Battery

Abstract

The utility model relates to the field of batteries, in particular to a battery. The battery comprises a first positive plate, the first positive plate comprises a positive current collector, a first safety coating is arranged on at least partial area of the first surface of the positive current collector, and a second safety coating is arranged on at least partial area of the surface, away from the positive current collector side, of the first safety coating. An active coating is also arranged on the outer surface of the first positive plate; in the first direction, the size of the first safety coating is larger than or equal to that of the second safety coating; the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is 1: (1-10). The battery disclosed by the utility model can reduce the energy density loss, effectively reduce the internal resistance and improve the rate capability on the premise of ensuring the needling safety and the heavy object impact safety.

Description

Technical Field

[0001] The utility model relates to the field of batteries, in particular to a battery. Background Art

[0002] Lithium-ion batteries are widely used in portable electronic devices such as mobile phones and laptops due to their high energy density and long cycle life, and their application in electric vehicles is also increasing. With the increase in energy density and charge and discharge rate, as well as the diversification of application scenarios, higher requirements are placed on the safety performance of lithium-ion batteries.

[0003] When lithium-ion batteries encounter mechanical abuse such as heavy impact, extrusion, and needle puncture, they are prone to trigger internal short circuits in the battery, causing fires, combustion, explosions, and other situations. When mechanical abuse occurs, many complex internal short-circuit sites will be generated inside the lithium-ion battery. Among various short-circuit methods, the contact between the positive electrode collector and the negative electrode sheet is the most dangerous, which can easily cause the battery to catch fire. In order to avoid this most dangerous short-circuit method, a common solution is to set a high-impedance safety primer layer in the positive electrode sheet to reduce the short-circuit current. However, the introduction of a high-impedance safety primer layer will increase the resistance of the positive electrode sheet, resulting in a decrease in the battery rate performance, and the presence of the safety primer layer will reduce the energy density of the battery.

[0004] Therefore, on the basis of ensuring the safety performance of the battery, it is particularly important to reduce the impact of the safety primer layer on the battery rate performance and energy density. Utility Model Content

[0005] The purpose of the utility model is to overcome the problem of the safety primer layer affecting the battery rate performance and energy density in the prior art, and to provide a battery. The battery of the utility model can reduce energy density loss, effectively reduce internal resistance, and improve rate performance while ensuring needle puncture safety and heavy object impact safety.

[0006] The safety primer layer in the related technology will have an adverse effect on the rate performance and energy density of the battery. After research, it was found that the structure of the safety primer layer and the position of the safety primer layer in the battery have a great influence on the battery's puncture safety, heavy object impact safety, energy density and rate performance. First, the safety primer layer is layered and the thickness ratio of the two is limited to give it a specific structure; then, by limiting the size of each layer of the safety primer layer in a specific direction, the energy density and rate performance of the battery can be improved while minimizing the adverse effects on puncture safety and heavy object impact safety.

[0007] The utility model provides a battery, the battery comprises a first positive electrode sheet, the first positive electrode sheet comprises a positive electrode collector, at least a portion of a first surface of the positive electrode collector is provided with a first safety coating, at least a portion of a surface of the first safety coating away from the positive electrode collector is provided with a second safety coating, and an active coating is further provided on the outer surface of the first positive electrode sheet; in a first direction, a size of the first safety coating is greater than or equal to a size of the second safety coating; a ratio of an average thickness of the first safety coating to an average thickness of the second safety coating is 1:(1-10).

[0008] In one example, in the first positive electrode sheet, at least a portion of the second surface of the positive electrode collector is provided with the first safety coating; or, in the first positive electrode sheet, at least a portion of the second surface of the positive electrode collector is provided with the first safety coating, and at least a portion of the surface of the first safety coating away from the positive electrode collector side is provided with the second safety coating.

[0009] In one example, the shape of the first safety coating on the cross section of the first positive electrode sheet along the thickness direction includes at least one of a rectangle and a triangle; and / or, the shape of the second safety coating on the cross section of the first positive electrode sheet along the thickness direction includes at least one of a rectangle and a triangle.

[0010] In one example, the ratio of the average thickness of the first safety coating to the average thickness of the active coating is 1:(4-500); and / or the ratio of the average thickness of the second safety coating to the average thickness of the active coating is 1:(4-500).

[0011] In one example, the first safety coatings are distributed at intervals in the first direction; and / or the second safety coatings are distributed at intervals in the first direction.

[0012] In one example, in the first direction, the ratio of the size of the first safety coating to the size of the positive electrode collector is 1:(1-20); and / or, in the first direction, the ratio of the size of the second safety coating to the size of the positive electrode collector is 1:(1-20).

[0013] In one example, the battery further includes a first negative electrode sheet and a separator, the first positive electrode sheet, the separator and the first negative electrode sheet are stacked and wound to form a winding core, and the winding core includes a straight area and a bending area.

[0014] In one example, along the winding direction of the first positive electrode sheet, starting from the winding start end, the orthographic projection area of ​​the second safety coating located in the front half of the first positive electrode sheet on the positive electrode collector accounts for a larger proportion than the orthographic projection area of ​​the second safety coating located in the rear half of the first positive electrode sheet on the positive electrode collector.

[0015] In one example, the straight area includes a first straight area and a second straight area located at the outermost side of the winding core, the bending area includes a first bending area and a second bending area connecting the first straight area and the second straight area, and the first positive electrode sheet located in the first straight area and / or the second straight area includes the first safety coating and / or the second safety coating; and / or, along the direction from the outer side of the winding core to the center of the winding core, at least one straight area of ​​the third to sixth turns of the first positive electrode sheet includes the first safety coating and / or the second safety coating.

[0016] In one example, the first positive electrode sheet located in the first bending region and / or the second bending region includes the first safety coating and / or the second safety coating.

[0017] In one example, the first positive electrode sheet includes the first safety coating on one side close to the center of the winding core, and the first positive electrode sheet includes the first safety coating and the second safety coating on one side away from the center of the winding core; and / or, the first positive electrode sheet includes the first safety coating and the second safety coating on one side close to the center of the winding core, and the first positive electrode sheet includes the first safety coating and the second safety coating on one side away from the center of the winding core, the thickness of the first safety coating close to the winding tail end of the first positive electrode sheet is equal to the thickness of the first safety coating away from the winding tail end of the first positive electrode sheet, and the thickness of the first safety coating close to the winding tail end of the first positive electrode sheet is equal to the thickness of the first safety coating away from the winding tail end of the first positive electrode sheet. The thickness of the second safety coating is greater than the thickness of the second safety coating away from the winding tail end of the first positive electrode sheet; and / or, the side of the first positive electrode sheet close to the center of the winding core includes the first safety coating and the second safety coating, the side of the first positive electrode sheet away from the center of the winding core includes the first safety coating and the second safety coating, the thickness of the first safety coating close to the winding tail end of the first positive electrode sheet is greater than the thickness of the first safety coating away from the winding tail end of the first positive electrode sheet, and the thickness of the second safety coating close to the winding tail end of the first positive electrode sheet is greater than the thickness of the second safety coating away from the winding tail end of the first positive electrode sheet.

[0018] In one example, the thickness of the first safety coating near the winding tail end of the first positive electrode sheet is greater than or equal to the thickness of the first safety coating far from the winding tail end of the first positive electrode sheet; and / or, the thickness of the second safety coating near the winding tail end of the first positive electrode sheet is greater than or equal to the thickness of the second safety coating far from the winding tail end of the first positive electrode sheet.

[0019] In one example, the battery includes a stacked core, the stacked core includes a plurality of the first positive electrode sheets, in the first direction, the ratio of the total size of the first safety coating to the total size of the positive electrode collector is 1:(1-20); and / or, in the first direction, the ratio of the total size of the second safety coating to the total size of the positive electrode collector is 1:(1-20).

[0020] In one example, the battery includes a stacked core, the stacked core includes a plurality of the first positive electrode sheets and a plurality of the second positive electrode sheets, the second positive electrode sheets include the positive electrode collector and the active coating located on at least one side of the surface of the positive electrode collector; in a first direction, the ratio of the total size of the first safety coating to the total size of the positive electrode collector is 1:(1-20); and / or, in the first direction, the ratio of the total size of the second safety coating to the total size of the positive electrode collector is 1:(1-20).

[0021] Through the above technical scheme, the utility model has at least the following advantages compared with the prior art: the battery of the utility model can reduce energy density loss, effectively reduce internal resistance and improve rate performance while ensuring needle puncture safety and heavy object impact safety.

[0022] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Shown is a schematic structural diagram of the first positive electrode sheet in an example of the utility model.

[0024] Figure 2 Shown is a schematic diagram of a first positive electrode sheet used for a winding core in an example of the utility model.

[0025] Figure 3 Shown is a schematic diagram of a first positive electrode sheet used for stacking cores in an example of the utility model.

[0026] Figure 4Shown is a schematic structural diagram of the first positive electrode sheet in an example of the utility model.

[0027] Figure 5 Shown is a schematic structural diagram of the first positive electrode sheet in an example of the utility model.

[0028] Figure 6 The figure shows a schematic diagram of the shape of the first safety coating and the second safety coating in a cross section along the thickness direction of the first positive electrode sheet in an example of the present invention.

[0029] Figure 7 Shown is a schematic diagram of the distribution of the first safety coating and the second safety coating in the first direction in an example of the utility model.

[0030] Figure 8 The figure shows a top view of the first positive electrode sheet in an example of the utility model.

[0031] Fig. 9 Shown is a schematic diagram of a winding core in an example of the present utility model.

[0032] Fig.10 The figure shows a schematic diagram of the dimensions of the first safety coating layer continuously distributed at the tail end of the first positive electrode sheet in an example of the present invention.

[0033] Fig.11 The figure shows a schematic diagram of the dimensions of the second safety coating layer continuously distributed at the tail end of the first positive electrode sheet in one example of the utility model.

[0034] Fig.12 The figure shows a top view of the first positive electrode sheet in an example of the utility model.

[0035] Fig.13 Shown is a schematic structural diagram of a stacked core in an example of the utility model.

[0036] Fig.14 Shown is a schematic diagram of a first positive electrode sheet in an example of the utility model.

[0037] Fig.15 Shown is a schematic diagram of a first positive electrode sheet in an example of the utility model. DETAILED DESCRIPTION

[0038] The specific implementation of the present invention is described in detail below. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0039] The utility model provides a battery, the battery may include a first positive electrode sheet, the first positive electrode sheet may include a positive electrode current collector, at least part of the first surface of the positive electrode current collector is provided with a first safety coating, at least part of the surface of the first safety coating away from the positive electrode current collector is provided with a second safety coating, and the outer surface of the first positive electrode sheet is also provided with an active coating. Figure 1 The figure shows a schematic diagram of the structure of the first positive electrode sheet in an example of the utility model. It can be seen from the figure that the first positive electrode sheet includes a positive electrode collector 1, and the first surface of the positive electrode collector 1 has a first safety coating 2, a second safety coating 3 located in a partial area of ​​the first safety coating 2 away from the positive electrode collector 1 side, and an active coating 4 located on the outer surface of the first positive electrode sheet.

[0040] In the present invention, in the first direction, the size of the positive electrode current collector may be greater than or equal to the size of the first safety coating layer. The size of the first safety coating layer may be greater than or equal to the size of the second safety coating layer.

[0041] When the first positive electrode sheet is used for winding core, the first direction refers to the length direction of the first positive electrode sheet. Figure 2 The schematic diagram of the first positive electrode sheet used for the winding core in one embodiment of the utility model is shown. Figure 2 In (a), in the length direction, the size of the positive electrode current collector 1 is equal to the size of the first safety coating 2, and the size of the first safety coating 2 is equal to the size of the second safety coating 3; Figure 2 In (b), in the length direction, the size of the positive electrode current collector 1 is larger than the size of the first safety coating 2, and the size of the first safety coating 2 is equal to the size of the second safety coating 3; Figure 2 In (c), in the length direction, the size of the positive electrode current collector 1 is equal to the size of the first safety coating 2, and the size of the first safety coating 2 is larger than the size of the second safety coating 3; Figure 2 In (d), in the length direction, the size of the positive electrode current collector 1 is larger than that of the first safety coating 2 , and the size of the first safety coating 2 is larger than that of the second safety coating 3 .

[0042] When the first positive electrode sheet is used for stacking, the first direction refers to the direction perpendicular to the extension direction of the positive electrode tab. Figure 3 The schematic diagram of the first positive electrode sheet used for stacking cores in one embodiment of the utility model is shown. Figure 3 In (a), in the direction perpendicular to the extension direction of the positive electrode tab, the size of the positive electrode current collector 1 is equal to the size of the first safety coating 2, and the size of the first safety coating 2 is equal to the size of the second safety coating 3; Figure 3In (b), in the direction perpendicular to the extension direction of the positive electrode tab, the size of the positive electrode current collector 1 is larger than the size of the first safety coating 2, and the size of the first safety coating 2 is equal to the size of the second safety coating 3; Figure 3 In (c), in the direction perpendicular to the extension direction of the positive electrode tab, the size of the positive electrode current collector 1 is equal to the size of the first safety coating 2, and the size of the first safety coating 2 is greater than the size of the second safety coating 3; Figure 3 In (d), in the direction perpendicular to the extension direction of the positive electrode tab, the size of the positive electrode current collector 1 is larger than the size of the first safety coating 2, and the size of the first safety coating 2 is larger than the size of the second safety coating 3; Figure 3 (e) Figure 3 (d) is a top view, from which it can be seen that the first direction is a direction perpendicular to the extension direction of the positive electrode tab 4.

[0043] After research, it was found that when the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is within a specific range, the rate performance and energy density can be improved without affecting the overall puncture safety and heavy object impact safety of the battery. The ratio of the average thickness of the first safety coating to the average thickness of the second safety coating can be 1: (1-10), for example, 1: 1, 1: 2, 1: 3, 1: 4, 1: 5, 1: 6, 1: 7, 1: 8, 1: 9 or 1: 10.

[0044] In one example, a ratio of an average thickness of the first safety coating layer to an average thickness of the second safety coating layer is 1:(2-5).

[0045] The specific testing method for the average thickness of the first safety coating and the average thickness of the second safety coating is as follows: take a first positive electrode sheet, take 30 measuring points at equal distances in a first direction, measure the thickness of the first safety coating and the thickness of the second safety coating at each measuring point respectively, and take the average value.

[0046] In one example, in the first positive electrode sheet, at least a portion of the second surface of the positive electrode collector is provided with the first safety coating.

[0047] In one example, in the first positive electrode sheet, at least a portion of the second surface of the positive current collector is provided with the first safety coating, and at least a portion of the surface of the first safety coating away from the positive current collector is provided with the second safety coating.

[0048] like Figure 4 The structure diagram of the first positive electrode sheet in an example of the utility model is shown in FIG. Figure 4 In (a), the second surface of the positive electrode current collector 1 has a first safety coating 2; Figure 4In (b), the second surface of the positive electrode current collector 1 has a first safety coating 2 and a second safety coating 3 located on the side of the first safety coating 2 away from the positive electrode current collector 1 .

[0049] In one example, in the first positive electrode sheet, the second surface of the positive current collector has a first safety coating layer and the active coating layer is located on a side of the first safety coating layer away from the first positive current collector.

[0050] In one example, in the first positive electrode sheet, the second surface of the positive electrode collector has a first safety coating, a second safety coating located on a side of the first safety coating away from the first positive electrode collector, and an active coating located on an outer surface of the first positive electrode sheet.

[0051] like Figure 5 The structure diagram of the first positive electrode sheet in an example of the utility model is shown in FIG. Figure 5 In (a), the second surface of the positive electrode current collector 1 has a first safety coating 2 and an active coating 4 located on the side of the first safety coating 2 away from the positive electrode current collector 1; Figure 5 In (b), the second surface of the positive current collector 1 has a first safety coating 2, a second safety coating 3 located on the side of the first safety coating 2 away from the positive current collector 1, and an active coating 4 located on the outer surface of the first positive electrode sheet.

[0052] In one example, the average thickness of the first safety coating can be 0.1μm-15μm, for example, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm.

[0053] In one example, the average thickness of the first security coating layer is 0.2 μm-0.5 μm.

[0054] In one example, the average thickness of the second safety coating can be 0.1μm-15μm, for example, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm.

[0055] In one example, the average thickness of the second security coating is 0.5 μm-2 μm.

[0056] In the present invention, there is no special limitation on the shapes of the first safety coating and the second safety coating in the cross section of the first positive electrode sheet along the thickness direction. The shape of the first safety coating in the cross section of the first positive electrode sheet along the thickness direction can be a rectangle or a triangle. The shape of the second safety coating in the cross section of the first positive electrode sheet along the thickness direction can be a rectangle or a triangle. Figure 6 The schematic diagram of the shape of the first safety coating and the second safety coating in the cross section of the first positive electrode sheet along the thickness direction in one example of the utility model is shown. Figure 6 In (a)-6(d), the shape of the first safety coating is a rectangle, and the shape of the second safety coating is a triangle; Figure 6 In (e), the shape of the first safety coating is a triangle, and the shape of the second safety coating is a triangle.

[0057] After research, it was found that when the ratio of the average thickness of the first safety coating to the average thickness of the active coating is too small (for example, less than 1:500), the average thickness of the first safety coating is thinner, and when mechanical damage occurs, the short-circuit impedance is too low to provide effective protection; and when the ratio of the average thickness of the first safety coating to the average thickness of the active coating is too large (for example, greater than 1:4), the average thickness of the first safety coating is thicker, which will not only cause a greater loss of energy density of the battery, but also reduce the transmission speed of electrons, thereby affecting the rate performance of the battery.

[0058] In one example, the ratio of the average thickness of the first safety coating to the average thickness of the active coating can be 1:(4-500), for example, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, 1:200, 1:300, 1:400 or 1:500.

[0059] In one example, the ratio of the average thickness of the first safety coating layer to the average thickness of the active coating layer is 1:(80-200).

[0060] After research, it was found that when the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is within a specific range, when the ratio of the average thickness of the second safety coating to the average thickness of the active coating is too small (for example, less than 1:500), the average thickness of the second safety coating is thinner, and when mechanical damage occurs, the short-circuit impedance is too low and cannot play an effective protective role; and when the ratio of the average thickness of the second safety coating to the average thickness of the active coating is too large (for example, greater than 1:4), the average thickness of the second safety coating is thicker, which will not only cause a large loss of energy density of the battery, but also reduce the transmission speed of electrons, thereby affecting the rate performance of the battery.

[0061] In one example, the ratio of the average thickness of the second safety coating to the average thickness of the active coating can be 1:(4-500), for example, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, 1:200, 1:300, 1:400 or 1:500.

[0062] In one example, the ratio of the average thickness of the second safety coating to the average thickness of the active coating is 1:(20-80).

[0063] In one example, the active coating layer may have an average thickness of 20 μm-100 μm, for example, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm.

[0064] In one example, the active coating has an average thickness of 30 μm to 50 μm.

[0065] The test method for the average thickness of the active coating is as follows: take a first positive electrode sheet, take 30 measurement points at equal distances in a first direction, measure the thickness of the active coating at each measurement point, and take the average value.

[0066] In the present invention, the first safety coating can be distributed continuously in the first direction, or can be distributed at intervals in the first direction. The second safety coating can be distributed continuously in the first direction, or can be distributed at intervals in the first direction. Figure 7 The diagram shows the distribution of the first safety coating and the second safety coating in the first direction in an example of the present invention. Figure 7 In (a), the first safety coating is continuously distributed in the first direction, and the second safety coating is distributed at intervals in the first direction; Figure 7 (b), the first safety coating is continuously distributed in the first direction, and the second safety coating is continuously distributed in the first direction; Figure 7 (c), the first safety coating is distributed at intervals in the first direction, and the second safety coating is distributed continuously in the first direction; Figure 7 In (d), the first safety coatings are distributed at intervals in the first direction, and the second safety coatings are distributed at intervals in the first direction.

[0067] In one example, the first safety coating and the second safety coating may each independently include inorganic particles, a binder and a conductive agent. The inorganic particles may be selected from inorganic particles conventionally used in the art, such as the following substances coated with carbon or not coated with carbon: aluminum oxide, barium sulfate, silicon dioxide, silicon monoxide, zirconium oxide, magnesium oxide, vanadium oxide, titanium oxide, boehmite, lithium iron manganese phosphate or lithium titanate. The binder may be selected from binders conventionally used in the art, such as polyvinylidene fluoride, polyacrylic acid, lithium polyacrylate, polyacrylate, polytetrafluoroethylene, styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The conductive agent may be selected from conductive agents conventionally used in the art, such as conductive carbon black, conductive carbon fiber or carbon nanotubes.

[0068] In one example, based on the total weight of the first safety coating, the content of the inorganic particles can be 30-99 weight % (for example, 30, 40, 50, 60, 70, 80, 90 or 99 weight %), the content of the binder can be 0.5-70 weight % (for example, 0.5, 1, 5, 10, 20, 30, 40, 50, 60 or 70 weight %), and the content of the conductive agent can be 0-25 weight % (for example, 0, 5, 10, 15, 20 or 25 weight %).

[0069] In one example, based on the total weight of the second safety coating, the content of the inorganic particles can be 30-99 weight % (for example, 30, 40, 50, 60, 70, 80, 90 or 99 weight %), the content of the binder can be 0.5-70 weight % (for example, 0.5, 1, 5, 10, 20, 30, 40, 50, 60 or 70 weight %), and the content of the conductive agent can be 0-25 weight % (for example, 0, 5, 10, 15, 20 or 25 weight %).

[0070] In one example, the active coating may include a positive electrode active material. The positive electrode active material may include a positive electrode active material conventionally used in the art, such as lithium cobalt oxide, lithium iron phosphate, lithium nickel oxide, lithium manganese oxide, lithium titanate, lithium vanadate, lithium manganese phosphate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium oxyvanadium phosphate, lithium-rich manganese material, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, nickel-cobalt-manganese-aluminum material, nickel-manganese binary material, or sodium-containing lithium cobalt oxide.

[0071] In one example, the active coating may further include a positive electrode conductor and a positive electrode binder. The positive electrode conductor may include a conductive agent conventionally used in the art, such as conductive carbon black, conductive carbon fiber or carbon nanotube. The positive electrode binder may include a binder conventionally used in the art, such as polyvinylidene fluoride, polyacrylic acid, lithium polyacrylate, polyacrylate, polytetrafluoroethylene, styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0072] In one example, based on the total weight of the active coating, the content of the positive electrode active material can be 80-99.8 weight % (for example, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 99 or 99.8 weight %), the content of the positive electrode conductor can be 0.1-10 weight % (for example, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5 or 0.1 weight %), and the content of the positive electrode binder can be 0.1-10 weight % (for example, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5 or 0.1 weight %).

[0073] In the utility model, in the first direction, the ratio of the size of the first safety coating to the size of the positive electrode collector can be 1:(1-20), for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20.

[0074] In one example, in the first direction, a ratio of a size of the first safety coating layer to a size of the positive electrode current collector is 1:(1-4).

[0075] After research, it was found that when the ratio of the size of the first safety coating to the size of the positive electrode collector in the first direction is within a specific range, the battery's needle puncture safety and heavy object impact safety can be significantly improved.

[0076] In the utility model, in the first direction, the ratio of the size of the second safety coating to the size of the positive electrode collector can be 1:(1-20), for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20.

[0077] In one example, in the first direction, the ratio of the size of the second safety coating layer to the size of the positive electrode current collector is 1:(2-4).

[0078] After research, it was found that when the ratio of the size of the second safety coating to the size of the positive electrode collector in the first direction is within a specific range, the battery's needle puncture safety and heavy object impact safety can be significantly improved.

[0079] In the utility model, the battery may include a rolled core or a stacked core.

[0080] <Core>

[0081] In the present invention, the battery further comprises a first negative electrode sheet and a separator. The first positive electrode sheet, the separator and the first negative electrode sheet are stacked and wound to form a winding core, and the winding core comprises a straight area and a bending area.

[0082] In one example, the first positive electrode sheet may include a positive electrode tab.

[0083] In one example, the first safety coating may include a groove exposing the positive electrode current collector, and the positive electrode tab may be located in the groove. Figure 8 The figure shows a schematic top view of the first positive electrode sheet in an example of the utility model. It can be seen from the figure that the first positive electrode sheet includes a positive electrode collector 1, a first safety coating 2 and a second safety coating 3 which are stacked in sequence; the first safety coating 2 includes a groove 5 exposing the positive electrode collector 1, and the first positive electrode sheet also includes a positive electrode ear 4, and the positive electrode ear 4 is located in the groove 5.

[0084] After research, it was found that when the positive electrode tab is located in the groove of the first safety coating, the battery's rate performance can be further improved.

[0085] After research, it was found that setting the second safety coating at least in the area prone to short circuit can improve the energy density and rate performance of the battery while minimizing the adverse effects on needle puncture safety and heavy object impact safety.

[0086] In one example, along the winding direction of the first positive electrode sheet, starting from the winding start end, the orthographic projection area of ​​the second safety coating located in the front half of the first positive electrode sheet on the positive electrode collector accounts for a larger proportion than the orthographic projection area of ​​the second safety coating located in the rear half of the first positive electrode sheet on the positive electrode collector.

[0087] In the present invention, the straight area may include a first straight area and a second straight area located at the outermost side of the winding core, and the bending area may include a first bending area and a second bending area connecting the first straight area and the second straight area. Fig. 9The figure shows a schematic diagram of a winding core in an example of the utility model. It can be seen from the figure that the winding core may include a straight area 7 and a bending area 6. The parts framed by dotted lines in the figure are the first straight area and the second straight area, and the first bending area and the second bending area are connected to the first straight area and the second straight area.

[0088] In one example, the first positive electrode sheet located in the first straight region and / or the second straight region includes the first safety coating and / or the second safety coating.

[0089] In one example, along the direction from the outside of the winding core to the center of the winding core, at least one straight area of ​​the third to sixth turns of the first positive electrode sheet includes the first safety coating and / or the second safety coating.

[0090] In one example, the first positive electrode sheet located in the first bending region and / or the second bending region includes the first safety coating and / or the second safety coating.

[0091] In one example, a side of the first positive electrode sheet close to the center of the winding core includes the first safety coating, and a side of the first positive electrode sheet away from the center of the winding core includes the first safety coating and the second safety coating.

[0092] In one example, a side of the first positive electrode sheet close to the center of the winding core includes the first safety coating and the second safety coating, a side of the first positive electrode sheet away from the center of the winding core includes the first safety coating and the second safety coating, a thickness of the first safety coating close to the winding tail end of the first positive electrode sheet is equal to a thickness of the first safety coating away from the winding tail end of the first positive electrode sheet, and a thickness of the second safety coating close to the winding tail end of the first positive electrode sheet is greater than a thickness of the second safety coating away from the winding tail end of the first positive electrode sheet.

[0093] In one example, a side of the first positive electrode sheet close to the center of the winding core includes the first safety coating and the second safety coating, a side of the first positive electrode sheet away from the center of the winding core includes the first safety coating and the second safety coating, a thickness of the first safety coating close to the winding tail end of the first positive electrode sheet is greater than a thickness of the first safety coating away from the winding tail end of the first positive electrode sheet, and a thickness of the second safety coating close to the winding tail end of the first positive electrode sheet is greater than a thickness of the second safety coating away from the winding tail end of the first positive electrode sheet.

[0094] In one example, the first positive electrode sheet is wound from the head end to the tail end, and in the first direction, the size of the first safety coating layer continuously distributed from the tail end of the first positive electrode sheet accounts for 1%-100% of the size of the positive electrode collector, for example, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%. Fig.10 The figure shows a schematic diagram of the size of the first safety coating layer continuously distributed at the tail end of the first positive electrode sheet in an example of the present invention. It can be seen from the figure that in the first direction, the size of the first safety coating layer 2 continuously distributed from the tail end of the first positive electrode sheet is L1, and the size of the positive electrode current collector 1 is L.

[0095] In one example, in the first direction, the size of the first safety coating layer continuously distributed from the tail end of the first positive electrode sheet accounts for 50%-100% of the size of the positive electrode current collector.

[0096] After research, it was found that when the percentage of the size of the first safety coating continuously distributed from the tail end of the first positive electrode sheet in the first direction to the size of the positive electrode collector is within a specific range, the battery's needle puncture safety and heavy object impact safety can be significantly improved.

[0097] In one example, the thickness of the first safety coating layer near the tail end of the first positive electrode sheet is greater than or equal to the thickness of the first safety coating layer far from the tail end of the first positive electrode sheet. Figure 6 As shown in (a), the thickness of the first safety coating 2 near the tail end of the first positive electrode sheet is equal to the thickness of the first safety coating 2 away from the tail end of the first positive electrode sheet; Figure 6 As shown in (e), the thickness of the first safety coating 2 near the tail end of the first positive electrode sheet is greater than the thickness of the first safety coating 2 away from the tail end of the first positive electrode sheet.

[0098] In one example, in the first direction, the size of the second safety coating layer continuously distributed from the tail end of the first positive electrode sheet may account for 1%-100% of the size of the positive electrode current collector, for example, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%. Fig.11 The figure shows a schematic diagram of the size of the second safety coating layer continuously distributed at the tail end of the first positive electrode sheet in an example of the present invention. It can be seen from the figure that in the first direction, the size of the second safety coating layer 3 continuously distributed from the tail end of the first positive electrode sheet is L2, and the size of the positive electrode current collector 1 is L.

[0099] In one example, in the first direction, the size of the second safety coating layer continuously distributed from the tail end of the first positive electrode sheet accounts for 25%-50% of the size of the positive electrode current collector.

[0100] In one example, the thickness of the second safety coating layer near the tail end of the first positive electrode sheet is greater than or equal to the thickness of the second safety coating layer far from the tail end of the first positive electrode sheet. Figure 5 As shown in (a), the thickness of the second safety coating 3 near the tail end of the first positive electrode sheet is equal to the thickness of the second safety coating 3 away from the tail end of the first positive electrode sheet; Figure 6 As shown in (a), the thickness of the second safety coating 3 near the tail end of the first positive electrode sheet is greater than the thickness of the second safety coating 3 away from the tail end of the first positive electrode sheet.

[0101] After research, it was found that when the size of the second safety coating continuously distributed from the tail end of the first positive electrode sheet in the first direction accounts for a percentage of the positive electrode collector size within a specific range, the battery's needle puncture safety and heavy object impact safety can be significantly improved.

[0102] In one example, in the winding direction, the size of the first straight region is equal to the size of the first safety coating. The size of the first straight region is equal to the size of the second safety coating.

[0103] In one example, in the winding direction, the size of the second straight area is equal to the size of the first safety coating. The size of the second straight area is equal to the size of the second safety coating.

[0104] <Stacked Core>

[0105] In one example, the battery includes a stacked core, and the stacked core includes the first positive electrode sheet.

[0106] In one example, the first positive electrode sheet may include a positive electrode tab extending outward from a surface of one side of the positive electrode current collector. The positive electrode tab is disposed in contact with the first safety coating. Fig.12 The figure shows a top view of the first positive electrode sheet in an example of the utility model. It can be seen from the figure that the first positive electrode sheet includes a positive electrode collector 1, a first safety coating 2 and a second safety coating 3 which are stacked in sequence. The first positive electrode sheet also includes a positive electrode ear 4 extending outward from one side surface of the positive electrode collector 1, and the positive electrode ear 4 is arranged in contact with the first safety coating 2.

[0107] After research, it was found that when the positive electrode tab is placed in contact with the first safety coating, the rate performance of the battery can be further improved.

[0108] In one example, the stacked core includes a plurality of the first positive electrode sheets. Fig.13 The figure shows a schematic structural diagram of a stacked core in an example of the present invention. It can be seen from the figure that the stacked core includes 7 first positive electrode sheets 8 .

[0109] In one example, in the first direction, the ratio of the total size of the first safety coating to the total size of the positive electrode collector can be 1:(1-20), for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20.

[0110] In one example, in the first direction, a ratio of a total size of the first safety coating layer to a total size of the positive electrode current collector is 1:(1-4).

[0111] After research, it was found that when the ratio of the total size of the first safety coating to the total size of the positive electrode collector in the first direction is within a specific range, the battery's needle puncture safety and heavy object impact safety can be significantly improved.

[0112] In one example, in the first direction, the ratio of the total size of the second safety coating to the total size of the positive electrode collector can be 1:(1-20), for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20.

[0113] In one example, in the first direction, a ratio of a total size of the second safety coating layer to a total size of the positive electrode current collector is 1:(2-4).

[0114] After research, it was found that when the ratio of the total size of the second safety coating to the total size of the positive electrode collector in the first direction is within a specific range, the battery's needle puncture safety and heavy object impact safety can be significantly improved.

[0115] In the present invention, in the first direction, the total size of the first safety coating refers to the sum of the sizes of the first safety coating on all the first positive electrode sheets in the stack in the first direction; in the first direction, the total size of the second safety coating refers to the sum of the sizes of the second safety coating on all the first positive electrode sheets in the stack in the first direction; the total size of the positive current collector refers to the sum of the sizes of the positive current collectors of all the first positive electrode sheets in the stack in the first direction.

[0116] In one example, the stacked core includes a plurality of the first positive electrode sheets and a plurality of the second positive electrode sheets. The second positive electrode sheet may include the positive electrode current collector and the active coating located on at least one side of the positive electrode current collector. In the first direction, the ratio of the total size of the first safety coating to the total size of the positive electrode current collector may be 1:(1-20), for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20. In the first direction, the ratio of the total size of the second safety coating to the total size of the positive electrode collector can be 1:(1-20), for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20.

[0117] In one example, in the first direction, a ratio of a total size of the first safety coating layer to a total size of the positive electrode current collector is 1:(1-4).

[0118] In one example, in the first direction, a ratio of a total size of the second safety coating layer to a total size of the positive electrode current collector is 1:(2-4).

[0119] The battery of the utility model can reduce energy density loss, effectively reduce internal resistance, and improve rate performance while ensuring needle puncture safety and heavy object impact safety.

[0120] It should be noted that the numerical expressions such as "first" and "second" in the present invention are only used to distinguish different substances or usage methods, and do not represent the difference in order.

[0121] The present invention will be described in detail below through embodiments. The embodiments described in the present invention are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0122] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0123] The following embodiments are used to illustrate the battery of the present invention.

[0124] Example 1

[0125] Prepare the battery as follows:

[0126] (1) Preparation of the first positive electrode sheet

[0127] Silicon dioxide, lithium polyacrylate and conductive carbon black are mixed evenly in a mass ratio of 55:40:5, added into deionized water, and stirred at high speed to obtain a safety coating slurry. The safety coating slurry is applied to the upper and lower surfaces of the aluminum foil using a gravure roller, and dried to obtain a first safety coating. The safety coating slurry is applied to the surface of the first safety coating, and dried to obtain a second safety coating. Lithium cobalt oxide, polyvinylidene fluoride and conductive carbon black are mixed evenly in a mass ratio of 96:2:2, added into N-methylpyrrolidone (NMP) and mixed evenly to obtain an active coating slurry. The active coating slurry is applied to both sides of the electrode containing the first safety coating and the second safety coating, and dried, rolled, cut and welded to the pole ears to obtain a first positive electrode sheet, wherein the structural schematic diagram of the first positive electrode sheet is shown as follows: Fig.14 As shown, Fig.14 (a) is a cross-sectional view, Fig.14 (b) is a top view, in which the first safety coating is continuously distributed in the first direction, and the second safety coating is continuously distributed in the first direction; the average thickness of the first safety coating is 0.5 μm, the average thickness of the second safety coating is 1 μm, the average thickness of the active coating is 40 μm, the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is 1:2, the ratio of the average thickness of the first safety coating to the average thickness of the active coating is 1:80, and the ratio of the average thickness of the second safety coating to the average thickness of the active coating is 1:40; in the first direction, the ratio of the size of the first safety coating to the size of the positive electrode collector is 1:1, the ratio of the size of the second safety coating to the size of the positive electrode collector is 1:2, the size of the first safety coating continuously distributed from the tail end of the first positive electrode accounts for 100% of the size of the positive electrode collector, and the size of the second safety coating continuously distributed from the tail end of the first positive electrode accounts for 50% of the size of the positive electrode collector; the thickness of the first safety coating near the tail end of the first positive electrode sheet is equal to the thickness of the first safety coating away from the tail end of the first positive electrode sheet, and the thickness of the second safety coating near the tail end of the first positive electrode sheet is equal to the thickness of the second safety coating away from the tail end of the first positive electrode sheet.

[0128] (2) Preparation of negative electrode sheet

[0129] Graphite, conductive carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed uniformly in a mass ratio of 98:1.5:0.5, dispersed in deionized water and stirred uniformly to obtain a negative electrode active slurry, which is coated on both sides of a copper foil, and dried, rolled and cut to obtain a negative electrode sheet.

[0130] (3) Preparation of batteries

[0131] The first positive electrode sheet, the separator (PE film), the negative electrode sheet and the separator (PE film) prepared in step (1) are stacked in sequence, and a core is obtained by winding. The core is placed in a punched aluminum-plastic film, and an electrolyte (a high-voltage electrolyte) is injected into the aluminum-plastic film package. After vacuum sealing, standing, forming, and secondary sealing, a battery is obtained, wherein the proportion of the positive projection area of ​​the second safety coating located in the outer area of ​​the battery on the positive electrode collector is greater than the proportion of the positive projection area of ​​the second safety coating located in the center area of ​​the battery on the positive electrode collector; in the winding direction, the first straight area, the second straight area, the first bending area, and the second bending area include the first safety coating and the second safety coating.

[0132] Example 2

[0133] The method is carried out with reference to Example 1, except that, in step (1), the coating thickness of the first safety coating, the coating area and thickness of the second safety coating, and the coating thickness of the active coating are changed as follows:

[0134] The average thickness of the first safety coating is 0.4μm, the average thickness of the second safety coating is 2μm, and the average thickness of the active coating is 40μm; the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is 1:5, the ratio of the average thickness of the first safety coating to the average thickness of the active coating is 1:100, and the ratio of the average thickness of the second safety coating to the average thickness of the active coating is 1:20; in the first direction, the ratio of the size of the second safety coating to the size of the positive electrode collector is 1:3, and the size of the second safety coating continuously distributed from the tail end of the first positive electrode accounts for 33% of the size of the positive electrode collector.

[0135] Example 3

[0136] The method is carried out with reference to Example 1, except that, in step (1), the coating thickness of the first safety coating, the coating area and thickness of the second safety coating, and the coating thickness of the active coating are changed as follows:

[0137] The average thickness of the first safety coating is 0.2μm, the average thickness of the second safety coating is 0.5μm, and the average thickness of the active coating is 40μm; the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is 1:2.5, the ratio of the average thickness of the first safety coating to the average thickness of the active coating is 1:200, and the ratio of the average thickness of the second safety coating to the average thickness of the active coating is 1:80; in the first direction, the ratio of the size of the second safety coating to the size of the positive electrode collector is 1:4, and the size of the second safety coating continuously distributed from the tail end of the first positive electrode accounts for 25% of the size of the positive electrode collector.

[0138] Example 4 Group

[0139] This group of embodiments is carried out with reference to Embodiment 3, except that, in step (1), the coating thickness of the second safety coating is changed as follows:

[0140] In Example 4a, the average thickness of the second safety coating is 1.4 μm, the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is 1:7, and the ratio of the average thickness of the second safety coating to the average thickness of the active coating is 1:29;

[0141] In Example 4b, the average thickness of the second safety coating is 1.6 μm, the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is 1:8, and the ratio of the average thickness of the second safety coating to the average thickness of the active coating is 1:25;

[0142] In Example 4c, the average thickness of the second safety coating is 2 μm, the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is 1:10, and the ratio of the average thickness of the second safety coating to the average thickness of the active coating is 1:20.

[0143] Example 5 Group

[0144] This group of examples is carried out with reference to Example 2 except that, in step (1), the thickness of the first safety coating is changed as follows:

[0145] Example 5a, the average thickness of the first safety coating is 1 μm, the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is 1:2, and the ratio of the average thickness of the first safety coating to the average thickness of the active coating is 1:40;

[0146] In Example 5b, the average thickness of the first safety coating is 2 μm, the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is 1:1, and the ratio of the average thickness of the first safety coating to the average thickness of the active coating is 1:20.

[0147] Example 6 Group

[0148] This group of examples is carried out with reference to Example 1, except that, in step (1), the thickness of the second safety coating is changed as follows:

[0149] Example 6a, the average thickness of the second safety coating is 3 μm, the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is 1:6, and the ratio of the average thickness of the second safety coating to the average thickness of the active coating is 1:13;

[0150] In Example 6b, the average thickness of the second safety coating is 4 μm, the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is 1:8, and the ratio of the average thickness of the second safety coating to the average thickness of the active coating is 1:10.

[0151] Example 7

[0152] The method is carried out in accordance with Example 1, except that, in step (1), the location of the tab is changed, as shown in FIG. Fig.15 shown.

[0153] Example 8 Group

[0154] This group of examples is carried out with reference to Example 1, except that, in step (1), the coating area of ​​the first safety coating is changed, as follows:

[0155] In Example 8a, in the first direction, the ratio of the size of the first safety coating to the size of the positive electrode current collector is 1:2, and the size of the first safety coating continuously distributed from the tail end of the first positive electrode accounts for 50% of the size of the positive electrode current collector;

[0156] In Example 8b, in the first direction, the ratio of the size of the first safety coating layer to the size of the positive electrode current collector is 1:4, and the size of the first safety coating layer continuously distributed from the tail end of the first positive electrode accounts for 25% of the size of the positive electrode current collector.

[0157] Example 9 Group

[0158] 9a and 9b in this group of embodiments are carried out with reference to embodiment 1, except that, in step (1), the coating area of ​​the second safety coating is changed; 9c in this group of embodiments is carried out with reference to embodiment 9b, except that, in step (3), the size of the battery is adjusted so that the size of the first straight area is larger than the size of the second safety coating in the winding direction, as follows:

[0159] In Example 9a, in the first direction, the ratio of the size of the second safety coating to the size of the positive electrode current collector is 1:5, and the size of the second safety coating continuously distributed from the tail end of the first positive electrode accounts for 20% of the size of the positive electrode current collector;

[0160] In Example 9b, in the first direction, the ratio of the size of the second safety coating to the size of the positive electrode current collector is 1:10, and the size of the second safety coating continuously distributed from the tail end of the first positive electrode accounts for 10% of the size of the positive electrode current collector.

[0161] Example 10 Group

[0162] The method is carried out in accordance with Example 1, except that, in step (1), the first safety coating or the second safety coating is distributed at intervals, as follows:

[0163] Embodiment 10a, the first safety coating is spaced apart in the first direction (such as Figure 7 (c)); In the first direction, the ratio of the size of the first safety coating to the size of the positive electrode current collector is 1:1.5, the size of the first safety coating continuously distributed from the tail end of the first positive electrode accounts for 50% of the size of the positive electrode current collector, and the size between the first safety coatings is 5% of the size of the positive electrode current collector;

[0164] Embodiment 10b, the second safety coating is spaced apart in the first direction (such as Fig.11 ); In the first direction, the ratio of the size of the second safety coating to the size of the positive electrode collector is 1:2, the size of the first safety coating continuously distributed from the tail end of the first positive electrode accounts for 25% of the size of the positive electrode collector, and the size between the second safety coatings is 5% of the size of the positive electrode collector.

[0165] Example 11 Group

[0166] This group of embodiments is carried out with reference to Embodiment 1, except that, in step (1), the shape of the first safety coating and / or the second safety coating on the cross section of the first positive electrode sheet along the thickness direction is changed as follows:

[0167] In Example 11a, the structure of the first positive electrode sheet is as follows Figure 6 (a)

[0168] In Example 11b, the structure of the first positive electrode sheet is as follows Figure 6 (b)

[0169] In Example 11c, the structure of the first positive electrode sheet is as follows Figure 6 (c)

[0170] In Example 11d, the structure of the first positive electrode sheet is as follows Figure 6 (d)

[0171] In embodiment 11e, the structure of the first positive electrode sheet is as follows Figure 6 (e) as shown.

[0172] Example 12

[0173] Prepare the battery as follows:

[0174] (1) Preparation of the first positive electrode sheet

[0175] Silicon dioxide, lithium polyacrylate and conductive carbon black are mixed evenly in a mass ratio of 55:40:5, added into deionized water, and stirred at high speed to obtain a safety coating slurry. The safety coating slurry is applied to the upper and lower surfaces of the aluminum foil using a gravure roller, and dried to obtain a first safety coating. The safety coating slurry is applied to the surface of the first safety coating, and dried to obtain a second safety coating. Lithium cobalt oxide, polyvinylidene fluoride and conductive carbon black are mixed evenly in a mass ratio of 96:2:2, added into N-methylpyrrolidone (NMP) and mixed evenly to obtain an active coating slurry. The active coating slurry is applied to the surface of the first safety coating. The first positive electrode sheet is obtained by drying, rolling, slitting and welding the pole ears on both sides of the pole sheet with the first safety coating and the second safety coating. The first safety coating is continuously distributed in the first direction, and the second safety coating is continuously distributed in the first direction; the average thickness of the first safety coating is 0.5μm, the average thickness of the second safety coating is 1μm, the average thickness of the active coating is 40μm, the ratio of the average thickness of the first safety coating to the average thickness of the second safety coating is 1:2, the ratio of the average thickness of the first safety coating to the average thickness of the active coating is 1:80, and the ratio of the average thickness of the second safety coating to the average thickness of the active coating is 1:40.

[0176] (2) Preparation of the second positive electrode sheet

[0177] Lithium cobalt oxide, polyvinylidene fluoride and conductive carbon black are mixed evenly in a mass ratio of 96:2:2, added into N-methylpyrrolidone (NMP) and mixed evenly to obtain an active coating slurry, and the active coating slurry is coated on the surface of aluminum foil, and a second positive electrode sheet is obtained after drying, rolling and slitting.

[0178] (3) Preparation of negative electrode sheet

[0179] Graphite, conductive carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed uniformly in a mass ratio of 98:1.5:0.5, dispersed in deionized water and stirred uniformly to obtain a negative electrode active slurry, which is coated on both sides of a copper foil, and dried, rolled and cut to obtain a negative electrode sheet.

[0180] (4) Preparation of batteries

[0181] The first positive electrode sheet and the second positive electrode sheet prepared in step (1) and step (2), the separator (PE film) and the negative electrode sheet prepared in step (3) are stacked in the order of the positive electrode sheet, the separator, the negative electrode sheet and the positive electrode sheet to obtain a stacked core, the stacked core is placed in a punched aluminum-plastic film, an electrolyte (a high-voltage electrolyte) is injected into the aluminum-plastic film package, and a battery is obtained after vacuum sealing, standing, forming, and secondary sealing. The proportion of the orthographic projection area of ​​the second safety coating located in the outer area of ​​the battery on the positive electrode collector is greater than the proportion of the orthographic projection area of ​​the second safety coating located in the center area of ​​the battery on the positive electrode collector; in the first direction, the ratio of the total size of the first safety coating to the total size of the positive electrode collector is 1:1, and the ratio of the total size of the second safety coating to the total size of the positive electrode collector is 1:2.

[0182] Embodiment 13

[0183] The method is carried out in accordance with Example 12, except that in step (4), the ratio of the total size of the second safety coating layer to the total size of the positive electrode collector in the first direction is controlled to be 1:3 by adjusting the number of the first positive electrode sheet and the second positive electrode sheet in the battery.

[0184] Embodiment 14

[0185] The method is carried out in accordance with Example 12, except that in step (4), the ratio of the total size of the second safety coating layer to the total size of the positive electrode collector in the first direction is controlled to be 1:4 by adjusting the number of the first positive electrode sheet and the second positive electrode sheet in the battery.

[0186] Comparative Example 1

[0187] The process is carried out in accordance with Example 1, except that, in step (1), the positive electrode sheet does not include the first safety coating and the second safety coating.

[0188] Comparative Example 2

[0189] The same procedure is carried out as in Example 1, except that in step (1), the positive electrode sheet does not include the second safety coating.

[0190] Comparative Example 3

[0191] The method is carried out in accordance with Example 1, except that, in step (1), the coating area of ​​the second safety coating is changed, specifically as follows: the ratio of the size of the second safety coating to the size of the positive electrode current collector is 1:1.

[0192] Comparative Example 4

[0193] The same is carried out as in Example 12, except that all the positive electrode sheets are second positive electrode sheets.

[0194] Comparative Example 5

[0195] The process is carried out in accordance with Example 12, except that in step (1), the first positive electrode sheet does not include the second safety coating, and in step (4), all the positive electrode sheets are the first positive electrode sheets.

[0196] Comparative Example 6

[0197] The process is carried out in accordance with Example 12, except that all the positive electrode sheets in step (4) are first positive electrode sheets.

[0198] Test Case

[0199] (1) Acupuncture safety

[0200] The batteries prepared in the examples and comparative examples were subjected to a needle puncture safety test. The specific test method is as follows: the battery is charged (upper limit voltage 4.5V) to 100% SOC, and a tungsten steel needle with a diameter of 2.5mm, a length of 100mm, and a needle tip cone angle of 45° is used to pierce the geometric center of the battery at a speed of 150mm / s and penetrate out. The test is maintained for 10 minutes. If the battery does not smoke, catch fire, or explode, it is considered to have passed. Ten batteries are tested in each group, and the results are recorded in Table 1.

[0201] (2) Safety against heavy object impact

[0202] The batteries prepared in the examples and comparative examples were subjected to a heavy object impact safety test. The specific test method is as follows: the battery is charged (upper limit voltage 4.5V) to 100% SOC, placed on a flat surface, a crossbar with a diameter of 15.8mm is placed in the middle of the battery, and a 9.1kg weight is used to perform free fall motion to impact the battery at a height of 610mm. If the battery does not smoke, catch fire or explode, it is considered to have passed the test. Ten batteries are tested in each group, and the results are recorded in Table 1.

[0203] (3) Constant current and constant voltage charging

[0204] The batteries prepared in the embodiment and the comparative example were subjected to constant current and constant voltage charging test. The specific testing method is as follows: a battery with a capacity of 5Ah is fully charged at 1C at room temperature, the charging cut-off voltage is 4.5V, and the charging cut-off current is 0.02C; the constant current charging ratio is the ratio of the capacity of the battery in the constant current charging stage to the total capacity of the battery, and the results are recorded in Table 1.

[0205] (4) Energy density test

[0206] The batteries prepared in the examples and comparative examples were subjected to energy density tests. The specific test method is as follows: the battery is charged and discharged to obtain the energy of the battery, and then the volume of the battery is tested to calculate the energy density (Wh / L) of the battery, and the energy density loss is recorded in Table 1.

[0207] Table 1

[0208]

[0209]

[0210] It can be seen from Table 1 that, compared with the comparative example, the battery of the utility model can reduce energy density loss and improve rate performance while ensuring needle puncture safety and heavy object impact safety.

[0211] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including combining various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A battery, characterized in that: The battery comprises a first positive electrode sheet, the first positive electrode sheet comprises a positive electrode current collector, at least a portion of a first surface of the positive electrode current collector is provided with a first safety coating, at least a portion of a surface of the first safety coating away from the positive electrode current collector is provided with a second safety coating, and an active coating is further provided on an outer surface of the first positive electrode sheet; In a first direction, the size of the first safety coating is greater than or equal to the size of the second safety coating; The ratio of the average thickness of the first safety coating layer to the average thickness of the second safety coating layer is 1:(1-10).

2. The battery according to claim 1, characterized in that In the first positive electrode sheet, at least a portion of the second surface of the positive electrode current collector is provided with the first safety coating; Alternatively, in the first positive electrode sheet, at least a portion of the second surface of the positive current collector is provided with the first safety coating, and at least a portion of the surface of the first safety coating away from the positive current collector is provided with the second safety coating.

3. The battery according to claim 1 or 2, characterized in that: The shape of the first safety coating on the cross section of the first positive electrode sheet along the thickness direction includes at least one of a rectangle and a triangle; And / or, the shape of the second safety coating layer in the cross section of the first positive electrode sheet along the thickness direction includes at least one of a rectangle and a triangle.

4. The battery according to claim 1 or 2, characterized in that: The ratio of the average thickness of the first safety coating to the average thickness of the active coating is 1:(4-500); And / or, the ratio of the average thickness of the second safety coating to the average thickness of the active coating is 1:(4-500).

5. The battery according to claim 1 or 2, characterized in that: The first safety coatings are distributed at intervals in the first direction; And / or, the second safety coating layers are distributed at intervals in the first direction.

6. The battery according to claim 1 or 2, characterized in that: In the first direction, the ratio of the size of the first safety coating layer to the size of the positive electrode current collector is 1:(1-20); And / or, in the first direction, the ratio of the size of the second safety coating layer to the size of the positive electrode current collector is 1:(1-20).

7. The battery according to claim 1 or 2, characterized in that: The battery further includes a first negative electrode sheet and a separator. The first positive electrode sheet, the separator and the first negative electrode sheet are stacked and wound to form a winding core. The winding core includes a straight area and a bending area.

8. The battery according to claim 7, characterized in that Along the winding direction of the first positive electrode sheet, starting from the winding start end, the proportion of the orthographic projection area of ​​the second safety coating located in the front half of the first positive electrode sheet on the positive electrode collector is greater than the proportion of the orthographic projection area of ​​the second safety coating located in the rear half of the first positive electrode sheet on the positive electrode collector.

9. The battery according to claim 7, characterized in that The straight area includes a first straight area and a second straight area located at the outermost side of the winding core, the bending area includes a first bending area and a second bending area connecting the first straight area and the second straight area, and the first positive electrode sheet located in the first straight area and / or the second straight area includes the first safety coating and / or the second safety coating; And / or, along the direction from the outside of the winding core to the center of the winding core, at least one straight area of ​​the third to sixth turns of the first positive electrode sheet includes the first safety coating and / or the second safety coating.

10. The battery according to claim 9, characterized in that The first positive electrode sheet located in the first bending zone and / or the second bending zone includes the first safety coating and / or the second safety coating.

11. The battery according to claim 7, characterized in that The first positive electrode sheet includes the first safety coating on one side close to the center of the winding core, and the first positive electrode sheet includes the first safety coating and the second safety coating on one side away from the center of the winding core; And / or, a side of the first positive electrode sheet close to the center of the winding core includes the first safety coating and the second safety coating, a side of the first positive electrode sheet away from the center of the winding core includes the first safety coating and the second safety coating, a thickness of the first safety coating close to the winding tail end of the first positive electrode sheet is equal to a thickness of the first safety coating away from the winding tail end of the first positive electrode sheet, and a thickness of the second safety coating close to the winding tail end of the first positive electrode sheet is greater than a thickness of the second safety coating away from the winding tail end of the first positive electrode sheet; And / or, the side of the first positive electrode sheet close to the center of the winding core includes the first safety coating and the second safety coating, the side of the first positive electrode sheet away from the center of the winding core includes the first safety coating and the second safety coating, the thickness of the first safety coating close to the winding tail end of the first positive electrode sheet is greater than the thickness of the first safety coating away from the winding tail end of the first positive electrode sheet, and the thickness of the second safety coating close to the winding tail end of the first positive electrode sheet is greater than the thickness of the second safety coating away from the winding tail end of the first positive electrode sheet.

12. The battery according to claim 7, characterized in that The thickness of the first safety coating layer close to the winding tail end of the first positive electrode sheet is greater than or equal to the thickness of the first safety coating layer far from the winding tail end of the first positive electrode sheet; And / or, the thickness of the second safety coating layer close to the winding tail end of the first positive electrode sheet is greater than or equal to the thickness of the second safety coating layer away from the winding tail end of the first positive electrode sheet.

13. The battery according to claim 1 or 2, characterized in that: The battery comprises a stacked core, the stacked core comprises a plurality of the first positive electrode sheets, and in the first direction, a ratio of a total size of the first safety coating layer to a total size of the positive electrode current collector is 1:(1-20); And / or, in the first direction, the ratio of the total size of the second safety coating layer to the total size of the positive electrode current collector is 1:(1-20).

14. The battery according to claim 1 or 2, characterized in that: The battery comprises a stacked core, the stacked core comprises a plurality of the first positive electrode sheets and a plurality of the second positive electrode sheets, the second positive electrode sheets comprise the positive electrode current collector and the active coating located on at least one side of the surface of the positive electrode current collector; in a first direction, a ratio of a total size of the first safety coating to a total size of the positive electrode current collector is 1:(1-20); And / or, in the first direction, the ratio of the total size of the second safety coating layer to the total size of the positive electrode current collector is 1:(1-20).

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