Secondary battery and electric device

Abstract

The invention relates to the technical field of lithium batteries, in particular to a secondary battery and a power utilization device.A positive pole piece of the secondary battery comprises a first film layer and a second film layer, the first film layer is close to the surface of a current collector, and at least part of the second film layer is located on the surface, away from the current collector, of the first film layer; the first film layer covers a partial region, close to the tab, of the current collector, the first film layer comprises porous ceramic and a first binder, at least a partial region of the second film layer is located on the surface, away from the current collector, of the first film layer, and the second film layer comprises a positive active material. The condition of service life attenuation of the secondary battery caused by insufficient electrolyte at the top of the secondary battery can be improved, and the condition that lithium dendrites or sodium dendrites are separated out of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to secondary batteries and electrical devices. Background Technology

[0002] In recent years, secondary batteries such as lithium-ion and sodium-ion batteries have seen tremendous development. These batteries can be widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in electric vehicles, power tools, military equipment, and aerospace. However, when applied to electric vehicles such as electric bicycles, electric motorcycles, and electric cars, the lifespan of these batteries needs further improvement as market demands for electric vehicles increase. Summary of the Invention

[0003] In view of this, the main technical problem to be solved by this application is to improve the lifespan of secondary batteries, thereby providing secondary batteries and electrical devices that can improve the lifespan of secondary batteries.

[0004] The first aspect of this application provides a secondary battery, which includes a positive electrode sheet, a current collector, and a positive electrode film. The positive electrode film is disposed on the surface of the current collector and includes a first film and a second film. The first film is close to the surface of the current collector and covers a portion of the current collector near the tab. The first film includes porous ceramic and a first binder. At least a portion of the second film is located on the surface of the first film away from the current collector, and the second film includes a positive electrode active material.

[0005] In this embodiment, the porous ceramic possesses insulation and liquid absorption properties. By setting the porous ceramic in the first film layer of the positive electrode sheet, and having the first film layer cover the portion of the current collector near the electrode tab (i.e., the edge region of the current collector covered by the first film layer), the conductivity of the first film layer can be reduced, and its resistivity increased. The first film layer is located between the second film layer and the current collector, further reducing the conductivity between the second film layer and the current collector. This results in a higher interfacial resistance of the positive electrode sheet during charging of the secondary battery, leading to a lower content of active ions such as lithium and sodium ions released. This reduces the occurrence of lithium or sodium dendrites depositing at the edge of the negative electrode sheet in the secondary battery, thereby improving the secondary battery's performance. Lifespan; Simultaneously, porous ceramics are disposed in the first membrane layer. The porous ceramics in the first membrane layer can adsorb electrolyte, which can improve the uniformity of electrolyte around the positive electrode in the secondary battery. This is beneficial to improving the lifespan degradation of the secondary battery caused by insufficient electrolyte at the top during cycling, and can improve the cycle life of the secondary battery; In the embodiments of this application, the second membrane layer contains positive electrode active material. The second membrane layer is located on the side of the first membrane layer away from the current collector, so that during charging and discharging, the electrolyte first contacts the surface of the positive electrode membrane layer (the surface away from the current collector), which is beneficial to the insertion or extraction of active ions into or out of the positive electrode active material, and improves the cycle performance of the secondary battery.

[0006] In any embodiment, the mass fraction of porous ceramic is 1%-10% based on the total mass of the first membrane layer. In the embodiments of this application, by controlling the mass fraction of porous ceramic within the above range, the content of adsorbed electrolyte is optimized.

[0007] In any embodiment, the current collector is made of aluminum, and the first film layer further includes an alkaline compound. The current collector for the positive electrode is typically aluminum foil. In this embodiment, the first film layer is located close to the surface of the current collector. The first film layer includes an alkaline compound, which can react with the aluminum foil current collector, making the surface of the aluminum foil uneven. This results in a stronger bond between the first film layer and the current collector, improving the problem of material shedding from the positive electrode during cycling, thus enhancing the stability of the positive electrode, improving the cycle stability of the battery, and increasing the battery's lifespan.

[0008] In any embodiment, the porosity of the porous ceramic is 20%-70%. In the embodiments of this application, by controlling the porosity within the above range, the porous ceramic has a larger specific surface area and can store more electrolyte, which is beneficial to improving the amount of electrolyte adsorbed at the top of the secondary battery.

[0009] In any embodiment, the pore size of the porous ceramic is 200 nm to 10 μm. In the embodiments of this application, by controlling the pore size of the porous ceramic within the above range, the electrolyte stored in the porous ceramic is less likely to escape, which is beneficial to ensuring better electrolyte uniformity in the secondary battery.

[0010] In any embodiment, the volume average particle size Dv50 of the porous ceramic is 0.5 μm-50 μm. In the embodiments of this application, the volume average particle size Dv50 of the porous ceramic is within the above range, which makes the uniformity of the first film layer in the embodiments of this application better and the film formation effect better.

[0011] In any embodiment, the alkaline compound includes one or more of calcium hydroxide, sodium hydroxide, lithium hydroxide, barium hydroxide, strontium hydroxide, radium hydroxide, cesium hydroxide, and rubidium hydroxide. These alkaline compounds are strong bases, exhibiting superior reaction with the aluminum foil of the current collector, resulting in a smoother surface finish.

[0012] In any embodiment, the mass fraction of the alkaline compound is 1%-5% based on the total mass of the first film layer. By controlling the mass fraction of the alkaline compound within the above range, it is beneficial to control the amount of alkaline compound reacting with aluminum within a preferred range.

[0013] In any embodiment, the resistivity of the first film layer is greater than that of the second film layer. In the embodiments of this application, by controlling the resistivity of the first film layer to be greater than that of the second film layer, the interfacial resistance between the current collector of the positive electrode and the second film layer is increased. During charging, due to the higher resistance, the amount of lithium ions released is less, which can reduce the occurrence of lithium dendrites or sodium dendrites deposited at the edge of the secondary battery.

[0014] In any embodiment, the ratio of the resistivity of the first film layer to the resistivity of the second film layer is greater than or equal to 1.2. In this embodiment, by controlling the ratio of the resistivity of the first film layer to the resistivity of the second film layer to be greater than or equal to 1.2, the interface resistance between the second film layer and the current collector is better, which can effectively improve the situation of lithium dendrites or sodium dendrites deposited at the edge of the secondary battery.

[0015] In any embodiment, the second film layer further includes a second binder. The mass fraction of the second binder in the second film layer is less than the mass fraction of the first binder in the first film layer. In the embodiments of this application, by controlling the mass fraction of the first binder in the first film layer to be larger, the adhesion between the first film layer and the current collector is stronger, thereby reducing the occurrence of positive electrode film layer detachment from the positive electrode sheet during battery charging and discharging.

[0016] In any embodiment, the first film layer includes a first conductive agent, and the second film layer includes a second conductive agent, wherein the mass fraction of the second conductive agent in the second film layer is less than the mass fraction of the first conductive agent in the first film layer. In this embodiment, by controlling the mass fraction of the first conductive agent in the first film layer to be greater than the mass fraction of the second conductive agent in the second film layer, it is beneficial that the resistance of the first film layer is greater than the resistance of the second film layer, which helps to reduce the precipitation of lithium dendrites or sodium dendrites at the edge of the negative electrode in the secondary battery.

[0017] In any embodiment, the mass ratio of the first conductive agent to the first binder in the first film layer is (1-40):(50-90). In this embodiment, by controlling the mass ratio of the first conductive agent to the first binder within the above range, the content of the first conductive agent and the first binder in the first film layer is optimal, resulting in a higher resistivity and better adhesion of the first film layer.

[0018] In any embodiment, the mass ratio of the positive electrode active material, the second conductive agent, and the second binder in the second film layer is (80-99):(1-10):(0.5-15). In this embodiment, by controlling the mass ratio of the positive electrode active material, the second conductive agent, and the second binder in the second film layer within the above range, the positive electrode active material in the second film layer of this embodiment can better extract or insert active ions.

[0019] In any embodiment, the width of the first film layer is 5mm-20mm. In this embodiment, the width of the first film layer refers to the distance from the center of the current collector to the long side of the current collector. By controlling the width of the first film layer to 5mm-20mm, the first film layer can effectively reduce the lithium ion extraction rate in the edge region, improve the situation of lithium dendrite or sodium dendrite precipitation at the edge, and reduce the occurrence of uneven electrolyte adsorption at the top of the battery.

[0020] In any embodiment, the width of the first film layer is 1%-10% of the width of the positive electrode film layer. By controlling the ratio of the width of the first film layer to the width of the positive electrode film layer within the above range, the first film layer can better improve the situation of lithium dendrites or sodium dendrites deposited at the edges.

[0021] In this embodiment of the application, the direction in which the width of the positive electrode film layer is located is parallel to the direction in which the width of the first film layer is located.

[0022] In any embodiment, the center of the current collector is oriented towards the tab, and the thickness of the first film layer gradually increases or remains constant. In this embodiment, by controlling the thickness of the first film layer to gradually increase or maintain a uniform thickness, the impact of thinner edge thickness caused during the fabrication of the positive electrode sheet on battery performance can be mitigated. Furthermore, by controlling the thickness of the first film layer to gradually increase, the precipitation of lithium dendrites or sodium dendrites at the edges of the secondary battery caused by the gradual thinning of the positive electrode sheet edge thickness can be mitigated.

[0023] In any embodiment, the areal density of the first film layer is 0.1 g / m³. 2 -10g / m 2 .

[0024] The second aspect of this application also includes an electrical device comprising the secondary battery of the first aspect. Since the electrical device of this application includes the secondary battery provided in the first aspect, it has at least the same advantages as the secondary battery of the first aspect.

[0025] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of a current collector according to an embodiment of this application.

[0027] Figure 2 This is a schematic diagram of the structure of an embodiment of the positive electrode sheet of this application.

[0028] Figure 3 This is a schematic diagram of another embodiment of the positive electrode sheet of this application.

[0029] Figure 4 This is a schematic diagram of the structure of a secondary battery according to an embodiment of this application.

[0030] Figure 5 This is an exploded structural diagram of an embodiment of the battery pack of this application.

[0031] Figure 6 This is a partial structural schematic diagram of an embodiment of the vehicle of this application.

[0032] 10. Secondary battery; 11. Cell assembly; 12. End cap; 12a. Electrode terminal; 13. Housing; 20. Box; 21. First part; 22. Second part; 100. Battery pack; 200. Controller; 300. Motor; 1000. Vehicle; 14. Positive electrode plate; 141. Current collector; 142. Positive electrode film; 1411. Main body area; 1412. Edge area; 1413. Tab; 1421. First film layer; 1422. Second film layer. Detailed Implementation

[0033] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the secondary battery, battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0034] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0036] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0037] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0038] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0039] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0040] In secondary batteries, the electrolyte is injected into the battery casing, but the electrolyte level within the casing does not reach the top of the cell. During cycling, insufficient electrolyte at the top of the cell leads to the precipitation of lithium or sodium dendrites at the edge of the negative electrode, resulting in a decrease in cell lifespan. Furthermore, the electrode fabrication typically involves coating a slurry containing active material onto the current collector. Generally, the positive electrode film layer near the tab is kept relatively thin. During charging and discharging of the secondary battery, the negative electrode layer near the tab (see

[1413] )... Figure 1 The charge density in the region is relatively high, which makes it easy for lithium dendrites or sodium dendrites to appear near the tab of the negative electrode, affecting the cycle performance of the secondary battery.

[0041] Based on this, the first aspect of this application provides a secondary battery, such as Figure 1 and Figure 2 As shown, the secondary battery includes a positive electrode 14, which includes a current collector 141 and a positive electrode film 142. The positive electrode film 142 is disposed on the surface of the current collector 141 and includes a first film layer 1421 and a second film layer 1422. The first film layer 1421 covers a portion of the current collector 141 near the tab 1413 and includes porous ceramic and a first binder. At least a portion of the second film layer 1422 is located on the surface of the first film layer 1421 away from the current collector 141, and the second film layer 1422 includes a positive electrode active material.

[0042] Specifically, in this embodiment, the current collector 141 includes a main region 1411 and an edge region 1412, with the edge region 1412 located between the main region 1411 and the tab 1413. A first film layer 1421 covers the edge region 1412; a second film layer 1422 covers the first film layer 1421 and the main region 1411 of the current collector 141.

[0043] In this embodiment, porous ceramics possess insulation and liquid absorption properties. By providing porous ceramics in the first film layer 1421 of the positive electrode 14, and with the first film layer 1421 covering a portion of the current collector near the tab 1413 (i.e., the first film layer 1421 covering the edge region 1412 of the current collector 141), the conductivity between the second film layer 1422 and the current collector 141 can be reduced. This results in a higher interface resistance of the positive electrode 14 during secondary battery charging, leading to a lower content of active ions such as lithium or sodium ions released. This reduces the occurrence of lithium dendrites or sodium dendrites depositing at the edge of the negative electrode in the secondary battery, thereby improving the battery's lifespan. Simultaneously, by providing porous ceramics... In the first film layer 1421, the porous ceramic in the first film layer 1421 can adsorb electrolyte, which can improve the uniformity of electrolyte around the positive electrode 14 in the secondary battery. This is beneficial to improving the secondary battery life degradation caused by insufficient electrolyte at the top during cycling. In this embodiment, the second film layer 1422 contains positive electrode active material. The second film layer 1422 is located on the side of the first film layer 1421 away from the current collector 141, so that during charging and discharging, the electrolyte first contacts the surface of the positive electrode film layer 142 (the surface away from the current collector 141), which is beneficial to the insertion or extraction of active ions into or out of the positive electrode active material and improves the cycle performance of the secondary battery.

[0044] In some embodiments, the mass fraction of porous ceramic is 1%-10% based on the total mass of the first membrane layer 1421. In this embodiment, controlling the mass fraction of porous ceramic within the above range optimizes the content of the adsorbed electrolyte. Specifically, the mass fraction of porous ceramic based on the total mass of the first membrane layer 1421 can be 1%, 3%, 4%, 5%, 8%, 8.6%, 9%, 9.3%, or 10%, or a range consisting of any two of the above values, such as 1%-3%, 3%-5%, 5%-8.6%, 8.6%-10%, etc.

[0045] In this embodiment, the porous ceramic can be made from metal oxides, silicon dioxide, silicon carbide, etc., through high-temperature calcination. It has open pores with a high porosity, and possesses both adsorption and insulation properties.

[0046] In some embodiments, the current collector 141 is made of aluminum, and the first film layer 1421 further includes an alkaline compound. The current collector 141 of the positive electrode 14 is generally aluminum foil. In this embodiment, the first film layer 1421 is close to the surface of the current collector 141. The first film layer 1421 includes an alkaline compound, which can react with the aluminum foil of the current collector 141, making the surface of the aluminum foil uneven. This results in a stronger bond between the first film layer 1421 and the current collector 141, improving the problem of material shedding during cycling of the positive electrode 14, thus enhancing the stability of the positive electrode 14, improving the cycle stability of the battery, and increasing the battery's lifespan.

[0047] In some embodiments, the porosity of the porous ceramic is 20%-70%. In this application, by controlling the porosity within the above range, the porous ceramic has a larger specific surface area and can store more electrolyte, which is beneficial for improving the amount of electrolyte adsorbed at the top of the secondary battery. The porosity of the porous ceramic can be 20%, 30%, 38%, 40%, 50%, 54%, 60%, 66%, 70%, etc., or a range of any two of the above values, such as 20%-38%, 38%-54%, 54%-70%, etc.

[0048] In some embodiments, the pore size of the porous ceramic is 200 nm to 10 μm. In the embodiments of this application, by controlling the pore size of the porous ceramic within the above range, the electrolyte stored in the porous ceramic is less likely to escape, which is beneficial to the better uniformity of the electrolyte in the secondary battery. The pore size of the porous ceramic can be 200 nm, 500 nm, 1 μm, 5 μm, 8 μm, 10 μm, etc., or any range of two of the above values, such as 200 nm-1 μm, 1 μm-5 μm, 5 μm-10 μm, etc.

[0049] In some embodiments, the volume average particle size Dv50 of the porous ceramic is 0.5 μm-50 μm. In the embodiments of this application, the volume average particle size Dv50 of the porous ceramic is within the above range, resulting in better uniformity of the first film layer and better film formation effect. The volume average particle size Dv50 of the porous ceramic is 0.5 μm, 1 μm, 10 μm, 30 μm, 40 μm, 46 μm, 50 μm, etc., or a range of any two of the above values, such as 0.5 μm-1 μm, 1 μm-30 μm, 30 μm-50 μm, etc.

[0050] In some embodiments, the alkaline compound includes one or more of calcium hydroxide, sodium hydroxide, lithium hydroxide, barium hydroxide, strontium hydroxide, radium hydroxide, cesium hydroxide, and rubidium hydroxide. These alkaline compounds are strong bases and react well with the aluminum foil of current collector 141, resulting in a smoother surface texture for current collector 141.

[0051] In some embodiments, the mass fraction of the alkaline compound is 1%-5% based on the total mass of the first film layer 1421. Controlling the mass fraction of the alkaline compound within the above range is beneficial for controlling the amount of alkaline compound reacting with aluminum within a preferred range. Specifically, the mass fraction of the alkaline compound based on the total mass of the first film layer 1421 can be 1%, 1.5%, 2%, 2.4%, 3%, 3.6%, 4%, or 5%, or a range consisting of any two of the above values, such as 1%-2.4%, 2.4%-3.6%, 3.6%-5%, etc.

[0052] In some embodiments, the resistivity of the first film layer 1421 is greater than the resistivity of the second film layer 1422. In this embodiment, by controlling the resistivity of the first film layer 1421 to be greater than the resistivity of the second film layer 1422, the interfacial resistance between the current collector 141 of the positive electrode 14 and the second film layer 1422 is increased. During charging, due to the higher resistance, the content of active ions such as lithium ions or sodium ions that are released is less, which can reduce the occurrence of lithium dendrites or sodium dendrites deposited at the edge of the secondary battery.

[0053] Among them, resistivity is common knowledge in the field, has a common meaning in the field, and can be measured by methods and instruments in the field.

[0054] In some embodiments, the ratio of the resistivity of the first film layer 1421 to the resistivity of the second film layer 1422 is greater than or equal to 1.2. In this embodiment, by controlling the ratio of the resistivity of the first film layer 1421 to the resistivity of the second film layer 1422 to be greater than or equal to 1.2, the interface resistance between the second film layer 1422 and the current collector 141 is optimized, which can effectively improve the situation of lithium dendrite or sodium dendrite precipitation at the edge of the secondary battery. The ratio of the resistivity of the first film layer 1421 to the resistivity of the second film layer 1422 can be 1.2, 1.5, 3, 5, 8, 8.5, 9, 10, 11, or 13, or a range of any two of the above values, such as 1.2-5, 5-8.5, 8.5-13, etc.

[0055] In some embodiments, the second film layer 1422 includes a second binder. The mass fraction of the second binder in the second film layer 1422 is less than the mass fraction of the first binder in the first film layer 1421. In this embodiment, by controlling the mass fraction of the first binder in the first film layer 1421 to be larger, the adhesion between the first film layer 1421 and the current collector 141 is stronger, thereby reducing the occurrence of the positive electrode film layer 142 of the positive electrode sheet 14 falling off during battery charging and discharging.

[0056] In some embodiments, the first film layer 1421 includes a first conductive agent, and the second film layer 1422 includes a second conductive agent, wherein the mass fraction of the second conductive agent in the second film layer 1422 is less than the mass fraction of the first conductive agent in the first film layer 1421. In this embodiment, by controlling the mass fraction of the first conductive agent in the first film layer 1421 to be greater than the mass fraction of the second conductive agent in the second film layer 1422, it is beneficial for the resistance of the first film layer 1421 to be greater than the resistance of the second film layer 1422, which helps to reduce the precipitation of lithium dendrites or sodium dendrites at the edge of the negative electrode in the secondary battery.

[0057] In some embodiments, the mass ratio of the first conductive agent to the first binder in the first film layer 1421 is (1-40):(50-90). In the embodiments of this application, by controlling the mass ratio of the first conductive agent to the first binder within the above range, the content of the first conductive agent and the first binder in the first film layer 1421 is optimal, resulting in a higher resistivity and better adhesion of the first film layer 1421. The mass ratio of the first conductive agent to the first adhesive can be 1:50, 20:50, 30:50, 40:50, 1:55, 1:60, 1:70, 1:80, 1:90, 20:60, 30:60, 30:70, 30:80, 30:90, 40:60, 40:80, 40:90, etc., or a range of any two of the above values, such as (1-20):(50-60), (20-30):(60-70), (30-40):(70-90), etc.

[0058] In some embodiments, the mass ratio of the positive electrode active material, the second conductive agent, and the second binder in the second film layer 1422 is (80-99):(1-10):(0.5-15). In this embodiment, by controlling the mass ratio of the positive electrode active material, the second conductive agent, and the second binder in the second film layer 1422 within the above range, the positive electrode active material in the second film layer 1422 in this embodiment can better extract or insert active ions. The mass ratio of the positive electrode active material, the second conductive agent, and the second binder can be 80:1:0.5, 80:3:0.5, 80:5:0.5, 80:8:0.5, 80:10:0.5, 82:1:0.5, 85:1:0.5, 88:1:0.5, 90:1:0.5, 95:1:0.5, 96:1:0.5, 99:1:0.5, 90:5:0.5, 90:5:10, 9 0:8:10, 90:10:10, 80:1:1, 80:1:3, 80:1:5, 80:1:8, 80:1:10, 80:1:12, 80:1:15, etc., or any range of values ​​composed of any two of the above, such as (80-88):(1-5):(0.5-5), (88-90):(5-8):(5-10), (90-99):(8-10):(10-15), etc.

[0059] Specific surface area is common knowledge in the field and has a common meaning in the field. It can be measured by methods and instruments in the field.

[0060] In some embodiments, the width of the first film layer 1421 is 5mm-20mm. In this embodiment, by controlling the width of the first film layer 1421, it is easier to control the rate at which lithium or sodium ions are removed from the edge region 1412, thus improving the situation of lithium or sodium dendrites depositing at the edge; and improving the uneven adsorption of electrolyte at the top of the secondary battery. The width of the first film layer 1421 can be 5mm, 8mm, 10mm, 12mm, 15mm, 18mm, 20mm, etc., or a range of any two of the above values, such as 5mm-10mm, 10mm-15mm, 15mm-20mm, etc.

[0061] In some embodiments, the width W1 of the first film layer 1421 is 1%-10% of the width W2 of the positive electrode film layer 142. By controlling the ratio of the width of the first film layer 1421 to that of the positive electrode film layer 142 within the above range, the first film layer 1421 can effectively reduce the occurrence of lithium dendrites or sodium dendrites at the edges. The width W1 of the first film layer 1421 can be 1%, 2%, 3%, 5%, 7%, 8%, 9%, 10%, etc., of the width W2 of the positive electrode film layer 142, or a range of any two of the above values, such as 1%-2%, 2%-5%, 5%-8%, 8%-10%, etc.

[0062] In some implementations, such as Figures 1-3 As shown, from the center of the current collector 141 toward the tab 1413, the thickness H of the first film layer 1421 gradually increases or remains constant. In this embodiment, by controlling the thickness H of the first film layer 1421 to gradually increase or remain uniform, the impact of the thin edge region 1412 on the performance of the secondary battery during the fabrication of the positive electrode 14 can be mitigated.

[0063] In some embodiments, the areal density of the first film layer 1421 is 0.1 g / m³. 2 -10g / m 2 The areal density of the first film layer 1421 can be 0.1 g / m³. 2 0.5g / m 2 0.8g / m 2 1g / m 2 3g / m 2 5g / m 2 7g / m 2 8g / m 2 9g / m 2 10g / m 2 etc., or a range of values ​​consisting of any two of the above values, such as 0.1 g / m 2 -3g / m 2 3g / m 2 -8g / m 2 8g / m 2 -10g / m 2 wait.

[0064] Among them, areal density is common knowledge in the field, has a common meaning in the field, and can be measured by methods and instruments in the field.

[0065] The second aspect of this application also includes an electrical device comprising the secondary battery of the first aspect. Since the electrical device of this application includes the secondary battery provided in the first aspect, it has at least the same advantages as the secondary battery of the first aspect.

[0066] In addition, please refer to the appendix as appropriate below. Figure 4 , Figure 5 and Figure 6 As shown, the secondary battery 10 and battery pack 100 of this application (see...) Figure 5 The description includes the electrical equipment.

[0067] In the embodiments of this application, the secondary battery 10 further includes an electrolyte and a separator, the separator being disposed on the positive electrode 14 (see...). Figure 2 The active ions (Li) between the positive and negative electrodes primarily prevent short circuits and allow ions to pass through. During the charging and discharging process of a secondary battery, the active ions (Li)... + The electrolyte moves back and forth between the positive electrode 14 and the negative electrode, inserting and removing itself, while also acting as a conductor for ions between them.

[0068] As an example, the current collector of the positive electrode 14 is called the positive current collector. The positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0069] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0070] In some embodiments, when the secondary battery 10 is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides, such as LiNi 1 / 3 Co 1 / 3Mn 1 / 3O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0071] In one embodiment, when the secondary battery 10 is a sodium-ion battery, the positive electrode material includes one or more of the following: polyanionic positive electrode materials, phosphate-based positive electrode materials, sulfate-based positive electrode materials, silicate-based positive electrode materials, and borate-based positive electrode materials. For example, in the positive electrode active material of a sodium-ion battery, the polyanionic compound includes compounds based on phosphoric acid and fluorophosphoric acid. Phosphoric acid-based compounds include Na... x1 Fe y1 P m1 O n1 For example, sodium iron phosphate has a high capacity, and sodium iron pyrophosphate has a high voltage platform. Polyanionic compounds include one or more of sodium vanadium trifluorophosphate Na3V2(PO4)2F3, sodium vanadium fluorophosphate NaVPO4F, sodium vanadium phosphate Na3V2(PO4)3, Na4Fe3(PO4)2P2O7, NaFePO4, and Na3V2(PO4)3. Prussian blue compounds are Na... x MM(CN)6, wherein M and M are one or more of Fe, Mn, Co, Ni, Cu, Zn, Cr, Ti, V, Zr, and Ce, and 0 < x ≤ 2. The positive electrode active material in a lithium metal battery may include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, or lithium manganese iron phosphate.

[0072] In some embodiments, the first adhesive and the second adhesive may each include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0073] In some embodiments, the first conductive agent and the second conductive agent may each include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0074] The negative electrode current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector. The active material layer of the negative electrode sheet is disposed on at least one surface of the negative electrode current collector.

[0075] In some embodiments, the current collector of the negative electrode may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0076] In some embodiments, the active material layer includes a negative electrode active material, which may include one or more of silicon-based materials, silicon-carbon materials, carbon materials, and selenium-based materials. Specifically, it includes one or more of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials, and selenium-based materials. Silicon-based materials may be selected from one or more of elemental silicon, silicon oxide compounds (e.g., silicon suboxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Selenium-based materials may be selected from one or more of elemental selenium, selenium oxide compounds, and selenium alloys.

[0077] In some embodiments, the active material layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0078] In some embodiments, the active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0079] In some embodiments, the active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0080] The electrolyte acts as a conductor of ions between the positive electrode 14 and the negative electrode. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements.

[0081] In some embodiments, the electrolyte includes an electrolyte salt and a solvent.

[0082] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0083] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0084] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0085] In some embodiments, the secondary battery 10 also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0086] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0087] In some implementations, the positive electrode 14, the negative electrode, and the separator can be manufactured into a cell assembly using a winding process or a stacking process.

[0088] In some implementations, such as Figure 4 As shown, the secondary battery 10 may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned cell assembly 11 and electrolyte. The outer packaging includes an end cap 12, a housing 13, and other functional components.

[0089] End cap 12 refers to a component that covers the opening of housing 13 to isolate the internal environment of secondary battery 10 from the external environment. The shape of end cap 12 can be adapted to the shape of housing 13 to fit it. Optionally, end cap 12 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 12 is not easily deformed under pressure and impact, giving secondary battery 10 higher structural strength and improved safety performance. Functional components such as electrode terminals 12a can be provided on end cap 12. Electrode terminals 12a can be used for electrical connection with cell assembly 11 to output or input electrical energy to secondary battery 10. In some embodiments, end cap 12 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of secondary battery 10 reaches a threshold. The material of end cap 12 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose special limitations on this. In some embodiments, an insulating element (not shown) may be provided on the inner side of the end cap 12. The insulating element can be used to isolate the electrical connection components within the housing 13 from the end cap 12 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0090] The housing 13 is a component used to cooperate with the end cap 12 to form the internal environment of the secondary battery 10. This internal environment can accommodate the cell assembly 11, electrolyte, and other components. The housing 13 and the end cap 12 can be independent components. An opening can be provided on the housing 13, and the end cap 12 closes the opening to form the internal environment of the secondary battery 10. Alternatively, the end cap 12 and the housing 13 can be integrated. Specifically, the end cap 12 and the housing 13 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 13, the end cap 12 closes the housing 13. The housing 13 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 13 can be determined according to the specific shape and size of the cell assembly 11. The material of the housing 13 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0091] The casing 13 may contain one or more battery cell assemblies 11. The portions of the positive and negative electrode plates that lack active material each constitute tabs 1413. The positive and negative tabs may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs 1413 connect to the electrode terminals to form a current loop.

[0092] Please refer to Figure 5 The battery pack 100 includes a housing 20 and a secondary battery 10, with the secondary battery 10 housed within the housing 20. The housing 20 provides a space for the secondary battery 10 and can have various structures. In some embodiments, the housing 20 may include a first portion 21 and a second portion 22, which overlap each other, jointly defining a space for accommodating the secondary battery 10. The second portion 22 may be a hollow structure with one open end, and the first portion 21 may be a plate-like structure, covering the open side of the second portion 22 so that the first portion 21 and the second portion 22 jointly define the space. Alternatively, both the first portion 21 and the second portion 22 may be hollow structures with one open side, with the open side of the first portion 21 covering the open side of the second portion 22. Of course, the housing 20 formed by the first portion 21 and the second portion 22 can have various shapes, such as a cylinder or a cuboid.

[0093] In the battery pack 100, there can be multiple secondary batteries 10, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that some of the secondary batteries 10 are connected in series and others in parallel. Multiple secondary batteries 10 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple secondary batteries 10 is housed within the housing 20. Alternatively, the battery pack 100 can also consist of multiple secondary batteries 10 first connected in series, parallel, or in a mixed manner to form battery modules, and then these battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 20. The battery pack 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple secondary batteries 10.

[0094] The battery pack 100 in this embodiment includes a lithium-ion battery as a secondary battery 10. In other embodiments, the battery pack 100 may further include any one or more of lithium-sulfur batteries, sodium-ion batteries, and magnesium-ion batteries, but is not limited thereto. The secondary battery 10 may be cylindrical, flat, cuboid, or other shapes.

[0095] In addition, this application also provides an electrical device, which includes at least one of the secondary battery 10 and / or battery pack 100 provided in this application. The secondary battery 10 or battery pack 100 can be used as the power source of the electrical device, or it can be used as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0096] As an electrical device, a secondary battery 10 and / or a battery pack 100 can be selected according to its usage requirements.

[0097] Figure 6 The diagram shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. A structural schematic diagram of the vehicle 1000 is provided. The vehicle 1000 internally houses a secondary battery 10 (see...). Figure 4 The secondary battery 10 or battery pack 100 can be located at the bottom, head, or tail of the vehicle 1000. The secondary battery 10 or battery pack 100 can be used to power the vehicle 1000; for example, it can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 controls the secondary battery 10 or battery pack 100 to supply power to the motor 300, for example, to meet the power requirements of the vehicle 1000 during startup, navigation, and driving.

[0098] In some embodiments of this application, the secondary battery 10 or battery pack 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0099] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0100] Example 1

[0101] 1) such as Figure 1 and Figure 2 As shown, the preparation method of the positive electrode 14 is as follows:

[0102] Conductive carbon black (Super-P), polyvinylidene fluoride (PVDF), strong calcium oxide and porous ceramics are mixed with N,N-dimethylpyrrolidone (NMP) in a mass ratio of 40%:54%:1%:5% and stirred evenly to obtain a first slurry, wherein the porosity of the porous ceramics is 20%.

[0103] Lithium iron phosphate, conductive carbon black (Super-P), and polyvinylidene fluoride (PVDF) were mixed with N,N-dimethylpyrrolidone (NMP) in a mass ratio of 96%:2%:2% and stirred until homogeneous to obtain a second slurry.

[0104] The first slurry is coated on both sides of the positive electrode current collector aluminum foil with a certain width. After drying, a first film layer 1421 is formed. The first film layer 1421 is located on the edge region 1412 of the positive electrode current collector, and the thickness of the first film layer 1421 is uniform, that is, the first film layer 1421 covers the edge region 1412. Then, a second slurry is coated on the first film layer 1421 and the main region 1411 of the positive electrode current collector to form a second film layer 1422. The second film layer 1422 covers the surface of the first film layer 1421 away from the positive electrode current collector and the main region 1411 of the positive electrode current collector to form a positive electrode film layer 142. Then, the positive electrode sheet 14 is obtained by cold pressing and slicing.

[0105] The first film layer 1421 has a width of 10 mm, and the positive electrode film layer 142 has a width of 500 mm. The width of the first film layer 1421 is 2% of the width of the positive electrode film layer 142. The resistivity of the first film layer 1421 is 0.42 Ω·cm. From the center of the current collector 141 towards the tab 1413, the thickness of the first film layer 1421 remains constant. In the positive electrode sheet 14, the areal density of the first film layer 1421 is 0.1 g / m³. 2 The resistivity of the second film layer 1422 is 0.3 Ω·cm, and the resistivity ratio of the first film layer to the second film layer is 1.2.

[0106] 2) Preparation method of negative electrode sheet:

[0107] Graphite, conductive carbon SP, and binder SBR are dry-mixed at a ratio of 97:1:2, then deionized water is added to adjust the solid content to 45%-55%. After stirring evenly, a negative electrode slurry is obtained, which is then coated, dried, cold-pressed, and slit to form a negative electrode sheet.

[0108] 3) Preparation method of secondary battery:

[0109] The positive electrode 14, the separator, and the negative electrode are wound into a cell assembly. The assembly is then welded with tabs 1413, packaged in an aluminum shell, injected with electrolyte, formed through encapsulation, and vacuum-formed to obtain a secondary battery. The injected electrolyte is a 1 mol / L LiPF6 solution, with ethylene carbonate (EC) and dimethyl carbonate (DMC) as solvents, in a volume ratio of 1:2. In this embodiment, the separator is made of 7 μm thick polyethylene (PE). The secondary battery obtained in this application embodiment includes a positive electrode 14 and a negative electrode. The positive electrode 14 includes a positive current collector and a positive electrode film 142 disposed on the surface of the positive current collector. The positive electrode film 142 includes a first film 1421 and a second film 1422. The first film 1421 is close to the surface of the current collector and covers the edge region 1412. The first film 1421 includes a first conductive agent, conductive carbon black (Super-P), porous ceramic, a first binder, polyvinylidene fluoride (PVDF), and calcium hydroxide.

[0110] The process parameters and performance parameters of Examples 2-10 are detailed in Table 1, and the others are similar to those of Example 1.

[0111] Comparative Example 1

[0112] The difference between this comparative example of a secondary battery and its preparation method and Example 1 lies in the preparation method of the positive electrode sheet: lithium iron phosphate, conductive carbon black (Super-P), and polyvinylidene fluoride (PVDF) are mixed with N,N-dimethylpyrrolidone (NMP) in a mass ratio of 96%:2%:2%, and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on both sides of the positive electrode current collector aluminum foil, dried to form a positive electrode film layer, and then cold-pressed and sliced ​​to obtain the positive electrode sheet. Other aspects are the same as in Example 1 and will not be repeated here.

[0113] The secondary batteries of Examples 1-11 and Comparative Example 1 were subjected to relevant tests:

[0114] 1) Test for precipitation of lithium dendrites or sodium dendrites.

[0115] At 25°C, charge at a constant current of 1 / 3C (nominal capacity) to a termination voltage of 3.8V, then charge at a constant voltage to 0.05C. 标 Let it sit for 5 minutes, then add 1 / 3C 标 Discharge to the discharge cutoff voltage of 2.0V to obtain the discharge energy E and capacity C. The obtained capacity is recorded as the initial capacity C0. Repeat the above steps for the same secondary battery, performing a cyclic test. Charge the battery to 3.8V, let it stand for 5 minutes, and determine whether the secondary battery has lithium plating based on the change in voltage and time (Dv / dt). If a significant peak appears, it is determined that the secondary battery has lithium plating. Disassemble the secondary battery to further observe whether there is lithium plating on the surface of the positive and negative electrode plates.

[0116] 2) Volume average particle size Dv50 test.

[0117] Equipment Model: Malvern 3000 (MasterSizer 3000) laser particle size analyzer; Reference Standard Procedure: GB / T19077~2016 / ISO 13320:2009; Specific Test Procedure: Take an appropriate amount of the sample to be tested (the sample concentration should be 8%~12% opacity), add 20ml of deionized water, and simultaneously incubate for 5 minutes (53KHz / 120W) to ensure complete dispersion of the sample. Then, measure the sample according to the GB / T19077~2016 / ISO 13320:2009 standard.

[0118] 3) Aperture testing.

[0119] The TriStarⅡ3020 pore size distribution instrument was used for testing. By adsorbing gas onto the test material under a series of gradually increasing pressures at a constant temperature, the pore size and pore volume distribution of porous ceramics can be characterized by the curves of the volume of each pore size versus the corresponding partial pressure; the average pore size can be obtained by further calculation.

[0120] 4) Porosity testing.

[0121] The true density of a material is obtained by testing it with a true density meter (e.g., AccuPycⅡ1340). The specific procedure involves weighing a sample of a certain mass, placing it in the true density meter, sealing the testing system, and introducing helium gas according to the prescribed procedure. By detecting the gas pressure in the sample chamber and the expansion chamber, and then applying Bohr's Law (PV = nRT), the true volume V can be calculated. r Then the true density ρ r =m / V r The apparent density of a material can be obtained by loading a certain mass of powder into a cylindrical mold with an inner diameter of 10 mm and applying a pressure of 200 MPa to obtain the apparent volume V0 of the powder. Then the apparent density of the material is ρ0 = m / V0.

[0122] 5) Resistivity test.

[0123] After the first film layer is coated on the positive electrode and dried, it is cut into small round pieces with a diameter of 3mm. The Yuaneng Technology electrode resistance meter is powered on, and the probe is positioned appropriately. The "Start" button is clicked, and the reading is taken once it stabilizes. Two locations are tested for each small round piece. The average of the six measurements is calculated to determine the resistance of the first film layer, and the resistivity is also calculated.

[0124] Cut the completed positive electrode sheet into small round pieces with a diameter of 3mm from the center. Turn on the Yuaneng Technology electrode resistance meter, place the probe at the appropriate position on the meter, and click the "Start" button. Once the reading stabilizes, take the reading. Test two positions for each small round piece, and finally calculate the average of the six measurements. This average value is the resistance of the second film layer, and the resistivity is also calculated.

[0125] 6) Surface density test.

[0126] 1) After the first film layer is coated on the positive electrode sheet and dried, the positive electrode sheet coated with the first film layer is punched to obtain a circular sample, and the cross-sectional area A on the thickness of the circular sample is measured.

[0127] 2) Weigh the mass m1 of the sample and measure the thickness d1 of the sample.

[0128] 3) Confirm the number of faces of the positive electrode sheet coated with the first film layer. The number of faces is 1 or 2.

[0129] 4) Clean the sample. Use NMP (N-methylpyrrolidone) solution to clean the positive electrode sample coated with the first film layer.

[0130] 5) Weigh the mass m2 of the substrate and measure the thickness d2 of the substrate.

[0131] 6) The areal density of the first film layer = (m1-m2) / (number of surfaces * A).

[0132] The process parameters and performance of each embodiment and comparative example are shown in Table 1 below.

[0133]

[0134] As shown in Table 1, the test results indicate that, compared to Comparative Example 1 where lithium dendrites began to precipitate after 400 cls of cycling, the number of cycles at which lithium dendrites began to precipitate in Examples 1-11 of this application was 410 cls-610 cls, a significant increase. This demonstrates that by setting a first film layer on the positive electrode and adding porous ceramic to the first film layer, Examples 1-11 of this application can improve the uniformity of electrolyte distribution in the secondary battery, resulting in sufficient electrolyte at the top of the cell and thus improving the cycle life of the secondary battery. Simultaneously, the porous ceramic located in the first film layer increases the resistance of the first film layer, which can improve the situation of lithium dendrite precipitation at the edge of the secondary battery. Based on Examples 6 and 7, it can be seen that adding alkaline compounds to the first film layer is beneficial to improving the cycle performance of the secondary battery.

[0135] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery characterized by comprising: The secondary battery comprises a positive electrode tab, the positive electrode tab comprises a current collector and a positive electrode film layer, the positive electrode film layer is arranged on the surface of the current collector, the positive electrode film layer comprises a first film layer and a second film layer, the first film layer is close to the surface of the current collector, the first film layer covers the partial area of the current collector close to the tab, the first film layer comprises porous ceramic and a first binder; the second film layer is at least partially located on the surface of the first film layer away from the current collector, and the second film layer comprises a positive electrode active material.

2. The secondary battery according to claim 1, characterized by The mass fraction of the porous ceramic is 1%-10% based on the total mass of the first film layer.

3. The secondary battery according to claim 1 or 2, characterized by The porosity of the porous ceramic is 20%-70%.

4. The secondary battery according to any one of claims 1 to 3, characterized by The material of the current collector comprises aluminum, and the first film layer further comprises an alkaline compound.

5. The secondary battery according to claim 4, characterized by The alkaline compound comprises one or two or more of calcium hydroxide, sodium hydroxide, lithium hydroxide, barium hydroxide, strontium hydroxide, radium hydroxide, cesium hydroxide and rubidium hydroxide.

6. The secondary battery according to claim 4 or 5, characterized by The mass fraction of the alkaline compound is 1%-5% based on the total mass of the first film layer.

7. The secondary battery according to any one of claims 1 to 6, characterized by The resistivity of the first film layer is greater than the resistivity of the second film layer.

8. The secondary battery according to any one of claims 1 to 7, characterized by The ratio of the resistivity of the first film layer to the resistivity of the second film layer is greater than or equal to 1.

2.

9. The secondary battery according to any one of claims 1 to 8, characterized by, The second film layer comprises a second binder, and the mass fraction of the second binder in the second film layer is less than the mass fraction of the first binder in the first film layer.

10. The secondary battery according to any one of claims 1 to 9, characterized by The first film layer comprises a first conductive agent, and the second film layer comprises a second conductive agent, and the mass fraction of the second conductive agent in the second film layer is less than the mass fraction of the first conductive agent in the first film layer.

11. The secondary battery according to claim 10, characterized by In the first film layer, the mass ratio of the first conductive agent to the first binder is (1-40):(50-90).

12. The secondary battery according to any one of claims 1 to 11, characterized by The width of the first film layer is 5mm-20mm.

13. The secondary battery according to any one of claims 1 to 12, characterized by The width of the first film layer is 1%-10% of the width of the positive electrode film layer.

14. The secondary battery according to claim 12 or 13, characterized by From the center position of the current collector towards the direction of the tab, the thickness of the first film layer gradually increases or remains equal.

15. An electric device comprising the secondary battery according to any one of claims 1-14.

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