Lithium ion secondary battery

Abstract

The invention relates to the technical field of batteries, in particular to a lithium ion secondary battery. Comprising a winding core formed by laminating and winding a positive plate, a diaphragm and a negative plate, the negative plate comprises a negative current collector and a negative active layer, the negative active layer comprises a negative active material, the negative active material comprises a silicon-based material, the positive plate comprises a positive current collector and a positive active layer, and the positive active layer comprises a positive active material and a solid electrolyte. The roll core comprises an arc area and a straight area connected with the arc area, the radius R of the arc area and the thickness T of the roll core meet the condition that 2R / T is larger than or equal to 0.9 and smaller than or equal to 4 / pi, and pi is the circumference ratio. According to the invention, the safety problem caused by gas production in the circulation and storage process of the battery can be effectively improved.

Description

Technical Field

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

[0002] As the requirements for the battery energy density of electronic products such as communication devices and electric vehicles are getting higher and higher, traditional graphite anode materials are difficult to meet the market demand. Silicon anodes are regarded as one of the key materials to improve the energy density of lithium-ion batteries due to their high theoretical specific capacity. However, after lithiation, silicon anodes will form lithium-silicon alloys, which will react with the electrolyte, seriously affecting the cycle life of the battery. Summary of the Invention

[0003] The object of the present invention is to overcome the above problems existing in the prior art, and provide a lithium-ion secondary battery. By introducing a solid electrolyte into the positive electrode sheet of the lithium-ion secondary battery of the present invention (hereinafter simply referred to as the battery), the amount of the electrolyte can be reduced, thereby alleviating the risk of side reactions between the silicon anode and the electrolyte, and improving the cycle life of the battery; at the same time, by regulating the relationship between the radius of the arc area and the thickness of the core, the gas generation problem of the solid electrolyte during battery cycling or storage can be effectively improved, and the safety performance and cycle life of the battery are improved.

[0004] The inventors of the present invention have conducted a large number of studies and found that adding a solid electrolyte to the positive electrode sheet of a silicon anode battery can significantly improve the risk of side reactions between the silicon anode and the electrolyte, and improve the cycle life of the battery. However, the addition of the solid electrolyte will cause the battery to easily generate gas during cycling or storage. The reason for the above problem is that the expansion stress in the arc area of the core is greater than that in the flat area. Especially when the negative electrode sheet contains silicon-based materials, the large expansion stress causes the electrolyte in the arc area to be squeezed into the flat area, resulting in a decrease in the electrolyte content in the arc area, thereby causing the kinetics in the arc area 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 generate gas. And with the decomposition of the CEI film, the electrolyte will be oxidized, further leading to a decrease in the electrolyte content. Such a vicious cycle leads to an increase in gas generation. When the radius R of the arc area and the thickness T of the core satisfy 2R / T < 0.9, it will cause the stress accumulation at the arc to be unable to be effectively released due to stress concentration during battery cycling or storage, resulting in a decrease in the electrolyte in the arc area, poor kinetics, and an increase in overpotential, and further leading to gas generation. In addition, the accumulation of gas generation may cause the battery to explode.

[0005] Based on the above findings, the inventors of the present invention introduced a solid electrolyte into the positive electrode sheet, reducing the safety hazards caused by side reactions with the electrolyte. In addition, the solid electrolyte itself has high ionic conductivity, which not only helps to improve the charge-discharge efficiency of the battery, but also helps to improve the interfacial impedance, enhancing the kinetic performance and cycle stability of the battery. At the same time, by increasing the thickness of the arc region, the relationship between the radius of the arc region and the thickness of the wound core is regulated, thereby improving the problem of gas generation that is prone to occur during cycling or storage of the solid electrolyte. This is because when 2R / T≥0.9, the arc region has a certain stress release space, which can relieve the stress concentration problem in the arc region. The expansion of the battery basically does not affect the amount of electrolyte in the arc region, enabling the arc region to retain sufficient electrolyte, reducing the concentration difference of the electrolyte between the arc region and the straight region, thereby avoiding an increase in the overpotential in the arc region and preventing the decomposition of the CEI film to generate gas.

[0006] Therefore, while introducing the solid electrolyte, by regulating the relationship between the radius of the arc region and the thickness of the wound core, it is possible to not only improve the charge-discharge efficiency and kinetic performance of the battery, but also reduce the explosion risk brought about by the large amount of gas generated in the arc region that cannot be discharged in time, enhancing the cycle stability and safety performance of the battery.

[0007] The present invention provides a lithium-ion secondary battery, comprising a wound core formed by laminating and winding a positive electrode sheet, a separator, and a negative electrode sheet; the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer provided on at least one side of the negative electrode current collector, the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material; the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer provided on at least one side of the positive electrode current collector, the positive electrode active layer includes a positive electrode active material and a solid electrolyte; the wound core includes an arc region and a straight region connected to the arc region; the radius R of the arc region and the thickness T of the wound core satisfy: 0.9≤2R / T≤4 / π, where π is the ratio of the circumference of a circle to its diameter.

[0008] Through the above technical solutions, the present invention has at least the following advantages compared with the prior art:

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

[0010] (2) The battery of the present invention can effectively reduce the safety risks caused by gas generation.

[0011] The endpoints and any values within the ranges disclosed in this document are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this document. Description of the Drawings

[0012] Figure 1 Shown is a schematic cross-sectional view of a core in an example of the present invention.

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

[0014] Figure 3 Shown is a schematic view of the interface between the positive electrode tab and the first adhesive tape of the present invention.

[0015] Figure 4 Shown is a partial schematic view of a positive electrode sheet in an example of the present invention; wherein, Figure 4 (a) does not show the first adhesive tape, Figure 4 (b) shows the first adhesive tape on the basis of Figure 4 (a).

[0016] Figure 5 Shown is a schematic view of the structure of the tab adhesive in an example of the present invention. Detailed Description of the Invention

[0017] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0018] The present invention provides a lithium-ion secondary battery, which includes a core formed by laminating and winding a positive electrode sheet, a separator, and a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer provided on at least one side of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material. The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer provided on at least one side of the positive electrode current collector. The positive electrode active layer includes a positive electrode active material and a solid electrolyte. The core includes an arc region and a flat region connected to the arc region; the radius R of the arc region and the thickness T of the core satisfy: 0.9 ≤ 2R / T ≤ 4 / π, where π is the ratio of the circumference of a circle to its diameter, such as 0.9, 1, 1.1, 1.2, or 4 / π.

[0019] In the present invention, the radius R of the arc region and the thickness T of the core have their conventional meanings in the art. As Figure 1The following is a schematic structural diagram of a core in an example of the present invention. As can be seen from the figure, the core includes an arc region 10 and a flat region 20 connected to the 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 arc region refers to the shortest distance from the outermost side to the innermost side of the arc region in a direction perpendicular to the thickness direction of the core.

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

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

[0022] In the present invention, the ratio of the thickness of the positive electrode sheet located in the arc region to the thickness of the positive electrode sheet located in the flat region is 0.7 - 1.5, such as 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 located in the arc region to the thickness of the positive electrode sheet located in the flat region is 1.01 - 1.3.

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

[0025] When the ratio of the thickness of the positive electrode sheet in the arc region to the thickness of the positive electrode sheet in the straight region is within a specific range, the pores or space structures reserved in the arc region will increase the thickness of the arc region after winding. The increase in the thickness of the arc region can reserve sufficient space for the expansion of the battery during the cycling process, preventing the vicious cycle phenomenon of the decrease in the electrolyte concentration in the arc region, the increase in overpotential, the decomposition of CEI to generate gas, and the further reduction of the electrolyte due to oxidation caused by the battery expansion.

[0026] In one example, the thickness of the positive electrode sheet in the straight region is 20 μm - 150 μm, such as 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 Figure 2 Shown is a schematic cross-sectional detail view of a winding core in an example of the present invention. The square in the figure is an enlarged view of a part of the winding core. It can be seen from the figure that compared with the thickness in the straight region, the thicknesses of the positive electrode sheet and the negative electrode sheet at the arc are significantly increased. It should be noted that the change in the radius of the arc region is achieved by increasing the interlayer gap and particle gap of the active material in the arc region, rather than simply increasing the thickness of the electrode sheets (including positive and negative electrode sheets) at the arc.

[0028] In the present invention, the thickness of the positive electrode sheet in the arc region and the thickness of the positive electrode sheet in the straight region can be obtained by testing using conventional methods in the art. For example, 10 different sites are taken on the positive electrode sheets in the arc region and the straight region respectively, the thickness of each site is measured, and the average value is taken.

[0029] In the present invention, the ratio of the tap density of the positive electrode active layer in the arc region to the tap density of the positive electrode active layer in the straight region is 0.5 - 0.99, such as 0.5, 0.6, 0.7, 0.8, or 0.99.

[0030] In one example, the ratio of the tap density of the positive electrode active layer in the arc region to the tap density of the positive electrode active layer in the straight region is 0.65 - 0.85.

[0031] In one example, the tap density of the positive electrode active layer in the straight region is 2 g / cm 3 - 5 g / cm 3 , such as 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 in the arc region is less than that of the positive electrode active layer in the straight region, the pores or space structures reserved in the arc region will increase the thickness of the arc region after winding. The increase in the thickness of the arc region can reserve sufficient space for the expansion of the battery during the cycling process, preventing the vicious cycle phenomenon that the electrolyte concentration in the arc region is small, the overpotential increases, gases are generated due to the decomposition of CEI, and the electrolyte is further reduced due to oxidation.

[0033] In the present invention, the compaction density of the positive electrode active layer in the arc region and the compaction density of the positive electrode active layer in the straight region can be obtained by testing through conventional methods in the art. For example, a certain area of the positive electrode active layer is intercepted from the arc region and the straight region respectively, and the coating thickness is measured at 5 randomly selected sites. The mass of the intercepted positive electrode active layer sample is weighed. According to the measured average thickness and the coating mass, substituting into the formula: compaction density = coating mass / coating volume, the compaction density of the positive electrode active layer in the arc region and the straight region is calculated respectively.

[0034] In the present invention, the ratio of the areal density of the positive electrode active layer in the arc region to the areal density of the positive electrode active layer in the straight region is 0.6 - 1, such as 0.6, 0.7, 0.8, 0.9, or 1.

[0035] In one example, the ratio of the areal density of the positive electrode active layer in the arc region to the areal density of the positive electrode active layer in the straight region is 0.7 - 0.95.

[0036] In one example, the areal density of the positive electrode active layer in the straight region is 8 mg / cm 2 -25 mg / cm 2 , such as 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 invention, the areal density of the positive electrode active layer located in the arc region and the areal density of the positive electrode active layer located in the straight region can be obtained by testing with conventional methods in the art. For example, a certain area of the positive electrode active layer is intercepted from the arc region and the straight region respectively, the mass of the intercepted positive electrode active layer sample is weighed, and according to the measured area and the coating mass, substituting into the formula: areal density = coating mass / coating area, the areal density of the positive electrode active layer located in the arc region and the straight region is calculated respectively.

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

[0039] In one example, the cross-sectional pore ratio of the positive electrode sheet located in the straight region is 1% - 3%, for example, 1%, 1.5%, 2%, 2.5% or 3%.

[0040] In the present invention, the ratio of the cross-sectional pore ratio of the positive electrode sheet located in the arc region to the cross-sectional pore ratio of the positive electrode sheet located in the straight region can be obtained by testing with conventional methods in the art. For example, the cross-sectional image of the positive electrode sheet is obtained by scanning electron microscopy (SEM) or X-ray tomography, and then the image is processed to obtain the cross-sectional pore ratio at the corresponding position.

[0041] In the present invention, the ratio of the thickness of the negative electrode sheet located in the arc region to the thickness of the negative electrode sheet located in the straight 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 one example, the thickness of the negative electrode sheet located in the straight region is 20 μm - 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 invention, the ratio of the tap density of the negative electrode active layer located in the arc region to the tap density of the negative electrode active layer located in the straight region is 0.5 - 0.99, for example, 0.5, 0.6, 0.7, 0.8, or 0.99.

[0044] In one example, the ratio of the tap density of the negative electrode active layer located in the arc region to the tap density of the negative electrode active layer located in the straight region is 0.65 - 0.95.

[0045] In one example, the tap density of the negative electrode active layer located in the straight 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 invention, the ratio of the areal density of the negative electrode active layer located in the arc region to the areal density of the negative electrode active layer located in the straight region is 0.6 - 1, for example, 0.6, 0.7, 0.8, 0.9, or 1.

[0047] In one example, the areal density of the negative electrode active layer located in the straight 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 invention, the ratio of the porosity ratio of the cross-section of the negative electrode sheet located in the arc region to the porosity ratio of the cross-section of the negative electrode sheet located in the straight region is 1.5 - 2, for example, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.

[0049] In one example, the porosity ratio of the cross-section of the negative electrode sheet located in the straight region is 1% - 3%, for example, 1%, 1.5%, 2%, 2.5%, or 3%.

[0050] In the present invention, the testing methods for the thickness and cross-sectional porosity ratio of the negative electrode sheet located in the straight region or the arc region, as well as the areal density and tap density of the negative electrode active layer, are the same as those of the positive electrode sheet, and will not be elaborated here.

[0051] In the present invention, 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 one 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-discharge cycle, the greater the stress generated in the arc region, resulting in a greater reduction in the electrolyte volume in the arc region, causing the kinetics in the arc region to deteriorate, increasing the overpotential in the arc region, leading to the decomposition of the CEI film to generate gas, and the decomposition of the CEI film will also cause the electrolyte to be oxidized, resulting in a further reduction in the electrolyte volume, and a large amount of gas accumulates in the arc region. 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 generation in the arc region. When the two satisfy a specific relationship, it can make the stress release space reserved in the arc region match the volume expansion of silicon, thereby further alleviating the stress concentration problem in the arc region, alleviating the reduction in the electrolyte volume in the arc region, reducing the concentration difference of the electrolyte between the arc region and the straight region, and further improving the problem of gas generation in the arc region; and by limiting the relationship between the two, the stress release space is not too large, so as not to affect the electrical contact inside the battery.

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

[0055] In one example, 3% ≤ c ≤ 15%.

[0056] In the present invention, the content c of elemental silicon in the negative electrode active layer can be obtained by testing through conventional methods in the art. For example, after discharging the battery to 0% SOC, disassemble and take out the negative electrode sheet. Soak it in dimethyl carbonate (DMC) solvent for 12 h, then rinse it with DMC solvent to remove the lithium salt attached to the negative electrode sheet. After drying, heat-treat the negative electrode sheet at 400 °C in an inert atmosphere for 2 h (for example, in a tube furnace under a nitrogen or argon atmosphere), and the negative electrode active layer can be peeled off from the negative electrode current collector. Collect the negative electrode active layer as a test sample. Use a thermogravimetric analyzer (such as TGA 550 thermogravimetric analyzer), with the test sample amount being 5 mg - 15 mg. Under an air or oxygen atmosphere, heat it from room temperature (25 °C) to 900 °C at a heating rate of 10 °C / min and keep it at 900 °C for 40 min, so that while the non-silicon components in the negative electrode active layer volatilize, silicon can be fully oxidized to silicon dioxide. Weigh the mass of the residual substance, and the content of elemental silicon in the negative electrode active layer can be obtained through the following calculation formula: Content of elemental silicon in the negative electrode active layer = 7 × mass of the residual substance / (15 × mass of the test sample).

[0057] In the present invention, the lithium-ion secondary battery further includes a casing; the positive electrode sheet further includes a positive electrode tab and a tab glue disposed on the surface of the positive electrode tab. The negative electrode sheet further includes a negative electrode tab and the tab glue disposed on the surface of the negative electrode tab. The tab glue includes a first glue layer, a second glue layer, and a third glue layer which are stacked in sequence. The first glue layer contacts the casing, the third glue layer contacts the positive electrode tab, and the second glue layer is located between the first glue layer and the third glue layer. As Figure 5 shown is a schematic structural diagram of the tab glue in an example of the present invention. As can be seen from the figure, the tab glue includes a first glue layer 7-1, a second glue layer 7-2, and a third glue layer 7-3 which are stacked in sequence.

[0058] In an example, the first glue layer contacts the casing, the third glue layer contacts the negative electrode tab, and the second glue layer is located between the first glue layer and the third glue layer.

[0059] In the present invention, the melting point of the first glue 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 glue 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 glue 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 undergoes safety tests such as furnace temperature and overcharge, or the battery is short-circuited due to abuse, it will cause thermal runaway of the battery, releasing a large amount of heat, thereby significantly increasing the internal temperature of the battery and further exacerbating the decomposition of the CEI film to generate gas. Therefore, it is relatively reliable to design the tab glue to exhaust gas in time to ensure the safety performance of the battery. The present invention applies a tab glue with three glue layers having different melting points, and the melting points of the first glue layer and the third glue layer are the same, both lower than the melting point of the second glue layer. When the battery undergoes 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 outer shell, providing an outlet for the gas generated inside the battery and preventing the battery from exploding due to excessive air pressure.

[0061] Specifically, the melting points of the first glue layer and the third glue layer are both 100°C - 130°C. The first glue layer and the third glue layer with melting points within the above range can melt in time when the internal temperature of the battery rises, causing the overall sealing interface tension between the outer shell and the tab to decay, making the interface easier to open, providing an exhaust channel for the battery, improving safety, and avoiding accidents such as fire and explosion caused by the inability to discharge a large amount of accumulated gas in time. In addition, it is necessary to coordinately control the melting point of the second glue layer so that the melting point of the second glue layer is 130°C - 160°C. The second glue layer with a melting point within the above range can play a good blocking role, prevent over-melting, avoid battery short-circuit; and ensure that there is no risk of interface segregation during the heat sealing process of the tab glue, avoiding battery leakage and swelling.

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

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

[0064] In the present invention, the thickness h1 of the positive tab, the thickness h3 of the negative tab, and the thickness h2 of the tab glue can be obtained by testing through conventional methods in the art. For example, 5 different sites are taken on the positive tab, the negative tab, and the tab glue respectively, and the thickness of each site is measured, and the average value is taken.

[0065] In the present invention, the size of the tab glue in the length direction of the positive electrode sheet (i.e., the width of the tab glue) is 5 mm - 20 mm, such as 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 or 20 mm. The size of the tab glue in the length direction of the negative electrode sheet (i.e., the width of the tab glue) is 5 mm - 20 mm, such as 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 or 20 mm.

[0066] In the present invention, the ratio of the size of the tab glue in the length direction of the positive electrode sheet to the size w2 of the positive tab in the length direction of the positive electrode sheet is 1.1 - 2, such as 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2. The ratio of the size of the tab glue in the length direction of the negative electrode sheet to the size w4 of the negative tab in the length direction of the negative electrode sheet is 1.1 - 2, such as 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2.

[0067] In the present invention, the positive electrode sheet further includes a positive tab welding area and a first adhesive tape, the positive tab is located in the positive tab welding area, and the first adhesive tape covers the positive tab welding area. As Figure 4 shown is a partial schematic diagram of the positive electrode sheet in an example of the present invention; among them, Figure 4 (a) does not show the first adhesive tape, Figure 4 (b) shows the first adhesive tape on the basis of Figure 4 (a). It can be seen from the figure that the positive electrode sheet 1 includes a positive tab 4, a positive tab welding area 6 and a first adhesive tape 5, the positive tab 4 is located in the positive tab welding area 6, and the first adhesive tape 5 covers the positive tab welding area 6.

[0068] In the present invention, the size of the first adhesive tape in the length direction of the positive electrode sheet is w1, the size of the positive tab in the length direction of the positive electrode sheet is w2, w1 is 15 mm - 50 mm (such as 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm or 50 mm), and w2 is 2 mm - 10 mm (such as 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm).

[0069] In the present invention, w1, w2 and the arc radius r1 of the layer where the positive electrode tab is located satisfy: w1 = k1×w2 + π×r1, where 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 Figure 3 Shown is a schematic diagram of the interface between the positive electrode tab and the first adhesive tape of the present invention. As can be seen from the figure, the core includes a positive electrode sheet 1, a negative electrode sheet 2 and a separator 3. The positive electrode sheet 1 has a positive electrode tab welding area and a positive electrode tab 4 located on the positive electrode tab welding area. The first adhesive tape 5 covers the positive electrode tab welding area, and the size of the first adhesive tape in the length direction of the positive electrode sheet is w1, and the size of the positive electrode tab 4 in the length direction of the positive electrode sheet is w2. The arc radius of the layer where the positive electrode tab 4 is located is r1.

[0071] In the present invention, the ratio of the distance from the first end of the positive electrode tab to the arc area to the arc radius r1 of the layer where the positive electrode 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 electrode tab close to the arc area.

[0072] In the present invention, the first adhesive tape covers at least part of the arc area.

[0073] In one example, the first adhesive tape completely covers the arc area.

[0074] By adjusting the setting positions of the positive electrode tab and the first adhesive tape, the first adhesive tape can pass through the arc area (partially cover the arc area or completely cover the arc area). Since the positive electrode tab is close to the arc area and the first adhesive tape passes through the arc area, it helps the gas generated in the arc area to burst and relieve pressure through the tab adhesive, thereby improving the safety performance of the battery.

[0075] In the present invention, the negative electrode sheet further includes a negative electrode tab welding area and a second adhesive tape. The negative electrode tab is located on the negative electrode tab welding area, and the second adhesive tape covers the negative electrode tab welding area.

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

[0077] In the present invention, w3, w4 and the arc radius r2 of the layer where the negative electrode tab is located satisfy: w3 = k2×w3 + π×r2, where 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 invention, the ratio of the distance from the first end of the negative electrode tab to the arc region to the arc radius r2 of the layer where the negative electrode 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 electrode tab close to the arc region.

[0079] In the present invention, the second adhesive tape covers at least a part of the arc region.

[0080] In one example, the second adhesive tape completely covers the arc region.

[0081] By adjusting the setting positions of the negative electrode tab and the second adhesive tape, the second adhesive tape can pass through the arc region (partially covering the arc region or completely covering the arc region). Since the negative electrode tab is close to the arc region and the second adhesive tape passes through the arc region, it helps the gas generated in the arc region to burst and release pressure through the tab adhesive, thereby improving the safety performance of the battery.

[0082] In the present invention, the mass content c2 of the solid electrolyte in the positive electrode active layer and the 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 one example, 0.06 ≤ R×c2 ≤ 0.45.

[0084] The mass content of the solid electrolyte is related to R: when R is larger, the amount of the solid electrolyte can be appropriately reduced, while when R is smaller, the amount of the solid electrolyte should be appropriately increased. This is because: when R is larger, the influence of battery swelling on the arc region is smaller, and the arc region retains sufficient electrolyte, avoiding the phenomenon that the overpotential in the arc region increases and causes the decomposition of CEI to generate gas; while when R is smaller, the influence of battery swelling on the arc region increases, resulting in the electrolyte in the arc region being extruded into the flat region, reducing the electrolyte concentration in the arc region, increasing the overpotential, decomposing CEI to generate gas, and then causing the electrolyte to be oxidized and the amount of electrolyte to further decrease, resulting in a vicious cycle. At this time, by increasing the amount of the solid electrolyte, the interfacial impedance of the active particles in the arc region can be further improved, reducing the overpotential in the arc region, thereby avoiding the decomposition of CEI to generate gas.

[0085] In the present invention, the solid electrolyte includes at least one of lithium aluminum titanium phosphate oxide, lithium lanthanum zirconium tantalum oxide, and lithium lanthanum titanium oxide. The lithium aluminum titanium phosphate oxide may be a superionic conductor type lithium aluminum titanium phosphate oxide with the molecular formula Li 1+x Al x Ti 2-x (PO4)3, where 0 < x ≤ 0.5. The lithium lanthanum zirconium tantalum oxide may be a garnet type lithium lanthanum zirconium tantalum oxide with the molecular formula Li 7-y La3Zr 2-y Ta y O 12 , where 0 ≤ y ≤ 0.5. The lithium lanthanum titanium oxide may be a perovskite type lithium lanthanum titanium oxide with the molecular formula Li 3z La 2 / 3-z TiO3, where 0 < z ≤ 0.2.

[0086] In one example, the solid electrolyte includes lithium aluminum titanium phosphate (LATP).

[0087] In the present invention, the average particle size of the solid 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 one example, the average particle size of the solid electrolyte is 0.05 μm - 2 μm.

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

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

[0091] In the present invention, the median particle size Dv50 of the solid electrolyte is 0.02 μm - 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 electrolyte can be obtained by testing through conventional methods in the art, such as a laser particle size analyzer.

[0092] In the present invention, the mass content c2 of the solid electrolyte in the positive electrode active layer is 0.1% - 5%, for example, 1%, 2%, 3%, 4% or 5%.

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

[0094] In the present invention, the content c of elemental silicon in the negative electrode active layer and the content c2 of the solid electrolyte in the positive electrode 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 electrode active layer is too large, the greater the volume expansion of the battery during the charge and discharge cycle, the greater the stress generated on the arc region, resulting in a reduction in the amount of electrolyte in the arc region, easily causing a decrease in the electrolyte concentration in the arc region, an increase in overpotential, and a vicious cycle of continuous decomposition and gas generation of CEI. At this time, by appropriately adding a solid electrolyte, the problem of CEI decomposition and gas generation caused by a large overpotential in the arc region can be effectively alleviated. However, the addition amount of the solid electrolyte should not be too much, otherwise it will cause an interfacial impedance. Therefore, it is necessary to control the ratio of the content c2 of the solid electrolyte to the content c of elemental silicon in the negative electrode active layer within a suitable range, which can not only ensure that the content of elemental silicon in the negative electrode active layer is not excessive, achieving the purpose of suppressing negative electrode expansion and improving the energy density of the battery, but also avoiding the gas generation problem in the arc region caused by the electrolyte concentration difference between the arc region and the flat region, thereby enhancing the safety performance of the battery.

[0097] In the present invention, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium nickel cobalt manganese aluminate, lithium manganate, lithium nickel manganate, lithium nickelate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate and lithium-rich manganese-based materials. The negative electrode active material may further include a carbon-based material, and the carbon-based material includes, for example, at least one of artificial graphite, natural graphite, mesocarbon microbead graphite, soft carbon and hard carbon.

[0098] In the present invention, the lithium ion secondary battery further includes an electrolyte. The electrolyte may optionally include propyl propionate. The term "optionally" means that the electrolyte may or may not include propyl propionate.

[0099] In the present invention, 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 one example, the mass content of propyl propionate in the electrolyte is ≤ 5%.

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

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

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

[0104] In a battery with a solid electrolyte in the positive electrode, when the overpotential of the positive electrode is large, the CEI film decomposes to generate gas. At this time, the electrolyte will be oxidized to form a new CEI film. When the content of propyl propionate is high, propyl propionate easily reacts with the solid electrolyte and decomposes to generate gases such as carbon dioxide, ethane, and propane, and a stable CEI film cannot be formed, resulting in a continuous increase in the gas generation amount. Therefore, when the content of propyl propionate in the electrolyte is low, the gas generation amount will be significantly reduced. Therefore, by regulating the composition of the electrolyte and controlling the content of propyl propionate in the electrolyte formulation, a stable CEI film can be formed on the surface of the positive electrode sheet, reducing the safety problem of gas generation in the battery.

[0105] In the present invention, the electrolyte further includes at least one of a lithium salt, a non-aqueous solvent, an additive, and a diluent; the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorophosphate, lithium difluoro(bis(oxalato))phosphate, or lithium tetrafluoro(oxalato)phosphate. The non-aqueous solvent includes carbonate substances, and the carbonate substances include at least one of ethylene carbonate (EC), vinylene carbonate, propylene carbonate (PC), propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, and fluoroethylene carbonate. The non-aqueous solvent further includes 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone, or diethyl sulfone. The additive includes at least one of fluoroethylene carbonate (FEC), vinylene carbonate, vinyl ethylene carbonate, ethylene sulfate (DTD), propylene sulfate, ethylene sulfite, 1,3-propane sultone (PS), 1,3-propylene sultone, cyclic quaternary ammonium sulfonate, succinic anhydride, succinonitrile (SN), adiponitrile, 1,3,6-hexanetricarbonitrile (HTCN), tris(trimethylsilyl) phosphate, or tris(trimethylsilyl) borate. The diluent includes 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 triglyme (TEP).

[0106] In the present invention, the silicon-based material includes, for example, at least one of elemental silicon, silicon carbide, silicon oxide, and silicon alloy.

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

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

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

[0110] In one 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 invention, the width of the recess may be 0.2mm-8mm, such as 0.2mm, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm or 8mm. The depth of the recess may be 3μm-40μm, such as 3μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm or 40μm. The spacing of the recesses may be 0.5mm-8mm, such as 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm or 8mm.

[0112] In the present invention, 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 with conventional methods in the art, for example, using SEM or 3D profiler to measure the depth of at least 20 or all the recesses on one side surface of the positive electrode sheet, and taking the average value.

[0113] In the present invention, the shape of the projection of the concave portion in the thickness direction of the positive electrode sheet is not limited, and it can be circular or rectangular. When the shape of the projection of the concave portion in the thickness direction of the positive electrode sheet is circular, the width of the concave portion is the diameter of the circle; when the shape of the projection of the concave portion in the thickness direction of the positive electrode sheet is non-circular, the width of the concave portion is the equivalent diameter of the circle with the same area as the non-circular shape. The width of the concave portion and the spacing between the concave portions can be obtained by conventional methods in the art. For example, through SEM, at least 10 concave portions are selected on the surface of the positive electrode sheet, the width of each concave portion is measured, and the average value is taken; at least 10 groups of adjacent concave portions are selected on the surface of the positive electrode sheet, the shortest distance between the edges of each group of concave portions is measured, and the average value is taken.

[0114] In the present invention, the height of the convex portion can be 2 μm - 40 μm, such as 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm or 40 μm. The width of the convex portion can be 0.2 mm - 8 mm, such as 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 between the convex portions can be 0.5 mm - 8 mm, such as 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm or 8 mm.

[0115] In the present invention, the height of the convex portion refers to the vertical distance from the highest point on the convex portion 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 profiler, the height of at least 20 convex portions or all convex portions on one side surface of the positive electrode sheet is measured, and the average value is taken.

[0116] In the present invention, the shape of the projection of the convex portion in the thickness direction of the positive electrode sheet is not limited, and it can be circular or rectangular. When the shape of the projection of the convex portion in the thickness direction of the positive electrode sheet is circular, the width of the convex portion is the diameter of the circle; when the shape of the projection of the convex portion in the thickness direction of the positive electrode sheet is non-circular, the width of the convex portion is the equivalent diameter of the circle with the same area as the non-circular shape. The width of the convex portion and the spacing between the convex portions can be obtained by conventional methods in the art. For example, through SEM, at least 10 convex portions are selected on the surface of the positive electrode sheet, the width of each convex portion is measured, and the average value is taken; at least 10 groups of adjacent convex portions are selected on the surface of the positive electrode sheet, the shortest distance between the edges of each group of convex portions (i.e., the shortest distance between the orthographic projections formed by each group of convex portions on the surface of the positive electrode sheet) is measured, and the average value is taken.

[0117] In the present invention, the thickness of the positive electrode sheet in the arc area and the straight area can also be controlled by adjusting the size of the concave and convex parts on the positive electrode sheet, so that the radius R of the arc area and the thickness T of the winding core satisfy: 0.9≤2R / T≤4 / π.

[0118] It should be noted that the numerical expressions such as "first" and "second" in the present invention are only used to distinguish different substances or usages, and do not represent the difference in order.

[0119] The present invention will be described in detail below by way of examples. The examples described in the present invention are only a part of the examples of the present invention, rather than all of the examples. Based on the examples in the present invention, all other examples obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0120] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

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

[0122] Example 1

[0123] The lithium ion secondary battery was prepared as follows:

[0124] (1) Preparation of positive electrode sheet

[0125] Evenly mix lithium cobalt oxide, lithium aluminum titanium phosphate (average particle size of 1.1 μm), carbon nanotubes and polyvinylidene fluoride in a mass ratio of 96.3:1.2:1.1:1.4, add N-methylpyrrolidone (NMP), and stir thoroughly in a stirring tank to prepare a positive electrode slurry; transfer the above positive electrode slurry evenly to the surface of the aluminum foil through an extrusion coating device, and then bake it in an oven at 80°C for 10 minutes, and reel it up with a reel after the solvent is completely removed; then unwind and compact the electrode piece on a variable roller gap roller press, and set the variable roller frequency according to the length of the electrode piece to adjust the radius R of the arc area. Note that the variable roller action stops when the rolling equipment runs to the single-sided area. The preparation of positive electrode pieces with the same surface density and different compaction densities can be achieved by continuously running the above variable roller action;

[0126] The rolled electrode sheet is cut into pieces according to the designed width size along the TD direction by a slitting device, and then the small roll electrode sheet is rolled up after the abnormality is eliminated by the charge coupled device image sensor (CCD) detection; the positive electrode ear (the dimension w2 of the positive electrode ear in the length direction of the positive electrode sheet is 6 mm, and the thickness h1 of the positive electrode ear is 40 μm) is welded and the first adhesive tape (acrylic adhesive tape, the dimension w1 in the length direction of the positive electrode sheet is 25.8 mm) is pasted; and the positive electrode sheet is cut;

[0127] Among them, the thickness of the positive electrode sheet in the arc region is 88 μm, the thickness of the positive electrode sheet in the straight region is 81 μm, and the ratio of the two is 1.09; the compaction density of the positive electrode active layer in the arc region is 3.21 g / cm 3 , and the compaction density of the positive electrode active layer in the straight region is 3.89 g / cm 3 , and the ratio of the two is 0.825; the areal density of the positive electrode active layer in the arc region is 12.5 mg / cm 2 , and the areal density of the positive electrode active layer in the straight 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 arc region is 2.89%, the cross-sectional porosity ratio of the positive electrode sheet in the straight 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] Mix artificial graphite, silicon carbide, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid evenly according to a mass ratio of 84.3:12.7:0.45:1.5:0.45:0.6, add deionized water, and stir well in a stirring tank to make a negative electrode slurry; transfer the above negative electrode slurry to the surface of the copper foil through an extrusion coating device, then bake it in an oven at 120 °C for 5 min, and wind it up with a reel after completely removing the solvent; then unwind and compact the electrode sheet on a variable roll gap rolling press, and set the variable roll frequency according to the length of the electrode segment to control the radius R of the arc region. Note that when the rolling equipment runs to the single-sided region, stop the variable roll action. By continuously running the above variable roll action, the preparation of the negative electrode sheet with the same areal density and different compaction densities can be achieved;

[0130] The rolled electrode sheet is slit along the TD direction according to the designed width dimension by a slitting device, and after excluding abnormalities through CCD detection, it is wound into small rolls of electrode sheets; the negative electrode tab (the dimension 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 tape (acrylic adhesive tape, the dimension w3 of which in the length direction of the negative electrode sheet is 25.8 mm) is pasted; then it is cut to obtain the negative electrode sheet;

[0131] Among them, the thickness of the negative electrode sheet in the arc region is 93.8 μm, the thickness of the negative electrode sheet in the straight 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 arc region is 1.1 g / cm 3 , and the compaction density of the negative electrode active layer in the straight region is 1.63 g / cm 3 , and the ratio of the two is 0.67; the areal density of the negative electrode active layer in the arc region is 4.9 mg / cm 2 , and the areal density of the negative electrode active layer in the straight region is 6.4 mg / cm2 The ratio of the two is 0.77; the cross-sectional pore ratio of the negative electrode sheet in the arc region is 2.8%, and the cross-sectional pore ratio of the negative electrode sheet in the straight 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 a glove box filled with argon (moisture < 1 ppm, oxygen content < 1 ppm), EC, PC, and EP are mixed into a homogeneous non-aqueous solvent in a mass ratio of 1:1:3. Then, 14% of lithium salt (lithium hexafluorophosphate), 5% of additive (FEC), 3% of additive (PS), 2.5% of additive (SN), 2% of additive (HTCN), and 0.5% of additive (DTD) based on the total mass of the electrolyte are slowly added thereto. After stirring evenly, the electrolyte is obtained;

[0134] Among them, 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) are aligned at the head, and then wound into a roll-like structure at a constant speed according to the designed size to obtain a core; the electrolyte prepared in step (3) is added; ear glue is provided between the positive electrode tab and the outer shell and between the negative electrode tab and the outer shell (the first glue layer contacts the outer shell, the third glue layer contacts the positive electrode tab / negative electrode tab, the second glue layer is located between the first glue layer and the third glue layer, the melting point of the first glue layer is 116 °C, the melting point of the second glue layer is 148 °C, the melting point of the third glue layer is 116 °C, the thickness h2 of the ear glue is 20 μm, and the size of the ear glue in the length direction of the positive electrode sheet / negative electrode sheet is 10 mm); after hot pressing, the radius R of the arc region and the thickness T of the core are observed and measured by X-Ray or a computed tomography scanner; it is aged for 24 h at room temperature (25 °C) and for 8 h at high temperature (65 °C) to fully infiltrate the electrolyte; it is transferred to a formation device, the positive electrode tab and the negative electrode tab are connected to the charging port, and the battery is charged and pressurized to activate the battery core under the conditions of a temperature of 80 °C and a pressure of 510 kgf per battery, forming a secondary lithium-ion battery that can be charged and discharged externally;

[0137] Among them, the radius R of the arc area 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 arc radius r1 of the layer where the positive tab is located is 3.6 mm; the arc radius r2 of the layer where the negative tab is located is 3.6 mm; k1 is 2.42; k2 is 2.42; the distance from the first end of the positive tab to the arc area is 4.5 mm, and the ratio of the distance from the first end of the positive tab to the arc area to r1 is 1.25; the distance from the first end of the negative tab to the arc area is 4.5 mm, and the ratio of the distance from the first end of the negative tab to the arc area to r2 is 1.25; the first adhesive tape and the second adhesive tape both completely cover the arc area; 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 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 tab in the length direction of the negative electrode sheet is 1.67.

[0138] Example 2

[0139] Prepare a lithium-ion secondary battery according to the following method:

[0140] (1) Prepare the positive electrode sheet

[0141] Mix lithium cobaltate, lithium titanium aluminum phosphate (average particle size of 0.05 μm), carbon nanotubes and polyvinylidene fluoride evenly according to a mass ratio of 94.7:2.8:1.1:1.4, add N-methylpyrrolidone (NMP), and stir well in a stirring tank to make a positive electrode paste; transfer the above positive electrode paste evenly onto the surface of the aluminum foil through an extrusion coating device, then bake it in an oven at 80 °C for 10 min, and wind it up with a reel after completely removing the solvent; then unwind and compact the electrode sheet on a variable roll gap roller press, set the variable roll frequency according to the length of the electrode segment to control the radius R of the arc area. Note that when the roller press runs to the single-sided area, stop the variable roll action. By continuously running the above variable roll action, the preparation of the positive electrode sheet with the same surface density and different compaction densities can be achieved;

[0142] The rolled electrode sheet is slit along the TD direction according to the designed width dimension by a slitting device, and then wound into small rolls of electrode sheets after detecting and excluding abnormalities through a charge-coupled device image sensor (CCD); weld the positive tab (the size w2 of the positive tab in the length direction of the positive electrode sheet is 10 mm, and the thickness h1 of the positive tab is 60 μm), and paste the first adhesive tape (acrylic adhesive tape, the size w1 in the length direction of the positive electrode sheet is 21.2 mm); then cut to obtain the positive electrode sheet;

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

[0144] (2) Preparation of negative electrode sheet

[0145] Mix artificial graphite, silicon carbon, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid evenly according to a mass ratio of 84.3:12.7:0.45:1.5:0.45:0.6, add deionized water, and stir well in a stirring tank to make a negative electrode slurry; transfer the above negative electrode slurry to the surface of a copper foil through an extrusion coating device, then bake it in an oven at 120 °C for 5 minutes, and wind it up with a reel after completely removing the solvent; then unwind and compact the electrode sheet on a variable roll gap rolling press, and set the variable roll frequency according to the length of the electrode segment to control the radius R of the arc area. Note that when the rolling equipment runs to the single-sided area, stop the variable roll action. By continuously running the above variable roll action, the preparation of negative electrode sheets with the same areal density and different tap densities can be achieved;

[0146] The rolled electrode sheet is slit along the TD direction according to the designed width dimension by a slitting device, and after excluding abnormalities through CCD detection, it is wound into small roll electrode sheets; the negative electrode tab (the size w4 of the negative electrode tab in the length direction of the negative electrode sheet is 10 mm, and the thickness h3 of the negative electrode tab is 60 μm) is welded, and the second adhesive tape (acrylic adhesive tape, the size w3 of which in the length direction of the negative electrode sheet is 21.2 mm) is pasted; then it is cut to obtain the negative electrode sheet;

[0147] Among them, the thickness of the negative electrode sheet in the arc area is 78 μm, and the thickness of the negative electrode sheet in the straight area is 74.6 μm, and the ratio of the two is 1.05; the tap density of the negative active material layer in the arc area is 1.37 g / cm 3 , and the tap density of the negative active material layer in the straight area is 1.49 g / cm 3 , and the ratio of the two is 0.92; the areal density of the negative active material layer in the arc area is 5 mg / cm 2 , and the areal density of the negative active material layer in the straight area is 5.2 mg / cm 2, the ratio of the two is 0.96; the cross-sectional pore ratio of the negative electrode sheet in the arc region is 2.49%, and the cross-sectional pore ratio of the negative electrode sheet in the straight region is 1.62%, and the ratio of the two is 1.54; the content c of elemental silicon in the negative electrode active layer is 7%.

[0148] (3) Preparation of electrolyte

[0149] In a glove box filled with argon (moisture < 1 ppm, oxygen content < 1 ppm), EC, PC, and EP are mixed into a uniform non-aqueous solvent in a mass ratio of 1:1:3. Slowly add 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. After stirring evenly, the electrolyte is obtained;

[0150] Among them, the content of propyl propionate in the electrolyte is 0%.

[0151] (4) Preparation of battery

[0152] Align 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 head of the negative electrode sheet prepared in step (2), and then wind them evenly into a roll structure at a constant speed according to the designed size to obtain a core; add the electrolyte prepared in step (3); set ear glue between the positive electrode tab and the outer shell and between the negative electrode tab and the outer shell (the first glue layer contacts the outer shell, the third glue layer contacts the positive electrode tab / negative electrode tab, the second glue layer is located between the first glue layer and the third glue layer, the melting point of the first glue layer is 102 °C, the melting point of the second glue layer is 133 °C, the melting point of the third glue layer is 102 °C, the thickness h2 of the ear glue is 16 μm, and the size of the ear glue in the length direction of the positive electrode sheet / negative electrode sheet is 12 mm); after hot pressing, observe and measure the radius R of the arc region and the core thickness T using X-Ray or a computed tomography scanner; age at room temperature (25 °C) for 24 h and at high temperature (65 °C) for 8 h to fully infiltrate the electrolyte; transfer to a forming device, connect the positive electrode tab and the negative electrode tab to the charging port, and charge and pressurize the battery at a temperature of 80 °C and a pressure of 510 kgf / battery to activate the battery core, forming a secondary lithium-ion battery that can be charged and discharged externally;

[0153] Among them, the radius R of the arc area 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 arc radius r1 of the layer where the positive tab is located is 1.9 mm; the arc radius r2 of 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 arc area is 1.5 mm, and the distance from the first end of the negative tab to the arc area is 1.5 mm; the ratio of the distance from the first end of the positive tab to the arc area to r1 is 0.79; the ratio of the distance from the first end of the negative tab to the arc area to r2 is 0.79; the first adhesive tape and the second adhesive tape both completely cover the arc area; 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 electrode sheet to the size of the positive tab in the length direction of the positive electrode sheet is 1.2, 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 tab in the length direction of the negative electrode sheet is 1.2.

[0154] Example 3

[0155] Prepare a lithium-ion secondary battery according to the following method:

[0156] (1) Prepare the positive electrode sheet

[0157] Mix lithium cobaltate, lithium titanium aluminum phosphate (average particle size of 1.93 μm), carbon nanotubes and polyvinylidene fluoride evenly according to a mass ratio of 93.3:4.2:1.1:1.4, add N-methylpyrrolidone (NMP), and stir well in a stirring tank to make a positive electrode slurry; transfer the above positive electrode slurry evenly onto the surface of the aluminum foil through an extrusion coating device, then bake it in an oven at 80 °C for 10 min, and wind it up with a reel after completely removing the solvent; then unwind and compact the electrode sheet on a variable roll gap rolling press, and set the variable roll frequency according to the length of the electrode segment to control the radius R of the arc area. Note that when the rolling equipment runs to the single-sided area, stop the variable roll action. By continuously running the above variable roll action, the preparation of the positive electrode sheet with the same surface density and different compaction densities can be achieved;

[0158] The rolled electrode sheet is slit along the TD direction according to the designed width dimension by a slitting device, and then wound into a small roll of electrode sheet after being detected and abnormal removed by a charge-coupled device image sensor (CCD); perform welding of the positive tab (the size w2 of the positive tab in the length direction of the positive electrode sheet is 8 mm, and the thickness h1 of the positive tab is 80 μm) and paste the first adhesive tape (acrylic adhesive tape, the size w1 in the length direction of the positive electrode sheet is 39.7 mm); then cut to obtain the positive electrode sheet;

[0159] Among them, the thickness of the positive electrode sheet located in the arc area is 120 μm, the thickness of the positive electrode sheet located in the flat area is 108 μm, and the ratio of the two is 1.11; the compaction density of the positive active layer located in the arc area is 3.39 g / cm3 , the tap density of the positive active material layer located in the straight area is 4.1 g / cm 3 , and the ratio of the two is 0.827; the areal density of the positive active material layer located in the arc area is 19 g / cm 2 , and the areal density of the positive active material layer located in the straight area is 20.5 g / cm 2 , and the ratio of the two is 0.93; the cross-sectional porosity ratio of the positive electrode sheet located in the arc area is 2.56%, and the cross-sectional porosity ratio of the positive electrode sheet located in the straight area is 1.68%, and the ratio of the two is 1.524; c2 is 4.2%.

[0160] (2) Preparation of the negative electrode sheet

[0161] Mix artificial graphite, silicon carbide, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose and polyacrylic acid evenly according to the mass ratio of 84.3:12.7:0.45:1.5:0.45:0.6, add deionized water, and stir well in a stirring tank to make a negative electrode slurry; transfer the above negative electrode slurry to the surface of the copper foil through an extrusion coating equipment, and then bake it in an oven at 120 °C for 5 minutes. After completely removing the solvent, wind it up with a reel; then unwind and compact the electrode sheet on a variable roll gap roll press, and set the variable roll frequency according to the length of the electrode segment to control the radius R of the arc area. Note that when the roll pressing equipment runs to the single-sided area, stop the variable roll action. By continuously running the above variable roll action, the preparation of the negative electrode sheet with the same areal density and different tap densities can be realized;

[0162] The rolled electrode sheet is slit along the TD direction according to the designed width dimension by a slitting equipment, and after excluding abnormalities through CCD detection, it is wound into a small roll of electrode sheet; the negative electrode tab (the dimension w4 of the negative electrode tab in the length direction of the negative electrode sheet is 8 mm, and the thickness h3 of the negative electrode tab is 80 μm) is welded and the second adhesive tape (acrylic adhesive tape, the dimension w3 of which in the length direction of the negative electrode sheet is 39.7 mm) is pasted; then it is cut to obtain the negative electrode sheet;

[0163] Among them, the thickness of the negative electrode sheet located in the arc area is 132 μm, and the thickness of the negative electrode sheet located in the straight area is 120 μm, and the ratio of the two is 1.1; the tap density of the negative active material layer located in the arc area is 1.38 g / cm 3 , and the tap density of the negative active material layer located in the straight area is 1.71 g / cm 3 , and the ratio of the two is 0.81; the areal density of the negative active material layer located in the arc area is 8.4 mg / cm 2 , and the areal density of the negative active material layer located in the straight area is 9.45 g / cm 2, the ratio of the two is 0.89; the cross-sectional pore ratio of the negative electrode sheet in the arc region is 2.42%, and the cross-sectional pore ratio of the negative electrode sheet in the straight 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 a glove box filled with argon (moisture < 1 ppm, oxygen content < 1 ppm), EC, PC, and EP are mixed into a homogeneous non-aqueous solvent in a mass ratio of 1:1:3. Then, 14% (by total mass of the electrolyte) of lithium salt (lithium hexafluorophosphate), 5% of additive (FEC), 3% of additive (PS), 2.5% of additive (SN), 2% of additive (HTCN), and 0.5% of additive (DTD) are slowly added thereto. After stirring evenly, the electrolyte is obtained;

[0166] Among them, the content of propyl propionate in the electrolyte is 0%.

[0167] (4) Preparation of battery

[0168] After aligning 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) at the head, they are wound into a roll-shaped structure at a uniform speed according to the designed size to obtain a core; the electrolyte prepared in step (3) is added; ear glue is set between the positive electrode tab and the outer shell and between the negative electrode tab and the outer shell (the first glue layer contacts the outer shell, the third glue layer contacts the positive electrode tab / negative electrode tab, the second glue layer is located between the first glue layer and the third glue layer, the melting point of the first glue layer is 130 °C, the melting point of the second glue layer is 159 °C, the melting point of the third glue layer is 130 °C, the thickness h2 of the ear glue is 36 μm, and the size of the ear glue in the length direction of the positive electrode sheet / negative electrode sheet is 15 mm); after hot pressing, the radius R of the arc region and the thickness T of the core are observed and measured by X-Ray or computer tomography scanner; it is aged at room temperature (25 °C) for 24 h and at high temperature (65 °C) for 8 h to fully infiltrate the electrolyte; it is transferred to a forming device, the positive electrode tab and the negative electrode tab are connected to the charging port, and the battery is charged and pressurized to activate the battery core at a temperature of 80 °C and a pressure of 510 kgf / battery to form a secondary lithium-ion battery that can be charged and discharged externally;

[0169] Among them, the radius R of the arc area is 10.1 mm, the thickness T of the core is 18.2 mm, and 2R / T is 1.11; c / (2R / T) is 0.063; the arc radius r1 of the layer where the positive tab is located is 7.5 mm; the arc radius r2 of the layer where the negative tab is located is 7.5 mm; k1 is 2.02; k2 is 2.02; the distance from the first end of the positive tab to the arc area is 6.8 mm, and the distance from the first end of the negative tab to the arc area is 6.8 mm; the ratio of the distance from the first end of the positive tab to the arc area to r1 is 0.91, and the ratio of the distance from the first end of the negative tab to the arc area to r2 is 0.91; both the first adhesive tape and the second adhesive tape completely cover the arc area; R×c2 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 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 tab in the length direction of the negative electrode sheet is 1.99.

[0170] 4 groups of examples

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

[0172] This group of examples is carried out with reference to Example 1. The difference is that 2R / T is regulated by changing the thickness T of the core, specifically as follows:

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

[0174] Example 4b, T is 8.2 mm, and 2R / T is 1.268; among them, the thickness of the positive electrode sheet in the arc region is 75 μm, and the thickness of the positive electrode sheet in the straight region is 68 μm, and the ratio of the two is 1.1; the tap density of the positive electrode active layer in the arc region is 2.93 g / cm 3 , and the tap density of the positive electrode active layer in the straight region is 4.02 g / cm 3 , and the ratio of the two is 0.729; the areal density of the positive electrode active layer in the arc region is 9.8 mg / cm 2 , and the areal density of the positive electrode active layer in the straight region is 12 mg / cm 2 , and the ratio of the two is 0.82; the cross-sectional porosity ratio of the positive electrode sheet in the arc region is 2.93%, and the cross-sectional porosity ratio of the positive electrode sheet in the straight region is 1.76%, and the ratio of the two is 1.665; the thickness of the negative electrode sheet in the arc region is 80 μm, and the thickness of the negative electrode sheet in the straight region is 72 μm, and the ratio of the two is 1.11; the tap density of the negative electrode active layer in the arc region is 1.14 g / cm 3 , and the tap density of the negative electrode active layer in the straight region is 1.48 g / cm 3 , and the ratio of the two is 0.77; the areal density of the negative electrode active layer in the arc region is 4.2 mg / cm 2 , and the areal density of the negative electrode active layer in the straight region is 4.9 mg / cm 2 , and the ratio of the two is 0.86; the cross-sectional porosity ratio of the negative electrode sheet in the arc region is 2.75%, and the cross-sectional porosity ratio of the negative electrode sheet in the straight region 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 electrode sheet in the arc region to the thickness of the positive electrode sheet in the straight region".

[0177] This group of examples is carried out with reference to Example 1. The difference is that the ratio of the thickness is regulated by changing the areal density of the positive electrode active layer in the arc region (keeping the tap density unchanged), specifically as follows:

[0178] Example 5a, the thickness of the positive electrode sheet located in the arc region is 60 μm, and the ratio of the thickness of the positive electrode sheet located in the arc region to the thickness of the positive electrode sheet located in the straight region is 0.74; among them, the areal density of the positive electrode active layer located in the arc region is 8.4 mg / cm 2 , the ratio of the areal density of the positive electrode active layer located in the arc region to the areal density of the positive electrode active layer located in the straight region is 0.59; the radius R of the arc region is 4.7 mm, the thickness T of the core is 10.3 mm, and 2R / T is 0.913;

[0179] Example 5b, the thickness of the positive electrode sheet located in the arc region is 106 μm, and the ratio of the thickness of the positive electrode sheet located in the arc region to the thickness of the positive electrode sheet located in the straight region is 1.31; among them, the areal density of the positive electrode active layer located in the arc region is 18.6 mg / cm 2 , the ratio of the areal density of the positive electrode active layer located in the arc region to the areal density of the positive electrode active layer located in the straight region is 1.31; the radius R of the arc region is 6.1 mm, the thickness T of the core is 10.3 mm, and 2R / T is 1.184.

[0180] Example 6

[0181] Used to verify the influence brought by the change of the "tab glue".

[0182] Carried out with reference to Example 1, the difference is that the tab glue is changed, specifically as follows: the tab glue is a single-layer structure with a melting point of 140 °C.

[0183] Example 7 group

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

[0185] This group of examples is carried out with reference to Example 1, the difference is that the melting point of at least one of the first glue layer, the second glue layer and the third glue layer is changed, specifically as follows:

[0186] Example 7a, the melting point of the first glue layer is 95 °C, and the melting point of the third glue layer is 95 °C;

[0187] Example 7b, the melting point of the first glue layer is 137 °C, and the melting point of the third glue layer is 137 °C;

[0188] Example 7c, the melting point of the second glue layer is 125 °C;

[0189] Example 7d, the melting point of the second glue layer is 169 °C.

[0190] Example 8

[0191] Used to verify the influence brought by whether the "first glue paper and the second glue paper cover the arc region".

[0192] This was carried out with reference to Example 1, except that by changing the setting positions of the positive electrode tab and the negative electrode tab, as well as the dimension w1 of the first adhesive tape in the length direction of the positive electrode sheet and the dimension w3 of the second adhesive tape in the length direction of the negative electrode sheet, it was regulated whether the first adhesive tape and the second adhesive tape covered the arc region, such that the first adhesive tape and the second adhesive tape did not cover the arc region. Among them, the radius R of the arc region was 5.18 mm, the thickness T of the core was 10.3 mm, and 2R / T was 1.006; w1 was 20.8 mm, w3 was 20.8 mm; the distance from the first end of the positive electrode tab to the arc region was 12.8 mm, and the distance from the first end of the negative electrode tab to the arc region was 12.8 mm.

[0193] Example 9 group

[0194] This group of examples was used to verify the influence brought about by the change of "the mass content c2 of the solid electrolyte in the positive electrode active layer".

[0195] This group of examples was carried out with reference to Example 1, except that c2 was regulated by changing the formulation of the positive electrode paste, specifically as follows:

[0196] Example 9a, the mass ratio of lithium cobaltate, lithium titanium aluminum phosphate, carbon nanotubes, and polyvinylidene fluoride was 97:0.5:1.1:1.4; among them, c2 was 0.5%; c / c2 was 14, and R×c2 was 0.026;

[0197] Example 9b, the mass ratio of lithium cobaltate, lithium titanium aluminum phosphate, carbon nanotubes, and polyvinylidene fluoride was 92.5:5:1.1:1.4; among them, c2 was 5%; c / c2 was 1.4, and R×c2 was 0.26.

[0198] Example 10

[0199] It was used to verify the influence brought about by the change of "R×c2".

[0200] This was carried out with reference to Example 2, except that R×c2 was regulated by changing c2, specifically as follows: the mass ratio of lithium cobaltate, lithium titanium aluminum phosphate, carbon nanotubes, and polyvinylidene fluoride was 96.3:1.2:1.1:1.4, c2 was 1.2%; R×c2 was 0.03.

[0201] Example 11 group

[0202] This group of examples was used to verify the influence brought about by the change of "the average particle size of the solid electrolyte".

[0203] This group of examples was carried out with reference to Example 1, except that the average particle size of lithium titanium aluminum phosphate was changed, specifically as follows:

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

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

[0206] Example 12 group

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

[0208] This group of examples is carried out with reference to Example 1. The difference is that c is regulated by changing the formula of the negative electrode slurry, specifically as follows:

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

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

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

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

[0213] Example 13

[0214] Used to verify the influence brought by the change of "c / c2".

[0215] Carried out with reference to Example 12a. The difference is that c / c2 is regulated by changing c2, specifically as follows: c2 is 4.2%, and c / c2 is 0.71.

[0216] Example 14 group

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

[0218] This group of examples is carried out with reference to Example 1. The difference is that the mass content of propyl propionate in the electrolyte is changed, specifically as follows:

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

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

[0221] The above examples all meet the following:

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

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

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

[0225] Comparative Example 1

[0226] It is carried out with reference to Example 1. The difference is that lithium titanium aluminum phosphate is not added to the positive electrode slurry, that is, lithium cobaltate, carbon nanotubes and polyvinylidene fluoride are in a mass ratio of 97.5:1.1:1.4.

[0227] Comparative Example 2 group

[0228] It is carried out with reference to Example 1. The difference is that 2R / T is regulated by changing the radius R of the arc area and the thickness T of the core, specifically as follows:

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

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

[0231] Test Example

[0232] (1) Furnace temperature safety test

[0233] The batteries prepared in the examples and comparative examples were subjected to furnace temperature safety tests. The specific test methods are as follows:

[0234] Under the environment of 25°C ± 3°C, discharge at 0.2C to 3.0V, stand still for 10 min, then charge at 0.5C to 4.53V, and the cut-off rate is 0.02C; put the battery into the test chamber, and the test chamber is heated at a temperature rise rate of (5 ± 2)°C / min. When the temperature in the test chamber reaches 130°C ± 2°C, keep it at a constant temperature for 60 min. During this period, if the battery does not smoke, catch fire or explode, it is regarded as passing the test. 5 batteries in each group of examples and comparative examples were tested, and the results were recorded in the form of "n / 5", where n represents the number of batteries passing the test. For example, 5 / 5 means that 5 batteries were tested and all passed the test. The larger n is, the better the furnace temperature safety performance of the battery. The results were recorded in Table 1.

[0235] (2) Overcharge safety test

[0236] The batteries prepared in the examples and comparative examples were subjected to overcharge safety tests. The specific test methods are as follows:

[0237] Under the environment of 25°C ± 3°C, discharge at 0.5C to 3.0V, and then put it into the explosion-proof box. Fix the contact point of the thermocouple at the center of the largest surface of the battery and connect it to the power supply for charging. Charge at a constant current of 3C to 4.6V, and then perform constant voltage charging at 4.6V. When the charging time reaches 7 h, stop the test and monitor the process voltage and temperature data. Among them, if the battery does not smoke, catch fire or explode, it is regarded as passing the test. 5 batteries in each group of examples and comparative examples were tested, and the results were recorded in the form of "m / 5", where m represents the number of batteries passing the test. For example, 5 / 5 means that 5 batteries were tested and all passed the test. The larger m is, the better the overcharge safety performance of the battery. The results were recorded in Table 1.

[0238] (3) Rate test

[0239] The batteries prepared in the examples and comparative examples were subjected to rate tests. The specific test methods are as follows:

[0240] Under the environment of 25°C ± 3°C, discharge at 0.2C to 3.0V, stand still for 10 min, then charge at 0.5C to 4.53V, and the cut-off rate is 0.02C; stand still for 10 min, discharge at 1C to 3.0V, record the discharge capacity retention rate, and record the results in Table 1.

[0241] (4) Cycle test

[0242] The batteries prepared in the examples and comparative examples were subjected to cycle tests. The specific test methods are as follows:

[0243] At an environment of 25°C ± 3°C, discharge at 0.7C until 3.0V, charge at 2C until 4.53V, and cut off at 0.2C. Cycle 400 times to calculate the cycle capacity retention rate of the battery, and record the results in Table 1.

[0244] (5) High-temperature storage test

[0245] Perform high-temperature storage tests on the batteries prepared in the examples and comparative examples. The specific test method is as follows:

[0246] At an environment of 25°C ± 3°C, charge at 0.5C until 4.53V, cut off at 0.05C, discharge at 0.2C until 3.0V, and record the discharge capacity; then charge the battery at 0.5C until 4.53V, cut off at 0.05C. After fully charging, test the full-charge thickness of the battery, place it in an environment of (60 ± 2)°C for 7 days, then take it out and place it in an environment of 25°C ± 3°C for 2h, test the battery thickness, and then discharge at 0.2C until 3.0V, record the discharge capacity, and record the capacity recovery rate and thickness expansion rate results in Table 1.

[0247] Table 1

[0248]

[0249]

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

[0251] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A lithium ion secondary battery, characterized in that: It includes a winding core formed by stacking and winding 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 disposed on at least one side of the negative electrode current collector, wherein the negative electrode active layer comprises a negative electrode active material, and 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 disposed on at least one side of the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode active material and a solid electrolyte; The winding core comprises an arc region and a straight region connected to the arc region; The radius R of the arc area and the thickness T of the winding core satisfy: 0.9≤2R / T≤4 / π, where π is pi.

2. The lithium ion secondary battery according to claim 1, wherein The radius R of the arc area is 1-100, in mm, and the thickness T of the winding core is 1-200, in mm; And / or, the ratio of the thickness of the positive electrode sheet located in the arc area to the thickness of the positive electrode sheet located in the straight area is 0.7-1.5; And / or, the thickness of the positive electrode sheet located in the flat area is 20 μm-150 μm; and / or, a ratio of the compaction density of the positive electrode active layer located in the arc region to the compaction density of the positive electrode active layer located in the straight region is 0.5-0.99; And / or, the compaction density of the positive electrode active layer located in the flat area is 2 g / cm 3 -5g / cm 3 ; and / or, the ratio of the surface density of the positive electrode active layer located in the arc region to the surface density of the positive electrode active layer located in the straight region is 0.6-1; And / or, the surface density of the positive electrode active layer located in the flat area is 8 mg / cm 2 -25mg / 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 arc area to the thickness of the negative electrode sheet located in the straight area is 1.01-1.5; And / or, the thickness of the negative electrode sheet located in the flat area is 20 μm-200 μm; and / or, a ratio of the compaction density of the negative electrode active layer located in the arc region to the compaction density of the negative electrode active layer located in the straight region is 0.5-0.99; And / or, the compaction density of the negative electrode active layer located in the flat area is 1 g / cm 3 -2.5g / cm 3 ; and / or, the ratio of the surface density of the negative electrode active layer located in the arc region to the surface density of the negative electrode active layer located in the straight region is 0.6-1; And / or, the surface density of the negative electrode active layer located in the flat area is 3 mg / cm 2 -12mg / 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; preferably, 0.06≤c / (2R / T)≤0.075; Preferably, 0 <c≤40%; Preferably, the silicon-based material comprises silicon carbon, and the silicon carbon comprises a porous carbon substrate and silicon material located inside the pores of the porous carbon substrate; More preferably, the mass content of silicon in the silicon carbon is 20%-70%; More preferably, 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.

5. The lithium ion secondary battery according to claim 1 or 2, wherein: The lithium-ion secondary battery further comprises a housing; the positive electrode sheet further comprises a positive electrode tab and a tab glue disposed on the surface of the positive electrode tab; And / or, the negative electrode sheet further includes a negative electrode tab and a tab glue disposed on the surface of the negative electrode tab; Preferably, the tab glue comprises a first glue layer, a second glue layer and a third glue layer stacked in sequence, the first glue layer contacts the shell, the third glue layer contacts the positive tab, and / or the third glue layer contacts the negative tab, and the second glue layer is located between the first glue layer and the third glue layer; More preferably, the melting point of the first adhesive layer is 100°C-130°C, the melting point of the second adhesive layer is 130°C-160°C, and the melting point of the third adhesive layer is 100°C-130°C; Preferably, the thickness h2 of the tab glue is 15 μm-50 μm.

6. The lithium ion secondary battery according to claim 5, wherein: The size of the ear glue in the length direction of the positive electrode sheet is 5mm-20mm; And / or, the size of the tab glue in the length direction of the negative electrode sheet is 5mm-20mm; And / or, the ratio of the dimension of the tab glue in the length direction of the positive electrode sheet to the dimension w2 of the positive electrode tab in the length direction of the positive electrode sheet is 1.1-2; And / or, the ratio of the dimension of the tab glue in the length direction of the negative electrode sheet to the dimension w4 of the negative electrode tab in the length direction of the negative electrode sheet is 1.1-2.

7. The lithium ion secondary battery according to claim 1 or 2, wherein: The positive electrode sheet further includes a positive electrode tab, 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; Preferably, the dimension w1 of the first adhesive tape in the length direction of the positive electrode sheet is 15mm-50mm, and the dimension w2 of the positive electrode tab in the length direction of the positive electrode sheet is 2mm-10mm; Preferably, the ratio of the distance from the first end of the positive electrode tab to the arc region to the arc radius r1 of the layer where the positive electrode tab is located is 0-2, wherein the first end is the end of the positive electrode tab close to the arc region; Preferably, the first adhesive tape at least covers a portion of the arc area.

8. The lithium ion secondary battery according to claim 1 or 2, wherein: The negative electrode sheet further includes a negative electrode tab, a negative electrode tab welding area, and a second adhesive tape, wherein the negative electrode tab is located in the negative electrode tab welding area, and the second adhesive tape covers the negative electrode tab welding area; Preferably, the dimension w3 of the second adhesive tape in the length direction of the negative electrode sheet is 15 mm-50 mm, and the dimension w4 of the negative electrode tab in the length direction of the negative electrode sheet is 2 mm-10 mm; Preferably, the ratio of the distance from the first end of the negative electrode tab to the arc region to the arc radius r2 of the layer where the negative electrode tab is located is 0-2, wherein the first end is the end of the negative electrode tab close to the arc region; Preferably, the second adhesive tape at least covers a portion of the arc area.

9. The lithium ion secondary battery according to claim 1 or 2, wherein: The solid 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 electrolyte is 0.02 μm-3 μm; preferably 0.05 μm-2 μm; And / or, the mass content c2 of the solid electrolyte in the positive electrode active layer is 0.1%-5%; preferably 1%-4.5%; and / or, the positive electrode active material comprises at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate and lithium-rich manganese-based materials; And / or, the negative electrode active material further includes a carbon-based material.

10. The lithium ion secondary battery according to claim 1 or 2, wherein: The lithium-ion secondary battery further comprises an electrolyte, wherein the mass content of propyl propionate in the electrolyte is ≤10%; Preferably, the electrolyte further includes a non-aqueous solvent, and the non-aqueous solvent includes a carbonate substance.

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