Positive pole piece, secondary battery and electric device

Abstract

The invention relates to a positive pole piece, a secondary battery and an electric device. The positive pole piece comprises an aluminum-based current collector, a first active material layer and a second active material layer, the second active material layer is arranged on at least one side of the aluminum-based current collector, and the first active material layer on at least one side is located between the aluminum-based current collector and the second active material layer. The first active material layer contains a first active substance and an aluminum passivator. The positive pole piece can be applied to a secondary battery of which the electrolyte contains fluorine-containing sulfonamide lithium salt, acid and the like, and the cycle performance can be improved on the basis of considering the power performance.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a positive electrode plate, a secondary battery and an electrical device. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their outstanding features such as light weight, no pollution, and no memory effect. The electrolyte of secondary batteries uses fluorinated sulfonamide lithium salts such as LiFSI, which can improve the power performance of the battery. However, the disadvantage is that the battery cycle performance deteriorates seriously under high voltage, especially at high temperature. Summary of the invention

[0004] Based on this, it is necessary to provide a positive electrode plate, a secondary battery and an electrical device that can improve the cycle performance while taking into account the power performance.

[0005] In a first aspect of the present application, a positive electrode plate is provided, which includes an aluminum-based current collector, a first active material layer and a second active material layer, wherein the second active material layer is arranged on at least one side of the aluminum-based current collector, and the first active material layer on at least one side is located between the aluminum-based current collector and the second active material layer, and the first active material layer contains a first active substance and an aluminum passivator.

[0006] Without wishing to be limited to any theory, the above-mentioned positive electrode plate of the present application is provided with a double-layer active material layer, and the aluminum passivator is provided in the first active material layer close to the aluminum-based current collector. The transmission path between the aluminum passivator and the aluminum-based current collector is short. Under the action of the electrolyte, the aluminum passivator dissolves and can fully contact with the aluminum-based current collector, so that a good passivation film layer is formed on the surface of the aluminum-based current collector; in this way, the corrosion problem of the aluminum-based current collector by electrolyte components such as fluorinated sulfonamide lithium salts and acids can be improved, and then the cycle performance of the secondary battery when working at high voltage, especially the cycle performance at high temperature, can be improved; at the same time, the setting of the double-layer active material layer can basically not affect the overall dynamic performance of the secondary battery, so it can have good power performance.

[0007] In any embodiment of the present application, the positive electrode sheet satisfies at least one of the following conditions:

[0008] (1) The aluminum passivator includes an alkali metal salt; optionally, the alkali metal salt includes at least one of a lithium salt and a sodium salt; optionally, the alkali metal salt includes at least one of lithium hexafluorophosphate, sodium hexafluorophosphate, lithium difluorooxalatoborate, sodium difluorooxalatoborate, lithium dioxalatoborate and sodium dioxalatoborate;

[0009] (2) In the first active material layer, the mass content of the aluminum passivator is 10% to 35%, optionally 10% to 35%; more optionally 10% to 25%.

[0010] In any embodiment of the present application, the alkali metal salt includes at least one of lithium hexafluorophosphate and sodium hexafluorophosphate;

[0011] Optionally, the alkali metal salt includes at least one of lithium difluorooxalatoborate, sodium difluorooxalatoborate, lithium dioxalatoborate and sodium dioxalatoborate, and at least one of lithium hexafluorophosphate and sodium hexafluorophosphate; more optionally, the mass ratio of at least one of lithium difluorooxalatoborate, sodium difluorooxalatoborate, lithium dioxalatoborate and sodium dioxalatoborate to the mass ratio of at least one of lithium hexafluorophosphate and sodium hexafluorophosphate is 1:(2-30), optionally 1:(4-20), and more optionally 1:(4-10).

[0012] In any embodiment of the present application, in the first active material layer, the mass content of at least one of the lithium hexafluorophosphate and the sodium hexafluorophosphate is 10% to 30%; further optionally 15% to 25%;

[0013] Optionally, in the first active material layer, the mass content of at least one of the lithium difluorooxalatoborate, sodium difluorooxalatoborate, lithium dioxalatoborate and sodium difluorooxalatoborate is 1% to 5%.

[0014] In any embodiment of the present application, the second active material layer contains a second active material, and the charge cutoff voltages of the first active material and the second active material are independently ≥ 4.2V;

[0015] Optionally, the first active material and the second active material each independently include a nickel-cobalt-manganese ternary positive electrode material, lithium cobalt oxide, LiMnO 2 and LiMn 2 O 4 At least one of .

[0016] In any embodiment of the present application, the percentage of nickel element in the total molar amount of nickel, cobalt and manganese in the nickel-cobalt-manganese ternary positive electrode material is 30% to 95%, and can be optionally 80% to 95%;

[0017] Optionally, the nickel-cobalt-manganese ternary positive electrode material includes Li x Ni a Co b Mn 1-a-b O 2-e , x is 0.8~1.2, 0.3≤a+b≤0.97, and e is 0~0.2.

[0018] In any embodiment of the present application, the positive electrode sheet satisfies at least one of the following conditions:

[0019] (1) The thickness ratio of the second active material layer to the first active material layer is (10 - 120):1, and optionally (20 - 50):1;

[0020] (2) The thickness of the first active material layer is 1 - 10 μm, and optionally 4 - 7 μm;

[0021] (3) The thickness of the second active material layer is 80 - 150 μm, and optionally 100 - 120 μm.

[0022] In the second aspect of the present application, a secondary battery is provided, including the positive electrode sheet, negative electrode sheet, and electrolyte as described in any one of the above.

[0023] In the third aspect of the present application, a secondary battery is provided, including a positive electrode sheet, a negative electrode sheet, and an electrolyte disposed between the positive electrode sheet and the negative electrode sheet;

[0024] The positive electrode sheet includes an aluminum-based current collector, a first active material layer, and a second active material layer. The second active material layer is disposed on at least one side of the aluminum-based current collector, and at least one side of the first active material layer is located between the aluminum-based current collector and the second active material layer. The porosity of the first active material layer is greater than the porosity of the second active material layer; the surface of the aluminum-based current collector contains a passivation film.

[0025] In any embodiment of the present application, the electrolyte includes a fluorosulfonamide-based lithium salt.

[0026] In any embodiment of the present application, the secondary battery satisfies at least one of the following conditions:

[0027] (1) The thickness of the passivation film is 1 - 2 μm;

[0028] ((2) The passivation film contains at least one of phosphorus element and boron element and fluorine element;

[0029] Optionally, the mass content of fluorine element in the passivation film is 100 - 20000 ppm, and more optionally 200 - 10000 ppm;

[0030] Optionally, the mass content of phosphorus element in the passivation film is 100 - 5000 ppm, and more optionally 200 - 2000 ppm;

[0031] Optionally, the passivation film includes at least one of AlF 3 and LiF, and more optionally, the passivation film further includes Li 3 PO4 ;

[0032] Optionally, the passivation film contains boron; more preferably, the mass content of boron in the passivation film is 100-1000 ppm; more preferably, the passivation film includes Li 3 BO 3 .

[0033] In any embodiment of the present application, the secondary battery satisfies at least one of the following conditions:

[0034] (1) The fluorinated sulfonamide lithium salt includes at least one of bis(fluorosulfonyl)imide lithium salt and bis(trifluoromethanesulfonyl)imide lithium salt;

[0035] (2) In the electrolyte, the mass content of the fluorinated sulfonamide lithium salt is ≥ 4%, which can be 4% to 20%, and more preferably 8% to 16%;

[0036] (3) The mass content of HF in the electrolyte is ≤200 ppm.

[0037] In a fourth aspect of the present application, an electrical device is provided, wherein the electrical device comprises any of the secondary batteries described above.

[0038] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0040] Figure 1 is a schematic cross-sectional view of a positive electrode sheet of a secondary battery according to an embodiment of the present application;

[0041] Figure 2 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0042] Figure 3 yes Figure 2 An exploded view of a battery cell according to an embodiment of the present application is shown;

[0043] Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application;

[0044] Figure 5 A schematic diagram of a battery pack according to an embodiment of the present application;

[0045] Figure 6 for Figure 5 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0046] Figure 7 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source;

[0047] Description of reference numerals:

[0048] 1. Battery cell; 11. Shell; 12. Electrode assembly; 13. Cover plate; 121. Positive electrode plate; 1211. First current collector; 1212. First active material layer; 1213. Second active material layer; 2. Battery pack; 21. Upper case; 22. Lower case; 3. Battery module; 4. Electrical device. DETAILED DESCRIPTION

[0049] Hereinafter, the embodiments of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be 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.

[0050] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a 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 a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present 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 real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it 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.

[0051] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0052] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0053] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0054] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0055] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A not only includes a1, a2 and a3, but also includes other members". In the present application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0056] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0057] The secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0058] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The electrolyte is located between the positive electrode sheet and the negative electrode sheet. During the battery charging and discharging process, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.

[0059] Secondary battery

[0060] A secondary battery is a battery that can be used again by recharging the active material after the battery is discharged. Generally, a secondary battery includes a positive electrode, a negative electrode and an electrolyte.

[0061] An embodiment of the present application provides a secondary battery and a positive electrode plate thereof. The secondary battery comprises a positive electrode plate, a negative electrode plate and an electrolyte.

[0062] Positive electrode

[0063] The positive electrode plate includes an aluminum-based current collector, a first active material layer and a second active material layer, wherein the second active material layer is arranged on at least one side of the aluminum-based current collector, and the first active material layer on at least one side is located between the aluminum-based current collector and the second active material layer, and the first active material layer contains a first active substance and an aluminum passivator.

[0064] In some embodiments, the electrolyte includes fluorinated sulfonamide lithium salt.

[0065] Without wishing to be limited to any theory, the above-mentioned positive electrode plate of the present application is provided with a double-layer active material layer, and the aluminum passivator is provided in the first active material layer close to the aluminum-based current collector. The transmission path between the aluminum passivator and the aluminum-based current collector is short. Under the action of the electrolyte, the aluminum passivator dissolves and can fully contact with the aluminum-based current collector, so that a good passivation film layer is formed on the surface of the aluminum-based current collector; in this way, the corrosion problem of the aluminum-based current collector by electrolyte components such as fluorinated sulfonamide lithium salts and acids can be improved, and then the cycle performance of the secondary battery when working at high voltage, especially the cycle performance at high temperature, can be improved; at the same time, the setting of the double-layer active material layer can basically not affect the overall dynamic performance of the secondary battery, so it can have good power performance.

[0066] It is understood that the "aluminum-based current collector" herein includes but is not limited to current collectors containing aluminum alone, such as aluminum foil and aluminum alloy current collectors.

[0067] As an example, the aluminum-based current collector has two surfaces facing each other in its own thickness direction, and the active material layer is provided on any one or both of the two facing surfaces of the positive electrode current collector.

[0068] In one embodiment, see Figure 1 , shows a schematic cross-sectional view of a positive electrode sheet 121. The positive electrode sheet 121 includes an aluminum-based current collector 1211, a first active material layer 1212, and a second active material layer 1213, wherein the second active material layer 1213 is disposed on at least one surface of the aluminum-based current collector 1211, the first active material layer 1212 is located between the aluminum-based current collector 1211 and the second active material layer 1213, and the first active material layer 1212 contains a first active material and an aluminum passivator.

[0069] In some of the embodiments, in the first active material layer, the mass content of the aluminum passivator is 10% to 35%; as an example, it can be 10%, 15%, 20%, 25%, 30%, 35%; in some examples, the mass content can also be a range consisting of any two of the above point values, and the following is similar.

[0070] In some embodiments, the aluminum passivator includes an alkali metal salt. Using an alkali metal salt as the aluminum passivator can not only play a passivation role, but also improve the capacity of the battery.

[0071] Furthermore, the alkali metal salt includes but is not limited to at least one of a lithium salt and a sodium salt.

[0072] Optionally, the lithium salt includes but is not limited to at least one of lithium hexafluorophosphate, lithium difluorooxalatoborate and lithium dioxalatoborate.

[0073] Optionally, the sodium salt includes but is not limited to at least one of sodium hexafluorophosphate, sodium difluorooxalatoborate and sodium dioxalatoborate.

[0074] Optionally, the alkali metal salt includes at least one of lithium hexafluorophosphate, sodium hexafluorophosphate, lithium difluorooxalatoborate, sodium difluorooxalatoborate, lithium dioxalatoborate and sodium dioxalatoborate.

[0075] In some embodiments, the alkali metal salt includes an alkali metal hexafluorophosphate salt, such as lithium hexafluorophosphate (LiPF 6 ) and at least one of sodium hexafluorophosphate. 6 Alkali metal hexafluorophosphate salts such as fluorinated phosphate have a good passivation effect on aluminum-based current collectors. The passivation film formed by them includes LiF, AlF 3 At least one of, optionally including Li 3PO 4 .

[0076] Furthermore, the alkali metal salt includes at least one of lithium difluorooxalatoborate (LiDFOB), sodium difluorooxalatoborate, lithium dioxalatoborate (LiBOB) and sodium dioxalatoborate, and lithium hexafluorophosphate (LiPF 6 ) and sodium hexafluorophosphate. In this way, two different alkali metal salts are used in combination as aluminum passivators, and the components of the passivation film formed include AlF 3 , LiF and Li 3 PO 4 and Li 3 BO 3 , which can not only passivate aluminum-based current collectors such as aluminum foil, but also the combined use of oxalate and borate alkali metal salts can appropriately reduce the use of hexafluorophosphate alkali metal salts, thereby appropriately reducing LiPF 6 The amount of LiF produced by the passivation reaction with the aluminum-based current collector reduces the deterioration of the battery's internal resistance DCR, which can further improve the battery's power performance and cycle performance.

[0077] Optionally, the mass ratio of at least one of lithium difluorooxalatoborate, sodium difluorooxalatoborate, lithium dioxalatoborate and sodium dioxalatoborate to the mass ratio of at least one of lithium hexafluorophosphate and sodium hexafluorophosphate is 1:(2-30), and as an example, it can be 1:2, 1:4, 1:6, 1:10, 1:15, 1:20, 1:25, 1:30; it can be optionally 1:(4-20), or 1:(4-10), and can further be 1:(8-10).

[0078] In some embodiments, in the first active material layer, the mass content of lithium hexafluorophosphate is 10% to 30%; further optionally, 15% to 25%. As an example, in the first active material layer, the mass content of lithium hexafluorophosphate may be 10%, 15%, 20%, 25%, 30%.

[0079] Optionally, in the first active material layer, the mass content of at least one of lithium difluorooxalatoborate and lithium dioxalatoborate is 1% to 5%, further 1% to 3%; as an example, it can be 1%, 2%, 3%, 4%, or 5%.

[0080] In some embodiments, no aluminum passivator is disposed in the second active material layer.

[0081] As the secondary battery is charged and discharged under the action of the electrolyte, the aluminum passivator in the above-mentioned positive electrode plate is able to fully contact with the aluminum-based current collector, so that a good passivation film layer is formed on the surface of the aluminum-based current collector. At the same time, the position of the aluminum passivator in the first active material layer becomes a pore, so that the porosity in the first active material layer is greater than the porosity in the second active material layer.

[0082] In other words, another embodiment of the present application also provides a secondary battery, whose positive electrode plate includes an aluminum-based current collector, a first active material layer and a second active material layer, the second active material layer is arranged on at least one surface of the aluminum-based current collector, the first active material layer is located between the aluminum-based current collector and the second active material layer, the porosity of the first active material layer is greater than the porosity of the second active material layer; the surface of the aluminum-based current collector contains a passivation film.

[0083] Porosity is defined by the following equation: Porosity = (1-(mass of porous material [g] / (volume of porous material [cm3]×material density)))×100[%]. The porosity of the membrane layer can be determined by the mercury intrusion method and gas adsorption method according to GB / T 21650.2-2008.

[0084] In some embodiments, the electrolyte includes a fluorinated sulfonamide lithium salt.

[0085] In some embodiments, the difference in porosity between the first active material layer and the second active material layer is 8% to 15%, and as examples, may be 8%, 10%, or 15%.

[0086] In some embodiments, the porosity of the first active material layer is 35% to 45%, and as examples, may be 35%, 40%, or 45%.

[0087] In some embodiments, the porosity of the second active material layer is 25% to 35%, and as examples, may be 25%, 30%, or 35%.

[0088] In some embodiments, the thickness of the passivation film is 1-2 μm.

[0089] In some embodiments, the passivation film contains at least one of phosphorus and boron and fluorine.

[0090] Optionally, the mass content of fluorine element in the passivation film is 100 to 20000 ppm, and further optionally 200 to 10000 ppm.

[0091] Optionally, the mass content of phosphorus in the passivation film is 100 to 5000 ppm, and further optionally 200 to 2000 ppm.

[0092] Further optionally, the passivation film comprises AlF 3 and Li 3 PO 4 .

[0093] Further, the passivation film contains boron; optionally, the content of boron in the passivation film is 100 to 1000 ppm; optionally, the passivation film includes Li3 BO 3 Optionally, the passivation film includes AlF 3 , LiF, and optionally also includes Li 3 PO 4 , and more optional include Li 3 BO 3 .

[0094] In some embodiments, the second active material layer contains a second active substance, and the charging cut-off voltage of the first active substance and the second active substance is greater than 4.2 V. The charging cut-off voltage of the second active substance, the first active substance and the second active substance is greater than 4.2 V. When the electrolyte contains a fluorinated sulfonamide lithium salt, the aluminum-based current collector is easily corroded by the fluorinated sulfonamide lithium salt at this higher voltage. The above-mentioned positive electrode plate can inhibit the corrosion of the aluminum-based current collector on the basis of having good power performance and improve the cycle performance of the secondary battery at high voltage due to its structure and component arrangement.

[0095] Optionally, the first active material and the second active material independently include a nickel-cobalt-manganese ternary positive electrode material, lithium cobalt oxide, LiMnO 2 and LiMn 2 O 4 At least one of the following. A wide variety of active materials can be used in this application.

[0096] Further, the percentage of nickel in the total molar amount of nickel, cobalt and manganese in the nickel-cobalt-manganese ternary positive electrode material is 30% to 95%, such as 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, and can be 80% to 95%. Studies have found that the smaller the percentage of nickel in the total molar amount of nickel, cobalt and manganese, the more serious the corrosion of the aluminum-based current collector when it works under high pressure. The use of the upper positive electrode plate can improve the corrosion problem of the aluminum-based current collector; further, when the percentage of nickel in the total molar amount of nickel, cobalt and manganese is 80% to 95%, the improvement effect is particularly obvious.

[0097] Optionally, the nickel-cobalt-manganese ternary positive electrode material includes Li x Ni a Co b Mn 1-a-b O 2-e , x is 0.8~1.2, 0.3≤a+b≤0.97, and e is 0~0.2.

[0098] Furthermore, a is 0.2 to 0.95. Still further, a is 0.8 to 0.95.

[0099] Non-limiting examples of nickel-cobalt-manganese ternary positive electrode materials (or lithium nickel-cobalt-manganese oxides) may include LiNi1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (Also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O 2 (Also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O 2 (Also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (Also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (Also referred to as NCM 811 ) etc. It is understandable that the nickel-cobalt-manganese ternary positive electrode material may also be doped with other metal elements.

[0100] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charging and discharging process, and the content of Li in the positive electrode active material is different when the battery is discharged to different states. In the enumeration of positive electrode active materials in this application, unless otherwise specified, the content of Li is the initial state of the material. The positive electrode active material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the content of Li in the positive electrode active material contained in the plate usually changes. Among them, the content of Li can be measured by molar content, but is not limited to this. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that the new material obtained by appropriate modification on the basis of the listed positive electrode active materials is also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to the acceptable modification method for the positive electrode active material, and non-limiting examples include coating modification.

[0101] In the list of positive electrode active materials in this application, the content of oxygen (O) is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by molar content, but is not limited to this.

[0102] It is understandable that the first active material and the second active material may also include active materials known in the art that can be used for the positive electrode of a secondary battery, and those skilled in the art may select them according to actual needs.

[0103] In some embodiments, the thickness ratio of the second active material layer to the first active material layer is (10-120): 1, for example, 10: 1, 20: 1, 30: 1, 40: 1, 50: 1, 60: 1, 70: 1, 80: 1, 90: 1, 100: 1, 110: 1, 120: 1, and may be (20-50): 1, or (30-50): 1. By controlling the thickness ratio, a better passivation effect and a lower internal resistance DCR can be taken into account, so as to take into account better cycle performance and power performance.

[0104] In some embodiments, the thickness of the first active material layer is 1-10 μm, for example, 1 μm, 2 μm, 4 μm, 5 μm, 6 μm, 7 μm, 10 μm, optionally 2-7 μm, or 4-7 μm.

[0105] In some embodiments, the thickness of the second active material layer is 80-150 μm, for example, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, and optionally 100-120 μm.

[0106] In some of the embodiments, the mass content of the first active substance in the first active material layer is 45% to 90%; as an example, it may be 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.

[0107] In some of the embodiments, the mass content of the second active material in the second active material layer is 75% to 98%; as examples, it may be 75%, 80%, 85%, 90%, 95%, or 98%.

[0108] In some embodiments, the mass content of the first active material in the first active material layer is less than the mass content of the second active material in the second active material layer.

[0109] The first active material layer and the second active material layer may also optionally include a binder, a conductive agent, and other optional auxiliary agents.

[0110] In some embodiments, in the positive electrode active material layer, the mass content of the conductive agent is 0.1% to 15%. For example, it may be 0.1%, 0.5%, 1%, 2%, 5%, 10%, or 15%.

[0111] In some embodiments, in the positive electrode active material layer, the mass content of the binder is 0.5% to 15%. For example, it may be 0.1%, 0.5%, 1%, 2%, 5%, 10%, or 15%.

[0112] As an example, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers.

[0113] As an example, the binder can be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0114] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the components of the first active material layer and the second active material layer for preparing the positive electrode plate, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to prepare the slurry for the first active material layer and the slurry for the second active material layer, coating the slurry for the first active material layer on the surface of the aluminum-based current collector, drying, and then coating the slurry for the second active material layer on the first active material layer. After processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0115] Negative electrode plate

[0116] The negative electrode plate generally includes a negative electrode current collector and a negative electrode film layer provided on the negative electrode current collector. It can be understood that in some examples, the negative electrode film layer can also be omitted.

[0117] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0118] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material on the polymer material substrate. Among them, the metal material includes but is not limited to at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy; the polymer material substrate includes but is not limited to at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0119] Furthermore, the negative electrode film layer includes a negative electrode active material. It can be understood that in some examples, the negative electrode film layer may not contain a negative electrode active material.

[0120] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0121] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0122] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0123] In some embodiments, the negative electrode film layer may further include other additives, such as a thickener. For example, the thickener may be sodium carboxymethyl cellulose (CMC-Na).

[0124] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent such as water to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0125] Electrolyte

[0126] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The electrolyte includes electrolyte salt and solvent.

[0127] As mentioned above, the electrolyte of the secondary battery includes a fluorinated sulfonamide lithium salt, which is an electrolyte salt. Further, the fluorinated sulfonamide lithium salt includes but is not limited to at least one of bis(fluorosulfonyl)imide lithium salt (LiFSI) and bis(trifluoromethanesulfonyl)imide lithium salt (LiTFSI).

[0128] In some embodiments, in the electrolyte, the mass content of the fluorinated sulfonamide lithium salt is ≥ 4%, and can be selected from 4% to 20%, for example, 4%, 5%, 8%, 10%, 15%, 20%; further, it can be selected from 5% to 20%, 8% to 16%. When the mass content of the fluorinated sulfonamide lithium salt in the electrolyte is within this range, on the one hand, better power performance can be obtained, and on the other hand, the positive electrode plate of the present application can improve the corrosion problem of the aluminum-based current collector, thereby improving the cycle performance and power performance of the battery.

[0129] In some embodiments, the mass content of HF in the electrolyte is ≤200ppm. HF will cause acid corrosion to aluminum-based current collectors such as aluminum foil. By treating the mass content of HF in the electrolyte with molecular sieves, the corrosion of the electrolyte to aluminum-based current collectors such as aluminum foil can be further inhibited.

[0130] In some of these embodiments, the electrolyte salt may further include other lithium salts.

[0131] As an example, the electrolyte salt may also include the following lithium salts: lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ) lithium hexafluoroarsenate (LiAsF 6 ), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), one or more of lithium difluorobis(oxalate) phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).

[0132] In some embodiments, the solvent includes at least one of an ether solvent, an ester solvent and a sulfone solvent.

[0133] As an example, the ether solvent may include at least one of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), and 1,3-dioxolane (DOL);

[0134] As an example, the ester solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), γ-butyrolactone (BL), 1,3-propane sultone (1,3-PS), methyl propionate (MP), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP) and ethyl butyrate (EB).

[0135] As an example, the sulfone-based solvent includes dimethyl sulfoxide (DMSO).

[0136] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0137] Isolation film

[0138] In some embodiments, the secondary battery further includes a separator, which is disposed between the positive electrode sheet and the negative electrode sheet to perform a separation function.

[0139] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0140] The isolation film can be a single-layer film or a multi-layer composite film. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different.

[0141] Unless otherwise specified, the above raw materials can be obtained from the market.

[0142] The shape of the secondary battery in the embodiment of the present application can be cylindrical, square or any other shape. Figure 2 The battery cell 1 is a square structure as an example.

[0143] In some embodiments, reference Figure 3The outer packaging may include a shell 11 and a cover plate 13. Among them, the shell 11 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 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The above-mentioned electrolyte is impregnated in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 1 can be one or more, and those skilled in the art can select according to specific actual needs.

[0144] The secondary battery may be a battery cell, a battery module or a battery pack.

[0145] Figure 4 3 is an example of a battery module. Figure 4 In the battery module 3, the plurality of battery cells 1 may be arranged in sequence along the length direction of the battery module 3. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 1 may be fixed by fasteners.

[0146] Optionally, the battery module 3 may further include a housing having a receiving space, and the plurality of battery cells 1 are received in the receiving space.

[0147] In some of the embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. A person skilled in the art may select a suitable number based on the application and capacity of the battery pack.

[0148] Figure 5 and Figure 6 2 is an example of a battery pack. Figure 5 and Figure 6 The battery pack 2 may include a battery box and a plurality of battery modules 3 disposed in the battery box. The battery box includes an upper box body 21 and a lower box body 22. The upper box body 21 can cover the lower box body 22 and form a closed space for accommodating the battery modules 3. The plurality of battery modules 3 can be arranged in the battery box in any manner.

[0149] In addition, the present invention further provides an electrical device, which includes the secondary battery provided by the present invention. The secondary battery can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.

[0150] As the electrical device, a secondary battery can be selected according to its usage requirements.

[0151] Figure 7 The power consumption device 4 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

[0152] As another example, the device may be a mobile phone, a tablet computer, a laptop computer, etc.

[0153] In order to make the purpose, technical solutions and advantages of the present invention more concise and clear, the present invention is described with the following specific embodiments, but the present invention is by no means limited to these embodiments. The embodiments described below are only preferred embodiments of the present invention, which can be used to describe the present invention and cannot be understood as limiting the scope of the present invention. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0154] In order to better illustrate the present invention, the present invention is further described below in conjunction with the embodiments. The following are specific embodiments.

[0155] Example 1

[0156] (1) Preparation of positive electrode sheet

[0157] The nickel-cobalt-manganese ternary positive electrode material (LiNi 0.8 Co 0.1 Mn 0.1 O 2 , NCM 811 ), aluminum passivator LiPF 6 , conductive agent carbon black, binder polyvinylidene fluoride (PVDF), add N-methyl pyrrolidone, mix and stir for 2 hours to obtain a first positive electrode slurry;

[0158] The nickel-cobalt-manganese ternary positive electrode material (LiNi 0.8 Co 0.1 Mn0.1 O 2 , NCM 811 ), conductive agent carbon black, binder polyvinylidene fluoride (PVDF), add N-methyl pyrrolidone, mix and stir for 2h to obtain a second positive electrode slurry;

[0159] The first positive electrode slurry is evenly coated on both sides of a 6 μm thick aluminum foil of the positive electrode current collector, and dried to form a first active material layer; the second positive electrode slurry is evenly coated on the first active material layer, dried and cold pressed to form a second active material layer, and cut to obtain positive electrode sheets.

[0160] (2) Preparation of negative electrode sheet

[0161] Graphite, binder styrene-butadiene rubber (SBR), dispersant (CMC-Na), and conductive carbon black (Super-P, SP) were fully stirred and mixed in an appropriate amount of deionized water at a weight ratio of 96:2:1:1 to prepare a negative electrode slurry. The negative electrode active slurry was then coated on both sides of a 6μm thick copper foil, dried and cold pressed to form a negative electrode active material layer, and cut into negative electrode sheets; the thickness of the negative electrode active layer was 150μm.

[0162] (3) Isolation film

[0163] Polypropylene film is used as the isolation film.

[0164] (4) Electrolyte

[0165] LiFSI is dissolved in a solvent of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a volume ratio of 1:1:1, and the mass content of LiFSI in the electrolyte is 10%; the mass content of HF in the electrolyte is ≤200ppm.

[0166] (5) Production of lithium-ion batteries

[0167] The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in order to obtain a bare cell; the bare cell is placed in a packaging shell, and after drying, an electrolyte is injected, and a lithium-ion battery is obtained through vacuum packaging, standing, forming, shaping and other processes.

[0168] Embodiments 2 to 4

[0169] It is basically the same as Example 1, except that the content of the aluminum passivator is different, and the content of the nickel-cobalt-manganese ternary positive electrode material is adjusted accordingly, and the total content of the nickel-cobalt-manganese ternary positive electrode material and the aluminum passivator remains unchanged, as shown in Table 1.

[0170] Embodiment 5-6

[0171] It is basically the same as Example 1, except that the type of aluminum passivator is different, and the corresponding aluminum passivator content remains unchanged, as shown in Table 1.

[0172] Embodiments 7 to 10

[0173] It is basically the same as Example 1, except that the type and content of the aluminum passivator are different, and the total content of the nickel-cobalt-manganese ternary positive electrode material and the aluminum passivator remains unchanged, as shown in Table 1.

[0174] Examples 11 to 15

[0175] It is basically the same as Example 1, except that the thickness of the first active material layer or the second active material layer is different, as shown in Table 1.

[0176] Embodiments 16 to 19

[0177] It is basically the same as Example 1, except that the nickel-cobalt-manganese ternary positive electrode materials in the first active material layer and the second active material layer are replaced by the first active material in Table 1 with the same mass as that in Example 1.

[0178] Embodiment 20-21

[0179] It is basically the same as Example 1, except that the mass content of LiFSI in the electrolyte is different, as shown in Table 1.

[0180] Comparative Example 1

[0181] The same as Example 1, except that the aluminum passivator is replaced by: adding LiPF in the electrolyte. 6 The content is 1mol / L.

[0182] Specifically, the first active material layer is omitted in the positive electrode sheet, that is, the positive electrode sheet includes an aluminum foil and a second active material layer disposed on the aluminum foil; the thickness remains unchanged. 1 mol / L LiPF 6 .

[0183] Comparative Example 2

[0184] It is basically the same as Example 1, except that the aluminum passivator is replaced by: added into the second active material layer.

[0185] Specifically, the preparation of the positive electrode sheets is different. The second positive electrode slurry is evenly coated on the 6μm thick aluminum foil of the positive electrode collector, and dried to form a 120μm thick first active material layer; the first positive electrode slurry is evenly coated on the first active material layer, dried and cold pressed to form a 5μm thick second active material layer, which is then cut to obtain the positive electrode sheets.

[0186] The following is the battery performance test

[0187] (1) The prepared battery was charged to 4.4 V at 0.1 C in a 25°C environment, and then discharged to 2.8 V at 0.1 C. The battery was disassembled and the porosity of the first active material layer and the second active material layer, as well as the thickness of the surface passivation film of the aluminum-based current collector were measured, as shown in Table 1.

[0188] The porosity of the first active material layer and the second active material layer is measured by mercury intrusion and gas adsorption according to GB / T 21650.2-2008. The thickness of the passivation film can be measured by scanning electron microscopy.

[0189] In addition, the components and content of the passivation film in Example 9 were also tested. The test method is as follows: After scraping off the first and second active material layers on the positive electrode plate, the scraped positive current collector is soaked in DMC for one hour and dried. After drying, the positive current collector is tested using SEM-EDS. It can be understood that the positive current collector includes the substrate and the passivation film. The test results show that AlF 3 , Li 3 PO 4 , Li 3 BO 3 The mass contents are 0.1%, 0.1% and 0.05% respectively.

[0190] (2) The cycle performance of the battery at high voltage and high temperature can reflect the passivation of the aluminum-based current collector. The cycle performance of the battery at high voltage and high temperature can be reflected by the capacity retention rate before and after storage at 60°C.

[0191] The capacity retention rate test method before and after 60℃ storage is as follows: the prepared battery is charged to 4.4V at 0.1C in a 25℃ environment, and then discharged to 2.8V at 0.1C, and the discharge capacity at this time is recorded as U 0 , then transferred to a 60℃ oven for storage for 100 days, the battery was taken out, charged to 4.4V at 0.1C in a 25℃ environment, and then discharged to 2.8V at 0.1C. The discharge capacity at this time was recorded as U 1 ;

[0192] High temperature storage capacity retention rate W = U 1 / U 2 ×100%.

[0193] (3) DC internal resistance DCR is an important factor affecting the power performance of the battery. The power performance of the battery can be reflected by DCR.

[0194] The DCR test method is as follows: the prepared battery is charged to 4.4V at 0.1C in a 25°C environment, and then discharged at 0.5C for 1h to adjust to 50% SOC. The voltage at this time is recorded as V 1, discharge at 4C for 30S, record the potential at this time as V 2 ;

[0195] DCR value = (V 1 -V 2 ) / 4C corresponding current value.

[0196] Some parameters and performance test results of the secondary batteries of various embodiments and comparative examples are shown in Table 1.

[0197] Table 1

[0198]

[0199] As shown in Table 1 above, in Comparative Example 1, no aluminum passivator is provided in the active material layer, but 1 mol / L LiPF 6 In Comparative Example 2, the aluminum passivator is placed in the second active material layer on the surface, and LiPF is not added to the electrolyte. 6 Compared with Comparative Examples 1 to 2, the high-temperature storage capacity retention rate of the embodiment is significantly improved, indicating that the passivation and cycle performance of the aluminum-based current collector are good, and the DC internal resistance DCR is significantly lower, which further indicates that the power performance of the battery is good.

[0200] It can be seen from Examples 1 and 7 to 10 that when the passivating agents in Examples 7 to 10 are used in combination, not only can the aluminum-based current collectors such as aluminum foil be passivated, but also the LiPF 6 The passivation reaction with the aluminum-based current collector produces LiF, thereby reducing the deterioration of the battery's internal resistance DCR, and can further improve the battery's power performance and cycle performance.

[0201] It can be seen from Examples 1 and 11 to 15 that the thickness of the first active material layer is 1 to 10 μm, and the thickness of the second active material layer is 80 to 150 μm, both of which have good power performance and cycle performance. Furthermore, the thickness of the first active material layer is 2 to 6 μm, and the thickness of the second active material layer is 100 to 120 μm, which can further improve the power performance and cycle performance of the battery.

[0202] It can be seen from Examples 1 and 16 to 19 that the present invention can use a wide variety of active materials, which are suitable for nickel-cobalt-manganese ternary positive electrode materials, lithium cobalt oxide, LiMnO 2 and LiMn 2 O 4 For active materials such as nickel, the improvement effect is particularly obvious when the percentage of nickel in the total molar amount of nickel, cobalt and manganese is 80% to 95%.

[0203] It can be seen from Examples 1 and 20 to 21 that the mass content of fluorinated sulfonamide lithium salt in the electrolyte is within 4% to 20%. On the one hand, better power performance can be obtained. On the other hand, the use of the positive electrode plate of the present application can improve the corrosion problem of the aluminum-based current collector, thereby improving the cycle performance and power performance of the battery.

[0204] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0205] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims, and the description and drawings can be used to interpret the content of the claims.

Claims

1. A positive electrode sheet, It is characterized in that The positive electrode plate includes an aluminum-based current collector, a first active material layer and a second active material layer, wherein the second active material layer is arranged on at least one side of the aluminum-based current collector, and the first active material layer is arranged between the aluminum-based current collector and the second active material layer on at least one side, and the first active material layer contains a first active substance and an aluminum passivator.

2. The positive electrode sheet according to claim 1, It is characterized in that The positive electrode sheet satisfies at least one of the following conditions: (1) The aluminum passivator includes an alkali metal salt; optionally, the alkali metal salt includes at least one of a lithium salt and a sodium salt; optionally, the alkali metal salt includes at least one of lithium hexafluorophosphate, sodium hexafluorophosphate, lithium difluorooxalatoborate, sodium difluorooxalatoborate, lithium dioxalatoborate and sodium dioxalatoborate; (2) In the first active material layer, the mass content of the aluminum passivator is 10% to 35%, optionally 10% to 35%; more optionally 10% to 25%.

3. The positive electrode sheet according to claim 2, It is characterized in that The alkali metal salt includes at least one of lithium hexafluorophosphate and sodium hexafluorophosphate; Optionally, the alkali metal salt includes at least one of lithium difluorooxalatoborate, sodium difluorooxalatoborate, lithium dioxalatoborate and sodium dioxalatoborate, and at least one of lithium hexafluorophosphate and sodium hexafluorophosphate; more optionally, the mass ratio of at least one of lithium difluorooxalatoborate, sodium difluorooxalatoborate, lithium dioxalatoborate and sodium dioxalatoborate to the mass ratio of at least one of lithium hexafluorophosphate and sodium hexafluorophosphate is 1:(2-30), optionally 1:(4-20), and more optionally 1:(4-10).

4. The positive electrode sheet according to claim 2, It is characterized in that In the first active material layer, the mass content of at least one of lithium hexafluorophosphate and sodium hexafluorophosphate is 10% to 30%; further optionally, 15% to 25%; Optionally, in the first active material layer, the mass content of at least one of the lithium difluorooxalatoborate, sodium difluorooxalatoborate, lithium dioxalatoborate and sodium difluorooxalatoborate is 1% to 5%.

5. The positive electrode sheet according to any one of claims 1 to 4, It is characterized in that The second active material layer contains a second active material, and the charge cutoff voltages of the first active material and the second active material are independently ≥ 4.2V; Optionally, the first active material and the second active material each independently include a nickel-cobalt-manganese ternary positive electrode material, lithium cobalt oxide, LiMnO 2 and LiMn 2 O 4 At least one of .

6. The positive electrode sheet according to claim 5, It is characterized in that The percentage of nickel in the total molar amount of nickel, cobalt and manganese in the nickel-cobalt-manganese ternary positive electrode material is 30% to 95%, and can be 80% to 95%; Optionally, the nickel-cobalt-manganese ternary positive electrode material includes Li x Ni a Co b Mn 1-a-b O 2-e , x is 0.8~1.2, 0.3≤a+b≤0.97, and e is 0~0.

2.

7. The positive electrode sheet according to any one of claims 1 to 6, It is characterized in that The positive electrode sheet satisfies at least one of the following conditions: (1) The thickness ratio of the second active material layer to the first active material layer is (10-120):1, and can be (20-50):1; (2) The thickness of the first active material layer is 1 to 10 μm, and can be 4 to 7 μm; (3) The thickness of the second active material layer is 80 to 150 μm, and can be 100 to 120 μm.

8. A secondary battery, It is characterized in that It comprises the positive electrode sheet, the negative electrode sheet and the electrolyte as described in any one of claims 1 to 7.

9. A secondary battery, It is characterized in that It includes a positive electrode sheet, a negative electrode sheet and an electrolyte disposed between the positive electrode sheet and the negative electrode sheet; The positive electrode sheet comprises an aluminum-based current collector, a first active material layer and a second active material layer, wherein the second active material layer is disposed on at least one side of the aluminum-based current collector, the first active material layer on at least one side is located between the aluminum-based current collector and the second active material layer, and the porosity of the first active material layer is greater than the porosity of the second active material layer; The surface of the aluminum-based current collector comprises a passivation film.

10. The secondary battery according to claim 8 or 9, It is characterized in that The electrolyte includes a fluorine-containing sulfonamide lithium salt.

11. The secondary battery according to claim 9, It is characterized in that The secondary battery satisfies at least one of the following conditions: (1) The thickness of the passivation film is 1 to 2 μm; (2) The passivation film contains at least one of phosphorus and boron and fluorine; Optionally, the mass content of fluorine element in the passivation film is 100 to 20000 ppm, and more preferably 200 to 10000 ppm; Optionally, the mass content of phosphorus in the passivation film is 100 to 5000 ppm, and more preferably 200 to 2000 ppm; Optionally, the passivation film comprises AlF 3 and LiF, more optionally, the passivation film further comprises Li 3 PO 4 ; Optionally, the passivation film contains boron; more preferably, the mass content of boron in the passivation film is 100-1000 ppm; more preferably, the passivation film includes Li 3 BO 3 .

12. The secondary battery according to any one of claims 8 to 11, It is characterized in that The secondary battery satisfies at least one of the following conditions: (1) The fluorinated sulfonamide lithium salt includes at least one of bis(fluorosulfonyl)imide lithium salt and bis(trifluoromethanesulfonyl)imide lithium salt; (2) In the electrolyte, the mass content of the fluorinated sulfonamide lithium salt is ≥ 4%, which can be 4% to 20%, and more preferably 8% to 16%; (3) The mass content of HF in the electrolyte is ≤200 ppm.

13. An electrical device, It is characterized in that The electric device comprises the secondary battery according to any one of claims 8 to 12.

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