Lithium-ion secondary battery

Abstract

The present disclosure relates to the technical field of batteries, and specifically relates to a lithium-ion secondary battery. The lithium-ion secondary battery comprises a jelly roll formed by laminating 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, 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, and the positive electrode active layer comprises a positive electrode active material and a solid-state electrolyte. The jelly roll comprises arc regions and flat regions connected to the arc regions, and the radius R of each arc region and the thickness T of the jelly roll satisfy: 0.9≤2R / T≤4 / π, wherein π is the mathematical constant pi. The present disclosure can effectively mitigate the safety problem caused by gas production during battery cycling and storage.

Description

Lithium-ion secondary batteries Technical Field

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

[0002] As electronic products such as communication devices and electric vehicles demand increasingly higher battery energy density, traditional graphite anode materials are no longer sufficient to meet market needs. Silicon anodes, due to their high theoretical specific capacity, are considered one of the key materials for improving the energy density of lithium-ion batteries. However, lithiation of silicon anodes forms lithium-silicon alloys, which undergo side reactions with the electrolyte, severely impacting the battery's cycle life. Summary of the Invention

[0003] The purpose of this disclosure is to overcome the aforementioned problems in the prior art and provide a lithium-ion secondary battery. The lithium-ion secondary battery of this disclosure (hereinafter referred to as the battery) reduces the amount of electrolyte used by introducing a solid electrolyte into the positive electrode, thereby mitigating the risk of side reactions between the silicon negative electrode and the electrolyte and improving the battery's cycle life. Simultaneously, by controlling the relationship between the radius of the arc region and the core thickness, the gas generation problem of the solid electrolyte during battery cycling or storage can be effectively improved, enhancing the battery's safety performance and cycle life.

[0004] Numerous studies have found that adding a solid electrolyte to the positive electrode of a silicon anode battery can significantly reduce the risk of side reactions between the silicon anode and the electrolyte, thus improving the battery's cycle life. However, the addition of a solid electrolyte can cause gas generation during cycling or storage. This is because the expansion stress in the arc-shaped region of the core is greater than in the flat region, especially when the anode contains silicon-based materials. This greater expansion stress forces the electrolyte in the arc-shaped region to be squeezed into the flat region, reducing the electrolyte content in the arc-shaped region. This leads to poorer kinetics in the arc-shaped region and an increased overpotential, further causing the CEI (Cathode Electrolyte Interphase) film on the positive electrode surface to decompose and generate gas. Furthermore, the decomposition of the CEI film causes the electrolyte to be oxidized, further reducing the electrolyte content, creating a vicious cycle that increases gas generation. When the radius R of the arc region and the thickness T of the core satisfy 2R / T < 0.9, stress concentration during battery cycling or storage can lead to stress accumulation at the arc region that cannot be effectively released. This results in reduced electrolyte in the arc region, deteriorated kinetics, increased overpotential, and ultimately, gas generation. Furthermore, the accumulation of gas may cause the battery to explode.

[0005] Based on the above findings, the inventors of this disclosure introduce a solid electrolyte into the positive electrode, reducing safety hazards caused by side reactions with the electrolyte. Furthermore, the solid electrolyte itself has high ionic conductivity, which not only helps improve the battery's charge and discharge efficiency but also helps improve interfacial impedance, enhancing the battery's kinetic performance and cycle stability. Simultaneously, by increasing the thickness of the arc-shaped region, the relationship between the radius of the arc-shaped region and the core thickness is controlled, thereby mitigating the problem of gas generation in the solid electrolyte during cycling or storage. This is because when 2R / T ≥ 0.9, the arc-shaped region has a certain stress release space, which can alleviate the stress concentration problem in the arc-shaped region. Battery expansion has virtually no impact on the amount of electrolyte in the arc-shaped region, ensuring sufficient electrolyte retention and reducing the concentration difference between the electrolyte in the arc-shaped and flat regions. This prevents an increase in overpotential in the arc-shaped region and prevents the CEI film from decomposing and generating gas.

[0006] Therefore, by introducing a solid electrolyte and adjusting the relationship between the radius of the arc region and the thickness of the core, the charging and discharging efficiency and dynamic performance of the battery can be improved, while the risk of explosion caused by the large amount of gas generated in the arc region that cannot be discharged in time is reduced, thus improving the cycle stability and safety performance of the battery.

[0007] This disclosure provides a lithium-ion secondary battery, including a core formed by stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet; the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one side of the negative electrode current collector, the negative electrode active layer including a negative electrode active material, the negative electrode active material including a silicon-based material; the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one side of the positive electrode current collector, the positive electrode active layer including a positive electrode active material and a solid electrolyte; the 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 core satisfy: 0.9≤2R / T≤4 / π, where π is pi.

[0008] Compared with the prior art, the present disclosure has at least the following advantages through the above technical solution:

[0009] (1) The battery disclosed herein has high charge and discharge efficiency, kinetic performance and cycle stability.

[0010] (2) The battery disclosed herein can effectively reduce the safety risks caused by gas production.

[0011] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0012] Figure 1 shows a cross-sectional schematic diagram of the core in an example of this disclosure.

[0013] Figure 2 shows a schematic diagram of the cross-sectional details of the core in an example of this disclosure.

[0014] Figure 3 shows a schematic diagram of the positive electrode tab and the first adhesive tape interface of this disclosure.

[0015] Figure 4 shows a partial schematic diagram of the positive electrode in an example of this disclosure, without showing the first adhesive tape.

[0016] Figure 5 shows a partial schematic diagram of the positive electrode in an example of this disclosure, with the first adhesive tape drawn based on Figure 4.

[0017] Figure 6 shows a schematic diagram of the tab adhesive structure in an example of this disclosure. Detailed Implementation

[0018] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0019] This disclosure provides a lithium-ion secondary battery, comprising a core formed by stacking and winding a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector, the negative active layer comprising a negative active material, the negative active material being a silicon-based material. The positive electrode includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector, the positive active layer comprising a positive active material and a solid electrolyte. The core includes an arc-shaped region and a straight region connected to the arc-shaped region; the radius R of the arc-shaped region and the thickness T of the core satisfy the condition: 0.9 ≤ 2R / T ≤ 4 / π, where π is pi, for example, 0.9, 1, 1.1, 1.2, or 4 / π.

[0020] In this disclosure, the radius R of the arc region and the thickness T of the core have conventional meanings in the art. Figure 1 shows a schematic diagram of the core structure in an example of this disclosure. As can be seen from the figure, the core includes an arc region 10 and a straight region 20 connected to the arc region 10. The thickness T of the core refers to the dimension of the middle portion 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 to the innermost side of the arc region in a direction perpendicular to the thickness direction of the core.

[0021] In this disclosure, the radius R of the arc can be 1-100 mm, for example, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm or 100 mm. The thickness T of the core can be 1-200 mm, for example, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, 21 mm, 22 mm, 23 mm, 24 mm, 25 mm, 26 mm, 27 mm, 28 mm, 29 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, 150 mm, or 200 mm.

[0022] In this disclosure, the thickness of the positive electrode sheet and / or negative electrode sheet located in the arc region and the straight 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 straight region, so that the radius R of the arc region and the thickness T of the core satisfy: 0.9≤2R / T≤4 / π.

[0023] In this disclosure, the radius R of the arc region and the thickness T of the core can be obtained by conventional testing methods in the art, such as by taking a computed tomography (CT) scan after discharging the lithium-ion secondary battery to 0% SOC and measuring the cross-section.

[0024] In this disclosure, 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 0.7-1.5, for example, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4 or 1.5.

[0025] In one example, the ratio of the thickness of the positive electrode in the arc region to the thickness of the positive electrode in the flat region is 1.01-1.3.

[0026] In one example, the ratio of the thickness of the positive electrode in the arc region to the thickness of the positive electrode in the flat region is 1.05-1.15.

[0027] When 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 within a specific range, the reserved pores or space structure 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 enough space for battery expansion during cycling, preventing a vicious cycle phenomenon that leads to low electrolyte concentration in the arc region, increased overpotential, CEI decomposition to produce gas, and further reduction of electrolyte due to oxidation caused by battery expansion.

[0028] In one example, the thickness of the positive electrode located in the flat region is 20μm-150μm, for example, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm or 150μm.

[0029] Figure 2 shows a detailed cross-sectional view of the core in an example of this disclosure. The box in the figure is an enlarged view of a part of the core. As can be seen from the figure, the thickness of the positive electrode and the negative electrode at the arc is significantly increased compared to the thickness in the flat area. It should be noted that the change in radius of the arc area is achieved by increasing the interlayer gap and particle gap of the active material in the arc area, rather than by increasing the thickness of the electrode (including the positive and negative electrode) at the arc in isolation.

[0030] In this disclosure, the thickness of the positive electrode sheet located in the arc region and the thickness of the positive electrode sheet located in the flat region can be obtained by conventional methods in the art, for example, taking 10 different sites on the positive electrode sheet located in the arc region and the flat region respectively, measuring the thickness of each site, and taking the average value.

[0031] In this disclosure, the 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 flat region is 0.5-0.99, for example, 0.5, 0.6, 0.7, 0.8, or 0.99.

[0032] In one example, the 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 flat region is 0.65-0.85.

[0033] In one example, the compaction density of the positive electrode active layer located in the flat region is 2 g / cm³. 3 -5g / cm 3 For example, 2g / cm 3 2.5g / cm 3 3g / cm 3 3.5g / cm 3 4g / cm 3 4.5g / cm 3 or 5g / cm 3 .

[0034] When the compaction density of the positive electrode active layer located in the arc region is less than that of the positive electrode active layer located in the flat region, the reserved pores or spatial structure 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 enough space for battery expansion during cycling, preventing a vicious cycle phenomenon that leads to low electrolyte concentration in the arc region, increased overpotential, CEI decomposition to produce gas, and further reduction of electrolyte due to oxidation caused by battery expansion.

[0035] In this disclosure, the compaction density of the positive electrode active layer located in the arc region and the compaction density of the positive electrode active layer located in the flat region can be obtained by conventional methods in the art. For example, a certain area of ​​the positive electrode active layer can be cut from the arc region and the flat region respectively, and the coating thickness can be measured at 5 randomly selected sites. The mass of the cut positive electrode active layer sample can be weighed. Based on the measured average thickness and coating mass, the compaction density of the positive electrode active layer located in the arc region and the flat region can be calculated respectively using the formula: compaction density = coating mass / coating volume.

[0036] In this disclosure, 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 flat region is 0.6-1, for example, 0.6, 0.7, 0.8, 0.9, or 1.

[0037] In one example, 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 flat region is 0.7-0.95.

[0038] In one example, the areal density of the positive electrode active layer located in the flat region is 8 mg / cm³. 2 -25mg / cm 2 For example, 8 mg / cm 2 9mg / cm 2 10mg / cm 2 11mg / cm 2 12mg / cm 2 13mg / cm2 14mg / cm 2 15mg / cm 2 16mg / cm 2 17mg / cm 2 18mg / cm 2 19mg / cm 2 20mg / cm 2 21mg / cm 2 22mg / cm 2 23mg / cm 2 24mg / cm 2 Or 25mg / cm 2 .

[0039] In this disclosure, 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 flat region can be obtained by conventional methods in the art. For example, a certain area of ​​the positive electrode active layer can be cut from the arc region and the flat region respectively, the mass of the cut positive electrode active layer sample can be weighed, and the areal density of the positive electrode active layer located in the arc region and the flat region can be calculated according to the measured area and coating mass: areal density = coating mass / coating area.

[0040] In this disclosure, the ratio of the cross-sectional porosity of the positive electrode sheet located in the arc region to the cross-sectional porosity 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.

[0041] In one example, the cross-sectional porosity of the positive electrode located in the flat region is 1%-3%, for example, 1%, 1.5%, 2%, 2.5% or 3%.

[0042] In this disclosure, the cross-sectional porosity of the positive electrode located in the arc region and the cross-sectional porosity of the positive electrode located in the straight region can be tested using conventional methods in the art, such as obtaining a cross-sectional image of the positive electrode by scanning electron microscopy (SEM) or X-ray tomography, and then processing the image to obtain the cross-sectional porosity at the corresponding position.

[0043] In this disclosure, 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.

[0044] In one example, the thickness of the negative electrode located in the flat region is 20μm-200μm, for example, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm or 200μm.

[0045] In this disclosure, the 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 flat region is 0.5-0.99, for example, 0.5, 0.6, 0.7, 0.8, or 0.99.

[0046] In one example, the 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 flat region is 0.65-0.95.

[0047] In one example, the compaction density of the negative electrode active layer located in the flat region is 1 g / cm³. 3 -2.5g / cm 3 For example, 1g / cm 3 1.5g / cm 3 2g / cm 3 Or 2.5g / cm 3 .

[0048] In this disclosure, 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 flat region is 0.6-1, for example, 0.6, 0.7, 0.8, 0.9 or 1.

[0049] In one example, the areal density of the negative electrode active layer located in the flat region is 3 mg / cm³. 2 -12mg / cm 2 For example, 3 mg / cm 2 4mg / cm 2 5mg / cm 2 6mg / cm 2 7mg / cm 2 8mg / cm 2 9mg / cm 2 10mg / cm 2 11mg / cm 2 Or 12mg / cm 2 .

[0050] In the present disclosure, the ratio of the cross-sectional porosity of the negative electrode plate located in the arc region to the cross-sectional porosity of the negative electrode plate located in the flat region is 1.5-2, for example, 1.5, 1.6, 1.7, 1.8, 1.9 or 2.

[0051] In an example, the cross-sectional porosity of the negative electrode plate located in the flat region is 1%-3%, for example, 1%, 1.5%, 2%, 2.5% or 3%.

[0052] In the present disclosure, the test methods for the thickness and cross-sectional porosity of the negative electrode plate located in the flat region or the arc region, and the areal density and compacted density of the negative electrode active layer are the same as those for the positive electrode plate, and will not be repeated herein.

[0053] In the present disclosure, 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.

[0054] In an example, 0.06≤c / (2R / T)≤0.075.

[0055] The higher the content c of elemental silicon in the negative electrode active layer, the greater the volume expansion of the battery during charge-discharge cycles, and the greater the stress generated on the arc region, which leads to a greater reduction in the amount of electrolyte in the arc region, causes deteriorated kinetics in the arc region, increases the overpotential in the arc region, leads to gas generation from the decomposition of the CEI film, and the decomposition of the CEI film in turn causes oxidation of the electrolyte, leading to a further reduction in the amount of electrolyte and accumulation of a large amount of gas 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, so as to further improve the problem of gas generation in the arc region. When the two satisfy the specific relationship, the reserved stress release space in the arc region can be matched with the volume expansion of silicon, thereby further alleviating the problem of stress concentration in the arc region, alleviating the reduction of the amount of electrolyte in the arc region, reducing the concentration difference of electrolyte between the arc region and the flat region, and thus further improving the problem of gas generation in the arc region; and by limiting the relationship between the two, the stress release space will not be too large, which would otherwise affect the electrical contact in the battery.

[0056] In the present disclosure, 0 < c ≤ 40%, for example, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40%.

[0057] In an example, 3% ≤ c ≤ 15%.

[0058] In this disclosure, the elemental silicon content c in the negative electrode active layer can be tested using conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled and soaked in dimethyl carbonate (DMC) solvent for 12 hours, then rinsed with DMC solvent to remove lithium salts adhering to the negative electrode sheet. After drying, the negative electrode sheet is subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active layer can then be peeled off from the negative electrode current collector, and the negative electrode active layer is collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer), the test sample amount is 5mg-15mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25°C) to 900°C at a rate of 10°C / min, and held at 900°C for 40 minutes. This allows the non-silicon components in the negative electrode active layer to volatilize while the silicon is fully oxidized to silicon dioxide. Weigh the residual material. The elemental silicon content in the negative electrode active layer can be obtained by the following formula: elemental silicon content in the negative electrode active layer = 7 × mass of residual material / (15 × mass of test sample).

[0059] In this disclosure, the lithium-ion secondary battery further includes a casing; the positive electrode further includes a positive electrode tab and a tab adhesive disposed on the surface of the positive electrode tab. The negative electrode further includes a negative electrode tab and a tab adhesive disposed on the surface of the negative electrode tab. The tab adhesive includes a first adhesive layer, a second adhesive layer, and a third adhesive layer stacked sequentially, the first adhesive layer being in contact with the casing, the third adhesive layer being in contact with the positive electrode tab, and the second adhesive layer being located between the first adhesive layer and the third adhesive layer. Figure 6 shows a schematic diagram of the tab adhesive structure in an example of this disclosure. As can be seen from the figure, the tab adhesive includes a first adhesive layer 7-1, a second adhesive layer 7-2, and a third adhesive layer 7-3 stacked sequentially.

[0060] In one example, the first adhesive layer is in contact with the outer casing, the third adhesive layer is in contact with the negative electrode tab, and the second adhesive layer is located between the first adhesive layer and the third adhesive layer.

[0061] In this disclosure, the melting point of the first adhesive layer is 100℃-130℃ (e.g., 100℃, 105℃, 110℃, 115℃, 120℃, 125℃ or 130℃), the melting point of the second adhesive layer is 130℃-160℃ (e.g., 130℃, 135℃, 140℃, 145℃, 150℃, 155℃ or 160℃), and the melting point of the third adhesive layer is 100℃-130℃ (e.g., 100℃, 105℃, 110℃, 115℃, 120℃, 125℃ or 130℃).

[0062] When a battery undergoes safety tests such as furnace temperature checks and overcharging, or short-circuits due to misuse, thermal runaway can occur, releasing a large amount of heat and significantly increasing the internal temperature of the battery. This further exacerbates the decomposition of the CEI film, generating gas. Therefore, designing the tab adhesive to release gas in a timely manner is a reliable way to ensure battery safety. This disclosure utilizes a three-layer adhesive with different melting points, where the first and third layers have the same melting point, both lower than the second layer. When thermal runaway occurs and the temperature exceeds the melting point of the first and / or third layers of the tab adhesive, the tab adhesive melts and separates from the tabs (including the positive and / or negative tabs) and / or the outer casing, providing an outlet for the gas generated inside the battery and preventing the battery from exploding due to excessive gas pressure.

[0063] Specifically, the melting points of the first and third adhesive layers are both between 100℃ and 130℃. These melting points allow the first and third adhesive layers to melt promptly when the internal temperature of the battery rises, reducing the tensile strength at the overall sealing interface between the casing and the tabs. This makes the interface easier to open, providing a venting channel for the battery, improving safety, and preventing accidents such as fires and explosions caused by the accumulation of large amounts of gas that cannot be released in time. Furthermore, the melting point of the second adhesive layer needs to be coordinated and controlled to be between 130℃ and 160℃. A second adhesive layer within this range provides good barrier properties, preventing over-melting and short circuits. It also ensures that there is no risk of interface segregation during the heat-sealing process of the tab adhesive, preventing battery leakage and gas buildup.

[0064] In this disclosure, the material of the tab adhesive is not limited, and it can be a tab adhesive commonly used in the art, such as polyolefin. The melting point can be controlled by changing the modifying groups on the surface of the tab adhesive, the degree of polymerization, etc.

[0065] In this disclosure, the thickness h1 of the positive electrode tab is 20μm-100μm, for example, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, or 100μm. The thickness h3 of the negative electrode tab is 20μm-100μm, for example, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, or 100μm. The thickness h2 of the tab adhesive is 15μm-50μm, for example, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, or 50μm.

[0066] In this disclosure, the thickness h1 of the positive electrode tab, the thickness h3 of the negative electrode tab, and the thickness h2 of the tab adhesive can be obtained by conventional methods in the art. For example, five different sites on the positive electrode tab, the negative electrode tab, and the tab adhesive can be taken respectively, the thickness of each site can be measured, and the average value can be taken.

[0067] In this disclosure, the dimension of the tab adhesive along the length of the positive electrode sheet (i.e., the width of the tab adhesive) is 5mm-20mm, for example, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, or 20mm. The dimension of the tab adhesive along the length of the negative electrode sheet (i.e., the width of the tab adhesive) is 5mm-20mm, for example, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, or 20mm.

[0068] In this disclosure, the width of the tab adhesive can be obtained by conventional testing methods in the art, such as by discharging the lithium-ion secondary battery to 0% SOC, disassembling and removing the core to observe and measure the tab adhesive.

[0069] In this disclosure, the ratio of the dimension of the tab adhesive along the length of the positive electrode sheet to the dimension w2 of the positive electrode tab along the length of the positive electrode sheet is 1.1-2, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2. The ratio of the dimension of the tab adhesive along the length of the negative electrode sheet to the dimension w4 of the negative electrode tab along the length of the negative electrode sheet is 1.1-2, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.

[0070] In this disclosure, the positive electrode sheet further includes a positive electrode tab welding area and a first adhesive tape. 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. Figures 4 and 5 show partial schematic diagrams of the positive electrode sheet in an example of this disclosure; the first adhesive tape is not shown in Figure 4, while it is shown in Figure 5 based on Figure 4. As can be seen from Figures 4 and 5, the positive electrode sheet 1 includes a positive electrode tab 4, a positive electrode tab welding area 6, and a first adhesive tape 5. The positive electrode tab 4 is located in the positive electrode tab welding area 6, and the first adhesive tape 5 covers the positive electrode tab welding area 6.

[0071] In this disclosure, the first adhesive tape has a dimension w1 along the length of the positive electrode sheet, and the positive electrode tab has a dimension w2 along the length of the positive electrode sheet. w1 is 15mm-50mm (e.g., 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm or 50mm), and w2 is 2mm-10mm (e.g., 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm).

[0072] In this disclosure, w1, w2 and the radius r1 of the arc 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.

[0073] Figure 3 shows a schematic diagram of the interface between the positive electrode tab and the first adhesive tape of this disclosure. 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 dimension of the first adhesive tape in the length direction of the positive electrode sheet is w1. The dimension of the positive electrode tab 4 in the length direction of the positive electrode sheet is w2. The radius of the arc of the layer containing the positive electrode tab 4 is r1.

[0074] In this disclosure, 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 (e.g., 0, 0.5, 1, 1.5 or 2), and the first end is the end of the positive electrode tab that is close to the arc region.

[0075] In this disclosure, the first adhesive tape at least partially covers the arcuate area.

[0076] In one example, the first adhesive tape completely covers the arc area.

[0077] By adjusting the positions of the positive electrode tab and the first adhesive tape, the first adhesive tape can pass through the arc-shaped area (partially or completely covering the arc-shaped area). Since the positive electrode tab is close to the arc-shaped area and the first adhesive tape passes through the arc-shaped area, it helps the gas generated in the arc-shaped area to burst and release pressure through the tab adhesive, thereby improving the safety performance of the battery.

[0078] In this disclosure, the negative electrode sheet further includes a negative electrode tab welding area and a second adhesive paper, wherein the negative electrode tab is located in the negative electrode tab welding area and the second adhesive paper covers the negative electrode tab welding area.

[0079] In this disclosure, the second adhesive tape has a dimension w3 in the length direction of the negative electrode sheet, and the negative electrode tab has a dimension w4 in the length direction of the negative electrode sheet. w3 is 15mm-50mm (e.g., 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm or 50mm), and w4 is 2mm-10mm (e.g., 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm).

[0080] In this disclosure, w1, w2, w3 and w4 can be obtained by conventional testing methods in the art, such as by discharging a lithium-ion secondary battery to 0% SOC, disassembling and removing the core, and observing and measuring the first adhesive tape, positive electrode tab, second adhesive tape and negative electrode tab respectively.

[0081] In this disclosure, the radius r2 of the arc of the layer where w3, w4 and the negative electrode tab are located satisfies: 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.

[0082] In this disclosure, 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 (e.g., 0, 0.5, 1, 1.5 or 2), and the first end is the end of the negative electrode tab that is close to the arc region.

[0083] In this disclosure, the second adhesive tape at least partially covers the arcuate area.

[0084] In one example, the second adhesive tape completely covers the arc area.

[0085] By adjusting the positions of the negative electrode tab and the second adhesive tape, the second adhesive tape can be positioned to cover the arc-shaped area (partially or completely). Because the negative electrode tab is closer to the arc-shaped area, and the second adhesive tape covers it, the gas generated in the arc-shaped area can be released through the tab adhesive, thus improving battery safety.

[0086] In this disclosure, the mass content c2 of the solid electrolyte in the positive electrode active layer and the radius R (in mm) of the arc satisfy the following condition: 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.

[0087] In one instance, 0.06 ≤ R × c2 ≤ 0.45.

[0088] The mass content of solid electrolyte is related to R: when R is large, the amount of solid electrolyte can be appropriately reduced, while when R is small, the amount of solid electrolyte should be appropriately increased. This is because: when R is large, the impact of battery expansion on the arc region is small, and the arc region retains sufficient electrolyte, avoiding the phenomenon of CEI decomposition and gas generation caused by the increase of overpotential in the arc region; however, when R is small, the impact of battery expansion on the arc region increases, causing the electrolyte in the arc region to be squeezed out into the flat region, resulting in a decrease in electrolyte concentration in the arc region, an increase in overpotential, CEI decomposition and gas generation, which in turn causes electrolyte oxidation, further reducing the amount of electrolyte, creating a vicious cycle. In this case, by increasing the amount of 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 CEI decomposition and gas generation.

[0089] In this disclosure, the solid electrolyte includes at least one of lithium aluminum titanium phosphorus oxide, lithium lanthanum zirconium tantalum oxide, and lithium lanthanum titanium oxide. The lithium aluminum titanium phosphorus oxide can be a superionic conductor type lithium aluminum titanium phosphorus oxide with the molecular formula Li. 1+x Al x Ti 2-x (PO4)3, 0 < x ≤ 0.5. The lithium lanthanum zirconium tantalum oxide can be a garnet-type lithium lanthanum zirconium tantalum oxide with the molecular formula Li. 7-y La3Zr 2-y Ta y O 12 , 0≤y≤0.5. The lithium lanthanum titanium oxide can be a perovskite type lithium lanthanum titanium oxide with the molecular formula Li. 3z La 2 / 3-z TiO3, 0 < z ≤ 0.2.

[0090] In one example, the solid electrolyte comprises lithium aluminum titanium phosphate (LATP).

[0091] In this disclosure, 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.

[0092] In one example, the average particle size of the solid electrolyte is 0.05 μm to 2 μm.

[0093] By controlling the content and average particle size of the solid electrolyte, the solid electrolyte particles can form a good interfacial contact with the positive electrode active layer, reducing interfacial impedance, promoting lithium-ion transport at the interface, and improving battery kinetic performance. Regarding gas generation in the arc region, reducing the interfacial impedance avoids CEI decomposition caused by increased overpotential in the arc region, thereby reducing gas generation and effectively improving the battery's cycle performance.

[0094] In this disclosure, the average particle size of the solid electrolyte can be obtained by methods conventional in the art. For example, by using SEM, at least 10 solid electrolyte particles are selected from the electron microscope image, the particle size of each solid electrolyte particle is measured, and the average value is taken.

[0095] In this disclosure, 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 measured by methods conventional in the art, such as a laser particle size analyzer.

[0096] In this disclosure, 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%.

[0097] In one instance, c2 ranges from 1% to 4.5%.

[0098] In this disclosure, the content of elemental silicon c in the negative electrode active layer and the content of solid electrolyte c2 in the positive electrode active layer satisfy the following condition: 0.5 ≤ c / c2 ≤ 35, for example, 0.5, 1, 5, 10, 15, 20, 25, 30 or 35.

[0099] In one instance, 1.5 ≤ c / c2 ≤ 13.

[0100] If the silicon content in the negative electrode active layer is too high, the battery volume expansion during charge-discharge cycles will be greater, resulting in increased stress on the arc-shaped region. This leads to a reduction in the electrolyte volume in the arc-shaped region, easily causing a decrease in electrolyte concentration, increased overpotential, and a vicious cycle of continuous CEI decomposition and gas production. In this case, adding an appropriate amount of solid electrolyte can effectively alleviate the CEI decomposition and gas production problem caused by the high overpotential in the arc-shaped region. However, the amount of solid electrolyte added should not be excessive, otherwise it will cause interfacial impedance. Therefore, it is necessary to control the ratio of the solid electrolyte content c2 to the silicon content c in the negative electrode active layer within a suitable range. This ensures that the silicon content in the negative electrode active layer is not excessive, thus suppressing negative electrode expansion and improving battery energy density. It also avoids the gas production problem in the arc-shaped region caused by the electrolyte concentration difference between the arc-shaped and flat regions, thereby improving battery safety performance.

[0101] In this disclosure, the positive electrode active material includes at least one selected from 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. The negative electrode active material may further include carbon-based materials, such as at least one selected from artificial graphite, natural graphite, mesophase carbon microsphere graphite, soft carbon, and hard carbon.

[0102] In this disclosure, the lithium-ion secondary battery further includes an electrolyte. The electrolyte may optionally include propyl propionate. "Optionally" means that the electrolyte may or may not include propyl propionate.

[0103] In this disclosure, 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%.

[0104] In one example, the electrolyte contains ≤5% propyl propionate by mass.

[0105] In one example, the electrolyte contains ≤1% propyl propionate by mass.

[0106] In one example, the electrolyte contains ≤0.5% propyl propionate by mass.

[0107] In one example, the electrolyte contains 0% propyl propionate by mass.

[0108] In batteries with a solid electrolyte at the positive electrode, when the overpotential at the positive electrode is high, the CEI film decomposes, producing gas. At this point, the electrolyte is oxidized, forming a new CEI film. When the propyl propionate content is high, propyl propionate readily reacts with the solid electrolyte, decomposing to produce gases such as carbon dioxide, ethane, and propane, preventing the formation of a stable CEI film and leading to a continuous increase in gas production. Therefore, when the propyl propionate content in the electrolyte is low, the gas production significantly decreases. Thus, by controlling the electrolyte composition, specifically adjusting the propyl propionate content in the electrolyte formulation, a stable CEI film can be formed on the positive electrode surface, reducing the safety issues related to battery gas production.

[0109] In this disclosure, the mass content of propyl propionate in the electrolyte can be obtained by conventional testing methods in the art, such as by gas chromatography or gas chromatography coupled with mass spectrometry.

[0110] In this disclosure, 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorophosphate, lithium difluorodioxalate phosphate, or lithium tetrafluorooxalate phosphate. The non-aqueous solvent includes carbonates, including at least one of ethylene carbonate (EC), ethylene carbonate, propylene carbonate (PC), propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl 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 additives include at least one of fluoroethylene carbonate (FEC), vinylene carbonate, vinyl ethylene carbonate, vinyl sulfate (DTD), propylene sulfate, vinyl sulfite, 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone, sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinic anhydride (SN), adiponitrile, 1,3,6-hexanetrionitrile (HTCN), tris(trimethylsilane) phosphate, or tris(trimethylsilane) 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 triethylene glycol dimethyl ether (TEP).

[0111] In this disclosure, the silicon-based material includes, for example, at least one of elemental silicon, silicon-carbon, silicon-oxygen, and silicon alloys.

[0112] In one example, the negative electrode material comprises graphite. The graphite material includes at least one of natural graphite, artificial graphite, or mesophase carbon microsphere graphite. The volumetric particle size distribution of the graphite material is: Dv10 is 5μm-10μm, Dv50 is 10μm-25μm, and Dv90 is 25μm-40μm; the interlayer spacing d002 of the graphite material is 0.3356nm-0.3359nm; and the reversible capacity of the graphite material is 350mAh / g-365mAh / g.

[0113] In one example, the negative electrode material comprises silicon-carbon, which for example includes a porous carbon substrate and silicon material located within the pores of the porous carbon substrate; the silicon content in the silicon-carbon is 20%-70% by mass; the volumetric particle size distribution of the silicon-carbon is: Dv10 is 1μm-6μm, Dv50 is 3μm-15μm, and Dv90 is 12μm-30μm; the specific surface area of ​​the silicon-carbon is 0.5m². 2 / g-10m 2 / g, the average sphericity of the silicon-carbon is 0.5-1.

[0114] In this disclosure, the positive electrode sheet has a first surface and a second surface disposed opposite to each other along the thickness direction. The first surface may have a plurality of recesses, and the second surface may have a plurality of protrusions. "A plurality of" means that the number of recesses on the first surface is greater than or equal to 2, and the number of protrusions on the second surface is greater than or equal to 2.

[0115] In one example, the recess on the first surface corresponds to the protrusion on the second surface.

[0116] In this disclosure, the width of the recess can be 0.2mm-8mm, for example, 0.2mm, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, or 8mm. The depth of the recess can be 3μm-40μm, for example, 3μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, or 40μm. The spacing between the recesses can be 0.5mm-8mm, for example, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, or 8mm.

[0117] In this disclosure, the depth of the recess refers to the vertical distance from the lowest point within the recess to the surface of the positive electrode. It can be measured using conventional methods in the art, such as using a SEM or 3D profilometer to measure the depth of at least 20 or all of the recesses on one side of the positive electrode surface and taking the average value.

[0118] In this disclosure, the shape of the projection of the recess in the thickness direction of the positive electrode sheet is not limited; it can be circular or rectangular. When the projection of the recess in the thickness direction of the positive electrode sheet is circular, the width of the recess is the diameter of the circle; when the projection of the recess in the thickness direction of the positive electrode sheet is non-circular, the width of the recess is the equivalent diameter of a circle with the same area as the non-circular shape. The width of the recess and the spacing between the recesses can be obtained by conventional methods in the art, such as by using SEM to select at least 10 recesses on the surface of the positive electrode sheet, measuring the width of each recess, and taking the average value; selecting at least 10 groups of adjacent recesses on the surface of the positive electrode sheet, measuring the shortest distance between the edges of each group of recesses, and taking the average value.

[0119] In this disclosure, the height of the protrusion can be 2μm-40μm, for example, 2μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, or 40μm. The width of the protrusion can be 0.2mm-8mm, for example, 0.2mm, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, or 8mm. The spacing between the protrusions can be 0.5mm-8mm, for example, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, or 8mm.

[0120] In this disclosure, the height of the protrusion refers to the vertical distance from the highest point of the protrusion to the surface of the positive electrode. It can be measured using conventional methods in the art, such as using a SEM or 3D profilometer to measure the height of at least 20 or all of the protrusions on one side of the positive electrode surface and taking the average value.

[0121] In this disclosure, the shape of the projection of the protrusion onto the thickness direction of the positive electrode sheet is not limited; it can be circular or rectangular. When the projection of the protrusion onto the thickness direction of the positive electrode sheet is circular, the width of the protrusion is the diameter of the circle; when the projection of the protrusion onto the thickness direction of the positive electrode sheet is non-circular, the width of the protrusion is the equivalent diameter of a circle with the same area as the non-circular shape. The width of the protrusion and the spacing between the protrusions can be obtained by conventional methods in the art, such as using SEM to select at least 10 protrusions on the surface of the positive electrode sheet, measuring the width of each protrusion, and taking the average value; selecting at least 10 groups of adjacent protrusions on the surface of the positive electrode sheet, measuring the shortest distance between the edges of each group of protrusions (i.e., the shortest distance between the orthographic projections formed by each group of protrusions on the surface of the positive electrode sheet), and taking the average value.

[0122] In this disclosure, the thickness of the positive electrode sheet located in the arc region and the straight region can also be controlled by adjusting the size of the concave and convex portions on the positive electrode sheet, so that the radius R of the arc region and the thickness T of the core satisfy: 0.9≤2R / T≤4 / π.

[0123] It should be noted that the numerical designations such as "first" and "second" in this disclosure are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0124] The present disclosure will be described in detail below through embodiments. The embodiments described in this disclosure are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0125] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0126] The following examples illustrate the lithium-ion secondary battery of this disclosure.

[0127] Example 1

[0128] Lithium-ion secondary batteries are prepared according to the following method:

[0129] (1) Preparation of positive electrode sheet

[0130] Lithium cobalt oxide, lithium aluminum titanium phosphate (average particle size 1.1 μm), carbon nanotubes, and polyvinylidene fluoride were mixed uniformly in a mass ratio of 96.3:1.2:1.1:1.4. N-methylpyrrolidone (NMP) was added, and the mixture was thoroughly stirred in a mixing tank to prepare a positive electrode slurry. The slurry was then uniformly transferred to the surface of aluminum foil using an extrusion coating device. After baking at 80°C for 10 minutes to completely remove the solvent, the foil was wound up onto a roll. The foil was then unwound and compacted using a variable roll gap press. The variable roll frequency was set according to the length of the foil fragment to control the radius R of the arc region. Note that the variable roll operation was stopped when the press reached the single-sided region. By continuously operating the variable roll operation, positive electrode fragments with the same surface density but different compaction densities could be prepared.

[0131] After being rolled, the electrode sheets are slit along the TD direction according to the designed width using a slitting device. After anomalies are detected and eliminated by a charge-coupled device image sensor (CCD), the small rolls of electrode sheets are wound up. The positive electrode tabs (with a dimension w2 of 6 mm in the length direction of the positive electrode sheet and a thickness h1 of 40 μm) are welded, and the first adhesive tape (acrylic adhesive tape with a dimension w1 of 25.8 mm in the length direction of the positive electrode sheet) is applied. Finally, the positive electrode sheets are cut to obtain the positive electrode sheets.

[0132] The thickness of the positive electrode sheet located in the arc region is 88 μm, and the thickness of the positive electrode sheet located in the flat region is 81 μm, with a ratio of 1.09; the compaction density of the positive electrode active layer located in the arc region is 3.21 g / cm³. 3 The compaction density of the positive electrode active layer located in the flat region is 3.89 g / cm³. 3 The ratio of the two is 0.825; the areal density of the positive electrode active layer located in the arc region is 12.5 mg / cm³. 2 The areal density of the positive electrode active layer located in the flat region is 14.2 g / cm³. 2 The ratio of the two is 0.88; the cross-sectional porosity of the positive electrode in the arc region is 2.89%, and the cross-sectional porosity of the positive electrode in the flat region is 1.92%, with a ratio of 1.505; c2 is 1.2%.

[0133] (2) Preparation of negative electrode sheet

[0134] Artificial graphite, silicon carbide, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid were mixed evenly in a mass ratio of 84.3:12.7:0.45:1.5:0.45:0.6. Deionized water was added, and the mixture was thoroughly stirred in a mixing tank to prepare a negative electrode slurry. The negative electrode slurry was transferred to the surface of copper foil using an extrusion coating device, and then baked in an oven at 120°C for 5 minutes to completely remove the solvent. After that, it was wound up on a roll and then unwound and compacted into an electrode sheet using a variable roll gap press. The variable roll frequency was set according to the electrode sheet length to control the radius R of the arc area. Note that the variable roll operation was stopped when the rolling equipment reached the single-sided area. By continuously running the above variable roll operation, negative electrode sheets with the same surface density but different compaction densities can be prepared.

[0135] After being rolled, the electrode sheets are cut along the TD direction according to the designed width using a slitting device. After eliminating abnormalities through CCD detection, the small rolls of electrode sheets are wound up. The negative electrode tabs (the dimension w4 of the negative electrode tab in the length direction of the negative electrode sheet is 6mm, and the thickness h3 of the negative electrode tab is 40μm) are welded, and the second adhesive tape (acrylic adhesive tape, the dimension w3 of the negative electrode sheet in the length direction of the negative electrode sheet is 25.8mm) is pasted on. Finally, the negative electrode sheets are cut to obtain the negative electrode sheets.

[0136] The thickness of the negative electrode sheet located in the arc region is 93.8 μm, and the thickness of the negative electrode sheet located in the flat region is 83.2 μm, with a ratio of 1.13; the compaction density of the negative electrode active layer located in the arc region is 1.1 g / cm³. 3 The compaction density of the negative electrode active layer located in the flat region is 1.63 g / cm³. 3 The ratio of the two is 0.67; the areal density of the negative electrode active layer located in the arc region is 4.9 mg / cm³. 2 The areal density of the negative electrode active layer located in the flat region is 6.4 mg / cm³.2 The ratio of the two is 0.77; the cross-sectional porosity of the negative electrode sheet located in the arc region is 2.8%, and the cross-sectional porosity of the negative electrode sheet located in the flat region is 1.42%, with a ratio of 1.97; the content of elemental silicon c in the negative electrode active layer is 7%.

[0137] (3) Preparation of electrolyte

[0138] In an argon-filled glove box (moisture content <1 ppm, oxygen content <1 ppm), EC, PC, and EP are mixed in a mass ratio of 1:1:3 to form a homogeneous non-aqueous solvent. Then, lithium salt (lithium hexafluorophosphate), 5% additive (FEC), 3% additive (PS), 2.5% additive (SN), 2% additive (HTCN), and 0.5% additive (DTD) are slowly added to the solvent based on the total mass of the electrolyte. After stirring until homogeneous, the electrolyte is obtained.

[0139] The electrolyte contains 0% propyl propionate.

[0140] (4) Battery fabrication

[0141] Align the heads of the positive electrode sheet, separator (oil-based 5+2+2 separator (5μm thick base film + 2μm thick ceramic layer + 2μm thick polyvinylidene fluoride adhesive layer) prepared in step (1) and the negative electrode sheet prepared in step (2), and wind them into a roll structure at a uniform speed according to the design dimensions to obtain a core; add the electrolyte prepared in step (3); and set electrode tab adhesive between the positive electrode tab and the outer shell and between the negative electrode tab and the outer shell (the first adhesive layer is in contact with the outer shell, the third adhesive layer is in contact with the positive electrode tab / negative electrode tab, and the second adhesive layer is located between the first adhesive layer and the third adhesive layer, the melting point of the first adhesive layer is 116℃, and the melting point of the second adhesive layer is 148℃). The melting point of the third adhesive layer is 116℃, the thickness h2 of the tab adhesive is 20μm, and the dimension of the tab adhesive in the length direction of the positive / negative electrode sheet is 10mm. After hot pressing, the radius R of the arc area and the core thickness T are observed and measured using X-ray or computed tomography. The battery is aged at room temperature (25℃) for 24h and at high temperature (65℃) for 8h to fully wet the electrolyte. The battery is then transferred to a formation device, and the positive and negative tabs are connected to the charging port. The battery is charged and pressurized to activate the cell under the conditions of 80℃ and 510kgf / cell to form a secondary lithium-ion battery that can be charged and discharged externally.

[0142] Among them, the radius R of the arc area is 5.2mm, the thickness T of the core is 10.3mm, 2R / T is 1.010, c / (2R / T) is 0.069, the arc radius r1 of the layer containing the positive electrode tab is 3.6mm, the arc radius r2 of the layer containing the negative electrode tab is 3.6mm, k1 is 2.42, k2 is 2.42, the distance from the first end of the positive electrode tab to the arc area is 4.5mm, and the ratio of the distance from the first end of the positive electrode tab to the arc area to r1 is 1.25; the negative electrode... The distance from the first end of the tab to the arc area is 4.5mm. The ratio of the distance from the first end of the negative electrode tab to the arc area to r2 is 1.25. Both the first and second adhesive tapes completely cover the arc area. R×c2 is 0.0624. c / c2 is 5.83. The ratio of the dimension of the tab adhesive in the length direction of the positive electrode sheet to the dimension of the positive electrode tab in the length direction of the positive electrode sheet is 1.67. The ratio of the dimension of the tab adhesive in the length direction of the negative electrode sheet to the dimension of the negative electrode tab in the length direction of the negative electrode sheet is 1.67.

[0143] Example 2

[0144] Lithium-ion secondary batteries are prepared according to the following method:

[0145] (1) Preparation of positive electrode sheet

[0146] Lithium cobalt oxide, lithium aluminum titanium phosphate (average particle size 0.05 μm), carbon nanotubes, and polyvinylidene fluoride were mixed uniformly in a mass ratio of 94.7:2.8:1.1:1.4. N-methylpyrrolidone (NMP) was added, and the mixture was thoroughly stirred in a mixing tank to prepare a positive electrode slurry. This slurry was then uniformly transferred to the surface of aluminum foil using an extrusion coating device. After baking at 80°C for 10 minutes to completely remove the solvent, the foil was wound up onto a roll. The foil was then unwound and compacted using a variable roll gap press. The variable roll frequency was set according to the length of the foil fragment to control the radius R of the arc region. Note that the variable roll operation was stopped when the press reached the single-sided region. By continuously operating the variable roll operation, positive electrode fragments with the same surface density but different compaction densities could be prepared.

[0147] After being rolled, the electrode sheets are slit along the TD direction according to the designed width using a slitting device. After anomalies are detected and eliminated by a charge-coupled device image sensor (CCD), the small rolls of electrode sheets are wound up. The positive electrode tabs (with a dimension w2 of 10 mm in the length direction of the positive electrode sheet and a thickness h1 of 60 μm) are welded, and the first adhesive tape (acrylic adhesive tape with a dimension w1 of 21.2 mm in the length direction of the positive electrode sheet) is applied. Finally, the positive electrode sheets are cut to obtain the positive electrode sheets.

[0148] The thickness of the positive electrode sheet located in the arc region is 65 μm, and the thickness of the positive electrode sheet located in the flat region is 62 μm, with a ratio of 1.05; the compaction density of the positive electrode active layer located in the arc region is 2.9 g / cm³.3 The compaction density of the positive electrode active layer located in the flat region is 4.2 g / cm³. 3 The ratio of the two is 0.69; the areal density of the positive electrode active layer located in the arc region is 8 mg / cm³. 2 The areal density of the positive electrode active layer located in the flat region is 11 mg / cm³. 2 The ratio of the two is 0.73; the cross-sectional porosity of the positive electrode in the arc region is 2.98%, and the cross-sectional porosity of the positive electrode in the flat region is 1.52%, with a ratio of 1.961; c2 is 2.8%.

[0149] (2) Preparation of negative electrode sheet

[0150] Artificial graphite, silicon carbide, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid were mixed evenly in a mass ratio of 84.3:12.7:0.45:1.5:0.45:0.6. Deionized water was added, and the mixture was thoroughly stirred in a mixing tank to prepare a negative electrode slurry. The negative electrode slurry was transferred to the surface of copper foil using an extrusion coating device, and then baked in an oven at 120°C for 5 minutes to completely remove the solvent. After that, it was wound up on a roll and then unwound and compacted into an electrode sheet using a variable roll gap press. The variable roll frequency was set according to the electrode sheet length to control the radius R of the arc area. Note that the variable roll operation was stopped when the rolling equipment reached the single-sided area. By continuously running the above variable roll operation, negative electrode sheets with the same surface density but different compaction densities can be prepared.

[0151] After being rolled, the electrode sheets are cut along the TD direction according to the designed width using a slitting device. After eliminating abnormalities through CCD detection, the small rolls of electrode sheets are wound up. The negative electrode tabs (the dimension w4 of the negative electrode tab in the length direction of the negative electrode sheet is 10mm, and the thickness h3 of the negative electrode tab is 60μm) are welded, and the second adhesive tape (acrylic adhesive tape with a dimension w3 of 21.2mm in the length direction of the negative electrode sheet) is pasted on. Finally, the negative electrode sheets are cut to obtain the negative electrode sheets.

[0152] The thickness of the negative electrode sheet located in the arc region is 78 μm, and the thickness of the negative electrode sheet located in the flat region is 74.6 μm, with a ratio of 1.05; the compaction density of the negative electrode active layer located in the arc region is 1.37 g / cm³. 3 The compaction density of the negative electrode active layer located in the flat region is 1.49 g / cm³. 3 The ratio of the two is 0.92; the areal density of the negative electrode active layer located in the arc region is 5 mg / cm³. 2 The areal density of the negative electrode active layer located in the flat region is 5.2 mg / cm³. 2The ratio of the two is 0.96; the cross-sectional porosity of the negative electrode sheet located in the arc region is 2.49%, and the cross-sectional porosity of the negative electrode sheet located in the flat region is 1.62%, with a ratio of 1.54; the content of elemental silicon c in the negative electrode active layer is 7%.

[0153] (3) Preparation of electrolyte

[0154] In an argon-filled glove box (moisture content <1 ppm, oxygen content <1 ppm), EC, PC, and EP are mixed in a mass ratio of 1:1:3 to form a homogeneous non-aqueous solvent. Then, lithium salt (lithium hexafluorophosphate), 5% additive (FEC), 3% additive (PS), 2.5% additive (SN), 2% additive (HTCN), and 0.5% additive (DTD) are slowly added to the solvent based on the total mass of the electrolyte. After stirring until homogeneous, the electrolyte is obtained.

[0155] The electrolyte contains 0% propyl propionate.

[0156] (4) Battery fabrication

[0157] Align the heads of the positive electrode sheet, separator (oil-based 5+2+2 separator (5μm thick base film + 2μm thick ceramic layer + 2μm thick polyvinylidene fluoride adhesive layer) prepared in step (1) and the negative electrode sheet prepared in step (2), and wind them into a roll structure at a uniform speed according to the design dimensions to obtain a core; add the electrolyte prepared in step (3); and set electrode tab adhesive between the positive electrode tab and the outer shell and between the negative electrode tab and the outer shell (the first adhesive layer is in contact with the outer shell, the third adhesive layer is in contact with the positive electrode tab / negative electrode tab, and the second adhesive layer is located between the first adhesive layer and the third adhesive layer, the melting point of the first adhesive layer is 102℃, and the melting point of the second adhesive layer is 133℃). The melting point of the third adhesive layer is 102℃, the thickness h2 of the tab adhesive is 16μm, and the dimension of the tab adhesive in the length direction of the positive / negative electrode sheet is 12mm. After hot pressing, the radius R of the arc area and the core thickness T are observed and measured using X-ray or computed tomography. The battery is aged at room temperature (25℃) for 24 hours and at high temperature (65℃) for 8 hours to fully wet the electrolyte. The battery is then transferred to a formation device, and the positive and negative tabs are connected to the charging port. The battery is charged and pressurized to activate the cell under the conditions of 80℃ and 510kgf / cell to form a secondary lithium-ion battery that can be charged and discharged externally.

[0158] Among them, the radius R of the arc area is 2.5mm, the thickness T of the core is 5.3mm, 2R / T is 0.943; c / (2R / T) is 0.074; the radius r1 of the arc of the layer containing the positive electrode tab is 1.9mm; the radius r2 of the arc of the layer containing the negative electrode tab is 1.9mm; k1 is 1.52; k2 is 1.52; the distance from the first end of the positive electrode tab to the arc area is 1.5mm, the distance from the first end of the negative electrode tab to the arc area is 1.5mm; the first end of the positive electrode tab... The ratio of the distance from one end to the arc region to r1 is 0.79; the ratio of the distance from the first end of the negative electrode tab to the arc region to r2 is 0.79; both the first and second adhesive tapes completely cover the arc region; R×c2 is 0.07; c / c2 is 2.5; the ratio of the dimension of the tab adhesive in the length direction of the positive electrode sheet to the dimension of the positive electrode tab in the length direction of the positive electrode sheet is 1.2, and the ratio of the dimension of the tab adhesive in the length direction of the negative electrode sheet to the dimension of the negative electrode tab in the length direction of the negative electrode sheet is 1.2.

[0159] Example 3

[0160] Lithium-ion secondary batteries are prepared according to the following method:

[0161] (1) Preparation of positive electrode sheet

[0162] Lithium cobalt oxide, lithium aluminum titanium phosphate (average particle size 1.93 μm), carbon nanotubes, and polyvinylidene fluoride were mixed uniformly in a mass ratio of 93.3:4.2:1.1:1.4. N-methylpyrrolidone (NMP) was added, and the mixture was thoroughly stirred in a mixing tank to prepare a positive electrode slurry. The slurry was then uniformly transferred to the surface of aluminum foil using an extrusion coating device. After baking at 80°C for 10 minutes to completely remove the solvent, the foil was wound up onto a roll. The foil was then unwound and compacted using a variable roll gap press. The variable roll frequency was set according to the length of the foil fragment to control the radius R of the arc region. Note that the variable roll operation was stopped when the press reached the single-sided region. By continuously operating the variable roll operation, positive electrode fragments with the same surface density but different compaction densities could be prepared.

[0163] After being rolled, the electrode sheets are slit along the TD direction according to the designed width using a slitting device. After anomalies are detected and eliminated by a charge-coupled device image sensor (CCD), the small rolls of electrode sheets are wound up. The positive electrode tabs (with a dimension w2 of 8 mm in the length direction of the positive electrode sheet and a thickness h1 of 80 μm) are welded, and the first adhesive tape (acrylic adhesive tape with a dimension w1 of 39.7 mm in the length direction of the positive electrode sheet) is applied. Finally, the positive electrode sheets are cut to obtain the positive electrode sheets.

[0164] The thickness of the positive electrode sheet located in the arc region is 120 μm, and the thickness of the positive electrode sheet located in the flat region is 108 μm, with a ratio of 1.11; the compaction density of the positive electrode active layer located in the arc region is 3.39 g / cm³.3 The compaction density of the positive electrode active layer located in the flat region is 4.1 g / cm³. 3 The ratio of the two is 0.827; the areal density of the positive electrode active layer located in the arc region is 19 g / cm³. 2 The areal density of the positive electrode active layer located in the flat region is 20.5 g / cm³. 2 The ratio of the two is 0.93; the cross-sectional porosity of the positive electrode in the arc region is 2.56%, and the cross-sectional porosity of the positive electrode in the flat region is 1.68%, with a ratio of 1.524; c2 is 4.2%.

[0165] (2) Preparation of negative electrode sheet

[0166] Artificial graphite, silicon carbide, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid were mixed evenly in a mass ratio of 84.3:12.7:0.45:1.5:0.45:0.6. Deionized water was added, and the mixture was thoroughly stirred in a mixing tank to prepare a negative electrode slurry. The negative electrode slurry was transferred to the surface of copper foil using an extrusion coating device, and then baked in an oven at 120°C for 5 minutes to completely remove the solvent. After that, it was wound up on a roll and then unwound and compacted into an electrode sheet using a variable roll gap press. The variable roll frequency was set according to the electrode sheet length to control the radius R of the arc area. Note that the variable roll operation was stopped when the rolling equipment reached the single-sided area. By continuously running the above variable roll operation, negative electrode sheets with the same surface density but different compaction densities can be prepared.

[0167] After being rolled, the electrode sheets are cut along the TD direction according to the designed width using a slitting device. After eliminating abnormalities through CCD detection, the small rolls of electrode sheets are wound up. The negative electrode tabs (the dimension w4 of the negative electrode tab in the length direction of the negative electrode sheet is 8mm, and the thickness h3 of the negative electrode tab is 80μm) are welded, and the second adhesive tape (acrylic adhesive tape, the dimension w3 of the negative electrode sheet in the length direction of the negative electrode sheet is 39.7mm) is pasted on. Finally, the negative electrode sheets are cut to obtain the negative electrode sheets.

[0168] The thickness of the negative electrode sheet located in the arc region is 132 μm, and the thickness of the negative electrode sheet located in the flat region is 120 μm, with a ratio of 1.1; the compaction density of the negative electrode active layer located in the arc region is 1.38 g / cm³. 3 The compaction density of the negative electrode active layer located in the flat region is 1.71 g / cm³. 3 The ratio of the two is 0.81; the areal density of the negative electrode active layer located in the arc region is 8.4 mg / cm³. 2 The areal density of the negative electrode active layer located in the flat region is 9.45 g / cm³. 2The ratio of the two is 0.89; the cross-sectional porosity of the negative electrode sheet located in the arc region is 2.42%, and the cross-sectional porosity of the negative electrode sheet located in the flat region is 1.3%, with a ratio of 1.86; the content of elemental silicon c in the negative electrode active layer is 7%.

[0169] (3) Preparation of electrolyte

[0170] In an argon-filled glove box (moisture content <1 ppm, oxygen content <1 ppm), EC, PC, and EP are mixed in a mass ratio of 1:1:3 to form a homogeneous non-aqueous solvent. Then, lithium salt (lithium hexafluorophosphate), 5% additive (FEC), 3% additive (PS), 2.5% additive (SN), 2% additive (HTCN), and 0.5% additive (DTD) are slowly added to the solvent based on the total mass of the electrolyte. After stirring until homogeneous, the electrolyte is obtained.

[0171] The electrolyte contains 0% propyl propionate.

[0172] (4) Battery fabrication

[0173] Align the heads of the positive electrode sheet, separator (oil-based 5+2+2 separator (5μm thick base film + 2μm thick ceramic layer + 2μm thick polyvinylidene fluoride adhesive layer) prepared in step (1) and the negative electrode sheet prepared in step (2), and then wind them into a roll structure at a uniform speed according to the design dimensions to obtain a core; add the electrolyte prepared in step (3); and place electrode tab adhesive between the positive electrode tab and the outer shell and between the negative electrode tab and the outer shell (the first adhesive layer is in contact with the outer shell, the third adhesive layer is in contact with the positive electrode tab / negative electrode tab, and the second adhesive layer is located between the first adhesive layer and the third adhesive layer, the melting point of the first adhesive layer is 130℃, and the melting point of the second adhesive layer is 159℃). The melting point of the third adhesive layer is 130℃, the thickness h2 of the tab adhesive is 36μm, and the dimension of the tab adhesive in the length direction of the positive / negative electrode sheet is 15mm. After hot pressing, the radius R of the arc area and the core thickness T are observed and measured using X-ray or computed tomography. The battery is aged at room temperature (25℃) for 24 hours and at high temperature (65℃) for 8 hours to fully wet the electrolyte. The battery is then transferred to a formation device, and the positive and negative tabs are connected to the charging port. The battery is charged and pressurized to activate the cell under the conditions of 80℃ and 510kgf / cell to form a secondary lithium-ion battery that can be charged and discharged externally.

[0174] Among them, the radius R of the arc area is 10.1 mm, the thickness T of the core is 18.2 mm, 2R / T is 1.11, c / (2R / T) is 0.063, the arc radius r1 of the layer containing the positive electrode tab is 7.5 mm, the arc radius r2 of the layer containing the negative electrode tab is 7.5 mm, k1 is 2.02, k2 is 2.02, the distance from the first end of the positive electrode tab to the arc area is 6.8 mm, the distance from the first end of the negative electrode tab to the arc area is 6.8 mm, the first end of the positive electrode tab... The ratio of the distance to the arc region to r1 is 0.91, and the ratio of the distance from the first end of the negative electrode tab to the arc region to r2 is 0.91; both the first and second adhesive tapes completely cover the arc region; R×c2 is 0.424; c / c2 is 1.67; the ratio of the dimension of the tab adhesive in the length direction of the positive electrode sheet to the dimension of the positive electrode tab in the length direction of the positive electrode sheet is 1.88, and the ratio of the dimension of the tab adhesive in the length direction of the negative electrode sheet to the dimension of the negative electrode tab in the length direction of the negative electrode sheet is 1.99.

[0175] Example 4 group

[0176] This set of examples is used to verify the impact of changes to "2R / T".

[0177] This set of embodiments refers to Embodiment 1, except that 2R / T is adjusted by changing the thickness T of the core, as follows:

[0178] Example 4a, T is 11.5 mm, 2R / T is 0.904; wherein, the thickness of the positive electrode sheet located in the arc region is 92 μm, the thickness of the positive electrode sheet located in the flat region is 86 μm, and the ratio of the two is 1.07; the compaction density of the positive electrode active layer located in the arc region is 3.27 g / cm³. 3 The compaction density of the positive electrode active layer located in the flat region is 4.11 g / cm³. 3 The ratio of the two is 0.796; the areal density of the positive electrode active layer located in the arc region is 13.4 mg / cm³. 2 The areal density of the positive electrode active layer located in the flat region is 15.6 mg / cm³. 2 The ratio of the two is 0.86; the cross-sectional porosity of the positive electrode in the arc region is 2.83%, and the cross-sectional porosity of the positive electrode in the flat region is 1.63%, with a ratio of 1.736; the thickness of the negative electrode in the arc region is 100 μm, and the thickness of the negative electrode in the flat region is 96 μm, with a ratio of 1.04; the compaction density of the negative electrode active layer in the arc region is 1.28 g / cm³. 3 The compaction density of the negative electrode active layer located in the flat region is 1.6 g / cm³. 3 The ratio of the two is 0.8; the areal density of the negative electrode active layer located in the arc region is 6 mg / cm³. 2The areal density of the negative electrode active layer located in the flat region is 7.2 mg / cm³. 2 The ratio of the two is 0.83; the cross-sectional porosity of the negative electrode in the arc region is 2.58%, and the cross-sectional porosity of the negative electrode in the flat region is 1.53%, with a ratio of 1.69.

[0179] Example 4b, T is 8.2 mm, 2R / T is 1.268; wherein, the thickness of the positive electrode sheet located in the arc region is 75 μm, and the thickness of the positive electrode sheet located in the flat region is 68 μm, with a ratio of 1.1; the compaction density of the positive electrode active layer located in the arc region is 2.93 g / cm³. 3 The compaction density of the positive electrode active layer located in the flat region is 4.02 g / cm³. 3 The ratio of the two is 0.729; the areal density of the positive electrode active layer located in the arc region is 9.8 mg / cm³. 2 The areal density of the positive electrode active layer located in the flat region is 12 mg / cm³. 2 The ratio of the two is 0.82; the cross-sectional porosity of the positive electrode in the arc region is 2.93%, and the cross-sectional porosity of the positive electrode in the flat region is 1.76%, with a ratio of 1.665; the thickness of the negative electrode in the arc region is 80 μm, and the thickness of the negative electrode in the flat region is 72 μm, with a ratio of 1.11; the compaction density of the negative electrode active layer in the arc region is 1.14 g / cm³. 3 The compaction density of the negative electrode active layer located in the flat region is 1.48 g / cm³. 3 The ratio of the two is 0.77; the areal density of the negative electrode active layer located in the arc region is 4.2 mg / cm³. 2 The areal density of the negative electrode active layer located in the flat region is 4.9 mg / cm³. 2 The ratio of the two is 0.86; the cross-sectional porosity of the negative electrode in the arc region is 2.75%, and the cross-sectional porosity of the negative electrode in the flat region is 1.72%, with a ratio of 1.6.

[0180] Example 5 group

[0181] This set of examples is used to verify the impact of changing 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.

[0182] This set of embodiments is based on Embodiment 1, except that the thickness ratio is controlled by changing the areal density of the positive electrode active layer located in the arc region (while keeping the compaction density constant), as follows:

[0183] In 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 in the arc region to the thickness of the positive electrode sheet in the flat region is 0.74; wherein, the areal density of the positive electrode active layer located in the arc region is 8.4 mg / cm³. 2 The ratio of the positive electrode active layer density in the arc region to that in the flat 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.

[0184] In Example 5b, the thickness of the positive electrode in the arc region is 106 μm, and the ratio of the thickness of the positive electrode in the arc region to the thickness of the positive electrode in the flat region is 1.31; wherein, the areal density of the positive electrode active layer in the arc region is 18.6 mg / cm³. 2 The ratio of the positive electrode active layer density in the arc region to that in the flat 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.

[0185] Example 6

[0186] Used to verify the effects of changes to the "ear gel".

[0187] The procedure was carried out in accordance with Example 1, except that the tab adhesive was changed as follows: the tab adhesive has a single-layer structure and a melting point of 140°C.

[0188] Example 7 group

[0189] This set of examples is used to verify the impact of changes in the melting points of the first, second, and third adhesive layers of the tab adhesive.

[0190] This set of embodiments is based on Embodiment 1, except that at least one of the melting points of the first adhesive layer, the second adhesive layer, and the third adhesive layer is changed, as follows:

[0191] In Example 7a, the melting point of the first adhesive layer is 95°C, and the melting point of the third adhesive layer is 95°C.

[0192] In Example 7b, the melting point of the first adhesive layer is 137°C, and the melting point of the third adhesive layer is 137°C.

[0193] In Example 7c, the melting point of the second adhesive layer is 125°C;

[0194] In Example 7d, the melting point of the second adhesive layer was 169°C.

[0195] Example 8

[0196] This is used to verify the impact of whether the first and second adhesive tapes cover the arc area.

[0197] Referring to Example 1, the difference is that the positions of the positive and negative electrode tabs, as well as the dimensions w1 of the first adhesive tape along the length of the positive electrode and w3 of the second adhesive tape along the length of the negative electrode, are adjusted to control whether the first and second adhesive tapes cover the arc area, so that the first and second adhesive tapes do not cover the arc area. The radius R of the arc area is 5.18 mm, the thickness T of the core is 10.3 mm, 2R / T is 1.006, w1 is 20.8 mm, w3 is 20.8 mm, the distance from the first end of the positive electrode tab to the arc area is 12.8 mm, and the distance from the first end of the negative electrode tab to the arc area is 12.8 mm.

[0198] Example 9 group

[0199] This set of examples is used to verify the impact of changes in the "mass content c2 of solid electrolyte in the positive electrode active layer".

[0200] This set of embodiments follows the same procedure as Embodiment 1, except that c2 is controlled by changing the formulation of the positive electrode slurry, as detailed below:

[0201] In Example 9a, the mass ratio of lithium cobalt oxide, lithium aluminum titanium phosphate, carbon nanotubes, and polyvinylidene fluoride was 97:0.5:1.1:1.4; wherein, c2 was 0.5%; c / c2 was 14, and R×c2 was 0.026.

[0202] In Example 9b, the mass ratio of lithium cobalt oxide, lithium titanium aluminum phosphate, carbon nanotubes, and polyvinylidene fluoride was 92.5:5:1.1:1.4; wherein, c2 was 5%; c / c2 was 1.4, and R×c2 was 0.26.

[0203] Example 10

[0204] Used to verify the impact of changes to "R×c2".

[0205] The experiment was conducted in accordance with Example 2, except that R×c2 was adjusted by changing c2, as follows: the mass ratio of lithium cobalt oxide, lithium aluminum titanium phosphate, carbon nanotubes and polyvinylidene fluoride was 96.3:1.2:1.1:1.4, c2 was 1.2% and R×c2 was 0.03.

[0206] Example 11 group

[0207] This set of examples is used to verify the impact of changes in the "average particle size of solid electrolytes".

[0208] This set of embodiments is based on Embodiment 1, except that the average particle size of lithium titanium aluminum phosphate is changed, as follows:

[0209] In Example 11a, the average particle size of lithium titanium aluminum phosphate was 0.02 μm;

[0210] Example 11b: The average particle size of lithium titanium aluminum phosphate is 3 μm.

[0211] Example 12 group

[0212] This set of examples is used to verify the impact of changing the "content of elemental silicon c in the negative electrode active layer".

[0213] This set of embodiments follows the same procedure as Embodiment 1, except that c is adjusted by changing the formulation of the negative electrode slurry, as detailed below:

[0214] In Example 12a, the mass ratio of artificial graphite, silicon carbide, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid was 91.5:5.5:0.45:1.5:0.45:0.6, where c was 3%; c / c2 was 2.5; and c / (2R / T) was 0.03.

[0215] In Example 12b, the mass ratio of artificial graphite, silicon carbide, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid was 69.7:27.3:0.45:1.5:0.45:0.6, where c was 15%; c / c2 was 12.5; and c / (2R / T) was 0.149.

[0216] In Example 12c, the mass ratio of artificial graphite, silicon carbide, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid was 60.6:36.4:0.45:1.5:0.45:0.6, where c was 20%; c / c2 was 16.67; and c / (2R / T) was 0.198.

[0217] In Example 12d, the mass ratio of artificial graphite, silicon carbide, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid was 24.3:72.7:0.45:1.5:0.45:0.6, where c was 40%; c / c2 was 33.33; and c / (2R / T) was 0.396.

[0218] Example 13

[0219] Used to verify the impact of changes to "c / c2".

[0220] The procedure was carried out in accordance with Example 12a, except that c / c2 was adjusted by changing c2, specifically as follows: c2 was 4.2% and c / c2 was 0.71.

[0221] Example 14 group

[0222] This set of examples is used to verify the impact of changes in the "mass content of propyl propionate in the electrolyte".

[0223] This set of embodiments is based on Example 1, except that the mass content of propyl propionate in the electrolyte is changed, as follows:

[0224] Example 14a: 0.5% propyl propionate was added to the electrolyte;

[0225] Example 14b: 1.5% propyl propionate was added to the electrolyte.

[0226] All of the above embodiments satisfy the following:

[0227] The median particle size Dv50 of lithium titanium aluminum phosphate is 0.02 μm-2 μm;

[0228] The volumetric particle size distribution of artificial graphite is as follows: Dv10 is 5μm-10μm, Dv50 is 10μm-25μm, and Dv90 is 25μm-40μm; the interlayer spacing d002 of artificial graphite is 0.3356nm-0.3359nm; and the reversible capacity of artificial graphite is 350mAh / g-365mAh / g.

[0229] Silicon-carbon comprises a porous carbon substrate and silicon material located within the pores of the porous carbon substrate; the volumetric particle size distribution of silicon-carbon is as follows: Dv10 is 1μm-6μm, Dv50 is 3μm-15μm, and Dv90 is 12μm-30μm; the specific surface area of ​​silicon-carbon is 0.5m². 2 / g-10m 2 / g, the average sphericity of silicon-carbon is 0.5-1.

[0230] Comparative Example 1

[0231] The experiment was conducted in accordance with Example 1, except that lithium titanium aluminum phosphate was not added to the positive electrode slurry. Instead, lithium cobalt oxide, carbon nanotubes, and polyvinylidene fluoride were prepared in a mass ratio of 97.5:1.1:1.4.

[0232] Comparative Example 2

[0233] The procedure is carried out in accordance with Example 1, except that 2R / T is adjusted by changing the radius R of the arc area and the core thickness T, as follows:

[0234] 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;

[0235] Comparative Example 2b has a radius R of 5.7 mm for the arc area, a core thickness T of 8.6 mm, and a 2R / T ratio of 1.326.

[0236] Test case

[0237] (1) Furnace temperature safety test

[0238] The batteries prepared in the examples and comparative examples were subjected to furnace temperature safety tests. The specific test methods are as follows:

[0239] In an environment of 25℃±3℃, the battery was discharged to 3.0V at 0.2C, left to stand for 10 minutes, and then charged to 4.53V at 0.5C, with a cutoff rate of 0.02C. The battery was placed in a test chamber, which was heated at a rate of (5±2)℃ / min. When the temperature inside the test chamber reached 130℃±2℃, it was kept at a constant temperature for 60 minutes. During this period, the battery was considered to have passed the test if it did not smoke, catch fire, or explode. Five batteries were tested in each set of examples and comparative examples, and the results were recorded in the form of "n / 5", where n represents the number of batteries that passed the test. For example, 5 / 5 means that all five batteries were tested and passed the test. The larger the n, the better the furnace temperature safety performance of the battery. The results are recorded in Table 1.

[0240] (2) Overcharge safety test

[0241] The batteries prepared in the examples and comparative examples were subjected to overcharge safety tests. The specific test methods are as follows:

[0242] The battery was discharged to 3.0V at 0.5C in an environment of 25℃±3℃, and then placed in an explosion-proof box. The thermocouple contacts were fixed at the center of the largest surface of the battery, and a power supply was connected for charging. The battery was charged at a constant current of 3C to 4.6V, and then charged at a constant voltage of 4.6V. When the charging time reached 7 hours, the test was stopped, and the voltage and temperature data were monitored. The battery was considered to have passed the test if it did not smoke, catch fire, or explode. Five batteries were tested in each example and comparative example, and the results were recorded in the form of "m / 5", where m represents the number of batteries that passed the test. For example, 5 / 5 means that all five batteries were tested and passed the test. The larger the value of m, the better the overcharge safety performance of the battery. The results are recorded in Table 1.

[0243] (3) Ratio Test

[0244] The batteries prepared in the examples and comparative examples were subjected to rate testing. The specific testing methods are as follows:

[0245] At 25℃±3℃, discharge at 0.2C to 3.0V, let stand for 10min, then charge at 0.5C to 4.53V, with a cutoff rate of 0.02C; let stand for 10min, then discharge at 1C to 3.0V, record the discharge capacity retention rate, and record the results in Table 1.

[0246] (4) Loop Test

[0247] The batteries prepared in the examples and comparative examples were subjected to cycle tests, and the specific test methods are as follows:

[0248] The battery was discharged at 0.7C to 3.0V, charged at 2C to 4.53V, and then cut off at 0.2C for 400 cycles. The cycle capacity retention rate of the battery was calculated and the results are recorded in Table 1.

[0249] (5) High-temperature storage test

[0250] The batteries prepared in the examples and comparative examples were subjected to high-temperature storage tests. The specific test methods are as follows:

[0251] In an environment of 25℃±3℃, the battery was charged at 0.5C to 4.53V, cut off at 0.05C, and discharged at 0.2C to 3.0V, and the discharge capacity was recorded. Then, the battery was charged at 0.5C to 4.53V, cut off at 0.05C, and the full-charge thickness of the battery was measured. The battery was then placed in an environment of (60±2)℃ for 7 days, and then placed in an environment of 25℃±3℃ for 2 hours to measure the battery thickness. The battery was then discharged at 0.2C to 3.0V, and the discharge capacity was recorded. The results of capacity recovery rate and thickness expansion rate are recorded in Table 1.

[0252] Table 1

[0253] As can be seen from Table 1, the battery disclosed herein has higher rate performance, cycle stability and high temperature storage stability compared with the comparative example, and can also effectively reduce the safety risks caused by gas production.

[0254] The preferred embodiments of this disclosure have been described in detail above; however, this disclosure is not limited thereto. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in this disclosure and are all within the protection scope of this disclosure.

Claims

1. A lithium-ion secondary battery, characterized by comprising: This includes a wound core composed of positive electrode plates, a separator, and negative electrode plates stacked and wound together; The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed 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 current collector and a positive active layer disposed on at least one side of the positive current collector, wherein the positive active layer includes a positive active material and a solid electrolyte; The 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 core satisfy the following condition: 0.9 ≤ 2R / T ≤ 4 / π, where π is the mathematical constant pi.

2. The lithium-ion secondary battery according to claim 1, wherein The radius R of the arc area is 1-100 mm, and the thickness T of the core is 1-200 mm. And / or, 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 0.7-1.5; And / or, the thickness of the positive electrode located in the flat region is 20μm-150μm; And / or, 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; And / or, the thickness of the negative electrode located in the flat region is 20μm-200μm.

3. The lithium-ion secondary battery according to claim 1 or 2, wherein The 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 in the flat area is 2 g / cm 3 -5 g / cm 3 ; And / or, 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 flat region is 0.6-1; and / or the surface density of the positive electrode active layer at the flat area is 8 mg / cm 2 - 25 mg / cm 2 .

4. The lithium-ion secondary battery according to any one of claims 1-3, wherein, The 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 active layer at the flat area is 1 g / cm 3 -2.5 g / cm 3 ; And / or, 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 flat region is 0.6-1; and / or the surface density of the negative active layer at the flat area is 3 mg / cm 2 - 12 mg / cm 2 .

5. The lithium-ion secondary battery according to any one of claims 1-4, wherein, The ratio of the cross-sectional porosity of the negative electrode sheet located in the arc region to the cross-sectional porosity of the negative electrode sheet located in the straight region is 1.5-2; And / or, the ratio of the cross-sectional porosity of the positive electrode located in the arc region to the cross-sectional porosity of the positive electrode located in the straight region is 1.5-2.

6. The lithium-ion secondary battery according to any one of claims 1-5, wherein, The silicon content c in the negative electrode active layer satisfies the following condition with respect to 2R / T: 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 silicon content in the silicon-carbon is 20%-70% by mass; More preferably, the volumetric particle size distribution of the silicon carbide is: Dv10 is 1μm-6μm, Dv50 is 3μm-15μm, and Dv90 is 12μm-30μm.

7. The lithium-ion secondary battery according to any one of claims 1-6, wherein, The lithium-ion secondary battery also includes a casing; the positive electrode sheet also includes a positive electrode tab and tab adhesive disposed on the surface of the positive electrode tab. And / or, the negative electrode sheet further includes a negative electrode tab and tab adhesive disposed on the surface of the negative electrode tab; Preferably, the tab adhesive includes a first adhesive layer, a second adhesive layer, and a third adhesive layer stacked sequentially, wherein the first adhesive layer is in contact with the outer shell, the third adhesive layer is in contact with the positive electrode tab, and / or the third adhesive layer is in contact with the negative electrode tab, and the second adhesive layer is located between the first adhesive layer and the third adhesive layer; More preferably, the melting point of the first adhesive layer is 100℃-130℃, the melting point of the second adhesive layer is 130℃-160℃, and the melting point of the third adhesive layer is 100℃-130℃; Preferably, the thickness h2 of the tab adhesive is 15μm-50μm.

8. The lithium-ion secondary battery according to claim 7, wherein, The tab adhesive has a dimension of 5mm-20mm along the length of the positive electrode sheet; And / or, the tab adhesive has a dimension of 5mm-20mm in the length direction of the negative electrode sheet; And / or, the ratio of the dimension of the tab adhesive 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 adhesive 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.

9. The lithium-ion secondary battery according to any one of claims 1-8, wherein, The positive electrode sheet further includes a positive electrode tab, a positive electrode tab welding area, and a first adhesive tape. 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 along the length of the positive electrode sheet is 15mm-50mm, and the dimension w2 of the positive electrode tab along the length 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 closest to the arc region; Preferably, the first adhesive tape covers at least a portion of the arc area.

10. The lithium-ion secondary battery according to any one of claims 1-9, wherein, The negative electrode sheet also includes a negative electrode tab, a negative electrode tab welding area, and a second adhesive paper. The negative electrode tab is located in the negative electrode tab welding area, and the second adhesive paper covers the negative electrode tab welding area. Preferably, the second adhesive tape has a dimension w3 of 15mm-50mm in the length direction of the negative electrode sheet, and the negative electrode tab has a dimension w4 of 2mm-10mm in the length direction of the negative electrode sheet; 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 closest to the arc region; Preferably, the second adhesive tape covers at least a portion of the arcuate area.

11. The lithium-ion secondary battery according to claim 9 or 10, wherein, w1, w2 and the radius r1 of the arc of the layer where the positive electrode tab is located satisfy: w1=k1×w2+π×r1, where k1 is 1.1-3; And / or, w3, w4 and the radius r2 of the arc of the layer where the negative electrode tab is located satisfy: w3=k2×w3+π×r2, where k2 is 1.1-3.

12. The lithium-ion secondary battery according to any one of claims 1-11, wherein, The solid electrolyte includes 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 includes 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.

13. The lithium-ion secondary battery according to any one of claims 1-12, wherein, The mass content c2 of the solid electrolyte in the positive electrode active layer and the radius R of the arc, in mm, satisfy: 0.02≤R×c2≤0.5; Preferably, 0.06≤R×c2≤0.

45.

14. The lithium-ion secondary battery according to any one of claims 1-13, wherein, The content of elemental silicon c in the negative electrode active layer and the content of solid electrolyte c2 in the positive electrode active layer satisfy the following condition: 0.5≤c / c2≤35; Preferably, 1.5 ≤ c / c2 ≤ 13.

15. The lithium-ion secondary battery according to any one of claims 1-14, wherein, The lithium-ion secondary battery also includes an electrolyte, wherein the mass content of propyl propionate in the electrolyte is ≤10%; Preferably, the electrolyte further includes a non-aqueous solvent, which includes carbonate substances.

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