Secondary battery and electronic device

Abstract

The present application provides a secondary battery and an electronic device. The secondary battery comprises an electrode assembly that is of a stack structure; the electrode assembly comprises positive electrode sheets, a separator, and a negative electrode sheet; the positive electrode sheets comprise a double-sided positive electrode sheet and a single-sided positive electrode sheet located on the outermost side of the electrode assembly in a stack direction; the single-sided positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer provided on one surface of the positive electrode current collector, and the positive electrode material layer faces the double-sided positive electrode sheet; the positive electrode material layer comprises a bonding coating area and a non-coating area, the bonding coating area comprises a first binder, the non-coating area comprises a second binder, and the bonding coating area comprises a plurality of sub-areas arranged at intervals. The bonding coating area of the single-sided positive electrode sheet comprises the plurality of sub-areas, so that the problems of curling and wrinkling of the single-sided positive electrode sheet can be mitigated, the wettability of the single-sided positive electrode sheet is improved, the problems of purple spots, lithium precipitation and capacity attenuation of the secondary battery can be mitigated, and the influence on the energy density of the secondary battery is also small.

Description

A secondary battery and an electronic device TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and in particular to a secondary battery and an electronic device. BACKGROUND

[0002] Secondary batteries, such as lithium ion batteries, are widely used in consumer, power, energy storage and other fields due to their high energy density, high kinetics, long service life and other characteristics, and are the focus of attention in the new energy field at the present stage. With the continuous progress and innovation of technology, people's demand for energy density and rate is becoming more and more urgent. Lithium ion batteries with a stacked structure, as an innovation in lithium ion battery technology, have become the direction of future development of lithium ion battery technology.

[0003] Lithium ion batteries with a stacked structure usually have single-sided positive electrode sheets or single-sided negative electrode sheets at the outermost side of the electrode assembly to reduce the waste of active materials and maximize the energy density. The middle of the electrode assembly is a double-sided positive electrode sheet and a double-sided negative electrode sheet. However, single-sided positive electrode sheets have curling and wrinkling problems due to different internal stresses on both sides. Currently, while solving the curling and wrinkling problems of single-sided positive electrode sheets, new problems are often brought about, such as a decrease in the liquid retention amount and wettability in the single-sided positive electrode sheet area, which leads to problems such as purple stains, lithium precipitation and capacity decay in the secondary battery.

[0004] SUMMARY

[0005] The purpose of the present application is to provide a secondary battery and an electronic device to improve the curling and wrinkling problems of single-sided positive electrode sheets, increase the liquid retention amount and wettability in the single-sided positive electrode sheet area, and thus improve the problems of purple stains, lithium precipitation and capacity decay in the secondary battery.

[0006] It should be noted that the present application is explained by taking lithium ion batteries as an example of a secondary battery in the summary of the present application, but the secondary battery of the present application is not limited to lithium ion batteries. The specific technical solutions are as follows:

[0007] The first aspect of the present application provides a secondary battery, which comprises an electrode assembly of a stack structure, the electrode assembly comprising a positive electrode tab, a separator and a negative electrode tab, the positive electrode tab comprising a double-sided positive electrode tab and a single-sided positive electrode tab located at the outermost side of the electrode assembly in the stacking direction; the single-sided positive electrode tab comprising a positive electrode current collector and a positive electrode material layer provided on one surface of the positive electrode current collector, the positive electrode material layer facing the double-sided positive electrode tab; the positive electrode material layer comprising a binder-coated region and a non-coated region, the binder-coated region comprising a first binder, the non-coated region comprising a second binder, and the binder-coated region comprising a plurality of spaced sub-regions. The binder-coated region of the single-sided positive electrode tab comprises a plurality of sub-regions, which can improve the problem of different internal stresses on both sides of the single-sided positive electrode tab, thereby improving the curling and wrinkling problems of the single-sided positive electrode tab; moreover, the provision of the binder-coated region can also improve the liquid retention and wettability of the single-sided positive electrode tab region, thereby improving the purple discoloration, lithium precipitation and capacity decay problems of the secondary battery. In addition, the binder-coated region only covers part of the surface of the positive electrode material layer, which has less impact on the energy density of the secondary battery.

[0008] In some embodiments of the present application, the plurality of sub-regions form a plurality of protrusions on the surface of the positive electrode material layer, and the mass ratio of the first binder to the second binder is X, 1 < X ≤ 5. The mass ratio X of the first binder to the second binder is within the above range, and the content of the first binder is greater than that of the second binder, thereby improving the adhesion between the binder-coated region and the separator, improving the liquid retention and wettability of the single-sided positive electrode tab region, and further improving the purple discoloration, lithium precipitation and capacity decay problems of the secondary battery. Moreover, the plurality of protrusions can alleviate the problem of different internal stresses on both sides of the single-sided positive electrode tab, thereby improving the curling and wrinkling problems of the single-sided positive electrode tab, and further improving the purple discoloration, lithium precipitation and capacity decay problems of the secondary battery.

[0009] In some embodiments of the present application, the plurality of protrusions are distributed in a stripe shape, the height of each protrusion is h1, 0 μm < h1 ≤ 1 μm, the width of each protrusion is L1, 50 μm ≤ L1 ≤ 1000 μm, and the minimum distance d1 between adjacent two protrusions is 0.5 mm ≤ d1 ≤ 5 mm. The plurality of protrusions formed by the binder-coated region are distributed in a stripe shape, and by adjusting h1, L1 and d1 within the above ranges, the height and distribution density of the plurality of protrusions are suitable, thereby improving the curling and wrinkling problems of the positive electrode tab, improving the liquid retention and wettability of the single-sided positive electrode tab region, and improving the purple discoloration, lithium precipitation and capacity decay problems of the secondary battery while having less impact on the energy density of the secondary battery.

[0010] In some embodiments of the present application, the angle between the convex part and the length direction of the single-face positive electrode tab is α, and the secondary battery satisfies: 0 μm < h1 < 0.5 μm, 0° ≤ α ≤ 90°; or, 0.5 μm ≤ h1 ≤ 1 μm, 20° ≤ α ≤ 75°. The height of different convex parts is matched with the angle α, which improves the curling and wrinkling problems of the positive electrode tab, improves the liquid retention and wettability of the single-face positive electrode tab area, and improves the purple stain, lithium precipitation, and capacity attenuation problems of the secondary battery, while on the one hand, the influence on the energy density of the secondary battery is reduced, and on the other hand, the single-face positive electrode tab is beneficial to winding in the production process.

[0011] In some embodiments of the present application, the plurality of convex parts are distributed in a dot shape, the shape of the convex part includes at least one of a circle, an ellipse, or a polygon, the height of a single convex part is h1, 0 μm < h1 ≤ 1 μm, the diameter D1 of the maximum circumscribed circle of the outer contour of a single convex part is 0.2 mm to 4 mm, and the minimum spacing d1 between two adjacent convex parts is 0.5 mm to 5 mm. The plurality of convex parts formed by the adhesive coating area are distributed in a dot shape, by adjusting h1, D1, and d1 within the above range, the height and distribution density of the plurality of convex parts are suitable, thereby improving the curling and wrinkling problems of the positive electrode tab, improving the liquid retention and wettability of the single-face positive electrode tab area, and improving the purple stain, lithium precipitation, and capacity attenuation problems of the secondary battery while having less influence on the energy density of the secondary battery. In addition, the dot-shaped distribution of the convex parts can better relieve the problem of different internal stresses on both sides of the single-face positive electrode tab, further improve the curling and wrinkling problems of the single-face positive electrode tab, and further improve the purple stain, lithium precipitation, and capacity attenuation problems of the secondary battery.

[0012] In some embodiments of the present application, the plurality of sub-areas form a plurality of recesses on the surface of the positive material layer, and the mass ratio of the first binder to the second binder is X, 0.2 ≤ X < 1. The plurality of recesses formed by the adhesive coating area provide channels for the transmission of electrolyte, so that the liquid retention and wettability of the electrolyte near the negative electrode of the single-face positive electrode tab area are improved, thereby improving the purple stain, lithium precipitation, and capacity attenuation problems of the secondary battery. Moreover, the plurality of recesses can relieve the problem of different internal stresses on both sides of the single-face positive electrode tab, improve the curling and wrinkling problems of the single-face positive electrode tab, and thus further improve the purple stain, lithium precipitation, and capacity attenuation problems of the secondary battery.

[0013] In some embodiments of the present application, the plurality of sub-regions are distributed in a striped manner, the depth of each of the recesses is h2, 0 < h2 < 1 μm, the minimum distance d2 between two adjacent recesses is 0.5 mm to 5 mm, and the width of each of the recesses is L2, 50 μm to 1000 μm. The plurality of recesses formed by the adhesive coating region are distributed in a striped manner. By adjusting h2, L2 and d2 within the above ranges, the height and distribution density of the plurality of recesses are suitable, thereby improving the curling and wrinkling problems of the positive electrode sheet, improving the liquid retention amount and wettability of the single-sided positive electrode sheet region, and improving the purple stain, lithium precipitation and capacity attenuation problems of the secondary battery while having little effect on the energy density of the secondary battery.

[0014] In some embodiments of the present application, the secondary battery satisfies: 0 < h2 < 0.5 μm, L2 < d2 < 5L2; or, 0.5 < h2 < 1 μm, 3L2 < d2 < 10L2. The height of different recesses and the minimum distance between two adjacent recesses are matched with each other, which on the one hand can reduce the effect on the energy density of the secondary battery, and on the other hand is conducive to the winding of the single-sided positive electrode sheet during the production process.

[0015] In some embodiments of the present application, the plurality of recesses are distributed in a dotted manner, the shape of the recesses includes at least one of a circle, an ellipse and a polygon, the depth of each of the recesses is h2, 0 < h2 < 1 μm, the diameter D2 of the maximum circumscribed circle of the outer contour of each of the recesses is 0.2 mm to 4 mm, and the minimum distance d2 between two adjacent recesses is 0.5 mm to 5 mm. The plurality of recesses formed by the adhesive coating region are distributed in a dotted manner. By adjusting h2, D2 and d2 within the above ranges, the height and distribution density of the plurality of recesses are suitable, thereby improving the curling and wrinkling problems of the positive electrode sheet, improving the liquid retention amount and wettability of the single-sided positive electrode sheet region, and improving the purple stain, lithium precipitation and capacity attenuation problems of the secondary battery while having little effect on the energy density of the secondary battery. In addition, the recesses distributed in a dotted manner can better relieve the problem of different internal stresses on both sides of the single-sided positive electrode sheet, further improve the curling and wrinkling problems of the single-sided positive electrode sheet, and further improve the purple stain, lithium precipitation and capacity attenuation problems of the secondary battery.

[0016] In some embodiments of the present application, the total area of the adhesive coating region orthographic projection along the thickness direction of the single-face positive electrode tab is S1, and the area of the single-face positive electrode tab is S2, 2%≤S1 / S2≤50%. By adjusting the value of S1 / S2 within the above range, the problems of curling and wrinkling of the positive electrode tab are improved, the liquid retention and wettability of the single-face positive electrode tab area are improved, and the problems of purple stain, lithium precipitation and capacity attenuation of the secondary battery are improved while the energy density of the secondary battery is less affected.

[0017] In some embodiments of the present application, the positive current collector is an aluminum foil, and 8μm≤H1≤20μm. The positive current collector is an aluminum foil, and by adjusting the thickness H1 of the positive current collector within the above range, the thickness of the positive current collector is appropriate, the energy density of the obtained secondary battery is high, and the production process yield is high, which is beneficial to industrialization.

[0018] In some embodiments of the present application, the first binder and the second binder each independently comprise at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, and polymethyl methacrylate. The above-mentioned first binder and second binder have high adaptability and can adapt to the design of more secondary battery material systems.

[0019] In some embodiments of the present application, the surface of the separator facing the positive electrode tab is provided with a ceramic coating.

[0020] The second aspect of the present application provides an electronic device comprising the secondary battery of any one of the preceding embodiments.

[0021] The beneficial effects of the present application are as follows:

[0022] The present application provides a secondary battery and an electronic device. The secondary battery comprises an electrode assembly in a stacked structure, the electrode assembly comprising a positive electrode tab, a separator, and a negative electrode tab, the positive electrode tab comprising a double-face positive electrode tab and a single-face positive electrode tab located at the outermost side of the electrode assembly in the stacking direction; the single-face positive electrode tab comprising a positive current collector and a positive electrode material layer arranged on one surface of the positive current collector, the positive electrode material layer facing the double-face positive electrode tab; the positive electrode material layer comprising an adhesive coating region and a non-coating region, the adhesive coating region comprising a first binder, and the non-coating region comprising a second binder, the adhesive coating region comprising a plurality of spaced sub-regions. The adhesive coating region of the single-face positive electrode tab comprises a plurality of sub-regions, and the adhesive coating region can eliminate part of the internal stress in the positive electrode material layer during the arrangement process. The structure design of the plurality of sub-regions can also improve the problem of different internal stresses on both sides of the single-face positive electrode tab, thereby improving the problems of curling and wrinkling of the single-face positive electrode tab. Moreover, the arrangement of the adhesive coating region can also improve the wettability of the single-face positive electrode tab, thereby improving the problems of purple stain, lithium precipitation, and capacity attenuation of the secondary battery. In addition, the adhesive coating region only covers part of the surface of the positive electrode material layer, and it also has less effect on the energy density of the secondary battery. Attached Figure Description

[0023] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0024] Figure 1 is a partial cross-sectional view of the secondary battery along the thickness direction in one embodiment of this application;

[0025] Figure 2 is a schematic cross-sectional view of a single-sided positive electrode sheet along the thickness direction according to one embodiment of this application;

[0026] Figure 3 is a schematic diagram of the structure of a single-sided positive electrode sheet according to one embodiment of this application;

[0027] Figure 4 is a schematic diagram of the structure of a single-sided positive electrode sheet according to another embodiment of this application;

[0028] Figure 5 is a schematic diagram of the structure of a single-sided positive electrode sheet according to another embodiment of this application;

[0029] Figure 6 is a schematic diagram of a partial cross-sectional structure of a single-sided positive electrode sheet along the thickness direction according to another embodiment of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0031] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0032] Currently, the problem of curling in single-sided positive electrode sheets is mostly addressed by increasing the thickness of the positive current collector to improve its stiffness, or by applying a coating with high bending strength to the side of the current collector that is not coated with the positive electrode material layer to counteract the curling. However, these methods all have a significant impact on the energy density of the secondary battery. Another approach is to coat the surface of the single-sided positive electrode sheet with a solvent, such as N-methylpyrrolidone, to eliminate residual stress after cold pressing and improve curling. However, this method leads to the loss of positive active material in the single-sided positive electrode sheet and a reduction in the surface binder, resulting in poor adhesion between the single-sided positive electrode sheet and the separator. This causes an increase in the distance between the single-sided positive electrode sheet and the separator, as well as between the adjacent negative electrode sheet, in the later stages of secondary battery cycling, leading to increased polarization and problems such as purple spots, lithium plating, and capacity decay.

[0033] Based on the above problems, the application provides a secondary battery and an electronic device, which improve the curling and wrinkling problems of the single-sided positive electrode sheet, increase the liquid retention and wettability of the single-sided positive electrode sheet region, and thus improve the purple stain, lithium precipitation, and capacity attenuation problems of the secondary battery without affecting the energy density of the secondary battery.

[0034] The first aspect of the application provides a secondary battery, which comprises an electrode assembly in a stacked structure, the electrode assembly comprising a positive electrode sheet, a separator, and a negative electrode sheet, the positive electrode sheet comprising a double-sided positive electrode sheet and a single-sided positive electrode sheet located at the outermost side of the electrode assembly in the stacking direction. Specifically, as shown in FIGS. 1-3, the secondary battery comprises a shell 100 and an electrode assembly 200 in a stacked structure, the outermost side of the electrode assembly 200 adjacent to the shell 100 is a single-sided positive electrode sheet 210, and the electrode assembly 200 further comprises a double-sided positive electrode sheet 220, a separator 230, and a negative electrode sheet 240. The single-sided positive electrode sheet 210 comprises a positive current collector 211 and a positive electrode material layer 212 arranged on one surface of the positive current collector 211, the positive electrode material layer 212 comprises a binder-coated region 213 and a non-coated region 214, and the binder-coated region 213 comprises a plurality of sub-regions arranged at intervals. The double-sided positive electrode sheet 220 comprises a double-sided positive current collector 221 and a double-sided positive electrode material layer 222 arranged on both surfaces of the double-sided positive current collector 221, and the positive electrode material layer 212 in the single-sided positive electrode sheet 210 faces the negative electrode sheet 240. The negative electrode sheet 240 is a double-sided negative electrode sheet, which comprises a negative current collector 241 and a negative electrode material layer 242 arranged on both surfaces of the negative current collector 241. In the secondary battery provided by the application, the binder-coated region of the single-sided positive electrode sheet comprises a plurality of sub-regions, the binder-coated region can eliminate part of the internal stress in the positive electrode material layer during the arrangement process, and the structure design of the plurality of sub-regions can also improve the problem of different internal stresses on both sides of the single-sided positive electrode sheet, thereby improving the curling and wrinkling problems of the single-sided positive electrode sheet. Moreover, the arrangement of the binder-coated region and the non-coated region can also improve the liquid retention and wettability of the single-sided positive electrode sheet region, thereby improving the purple stain, lithium precipitation, and capacity attenuation problems of the secondary battery. In addition, the binder-coated region only covers part of the surface of the positive electrode material layer, which also has little effect on the energy density of the secondary battery. It can be understood that the size, number, etc. of the double-sided positive electrode sheet, the negative electrode sheet, and the separator in FIG. 1 are only examples, and the size, number, and shape of the binder-coated region in FIGS. 2 and 3 are only examples, which do not limit the protection scope of the application.

[0035] In the present application, the adhesive coating area and the non-coating area refer to the area of the surface of the positive material layer; the positive current collector is the positive current collector in the single-sided positive electrode sheet, and the positive material layer is the positive material layer in the single-sided positive electrode sheet; the double-sided positive current collector is the positive current collector in the double-sided positive electrode sheet, and the double-sided positive material layer is the positive material layer in the double-sided positive electrode sheet.

[0036] In some embodiments of the present application, as shown in FIG. 2, the plurality of spaced sub-areas of the adhesive coating area 213 form a plurality of convex parts on the surface of the positive material layer 212. The mass ratio of the first adhesive to the second adhesive is X, and 1X≤5. For example, X can be 1.1, 1.2, 1.3, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a range between any two of them. The mass ratio X of the first adhesive to the second adhesive is within the above range, and the content of the first adhesive is greater than that of the second adhesive, so that the single-sided positive electrode sheet has good adhesion with the separator, and the plurality of sub-areas form a plurality of convex parts on the surface of the positive material layer, which can provide a channel for the electrolyte as a supporting structure, so that the liquid retention amount and wettability of the electrolyte near the negative electrode in the area of the single-sided positive electrode sheet are improved, thereby improving the purple stain, lithium precipitation, and capacity decay problems of the secondary battery. Moreover, the adhesive coating area can eliminate part of the internal stress in the positive material layer during the setting process, and the structural design of the plurality of convex parts can also alleviate the problem of different internal stresses on both sides of the single-sided positive electrode sheet, improve the curling and wrinkling problems of the single-sided positive electrode sheet, and thus further improve the purple stain, lithium precipitation, and capacity decay problems of the secondary battery. In the present application, the mass ratio of the first adhesive to the second adhesive refers to the mass ratio of the first adhesive in the adhesive coating area on the surface of the positive material layer to the second adhesive in the non-coating area.

[0037] In some embodiments of the present application, as shown in FIG. 2 and FIG. 3, the plurality of protrusions formed by the adhesive coating area 213 are distributed in a stripe shape, the height of a single protrusion is h1, 0 < h1 < 1 μm, the width of a single protrusion L1 is 50 μm to 1000 μm, and the minimum spacing d1 between adjacent two protrusions is 0.5 mm to 5 mm. For example, h1 can be 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, or a range between any two of them. For example, L1 can be 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, or a range between any two of them. For example, d1 can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or a range between any two of them. By adjusting h1, L1 and d1 within the above ranges, the height and distribution density of the plurality of protrusions are suitable, thereby improving the curling and wrinkling problems of the positive electrode sheet, improving the liquid retention and wettability of the single-sided positive electrode sheet area, and improving the purple stain, lithium precipitation, and capacity decay problems of the secondary battery while having little effect on the energy density of the secondary battery.

[0038] In some embodiments of the present application, as shown in FIG. 4, the plurality of protrusions formed by the adhesive coating area 213 are distributed in a stripe shape, the adhesive coating area 213 forms an angle a between the protrusion and the length direction of the single-face positive electrode sheet, and the secondary battery satisfies: 0 μm < h1 < 0.5 μm, 0°≤a≤90°. For example, when h1 is 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.49 μm, or any value in the range formed by any two of them, a can be 0°, 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, or a range formed by any two of them. In some embodiments of the present application, the secondary battery satisfies: 0.5 μm≤h1≤1 μm, 20°≤a≤75°. For example, when h1 is 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, or any value in the range formed by any two of them, a can be 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, or a range formed by any two of them. The height of different protrusions and the angle a are matched with each other, which can improve the curling and wrinkling problems of the positive electrode sheet, improve the liquid retention and wettability of the single-face positive electrode sheet area, and improve the purple stain, lithium precipitation, and capacity attenuation problems of the secondary battery, while on the one hand reducing the impact on the energy density of the secondary battery, and on the other hand facilitating the winding of the single-face positive electrode sheet during production. In the present application, the length direction of the single-face positive electrode sheet refers to the direction of the longer side of the single-face positive electrode sheet.

[0039] In the present application, the width L1 of a single protrusion is the maximum value of the orthogonal projection width of a single protrusion in the thickness direction of the single-face positive electrode sheet. When the plurality of protrusions are distributed in a stripe shape, the widths L1 of adjacent two protrusions can be the same or different, the lengths of the strips can be the same or different, and h1 and d1 can also be the same or different, as long as the purpose of the present application can be achieved. The present application does not particularly limit the length of the strip, which can be designed according to the size of the single-face positive electrode sheet, as long as the purpose of the present application can be achieved.

[0040] In some embodiments of the present application, the plurality of protrusions formed by the adhesive coating region are distributed in a dot-like manner, and the shape of the protrusions includes at least one of a circle, an ellipse, or a polygon. The height of a single protrusion is h1, and 0 < h1 < 1 μm. The diameter D1 of the maximum circumscribed circle of the outer contour of a single protrusion is 0.2 mm to 4 mm. The minimum spacing d1 between two adjacent protrusions is 0.5 mm to 5 mm. For example, h1 can be 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, or a range defined by any two of these values. For example, D1 can be 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.7 mm, 0.9 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, or a range defined by any two of these values. For example, d1 can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or a range defined by any two of these values. The plurality of protrusions formed by the adhesive coating region are distributed in a dot-like manner. By adjusting h1, D1, and d1 within the above ranges, the height and distribution density of the plurality of protrusions are suitable, thereby improving the curling and wrinkling problems of the positive electrode sheet, increasing the liquid retention and wettability of the single-sided positive electrode sheet region, and improving the purple stain, lithium precipitation, and capacity attenuation problems of the secondary battery while having little effect on the energy density of the secondary battery. In addition, the dot-like distributed protrusions can better alleviate the problem of different internal stresses on both sides of the single-sided positive electrode sheet, further improve the curling and wrinkling problems of the single-sided positive electrode sheet, and further improve the purple stain, lithium precipitation, and capacity attenuation problems of the secondary battery. In the present application, the shape of the protrusion is the shape of the orthogonal projection of the protrusion along the thickness direction of the single-sided positive electrode sheet. The outer contour of the orthogonal projection of a single protrusion is the outer contour of the orthogonal projection along the thickness direction of the single-sided positive electrode sheet. The minimum spacing d1 between two adjacent protrusions is the minimum spacing d1 between the outer contours of the orthogonal projections of two adjacent protrusions.

[0041] Specifically, as shown in FIG. 5, the protrusions formed by the adhesive coating region 213 are distributed in a dot-like array. The shapes of the protrusions formed by the adhesive coating region 213 are a circle and a triangle. The diameter D1 of the maximum circumscribed circle of the circle is the diameter of the circle. The diameter D1 of the circumscribed circle of the triangle is the diameter of the circumscribed circle. The minimum spacing d1 between two adjacent circles or triangles is d1. It can be understood that when the protrusions are distributed in a dot-like manner, they can also be distributed in a scattered dot-like manner. The diameter D1 of the maximum circumscribed circle of the outer contour of a single protrusion and the minimum spacing d1 between two adjacent protrusions both satisfy the above ranges. It can be understood that the size in FIG. 5 and the number and shape of the protrusions are only examples and do not limit the scope of protection of the present application.

[0042] In the present application, the shape of the convex part is polygonal, and the polygonal shape can be triangular, square, rectangular, pentagonal, hexagonal, octagonal, etc. When the plurality of convex parts are distributed in a dot-like manner, the shapes of the orthographic projections of two adjacent convex parts can be the same or different, and h1, D1 and d1 can also be the same or different, as long as the purpose of the present application can be achieved.

[0043] The present application does not have special restrictions on the preparation method of the single-sided positive electrode sheet with a plurality of convex parts formed in the adhesive coating area, as long as the purpose of the present application can be achieved. The preparation method of the single-sided positive electrode sheet can include, but is not limited to, the following steps: (1) mixing the positive electrode active material, the second binder and the conductive agent, adding a solvent to prepare a positive electrode slurry, then setting the positive electrode slurry on one surface of the positive electrode current collector, drying and cold pressing to obtain a sheet with a positive electrode active material layer set on one surface of the positive electrode current collector; (2) adding the first binder to the solvent to prepare an adhesive coating area slurry, coating the adhesive coating area slurry on the surface of the positive electrode active material layer, and drying to obtain a single-sided positive electrode sheet. The solid content W of the adhesive coating area slurry is 1% to 5%. The content of the adhesive in the adhesive coating area slurry is high, so that the convex part can be formed on the surface of the positive electrode material layer, and the solvent in the adhesive coating area slurry can soften the second binder in the positive electrode active material layer, so that part of the internal stress in the positive electrode active material layer can be eliminated. The present application does not have special restrictions on the above-mentioned solvent, as long as the purpose of the present application can be achieved. The above-mentioned solvent can be selected from conventional solvents used in the preparation of positive electrode slurry in the art, which is not limited in the present application.

[0044] The present application does not have special restrictions on the way to regulate h1, L1, d1 and D1, as long as the purpose of the present application can be achieved. The size of h1, L1, d1 and D1 can be regulated by regulating the solid content and content of the adhesive coating area slurry in the coating process, and the coating method.

[0045] In some embodiments of the present application, as shown in FIG. 6, the plurality of sub-regions of the adhesive coating region 213 form a plurality of recesses on the surface of the positive electrode material layer, and the mass ratio of the first adhesive to the second adhesive is X, 0.2≤X<1. For example, X can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.99, or a range between any two of the values. The plurality of recesses formed by the adhesive coating region provide channels for the transmission of electrolyte, thereby improving the electrolyte retention and wettability of the electrolyte near the negative electrode of the single-sided positive electrode tab region, and maintaining good adhesion between the non-coated region and the separator, thereby improving the purple stain, lithium precipitation, and capacity decay problems of the secondary battery. Moreover, the adhesive coating region can eliminate part of the internal stress in the positive electrode material layer during the setting process, and the structural design of the plurality of recesses can also alleviate the problem of different internal stresses on both sides of the single-sided positive electrode tab, thereby improving the curling and wrinkling problems of the single-sided positive electrode tab, and further improving the purple stain, lithium precipitation, and capacity decay problems of the secondary battery. It should be understood that the size, number, and shape of the adhesive coating region in FIG. 6 are only examples and do not limit the scope of protection of the present application.

[0046] In some embodiments of the present application, the plurality of sub-regions are distributed in a stripe shape, the depth of a single recess is h2, 0 pm < h2≤ 1 pm, the minimum distance d2 between adjacent two recesses is 0.5 mm to 5 mm, and the width L2 of a single recess is 50 pm to 1000 pm. For example, h2 can be 0.1 pm, 0.2 pm, 0.3 pm, 0.4 pm, 0.5 pm, 0.6 pm, 0.7 pm, 0.8 pm, 0.9 pm, 1 pm, or a range between any two of the values. For example, L2 can be 50 pm, 100 pm, 200 pm, 300 pm, 400 pm, 500 pm, 600 pm, 700 pm, 800 pm, 900 pm, 1000 pm, or a range between any two of the values. For example, d2 can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or a range between any two of the values. The plurality of recesses formed by the adhesive coating region are distributed in a stripe shape, and by adjusting h2, L2, and d2 within the above ranges, the height and distribution density of the plurality of recesses are suitable, thereby improving the curling and wrinkling problems of the positive electrode tab, improving the electrolyte retention and wettability of the single-sided positive electrode tab region, and improving the purple stain, lithium precipitation, and capacity decay problems of the secondary battery while having little effect on the energy density of the secondary battery.

[0047] In some embodiments of the present application, the plurality of recesses formed by the adhesive coating region are distributed in a stripe shape, and the secondary battery satisfies: 0 μm < h2 < 0.5 μm, L2 < d2 < 5L2; for example, when h2 is 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.49 μm, or any value in a range between any two of them, d2 can be 1.1L2, 1.2L2, 1.3L2, 1.5L2, 2L2, 2.5L2, 3L2, 3.5L2, 4L2, 4.5L2, 4.9L2, or a range between any two of them. In some embodiments of the present application, the plurality of recesses formed by the adhesive coating region are distributed in a stripe shape, and the secondary battery satisfies: 0 μm < h2 < 0.5 μm, 0.5 mm ≤ d2 ≤ 5 mm; for example, when h2 is 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.49 μm, or any value in a range between any two of them, d2 can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or a range between any two of them. In some embodiments of the present application, the plurality of recesses formed by the adhesive coating region are distributed in a stripe shape, and the secondary battery satisfies: 0.5 μm ≤ h2 ≤ 1 μm, 3L2 < d2 ≤ 10L2; for example, when h2 is 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, or any value in a range between any two of them, d2 can be 3.1L2, 4L2, 5L2, 6L2, 7L2, 8L2, 9L2, 10L2, or a range between any two of them. In some embodiments of the present application, the plurality of recesses formed by the adhesive coating region are distributed in a stripe shape, and the secondary battery satisfies: 0.5 μm ≤ h2 ≤ 1 μm, 0.5 mm ≤ d2 ≤ 5 mm; for example, when h2 is 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, or any value in a range between any two of them, d2 can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or a range between any two of them.The height of the different recesses matches the minimum distance between two adjacent recesses, which improves the curling and wrinkling of the positive electrode sheet, increases the liquid retention and wettability of the single-sided positive electrode sheet area, and improves the purple stain, lithium precipitation, and capacity decay problems of the secondary battery. On the one hand, it reduces the impact on the energy density of the secondary battery, and on the other hand, it is beneficial to the winding of the single-sided positive electrode sheet during production.

[0048] In the present application, the width L2 of a single recess is the maximum value of the orthogonal projection width of the single recess along the thickness direction of the single-sided positive electrode sheet. When the plurality of recesses are distributed in a stripe shape, the widths L2 of two adjacent recesses can be the same or different, the lengths of the strips can be the same or different, and h2 and d2 can also be the same or different, as long as the purpose of the present application can be achieved. The present application does not have a special limitation on the length of the strip, which can be designed according to the size of the single-sided positive electrode sheet, as long as the purpose of the present application can be achieved.

[0049] In some embodiments of the present application, the plurality of recesses are distributed in a dot pattern, the shape of the recesses comprises at least one of a circle, an ellipse, a polygon, the depth of a single recess is h2, 0 < h2 < 1 μm, the diameter D2 of the maximum circumscribed circle of the outer contour of a single recess is 0.2 mm to 4 mm, and the minimum spacing d2 between two adjacent recesses is 0.5 mm to 5 mm. For example, h2 can be 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, or a range formed by any two of these values. For example, D2 can be 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.7 mm, 0.9 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, or a range formed by any two of these values. For example, d2 can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or a range formed by any two of these values. The plurality of recesses formed by the bonding coating area are distributed in a dot pattern, by adjusting h2, D2 and d2 within the above ranges, the height and distribution density of the plurality of recesses are suitable, thereby improving the curling and wrinkling problems of the positive electrode sheet, improving the liquid retention and wettability of the single-sided positive electrode sheet area, and improving the purple stain, lithium precipitation and capacity attenuation problems of the secondary battery while having little effect on the energy density of the secondary battery. In addition, the dot pattern of the recesses can better relieve the problem of different internal stresses on both sides of the single-sided positive electrode sheet, further improve the curling and wrinkling problems of the single-sided positive electrode sheet, and further improve the purple stain, lithium precipitation and capacity attenuation problems of the secondary battery. In the present application, the shape of the recess is the shape of the orthographic projection of the recess along the thickness direction of the single-sided positive electrode sheet; the outer contour of the orthographic projection of a single recess is the outer contour of the orthographic projection along the thickness direction of the single-sided positive electrode sheet; and the minimum spacing d2 between two adjacent recesses is the minimum spacing d2 between the outer contours of the orthographic projections of two adjacent recesses.

[0050] In the present application, the plurality of recesses formed by the bonding coating area are distributed in a dot pattern, and the plurality of recesses can be distributed in a dot array or in a scattered dot pattern. In the present application, the shape of the recess is a polygon, and exemplary polygons can be a triangle, a square, a rectangle, a pentagon, a hexagon, an octagon, etc. When the plurality of recesses are distributed in a dot pattern, the shapes of the orthographic projections of two adjacent recesses can be the same or different, and h2, D2 and d2 can be the same or different, as long as the purpose of the present application can be achieved.

[0051] The preparation method of the single-face positive electrode sheet with the adhesive coating area forming a plurality of recesses is not particularly limited in the present application, as long as the purpose of the present application can be achieved. Illustratively, the preparation method of the single-face positive electrode sheet can include, but is not limited to, the following steps: (1) mixing the positive electrode active material, the second binder and the conductive agent, adding a solvent to prepare a positive electrode slurry, then setting the positive electrode slurry on one surface of the positive electrode current collector, drying and cold pressing to obtain a sheet with a positive electrode active material layer set on one surface of the positive electrode current collector; (2) adding the first binder to the solvent to prepare an adhesive coating area slurry, coating the adhesive coating area slurry on the surface of the positive electrode active material layer, and drying to obtain a single-face positive electrode sheet. The solid content W of the adhesive coating area slurry is greater than or equal to 0% and less than or equal to 0.8%. The content of the adhesive in the adhesive coating area slurry is low, so that recesses can be formed on the surface of the positive electrode material layer. The solvent is not particularly limited in the present application, as long as the purpose of the present application can be achieved. Illustratively, the solvent can be selected from conventional solvents used in the preparation of positive electrode slurries in the art, which are not limited in the present application.

[0052] The manner of regulating h2, L2, d2 and D2 is not particularly limited in the present application, as long as the purpose of the present application can be achieved. Illustratively, the size of h2, L2, d2 and D2 can be regulated by regulating the solid content and content of the adhesive coating area slurry in the coating process, and the manner of coating.

[0053] In some embodiments of the present application, the total area of the adhesive coating area orthographic projection along the thickness direction of the single-face positive electrode sheet is S1, and the area of the single-face positive electrode sheet is S2, 2%≤S1 / S2≤50%. For example, S1 / S2 can be 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or a range composed of any two of the above values. By regulating the value of S1 / S2 within the above range, the problems of curling and wrinkling of the positive electrode sheet are improved, and the liquid retention and wettability of the single-face positive electrode sheet area are improved, thereby improving the purple stain, lithium precipitation and capacity decay problems of the secondary battery while having little effect on the energy density of the secondary battery.

[0054] In some embodiments of the present application, the positive electrode current collector is an aluminum foil, and 8 μm≤H1≤20 μm. For example, H1 can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm or a range composed of any two of the above values. The positive electrode current collector is an aluminum foil, and by regulating the thickness H1 of the positive electrode current collector within the above range, the thickness of the positive electrode current collector is appropriate, the energy density of the obtained secondary battery is high, and the production process yield is high, which is beneficial to industrialization.

[0055] In some embodiments of the present application, the double-sided positive electrode current collector is an aluminum foil, 8 pm ≤ H2≤ 20 pm. For example, H2may be 8 pm, 9 pm, 10 pm, 11 pm, 12 pm, 13 pm, 14 pm, 15 pm, 16 pm, 17 pm, 18 pm, 19 pm, 20 pm, or a range between any two of them.

[0056] In the present application, positive electrode current collectors of different thicknesses can be purchased and measured by micrometer, and the positive electrode current collector of the desired thickness can be selected.

[0057] In some embodiments of the present application, the first binder and the second binder each independently include at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, or polymethyl methacrylate, and the first binder and the second binder can be the same or different. The above-mentioned first binder and second binder have high adaptability and can adapt to the design of more secondary battery material systems.

[0058] In the present application, the positive electrode material layer and the double-sided material layer each independently include a positive electrode active material, and the present application does not have a particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material can include, but is not limited to, at least one of nickel-cobalt-manganese lithium phosphate (e.g., NCM811, NCM622, NCM523, NCM111), nickel-cobalt-aluminum lithium phosphate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate, lithium manganese iron phosphate, or lithium titanate.

[0059] The positive electrode material layer and the double-sided material layer can further include a conductive agent, and the present application does not have a particular limitation on the type of conductive agent as long as the purpose of the present application can be achieved. For example, the conductive agent can include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials, or conductive polymers, and the conductive carbon black can include, but is not limited to, at least one of acetylene black or ketjen black. The above-mentioned carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanocarbon fibers. The above-mentioned metal materials can include, but are not limited to, metal powder and / or metal fibers, and in particular, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymers can include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0060] The double-sided material layer can further include a binder, which can include at least one of the first binder and the second binder described above, or at least one of sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, or styrene butadiene rubber.

[0061] The present application does not have a particular limitation on the mass ratio of the positive active material, the conductive agent, and the second binder in the positive electrode material layer, and a person skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved. The present application does not have a particular limitation on the mass ratio of the positive active material, the conductive agent, and the binder in the double-sided positive electrode material layer, and a person skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved. The present application does not have a particular limitation on the thickness of the single-layer positive electrode material layer and the double-sided positive electrode material layer, as long as the purpose of the present application can be achieved, for example, the thickness can be 30 μm to 120 μm.

[0062] In the present application, the positive electrode material layer includes a bonding coated area and a non-coated area, the bonding coated area of the single-sided positive electrode sheet contains a plurality of sub-areas, the bonding coated area forms a convex part or a concave part, so that the roughness Ra of the bonding coated area is greater than the roughness Rb of the non-coated area. It can improve the purple stain, lithium precipitation, capacity attenuation problem of the secondary battery, and the influence on the energy density of the secondary battery is also small.

[0063] In some embodiments of the present application, the separator includes a base material layer and a ceramic coating layer disposed on one surface of the base material layer, and the ceramic coating layer faces the positive electrode sheet.

[0064] In some embodiments of the present application, the ceramic coating layer includes an inorganic particle layer including inorganic particles and a binder. The present application does not have a particular limitation on the inorganic particles, for example, the inorganic particles can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The present application does not have a particular limitation on the binder, for example, the binder can be at least one of the binders described above. The present application does not have a particular limitation on the mass ratio of the inorganic particles and the binder, as long as the purpose of the present application can be achieved, for example, the mass ratio of the inorganic particles and the binder can be 1:(0.05 to 0.12).

[0065] In some embodiments of the present application, the thickness of the ceramic coating layer does not have a particular limitation, as long as the purpose of the present application can be achieved, for example, the thickness of the ceramic coating layer can be 2 μm to 6 μm. For example, the thickness of the ceramic coating layer can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, or a range composed of any two of the above values.

[0066] The material of the substrate layer can include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP)-based polyolefin (PO), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator can include at least one of a woven film, a non-woven film, a microporous film, a composite film, a calendered film, or a spunlaced film. Exemplarily, the substrate layer can use a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film.

[0067] In the present application, the thickness of the separator is not particularly limited as long as the purpose of the present application can be achieved, for example, the thickness of the separator can be 3 μm to 30 μm.

[0068] The negative electrode current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, it can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper, or a composite current collector, and exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0069] The negative electrode material layer includes a negative electrode active material, and the negative electrode active material is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the negative electrode active material can include, but is not limited to, at least one of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O 12 or Li-Al alloy.

[0070] In some embodiments of the present application, the negative electrode material layer can further include a conductive agent and a binder, and the type of the conductive agent and the binder is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, it can be at least one of the above-mentioned conductive agent and the above-mentioned binder. The mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode material layer is not particularly limited in the present application, and a person skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0071] The thickness of the negative electrode material layer is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode material layer is 30 μm to 120 μm. The thickness of the negative electrode current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0072] In the present application, the secondary battery further includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.

[0073] The lithium salt is not particularly limited as long as the object of the present application can be achieved. For example, the lithium salt can include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. The content of the lithium salt in the electrolyte is not particularly limited as long as the object of the present application can be achieved.

[0074] The non-aqueous solvent is not particularly limited as long as the object of the present application can be achieved, for example, the non-aqueous solvent can include, but is not limited to, at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, or other organic solvents.

[0075] The carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluoro-carbonate compound. The chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The cyclic carbonate compound can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The fluoro-carbonate compound can include, but is not limited to, at least one of fluoro-ethylene carbonate (FEC), 1,2-difluoro-ethylene carbonate, 1,1-difluoro-ethylene carbonate, 1,1,2-trifluoro-ethylene carbonate, 1,1,2,2-tetrafluoro-ethylene carbonate, 1-fluoro-2-methyl-ethylene carbonate, 1-fluoro-1-methyl-ethylene carbonate, 1,2-difluoro-1-methyl-ethylene carbonate, 1,1,2-trifluoro-2-methyl-ethylene carbonate, or trifluoromethyl-ethylene carbonate. The carboxylic acid ester compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or hexanolactone. The ether compound can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvent can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The content of the non-aqueous solvent in the electrolyte is not particularly limited in the present application, as long as the object of the present application can be achieved.

[0076] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, the preparation process of the secondary battery can include, but is not limited to, the following steps: stacking the separator, the negative electrode sheet, the separator, the double-sided positive electrode sheet, the separator, the negative electrode sheet, the separator in order, and setting the single-sided positive electrode sheet on the outermost side on both sides with the first material layer facing the negative electrode sheet, then fixing the four corners of the entire stack structure with tape to obtain an electrode assembly of the stack structure, placing the electrode assembly into the case, injecting the electrolyte into the case and sealing, to obtain the secondary battery. In addition, the overcurrent prevention element, the guide plate, etc. can also be placed in the case as needed, so as to prevent the pressure inside the secondary battery from rising, overcharging and discharging.

[0077] The second aspect of the present application provides an electronic device comprising the secondary battery of any of the preceding embodiments. Thus, the electronic device provided by the present application has good use performance.

[0078] The kind of the electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, an illuminating appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0079] Embodiments

[0080] Hereinafter, embodiments and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0081] Test methods and apparatus:

[0082] Mass ratio X of the first binder to the second binder:

[0083] (1) Take the single-sided positive electrode sheet to be tested with a radius r of 10 mm, first soak it in dimethyl carbonate (DMC) with a purity of 99.9% for 24 h, and then wash away the residual electrolyte. Replace the DMC every 8 h during soaking, and then place it in a vacuum box at room temperature for 12 h to dry until there is no residual DMC on the surface;

[0084] (2) Place the single-sided positive electrode sheet in the sample chamber of a scanning electron microscope (SEM), select a magnification of 100 to 2000 times, and observe and determine the coated and uncoated areas on the surface of the positive electrode material layer under the SEM field of view;

[0085] (3) Perform EDS distribution analysis on the areas within the field of view in backscattering mode; select the coated and uncoated areas for composition content analysis of the specified elements;

[0086] (4) Take PVDF as an example, the specified element is F, and output the specific values of the F element content data in the coated area and the F element content in the uncoated area; if it is polyacrylonitrile, the specified element is N, and output the specific values of the N element content data in the coated area and the N element content in the uncoated area;

[0087] (5) Calculate the mass ratio of the coated area and the non-coated area of the specified element, which is the mass ratio value X of the first binder and the second binder;

[0088] (6) Repeat steps (2) to (4) 3 times, and take the average as the final output result.

[0089] Test of h1, L1, d1, D1, h2, L2, d2, D2:

[0090] Disassemble the lithium ion battery, observe the positive material layer surface of the single-sided positive electrode sheet, whether the coated and bonded area is a convex part or a concave part, and its distribution state. The cross section of the single-sided positive electrode sheet along the thickness direction of itself is ion polished, the convex part or the concave part is observed, and one of them can be selected to measure h1, L1, d1, h2, L2, d2. Under the scanning electron microscope, a convex part or a concave part is selected, D1 or D2 can be measured, and S1 can be calculated. The above size measurement is measured for 10 times, and the average value is taken as the final result. S2=55×91.5=5032.5mm 2 , and then S1 / S2 is calculated.

[0091] Single-sided positive electrode sheet curling test:

[0092] 1. Take a single-sided positive electrode sheet, and then cut the single-sided positive electrode sheet into a rectangular sheet of 91.5mm×55mm;

[0093] 2. Lay the rectangular sheet on a flat marble table, with the first material layer facing down, in a natural relaxed state, measure the size of the rectangular sheet in the transverse TD and longitudinal MD directions in the relaxed state, denoted as T1 and M1;

[0094] 3. Use a glass plate to flatten the rectangular sheet to be flat with the desktop, measure the actual transverse TD and longitudinal MD directions of the rectangular sheet, denoted as T2 and M2;

[0095] 4. Calculate the curling rate of the single-sided positive electrode sheet: TD curling rate=(T2-T1) / T2×100%; MD curling rate=(M2-M1) / M2×100%;

[0096] Take the larger one of TD curling rate and MD curling rate as the final result. When the curling rate is greater than or equal to 2%, it means that the curling of the single-sided positive electrode sheet is serious, and the risk in the processing process is high; when the curling rate is less than 2%, it means that the curling of the single-sided positive electrode sheet is not serious, and there is basically no risk in the processing process.

[0097] Observation of purple spots and lithium precipitation:

[0098] The lithium ion battery was placed in an environment of 25°C, charged at 0.5C constant current to 4.5V, then charged at 4.5V constant voltage to the cutoff current 0.05C, and rested for 5min, discharged at 0.5C constant current to 3.0V, and rested for 5min, which was one charge and discharge cycle. The same steps were repeated for 500 cycles. Then charged to 4.5V, then charged at 4.5V constant voltage to the cutoff current 0.05C, and rested for 5min. The lithium ion battery was disassembled, and whether there was purple stain and lithium precipitation on the surface of the negative electrode plate adjacent to the single-sided positive electrode plate was observed. If there was, it was recorded as "yes", and if there was not, it was recorded as "no".

[0099] Cycle capacity retention rate test:

[0100] The lithium ion battery was placed in an environment of 25°C, charged at 1C constant current to 4.5V, then charged at 4.5V constant voltage to the cutoff current 0.2C, and rested for 5min, discharged at 0.5C constant current to 3.0V, and rested for 5min, which was one charge and discharge cycle. The discharge capacity at this time was recorded as C1. The same steps were repeated for x cycles, and the discharge capacity of the xth cycle was taken as Cx. The battery capacity retention rate of the xth cycle was Cx / C1x100%, and x=500.

[0101] Example 1

[0102] Preparation of the positive electrode slurry

[0103] The positive electrode active material LiCoO2, the conductive agent acetylene black, and the second binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97:1:2, N-methyl pyrrolidone (NMP) was added as a solvent, and a slurry with a solid content of 75wt% was prepared. After uniform stirring under vacuum, the positive electrode slurry was obtained.

[0104] Preparation of the single-sided positive electrode plate

[0105] (1) The positive electrode slurry was uniformly coated on one surface of the positive electrode current collector aluminum foil with a thickness H1 of 10μm, and dried at 85°C to obtain a positive electrode plate with a material layer of 100μm thick. After cold pressing, it was ready for use.

[0106] (2) The first binder PVDF is added into NMP and dispersed at a high speed of 1000 r / min for 60 min to prepare a binder coating area slurry with a solid content W of 2%, and then the binder coating area slurry is coated on the surface of the material layer and dried at 100°C to form a plurality of convex parts in a stripe distribution, h1 = 0.2 μm, L1 = 100 μm, d1 = 0.8 mm, and a = 90°. Then, the single-face positive electrode tab is obtained by vacuum drying at 85°C for 8 h, cutting, and welding the tab, and the specification of the single-face positive electrode tab is 55 mm x 91.5 mm, and the thickness of the positive electrode material layer is 53.7 μm.

[0107] <Preparation of a double-face positive electrode tab>

[0108] The positive electrode slurry is uniformly coated on one surface of a double-face positive electrode current collector aluminum foil with a thickness H2 of 10 μm, and dried at 85°C to obtain a positive electrode tab with a double-face positive electrode material layer coated on one surface with a thickness of 100 μm. Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode tab with a double-face positive electrode material layer coated on both surfaces. Then, the positive electrode tab is subjected to cold pressing and vacuum drying at 85°C for 8 h, and then cut and the tab is welded to obtain a double-face positive electrode tab with a specification of 55 mm x 91.5 mm. The thickness of the single-layer double-face positive electrode material layer is 53.7 μm.

[0109] <Preparation of a negative electrode tab>

[0110] The negative electrode active material artificial graphite, the binder styrene-butadiene rubber, and the conductive agent acetylene black are mixed in a mass ratio of 96:2:2, and deionized water is added as a solvent to prepare a slurry with a solid content of 45 wt%, and the negative electrode slurry is obtained after uniform stirring by a vacuum stirrer. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and dried at 85°C to obtain a negative electrode tab with a single-face negative electrode material layer coated with a thickness of 100 μm. Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode tab with a double-face negative electrode material layer coated. After cold pressing, cutting, and welding of the tab, the negative electrode tab is vacuum dried at 120°C for 12 h to obtain a negative electrode tab with a specification of 56 mm x 93 mm. The thickness of the single-face negative electrode material layer is 66.5 μm.

[0111] <Preparation of an electrolyte>

[0112] Ethylene carbonate, propylene carbonate, and diethyl carbonate are mixed in a mass ratio of 1:1:1 to obtain an organic solvent, and then electrolyte salt LiPF6 is added into the organic solvent to obtain an electrolyte. The molar concentration of the electrolyte salt is 1.15 mol / L based on the mass of the electrolyte.

[0113] <Separator>

[0114] A porous polyethylene film (provided by Celgard) with a thickness of 5 μm was used as a base film, and a ceramic coating layer was formed on one surface of the base film by disposing a ceramic coating slurry to form a ceramic coating layer, and the thickness of the single ceramic coating layer was 3 μm. The ceramic coating slurry was prepared by mixing aluminum oxide and polyvinylidene fluoride at a mass ratio of 9:1, then adding NMP and mixing uniformly to obtain a solid content of 45 wt%.

[0115] <Preparation of a lithium ion battery>

[0116] The above-prepared separator, negative electrode sheet, separator, double-sided positive electrode sheet, separator, negative electrode sheet, separator were stacked in sequence, and single-sided positive electrode sheets were disposed on the outermost sides of both sides with the first material layer facing the negative electrode sheet and the ceramic coating layer facing the positive electrode sheet, and then the four corners of the entire stack structure were fixed with adhesive tape to obtain an electrode assembly of a stack structure. The electrode assembly was loaded into an aluminum plastic film packaging bag, and the water was removed at 80°C, and the above-prepared electrolyte was injected, and then vacuum packaging, standing, formation, shaping, capacity, degassing, and edge cutting were performed to obtain a lithium ion battery. The formation temperature was 80°C, and the standing time was 2 h.

[0117] Examples 2 to 37

[0118] Except for adjusting the relevant preparation parameters according to Table 1, the rest was the same as Example 1.

[0119] Comparative Example 1

[0120] Except for preparing a single-sided positive electrode sheet according to the following preparation method, the rest was the same as Example 1:

[0121] <Preparation of a single-sided positive electrode sheet>

[0122] The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness H1 of 10 μm, and dried at 85°C to obtain a positive electrode sheet with a single-sided positive electrode material layer of 100 μm in thickness. Then, cold pressing was performed, and vacuum drying was performed at 85°C for 8 h, and then the sheet was cut and the tabs were welded to obtain a single-sided positive electrode sheet with a size of 55 mm x 91.5 mm for use. The thickness of the positive electrode material layer was 53.7 μm.

[0123] Comparative Example 2

[0124] Except for preparing a single-sided positive electrode sheet according to the following preparation method, the rest was the same as Example 1:

[0125] <Preparation of a single-sided positive electrode sheet>

[0126] (1) The positive electrode slurry was uniformly coated on one surface of the positive current collector aluminum foil with a thickness H1 of 10 μm, and dried at 85°C to obtain a positive electrode sheet with a 100 μm thick positive electrode material layer on one surface.

[0127] (2) The boehmite with a D50 of 1 μm and the binder PVDF were mixed in a mass ratio of 95:5, deionized water was added as a solvent, and a slurry with a solid content of 45wt% was prepared. After uniform vacuum stirring, a coating slurry was obtained. Then the coating slurry was coated on the other surface of the aluminum foil, and then dried, cold-pressed, and vacuum dried at 85°C for 8h. After cutting and welding the tabs, a single-sided positive electrode sheet with a size of 55mm x 91.5mm was obtained for use. The thickness of the positive electrode material layer was 53.7 μm, and the thickness of the coating was 10 μm.

[0128] Comparative Example 3

[0129] Except that a single-sided positive electrode sheet was prepared according to the following preparation method, the rest was the same as Example 1.

[0130] Preparation of a single-sided positive electrode sheet

[0131] (1) The positive electrode slurry was uniformly coated on one surface of the positive current collector aluminum foil with a thickness H1 of 10 μm, and dried at 85°C to obtain a positive electrode sheet with a 100 μm thick positive electrode material layer on one surface. After cold-pressing, 30mg / 1540.25mm of NMP was uniformly coated on the surface of the positive electrode material layer, dried, and then vacuum dried at 85°C for 8h. After cutting and welding the tabs, a single-sided positive electrode sheet with a size of 55mm x 91.5mm was obtained for use. The thickness of the positive electrode material layer was 53.7 μm. 2

[0132] The preparation parameters and performance tests of each example and comparative example are shown in Table 1.

[0133] ​As can be seen from Examples 1 to 37 and Comparative Examples 1 to 3, the lithium ion batteries in the examples have the positive electrode material layer of the single-sided positive electrode tab provided with the adhesive coating area and the non-coating area, and the adhesive coating area comprises a plurality of sub-areas; the surface of the single-sided positive electrode tab in Comparative Example 1 is not treated in any way, the other surface of the single-sided tab in Comparative Example 2 is provided with a bending-resistant coating, and the single-sided positive electrode tab in Comparative Example 3 is coated with a solvent on the surface of the positive electrode material layer after being prepared. The above comparative examples do not simultaneously have the adhesive coating area and the non-coating area. The single-sided positive electrode tab obtained in Comparative Example 1 has a very high curling rate and cannot be processed into a lithium ion battery; the single-sided positive electrode tab obtained in Comparative Example 2 has improved curling by providing a bending-resistant coating, the lithium ion battery does not have black spots and lithium precipitation problems, but has a low cycle capacity retention rate, and the provision of the coating also greatly affects the energy density of the lithium ion battery; in Comparative Example 3, the lithium ion battery has black spots and lithium precipitation problems, and has a low cycle capacity retention rate. The single-sided positive electrode tab obtained in the examples of the present application has a curling rate of less than 2%, and there is basically no risk in the processing process, and the lithium ion battery does not have black spots and lithium precipitation problems at the same time, and has a high cycle capacity retention rate, thereby indicating that the curling problem of the single-sided positive electrode tab in the examples of the present application is improved, and the black spot, lithium precipitation and capacity decay problems of the lithium ion battery are improved compared with the lithium ion batteries in the comparative examples, and the lithium ion battery has better cycle performance. In addition, the existence of the adhesive coating area and the non-coating area basically has no effect on the energy density of the secondary battery.

[0134] The form of the adhesive coating area usually affects the cycle performance of the lithium ion battery. As can be seen from Examples 1 to 37, the adhesive coating area exists in the form of a convex portion or a concave portion, the obtained single-sided positive electrode tab has a low curling rate, the lithium ion battery does not have black spots and lithium precipitation problems at the same time, and has a high cycle capacity retention rate, thereby indicating that the curling problem of the single-sided positive electrode tab in the above examples is improved, and the black spot, lithium precipitation and capacity decay problems of the lithium ion battery are improved, and the lithium ion battery has good cycle performance.

[0135] The size and distribution of the protrusions generally affect the cycle performance of the lithium ion battery. As can be seen from Examples 1 to 18, when the protrusions are distributed in a stripe shape or a matrix point shape, the single-face positive electrode sheet obtained has low curling rate, the lithium ion battery does not have problems of black spots and lithium precipitation at the same time, and has high cycle capacity retention rate, thereby indicating that the curling problem of the single-face positive electrode sheet is improved, the problems of black spots, lithium precipitation and capacity attenuation of the lithium ion battery are improved, and the lithium ion battery has good cycle performance. Moreover, when the height h1 of the protrusions, the minimum distance d1 between two adjacent protrusions, the width L1 of the protrusions, the diameter D1 of the maximum circumscribed circle of the outer contour of a single protrusion, and the mass ratio X of the first binder to the second binder are within the ranges of the present application, the single-face positive electrode sheet obtained has low curling rate, the lithium ion battery does not have problems of black spots and lithium precipitation, and has high cycle capacity retention rate, thereby indicating that when h1, d1, L1, D1 and X are within the ranges of the present application, the curling problem of the single-face positive electrode sheet is improved, the problems of black spots, lithium precipitation and capacity attenuation of the lithium ion battery are improved, and the lithium ion battery has better cycle performance.

[0136] The size and distribution of the recesses generally affect the cycle performance of the lithium ion battery. As can be seen from Examples 19 to 34, when the recesses are distributed in a stripe shape or a matrix point shape, the single-face positive electrode sheet obtained has low curling rate, the lithium ion battery does not have problems of black spots and lithium precipitation at the same time, and has high cycle capacity retention rate, thereby indicating that the curling problem of the single-face positive electrode sheet is improved, the problems of black spots, lithium precipitation and capacity attenuation of the lithium ion battery are improved, and the lithium ion battery has good cycle performance. Moreover, when the height h2 of the recesses, the minimum distance d2 between two adjacent recesses, the width L2 of the recesses, the diameter D2 of the maximum circumscribed circle of the outer contour of a single recess, and the mass ratio X of the first binder to the second binder are within the ranges of the present application, the single-face positive electrode sheet obtained has low curling rate, the lithium ion battery does not have problems of black spots and lithium precipitation, and has high cycle capacity retention rate, thereby indicating that when h2, d2, L2, D2 and X are within the ranges of the present application, the curling problem of the single-face positive electrode sheet is improved, the problems of black spots, lithium precipitation and capacity attenuation of the lithium ion battery are improved, and the lithium ion battery has better cycle performance.

[0137] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery comprising an electrode assembly of a stacked structure, the electrode assembly comprising a positive electrode tab, a separator, and a negative electrode tab, the positive electrode tab comprising a double-sided positive electrode tab and a single-sided positive electrode tab located at the outermost side of the electrode assembly in a stacking direction; the single-sided positive electrode tab comprising a positive electrode current collector and a positive electrode material layer provided on one surface of the positive electrode current collector, the positive electrode material layer facing the double-sided positive electrode tab; the positive electrode material layer comprising a binder-coated region and a non-coated region, the binder-coated region comprising a first binder, the non-coated region comprising a second binder, the binder-coated region comprising a plurality of sub-regions arranged at intervals.

2. The secondary battery according to claim 1, wherein the plurality of sub-regions forming a plurality of protrusions on the surface of the positive electrode material layer, a mass ratio of the first binder to the second binder being X, 1 < X ≤ 5.

3. The secondary battery according to claim 2, wherein the plurality of protrusions being distributed in a stripe shape, a height of an individual protrusion being h1, 0 μm < h1 ≤ 1 μm, a width L1 of the individual protrusion being 50 μm to 1000 μm, and a minimum distance d1 between adjacent two protrusions being 0.5 mm to 5 mm.

4. The secondary battery according to claim 3, wherein an angle between the protrusion and a length direction of the single-sided positive electrode tab being α, the secondary battery satisfying: 0 μm < h1 < 0.5 μm, 0° ≤ α ≤ 90°; or 0.5 μm ≤ h1 ≤ 1 μm, 20° ≤ α ≤ 75°.

5. The secondary battery according to claim 2, wherein the plurality of protrusions being distributed in a dot shape, a shape of the protrusion comprising at least one of a circle, an ellipse, or a polygon, a height of an individual protrusion being h1, 0 μm < h1 ≤ 1 μm, a diameter D1 of a maximum circumscribed circle of an outer contour of the individual protrusion being 0.2 mm to 4 mm, and a minimum distance d1 between adjacent two protrusions being 0.5 mm to 5 mm.

6. The secondary battery according to claim 1, wherein the plurality of sub-regions forming a plurality of recesses on the surface of the positive electrode material layer, a mass ratio of the first binder to the second binder being X, 0.2 ≤ X < 1.

7. The secondary battery according to claim 6, wherein the plurality of sub-regions being distributed in a stripe shape, a depth of an individual recess being h2, 0 μm < h2 ≤ 1 μm, a minimum distance d2 between adjacent two recesses being 0.5 mm to 5 mm, and a width L2 of the individual recess being 50 μm to 1000 μm. 8.The secondary battery according to claim 7, satisfying: 0 μm < h2 < 0.5 μm, L2 < d2 < 5L2; or 0.5 μm ≤ h2 ≤ 1 μm, 3L2 < d2 ≤ 10L2.

9. The secondary battery according to claim 6, wherein the plurality of recesses being distributed in a dot shape, a shape of the recess comprising at least one of a circle, an ellipse, or a polygon, a depth of an individual recess being h2, 0 μm < h2 ≤ 1 μm, a diameter D2 of a maximum circumscribed circle of an outer contour of the individual recess being 0.2 mm to 4 mm, and a minimum distance d2 between adjacent two recesses being 0.5 mm to 5 mm.

10. The secondary battery according to any one of claims 1 to 9, wherein the positive electrode current collector being an aluminum foil, 8 μm ≤ H1 ≤ 20 μm.

11. The secondary battery according to any one of claims 1 to 9, wherein the first binder and the second binder each independently comprising at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, or polymethyl methacrylate.

12. The secondary battery according to any one of claims 1 to 9, wherein a surface of the separator facing the positive electrode tab being provided with a ceramic coating. 13.An electronic device comprising the secondary battery of any one of claims 1 to 12.

Images