WO2024011540A1

WO2024011540A1 - Electrode plate, secondary battery, battery module, battery pack, and electrical device

Info

Publication number: WO2024011540A1
Application number: PCT/CN2022/105826
Authority: WO
Inventors: 张翠平; 韩昌隆; 范朋; 吴则利; 黄磊; 陈慧玲
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-07-14
Filing date: 2022-07-14
Publication date: 2024-01-18

Abstract

The present application provides an electrode plate, a secondary battery, a battery module, a battery pack, and an electrical device. The electrode plate comprises: a current collector, comprising a base material and a protective coating, the base material comprising a main body portion and a tab portion arranged in a first direction, the tab portion being provided with a first edge extending in a second direction, the protective coating being disposed on at least part of the surface of the main body portion to form a second edge adjacent to the tab portion and extending in the second direction, and the protective coating extending in the first direction and forming a third edge extending in the second direction; and an electrode active material layer disposed on a side of the protective coating facing away from the main body portion, wherein an area A₁ of the tab portion defined by the second edge and the first edge, and an area A₂ of the protective coating defined by the second edge and the third edge satisfy the following relation: 0.05 ≤ A₂/A₁ ≤ 6. The electrode plate in embodiments of the present application can enhance the stability of secondary batteries operating under high-temperature conditions, and extend the cycle life thereof.

Description

Electrode plates, secondary batteries, battery modules, battery packs and electrical devices

Technical field

The present application relates to the technical field of lithium batteries, and in particular to an electrode pole piece, a secondary battery, a battery module, a battery pack and an electrical device.

Background technique

Lithium-ion secondary batteries have many advantages such as high specific energy density, long cycle life, high nominal voltage, low self-discharge rate, small size, and light weight. They are widely used in various fields, including electric bicycles, electric vehicles, and other fields.

In addition to how to improve the electrical performance of secondary batteries, the safety of secondary batteries during operation is also one of the focuses of research in this field. Since the probability of safety accidents occurring in electrode plates of secondary batteries in high-temperature environments is greatly increased, how to improve the safety performance of electrode plates in high-temperature environments is also one of the issues that urgently need to be solved.

Contents of the invention

This application was made in view of the above-mentioned issues, and its purpose is to provide an electrode pole piece that can improve the stability of secondary batteries operating under high-temperature conditions and extend their cycle life.

In order to achieve the above objectives, the present application provides an electrode pole piece, a secondary battery, a battery module, a battery pack and a power device.

The first aspect of this application provides an electrode pole piece, including:

A current collector includes a base material and a protective coating. The base material includes a main body portion and a tab portion arranged along a first direction. The tab portion has a first edge extending along a second direction, and the first direction intersects the second direction; The protective coating is disposed on a portion of the surface of the main body portion to form a second edge extending in the second direction adjacent to the tab portion, and the protective coating extends in the first direction and forms a third edge extending in the second direction. ;as well as

An electrode active material layer is provided on the protective coating and at least part of the surface of the main body part,

Among them, the area A ₁ of the pole portion defined by the second edge and the first edge, and the area A ₂ of the protective coating defined by the second edge and the third edge satisfy: 0.05 ≤ _{A 2} /A ₁ ≤ 6, optional ,0.1≤A ₂ /A ₁ ≤5.

This application effectively reduces the probability that the base material in the protective coating area contacts and reacts with the electrolyte by arranging a protective coating on the area of the current collector substrate close to the pole lug, and reasonably limiting the area of the protective coating. At the same time, It ensures the heat dissipation efficiency of the electrode pole piece, improves the integrity of the substrate in the protective coating area, improves the stability of the secondary battery operation and extends its cycle life.

In some embodiments, the first edge, the second edge and the third edge are substantially parallel to each other, and the distance L ₁ between the second edge and the first edge and the distance L ₂ between the second edge and the third edge satisfy: 0.05≤L ₂ /L ₁ ≤6, optional, 0.1≤L ₂ /L ₁ ≤5.

Therefore, the above three edges are substantially parallel, so that the planar shape of the protective coating and the tab portion is substantially rectangular. Such a solution can improve the convenience of manufacturing current collectors, and by limiting the reasonable value range of L ₂ /L ₁ , it can reduce the coating area of the protective coating while ensuring that the protective coating plays a protective role. , beneficially improving the energy density of secondary batteries.

In some embodiments, the substrate is selected from aluminum foil or aluminum polymer composite substrate. When aluminum substrates (such as aluminum foil or aluminum polymer composite substrates) are used, aluminum is prone to chemical reactions with some substances in the electrolyte, such as certain electrolytes, and is corroded, especially at elevated temperatures, resulting in the substrate being corroded. There are holes or broken strips on the surface of the material. Therefore, applying a protective coating on an aluminum-containing substrate can prevent the electrolyte from corroding the aluminum, thereby preventing pits or breakage on the surface of the substrate.

In some embodiments, the protective coating includes a binder and a conductive agent. Optionally, the binder is selected from the group consisting of polyacrylic resin, PVDF and its copolymers, polyacrylonitrile, epoxy resin conductive glue, and phenolic resin conductive resin. At least one of the glue, optionally, the conductive agent is selected from at least one of carbon black, graphite, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene. In the above technical solution, the conductive agent can ensure that the protective coating has good conductivity, and the adhesive can ensure the bonding strength between the protective coating and the substrate.

In some embodiments, the electrode active material layer includes an active material, an electrode binder, and an electrode conductive agent. Optionally, the active material is selected from _LiNix Co _y N _z M _1-xyz O ₂ , LiMn ₂ O ₄ , Li ₂ MnO _3·(1-a) At least one of LiPO ₂ and LiFePO ₄ ; optionally, the electrode binder is selected from polyacrylic resin, PVDF and its copolymers, polyacrylonitrile, and epoxy resin conductive adhesive , at least one of phenolic resin conductive glue; optionally, the electrode conductive agent is selected from at least one of carbon black, graphite, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

In some embodiments, the thickness H ₁ of the protective coating and the thickness H ₂ of the substrate satisfy the relationship: H ₂ /26 ≤ H ₁ ≤ _{H 2} /2.6. Therefore, by setting a reasonable coating thickness of the protective coating, the heat dissipation effect of the pole piece can be improved while ensuring the protective effect and preventing holes or breaks in the substrate, and the total thickness of the pole piece can be reduced as much as possible to ensure Energy density of secondary batteries.

In some embodiments, the protective coating includes a binder with a mass of W ₁ and a conductive agent with a mass of W ₂ , and the ratio B of W ₁ to W ₁ + W ₂ satisfies the relationship: 0.05≤B≤0.5. In the above technical solution, by setting a reasonable mass ratio of conductive agent to binder, it is possible to ensure the bonding and conductive effects while improving the process performance of protective coating coating and drying.

In some embodiments, the thickness D ₁ of the electrode active material layer and the thickness H ₁ of the protective coating satisfy the relationship: D ₁ /200 ≤ _{H 1} ≤ _{D 1} /30. In the above technical solution, by setting a reasonable thickness of the active material layer and protective coating, while ensuring the protective effect of the protective coating area and the electrical performance of the pole piece, the total thickness of the electrode pole is controlled to ensure the energy density of the secondary battery.

A second aspect of the application provides a secondary battery, including the electrode pole piece of the first aspect of the application, a separator, and an electrolyte. The electrolyte includes a solvent and an electrolyte.

In some embodiments, the electrolyte includes lithium hexafluorophosphate and lithium fluorine-containing sulfonyl imide. Optionally, the molar concentration C ₁ of the lithium hexafluorophosphate salt is 0.1 mol/L ≤ C ₁ ≤ 1 mol/L, and the lithium fluorine-containing sulfonyl imide is optional. The molar concentration C ₂ is 0.5mol/L ≤ C ₂ ≤ 1.5mol/L. In the above technical solution, the fluorine-containing sulfonyl imide lithium salt can withstand high temperatures and is insoluble in water. Therefore, adding a certain amount of fluorine-containing sulfonyl imide lithium salt can improve the safety of the secondary battery to a certain extent.

In some embodiments, the molar concentration C ₁ of the lithium hexafluorophosphate salt and the molar concentration C ₂ of the lithium fluorine-containing sulfonylimide satisfy: 0.6mol/L≤C ₁ +C ₂ ≤2mol/L, and 1≤C ₂ /C ₁ ≤ 5. Therefore, by setting a reasonable proportion of lithium hexafluorophosphate and lithium fluorine-containing sulfonimide in the electrolyte, the ionic conductivity of the electrolyte can be ensured while the chemical stability and thermal stability of the electrolyte can be improved, thereby improving the safety performance of the battery.

In some embodiments, the tab area A ₁ , the protective coating area A ₂ , the molar concentration C ₁ of the lithium hexafluorophosphate salt, and the molar concentration C ₂ of the lithium fluorine-containing sulfonylimide satisfy: C ₂ /(10C ₁ )≤ A ₂ /A ₁ ≤C ₂ /(2C ₁ )+2.5.

Fluorine-containing lithium sulfonylimide easily reacts chemically with aluminum. When the electrolyte contains a certain molar concentration of lithium hexafluorophosphate and fluorine-containing lithium sulfonylimide, by setting the area of the protective coating so that it meets the requirements stipulated in this embodiment, it can be ensured that even if an aluminum substrate is used, Prevents the corrosion of aluminum by lithium fluorosulfonyl imide, thereby preventing pits or breakage on the surface of the substrate.

In any embodiment, the fluorine-containing sulfonyl imide lithium salt includes a compound represented by Formula I,

Wherein, R ₁ is selected from any one of F atom and C1-C3 alkyl group substituted by F;

R ₂ is selected from any one of F atoms and C1-C3 alkyl groups substituted by F,

Optionally, R ₁ is an F atom and R ₂ is an F atom.

Among the above technical solutions, the selected fluorosulfonimide lithium salt compound has a high thermal decomposition temperature and good water resistance, which can effectively improve the safety of the secondary battery operation process, and the raw materials of the above compound are easy to produce. Obtain and manufacture convenience.

In any embodiment, the electrolyte further includes an additive selected from the group consisting of vinylene carbonate, vinyl sulfate, lithium difluoroxaloborate, lithium difluorophosphate, lithium tetrafluoroborate, 1,3-propanesultone, At least one of lithium trifluoromethanesulfonate and lithium diacetate borate. In the above technical solution, by adding at least one additive to the electrolyte, the efficiency and/or safety of battery operation can be improved.

A third aspect of the present application provides a battery module including the secondary battery of the second aspect of the present application.

A fourth aspect of the application provides a battery pack, including the battery module of the third aspect of the application.

A fifth aspect of the present application provides an electrical device, including at least one selected from the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application, or the battery pack of the fourth aspect of the present application. kind.

By arranging a protective coating in the area close to the pole lug and reasonably limiting the area of the protective coating, this application effectively reduces the probability that the base material in the protective coating area contacts and reacts with the electrolyte in a high-temperature environment, while ensuring The heat dissipation efficiency of the electrode plate improves the integrity of the substrate in the protective coating area, improves the stability of the secondary battery operation and extends its cycle life.

Description of drawings

Figure 1 is a schematic structural diagram of an electrode pole piece according to an embodiment of the present application.

Figure 2 is a schematic diagram of the B-B section in Figure 1.

FIG. 3 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 4 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 3 .

Figure 5 is a schematic diagram of a battery module according to an embodiment of the present application.

Figure 6 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 7 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 6 .

FIG. 8 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.

Explanation of reference symbols:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly; X first direction; Y second direction;

6 electrode pole piece; 61 current collector; 611 base material; 612 protective coating; 613 main body part; 614 pole ear part; 615 first edge; 616 second edge; 617 third edge; 62 electrode active material layer.

Detailed ways

Hereinafter, embodiments specifically disclosing the conductive paste, current collector, secondary battery, battery module, battery pack, and electrical device of the present application will be described in detail with reference to the accompanying drawings as appropriate. However, unnecessary detailed explanations may be omitted. For example, detailed descriptions of well-known matters may be omitted, or descriptions of substantially the same structure may be repeated. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

"Ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

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 stated otherwise, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

If there is no special instructions, all steps of the present application can be performed sequentially or randomly, and are preferably performed sequentially. For example, a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, mentioning that the method may also include step (c) means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), and may also include step (a). , (c) and (b), and may also include steps (c), (a) and (b), etc.

If there is no special explanation, the words "include" and "include" mentioned in this application represent open expressions, which may also be closed expressions. For example, "comprises" and "comprises" may mean that other components not listed may also be included or included, or that only the listed components may be included or included.

In this application, the term "or" is inclusive unless otherwise specified. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, 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).

Generally, the preparation process of the electrode plate includes coating the active material slurry on the surface of the current collector substrate, and then cold pressing the current collector substrate coated with the active material slurry. On the one hand, the cold pressing process can increase the compaction density of the active material layer, thereby increasing the energy density of the battery core. On the other hand, it can enhance the contact between the active material and the substrate. However, during the cold pressing process, some active material particles will be pressed into the material of the current collector substrate, causing damage to the surface of the current collector substrate. When such an electrode piece is used in a battery, the surface of the damaged current collector base material comes into contact with the electrolyte, causing the materials inside the base material to be exposed to the electrolyte. Certain substances in the electrolyte may react chemically with materials inside the substrate, especially when the battery is being charged and discharged. Such chemical reactions will cause corrosion pits or broken belts on the current collector substrate, creating safety risks and reducing the service life of the secondary battery.

In addition, after extensive research and observation by the inventor, it was found that the above-mentioned corrosion reaction is affected by temperature, and the reaction rate accelerates as the temperature increases. During the operation of the battery, the current generated by the active material of the electrode plate is collected into the tab through the current collector to be provided to the outside. Therefore, the temperature of the current collector near the pole ear is usually higher, and it is also the area where corrosion or breakage occurs most frequently.

Based on this, this application has developed an electrode piece to address the above problems, which effectively reduces the probability that the base material in the protective coating area contacts and reacts with the electrolyte, while ensuring the heat dissipation efficiency of the electrode piece and improving the protective coating. The integrity of the substrate in the area improves the operational stability of the secondary battery and extends its cycle life.

Electrode pole piece

In the first aspect of this application, an electrode piece 6 is proposed. As shown in FIGS. 1 and 2 , the electrode piece 6 in this application includes a current collector 61 and an electrode active material layer 62 .

The current collector 61 includes a base material 611 and a protective coating 612. The base material 611 includes a main body portion 613 and a tab portion 614 arranged along the first direction X. The tab portion 614 has a first edge 615 extending along the second direction Y, The first direction 612 expands along the first direction X and forms a third edge 617 extending along the second direction Y.

The electrode active material layer 62 is provided on the protective coating 612 and on at least part of the surface of the main body portion 613 .

Wherein, the area A ₁ of the pole portion 614 defined by the second edge 616 and the first edge 615 and the area A ₂ of the protective coating 612 defined by the second edge 616 and the third edge 617 satisfy: 0.05≤A ₂ /A ₁ ≤6, optional, 0.1≤A ₂ /A ₁ ≤5.

In the embodiment of the present application, the base material 611 can be divided into a main body part 613 and a tab part 614 according to functions. The main part 613 is used to carry active materials in which electrochemical reactions will occur, and the tab parts 614 are used to draw out current. part. The tab portion 614 is used to connect the tab, and no electrode active material is provided on the tab portion 614 . The protective coating 612 is provided on the main body 613 , and the protective coating 612 covers part of the main body 613 . The electrode active material layer 62 contains electrode active material and is a main component for electrochemical reactions. As shown in FIG. 1 , the electrode active material layer 62 is provided on the protective coating 612 and at least part of the surface of the main body portion 613 .

In this application, the protective coating 612 is used to protect the current collector substrate 611 from surface damage caused by the intrusion of active material particles. By providing the protective coating 612 in the area of the current collector base material 611 close to the tab 614 and reasonably limiting the area of the protective coating 612, the probability that the base material in the protective coating area comes into contact with the electrolyte and reacts is effectively reduced. , while ensuring the heat dissipation efficiency of the electrode pole piece, improving the integrity of the substrate in the protective coating area, improving the stability of the secondary battery operation and extending its cycle life.

In addition, providing the protective coating 612 in the area of the main body 613 close to the tab portion 614 can effectively improve the gravimetric energy density of the secondary battery compared to coating the entire main body 613 with the protective coating 612. The contact area between the electrode active material and the base material 611 is expanded, the internal impedance of the electrode is reduced, and the rate performance is improved.

Therefore, according to the present application, coating a certain area of the protective coating on a specific area of the current collector substrate can protect the current collector substrate from breakage due to chemical corrosion without coating the entire area of the substrate. The protective layer can improve the operational stability of the secondary battery and extend its cycle life, while also increasing the energy density of the electrode plate.

In some embodiments, electrode active material layer 62 completely covers body portion 613 . As a result, the coating amount of the active material can be increased and the efficiency of the secondary battery can be improved.

In the embodiment of the present application, the first edge 615, the second edge 616 and the third edge 617 are substantially parallel to each other, and the distance L 1 between the second edge 616 and the first edge 615 is the same as the distance L ₁ between the second edge 616 and the third edge. The spacing L ₂ between 617 satisfies: 0.05≤L ₂ /L ₁ ≤6, optional, 0.1≤L ₂ /L ₁ ≤5.

In the above technical solution, the fact that the first edge 615, the second edge 616 and the third edge 617 are substantially parallel to each other means that the angle α ≤ 3° formed by the intersection of the straight lines of any two edges. Therefore, the first edge 615 , the second edge 616 and the third edge 617 are substantially parallel, so that the planar shape of the protective coating 612 and the tab portion 614 is substantially rectangular. Such a solution can improve the convenience of manufacturing the current collector 61, and by limiting the reasonable value range of L ₂ /L ₁ , it can ensure that the coating of the protective coating 612 plays a protective role while reducing the application cost of the protective coating 612. Coverage area, beneficially improve the energy density of secondary batteries.

In the embodiment of the present application, the first direction X is perpendicular to the second direction Y. In the above technical solution, the protective coating 612 is applied in a direction perpendicular to the edge and covers along the width direction of the tab portion 614, which can improve the protective performance of the protective coating 612 and prevent the base material 611 from breaking. At the same time, it can ensure the regularity of the shape of the protective coating 612 and improve the convenience of manufacturing and installation.

In some embodiments of the present application, the substrate 611 is selected from aluminum foil or aluminum polymer composite substrates.

Aluminum has properties such as good electrical conductivity and flexibility, making it a good conductor of electricity and easy to process. Fresh aluminum foil is easily oxidized in the air, and then an oxide film will be formed on the surface. This oxide film can block the corrosion of aluminum by external moisture and air, further ensuring the thermodynamic stability of the aluminum foil. Therefore, aluminum is often used as a material for the positive electrode current collector of secondary batteries.

However, when the current collector substrate coated with the active material slurry is cold pressed to prepare the electrode piece, the active material particles will crush the protective oxide film on the surface of the aluminum foil, thus destroying the integrity of the oxide film, causing some Aluminum exposed. Because aluminum has strong reducing properties, it is prone to chemical reactions with certain substances in the electrolyte and is corroded. In particular, when the electrolyte contains a fluorine-containing sulfonyl imide lithium salt, during the charging process, the fluorine-containing sulfonyl imide lithium salt is oxidized, and the anions of the oxidation product react with the exposed fresh aluminum to form a product and Soluble in electrolyte. And the corrosion reaction is affected by temperature and accelerates as the temperature increases. Therefore, corrosion pits or broken strips will appear in the area of the current collector close to the tabs, causing safety risks and reducing the service life of the secondary battery.

According to embodiments of the present application, by coating a certain area of the protective coating 612 on a specific area of the aluminum-containing substrate 611, it is possible to effectively prevent strip breakage due to corrosion of aluminum.

In the embodiment of the present application, the thickness of the substrate 611 ranges from 8 μm to 20 μm. By setting a reasonable thickness range of the base material 611, the energy density of the secondary battery can be improved while ensuring the conductive effect of the electrode plate.

In the embodiment of the present application, the protective coating 612 includes a binder and a conductive agent. Optionally, the binder is selected from polyacrylic resin, PVDF and its copolymers, polyacrylonitrile, epoxy resin conductive glue, At least one of the phenolic resin conductive adhesives, optionally, the conductive agent is selected from at least one of carbon black, graphite, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

In the above technical solution, the conductive agent can ensure that the protective coating 612 has good conductivity, and the adhesive can ensure the bonding strength between the protective coating 612 and the base material 611 .

In the embodiment of the present application, the electrode active material layer 62 includes an active material, an electrode binder and an electrode conductive agent. Optionally, the active material is selected from _LiNix Co _y N _z M _1-xyz O ₂ , LiMn ₂ O _4. At least one of Li ₂ MnO _3·(1-a) LiPO ₂ and LiFePO ₄ ; optionally, the electrode binder is selected from polyacrylic resin, PVDF and its copolymers, polyacrylonitrile, and epoxy At least one of resin conductive glue and phenolic resin conductive glue; optionally, the electrode conductive agent is selected from at least one of carbon black, graphite, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

Optionally, the cathode active material in the embodiment of the present application can be selected from:

1) _LiNix Co _y N _z M _1-xyz O ₂ , where N is selected from Mn and Al, M is selected from Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Any one of V and Ti, 0≤x<1, 0≤y≤1, 0≤z≤1, x+y+z≤1,

2) At least one of LiMn ₂ O ₄ , Li ₂ MnO _3·(1-a) LiPO ₂ (P=Ni, Co, Mn)0<a<1,

3) LiFePO ₄

Any one of them can also be a positive electrode material mixed with the above three types of materials in any proportion.

Optionally, the negative active material in the embodiment of the present application can be selected from: natural graphite, artificial graphite, mesophase microcarbon balls (MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composite, Li- One or more of Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO ₂ , spinel structure lithiated TiO ₂ -Li ₄ Ti ₅ O ₁₂ , and Li-Al alloy.

In the embodiment of the present application, the thickness H ₁ of the protective coating 612 and the thickness H ₂ of the substrate satisfy the relationship: H ₂ /26 ≤ H ₁ ≤ _{H 2} /2.6. Therefore, by setting a reasonable coating thickness of the protective coating 612, the heat dissipation effect of the pole piece can be improved while ensuring the protection effect and preventing the occurrence of holes or breaks in the base material 611, and the total thickness of the pole piece can be reduced as much as possible. , ensuring the energy density of secondary batteries.

In the embodiment of the present application, the protective coating 612 includes a binder with a mass of W ₁ and a conductive agent with a mass of W ₂ . The ratio B of W ₁ to W ₁ + W ₂ satisfies the relationship: 0.05≤B≤0.5. In the above technical solution, by setting a reasonable mass ratio of conductive agent to binder, the bonding strength and conductive effect can be ensured, while the process performance of protective coating coating and drying can be improved.

In the embodiment of the present application, the thickness D ₁ of the active material layer and the thickness H ₁ of the protective coating satisfy the relationship: D ₁ /200 ≤ _{H 1} ≤ _{D 1} /30. In the above technical solution, by setting a reasonable thickness of the active material layer and protective coating, the protective effect of the protective coating area and the electrical performance of the electrode piece are ensured, while the total thickness of the electrode piece is controlled.

In the embodiments of this application, the electrode pole pieces are prepared by the following method:

Take aluminum foil as the base material, mix the adhesive and conductive agent evenly to make a protective coating slurry, apply the protective coating slurry to the preset area of the main body of the base material near the tab, and dry it to form protective coating;

Mix the active material, electrode binder and electrode conductive agent evenly to obtain an electrode active material slurry, apply the electrode active material slurry on the main body of the base material with a protective coating, cold-press and air-dry to obtain an electrode pole piece . The preparation method of the above electrode pole piece is simple and has high manufacturability.

secondary battery

In the embodiments of the present application, there is no particular restriction on the type of isolation membrane, and any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.

In the embodiment of the present application, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

In the embodiment of the present application, the positive electrode piece, the negative electrode piece and the isolation film can be made into an electrode assembly through a winding process or a lamination process.

In the embodiments of the present application, the solvent is selected from at least two of dimethyl carbonate, diethyl carbonate, propylene carbonate, ethyl methyl carbonate, fluoroethylene carbonate, ethyl formate, ethyl acetate, and tetrahydrofuran. .

Optionally, the solvent may also include dipropyl carbonate, methylpropyl carbonate, ethylene carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, ethyl propyl carbonate, γ-butyrolactone, methyl formate. Select one or more from ester, propyl acetate, methyl propionate, ethyl propionate, methyl propionate and tetrahydrofuran.

In the embodiment of the present application, the mass percentage of the solvent in the electrolyte is 65% to 85%. The above technical solution, by setting a reasonable mass fraction of the solvent, can ensure the performance of the electrolyte in dispersing active materials while ensuring its wettability to the electrode assembly.

In the embodiment of the present application, the electrolyte includes lithium hexafluorophosphate and fluorine-containing sulfonyl imide lithium salt. Optionally, the molar concentration C ₁ of the lithium hexafluorophosphate salt is 0.1 mol/L ≤ C ₁ ≤ 1 mol/L, and the fluorine-containing sulfonyl imide lithium salt is The molar concentration C ₂ of lithium amine is 0.5 mol/L ≤ C ₂ ≤ 1.5 mol/L. In the above technical solution, the fluorine-containing sulfonyl imide lithium salt can withstand high temperatures and is insoluble in water. By adding a certain amount of fluorine-containing sulfonyl imide lithium salt, the safety of the secondary battery can be improved to a certain extent.

In the embodiment of the present application, the molar concentration C ₁ of the lithium hexafluorophosphate salt and the molar concentration C ₂ of the lithium fluorine-containing sulfonylimide satisfy: 0.6mol/L≤C ₁ +C ₂ ≤2mol/L, and 1≤C ₂ /C ₁ ≤5.

Therefore, by adding a reasonable concentration ratio of lithium hexafluorophosphate and lithium fluorine-containing sulfonylimide to the electrolyte, the ionic conductivity of the electrolyte can be ensured while the chemical stability and thermal stability of the electrolyte can be improved, thereby improving the safety of the battery. performance.

In the embodiment of the present application, the tab area A ₁ , the protective coating area A ₂ , the molar concentration C ₁ of the lithium hexafluorophosphate salt, and the molar concentration C ₂ of the fluorinated sulfonylimide lithium salt satisfy: C ₂ /(10C ₁ )≤A ₂ /A ₁ ≤C ₂ /(2C ₁ )+2.5.

Fluorine-containing lithium sulfonylimide easily reacts chemically with aluminum. When the electrolyte contains a certain molar concentration of lithium hexafluorophosphate and lithium fluorine-containing sulfonimide, by setting the area of the protective coating so that it meets the requirements stipulated in this embodiment, it can be ensured that even if an aluminum substrate is used, It can prevent the corrosion of aluminum by lithium fluorosulfonyl imide, thus preventing pits or breakage on the surface of the substrate.

In the embodiments of the present application, the fluorine-containing sulfonyl imide lithium salt includes compounds represented by formula I,

Optionally, R ₁ is an F atom and R ₂ is an F atom.

In the embodiment of the present application, the electrolyte further includes additives selected from the group consisting of vinylene carbonate, vinyl sulfate, lithium difluoroxalate borate, lithium difluorophosphate, lithium tetrafluoroborate, and 1,3-propanesulfonic acid. At least one of ester, lithium trifluoromethanesulfonate, and lithium diacetate borate. In the above technical solution, by adding at least one additive to the electrolyte, the efficiency and/or safety of battery operation can be improved.

This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, FIG. 3 shows a square-structured secondary battery 5 as an example.

In some embodiments, referring to FIG. 4 , the outer package may include a housing 51 and a cover 53 . The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.

Figure 5 shows a battery module 4 as an example. Referring to 5, in the battery module 4, a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, it can also be arranged in any other way. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

Figures 6 and 7 show the battery pack 1 as an example. Referring to FIGS. 6 and 7 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3 . The upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack may be used as a power source for the electrical device, or may be used as an energy storage unit for the electrical device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

As the power-consuming device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

FIG. 8 shows an electrical device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the electrical device, a battery pack or battery module can be used.

As another example, the device may be a mobile phone, a tablet, a laptop, etc. The device is usually required to be thin and light, and a secondary battery can be used as a power source.

Example

Hereinafter, examples of the present application will be described. The embodiments described below are illustrative and are only used to explain the present application and are not to be construed as limitations of the present application. If specific techniques or conditions are not specified in the examples, the techniques or conditions described in literature in the field or product instructions will be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

Examples 1 to 6

1. Preparation of electrolyte

In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), add 2% mass concentration of vinylene carbonate to the organic solvent (EC:EMC=3:7W%/W%), and mix After uniformity, slowly add an appropriate amount of lithium salt to the non-aqueous organic solvent (see Table 1 below for the specific contents of LiPF ₆ and lithium bisfluorosulfonimide). After the lithium salt of bisfluorosulfonimide is completely dissolved, the target is obtained. The electrolyte is the electrolyte used in the examples and comparative examples of this application.

In Examples 1-6 and Comparative Examples 1-3, the ratios of solvents and additives used are shown in Table 1.

Table 1 Electrolyte raw material ratio table

2. Preparation of positive electrode plates (Examples 1 to 6 and Comparative Examples 2 to 3):

First, mix the aqueous solution containing conductive carbon (mass content W1 = 50%) and polyacrylate (mass content W2 = 50%) evenly to prepare a protective coating slurry.

Coat the protective coating slurry on the aluminum foil substrate, the ratio of the coated area to the area of the tab (A ₂ /A ₁ ) and the ratio of the distance between the edges of the coating area (L ₂ /L ₁ ) Make the settings as in Table 2 to obtain the current collector.

Dry the current collector in an oven at 85°C and set aside.

Put the positive active material LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMnO ₂ electrode conductive agent Super P, and electrode binder polyvinylidene fluoride (PVDF) in N -Cathode active slurry is made from methylpyrrolidone (NMP). The solid content of the cathode active slurry is 50wt%, and the mass ratio of LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , Super P, and PVDF in the solid component is 8:1: 1.

Coat the positive electrode active slurry on the current collector obtained in the above steps, and the positive electrode active slurry completely covers the main body.

After drying at 85°C, cold pressing is performed, and then trimming, cutting, and slitting are performed, and then dried under vacuum conditions at 85°C for 4 hours to make the positive electrode piece.

Table 2 Protective coating coating proportion table

	L ₂/L ₁ L ₂ /L ₁	A ₂/A ₁ A ₂ /A ₁	热失控温度℃Thermal runaway temperature °C	倍率放电容量保持率Rate discharge capacity retention rate
实施例1Example 1	0.50.5	0.50.5	145145	84.50％84.50%
实施例2Example 2	0.80.8	1.01.0	140140	85.60％85.60%
实施例3Example 3	1.01.0	2.02.0	151151	86.30％86.30%

实施例4Example 4	2.52.5	2.52.5	150150	86.70％86.70%
实施例5Example 5	2.02.0	2.52.5	146146	86.80％86.80%
实施例6Example 6	2.52.5	4.54.5	150150	83.30％83.30%
对比例1Comparative example 1	无保护涂层No protective coating	无保护涂层No protective coating	9090	73.80％73.80%
对比例2Comparative example 2	0.450.45	0.450.45	100100	76.50％76.50%
实施例3Example 3	44	5.55.5	121121	73.20％73.20%

3. Preparation of positive electrode plate (Comparative Example 1):

Combine the positive active material LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMnO ₂ ), electrode conductive agent Super P, and electrode binder polyvinylidene fluoride (PVDF) The positive electrode active slurry was prepared in N-methylpyrrolidone (NMP). The solid content of the positive electrode active slurry is 50wt%, and the mass ratio of LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , Super P, and PVDF in the solid content is 8:1:1.

The positive electrode active slurry is coated on the aluminum foil and dried at 85°C, then cold-pressed, then trimmed, cut into pieces, and slit, and then dried under vacuum conditions at 85°C for 4 hours to make positive electrode sheets.

4. Preparation of negative electrode plates (Examples 1 to 6 and Comparative Examples 1 to 3):

Mix the graphite as the negative active material, the electrode conductive agent Super P, the thickener CMC, and the electrode binder styrene-butadiene rubber (SBR) in deionized water evenly to make a negative active slurry. The solid content of the negative active slurry is 30wt%, and the mass ratio of graphite, Super P, CMC and adhesive styrene-butadiene rubber (SBR) in the solid components is 80:15:3:2.

The negative electrode active slurry is coated on the copper foil and dried at 85°C, then cold pressed, trimmed, cut into pieces, and slit, and then dried under vacuum conditions at 120°C for 12 hours to make the negative electrode piece.

5. Preparation of secondary batteries (Examples 1 to 6 and Comparative Examples 1 to 3):

Use 16 μm polyethylene film (PE) as the isolation film. Stack the prepared positive electrode pieces, isolation film, and negative electrode pieces in order so that the isolation film is between the positive and negative electrode pieces to isolate the positive and negative electrodes. The electrode assembly is obtained by winding, the tabs are welded, and the bare electrode is The core is placed in the outer package, and the electrolyte prepared above is injected into the dried electrode assembly, followed by packaging, standing, formation, shaping, capacity testing, etc., to complete the preparation of the secondary battery (the thickness of the soft-pack battery is 4.0 mm , width 60mm, length 140mm).

Next, the testing process of the secondary battery will be explained.

(1) Thermal runaway performance test of secondary batteries.

Adjust the ambient temperature to 25°C, charge the battery core at 1C to 4.2V, and then charge it to 0.05C at a constant voltage. Place the battery core in the heating furnace. The furnace heats up at 10°C/min and keeps it warm for 10 minutes until the battery core experiences thermal runaway ( The battery core releases heat rapidly, and the temperature rise rate of the battery core surface is higher than the furnace temperature rise rate. At this time, the battery core begins to thermally run out of control), and the process ends. Record the temperature monitored by the furnace when the cell thermal runaway occurs.

The cells in the secondary battery will release temperature during operation, so this test tests the high temperature resistance of the secondary battery by simulating the high temperature environment in the use environment. Specifically, by testing the thermal runaway temperature of the secondary battery, the reaction between the aluminum foil in the electrode plate of the secondary battery and the fluorine-containing sulfonimide lithium salt in the electrolyte can be obtained. When the reaction efficiency is high, the faster the positive electrode piece breaks, the lower the thermal runaway temperature, and the worse the performance of the electrode piece. When the reaction efficiency is low, the slower the positive electrode piece breaks, the higher the thermal runaway temperature, and the better the performance of the electrode piece.

(2)Lithium-ion battery rate performance test

At 25℃, charge 1C to 4.2V, then charge with constant voltage to 0.05C, let it stand for 20 minutes, discharge 1C to 2.8V, record the discharge capacity D0 at this time, then charge with 1C to 4.2V, and then charge with constant voltage to 0.05C. Let stand for 20 minutes, discharge at 3C to 2.8V, record the discharge capacity D1, and rate discharge capacity retention rate M=D1/D0.

Table 3 Thermal runaway temperature performance and capacity retention rate of secondary batteries

电池编号Battery number	热失控温度℃Thermal runaway temperature °C	MM
实施例1Example 1	145145	84.5％84.5%
实施例2Example 2	140140	85.6％85.6%
实施例3Example 3	151151	86.3％86.3%
实施例4Example 4	150150	86.7％86.7%
实施例5Example 5	146146	86.8％86.8%
实施例6Example 6	150150	83.3％83.3%
对比例1Comparative example 1	9090	73.8％73.8%
对比例2Comparative example 2	100100	76.5％76.5%

Comparative example 3

121

73.2%

As shown in Table 3, in Examples 1 to 6, 0.05≤A ₂ /A ₁ ≤6 is satisfied. Therefore, the thermal runaway temperatures in the above-mentioned examples are all higher than 140 degrees Celsius. The above-mentioned thermal runaway temperature is relatively high and meets the thermal runaway temperature requirements of secondary batteries. Moreover, the rate discharge capacity retention rates of the above embodiments are significantly improved compared with the comparative examples. It shows that the electrode pole pieces in the above embodiments can effectively improve the electrical performance of the battery core.

Specifically, in Example 1, A ₂ /A ₁ =0.5, L ₂ /L ₁ =0.5. Compared with Examples 2-5, the area of the protective coating in Example 1 is smaller, so its thermal runaway temperature is lower. . However, due to the small area of the protective layer, the active material and the aluminum foil have good conductivity, so it has a high rate discharge capacity retention rate.

In Example 2, A ₂ /A ₁ =0.8, L ₂ /L ₁ =1.0. Compared with other examples, the area of the protective coating in Example 2 is smaller, so its thermal runaway temperature is lower. However, due to the small area of the protective layer, the active material and the aluminum foil have good conductivity, so it has a high rate discharge capacity retention rate.

In Example 3, A ₂ /A ₁ =1.0, L ₂ /L ₁ =2.0, and the protective coating area of Example 3 is larger than the protective coating area of Example 1 and Example 2. Therefore, it can better protect the area near the pole lug from high temperatures, and the thermal runaway temperature is higher. And the area of the protective layer is relatively reasonable, so it has a high rate discharge capacity retention rate.

In Example 4, A ₂ /A ₁ =2.5 and L ₂ /L ₁ =2.5. The protective coating area of Example 4 is larger than that of Example 1, Example 2 and Example 3. Therefore, it can better protect the area near the pole lug from high temperatures, and the thermal runaway temperature is higher. And the area of the protective layer is relatively reasonable, so it has a high rate discharge capacity retention rate.

In Example 5, A ₂ /A ₁ =2.0 and L ₂ /L ₁ =2.5. The protective coating area of Example 5 is larger than the protective coating area of Example 1, Example 2 and Example 3. Therefore, it can better protect the area near the pole lug from high temperatures, and the thermal runaway temperature is higher. And the area of the protective layer is relatively reasonable, so it has a high rate discharge capacity retention rate.

In Example 6, A ₂ /A ₁ =2.5, L ₂ /L ₁ =4.5, and Example 5 has the largest protective coating area. Therefore, it can better protect the area near the pole lug from high temperatures, and the thermal runaway temperature is higher. However, its protective coating will affect the heat dissipation of the electrode pole piece, so its rate discharge capacity retention rate is slightly lower than the above-mentioned embodiments.

In Comparative Example 1, there is no protective coating. The surface of the aluminum foil punctured by the active material particles reacts rapidly with the fluorine-containing lithium sulfonyl imide in the electrolyte, causing the aluminum foil to break and causing a short circuit inside the battery. Therefore, it is damaged at 90°C. That is, thermal runaway occurs, and its rate discharge capacity retention rate is low and its electrical performance is poor.

In Comparative Example 2, A ₂ /A ₁ =0.45 and L ₂ /L ₁ =0.45. The protective coating area of Comparative Example 2 is smaller. Therefore, the area near the pole lug cannot be effectively protected, and the aluminum foil will still be corroded and fractured at a lower temperature. And its rate discharge capacity retention rate is lower than that of the above-mentioned embodiments.

In Comparative Example 3, A ₂ /A ₁ =4 and L ₂ /L ₁ =5.5. Comparative Example 3 has the largest protective coating area. Therefore, the area near the pole lug can be protected to a certain extent. However, the protective coating area is too large and the electrode piece cannot effectively dissipate heat, causing the temperature of the pole piece surface to rise rapidly, and the area near the pole lug will still undergo relatively large heat dissipation. Violent corrosion. Therefore, its thermal runaway temperature is lower. Moreover, its rate discharge capacity retention rate is lower than that of the above-mentioned embodiments.

The above results show that when the electrolyte contains lithium fluorosulfonate imine, only by setting a protective coating in the area close to the pole lug and reasonably limiting the area of the protective coating can the base of the protective coating area be effectively reduced. It reduces the probability that the material will come into contact with the electrolyte and react, while ensuring the heat dissipation efficiency of the electrode plate, improving the integrity of the substrate in the protective coating area, improving the stability of the secondary battery operation and extending its cycle life.

It should be noted that the present application is not limited to the above-described embodiment. The above-mentioned embodiments are only examples. Within the scope of the technical solution of the present application, embodiments that have substantially the same structure as the technical idea and exert the same functions and effects are included in the technical scope of the present application. In addition, within the scope that does not deviate from the gist of the present application, various modifications to the embodiments that can be thought of by those skilled in the art, and other forms constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application. .

Claims

An electrode pole piece, including:

A current collector includes a base material and a protective coating. The base material includes a main body portion and a tab portion arranged along a first direction. The tab portion has a first edge extending along a second direction. The first direction Intersecting with the second direction; the protective coating is disposed on part of the surface of the main body portion to form a second edge adjacent to the tab portion and extending along the second direction, and the protective coating The coating extends along the first direction and forms a third edge extending along the second direction; and

An electrode active material layer is provided on the protective coating and at least part of the surface of the main body part,

Wherein, the ear portion area A 1 defined by the second edge and the first edge, and the protective coating area A 2 defined by the second edge and the third edge satisfy:

0.05≤A 2 /A 1 ≤6, optional, 0.1≤A 2 /A 1 ≤5.
The electrode pole piece according to claim 1, wherein the first edge, the second edge and the third edge are substantially parallel to each other, and a distance L between the second edge and the first edge 1 and the distance L 2 between the second edge and the third edge satisfies:

0.05≤L 2 /L 1 ≤6, optional, 0.1≤L 2 /L 1 ≤5.
The electrode pole piece according to claim 1 or 2, wherein the substrate is selected from aluminum foil or aluminum polymer composite substrate.
The electrode pole piece according to claim 3, wherein the protective coating includes a binder and a conductive agent,

Optionally, the binder is selected from at least one of polyacrylic resin, PVDF and its copolymers, polyacrylonitrile, epoxy resin conductive glue, and phenolic resin conductive glue,

Optionally, the conductive agent is selected from at least one of carbon black, graphite, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.
The electrode pole piece according to claim 3, wherein the electrode active material layer includes an active material, an electrode binder and an electrode conductive agent,

Optionally, the active material is selected from at least one of LiNix Co y N z M 1-xyz O 2 , LiMn 2 O 4 , Li 2 MnO 3·(1-a) LiPO 2 and LiFePO 4 ;

Optionally, the electrode binder is selected from at least one of polyacrylic resin, PVDF and its copolymers, polyacrylonitrile, epoxy resin conductive glue, and phenolic resin conductive glue;

Optionally, the electrode conductive agent is selected from at least one of carbon black, graphite, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.
The electrode pole piece according to claim 3, wherein the thickness H 1 of the protective coating and the thickness H 2 of the substrate satisfy the relationship: H 2 /26 ≤ H 1 ≤ H 2 /2.6.
The electrode pole piece according to claim 4, wherein the protective coating includes the binder with a mass of W 1 and the conductive agent with a mass of W 2 , the ratio of W 1 to W 1 + W 2 B satisfies the relationship: 0.05≤B≤0.5.
The electrode pole piece according to claim 7, wherein the thickness D 1 of the active material layer and the thickness H 1 of the protective coating satisfy the relationship: D 1 /200 ≤ H 1 ≤ D 1 /30.
A secondary battery including:

The electrode pole piece according to any one of claims 1 to 8;

isolation film;

Electrolyte, including solvent and electrolyte.
The secondary battery according to claim 9, wherein

The electrolyte includes lithium hexafluorophosphate and lithium fluorine-containing sulfonimide,

Optionally, the molar concentration C 1 of the lithium hexafluorophosphate salt is 0.1 mol/L ≤ C 1 ≤ 1 mol/L, and the molar concentration C 2 of the fluorine-containing lithium sulfonylimide is 0.5 mol/L ≤ C 2 ≤ 1.5 mol/L.
The secondary battery according to claim 10, wherein the molar concentration C1 of the lithium hexafluorophosphate salt and the molar concentration C2 of the fluorine-containing lithium sulfonylimide satisfy:

0.6mol/L≤C 1 +C 2 ≤2mol/L, and 1≤C 2 /C 1 ≤5.
The secondary battery according to claim 11, wherein the tab area A 1 , the protective coating area A 2 , the molar concentration C 1 of the lithium hexafluorophosphate salt, the fluorine-containing lithium sulfonyl imide The molarity of C2 satisfies:

C 2 /(10C 1 )≤A 2 /A 1 ≤C 2 /(2C 1 )+2.5.
The secondary battery according to any one of claims 9 to 12, wherein the fluorine-containing sulfonimide lithium salt includes a compound represented by formula I,

Wherein, R 1 is selected from any one of F atom and C1-C3 alkyl group substituted by F;

R 2 is selected from any one of F atoms and C1-C3 alkyl groups substituted by F. Alternatively, R 1 is an F atom and R 2 is an F atom.
The secondary battery according to claim 13, wherein the electrolyte further includes an additive selected from the group consisting of vinylene carbonate, vinyl sulfate, lithium difluoroborate, lithium difluorophosphate, and lithium tetrafluoroborate. , at least one of 1,3-propanesultone, lithium trifluoromethanesulfonate, and lithium diacetate borate.
A battery module including the secondary battery according to any one of claims 9 to 14.
A battery pack including the battery module according to claim 15.
An electric device including at least one selected from the group consisting of the secondary battery according to any one of claims 9 to 14, the battery module according to claim 15, or the battery pack according to claim 16.