Lithium ion secondary battery

Abstract

The invention relates to the technical field of batteries, in particular to a lithium ion secondary battery. Comprising a laminated core and an aluminum-plastic film, the laminated core comprises a positive plate, a diaphragm and a negative plate which are laminated, the positive plate comprises a single-sided positive plate and a double-sided positive plate in the thickness direction, the single-sided positive plate is located on the outer side of the laminated core, and a positive active layer is close to the center of the laminated core; the laminated core comprises an upper end face and a lower end face along the height direction of the laminated core, and the shortest distances between the top seal and the bottom of the aluminum-plastic film and the negative plates positioned on the upper end face and the lower end face are respectively 1-4mm and 0.1-2mm; the negative plate exceeds the positive plate; the positive electrode active material includes lithium cobalt oxide having a matrix and a first region; the first region comprises Al and / or Ti, and the content of the Al in the lithium cobalt oxide is 500-12000ppm, and the content of the Ti in the lithium cobalt oxide is 10-1000ppm; and the lithium cobalt oxide Dv99 is 32 to 55 [mu] m. According to the battery, aluminum plastic film abrasion is relieved, and the safety performance is improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and specifically to a lithium-ion secondary battery. Background Technology

[0002] Lithium-ion rechargeable batteries are widely used due to their high energy density and long lifespan. Among them, stacked batteries, compared to wound batteries, have higher energy density, safety, and a more stable internal structure, making them more suitable for high-rate, large-size, and irregularly shaped batteries, and thus attracting much attention. Because the outermost layer of a stacked battery is a single-sided positive electrode sheet, meaning the positive electrode current collector only has an active layer on one side facing the center of the stack, the side of the positive electrode current collector without paste will wear down the aluminum-plastic film, causing the positive electrode active material particles to detach and the aluminum foil on one side to fold, thereby affecting the battery's safety and electrochemical performance. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned defects in the prior art and propose a lithium-ion secondary battery. The lithium-ion secondary battery (hereinafter referred to as the battery) includes a stack of cores, tabs and an aluminum-plastic film, which alleviates the wear and tear of the positive and negative electrode plates on the aluminum-plastic film, avoids short circuits between the positive and negative electrodes, and improves the safety performance of the battery. Furthermore, by setting a second region on the surface of lithium cobalt oxide, the stability of the positive electrode is improved and the detachment of the positive electrode active material is prevented.

[0004] The inventors of this invention discovered that the thickness of the positive current collector in a single-sided positive electrode sheet of a stacked battery is usually large, resulting in excessively high current density in the single-sided region. When the positive electrode active material of the single-sided sheet uses lithium cobalt oxide with a large particle size, overcharging is likely to occur during dynamic cycling, leading to structural instability of the positive electrode active material and thus affecting the cycle stability of the battery. The inventors of this invention improved the structural stability of the positive electrode active material by controlling the particle size distribution and structure of lithium cobalt oxide (forming a matrix and a first region on the matrix surface) to keep the lithium cobalt oxide particle size within a suitable range, and by forming a protective layer in the first region. When the current density is too high, it can prevent the positive electrode from being overcharged and causing the positive electrode active material structure to collapse, thus avoiding the detachment of the positive electrode active material during drop and micro-drop tests. On the other hand, since the positive electrode active layer is only set on one side of the single-sided positive electrode sheet, the corners of the single-sided positive electrode sheet and the positive electrode current collector will severely wear down the inner layer of the aluminum-plastic film, causing the aluminum foil in the single-sided positive electrode sheet to fold, electrolyte to leak, and the battery to bulge and swell. In drop and micro-drop tests, the wear of the aluminum-plastic film at the corners of the single-sided positive electrode sheet will further aggravate the detachment of the positive electrode active material, resulting in damage to the internal electrode structure of the battery and affecting the battery's electrochemical performance and safety performance. In order to further improve the above problems, the inventors of this invention have adjusted the distance between the upper and lower end faces of the stack and the aluminum-plastic film to avoid the aggravated wear caused by the positive and negative electrodes extending and contacting the aluminum-plastic film. In addition, by adjusting the negative electrode sheet to extend beyond the positive electrode sheet in the height and width directions of the stack, the inventors have prevented the positive electrode sheet from displacing beyond the negative electrode sheet and causing a short circuit, thus improving the battery's safety performance.

[0005] Based on this, the present invention proposes the following technical solution:

[0006] This invention proposes a lithium-ion secondary battery, which includes a stacked core and an aluminum-plastic film. The stacked core includes a positive electrode sheet, a separator, and a negative electrode sheet stacked together. Along the thickness direction of the stacked core, the positive electrode sheet includes a single-sided positive electrode sheet and a double-sided positive electrode sheet. The single-sided positive electrode sheet is located on the outside of the stacked core. The single-sided positive electrode sheet includes a positive current collector and a positive active layer located on one side surface of the positive current collector. The positive active layer is close to the center of the stacked core.

[0007] The lithium-ion secondary battery also includes a positive electrode tab, which is electrically connected to the positive current collector. Along the height direction of the stacked core, the stacked core includes an upper end face and a lower end face, with the upper end face close to the positive electrode tab and the lower end face away from the positive electrode tab. The shortest distance between the top seal of the aluminum-plastic film and the negative electrode sheet located on the upper end face is d1, where d1 is 1mm-4mm. The shortest distance between the bottom of the aluminum-plastic film and the negative electrode sheet located on the lower end face is d2, where d2 is 0.1mm-2mm.

[0008] The negative electrode extends beyond the positive electrode in the height direction of the stacked core, and the negative electrode extends beyond the positive electrode in the width direction of the stacked core;

[0009] The positive electrode active layer includes a positive electrode active material, which includes lithium cobalt oxide, and the lithium cobalt oxide comprises a compound with the chemical formula Li. a Co x A k The substance containing O2, wherein 0.85≤a≤1.1, 0.8≤x≤1.05, 0<k≤0.15, and A includes at least one of the elements Al, Mg, Ti, Zr, Y, La, W, B, Nb, Sr, F, Ni, Mn, and P, wherein the lithium cobalt oxide includes a matrix and a first region located on the surface of the matrix; the first region includes the elements Al and / or Ti, wherein the mass content of element Al in the lithium cobalt oxide is 5000ppm-12000ppm, and the mass content of element Ti in the lithium cobalt oxide is 10ppm-1000ppm;

[0010] The lithium cobalt oxide has a particle size Dv99 of 12μm-50μm.

[0011] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0012] (1) The lithium-ion secondary battery of the present invention improves the wear problem of aluminum-plastic film and aluminum-plastic film on single-sided positive electrode sheet and improves the safety performance of battery.

[0013] (2) The lithium-ion secondary battery of the present invention improves the structural stability of the positive electrode active material, avoids shedding, and improves the cycle performance of the battery.

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0015] Figure 1 The figure shown is a three-dimensional schematic diagram of a stacked core in one embodiment of the present invention.

[0016] Figure 2 The diagram shown is a structural schematic along the thickness direction of the stacked core in one embodiment of the present invention.

[0017] Figure 3 The figure shown is a planar schematic diagram of the stacked core along the height direction of the stacked core in one embodiment of the present invention.

[0018] Figure 4 The image shown is a cross-sectional scanning electron microscope (SEM) image of the positive electrode sheet in one embodiment of the present invention.

[0019] Figure 5 The diagram shown is a schematic diagram of the structure of lithium cobalt oxide in one embodiment of the present invention.

[0020] Figure 6 The image shown is a SEM image of the positive electrode active layer in one embodiment of the present invention.

[0021] Figure 7 The image shown is an EDS spot scan map of the second region surface in one embodiment of the present invention.

[0022] Figure 8 The figure shown is a schematic diagram of the planar structure of the stacked core and aluminum-plastic film in one embodiment of the present invention.

[0023] Figure 9 The diagram shown is a schematic diagram of a single-pit aluminum-plastic film in one embodiment of the present invention.

[0024] Figure 10 The diagram shown is a schematic diagram of a double-pit aluminum-plastic film in one embodiment of the present invention.

[0025] Figure 11 The figure shown is a cross-sectional schematic diagram of the perforated aluminum-plastic film along the thickness direction in one embodiment of the present invention.

[0026] Figure 12 The diagram shown is a chamfered schematic of the negative electrode sheet in one embodiment of the present invention.

[0027] Figure 13 The diagram shown is a chamfered schematic of the negative electrode sheet in one embodiment of the present invention.

[0028] Figure 14 The diagram shown is a schematic diagram of the bonding area along the thickness direction of the stacked core in one embodiment of the present invention.

[0029] Figure 15 The diagram shown is a schematic diagram of the insulating layer arrangement in one embodiment of the present invention.

[0030] Figure 16 The figure shown is a planar schematic diagram of the negative electrode sheet in one embodiment of the present invention.

[0031] Figure 17 The figure shown is a cross-sectional schematic diagram of a single-sided positive electrode sheet in one embodiment of the present invention.

[0032] Reference numerals: 1 for positive electrode, 11 for single-sided positive electrode, 12 for double-sided positive electrode, 13 for positive current collector, 14 for positive active layer, 15 for protrusion, 16 for concave portion; 2 for negative electrode, 21 for negative current collector, 22 for negative active layer, 23 for first edge of negative electrode, 24 for second edge of negative electrode, 25 for first edge of negative electrode, 26 for second edge of negative electrode; 3 for separator, 31 for bonding. Area; 4 is the tab, 41 is the positive tab, 42 is the negative tab; 5 is the first surface, 6 is the second surface; 7 is the aluminum-plastic film, 71 is the inner layer located on the first surface of the stacked core, 72 is the edge of the connecting corner area, 73 is the inner layer, 74 is the middle layer, 75 is the outer layer, 8 is the upper end surface, 9 is the lower end surface, 10 is the third surface, 17 is the fourth surface, 18 is the side surface, 19 is the first bonding position, 20 is the third bonding position. Detailed Implementation

[0033] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0034] This invention provides a lithium-ion secondary battery, which includes a stacked core and an aluminum-plastic film. The stacked core includes a positive electrode sheet, a separator, and a negative electrode sheet stacked together. Along the thickness direction of the stacked core, the positive electrode sheet includes a single-sided positive electrode sheet and a double-sided positive electrode sheet. The single-sided positive electrode sheet is located on the outer side of the stacked core. The single-sided positive electrode sheet includes a positive current collector and a positive active layer located on one side surface of the positive current collector. The positive active layer is close to the center of the stacked core.

[0035] In this invention, the positive electrode sheet further includes a double-sided positive electrode sheet, which includes the positive current collector and positive active layers located on both sides of the positive current collector.

[0036] It is understood that the single-sided positive electrode is located at the top and bottom layers of the stacked core along the thickness direction. A plurality of double-sided positive electrode sheets are disposed between the single-sided positive electrode sheets.

[0037] In this invention, the thickness of the positive current collector of the single-sided positive electrode is greater than the thickness of the positive current collector of the double-sided positive electrode.

[0038] It is understood that "several" refers to the number of double-sided positive electrodes ≥ 2.

[0039] like Figure 1 The figure shown is a three-dimensional schematic diagram of a stacked core according to an embodiment of the present invention, as follows: Figure 2The diagram shows a structural schematic along the thickness direction of the stacked core in one embodiment of the present invention; wherein, 1 is a positive electrode sheet, 11 is a single-sided positive electrode sheet, 12 is a double-sided positive electrode sheet, 13 is a positive current collector, 14 is a positive active layer, 2 is a negative electrode sheet, 21 is a negative current collector, 22 is a negative active layer, 3 is a separator, 4 is a tab (41 is a positive tab, 42 is a negative tab), 5 is a first surface, and 6 is a second surface. As can be seen from the figure, the stacked core includes the positive electrode sheet, the separator, and the negative electrode sheet stacked together. The direction indicated by the arrow is the thickness direction of the stacked core. The outermost part of the stacked core is the single-sided positive electrode sheet, and the positive active layer is close to the center of the stacked core.

[0040] In this invention, the lithium-ion secondary battery further includes a positive electrode tab, which is electrically connected to the positive current collector. Along the height direction of the stacked core, the stacked core includes an upper end face and a lower end face, with the upper end face close to the positive electrode tab and the lower end face away from the positive electrode tab. The shortest distance between the top seal of the aluminum-plastic film and the negative electrode sheet located on the upper end face is d1, where d1 is 1mm-4mm, for example, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, or 1.5mm. The minimum distance between the bottom of the aluminum-plastic film and the negative electrode sheet located on the lower end face is d2, which is 0.1mm-2mm, for example, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.6mm, 0.8mm, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm or 2mm.

[0041] In one embodiment, d1 is 1.5mm-3mm.

[0042] In one embodiment, d2 is 0.3mm-1.5mm.

[0043] In this invention, 1mm≤d1+d2≤5mm, for example, 1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.8mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.2mm, 4.5mm or 5mm.

[0044] In one embodiment, 1.3mm ≤ d1 + d2 ≤ 4.2mm.

[0045] It is understood that the top seal of the aluminum-plastic film is located on the side extending from the electrode tab, the bottom of the aluminum-plastic film is located on the side away from the electrode tab, and the top seal and the bottom are arranged opposite to each other.

[0046] In this invention, the negative electrode extends beyond the positive electrode in the height direction of the stacked core, and the negative electrode extends beyond the positive electrode in the width direction of the stacked core.

[0047] In this invention, along the height direction of the stacked core, the size difference between the negative electrode and the positive electrode located on the upper end face is 0.4mm-2mm, for example, 0.4mm, 0.45mm, 0.5mm, 0.55mm, 0.6mm, 0.65mm, 0.7mm, 0.75mm, 0.8mm, 0.85mm, 0.9mm, 0.95mm, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, or 2mm. mm; the size difference between the negative electrode and the positive electrode located on the lower end face is 0.3mm-1.8mm, for example, 0.3mm, 0.32mm, 0.34mm, 0.36mm, 0.38mm, 0.4mm, 0.42mm, 0.44mm, 0.46mm, 0.48mm, 0.5mm, 0.6mm, 0.8mm, 1mm, 1.2mm, 1.4mm, 1.5mm, 1.6mm or 1.8mm.

[0048] In this invention, the stacked core further includes a third surface and a fourth surface disposed opposite to each other along the width direction of the stacked core. The size difference between the negative electrode and the positive electrode located on the third surface is 0.3mm-1.8mm, for example, 0.3mm, 0.32mm, 0.34mm, 0.36mm, 0.38mm, 0.4mm, 0.42mm, 0.44mm, 0.46mm, 0.48mm, 0.5mm, 0.6mm, 0.8mm, 1mm, 1.2mm, and 1.4mm. The size difference between the negative electrode and the positive electrode on the fourth surface is 0.3mm-1.8mm, for example, 0.3mm, 0.32mm, 0.34mm, 0.36mm, 0.38mm, 0.4mm, 0.42mm, 0.44mm, 0.46mm, 0.48mm, 0.5mm, 0.6mm, 0.8mm, 1mm, 1.2mm, 1.4mm, 1.5mm, 1.6mm or 1.8mm.

[0049] In this invention, the negative electrode sheet includes a negative current collector and a negative active layer located on at least one side of the surface of the negative current collector, and the lithium-ion secondary battery further includes a negative tab, which is electrically connected to the negative current collector.

[0050] In this invention, the positive electrode tab is connected to each of the positive electrode sheets in the stacked core.

[0051] In this invention, the negative electrode tab is connected to each of the negative electrode sheets in the stacked core.

[0052] like Figure 3 The figure shows a planar schematic diagram of the stacked core along its height direction in one embodiment of the present invention, wherein 1 is the positive electrode sheet, 2 is the negative electrode sheet, 7 is the aluminum-plastic film, 8 is the upper end surface, 9 is the lower end surface, 10 is the third surface, and 17 is the fourth surface. As can be seen from the figure, along the height direction of the stacked core, the shortest distance between the top seal of the aluminum-plastic film and the negative electrode sheet located on the upper end surface is d1, and the shortest distance between the bottom of the aluminum-plastic film and the negative electrode sheet located on the lower end surface is d2; the dimensions of the negative electrode sheets located on the upper end surface, lower end surface, third surface, and fourth surface are w1, w2, w3, and w4 respectively, which are differences between the dimensions of the positive electrode sheets at their corresponding positions.

[0053] It is understood that the stacked core has six surfaces, the upper end surface and the lower end surface are two surfaces arranged opposite each other along the height direction of the stacked core, the first surface and the second surface are two surfaces arranged opposite each other along the thickness direction of the stacked core, and the third surface and the fourth surface are two surfaces arranged opposite each other along the width direction of the stacked core.

[0054] By limiting the dimensional difference between the negative electrode sheet and the corresponding positive electrode sheet in the four directions (top, bottom, left, and right), the negative electrode sheet extends beyond the positive electrode sheet while maintaining a certain dimensional margin. This provides sufficient space for lithium intercalation during battery charging, preventing lithium dendrite growth from piercing the separator and causing a short circuit. It also covers the edge of the positive electrode sheet, preventing it from shifting beyond the negative electrode sheet and causing a short circuit, which would negatively impact safety. Furthermore, by limiting the minimum distance between the negative electrode sheet located on the upper and lower surfaces of the stack and the top and bottom of the aluminum-plastic film, a certain gap can be controlled between the aluminum-plastic film and the stack. This provides space for the stack to release internal stress and acts as a buffer when the battery is subjected to external stress or impact, reducing the possibility of stack damage.

[0055] Setting gaps between the upper and lower end faces of the aluminum-plastic film and the stacked core can improve battery safety while ensuring electrolyte wetting and good energy density. When d1 and d2 are too large, the probability of the electrode stretching and squeezing the aluminum-plastic film during battery cycling and aggravating wear of the aluminum-plastic film is reduced, providing buffer space for the volume change of the negative electrode. However, it will significantly reduce the energy density of the battery and increase the possibility of internal component displacement during micro-drop or drop tests, resulting in poor structural stability and potentially causing local wear of the aluminum-plastic film. When d1 and d2 are too small, although it is beneficial to optimize battery energy density, it increases the risk of battery short circuit. Under the action of expansion stress, it accelerates the wear of the aluminum-plastic film at the edge of the electrode, leading to short circuits, corner breakage, and leakage, which is not conducive to improving safety performance. Furthermore, too small a gap cannot provide sufficient expansion space, reducing the ability to withstand expansion stress and leading to capacity decay.

[0056] In this invention, d1 and d2 can be obtained by conventional testing methods in the art, such as by measuring them by CT testing.

[0057] In this invention, w1, w2, w3 and w4 can be obtained by conventional testing methods in the art, for example by discharging the battery to 0% SOC, disassembling the battery, and measuring the dimensions of the positive and negative electrodes.

[0058] In this invention, the positive electrode active layer comprises a positive electrode active material, the positive electrode active material comprises lithium cobalt oxide, and the lithium cobalt oxide comprises a material with the chemical formula Li. a Co x A k The substance of O2, wherein 0.85≤a≤1.1 (e.g., 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.92, 0.94, 0.96, 0.98, 1, 1.05 or 1.1), 0.8≤x≤1.05 (e.g., 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, 1 or 1.05), 0<k≤0.15 (e.g., 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14 or 0.15), and A includes at least one of the elements Al, Mg, Ti, Zr, Y, La, W, B, Nb, Sr, F, Ni, Mn and P.

[0059] In this invention, the lithium cobalt oxide includes a matrix and a first region located on the surface of the matrix; the first region includes the elements Al and / or Ti.

[0060] In this invention, the mass content of element Al in the lithium cobalt oxide is 5000ppm-12000ppm, for example, 5000ppm, 5500ppm, 6000ppm, 6500ppm, 7000ppm, 7500ppm, 8000ppm, 9000ppm, 10000ppm, 11000ppm or 12000ppm.

[0061] In this invention, the mass content of element Ti in the lithium cobalt oxide is 10ppm-1000ppm, for example, 10ppm, 15ppm, 20ppm, 25ppm, 30ppm, 40ppm, 50ppm, 60ppm, 80ppm, 100ppm, 200ppm, 400ppm, 600ppm, 800ppm or 1000ppm.

[0062] In one embodiment, the mass content of element Ti in the lithium cobalt oxide is 100ppm-900ppm.

[0063] In one embodiment, the mass content of Al in the lithium cobalt oxide is 7000ppm-11000ppm.

[0064] In this invention, the particle size Dv1 of the lithium cobalt oxide is 1μm-2μm, for example, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm or 2μm.

[0065] In this invention, the particle size Dv10 of the lithium cobalt oxide is 4μm-10μm, for example, 4μm, 4.2μm, 4.4μm, 4.6μm, 4.8μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 8μm, 9μm or 10μm.

[0066] In this invention, the median particle size Dv50 of the lithium cobalt oxide is 11μm-20μm, for example, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm.

[0067] In this invention, the particle size Dv90 of the lithium cobalt oxide is 22μm-30μm, for example, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm or 30μm.

[0068] In this invention, the lithium cobalt oxide has a particle size Dv99 of 32μm-55μm, for example, 32μm, 34μm, 36μm, 38μm, 40μm, 45μm, 50μm or 55μm.

[0069] By defining the structural characteristics of lithium cobalt oxide, it is made to have a matrix and a first region on the surface of the matrix. The first region can act as a protective layer for the matrix, which not only prevents direct contact between the electrolyte and the matrix, reducing Co dissolution and thus suppressing interfacial side reactions and improving the cycle stability of the battery, but also improves the structural stability of lithium cobalt oxide particles, reduces cracks, and improves the stability of the positive electrode active material. On the one hand, it prevents wear on the inner layer of the aluminum-plastic film at the corners and edges of the single-sided positive electrode sheet, and even causes the single-sided positive electrode sheet to embed into the inner layer. When the electrode sheet extends, it causes the single-sided positive electrode sheet to fold, resulting in the shedding of lithium cobalt oxide particles. On the other hand, it can also prevent the shedding of lithium cobalt oxide during dynamic cycling, especially when the particle size of lithium cobalt oxide is too large. Due to the battery design, the thickness of the positive current collector of the single-sided positive electrode sheet is large, and the current density of the single-sided area increases, which leads to overcharging on one side of the positive active layer of the single-sided positive electrode sheet, making the lithium cobalt oxide structure unstable and affecting the cycle stability of the battery.

[0070] In this invention, the values ​​of a, x, and k can be determined by conventional testing methods in the art, for example, by the following method: After discharging a lithium-ion secondary battery to 0% SOC, the positive electrode sheet is disassembled and removed. It is then soaked in dimethyl carbonate (DMC) solvent for 12 hours, followed by rinsing with DMC to remove the lithium salts adhering to the positive electrode sheet. The positive electrode sheet is then kept at 450°C for 180 minutes. After cooling, the positive electrode sheet is brushed off with a brush to obtain positive electrode active material powder. The collected positive electrode active material powder is taken as a sample. Approximately 0.1 g of the sample is added to 10 mL of hydrochloric acid and digested on a hot plate at 350°C for 10 minutes. After cooling, the volume is adjusted to 100 mL, and then diluted 10 times. A portion of the solution is analyzed using an ICP spectrometer. The corresponding test parameters are obtained and can be converted using a formula.

[0071] In this invention, the mass content of elements Al and Ti in the lithium cobalt oxide can be obtained by conventional testing methods in the art, for example, by the following method: After discharging the lithium-ion secondary battery to 0% SOC, the positive electrode sheet is disassembled and taken out. After soaking in dimethyl carbonate (DMC) solvent for 12 hours, it is rinsed with DMC to remove the lithium salt attached to the positive electrode sheet. The positive electrode sheet is then kept at 450°C for 180 minutes. The cooled positive electrode sheet is brushed off with a brush to obtain positive electrode active material powder. The collected positive electrode active material powder is taken as a sample. About 0.1g of the sample is added to 10mL of hydrochloric acid and digested on a hot plate at 350°C for 10 minutes. After cooling, the volume is adjusted to 100ml, and then diluted 10 times. A portion of the solution is analyzed by an ICP spectrometer.

[0072] In this invention, the lithium cobalt oxide includes a first lithium cobalt oxide and a second lithium cobalt oxide. The median particle size Dv50 of the first lithium cobalt oxide is 2μm-8μm, for example, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm or 8μm; the median particle size Dv50 of the second lithium cobalt oxide is 9μm-25μm, for example, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 16μm, 20μm or 25μm.

[0073] In this invention, the length of the shortest axis of the second lithium cobalt oxide is Rc, and the length of the longest axis is Ri, where 1 < Ri / Rc ≤ 5, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.5, 3, 3.5, 4, 4.5 or 5.

[0074] In one embodiment, 1 < Ri / Rc ≤ 2.

[0075] The shape of the second lithium cobalt oxide (LiCO) can be controlled by adjusting the ratio of its longest and shortest axes. When Ri / Rc is too large (e.g., >5), the LiCO is too elongated or flat, leading to a longer diffusion path for lithium ions during charging and discharging, and the particles are prone to breakage. This is especially true when lithium ions are inserted along their long axis, significantly increasing the diffusion time and affecting the battery's high-rate performance. Ideally, when the LiCO particles are nearly spherical (i.e., Ri / Rc is close to 1), the tap density of the positive electrode is improved, the lithium-ion diffusion path is shortened, and the diffusion paths in all directions are made closer, improving the battery's rate performance and cycle stability. Conversely, when Ri / Rc is too small (e.g., <1), lithium-ion diffusion kinetics deteriorate, particles break easily, or the positive electrode coating becomes uneven.

[0076] like Figure 4 The image shown is a cross-sectional scanning electron microscope (SEM) image of the positive electrode sheet in one embodiment of the present invention. As can be seen from the image, the positive electrode active layer contains first lithium cobalt oxide (small particle size) and second lithium cobalt oxide (large particle size) with different particle sizes.

[0077] In this invention, Ri / Rc can be obtained using conventional methods in the art. For example, the battery is discharged to 0% SOC, the positive electrode is disassembled and removed, or the positive electrode is directly removed. The cross-section of the positive electrode is polished using an argon-ion polisher, and then observed using backscatter imaging mode on a scanning electron microscope (SEM). The second lithium cobalt oxide (distinguished by particle size from the first and second lithium cobalt oxide) is located. Any two points on the edge of the second lithium cobalt oxide particle are connected to form a straight line segment inside the particle. The longest straight line segment inside the particle is selected, and its length is denoted as Ri. The midpoint of this longest straight line segment is taken, and a straight line is drawn through this midpoint to form a straight line segment with both ends at the edge of the particle. The shortest straight line segment is selected, and its length is denoted as Rc. Ri / Rc is calculated. At least 10 second lithium cobalt oxide particles are selected, and the average value is taken after measurement. Figure 4 As shown, the black dashed line represents the longest axis with a length of Ri, and the white dashed line represents the shortest axis with a length of Rc.

[0078] In this invention, the particle sizes Dv1, Dv10, Dv50, Dv90, and Dv99 of the lithium cobalt oxide, as well as the median particle sizes Dv50 of the first and second lithium cobalt oxides, can be obtained by conventional testing methods in the art. For example, after discharging a lithium-ion secondary battery to 0% SOC, the positive electrode sheet is disassembled and removed. After soaking in dimethyl carbonate (DMC) solvent for 12 hours, it is rinsed with DMC to remove the lithium salts attached to the positive electrode sheet. The positive electrode sheet is then kept at 450°C for 180 minutes. The cooled positive electrode sheet is brushed off with a brush to obtain positive electrode active material powder. The collected positive electrode active material powder is taken as a sample, and the volume distribution curve is measured using a laser diffraction particle size analyzer. The volume distribution curve has a bimodal structure, and the volume distribution curve and the test values ​​of the equipment are used to determine the distribution.

[0079] In this invention, the thickness of the first region is 0.5nm-100nm, for example, 0.5nm, 1nm, 2nm, 4nm, 6nm, 8nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm.

[0080] In one embodiment, the thickness of the first region is 0.5 nm to 50 nm.

[0081] Controlling the thickness of the first region within a suitable range not only ensures its protective effect on the lithium cobalt oxide matrix but also takes into account kinetic performance. When the thickness of the first region is too small (e.g., <0.5 nm), it cannot completely block the electrolyte, and its effect on improving interfacial impedance and Co dissolution is not significant. When the thickness of the first region is too large (e.g., >100 nm), it will increase the lithium-ion insertion path and even block its transport, resulting in lithium dendrites, which is detrimental to battery capacity and kinetic performance.

[0082] In this invention, the lithium cobalt oxide further includes a second region located on the surface of the first region, the second region at least partially covering the first region, the second region including at least one of the elements Ti, Zr, Y, La and Al, and the thickness of the second region being 10nm-500nm, for example 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 150nm, 200nm, 300nm, 400nm or 500nm.

[0083] It is understood that the thickness of the second region is the maximum distance between the highest point of the second region and the surface of the first region.

[0084] In this invention, the second region includes Y and / or La, wherein the mass content of Y in the lithium cobalt oxide is 100ppm-900ppm, for example 100ppm, 120ppm, 140ppm, 160ppm, 180ppm, 200ppm, 240ppm, 280ppm, 300ppm, 350ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm or 900ppm, and the mass content of La is 100ppm-600ppm, for example 100ppm, 120ppm, 140ppm, 160ppm, 180ppm, 200ppm, 220ppm, 240ppm, 260ppm, 280ppm, 300ppm, 340ppm, 380ppm, 400ppm, 450ppm, 500ppm, 550ppm or 600ppm.

[0085] Furthermore, by setting a second region on the surface of the first region of lithium cobalt oxide, the structural stability and interfacial compatibility of the cathode active material can be further optimized. For example, when the second region includes Y, the thermal stability of the cathode active material can be enhanced, and O can be suppressed. 2- Release; when the second region includes La, it can stabilize the lattice structure of the positive electrode active material and suppress Li / Co mixing.

[0086] In this invention, the thickness of the first region and the thickness of the second region can be obtained by conventional testing methods in the art, such as the following method: discharge the battery to 0% SOC, disassemble and remove the positive electrode sheet, or directly remove the positive electrode sheet, polish its cross-section with an argon ion mill, observe it using backscatter imaging mode on a scanning electron microscope (SEM), randomly select 10 different lithium cobalt oxide particles, measure the thickness of the first region at 3 different locations for each lithium cobalt oxide particle, and take the average value as the thickness of the first region; then randomly select different lithium cobalt oxide particles with the second region, measure the thickness of the second region of a total of 20 different particles, and take the average value as the thickness of the second region; the thickness of the second region can also be determined by atomic force microscopy.

[0087] In this invention, the mass content of Y and La in the lithium cobalt oxide can be obtained by conventional testing methods in the art, such as scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). After discharging the lithium-ion secondary battery to 0% SOC, the battery is disassembled, the positive electrode is removed, and the backscatter mode of the scanning electron microscope is used for testing. Five different lithium cobalt oxide particles are selected, and five different points in the second region are randomly selected for EDS analysis to obtain the mass content of Y and La in the lithium cobalt oxide and calculate the average value. Alternatively, ICP determination can be performed as follows: After discharging the lithium-ion secondary battery to 0% SOC, disassemble and remove the positive electrode sheet. Soak it in dimethyl carbonate (DMC) solvent for 12 hours, then rinse it with DMC to remove the lithium salts adhering to the positive electrode sheet. Then, keep the positive electrode sheet at 450℃ for 180 minutes. After cooling, brush off the positive electrode active material to obtain positive electrode active material powder. Take the collected positive electrode active material powder as a sample. Take about 0.1g of the sample and add 10mL of hydrochloric acid for digestion on a 350℃ hot plate for 10 minutes. After cooling, make up to 100ml, then dilute it 10 times. Take a portion of the solution for analysis using an ICP spectrometer.

[0088] like Figure 5 The diagram shows a schematic representation of lithium cobalt oxide in one embodiment of the present invention. From the center outwards, the diagram shows the substrate (represented by a light-colored portion), the first region (represented by black diagonal lines, located on the outer surface of the substrate), and the second region (represented by a gray portion, located on the surface of the first region). Figure 6 The image shown is a SEM image of the positive electrode active layer in one embodiment of the present invention. Figure 7 The image shown is an EDS spot scan of the surface of the second region in one embodiment of the present invention; from Figure 7 It can be seen that the surface of the lithium cobalt oxide has a second region, so as to Figure 6 Point 1 (Spectrum1) is the target area for EDS point scanning, and the results are obtained. Figure 7The EDS spectrum shown is as follows, where the horizontal axis represents energy (keV) and the vertical axis represents signal strength (cps / eV). It can be seen from the spectrum that the second region contains the elements Ti, Zr, Y, La and Al.

[0089] In this invention, based on the total mass of the lithium cobalt oxide, the proportion of the first lithium cobalt oxide is 10%-60%, for example, 10%, 12%, 14%, 16%, 18%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%; and the proportion of the second lithium cobalt oxide is 40%-90%, for example, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.

[0090] In this invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector.

[0091] In this invention, the thickness of the negative electrode current collector is 5μm-10μm, for example, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm or 10μm.

[0092] In this invention, the tensile strength of the negative electrode current collector is ≥350MPa, for example, 350MPa, 400MPa, 420MPa, 440MPa, 460MPa, 480MPa, 500MPa, 520MPa, 540MPa, 560MPa, 600MPa, or 650MPa.

[0093] In this invention, the elongation at break of the negative electrode current collector is ≥2%, for example, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9% or 10%.

[0094] The elongation at break is calculated using the following formula: Elongation at break = (Length at break - Initial length) / Initial length × 100%.

[0095] In this invention, the tensile strength of the negative electrode current collector is ≥350MPa in both the width and length directions, for example, 350MPa, 400MPa, 420MPa, 440MPa, 460MPa, 480MPa, 500MPa, 520MPa, 540MPa, 560MPa, 600MPa, or 650MPa.

[0096] In this invention, the elongation at break of the negative electrode current collector is ≥2% in both the width direction and the length direction, for example, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9% or 10%.

[0097] By limiting the thickness, tensile strength, and elongation at break of the negative electrode current collector, it is possible to prevent the silicon-based negative electrode from expanding in volume during battery cycling, which would cause the negative electrode sheet to stretch and break. This would suppress battery deformation and improve battery safety and cycle life.

[0098] In this invention, the thickness of the negative electrode current collector can be obtained by conventional testing methods in the art, such as the following method: discharge the battery to 0% SOC, disassemble and remove the negative electrode sheet, soak it in DMC solvent for 12 hours, rinse it with DMC solvent to remove the lithium salt attached to the negative electrode sheet, dry the negative electrode sheet and polish its cross-section with an argon ion mill, image the obtained cross-section using backscatter imaging mode on a scanning electron microscope (SEM) device, locate the negative electrode current collector and measure its thickness at 5 different locations and take the average value.

[0099] In this invention, the tensile strength and elongation at break of the negative electrode current collector can be obtained by conventional testing methods in the art, such as the following method: Discharge the battery to 0% SOC, disassemble and remove the negative electrode sheet, or directly remove the negative electrode sheet and remove the negative electrode active coating on the surface of the negative electrode sheet to obtain the negative electrode current collector. After preparing the obtained negative electrode current collector samples (more than 5), first measure the initial length l0 (unit: mm), and then vertically install them on the fixture of a universal testing machine, ensuring that the sample axis coincides with the tensile direction, and that the clamping length of the fixture on the sample is not less than 20 mm, with moderate clamping force to prevent the sample from sliding or being broken during the tensile process. The tensile speed is 20 mm / min, and the force and displacement data during the tensile process are recorded in real time, and the sample is stretched at a uniform speed. The tensile process is continuously observed. When the sample breaks, the equipment automatically stops the tensile process and records the maximum tensile force F at the moment of fracture and the length lt (unit: mm) of the sample at the moment of fracture. Tensile strength = F / S is used to calculate the tensile strength (unit: MPa) of each specimen. Elongation at break = (lt - l0) / l0 × 100% is used to calculate the elongation at break of each specimen, and the average value is taken. Where F is the maximum tensile force (N) at which the specimen breaks, and S is the original cross-sectional area of ​​the specimen (mm²). 2 ).

[0100] In this invention, the negative electrode active layer comprises a negative electrode active material, which includes silicon carbon and graphite.

[0101] In this invention, the silicon-carbon comprises a porous carbon matrix, silicon material located in the internal channels of the porous carbon matrix, and a carbon layer located on the surface of the porous carbon matrix.

[0102] In this invention, the graphite includes artificial graphite and / or natural graphite.

[0103] In this invention, the silicon content in the silicon carbon is 20%-80% by mass, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 80%.

[0104] In this invention, based on the total weight of the negative electrode active layer, the silicon content is 2%-20%, for example, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18% or 20%.

[0105] In this invention, the average particle size of the silicon carbide is 2μm-15μm, for example, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 6μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm.

[0106] By limiting the silicon content in silicon-carbon and the silicon content in the negative electrode active layer to appropriate ranges, not only can the specific capacity of the negative electrode active material be improved and the energy density increased, but also excessive silicon content can be avoided, which would lead to excessive cycle expansion, causing the negative electrode active material to detach and the negative electrode sheet to stretch, thus hindering the improvement of battery cycle stability. Furthermore, controlling the average particle size of silicon-carbon within an appropriate range is beneficial for increasing the compaction density of the negative electrode sheet and dispersing expansion stress, preventing stress concentration that could lead to particle breakage.

[0107] In this invention, the average particle size of the silicon carbon can be obtained by conventional testing methods in the art, such as the following method: discharging the battery to 0% SOC, disassembling and removing the negative electrode, or directly removing the negative electrode, polishing its cross-section with an argon ion mill, and then imaging the obtained cross-section using backscatter imaging mode on a scanning electron microscope (SEM) device; the silicon carbon particles in the image appear grayish-white, and then the particle size is measured and the distribution is statistically analyzed using electron microscope image analysis software such as ImageJ to obtain the average particle size of the silicon carbon.

[0108] In this invention, the mass content of silicon in the silicon-carbon can be obtained by conventional testing methods in the art, such as scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). The battery is discharged to empty charge at a low rate, the battery is disassembled, the negative electrode is taken out, and after processing by argon ion polishing technology, a cross-sectional sample of the negative electrode can be obtained. Then, it is tested by scanning electron microscopy in backscatter mode at a magnification of 10K. The middle region of a single silicon-carbon particle is selected for EDS analysis, and only the content of carbon and silicon is tested to obtain the mass content of silicon in the silicon-carbon.

[0109] In this invention, the mass content of silicon in the negative electrode active layer can be tested using conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled and soaked in dimethyl carbonate (DMC) solvent for 12 hours, then rinsed with DMC solvent to remove lithium salts adhering to the negative electrode sheet. After drying, the negative electrode sheet is subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active layer can then be peeled off from the negative electrode current collector, and the negative electrode active layer is collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer), the test sample amount is 5mg-15mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25°C) to 900°C at a rate of 10°C / min, and held at 900°C for 40 minutes, so that the non-silicon components in the negative electrode active layer volatilize while the silicon is fully oxidized to silicon dioxide. The remaining substance is the ash of the negative electrode active layer. The mass content of silicon in the negative electrode active layer can be calculated based on the mass of ash. The calculation formula is as follows: Mass content of silicon in the negative electrode active layer = 7 × mass of ash / (15 × mass of test sample).

[0110] In this invention, the aluminum-plastic film includes an inner layer, an outer layer, and an intermediate layer located between the inner layer and the outer layer. The inner layer includes a polypropylene layer (PP layer) or a polypropylene carbonate layer (PPC layer). The intermediate layer includes element Al. The outer layer includes nylon. The inner layer is close to the core, and the outer layer is away from the core.

[0111] In this invention, the thickness of the inner layer located in the corner region of the aluminum-plastic film is h1, the thickness of the inner layer located on the edge connecting the corner region is h2, the stacked core includes a first surface and a second surface arranged opposite to each other along the thickness direction, and the thickness of the inner layer located on the first surface and / or the second surface of the stacked core is h3, h1≤h2≤h3.

[0112] In this invention, 4μm≤h3-h1≤15μm, for example, h3-h1 is 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm.

[0113] In this invention, 2μm≤h3-h2≤12μm, for example, h3-h2 is 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm or 12μm.

[0114] like Figure 8 The diagram shows a planar structural schematic of the stacked core and aluminum-plastic film in one embodiment of the present invention. 71 is the inner layer located on the first surface of the stacked core (the inner layer located on the second surface of the stacked core is opposite to 71 and is not shown in the diagram), 72 are the edges connecting the corner regions, totaling four, and the circular dashed lines indicate the corner regions of the aluminum-plastic film, which also total four. Figure 9 The diagram shown is a schematic of a single-corrugated aluminum-plastic film in one embodiment of the present invention. Figure 10 The diagram shown is a schematic of a double-corrugated aluminum-plastic film in one embodiment of the present invention, where 7 represents the aluminum-plastic film. It can be understood that a single-corrugated aluminum-plastic film has four corner regions, while a double-corrugated aluminum-plastic film has eight corner regions. Figure 11 The figure shown is a cross-sectional schematic diagram of the perforated aluminum-plastic film along the thickness direction in one embodiment of the present invention, wherein 73 is the inner layer, 74 is the middle layer, 75 is the outer layer, and the circular dashed line indicates the corner area.

[0115] It is understood that the corner area refers to the area formed by the recessed area created after the aluminum-plastic film is punched, with the center of the transition arc where the bottom and side surfaces of the recess intersect as the corner center and a radius of α (e.g., α is 3mm). The straight segment between any two corner areas is the edge connecting the corner areas.

[0116] In this invention, h1, h2, h3 and h4 can be determined by conventional testing methods in the art, such as by observing and measuring after processing with a 3D microscope.

[0117] In this invention, the negative electrode and the positive electrode each include four corner positions, and the corner positions have chamfers.

[0118] In this invention, the chamfer is composed of a bevel and / or an arc.

[0119] In one embodiment, the chamfer consists of a bevel and an arc.

[0120] In this invention, the angle formed between the tangent of at least one of the chamfered arcs and the edge of the negative electrode sheet is 30°-80°, for example, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75° or 80°.

[0121] In this invention, the angle formed between the chamfered line of at least one of the chamfers and the edge of the negative electrode sheet is 30°-80°, for example, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75° or 80°.

[0122] In this invention, the chamfer includes at least one arc, the radius (R) of which is 0.5mm-3mm, for example 0.5mm, 0.6mm, 0.8mm, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm or 3mm.

[0123] It is understood that the R-angle of the arc is the radius of the circle in which the arc is located.

[0124] like Figure 12 The diagram shown is a chamfered profile of the negative electrode sheet in one embodiment of the present invention. It can be seen that the chamfer includes two arcs and a diagonal line between the two arcs. The angle formed by the diagonal line and the edge of the negative electrode sheet is ∠1. The radius (R) angles of the arcs are R1 and R2. Taking the arc with radius R2 as an example, the angle formed by the tangent of the arc and the edge of the negative electrode sheet is ∠2. Figure 13 The diagram shown is a chamfered profile of the negative electrode sheet in one embodiment of the present invention. It can be seen that the chamfer includes an arc and a diagonal line. The angle formed by the diagonal line and the edge of the negative electrode sheet is ∠1. The R angle of the arc is R1, and the angle formed by the tangent of the arc and the edge of the negative electrode sheet is ∠3.

[0125] In this invention, the total area of ​​the chamfered notches of the positive electrode sheet is 1 mm. 2 -10mm 2 For example, 1mm 2 1.2mm 2 1.4mm 2 1.6mm 2 1.8mm 2 2mm 2 2.5mm 2 3mm 2 3.5mm 2 4mm 2 5mm 2 6mm 2 7mm 28mm 2 9mm 2 or 10mm 2 The total area of ​​the chamfered notches on the negative electrode is 2 mm. 2 -9mm 2 For example, 2mm 2 2.2mm 2 2.4mm 2 2.6mm 2 2.8mm 2 3mm 2 3.5mm 2 4mm 2 4.5mm 2 5mm 2 6mm 2 7mm 2 8mm 2 or 9mm 2 .

[0126] In this invention, the total chamfered notch area of ​​the positive electrode is the sum of the chamfered notch areas at the four corners of a single positive electrode; the total chamfered notch area of ​​the negative electrode is the sum of the chamfered notch areas at the four corners of a single negative electrode.

[0127] It is understood that the chamfer notch area has a conventional meaning in the art. Taking any chamfer on the positive and / or negative electrode as an example, the original corner position refers to the corner position without a chamfer (presenting a right angle), and the two right-angled sides of the original corner position are the original edge. When the chamfer is a diagonal line, the chamfer notch area refers to the area of ​​the right-angled triangle formed by the intersection of the diagonal line and the two right-angled sides of the original corner position, with the original corner position as the vertex. When the chamfer is an arc, the chamfer notch area refers to the area of ​​the right-angled triangle formed by the intersection of the diagonal line and the two right-angled sides of the original corner position, with the original corner position as the vertex. The area of ​​the region formed by the arc (R angle is R1) extending from the original edge and the original edge; when the chamfer is composed of an arc and a diagonal line, the area of ​​the chamfer gap refers to: the area of ​​the region formed by the arc (R angle is R1) that is tangent to one of the original edges of the original corner and connected to the diagonal line at the other end, and the vertex of the original corner, denoted as β1; the area of ​​the region formed by the two ends of the diagonal line and the vertex of the original corner, denoted as β2; then the area of ​​the chamfer gap is β1 + β2. Figure 13 The shaded area is shown in the figure; similarly, when the chamfer consists of two arcs and one diagonal line, the area of ​​the chamfer notch is as shown in the figure. Figure 12 The shaded area is shown in the image.

[0128] In this invention, along the height direction of the stacked core, the sum of the chamfered notch areas of the positive and negative electrode plates located on the upper end face is less than or equal to the sum of the chamfered notch areas of the positive and negative electrode plates located on the lower end face.

[0129] When aluminum-plastic film is dented, localized damage occurs to the corner areas and edges connecting these areas, leading to thinning of the inner layer. This makes the film more susceptible to aluminum leakage (exposed aluminum layer of the aluminum-plastic film), electrolyte leakage, and corrosion of the stack when subjected to wear from the corners of the stack and the aluminum foil of the single-sided positive electrode. This results in battery swelling and bulging, negatively impacting battery safety. To mitigate these issues, chamfers are used instead of right angles at the four corners of the positive and negative electrodes, giving the stack a certain curvature. This reduces wear on the corner areas of the aluminum-plastic film during battery cycling, prevents active material detachment at the corners, improves electrode structure stability, and enhances battery safety. Furthermore, ensuring that the total area of ​​the chamfered notches on the upper positive electrode and the lower negative electrode is less than or equal to the total area of ​​the chamfered notches on the lower positive and negative electrodes reduces energy density loss and improves the pass rate of drop and micro-drop tests, ensuring battery safety.

[0130] In this invention, the angle formed by the tangent of the arc and the edge of the negative electrode and the angle formed by the oblique line and the edge of the negative electrode can be obtained by conventional testing methods in the art, such as discharging the battery to 0% SOC, disassembling and removing the negative electrode, and then testing it with a 2.5D microscope.

[0131] In this invention, the R-angle of the arc can be obtained by conventional testing methods in the art, such as by testing with a 2.5D microscope.

[0132] In this invention, the notch area of ​​the chamfer of the positive electrode and the notch area of ​​the chamfer of the negative electrode can be obtained by conventional testing methods in the art, such as discharging the battery to 0% SOC, disassembling and removing the positive and negative electrodes, and then testing them with a 2.5D microscope.

[0133] In this invention, the separator includes a base film and a ceramic layer located on at least one side surface of the base film opposite each other along the thickness direction. The separator also includes an adhesive layer located on at least one outer surface of the separator. The adhesive force between the single-sided positive electrode and the separator is 1N / m-30N / m, for example, 1N / m, 2N / m, 4N / m, 6N / m, 8N / m, 10N / m, 12N / m, 14N / m, 16N / m, 18N / m, 20N / m, 22N / m, 24N / m, 26N / m, 28N / m or 30N / m.

[0134] In one embodiment, the adhesive layer is located on the side surface of the ceramic layer opposite to the base film that is facing the positive electrode and on the side surface of the base film that is facing the negative electrode.

[0135] In one embodiment, the adhesive layer is located on the side of the ceramic layer opposite to the base film that is facing the positive electrode and on the side of the ceramic layer opposite to the base film that is facing the negative electrode.

[0136] It is understood that the separator is bonded to the positive electrode and / or the negative electrode through thermal bonding of the adhesive layer. The side of the single-sided positive electrode with the positive active layer is in contact with the separator, and the adhesive force between the single-sided positive electrode and the separator is the adhesive force between the positive active layer of the single-sided positive electrode and the separator.

[0137] When preparing a stacked core by stacking positive electrode, separator, and negative electrode, a hot pressing process is used to ensure that the components in the stack are tightly bonded together.

[0138] Adjusting the adhesion between the side of the single-sided positive electrode sheet with the positive active layer and the separator can prevent the single-sided positive electrode sheet from delaminating and suppress the aluminum foil folding of the single-sided positive electrode sheet, which would lead to a decrease in safety performance.

[0139] In this invention, the separator covers the negative electrode sheet, and the edges of the separator extend beyond the corresponding edges of the negative electrode sheet.

[0140] In this invention, portions of at least two adjacent layers of the separator that extend beyond the negative electrode sheet are bonded together to form a bonding area.

[0141] In this invention, the adhesive force between the diaphragms in the adhesive area is ≥5N / m, for example, 5N / m, 6N / m, 7N / m, 8N / m, 9N / m, 10N / m, 12N / m, 14N / m, 16N / m, 18N / m, 20N / m, 22N / m, 24N / m or 25N / m.

[0142] In this invention, the shortest distance between the edge of the bonding area near the negative electrode sheet and the corresponding edge of the negative electrode sheet parallel to the bonding area is ≥0.2mm, for example, 0.2mm, 0.3mm, 0.4mm or 0.5mm.

[0143] like Figure 14 The diagram shows a bonding area along the thickness direction of the stacked core in one embodiment of the present invention. 31 is the bonding area. It can be seen that the separator extends out of the negative electrode sheet, and the extended portions of two adjacent separator layers are bonded to each other to form a bonding area. The shortest distance between the edge of the bonding area near the negative electrode sheet and the corresponding edge of the negative electrode sheet parallel to the bonding area is d3.

[0144] An adhesive structure is provided between at least two adjacent separator layers. This adhesive structure can tighten the separator, improve the limiting ability of the electrode, effectively restrain the negative electrode, reduce battery expansion, and prevent the expansion stress of the negative electrode from being transferred and concentrated on the insulating layer, which would cause the insulating layer to break due to excessive expansion stress. When the battery is subjected to vibration or drops, it prevents the electrode from moving or even delaminating, avoiding problems such as lithium plating, short circuits, or reduced overcurrent capacity, thus ensuring the safety and effectiveness of the battery. It can also prevent safety issues caused by separator folding.

[0145] In this invention, the adhesion between the side of the single-sided positive electrode sheet with the positive active layer and the separator can be obtained by conventional testing methods in the art, for example, by the following method: discharge the battery to 0% SOC, disassemble and remove the single-sided positive electrode sheet-separator composite structure, keep the interface intact, rinse with DMC solvent and cut the single-sided positive electrode sheet-separator composite structure into a suitable size, keep the sample width uniform, fix the obtained sample and fold the free end of the separator 180° in the opposite direction so that it is parallel to itself, use a tensile testing machine to clamp the folded free end and peel it horizontally at a constant speed, record the peeling force and calculate the average peel strength per unit width to obtain the adhesion between the side of the single-sided positive electrode sheet with the positive active layer and the separator.

[0146] In this invention, the adhesive force between the membranes within the bonding area can be obtained by conventional testing methods in the art, such as the following method: discharge the battery to 0% SOC, disassemble and remove the membrane, keep the bonding area interface intact, rinse with DMC solvent, cut the membrane to a suitable size to form a structure with one end as a free end and the other end as the bonding area, keep the sample width uniform, fix the obtained sample and fold a layer of the free end of the membrane in the opposite direction by 180° so that it is parallel to itself, use a tensile testing machine to clamp the folded free end, peel horizontally at a constant speed, record the peel force and calculate the average peel strength per unit width to obtain the adhesive force between the membranes within the bonding area.

[0147] In this invention, the shortest distance between the edge of the bonding area near the negative electrode sheet and the corresponding edge of the negative electrode sheet parallel to the bonding area can be obtained by conventional testing methods in the art, such as: discharging the battery to 0% SOC, disassembling and removing the stacked core, measuring the distance between the separator bonding area and the corresponding negative electrode sheet, measuring 5 different points and taking the average value.

[0148] In this invention, the stacked core includes a first surface and a second surface disposed opposite to each other along the thickness direction. The first surface and the second surface include an insulating layer. Along the thickness direction of the stacked core, the orthographic projection of the insulating layer and the orthographic projection of the bonding area at least partially overlap.

[0149] In this invention, the side surface includes a continuous side surface formed around the first surface and the second surface; the insulating layer is bonded to the first surface to form a first bonding position, the insulating layer is bonded to the second surface to form a second bonding position, and the insulating layer is bonded to the side surface to form a third bonding position.

[0150] In this invention, the insulating layer includes a first insulating layer, a second insulating layer, and a third insulating layer; the first insulating layer is located on the lower end face, and the first insulating layer adheres to at least a portion of the first surface, the second surface, and the side surface.

[0151] It is understood that the first insulating layer being bonded to at least a portion of the first surface, the second surface, and the side surface means that the first insulating layer is bonded to at least a portion of the first surface, the first insulating layer is bonded to at least a portion of the second surface, and the first insulating layer is bonded to at least a portion of the side surface.

[0152] In this invention, the second insulating layer is located on the third surface, and the second insulating layer adheres to at least a portion of the first surface, the second surface, and the side surface.

[0153] It is understood that the second insulating layer being bonded to at least a portion of the first surface, the second surface, and the side surface means that the second insulating layer is bonded to at least a portion of the first surface, the second insulating layer is bonded to at least a portion of the second surface, and the second insulating layer is bonded to at least a portion of the side surface.

[0154] In this invention, the third insulating layer is located on the fourth surface, and the third insulating layer adheres to at least a portion of the first surface, the second surface, and the side surface.

[0155] It is understood that the third insulating layer being bonded to at least a portion of the first surface, the second surface, and the side surface means that the third insulating layer is bonded to at least a portion of the first surface, the third insulating layer is bonded to at least a portion of the second surface, and the third insulating layer is bonded to at least a portion of the side surface.

[0156] In this invention, the thickness of the first insulating layer is 2μm-24μm, for example, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm or 24μm.

[0157] In this invention, the thickness of the second insulating layer is 2μm-24μm, for example, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm or 24μm.

[0158] In this invention, the thickness of the third insulating layer is 2μm-24μm, for example, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm or 24μm.

[0159] In this invention, the dimension t1 of the first insulating layer located on the first surface in the stack height direction is 2mm-10mm, for example, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 7mm, 8mm, 9mm or 10mm.

[0160] In this invention, the dimension t2 of the first insulating layer located on the second surface in the stack height direction is 2mm-10mm, for example, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 7mm, 8mm, 9mm or 10mm.

[0161] In this invention, the dimension t3 of the second insulating layer located on the first surface in the width direction of the stacked core is 2mm-10mm, for example, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 7mm, 8mm, 9mm or 10mm.

[0162] In this invention, the dimension t4 of the second insulating layer located on the second surface in the width direction of the stacked core is 2mm-10mm, for example, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 7mm, 8mm, 9mm or 10mm.

[0163] In this invention, the dimension t5 of the third insulating layer located on the first surface in the width direction of the stacked core is 2mm-10mm, for example, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 7mm, 8mm, 9mm or 10mm.

[0164] In this invention, the dimension t6 of the third insulating layer located on the second surface in the width direction of the stacked core is 2mm-10mm, for example, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 7mm, 8mm, 9mm or 10mm.

[0165] It is understood that the portions of the first insulating layer, the second insulating layer, and the third insulating layer that are bonded to the first surface are all the first bonding positions; the portions of the first insulating layer, the second insulating layer, and the third insulating layer that are bonded to the second surface are all the second bonding positions; and the portions of the first insulating layer, the second insulating layer, and the third insulating layer that are bonded to the side surface are all the first bonding positions.

[0166] In this invention, the insulating layer includes at least one of the first insulating layer, the second insulating layer, and the third insulating layer.

[0167] In this invention, the area of ​​the side surface is S1, the area of ​​the third mating position is S2, and 0.1≤S2 / S1≤0.9, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9.

[0168] In one embodiment, 0.3 ≤ S2 / S1 ≤ 0.8.

[0169] like Figure 15 The diagram shows an embodiment of the insulating layer arrangement, where 5 is the first surface, 6 is the second surface, 18 is the side surface (composed of the two surfaces marked in the figure and the two opposite side surfaces), 19 is the first bonding position, and 20 is the third bonding position. The second bonding position is located on the second surface and is not shown in the figure. It can be understood that the darker areas in the figure represent the insulating layer, with the first insulating layer located on the lower end surface, the second insulating layer located on the third surface, and the third insulating layer located on the fourth surface.

[0170] By setting an insulating layer (adhesive tape) on the stacked core, a safety protection layer is essentially placed between the edge of the single-sided positive electrode and the inner layer of the aluminum-plastic film. The location with this protective layer prevents wear on the inner layer from the edge of the single-sided positive electrode during formation and cycling. Furthermore, it applies inward restraint to the stacked core, suppressing the expansion force generated by the electrode. Additionally, increasing the restraint of the insulating layer improves the overall stability of the stacked core, preventing localized delamination issues during drops or special tests (such as roller tests). Further, by limiting the number of insulating layers, their coverage size on the first and second surfaces, and their coverage area on the side surfaces, the overall coverage details of the insulating layer on the stacked core can be controlled. Excessive insulation coverage may affect the electrolyte wetting effect, while insufficient coverage cannot prevent delamination and improve overall stability. By limiting S2 / S1 within a suitable range, the wetting effect of the electrolyte on the stacked core can be ensured while improving delamination and overall stability, thus avoiding impact on battery performance.

[0171] In this invention, the negative electrode active layer includes a plurality of grooves. The distance between the first edge of the groove and the first edge of the negative electrode sheet is 1mm-3mm, for example, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm, or 3mm. The distance between the second edge of the groove and the second edge of the negative electrode sheet is 1mm-3mm, for example, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm, or 3mm. The distance between the upper edge of the groove and the upper edge of the negative electrode sheet is 1mm-3mm, for example, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm, or 3mm. The distance between the lower edge of the groove and the lower edge of the negative electrode sheet is 1mm-3mm, for example, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm or 3mm.

[0172] In this invention, the first edge and the second edge are two side edges along the width direction of the stacked core. The first edge is one side edge located on the third surface, and the second edge is one side edge located on the fourth surface.

[0173] In this invention, the upper edge and the lower edge are the two side edges along the height direction of the stacked core. The upper edge is close to the electrode tab, and the lower edge is away from the electrode tab.

[0174] In this invention, the depth of the groove is 5μm-30μm, for example, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 8μm, 9μm, 10μm, 15μm, 20μm, 25μm, or 30μm. The spacing between the grooves is 1mm-3mm, for example, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm, or 3mm. The width of the groove is 50μm-150μm, for example, 50μm, 55μm, 60μm, 65μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, or 150μm.

[0175] In this invention, "several" refers to a quantity ≥ 2.

[0176] In this invention, the shape of the groove is not limited, and the groove can be achieved by drilling or by wire.

[0177] In one embodiment, the groove is achieved by laser etching.

[0178] In this invention, the distance between the first edge of the groove and the first edge of the negative electrode refers to the distance between the leftmost point of the first edge of the groove and the first edge of the negative electrode, which is the shortest distance between the first edge of the groove and the first edge of the negative electrode; the distance between the second edge of the groove and the second edge of the negative electrode refers to the distance between the rightmost point of the second edge of the groove and the second edge of the negative electrode, which is the shortest distance between the second edge of the groove and the second edge of the negative electrode.

[0179] In this invention, the distance between the upper edge of the groove and the upper edge of the negative electrode sheet refers to the distance between the highest point of the upper edge of the groove and the upper edge of the negative electrode sheet, which is the shortest distance between the upper edge of the groove and the upper edge of the negative electrode sheet; the distance between the lower edge of the groove and the lower edge of the negative electrode sheet refers to the distance between the lowest point of the lower edge of the groove and the lower edge of the negative electrode sheet, which is the shortest distance between the lower edge of the groove and the lower edge of the negative electrode sheet.

[0180] In this invention, the width of the groove, the depth of the groove, and the spacing of the grooves have conventional meanings in the art. The width of the groove refers to the shortest distance between two opposite edges of the orthographic projection of a single groove on the negative electrode sheet. The depth of the groove refers to the vertical distance from the lowest point in the groove to the surface of the negative electrode active layer. The spacing of the grooves refers to the average distance between the contour edges of two adjacent grooves in the length or width direction of the negative electrode sheet.

[0181] like Figure 16 The figure shows a planar schematic diagram of the negative electrode sheet in one embodiment of the present invention. 23 is the upper edge of the negative electrode sheet, 24 is the lower edge of the negative electrode sheet, 25 is the first edge of the negative electrode sheet, and 26 is the second edge of the negative electrode sheet. As can be seen from the figure, the surface of the negative electrode sheet includes several grooves, which are linear in shape.

[0182] By creating grooves on the negative electrode active layer, the expansion of the negative electrode sheet in the XYZ direction during battery cycling can be mitigated, reducing volume changes and thus avoiding wear on the inner layer. This reduces the probability of lithium cobalt oxide particles detaching from the single-sided positive electrode sheet, improving electrode structure stability. Furthermore, ensuring that the distances between the first and second edges of the grooves and the first and second edges of the negative electrode sheet, as well as the distances between the upper and lower edges of the grooves and the upper and lower edges of the negative electrode sheet, provides a clearance area for the grooves. This prevents cutting into the groove location during die-cutting, which could lead to powder shedding from the negative electrode sheet edges, severe battery self-discharge, and poor cycle performance.

[0183] In this invention, the width, depth, and spacing of the grooves can be obtained using conventional testing methods in the art, for example, by the following method: After discharging the lithium-ion secondary battery to 0% SOC, disassemble and remove the negative electrode sheet. Five samples (1cm × 1cm) are taken. The grooves are observed under a scanning electron microscope (SEM). Ten grooves are randomly selected, and the shortest distance between their opposite edges is measured. The average value is taken as the width of the groove. Then, two adjacent grooves are grouped together, and ten groups are randomly selected. The shortest distance between the edges of the two adjacent groove contours in each group is measured using image analysis software, and the average value is taken as the spacing of the grooves. The depth of the grooves can also be obtained using conventional testing methods in the art, for example: After discharging the lithium-ion secondary battery to 0% SOC, the negative electrode sheet is disassembled, its cross-section is polished using an argon ion mill, the grooves are observed under a scanning electron microscope (SEM), and their depth is measured using image analysis software. Ten different grooves are measured, and the average value is taken as the depth of the groove. The width and spacing of the grooves can also be obtained using a 3D microscope.

[0184] In this invention, the distance between the first edge of the groove and the first edge of the negative electrode sheet, and the distance between the second edge of the groove and the second edge of the negative electrode sheet, can be obtained by conventional testing methods in the art. For example, by the following method: after discharging the lithium-ion secondary battery to 0% SOC, disassemble and remove the negative electrode sheet, observe 10 grooves using a 2.5D or 3D microscope, measure the average distance between the leftmost point of its first edge and the first edge of the negative electrode sheet, and then measure the average distance between the rightmost point of its second edge and the second edge of the negative electrode sheet. The distance between the upper edge of the groove and the upper edge of the negative electrode sheet, and the distance between the lower edge of the groove and the lower edge of the negative electrode sheet, can be obtained by conventional testing methods in the art. For example, by the following method: after discharging the lithium-ion secondary battery to 0% SOC, disassemble and remove the negative electrode sheet, observe 10 grooves using a 2.5D or 3D microscope, measure the average distance between the highest point of its upper edge and the upper edge of the negative electrode sheet, and then measure the average distance between the lowest point of its lower edge and the lower edge of the negative electrode sheet.

[0185] In this invention, the single-sided positive electrode sheet has a plurality of recesses on one side of the positive electrode active layer and a plurality of protrusions on the side of the positive electrode current collector.

[0186] In this invention, the height of the protrusion is 0.5μm-20μm, for example, 0.5μm, 1μm, 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm or 20μm.

[0187] In this invention, the depth of the recess is 0.5μm-20μm, for example, 0.5μm, 1μm, 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm or 20μm.

[0188] In one embodiment, the positions of the protrusion and the recess correspond one-to-one.

[0189] In this invention, "several" refers to a quantity ≥ 2.

[0190] In this invention, the protrusions and the recesses can be obtained by methods conventional in the art, such as by using an embossing roller (with protrusions).

[0191] In this invention, the shape of the orthographic projection of the protrusion onto the positive electrode current collector is not limited; it can be circular or rectangular. The height of the protrusion refers to the vertical distance from the highest point within the protrusion to the positive electrode current collector.

[0192] In this invention, the shape of the orthographic projection onto the positive electrode active layer is not limited; it can be circular or rectangular. The depth of the recess refers to the vertical distance from the lowest point within the recess to the positive electrode active layer.

[0193] In this invention, the distance between the highest points of two adjacent protrusions is L1, and the shortest distance between the edges of two adjacent protrusions is L2. L1 / L2 is 1.05-3, for example, 1.05, 1.06, 1.07, 1.08, 1.1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8 or 3.

[0194] In one embodiment, L1 / L2 is 1.1-2.

[0195] In this invention, L1 is 3mm-10mm, for example, 3mm, 3.2mm, 3.4mm, 3.6mm, 3.8mm, 4mm, 4.5mm, 5mm, 6mm, 7mm, 8mm or 10mm.

[0196] In one embodiment, L1 is 2mm-8mm.

[0197] In this invention, L2 is 0.5mm-8mm, for example, 0.5mm, 0.6mm, 0.8mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm, 6mm, 7mm or 8mm.

[0198] In one embodiment, L2 is 1mm-4mm.

[0199] like Figure 17 The figure shows a cross-sectional schematic diagram of a single-sided positive electrode sheet in one embodiment of the present invention, wherein 19 is a convex portion and 20 is a concave portion. As can be seen from the figure, the single-sided positive electrode sheet includes several convex portions, the vertical distance between the highest point of the convex portion and the positive current collector is the height H of the convex portion; the distance between the highest points of two adjacent convex portions is L1, and the shortest distance between the contour edges of two adjacent convex portions is a straight segment with a length of L2.

[0200] By setting convex and concave portions on both sides of the single-sided positive electrode sheet, the curling of the single-sided positive electrode sheet can be avoided. Since the single-sided positive electrode sheet has a positive active layer on one side and a positive current collector on the other side, there is curling stress, which aggravates the severity of inner layer wear and the probability of positive active material particles falling off the single-sided positive electrode sheet.

[0201] In this invention, L1, L2, and the height of the protrusion can be obtained using conventional testing methods in the art, such as measurement using a 3D profilometer: After discharging the lithium-ion secondary battery to 0% SOC, the positive electrode sheet is disassembled, a sample is prepared, and fixed on a stage. Five different regions with complete and clear protrusion structures are selected for measurement. After magnification to a certain degree and setting parameters, the height is measured on the collected images using analysis software, and the average value is taken as the height of the protrusion. Five groups are randomly selected, with each pair of adjacent protrusions forming a group. The distance between the highest points of the two adjacent protrusions in each group is measured using image analysis software, and the average value is taken as L1. The shortest distance between the edges of the contours of the two adjacent protrusions in each group is then measured, and the average value is taken as L2. L1, L2, and the height of the protrusion can also be obtained using a 3D microscope.

[0202] In this invention, the depth of the recess can be obtained by conventional testing methods in the art. For example, after the cell is discharged to 0% SOC, the positive electrode is disassembled and removed. After sample preparation, it is fixed on a stage. Five different areas with complete and clear recess structures are selected for measurement. After magnification to a certain factor, parameters are set, and the depth is determined by combining the collected images with analysis software. After measuring five different recesses, the average value is taken as the depth of the recess.

[0203] In this invention, the lithium-ion secondary battery further includes an electrolyte, which includes ethyl difluoroacetate, wherein ethyl difluoroacetate refers to ethyl acetate in which two fluorine atoms are substituted at any position.

[0204] In this invention, the ethyl difluoroacetate includes at least one of 2,2-difluoroethyl acetate (DFEA) and ethyl 2,2-difluoroacetate.

[0205] In this invention, the content of ethyl difluoroacetate is 20%-60% based on the total weight of the electrolyte, for example, 20%, 22%, 24%, 26%, 28%, 30%, 35%, 40%, 45%, 50%, 55% or 60%.

[0206] In this invention, the content of the ethyl difluoroacetate can be obtained by gas chromatography or gas chromatography coupled with mass spectrometry.

[0207] In this invention, the electrolyte further includes ethyl propionate and / or propyl propionate.

[0208] Because lithium cobalt oxide has a first-region and second-region structure, although it can reduce electrolyte side reactions to a certain extent, the lithium ion transport rate decreases. By adjusting the content of carboxylic acid esters in the electrolyte, the ionic conductivity of the electrolyte can be improved. At the same time, after the stacked cores are hot-pressed, the wettability of the electrolyte to the stacked cores decreases. By adjusting the content of carboxylic acid esters, the wettability of the electrolyte to the stacked cores can be improved.

[0209] In this invention, the term "0% SOC" refers to the battery being discharged to 2.8V at 0.1C.

[0210] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0211] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0212] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0213] The following examples illustrate the lithium-ion secondary battery of the present invention.

[0214] Example 1:

[0215] Lithium-ion secondary batteries are prepared according to the following method:

[0216] (1) Preparation of double-sided positive electrode:

[0217] Lithium cobalt oxide (LiCo) 0.92 A 0.08 O2, A includes Al, Ti, La and Y, where the content of Al is 9635 ppm, the content of Y is 505 ppm, the content of La is 312 ppm, and the content of Ti is 584 ppm), positive electrode conductive agent (conductive carbon black and carbon nanotubes mixed in a 6:4 ratio), and polyvinylidene fluoride (PVDF) are placed in N-methylpyrrolidone (NMP) at a mass ratio of 98.2:1:0.8 and stirred evenly to obtain the first positive electrode slurry; the first positive electrode slurry is uniformly coated on both sides of aluminum foil in a zebra coating manner to obtain the positive electrode active layer; and then dried and rolled (roller compaction is 4.25 g / cm). 3 The double-sided positive electrode is obtained through die-cutting and other processes. Chamfers are set at the corners of the double-sided positive electrode, and the radius (R) of the double-sided positive electrode is 2mm. The first lithium cobalt oxide and the second lithium cobalt oxide are mixed at a mass ratio of 1:1.

[0218] (2) Preparation of single-sided positive electrode:

[0219] Lithium cobalt oxide (LiCo) 0.92 A 0.08 O2, A includes Al, Ti, La and Y, where the content of Al is 9635 ppm, the content of Y is 505 ppm, the content of La is 312 ppm, and the content of Ti is 584 ppm), positive electrode conductive agent (conductive carbon black and carbon nanotubes mixed at a mass ratio of 6:4), and PVDF at a mass ratio of 98.2:1:0.8 are placed in NMP and stirred evenly to obtain a second positive electrode slurry; the second positive electrode slurry is uniformly coated on one side of aluminum foil in a zebra coating manner to obtain the positive electrode active layer; and then dried and rolled (roller compaction is 4.15 g / cm). 3 The electrode is then processed using a roller with an uneven structure, forming several recesses on one side of the positive electrode active layer and several protrusions on the aluminum foil side. The height of the protrusions is 10 μm, L1 is 5.2 mm, L2 is 3 mm, and L1 / L2 is 1.73. After die-cutting, a single-sided positive electrode sheet is obtained, with chamfers at the corners. The radius (R) of the single-sided positive electrode sheet is 2 mm. The first lithium cobalt oxide and the second lithium cobalt oxide are mixed at a mass ratio of 1:1.

[0220] (3) Preparation of negative electrode:

[0221] The negative electrode active material (a mixture of 39% silicon carbide and 61% artificial graphite), conductive carbon black, negative electrode binder, and sodium carboxymethyl cellulose were placed in deionized water at a mass ratio of 96.6:0.4:2.8:0.2. The above slurry was stirred evenly to obtain the negative electrode slurry. The negative electrode binder was a mixture of polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) at a mass ratio of 8:2. The negative electrode slurry is uniformly coated onto copper foil (6.5 μm thick) to form a negative electrode active layer. The coating is then subjected to drying, rolling, cleaning, and slitting processes. After slitting, grooves are laser-etched onto the entire surface of the negative electrode sheet. The distance between the grooves and the first and second edges is 2.2 mm, and the distance between the grooves and the upper and lower edges is 1.5 mm. The grooves are elongated diagonal lines with an angle of 45° to the horizontal line. The spacing between adjacent grooves is 1.5 mm, the groove depth is 20 μm, and the groove width is 85 μm. The laser-treated negative electrode sheet is then cleaned and die-cut to obtain the final negative electrode sheet. Chamfers are applied to the corners of the negative electrode sheet, with a radius (R) of 2 mm.

[0222] The silicon content in the silicon-carbon material is 40% by mass, the silicon content in the negative electrode active layer is 15% by mass, and the median particle size Dv50 of the silicon-carbon material is 11.3 μm.

[0223] (4) Preparation of lithium-ion secondary batteries:

[0224] The diaphragm is made of a 9μm thick substrate (polyethylene) + alumina ceramic + adhesive (PVDF) diaphragm. The electrolyte includes lithium salt LiPF6 and solvent. The solvent is composed of ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) in a mass ratio of 1:1:1, and then mixed with 45% DFEA.

[0225] The die-cut positive electrode sheet, separator, and negative electrode sheet are stacked in sequence to form a core (the negative electrode sheet extends beyond the positive electrode sheet). The top and bottom layers of the core are single-sided positive electrode sheets, and the middle part is a double-sided positive electrode sheet. The positive active layer of the single-sided positive electrode sheet faces the geometric center of the core. The portion of the separator that extends beyond the negative electrode sheet is bonded together to form a bonding area. A first insulating layer is attached to the lower end face of the stack core, simultaneously bonding it to the first, second, and side surfaces of the stack core. One first insulating layer is applied. Two second insulating layers are attached to the third surface of the stack core, simultaneously bonding it to the first, second, and side surfaces of the stack core. These two second insulating layers cover the upper and lower corners of the third surface, respectively. Two third insulating layers are attached to the fourth surface of the stack core, simultaneously bonding it to the first, second, and side surfaces of the stack core. These two third insulating layers cover the upper and lower corners of the fourth surface, respectively. Finally, the stack core is encapsulated using a 105μm thick double-perforated aluminum-plastic film (with gaps between the upper and lower end faces of the stack core and the top and bottom seals of the aluminum-plastic film, respectively). After encapsulation, electrolyte injection, formation, secondary sealing, and sorting are performed to obtain a lithium-ion secondary battery.

[0226] The thickness of the first region is 26 nm, the thickness of the second region is 181 nm, the median particle size Dv50 of the first lithium cobalt oxide is 5.7 μm, the median particle size Dv50 of the second lithium cobalt oxide is 17.2 μm, the Ri / Rc of the first lithium cobalt oxide is 1.5, the particle size Dv1 of lithium cobalt oxide is 1.6 μm, the particle size Dv10 is 6.8 μm, the median particle size Dv50 is 11.5 μm, the particle size Dv90 is 26.2 μm, the particle size Dv99 is 36.5 μm, and d2 is 0.7 m. m, d1 is 2mm, d1+d2 is 2.7mm; w1 is 0.9mm, w2 is 1.2mm, w3 is 1.2mm, w4 is 1.2mm; the thickness of the first insulating layer = the thickness of the second insulating layer = the thickness of the third insulating layer = 15μm; t1 = t2 = t3 = t4 = t5 = t6 = 7μm; S2 / S1 is 0.56; the total area of ​​the chamfered notches of the positive and negative electrode plates on the upper end face is ≤ the total area of ​​the chamfered notches of the positive and negative electrode plates on the lower end face.

[0227] Example 2:

[0228] Lithium-ion secondary batteries are prepared according to the following method:

[0229] (1) Preparation of double-sided positive electrode:

[0230] Lithium cobalt oxide (LiCo) 0.92 A 0.08 O2, A includes Al, Ti, La and Y, where the content of Al is 7027 ppm, the content of Y is 107 ppm, the content of La is 105 ppm, and the content of Ti is 112 ppm; positive electrode conductive agent (conductive carbon black and carbon nanotubes mixed in a 6:4 ratio); and polyvinylidene fluoride (PVDF) are placed in N-methylpyrrolidone (NMP) at a mass ratio of 98.2:1:0.8 and stirred evenly to obtain the first positive electrode slurry; the first positive electrode slurry is uniformly coated on both sides of aluminum foil in a zebra coating manner to obtain the positive electrode active layer; and then dried and rolled (roller compaction is 4.25 g / cm³). 3 The double-sided positive electrode is obtained through die-cutting and other processes. Chamfers are set at the corners of the double-sided positive electrode, and the radius (R) of the double-sided positive electrode is 1.5 mm. The first lithium cobalt oxide and the second lithium cobalt oxide are mixed at a mass ratio of 1:1.

[0231] (2) Preparation of single-sided positive electrode:

[0232] Lithium cobalt oxide (LiCo) 0.92 A 0.08 O2, A includes Al, Ti, La and Y, where the content of Al is 7027 ppm, the content of Y is 107 ppm, the content of La is 105 ppm, and the content of Ti is 112 ppm), positive electrode conductive agent (conductive carbon black and carbon nanotubes mixed at a mass ratio of 6:4), and PVDF at a mass ratio of 98.2:1:0.8 are placed in NMP and stirred evenly to obtain a second positive electrode slurry; the second positive electrode slurry is uniformly coated on one side of aluminum foil in a zebra coating manner to obtain the positive electrode active layer; and then dried and rolled (roller compaction is 4.15 g / cm). 3 The electrode is then processed using a roller with an uneven structure, forming several recesses on one side of the positive electrode active layer and several protrusions on the other side of the aluminum foil. The height of the protrusions is 15 μm, L1 is 2 mm, L2 is 1.8 mm, and L1 / L2 is 1.11. After die-cutting, a single-sided positive electrode sheet is obtained, with chamfers at the corners. The radius (R) of the single-sided positive electrode sheet is 1.5 mm. The first lithium cobalt oxide and the second lithium cobalt oxide are mixed at a mass ratio of 1:1.

[0233] (3) Preparation of negative electrode:

[0234] The negative electrode active material (a mixture of 39% silicon carbide and 61% artificial graphite), conductive carbon black, negative electrode binder, and sodium carboxymethyl cellulose were placed in deionized water at a mass ratio of 96.6:0.4:2.8:0.2. The above slurry was stirred evenly to obtain the negative electrode slurry. The negative electrode binder was a mixture of polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) at a mass ratio of 8:2. The negative electrode slurry is uniformly coated onto copper foil (5 μm thick) to form a negative electrode active layer. The negative electrode is then subjected to drying, rolling, cleaning, and slitting processes. After slitting, grooves are laser-etched onto the entire surface of the negative electrode sheet. The distance between the grooves and the first and second edges is 1 mm, and the distance between the grooves and the upper and lower edges is 1.2 mm. The grooves are elongated diagonal lines with an angle of 45° to the horizontal line. The spacing between adjacent grooves is 1 mm, the depth of the grooves is 15 μm, and the width of the grooves is 72 μm. The laser-treated negative electrode sheet is then cleaned and die-cut to obtain the final negative electrode sheet. Chamfers are applied to the corners of the negative electrode sheet, with a radius (R) of 1.5 mm.

[0235] The silicon content in the silicon-carbon material is 40% by mass, the silicon content in the negative electrode active layer is 15% by mass, and the median particle size Dv50 of the silicon-carbon material is 2.1 μm.

[0236] (4) Preparation of lithium-ion secondary batteries:

[0237] The diaphragm is made of a 9μm thick substrate (polyethylene) + alumina ceramic + adhesive (PVDF) diaphragm. The electrolyte includes lithium salt LiPF6 and solvent. The solvent is composed of ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) in a mass ratio of 1:1:1, and then mixed with 20% DFEA.

[0238] The die-cut positive electrode sheet, separator, and negative electrode sheet are stacked in sequence to form a core (the negative electrode sheet extends beyond the positive electrode sheet). The top and bottom layers of the core are single-sided positive electrode sheets, and the middle part is a double-sided positive electrode sheet. The positive active layer of the single-sided positive electrode sheet faces the geometric center of the core. The portion of the separator that extends beyond the negative electrode sheet is bonded together to form a bonding area. A first insulating layer is attached to the lower end face of the stack core, simultaneously bonding it to the first, second, and side surfaces of the stack core. One first insulating layer is applied. Two second insulating layers are attached to the third surface of the stack core, simultaneously bonding it to the first, second, and side surfaces of the stack core. These two second insulating layers cover the upper and lower corners of the third surface, respectively. Two third insulating layers are attached to the fourth surface of the stack core, simultaneously bonding it to the first, second, and side surfaces of the stack core. These two third insulating layers cover the upper and lower corners of the fourth surface, respectively. Finally, the stack core is encapsulated using a 105μm thick double-perforated aluminum-plastic film (with gaps between the upper and lower end faces of the stack core and the top and bottom seals of the aluminum-plastic film, respectively). After encapsulation, electrolyte injection, formation, secondary sealing, and sorting are performed to obtain a lithium-ion secondary battery.

[0239] The thickness of the first region is 0.8 nm, and the thickness of the second region is 11 nm. The median particle size Dv50 of the first lithium cobalt oxide is 2.5 μm, and the median particle size Dv50 of the second lithium cobalt oxide is 13.5 μm. The Ri / Rc ratio of the first lithium cobalt oxide is 1.1. The particle sizes of lithium cobalt oxide are Dv1, Dv10, and Dv90: 1.2 μm, 5.2 μm, 8 μm, 23.8 μm, and 33.6 μm respectively; d2 is 0.3 mm. d1 is 1.5mm, d1+d2 is 1.8mm; w1 is 0.5mm, w2 is 0.3mm, w3 is 0.3mm, w4 is 0.3mm; the thickness of the first insulating layer = the thickness of the second insulating layer = the thickness of the third insulating layer = 24μm; t1 = t2 = t3 = t4 = t5 = t6 = 2μm; S2 / S1 is 0.31; the total area of ​​the chamfered notches of the positive and negative electrode plates on the upper end face is ≤ the total area of ​​the chamfered notches of the positive and negative electrode plates on the lower end face.

[0240] Example 3:

[0241] Lithium-ion secondary batteries are prepared according to the following method:

[0242] (1) Preparation of double-sided positive electrode:

[0243] Lithium cobalt oxide (LiCo) 0.92 A 0.08O2, A includes Al, Ti, La and Y, where the content of Al is 10987 ppm, the content of Y is 992 ppm, the content of La is 586 ppm, and the content of Ti is 875 ppm), positive electrode conductive agent (conductive carbon black and carbon nanotubes mixed in a 6:4 ratio), and polyvinylidene fluoride (PVDF) are placed in N-methylpyrrolidone (NMP) at a mass ratio of 98.2:1:0.8 and stirred evenly to obtain the first positive electrode slurry; the first positive electrode slurry is uniformly coated on both sides of aluminum foil in a zebra coating manner to obtain the positive electrode active layer; and then dried and rolled (roller compaction is 4.25 g / cm). 3 The double-sided positive electrode is obtained through die-cutting and other processes. Chamfers are set at the corners of the double-sided positive electrode, and the radius (R) of the double-sided positive electrode is 2mm. The first lithium cobalt oxide and the second lithium cobalt oxide are mixed at a mass ratio of 1:1.

[0244] (2) Preparation of single-sided positive electrode:

[0245] Lithium cobalt oxide (LiCo) 0.92 A 0.08 O2, A includes Al, Ti, La and Y, where the content of Al is 10987 ppm, the content of Y is 992 ppm, the content of La is 586 ppm, and the content of Ti is 875 ppm), positive electrode conductive agent (conductive carbon black and carbon nanotubes mixed at a mass ratio of 6:4), and PVDF at a mass ratio of 98.2:1:0.8 are placed in NMP and stirred evenly to obtain a second positive electrode slurry; the second positive electrode slurry is uniformly coated on one side of aluminum foil in a zebra coating manner to obtain the positive electrode active layer; and then dried and rolled (rolled compaction is 4.15 g / cm). 3 The electrode is then processed using a roller with an uneven structure, forming several recesses on one side of the positive electrode active layer and several protrusions on the other side of the aluminum foil. The height of the protrusions is 5 μm, L1 is 7.8 mm, L2 is 4 mm, and L1 / L2 is 1.95. After die-cutting, a single-sided positive electrode sheet is obtained, with chamfers at the corners. The radius (R) of the single-sided positive electrode sheet is 2 mm. The first lithium cobalt oxide and the second lithium cobalt oxide are mixed at a mass ratio of 1:1.

[0246] (3) Preparation of negative electrode:

[0247] The negative electrode active material (a mixture of 39% silicon carbide and 61% artificial graphite), conductive carbon black, negative electrode binder, and sodium carboxymethyl cellulose were placed in deionized water at a mass ratio of 96.6:0.4:2.8:0.2. The above slurry was stirred evenly to obtain the negative electrode slurry. The negative electrode binder was a mixture of PAA and SBR at a mass ratio of 8:2. The negative electrode slurry is uniformly coated onto copper foil (10 μm thick) to form a negative electrode active layer. The coating is then subjected to drying, rolling, cleaning, and slitting processes. After slitting, grooves are laser-etched onto the entire surface of the negative electrode sheet. The distance between the grooves and the first and second edges is 2.9 mm, and the distance between the grooves and the upper and lower edges is 2.7 mm. The grooves are elongated diagonal lines with an angle of 45° to the horizontal line. The spacing between adjacent grooves is 2.3 mm, the groove depth is 10 μm, and the groove width is 97 μm. The laser-treated negative electrode sheet is then cleaned and die-cut to obtain the final negative electrode sheet. Chamfers are applied to the corners of the negative electrode sheet, with a radius (R) of 2 mm.

[0248] The silicon content in the silicon-carbon material is 40% by mass, the silicon content in the negative electrode active layer is 15% by mass, and the median particle size Dv50 of the silicon-carbon material is 14.8 μm.

[0249] (4) Preparation of lithium-ion secondary batteries:

[0250] The diaphragm is made of a 9μm thick substrate (polyethylene) + alumina ceramic + adhesive (PVDF) diaphragm. The electrolyte includes lithium salt LiPF6 and solvent. The solvent is composed of ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) in a mass ratio of 1:1:1, and then mixed with 60% DFEA.

[0251] The die-cut positive electrode sheet, separator, and negative electrode sheet are stacked in sequence to form a core (the negative electrode sheet extends beyond the positive electrode sheet). The top and bottom layers of the core are single-sided positive electrode sheets, and the middle part is a double-sided positive electrode sheet. The positive active layer of the single-sided positive electrode sheet faces the geometric center of the core. The portion of the separator that extends beyond the negative electrode sheet is bonded together to form a bonding area. A first insulating layer is attached to the lower end face of the stack core, simultaneously bonding it to the first, second, and side surfaces of the stack core. One first insulating layer is applied. Two second insulating layers are attached to the third surface of the stack core, simultaneously bonding it to the first, second, and side surfaces of the stack core. These two second insulating layers cover the upper and lower corners of the third surface, respectively. Two third insulating layers are attached to the fourth surface of the stack core, simultaneously bonding it to the first, second, and side surfaces of the stack core. These two third insulating layers cover the upper and lower corners of the fourth surface, respectively. Finally, the stack core is encapsulated using a 105μm thick double-perforated aluminum-plastic film (with gaps between the upper and lower end faces of the stack core and the top and bottom seals of the aluminum-plastic film, respectively). After encapsulation, electrolyte injection, formation, secondary sealing, and sorting are performed to obtain a lithium-ion secondary battery.

[0252] The thickness of the first region is 58 nm, and the thickness of the second region is 495 nm. The median particle size Dv50 of the first lithium cobalt oxide is 7.2 μm, the median particle size Dv50 of the second lithium cobalt oxide is 21.8 μm, the Ri / Rc ratio of the first lithium cobalt oxide is 2, the particle size Dv1 of lithium cobalt oxide is 1.8 μm, the particle size Dv10 is 7.9 μm, the median particle size Dv50 is 14.5 μm, the particle size Dv90 is 27.7 μm, the particle size Dv99 is 49.7 μm, and d1 is 2.7 μm. m, d2 is 1.3mm, d1+d2 is 4mm; w1 is 2mm, w2 is 1.8mm, w3 is 1.8mm, w4 is 1.8mm; the thickness of the first insulating layer = the thickness of the second insulating layer = the thickness of the third insulating layer = 3μm; t1 = t2 = t3 = t4 = t5 = t6 = 10μm; S2 / S1 is 0.78; the total area of ​​the chamfered notches of the positive and negative electrode plates on the upper end face is ≤ the total area of ​​the chamfered notches of the positive and negative electrode plates on the lower end face.

[0253] Example 4 group:

[0254] This set of examples is used to verify the impact of the change in "d1+d2", which is achieved by changing the distance between the upper and lower end faces of the stacked core and the aluminum-plastic film, as follows:

[0255] Example 4a is based on Example 1, except that d1 is 1.1 mm, d2 is 0.1 mm, and d1+d2 is 1.2 mm;

[0256] Example 4b is based on Example 1, except that d1 is 3.3 mm, d2 is 1.7 mm, and d1+d2 is 5 mm.

[0257] Example 5 group:

[0258] This set of examples is used to verify the impact of changes in the particle size Dv99 of lithium cobalt oxide. This is achieved by changing the particle size distribution of the first and second lithium cobalt oxides, as detailed below:

[0259] Example 5a is based on Example 1, except that the median particle size Dv50 of the first lithium cobalt oxide is 2.2 μm and the median particle size Dv50 of the second lithium cobalt oxide is 9.2 μm. In this case, the particle size Dv1 of the lithium cobalt oxide is 1 μm, the particle size Dv10 is 4.2 μm, the median particle size Dv50 is 6.15 μm, the particle size Dv90 is 22.5 μm, and the particle size Dv99 is 32.4 μm.

[0260] Example 5b is based on Example 1, except that the median particle size Dv50 of the first lithium cobalt oxide is 7.9 μm and the median particle size Dv50 of the second lithium cobalt oxide is 24.7 μm. In this case, the particle size Dv1 of lithium cobalt oxide is 1.9 μm, the particle size Dv10 is 9.8 μm, the median particle size Dv50 is 16.3 μm, the particle size Dv90 is 29.7 μm, and the particle size Dv99 is 54.7 μm.

[0261] Example 6 group:

[0262] This set of examples is used to verify the impact of changes in the "mass content of Al and Ti in lithium cobalt oxide", as detailed below:

[0263] Example 6a is based on Example 1, except that the mass content of Al in lithium cobalt oxide is 5012 ppm, the mass content of Ti is 15 ppm, and the thickness of the first region is 0.5 nm.

[0264] Example 6b is based on Example 1, except that the mass content of Al in lithium cobalt oxide is 11994 ppm, the mass content of Ti is 9986 ppm, and the thickness of the first region is 196 nm.

[0265] Example 7 group:

[0266] This set of examples is used to verify the impact of changes in the "Ri / Rc ratio of the first lithium cobalt oxide", which is achieved by changing the shape of the first lithium cobalt oxide, as follows:

[0267] Example 7a is based on Example 1, except that Ri / Rc is 0.6;

[0268] Example 7b is based on Example 1, except that Ri / Rc is 4.8.

[0269] Example 8 group:

[0270] This set of examples is used to verify the impact of changes in the "mass content of silicon in the negative electrode active layer". This is achieved by changing the silicon content in silicon-carbon and / or the ratio of silicon-carbon in the negative electrode active layer, as detailed below:

[0271] Example 8a is based on Example 1, except that the negative electrode active material is a mixture of 10% silicon carbon and 90% artificial graphite, the silicon carbon has a silicon content of 21% by mass, and the negative electrode active layer has a silicon content of 2% by mass.

[0272] Example 8b is based on Example 1, except that the negative electrode active material is a mixture of 25% silicon carbon and 75% artificial graphite, the silicon carbon has a silicon content of 78% by mass, and the negative electrode active layer has a silicon content of 19% by mass.

[0273] Example 9:

[0274] Based on Example 1, the difference is that the positive and negative electrode plates are not chamfered.

[0275] Example 10:

[0276] Based on Example 1, the difference is that the sum of the chamfered notch areas of the positive and negative electrode plates on the upper end face is greater than the sum of the chamfered notch areas of the positive and negative electrode plates on the lower end face.

[0277] Example 11:

[0278] Based on Example 1, the difference is that the number of insulating layers is 0.

[0279] Example 12 group:

[0280] This set of examples is used to verify the impact of the change in "S2 / S1", which is achieved by changing the width of the insulating layer, as follows:

[0281] Example 12a is based on Example 1, except that S2 / S1 is 0.1;

[0282] Example 12b is based on Example 1, except that S2 / S1 is 0.9.

[0283] Example 13 group:

[0284] This set of examples is used to verify the impact of changes in the "protrusion disposed on a single-sided positive electrode sheet", as detailed below:

[0285] Example 13a is based on Example 1, except that the height of the protrusion is 0.8 μm, L1 is 3 mm, L2 is 1 mm, and L1 / L2 is 3.

[0286] Example 13b is based on Example 1, except that the height of the protrusion is 19 μm, L1 is 9 mm, L2 is 8.5 mm, and L1 / L2 is 1.06.

[0287] In Examples 1-13, the tensile strength of the negative electrode current collector was ≥350MPa, and the elongation at break of the negative electrode current collector was ≥2%; the inner layer thickness of the aluminum-plastic film was h1≤h2≤h3, h3-h1 was in the range of 4μm-15μm, and h3-h2 was in the range of 2μm-12μm.

[0288] In Examples 1-8 and Examples 10-13, the chamfer includes oblique lines and arcs. The angle formed by the tangent of the arc and the edge of the negative electrode is in the range of 30°-80°; the angle formed by the oblique line and the edge of the negative electrode is in the range of 30°-80°; and the total area of ​​the chamfer notch of the positive electrode is in the range of 1 mm. 2 -10mm 2 Within the specified range, the total area of ​​the chamfered notches of the negative electrode is all within 2mm. 2 -9mm 2 Within the range.

[0289] In Examples 1-13, the adhesive force between the single-sided positive electrode and the separator is in the range of 2N / m-30N / m; the adhesive force between the separators in the bonding area is ≥5N / m; and the shortest distance between the edge of the bonding area near the negative electrode and the corresponding edge of the negative electrode parallel to the bonding area is ≥0.2mm.

[0290] Comparative Example 1:

[0291] This set of comparative figures is used to verify the impact of the change in "d1+d2", which is achieved by changing the distance between the upper and lower end faces of the stacked core and the aluminum-plastic film, as follows:

[0292] Comparative Example 1a is based on Example 1, except that d1+d2 is 0 mm;

[0293] Comparative Example 1b is based on Example 1, except that d1 is 1.8 mm, d2 is 3.3 mm, and d1+d2 is 5.1 mm.

[0294] Comparative Example 2:

[0295] This set of examples is used to verify the impact of changes in the "mass content of elements Al and Ti in lithium cobalt oxide", as detailed below:

[0296] Comparative Example 2a is based on Example 1, except that the mass content of element Al in lithium cobalt oxide is 0 ppm, the mass content of element Ti in lithium cobalt oxide is 1300 ppm, and the thickness of the first region is 6.1 nm.

[0297] Comparative Example 2b is based on Example 1, except that the mass content of element Al in lithium cobalt oxide is 15000 ppm, the mass content of element Ti in lithium cobalt oxide is 0 ppm, and the thickness of the first region is 315 nm.

[0298] Comparative Example 3:

[0299] This comparative group is used to verify the impact of changes in the particle size Dv99 of lithium cobalt oxide. This is achieved by altering the particle size distribution of the first and second lithium cobalt oxides, as detailed below:

[0300] Comparative Example 3a, based on Example 1, differs in that the median particle size Dv50 of the first lithium cobalt oxide is 1.2 μm, the median particle size Dv50 of the second lithium cobalt oxide is 4.3 μm, and in this case, the particle size Dv1 of lithium cobalt oxide is 0.8 μm, the particle size Dv10 is 2.2 μm, the median particle size Dv50 is 5.4 μm, the particle size Dv90 is 14.3 μm, and the particle size Dv99 is 18.2 μm;

[0301] Comparative Example 3b is based on Example 1, except that the median particle size Dv50 of the first lithium cobalt oxide is 12 μm, the median particle size Dv50 of the second lithium cobalt oxide is 32.5 μm, the particle size Dv1 is 2.7 μm, the particle size Dv10 is 6.4 μm, the median particle size Dv50 is 22.3 μm, the particle size Dv90 is 52.4 μm, and the particle size Dv99 of the lithium cobalt oxide is 57.5 μm.

[0302] It is understood that the proportions between components in the embodiments refer to weight ratios. For example, 39% silicon carbon and 61% artificial graphite means that, based on the total weight of the negative electrode active material, silicon carbon accounts for 39% and artificial graphite accounts for 61%.

[0303] Test example:

[0304] (1) 500T cycle capacity retention rate:

[0305] The batteries prepared according to the embodiments and comparative examples of this invention were subjected to cyclic testing on a blue battery testing cabinet. The test conditions were 25℃±2℃, charging at 2.0C to 4.37V, charging at 1.8C to 4.37V, charging at 1.2C to 4.53V, charging at 1C to 4.58V, and then stopping at 0.05C; discharging at 0.7C to 3V. The specific method was as follows:

[0306] (a) Let stand at 25℃±2℃ for 5 min, then discharge at 0.2C to the lower limit voltage of 3.0V;

[0307] (b) Let stand for 5 minutes, charge at 0.7C to the upper limit voltage of 4.58V, cut off at 0.025C, let stand for 5 minutes, and discharge at 0.2C to the lower limit voltage;

[0308] (c) Initial capacity test: After standing for 5 minutes, charge at 2.0C to 4.37V, 1.8C to 4.37V, 1.2C to 4.53V, 1C to 4.58V, cut off at 0.05C, and then discharge at 1C to the cutoff voltage of 3.0V; measure and record the initial capacity C0 of the battery under discharge conditions.

[0309] (d) Let stand at 25℃±2℃ for 5 min, discharge at 0.7C to 3V, let stand for 5 min, charge at 2.0C to 4.37V, charge at 1.8C to 4.37V, charge at 1.2C to 4.53V, charge at 1C to 4.58V, cut off at 0.05C, let stand for 5 min, discharge at 0.7C to 3V, repeat this process 500 times.

[0310] The battery discharge capacity was recorded as C1 after 500T cycles.

[0311] The capacity retention rate of the battery after 500T cycles is calculated as C1 / C0 × 100%.

[0312] The test results are recorded in Table 1.

[0313] (2) 500T discharge capacity:

[0314] The batteries prepared in the embodiments and comparative examples of the present invention were subjected to cyclic testing on the Blue Electric Test Cabinet. The test conditions and cyclic mechanism are as described in (1). After 500T cycles, the discharge capacity was recorded under full charge.

[0315] The test results are recorded in Table 1.

[0316] (3) Expansion rate of 500T:

[0317] The batteries prepared in the embodiments and comparative examples of the present invention were subjected to cyclic testing on the Blue Electric Test Cabinet. The test conditions and cyclic mechanism are as described in (1). In step (c), the battery thickness N1 under full charge was recorded. After 500T cycles, the battery thickness under full charge was recorded as N2. Then, the expansion rate of the battery after 500T cycles is (N2-N1) / N1×100%.

[0318] The test results are recorded in Table 1.

[0319] (4) Drop test:

[0320] Pre-discharge treatment: The samples prepared in the embodiments and comparative examples of the present invention were discharged to the lower limit voltage at 0.2C and charged to the upper limit voltage of 4.58V at 0.7C (cut off at 0.025C) in an environment of 25℃±2℃. They were then left to stand in a test cabinet for 24h (sampled every 1min) and the voltage drop was recorded (the voltage value after 14h of standing is marked as V1 and the time is recorded as t1; the voltage value after 24h of standing is marked as V2 and the time is recorded as t2).

[0321] Drop test: The batteries prepared in the embodiments and comparative examples of the present invention were fully charged at an ambient temperature of (25±2)℃. The batteries were dropped onto a marble surface from a height of 1m, 10 times each on 6 sides and 4 corners. During the test, the batteries were dropped directionally with a clamping arm. After the drops, the presence of aluminum-plastic film damage and leakage was judged by visual inspection, and the presence of positive electrode particles was observed by 3D microscope.

[0322] Post-test processing: After the micro-drop test, the battery was discharged at 0.2C to the lower limit voltage of 3.0V at 25℃, and then charged at 0.7C to the upper limit voltage of 4.58V. The battery was then left to stand in the test cabinet for 24 hours (sampled every 1 minute) and the voltage drop was recorded (the voltage value after 14 hours of standing is marked as V3 and the time is recorded as t3; the voltage value after 24 hours of standing is marked as V4 and the time is recorded as t4).

[0323] The increment of K is calculated as follows: K1 = (V1 - V2) / (t2 - t1); K2 = (V3 - V4) / (t4 - t3); K increment = K2 - K1.

[0324] The test results are recorded in Table 2.

[0325] (5) Slight dip test:

[0326] Pre-discharge treatment: The samples prepared in the embodiments and comparative examples of the present invention were discharged to the lower limit voltage at 0.2C and charged to the upper limit voltage of 4.58V at 0.7C (cutoff at 0.025C) at 25℃±2℃. They were then left to stand in a test cabinet for 24h (sampled every 1min) and the voltage drop was recorded (the voltage value after 14h of standing was marked as V1' and the time was recorded as t1', and the voltage value after 24h of standing was marked as V2' and the time was recorded as t2').

[0327] Micro-drop test: The batteries prepared in the embodiments and comparative examples of this invention were fully charged. At 25°C, the fully charged batteries were placed in a drop fixture and the drop test was initiated. The height was set to 10cm, with the drop surface facing the battery's micrometer. The drop sequence was as follows: upper surface, lower surface, first surface, second surface, third surface, and fourth surface, totaling six surfaces in one round. Each surface was dropped 800 times, for a total of 4800 drops. After each surface drop, the voltage and K-value data were measured. After the micro-drop test, the presence of aluminum-plastic film damage and leakage was visually assessed, and the presence of positive electrode particle detachment was observed using a 3D microscope.

[0328] Post-test processing: After the micro-drop test, the battery was discharged at 0.2C to the lower limit voltage of 3.0V at 25℃, and then charged at 0.7C to the upper limit voltage of 4.58V. The battery was then left to stand in the test cabinet for 24 hours (sampled every 1 minute) and the voltage drop was recorded (the voltage value after 14 hours of standing is marked as V3' and the time is recorded as t3', and the voltage value after 24 hours of standing is marked as V4' and the time is recorded as t4').

[0329] The increment of K is calculated as follows: K1 = (V1'-V2') / (t2'-t1'); K2 = (V3'-V4') / (t4'-t3'); K increment = K2'-K1'.

[0330] The test results are recorded in Table 3.

[0331] Table 1:

[0332]

[0333]

[0334] Table 2:

[0335]

[0336]

[0337] Table 3:

[0338]

[0339]

[0340] As can be seen from Tables 1-3, the lithium-ion battery prepared by this invention improves the problem of positive electrode particle shedding and enhances battery safety and cycle performance compared to the comparative example.

[0341] 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 inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A lithium-ion secondary battery, characterized by comprising: The lithium ion secondary battery comprises a laminated core and an aluminum plastic film, the laminated core comprises a positive electrode sheet, a separator and a negative electrode sheet arranged in layers, along the thickness direction of the laminated core, the positive electrode sheet comprises a single-sided positive electrode sheet and a double-sided positive electrode sheet, the single-sided positive electrode sheet is located on the outer side of the laminated core, the single-sided positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on one side surface of the positive electrode current collector, and the positive electrode active layer is close to the center of the laminated core; The lithium ion secondary battery further comprises a positive electrode tab, the positive electrode tab and the positive electrode current collector are electrically connected, along the height direction of the laminated core, the laminated core comprises an upper end surface and a lower end surface, the upper end surface is close to the positive electrode tab, and the lower end surface is away from the positive electrode tab; the shortest distance between the top seal of the aluminum plastic film and the negative electrode sheet located on the upper end surface is d1, d1 is 1mm-4mm; the shortest distance between the bottom of the aluminum plastic film and the negative electrode sheet located on the lower end surface is d2, d2 is 0.1mm-2mm; The negative electrode sheet extends beyond the positive electrode sheet in the height direction of the laminated core, and the negative electrode sheet extends beyond the positive electrode sheet in the width direction of the laminated core; The positive electrode active layer includes a positive electrode active material including lithium cobaltate including a substance of a chemical formula of Li a Co x A k O2, wherein 0.85≤a≤1.1, 0.8≤x≤1.05, 0 The positive electrode active layer includes a positive electrode active material including lithium cobaltate including a substance of a chemical formula of Li The particle size Dv99 of the lithium cobaltate is 32μm-55μm.

2. The lithium-ion secondary battery according to claim 1, wherein The mass content of element Al in the lithium cobaltate is 7000ppm-11000ppm; And / or, the mass content of element Ti in the lithium cobaltate is 100ppm-900ppm; And / or, 1mm≤d1+d2≤5mm; Preferably, 1.3mm≤d1+d2≤4.2mm.

3. The lithium-ion secondary battery according to claim 1 or 2, wherein The particle size Dv10 of the lithium cobaltate is 4μm-10μm, the median particle size Dv50 is 11μm-20μm, and the particle size Dv90 is 22μm-30μm; Preferably, the lithium cobaltate comprises a first lithium cobaltate and a second lithium cobaltate, the median particle size Dv50 of the first lithium cobaltate is 2μm-8μm, and the median particle size Dv50 of the second lithium cobaltate is 9μm-25μm; And / or, the length of the shortest axis of the second lithium cobaltate is Rc, the length of the longest axis is Ri, and 1 Preferably, 1 And / or, the thickness of the first region is 0.5nm-100nm; Preferably, the thickness of the first region is 0.5nm-50nm; Preferably, the lithium cobaltate further comprises a second region located on the surface of the first region, the second region at least partially covers the first region, the second region comprises at least one of elements Ti, Zr, Y, La and Al, and the thickness of the second region is 10nm-500nm; More preferably, the second region comprises Y and / or La, in the lithium cobaltate, the mass content of Y is 100ppm-900ppm, and the mass content of La is 100ppm-600ppm.

4. The lithium-ion secondary battery according to claim 1, wherein The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector; And / or, the thickness of the negative electrode current collector is 5μm-10μm; And / or, the tensile strength of the negative electrode current collector is ≥350MPa; And / or, the breaking elongation of the negative current collector is ≥ 2%; Preferably, the negative active layer comprises a negative active material, the negative active material comprises silicon carbon and graphite, the silicon carbon comprises a porous carbon matrix and a silicon material in the internal channel of the porous carbon matrix and a carbon layer on the surface of the porous carbon matrix; And / or, the mass content of silicon element in the silicon carbon is 20%-80%; And / or, the content of silicon element is 2%-20% based on the total weight of the negative active layer; And / or, the median particle size Dv50 of the silicon carbon is 2 μm-15 μm.

5. The lithium-ion secondary battery according to claim 1, wherein The aluminum plastic film comprises an inner layer, an outer layer and an intermediate layer between the inner layer and the outer layer, the inner layer comprises a polypropylene layer or a polypropylene carbonate layer, the inner layer is close to the core, and the outer layer is away from the core; And / or, the thickness of the inner layer in the corner position area of the aluminum plastic film is h1, the thickness of the inner layer in the edge connecting the corner position area is h2, the core comprises a first surface and a second surface oppositely arranged in the thickness direction, and the thickness of the inner layer in the first surface and / or the second surface of the core is h3, h1≤h2≤h3; Preferably, 4 μm≤h3-h1≤15 μm, 2 μm≤h3-h2≤12 μm.

6. The lithium-ion secondary battery according to claim 1, wherein The negative sheet and the positive sheet respectively comprise four corner positions, and the corner position has a chamfer; And / or, the included angle between the tangent of the arc in at least one of the chamfers and the edge of the negative sheet is 30°-80°; And / or, the included angle between the slant line in at least one of the chamfers and the edge of the negative sheet is 30°-80°; Preferably, the chamfer comprises at least one of the arc lines, and the R angle of the arc line is 0.5 mm-3 mm; Preferably, the sum of the notched area of the chamfer of the positive electrode sheet is 1 mm 2 - 10 mm 2 , the sum of the notched area of the chamfer of the negative electrode sheet is 2 mm 2 - 9 mm 2 ; Preferably, along the height direction of the core, the total area of the notches of the chamfers of the positive sheet and the negative sheet located on the upper end surface is ≤ the total area of the notches of the chamfers of the positive sheet and the negative sheet located on the lower end surface.

7. The lithium-ion secondary battery according to claim 1, wherein The separator comprises a base film and a ceramic layer on at least one side surface of the base film in the thickness direction, and the separator further comprises a glue layer on at least one outer surface of the separator, the adhesion between the single-sided positive sheet and the separator is 1 N / m-30 N / m; And / or, the separator covers the negative sheet, and the edges of the separator all extend beyond the corresponding edges of the negative sheet; Preferably, the parts of at least two adjacent separators extending beyond the negative sheet are adhered to each other to form an adhesive area; And / or, the adhesion between the separators in the adhesive area is ≥ 5 N / m; And / or, the shortest distance between the edge of the adhesive area close to the negative sheet and the corresponding edge of the negative sheet parallel to the adhesive area is ≥ 0.2 mm.

8. The lithium ion secondary battery according to claim 7, the core comprises a first surface and a second surface oppositely arranged in the thickness direction, the first surface and the second surface comprise an insulating layer, and the positive projection of the insulating layer and the positive projection of the adhesive area at least partially overlap in the thickness direction of the core. And / or, the electrode assembly further comprises a side surface, the side surface comprises a continuous side surface formed around the first surface and the second surface; the insulating layer is bonded with the first surface to form a first bonding site, the insulating layer is bonded with the second surface to form a second bonding site, and the insulating layer is bonded with the side surface to form a third bonding site; And / or, the insulating layer comprises a first insulating layer, a second insulating layer and a third insulating layer; the first insulating layer is located on the lower end surface, and the first insulating layer is bonded with at least part of the first surface, the second surface and the side surface; And / or, the second insulating layer is located on the third surface, and the second insulating layer is bonded with at least part of the first surface, the second surface and the side surface; And / or, the third insulating layer is located on the fourth surface, and the third insulating layer is bonded with at least part of the first surface, the second surface and the side surface; And / or, the thickness of the first insulating layer is 2-24 μm; the thickness of the second insulating layer is 2-24 μm; and the thickness of the third insulating layer is 2-24 μm; Preferably, the area of the side surface is S1, the area of the third bonding site is S2, and 0.1≤S2 / S1≤0.

9.

9. The lithium-ion secondary battery according to claim 1, wherein, The negative electrode active layer comprises a plurality of grooves, the distance between the first edge of the groove and the first edge of the negative electrode sheet is 1-3 mm; the distance between the second edge of the groove and the second edge of the negative electrode sheet is 1-3 mm; the first edge and the second edge are two side edges along the width direction of the core; And / or, the distance between the upper edge of the groove and the upper edge of the negative electrode sheet is 1-3 mm; the distance between the lower edge of the groove and the lower edge of the negative electrode sheet is 1-3 mm; the upper edge and the lower edge are two side edges along the height direction of the core; And / or, the depth of the groove is 5-30 μm, the pitch of the groove is 1-3 mm, and the width of the groove is 50-150 μm; And / or, the single-sided positive electrode sheet comprises a plurality of recesses on one side of the positive electrode active layer, and a plurality of convex parts on one side of the positive electrode current collector of the single-sided positive electrode sheet; the height of the convex part is 0.5-20 μm; the distance between the highest points of adjacent two convex parts is L1, the shortest distance between the edges of adjacent two convex parts is L2, L1 / L2 is 1.05-3, preferably 1.1-2; And / or, L1 is 3-10 mm; preferably 2-8 mm; And / or, L2 is 0.5-8 mm; preferably 1-4 mm.

10. The lithium-ion secondary battery according to claim 1, wherein The lithium ion secondary battery further comprises an electrolyte, and the electrolyte comprises ethyl difluoroacetate; Preferably, the ethyl difluoroacetate comprises at least one of 2,2-difluoroethyl acetate and ethyl 2,2-difluoroacetate; Preferably, the content of the ethyl difluoroacetate is 20%-60% based on the total weight of the electrolyte.

Images