Secondary battery and electric device

Abstract

The present application relates to a secondary battery and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte disposed between the positive electrode sheet and the negative electrode sheet, wherein the electrolyte contains LiFSI having a mass content of a; the positive electrode sheet contains a positive active material, Dv99 of the positive active material is y1 μm, and y1 ranges from 5 to 15; and the secondary battery meets the following condition: 100≤y1 / a≤10000. Regarding the secondary battery, the addition of LiFSI to the electrolyte can alleviate temperature rise, but when there is excess LiFSI, the service life of the battery is affected because LiFSI itself is not resistant to oxidation; and using a positive active material having a relatively small Dv99 value can alleviate temperature rise, but if the Dv99 value is overly small, the service life of the battery deteriorates. In the present application, by means of controlling the relationship between Dv99 and the LiFSI content, temperature rise during fast charging is alleviated, and the service life problems caused by LiFSI and Dv99 are also avoided.

Description

Secondary batteries and electrical devices

[0001] Related applications

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on November 17, 2023, with application number 2023115348647 and titled “Secondary Batteries and Electrical Devices,” the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the field of new energy technology, and in particular to a secondary battery and an electrical device. Background Art

[0004] In recent years, the application range of secondary batteries, such as lithium-ion batteries, has become increasingly broad. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the rapid development of lithium-ion batteries, higher requirements have been placed on their fast-charging performance, especially how to solve the problem of thermal runaway caused by the rapid temperature rise during fast charging. Summary of the Invention

[0005] The present application provides a secondary battery and an electrical device that can improve fast charging performance and the thermal runaway problem caused by excessive temperature rise during fast charging.

[0006] In order to achieve the above-mentioned object, the first aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte disposed between the positive electrode sheet and the negative electrode sheet;

[0007] The electrolyte includes LiFSI with a mass content of a; the positive electrode sheet contains a positive electrode active material, the Dv99 of the positive electrode active material is y1μm, and y1 is 5 to 15; the secondary battery meets the following conditions: 100≤y1 / a≤10000.

[0008] Without wishing to be bound by any theory, in the secondary battery described above, adding LiFSI to the electrolyte can improve temperature rise. However, excessive LiFSI can affect battery life due to its inherent oxidation resistance. Using a positive electrode active material with a smaller Dv99 value can also improve temperature rise, but too low a Dv99 value can worsen battery life. This application achieves temperature rise during fast charging by controlling the relationship between Dv99 and LiFSI content, while also avoiding the lifespan issues associated with LiFSI and Dv99.

[0009] In some embodiments of the present application, the secondary battery satisfies at least one of the following conditions:

[0010] (1) y1 is 5 to 12;

[0011] (2) 0<a≤10%;

[0012] (3)200≤y1 / a≤5000.

[0013] In some embodiments of the present application, y1 is 5-10.

[0014] In some embodiments of the present application, 0.01%≤a≤10%.

[0015] In some embodiments of the present application, 0.1%≤a≤5%.

[0016] In some embodiments of the present application, the secondary battery satisfies at least one of the following conditions:

[0017] (1) 1% ≤ a ≤ 5%;

[0018] (2)200≤y1 / a≤600.

[0019] In some embodiments of the present application, 2%≤a≤4%.

[0020] In some embodiments of the present application, the Dv50 of the positive electrode active material is y2 μm, and the secondary battery satisfies the following condition: 1.2≤y1 / y2≤7.

[0021] By controlling the ratio of Dv99 to Dv50 of the positive electrode active material, the secondary battery can achieve excellent fast charging performance, cycle life and hot box safety performance while having a lower temperature rise.

[0022] In some embodiments of the present application, the secondary battery satisfies at least one of the following conditions:

[0023] (1) y2 is 1.5 to 6;

[0024] (2)2≤y1 / y2≤6.

[0025] In some embodiments of the present application, y2 is 2 to 5. Optionally, y2 is 3 to 5.

[0026] When y2 is in the range of 1.5-6, 2-5 and 3-5, and y1 / y2 is in the range of 2-6, the battery has better cycle life and hot box safety performance.

[0027] In some embodiments of the present application, the positive electrode active material includes a nickel-cobalt-manganese ternary positive electrode material.

[0028] In some embodiments of the present application, in the total molar amount of nickel, cobalt and manganese elements in the nickel-cobalt-manganese ternary positive electrode material, the molar proportion of cobalt is 5% to 15%, and the molar proportion of nickel is 50% to 90%;

[0029] In some embodiments of the present application, in the total molar amount of nickel, cobalt and manganese elements in the nickel-cobalt-manganese ternary positive electrode material, the molar proportion of cobalt element is 9% to 15%, and the molar proportion of nickel element is 50% to 70%.

[0030] The molar ratio of nickel and cobalt is controlled within this range, so that the battery has better cycle life and hot box safety performance.

[0031] In some embodiments of the present application, the compaction density of the negative electrode sheet is ≤1.6 g / cm 3 .

[0032] In some embodiments of the present application, the secondary battery further includes a separator provided between the positive electrode sheet and the negative electrode sheet, and the Gurley value of the separator is 100s to 600s;

[0033] In some embodiments of the present application, the isolation film has a Gurley value of 400s to 500s.

[0034] The second aspect of the present application further provides an electrical device comprising the secondary battery of the first aspect of the present application.

[0035] The electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0036] 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

[0037] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0038] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0039] FIG. 2 is an exploded view of the battery cell according to one embodiment of the present application shown in FIG. 1 .

[0040] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0041] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0042] FIG5 is an exploded view of the battery pack shown in FIG4 according to an embodiment of the present application.

[0043] FIG6 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] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0045] Below, some embodiments of the secondary battery and the 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 may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure 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.

[0046] " scope " disclosed in the present application can be 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 any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can form a scope 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 listed, and if the maximum range value 3,4 and 5 are also listed, then the following scope can all be 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 all real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10", this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0047] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0048] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0049] References to "embodiments" herein mean 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 such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0050] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply 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 inherent logic. Unless otherwise specified, all steps of the present application may 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 further include step (c), indicating that step (c) may 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.

[0051] In this application, in the open technical features or technical solutions described with words such as "contain", "include", and "include", 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 that also include 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 includes not only a1, a2, and a3, but also other members". In this 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.

[0052] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0053] The secondary battery and the electric device of the present application will be described below with reference to the accompanying drawings as appropriate.

[0054] Typically, a secondary battery consists of a positive electrode, a negative electrode, and an electrolyte. The electrolyte is located between the positive and negative electrodes. During the battery's charge and discharge processes, active ions are inserted and removed from the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. Typically, the electrolyte is a liquid, or electrolyte solution.

[0055] In addition, secondary batteries generally also include a separator, which is placed between the positive electrode and the negative electrode to prevent a short circuit between the positive and negative electrodes while allowing ions to pass through.

[0056] One embodiment of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte disposed between the positive and negative electrode sheets. The electrolyte comprises LiFSI having a mass content a. The positive electrode sheet contains a positive electrode active material having a Dv99 of y1 μm, where y1 is 5 to 15. The secondary battery satisfies the following condition: 100 ≤ y1 / a ≤ 1000.

[0057] Without wishing to be bound by any theory, in the secondary battery described above, adding LiFSI to the electrolyte can improve temperature rise. However, excessive LiFSI can affect battery life due to its inherent oxidation resistance. Using a positive electrode active material with a smaller Dv99 value can also improve temperature rise, but too low a Dv99 value can worsen battery life. This application achieves temperature rise during fast charging by controlling the relationship between Dv99 and LiFSI content, while also avoiding the lifespan issues associated with LiFSI and Dv99.

[0058] y1 / a reflects the relationship between the Dv99 value and the LiFSI content of the positive electrode active material. A large y1 / a indicates excessive Dv99 or insufficient LiFSI content, both of which affect the battery's temperature rise. A small y1 / a, on the other hand, indicates either a low y1 or excessive LiFSI content, both of which affect the battery's cycle life. By controlling the Dv99 value and LiFSI content within appropriate ranges, a secondary battery with improved temperature rise performance and cycle life can be achieved.

[0059] Dv99 is a well-known term in the art and can be measured using methods known in the art. For example, it can be measured using a laser particle size analyzer (e.g., Malvern Master Size 3000). Dv99 represents the particle size corresponding to the 99th percentile of the volume distribution of particles starting from the smallest particle size, based on the particle size volume distribution. Dv50 represents the particle size corresponding to the 50th percentile of the volume distribution of particles starting from the smallest particle size, based on the particle size volume distribution.

[0060] Particle size and volume distribution can be determined by the following method: Add an appropriate amount of the sample to be tested to a clean beaker and thoroughly sonicate to ensure complete dispersion. The test instrument is a Malvern 2000 (USA). The sample is poured into the injection tower and then circulated with the solution into the test optical system. The particles are illuminated by a laser beam, and the energy distribution of the scattered light is measured to determine the particle size distribution (shading degree: 8-12%). A particle size and volume distribution graph is then plotted based on the test data.

[0061] Positive electrode

[0062] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material mentioned above.

[0063] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0064] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0065] In some embodiments, the thickness of the single-sided positive electrode active material layer is 26-68 μm.

[0066] As an example, the Dv99 of the positive electrode active material is y1μm, where y1 can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or a range consisting of any two of the above values. In some embodiments, y1 is 5-12; in other words, the Dv99 of the positive electrode active material is 5-12μm. By controlling the Dv99 of the positive electrode active material within an appropriate range, a large temperature rise in the battery can be avoided, while also preventing serious side reactions, resulting in a secondary battery with a longer cycle life and a lower temperature rise. Furthermore, y1 is 5-10.

[0067] The positive electrode active material with the above particle size can be purchased from the market or prepared by yourself. The specific preparation method can adopt the known preparation method. Taking the nickel-cobalt-manganese ternary material as an example, the specific preparation steps can be:

[0068] Step 1: Preparation of hydroxide precursor Ni x Co y M 1-x-y (OH)2; Ni salt, Co salt and M salt are used to prepare a metal salt solution with a total metal ion concentration of 1.0 to 5.0 mol / L; the metal salt solution and the ammonia-alkali mixed solution are subjected to a coprecipitation reaction in a reactor to prepare a precursor Ni x Co y M 1-x-y (OH)2; wherein, 0<x<1, 0<y<1, 0<1-xy<1.

[0069] Step 2: Preparation of ternary cathode material LiNi x Co y M 1-x-y O2; grind and mix the precursor obtained in step 1 with flux and LiOH·H2O; sinter the mixture in an oxygen atmosphere at a temperature of 700-1000°C for 8-20 hours; grind, wash, filter and dry the sintered material; after drying, sinter the material in an oxygen atmosphere at a temperature of 750-1000°C for 1-10 hours to obtain the ternary positive electrode material LiNi x Co y M 1-x-y O2;

[0070] Optionally, the above ternary cathode material can also be surface coated. Specifically, the ternary cathode material obtained in step 2 is ground and mixed with the coating raw material; the mixture is sintered in an oxygen atmosphere, and the sintering conditions are controlled to be 700-1000° C. and 3-15 hours. The coating raw material can be one or both of LiOH·H2O and Li2O.

[0071] In some embodiments, the Dv50 of the positive electrode active material is y2 μm, and the secondary battery satisfies the following condition: 1.2≤y1 / y2≤7. Alternatively, 2≤y1 / y2≤6.

[0072] As an example, the value of y1 / y2 can be 1.2, 1.5, 1.8, 2, 2.5, 2.8, 2.9, 3, 3.4, 3.5, 3.8, 4, 4.2, 4.5, 6, 6.5, 7, or a range consisting of any two of the above values.

[0073] Optionally, y2 is 1.5 to 6; more optionally, y2 is 2 to 5; more optionally, y2 is 3 to 5.

[0074] As an example, the Dv50 of the positive electrode active material can be 1.5μm, 2μm, 2.5μm, 2.9μm, 2.9μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 5.6μm, 5.8μm, 6μm, or a range consisting of any two of the foregoing values. By controlling the Dv50 of the material within an appropriate range, a large temperature rise of the battery can be avoided, while also preventing serious side reactions, thereby enabling the secondary battery to have a longer cycle life and a lower temperature rise.

[0075] By controlling the ratio of Dv99 to Dv50 of the positive electrode active material, and thus controlling the Dv50 of the positive electrode active material within an appropriate range, the particle size distribution of the positive electrode active material can be limited, which can take into account excellent fast charging performance, cycle life and hot box safety performance, while having a lower temperature rise.

[0076] When y2 is in the ranges of 1.5-6, 2-5, and 3-5, and y1 / y2 is in the range of 2-6, the battery exhibits excellent cycle life and hot box safety. y1 / y2 represents the difference between the Dv99 and Dv50 values. A larger ratio indicates a greater difference between the two, while a smaller ratio indicates a smaller difference. A smaller difference indicates a more uniform particle size of the positive electrode active material, making it easier to form a lithium ion transmission path and improve fast charging performance. However, a larger Dv50 can increase the fast charging temperature rise. A larger difference indicates an uneven particle size of the positive electrode active material. Combining different particle sizes can increase energy density, but a smaller Dv50 helps reduce temperature rise, but it increases side reactions, reducing cycle life and hot box safety. By controlling the ratio range of the Dv99 and Dv50 values ​​of the positive electrode active material, the battery can achieve better overall performance.

[0077] In some of these embodiments, the positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, nickel cobalt manganese ternary positive electrode materials (or lithium nickel cobalt manganese oxide), lithium nickel cobalt aluminum oxide, and its modified compounds.

[0078] Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0079] Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt aluminum oxides may include LiNi 0.85 Co 0.15 Al 0.05 O2.

[0080] Non-limiting examples of nickel-cobalt-manganese ternary positive electrode materials (also known as lithium nickel-cobalt-manganese oxide) may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.5 Co 0.15 Mn 0.35 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1Mn 0.1 O2 (also referred to as NCM 811 ), LiNi 0.85 Co 0.05 Mn 0.1 O2、LiNi 0.64 Co 0.09 Mn 0.27 O2、LiNi 0.68 Co 0.10 Mn 0.22 O2, etc. It is understandable that the nickel-cobalt-manganese ternary positive electrode material may also be doped with other metal elements.

[0081] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the content of Li in the positive electrode active material is different when the battery is discharged to different states. In the list of positive electrode active materials in this application, unless otherwise specified, the Li content 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 Li content in the positive electrode active material contained in the plate will usually change. Among them, the Li content can be measured by molar ratio, but is not limited to this. Regarding "the Li content 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 new materials obtained by appropriate modification on the basis of the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode active materials, and non-limiting examples include coating modification.

[0082] In the examples of positive electrode active materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the molar percentage of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar percentage, but is not limited to this.

[0083] In some embodiments, the positive electrode active material includes a nickel-cobalt-manganese ternary positive electrode material.

[0084] Furthermore, of the total molar amount of nickel, cobalt, and manganese in the nickel-cobalt-manganese ternary cathode material, the molar proportion of cobalt is 5% to 15%, and the molar proportion of Ni is 50% to 90%. Alternatively, the molar proportion of cobalt is 9% to 15%, and the molar proportion of Ni is 50% to 70%. For example, the molar proportion of Ni can be 50%, 55%, 60%, 64%, 65%, 68%, 70%, 75%, 80%, 85%, or 90%. The molar proportion of cobalt can be 5%, 6%, 9%, 10%, 12%, or 15%. Controlling the Ni and Co contents of the cathode active material ensures that the battery has an optimal cycle life and hot box safety. A higher Ni content can achieve a higher energy density, but an excessively high Ni content can deteriorate the battery's cycle life and hot box safety.

[0085] The molar content of each element (such as nickel, cobalt and manganese) in the positive electrode active material can be measured by methods known in the art, such as the ICP method (trace element analysis-inductively coupled plasma optical emission spectrometry) using an inductively coupled plasma optical emission spectrometer iCAP 7400.

[0086] Optionally, the molar fraction of cobalt in the surface layer of the nickel-cobalt-manganese ternary cathode material is greater than the molar fraction of cobalt in the inner layer. In other words, the composition of the inner and surface layers of the nickel-cobalt-manganese ternary cathode material differs, with the molar fraction of cobalt in the inner layer being lower and the molar fraction of cobalt in the surface layer being higher. This gradient setting of Co in the nickel-cobalt-manganese ternary cathode material can effectively stabilize the structure of the cathode active material and improve the kinetic performance of the cathode electrode sheet.

[0087] It is understood that in some examples, the molar ratio of cobalt in the inner layer and the surface layer can be differentiated by using multiple coatings with precursors of different compositions. It is understood that the specific implementation method is not limited to this.

[0088] In some embodiments, the positive electrode active material layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0089] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] In some embodiments, in the positive electrode active material layer, the mass content of the positive electrode active material is 75% to 98%.

[0091] In some embodiments, in the positive electrode active material layer, the mass content of the conductive agent is 0.1% to 15%.

[0092] In some embodiments, in the positive electrode active material layer, the binder has a mass content of 0.5% to 15%.

[0093] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0094] The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 to 25000 mPa·s. When applying the positive electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 15 to 35 mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 to 3.6 g / cm 3 , can be selected as 3.3~3.5g / cm 3 .

[0095] Negative electrode

[0096] Generally, a negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0097] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0098] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0099] Furthermore, the negative electrode film layer may include a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material.

[0100] In some embodiments, the thickness of the single-sided negative electrode active material layer is 22-110 μm.

[0101] In some of these embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0102] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include one or more 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).

[0103] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0104] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0105] In some embodiments, the mass content of the negative electrode active material in the negative electrode film layer is 75% to 98%.

[0106] In some embodiments, the mass content of the conductive agent in the negative electrode film layer is 0.1% to 15%.

[0107] In some embodiments, the mass content of the binder in the negative electrode film layer is 0.5% to 15%.

[0108] In some embodiments, the compaction density of the negative electrode sheet is less than 1.6 g / cm 2 ; Optional: 1.3~1.5g / cm 2 Controlling the smaller compaction density of the negative electrode can make the negative electrode have larger pores inside, thereby improving the infiltration of the electrolyte and improving Li + transmission, thereby improving the overall dynamic performance of the secondary battery, which is beneficial to improving the fast charging performance. It can be understood that the compaction density of the negative electrode plate refers to the compaction density of the negative electrode film layer on the negative electrode plate. Compaction density test: disassemble the battery cell to take the electrode plate, and punch it into small discs with an area of ​​S, measure the weight M and thickness L of the small discs, take another layer of electrode plates, wipe off the surface membrane layer and leave the remaining empty current collector foil, and also punch it into small discs of S, weigh the mass of the empty aluminum foil M0, then the compaction density PD = (M-M0) / (S*n*L), where n is the number of membrane layers coated on the current collector, which is 1 or 2, single-sided coating or double-sided coating. In a specific example, S is 1540.25mm 2 .

[0109] In some embodiments, the negative electrode sheet can be prepared by the following method: 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 (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0110] The negative electrode slurry may be applied to a single surface of the negative electrode current collector or to both surfaces of the negative electrode current collector. The negative electrode slurry may have a solid content of 40 wt % to 60 wt %. The viscosity of the negative electrode slurry at room temperature may be adjusted to 2000-10000 mPa·s.

[0111] electrolytes

[0112] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The electrolyte of this application is an electrolyte. The electrolyte includes an electrolyte salt and a solvent. As described above, the electrolyte includes LiFSI with a mass content of a.

[0113] In some embodiments, 0 < a ≤ 10%. As an example, the value of a can be 0.01%, 0.02%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of the foregoing values. Alternatively, 0.01% ≤ a ≤ 10%, alternatively, 0.1% ≤ a ≤ 5%, further, 1% ≤ a ≤ 5%, and even more alternatively, 1% < a ≤ 5%.

[0114] Further, 2%≤a≤4%, more optionally, 2%<a≤4%.

[0115] As an example, the value of y1 / a can be 100, 120, 150, 160, 167, 170, 200, 233, 300, 330, 333, 340, 400, 500, 600, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, or 10000. The value range of y1 / a can be a range consisting of any two of the above values. Furthermore, 200 ≤ y1 / a ≤ 5000, or 100 ≤ y1 / a ≤ 5000; 200 ≤ y1 / a ≤ 600; or a range consisting of any two of the above values.

[0116] In some embodiments, the electrolyte includes LiFSI having a mass content a, where 0.1% ≤ a ≤ 5%. The positive electrode sheet includes a positive electrode active material having a Dv99 of y1 μm, where y1 is 5 to 10. Thus, the secondary battery satisfies the following condition: 100 ≤ y1 / a ≤ 1000.

[0117] In some embodiments, the electrolyte salt may also include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorodioxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0118] In some embodiments, the solvent may include one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0119] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include 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, and additives that improve battery high or low temperature performance.

[0120] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0121] Isolation film

[0122] The isolation membrane is set between the positive electrode and the negative electrode, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0123] In some embodiments, the isolation film has a Gurley value of 100s to 600s.

[0124] Optionally, the Gurley value of the isolation film is 150s to 600s; more optionally, the Gurley value of the isolation film is 400s to 600s; or 400s to 500s.

[0125] By controlling the Gurley value of the isolation membrane within the aforementioned smaller range, its impedance is smaller and its kinetic performance is better. When used in combination with an electrolyte containing LiFSI, it can achieve better fast charging capability.

[0126] The Gurley value of the isolation membrane can be obtained by testing in the following manner: placing the isolation membrane in an air permeability tester and testing the time required for 100 mL of air to pass through 1 square inch of the isolation membrane under a pressure of 1.22 kPa, in seconds (s).

[0127] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0128] In some embodiments, the thickness of the isolation film is 6 μm to 40 μm, and optionally 12 μm to 20 μm.

[0129] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0130] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0131] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0132] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells. In one example, a secondary battery may also be a battery cell.

[0133] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0134] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0135] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The 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 impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0136] The secondary battery may be a battery module 4 or a battery pack 1 .

[0137] A battery module includes at least one battery cell. The number of battery cells contained in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0138] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0139] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0140] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0141] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , 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 placed 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.

[0142] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0143] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0144] Figure 6 shows an example of an electric device 6. 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.

[0145] 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.

[0146] The following are specific examples.

[0147] Below, the embodiment of the present application is described. The embodiment described below is exemplary, is only used to explain the present application, and is not to be construed as limiting the present application. Where the technology or conditions are not specified in the embodiment, the technology or conditions described in the literature in this area or the product instructions are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0148] Example 1

[0149] 1) Preparation of positive electrode sheet

[0150] The positive electrode active material LiNi 0.68 Co 0.10 Mn 0.22 O2, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were mixed uniformly in an appropriate amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.2:2.7:1.1 to produce a positive electrode slurry. The slurry was then coated onto aluminum foil, the positive electrode current collector. The slurry was then dried, cold-pressed, slit, and cut to form a 38μm thick positive electrode active material layer, resulting in a positive electrode sheet. The Dv99 and Dv50 values ​​of the positive electrode active material were 1μm and 2μm, respectively. See Table 1 for specific values.

[0151] 2) Preparation of negative electrode sheet

[0152] The negative electrode active material artificial graphite, conductive agent carbon black (Super P), binder styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) were mixed uniformly in an appropriate amount of deionized water according to a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry; the negative electrode slurry was coated on the negative electrode current collector copper foil, and through the processes of drying, cold pressing, slitting and cutting, a negative electrode active material layer with a single-side thickness of 54μm was formed to obtain a negative electrode sheet. The compacted density of the negative electrode sheet is 1.45g / cm 3 .

[0153] 3) Isolation film

[0154] A 12 μm thick polypropylene separator was selected; for the Gurley value of the separator, please refer to Table 1.

[0155] 4) Preparation of electrolyte

[0156] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 30:70 to obtain an organic solvent. LiFSI, which accounts for 3 wt% of the entire electrolyte, is dissolved in the mixed solvent. Fully dried LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0157] 5) Preparation of secondary batteries

[0158] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to form an electrode assembly. The electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum packaging, standing, forming, and shaping, a secondary battery is obtained. The ratio of the electrolyte mass to the secondary battery capacity is 2.2g / Ah. See Table 1 for some specific parameters.

[0159] Examples 2 to 6

[0160] The secondary batteries of Examples 2 to 6 were prepared in a similar manner to the secondary battery of Example 1, except that the mass content a of LiFSI in the electrolyte was different. Please see Table 1 for the specific differences.

[0161] Examples 7 to 15

[0162] The secondary batteries of Examples 7 to 15 are prepared in a similar manner to the secondary battery of Example 1, except that the positive electrode active material LiNi 0.68 Co 0.10 Mn 0.22 Different Dv99 (i.e. y1) of O2 and / or positive electrode active material LiNi 0.68 Co 0.10 Mn 0.22 The Dv50 of O2 is different. Please see Table 1 for the specific differences.

[0163] Examples 16 to 19

[0164] The secondary batteries of Examples 16 to 19 are prepared in a similar manner to the secondary battery of Example 1, except that the molar ratio of the nickel element and the molar ratio of the cobalt element in the positive electrode active material NCM ternary material are different.

[0165] Examples 20 to 22

[0166] The secondary batteries of Examples 20 to 22 were prepared in a similar manner to the secondary battery of Example 1, except that the Gurley values ​​of the separators were different. Please see Table 1 for the specific differences.

[0167] Comparative Examples 1-2

[0168] The preparation method of the secondary battery of Comparative Examples 1 to 2 is similar to that of the secondary battery of Example 1, except that the mass content of LiFSI in the electrolyte and the positive electrode active material LiNi 0.68 Co 0.10 Mn 0.22 The Dv99 (i.e., y1) of O2 is different and the value of y1 / a is different. Please refer to Table 1 for the specific differences. Please refer to Table 1 for the specific differences.

[0169] Table 1

[0170] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0171] The following is a performance test.

[0172] (1) Fast charging capability test: The batteries of the above-mentioned embodiments and comparative examples were charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour). Specifically, at 35°C, the batteries were charged at a constant current rate of 1C to a voltage of 4.4V, then charged at a constant voltage to a current of ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.8V. The actual capacity was recorded as C0. Then each battery is charged with a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 in sequence to the full battery charge cut-off voltage of 4.4V or the negative electrode cut-off potential of 0V (whichever is reached first). After each charge is completed, it is discharged with 1C0 to the full battery discharge cut-off voltage of 2.8V. Record the state of charge (SOC) at different charge rates to 10%, 20%, 30%, ..., 80%. Charge, state of charge, when "SOC = 0" means the battery is fully discharged, when "SOC = 100%" means the battery is fully charged) the corresponding negative electrode potential, draw the charge rate-negative electrode potential curve under different SOC states, and after linear fitting, obtain the charge rate corresponding to the negative electrode potential of 0V under different SOC states. This charge rate is the charging window under this SOC state, which is recorded as C(10% SOC), C(20% SOC), C(30% SOC), and C(40% SOC) respectively. , C(50% SOC), C(60% SOC), C(70% SOC), C(80% SOC), and the charging time T (in minutes) for charging the battery from 10% SOC to 80% SOC are calculated according to the formula (60 / C(20% SOC) + 60 / C(30% SOC) + 60 / C(40% SOC) + 60 / C(50% SOC) + 60 / C(60% SOC) + 60 / C(70% SOC) + 60 / (C80% SOC)) × 10%. The shorter this time, the better the battery's fast charging performance.

[0173] (2) Fast charge cycle life: The battery is charged step by step at the charge rate under each SOC obtained from the fast charge capability test. The battery is charged at a charge rate of C(10% SOC) to 10% SOC, then at a charge rate of C(20% SOC) to 20% SOC, then at a charge rate of C(30% SOC) to 30% SOC, then at a charge rate of C(40% SOC) to 40% SOC, then at a charge rate of C(50% SOC) to 60% SOC. The battery was charged at a constant current of 0.33 C to 50% SOC, then charged at a constant current of C(60% SOC) to 60% SOC, then charged at a constant current of C(70% SOC) to 70% SOC, then charged at a constant current of C(80% SOC) to 80% SOC, then charged at a constant current of 0.33 C to 100% SOC, and then discharged at a rate of 0.33 C to 2.5 V. Cycle according to the above process and record the number of cycles when the battery decays to 80% SOC.

[0174] Among them, the number of cycles when decaying to 80% SOH is calculated by the following method: divide the discharge capacity of the nth cycle by the discharge capacity of the first cycle from small to large, and record the ratio respectively; when the ratio is equal to or less than 80% SOH for the first time, this number of cycles is the number of cycles when decaying to 80% SOH, that is, the fast charge cycle life parameter in Table 2.

[0175] The larger the number of cycles, the better the fast charging cycle life.

[0176] (3) Fast charge temperature rise test: Use the same charge and discharge process as the fast charge cycle life test to charge and discharge for one cycle, and use a temperature sensing wire to test and record the temperature rise of the large surface of the battery cell during this process (i.e. the temperature difference before and after charging and discharging).

[0177] (4) Hot box safety test: The battery cell is first fully charged to the corresponding design upper limit voltage. The battery cell is equipped with a clamp. The temperature inside the hot box is raised from room temperature at a rate of 2°C / min to 100°C and maintained for 1 hour. The temperature is then raised at a rate of 5°C / min and maintained for 30 minutes at every 5°C until the battery cell fails (smoke or fire occurs when the valve is opened). The test is stopped and the upper limit temperature is set to 250°C. The temperature inside the hot box when the battery cell fails is recorded. The temperature inside the hot box can represent the safety performance of the hot box. The specific values ​​are shown in Table 2, Hot Box Safety Performance (°C).

[0178] The test results are shown in Table 2.

[0179] Table 2

[0180] The fast-charge time in Table 2 can be used to characterize the fast-charge performance of a secondary battery. The shorter the fast-charge time, the better the fast-charge performance of the battery. The fast-charge cycle life (number of cycles to 80% SOH) can be used to characterize the cycle life of the battery. A greater fast-charge cycle life (number of cycles to 80% SOH) indicates a better fast-charge cycle life.

[0181] The fast-charge temperature rise and hot box safety tests in Table 2 can indicate thermal runaway caused by excessive temperature rise during fast charging. The smaller the fast-charge temperature rise, the lower the risk of thermal runaway caused by excessive temperature rise during fast charging, and the better the temperature rise performance. The higher the furnace temperature at which the hot box safety test cell fails, the lower the risk of thermal runaway caused by excessive temperature rise during fast charging, and the better the hot box safety performance.

[0182] From Tables 1 and 2, it can be seen that the preparation methods of the secondary batteries of Comparative Examples 1 and 2 are similar to those of the secondary batteries of Example 1. The difference is that at least one of the mass content a of LiFSI in the electrolyte and the Dv99 (i.e., y1) of the positive electrode active material is different. The Dv99 of the positive electrode active material of Comparative Example 1 is larger, and y1 / a is larger. The fast charging time T of its secondary battery is longer, the cycle life is shorter, and the temperature rise is larger, indicating that the battery has poor fast charging performance, poor cycle life, and large temperature rise; in Comparative Example 2, a is larger, y1 / a is smaller, the cycle life of the secondary battery is deteriorated, the furnace temperature when the battery cell fails is lower, and the hot box safety performance is poor.

[0183] Compared with the comparative example, each embodiment can ensure that the secondary battery has a better fast charge cycle life.

[0184] It can be seen from Examples 1 to 10 that controlling 200≤y1 / a≤5000 can further improve the fast charging performance and cycle life of the battery, while having a lower temperature rise and better hot box safety performance. Controlling 200≤y1 / a≤600 can further improve the comprehensive performance of the secondary battery.

[0185] The secondary batteries of Examples 7-9 differ from those of Example 1 in that the Dv99 (i.e., y1) of the positive electrode active material is different. All batteries exhibit good overall performance. Furthermore, by controlling the Dv99 of the positive electrode active material to 5-12 μm, the secondary batteries exhibit better fast-charging performance and lower temperature rise.

[0186] The secondary batteries of Examples 12 to 15 differ from Example 1 in that the positive electrode active material Dv50 (i.e., y2) and correspondingly different y1 / y2 ratios are employed. All batteries exhibit excellent overall performance. Furthermore, when y2 is within the range of 2 to 5 and y1 / y2 is within the range of 2 to 6, the secondary batteries exhibit improved fast-charging performance and cycle life, while also exhibiting lower temperature rise and superior safety performance.

[0187] The secondary batteries of Examples 16 to 19 differ from those of Example 1 in that the nickel content and cobalt content of the positive electrode active material are different. When the molar ratio of the cobalt element is 9% to 15% and the molar ratio of the nickel element is 50% to 70%, the secondary batteries have better cycle life and better hot box safety performance.

[0188] The secondary batteries of Examples 20-22 differ from those of Example 1 in that the Gurley values ​​of the separators differ. All batteries exhibit excellent fast-charging performance and reduce the risk of thermal runaway caused by rapid temperature rise during fast charging. Furthermore, the separators have Gurley values ​​in the range of 400-600s, resulting in improved cycle life and superior hot box safety.

[0189] 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. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte disposed between the positive electrode sheet and the negative electrode sheet; the electrolyte comprises LiFSI with a mass content of a; the positive electrode sheet contains a positive electrode active material, the Dv99 of the positive electrode active material is y1μm, and y1 is 5 to 15; the secondary battery satisfies the following conditions: 100≤y1 / a≤10000.

2. The secondary battery according to claim 1, wherein The secondary battery satisfies at least one of the following conditions: (1) y1 is 5 to 12; (2)0＜a≤10％； (3)200≤y1 / a≤5000.

3. The secondary battery according to any one of claims 1 to 2, wherein: y1 is 5 to 10.

4. The secondary battery according to any one of claims 1 to 3, wherein: 0.01％≤a≤10％。 5. The secondary battery according to any one of claims 1 to 4, wherein: 0.1％≤a≤5％。 6. The secondary battery according to any one of claims 1 to 5, wherein: The secondary battery satisfies at least one of the following conditions: (1)1％≤a≤5％； (2)200≤y1 / a≤600.

7. The secondary battery according to claim 6, wherein: 2％≤a≤4％。 8. The secondary battery according to any one of claims 1 to 7, wherein: The Dv50 of the positive electrode active material is y2 μm, and the secondary battery satisfies the following condition: 1.2≤y1 / y2≤7.

9. The secondary battery according to claim 8, wherein: The secondary battery satisfies at least one of the following conditions: (1) y2 is 1.5 to 6; (2)2≤y1 / y2≤6.

10. The secondary battery according to claim 9, wherein y2 is 2 to 5.

11. The secondary battery according to any one of claims 1 to 10, wherein: The positive electrode active material includes a nickel-cobalt-manganese ternary positive electrode material.

12. The secondary battery according to claim 11, wherein In the total molar amount of nickel, cobalt and manganese elements in the nickel-cobalt-manganese ternary positive electrode material, the molar proportion of cobalt is 5% to 15%, and the molar proportion of nickel is 50% to 90%.

13. The secondary battery according to claim 12, wherein In the total molar amount of nickel, cobalt and manganese elements in the nickel-cobalt-manganese ternary positive electrode material, the molar proportion of cobalt is 9% to 15%, and the molar proportion of nickel is 50% to 70%.

14. The secondary battery according to any one of claims 1 to 13, wherein: The secondary battery further includes a separator disposed between the positive electrode plate and the negative electrode plate, and the Gurley value of the separator is 100s to 600s.

15. The secondary battery according to claim 14, wherein The Gurley value of the isolation film is 400s to 500s.

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

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