Lithium ion secondary battery

Abstract

The application relates to the technical field of batteries, in particular to a lithium ion secondary battery. The lithium ion secondary battery comprises a winding core formed by stacking and winding a positive electrode sheet, a diaphragm and a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer, the negative electrode active layer comprises a negative electrode active material, the negative electrode active material comprises a silicon-based material, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer, the positive electrode active layer comprises a positive electrode active material and a solid-state electrolyte, the winding core comprises a circular arc area and a flat area connected with the circular arc area, and the radius R of the circular arc area and the thickness T of the winding core satisfy the relationship of 0.9 <= 2R / T <= 4 / PI, wherein PI is a circular constant. The application can effectively improve the safety problem of the battery caused by gas production during the cycle and storage processes.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium ion secondary battery. BACKGROUND

[0002] With the increasing demand for energy density of batteries in electronic products such as communication equipment and electric vehicles, the traditional graphite negative electrode material has been difficult to meet market demand. Silicon negative electrode is considered as one of the key materials for improving the energy density of lithium ion batteries due to its high theoretical specific capacity. However, the lithiation of silicon negative electrode will form lithium-silicon alloy and cause side reactions with electrolyte, which seriously affects the cycle life of the battery. SUMMARY

[0003] The present application aims to overcome the above-mentioned problems in the prior art and provides a lithium ion secondary battery. The lithium ion secondary battery (hereinafter referred to as battery) of the present application can reduce the amount of electrolyte by introducing a solid-state electrolyte into the positive electrode sheet, thereby reducing the risk of side reactions between the silicon negative electrode and the electrolyte and improving the cycle life of the battery. At the same time, by adjusting the relationship between the radius of the circular arc region and the thickness of the winding core, the gas production problem of the solid-state electrolyte during the cycle or storage process of the battery can be effectively improved, and the safety performance and cycle life of the battery are improved.

[0004] The present inventors have found that the addition of a solid-state electrolyte to the positive electrode sheet of a silicon negative electrode battery can significantly improve the risk of side reactions between the silicon negative electrode and the electrolyte and improve the cycle life of the battery. However, the addition of a solid-state electrolyte can cause the battery to produce gas during the cycle or storage process, and the reason for the above-mentioned problem is that the expansion stress of the circular arc region in the winding core is greater than that of the flat region, especially when the negative electrode sheet contains silicon-based materials, the greater expansion stress causes the electrolyte located in the circular arc region to be squeezed into the flat region, resulting in a decrease in the electrolyte content in the circular arc region, which in turn causes the kinetics of the circular arc region to deteriorate and the overpotential to increase, further causing the decomposition of the CEI (Cathode Electrolyte Interphase) film on the surface of the positive electrode sheet to produce gas. And the decomposition of the CEI film will also cause the electrolyte to be oxidized, further reducing the electrolyte content, thus creating a vicious cycle that increases gas production. When the radius R of the circular arc region and the thickness T of the winding core satisfy 2R / T < 0.9, the stress accumulation at the circular arc region caused by stress concentration during the cycle or storage process of the battery cannot be effectively released, resulting in a decrease in the electrolyte content in the circular arc region, a deterioration in the kinetics, an increase in the overpotential, and further gas production. In addition, the accumulation of gas may cause the battery to explode.

[0005] Based on the above findings, the inventors of the present application introduce a solid-state electrolyte into the positive electrode sheet, reducing the safety hazards caused by side reactions with the electrolyte. In addition, the solid-state electrolyte itself has high ionic conductivity, which not only helps to improve the charge and discharge efficiency of the battery, but also helps to improve the interface impedance, improve the dynamic performance and cycle stability of the battery. At the same time, by increasing the thickness of the circular arc area, the relationship between the radius of the circular arc area and the thickness of the winding core is adjusted to improve the problem of easy gas production of the solid-state electrolyte during the cycle or storage process. This is because when 2R / T≥0.9, the circular arc area has a certain stress release space, which can relieve the stress concentration problem of the circular arc area, and the battery expansion basically will not affect the amount of electrolyte in the circular arc area, so that the circular arc area retains enough electrolyte, reduces the concentration difference of electrolyte in the circular arc area and the flat area, thereby avoiding the increase of overpotential of the circular arc area and preventing the decomposition of CEI film to produce gas.

[0006] Therefore, by introducing a solid-state electrolyte and adjusting the relationship between the radius of the circular arc area and the thickness of the winding core, the charge and discharge efficiency and dynamic performance of the battery can be improved, while the risk of explosion caused by excessive gas production in the circular arc area and the inability to timely discharge is reduced, and the cycle stability and safety performance of the battery are improved.

[0007] The present application provides a kind of lithium ion secondary battery, including by positive electrode sheet, diaphragm and negative electrode sheet layering winding arrangement into winding core;The negative electrode sheet includes negative electrode current collector and the negative electrode active layer of at least one side of the negative electrode current collector, and the negative electrode active layer includes negative electrode active material, and the negative electrode active material includes silicon-based material;The positive electrode sheet includes positive electrode current collector and the positive electrode active layer of at least one side of the positive electrode current collector, and the positive electrode active layer includes positive electrode active material and solid-state electrolyte;The winding core includes circular arc area and flat area connected with the circular arc area;The radius R of the circular arc area and the thickness T of the winding core satisfy: 0.9≤2R / T≤4 / π, and π is circular constant.

[0008] Compared with the prior art, the present application has at least the following advantages:

[0009] (1) The battery of the present application has high charge and discharge efficiency, dynamic performance and cycle stability;

[0010] (2) The battery of the present application can effectively reduce the safety risk caused by gas production.

[0011] 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

[0012] Figure 1 The figure shown is a cross-sectional schematic diagram of the core in an example of the present invention.

[0013] Figure 2 The diagram shown is a detailed cross-sectional view of the core in an example of the present invention.

[0014] Figure 3 The diagram shown is a schematic diagram of the positive electrode tab and the first adhesive paper interface of the present invention.

[0015] Figure 4 The diagram shown is a partial schematic of the positive electrode sheet in an embodiment of the present invention; wherein, Figure 4 The first adhesive tape is not shown in (a). Figure 4 (b) in Figure 4 The first adhesive paper was drawn based on (a).

[0016] Figure 5 The diagram shown is a schematic diagram of the tab adhesive in an example of the present invention. Detailed Implementation

[0017] 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.

[0018] This invention provides a lithium-ion secondary battery, comprising a core formed by stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet. The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector, the negative active layer comprising a negative active material, the negative active material being a silicon-based material. The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector, the positive active layer comprising a positive active material and a solid electrolyte. The core includes an arc-shaped region and a straight region connected to the arc-shaped region; the radius R of the arc-shaped region and the thickness T of the core satisfy the condition: 0.9 ≤ 2R / T ≤ 4 / π, where π is pi, for example, 0.9, 1, 1.1, 1.2, or 4 / π.

[0019] In this invention, the radius R of the arc region and the thickness T of the core have conventional meanings in the art. For example... Figure 1The structure of the core in an example of the present application is shown in the diagram. As can be seen from the diagram, the core comprises a circular arc region 10 and a flat region 20 connected to the circular arc region 10. The thickness T of the core refers to the dimension of the middle part of the core in the thickness direction of the negative electrode sheet. The radius R of the circular arc refers to the shortest distance from the outermost side of the circular arc region to the innermost side of the circular arc region in a direction perpendicular to the thickness direction of the core.

[0020] In the present application, the radius R of the circular arc can be 1-100 mm, for example, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm or 100 mm. The thickness T of the core can be 1-200 mm, for example, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, 21 mm, 22 mm, 23 mm, 24 mm, 25 mm, 26 mm, 27 mm, 28 mm, 29 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, 150 mm or 200 mm.

[0021] In the present application, the thickness of the positive electrode sheet and / or the negative electrode sheet in the circular arc region and the flat region can be controlled by adjusting the area density and / or the compaction density of the positive electrode active layer and / or the negative electrode active layer in the circular arc region and the flat region, so that the radius R of the circular arc and the thickness T of the core satisfy: 0.9≤2R / T≤4 / π.

[0022] In the present application, the ratio of the thickness of the positive electrode sheet in the circular arc region to the thickness of the positive electrode sheet in the flat region is 0.7-1.5, for example, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4 or 1.5.

[0023] In an example, the ratio of the thickness of the positive electrode sheet in the circular arc region to the thickness of the positive electrode sheet in the flat region is 1.01-1.3.

[0024] In an example, the ratio of the thickness of the positive electrode sheet in the circular arc region to the thickness of the positive electrode sheet in the flat region is 1.05-1.15.

[0025] When the ratio of the thickness of the positive electrode sheet in the circular arc region to the thickness of the positive electrode sheet in the flat region is within a certain range, the porosity or space structure reserved in the circular arc region can increase the thickness of the circular arc region after winding, and the increase in the thickness of the circular arc region can reserve sufficient space for battery swelling during the cycle process, preventing the vicious cycle phenomenon of electrolyte concentration in the circular arc region being small, overpotential being increased, CEI being decomposed to generate gas, and electrolyte being further oxidized.

[0026] In an example, the thickness of the positive electrode sheet in the flat region is 20 μm-150 μm, for example, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, or 150 μm.

[0027] As shown in FIG. 1, the thickness of the positive electrode sheet in the circular arc region is greater than the thickness of the positive electrode sheet in the flat region. Figure 2 FIG. 2 shows a cross-sectional detail view of a winding core in an example of the present application, in which the box in the figure is an enlarged view of a part of the winding core. As can be seen from the figure, the thickness of the positive electrode sheet and the thickness of the negative electrode sheet in the circular arc region are significantly greater than the thickness in the flat region. It should be noted that the change in the radius of the circular arc region is achieved by increasing the interlayer gap of the active material layer, the intergranular gap of the active material, etc. in the circular arc region, rather than by increasing the thickness of the electrode sheet (including the positive electrode sheet and the negative electrode sheet) in the circular arc region in isolation.

[0028] In the present application, the thickness of the positive electrode sheet in the circular arc region and the thickness of the positive electrode sheet in the flat region can be obtained by conventional methods in the art, for example, by taking 10 different points on the positive electrode sheet in the circular arc region and the flat region respectively, measuring the thickness of each point, and taking the average.

[0029] In the present application, the ratio of the compaction density of the positive electrode active layer in the circular arc region to the compaction density of the positive electrode active layer in the flat region is 0.5-0.99, for example, 0.5, 0.6, 0.7, 0.8, or 0.99.

[0030] In an example, the ratio of the compaction density of the positive electrode active layer in the circular arc region to the compaction density of the positive electrode active layer in the flat region is 0.65-0.85.

[0031] In an example, the compaction density of the positive electrode active layer in the flat region is 2 g / cm 3 -5 g / cm 3 , for example, 2 g / cm 3 , 2.5 g / cm 3 , 3 g / cm 3 , 3.5 g / cm 3 , 4 g / cm 3, 4.5 g / cm 3 or 5 g / cm 3 .

[0032] When the compaction density of the positive electrode active layer located in the circular arc region is less than the compaction density of the positive electrode active layer located in the flat region, the circular arc region reserves a pore or space structure, which can increase the thickness of the circular arc region after winding, and the increase in the thickness of the circular arc region can reserve sufficient space for battery swelling during the cycle process, preventing the vicious cycle phenomenon of decreasing electrolyte concentration, increasing overpotential, CEI decomposition to produce gas, and further oxidation of electrolyte in the circular arc region due to battery swelling.

[0033] In the present application, the compaction density of the positive electrode active layer located in the circular arc region and the compaction density of the positive electrode active layer located in the flat region can be tested by conventional methods in the art, for example, cutting a certain area of the positive electrode active layer from the circular arc region and the flat region, respectively, and optionally measuring the coating thickness at 5 sites, weighing the mass of the cut positive electrode active layer sample, and according to the measured average thickness and coating mass, substituting into the formula: compaction density = coating mass / coating volume, to calculate the compaction density of the positive electrode active layer located in the circular arc region and the flat region, respectively.

[0034] In the present application, the ratio of the surface density of the positive electrode active layer located in the circular arc region to the surface density of the positive electrode active layer located in the flat region is 0.6-1, for example, 0.6, 0.7, 0.8, 0.9, or 1.

[0035] In an example, the ratio of the surface density of the positive electrode active layer located in the circular arc region to the surface density of the positive electrode active layer located in the flat region is 0.7-0.95.

[0036] In an example, the surface density of the positive electrode active layer located in the flat region is 8 mg / cm 2 -25 mg / cm 2 , for example, 8 mg / cm 2 , 9 mg / cm 2 , 10 mg / cm 2 , 11 mg / cm 2 , 12 mg / cm 2 , 13 mg / cm 2 , 14 mg / cm 2 , 15 mg / cm 2 , 16 mg / cm 2 , 17 mg / cm 2 , 18 mg / cm 2 , 19 mg / cm 2 , 20 mg / cm 2 , 21 mg / cm2 22 mg / cm 2 23 mg / cm 2 24 mg / cm 2 or 25 mg / cm 2 .

[0037] In the present application, the area density of the positive active layer located in the circular arc region and the area density of the positive active layer located in the flat region can be tested by conventional methods in the art, for example, respectively cutting a certain area of the positive active layer from the circular arc region and the flat region, weighing the mass of the cut positive active layer sample, and according to the measured area and coating mass, substituting into the formula: area density = coating mass / coating area, to calculate the area density of the positive active layer located in the circular arc region and the flat region, respectively.

[0038] In the present application, the ratio of the cross-sectional porosity of the positive electrode sheet located in the circular arc region to the cross-sectional porosity of the positive electrode sheet located in the flat region is 1.5-2, for example, 1.5, 1.6, 1.7, 1.8, 1.9 or 2.

[0039] In an example, the cross-sectional porosity of the positive electrode sheet located in the flat region is 1%-3%, for example, 1%, 1.5%, 2%, 2.5% or 3%.

[0040] In the present application, the cross-sectional porosity of the positive electrode sheet located in the circular arc region and the cross-sectional porosity of the positive electrode sheet located in the flat region can be tested by conventional methods in the art, for example, by scanning electron microscopy (SEM) or X-ray tomography to obtain a cross-sectional image of the positive electrode sheet, and then processing the image to obtain the cross-sectional porosity of the corresponding position.

[0041] In the present application, the ratio of the thickness of the negative electrode sheet located in the circular arc region to the thickness of the negative electrode sheet located in the flat region is 1.01-1.5, for example, 1.01, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45 or 1.5.

[0042] In an example, the thickness of the negative electrode sheet located in the flat region is 20-200 μm, for example, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm or 200 μm.

[0043] In the present application, the ratio of the compaction density of the negative electrode active layer located in the circular arc region to the compaction density of the negative electrode active layer located in the flat region is 0.5-0.99, for example, 0.5, 0.6, 0.7, 0.8, or 0.99.

[0044] In an example, the ratio of the compaction density of the negative electrode active layer located in the circular arc region to the compaction density of the negative electrode active layer located in the flat region is 0.65-0.95.

[0045] In an example, the compaction density of the negative electrode active layer located in the flat region is 1 g / cm 3 -2.5 g / cm 3 , for example, 1 g / cm 3 , 1.5 g / cm 3 , 2 g / cm 3 , or 2.5 g / cm 3 .

[0046] In the present application, the ratio of the surface density of the negative electrode active layer located in the circular arc region to the surface density of the negative electrode active layer located in the flat region is 0.6-1, for example, 0.6, 0.7, 0.8, 0.9, or 1.

[0047] In an example, the surface density of the negative electrode active layer located in the flat region is 3 mg / cm 2 -12 mg / cm 2 , for example, 3 mg / cm 2 , 4 mg / cm 2 , 5 mg / cm 2 , 6 mg / cm 2 , 7 mg / cm 2 , 8 mg / cm 2 , 9 mg / cm 2 , 10 mg / cm 2 , 11 mg / cm 2 , or 12 mg / cm 2 .

[0048] In the present application, the ratio of the cross-sectional porosity of the negative electrode sheet located in the circular arc region to the cross-sectional porosity of the negative electrode sheet located in the flat region is 1.5-2, for example, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.

[0049] In an example, the cross-sectional porosity of the negative electrode sheet located in the flat region is 1%-3%, for example, 1%, 1.5%, 2%, 2.5%, or 3%.

[0050] In the present application, the test method of the thickness and cross-sectional porosity of the negative electrode sheet and the area density and the compaction density of the negative electrode active layer in the flat area or the circular arc area is the same as that of the positive electrode sheet, which will not be described here.

[0051] In the present application, the content c of elemental silicon in the negative electrode active layer and 2R / T satisfy: 0.03≤c / (2R / T)≤0.5, for example, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4 or 0.5.

[0052] In an example, 0.06≤c / (2R / T)≤0.075.

[0053] The greater the content c of elemental silicon in the negative electrode active layer, the greater the volume expansion of the battery during the charge and discharge cycle, the greater the stress generated on the circular arc area, the greater the reduction of the electrolyte amount in the circular arc area, causing the kinetics of the circular arc area to deteriorate, resulting in an increase in the overpotential of the circular arc area, leading to the decomposition of the CEI film to produce gas, and the decomposition of the CEI film will cause the electrolyte to be oxidized, resulting in a further reduction of the electrolyte amount, and a large amount of gas accumulating in the circular arc area. Therefore, it is necessary to limit the relationship between the content of elemental silicon in the negative electrode active layer and 2R / T to further improve the problem of gas production in the circular arc area. When the two satisfy a certain relationship, the stress release space reserved in the circular arc area can match the volume expansion of silicon, thereby further relieving the stress concentration problem of the circular arc area, relieving the reduction of the electrolyte amount in the circular arc area, reducing the concentration difference of the electrolyte in the circular arc area and the flat area, thereby further improving the problem of gas production in the circular arc area; and by limiting the relationship between the two, the stress release space is not too large, thereby affecting the electrical contact in the battery.

[0054] In the present application, 0<c≤40%, for example, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40%.

[0055] In an example, 3%≤c≤15%.

[0056] In the present application, the content c of elemental silicon in the negative electrode active layer can be tested by conventional methods in the art, for example, after discharging the battery to 0% SOC, disassembling and taking out the negative electrode sheet, soaking in dimethyl carbonate (DMC) solvent for 12 h, then rinsing with DMC solvent to remove the lithium salt attached to the negative electrode sheet, drying, then high temperature treatment of the negative electrode sheet at 400°C in an inert atmosphere for 2h (for example, in a tube furnace, under nitrogen or argon atmosphere), the negative electrode active layer can be peeled off from the negative electrode current collector, and the negative electrode active layer is collected as a test sample. Using a thermal gravimetric analyzer (for example, TGA 550 thermal gravimetric analyzer), the test sample amount is 5mg-15mg, under air or oxygen atmosphere, the temperature is raised from room temperature (25°C) to 900°C at a rate of 10°C / min, and is kept at 900°C for 40min, so that the non-silicon components in the negative electrode active layer volatilize, while the silicon is fully oxidized to silicon dioxide. The mass of the residual material is weighed, and the content of elemental silicon in the negative electrode active layer can be calculated by the following formula: content of elemental silicon in the negative electrode active layer = 7 x mass of residual material / (15 x mass of test sample).

[0057] In the present application, the lithium ion secondary battery further comprises a shell; the positive electrode sheet further comprises a positive electrode tab and a tab adhesive arranged on the surface of the positive electrode tab. The negative electrode sheet further comprises a negative electrode tab and the tab adhesive arranged on the surface of the negative electrode tab. The tab adhesive comprises a first adhesive layer, a second adhesive layer and a third adhesive layer arranged in sequence, the first adhesive layer is in contact with the shell, the third adhesive layer is in contact with the negative electrode tab, and the second adhesive layer is located between the first adhesive layer and the third adhesive layer. Figure 5 As shown in the structure schematic diagram of the tab adhesive in an example of the present application, the tab adhesive comprises a first adhesive layer 7-1, a second adhesive layer 7-2 and a third adhesive layer 7-3 arranged in sequence.

[0058] In an example, the first adhesive layer is in contact with the shell, the third adhesive layer is in contact with the negative electrode tab, and the second adhesive layer is located between the first adhesive layer and the third adhesive layer.

[0059] In the present application, the melting point of the first adhesive layer is 100°C-130°C (for example, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C or 130°C), the melting point of the second adhesive layer is 130°C-160°C (for example, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C or 160°C), and the melting point of the third adhesive layer is 100°C-130°C (for example, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C or 130°C).

[0060] When the battery is subjected to safety tests such as oven temperature and overcharge, or short-circuit caused by misuse, thermal runaway of the battery will occur, releasing a large amount of heat, thereby significantly increasing the internal temperature of the battery, further exacerbating the decomposition of the CEI film to produce gas. Therefore, it is more reliable to design the tab glue to vent in time to ensure the safety performance of the battery. The tab glue with three layers of glue layers with different melting points is applied in the present application, and the melting points of the first glue layer and the third glue layer are the same, which are lower than that of the second glue layer. When the battery is in thermal runaway and the temperature is higher than the melting point of the first glue layer and / or the third glue layer of the tab glue, the tab glue melts and separates from the tab (including the positive tab and / or the negative tab) and / or the shell, providing an outlet for the gas generated in the battery, avoiding explosion of the battery due to excessive gas pressure.

[0061] Specifically, the melting points of the first glue layer and the third glue layer are both 100-130℃. The first glue layer and the third glue layer with the melting point in the above range can melt in time when the internal temperature of the battery rises, so that the overall sealing interface tension of the shell and the tab decreases, the interface is more prone to opening, providing a venting channel for the battery, improving safety, and avoiding accidents such as fire and explosion caused by the inability to vent in time due to the accumulation of a large amount of gas. In addition, the melting point of the second glue layer needs to be synergistically controlled, so that the melting point of the second glue layer is 130-160℃. The second glue layer with the melting point in the above range can play a better barrier role, prevent over-melting, avoid battery short circuit; and ensure that the tab glue has no interface segregation risk during heat sealing process, avoiding battery leakage and gas swelling.

[0062] In the present application, the material of the tab glue is not limited, which can be a tab glue commonly used in the art, such as polyolefin. The melting point can be adjusted by changing the modified groups, polymerization degree, etc. on the surface of the tab glue.

[0063] In the present application, the thickness h1 of the positive tab is 20-100μm, for example, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm. The thickness h3 of the negative tab is 20-100μm, for example, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm. The thickness h2 of the tab glue is 15-50μm, for example, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm or 50μm.

[0064] In the present application, the thickness h1 of the positive tab, the thickness h3 of the negative tab and the thickness h2 of the tab glue can be tested by conventional methods in the art, for example, taking 5 different points on the positive tab, the negative tab and the tab glue respectively, measuring the thickness of each point, and taking the average value.

[0065] In this invention, the dimension of the tab adhesive along the length of the positive electrode sheet (i.e., the width of the tab adhesive) is 5mm-20mm, for example, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, or 20mm. The dimension of the tab adhesive along the length of the negative electrode sheet (i.e., the width of the tab adhesive) is 5mm-20mm, for example, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, or 20mm.

[0066] In this invention, the ratio of the dimension of the tab adhesive along the length of the positive electrode sheet to the dimension w2 of the positive electrode tab along the length of the positive electrode sheet is 1.1-2, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2. The ratio of the dimension of the tab adhesive along the length of the negative electrode sheet to the dimension w4 of the negative electrode tab along the length of the negative electrode sheet is 1.1-2, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.

[0067] In this invention, the positive electrode sheet further includes a positive electrode tab welding area and a first adhesive tape, wherein the positive electrode tab is located in the positive electrode tab welding area, and the first adhesive tape covers the positive electrode tab welding area. Figure 4 The diagram shown is a partial schematic of the positive electrode sheet in an embodiment of the present invention; wherein, Figure 4 The first adhesive tape is not shown in (a). Figure 4 (b) in Figure 4 Based on (a), the first adhesive tape is drawn. As can be seen from the figure, the positive electrode 1 includes a positive electrode tab 4, a positive electrode tab welding area 6, and a first adhesive tape 5. The positive electrode tab 4 is located in the positive electrode tab welding area 6, and the first adhesive tape 5 covers the positive electrode tab welding area 6.

[0068] In this invention, the first adhesive tape has a dimension w1 along the length of the positive electrode sheet, and the positive electrode tab has a dimension w2 along the length of the positive electrode sheet. w1 is 15mm-50mm (e.g., 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm or 50mm), and w2 is 2mm-10mm (e.g., 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm).

[0069] In the present application, w1, w2 and the circular arc radius r1 of the layer where the positive tab is located satisfy: w1=k1×w2+π×r1, wherein k1 is 1.1-3, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.

[0070] As shown in Figure 3 The positive tab and the first adhesive paper interface of the present application are shown in the figure, from which it can be seen that the core includes a positive sheet 1, a negative sheet 2 and a separator 3, the positive sheet 1 has a positive tab welding area and a positive tab 4 located on the positive tab welding area, a first adhesive paper 5 covers the positive tab welding area, and the size of the first adhesive paper in the length direction of the positive sheet is w1, the size of the positive tab 4 in the length direction of the positive sheet is w2. The circular arc radius of the layer where the positive tab 4 is located is r1.

[0071] In the present application, the ratio of the distance from the first end of the positive tab to the circular arc area to the circular arc radius r1 of the layer where the positive tab is located is 0-2 (for example, 0, 0.5, 1, 1.5 or 2), and the first end is the end of the positive tab close to the circular arc area.

[0072] In the present application, the first adhesive paper at least covers part of the circular arc area.

[0073] In an example, the first adhesive paper completely covers the circular arc area.

[0074] By adjusting the setting position of the positive tab and the first adhesive paper, the first adhesive paper can pass through the circular arc area (partially cover the circular arc area or completely cover the circular arc area). Since the positive tab is close to the circular arc area, and the first adhesive paper passes through the circular arc area, it helps the gas generated in the circular arc area to be released through the tab adhesive explosion, thereby improving the safety performance of the battery.

[0075] In the present application, the negative sheet further comprises a negative tab welding area and a second adhesive paper, the negative tab is located in the negative tab welding area, and the second adhesive paper covers the negative tab welding area.

[0076] In the present application, the size of the second adhesive paper in the length direction of the negative sheet is w3, and the size of the negative tab in the length direction of the negative sheet is w4, w3 is 15mm-50mm (for example, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm or 50mm), and w4 is 2mm-10mm (for example, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm).

[0077] In the present application, w3, w4 and the circular arc radius r2 of the layer where the negative tab is located satisfy: w3=k2×w3+π×r2, wherein k2 is 1.1-3, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.

[0078] In the present application, the ratio of the distance from the first end of the negative tab to the circular arc region to the circular arc radius r2 of the layer where the negative tab is located is 0-2 (for example, 0, 0.5, 1, 1.5 or 2), and the first end is the end of the negative tab close to the circular arc region.

[0079] In the present application, the second adhesive paper covers at least part of the circular arc region.

[0080] In an example, the second adhesive paper completely covers the circular arc region.

[0081] By adjusting the setting position of the negative tab and the second adhesive paper, the second adhesive paper can pass through the circular arc region (partially covering the circular arc region or completely covering the circular arc region). Since the negative tab is close to the circular arc region, and the second adhesive paper passes through the circular arc region, it helps the gas generated in the circular arc region to be discharged through the tab adhesive, thereby improving the safety performance of the battery.

[0082] In the present application, the mass content c2 of the solid-state electrolyte in the positive active layer and the circular arc radius R (unit: mm) satisfy: 0.02≤R×c2≤0.5, for example, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4 or 0.5.

[0083] In an example, 0.06≤R×c2≤0.45.

[0084] The mass content of the solid-state electrolyte is related to R: when R is larger, the amount of solid-state electrolyte can be appropriately reduced, and when R is smaller, the amount of solid-state electrolyte should be appropriately increased. This is because: when R is larger, the battery expansion has less effect on the circular arc region, the circular arc region retains sufficient electrolyte, and the phenomenon of increased overpotential in the circular arc region causing CEI decomposition to generate gas is avoided; and when R is smaller, the battery expansion has a greater effect on the circular arc region, causing the electrolyte in the circular arc region to be squeezed out to the flat region, resulting in a decrease in the electrolyte concentration in the circular arc region, an increase in the overpotential, CEI decomposition to generate gas, and further oxidation of the electrolyte, further reducing the amount of electrolyte, and a vicious cycle is formed. At this time, the amount of solid-state electrolyte can be increased to further improve the interface impedance of the active particles in the circular arc region, thereby reducing the overpotential in the circular arc region and avoiding CEI decomposition to generate gas.

[0085] In the present application, the solid-state electrolyte comprises at least one of lithium aluminum titanium phosphorous oxide, lithium lanthanum zirconium tantalum oxide and lithium lanthanum titanium oxide. The lithium aluminum titanium phosphorous oxide can be superionic conductor type lithium aluminum titanium phosphorous oxide with a molecular formula of Li 1+x Al x Ti 2-x (PO4)3, 0 7-y La3Zr 2-y Ta y O 12 , 0 3z La 2 / 3-z TiO3, 0

[0086] In an example, the solid-state electrolyte comprises lithium aluminum titanium phosphorous (LATP).

[0087] In the present application, the average particle size of the solid-state electrolyte is 0.02 μm-3 μm, for example, 0.02 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.5 μm or 3 μm.

[0088] In an example, the average particle size of the solid-state electrolyte is 0.05 μm-2 μm.

[0089] By adjusting the content and average particle size of the solid-state electrolyte, the solid-state electrolyte particles can form good interface contact with the positive active layer, reduce the interface impedance, promote the transmission of lithium ions at the interface and improve the battery kinetic performance. For the gas production in the circular arc region, when the interface impedance is reduced, the decomposition of CEI caused by the increase of overpotential in the circular arc region is avoided, thereby achieving the purpose of reducing gas production and effectively improving the cycle performance of the battery.

[0090] In the present application, the average particle size of the solid-state electrolyte can be obtained by conventional methods in the art. For example, by SEM, at least 10 solid-state electrolyte particles are selected in the electron microscope image, the particle size of each solid-state electrolyte particle is measured, and the average value is taken.

[0091] In the present application, the solid-state electrolyte has a median particle size Dv50 of 0.02 μm to 2 μm, for example 0.02 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2 μm. The median particle size Dv50 of the solid-state electrolyte can be tested by a method conventional in the art, for example a laser particle size analyzer.

[0092] In the present application, the positive active layer has a mass content c2 of the solid-state electrolyte of 0.1% to 5%, for example 1%, 2%, 3%, 4% or 5%.

[0093] In one example, c2 is 1% to 4.5%.

[0094] In the present application, the content c of elemental silicon in the negative active layer and the content c2 of the solid-state electrolyte in the positive active layer satisfy: 0.5≤c / c2≤35, for example 0.5, 1, 5, 10, 15, 20, 25, 30 or 35.

[0095] In one example, 1.5≤c / c2≤13.

[0096] If the content of elemental silicon in the negative active layer is too large, the volume expansion of the battery during the charge and discharge cycle is greater, and the stress on the circular arc region is greater, resulting in a decrease in the amount of electrolyte in the circular arc region, which easily causes a decrease in the electrolyte concentration in the circular arc region, an increase in the overpotential, and a vicious cycle of continuous decomposition of CEI to produce gas. At this time, by appropriately adding the solid-state electrolyte, the problem of CEI decomposition to produce gas caused by a large overpotential in the circular arc region can be effectively alleviated. However, the amount of the solid-state electrolyte added should not be too much, otherwise it will cause interface impedance. Therefore, it is necessary to control the ratio of the content c2 of the solid-state electrolyte to the content c of elemental silicon in the negative active layer within a suitable range, so that the content of elemental silicon in the negative active layer can not be excessive, achieving the purpose of inhibiting the expansion of the negative electrode and improving the energy density of the battery, and the problem of gas production in the circular arc region caused by the difference in electrolyte concentration between the circular arc region and the flat region can be avoided, and the safety performance of the battery is improved.

[0097] In the present application, the positive active material includes at least one of lithium cobaltate, lithium nickel cobalt manganese acid, lithium nickel cobalt aluminum acid, lithium nickel cobalt manganese aluminum acid, lithium manganese acid, lithium nickel manganese acid, lithium nickel acid, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate and lithium-rich manganese-based material. The negative active material can also include a carbon-based material, for example including at least one of artificial graphite, natural graphite, mesocarbon microbead graphite, soft carbon and hard carbon.

[0098] In the present application, the lithium ion secondary battery further comprises an electrolyte. The electrolyte can optionally comprise propyl propionate. The "optionally" means that the electrolyte can comprise propyl propionate or can not comprise propyl propionate.

[0099] In the present application, the mass content of propyl propionate in the electrolyte is ≤10%, for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, or 0%.

[0100] In an example, the mass content of propyl propionate in the electrolyte is ≤5%.

[0101] In an example, the mass content of propyl propionate in the electrolyte is ≤1%.

[0102] In an example, the mass content of propyl propionate in the electrolyte is ≤0.5%.

[0103] In an example, the mass content of propyl propionate in the electrolyte is 0%.

[0104] In a battery containing a solid-state electrolyte in the positive electrode, when the positive electrode overpotential is large, the CEI film is decomposed to produce gas, at this time, the electrolyte is oxidized to form a new CEI film. When the content of propyl propionate is high, propyl propionate is easy to react with the solid-state electrolyte, and decompose to produce carbon dioxide, ethane, propane and other gases, which cannot form a stable CEI film, resulting in continuous increase in gas production. Therefore, when the content of propyl propionate in the electrolyte is low, the gas production will be significantly reduced. Therefore, by regulating the composition of the electrolyte, the content of propyl propionate in the electrolyte formula can make the positive electrode sheet surface form a stable CEI film, and reduce the safety problem of battery gas production.

[0105] In the present application, the electrolyte further comprises at least one of a lithium salt, a non-aqueous solvent, an additive, and a diluent; the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium trifluoromethanesulfonate, lithium difluoro oxalate borate, lithium bisoxalate borate, lithium difluorophosphate, lithium difluoro bisoxalate phosphate, or lithium tetrafluoro oxalate phosphate. The non-aqueous solvent comprises a carbonic ester, which comprises at least one of ethylene carbonate (EC), ethylene carbonate, propylene carbonate (PC), propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, and fluoroethylene carbonate. The non-aqueous solvent further comprises at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butyrosulfone, dimethyl sulfone, methyl ethyl sulfone, or diethyl sulfone. The additive comprises at least one of fluoroethylene carbonate (FEC), vinylene carbonate, vinyl ethylene carbonate, vinyl sulfate (DTD), propylene sulfate, ethylene sulfite, 1,3-propane sulfone lactone (PS), 1,3-propylene sulfone lactone, sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN), adiponitrile, 1,3,6-hexanetricarbonitrile (HTCN), tris(trimethylsilyl)phosphate, or tris(trimethylsilyl)borate. The diluent comprises at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), and triethylene glycol dimethyl ether (TEP).

[0106] In the present application, the silicon-based material comprises at least one of elemental silicon, silicon-carbon, silicon-oxygen, and silicon alloy, for example.

[0107] In an example, the negative electrode material comprises a graphite material. The graphite material comprises at least one of the natural graphite, the artificial graphite, or the mesocarbon microbead graphite. The graphite material has a volume distribution particle size of Dv10 of 5 μm-10 μm, Dv50 of 10 μm-25 μm, and Dv90 of 25 μm-40 μm; an interlayer spacing d002 of the graphite material of 0.3356 nm-0.3359 nm; and a reversible capacity of the graphite material of 350 mAh / g-365 mAh / g.

[0108] In an example, the negative material comprises silicon-carbon, for example, comprising a porous carbon substrate and silicon material inside the pores of the porous carbon substrate; the mass content of silicon in the silicon-carbon is 20%-70%; the volume distribution particle size of the silicon-carbon is: Dv10 is 1-6 μm, Dv50 is 3-15 μm, and Dv90 is 12-30 μm; the specific surface area of the silicon-carbon is 0.5-10 m 2 / g-10 m 2 / g, and the average sphericity of the silicon-carbon is 0.5-1.

[0109] In the present application, the positive electrode sheet has a first surface and a second surface oppositely arranged along the thickness direction. The first surface can have a plurality of recesses, and the second surface can have a plurality of protrusions. The "plurality" means that the number of recesses on the first surface is greater than or equal to 2, and the number of protrusions on the second surface is greater than or equal to 2.

[0110] In an example, the positions of the recesses on the first surface correspond to the positions of the protrusions on the second surface.

[0111] In the present application, the width of the recess can be 0.2-8 mm, for example, 0.2 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, or 8 mm. The depth of the recess can be 3-40 μm, for example, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, or 40 μm. The pitch of the recess can be 0.5-8 mm, for example, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, or 8 mm.

[0112] In the present application, the depth of the recess refers to the vertical distance from the lowest point in the recess to the surface of the positive electrode sheet. It can be obtained by testing by conventional methods in the art, for example, using SEM or a 3D profilometer to measure the depth of at least 20 recesses or all recesses on one side surface of the positive electrode sheet, and taking the average value.

[0113] In the present application, the shape of the projection of the recess in the thickness direction of the positive electrode sheet is not limited, and can be circular or rectangular. When the shape of the projection of the recess in the thickness direction of the positive electrode sheet is circular, the width of the recess is the diameter of the circle; when the shape of the projection of the recess in the thickness direction of the positive electrode sheet is non-circular, the width of the recess is the equivalent diameter of a circle equal to the area of the non-circular shape. The width of the recess and the spacing of the recesses can be obtained by conventional methods in the art, for example, by SEM, selecting at least 10 recesses on the surface of the positive electrode sheet, measuring the width of each recess, and taking the average; selecting at least 10 groups of adjacent recesses on the surface of the positive electrode sheet, measuring the shortest distance between the edges of each group of recesses, and taking the average.

[0114] In the present application, the height of the protrusion can be 2 pm to 40 pm, for example, 2 pm, 5 pm, 10 pm, 15 pm, 20 pm, 25 pm, 30 pm, 35 pm, or 40 pm. The width of the protrusion can be 0.2 mm to 8 mm, for example, 0.2 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, or 8 mm. The spacing of the protrusions can be 0.5 mm to 8 mm, for example, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, or 8 mm.

[0115] In the present application, the height of the protrusion refers to the vertical distance from the highest point of the protrusion to the surface of the positive electrode sheet. It can be obtained by conventional methods in the art, for example, using SEM or a 3D profilometer, measuring the height of at least 20 protrusions or all the protrusions on one side of the surface of the positive electrode sheet, and taking the average.

[0116] In the present application, the shape of the projection of the protrusion in the thickness direction of the positive electrode sheet is not limited, and can be circular or rectangular. When the shape of the projection of the protrusion in the thickness direction of the positive electrode sheet is circular, the width of the protrusion is the diameter of the circle; when the shape of the projection of the protrusion in the thickness direction of the positive electrode sheet is non-circular, the width of the protrusion is the equivalent diameter of a circle equal to the area of the non-circular shape. The width of the protrusion and the spacing of the protrusions can be obtained by conventional methods in the art, for example, by SEM, selecting at least 10 protrusions on the surface of the positive electrode sheet, measuring the width of each protrusion, and taking the average; selecting at least 10 groups of adjacent protrusions on the surface of the positive electrode sheet, measuring the shortest distance between the edges of each group of protrusions (i.e., the shortest distance between the orthographic projections of each group of protrusions on the surface of the positive electrode sheet), and taking the average.

[0117] In the present application, the thickness of the positive plate in the circular arc region and the flat region can also be controlled by adjusting the size of the concave and convex parts on the positive plate, so that the radius R of the circular arc region and the thickness T of the roll core satisfy: 0.9≤2R / T≤4 / π.

[0118] It should be noted that the "first", "second" and the like in the present application are only used to distinguish different substances or use methods, and do not represent the difference in order.

[0119] The present application will be described in detail below by way of examples. The examples described in the present application are only a part of the examples of the present application, not all examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0120] In the following examples, the materials used are commercially available analytical pure unless otherwise specified.

[0121] The following examples are used to illustrate the lithium ion secondary battery of the present application.

[0122] Example 1

[0123] The lithium ion secondary battery is prepared according to the following method:

[0124] (1) Preparation of positive plate

[0125] Lithium cobaltate, lithium titanium aluminum phosphate (average particle size 1.1 μm), carbon nanotubes and polyvinylidene fluoride were mixed in a mass ratio of 96.3:1.2:1.1:1.4, N-methyl pyrrolidone (NMP) was added, and the positive slurry was prepared by stirring in a stirring tank; the above-mentioned positive slurry was uniformly transferred to the surface of aluminum foil by extrusion coating equipment, and then baked in an oven at 80℃ for 10 min, and then wound by a winding drum after completely removing the solvent; then the positive plate was wound and compacted by a variable roll gap roller, and the variable roll frequency was set according to the length of the positive plate segment to control the radius R of the circular arc region. Note that the variable roll action is stopped when the roller pressing equipment runs to the single-sided region. The preparation of positive plate with uniform surface density and different compaction densities can be realized by continuous operation of the above-mentioned variable roll action;

[0126] The rolled positive plate was cut by a cutting device along the TD direction according to the designed width size, and then wound into a small roll after being detected by a charge-coupled device image sensor (CCD) to exclude abnormalities; positive tab welding (the size w2 of the positive tab in the length direction of the positive plate is 6 mm, and the thickness h1 of the positive tab is 40 μm) and first adhesive tape (acrylic adhesive tape, the size w1 in the length direction of the positive plate is 25.8 mm) were pasted; and then the positive plate was cut;

[0127] The thickness of the positive electrode sheet in the circular arc region is 88 μm, the thickness of the positive electrode sheet in the flat region is 81 μm, and the ratio of the two is 1.09; the compaction density of the positive electrode active layer in the circular arc region is 3.21 g / cm 3 , the compaction density of the positive electrode active layer in the flat region is 3.89 g / cm 3 , and the ratio of the two is 0.825; the surface density of the positive electrode active layer in the circular arc region is 12.5 mg / cm 2 , the surface density of the positive electrode active layer in the flat region is 14.2 g / cm 2 , and the ratio of the two is 0.88; the cross-sectional porosity ratio of the positive electrode sheet in the circular arc region is 2.89%, the cross-sectional porosity ratio of the positive electrode sheet in the flat region is 1.92%, and the ratio of the two is 1.505; c2 is 1.2%.

[0128] (2) Preparation of the negative electrode sheet

[0129] The artificial graphite, silicon carbon, carbon nanotube, butadiene rubber, sodium carboxymethyl cellulose and polyacrylic acid are uniformly mixed in a mass ratio of 84.3:12.7:0.45:1.5:0.45:0.6, deionized water is added, and the mixture is fully stirred in a stirring tank to prepare a negative electrode slurry; the negative electrode slurry is transferred to the surface of a copper foil through an extrusion coating device, and then baked in an oven at 120°C for 5 min; after the solvent is completely removed, the negative electrode sheet is wound on a winding drum; the wound negative electrode sheet is then placed on a variable roll gap roller press, the variable roll frequency is set according to the length of the negative electrode sheet, and the radius R of the circular arc region is adjusted. It should be noted that the variable roll action is stopped when the roller press device reaches the single-sided region. The continuous operation of the above variable roll action can realize the preparation of negative electrode sheets with different surface densities and different compaction densities;

[0130] The rolled negative electrode sheet is cut along the TD direction according to the designed width size through a cutting device, and then wound on a small roll after the abnormality is detected and excluded by a CCD; the negative electrode tab (the size w4 of the negative electrode tab in the length direction of the negative electrode sheet is 6 mm, and the thickness h3 of the negative electrode tab is 40 μm) is welded, and the second adhesive paper (acrylic adhesive paper, the size w3 of the negative electrode sheet in the length direction is 25.8 mm) is pasted; and then the negative electrode sheet is cut to obtain the negative electrode sheet;

[0131] The thickness of the negative electrode sheet in the circular arc region is 93.8 μm, the thickness of the negative electrode sheet in the flat region is 83.2 μm, and the ratio of the two is 1.13; the compaction density of the negative electrode active layer in the circular arc region is 1.1 g / cm 3 , the compaction density of the negative electrode active layer in the flat region is 1.63 g / cm 3 , and the ratio of the two is 0.67; the surface density of the negative electrode active layer in the circular arc region is 4.9 mg / cm 2 , the surface density of the negative electrode active layer in the flat region is 6.4 mg / cm2 The ratio of the two is 0.77; the cross-sectional porosity of the negative electrode sheet in the circular arc region is 2.8%, and the cross-sectional porosity of the negative electrode sheet in the flat region is 1.42%, and the ratio of the two is 1.97; the content c of elemental silicon in the negative active layer is 7%.

[0132] (3) Preparation of electrolyte

[0133] In an argon-filled glove box (moisture <1 ppm, oxygen <1 ppm), EC, PC and EP were mixed into a uniform non-aqueous solvent at a mass ratio of 1:1:3, and 14% lithium salt (lithium hexafluorophosphate), 5% additive (FEC), 3% additive (PS), 2.5% additive (SN), 2% additive (HTCN) and 0.5% additive (DTD) based on the total mass of the electrolyte were slowly added, and stirred uniformly to obtain the electrolyte;

[0134] The content of propyl propionate in the electrolyte is 0%.

[0135] (4) Preparation of battery

[0136] The positive electrode sheet prepared in step (1), the separator (oil-based 5+2+2 separator (5 μm thick base film+2 μm thick ceramic layer+2 μm thick polyvinylidene fluoride adhesive layer)) and the negative electrode sheet prepared in step (2) were aligned at the head, and then uniformly rolled into a roll-shaped structure according to the designed size to obtain a roll core; the electrolyte prepared in step (3) was added; the tab adhesive (the first adhesive layer is in contact with the shell, the third adhesive layer is in contact with the positive / negative tab, the second adhesive layer is between the first and third adhesive layers, the melting point of the first adhesive layer is 116℃, the melting point of the second adhesive layer is 148℃, the melting point of the third adhesive layer is 116℃, the thickness h2 of the tab adhesive is 20 μm, and the size of the tab adhesive in the length direction of the positive / negative electrode sheet is 10 mm) was arranged between the positive tab and the shell and between the negative tab and the shell; after hot pressing, the radius R of the circular arc region and the thickness T of the roll core were observed and measured by X-Ray or computed tomography; the electrolyte was fully infiltrated by aging at room temperature (25℃) for 24 h and at high temperature (65℃) for 8 h; the battery was transferred to the formation equipment, the positive and negative tabs were connected to the charging port, and the battery was charged and pressurized to activate the core at a temperature of 80℃ and a pressure of 510 kgf per battery, forming a secondary lithium ion battery that can charge and discharge externally;

[0137] The radius R of the circular arc region is 5.2 mm, the thickness T of the core is 10.3 mm, 2R / T is 1.010, c / (2R / T) is 0.069, the radius r1 of the circular arc of the layer where the positive electrode tab is located is 3.6 mm, the radius r2 of the circular arc of the layer where the negative electrode tab is located is 3.6 mm, k1 is 2.42, k2 is 2.42, the distance from the first end of the positive electrode tab to the circular arc region is 4.5 mm, the ratio of the distance from the first end of the positive electrode tab to the circular arc region to r1 is 1.25, the distance from the first end of the negative electrode tab to the circular arc region is 4.5 mm, the ratio of the distance from the first end of the negative electrode tab to the circular arc region to r2 is 1.25, the first and second adhesive papers completely cover the circular arc region, R×c2 is 0.0624, c / c2 is 5.83, the ratio of the size of the tab adhesive in the length direction of the positive electrode sheet to the size of the positive electrode tab in the length direction of the positive electrode sheet is 1.67, and the ratio of the size of the tab adhesive in the length direction of the negative electrode sheet to the size of the negative electrode tab in the length direction of the negative electrode sheet is 1.67.

[0138] Example 2

[0139] The lithium ion secondary battery was prepared according to the following method:

[0140] (1) Preparation of a positive electrode sheet

[0141] Lithium cobaltate, lithium titanium aluminum phosphate (average particle size 0.05 μm), carbon nanotubes and polyvinylidene fluoride were mixed in a mass ratio of 94.7:2.8:1.1:1.4, N-methyl pyrrolidone (NMP) was added, and the mixture was stirred in a stirring tank to prepare a positive electrode slurry; the positive electrode slurry was uniformly transferred to the surface of an aluminum foil through an extrusion coating device, and then baked in an oven at 80°C for 10 min; after the solvent was completely removed, the positive electrode sheet was wound on a winding drum; then the positive electrode sheet was unwound on a variable roll gap roller press machine, the variable roll frequency was set according to the length of the positive electrode sheet, and the radius R of the circular arc region was adjusted; attention should be paid to stopping the variable roll action when the roller press machine runs to the single-sided region; and the positive electrode sheet with the same surface density and different compaction densities was prepared by continuously running the above variable roll action.

[0142] The positive electrode tab (the size w2 of the positive electrode tab in the length direction of the positive electrode sheet is 10 mm, and the thickness h1 of the positive electrode tab is 60 μm) was welded, and the first adhesive paper (acrylic adhesive paper, the size w1 in the length direction of the positive electrode sheet is 21.2 mm) was pasted; and then the positive electrode sheet was obtained by cutting.

[0143] The thickness of the positive electrode sheet in the circular arc region is 65 μm, the thickness of the positive electrode sheet in the flat region is 62 μm, and the ratio of the two is 1.05; the compaction density of the positive electrode active layer in the circular arc region is 2.9 g / cm3 The compaction density of the positive active layer in the flat area is 4.2 g / cm 3 , and the ratio of the two is 0.69; the surface density of the positive active layer in the circular arc area is 8 mg / cm 2 , and the surface density of the positive active layer in the flat area is 11 mg / cm 2 , and the ratio of the two is 0.73; the cross-sectional porosity of the positive plate in the circular arc area is 2.98%, the cross-sectional porosity of the positive plate in the flat area is 1.52%, and the ratio of the two is 1.961; c2 is 2.8%.

[0144] (2) Preparation of the negative plate

[0145] The artificial graphite, silicon carbon, carbon nanotube, butadiene rubber, sodium carboxymethyl cellulose and polyacrylic acid are uniformly mixed in a mass ratio of 84.3:12.7:0.45:1.5:0.45:0.6, deionized water is added, and the negative electrode slurry is prepared by fully stirring in a stirring tank; the above-mentioned negative electrode slurry is transferred to the surface of the copper foil through the extrusion coating equipment, and then baked in an oven at 120°C for 5 min, and after the solvent is completely removed, the roll is used for winding; then the roll is unwound and the electrode plate is compacted on the variable roll gap roller press, and the variable roll frequency is set according to the length of the electrode plate to control the radius R of the circular arc area. Note that the variable roll action is stopped when the roll pressing equipment runs to the single-sided area. The preparation of the negative plate with the same surface density and different compaction densities can be realized by continuously running the above-mentioned variable roll action;

[0146] The electrode plate after rolling is cut along the TD direction according to the designed width size by the cutting equipment, and after the abnormality is detected by the CCD, the small roll electrode plate is wound; the negative tab (the size w4 of the negative tab in the length direction of the negative plate is 10 mm, and the thickness h3 of the negative tab is 60 μm) is welded, and the second adhesive paper (acrylic adhesive paper, the size w3 in the length direction of the negative plate is 21.2 mm) is pasted; then the negative plate is cut;

[0147] The thickness of the negative plate in the circular arc area is 78 μm, the thickness of the negative plate in the flat area is 74.6 μm, and the ratio of the two is 1.05; the compaction density of the negative active layer in the circular arc area is 1.37 g / cm 3 , and the compaction density of the negative active layer in the flat area is 1.49 g / cm 3 , and the ratio of the two is 0.92; the surface density of the negative active layer in the circular arc area is 5 mg / cm 2 , and the surface density of the negative active layer in the flat area is 5.2 mg / cm 2The ratio of the two is 0.96; the cross-sectional porosity of the negative electrode sheet located in the circular arc region is 2.49%, the cross-sectional porosity of the negative electrode sheet located in the flat region is 1.62%, and the ratio of the two is 1.54; the content c of elemental silicon in the negative active layer is 7%.

[0148] (3) Preparation of electrolyte

[0149] In an argon-filled glove box (moisture <1 ppm, oxygen <1 ppm), EC, PC and EP were mixed into a uniform non-aqueous solvent at a mass ratio of 1:1:3, and 14% lithium salt (lithium hexafluorophosphate), 5% additive (FEC), 3% additive (PS), 2.5% additive (SN), 2% additive (HTCN) and 0.5% additive (DTD) based on the total mass of the electrolyte were slowly added, and stirred uniformly to obtain the electrolyte;

[0150] The content of propyl propionate in the electrolyte is 0%.

[0151] (4) Preparation of battery

[0152] The positive electrode sheet prepared in step (1), the separator (oil-based 5+2+2 separator (5 μm thick base film+2 μm thick ceramic layer+2 μm thick polyvinylidene fluoride adhesive layer)) and the negative electrode sheet prepared in step (2) were aligned at the head, and then uniformly rolled into a roll-shaped structure according to the designed size to obtain a roll core; the electrolyte prepared in step (3) was added; the tab adhesive (the first adhesive layer is in contact with the shell, the third adhesive layer is in contact with the positive / negative tab, the second adhesive layer is between the first and third adhesive layers, the melting point of the first adhesive layer is 102°C, the melting point of the second adhesive layer is 133°C, the melting point of the third adhesive layer is 102°C, the thickness h2 of the tab adhesive is 16 μm, and the size of the tab adhesive in the length direction of the positive / negative electrode sheet is 12 mm) was arranged between the positive tab and the shell and between the negative tab and the shell; after hot pressing, the radius R of the circular arc region and the thickness T of the roll core were observed and measured by X-Ray or computed tomography; the electrolyte was fully soaked by aging at room temperature (25°C) for 24 h and at high temperature (65°C) for 8 h; the battery was transferred to the formation equipment, the positive and negative tabs were connected to the charging port, and the battery was charged and activated at a temperature of 80°C and a pressure of 510 kgf per battery to form a secondary lithium ion battery that can charge and discharge externally;

[0153] The radius R of the circular arc region is 2.5 mm, the thickness T of the core is 5.3 mm, 2R / T is 0.943, c / (2R / T) is 0.074, the radius r1 of the circular arc in the layer where the positive tab is located is 1.9 mm, the radius r2 of the circular arc in the layer where the negative tab is located is 1.9 mm, k1 is 1.52, k2 is 1.52, the distance from the first end of the positive tab to the circular arc region is 1.5 mm, the distance from the first end of the negative tab to the circular arc region is 1.5 mm, the ratio of the distance from the first end of the positive tab to the circular arc region to r1 is 0.79, the ratio of the distance from the first end of the negative tab to the circular arc region to r2 is 0.79, the first and second adhesive papers completely cover the circular arc region, R×c2 is 0.07, c / c2 is 2.5, the ratio of the size of the tab adhesive in the length direction of the positive tab to the size of the positive tab in the length direction of the positive tab is 1.2, and the ratio of the size of the tab adhesive in the length direction of the negative tab to the size of the negative tab in the length direction of the negative tab is 1.2.

[0154] Example 3

[0155] A lithium ion secondary battery was prepared according to the following method:

[0156] (1) Preparation of a positive tab

[0157] Lithium cobaltate, lithium titanium aluminum phosphate (average particle size 1.93 μm), carbon nanotubes and polyvinylidene fluoride were mixed in a mass ratio of 93.3:4.2:1.1:1.4, N-methyl pyrrolidone (NMP) was added, and the mixture was stirred in a stirring tank to prepare a positive electrode slurry; the above-mentioned positive electrode slurry was uniformly transferred to the surface of an aluminum foil by an extrusion coating device, and then baked in an oven at 80°C for 10 min; after the solvent was completely removed, the positive tab was wound on a winding drum; then the positive tab was unwound on a variable gap roller press machine, the variable roller frequency was set according to the length of the positive tab segment, and the variable roller frequency was used to control the radius R of the circular arc region. It should be noted that the variable roller action should be stopped when the roller pressing equipment runs to the single-sided region. The continuous operation of the above-mentioned variable roller action can realize the preparation of positive tabs with the same surface density and different compaction densities;

[0158] The rolled tab was cut along the TD direction according to the designed width size by a cutting device, and then wound into a small roll after being detected by a charge-coupled device image sensor (CCD) to exclude abnormalities; the positive tab (the size w2 of the positive tab in the length direction of the positive tab is 8 mm, and the thickness h1 of the positive tab is 80 μm) was welded, and the first adhesive paper (acrylic adhesive paper, the size w1 in the length direction of the positive tab is 39.7 mm) was pasted; then the positive tab was cut to obtain a positive tab;

[0159] The thickness of the positive tab in the circular arc region is 120 μm, the thickness of the positive tab in the flat region is 108 μm, and the ratio of the two is 1.11; the compaction density of the positive active layer in the circular arc region is 3.39 g / cm3 The compaction density of the positive active layer in the flat area is 4.1 g / cm 3 , and the ratio of the two is 0.827; the surface density of the positive active layer in the circular arc area is 19 g / cm 2 , and the surface density of the positive active layer in the flat area is 20.5 g / cm 2 , and the ratio of the two is 0.93; the cross-sectional porosity of the positive plate in the circular arc area is 2.56%, the cross-sectional porosity of the positive plate in the flat area is 1.68%, and the ratio of the two is 1.524; c2 is 4.2%.

[0160] (2) Preparation of the negative plate

[0161] The artificial graphite, silicon carbon, carbon nanotube, butadiene rubber, sodium carboxymethyl cellulose and polyacrylic acid are uniformly mixed in a mass ratio of 84.3:12.7:0.45:1.5:0.45:0.6, deionized water is added, and the negative electrode slurry is prepared by fully stirring in a stirring tank; the above-mentioned negative electrode slurry is transferred to the surface of the copper foil through the extrusion coating equipment, and then baked in an oven at 120°C for 5 min, and after the solvent is completely removed, the roll is used for winding; then the roll is unwound and the plate is compacted on the variable roll gap roller press, and the variable roll frequency is set according to the length of the plate to control the radius R of the circular arc area. Note that the variable roll action is stopped when the roll pressing equipment runs to the single-sided area. The preparation of the negative plate with the same surface density and different compaction densities can be realized by continuously running the above-mentioned variable roll action;

[0162] The roll-pressed plate is cut along the TD direction according to the designed width size by the cutting equipment, and after the abnormality is detected by the CCD, the small roll plate is wound; the negative tab (the size w4 of the negative tab in the length direction of the negative plate is 8 mm, and the thickness h3 of the negative tab is 80 μm) is welded, and the second adhesive paper (acrylic adhesive paper, the size w3 in the length direction of the negative plate is 39.7 mm) is pasted; then the negative plate is cut;

[0163] The thickness of the negative plate in the circular arc area is 132 μm, the thickness of the negative plate in the flat area is 120 μm, and the ratio of the two is 1.1; the compaction density of the negative active layer in the circular arc area is 1.38 g / cm 3 , and the compaction density of the negative active layer in the flat area is 1.71 g / cm 3 , and the ratio of the two is 0.81; the surface density of the negative active layer in the circular arc area is 8.4 mg / cm 2 , and the surface density of the negative active layer in the flat area is 9.45 g / cm 2The ratio of the two is 0.89; the cross-sectional porosity of the negative electrode sheet located in the circular arc region is 2.42%, the cross-sectional porosity of the negative electrode sheet located in the flat region is 1.3%, and the ratio of the two is 1.86; the content c of elemental silicon in the negative active layer is 7%.

[0164] (3) Preparation of electrolyte

[0165] In an argon-filled glove box (moisture <1 ppm, oxygen <1 ppm), EC, PC and EP were mixed into a uniform non-aqueous solvent at a mass ratio of 1:1:3, and 14% lithium salt (lithium hexafluorophosphate), 5% additive (FEC), 3% additive (PS), 2.5% additive (SN), 2% additive (HTCN) and 0.5% additive (DTD) based on the total mass of the electrolyte were slowly added, and stirred uniformly to obtain the electrolyte;

[0166] The content of propyl propionate in the electrolyte is 0%.

[0167] (4) Preparation of battery

[0168] The positive electrode sheet prepared in step (1), the separator (oil-based 5+2+2 separator (5 μm thick base film+2 μm thick ceramic layer+2 μm thick polyvinylidene fluoride adhesive layer)) and the negative electrode sheet prepared in step (2) were aligned at the head, and then uniformly rolled into a roll-shaped structure according to the designed size to obtain a roll core; the electrolyte prepared in step (3) was added; the tab adhesive (the first adhesive layer is in contact with the shell, the third adhesive layer is in contact with the positive / negative tab, the second adhesive layer is between the first and third adhesive layers, the melting point of the first adhesive layer is 130°C, the melting point of the second adhesive layer is 159°C, the melting point of the third adhesive layer is 130°C, the thickness h2 of the tab adhesive is 36 μm, and the size of the tab adhesive in the length direction of the positive / negative electrode sheet is 15 mm) was arranged between the positive tab and the shell and between the negative tab and the shell; after hot pressing, the radius R of the circular arc region and the thickness T of the roll core were observed and measured by X-Ray or computed tomography; the electrolyte was fully soaked by aging at room temperature (25°C) for 24 h and at high temperature (65°C) for 8 h; the battery was transferred to the formation equipment, the positive and negative tabs were connected to the charging port, and the battery was charged and activated at a temperature of 80°C and a pressure of 510 kgf per battery to form a secondary lithium ion battery that can charge and discharge externally;

[0169] The radius R of the arc region is 10.1 mm, the thickness T of the winding core is 18.2 mm, 2R / T is 1.11, c / (2R / T) is 0.063, the radius r1 of the arc in the layer where the positive electrode tab is located is 7.5 mm, the radius r2 of the arc in the layer where the negative electrode tab is located is 7.5 mm, k1 is 2.02, k2 is 2.02, the distance from the first end of the positive electrode tab to the arc region is 6.8 mm, the distance from the first end of the negative electrode tab to the arc region is 6.8 mm, the ratio of the distance from the first end of the positive electrode tab to the arc region to r1 is 0.91, the ratio of the distance from the first end of the negative electrode tab to the arc region to r2 is 0.91, the first and second adhesive papers completely cover the arc region, Rxc2 is 0.424, c / c2 is 1.67, the ratio of the size of the tab adhesive in the length direction of the positive electrode sheet to the size of the positive electrode tab in the length direction of the positive electrode sheet is 1.88, and the ratio of the size of the tab adhesive in the length direction of the negative electrode sheet to the size of the negative electrode tab in the length direction of the negative electrode sheet is 1.99.

[0170] Example 4 group

[0171] This group of examples is used to verify the influence of the change of "2R / T".

[0172] This group of examples refers to Example 1, except that the thickness T of the winding core is changed to regulate 2R / T, as follows:

[0173] In Example 4a, T is 11.5 mm, and 2R / T is 0.904; wherein the thickness of the positive electrode sheet in the arc region is 92 μm, the thickness of the positive electrode sheet in the flat region is 86 μm, and the ratio of the two is 1.07; the compaction density of the positive electrode active layer in the arc region is 3.27 g / cm 3 , the compaction density of the positive electrode active layer in the flat region is 4.11 g / cm 3 , and the ratio of the two is 0.796; the area density of the positive electrode active layer in the arc region is 13.4 mg / cm 2 , the area density of the positive electrode active layer in the flat region is 15.6 mg / cm 2 , and the ratio of the two is 0.86; the cross-sectional porosity ratio of the positive electrode sheet in the arc region is 2.83%, the cross-sectional porosity ratio of the positive electrode sheet in the flat region is 1.63%, and the ratio of the two is 1.736; the thickness of the negative electrode sheet in the arc region is 100 μm, the thickness of the negative electrode sheet in the flat region is 96 μm, and the ratio of the two is 1.04; the compaction density of the negative electrode active layer in the arc region is 1.28 g / cm 3 , the compaction density of the negative electrode active layer in the flat region is 1.6 g / cm 3 , and the ratio of the two is 0.8; the area density of the negative electrode active layer in the arc region is 6 mg / cm 2, the surface density of the negative active layer in the flat area is 7.2 mg / cm 2 , the ratio of the two is 0.83; the cross-sectional porosity of the negative sheet in the circular arc area is 2.58%, the cross-sectional porosity of the negative sheet in the flat area is 1.53%, and the ratio of the two is 1.69;

[0174] Example 4b, T is 8.2 mm, 2R / T is 1.268; wherein the thickness of the positive sheet in the circular arc area is 75 μm, the thickness of the positive sheet in the flat area is 68 μm, and the ratio of the two is 1.1; the compaction density of the positive active layer in the circular arc area is 2.93 g / cm 3 , the compaction density of the positive active layer in the flat area is 4.02 g / cm 3 , the ratio of the two is 0.729; the surface density of the positive active layer in the circular arc area is 9.8 mg / cm 2 , the surface density of the positive active layer in the flat area is 12 mg / cm 2 , the ratio of the two is 0.82; the cross-sectional porosity of the positive sheet in the circular arc area is 2.93%, the cross-sectional porosity of the positive sheet in the flat area is 1.76%, and the ratio of the two is 1.665; the thickness of the negative sheet in the circular arc area is 80 μm, the thickness of the negative sheet in the flat area is 72 μm, and the ratio of the two is 1.11; the compaction density of the negative active layer in the circular arc area is 1.14 g / cm 3 , the compaction density of the negative active layer in the flat area is 1.48 g / cm 3 , the ratio of the two is 0.77; the surface density of the negative active layer in the circular arc area is 4.2 mg / cm 2 , the surface density of the negative active layer in the flat area is 4.9 mg / cm 2 , the ratio of the two is 0.86; the cross-sectional porosity of the negative sheet in the circular arc area is 2.75%, the cross-sectional porosity of the negative sheet in the flat area is 1.72%, and the ratio of the two is 1.6.

[0175] Example 5 group

[0176] This group of examples is used to verify the influence brought by the change of the ratio of the thickness of the positive sheet in the circular arc area to the thickness of the positive sheet in the flat area.

[0177] This group of examples refers to Example 1, except that the ratio of the thickness is regulated by changing the surface density of the positive active layer in the circular arc area (while keeping the compaction density unchanged), as follows:

[0178] The thickness of the positive electrode tab in the circular arc region is 60 μm, and the ratio of the thickness of the positive electrode tab in the circular arc region to the thickness of the positive electrode tab in the flat region is 0.74; wherein the areal density of the positive electrode active layer in the circular arc region is 8.4 mg / cm 2 , the ratio of the areal density of the positive electrode active layer in the circular arc region to the areal density of the positive electrode active layer in the flat region is 0.59; the radius R of the circular arc region is 4.7 mm, the thickness T of the winding core is 10.3 mm, and 2R / T is 0.913;

[0179] The thickness of the positive electrode tab in the circular arc region is 60 μm, and the ratio of the thickness of the positive electrode tab in the circular arc region to the thickness of the positive electrode tab in the flat region is 0.74; wherein the areal density of the positive electrode active layer in the circular arc region is 8.4 mg / cm 2 , the ratio of the areal density of the positive electrode active layer in the circular arc region to the areal density of the positive electrode active layer in the flat region is 0.59; the radius R of the circular arc region is 4.7 mm, the thickness T of the winding core is 10.3 mm, and 2R / T is 0.913;

[0180] Example 6

[0181] To verify the influence brought by the change of the "tab adhesive".

[0182] Example 1 is referred to, except that the tab adhesive is changed, specifically as follows: the tab adhesive is a single-layer structure, and the melting point is 140 ℃.

[0183] Example 7 group

[0184] This group of examples is used to verify the influence brought by the change of the "melting point of the first, second and third adhesive layers of the tab adhesive".

[0185] This group of examples refers to Example 1, except that the melting point of at least one of the first, second and third adhesive layers is changed, specifically as follows:

[0186] Example 7a, the melting point of the first adhesive layer is 95 ℃, and the melting point of the third adhesive layer is 95 ℃;

[0187] Example 7b, the melting point of the first adhesive layer is 137 ℃, and the melting point of the third adhesive layer is 137 ℃;

[0188] Example 7c, the melting point of the second adhesive layer is 125 ℃;

[0189] Example 7d, the melting point of the second adhesive layer is 169 ℃.

[0190] Example 8

[0191] To verify the influence brought by "whether the first and second adhesive papers cover the circular arc region".

[0192] Refer to Example 1, except that whether the first adhesive paper and the second adhesive paper cover the arcuate region is regulated by changing the setting positions of the positive electrode tabs and the negative electrode tabs and the size w1 of the first adhesive paper in the length direction of the positive electrode sheet and the size w3 of the second adhesive paper in the length direction of the negative electrode sheet, so that the first adhesive paper and the second adhesive paper do not cover the arcuate region, wherein the radius R of the arcuate region is 5.18 mm, the thickness T of the jelly-roll core is 10.3 mm, 2R / T is 1.006; w1 is 20.8 mm, w3 is 20.8 mm; the distance from the first end of the positive electrode tab to the arcuate region is 12.8 mm, and the distance from the first end of the negative electrode tab to the arcuate region is 12.8 mm.

[0193] Example 9 group

[0194] The examples in this group are used to verify the influence brought by the change of "the mass content c2 of the solid-state electrolyte in the positive electrode active layer".

[0195] The examples in this group refer to Example 1, except that c2 is regulated by changing the formula of the positive electrode slurry, as follows:

[0196] Example 9a, the mass ratio of lithium cobaltate, lithium aluminum titanium phosphate, carbon nanotube and polyvinylidene fluoride is 97:0.5:1.1:1.4; wherein c2 is 0.5%; c / c2 is 14, Rxc2 is 0.026;

[0197] Example 9b, the mass ratio of lithium cobaltate, lithium aluminum titanium phosphate, carbon nanotube and polyvinylidene fluoride is 92.5:5:1.1:1.4; wherein c2 is 5%; c / c2 is 1.4, Rxc2 is 0.26.

[0198] Example 10

[0199] The examples in this group are used to verify the influence brought by the change of "Rxc2".

[0200] The examples in this group refer to Example 2, except that Rxc2 is regulated by changing c2, as follows: the mass ratio of lithium cobaltate, lithium aluminum titanium phosphate, carbon nanotube and polyvinylidene fluoride is 96.3:1.2:1.1:1.4, c2 is 1.2%; Rxc2 is 0.03.

[0201] Example 11 group

[0202] The examples in this group are used to verify the influence brought by the change of "the average particle size of the solid-state electrolyte".

[0203] The examples in this group refer to Example 1, except that the average particle size of lithium aluminum titanium phosphate is changed, as follows:

[0204] Example 11a, the average particle size of lithium aluminum titanium phosphate is 0.02 μm;

[0205] Example 11b, the average particle size of the lithium aluminum titanium phosphate is 3 μm.

[0206] Example 12 group

[0207] The examples in this group are used to verify the influence brought by the change of "the content c of elemental silicon in the negative active layer".

[0208] The examples in this group are implemented with reference to Example 1, except that c is regulated by changing the formulation of the negative electrode slurry, as follows:

[0209] Example 12a, the mass ratio of artificial graphite, silicon carbon, carbon nanotube, styrene butadiene rubber, sodium carboxymethyl cellulose and polyacrylic acid is 91.5:5.5:0.45:1.5:0.45:0.6, wherein c is 3%; c / c2 is 2.5; c / (2R / T) is 0.03;

[0210] Example 12b, the mass ratio of artificial graphite, silicon carbon, carbon nanotube, styrene butadiene rubber, sodium carboxymethyl cellulose and polyacrylic acid is 69.7:27.3:0.45:1.5:0.45:0.6, wherein c is 15%; c / c2 is 12.5; c / (2R / T) is 0.149;

[0211] Example 12c, the mass ratio of artificial graphite, silicon carbon, carbon nanotube, styrene butadiene rubber, sodium carboxymethyl cellulose and polyacrylic acid is 60.6:36.4:0.45:1.5:0.45:0.6, wherein c is 20%; c / c2 is 16.67; c / (2R / T) is 0.198;

[0212] Example 12d, the mass ratio of artificial graphite, silicon carbon, carbon nanotube, styrene butadiene rubber, sodium carboxymethyl cellulose and polyacrylic acid is 24.3:72.7:0.45:1.5:0.45:0.6, wherein c is 40%; c / c2 is 33.33; c / (2R / T) is 0.396.

[0213] Example 13

[0214] The examples in this group are used to verify the influence brought by the change of "c / c2".

[0215] The examples in this group are implemented with reference to Example 12a, except that c / c2 is regulated by changing c2, as follows: c2 is 4.2%, c / c2 is 0.71.

[0216] Example 14 group

[0217] The examples in this group are used to verify the influence brought by the change of "the mass content of propyl propionate in the electrolyte".

[0218] The present examples are performed according to Example 1, except that the mass content of propyl propionate in the electrolyte is changed, as follows:

[0219] Example 14a, 0.5% propyl propionate is added to the electrolyte by mass;

[0220] Example 14b, 1.5% propyl propionate is added to the electrolyte by mass.

[0221] The above examples all meet:

[0222] The median particle size Dv50 of the lithium aluminum titanium phosphate is 0.02-2 μm;

[0223] The volume distribution particle size of the artificial graphite is: Dv10 is 5-10 μm, Dv50 is 10-25 μm, and Dv90 is 25-40 μm; the interlayer spacing d002 of the artificial graphite is 0.3356-0.3359 nm; the reversible capacity of the artificial graphite is 350-365 mAh / g;

[0224] The silicon-carbon is a porous carbon substrate and a silicon material inside the pore channel of the porous carbon substrate; the volume distribution particle size of the silicon-carbon is: Dv10 is 1-6 μm, Dv50 is 3-15 μm, and Dv90 is 12-30 μm; the specific surface area of the silicon-carbon is 0.5-10 m 2 / g, and the average sphericity of the silicon-carbon is 0.5-1. 2

[0225] Comparative Example 1

[0226] According to Example 1, except that no lithium aluminum titanium phosphate is added to the positive electrode slurry, i.e., the mass ratio of lithium cobaltate, carbon nanotubes and polyvinylidene fluoride is 97.5:1.1:1.4.

[0227] Comparative Example 2 group

[0228] According to Example 1, except that 2R / T is regulated by changing the radius R of the arc region and the thickness T of the winding core, as follows:

[0229] Comparative Example 2a, the radius R of the arc region is 4.8 mm, the thickness T of the winding core is 10.9 mm, and 2R / T is 0.881;

[0230] Comparative Example 2b, the radius R of the arc region is 5.7 mm, the thickness T of the winding core is 8.6 mm, and 2R / T is 1.326.

[0231] Test Example

[0232] (1) Furnace temperature safety test

[0233] ​The batteries prepared from the examples and comparative examples were subjected to oven temperature safety test, and the specific test method was as follows:

[0234] The batteries were placed in a test chamber, and the test chamber was subjected to temperature rise at a rate of (5±2) °C / min. When the temperature in the test chamber reached 130 °C±2 °C, the temperature was kept constant for 60 min. During this period, if the battery did not smoke, did not catch fire, and did not explode, it was considered to pass the test. Five batteries of each example and comparative example were tested, and the results were recorded in the form of "n / 5", wherein n represented the number of batteries that passed the test. For example, 5 / 5 indicated that 5 batteries were tested and all passed the test. The larger n was, the better the oven temperature safety performance of the battery was. The results were recorded in Table 1.

[0235] (2) Overcharge safety test

[0236] The batteries prepared from the examples and comparative examples were subjected to overcharge safety test, and the specific test method was as follows:

[0237] The batteries were placed in a test chamber, and the test chamber was subjected to temperature rise at a rate of (5±2) °C / min. When the temperature in the test chamber reached 130 °C±2 °C, the temperature was kept constant for 60 min. During this period, if the battery did not smoke, did not catch fire, and did not explode, it was considered to pass the test. Five batteries of each example and comparative example were tested, and the results were recorded in the form of "n / 5", wherein n represented the number of batteries that passed the test. For example, 5 / 5 indicated that 5 batteries were tested and all passed the test. The larger n was, the better the oven temperature safety performance of the battery was. The results were recorded in Table 1.

[0238] (3) Rate test

[0239] The batteries prepared from the examples and comparative examples were subjected to rate test, and the specific test method was as follows:

[0240] The batteries were placed in a test chamber, and the test chamber was subjected to temperature rise at a rate of (5±2) °C / min. When the temperature in the test chamber reached 130 °C±2 °C, the temperature was kept constant for 60 min. During this period, if the battery did not smoke, did not catch fire, and did not explode, it was considered to pass the test. Five batteries of each example and comparative example were tested, and the results were recorded in the form of "n / 5", wherein n represented the number of batteries that passed the test. For example, 5 / 5 indicated that 5 batteries were tested and all passed the test. The larger n was, the better the oven temperature safety performance of the battery was. The results were recorded in Table 1.

[0241] (4) Cycle test

[0242] The batteries prepared from the examples and comparative examples were subjected to cycle test, and the specific test method was as follows:

[0243] The cycle capacity retention rate of the battery was calculated by discharging at 0.7C to 3.0V, charging at 2C to 4.53V, and cutting off at 0.2C, and repeating the cycle for 400 cycles at 25℃±3℃, and the results were recorded in Table 1.

[0244] (5) High-temperature storage test

[0245] The batteries prepared in the examples and comparative examples were subjected to high-temperature storage test, and the specific test method was as follows:

[0246] The batteries were charged at 0.5C to 4.53V and cut off at 0.05C, discharged at 0.2C to 3.0V, and the discharge capacity was recorded; then the batteries were charged at 0.5C to 4.53V and cut off at 0.05C, and the full charge thickness of the batteries was tested after being fully charged, and the batteries were placed in an environment of (60±2)℃ for 7 days, then taken out and placed in an environment of 25℃±3℃ for 2h, the thickness of the batteries was tested, and then the batteries were discharged at 0.2C to 3.0V, and the discharge capacity was recorded, and the capacity recovery rate and thickness expansion rate were recorded in Table 1.

[0247] Table 1

[0248]

[0249]

[0250] As can be seen from Table 1, the battery of the present application has higher rate performance, cycle stability and high-temperature storage stability compared with the comparative examples, and can effectively reduce the safety risk caused by gas production.

[0251] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application, and all fall within the protection scope of the present application.

Claims

1. A lithium-ion secondary battery, characterized by comprising: The lithium ion secondary battery comprises a roll core formed by stacking and rolling a positive electrode sheet, a separator and a negative electrode sheet; The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer arranged on at least one side of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising a silicon-based material; The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer arranged on at least one side of the positive electrode current collector, the positive electrode active layer comprising a positive electrode active material and a solid-state electrolyte; The roll core comprises a circular arc region and a flat region connected to the circular arc region; The radius R of the circular arc region and the thickness T of the roll core satisfy: 0.9≤2R / T≤4 / π, π being the circular constant; The mass content c2 of the solid-state electrolyte in the positive electrode active layer and the circular arc radius R satisfy: 0.02≤R×c2≤0.5, the unit of the circular arc radius being mm; The content of elemental silicon in the negative electrode active layer is c, and 0 2. The lithium-ion secondary battery according to claim 1, wherein The radius R of the circular arc region is 1-100 mm, and the thickness T of the roll core is 1-200 mm; And / or, the ratio of the thickness of the positive electrode sheet located in the circular arc region to the thickness of the positive electrode sheet located in the flat region is 0.7-1.5; And / or, the thickness of the positive electrode sheet located in the flat region is 20 μm-150 μm; And / or, the ratio of the compaction density of the positive electrode active layer located in the circular arc region to the compaction density of the positive electrode active layer located in the flat region is 0.5-0.99; and / or the compaction density of the positive electrode active layer in the flat area is 2 g / cm 3 -5 g / cm 3 ; And / or, the ratio of the surface density of the positive electrode active layer located in the circular arc region to the surface density of the positive electrode active layer located in the flat region is 0.6-1; and / or the surface density of the positive electrode active layer at the flat area is 8 mg / cm 2 - 25 mg / cm 2 .

3. The lithium-ion secondary battery according to claim 1 or 2, wherein The ratio of the thickness of the negative electrode sheet located in the circular arc region to the thickness of the negative electrode sheet located in the flat region is 1.01-1.5; And / or, the thickness of the negative electrode sheet located in the flat region is 20 μm-200 μm; And / or, the ratio of the compaction density of the negative electrode active layer located in the circular arc region to the compaction density of the negative electrode active layer located in the flat region is 0.5-0.99; and / or the compaction density of the negative active layer at the flat area is 1 g / cm 3 -2.5 g / cm 3 ; And / or, the ratio of the surface density of the negative electrode active layer located in the circular arc region to the surface density of the negative electrode active layer located in the flat region is 0.6-1; and / or the surface density of the negative active layer at the flat area is 3 mg / cm 2 - 12 mg / cm 2 .

4. The lithium-ion secondary battery according to claim 1 or 2, wherein The content c of elemental silicon in the negative electrode active layer and 2R / T satisfy: 0.03≤c / (2R / T)≤0.

5.

5. The lithium-ion secondary battery according to claim 4, wherein 0.06 0.075； And / or, the silicon-based material comprises silicon-carbon, the silicon-carbon comprising a porous carbon substrate and a silicon material located inside the pores of the porous carbon substrate.

6. The lithium-ion secondary battery according to claim 5, wherein The mass content of silicon in the silicon-carbon is 20%-70%; And / or, the volume distribution particle size of the silicon-carbon is: Dv10 is 1 μm-6 μm, Dv50 is 3 μm-15 μm, and Dv90 is 12 μm-30 μm.

7. The lithium-ion secondary battery according to claim 1 or 2, wherein The lithium ion secondary battery further comprises a shell; the positive electrode sheet further comprises a positive electrode tab and a tab adhesive arranged on the surface of the positive electrode tab; And / or, the negative electrode sheet further comprises a negative electrode tab and a tab adhesive arranged on the surface of the negative electrode tab.

8. The lithium-ion secondary battery according to claim 7, wherein The tab adhesive comprises a first adhesive layer, a second adhesive layer and a third adhesive layer arranged in sequence, the first adhesive layer is in contact with the shell, the third adhesive layer is in contact with the positive tab, and / or the third adhesive layer is in contact with the negative tab, and the second adhesive layer is located between the first adhesive layer and the third adhesive layer. And / or, the thickness h2 of the tab adhesive is 15-50 μm.

9. The lithium-ion secondary battery according to claim 8, wherein The melting point of the first adhesive layer is 100-130 ℃, the melting point of the second adhesive layer is 130-160 ℃, and the melting point of the third adhesive layer is 100-130 ℃.

10. The lithium-ion secondary battery according to claim 7, wherein The size of the tab adhesive in the length direction of the positive plate is 5-20 mm; And / or, the size of the tab adhesive in the length direction of the negative plate is 5-20 mm; And / or, the ratio of the size of the tab adhesive in the length direction of the positive plate to the size w2 of the positive tab in the length direction of the positive plate is 1.1-2; And / or, the ratio of the size of the tab adhesive in the length direction of the negative plate to the size w4 of the negative tab in the length direction of the negative plate is 1.1-2.

11. The lithium-ion secondary battery according to claim 1 or 2, wherein The positive plate further comprises a positive tab, a positive tab welding area and a first adhesive paper, the positive tab is located in the positive tab welding area, and the first adhesive paper covers the positive tab welding area.

12. The lithium-ion secondary battery according to claim 11, wherein The size w1 of the first adhesive paper in the length direction of the positive plate is 15-50 mm, and the size w2 of the positive tab in the length direction of the positive plate is 2-10 mm; And / or, the ratio of the distance from the first end of the positive tab to the circular arc area to the circular arc radius r1 of the layer where the positive tab is located is 0-2, wherein the first end is the end of the positive tab close to the circular arc area; And / or, the first adhesive paper covers at least part of the circular arc area.

13. The lithium-ion secondary battery according to claim 1 or 2, wherein The negative plate further comprises a negative tab, a negative tab welding area and a second adhesive paper, the negative tab is located in the negative tab welding area, and the second adhesive paper covers the negative tab welding area.

14. The lithium-ion secondary battery according to claim 13, wherein, The size w3 of the second adhesive paper in the length direction of the negative plate is 15-50 mm, and the size w4 of the negative tab in the length direction of the negative plate is 2-10 mm; And / or, the ratio of the distance from the first end of the negative tab to the circular arc area to the circular arc radius r2 of the layer where the negative tab is located is 0-2, wherein the first end is the end of the negative tab close to the circular arc area; And / or, the second adhesive paper covers at least part of the circular arc area.

15. The lithium-ion secondary battery according to claim 1 or 2, wherein The solid-state electrolyte comprises at least one of lithium aluminum titanium phosphorus oxide, lithium lanthanum zirconium tantalum oxide and lithium lanthanum titanium oxide; And / or, the average particle size of the solid-state electrolyte is 0.02-3 μm; And / or, the mass content c2 of the solid-state electrolyte in the positive active layer is 0.1%-5%; And / or, the positive active material comprises at least one of lithium cobaltate, lithium nickel cobalt manganese acid, lithium nickel cobalt aluminum acid, lithium nickel cobalt manganese aluminum acid, lithium manganese acid, lithium nickel manganese acid, lithium nickel acid, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate and lithium-rich manganese-based material; And / or, the negative active material further comprises a carbon-based material.

16. The lithium-ion secondary battery according to claim 15, wherein The average particle size of the solid-state electrolyte is 0.05-2 microns. And / or, the mass content c2 of the solid-state electrolyte in the positive active layer is 1-4.5%.

17. The lithium-ion secondary battery according to claim 1 or 2, wherein The lithium ion secondary battery further comprises an electrolyte, and the mass content of propyl propionate in the electrolyte is ≤10%.

18. The lithium-ion secondary battery according to claim 10, wherein, The electrolyte further comprises a non-aqueous solvent, and the non-aqueous solvent comprises a carbonic acid ester.

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