Electrochemical device and electric equipment

Abstract

The application relates to an electrochemical device and an electric equipment, the electrochemical device comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector, a first safety layer and a first positive electrode active material layer, the positive electrode sheet comprising a first region provided with the first positive electrode active material layer, the first safety layer comprising a first part located in the first region, the first part being arranged between the positive electrode current collector and the first positive electrode active material layer. The coefficient of variation delta 1 of the resistance R of the positive electrode sheet in the first region of the electrochemical device at 25 DEG C in a full charge state is less than or equal to 15%. The electrochemical device can have good low-temperature performance while meeting the safety performance of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to an electrochemical device and electrical equipment. Background Technology

[0002] With the widespread use of electronic products such as laptops, mobile phones, and tablets, and the rapid development of the electric vehicle industry, people are placing increasingly stringent safety requirements on electrochemical devices (such as lithium-ion batteries). Currently, lithium-ion batteries still experience safety incidents such as fires and explosions due to external impacts or compression during use. Furthermore, the capacity of lithium-ion batteries is limited in cold winters, further hindering their widespread application. Summary of the Invention

[0003] In view of this, this application provides an electrochemical device and electrical equipment that, while meeting the safety performance requirements of the electrochemical device, also possesses excellent low-temperature performance.

[0004] In a first aspect, this application provides an electrochemical device including a positive electrode sheet. The positive electrode sheet includes a positive current collector, a first safety layer, and a first positive active material layer. The positive electrode sheet includes a first region where the first positive active material layer is disposed. The first safety layer includes a first portion located in the first region, the first portion being disposed between the positive current collector and the first positive active material layer. Under full charge at 25°C, the coefficient of variation δ1 of the resistance R of the positive electrode sheet in the first region is ≤15%.

[0005] In the above technical solution, when the electrochemical device is fully charged at 25°C, the coefficient of variation of the resistance R of the first region of the positive electrode (the first part having the first positive electrode active material layer and the first safety layer) is small. This not only ensures the safety performance of the electrochemical device, but also maintains a better transmission interface between the first safety layer and the first positive electrode active material layer, reducing the risk that the first positive electrode active material layer cannot be effectively charged and discharged at low temperatures, thereby improving the low-temperature performance of the electrochemical device.

[0006] In some embodiments, when the electrochemical device is fully charged at 25°C, the average resistance R1 of the positive electrode in the first region satisfies: 8Ω / cm. 2 ≤R1≤100Ω / cm 2 If the average resistance R1 of the first region of the positive electrode is within the above range, the low-temperature performance of the electrochemical device can be further improved while enhancing its safety performance.

[0007] In some embodiments, the positive electrode sheet further includes a second region without the first positive electrode active material layer, and the first safety layer includes a second portion located in the second region; when the electrochemical device is fully charged at 25°C, the coefficient of variation δ2 of the resistance R of the positive electrode sheet in the second region is ≤10%. In the above technical solution, the region without the first positive electrode active material layer is the empty foil region of the positive electrode current collector. During the extrusion process, the empty foil region is prone to contact with the negative electrode, which affects the safety performance. Both the first and second regions contain the first safety layer, which can improve the safety of the electrochemical device and greatly improve the preparation efficiency of the positive electrode sheet. At the same time, the coefficient of variation of the resistance R of the second region of the positive electrode sheet (the second portion with the first safety layer) is small, which can reduce the risk of local leakage of the second portion of the first safety layer, thereby reducing the risk of the empty foil region contacting the negative electrode during the extrusion process, and thus further improving the safety performance of the electrochemical device.

[0008] In some embodiments, when the electrochemical device is fully charged at 25°C, the average resistance R2 of the positive electrode in the second region satisfies: 5Ω / cm. 2 ≤R2≤100Ω / cm 2 The average resistance R2 of the second region of the positive electrode is within the above range, which can further improve the safety performance of the electrochemical device while further improving its low-temperature performance.

[0009] In some embodiments, when the electrochemical device is fully charged at 25°C, the average resistance R1 of the positive electrode in the first region and the average resistance R2 of the positive electrode in the second region satisfy the condition that R2 / R1 ≥ 60%. This improves the safety performance of the electrochemical device.

[0010] In some embodiments, the positive electrode sheet further includes a second safety layer and a second positive electrode active material layer. The second safety layer includes a third portion located in the first region and a fourth portion located in the second region. The second positive electrode active material layer includes a fifth portion located in the first region and a sixth portion located in the second region. The third portion is disposed between the positive electrode current collector and the fifth portion, and the fourth portion is disposed between the positive electrode current collector and the sixth portion.

[0011] In some embodiments, the thickness of the first safety layer is 0.5 μm to 10 μm. In some embodiments, the thickness of the second safety layer is 0.5 μm to 10 μm. This can improve the safety performance of the electrochemical device while ensuring its energy density.

[0012] In some embodiments, the diameter of the missed coating point in the second part is Diameter satisfies The number of missed spots should not exceed 30 / m 2 The diameter satisfies The number of missed coating spots should not exceed 5 / m2 It does not exist. The number of uncoated spots with larger diameters is smaller, which makes the first safety layer more uniform, thereby achieving a coefficient of variation δ2 ≤ 10% for the resistance R of the second region of the positive electrode.

[0013] In some embodiments, the material of the first safety layer includes first inorganic insulating particles, a first conductive agent, a first binder, and optionally a first leveling agent; the material of the second safety layer includes second inorganic insulating particles, a second conductive agent, a second binder, and optionally a second leveling agent. Both the first and second portions of the first safety layer contain the first inorganic insulating particles, the first conductive agent, and the first binder, which makes the first safety layer more uniform and facilitates the preparation of the positive electrode sheet. Simultaneously, the second safety layer contains the second inorganic insulating particles, the second conductive agent, and the second binder, which can meet the safety performance requirements of the electrochemical device.

[0014] In some embodiments, the specific surface area of ​​the first inorganic insulating particle is 1 m². 2 / g~50m 2 / g. In some embodiments, the specific surface area of ​​the second inorganic insulating particles is 1m². 2 / g~50m 2 / g. This can reduce the number of missed spots in the first / second safety layer.

[0015] In some embodiments, based on the mass of the first safety layer, the mass percentage of the first inorganic insulating particles is 65% to 98.9%, the mass percentage of the first binder is 1% to 20%, the mass percentage of the first conductive agent is 0.1% to 10%, and the mass percentage of the first leveling agent is 0% to 5%. A higher content of the first insulating particles and a relatively lower content of the first conductive agent allows for better safety performance of the electrochemical device while still satisfying current collection requirements.

[0016] In some embodiments, based on the mass of the second safety layer, the mass percentage of the second inorganic insulating particles is 65%–98.9%, the mass percentage of the second binder is 1%–20%, the mass percentage of the second conductive agent is 0.1%–10%, and the mass percentage of the second leveling agent is 0%–5%. A higher content of second insulating particles and a relatively lower content of the second conductive agent allows for better safety performance of the electrochemical device while still satisfying current collection requirements.

[0017] In some embodiments, the first adhesive and / or the second adhesive each independently include at least one of olefin polymers, acrylic polymers, amide polymers, fluoroolefin polymers, carboxymethyl cellulose salts, and rubbers.

[0018] In some embodiments, the first inorganic insulating particle and / or the second inorganic insulating particle each independently comprise at least one of boehmite, alumina, titanium oxide, silicon oxide, magnesium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium sulfate, calcium sulfate, calcium silicate, and silicon carbide.

[0019] In some embodiments, the first conductive agent and / or the second conductive agent each independently include at least one of particulate, sheet-like, mesh-like, or linear conductive agents.

[0020] In some embodiments, the first leveling agent and / or the second leveling agent each independently comprise at least one of an olefin derivative polymer, an acrylate polymer, a siloxane polymer, an acrylate polymer, an alcohol compound, an ether compound, or a fluorocarbon compound.

[0021] In a first aspect, this application provides an electrical device that includes the electrochemical device provided in any of the embodiments of the first aspect described above. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings.

[0023] Figure 1 This is a schematic diagram of the structure of an electrode assembly provided in some embodiments of this application;

[0024] Figure 2 This is a schematic diagram of the structure of the positive electrode sheet provided in some embodiments of this application;

[0025] Figure 3 This is a schematic diagram of the structure of a wound electrode assembly provided in some embodiments of this application;

[0026] Figure 4 This is a schematic diagram of the structure of the negative electrode sheet provided in some embodiments of this application.

[0027] Icons: 10-Electrode assembly; 11-Positive electrode; 12-Negative electrode; 13-Separator; 131-First separator; 132-Second separator;

[0028] 111-Positive current collector; 112-First safety layer; 113-First positive active material layer; 114-First region; 115-Second region; 1121-First part; 1122-Second part; 116-Second safety layer; 117-Second positive active material layer; 1161-Third part; 1162-Fourth part; 1171-Fifth part; 1172-Sixth part; 118-Wound single-sided area tail section;

[0029] 121-Second negative electrode active material layer; 122-Negative electrode current collector; 123-First negative electrode active material layer; 124-Third region; 125-Fourth region; 126-Starting section of single-sided winding region; 141-Positive electrode tab; 142-Negative electrode tab. Detailed Implementation

[0030] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0032] In the description of the embodiments of this application, the terms "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order, or primary and secondary relationship of the indicated technical features.

[0033] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0034] In the description of the embodiments of this application, the technical 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" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0035] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" 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. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0036] The electrochemical device includes an electrode assembly and a housing, with the electrode assembly housed within the housing. The electrode assembly can be a wound structure or a stacked structure. Figure 1 For a schematic diagram of the structure of the electrode assembly 10 provided in some embodiments of this application, please refer to... Figure 1 The electrode assembly 10 includes a positive electrode 11, a negative electrode 12, and a separator 13 disposed between the positive electrode 11 and the negative electrode 12. The positive electrode 11, the first separator 131, the negative electrode 12, and the second separator 132 can be used as one electrode unit, which is then wound to form a wound structure; alternatively, the positive electrode 11, the first separator 131, the negative electrode 12, and the second separator 132 can be used as one electrode unit, and multiple electrode units can be stacked sequentially to form a laminated structure.

[0037] The separator 13 is a component that separates the positive electrode 11 and the negative electrode 12. The separator 13 can be made of various materials, such as PP (polypropylene) and PE (polyethylene).

[0038] Figure 2 This is a schematic diagram of the structure of the positive electrode 11 provided in some embodiments of this application. Please refer to... Figure 2 The positive electrode 11 includes a positive current collector 111, a first safety layer 112, and a first positive active material layer 113. The positive electrode 11 includes a first region 114 where the first positive active material layer 113 is disposed. The first safety layer 112 includes a first portion 1121 located in the first region 114, and the first portion 1121 is disposed between the positive current collector 111 and the first positive active material layer 113. In a fully charged state at 25°C, the coefficient of variation δ1 of the resistance R of the positive electrode 11 in the first region 114 is ≤15%.

[0039] The positive electrode current collector 111 can be aluminum foil, aluminum foam, aluminum composite current collector (with a polymer support layer in the middle, and aluminum metal layers on both surfaces of the support layer), nickel foil, nickel foam, etc. The first positive electrode active material layer 113 refers to a layer structure containing positive electrode active material, which can be lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, etc.

[0040] The first safety layer 112 has a certain degree of conductivity, which can improve the safety performance of the electrochemical device while ensuring the current collection of the positive electrode current collector 111. At the same time, when the electrochemical device is fully charged at 25°C, the coefficient of variation of the resistance R of the first region 114 of the positive electrode 11 is small, which can reduce the polarization difference of the first region 114 at low temperature, reduce the risk of ineffective charging and discharging of the first region 114 at low temperature, and thus improve the low-temperature performance of the electrochemical device.

[0041] Please continue to refer to Figure 2 Along the thickness direction of the positive electrode sheet 11, the first region 114 includes a positive current collector 111, a first part 1121 of the first safety layer 112, and a first positive active material layer 113 stacked sequentially.

[0042] The 25°C full charge state of an electrochemical device refers to the following: at 25°C, the electrochemical device is charged to the design voltage by a constant current, and then charged to the design cutoff current by a constant voltage at the design voltage. At this point, the electrochemical device has reached the full charge state.

[0043] The coefficient of variation δ1 of the resistance R of the positive electrode 11 in the first region 114 refers to: using a film resistance tester to test the resistance of the first region 114 of the positive electrode 11, at least 15 different points are tested, and then the resistance value of a single test point is recorded as Ra. Each test point has a Ra, the average value of all Ra is recorded as R1, and then the standard deviation of all Ra is calculated and recorded as σa. The coefficient of variation δ1 = σa / R1.

[0044] As an example, in the fully charged state at 25°C, the coefficient of variation δ1 of the resistance R of the positive electrode 11 in the first region 114 is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%, and it can also be any value within the above range.

[0045] Optionally, under full charge at 25°C, the coefficient of variation δ1 of the resistance R of the positive electrode 11 in the first region 114 is ≤8%, which can further improve the low-temperature performance of the electrochemical device. Further, the coefficient of variation δ1 of the resistance R of the positive electrode 11 in the first region 114 is ≤5%.

[0046] In some embodiments, when the electrochemical device is fully charged at 25°C, the average resistance R1 of the positive electrode 11 in the first region 114 satisfies: 8Ω / cm. 2 ≤R1≤100Ω / cm 2 The resistance values ​​of multiple test points in the first region 114 of the positive electrode 11, measured by the aforementioned diaphragm resistance tester, are denoted as Ra, and the average value of the multiple Ra values ​​is denoted as R1, 8Ω / cm. 2≤R1≤100Ω / cm 2 The average resistance R1 of the first region 114 of the positive electrode 11 is within the above-mentioned range, which can improve the safety performance of the electrochemical device while further improving its low-temperature performance.

[0047] As an example, the average resistance R1 of the positive electrode 11 in the first region 114 is 8 Ω / cm. 2 10Ω / cm 2 15Ω / cm 2 20Ω / cm 2 30Ω / cm 2 40Ω / cm 2 50Ω / cm 2 60Ω / cm 2 70Ω / cm 2 80Ω / cm 2 90Ω / cm 2 Or 100Ω / cm 2 It can also be any value within the above range.

[0048] Optionally, the average resistance R1 of the positive electrode 11 in the first region 114 satisfies: 10Ω / cm 2 ≤R1≤40Ω / cm 2 This can improve the safety performance of the electrochemical device while further enhancing its low-temperature performance. Further, optionally, the average resistance R1 of the positive electrode 11 in the first region 114 satisfies: 25 Ω / cm. 2 ≤R1≤32Ω / cm 2 .

[0049] Please continue to refer to Figure 2 The positive electrode 11 also includes a second region 115 without the first positive electrode active material layer 113, and the first safety layer 112 includes a second part 1122 located in the second region 115; when the electrochemical device is fully charged at 25°C, the coefficient of variation δ2 of the resistance R of the positive electrode 11 in the second region 115 is ≤10%.

[0050] Please continue to refer to Figure 2 The positive electrode 11 includes a first region 114 and a second region 115. Along the thickness direction of the positive electrode, the first region 114 includes a positive current collector 111, a first portion 1121 of a first safety layer 112, and a first positive active material layer 113, stacked sequentially. The second region 115 includes the positive current collector 111 and a second portion 1122 of the first safety layer 112, stacked sequentially. Figure 2 The dotted lines in the diagram represent divisions; the area to the left of the dotted lines is the first region 114, and the area to the right of the dotted lines is the second region 115.

[0051] Figure 3 This is a schematic diagram of the structure of a wound electrode assembly 10 provided in some embodiments of this application. A positive electrode 11, a first separator 131, a negative electrode 12, and a second separator 132 are stacked to form an electrode unit, which is then wound to form the wound electrode assembly 10. At this time, the second region 115 of the positive electrode 11 is located on the outer ring of the wound electrode assembly 10 relative to the first region 114. That is, after forming the electrode assembly 10, the second region 115 of the positive electrode 11 is the tail section 118 of the single-sided winding area of ​​the positive electrode 11. Since there is no corresponding negative active material layer on the outer side of the second region 115 of the positive electrode 11 in the wound electrode assembly 10, the second region 115 does not have a first positive active material layer 113, which can improve the energy density of the electrochemical device.

[0052] The single-sided winding section 118 of the positive electrode 11 refers to... Figure 3 The portion of the electrode assembly 10 shown is enclosed in the dashed box, which represents the area furthest from the winding center. The single-sided winding end section 118 of the positive electrode 11 refers to the section where, at the winding end of the positive electrode 11, one surface is provided with a positive active material layer, while the opposite surface is not provided with a positive active material layer, thus forming the single-sided winding end section 118 of the positive electrode 11. When the electrode assembly 10 is formed by winding, the section at the end of the winding of the positive electrode 11 is the winding single-sided area termination section 118 of the positive electrode 11. After the electrode assembly 10 is formed, the winding single-sided area termination section 118 of the positive electrode 11 is located in the part of the electrode assembly 10 away from the winding center of the electrode assembly 10. The side of the winding single-sided area termination section 118 of the positive electrode 11 facing the center of the electrode assembly 10 is provided with a positive active material layer, and the side of the winding single-sided area termination section 118 of the positive electrode 11 away from the center of the electrode assembly 10 is not provided with a positive active material layer.

[0053] The second region 115 of the positive electrode 11 does not have the first positive electrode active material layer 113, which can improve the energy density of the electrochemical device after winding. At the same time, the second region 115 of the positive electrode 11 has the second part 1122 of the first safety layer 112, which can improve the safety performance of the electrochemical device.

[0054] The coefficient of variation δ2 of the resistance R of the positive electrode 11 in the second region 115 refers to: using a film resistance tester to test the resistance of the second region 115 of the positive electrode 11, at least 15 different points are tested, and then the resistance value of a single test point is recorded as Rb. Each test point has one Rb, the average value of all Rb is recorded as R2, and then the standard deviation of all Rb is calculated and recorded as σb. The coefficient of variation δ2 = σb / R2.

[0055] As an example, in the fully charged state at 25°C, the coefficient of variation δ2 of the resistance R of the positive electrode 11 in the second region 115 is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, and it can also be any value within the above range.

[0056] The area without the first positive electrode active material layer 113 is the empty foil area of ​​the positive electrode current collector 111. During the extrusion process, the empty foil area is prone to contact with the negative electrode after breaking, which affects the safety performance. Both the first region 114 and the second region 115 contain a first safety layer 112, which can improve the safety of the electrochemical device and greatly improve the preparation efficiency of the positive electrode sheet. At the same time, the coefficient of variation δ2 of the resistance R of the second region 115 of the positive electrode sheet 11 is ≤10%, which can not only reduce the risk of the empty foil area contacting the negative electrode during the extrusion process and further improve the safety performance of the electrochemical device, but also further improve the low-temperature performance of the electrochemical device.

[0057] Optionally, under full charge at 25°C, the coefficient of variation δ2 of the resistance R of the positive electrode 11 in the second region 115 is ≤7%, which can further improve the low-temperature performance of the electrochemical device. Further, the coefficient of variation δ2 of the resistance R of the positive electrode 11 in the second region 115 is ≤3%.

[0058] In some embodiments, when the electrochemical device is fully charged at 25°C, the average resistance R2 of the positive electrode 11 in the second region 115 satisfies: 5Ω / cm. 2 ≤R2≤100Ω / cm 2 The resistance values ​​at multiple test points in the second region 115 of the positive electrode 11, measured by the aforementioned diaphragm resistance tester, are denoted as Rb, and the average value of the multiple Rb values ​​is denoted as R2, 5Ω / cm. 2 ≤R2≤100Ω / cm 2 The average resistance R2 of the second region 115 of the positive electrode 11 is within the above-mentioned range, which can improve the safety performance of the electrochemical device while further improving its low-temperature performance.

[0059] As an example, the average resistance R2 of the positive electrode 11 in the second region 115 is 5Ω / cm. 2 10Ω / cm 2 15Ω / cm 2 20Ω / cm 2 30Ω / cm 2 40Ω / cm 2 50Ω / cm 2 60Ω / cm 2 70Ω / cm 2 80Ω / cm 2 90Ω / cm 2Or 100Ω / cm 2 It can also be any value within the above range.

[0060] Optionally, the average resistance R2 of the positive electrode 11 in the second region 115 satisfies: 8Ω / cm 2 ≤R2≤40Ω / cm 2 This can further improve the low-temperature performance of the electrochemical device while ensuring its safety. Further, optionally, the average resistance R2 of the positive electrode 11 in the second region 115 satisfies: 23 Ω / cm. 2 ≤R2≤32Ω / cm 2 .

[0061] In some embodiments, when the electrochemical device is fully charged at 25°C, the average resistance R2 of the positive electrode 11 in the second region 115 is less than the average resistance R1 of the positive electrode 11 in the first region 114.

[0062] In some embodiments, when the electrochemical device is fully charged at 25°C, the average resistance R1 of the positive electrode 11 in the first region 114 and the average resistance R2 of the positive electrode 11 in the second region 115 satisfy the condition that R2 / R1 ≥ 60%. Meeting this range for R2 / R1 improves the safety performance of the electrochemical device.

[0063] As an example, the average resistance R1 of the positive electrode 11 in the first region 114 and the average resistance R2 of the positive electrode 11 in the second region 115 satisfy the following: R2 / R1 is 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%, and it can also be any value within the above range.

[0064] Optionally, the average resistance R1 of the positive electrode 11 in the first region 114 and the average resistance R2 of the positive electrode 11 in the second region 115 satisfy: R2 / R1 ≥ 80%. This can further improve the safety performance of the electrochemical device while ensuring its low-temperature performance. Further, optionally, the average resistance R1 of the positive electrode 11 in the first region 114 and the average resistance R2 of the positive electrode 11 in the second region 115 satisfy: R2 / R1 ≥ 90%.

[0065] Please continue to refer to Figure 2The positive electrode 11 also includes a second safety layer 116 and a second positive electrode active material layer 117. The second safety layer 116 includes a third portion 1161 located in the first region 114 and a fourth portion 1162 located in the second region 115. The second positive electrode active material layer 117 includes a fifth portion 1171 located in the first region 114 and a sixth portion 1172 located in the second region 115. The third portion 1161 is disposed between the positive electrode current collector 111 and the fifth portion 1171, and the fourth portion 1162 is disposed between the positive electrode current collector 111 and the sixth portion 1172.

[0066] Please continue to refer to Figure 2 The first positive electrode active material layer 113 and the second positive electrode active material layer 117 are respectively disposed on the two surfaces of the positive electrode current collector 111. The first positive electrode active material layer 113 is disposed on the upper surface of the positive electrode current collector 111, partially covering the first safety layer 112. The second positive electrode active material layer 117 is disposed on the lower surface of the positive electrode current collector 111, and the projection of the second positive electrode active material layer 117 on the positive electrode current collector 111 extends to the right beyond the projection of the first positive electrode active material layer 113 on the positive electrode current collector 111.

[0067] Please continue to refer to Figure 2 The positive electrode 11 includes a first region 114 and a second region 115. Along the thickness direction of the positive electrode 11, the first region 114 includes a fifth portion 1171 of a second positive active material layer 117, a third portion 1161 of a second safety layer 116, a positive current collector 111, a first portion 1121 of a first safety layer 112, and a first positive active material layer 113, all stacked sequentially. The second region 115 includes a sixth portion 1172 of a second positive active material layer 117, a fourth portion 1162 of a second safety layer 116, a positive current collector 111, and a second portion 1122 of a first safety layer 112, all stacked sequentially. Figure 2 The dotted lines in the diagram represent divisions; the area to the left of the dotted lines is the first region 114, and the area to the right of the dotted lines is the second region 115.

[0068] Please continue to refer to Figure 3 After the winding electrode assembly 10 is formed, the winding single-sided area ending section 118 of the positive electrode sheet 11 is located in the part of the electrode assembly 10 away from the winding center of the electrode assembly 10. One surface of the winding single-sided area ending section 118 of the positive electrode sheet 11 (the surface facing the center of the electrode assembly 10) contains the second positive electrode active material layer 117, and the other surface (the surface away from the center of the electrode assembly 10) does not contain the first positive electrode active material layer 113.

[0069] The first region 114 and the second region 115 of the positive electrode are both provided with a second safety layer 116 and a second positive electrode active material layer 117, which can improve the energy density of the electrochemical device while also satisfying the requirements for safety performance and low temperature performance.

[0070] In some embodiments, the thickness of the first safety layer is 0.5 μm to 10 μm. This can improve the safety performance of the electrochemical device while ensuring its energy density.

[0071] Please continue to refer to Figure 2 The thickness of the first security layer 112 is D1, which can be 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, or any value within the above range.

[0072] Optionally, the thickness of the first safety layer 112 is 2 μm to 5 μm, which can further improve the safety performance of the electrochemical device. Further, the thickness of the first safety layer 112 is 2 μm to 4 μm.

[0073] In some embodiments, the thickness of the second safety layer is 0.5 μm to 10 μm. This can improve the safety performance of the electrochemical device while ensuring its energy density.

[0074] Please continue to refer to Figure 2 The thickness of the second safety layer 116 is D2, which can be 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, or 10μm, or any value within the aforementioned range. Optionally, the thickness D1 of the first safety layer 112 and the thickness D2 of the second safety layer 116 can be the same or different.

[0075] In some embodiments, the diameter of the missed coating point in the second portion 1122 is Diameter satisfies The number of missed spots should not exceed 30 / m 2 The diameter satisfies The number of missed coating spots should not exceed 5 / m 2 It does not exist. The number of missing coating points with larger diameters is smaller, which makes the first safety layer 112 more uniform and makes it easier to achieve a coefficient of variation δ2 ≤ 10% for the resistance R of the second region 115, so as to better improve the low-temperature performance while meeting the safety performance of the electrochemical device.

[0076] During the coating process to form the first safety layer 112, due to differences in component dispersion, interfacial tension, coating thickness, etc., after the coating dries, the second portion 1122 of the first safety layer 112 may develop uncoated spots. For example, under otherwise equal conditions, the thicker the coating, the fewer the number and the smaller the diameter of the uncoated spots in the second portion 1122 of the first safety layer 112; conversely, the thinner the coating, the more numerous and larger the diameter of the uncoated spots in the second portion 1122 of the first safety layer 112. Uncoated spots can be regular circular structures, but more often they are irregular shapes. The diameter of an uncoated spot refers to the average of its maximum and minimum diameters.

[0077] The diameter of the missed coating point in Part 2, 1122 is Diameter satisfies The number of missed spots can be 0 / m 2 2 per m 2 4 units / m 2 8 per m 2 12 per m 2 16 per m 2 20 pieces / m 2 25 pieces / m 2 Or 30 per m 2 It can also be any value within the above range; the diameter satisfies The number of missed spots can be 0 / m 2 1 per m 2 2 per m 2 3 / m 2 4 units / m 2 Or 5 per m 2 It can also be any value within the above range; it does not exist. Spots where coating was missed.

[0078] Optionally, the diameter of the missed coating point in the second part 1122 is Diameter satisfies The number of missed spots should not exceed 10 / m 2 The diameter satisfies The number of missed spots should not exceed 2 / m 2 It does not exist. Spots where coating was missed.

[0079] In some embodiments, the material of the first safety layer 112 includes first inorganic insulating particles, a first conductive agent, a first binder, and optionally a first leveling agent; the material of the second safety layer 116 includes second inorganic insulating particles, a second conductive agent, a second binder, and optionally a second leveling agent. After mixing the inorganic insulating particles, conductive agent, binder, and optionally leveling agent, a slurry is formed. This slurry can be coated on both surfaces of the positive electrode current collector 111, thereby forming the first safety layer 112 and the second safety layer 116 to improve the safety performance of the electrochemical device.

[0080] The first part 1121 and the second part 1122 of the first safety layer 112 both contain first inorganic insulating particles, first conductive agent and first binder, which can make the first safety layer 112 more uniform and facilitate the preparation of the positive electrode 11; at the same time, the second safety layer 116 contains second inorganic insulating particles, second conductive agent and second binder, which can meet the safety performance of the electrochemical device.

[0081] In some embodiments, the specific surface area of ​​the first inorganic insulating particles in the first safety layer 112 is 1 m². 2 / g~50m 2 / g. The specific surface area of ​​the first inorganic insulating particles is within the above range, which can reduce the number of uncoated spots in the second part 1122 of the first safety layer 112, and make the slurry more uniform, avoiding agglomeration. This ensures that, under full charge at 25°C, the coefficient of variation δ1 of the resistance R of the positive electrode 11 in the first region 114 is ≤15%, and the coefficient of variation δ2 of the resistance R of the positive electrode 11 in the second region 115 is ≤10%, thereby improving the safety performance and low-temperature performance of the electrochemical device.

[0082] As an example, the specific surface area of ​​the first inorganic insulating particles in the first safety layer 112 is 1m². 2 / g、2m 2 / g、3m 2 / g、5m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、30m 2 / g、40m 2 / g or 50m 2 / g, which can also be any value within the above range. Optionally, the specific surface area of ​​the first inorganic insulating particles in the first safety layer 112 is 5m². 2 / g~20m 2 / g.

[0083] In some embodiments, the specific surface area of ​​the second inorganic insulating particles in the second safety layer 116 is 1 m². 2 / g~50m2 / g. The specific surface area of ​​the second inorganic insulating particles is within the above range, which can reduce the number of missed spots in the second safety layer 116 and make the slurry more uniform, avoiding agglomeration, thereby improving the safety performance and low-temperature performance of the electrochemical device.

[0084] As an example, the specific surface area of ​​the second inorganic insulating particles in the second safety layer 116 is 1m². 2 / g、2m 2 / g、3m 2 / g、5m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、30m 2 / g、40m 2 / g or 50m 2 / g, which can also be any value within the above range. Optionally, the specific surface area of ​​the second inorganic insulating particles in the second safety layer 116 is 5m². 2 / g~20m 2 / g. The specific surface area of ​​the first inorganic insulating particle can be the same as or different from that of the second inorganic insulating particle.

[0085] In some embodiments, based on the mass of the first safety layer 112, the mass percentage of the first inorganic insulating particles is 65% to 98.9%, the mass percentage of the first adhesive is 1% to 20%, the mass percentage of the first conductive agent is 0.1% to 10%, and the mass percentage of the first leveling agent is 0% to 5%.

[0086] As an example, based on the mass of the first safety layer 112, the mass percentage of the first inorganic insulating particles is 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 98.9%, or any value within the aforementioned range; the mass percentage of the first adhesive is 1%, 3%, 5%, 10%, 15%, or 20%, or any value within the aforementioned range; the mass percentage of the first conductive agent is 0.1%, 0.3%, 0.5%, 1%, 3%, 5%, or 10%, or any value within the aforementioned range; and the mass percentage of the first leveling agent is 0%, 1%, 2%, 3%, 4%, or 5%, or any value within the aforementioned range.

[0087] The higher content of the first insulating particles and the relatively lower content of the first conductive agent allow for better safety performance while satisfying current collection requirements.

[0088] In some embodiments, based on the mass of the second safety layer 116, the mass percentage of the second inorganic insulating particles is 65% to 98.9%, the mass percentage of the second adhesive is 1% to 20%, the mass percentage of the second conductive agent is 0.1% to 10%, and the mass percentage of the second leveling agent is 0% to 5%.

[0089] As an example, based on the mass of the second safety layer 116, the mass percentage of the second inorganic insulating particles is 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 98.9%, or any value within the aforementioned range; the mass percentage of the second adhesive is 1%, 3%, 5%, 10%, 15%, or 20%, or any value within the aforementioned range; the mass percentage of the second conductive agent is 0.1%, 0.3%, 0.5%, 1%, 3%, 5%, or 10%, or any value within the aforementioned range; and the mass percentage of the second leveling agent is 0%, 1%, 2%, 3%, 4%, or 5%, or any value within the aforementioned range.

[0090] The higher content of the second insulating particles and the relatively lower content of the second conductive agent allow for better safety performance of the electrochemical device while satisfying the current collection requirement.

[0091] In some embodiments, the first adhesive and / or the second adhesive each independently comprise at least one of olefin polymers, acrylic polymers, amide polymers, fluoroolefin polymers, carboxymethyl cellulose salts, and rubbers. The materials of the first adhesive and the second adhesive may be the same or different.

[0092] In some embodiments, the first inorganic insulating particle and / or the second inorganic insulating particle each independently comprise at least one of boehmite, alumina, titanium oxide, silicon oxide, magnesium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium sulfate, calcium sulfate, calcium silicate, and silicon carbide. The material of the first inorganic insulating particle and the material of the second inorganic insulating particle may be the same or different.

[0093] In some embodiments, the first conductive agent and / or the second conductive agent each independently comprise at least one of particulate, sheet-like, mesh-like, or linear conductive agents. The shapes of the first conductive agent and the second conductive agent may be the same or different.

[0094] The first conductive agent and / or the second conductive agent each independently include at least one of conductive carbon black, carbon fiber, carbon nanotubes, Ketjen black, graphene, or acetylene black. The materials of the first conductive agent and the second conductive agent may be the same or different.

[0095] In some embodiments, the first leveling agent and / or the second leveling agent each independently comprise at least one of a polymer of an olefin derivative, an acrylate polymer, a siloxane polymer, an acrylate polymer, an alcohol compound, an ether compound, or a fluorocarbon compound. The materials of the first leveling agent and the second leveling agent may be the same or different.

[0096] Figure 4 This is a schematic diagram of the structure of the negative electrode 12 provided in some embodiments of this application. Please refer to... Figure 4 The negative electrode sheet 12 includes a second negative electrode active material layer 121, a negative electrode current collector 122, and a first negative electrode active material layer 123, which are sequentially stacked along the thickness direction. The negative electrode sheet 12 includes a third region 124 with the first negative electrode active material layer 123 and a fourth region 125 without the first negative electrode active material layer 123. It can be used to... Figure 4 The dashed lines in the diagram represent divisions; the right side of the dashed lines represents the third region 124, and the left side represents the fourth region 125. Both the third region 124 and the fourth region 125 are provided with a second negative electrode active material layer 121.

[0097] Please continue reading. Figure 4 The first negative electrode active material layer 123 and the second negative electrode active material layer 121 are respectively disposed on the two surfaces of the negative electrode current collector 122. The first negative electrode active material layer 123 is disposed on the upper surface of the negative electrode current collector 122; the second negative electrode active material layer 121 is disposed on the lower surface of the negative electrode current collector 122, and the projection of the second negative electrode active material layer 121 on the negative electrode current collector 122 extends to the left beyond the projection of the first negative electrode active material layer 123 on the negative electrode current collector 122.

[0098] For example, the negative electrode current collector 122 can be copper foil, copper foam, copper composite current collector (with a polymer support layer in the middle, and copper metal layers on both surfaces of the support layer), nickel foil, nickel foam, etc. The negative electrode active material layer refers to the layer structure containing negative electrode active material, which can be graphite, silicon, etc.

[0099] Please continue reading. Figure 3The positive electrode 11, the first separator 131, the negative electrode 12, and the second separator 132 are stacked to form an electrode unit, which is then wound to form a wound electrode assembly 10. At this time, the fourth region 125 of the negative electrode 12 is located in the inner circle of the wound electrode assembly 10 relative to the third region 124. That is to say, after the electrode assembly 10 is formed, the fourth region 125 of the negative electrode 12 is the starting segment 126 of the wound single-sided area of ​​the negative electrode 12. Since there is no corresponding positive active material layer on the inner side of the wound fourth region 125 of the negative electrode 12 in the wound electrode assembly 10, the fourth region 125 does not have a first negative active material layer 123, which can improve the energy density of the electrochemical device.

[0100] The starting segment 126 of the single-sided winding region of the negative electrode 12 refers to Figure 3 The portion within the dashed box near the winding center of the electrode assembly 10 shown. The starting segment 126 of the single-sided winding area of ​​the negative electrode sheet 12 refers to the following: at the starting end of the winding of the negative electrode sheet 12, one surface is provided with a negative electrode active material layer, while the opposite surface is not provided with a negative electrode active material layer, thus forming the starting segment 126 of the single-sided winding area of ​​the negative electrode sheet 12. In particular, a negative electrode current collector segment 122 may also be provided in the starting segment 126 of the single-sided winding area of ​​the negative electrode sheet 12, where neither surface is provided with a negative electrode active material layer. When the electrode assembly 10 is formed by winding, the starting section of the winding of the negative electrode sheet 12 has a single-sided starting section 126 of the winding of the negative electrode sheet 12. After the electrode assembly 10 is formed, the single-sided starting section 126 of the winding of the negative electrode sheet 12 is located in the part of the electrode assembly 10 close to the winding center of the electrode assembly 10. The side of the single-sided starting section 126 of the winding of the negative electrode sheet 12 facing the center of the electrode assembly 10 does not have a negative active material layer, and the side of the single-sided starting section 126 of the winding of the negative electrode sheet 12 away from the center of the electrode assembly 10 has a negative active material layer.

[0101] Please continue reading. Figure 3 The electrode assembly 10 also includes a positive electrode tab 141 and a negative electrode tab 142. The positive electrode tab 141 is disposed on one side of the positive electrode plate 11 and electrically connected to the positive current collector 111. The negative electrode tab 142 is disposed on one side of the negative electrode plate 12 and electrically connected to the negative current collector 122. The positive electrode tab 141 and the negative electrode tab 142 are used to output current.

[0102] In some embodiments, please continue to refer to Figure 2 and Figure 3The electrochemical device includes a wound electrode assembly 10 formed by stacking and winding a positive electrode 11, a first separator 131, a negative electrode 12, and a second separator 132. The positive electrode 11 includes a second positive active material layer 117, a second safety layer 116, a positive current collector 111, a first safety layer 112, and a first positive active material layer 113. The positive electrode 11 includes a first region 114 containing the first positive active material layer 113. The first safety layer 112 includes a first portion 1121 located in the first region 114, which is disposed between the positive current collector 111 and the first positive active material layer 113. In a fully charged state at 25°C, the coefficient of variation δ1 of the resistance R of the positive electrode 11 in the first region 114 is ≤15%. The positive electrode 11 also includes a second region 115 without the first positive electrode active material layer 113. The first safety layer 112 includes a second portion 1122 located in the second region 115. In a fully charged state at 25°C, the coefficient of variation δ2 of the resistance R of the positive electrode 11 in the second region 115 is ≤10%. The second safety layer 116 includes a third portion 1161 located in the first region 114 and a fourth portion 1162 located in the second region 115. The second positive electrode active material layer 117 includes a fifth portion 1171 located in the first region 114 and a sixth portion 1172 located in the second region 115. The second region 115 of the positive electrode 11 is located on the outer ring of the wound electrode assembly 10 relative to the first region 114, and the second portion 1122 of the first safety layer 112 is located on the side of the positive electrode 11 away from the center of the wound electrode assembly 10.

[0103] In this embodiment, the electrochemical device contains the aforementioned positive electrode 11, which can improve the safety performance and low-temperature performance of the electrochemical device, and also enable the electrochemical device to have a high energy density.

[0104] In a second aspect, this application provides an electrical device comprising the electrochemical apparatus described above.

[0105] In some embodiments, the electrical device may include, but is not limited to: mobile phones, laptops, headphones, video recorders, calculators, vehicles, ships, spacecraft, power tools, electric toys, etc. This application does not impose any special limitations on the aforementioned electrical devices.

[0106] The technical solution of this application will be described in further detail below with reference to embodiments and comparative examples. However, it should be understood that the following embodiments are merely examples, and the implementation of this application is not limited thereto.

[0107] Example

[0108] Preparation of negative electrode sheet:

[0109] The negative electrode active material granules (graphite), conductive agent Super P, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly mixed in deionized water at a mass ratio of 95:2:2:1 to obtain the negative electrode slurry. Figure 4 As shown, the negative electrode slurry is coated on one side of a 6μm copper foil current collector and dried. Then, the negative electrode slurry is coated on the other side of the copper foil current collector and dried. After cold pressing, a negative electrode sheet containing a first negative electrode active material layer 123 and a second negative electrode active material layer 121 is obtained.

[0110] Preparation of positive electrode sheet:

[0111] Step 1: Prepare the positive electrode slurry. Mix the positive electrode active material particles LiCoO2, conductive agent Super P, carbon nanotubes and binder polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of 97.3:0.6:0.5:1.6 to obtain the positive electrode slurry.

[0112] Step 2: Prepare the safety layer slurry by adding inorganic insulating particles, binder, conductive agent and optional leveling agent to water and mixing them evenly to obtain the safety layer slurry.

[0113] Step 3: Follow Figure 2 The first safety layer 112 is obtained by coating a safety layer slurry onto one side of a 9μm aluminum foil current collector and drying it; then proceeding according to... Figure 2 The second safety layer 116 is obtained by coating the safety layer slurry onto the other side of the aluminum foil current collector.

[0114] Step 4: According to Figure 2 The positive electrode slurry is coated onto the first safety layer 112 and dried to form the first positive electrode active material layer 113; then the process continues according to... Figure 2 The positive electrode slurry is coated onto the second safety layer 116 and dried to form the second positive electrode active material layer 117. After cold pressing, the positive electrode sheet is obtained. The thickness of the first positive electrode active material layer 113 and the second positive electrode active material layer 117 is 50 μm.

[0115] Preparation of electrode assembly 10:

[0116] The separator 13 is made of porous polyethylene polymer film.

[0117] After stacking the positive electrode 11, the first separator 131, the negative electrode 12, and the second separator 132, they are arranged as follows: Figure 3The electrode assembly 10 is formed by winding in a manner whereby the fourth region 125 of the negative electrode 12 is located in the innermost circle of the electrode assembly 10, and the side of the fourth region 125 of the negative electrode 12 that is not provided with a negative active material layer faces the center of the electrode assembly 10; the second region 115 of the positive electrode 11 is located in the outer circle of the electrode assembly 10, and the side of the second region 115 of the positive electrode 11 that is not provided with a positive active material layer faces away from the center of the electrode assembly 10.

[0118] Preparation of lithium-ion batteries:

[0119] A wound electrode assembly 10 is placed inside an aluminum-plastic film, an electrolyte is injected, and the assembly is encapsulated. A lithium-ion battery is obtained through formation, degassing, and edge trimming processes. The electrolyte is prepared as follows: In an argon-atmosphere glove box with a water content of <10 ppm, ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) are mixed uniformly in a weight ratio of 2:6:2. Thoroughly dried lithium salt LiPF6 is then dissolved in the solvent, and 1,3-propanesulfonyl lactone, fluoroethylene carbonate, and adiponitrile are added to obtain the electrolyte. The content of LiPF6 is 12.5%, 1,3-propanesulfonyl lactone is 1.5%, fluoroethylene carbonate is 3%, and adiponitrile is 2%, with each component based on the total weight of the electrolyte.

[0120] The parameters of the positive electrode are described in detail in Table 1 below.

[0121] Table 1 Parameters of the positive electrode sheet

[0122]

[0123]

[0124] Test method:

[0125] (1) Specific surface area (BET):

[0126] The electrode sheet from the second region 115 of the positive electrode sheet 11 was soaked in dimethyl carbonate (DMC) for 30 minutes and then air-dried in a fume hood. The safety layer was scraped off with a scraper, and the conductive agent, binder, and leveling agent were burned off to obtain inorganic insulating particle powder. The specific surface area (BET) of the inorganic insulating particle powder was determined using the nitrogen adsorption method. 2 / g -1 ).

[0127] (1) Full charge resistance and coefficient of variation:

[0128] 1) At 25℃, the lithium-ion battery is charged to the designed full charge voltage of 4.45V by a constant current of 0.05C. Then, it is charged at a constant voltage of 0.025C (cutoff current) to bring the lithium-ion battery to a fully charged state.

[0129] 2) Disassemble the lithium-ion battery to obtain the positive electrode 11.

[0130] 3) After soaking the positive electrode 11 obtained in 2) in dimethyl carbonate (DMC) at 25°C for 1 hour, it is dried in a fume hood and then sealed and transferred to the resistance test location.

[0131] 4) Use a BER1200 film resistance tester to test the resistance of the first region 114 of the positive electrode 11 obtained in 3) (the indenter is set on the first positive active material layer 113 of the first region 114 of the positive electrode 11). The adjacent test points are spaced 2mm to 3mm apart. Test 20 different points and record the resistance Ra of all test points. Calculate the average value of the 20 Ra values ​​as R1. Then calculate the standard deviation of the 20 Ra values ​​as σa. The coefficient of variation δ1 = σa / R1.

[0132] 5) Use a BER1200 model film resistance tester to test the resistance of the second region 115 of the positive electrode 11 obtained in 3) (the pressure head is set on the second part 1122 of the first safety layer 112 of the second region 115 of the positive electrode 11). The adjacent test points are spaced 2mm to 3mm apart. Test 20 different points and record the resistance Rb of all test points. Calculate the average value of the 20 Rb as R2. Then calculate the standard deviation of the 20 Rb and record it as σb. The coefficient of variation δ2=σb / R2.

[0133] The resistance test parameters are as follows: indenter area is 153.94 mm². 2 The pressure is 3.5t, and the holding time is 50s.

[0134] (3) Thickness of the safety layer:

[0135] 1) Remove the positive electrode 11 from the lithium-ion battery. 2) Bake the positive electrode 11 at 80°C for 60 minutes. 3) Take the positive electrode 11 from step 2) and perform plasma cutting on the part of the positive electrode 11 with the safety layer to obtain its cross-section. 4) Observe the cross-section of the electrode obtained in step 3) under a scanning electron microscope (SEM) and test the thickness of the first safety layer 112. Test 20 different points with adjacent test points spaced 2mm to 3mm apart, and record the average value of all test points as the thickness D1 of the first safety layer 112. Test the thickness D2 of the second safety layer 116 using the same method.

[0136] (4) The diameter of the missed coating point is

[0137] Take an electrode sheet coated with the first safety layer 112 from the second region 115, locate the missed coating points under a 300x optical microscope, and measure the longest and shortest diameters of each missed coating point, denoted as . and Diameter of the missed coating point

[0138] (5) Side extrusion pass rate:

[0139] At 25℃, the lithium-ion battery under test was charged at a constant current rate of 0.05C to the designed full charge voltage of 4.45V. Then, it was charged at a constant voltage until the current reached 0.025C (cutoff current) to achieve a fully charged state. The appearance of the lithium-ion battery before the test was recorded. A side-extrusion test was performed on the lithium-ion battery in an environment of 25±3℃. The diameter of the steel nail was 5mm, and the extrusion speed was 150mm / s. Extrusion started from the side of the lithium-ion battery and continued for 3 minutes or until the surface temperature of the lithium-ion battery dropped to 50℃. Twenty lithium-ion batteries were used as a group, and the state of the lithium-ion batteries during the test was observed. The passing standard was that the lithium-ion battery did not burn or explode. The side-extrusion pass rate was recorded as: number of passes / 20.

[0140] (6) Low temperature performance:

[0141] 1) Let it stand at 25℃ for 60 minutes, then charge it at a constant current rate of 1.5C to the full charge design voltage of 4.45V. Then charge it at a constant voltage of the full charge design voltage until the current is 0.025C (cutoff current) to bring the lithium-ion battery to a full charge state.

[0142] 2) At 25°C, the lithium-ion battery in 1) was discharged at a constant current rate of 0.2C to 3.0V, and the discharge capacity at 25°C was recorded as C1.

[0143] 3) Repeat step 1) at 25°C to fully charge the lithium-ion battery.

[0144] 4) Then, let the lithium-ion battery from step 3) stand at -20℃ for 60 minutes, and then discharge it at a constant current rate of 0.2C to 3.0V. Record the discharge capacity at -20℃ as C2.

[0145] 5) Low-temperature performance = C2 / C1 × 100%.

[0146] The parameters and performance of lithium-ion batteries are described in detail in Tables 4 and 5 below.

[0147] Table 2 Parameters and performance of the electrochemical device

[0148]

[0149] As can be seen from Tables 1 and 2, the specific surface area and amount of inorganic insulating particles, the type and amount of binder, the type and amount of leveling agent, the type and amount of conductive agent, the thickness of the safety layer, etc., all affect the side extrusion pass rate and low-temperature performance of lithium-ion batteries.

[0150] Through extensive research, the inventors discovered that the reason for this is that the aforementioned characteristics collectively affect the average resistance R1 and coefficient of variation δ1 of the first region 114 of the positive electrode 11 when the lithium-ion battery is fully charged at 25°C. They also affect the average resistance R2 and coefficient of variation δ2 of the second region 115 of the positive electrode 11. Furthermore, they also affect the size and number of uncoated spots in the first safety layer 112, thereby impacting the side extrusion pass rate and low-temperature performance of the lithium-ion battery.

[0151] As shown in Tables 1 and 2, the smaller the coefficient of variation δ1 of the resistance in the first region 114 and the coefficient of variation δ2 of the resistance in the second region 115, the more significant the improvement in the low-temperature performance of the lithium-ion battery (the value of C2 / C1 gradually increases). Examples 1 to 24 not only meet the requirements for low-temperature performance of lithium-ion batteries (larger value of C2 / C1), but also have excellent safety performance (higher side extrusion pass rate).

[0152] As can be seen from Comparative Example 1 in Tables 1 and 2, if the positive electrode 11 does not have a safety layer, although the low-temperature performance of the lithium-ion battery can be met, the safety performance is very poor.

[0153] As can be seen from Comparative Examples 2-3 in Tables 1 and 2, under full charge at 25°C, the coefficients of variation δ1 of the resistance in the first region 114 and δ2 of the resistance in the second region 115 are both relatively large (δ1 > 15%, δ2 > 10%). Furthermore, the diameters of the uncoated spots in the first safety layer 112 are large and numerous, and the diameters meet the requirements... The number of missed coating spots exceeds 30 / m 2 The diameter satisfies The number of missed coating spots exceeds 5 / m 2 ,exist The lack of coating points leads to poor low-temperature performance and safety performance of lithium-ion batteries.

[0154] Compared to Comparative Examples 2 and 3, in Example 1, the coefficient of variation δ1 of the resistance in the first region 114 and the coefficient of variation δ2 of the resistance in the second region 115 are both smaller (δ1 = 10%, δ2 = 8%), and there are no large-diameter uncoated spots, which can simultaneously improve the low-temperature performance and safety performance of the lithium-ion battery.

[0155] A comparison of Examples 1 and 3 shows that in each example, when the coefficient of variation δ1 of the resistance in the first region 114 and the coefficient of variation δ2 of the resistance in the second region 115 are the same (δ1 = 10%, δ2 = 8%), the average value R1 (R1 ≥ 10Ω) of the resistance in the first region 114 and the average value R2 (R2 ≥ 8Ω) of the resistance in the second region 115 are larger (Example 3). This can maintain the low-temperature performance of the lithium-ion battery while further improving its safety performance.

[0156] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The embodiments described above are only some, not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

Claims

1. An electrochemical device, characterized in that, The device includes a positive electrode sheet, which includes a positive current collector, a first safety layer, and a first positive active material layer. The positive electrode sheet includes a first region having the first positive active material layer and a second region not having the first positive active material layer. The first safety layer includes a first portion located in the first region and a second portion located in the second region. The first portion is disposed between the positive current collector and the first positive active material layer. The positive electrode sheet further includes a second safety layer and a second positive electrode active material layer. The second safety layer includes a third part located in the first region and a fourth part located in the second region. The second positive electrode active material layer includes a fifth part located in the first region and a sixth part located in the second region. The third part is disposed between the positive electrode current collector and the fifth part, and the fourth part is disposed between the positive electrode current collector and the sixth part. The material of the first safety layer includes first inorganic insulating particles, a first conductive agent, and a first adhesive; The material of the second safety layer includes second inorganic insulating particles, a second conductive agent, and a second adhesive; When the electrochemical device is fully charged at 25°C, the coefficient of variation δ1 of the resistance R of the positive electrode in the first region is ≤15%. When the electrochemical device is fully charged at 25°C, the coefficient of variation δ2 of the resistance R of the positive electrode in the second region is ≤10%.

2. The electrochemical device according to claim 1, characterized in that, When the electrochemical device is fully charged at 25°C, the average resistance R1 of the positive electrode in the first region satisfies: 8 Ω / cm. 2 ≤R1≤100 Ω / cm 2 .

3. The electrochemical device according to claim 1, characterized in that, When the electrochemical device is fully charged at 25°C, the average resistance R2 of the positive electrode in the second region satisfies: 5 Ω / cm. 2 ≤R2≤100 Ω / cm 2 .

4. The electrochemical device according to claim 1, characterized in that, The electrochemical device meets the following conditions: When the electrochemical device is fully charged at 25°C, the average resistance R1 of the positive electrode in the first region and the average resistance R2 of the positive electrode in the second region satisfy the following condition: R2 / R1≥60%.

5. The electrochemical device according to claim 1, characterized in that, The electrochemical device satisfies at least one of the following conditions: (c) The thickness of the first safety layer is 0.5 μm to 10 μm; (d) The thickness of the second security layer is 0.5 μm to 10 μm.

6. The electrochemical device according to claim 1, characterized in that, The diameter of the missed coating points in the second part is φ, and the number of missed coating points with a diameter of 0.5 mm ≤ φ ≤ 1.5 mm does not exceed 30 per m. 2 The number of uncoated spots with a diameter of 1.5 mm < φ ≤ 2.5 mm shall not exceed 5 per m. 2 There are no uncoated spots with a diameter greater than 2.5 mm.

7. The electrochemical device according to claim 1, characterized in that, The electrochemical device satisfies at least one of the following conditions: (e) The specific surface area of ​​the first inorganic insulating particle is 1 m². 2 / g~50 m 2 / g; (f) The specific surface area of ​​the second inorganic insulating particle is 1 m². 2 / g~50 m 2 / g; (g) The material of the first safety layer includes a first leveling agent, and based on the mass of the first safety layer, the mass percentage of the first inorganic insulating particles is 65% to 98.9%, the mass percentage of the first adhesive is 1% to 20%, the mass percentage of the first conductive agent is 0.1% to 10%, and the mass percentage of the first leveling agent is 0% to 5%. (h) The material of the second safety layer includes a second leveling agent, and based on the mass of the second safety layer, the mass percentage of the second inorganic insulating particles is 65% to 98.9%, the mass percentage of the second adhesive is 1% to 20%, the mass percentage of the second conductive agent is 0.1% to 10%, and the mass percentage of the second leveling agent is 0% to 5%.

8. The electrochemical device according to claim 7, characterized in that, The electrochemical device satisfies at least one of the following conditions: (i) The first adhesive and / or the second adhesive each independently comprise at least one of olefin polymers, acrylic polymers, amide polymers, fluoroolefin polymers, carboxymethyl cellulose salts, and rubbers; (j) The first inorganic insulating particle and / or the second inorganic insulating particle each independently comprise at least one of boehmite, alumina, titanium oxide, silicon oxide, magnesium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium sulfate, calcium sulfate, calcium silicate, and silicon carbide; (k) The first conductive agent and / or the second conductive agent each independently comprise at least one of the following: particulate, sheet-like, mesh-like, or linear conductive agents; (l) The first leveling agent and / or the second leveling agent each independently comprise at least one of the following: an olefin derivative polymer, an acrylate polymer, a siloxane polymer, an acrylate polymer, an alcohol compound, an ether compound, or a fluorocarbon compound.

9. An electrical appliance, characterized in that, It includes the electrochemical device according to any one of claims 1 to 8.

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