-acrylonitrile copolymer, a styrene-vinyl acetate copolymer, a styrene-vinyl acetate-pyrrolidone copolymer, and a modified compound of the above copolymers.

[0074] In some embodiments, the second polymer has a number average molecular weight of 100,000 to 500,000 (e.g., 100,000, 200,000, 300,000, 400,000, 500,000).

[0075] In some embodiments, the second polymer has a softening point of -30°C to 180°C (e.g., -30°C, -10°C, 0°C, 10°C, 30°C, 50°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, or 180°C). When the softening point is too low (e.g., less than 30°C), the second polymer can self-adhere and stick to the roll during use, causing damage to the second polymer layer and affecting the performance of the interlayer separator (e.g., the tensile strength, adhesion performance, etc. decrease). When the softening point is too high (e.g., greater than 180°C), the second polymer requires a high temperature to achieve good adhesion, and the high temperature can damage the uniformity and compactness of the solid electrolyte interface film on the surface of the electrode, increase the interface impedance, reduce the transmission efficiency of lithium ions, and thus affect the performance of the lithium ion battery.

[0076] In some embodiments, the second polymer layer has a thickness of 0.3 μm to 5 μm, for example 0.3 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm. And / or, the second polymer layer has an area density of 0.05 g / m 2 ~ 1 g / m 2 , for example 0.05 g / m 2 , 0.1 g / m 2 , 0.2 g / m 2 , 0.3 g / m 2 , 0.4 g / m 2 , 0.5 g / m 2 , 0.6 g / m 2 , 0.7 g / m 2 , 0.8 g / m 2 , 1 g / m 2 , preferably 0.1 g / m 2 ~ 0.5 g / m 2 . When the area density of the second polymer layer is too low (for example, lower than 0.05 g / m 2 ), the amount of the first polymer added is insufficient to provide sufficient adhesion, the battery is soft, and safety accidents are easily triggered; when the area density is too high (for example, higher than 1 g / m 2 ), the amount of the second polymer coated is too high, which hinders the transmission channel of the electrolyte, and is not conducive to the rate performance and cycle performance of the lithium ion battery.

[0077] In some preferred embodiments, the area density of the first polymer layer is greater than the area density of the second polymer layer, so that the adhesion of the surface layer separator is higher than the adhesion of the intermediate layer separator, the adhesion of the surface layer separator to the single-sided positive electrode sheet > the adhesion of the intermediate layer separator to the double-sided positive electrode sheet, the adhesion of the surface layer separator to the double-sided negative electrode sheet > the adhesion of the intermediate layer separator to the double-sided negative electrode sheet, and the adhesion of the surface layer separator to the single-sided positive electrode sheet > the adhesion of the surface layer separator to the double-sided negative electrode sheet.

[0078] In the present application, by adjusting the type, molecular weight and softening point of the second polymer within the above range, or by adjusting the thickness and area density of the second polymer layer within the above range, the adhesion of the intermediate layer separator to the positive electrode sheet and the negative electrode sheet can be relatively small, and then the adhesion of the surface layer separator to the single-sided positive electrode sheet > the adhesion of the intermediate layer separator to the double-sided positive electrode sheet, thereby reducing the occurrence of purple spots and lithium precipitation of the single-sided positive electrode sheet, and improving the rate performance and cycle performance of the overall jelly-roll battery.

[0079] In some embodiments, the intermediate layer separator further comprises at least one second heat-resistant layer disposed on at least one side of the second substrate and / or between the second substrate and the second polymer layer. The second heat-resistant layer comprises second inorganic particles and a second binder; preferably, the second heat-resistant layer comprises 80 wt% to 99 wt% of the second inorganic particles and 1 wt% to 20 wt% of the second binder. The second heat-resistant layer helps to keep the adhesion of the separator more stable during long-term use, and enhances the mechanical strength and heat resistance of the separator, which helps to prevent short circuit or failure of the battery due to deformation or rupture of the separator caused by thermal shrinkage during charging and discharging.

[0080] In some embodiments, the second inorganic particles comprise, but are not limited to, at least one of alumina, magnesia, boehmite, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, and nickel oxide. The second binder comprises, but is not limited to, at least one of polyacrylate, polytetrafluoroethylene, polyvinylidene fluoride, hexafluoropropylene-vinylidene fluoride copolymer (e.g., polyvinylidene fluoride-hexafluoropropylene copolymer), polyimide, polyacrylonitrile, and polymethyl methacrylate. The second heat-resistant layer has a thickness of 0.2 μm to 5 μm, such as 0.2 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm. When the type of the second inorganic particles and the thickness of the second heat-resistant layer are within the above ranges, the second heat-resistant layer can further enhance the stability of the structure and performance of the intermediate layer separator.

[0081] In this application, the softening point of the first polymer and the second polymer can be obtained by methods commonly used in the art. For example, using a universal differential scanning calorimeter (DSC) method: taking 5 mg of the first polymer or the second polymer sample, heating to 150°C at a heating rate of 5°C / min, collecting the DSC curve, and determining the softening point of the first polymer or the second polymer, i.e., the softening temperature, from the obtained DSC curve.

[0082] In the present application, the areal density of the first polymer layer and the second polymer layer can be tested by conventional methods in the art. For example, the test of areal density includes: mode one, the polymer coated sample is cut into a rectangular sample with a 100mm*50mm die. The length L and width W of the rectangular sample are measured respectively, the weight of the sheet-shaped sample before coating is measured and recorded as M1, the weight of the sample after coating is measured and recorded as M2, and then the areal density of the polymer layer is (M2-M1) / (L*W). Or mode two, the separator is cut into a rectangular sample with a 100mm*50mm die. The length L and width W of the rectangular sample are measured respectively, the weight of the rectangular sample is measured and recorded as M1, the weight of the rectangular sample after removing the polymer coating on one side surface is measured and recorded as M2, and then the areal density of the polymer layer is (M2-M1) / (L*W).

[0083] In some embodiments, the surface layer separator and / or the intermediate layer separator satisfy: the tensile strength in the TD direction is ≥50Mpa; and / or the tensile strength in the MD direction is ≥50Mpa. When the tensile strength of the surface layer separator and / or the intermediate layer separator is in the above range, the mechanical stress generated during the charging and discharging process of the battery can be resisted, the separator can be prevented from being broken or deformed, and the mechanical integrity and structural stability of the battery can be maintained.

[0084] In the present application, the TD direction (Transverse Direction) refers to the transverse direction perpendicular to the mechanical direction, which is used to describe the performance of the material in the transverse direction; the MD direction (Machine Direction) refers to the mechanical direction or the longitudinal direction of the material, which is used to describe the performance of the material in the longitudinal direction.

[0085] In some embodiments, the adhesion force d1 between the surface layer separator and the single-sided positive electrode sheet is greater than the adhesion force d3 between the intermediate layer separator and the double-sided positive electrode sheet after 800 cycles of the battery of the present application, the adhesion performance of the battery is good in the later cycle period, the distance consistency between the positive electrode and the negative electrode is good, the lithium precipitation in the later cycle period can be improved, and the rate performance and the cycle performance of the battery can be improved.

[0086] In some embodiments, the adhesion force d2 between the surface layer separator and the double-sided negative electrode sheet is greater than the adhesion force d4 between the intermediate layer separator and the double-sided negative electrode sheet, the adhesion performance of the battery is good in the later cycle period, the distance consistency between the positive electrode and the negative electrode is good, the lithium precipitation in the later cycle period can be improved, and the rate performance and the cycle performance of the battery can be improved.

[0087] In some embodiments, the structure of the surface layer separator includes, for example: a first substrate layer+ a first polymer layer; a first substrate layer+ a first heat-resistant layer+ a first polymer layer; a first polymer layer+ a first substrate layer+ a first polymer layer, a first polymer layer+ a first substrate layer+ a first heat-resistant layer+ a first polymer layer; a first polymer layer+ a first heat-resistant layer+ a first substrate layer+ a first heat-resistant layer+ a first polymer layer.

[0088] In some embodiments, the structure of the intermediate layer separator film comprises, for example: a second substrate layer + a second polymer layer; a second substrate layer + a second heat-resistant layer + a second polymer layer; a second polymer layer + a second substrate layer + a second polymer layer, a second polymer layer + a second substrate layer + a second heat-resistant layer + a second polymer layer; a second polymer layer + a second heat-resistant layer + a second substrate layer + a second heat-resistant layer + a second polymer layer.

[0089] In the present application, the structures of the surface layer separator film and the intermediate layer separator film can be the same or different, the first polymer layer and the second polymer layer can be the same or different, the first heat-resistant layer and the second heat-resistant layer can be the same or different, the face density, thickness and composition of the first polymer layer and the second polymer layer can be the same or different, as long as the adhesion of the surface layer separator film and the intermediate layer separator film to the pole piece meets the requirements of the present application. The present application can adjust the adhesion of the two separator films to the pole piece by adjusting one or more parameters such as the thickness, face density, composition and ratio of the first polymer layer and the second polymer layer.

[0090] In some embodiments, the double-sided negative pole piece comprises a negative current collector and a negative active layer located on both sides of the negative current collector. The negative active layer comprises a negative active material, which can be one or more layers, and each layer of active material or ratio can be the same or different; the negative active material can use the negative active material commonly known in the art for batteries, such as one or more of carbon-based materials, silicon-based materials, tin-based materials, titanium-based materials; specifically, one or more of artificial graphite, natural graphite, soft carbon, hard carbon, elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, silicon alloys, elemental tin, tin oxides, tin alloys, elemental titanium, titanium oxides, titanium alloys.

[0091] In some embodiments, the single-sided positive pole piece comprises a positive current collector and a positive active layer located on one side of the positive current collector.

[0092] In some embodiments, the double-sided positive pole piece comprises a positive current collector and a positive active layer located on both sides of the positive current collector.

[0093] The positive electrode active layer is not particularly limited, and the positive electrode active layer can include a positive electrode active material, a conductive agent, a binder, and the like according to a conventional composition in the art. Among them, the positive electrode active material, the conductive agent, the binder, and the like can all be selected from conventional materials in the art, for example, the positive electrode active material can be selected from one or more of lithium nickelate, lithium titanate, lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganate, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotube, conductive graphite, and graphene, and the binder can be selected from one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymer, polyimide, butadiene styrene rubber, and styrene propylene rubber.

[0094] In some embodiments, the battery further comprises a non-aqueous electrolyte. The non-aqueous electrolyte can be a conventional selection in the art.

[0095] In some embodiments, the battery is a lithium ion battery.

[0096] In some embodiments, the battery is a lithium ion secondary battery.

[0097] The technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0098] The materials, reagents, and the like used in the following examples can be obtained from commercial channels unless otherwise specified.

[0099] The present application will be described in detail below in conjunction with specific examples, which are used for understanding rather than limiting the present application.

[0100] Example 1-1

[0101] (1) Preparation of the separator:

[0102] A certain mass of the first polymer polymethacrylate copolymer (molecular weight 330,000, softening point 45°C) and auxiliary additives (thickener sodium carboxymethyl cellulose, wetting agent dimethyl silicone, adhesive methacrylic acid) were added to deionized water at a solid content of 10%, and stirred at a stirring speed of 1500 rpm for 60 min to obtain a polymer slurry S1.

[0103] A first heat resistant layer (alumina layer, composition: 92wt% alumina, 4wt% methacrylic acid, 4wt% sodium polymethyl cellulose) having a thickness of 2 μm was coated on the first surface of a polyethylene substrate having a thickness of 7 μm and a porosity of 40%, and a second heat resistant layer (alumina layer, composition: 92wt% alumina, 4wt% methacrylic acid, 4wt% sodium polymethyl cellulose) having a thickness of 1.5 μm was coated on the second surface of the polyethylene substrate opposite to the first surface and the surface of the first heat resistant layer. After drying in an oven, a surface layer separator was obtained. 2 A second heat resistant layer (alumina layer, composition: 92wt% alumina, 4wt% methacrylic acid, 4wt% sodium polymethyl cellulose) having a thickness of 1.5 μm was coated on the first surface of a polyethylene substrate having a thickness of 5 μm and a porosity of 35%, and a third heat resistant layer (alumina layer, composition: 92wt% alumina, 4wt% methacrylic acid, 4wt% sodium polymethyl cellulose) having a thickness of 1.5 μm was coated on the second surface of the polyethylene substrate opposite to the first surface and the surface of the second heat resistant layer. After drying in an oven, an intermediate layer separator was obtained.

[0104] A second polymer, polyvinylidene fluoride-hexafluoropropylene copolymer (molecular weight: 550,000, softening point: -19°C), and auxiliary additives (thickener sodium carboxymethyl cellulose, wetting agent dimethylsiloxane, adhesive methacrylic acid, etc.) were added to deionized water at a solid content of 15%, and the mixture was stirred at 1500 rpm for 60 min to obtain a polymer slurry S2.

[0105] A second heat resistant layer (alumina layer, composition: 92wt% alumina, 4wt% methacrylic acid, 4wt% sodium polymethyl cellulose) having a thickness of 1.5 μm was coated on the first surface of a polyethylene substrate having a thickness of 5 μm and a porosity of 35%, and a third heat resistant layer (alumina layer, composition: 92wt% alumina, 4wt% methacrylic acid, 4wt% sodium polymethyl cellulose) having a thickness of 1.5 μm was coated on the second surface of the polyethylene substrate opposite to the first surface and the surface of the second heat resistant layer. After drying in an oven, an intermediate layer separator was obtained. 2 A second heat resistant layer (alumina layer, composition: 92wt% alumina, 4wt% methacrylic acid, 4wt% sodium polymethyl cellulose) having a thickness of 1.5 μm was coated on the first surface of a polyethylene substrate having a thickness of 5 μm and a porosity of 35%, and a third heat resistant layer (alumina layer, composition: 92wt% alumina, 4wt% methacrylic acid, 4wt% sodium polymethyl cellulose) having a thickness of 1.5 μm was coated on the second surface of the polyethylene substrate opposite to the first surface and the surface of the second heat resistant layer. After drying in an oven, an intermediate layer separator was obtained.

[0106] (2) Preparation of the positive electrode sheet: lithium cobaltate, PVDF, and superconducting carbon black were mixed in a mass ratio of 97:2:1 in N-methylpyrrolidone to prepare a positive electrode slurry. The positive electrode slurry was coated on both surfaces of the second positive current collector (aluminum foil, thickness: 10 μm), and after drying and rolling, a double-sided positive electrode sheet was obtained. The positive electrode slurry was coated on one surface of the first positive current collector (aluminum foil, thickness: 20 μm), and after drying and rolling, a single-sided positive electrode sheet was obtained.

[0107] (3) Preparation of the negative electrode sheet: the negative electrode active material graphite, styrene diene rubber (SBR), sodium hydroxymethyl cellulose, and conductive carbon black were mixed in a weight ratio of 94:3:2:1, and the mixture was dispersed in water and subjected to double planetary mixing to obtain a negative electrode slurry. The slurry was coated on a copper current collector, and then dried and rolled to obtain a negative electrode sheet.

[0108] (4) Preparation of the non-aqueous electrolyte: ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) were mixed in a mass ratio of 2:1.5:2 in an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), and LiPF6 (14wt% based on the total mass of the non-aqueous electrolyte) and ethyl propionate (20wt% based on the total mass of the non-aqueous electrolyte) were slowly added to the mixed solution and stirred to obtain a non-aqueous electrolyte.

[0109] (5) Lithium ion battery preparation: the single-sided positive electrode sheet, the surface layer separator, the negative electrode sheet, the intermediate layer separator, the positive electrode sheet, the intermediate layer separator, the negative electrode sheet, the surface layer separator, and the single-sided positive electrode sheet are sequentially stacked to form a bare battery cell. Whether the single-sided positive electrode sheet is curled is observed. Then, after processes such as packaging, battery cell baking, liquid injection, and hot pressing formation, the battery is prepared.

[0110] (6) Battery performance test

[0111] (i) Adhesion test between separator and electrode sheet:

[0112] After sorting the batteries obtained in the above examples and comparative examples, the batteries were placed in an environment of (25±2) °C for 2-3 h. The batteries were charged at a constant current of 0.7C, and the cutoff current was 0.05C. When the terminal voltage of the battery reached the charge limit voltage, the battery was charged at a constant voltage until the charging current was less than or equal to the cutoff current. The battery was stopped charging and rested for 5 min. The fully charged battery was disassembled, and the adhesion between the separator and the positive or negative electrode sheet was tested according to the national standard GB / T 2790-1995, i.e., the 180° peeling test standard. The separator and the positive or negative electrode sheet were cut into small strips of 15 mm x 54.2 mm, and the adhesion between the separator and the positive or negative electrode sheet was tested according to the 180° peeling test standard.

[0113] (ii) Hot box test

[0114] Under the condition of 25℃±3℃, discharge at 0.2C to the cutoff voltage 3.0V, and rest for 10 min; charge at 0.5C constant current and constant voltage to the upper limit voltage 4.2V, and the cutoff current is 0.02C. Test the full charge state voltage, internal resistance, and thickness at 25℃±3℃. Place the fully charged battery cell in the test chamber, and heat the test chamber at a temperature rise rate of (5±2)℃ / min. When the temperature in the chamber reaches the test temperature 130℃±2℃, keep the temperature constant for 60 min. After the test is completed, observe whether the battery cell catches fire. If it catches fire, it does not pass. If it does not catch fire, it passes. Each sample is tested ten times, and the result is represented by "passing times / 10". For example, "10 / 10" means that 10 times pass, and "5 / 10" means that 5 out of 10 times pass.

[0115] (iii) 25℃ cycle test

[0116] The initial voltage and initial thickness of the batteries of the above examples and comparative examples were tested. Then the lithium ion batteries were placed at 25°C, charged at 1C constant current to the upper limit voltage, then charged at the upper limit voltage constant voltage to 0.05C, and rested for 5 minutes; then discharged at 0.5C constant current to 3V, and rested for 5 minutes, which was one charge-discharge cycle. Such charging / discharging was carried out, and the capacity retention rate of the lithium ion battery at 800T was recorded. The final thickness was tested, the thickness expansion rate was calculated = (final thickness-initial thickness) / initial thickness. The adhesion between the separator and the pole piece after 800T of the lithium ion battery was tested, and the test method was as described in (i) above.

[0117] (iv) Lithium precipitation test

[0118] The lithium ion batteries of the examples and comparative examples were placed at 25°C, and charged at 5C and 6C constant current to the upper limit voltage, respectively, then charged at the upper limit voltage constant voltage to 0.05C, and rested for 5 minutes; then discharged at 0.5C constant current to 3V, and rested for 5 minutes, which was one charge-discharge cycle. After 20T of charge-discharge cycle, the battery was disassembled, and the lithium precipitation of the pole piece was observed.

[0119] Reference was made to Example 1-1, except for the differences as shown in Table 1. Among them, the values of d1 in Example 1 group and Comparative Examples 3 and 4 were changed by adjusting the surface density of the polymer slurry S1 coated on the surface layer separator; the values of d3 in Example 2 group were changed by adjusting the surface density of the polymer slurry S2 coated on the middle layer separator; in Example 3 group, the values of c were adjusted by changing the thickness of the current collector of the single-sided positive pole piece.

[0120] Table 1

[0121] " / " means that the data is not counted.

[0122] Comparative Example 1: Reference was made to Example 1-1, except for the difference that only the surface layer separator was used to assemble the battery. The positive pole piece, the surface layer separator, and the negative pole piece were stacked in sequence to form a bare battery core, and then the battery was prepared after the processes of packaging, battery core baking, liquid injection, and hot pressing formation.

[0123] Comparative Example 2: Reference was made to Example 1-1, except for the difference that only the middle layer separator was used to assemble the battery. The positive pole piece, the middle layer separator, and the negative pole piece were stacked in sequence to form a bare battery core, and then the battery was prepared after the processes of packaging, battery core baking, liquid injection, and hot pressing formation.

[0124] The test data of Example 1 group-3 group and Comparative Examples 1-4 are recorded in Table 2.

[0125] Table 2

[0126] " / " means that the data is not tested.

[0127] As can be seen from Table 2, when the adhesion d1 between the surface layer separator and the single-sided positive electrode sheet is greater than the adhesion d3 between the intermediate layer separator and the double-sided positive electrode sheet, the generation of lithium precipitation in the single-sided positive electrode sheet can be reduced. Further adjusting a and c to satisfy 0.025≤a / c≤19.5 can make the single-sided positive electrode sheet of the stacked battery and the surface layer separator maintain good adhesion, and further improve the lithium precipitation in the single-sided positive electrode sheet.

[0128] Refer to Example 1-1, except for the differences shown in Table 3. In the Example 4 group, the surface layer separator is adjusted by adjusting the areal density of the polymer slurry S1 coating to change the value of d2; in the Example 5 group, the intermediate layer separator is adjusted by adjusting the areal density of the polymer slurry S2 coating to change the value of d4, and in Example 5-3, d2<d4.

[0129] Table 3

[0130] " / " means that the data is not tested.

[0131] The test data of Example 4 group-5 group is recorded in Table 4.

[0132] Table 4

[0133] As can be seen from Table 4, adjusting a, b and c to satisfy 0.05≤(a+b) / c≤20 makes the surface layer separator and the single-sided positive electrode sheet and the double-sided negative electrode sheet maintain good adhesion, reduces lithium precipitation in the single-sided positive electrode sheet, and improves the overall rate performance and cycle performance of the stacked battery.

[0134] Refer to Example 1-1, except for the differences shown in Table 5. In the Example 6 group, the surface layer separator is adjusted by adjusting the areal density of the polymer slurry S1 coating to change the values of d1 and d2, and the intermediate layer separator is adjusted by adjusting the areal density of the polymer slurry S2 coating to change the values of d3 and d4, and the thickness of the first positive electrode current collector is adjusted to change the value of d / c.

[0135] Table 5

[0136] The test data of Example 6 group is recorded in Table 6.

[0137] Table 6

[0138] As can be seen from Table 6, when d and c satisfy 0.05≤d / c≤10, the surface layer separator of the laminated battery has good adhesion to the single-face positive electrode sheet and the double-face negative electrode, the lithium ion transmission distance is short, the single-face positive electrode sheet is less likely to produce lithium precipitation, the problem of lithium precipitation in the single-face area is reduced, and the cycle performance and rate performance of the battery are improved.

[0139] Reference is made to Example 1-1, except for the differences shown in Table 7. In the example, the air permeability of the surface layer separator and the intermediate layer separator is adjusted by changing the porosity of the first substrate and the second substrate.

[0140] Table 7

[0141] As can be seen from Table 7, when the air permeability of the surface layer separator is adjusted within the protection scope of the present application, the lithium ion transmission of the surface layer is promoted, and the single-face positive electrode sheet is less likely to produce lithium precipitation; and when the air permeability of the intermediate layer separator is adjusted within the protection scope of the present application, the lithium ion is quickly transmitted through the separator during the charging and discharging process, and the rate performance and cycle performance of the battery are improved.

[0142] It should be noted that in this document, the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusions, such that processes, methods, articles, or devices that comprise a list of elements are not limited to those elements, but can also include other elements not expressly listed, or inherent to such processes, methods, articles, or devices. Without more limitations, the element defined by the phrase "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or device that includes the element. In addition, it should be noted that the scope of the methods and devices in the embodiments of the present application is not limited to the order of performing the functions shown or discussed, and can also include performing the functions in a substantially simultaneous manner or in reverse order, for example, the described method can be performed in an order different from that described, and various steps can be added, omitted, or combined. In addition, the features described with reference to certain examples can be combined in other examples.

[0143] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A battery, wherein, An electrode assembly comprising a laminated structure, the electrode assembly comprising: a plurality of laminated electrode plates, the electrode plates comprising two surface layer electrode plates at the outermost layers and a plurality of intermediate layer electrode plates between the two surface layer electrode plates, the surface layer electrode plates being single-sided positive electrode plates, and the intermediate layer electrode plates being double-sided positive electrode plates and double-sided negative electrode plates; a surface layer separator between the single-sided positive electrode plates and the double-sided negative electrode plates; and an intermediate layer separator between the double-sided positive electrode plates and the double-sided negative electrode plates; wherein the adhesion of the surface layer separator to the single-sided positive electrode plates is greater than the adhesion of the intermediate layer separator to the double-sided positive electrode plates.

2. The battery of claim 1, wherein, The single-sided positive electrode plates comprise a first positive current collector, and the double-sided positive electrode plates comprise a second positive current collector; the thickness of the first positive current collector is greater than the thickness of the second positive current collector, and the difference is c μm.

3. The battery according to claim 1 or 2, wherein The adhesion of the surface layer separator to the double-sided negative electrode plates is greater than the adhesion of the intermediate layer separator to the double-sided negative electrode plates.

4. The battery of any one of claims 1-3, wherein, The adhesion of the surface layer separator to the single-sided positive electrode plates is greater than the adhesion of the surface layer separator to the double-sided negative electrode plates.

5. The battery of claim 2, wherein, The adhesion of the surface layer separator to the single-sided positive electrode plates is d1 N / m, the adhesion of the intermediate layer separator to the double-sided positive electrode plates is d3 N / m, and the difference a = d1 - d3, with the unit of N / m; a and c satisfy: 0.025 ≤ a / c ≤ 19.5, preferably 0.5 ≤ a / c ≤ 5; Preferably, a satisfies: 0.5 N / m ≤ a N / m ≤ 19.5 N / m; Preferably, c satisfies: 1 μm ≤ c μm ≤ 20 μm.

6. The battery of claim 5, wherein, The adhesion of the surface layer separator to the double-sided negative electrode plates is d2 N / m, and the adhesion of the intermediate layer separator to the double-sided negative electrode plates is d4 N / m, and the difference b = d2 - d4, with the unit of N / m; a, b and c satisfy: 0.05 ≤ (a+b) / c ≤ 20, preferably 0.1 ≤ (a+b) / c ≤ 6; Preferably, b satisfies: 0.5 N / m ≤ b N / m ≤ 19.5 N / m.

7. The battery of claim 2, wherein, The adhesion of the surface layer separator to the single-sided positive electrode plates is d1, and the adhesion of the surface layer separator to the double-sided negative electrode plates is d2; d = d1 - d2; d and c satisfy: 0.05 ≤ d / c ≤ 10, preferably 0.1 ≤ d / c ≤ 4; Preferably, d satisfies: 1 N / m ≤ d ≤ 20 N / m; Preferably, 5 N / m ≤ d1 ≤ 50 N / m; Preferably, 5 N / m ≤ d2 ≤ 50 N / m; Preferably, c satisfies: 1 μm ≤ c ≤ 20 μm.

8. The battery of claim 1, wherein, The surface layer separator has a gas permeability of 80 s / 100 ml to 300 s / 100 ml.

9. The battery of claim 1, wherein, The intermediate layer separator has a gas permeability of 100 s / 100 ml to 350 s / 100 ml.

10. The battery of claim 1, wherein, The absolute value of the difference between the gas permeability of the surface layer separator and the gas permeability of the intermediate layer separator is ≥ 5 s / 100 ml.

11. The battery of claim 1, wherein, The surface layer separator comprises a first substrate and a first polymer layer provided on at least one side surface of the first substrate; Preferably, the first polymer layer comprises a first polymer; the mass fraction of the first polymer in the total mass of the first polymer layer is 60% to 100%. Preferably, the first polymer layer has a thickness of 0.3 μm to 5 μm; and / or, the first polymer layer has an areal density of 0.1 g / m 2 ~ 1 g / m 2 ; Preferably, the first polymer comprises one or more of polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, a copolymer of different fluorine-containing olefin monomer units, a copolymer of fluorine-containing olefin monomer units and olefin monomer units, a copolymer of fluorine-containing olefin monomer units and acrylic monomer units, a copolymer of fluorine-containing olefin monomer units and acrylate monomer units, butyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate copolymer, isooctyl methacrylate-styrene copolymer, methacrylate-methacrylic acid-styrene copolymer, methyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl acrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, methyl acrylate-isooctyl methacrylate-styrene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, methyl acrylate-styrene-acrylonitrile copolymer, isooctyl methacrylate-styrene-acrylonitrile copolymer, styrene-vinyl acetate copolymer, styrene-vinyl acetate-pyrrolidone copolymer, and modified compounds of the above copolymers. Preferably, the number average molecular weight of the first polymer is 100,000-800,000; and / or, the softening point of the first polymer is -30°C-180°C.

12. The battery of claim 11, wherein, The surface layer separator further comprises at least one first heat-resistant layer, which is arranged on at least one side of the first substrate and / or between the first substrate and the first polymer layer. Preferably, the first heat-resistant layer comprises first inorganic particles and a first binder. Preferably, the thickness of the first heat-resistant layer is 0.2-5 μm. Preferably, the porosity of the first substrate is 35%-60%; and / or, the pore size is 20-90 nm.

13. The battery of claim 1, wherein, The intermediate layer separator comprises a second substrate and a second polymer layer arranged on at least one side of the second substrate. Preferably, the second polymer layer comprises a second polymer, and the mass fraction of the second polymer in the total mass of the second polymer layer is 60%-100%. Preferably, the second polymer layer has a thickness of 0.3 μm to 5 μm; and / or, the second polymer layer has an areal density of 0.05 g / m 2 ~ 1 g / m 2 ; Preferably, the second polymer comprises one or more of polytetrafluoroethylene, polychlorotrifluoroethylene, polyfluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, a copolymer of different fluorine-containing olefin monomer units, a copolymer of fluorine-containing olefin monomer units and olefin monomer units, a copolymer of fluorine-containing olefin monomer units and acrylic monomer units, a copolymer of fluorine-containing olefin monomer units and acrylate monomer units, a butyl acrylate-styrene copolymer, a butyl methacrylate-isooctyl methacrylate copolymer, an isooctyl methacrylate-styrene copolymer, a methacrylate-methacrylic acid-styrene copolymer, a methyl acrylate-isooctyl methacrylate-styrene copolymer, a butyl acrylate-isooctyl acrylate-styrene copolymer, a butyl acrylate-isooctyl methacrylate-styrene copolymer, a butyl methacrylate-isooctyl acrylate-styrene copolymer, a butyl methacrylate-isooctyl methacrylate-styrene copolymer, a methyl acrylate-butyl methacrylate-styrene copolymer, a styrene-acrylonitrile copolymer, a styrene-butadiene-acrylonitrile copolymer, a methyl acrylate-styrene-acrylonitrile copolymer, an isooctyl methacrylate-styrene-acrylonitrile copolymer, a styrene-vinyl acetate copolymer, a styrene-vinyl acetate-pyrrolidone copolymer, and a modified compound of the above copolymers. Preferably, the second polymer has a number average molecular weight of 100,000 to 500,000; and / or, a softening point of -30°C to 180°C.

14. The battery of claim 13, wherein, The intermediate layer separator further comprises at least one second heat-resistant layer disposed on at least one side of the second substrate and / or between the second substrate and the second polymer layer. Preferably, the second heat-resistant layer comprises second inorganic particles and a second binder. Preferably, the second heat-resistant layer has a thickness of 0.2 μm to 5 μm. Preferably, the second substrate has a porosity of 30% to 50%; and / or, a pore size of 20 nm to 90 nm.

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