Electrode piece, secondary battery, battery module, battery pack and electric device

Abstract

The invention provides an electrode plate, a secondary battery, a battery module, a battery pack and an electric device. The electrode pole piece comprises a current collector, the current collector comprises a base material and a protective coating, the base material comprises a main body part and a tab part which are arranged along a first direction, and the tab part is provided with a first edge extending along a second direction; the protective coating is arranged on at least part of the surface of the main body part so as to form a second edge which is adjacent to the tab part and extends along the second direction, and the protective coating extends along the first direction and forms a third edge which extends along the second direction; the electrode active material layer is arranged on the side, away from the main body part, of the protective coating, and the area A1 of the tab part defined by the second edge and the first edge and the area A2 of the protective coating defined by the second edge and the third edge meet the condition that A2 / A1 is larger than or equal to 0.05 and smaller than or equal to 6. According to the electrode plate provided by the embodiment of the invention, the operation stability of the secondary battery under a high-temperature condition can be improved, and the cycle life of the secondary battery is prolonged.

Description

Electrode sheets, secondary batteries, battery modules, battery packs and electrical devices Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to an electrode plate, a secondary battery, a battery module, a battery pack, and an electrical device. Background Art

[0002] 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 and electric vehicles.

[0003] In addition to improving the electrical performance of secondary batteries, the safety of secondary batteries during operation is also a key research focus in this field. Since the probability of safety accidents involving secondary battery electrodes in high-temperature environments is greatly increased, improving the safety performance of electrodes in high-temperature environments is also an urgent issue that needs to be addressed.

[0004] Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide an electrode plate that can improve the stability of secondary batteries operating under high temperature conditions and extend their cycle life.

[0006] In order to achieve the above-mentioned objectives, the present application provides an electrode plate, a secondary battery, a battery module, a battery pack and an electrical device.

[0007] A first aspect of the present application provides an electrode plate, comprising:

[0008] A current collector comprising a substrate and a protective coating, wherein the substrate comprises a main body portion and a pole ear portion arranged along a first direction, the pole ear portion having a first edge extending along a second direction, the first direction intersecting the second direction; the protective coating is disposed on a portion of a surface of the main body portion to form a second edge adjacent to the pole ear portion and extending along the second direction, and the protective coating extends along the first direction and forms a third edge extending along the second direction; and

[0009] an electrode active material layer disposed on at least a portion of the surface of the protective coating and the main body;

[0010] The area A1 of the pole ear defined by the second edge and the first edge and the area A2 of the protective coating defined by the second edge and the third edge satisfy: 0.05≤A2 / A1≤6, optionally, 0.1≤A2 / A1≤5.

[0011] The present application provides a protective coating in the area of ​​the current collector substrate close to the pole ear and reasonably limits the area of ​​the protective coating, thereby effectively reducing the probability of the substrate in the protective coating area contacting and reacting with the electrolyte, 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.

[0012] In some embodiments, the first edge, the second edge, and the third edge are substantially parallel to each other, and the spacing L1 between the second edge and the first edge and the spacing L2 between the second edge and the third edge satisfy: 0.05≤L2 / L1≤6, optionally, 0.1≤L2 / L1≤5.

[0013] As a result, the three edges are roughly parallel, making the protective coating and the tabs roughly rectangular in plan. This solution improves the manufacturing convenience of the current collector and, by limiting the reasonable value range of L2 / L1, reduces the coating area while ensuring the protective effect of the protective coating, thereby effectively improving the energy density of the secondary battery.

[0014] In some embodiments, the substrate is selected from aluminum foil or an aluminum-polymer composite substrate. When using an aluminum substrate (such as aluminum foil or an aluminum-polymer composite substrate), aluminum is susceptible to chemical reactions with certain substances in the electrolyte, such as certain electrolytes, causing corrosion, particularly at elevated temperatures, which can lead to pitting or broken strips on the substrate surface. Therefore, applying a protective coating to the aluminum-containing substrate can prevent electrolyte corrosion of the aluminum, thereby preventing pitting or broken strips on the substrate surface.

[0015] In some embodiments, 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 adhesive, and phenolic resin conductive adhesive. 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 ensures good conductivity of the protective coating, and the binder ensures bond strength between the protective coating and the substrate.

[0016] 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 LiNi x Co y N z M 1-x-y-z O2, LiMn2O4, Li2MnO 3·(1-a)At least one of LiPO2 and LiFePO4; optionally, the electrode binder is selected from at least one of polyacrylic resin, PVDF and its copolymers, polyacrylonitrile, epoxy resin conductive adhesive, phenolic resin conductive adhesive; 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.

[0017] In some embodiments, the thickness H1 of the protective coating and the thickness H2 of the substrate satisfy the relationship: H2 / 26≤H1≤H2 / 2.6. Thus, by setting a reasonable coating thickness for the protective coating, while ensuring protection and preventing pits or breakage in the substrate, the heat dissipation of the electrode is improved, and the total thickness of the electrode is minimized to ensure the energy density of the secondary battery.

[0018] In some embodiments, the protective coating comprises a binder having a mass W1 and a conductive agent having a mass W2, wherein the ratio B of W1 to W1 + W2 satisfies the relationship: 0.05 ≤ B ≤ 0.5. In the above technical solution, by setting a reasonable mass ratio of the conductive agent to the binder, the coating and drying process performance of the protective coating can be improved while ensuring bonding and conductivity.

[0019] In some embodiments, the thickness D1 of the electrode active material layer and the thickness H1 of the protective coating satisfy the relationship: D1 / 200≤H1≤D1 / 30. In the above technical solution, by setting reasonable thicknesses of the active material layer and protective coating, the protective effect of the protective coating area and the electrical performance of the electrode sheet are guaranteed, while the total thickness of the electrode sheet is controlled to ensure the energy density of the secondary battery.

[0020] A second aspect of the present application provides a secondary battery, comprising the electrode plate, a separator and an electrolyte according to the first aspect of the present application, wherein the electrolyte comprises a solvent and an electrolyte.

[0021] In some embodiments, the electrolyte includes lithium hexafluorophosphate and a fluorinated lithium sulfonyl imide salt. Optionally, the molar concentration C1 of the lithium hexafluorophosphate salt is 0.1 mol / L ≤ C1 ≤ 1 mol / L, and the molar concentration C2 of the fluorinated lithium sulfonyl imide salt is 0.5 mol / L ≤ C2 ≤ 1.5 mol / L. In the above technical solution, the fluorinated lithium sulfonyl imide salt is resistant to high temperatures and insoluble in water. Therefore, adding a certain amount of the fluorinated lithium sulfonyl imide salt can improve the safety of the secondary battery to a certain extent.

[0022] In some embodiments, the molar concentration C1 of the lithium hexafluorophosphate salt and the molar concentration C2 of the lithium fluorinated sulfonyl imide satisfy the following conditions: 0.6 mol / L ≤ C1 + C2 ≤ 2 mol / L, and 1 ≤ C2 / C1 ≤ 5. Thus, by setting a reasonable ratio of lithium hexafluorophosphate salt and lithium fluorinated sulfonyl imide salt in the electrolyte, the ionic conductivity of the electrolyte can be maintained while improving the chemical and thermal stability of the electrolyte, thereby enhancing the safety performance of the battery.

[0023] In some embodiments, the lug area A1, the protective coating area A2, the molar concentration C1 of lithium hexafluorophosphate salt, and the molar concentration C2 of lithium fluorinated sulfonyl imide satisfy: C2 / (10C1)≤A2 / A1≤C2 / (2C1)+2.5.

[0024] Fluorinated lithium sulfonyl imide readily reacts chemically with aluminum. When the electrolyte contains a certain molar concentration of lithium hexafluorophosphate and lithium fluorinated lithium sulfonyl imide, by setting the area of ​​the protective coating to meet the requirements of this embodiment, it is possible to prevent corrosion of the aluminum by the lithium fluorinated lithium sulfonyl imide even when using an aluminum substrate, thereby preventing pitting or tape breakage on the substrate surface.

[0025] In any embodiment, the fluorinated sulfonyl imide lithium salt comprises a compound represented by Formula I,

[0026]

[0027] Wherein, R1 is selected from any one of a F atom and a C1-C3 alkyl group substituted by F;

[0028] R2 is selected from any one of a F atom and a C1-C3 alkyl group substituted by F,

[0029] Optionally, R1 is a F atom, and R2 is a F atom.

[0030] In the above technical solution, the selected fluorinated sulfonyl imide 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. In addition, the raw materials of the above compound are easily available and easy to manufacture.

[0031] In any embodiment, the electrolyte further includes an additive selected from at least one of vinylene carbonate, vinyl sulfate, lithium difluorooxalatoborate, lithium difluorophosphate, lithium tetrafluoroborate, 1,3-propane sultone, 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 the battery can be improved.

[0032] A third aspect of the present application provides a battery module including the secondary battery according to the second aspect of the present application.

[0033] A fourth aspect of the present application provides a battery pack comprising the battery module of the third aspect of the present application.

[0034] The fifth aspect of the present application provides an electrical device comprising 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.

[0035] This application provides a protective coating in the area near the pole ear and reasonably limits the area of ​​the protective coating, thereby effectively reducing the probability of the substrate in the protective coating area contacting and reacting with the electrolyte in a high-temperature environment, 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG1 is a schematic structural diagram of an electrode plate according to an embodiment of the present application.

[0037] FIG2 is a schematic diagram of the BB section in FIG1 .

[0038] FIG3 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0039] FIG. 4 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 3 .

[0040] FIG5 is a schematic diagram of a battery module according to an embodiment of the present application.

[0041] FIG6 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0042] FIG. 7 is an exploded view of the battery pack shown in FIG. 6 according to an embodiment of the present application.

[0043] FIG8 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0044] Description of reference numerals:

[0045] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly; X first direction; Y second direction;

[0046] 6 Electrode pole piece; 61 Current collector; 611 Substrate; 612 Protective coating; 613 Main body; 614 Ear; 615 First edge; 616 Second edge; 617 Third edge; 62 Electrode active material layer. DETAILED DESCRIPTION

[0047] Below, the embodiments of the conductive paste, current collector, secondary battery, battery module, battery pack and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of 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.

[0048] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0050] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0051] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0052] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may indicate that other components not listed may also be included or that only the listed components are included.

[0053] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0054] Typically, the preparation process of an electrode pole piece includes coating an active material slurry on the surface of a 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 cell, and 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, thereby damaging the surface of the current collector substrate. When such an electrode pole piece is used in a battery, the damaged surface of the current collector substrate comes into contact with the electrolyte, causing the material inside the substrate to be exposed to the electrolyte. Certain substances in the electrolyte may react chemically with the material inside the substrate, especially when the battery is charged and discharged. Such chemical reactions can cause corrosion pits or broken bands in the current collector substrate, creating safety risks and reducing the service life of the secondary battery.

[0055] Furthermore, through extensive research and observation, the inventors discovered that the aforementioned corrosion reaction is affected by temperature, accelerating as the temperature rises. During battery operation, the current generated by the active material in the electrode sheet is collected by the current collector and then fed to the tab for external supply. Therefore, the area near the tab where the current collector is located is typically hotter, and this is also where corrosion or fractures are most likely to occur.

[0056] Based on this, the present application addresses the above problems and develops an electrode plate, which effectively reduces the probability of the substrate in the protective coating area contacting and reacting with the electrolyte, 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.

[0057] Electrode plate

[0058] In a first aspect of the present application, an electrode plate 6 is proposed. As shown in FIG. 1 and FIG. 2 , the electrode plate 6 in the present application includes: a current collector 61 and an electrode active material layer 62 .

[0059] The current collector 61 includes a substrate 611 and a protective coating 612. The substrate 611 includes a main body 613 and a pole ear 614 arranged along a first direction X. The pole ear 614 has a first edge 615 extending along a second direction Y. The first direction X intersects with the second direction Y. The protective coating 612 is arranged on a portion of the surface of the main body 613 to form a second edge 616 adjacent to the pole ear 614 and extending along the second direction Y. The protective coating 612 extends along the first direction X and forms a third edge 617 extending along the second direction Y.

[0060] The electrode active material layer 62 is provided on the protective coating layer 612 and on at least a portion of the surface of the main body portion 613 .

[0061] The area A1 of the pole ear portion 614 defined by the second edge 616 and the first edge 615 and the area A2 of the protective coating 612 defined by the second edge 616 and the third edge 617 satisfy: 0.05≤A2 / A1≤6, optionally, 0.1≤A2 / A1≤5.

[0062] In the embodiment of the present application, the substrate 611 can be divided into a main body 613 and a tab 614 according to its function, wherein the main body 613 is used to carry the active material in which the electrochemical reaction will occur, and the tab 614 is a component for drawing out the current. The tab 614 is used to connect the tabs, and no electrode active material is provided on the tab 614. The protective coating 612 is provided on the main body 613, and the protective coating 612 covers a portion of the main body 613. The electrode active material layer 62 contains electrode active material and is the main component for the electrochemical reaction. As shown in Figure 1, the electrode active material layer 62 is provided on the protective coating 612 and at least a portion of the surface of the main body 613.

[0063] 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 substrate 611 near the electrode ear portion 614 and reasonably limiting the area of ​​the protective coating 612, the probability of the substrate in the protective coating area contacting and reacting with the electrolyte is effectively reduced, while ensuring the heat dissipation efficiency of the electrode plate, improving the integrity of the substrate in the protective coating area, and enhancing the stability of the secondary battery operation and extending its cycle life.

[0064] In addition, a protective coating 612 is provided in the area of ​​the main body 613 close to the pole ear 614. Compared with coating the entire main body 613 with the protective coating 612, this can effectively improve the weight energy density of the secondary battery, expand the contact area between the electrode active material and the substrate 611, reduce the internal impedance of the electrode, and improve the rate performance.

[0065] Therefore, according to the present application, applying a certain area of ​​protective coating on a specific area of ​​the current collector substrate can protect the current collector substrate from breaking due to chemical corrosion without the need to apply a protective layer on the entire area of ​​the substrate, thereby improving the stability of the secondary battery operation and extending its cycle life while increasing the energy density of the electrode plate.

[0066] In some embodiments, the electrode active material layer 62 completely covers the main body 613. This can increase the amount of active material coated and improve the efficiency of the secondary battery.

[0067] In an 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 spacing L1 between the second edge 616 and the first edge 615 and the spacing L2 between the second edge 616 and the third edge 617 satisfy: 0.05≤L2 / L1≤6, optionally, 0.1≤L2 / L1≤5.

[0068] In the above technical solution, the first edge 615, the second edge 616 and the third edge 617 are roughly parallel to each other, which means that the angle α formed by the intersection of the straight lines on which any two edges are located is ≤3°. As a result, the first edge 615, the second edge 616 and the third edge 617 are roughly parallel, so that the planar shape of the protective coating 612 and the pole ear portion 614 is roughly rectangular. Such a solution can improve the convenience of manufacturing the current collector 61, and by limiting the reasonable value range of L2 / L1, it ensures that the coating of the protective coating 612 plays a protective role while reducing the coating area of ​​the protective coating 612, which is beneficial to improving the energy density of the secondary battery.

[0069] In the embodiment of the present application, the first direction X is perpendicular to the second direction Y. The above-described technical solution applies the protective coating 612 perpendicular to the edge, covering the width of the tab 614. This improves the protective performance of the protective coating 612 and prevents breakage of the substrate 611. It also ensures the regularity of the shape of the protective coating 612, improving manufacturing and installation convenience.

[0070] In some embodiments of the present application, the substrate 611 is selected from aluminum foil or aluminum polymer composite substrate.

[0071] Aluminum boasts excellent electrical conductivity and flexibility, making it a good conductor of electricity and easy to process. Fresh aluminum foil readily oxidizes in air, forming an oxide film on its surface. This film protects the aluminum from corrosion from moisture and air, further ensuring its thermodynamic stability. Therefore, aluminum is commonly used as the positive electrode current collector material in secondary batteries.

[0072] However, when the current collector substrate coated with active material slurry is cold-pressed to prepare electrode plates, the active material particles will break the protective oxide film on the surface of the aluminum foil, thereby destroying the integrity of the oxide film and exposing part of the aluminum. Because aluminum has a strong reducing property, it easily reacts chemically with certain substances in the electrolyte and is corroded. In particular, when the electrolyte contains a fluorinated sulfonyl imide lithium salt, during the charging process, the fluorinated sulfonyl imide lithium salt is oxidized, and the anions of the oxidation product react with the exposed fresh aluminum to generate products that dissolve in the electrolyte. In addition, this corrosion reaction is affected by temperature and accelerates as the temperature rises. Therefore, corrosion pits or broken strips will appear in the area of ​​the current collector near the tab, creating a safety risk and reducing the service life of the secondary battery.

[0073] According to an embodiment of the present application, by applying a certain area of ​​the protective coating 612 to a specific region of the aluminum-containing substrate 611 , it is possible to effectively prevent the strip from being broken due to aluminum corrosion.

[0074] In the embodiment of the present application, the thickness of the substrate 611 is in the range of 8 μm to 20 μm. By setting a reasonable thickness range of the substrate 611, the energy density of the secondary battery can be improved while ensuring the conductive effect of the electrode sheet.

[0075] In an embodiment of the present application, the protective coating 612 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 adhesive, and phenolic resin conductive adhesive. Optionally, the conductive agent is selected from at least one of carbon black, graphite, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

[0076] 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 substrate 611.

[0077] 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 LiNi x Co y N z M 1-x-y-z O2, LiMn2O4, Li2MnO 3·(1-a) At least one of LiPO2 and LiFePO4; optionally, the electrode binder is selected from at least one of polyacrylic resin, PVDF and its copolymers, polyacrylonitrile, epoxy resin conductive adhesive, phenolic resin conductive adhesive; 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.

[0078] Optionally, the positive electrode active material in the embodiment of the present application may be selected from:

[0079] 1) LiNi x Co y N z M 1-x-y-z O2, wherein N is selected from Mn and Al, M is selected from any one of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, 0≤x<1, 0≤y≤1, 0≤z≤1, x+y+z≤1,

[0080] 2) LiMn2O4, Li2MnO 3·(1-a) At least one of LiPO2 (P = Ni, Co, Mn) 0 < a < 1,

[0081] 3) LiFePO4

[0082] Any one of them, or it can be a positive electrode material in which the above three types of materials are mixed in any proportion.

[0083] Alternatively, the negative electrode active material in the embodiment of the present application can be selected from: natural graphite, artificial graphite, mesophase microcarbon beads (abbreviated as MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 , one or more of Li-Al alloys.

[0084] In the embodiment of the present application, the thickness H1 of the protective coating 612 and the thickness H2 of the substrate satisfy the relationship: H2 / 26≤H1≤H2 / 2.6. Thus, by setting a reasonable coating thickness for the protective coating 612, while ensuring protection and preventing pits or breaks in the substrate 611, the heat dissipation of the electrode is improved, and the total thickness of the electrode is minimized to ensure the energy density of the secondary battery.

[0085] In the embodiment of the present application, the protective coating 612 comprises a binder having a mass W1 and a conductive agent having a mass W2, wherein the ratio B of W1 to W1 + W2 satisfies the relationship: 0.05 ≤ B ≤ 0.5. In the above technical solution, by setting a reasonable mass ratio of the conductive agent to the binder, the bonding strength and conductivity can be ensured while improving the process performance of the protective coating application and drying process.

[0086] In the embodiment of the present application, the thickness D1 of the active material layer and the thickness H1 of the protective coating satisfy the relationship: D1 / 200≤H1≤D1 / 30. In the above technical solution, by setting reasonable thicknesses of the active material layer and the protective coating, the protective effect of the protective coating area and the electrical performance of the electrode sheet are guaranteed while controlling the total thickness of the electrode sheet.

[0087] In the embodiments of the present application, the electrode sheet is prepared by the following method:

[0088] Aluminum foil is used as a substrate, and a binder and a conductive agent are mixed evenly to form a protective coating slurry. The protective coating slurry is applied to a predetermined area of ​​the main body of the substrate near the tab portion, and dried to form a protective coating;

[0089] The active material, electrode binder, and electrode conductive agent are uniformly mixed to obtain an electrode active material slurry. The electrode active material slurry is applied to the main body of the substrate with the protective coating, and then cold-pressed and air-dried to obtain an electrode plate. The above-mentioned electrode plate preparation method is simple and has high manufacturability.

[0090] secondary batteries

[0091] A second aspect of the present application provides a secondary battery, comprising the electrode plate, a separator and an electrolyte according to the first aspect of the present application, wherein the electrolyte comprises a solvent and an electrolyte.

[0092] In the embodiments of the present application, there is no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0093] In the embodiments of the present application, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0094] In an embodiment of the present application, the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a winding process or a lamination process.

[0095] In an embodiment 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.

[0096] Optionally, the solvent may also include one or more selected from dipropyl carbonate, methylpropyl carbonate, ethylene carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, ethylpropyl carbonate, γ-butyrolactone, methyl formate, propyl acetate, methyl propionate, ethyl propionate, methyl propionate and tetrahydrofuran.

[0097] 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 the active material while ensuring its wettability to the electrode assembly.

[0098] In an embodiment of the present application, the electrolyte includes lithium hexafluorophosphate and a fluorinated lithium sulfonyl imide salt. Optionally, the molar concentration C1 of the lithium hexafluorophosphate salt is 0.1 mol / L ≤ C1 ≤ 1 mol / L, and the molar concentration C2 of the fluorinated lithium sulfonyl imide salt is 0.5 mol / L ≤ C2 ≤ 1.5 mol / L. In the above technical solution, the fluorinated lithium sulfonyl imide salt is resistant to high temperatures and insoluble in water. By adding a certain amount of the fluorinated lithium sulfonyl imide salt, the safety of the secondary battery can be improved to a certain extent.

[0099] In the embodiment of the present application, the molar concentration C1 of the lithium hexafluorophosphate salt and the molar concentration C2 of the lithium fluorinated sulfonyl imide satisfy: 0.6 mol / L≤C1+C2≤2 mol / L, and 1≤C2 / C1≤5.

[0100] Therefore, by adding lithium hexafluorophosphate and fluorinated sulfonyl imide lithium salt in a reasonable concentration ratio to the electrolyte, the ionic conductivity of the electrolyte can be guaranteed while the chemical stability and thermal stability of the electrolyte can be improved, thereby improving the safety performance of the battery.

[0101] In the embodiment of the present application, the lug area A1, the protective coating area A2, the molar concentration C1 of lithium hexafluorophosphate salt, and the molar concentration C2 of lithium fluorinated sulfonyl imide salt satisfy: C2 / (10C1)≤A2 / A1≤C2 / (2C1)+2.5.

[0102] Fluorinated lithium sulfonyl imide readily reacts chemically with aluminum. When the electrolyte contains a certain molar concentration of lithium hexafluorophosphate and a fluorinated lithium sulfonyl imide, by setting the area of ​​the protective coating to meet the requirements of this embodiment, it is possible to prevent corrosion of the aluminum by the lithium fluorinated lithium sulfonyl imide even when using an aluminum substrate, thereby preventing pitting or tape breakage on the substrate surface.

[0103] In the embodiment of the present application, the fluorine-containing lithium sulfonyl imide salt includes a compound shown in Formula I,

[0104]

[0105] Wherein, R1 is selected from any one of a F atom and a C1-C3 alkyl group substituted by F;

[0106] R2 is selected from any one of a F atom and a C1-C3 alkyl group substituted by F,

[0107] Optionally, R1 is a F atom, and R2 is a F atom.

[0108] In the above technical solution, the selected fluorinated sulfonyl imide 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. In addition, the raw materials of the above compound are easily available and easy to manufacture.

[0109] In an embodiment of the present application, the electrolyte further includes an additive selected from at least one of vinylene carbonate, vinyl sulfate, lithium difluorooxalatoborate, lithium difluorophosphate, lithium tetrafluoroborate, 1,3-propane sultone, 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 the battery can be improved.

[0110] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG3 shows a secondary battery 5 with a square structure as an example.

[0111] In some embodiments, referring to Figure 4, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in 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.

[0112] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0113] FIG5 shows an example battery module 4. Referring to FIG5 , in the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, the arrangement may also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be secured using fasteners.

[0114] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0115] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0116] Figures 6 and 7 illustrate an example battery pack 1. Referring to Figures 6 and 7 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0117] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric 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, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0118] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0119] FIG8 shows an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0120] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0121] Example

[0122] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0123] Examples 1 to 6

[0124] 1. Preparation of Electrolyte

[0125] In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), 2% mass concentration of vinylene carbonate was added to an organic solvent (EC:EMC=3:7W% / W%), and after mixing evenly, an appropriate amount of lithium salt (the specific content of LiPF6 and lithium bis(fluorosulfonyl)imide is shown in Table 1 below) was slowly added to the non-aqueous organic solvent. After the lithium bis(fluorosulfonyl)imide salt was completely dissolved, the target electrolyte was obtained, which is the electrolyte used in this embodiment and the comparative example.

[0126] In Examples 1-6 and Comparative Examples 1-3, the ratios of solvents and additives used are shown in Table 1.

[0127] Table 1 Electrolyte raw material ratio table

[0128]

[0129]

[0130] 2. Preparation of positive electrode sheets (Examples 1 to 6 and Comparative Examples 2 to 3):

[0131] First, an aqueous solution containing conductive carbon (mass content W1 = 50%) and polyacrylate (mass content W2 = 50%) is mixed evenly to prepare a protective coating slurry.

[0132] The protective coating slurry is coated on an aluminum foil substrate, and the ratio of the coating area to the lug area (A2 / A1) and the ratio of the distance between the edges of the coating area (L2 / L1) are set as shown in Table 2 to obtain a current collector.

[0133] The current collector was dried in an oven at 85°C and set aside.

[0134] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2(LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMnO2 electrode conductive agent Super P, electrode binder polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) to prepare positive electrode active slurry. The solid content in the positive electrode active slurry is 50wt%, and the solid content of LiNi 0.5 Co 0.2 Mn 0.3 The mass ratio of O2, Super P, and PVDF is 8:1:1.

[0135] The positive electrode active slurry is coated on the current collector obtained in the above step, and the positive electrode active slurry completely covers the main body.

[0136] After drying at 85°C, cold pressing is performed, and then trimming, cutting, and striping are performed, and then drying is performed at 85°C under vacuum conditions for 4 hours to produce positive electrode sheets.

[0137] Table 2 Protective coating coating ratio

[0138] L2 / L1A2 / A1 Thermal runaway temperature ℃ Rate discharge capacity retention rate Example 1 0.5 0.5 145 8 4.50% Example 2 0.8 1.0 140 8 5.60% Example 3 1.0 20 151 8 6.30%

[0139] Example 4 2.5 2.5 150 86.70% Example 5 2.0 2.5 146 86.80% Example 6 2.5 4.5 150 83.30% Comparative Example 1 No protective coating No protective coating 90 73.80% Comparative Example 2 0.4 5 0.4 5 100 76.50% Example 3 4 5.5 121 73.20%

[0140] 3. Preparation of positive electrode sheet (Comparative Example 1):

[0141] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2(LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O2, LiMnO2), electrode conductive agent Super P, electrode binder polyvinylidene fluoride (PVDF) are prepared in N-methylpyrrolidone (NMP) to prepare positive electrode active slurry. The solid content in the positive electrode active slurry is 50wt%, and the solid content of LiNi 0.5 Co 0.2 Mn 0.3 The mass ratio of O2, Super P, and PVDF is 8:1:1.

[0142] The positive electrode active slurry is coated on aluminum foil and dried at 85°C before cold pressing. It is then trimmed, cut into pieces, and divided into strips, and then dried at 85°C under vacuum conditions for 4 hours to make a positive electrode sheet.

[0143] 4. Preparation of negative electrode sheet (Examples 1 to 6 and Comparative Examples 1 to 3):

[0144] Graphite, the negative electrode active material, was mixed with Super P (a conductive agent), CMC (a thickener), and SBR (a binder) in deionized water to create a negative electrode active slurry. The slurry had a solids content of 30% by weight, and the mass ratio of graphite, Super P, CMC, and SBR was 80:15:3:2.

[0145] 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 sheet.

[0146] 5. Preparation of Secondary Batteries (Examples 1 to 6 and Comparative Examples 1 to 3):

[0147] Using a 16μm polyethylene film (PE) as a separator, the prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative sheets to separate the positive and negative electrodes. The electrode assembly is wound and the tabs are welded. The bare cell is placed in an outer package and the prepared electrolyte is injected into the dried electrode assembly. The secondary battery is then packaged, left to rest, formed, shaped, and capacity tested to complete the process (the soft-pack battery has a thickness of 4.0mm, a width of 60mm, and a length of 140mm).

[0148] Next, the test process of the secondary battery is described.

[0149] (1) Thermal runaway performance test of secondary batteries.

[0150] The ambient temperature was adjusted to 25°C. The battery cells were charged at 1C to 4.2V, then charged at a constant voltage to 0.05C. The cells were placed in a heating furnace and heated at 10°C / min. The furnace was held at this temperature for 10 minutes until thermal runaway occurred (the cell rapidly released heat, with the surface temperature rising faster than the furnace temperature, at which point thermal runaway began). The process was terminated. The furnace temperature at the time of thermal runaway was recorded.

[0151] The cells in a secondary battery release heat during operation, so this test tests the high-temperature resistance of the secondary battery by simulating a 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 and the fluorinated sulfonyl imide lithium salt in the electrolyte can be obtained. When the reaction efficiency is high, the faster the positive electrode plate breaks, the lower the thermal runaway temperature, and the worse the performance of the electrode plate. When the reaction efficiency is low, the slower the positive electrode plate breaks, the higher the thermal runaway temperature, and the better the performance of the electrode plate.

[0152] (2) Lithium-ion battery rate performance test

[0153] At 25°C, charge at 1C to 4.2V, then charge at constant voltage to 0.05C, let stand for 20 minutes, discharge at 1C to 2.8V, record the discharge capacity D0 at this time, then charge at 1C to 4.2V, then charge at constant voltage to 0.05C, let stand for 20 minutes, discharge at 3C to 2.8V, record the discharge capacity D1, and the rate discharge capacity retention rate M=D1 / D0.

[0154] Table 3 Thermal runaway temperature performance and capacity retention rate of secondary batteries

[0155] Battery No. Thermal runaway temperature ℃ M Example 1 14584.5% Example 2 14085.6% Example 3 15186.3% Example 4 15086.7% Example 5 14686.8% Example 6 15083.3% Comparative Example 1 9073.8% Comparative Example 2 10076.5%

[0156] Comparative Example 312173.2%

[0157] As shown in Table 3, Examples 1 to 6 all meet the requirement of 0.05≤A2 / A1≤6. Therefore, the thermal runaway temperatures in the above-mentioned embodiments are all higher than 140 degrees Celsius. These relatively high thermal runaway temperatures meet the thermal runaway temperature requirements of secondary batteries. Furthermore, the rate discharge capacity retention rates of the above-mentioned embodiments are significantly improved compared to the comparative examples. This indicates that the electrode plates in the above-mentioned embodiments can effectively improve the electrical performance of the battery cell.

[0158] Specifically, in Example 1, A2 / A1 = 0.5 and L2 / L1 = 0.5. Compared to Examples 2-5, Example 1 has a smaller protective coating area, resulting in a lower thermal runaway temperature. However, due to the smaller protective layer area, the active material and aluminum foil have good conductivity, resulting in a higher rate discharge capacity retention.

[0159] In Example 2, A2 / A1 = 0.8 and L2 / L1 = 1.0. Compared to the other examples, Example 2 has a smaller protective coating area, resulting in a lower thermal runaway temperature. However, due to the smaller protective layer area, the active material and aluminum foil have good conductivity, resulting in a higher rate discharge capacity retention.

[0160] In Example 3, A2 / A1 = 1.0 and L2 / L1 = 2.0. The protective coating area in Example 3 is larger than that in Examples 1 and 2. Therefore, it provides better high-temperature protection near the lug, resulting in a higher thermal runaway temperature. Furthermore, the area of ​​the protective layer is reasonably designed, resulting in a higher rate discharge capacity retention.

[0161] In Example 4, A2 / A1 = 2.5, and L2 / L1 = 2.5. The protective coating area of ​​Example 4 is larger than that of Examples 1, 2, and 3. Therefore, it provides better high-temperature protection near the lug, resulting in a higher thermal runaway temperature. Furthermore, the area of ​​the protective layer is reasonably designed, resulting in a higher rate discharge capacity retention.

[0162] In Example 5, A2 / A1 = 2.0 and L2 / L1 = 2.5. The protective coating area in Example 5 is larger than that in Examples 1, 2, and 3. Therefore, it provides better high-temperature protection near the lug, resulting in a higher thermal runaway temperature. Furthermore, the area of ​​the protective layer is reasonably designed, resulting in a higher rate discharge capacity retention.

[0163] In Example 6, A2 / A1 = 2.5 and L2 / L1 = 4.5, indicating that Example 5 has the largest protective coating area. Therefore, it provides better high-temperature protection near the lug, resulting in a higher thermal runaway temperature. However, the protective coating affects heat dissipation from the electrode sheet, resulting in a slightly lower rate discharge capacity retention than the aforementioned examples.

[0164] In Comparative Example 1, no protective coating is provided. The surface of the aluminum foil punctured by the active material particles reacts rapidly with the lithium fluorinated sulfonyl imide in the electrolyte, causing the aluminum foil to break and a short circuit inside the battery. As a result, thermal runaway occurs at 90°C, and its rate discharge capacity retention rate is low, resulting in poor electrical performance.

[0165] In Comparative Example 2, A2 / A1 = 0.45 and L2 / L1 = 0.45. The protective coating area in Comparative Example 2 is relatively small. Therefore, it fails to effectively protect the area near the tabs, and the aluminum foil still corrodes and breaks at relatively low temperatures. Furthermore, its rate discharge capacity retention is lower than that of the aforementioned examples.

[0166] In Comparative Example 3, A2 / A1 = 4 and L2 / L1 = 5.5, resulting in the largest protective coating area. Therefore, while the area near the electrode lug can be protected to a certain extent, the excessively large protective coating prevents effective heat dissipation from the electrode plate, causing a rapid increase in the surface temperature of the electrode plate and significant corrosion near the lug. Consequently, the thermal runaway temperature is relatively low. Furthermore, the rate discharge capacity retention is lower than in the aforementioned examples.

[0167] The above results show that when the electrolyte contains fluorinated sulfonic acid imide lithium salt, a protective coating is provided in the area near the pole ear and the area of ​​the protective coating is reasonably limited. This can effectively reduce the probability of the substrate in the protective coating area contacting and reacting with the electrolyte, 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.

[0168] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An electrode plate, comprising: A current collector comprising a substrate and a protective coating, wherein the substrate comprises a main body portion and a tab portion arranged along a first direction, the tab portion having a first edge extending along a second direction, the first direction intersecting the second direction; the protective coating being disposed on a portion of a 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 extending along the first direction to form a third edge extending along the second direction; as well as an electrode active material layer disposed on at least a portion of the surface of the protective coating and the main body; The tab area A1 defined by the second edge and the first edge, and the protective coating area A2 defined by the second edge and the third edge satisfy: 0.05≤A2 / A1≤6, optional, 0.1≤A2 / A1≤5.

2. The electrode plate according to claim 1, wherein: The first edge, the second edge, and the third edge are substantially parallel to each other, and a distance L1 between the second edge and the first edge and a distance L2 between the second edge and the third edge satisfy: 0.05≤L2 / L1≤6, optional, 0.1≤L2 / L1≤5.

3. The electrode plate according to claim 1 or 2, wherein: The substrate is selected from aluminum foil or aluminum polymer composite substrate.

4. The electrode plate according to claim 3, wherein: The protective coating comprises 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 adhesive, and phenolic resin conductive adhesive. Optionally, the conductive agent is selected from at least one of carbon black, graphite, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

5. The electrode plate according to claim 3, wherein: The electrode active material layer includes active material, electrode binder and electrode conductive agent, Optionally, the active material is selected from LiNi x Co y N z M 1-x-y-z O2, LiMn2O4, Li2MnO 3·(1-a) At least one of LiPO2 and LiFePO4; Optionally, the electrode binder is selected from at least one of polyacrylic resin, PVDF and its copolymer, polyacrylonitrile, epoxy resin conductive adhesive, and phenolic resin conductive adhesive; 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.

6. The electrode plate according to claim 3, wherein: The thickness H1 of the protective coating and the thickness H2 of the substrate satisfy the relationship: H2 / 26≤H1≤H2 / 2.

6.

7. The electrode plate according to claim 4, wherein: The protective coating layer includes the binder with a mass of W1 and the conductive agent with a mass of W2, and a ratio B of W1 to W1+W2 satisfies the relationship: 0.05≤B≤0.

5.

8. The electrode plate according to claim 7, wherein: The thickness D1 of the active material layer and the thickness H1 of the protective coating layer satisfy the relationship: D1 / 200≤H1≤D1 / 30.

9. A secondary battery comprising: The electrode plate according to any one of claims 1 to 8; Isolation film; Electrolyte, including solvent and electrolyte.

10. The secondary battery according to claim 9, wherein The electrolyte includes lithium hexafluorophosphate and fluorinated lithium sulfonyl imide salt. Optionally, the molar concentration C1 of the lithium hexafluorophosphate salt is 0.1 mol / L≤C1≤1 mol / L, and the molar concentration C2 of the fluorinated lithium sulfonyl imide is 0.5 mol / L≤C2≤1.5 mol / L.

11. The secondary battery according to claim 10, wherein The molar concentration C1 of the lithium hexafluorophosphate salt and the molar concentration C2 of the fluorinated lithium sulfonyl imide satisfy: 0.6mol / L≤C1+C2≤2mol / L, and 1≤C2 / C1≤5.

12. The secondary battery according to claim 11, wherein The area A1 of the tab, the area A2 of the protective coating, the molar concentration C1 of the lithium hexafluorophosphate salt, and the molar concentration C2 of the fluorinated lithium sulfonyl imide satisfy the following conditions: C2 / (10C1)≤A2 / A1≤C2 / (2C1)+2.

5.

13. The secondary battery according to any one of claims 9 to 12, wherein The fluorine-containing sulfonyl imide lithium salt includes a compound shown in Formula I, Wherein, R1 is selected from any one of a F atom and a C1-C3 alkyl group substituted by F; R2 is selected from any one of a F atom and a C1-C3 alkyl group substituted by F. Optionally, R1 is a F atom and R2 is a F atom.

14. The secondary battery according to claim 13, wherein The electrolyte further includes an additive, and the additive is selected from at least one of vinylene carbonate, vinyl sulfate, lithium difluorooxalatoborate, lithium difluorophosphate, lithium tetrafluoroborate, 1,3-propane sultone, lithium trifluoromethanesulfonate, and lithium diacetate borate. 15 . A battery module comprising the secondary battery according to claim 9 .

16. A battery pack comprising the battery module according to claim 15. 17 . An electrical device comprising at least one selected from the secondary battery according to claim 9 , the battery module according to claim 15 , or the battery pack according to claim 16 .

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