A type of battery

Abstract

This invention provides a battery comprising a wound electrode assembly. The electrode assembly includes a negative electrode sheet, a separator, and a positive electrode sheet sequentially stacked and wound. The electrode assembly includes an arc-shaped region and a straight region connected to the arc-shaped region. The positive electrode sheet includes a positive current collector, which has a main body region and a passivation region along its length. The passivation region is located in the arc-shaped region, and the main body region is located in the straight region. At least one surface of the positive current collector located in the main body region includes a first active material layer, and at least one surface of the positive current collector located in the passivation region includes a second active material layer. The impedance of the first active material layer is less than the impedance of the second active material layer. The battery provided by this invention can effectively reduce the cycle expansion caused by excessive negative electrode embedding in the arc-shaped region of the wound battery due to excessive positive electrode activity, thereby effectively improving the bulging and cracking problem at the arc-shaped region of the lithium-ion battery, enhancing the cycle stability and safety of the battery.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, and more particularly to a battery. Background Technology

[0002] With the global trend towards energy conservation and emission reduction, and the rise of green energy, lithium-ion battery (LIB) technology has become extremely important, reducing reliance on fossil fuels. LIBs are the most widely used batteries in portable electronics, electric vehicles, power tools, and various grid applications due to their high power and energy density, low cost, and better lifespan. Since the energy density of a LIB is primarily determined by its output voltage and specific capacity, the electrode becomes a crucial component. The LIB electrode assembly consists of active materials and current collectors, with the current collectors having a large surface area for electrochemical processes during charge-discharge cycles. To meet the rapidly growing customer demands in the electronics industry, further performance development of LIBs in fast charging is essential.

[0003] Most researchers focus on improving the properties and chemical composition of the active materials in the electrodes, reducing electrode thickness, and decreasing the mass load (amount of active material per unit area). However, these methods do not significantly improve the rapid swelling of batteries during fast charging. In particular, the curved areas of wound-structured batteries often experience over-intercalation of the negative electrode due to excessive positive electrode activity, leading to a continuously increasing cycle expansion rate and severe swelling at the curved areas. This results in capacity decay and even short circuits and fires, severely impacting the cycle life and safety of high-rate charge / discharge lithium-ion batteries. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a battery that can effectively reduce the cyclic expansion caused by excessive negative electrode embedding in the arc region of the wound battery due to excessive positive electrode activity, thereby effectively improving the bulging and cracking problem at the arc of the lithium-ion battery, enhancing the battery's cycle stability and safety.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A first aspect of the present invention provides an electrode assembly comprising a wound structure, the electrode assembly comprising a negative electrode, a separator, and a positive electrode sequentially stacked and wound, the electrode assembly comprising an arc region and a straight region connected to the arc region, the positive electrode comprising a positive current collector, the positive current collector having a main body region and a passivation region disposed along its length direction, the passivation region being located in the arc region, and the main body region being located in the straight region;

[0007] At least one side surface of the positive current collector located in the main body region includes a first active material layer, and at least one side surface of the positive current collector located in the passivation region includes a second active material layer;

[0008] The impedance of the first active material layer is less than the impedance of the second active material layer.

[0009] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0010] The battery of the present invention employs a partitioned coating technique on the arc and straight regions of the wound electrode assembly, which is formed by winding. This allows the impedance of the first active material coating in the main body region located in the straight region of the positive electrode current collector to be less than the impedance of the second active material coating in the passivation region located in the arc region of the current collector. This effectively improves the electrode impedance and electrode strength at specific locations on the positive electrode sheet, enabling the passivated positive electrode sheet to better match the negative electrode region, which is prone to lithium plating bulging. This effectively improves the arc bulging and cracking of lithium-ion batteries caused by excessive lithium intercalation in the arc region of the negative electrode, while alleviating problems such as deformation and cracking of the battery cell during subsequent use due to stress concentration in the arc region of the cell. This enhances the cycle stability and safety of the battery.

[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 This is a cross-sectional schematic diagram of an electrode assembly with a core structure provided in an embodiment of the present invention;

[0013] Figure 2 This is a top view schematic diagram of a positive electrode structure with a centrally located tab provided in an embodiment of the present invention;

[0014] Figure 3 This is a top view schematic diagram of the positive electrode structure of the multi-tab provided in an embodiment of the present invention;

[0015] Figure 4 This is a top view schematic diagram of the positive electrode structure of a conventional electrode tab provided in an embodiment of the present invention;

[0016] Figure 5 Here are cross-sectional SEM images of the first active material layer and the second active material layer of the positive electrode in an example of the present invention.

[0017] Figure 6 This is a planar SEM image of the second active material layer of the positive electrode in an example of the present invention.

[0018] Explanation of reference numerals in the attached figures:

[0019] 1-Main region, 11-Main region, 2-Passivation region, 21-Passivation region, 3-Electrode, 4-Empty foil region. Detailed Implementation

[0020] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0021] The first aspect of the present invention provides a battery, such as Figure 1 The diagram shows a cross-sectional view of an electrode assembly with a wound core structure provided in an embodiment of the present invention. The battery includes a wound electrode assembly comprising a negative electrode sheet, a separator, and a positive electrode sheet sequentially stacked and wound. The electrode assembly includes an arc region 2 and a straight region 1 connected to the arc region 2. The positive electrode sheet includes a positive current collector. The positive current collector has a main body region 11 and a passivation region 21 arranged along its length. The passivation region 21 is located in the arc region 2, and the main body region 11 is located in the straight region 1. When the above-mentioned electrode assembly with a wound structure is unfolded, the main body region 11 and the passivation region 21 are alternately arranged along the length direction of the positive current collector according to the structural characteristics of the wound cell, such as... Figure 2 As shown, Figure 2 This is a top view schematic diagram of a positive electrode structure with a centrally located tab provided in an embodiment of the present invention.

[0022] like Figure 2 , 3 As shown in Figure 4, at least one surface of the positive current collector located in the main body region 11 includes a first active material layer, and at least one surface of the positive current collector located in the passivation region 21 includes a second active material layer; the impedance of the first active material layer is less than the impedance of the second active material layer. The lower impedance of the first active material layer compared to the second active material layer is equivalent to passivating the positive current collector region where the second active material layer is located, thus forming a passivation region with higher impedance. The positive current collector region without passivation treatment has lower impedance and constitutes the main body region.

[0023] Conventional technology does not passivate the arc of the positive electrode sheet. During the winding process, the CB value (the margin by which the capacity of the negative electrode exceeds the capacity of the positive electrode under the same conditions and in the same stage) at the arc of the negative electrode convex side corresponding to the positive electrode concave side decreases. This decrease is due to insufficient CB value in certain areas during charging and discharging, which can lead to excessive lithium insertion in the corresponding negative electrode arc, causing the battery arc to bulge and the electrode to break. This seriously affects the long-cycle performance and safety performance of lithium-ion batteries. Therefore, the positive electrode sheet of the present invention employs a partitioned coating technique in the arc region and non-arc region (flat region) of its wound core. This allows the impedance of the first active material coating located in the non-arc region of the positive electrode current collector to be less than the impedance of the second active material coating located in the arc region of the current collector. In other words, passivating the active coating located in the arc region of the electrode sheet can effectively improve the electrode impedance and electrode strength at specific locations. This allows the passivated positive electrode sheet to better match the negative electrode region, which is prone to lithium plating bulging, and reduces the lithium intercalation SOC on the negative electrode side (SOC represents the state of charge, the ratio of the current remaining charge Qc to its total capacity Qn when fully charged, SOC = (Qc / Qn) × 100%). This improves the bulging and cracking of the lithium-ion battery arc caused by the transitional lithium intercalation at the negative electrode arc, and alleviates the problems of deformation and cracking of the cell during subsequent use caused by stress concentration in the arc region of the cell. This enhances the cycle stability and safety of the battery.

[0024] In this invention, such as Figure 2 , 3 As shown in Figures 4 and 5, the passivation region 21 includes N 钝 passivation region, N 钝 = The total number of arcs in the winding structure of the electrode assembly formed by winding the positive electrode sheet, that is, the number of sub-passivation regions included in the passivation region of the positive current collector, depends on the total number of arcs in the winding structure of the electrode assembly formed by winding the positive electrode sheet. Furthermore, the main body region 11 has arc regions on both sides along the winding direction of the electrode assembly. Therefore, N 钝 The value of is actually equal to the sum of the number of arcs on both sides of the electrode assembly; however, it should be noted that the arc area only represents the division of a specific area on the electrode assembly, and does not mean that the entire specific area is a passivation area or that the entire area needs to be passivated.

[0025] In one specific embodiment, at least one side surface of the positive current collector located in the sub-passivation region includes the second active material layer, or at least one side surface of the positive current collector located in the sub-passivation region includes both the first active material layer and the second active material layer. There are a large number of sub-passivation regions. Sub-passivation regions requiring passivation modification include the second active material layer or simultaneously include both the first and second active material layers. Sub-passivation regions not requiring passivation modification simply include the first active material layer, consistent with the main region. Furthermore, when a sub-passivation region simultaneously includes both the first and second active material layers, the first and second active material layers are sequentially arranged along the length direction of the positive current collector, not stacked. It is understood that N 钝 The second active material layer may not be fully coated in all sub-passivation regions. Some sub-passivation regions may be coated with both the first and second active material layers simultaneously. This ensures that the impedance of the positive current collector surface coating in the arc region is less than that in the flat region, thereby effectively improving the arc bulging and cracking of lithium-ion batteries caused by excessive lithium intercalation in the negative arc, enhancing the cycle stability and safety of the battery.

[0026] In one specific implementation, such as Figure 2 , 3 As shown in Figure 4, in any of the sub-passivation regions, along the length direction of the positive current collector, the length of the second active material layer is L, and the circumference of the arc formed by the sub-passivation region corresponding to the second active material layer is C. The L and C satisfy 1 / 3*C≤L≤1 / 2*C; that is, the length L of the second active material layer is 1 / 3 to 1 / 2 of the circumference C of the entire circle completed by the arc region formed by the winding structure of the electrode assembly formed by the winding of the sub-passivation region corresponding to the second active material layer.

[0027] In one specific implementation, such as Figure 2 As shown, along the width direction of the positive electrode current collector, the width of the second active material layer is D. 活 The width of the positive electrode is D. 极 The D 活 and D 极 Satisfying D 活 ≤D 极 That is, the second active material layer can be fully coated in the width direction of the positive electrode current collector, at which point D 活 =D 极 Alternatively, it can be left unpainted; in this case, D... 活 <D 极 .

[0028] In one specific implementation, such as Figure 1As shown, along the length direction of the positive electrode current collector, the spacing between adjacent second active material layers is I, and the width of the flat region is D. 平 The width of the arc region is D. 圆 The I and D 平 and D 圆 , satisfying 0≤(ID) 平 ) / D 圆 ≤1. The width of the second active material layer coating area along the length of the positive electrode current collector in the passivation region can be equal to or less than the width of the passivation region along the length of the positive electrode current collector. That is, the passivation region may not be completely coated along its length. Therefore, the spacing I between adjacent second active material layers will be greater than or equal to the width of the flat region along the length of the positive electrode current collector, and less than or equal to the sum of the width of the flat region along the length of the positive electrode current collector and the width of the arc region along the length of the positive electrode current collector. Therefore, the spacing I and D... 平 and D 圆 , satisfying 0≤(ID) 平 ) / D 圆 ≤1. In addition, it should be noted that when the passivation region is not fully coated in the length direction, the remaining width of the positive current collector in the passivation region needs to be provided with a first active material layer.

[0029] In one specific embodiment, the coverage area of ​​the second active material layer on the surface of the positive electrode current collector accounts for 3%-20% of the total area of ​​the positive electrode current collector, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20%. When the area of ​​the second active material layer is too large, the actual capacity of the battery cannot be fully utilized, the rate performance of the battery deteriorates, and the capacity decreases; when the area of ​​the second active material layer is too small, the bulging and cracking problem at the arc cannot be effectively improved, affecting the cycle and safety performance of the battery.

[0030] In a preferred embodiment, the coverage area of ​​the second active material layer on the surface of the positive electrode current collector accounts for 3%-8% of the total area of ​​the positive electrode current collector.

[0031] In this invention, the first active material layer and the second active material layer may include a positive electrode active material, a binder, and a conductive agent; the mass ratio of the binder to the conductive agent in the first active material layer is a1, 0.5≤a1≤2, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2; the mass ratio of the binder to the conductive agent in the second active material layer is a2, 1.5≤a2≤6, for example, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 3, 4, 5, 6.

[0032] In one specific implementation, 0.13 ≤ a1 / a2 ≤ 0.6, for example, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.55, 0.6.

[0033] This invention adjusts the content relationship between the conductive agent and the binder in the first and second active material layers simultaneously to satisfy 0.5≤a1≤2 and / or 1.5≤a2≤6, and further satisfies 0.13≤a1 / a2≤0.6. This not only does not affect any electrical performance of the battery, but also significantly reduces the material shedding problem in the electrode passivation area during winding, significantly increases the flexibility of the arc electrode sheet, significantly reduces the amount of lithium intercalation in the arc during full charge, and significantly reduces the expansion rate of the negative electrode at the arc, thereby alleviating the expansion force in the arc area. This avoids the problems of arc breakage, arc lithium plating, and significant thickness increase caused by excessive lithium intercalation and expansion in the arc, and further improves the cycle stability and safety of lithium-ion batteries.

[0034] In a preferred embodiment, 0.7 ≤ a1 ≤ 1.5.

[0035] In a preferred embodiment, 1.9 ≤ a2 ≤ 5.

[0036] In a preferred embodiment, 0.2 ≤ a1 / a2 ≤ 0.5.

[0037] In one specific embodiment, the positive electrode active material includes lithium transition metal oxides and / or lithium-containing phosphates.

[0038] In one specific embodiment, the lithium transition metal oxide includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds.

[0039] In one specific embodiment, the lithium-containing phosphate includes at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and modified compounds thereof.

[0040] In one specific embodiment, the adhesive includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, and aluminate coupling agent.

[0041] In one specific embodiment, the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0042] In one specific embodiment, the positive electrode active material has a mass content of 90wt%-98wt% in the second active material layer, for example, 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, or 98wt%; the binder has a mass content of 2wt%-10wt% in the second active material layer, for example, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%; and the conductive agent has a mass content of 0.1wt%-1wt% in the second active material layer, for example, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, or 1wt%.

[0043] In one specific embodiment, the positive electrode active material has a mass content of 90wt%-98wt% in the first active material layer, for example, 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, or 98wt%; the binder has a mass content of 1wt%-5wt% in the first active material layer, for example, 1wt%, 2wt%, 3wt%, 4wt%, or 5wt%; and the conductive agent has a mass content of 0.5wt%-5wt% in the first active material layer, for example, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, or 5wt%.

[0044] This invention, by reducing the amount of conductive agent used in the second active material layer and increasing the amount of binder used, can increase the difficulty of delithiation in the passivation zone at the positive electrode arc and improve the strength of the positive electrode arc. It also reduces the conductivity of the second active material layer material and increases the impedance of the second active material layer material in the passivation zone, making the impedance of the second active material layer greater than that of the first active material layer. This improves the reaction rate of the active material material in the corresponding sensitive area at the arc due to local passivation modification. When the value is within this range, the expansion stress in the arc area during charging and discharging will be significantly lower than that in the central core area, which can effectively alleviate the problem of electrolyte leakage caused by stress compression at the arc. Further reduction of arc stress can effectively alleviate the problem of electron transport obstruction caused by arc material loss and breakage, significantly improving the safety and cycle stability of lithium batteries.

[0045] In this invention, the first active material layer may include a positive electrode active material, a binder, and a conductive agent, and the second active material layer may include an active material, a filler, a binder, and a conductive agent. Alternatively, a filler may be added to the second active material layer as a passivation modifier for the passivation region active material, thereby reducing the impedance of the second active material layer.

[0046] In one specific embodiment, the filler comprises inorganic particles, which include at least one of oxide ceramics, nitride ceramics, and carbide ceramics.

[0047] In one specific embodiment, the oxide ceramic includes at least one of aluminum oxide, titanium oxide, calcium oxide, chromium oxide, zinc oxide, zirconium oxide, and silicon oxide.

[0048] In one specific embodiment, the nitride ceramic includes at least one of silicon nitride, boron nitride, aluminum nitride, and gallium nitride.

[0049] In one specific embodiment, the carbide ceramic includes at least one of titanium carbide, tungsten carbide, and silicon carbide.

[0050] In one specific embodiment, the positive electrode active material is a ternary material or a lithium cobalt oxide material, and the filler includes a lithium-containing phosphate; the lithium-containing phosphate includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium manganese oxide, and lithium titanate.

[0051] This invention increases the impedance of the positive electrode passivation region by adding a filler to the active material. This increases the impedance of the second active material layer in the positive electrode passivation region, reduces the positive electrode reaction rate, and decreases the capacity utilization of the negative electrode. As a result, it significantly improves the electrolyte storage capacity of the passivation region. During cycling, especially in the later stages of cycling, it significantly increases the electrolyte content in the arc region, preventing arc lithium plating caused by insufficient electrolyte due to stress compression. This, in turn, improves the cycle stability and safety of lithium-ion batteries.

[0052] In one specific embodiment, the Dv50 particle size of the inorganic particles is 0.5μm-30μm, for example, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, and 30μm. If the filler Dv50 particle size is too large, it will cause a significant decrease in the capacity of the active material layer. In a preferred embodiment, the inorganic particles have a Dv50 particle size of 0.5 μm to 5 μm.

[0053] In one specific embodiment, the Dv50 particle size of the positive electrode active material is 10μm-19μm, for example, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, or 19μm.

[0054] In one specific embodiment, the ratio of the Dv50 particle size of the inorganic particles to the Dv50 particle size of the positive electrode active material is 0.05-1, for example, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.

[0055] When the particle size of the filler is within the above range, it can significantly increase the specific surface area of ​​the second active material layer in the passivation region, and further control the particle size ratio of inorganic particles to active material particles, which can significantly improve the liquid retention capacity of the positive electrode active material particles at the arc, thereby reducing the problem of lithium plating due to insufficient electrolyte during long-term cycling, and improving the long-cycle performance of lithium-ion batteries.

[0056] In one specific embodiment, the mass content of the filler in the second active material layer to the mass content of the positive electrode active material in the second active material layer is 0.01-0.11, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or 0.11. Too much filler in the second active material layer will lead to excessively high positive electrode impedance, which will prevent the arc-shaped positive electrode from functioning properly and worsen the arc-shaped lithium plating.

[0057] In a preferred embodiment, the mass content of the filler in the second active material layer to the mass content of the positive electrode active material in the second active material layer is 0.02-0.1.

[0058] In one specific embodiment, the positive electrode active material has a mass content of 90wt%-97wt% in the second active material layer, for example, 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, or 97wt%; the filler has a mass content of 1wt%-11wt% in the second active material layer, for example, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, or 8wt%. The binder comprises 9 wt%, 10 wt%, and 11 wt% of the second active material layer, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, and 5 wt% by mass; the conductive agent comprises 0.5 wt% to 5 wt% of the second active material layer, for example, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, and 5 wt% by mass.

[0059] In a preferred embodiment, the filler accounts for 2wt%-10wt% of the mass content in the second active material layer.

[0060] In one specific embodiment, the positive electrode active material has a mass content of 90wt%-98wt% in the first active material layer, for example, 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, or 98wt%; the binder has a mass content of 1wt%-5wt% in the first active material layer, for example, 1wt%, 2wt%, 3wt%, 4wt%, or 5wt%; and the conductive agent has a mass content of 0.5wt%-5wt% in the first active material layer, for example, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, or 5wt%.

[0061] In one specific embodiment, the ratio of the specific surface area of ​​the second active material layer to that of the first active material layer is 3-10, for example, 3, 4, 5, 6, 7, 8, 9, or 10. The specific surface area of ​​the first and second active material layers refers to the specific surface area of ​​the particulate material in the active material layer as measured by a BET analyzer. The specific operation steps are as follows: a certain amount of sample is loaded into a sample tube, a certain amount of inert gas is introduced into the sample in a liquid nitrogen environment, and the instrument calculates the specific surface area of ​​the material based on the amount of inert gas adsorbed.

[0062] In a preferred embodiment, the ratio of the specific surface area of ​​the second active material layer to the specific surface area of ​​the first active material layer is 3-6.

[0063] In one specific embodiment, the specific surface area of ​​the first active material layer is 0.1 m². 2 / g-0.3m 2 / g, for example, 0.1m 2 / g, 0.12m 2 / g, 0.13m 2 / g, 0.14m 2 / g, 0.15m 2 / g, 0.2m 2 / g, 0.25m 2 / g, 0.3m 2 / g; the specific surface area of ​​the second active material layer is 0.5m². 2 / g-3m 2 / g, for example, 0.5m 2 / g, 1m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g.

[0064] In a preferred embodiment, the specific surface area of ​​the first active material layer is 0.15 m². 2 / g-0.25m 2 / g.

[0065] In a preferred embodiment, the specific surface area of ​​the second active material layer is 0.7 m². 2 / g-1.5m 2 / g.

[0066] A larger specific surface area of ​​the second active material layer facilitates electrolyte storage, significantly increasing electrolyte content in the arc-shaped region during cycling, especially in the later stages. This prevents insufficient electrolyte in the arc-shaped region due to stress compression, thus improving the cycle stability and safety of the lithium-ion battery. However, the specific surface area of ​​the second active material layer should not be excessive. A large specific surface area implies a smaller particle size of the filler material, leading to a significant decrease in the porosity of the positive electrode active material. This increases the pore resistance of the positive electrode active material and can, in severe cases, cause lithium plating on the negative electrode, affecting the battery's cycle performance. Therefore, it is necessary to control the specific surface area of ​​the second active material layer within a suitable range.

[0067] In this invention, the first positive electrode active material layer and the second positive electrode active material layer contain doping elements, and the doping elements include at least one of Al, Mg, Ti and Zr.

[0068] In a preferred embodiment, the doping elements in the first active material layer include Al, Mg, Ti, and Zr. The Al doping amount is 1000ppm-5000ppm (e.g., 1000ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm), and the Mg doping amount is 600ppm-2000ppm (e.g., 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1100ppm, 1200ppm, 1300ppm, 1400ppm, 1500ppm, 1600ppm, 1700ppm, 1800ppm). Ti doping levels range from 600ppm to 2000ppm (e.g., 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1100ppm, 1200ppm, 1300ppm, 1400ppm, 1500ppm, 1600ppm, 1700ppm, 1800ppm, 1900ppm, 2000ppm), while Zr doping levels range from 500ppm to 1000ppm (e.g., 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm).

[0069] In a preferred embodiment, the doping elements in the second active material layer include Al, Mg, Ti, and Zr, wherein the Al doping amount is 500ppm-2000ppm (e.g., 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1100ppm, 1200ppm, 1300ppm, 1400ppm, 1500ppm, 1600ppm, 1700ppm, 1800ppm, 1900ppm, 2000ppm), and the Mg doping amount is 20%. The doping levels for Ti and Zr are 0ppm-1000ppm (e.g., 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm), 100ppm-500ppm (e.g., 100ppm, 200ppm, 300ppm, 400ppm, 500ppm), and 100ppm-500ppm (e.g., 100ppm, 200ppm, 300ppm, 400ppm, 500ppm).

[0070] The doping amount of all dopants in the above active coatings can be determined by ICP dopant metal content test.

[0071] In a preferred embodiment, the amount of dopant element in the second active material layer is reduced by 10%-50% compared to the amount of dopant element in the first active material layer, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%.

[0072] This invention improves the lithium removal resistance of the positive electrode active material and reduces the amount of lithium removal in the positive electrode material by reducing the doping amount of doping elements such as Al in the second active material layer. This reduces the reaction rate of the positive electrode in the passivation region, reduces the capacity utilization of the negative electrode, and thus improves the cycle stability of the lithium-ion battery.

[0073] This invention also provides a method for preparing a positive electrode sheet, wherein the passivated second active material layer slurry and the first active material layer slurry are co-coated onto a foil at a preset frequency and areal density to form the positive electrode sheet of this invention. Specifically, the ratio of the passivated second active material layer slurry to the first active material layer slurry is as described above, and will not be repeated here. Solvent is added according to actual needs; for example, for a 40% solid content, 60 parts of solvent are required per 100 parts of slurry. NMP is typically used as the solvent. After thoroughly stirring and filtering the above materials in a mixing tank, the first active material layer slurry is obtained. The first active material layer slurry and the passivated second active material layer slurry are then placed in two separate coating tanks. The feeding system picks up two materials into the double-layer coating die head according to the feeding settings parameters. The first coating die head extrudes the first active material layer slurry at the set frequency and speed, and the second coating die head extrudes the second active material layer slurry in the passivation zone at the set frequency and speed. After the two slurries are mixed at the die head lip, they are uniformly coated on the first and / or second surfaces of the current collector to form the positive electrode sheet of the present invention as described above.

[0074] The positive electrode preparation method of the present invention adopts a double-layer partitioned coating technology, which can adjust the extrusion frequency and speed of the two slurries, and efficiently achieve local coating of the passivation region, thereby reducing the reaction rate of the passivation region, reducing the negative electrode arc lithium intercalation SOC, and improving the cycle performance of lithium-ion batteries.

[0075] The tab 3 of the positive electrode of the present invention can be a centrally located tab structure (e.g.) Figure 2 As shown), multipole ear structure (such as...) Figure 3 (as shown) or conventional electrode structures (such as Figure 4 As shown), an empty foil region 4 is also provided on one side of the positive electrode sheet along the length direction of the positive electrode current collector, such as... Figure 2 , 3 As shown in Figure 4.

[0076] In this invention, the electrode assembly comprises a negative electrode sheet, a separator, and a positive electrode sheet sequentially stacked and wound; the negative electrode sheet can be prepared according to conventional methods in the art. For example, a uniform negative electrode active material slurry is formed by adding an optional conductive agent, an optional binder, and an optional negative electrode active material to a solvent and stirring; the negative electrode active material slurry is coated on the first and / or second surfaces of the negative electrode current collector, and then dried and cold-pressed to obtain the negative electrode sheet. Alternatively, tabs can be welded or laser-cut at the positions where aluminum foil is pre-reserved on the negative electrode current collector for negative electrode charge transfer.

[0077] The electrolyte in this invention includes lithium salt, organic solvent and optional additives. The types of organic solvent, lithium salt and additives are not specifically limited and can be selected according to requirements.

[0078] In one specific embodiment, the lithium salt includes, but is not limited to, at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium bistrifluoromethanesulfonylimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate), which can be used alone or in combination with two or more of them.

[0079] In one specific embodiment, the organic solvent includes, but is not limited to, at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), diethyl carbonate (DEC), butyl carbonate (BC), propylene carbonate (PC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), methyl sulfone (EMS), dimethyl sulfone (MSM), diethyl sulfone (ESE), and sulfolane (SF). The above organic solvents can be used alone or in combination of two or more.

[0080] In one specific embodiment, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain battery performance, such as additives improving battery overcharge performance, additives improving battery high-temperature or low-temperature performance, flame-retardant additives, etc. As an example, the additives include, but are not limited to, at least one of the following: fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinic anhydride (SN), adiponitrile (AND), tris(trimethylsilane) phosphate (TMSP), and tris(trimethylsilane) borate (TMSB). The electrolyte can be prepared according to methods conventional in the art. For example, an organic solvent, lithium salt, and optional additives can be mixed uniformly in a set ratio to obtain the electrolyte. There are no particular restrictions on the order in which the materials are added. For example, lithium salt and optional additives can be added to an organic solvent and mixed evenly to obtain an electrolyte; or, lithium salt can be added to an organic solvent first, and then optional additives can be added to an organic solvent and mixed evenly to obtain an electrolyte.

[0081] The membrane material in this invention can be selected from one or more porous materials formed by processing fibers, non-woven fabrics, polyethylene, polypropylene, and polyvinylidene fluoride. Optionally, the membrane material may include polyethylene or polypropylene. The membrane can be a substrate membrane or a multilayer composite membrane. When the membrane is a multilayer composite membrane, the materials of each layer may be the same or different. For example, a ceramic coating, an adhesive layer, or a metal oxide coating may also be provided on the membrane.

[0082] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0083] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0084] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0085] Example 1

[0086] The lithium-ion battery of the present invention is obtained by the following method:

[0087] (1) Preparation of positive electrode

[0088] Preparation of doped lithium cobalt oxide I: 9.6 wt% cobalt tetroxide and 90 wt% lithium carbonate, with Al doping levels of 3000 ppm, Mg doping level of 1000 ppm, Ti doping level of 1000 ppm, and Zr doping level of 800 ppm, were added and thoroughly mixed. The mixture was then compacted using a press and placed into saggers. The kiln was powered on and the temperature of the high-temperature zone was adjusted to 800℃~1000℃. The saggers were then stacked on the pusher plate of the outer pusher frame and sintered for 15~20 hours. The compacted mixture after the first sintering was then pulverized to obtain the doped lithium cobalt oxide I of this embodiment.

[0089] Preparation of the first active material layer paste in the main region: Add an appropriate amount of NMP to doped lithium cobalt oxide I at a ratio of 96.06 wt% + carbon nanotubes at a ratio of 2 wt% + polyvinylidene fluoride at a ratio of 1.94 wt%, and stir thoroughly in a mixing tank to prepare the first active material layer slurry, which is designated as type 1 slurry.

[0090] Preparation of doped lithium cobalt oxide ⅠⅠ: 9.6 wt% cobalt tetroxide and 90 wt% lithium carbonate, with Al doping levels of 1500 ppm, Mg doping levels of 500 ppm, Ti doping levels of 500 ppm, and Zr doping levels of 400 ppm, were added and thoroughly mixed. The mixture was then compacted using a sagger press and placed into saggers. The kiln was powered on and the temperature of the high-temperature zone was adjusted to 800℃~1000℃. The saggers were then stacked on the pusher plate of the outer pusher frame and sintered for 15~20 hours. The compacted mixture after the first sintering was then pulverized to obtain the doped lithium cobalt oxide ⅠⅠ of this embodiment.

[0091] The doping amount of the above-mentioned doping elements in the second positive electrode active material layer is reduced by 50% compared with their doping amount in the first positive electrode active material layer;

[0092] Preparation method of the second active material layer paste in the passivation region: 90 wt% of doped lithium cobalt oxide ⅠⅠ (Dv50 particle size of 10 μm) + 1.2 wt% of carbon nanotubes + 1.8 wt% of polyvinylidene fluoride + 7 wt% of alumina (filler, Dv50 particle size of 3 μm) are added to an appropriate amount of NMP and stirred thoroughly in a mixing tank to prepare the second active material layer slurry, which is referred to as type 2 slurry;

[0093] The mass content of alumina in the second active material layer is 0.078 to the mass content of lithium cobalt oxide in the second active material layer, and the ratio of the Dv50 particle size of alumina to the Dv50 particle size of the active material is 0.3.

[0094] Preparation of the positive electrode sheet: The positive electrode sheet of this invention consists of a positive current collector and a double-sided coating. An aluminum foil with a width of 100 mm and a length of 890 mm is used as the positive current collector. A type 1 slurry with a length of 80 mm and a width of 68 mm is sequentially coated and dried on the first and second surfaces of the aluminum foil along the length of the positive current collector to form the first active material layer. A type 2 slurry with a length of 6 mm and a width of 68 mm is then coated and dried to form the second active material layer. This process is repeated multiple times. The coating length of the type 1 slurry (80 mm) decreases by 2 mm each time, while the coating length of the type 2 slurry (6 mm) increases by 1 mm each time. Coating is stopped when the coating length of the type 2 slurry reaches 10 mm. The sheet is then calendered once using a roller press to a compaction density of 4.05 g / cm³. 3 The foil with a 32mm width edge is cut off, and tabs are welded to the middle area. Insulating tape is then applied to prepare a rolled positive electrode sheet. The cross-sectional SEM images of the first and second active material layers of the positive electrode sheet are shown below. Figure 5 As shown, where Figure 5 Figure a) shows the cross-sectional SEM morphology of the first active material layer. Figure 5 Figure b) shows the cross-sectional SEM morphology of the second active material layer; the planar SEM morphology of the second active material layer of the positive electrode is shown below. Figure 6 As shown.

[0095] (2) Preparation of negative electrode

[0096] Preparation method of negative electrode slurry: Graphite, carbon nanotubes and styrene-butadiene rubber are mixed in a mass content ratio of 97wt%:1.1wt%:2.9wt%, and then an appropriate amount of deionized water is added. After stirring thoroughly, the negative electrode slurry is obtained.

[0097] The method for preparing the negative electrode sheet of this invention is as follows: A copper foil with a width of 100 mm and a length of 910 mm along the length direction of the negative electrode current collector is used as the negative electrode current collector. A 60 mm wide portion of the aforementioned negative electrode slurry is coated onto the first and second surfaces of the copper foil and dried; the coating length is 910 mm. The coating is then compacted to a density of 1.76 g / cm³ using a roller press. 3 Cut off the 40mm edge of the foil in the width direction, weld the tabs in the middle of the foil area, and attach insulating tape to prepare a roll of negative electrode sheet.

[0098] (3) Battery preparation method: Using the positive electrode sheet obtained in step (1), the negative electrode sheet obtained in step (2), and the separator and non-aqueous electrolyte known in the industry, the lithium-ion battery is wound into a core according to the design structure. After adding an appropriate amount of electrolyte and performing formation and sealing, the core is activated to enable it to charge and discharge. After packaging, the battery of this embodiment is assembled.

[0099] Example 2 group

[0100] The preparation method of Example 2 is similar to that of Example 1, except that the Dv50 particle size of alumina is changed in the preparation method of the second active material layer paste in the passivation region. Specifically:

[0101] Example 2-1: The Dv50 particle size of alumina is 0.5 μm, and the ratio of the Dv50 particle size of alumina to the Dv50 particle size of the positive electrode active material is 0.05.

[0102] In Example 2-2, the Dv50 particle size of alumina is 5 μm, and the ratio of the Dv50 particle size of alumina to the Dv50 particle size of the positive electrode active material is 0.5.

[0103] In Examples 2-3, the Dv50 particle size of alumina is 10 μm, and the ratio of the Dv50 particle size of alumina to the Dv50 particle size of the positive electrode active material is 1.

[0104] In Examples 2-4, the Dv50 particle size of alumina is 30 μm, and the ratio of the Dv50 particle size of alumina to the Dv50 particle size of the positive electrode active material is 3.

[0105] In Examples 2-5, the Dv50 particle size of alumina is 0.3 μm, and the ratio of the Dv50 particle size of alumina to the Dv50 particle size of the positive electrode active material is 0.03.

[0106] In Examples 2-6, the Dv50 particle size of alumina was 35 μm, and the ratio of the Dv50 particle size of alumina to the Dv50 particle size of the positive electrode active material was 3.5.

[0107] Example 3 Group

[0108] The preparation method of Example 3 is similar to that of Example 1, except that the mass content ratio of lithium cobalt oxide and aluminum oxide in the preparation method of the second active material layer paste in the passivation region is changed. Specifically:

[0109] Example 3-1: Lithium cobalt oxide is 95.8 wt% and alumina is 1.2 wt%. In this case, the mass content of alumina in the second active material layer and the mass content of lithium cobalt oxide in the second active material layer are 0.013.

[0110] In Example 3-2, lithium cobalt oxide was used at 87.1 wt% and alumina at 9.9 wt%. In this case, the mass content of alumina in the second active material layer to the mass content of lithium cobalt oxide in the second active material layer was 0.114.

[0111] In Example 3-3, lithium cobalt oxide was used at 84 wt% and alumina at 13 wt%. In this case, the mass content of alumina in the second active material layer and the mass content of lithium cobalt oxide in the second active material layer were 0.155.

[0112] The relevant parameter settings for the above-mentioned Example 1, Example 2 and Example 3 are recorded in Table 1.

[0113] Table 1

[0114]

[0115] Example 4

[0116] Example 4 is prepared in a similar manner to Example 1, except that the preparation method of the second active material layer coating in the passivation region is changed:

[0117] Preparation method of the second active material layer paste in the passivation zone: Lithium cobalt oxide at a ratio of 97.03 wt% + carbon nanotubes at a ratio of 1 wt% + polyvinylidene fluoride at a ratio of 1.97 wt% is added to an appropriate amount of NMP, and the mixture is stirred thoroughly in a mixing tank to prepare the second active material layer slurry.

[0118] The mass ratio of binder to conductive agent in the first active material layer is a1 = 0.97; the mass ratio of binder to conductive agent in the second active material layer is a2 = 1.97; and a1 / a2 = 0.492.

[0119] Example 5 group

[0120] The preparation method of Example 5 is similar to that of Example 4, except that the mass content of the positive electrode active material, conductive agent, and binder in the preparation method of the second active material layer paste in the passivation region is changed, which changes the mass content ratio a2 of binder and conductive agent in the second active material layer:

[0121] In Example 5-1, the mass ratio of binder to conductive agent in the second active material layer is a2 = 1.51; a1 / a2 = 0.642.

[0122] In Example 5-2, the mass ratio of binder to conductive agent in the second active material layer is a2 = 5.59; a1 / a2 = 0.174.

[0123] In Examples 5-3, the mass content ratio of binder to conductive agent in the second active material layer is a2 = 7.95; a1 / a2 = 0.122.

[0124] Example 6 group

[0125] The preparation method of Example 6 is similar to that of Example 4, except that the mass content of the positive electrode active material, conductive agent, and binder in the preparation method of the first active material layer paste in the passivation region is changed, which changes the mass content ratio a1 of binder and conductive agent in the first active material layer:

[0126] In Example 6-1, the mass ratio of binder to conductive agent in the first active material layer is a1 = 0.55; a1 / a2 = 0.279.

[0127] In Example 6-2, the mass ratio of binder to conductive agent in the first active material layer is a1 = 1.55; a1 / a2 = 0.787.

[0128] The relevant parameter settings for the above-mentioned Examples 4, 5 and 6 are recorded in Table 2.

[0129] Table 2

[0130]

[0131]

[0132] Example 7 group

[0133] Example 7 is prepared in a similar manner to Example 1, except that the amount of lithium cobalt oxide doped in the preparation of the second active material layer paste in the passivation region is changed. Specifically:

[0134] Example 7-1: Preparation of doped lithium cobalt oxide ⅠⅠ: The doping amount of Al is 2700ppm, the doping amount of Mg is 900ppm, the doping amount of Ti is 900ppm, and the doping amount of Zr is 720ppm.

[0135] The doping amount of the above-mentioned doping elements in the second positive electrode active material layer is reduced by 10% compared with their doping amount in the first positive electrode active material layer;

[0136] Example 7-2: Preparation of doped lithium cobalt oxide ⅠⅠ: The doping amount of Al is 1200ppm, the doping amount of Mg is 400ppm, the doping amount of Ti is 400ppm, and the doping amount of Zr is 320ppm.

[0137] The doping amount of the above-mentioned doping elements in the second positive electrode active material layer is reduced by 60% compared with their doping amount in the first positive electrode active material layer.

[0138] Example 7-3: Preparation of doped lithium cobalt oxide ⅠⅠ: Al doping amount is 2850ppm, Mg doping amount is 950ppm, Ti doping amount is 950ppm, and Zr doping amount is 760ppm.

[0139] The doping amount of the above-mentioned doping elements in the second positive electrode active material layer is 5% lower than that in the first positive electrode active material layer.

[0140] Comparative Example 1

[0141] The preparation method of Comparative Example 1 is similar to that of Example 1, except that the preparation method of the positive electrode sheet is changed:

[0142] Aluminum foil with a width of 100 mm and a length of 890 mm was used as the positive electrode current collector. A type 1 slurry with a width of 60 mm and a length of 890 mm was coated on both the first and second surfaces of the aluminum foil and dried. The slurry was then calendered to a compacted density of 4.05 g / cm³ using a roller press. 3 Cut off the 40mm edge of the foil in the width direction, weld the tabs in the middle of the foil area, and attach insulating tape to prepare a roll of conventional positive electrode sheet.

[0143] Test case

[0144] The batteries prepared in the above embodiments and comparative examples were subjected to the following tests:

[0145] (1) Charge transfer impedance (Rct) test of the first active material coating and the second active material coating:

[0146] The testing method involved disassembling the batteries prepared in the above examples and comparative examples after formation at 50% SOC to obtain the positive electrode sheet. A slicing machine was used to cut the main body region and passivation region of the positive electrode sheet into 1cm square pieces, leaving tabs. The main body region and the positive electrode were assembled into a single cell in a 1-to-1 ratio, and the passivation region was also assembled into a single cell in a 1-to-1 ratio. 0.5g of electrolyte was injected, and the cells were packaged into a pouch-type symmetrical single-cell battery. The symmetrical battery was measured on a Zahner electrochemical workstation at a frequency of 50mHz to 200MHz. After testing, the data was fitted using an equivalent circuit, and the Rct impedance values ​​of the main body region and the passivation region were read. These are the Rct impedances of the first active material coating and the second active material coating, in mΩ.

[0147] (3) Battery charge / discharge capacity retention test:

[0148] Test method: The full batteries prepared in the above examples and comparative examples were cycled for 800T on the Blue Electric Test System under the 3C stepped charging regime, and the charge and discharge capacity retention rate (%) of the batteries was calculated.

[0149] (4) Battery cycle expansion rate test:

[0150] Test method: The full cells prepared in the above examples and comparative examples were placed under a PPG test device for 1000T cycles. The thickness of the upper cell was recorded, and the cycle expansion rate (%) of the cell was calculated.

[0151] Table 2

[0152]

[0153] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A battery, characterized in that, An electrode assembly with a wound structure includes a negative electrode, a separator, and a positive electrode, which are sequentially stacked and wound. The electrode assembly includes an arc-shaped region and a straight region connected to the arc-shaped region. The positive electrode includes a positive current collector, which has a main body region and a passivation region along its length. The passivation region is located in the arc-shaped region, and the main body region is located in the straight region. The passivation region includes N... 钝 passivation region, N 钝 =The total number of arcs in the winding structure of the electrode assembly formed by winding the positive electrode sheet; At least one side surface of the positive current collector located in the main body region includes a first active material layer, and at least one side surface of the positive current collector located in the sub-passivation region includes the first active material layer and a second active material layer. Along the length of the positive electrode current collector, the spacing between adjacent second active material layers is I, and the width of the flat region is D. 平 The width of the arc region is D. 圆 The I and D 平 and D 圆 , satisfying 0 < ID 平 <D 圆 ; The impedance of the first active material layer is less than that of the second active material layer.

2. The battery according to claim 1, wherein, In any of the sub-passivation regions, along the length direction of the positive electrode current collector, the length of the second active material layer is L, and the circumference of the arc formed by the sub-passivation region corresponding to the second active material layer is C. L and C satisfy 1 / 3 C≤L≤1 / 2 C; And / or, along the width direction of the positive electrode current collector, the width of the second active material layer is D. 活 The width of the positive electrode is D. 极 The D 活 and D 极 Satisfying D 活 ≤D 极 .

3. The battery according to claim 1, wherein, The second active material layer covers 3%-20% of the total area of ​​the positive electrode current collector.

4. The battery according to claim 1, wherein, The first active material layer and the second active material layer include a positive electrode active material, a binder, and a conductive agent; The mass ratio of the binder to the conductive agent in the first active material layer is a1, where 0.5 ≤ a1 ≤ 2; The mass ratio of the binder to the conductive agent in the second active material layer is a2, where 1.5 ≤ a2 ≤ 6.

5. The battery according to claim 4, wherein, 0.13≤a1 / a2≤0.

6.

6. The battery according to claim 4, wherein, The positive electrode active material has a mass content of 90wt%-98wt% in the second active material layer, the binder has a mass content of 2wt%-10wt% in the second active material layer, and the conductive agent has a mass content of 0.1wt%-1wt% in the second active material layer. And / or, the positive electrode active material accounts for 90wt%-98wt% of the mass content in the first active material layer, the binder accounts for 1wt%-5wt% of the mass content in the first active material layer, and the conductive agent accounts for 0.5wt%-5wt% of the mass content in the first active material layer.

7. The battery according to claim 1, wherein, The first active material layer includes a positive electrode active material, a binder, and a conductive agent, and the second active material layer includes a positive electrode active material, a filler, a binder, and a conductive agent.

8. The battery according to claim 7, wherein, The filler includes inorganic particles, which include at least one of oxide ceramics, nitride ceramics, and carbide ceramics. The inorganic particles have a Dv50 particle size of 0.5μm-30μm; The ratio of the Dv50 particle size of the inorganic particles to the Dv50 particle size of the positive electrode active material is 0.05-1.

9. The battery according to claim 7, wherein, The ratio of the mass content of the filler in the second active material layer to the mass content of the positive electrode active material in the second active material layer is 0.01-0.

11.

10. The battery according to claim 9, wherein, The positive electrode active material has a mass content of 90wt%-97wt% in the second active material layer, the filler has a mass content of 1wt%-11wt% in the second active material layer, the binder has a mass content of 1wt%-5wt% in the second active material layer, and the conductive agent has a mass content of 0.5wt%-5wt% in the second active material layer. The positive electrode active material accounts for 90wt%-98wt% of the mass content in the first active material layer, the binder accounts for 1wt%-5wt% of the mass content in the first active material layer, and the conductive agent accounts for 0.5wt%-5wt% of the mass content in the first active material layer.

11. The battery according to claim 7, wherein, The ratio of the specific surface area of ​​the second active material layer to the specific surface area of ​​the first active material layer is 3-10; The specific surface area of ​​the first active material layer is 0.1 m². 2 / g-0.3m 2 / g, the specific surface area of ​​the second active material layer is 0.5m². 2 / g-3m 2 / g.

12. The battery according to claim 1, wherein, The first active material layer and the second active material layer contain doping elements, and the doping elements include at least one of Al, Mg, Ti and Zr; In the first active material layer, the doping elements include Al, Mg, Ti and Zr, with Al doping amount of 1000ppm-5000ppm, Mg doping amount of 600ppm-2000ppm, Ti doping amount of 600ppm-2000ppm and Zr doping amount of 500ppm-1000ppm. In the second active material layer, the doping elements include Al, Mg, Ti and Zr, with Al doping amount of 500ppm-2000ppm, Mg doping amount of 200ppm-1000ppm, Ti doping amount of 100ppm-500ppm and Zr doping amount of 100ppm-500ppm.

13. The battery according to claim 12, wherein, The amount of dopant element in the second active material layer is 10%-50% lower than the amount of dopant element in the first active material layer.

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