battery

Abstract

The application belongs to the technical field of batteries, and discloses a battery, which comprises a shell, an explosion-proof valve and an electrode assembly. The explosion-proof valve is installed on the shell wall of the shell, and the electrode assembly is arranged in the shell. The electrode assembly comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector, a first active layer, a second active layer and a third active layer, the first active layer is arranged on at least one side surface of the positive electrode current collector along the thickness direction, the second active layer is arranged on the side of the first active layer away from the positive electrode current collector, and the third active layer is arranged on at least one side of the positive electrode current collector along the thickness direction. The positive projection of the third active layer along the first direction at least partially overlaps the positive projection of the explosion-proof valve along the first direction, the thermal decomposition temperature of the third active layer is lower than the thermal decomposition temperature of the first active layer, and the thermal decomposition temperature of the third active layer is lower than the thermal decomposition temperature of the second active layer. The first direction is the thickness direction of the shell wall on which the explosion-proof valve is arranged. The battery provided by the application has high safety and reliability.

Description

Technical Field

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

[0002] Ternary materials stand out among battery electrode materials due to their excellent fast-charging performance and low-temperature performance.

[0003] To improve battery capacity, related technologies typically employ a double-layer coating structure for battery electrodes. For example, the first active material coating near the current collector aluminum foil is made of ternary lithium, while the second active material coating further away is made of lithium iron phosphate. This improves battery cycle performance and energy density. However, ternary lithium materials have high reactivity and poor thermal stability. When the battery is heated, the internal pressure increases, posing a risk that the explosion-proof valve may fail to open in time, leading to a sudden increase in internal pressure and potentially causing a valve explosion. In severe cases, this could even cause the battery casing to burst open, posing a significant safety hazard. Summary of the Invention

[0004] This application provides a battery to address the technical problem of low battery safety.

[0005] Based on the above concept, the technical solution adopted in this application is: The battery includes: case; An explosion-proof valve, wherein the explosion-proof valve is installed on the shell wall of the housing; An electrode assembly is disposed within the housing. The electrode assembly includes a positive electrode sheet, which comprises a positive current collector, a first active layer, a second active layer, and a third active layer. The first active layer is disposed on at least one side surface of the positive current collector along its thickness direction. The second active layer is disposed on the side of the first active layer opposite to the positive current collector. The third active layer is disposed on at least one side of the positive current collector along its thickness direction. The orthographic projection of the third active layer along a first direction at least partially overlaps with the orthographic projection of the explosion-proof valve along the first direction. Furthermore, the thermal decomposition temperature of the third active layer is less than the thermal decomposition temperature of the first active layer, and the thermal decomposition temperature of the third active layer is less than the thermal decomposition temperature of the second active layer. The first direction is the thickness direction of the housing wall where the explosion-proof valve is disposed.

[0006] In one or more embodiments of this application, the third active layer is disposed on the side of the first active layer away from the positive current collector, and is disposed in the same layer as the second active layer; Alternatively, the third active layer is connected to the surface of the positive current collector facing the positive current collector in the thickness direction, and the surface of the third active layer facing away from the positive current collector in the thickness direction is coplanar with the surface of the second active layer facing away from the positive current collector.

[0007] In one or more embodiments of this application, the third active layer extends from one end toward the explosion-proof valve to the edge of the positive current collector near the explosion-proof valve; Alternatively, there may be a gap between the end of the third active layer facing the explosion-proof valve and the edge of the positive current collector near the explosion-proof valve.

[0008] In one or more embodiments of this application, in a second direction, the second active layer is disposed further away from the explosion-proof valve than the third active layer, and the second direction is perpendicular to the first direction and perpendicular to the thickness direction of the positive current collector.

[0009] In one or more embodiments of this application, the width of the third active layer is c1, and the dimension of the explosion-proof valve in the width direction of the third active layer is c2, satisfying the relationship: c2≤c1≤1.7c2; And / or, the width of the third active layer is in the range of 20mm-50mm.

[0010] In one or more embodiments of this application, the thermal decomposition temperature satisfies at least one of the following characteristics (1) to (6): (1) 40℃≤ thermal decomposition temperature of the second active layer - thermal decomposition temperature of the third active layer≤170℃; (2) 40℃≤ thermal decomposition temperature of the first active layer - thermal decomposition temperature of the third active layer≤90℃; (3) The thermal decomposition temperature of the second active layer is greater than that of the first active layer; (4) The thermal decomposition temperature of the third active layer is 180℃-230℃; (5) The thermal decomposition temperature of the second active layer is 270℃-350℃; (6) The thermal decomposition temperature of the first active layer is 220℃-270℃.

[0011] In one or more embodiments of this application, the material of the first active layer includes LiNi. x1 Co y1 Mn z1 O2, where 0.4 ≤ x1 < 0.75, y1 > 0, z1 > 0; and / or, The material of the second active layer includes lithium iron phosphate; and / or, The material of the third active layer includes lithium nickel cobalt manganese oxide, and the material of the third active layer includes LiNi x2 Co y2 Mn z2 O2, where x2≥0.75, y2>0, z2>0.

[0012] In one or more embodiments of this application, the positive electrode sheet further includes a positive electrode tab, which is connected to at least one side of the positive current collector in the width direction; The positive electrode further includes a fourth active layer, which is disposed on the side of the first active layer away from the positive current collector and is disposed in the same layer as the second active layer. The fourth active layer is closer to the positive electrode tab than the second active layer, and the resistivity of the fourth active layer is greater than that of the second active layer. Optionally, the resistivity of the fourth active layer minus the resistivity of the second active layer is ≥50 Ω·m; Preferably, the resistivity of the fourth active layer is 50 Ω·m-200 Ω·m; Preferably, the resistivity of the second active layer is <0.3Ωm.

[0013] In one or more embodiments of this application, the material of the fourth active layer includes LiNi. x3 Co y3 Mn z3 O2, where 0 < x3 < 0.4, y3 > 0, z3 > 0.

[0014] In one or more embodiments of this application, the positive electrode tab is located on the side of the electrode assembly closer to the explosion-proof valve.

[0015] The beneficial effects of this application include at least the following: At least one side of the positive electrode current collector in the thickness direction not only has a first active layer and a second active layer, but also a third active layer. The thermal decomposition temperature of the third active layer is lower than that of the first active layer and also lower than that of the second active layer. The orthographic projection of the third active layer along the first direction overlaps with at least a portion of the orthographic projection of the explosion-proof valve along the first direction, so that the third active layer and at least a portion of the explosion-proof valve are arranged opposite each other in the first direction. As a result, when the battery temperature rises abnormally, the third active layer undergoes thermal decomposition first, and the gas generated by thermal decomposition can quickly reach the explosion-proof valve. In some cases, it can directly rush towards the explosion-proof valve, allowing the explosion-proof valve to be quickly ruptured. This achieves a rapid response to battery thermal runaway, allowing the gas inside the battery to be released to the outside through the explosion-proof valve, preventing the temperature and pressure inside the battery from rising further. This reduces the risk of instantaneous valve rupture due to a sudden increase in internal battery pressure, thereby reducing the risk of the casing wall with the explosion-proof valve being blown open and also reducing the risk of explosion, improving the safety and reliability of the battery. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the content of the embodiments of this application and these drawings without creative effort.

[0017] Figure 1 This is a cross-sectional view of a battery provided in an embodiment of this application; Figure 2 This is a side view of the positive electrode sheet provided in an embodiment of this application; Figure 3 This is a schematic diagram of a battery structure provided in one embodiment of this application; Figure 4 This is a schematic diagram of the structure of one type of battery provided in an embodiment of this application; Figure 5 This is a cross-sectional view of a positive electrode sheet provided in an embodiment of this application; Figure 6 This is a cross-sectional view of another positive electrode sheet provided in one embodiment of this application; Figure 7 This is a top view of a positive electrode sheet provided in an embodiment of this application; Figure 8 This is a schematic diagram of the structure of another battery provided in one embodiment of this application; Figure 9 This is a schematic diagram of the structure of another battery provided in an embodiment of this application; Figure 10This is a schematic diagram of the structure of another battery provided in one embodiment of this application.

[0018] Explanation of reference numerals in the attached figures: 1. Shell; 11. Shell body; 12. Top cover; 2. Explosion-proof valve; 3. Electrode assembly; 31. Positive electrode plate; 311. Positive current collector; 312. First active layer; 313. Second active layer; 314. Third active layer; 315. Positive electrode tab; 316. Fourth active layer. Detailed Implementation

[0019] To make the technical problems solved by this application, the technical solutions adopted, and the technical effects achieved clearer, the technical solutions of this application will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely for explaining this application and not for limiting it. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not all of them.

[0020] It should be understood that the phrase "an embodiment" or "one embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "in one embodiment" or "in one embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] In the description of this application, unless otherwise expressly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0023] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature. In the description of this embodiment, unless otherwise specified, "multiple" specifically refers to two or more.

[0024] In the description of this embodiment, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of description and simplification of operation. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. In addition, the terms "first" and "second" are only used for distinction in description and have no special meaning.

[0025] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly on the other component or it can be located in between the component.

[0026] The technical solution of this application will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] The electrode assembly is formed by stacking and winding a positive electrode, a separator, and a negative electrode. The positive electrode typically employs a double-coated structure. Specifically, the positive electrode includes a current collector aluminum foil and an active material coating. The current collector aluminum foil has active material coatings on both sides along its thickness direction, and each side of the current collector aluminum foil has two active material coatings. The first active material coating is a ternary material, and the second active material coating, located away from the current collector aluminum foil, is lithium iron phosphate. While the double-coating structure can improve the battery's cycle life, it presents a problem where excessive internal pressure can cause the battery's top cover to open. Specifically, during thermal runaway, the separator shrinks due to heat, and the lithium iron phosphate coating, located away from the current collector, preferentially contacts the negative electrode of the electrode assembly, leading to a short circuit. After the short circuit, side reactions occur inside the battery, but the gas produced is insufficient to immediately open the explosion-proof valve. However, side reactions will gradually consume the lithium iron phosphate in the positive electrode. When the consumption of lithium iron phosphate reaches a certain level, the ternary material coating near the current collector aluminum foil will come into contact with the negative electrode, causing a continuous short circuit. Due to the high reactivity of ternary materials, the internal pressure of the battery will increase sharply, causing the battery's explosion-proof valve to open and the battery's top cover to be lifted. In severe cases, it can even cause the electrode components inside the battery to be ejected, resulting in an explosion and affecting the battery's safety.

[0028] Based on the above problems, this embodiment provides a battery that reduces the risk of the battery casing wall being opened by the explosion-proof valve 2, and can have high safety and reliability.

[0029] For example, such as Figures 1 to 10 As shown, the battery includes a housing 1, an explosion-proof valve 2, and an electrode assembly 3. The housing 1 has a receiving cavity (not shown) for housing the electrode assembly 3. The explosion-proof valve 2 is installed on the wall of the housing 1. When the pressure inside the housing 1 exceeds a preset value, the explosion-proof valve 2 is opened, thereby quickly releasing the pressure inside the battery.

[0030] In this embodiment, as Figure 1 As shown, the electrode assembly 3 is disposed within the housing 1; specifically, the electrode assembly 3 is located within the receiving cavity. Furthermore, the electrode assembly 3 includes a positive electrode plate 31, such as... Figure 2 As shown, the positive electrode 31 includes a positive current collector 311, a first active layer 312, a second active layer 313, and a third active layer 314. The first active layer 312 is disposed on at least one surface of the positive current collector 311 along its thickness direction; that is, the first active layer 312 may be disposed on one side of the positive current collector 311 along its thickness direction, or it may be disposed on both sides of the positive current collector 311 along its thickness direction. In this embodiment... Figure 2 This is a schematic diagram of the first active layer 312 disposed on one side surface of the positive electrode current collector 311 along the thickness direction.

[0031] Please continue reading Figure 2 The second active layer 313 is disposed on the side of the first active layer 312 away from the positive current collector 311, that is, the second active layer 313 and the first active layer 312 are stacked.

[0032] In this embodiment, as Figure 3 As shown, the third active layer 314 is disposed on at least one side of the positive electrode current collector 311 along the thickness direction. The orthographic projection of the third active layer 314 along the first direction X overlaps with at least a portion of the orthographic projection of the explosion-proof valve 2 along the first direction X, such that the third active layer 314 and at least a portion of the explosion-proof valve 2 are disposed opposite each other. Furthermore, the thermal decomposition temperature of the third active layer 314 is less than (less than) the thermal decomposition temperature of the first active layer 312, and the thermal decomposition temperature of the third active layer 314 is less than (less than) the thermal decomposition temperature of the second active layer 313. With this configuration, the third active layer 314 undergoes thermal decomposition before the first active layer 312 and the second active layer 313 after being heated, resulting in the generation of a large amount of gas after the thermal decomposition of the third active layer 314. Since the orthographic projection of the third active layer 314 along the first direction X overlaps with at least a portion of the explosion-proof valve 2, the gas generated by the third active layer 314 can move towards the explosion-proof valve 2, allowing the explosion-proof valve 2 to open quickly and achieve pressure relief.

[0033] It should be noted that the first active layer 312, the second active layer 313, and the third active layer 314 all include active materials. The thermal decomposition temperature of the first active layer 312 refers to the thermal decomposition temperature of the active material in the first active layer 312; the thermal decomposition temperature of the second active layer 313 refers to the thermal decomposition temperature of the active material in the second active layer 313; and the thermal decomposition temperature of the third active layer 314 refers to the thermal decomposition temperature of the active material in the third active layer 314. The thermal decomposition temperature of a substance generally refers to the temperature range or starting temperature at which the chemical structure of the substance begins to undergo irreversible decomposition when heated, generating simpler substances (usually gases and small-molecule solids).

[0034] It should also be noted that the first direction X is the thickness direction of the shell wall of the explosion-proof valve 2, that is, the direction perpendicular to the shell wall of the explosion-proof valve 2. The explosion-proof valve 2 and the third active layer 314 can be arranged opposite each other in the first direction X, so that the gas generated by the third active layer 314 can quickly break through the explosion-proof valve 2. Optionally, the first direction X can be the length direction of the positive electrode 31, or it can be the width direction of the positive electrode 31; this embodiment does not limit this.

[0035] It is understandable that the electrode assembly also includes structures such as the negative electrode plate and the separator, with the separator located between the positive electrode plate 31 and the negative electrode plate.

[0036] The battery provided in this embodiment has a first active layer 312 and a second active layer 313 on at least one side of the positive electrode current collector 311 in the thickness direction, as well as a third active layer 314. The thermal decomposition temperature of the third active layer 314 is lower than that of the first active layer 312 and lower than that of the second active layer 313. The orthographic projection of the third active layer 314 along the first direction X overlaps with at least a portion of the orthographic projection of the explosion-proof valve 2 along the first direction X, so that the third active layer 314 and at least a portion of the explosion-proof valve 2 are arranged opposite each other in the first direction X. As a result, when the battery temperature rises abnormally, the third active layer 314 undergoes thermal decomposition first, and the gas generated by thermal decomposition can quickly reach the explosion-proof valve 2. In some cases, it can directly rush towards the explosion-proof valve 2, so that the explosion-proof valve 2 can be quickly ruptured. This achieves a rapid response to battery thermal runaway, allowing the gas inside the battery to be released to the outside through the explosion-proof valve 2, preventing the temperature and pressure inside the battery from rising further, thereby reducing the risk of instantaneous valve blowout due to a sudden increase in internal battery pressure, and improving the safety and reliability of the battery.

[0037] Furthermore, by setting a third active layer 314, when the battery experiences thermal runaway and the pressure inside the battery reaches the valve opening pressure, the explosion-proof valve 2 can open before the first active layer 312 contacts and short-circuits with the negative electrode of the electrode assembly 3, so that the pressure inside the battery will not increase sharply, thereby reducing the risk of the shell wall of the casing 1 being directly blown open, and also reducing the risk of the electrode assembly 3 being ejected and exploding, ensuring that the battery has a high level of safety.

[0038] In one or more embodiments of this application, such as Figure 5 As shown, the third active layer 314 is disposed on the side of the first active layer 312 away from the positive current collector 311, and is disposed in the same layer as the second active layer 313. With this arrangement, the third active layer 314 can make full use of the space of the second active layer 313, and the thickness of the positive electrode 31 will not increase excessively due to the placement of the third active layer 314, which is beneficial to the thinning of the positive electrode 31.

[0039] In some embodiments, the fact that the third active layer 314 and the second active layer 313 are disposed in the same layer can be understood as the second active layer 313 being provided with a groove structure, and the third active layer 314 being embedded in the groove structure.

[0040] It should be noted that when the third active layer 314 and the second active layer 313 are disposed in the same layer, the thickness of the third active layer 314 can be the same as the thickness of the second active layer 313. The surface of the third active layer 314 facing away from the positive electrode current collector 311 is coplanar with the surface of the second active layer 313 facing away from the positive electrode current collector 311, so as to ensure the flatness of the active coating.

[0041] In other embodiments of this application, such as Figure 6As shown, the third active layer 314 can also be directly disposed on the positive current collector 311. For example, the surface of the third active layer 314 facing the positive current collector 311 in the thickness direction is connected to the positive current collector 311, and the surface of the third active layer 314 away from the positive current collector 311 in the thickness direction is coplanar with the surface of the second active layer 313 away from the positive current collector 311. In this case, the thickness of the third active layer 314 is the sum of the thicknesses of the first active layer 312 and the second active layer 313. With this configuration, the third active layer 314 is equivalent to being embedded in the first active layer 312 and the second active layer 313, which improves the fixing strength of the third active layer 314. Furthermore, the third active layer 314 has a larger thickness and volume. After thermal runaway of the battery, the third active layer 314 can quickly generate a large amount of gas, allowing the explosion-proof valve 2 to respond and open more quickly, further improving the safety of the battery.

[0042] In some alternative embodiments, the third active layer 314 may also be disposed in the same layer as the first active layer 312 and connected to the surface of the second active layer 313 facing the positive current collector 311, that is, the third active layer 314 is embedded in the first active layer 312.

[0043] The specific location of the third active layer 314 can be flexibly selected according to requirements, and this embodiment does not limit it.

[0044] In some embodiments, such as Figure 4 As shown, the third active layer 314 extends from one end toward the explosion-proof valve 2 to the edge of the positive current collector 311 near the explosion-proof valve 2. This arrangement ensures that, in the first direction X, the second active layer 313 does not have a portion located between the third active layer 314 and the explosion-proof valve 2, thereby preventing the second active layer 313 from affecting the flow of gas generated by the third active layer 314 toward the explosion-proof valve 2.

[0045] In other embodiments, such as Figure 3 As shown, there is a gap between the end of the third active layer 314 facing the explosion-proof valve 2 and the edge of the positive current collector 311 near the explosion-proof valve 2, which is not limited here.

[0046] In one embodiment of this application, such as Figure 3 , Figure 4 and Figure 8As shown, the third active layer 314 and the explosion-proof valve 2 are centered in the first direction X. This centered alignment of the third active layer 314 and the explosion-proof valve 2 in the first direction X can be understood as the line connecting the center of the third active layer 314 and the center of the explosion-proof valve 2 extending along the first direction X. This arrangement allows the third active layer 314 and the explosion-proof valve 2 to have a large facing area, enabling the gas generated by the thermal decomposition of the third active layer 314 during battery thermal runaway to move along the first direction X and accumulate at the explosion-proof valve 2. This allows the gas to more quickly break through the explosion-proof valve 2, achieving battery depressurization.

[0047] It is understandable that the third active layer 314 and the explosion-proof valve 2 can be eccentrically arranged in the first direction X, but this embodiment does not limit this.

[0048] In some optional embodiments, the width of the third active layer 314 is c1, and the dimension of the explosion-proof valve 2 in the width direction of the third active layer 314 is c2, satisfying the relationship: c2≤c1≤1.7c2. The width direction of the third active layer 314 is perpendicular to the first direction X. In some embodiments, the width direction of the third active layer 314 is a second direction Y, which is perpendicular to the first direction X. Based on the alignment of the third active layer 314 and the explosion-proof valve 2 in the first direction X, when the width of the third active layer 314 and the dimension of the explosion-proof valve 2 in the width direction of the third active layer 314 satisfy the relationship, the gas generated by the thermal decomposition of the third active layer 314 can effectively and promptly open the explosion-proof valve 2, achieving rapid pressure relief and further improving the safety and reliability of the battery. In this embodiment, Figure 3 , Figure 4 , Figure 9 and Figure 10 All of these are examples where c2=c1. Figure 8 This is an embodiment where c1 > c2. It should be noted that the width of the third active layer 314 is less than the length of the third active layer 314 but greater than the thickness of the third active layer 314.

[0049] Optionally, c1 can satisfy multiple value ranges such as c2≤c1≤1.4c2, 1.1c2≤c1≤1.4c2, 1.2c2≤c1≤1.7c2, etc. For example, c1=c2, c1=1.1c2, c1=1.2c2, c1=1.3c2, c1=1.4c2, c1=1.5c2, c1=1.7c2, etc., but this embodiment does not limit this.

[0050] In some optional embodiments, the width c1 of the third active layer 314 can be in the range of 20mm-50mm. Exemplarily, the width c1 of the third active layer 314 can be any value or a range between any two values, such as 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, etc., and this embodiment does not limit this.

[0051] In one or more embodiments of this application, such as Figure 4 As shown, the housing 1 may include a housing body 11 and a top cover 12, wherein the housing body 11 has an opening and the top cover 12 is connected to the opening of the housing body 11 to form a relatively sealed receiving cavity for accommodating the electrode assembly 3.

[0052] In some embodiments, such as Figure 3 and Figure 4 As shown, the explosion-proof valve 2 can be installed on the top cover 12. With this configuration, in the event of thermal runaway of the battery and the contraction of the separator of the electrode assembly 3, the generated gas can be discharged directly and unimpeded from the gaps in the electrode assembly 3, quickly reaching the explosion-proof valve 2. At this time, the installation of the third active layer 314 prevents a sharp increase in the internal pressure of the battery, thereby reducing the risk of the top cover 12 with the explosion-proof valve 2 being directly opened and improving battery safety.

[0053] In other alternative embodiments, such as Figure 10 As shown, the explosion-proof valve 2 can be installed on one of the side walls of the shell body 11. The specific location can be flexibly selected according to the requirements, and this embodiment does not limit it.

[0054] In some optional embodiments, there may be one or more explosion-proof valves 2. When there are multiple explosion-proof valves 2, there may be one or more third active layers 314, as long as the orthographic projection of the third active layer 314 along the first direction X overlaps with at least a portion of the orthographic projection of the explosion-proof valve 2 along the first direction X. This embodiment does not limit this.

[0055] In some optional embodiments, the thermal decomposition temperature in this embodiment satisfies at least one of the following characteristics (1) to (6): (1) 40℃≤ thermal decomposition temperature of the second active layer 313 - thermal decomposition temperature of the third active layer 314≤170℃.

[0056] Specifically, the thermal decomposition temperature difference between the second active layer 313 and the third active layer 314 is calculated by subtracting the thermal decomposition temperature of the third active layer 314 from the thermal decomposition temperature of the second active layer 313. The difference between these two temperatures should be between 40℃ and 170℃. This ensures that the third active layer 314 can undergo thermal decomposition before the second active layer 313, while maintaining the conductivity of both layers. However, the difference should not be too small. If it is too small, it indicates that the thermal decomposition temperatures of the second and third active layers are similar, posing a risk that the gas generated by the third active layer 314 may not break through the explosion-proof valve in time before the second active layer 313 has already undergone thermal decomposition, resulting in lower safety. The difference between the thermal decomposition temperature of the second active layer 313 and the thermal decomposition temperature of the third active layer 314 should not be too large. If it is too large, it means that the decomposition temperature of the third active layer 314 is too low, which will cause the third active layer 314 to decompose prematurely and affect the safety of the battery.

[0057] Optionally, the difference between the thermal decomposition temperature of the second active layer 313 and the thermal decomposition temperature of the third active layer 314 can be any value or a range between any two values, such as 40℃, 60℃, 80℃, 100℃, 110℃, 130℃, 150℃, 160℃, 170℃, etc. This embodiment does not limit this.

[0058] (2) 40℃≤ thermal decomposition temperature of the first active layer 312 - thermal decomposition temperature of the third active layer 314≤90℃.

[0059] Specifically, the thermal decomposition temperature difference between the first active layer 312 and the third active layer 314 is calculated by subtracting the thermal decomposition temperature of the third active layer 314 from the thermal decomposition temperature of the first active layer 312. The difference between these two temperatures should be between 40℃ and 90℃. This ensures that the third active layer 314 can undergo thermal decomposition before the first active layer 312, while maintaining the conductivity of both layers. However, the difference should not be too small. If it is too small, it indicates that the thermal decomposition temperatures of the first and third active layers are similar, posing a risk that the gas generated by the third active layer 314 may not break through the explosion-proof valve in time before the first active layer 312 has already undergone thermal decomposition, resulting in lower safety. The difference between the thermal decomposition temperature of the first active layer 312 and the thermal decomposition temperature of the third active layer 314 should not be too large. If it is too large, the thermal decomposition temperature of the third active layer 314 will be too low, causing the third active layer 314 to decompose prematurely, which will affect the safety of the battery.

[0060] Optionally, the difference between the thermal decomposition temperature of the first active layer 312 and the thermal decomposition temperature of the third active layer 314 can be any value or a range between any two values, such as 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, etc., and this embodiment does not limit this.

[0061] (3) The thermal decomposition temperature of the second active layer 313 is greater than that of the first active layer 312.

[0062] The thermal decomposition temperature of the second active layer 313 is higher than that of the first active layer 312. The second active layer 313 is located on the side of the first active layer 312 away from the positive electrode current collector 311. The first active layer 312 is closer to the positive electrode current collector 311 than the second active layer 313. Since the temperature of the positive electrode current collector 311 is usually higher, the first active layer 312 is close to the area with a higher temperature, which enables the first active layer 312 to decompose quickly, realize a rapid response to thermal runaway, and further improve the safety of the battery.

[0063] (4) The thermal decomposition temperature of the third active layer 314 is 180℃-230℃.

[0064] The thermal decomposition temperature of the third active layer 314 can be any value or a range between any two values, such as 180℃, 190℃, 200℃, 210℃, 220℃, 230℃.

[0065] (5) The thermal decomposition temperature of the second active layer 313 is 270℃-350℃.

[0066] The thermal decomposition temperature of the second active layer 313 can be any value or a range between any two values, such as 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, and 350℃.

[0067] (6) The thermal decomposition temperature of the first active layer 312 is 220℃-270℃.

[0068] The thermal decomposition temperature of the first active layer 312 can be any value or a range between any two values, such as 220℃, 230℃, 240℃, 250℃, 260℃, 270℃.

[0069] In one or more embodiments of this application, the first active layer 312 is made of lithium nickel manganese cobalt oxide in the medium nickel range. For example, the material of the first active layer 312 includes LiNi. x1 Co y1 Mn z1 O2, where 0.4≤x1<0.75, y1>0, z1>0.

[0070] For example, the value of x1 can be any value such as 0.4, 0.5, 0.6, 0.7, 0.74, or a range between any two values; this embodiment does not limit this. The value of y1 can be 0.1, 0.2, 0.3, 0.4, 0.5, etc., and the value of z1 can be 0.1, 0.2, 0.3, 0.4, 0.5, etc.; this embodiment does not limit this.

[0071] In some optional embodiments, the material of the first active layer 312 may also be NCM523, that is, x1:y1:z1=5:2:3, and x1=0.5, y1=0.2, z1=0.3.

[0072] In some optional embodiments, the material of the first active layer 312 may also be NCM442, that is, x1:y1:z1=4:4:2, and x1=0.4, y1=0.4, z1=0.2.

[0073] In some optional embodiments, the material of the first active layer 312 may also be NCM532, that is, x1:y1:z1=5:3:2, and x1=0.5, y1=0.3, z1=0.2.

[0074] For example, the resistivity of the first active layer 312 is in the range of 10 Ω·m to 80 Ω·m. For instance, the resistivity of the first active layer 312 can be any value or any two values ​​between 10 Ω·m, 20 Ω·m, 30 Ω·m, 40 Ω·m, 60 Ω·m, and 80 Ω·m.

[0075] In some optional embodiments, the first active layer 312 comprises a first conductive agent and a first adhesive. The ratio of the first conductive agent to the first adhesive is 92–96:2–4:2–4.

[0076] In one or more embodiments of this application, the material of the second active layer 313 includes lithium iron phosphate. Lithium iron phosphate can effectively mitigate structural damage during battery decomposition and cycling, thereby effectively improving the overall cycle life of the battery.

[0077] In some embodiments, the resistivity of the second active layer 313 is less than 0.3 Ω·m. Exemplarily, the resistivity of the second active layer 313 can be any value such as 0.29 Ω·m, 0.25 Ω·m, 0.2 Ω·m, 0.1 Ω·m, etc., and this embodiment does not limit it.

[0078] In some optional embodiments, the second active layer 313 comprises a second conductive agent and a second binder. The ratio of the second conductive agent to the second binder is 90–94:1–6:2–4.

[0079] In one embodiment of this application, the third active layer 314 is made of lithium nickel cobalt manganese oxide in the high nickel range. For example, the material of the third active layer 314 includes LiNi. x2 Co y2 Mn z2 O2, where x2≥0.75, y2>0, z2>0. The material of the third active layer 314 is set to lithium nickel cobalt manganese oxide in the high nickel range, which has strong activity and can achieve the purpose of low-temperature pyrolysis, thereby ensuring that the explosion-proof valve 2 can be opened in time in the event of thermal runaway.

[0080] For example, the value of x2 can be any value or a range between any two values, such as 0.75, 0.8, 0.82, 0.85, 0.9, 0.92, 0.95, etc., and this embodiment does not limit this. The value of y3 can be 0.1, 0.15, 0.18, 0.2, 0.22, etc., and the value of z3 can be 0.1, 0.15, 0.18, 0.2, 0.22, etc., and this embodiment does not limit this.

[0081] In some optional embodiments, the material of the third active layer 314 can be NCM811, that is, x2:y2:z2=8:1:1, and x2=0.8, y2=0.1, z2=0.1.

[0082] In some optional embodiments, the material of the third active layer 314 can be NCM9055, that is, x2:y2:z2=9:0.5:0.5, and x2=0.9, y2=0.05, z2=0.05.

[0083] In some embodiments, the resistivity of the third active layer 314 ranges from 1 Ω·m to 20 Ω·m. Exemplarily, the resistivity of the third active layer 314 can be any value or a range between any two values, such as 1 Ω·m, 3 Ω·m, 5 Ω·m, 8 Ω·m, 10 Ω·m, 12 Ω·m, 14 Ω·m, 16 Ω·m, 18 Ω·m, or 20 Ω·m.

[0084] In some optional embodiments, the third active layer 314 comprises a third conductive agent and a third binder. The ratio of the third conductive agent to the third binder is 92–96:2–4:2–4.

[0085] In one or more embodiments of this application, such as Figure 3 , Figure 4 , Figure 9 or Figure 10 As shown, the positive electrode 31 also includes a positive electrode tab 315. The positive electrode tab 315 is connected to at least one side of the positive current collector 311 in the width direction. The width direction of the positive current collector 311 is the same as the height direction of the battery.

[0086] In some alternative embodiments, please continue to refer to Figure 3 , Figure 4 , Figure 9 or Figure 10 The positive electrode 31 also includes a fourth active layer 316. The fourth active layer 316 is disposed on the side of the first active layer 312 away from the positive current collector 311, and is disposed in the same layer as the second active layer 313. That is, the fourth active layer 316 and the second active layer 313 are distributed in a direction perpendicular to the thickness direction of the positive current collector 311. Furthermore, the fourth active layer 316 is closer to the positive electrode tab 315 than the second active layer 313, and the resistivity of the fourth active layer 316 is greater than that of the second active layer 313. By setting the fourth active layer 316 close to the positive electrode tab 315, and by having the resistivity of the fourth active layer 316 greater than that of the second active layer 313, lithium plating caused by insufficient electrochemical kinetics during high-rate fast charging can be effectively mitigated, thereby ensuring the battery's fast charging performance while extending its service life.

[0087] It should be noted that the fourth active layer 316 is disposed on the first active layer 312, and the surface of the fourth active layer 316 facing away from the first active layer 312 is coplanar with the surface of the second active layer 313 facing away from the first active layer 312, making the positive electrode sheet 31 relatively flat.

[0088] In some optional embodiments, the resistivity of the fourth active layer 316 minus the resistivity of the second active layer 313 is ≥ 50 Ω·m. That is, the difference between the resistivity of the fourth active layer 316 and the resistivity of the second active layer 313 is greater than or equal to 50 Ω·m. This setting reduces the risk of lithium plating. The difference between the resistivity of the fourth active layer 316 and the resistivity of the second active layer 313 cannot be too small. If it is too small, the improvement in conductivity of the fourth active layer 316 on the second active layer 313 and the overall conductivity of the fourth active layer 316 will not be significant, leading to insufficient electrochemical kinetics and still affecting the battery's fast-charging performance and lifespan.

[0089] For example, the resistivity of the fourth active layer 316 minus the resistivity of the second active layer 313 can be any value such as 50Ω·m, 60Ω·m, 65Ω·m, 70Ω·m, 75Ω·m, 80Ω·m, 85Ω·m, etc., and this embodiment does not limit it.

[0090] In some optional embodiments, the resistivity of the fourth active layer 316 is 50 Ω·m to 200 Ω·m. Exemplarily, the resistivity of the fourth active layer 316 can be any value or a range between any two values, such as 50 Ω·m, 80 Ω·m, 90 Ω·m, 100 Ω·m, 120 Ω·m, 150 Ω·m, 160 Ω·m, 180 Ω·m, 190 Ω·m, 200 Ω·m.

[0091] In one or more embodiments of this application, the fourth active layer 316 is made of lithium nickel manganese cobalt oxide in the low nickel range. For example, the material of the fourth active layer 316 includes LiNi. x3 Co y3 Mn z3 O2, where 0 < x3 < 0.4, y3 > 0, z3 > 0.

[0092] For example, the value of x3 can be any value such as 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or any range between any two values; this embodiment does not limit this. The value of y3 can be 0.1, 0.2, 0.3, 0.4, 0.5, etc., and the value of z3 can be 0.1, 0.2, 0.3, 0.4, 0.5, etc.; this embodiment does not limit this.

[0093] In some alternative embodiments, the material of the fourth active layer 316 can be NCM111, that is, x3:y3:z3=1:1:1, and x3=0.33, y3=0.33, z3=0.33.

[0094] In some alternative embodiments, the material of the fourth active layer 316 can be NCM226, that is, x3:y3:z3=2:2:6, and x3=0.2, y3=0.2, z3=0.6.

[0095] In some embodiments, the thermal decomposition temperature of the fourth active layer 316 is in the range of 250°C to 300°C.

[0096] In some optional embodiments, the fourth active layer 316 comprises a fourth conductive agent and a fourth binder. The ratio of the fourth conductive agent to the fourth binder is 92–96:2–4:2–4.

[0097] Exemplarily, the conductive agent and binder in this embodiment are conventionally configured. For example, the conductive agent is at least one selected from SP, acetylene black, Ketjen black, conductive graphite, and carbon black. The binder is at least one selected from polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC-Na).

[0098] In one or more embodiments of this application, such as Figure 3 and Figure 4 As shown, a positive electrode tab 315 is provided on one side of the positive current collector 311 in the width direction, and the positive electrode tab 315 is located on the side of the electrode assembly 3 near the explosion-proof valve 2.

[0099] In one embodiment of this application, such as Figure 3As shown, the third active layer 314 and the second active layer 313 are located on the same side of the fourth active layer 316. That is, the end of the third active layer 314 facing the fourth active layer 316 does not extend to the edge of the positive electrode current collector 311, but rather abuts against the fourth active layer 316. With this arrangement, the fourth active layer 316 is closer to the positive electrode tab 315 than the third active layer 314 and the second active layer 313, which can reduce the risk of lithium plating in the area near the positive electrode tab 315.

[0100] In another alternative embodiment, such as Figure 4 As shown, the third active layer 314 extends along the first direction X to the two edges of the positive current collector 311. That is, a part of the third active layer 314 is adjacent to the second active layer 313 in the second direction Y, and another part of the third active layer 314 is adjacent to the fourth active layer 316 in the second direction Y.

[0101] In some embodiments of this application, the thickness of the first active layer 312 is greater than or equal to the thickness of the second active layer 313. This configuration ensures high capacity and high energy density of the positive electrode 31 while improving battery safety.

[0102] For example, the thickness of the first active layer 312 is in the range of 60μm-120μm. For example, the thickness of the first active layer 312 is any value or any two values ​​of 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm.

[0103] In some optional embodiments, the thickness of the second active layer 313 ranges from 40 μm to 80 μm. Exemplarily, the thickness of the second active layer 313 is any value or a range between any two values, such as 40 μm, 50 μm, 60 μm, 70 μm, or 80 μm.

[0104] It should be noted that the thickness of the third active layer 314 is equal to the thickness of the second active layer 313, and the thickness of the fourth active layer 316 is equal to the thickness of the second active layer 313.

[0105] In one or more embodiments of this application, such as Figure 7As shown, the dimension of the fourth active layer 316 in the width direction of the positive electrode current collector 311 is 'a', and the dimension of the first active layer 312 in the width direction of the positive electrode current collector 311 is 'b'. 'a' and 'b' satisfy the relationship: 0.04b ≤ a ≤ 0.2b. When 'a' and 'b' satisfy this relationship, the risk of lithium plating occurring on the side of the positive electrode tab 315 on the positive electrode sheet 31 can be reduced, thereby improving battery safety. In this embodiment, the dimension of the fourth active layer 316 in the width direction of the positive electrode current collector 311 can be understood as the width of the fourth active layer 316. The dimension of the first active layer 312 in the width direction of the positive electrode current collector 311 can be understood as the width of the first active layer 312.

[0106] For example, the value of a can be 0.04b, 0.05b, 0.08b, 0.1b, 0.15b, 0.18b, 0.2b, etc., and this embodiment does not limit it.

[0107] In some optional embodiments, the dimension of the fourth active layer 316 in the width direction of the positive current collector 311 ranges from 5mm to 20mm. For example, the dimension of the fourth active layer 316 in the width direction of the positive current collector 311 is any value or any range between two values ​​such as 5mm, 8mm, 9mm, 10mm, 12mm, 14mm, 16mm, 18mm, 20mm.

[0108] In some optional embodiments, the dimension of the first active layer 312 in the width direction of the positive current collector 311 ranges from 80mm to 120mm. For example, the dimension of the first active layer 312 in the width direction of the positive current collector 311 can be any value or a range between any two values ​​such as 80mm, 90mm, 100mm, 110mm, 120mm.

[0109] In the battery provided in this embodiment, the second active layer 313, the third active layer 314, and the fourth active layer 316 of the positive electrode 31 are positioned in a reasonable and coordinated manner. Their synergistic effect optimizes the battery's fast-charging performance, safety, and cycle life simultaneously, resulting in a battery that simultaneously possesses high fast-charging performance, high safety, and long cycle life. The fourth active layer 316 is a low-nickel lithium nickel cobalt manganese oxide, which effectively mitigates lithium plating caused by insufficient electrochemical kinetics during high-rate fast charging, ensuring fast-charging performance while extending battery life. The third active layer 314 is a high-nickel lithium nickel cobalt manganese oxide, which effectively reduces the risk of the top cover opening and explosion caused by the instantaneous valve ejection during thermal runaway, improving battery safety. The second active layer 313 is made of lithium iron phosphate, effectively mitigating structural damage and improving the overall cycle life of the battery. The second active layer 313, the third active layer 314, and the fourth active layer 316 complement each other from different dimensions, which not only solves the problems of battery fast charging shortcomings, safety hazards, and structural degradation under a single material system, but also achieves simultaneous optimization and improvement of battery fast charging performance, safety factor, and overall cycle life.

[0110] This embodiment provides some examples and comparative examples to compare the performance of the battery provided in this application with batteries in related technologies. The relevant parameters and results are presented in Table 1.

[0111] Example 1: S1: The material of the fourth active layer 316 is NCM111, the conductive agent of the fourth active layer 316 is SP, and the binder of the fourth active layer 316 is PVDF. NCM111, SP and PVDF are weighed in a mass ratio of 93:3:4, and NMP is added in a mass ratio of 1:2 with the ternary material NCM111. The mixture is dispersed at high speed and mixed evenly to obtain slurry A. S2: The material of the third active layer 314 is NCM811, the conductive agent of the third active layer 314 is SP, and the binder of the third active layer 314 is PVDF. NCM811, SP and PVDF are weighed in a mass ratio of 92:4:4, and NMP is added in a mass ratio of 1:2 with the ternary material NCM811. The mixture is dispersed at high speed and mixed evenly to obtain slurry B. S3: The material of the second active layer 313 is LiFePO4, the conductive agent of the second active layer 313 is SP, and the binder of the second active layer 313 is PVDF. LiFePO4, SP and PVDF are weighed in a mass ratio of 90:6:4, and NMP is added in a mass ratio of 1:2 of LiFePO4. The mixture is dispersed at high speed and mixed evenly to obtain slurry C. S4: The material of the first active layer 312 is NCM523, the conductive agent of the first active layer 312 is SP, and the binder of the first active layer 312 is PVDF. The first active materials NCM523, SP, and PVDF are weighed in a mass ratio of 92:4:4. NMP is added in a mass ratio of 1:2 to NCM523, and the mixture is dispersed at high speed and mixed evenly to obtain slurry D. S5: Set the coating machine parameters to a coating thickness of 100μm, and uniformly coat the slurry D onto the aluminum foil (i.e., the positive electrode current collector 311) to obtain the first active layer 312. That is, the coating thickness of the first layer is 100μm. After coating, the electrode is dried at 110℃ for 1.5h to obtain electrode A. The dimension of the first active layer 312 in the width direction of the positive electrode current collector 311 (i.e., the width of the first active layer 312) is 100mm. The width direction of the positive electrode current collector 311 is perpendicular to the length direction and the thickness direction of the positive electrode current collector 311, and the width direction of the positive electrode current collector 311 is the same as the width direction of the positive electrode 31.

[0112] S6: Apply slurry A, slurry B, and slurry C evenly onto the dried electrode A according to the required distribution, so that the overall coating thickness of the second layer is 50 μm, resulting in a second active layer 313, a third active layer 314, and a fourth active layer 316. The arrangement of the second active layer 313, the third active layer 314, and the fourth active layer 316 is as follows: Figure 8 The arrangement is shown. The fourth active layer 316 has a width of 12 mm in the width direction of the positive current collector 311 (i.e., the width of the fourth active layer 316), and the third active layer 314 has a width of 35 mm in the length direction of the positive current collector 311 (i.e., the width of the third active layer 314). After drying the coated electrode at 100°C for 1 hour, electrode B is obtained, which is a double-coated composite positive electrode. The coating width of the active material layer on the positive electrode 31 (i.e., the dimension of the active material layer on the positive current collector 311 in the width direction) is 100 mm. At this time, the second active layer 313 has a width of 88 mm in the width direction of the positive current collector 311.

[0113] Negative electrode sheet: Graphite:SBR:CMC:SP is dispersed in water at a mass ratio of 96:1:2:1, then coated onto a 7μm copper foil (i.e., negative electrode current collector), and dried to form a negative electrode sheet.

[0114] The separator located between the positive electrode 31 and the negative electrode is a polypropylene base film with a thickness of 12 μm.

[0115] The lithium salt in the electrolyte is 1 mol / L lithium hexafluorophosphate (LiPF6), and the organic solvent in the electrolyte is ethylene carbonate (EC) and dimethyl carbonate (DMC), with a volume ratio of ethylene carbonate (EC) to dimethyl carbonate (DMC) of 1:1.

[0116] The battery casing 1 is made of aluminum and includes a casing body 11 and a top cover 12. The casing body 11 and the top cover 12 are connected to form a receiving cavity. Figure 8 As shown, the explosion-proof valve 2 is installed on the top cover 12, and the dimension of the explosion-proof valve 2 in the width direction of the third active layer 314 is 30mm.

[0117] Battery fabrication: The positive electrode 31, the separator and the negative electrode are wound together to obtain the electrode assembly 3; the electrode assembly 3 is installed in the housing 1 and injected with electrolyte and sealed to obtain a square aluminum-cased lithium-ion battery.

[0118] Example 2: The difference between Example 2 and Example 1 lies in steps S1 to S4, specifically: S1: The material of the fourth active layer 316 is NCM226, the conductive agent of the fourth active layer 316 is SP, and the binder of the fourth active layer 316 is PVDF. NCM226, SP and PVDF are weighed in a mass ratio of 93:3:4, and NMP is added in a mass ratio of 1:2 with the ternary material NCM226. The mixture is dispersed at high speed and mixed evenly to obtain slurry A. S2: The material of the third active layer 314 is NCM9055, the conductive agent of the third active layer 314 is SP, and the binder of the third active layer 314 is PVDF. NCM9055, SP and PVDF are weighed in a mass ratio of 92:4:4, and NMP is added in a mass ratio of 1:2 with the ternary material NCM9055. The mixture is dispersed at high speed and mixed evenly to obtain slurry B. S3: The material of the second active layer 313 is LiFePO4, the conductive agent of the second active layer 313 is SP, and the binder of the second active layer 313 is PVDF. LiFePO4, SP and PVDF are weighed in a mass ratio of 90:6:4, and NMP is added in a mass ratio of 1:2 of LiFePO4. The mixture is dispersed at high speed and mixed evenly to obtain slurry C. S4: The material of the first active layer 312 is NCM442, the conductive agent of the first active layer 312 is SP, and the binder of the first active layer 312 is PVDF. The first active materials NCM442, SP, and PVDF are weighed in a mass ratio of 92:4:4. NMP is added in a mass ratio of 1:2 to NCM442, and the mixture is dispersed at high speed and mixed evenly to obtain slurry D. The remaining steps are the same as in Example 1, and will not be described in detail here.

[0119] Example 3: The difference between Example 3 and Example 1 lies in step S6, specifically: S6: Apply slurry A, slurry B, and slurry C evenly onto the dried electrode A according to the required distribution, so that the overall coating thickness of the second layer is 50 μm, resulting in a second active layer 313, a third active layer 314, and a fourth active layer 316. The arrangement of the second active layer 313, the third active layer 314, and the fourth active layer 316 is as follows: Figure 8 The arrangement is shown. The fourth active layer 316 has a width of 20 mm in the width direction of the positive current collector 311 (i.e., the width of the fourth active layer 316), and the third active layer 314 has a width of 35 mm in the length direction of the positive current collector 311 (i.e., the width of the third active layer 314). After drying the coated electrode at 100°C for 1 hour, electrode B is obtained, which is a double-coated composite positive electrode. The coating width of the active material layer on the positive electrode 31 (i.e., the dimension of the active material layer on the positive current collector 311 in the width direction) is 100 mm. At this time, the second active layer 313 has a width of 80 mm in the width direction of the positive current collector 311.

[0120] The remaining steps are the same as in Example 1, and will not be described in detail here.

[0121] Example 4: The difference between Example 4 and Example 1 lies in step S6, specifically: S6: Apply slurry A, slurry B, and slurry C evenly onto the dried electrode A according to the required distribution, so that the overall coating thickness of the second layer is 50 μm, resulting in a second active layer 313, a third active layer 314, and a fourth active layer 316. The arrangement of the second active layer 313, the third active layer 314, and the fourth active layer 316 is as follows: Figure 8 The arrangement is shown. The fourth active layer 316 has a width of 5 mm in the width direction of the positive current collector 311 (i.e., the width of the fourth active layer 316), and the third active layer 314 has a width of 35 mm in the length direction of the positive current collector 311 (i.e., the width of the third active layer 314). After drying the coated electrode at 100°C for 1 hour, electrode B is obtained, which is a double-layer coated composite positive electrode. The coating width of the active material layer on the positive electrode 31 (i.e., the dimension of the active material layer on the positive current collector 311 in the width direction) is 100 mm. At this time, the second active layer 313 has a width of 95 mm in the width direction of the positive current collector 311.

[0122] The remaining steps are the same as in Example 1, and will not be described in detail here.

[0123] Example 5: The difference between Example 5 and Example 1 lies in step S6, specifically: S6: Apply slurry A, slurry B, and slurry C evenly onto the dried electrode A according to the required distribution, so that the overall coating thickness of the second layer is 50 μm, resulting in a second active layer 313, a third active layer 314, and a fourth active layer 316. The arrangement of the second active layer 313, the third active layer 314, and the fourth active layer 316 is as follows: Figure 8 The arrangement is shown. The fourth active layer 316 has a width of 12 mm in the width direction of the positive current collector 311 (i.e., the width of the fourth active layer 316), and the third active layer 314 has a width of 50 mm in the length direction of the positive current collector 311 (i.e., the width of the third active layer 314). After drying the coated electrode at 100°C for 1 hour, electrode B is obtained, which is a double-coated composite positive electrode. The coating width of the active material layer on the positive electrode 31 (i.e., the dimension of the active material layer on the positive current collector 311 in the width direction) is 100 mm. At this time, the second active layer 313 has a width of 88 mm in the width direction of the positive current collector 311.

[0124] The remaining steps are the same as in Example 1, and will not be described in detail here.

[0125] Example 6: The difference between Example 6 and Example 1 lies in step S6, specifically: S6: Apply slurry A, slurry B, and slurry C evenly onto the dried electrode A according to the required distribution, so that the overall coating thickness of the second layer is 50 μm, resulting in a second active layer 313, a third active layer 314, and a fourth active layer 316. The arrangement of the second active layer 313, the third active layer 314, and the fourth active layer 316 is as follows: Figure 8 The arrangement is shown. The fourth active layer 316 has a width of 12 mm in the width direction of the positive current collector 311 (i.e., the width of the fourth active layer 316), and the third active layer 314 has a width of 20 mm in the length direction of the positive current collector 311 (i.e., the width of the third active layer 314). After drying the coated electrode at 100°C for 1 hour, electrode B is obtained, which is a double-coated composite positive electrode. The coating width of the active material layer on the positive electrode 31 (i.e., the dimension of the active material layer on the positive current collector 311 in the width direction) is 100 mm. At this time, the second active layer 313 has a width of 88 mm in the width direction of the positive current collector 311.

[0126] The remaining steps are the same as in Example 1, and will not be described in detail here.

[0127] Example 7: The difference between Example 7 and Example 1 lies in the position of the explosion-proof valve 2. Specifically: The explosion-proof valve 2 is located on the side wall of the shell body 11, not on the top cover 12. The corresponding third active layer 314 is transverse, that is, the arrangement of the second active layer 313, the third active layer 314, and the fourth active layer 316 is as follows: Figure 10 The arrangement shown is as follows. The position of explosion-proof valve 2 is... Figure 10 The positions are shown. The fourth active layer 316 has a width of 12 mm in the width direction of the positive current collector 311 (i.e., the width of the fourth active layer 316), and the third active layer 314 has a width of 35 mm in the width direction of the positive current collector 311 (i.e., the width of the third active layer 314). After drying the coated electrode at 100°C for 1 hour, electrode B is obtained, which is a double-coated composite positive electrode. The coating width of the active material layer on the positive electrode 31 (i.e., the dimension of the active material layer on the positive current collector 311 in the width direction) is 100 mm. At this time, the second active layer 313 has a width of 53 mm in the width direction of the positive current collector 311.

[0128] Furthermore, the explosion-proof valve 2 has a width dimension of 30 mm in the third active layer 314.

[0129] The remaining steps are the same as in Example 1, and will not be described in detail here.

[0130] Example 8: The difference between Example 8 and Example 1 is that in step S5, the coating thickness of the first layer is 75 μm, that is, the thickness of the first active layer 312 is 75 μm. In step S6, the coating thickness of the second layer is 75 μm, that is, the thickness of the second active layer 313, the third active layer 314, and the fourth active layer 316 is all 75 μm.

[0131] The remaining steps are the same as in Example 1, and will not be described in detail here.

[0132] Example 9: The difference between Example 9 and Example 1 is that in step S5, the coating thickness of the first layer is 70 μm, that is, the thickness of the first active layer 312 is 70 μm. In step S6, the coating thickness of the second layer is 80 μm, that is, the thickness of the second active layer 313, the third active layer 314, and the fourth active layer 316 are all 80 μm.

[0133] The remaining steps are the same as in Example 1, and will not be described in detail here.

[0134] Comparative Example 1: S1: Weigh NCM523, SP and PVDF according to a mass ratio of 92:4:4, add NMP at a mass ratio of 1:2 with the ternary material, disperse at high speed, and mix evenly to obtain slurry D; S2: Weigh LiFePO4, SP and PVDF according to a mass ratio of 90:6:4, add NMP according to a mass ratio of 1:2 for LiFePO4, disperse at high speed, and mix evenly to obtain slurry C; S3: Set the coating machine parameters to a coating thickness of 100μm, and uniformly coat slurry D onto the aluminum foil (positive electrode current collector 311), which is the first active layer 312. After coating, the electrode is dried at 110℃ for 1.5h to obtain electrode A. Then, slurry C is coated onto electrode A to a coating thickness of 50μm. After coating, the electrode is dried at 110℃ for 1.5h to obtain the positive electrode.

[0135] Test methods First-cycle capacity test: Lithium-ion batteries prepared in the example and comparative examples were tested under the following conditions: charging at 0.33C rate to the cutoff voltage of 4.2V and discharging at 0.33C rate to the cutoff voltage of 2.5V at 25°C.

[0136] 2C / 1C fast charging cycle life test: Lithium-ion aluminum-cased batteries prepared in the examples and comparative examples were subjected to 2C / 1C cycle tests at 25°C. Powder shedding and lithium plating on the tab side material after 1000 cycles: The battery after 1000 cycles was fully charged to 4.2V at 1C.

[0137] Thermal runaway test: A 1000W heating element is attached to the center of the large surface of a fully charged (1C charging to 4.5V) battery, and the two are clamped together. Then, the heating element is powered on for testing. The thermal runaway trigger condition is as follows: a) The triggering object generates a voltage drop, and the drop value exceeds 25% of the initial voltage; b) The temperature at the monitoring point (back of the battery) reaches 300℃; c) The rate of temperature rise at the monitoring point (back of the battery) (the rate of temperature rise outside the battery) dT / dt is ≥1℃ / s and lasts for more than 3s.

[0138] When a)+c) or b)+c) is satisfied, thermal runaway is determined to have occurred, and the test is stopped at that time.

[0139] As can be seen from Examples 1 to 9 in Tables 1 and 2, the battery provided in this embodiment has a third active layer 314 on at least one side of the positive electrode current collector 311 in the thickness direction. The thermal decomposition temperature of the third active layer 314 is lower than the thermal decomposition temperature of the first active layer 312 and lower than the thermal decomposition temperature of the second active layer 313. The orthographic projection of the third active layer 314 along the first direction X overlaps with at least part of the orthographic projection of the explosion-proof valve 2 along the first direction X, so that when the battery experiences thermal runaway, the explosion-proof valve 2 can be opened normally and smoothly, and the top cover 12 does not have to be lifted.

[0140] As can be seen from Comparative Example 1, although two active material layers are set on the current collector of the positive electrode, the material of the second active material layer away from the current collector is lithium iron phosphate. Although it can meet the high current requirements, after the battery thermal runaway, the explosion-proof valve 2 did not open normally, and the top cover was lifted. Obviously, the above embodiments of this application are merely examples for clear illustration and are not intended to limit the implementation of this application. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of the claims of this application.

Claims

1. A battery, characterized in that, include: case; An explosion-proof valve, wherein the explosion-proof valve is installed on the shell wall of the housing; An electrode assembly is disposed within the housing. The electrode assembly includes a positive electrode sheet, which comprises a positive current collector, a first active layer, a second active layer, and a third active layer. The first active layer is disposed on at least one side surface of the positive current collector along its thickness direction. The second active layer is disposed on the side of the first active layer opposite to the positive current collector. The third active layer is disposed on at least one side of the positive current collector along its thickness direction. The orthographic projection of the third active layer along a first direction at least partially overlaps with the orthographic projection of the explosion-proof valve along the first direction. Furthermore, the thermal decomposition temperature of the third active layer is less than the thermal decomposition temperature of the first active layer, and the thermal decomposition temperature of the third active layer is less than the thermal decomposition temperature of the second active layer. The first direction is the thickness direction of the housing wall where the explosion-proof valve is disposed.

2. The battery according to claim 1, characterized in that, The third active layer is disposed on the side of the first active layer away from the positive electrode current collector, and is disposed in the same layer as the second active layer; Alternatively, the third active layer is connected to the surface of the positive current collector facing the positive current collector in the thickness direction, and the surface of the third active layer facing away from the positive current collector in the thickness direction is coplanar with the surface of the second active layer facing away from the positive current collector.

3. The battery according to claim 1, characterized in that, The third active layer extends from one end toward the explosion-proof valve to the edge of the positive current collector near the explosion-proof valve; Alternatively, there may be a gap between the end of the third active layer facing the explosion-proof valve and the edge of the positive current collector near the explosion-proof valve.

4. The battery according to claim 1, characterized in that, In the first direction, the third active layer is centered with the explosion-proof valve.

5. The battery according to claim 4, characterized in that, The width of the third active layer is c1, and the dimension of the explosion-proof valve in the width direction of the third active layer is c2, satisfying the relationship: c2≤c1≤1.7c2; And / or, the width of the third active layer is in the range of 20mm-50mm.

6. The battery according to any one of claims 1-5, characterized in that, The thermal decomposition temperature satisfies at least one of the following characteristics (1) to (6): (1) 40℃≤ thermal decomposition temperature of the second active layer - thermal decomposition temperature of the third active layer≤170℃; (2) 40℃≤ thermal decomposition temperature of the first active layer - thermal decomposition temperature of the third active layer≤90℃; (3) The thermal decomposition temperature of the second active layer is greater than that of the first active layer; (4) The thermal decomposition temperature of the third active layer is 180℃-230℃; (5) The thermal decomposition temperature of the second active layer is 270℃-350℃; (6) The thermal decomposition temperature of the first active layer is 220℃-270℃.

7. The battery according to any one of claims 1-5, characterized in that, The material of the first active layer includes LiNi x1 Co y1 Mn z1 O2, where 0.4 ≤ x1 < 0.75, y1 > 0, z1 > 0; and / or, The material of the second active layer includes lithium iron phosphate; and / or, The material of the third active layer includes LiNi. x2 Co y2 Mn z2 O2, where x2≥0.75, y2>0, z2>0.

8. The battery according to any one of claims 1-5, characterized in that, The positive electrode plate further includes a positive electrode tab, which is connected to at least one side of the positive current collector in the width direction; The positive electrode further includes a fourth active layer, which is disposed on the side of the first active layer away from the positive current collector and is disposed in the same layer as the second active layer. The fourth active layer is closer to the positive electrode tab than the second active layer, and the resistivity of the fourth active layer is greater than that of the second active layer. Optionally, the resistivity of the fourth active layer minus the resistivity of the second active layer is ≥50 Ω·m; Preferably, the resistivity of the fourth active layer is 50 Ω·m-200 Ω·m; Preferably, the resistivity of the second active layer is <0.3Ωm.

9. The battery according to claim 8, characterized in that, The material of the fourth active layer includes LiNi. x3 Co y3 Mn z3 O2, where 0 < x3 < 0.4, y3 > 0, z3 > 0.

10. The battery according to claim 8, characterized in that, The positive electrode tab is located on the side of the electrode assembly closest to the explosion-proof valve.

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