Secondary battery, modified graphite, method for producing the same, and electric device

Abstract

The application discloses a secondary battery, modified graphite, a preparation method of the modified graphite and an electric device. The secondary battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector, the positive electrode active material layer comprises modified graphite, the modified graphite has intercalated ions in the interlayer and / or surface, the intercalated ions contain non-oxygen non-metal elements and oxygen elements, the non-oxygen non-metal elements comprise at least one of sulfur elements, phosphorus elements and nitrogen elements, and the mass percentage of the intercalated ions is 0.001% to 0.25% based on the total mass of the positive electrode active material layer. During overcharging, the intercalated ions are gradually deposited on the surface of the positive electrode active material under the action of an electric field, the surface of the positive electrode is passivated in situ, the side reaction of the positive electrode is reduced, the voltage of the secondary battery is rapidly increased, the overcharging time of the secondary battery is shortened, the total energy input during the overcharging of the secondary battery is reduced, and therefore, the risk of thermal runaway of the battery is reduced.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to secondary batteries, modified graphite, methods for preparing the same, and electrical devices thereof. Background Technology

[0002] With the acceleration of global carbon neutrality, lithium-ion batteries, with their excellent cycle performance, high energy density, and low self-discharge, have become an ideal choice for reducing carbon emissions. They are widely used in electric vehicles and energy storage grids. To meet the demands for longer driving ranges in electric vehicles and other electric transportation, and higher land utilization rates for energy storage systems, the energy density of battery cells is gradually increasing. This increases the risk of thermal runaway under abuse conditions (overcharging, overheating, mechanical short circuits, etc.). As the energy density and charging capacity of battery cells continue to improve, the problem of overcharging thermal runaway is receiving increasing attention, and reducing the risk of overcharging thermal runaway has become a major challenge in the field. Summary of the Invention

[0003] In view of the technical problems existing in the background art, this application provides a secondary battery, which aims to reduce the risk of thermal runaway of secondary batteries.

[0004] In one aspect of this application, a secondary battery is proposed. In some embodiments of this application, the secondary battery includes a positive electrode sheet, which includes a positive current collector and a positive active material layer located on at least one side of the positive current collector. The positive active material layer includes modified graphite, and the interlayer and / or surface of the modified graphite have intercalated ions. The intercalated ions contain non-oxygen non-metallic elements and oxygen elements. The non-oxygen non-metallic elements include at least one of sulfur, phosphorus, and nitrogen. Based on the total mass of the positive active material layer, the mass percentage of the intercalated ions is 0.001% to 0.25%. Thus, the modified graphite contains a certain amount of intercalated ions. During overcharging, the intercalated ions in the modified graphite will gradually deposit onto the surface of the positive active material under the action of an electric field, passivating the positive electrode surface in situ, reducing side reactions on the positive electrode side, causing the voltage of the secondary battery to rise rapidly, shortening the overcharging time of the secondary battery, reducing the total energy input during the overcharging process, thereby reducing the risk of thermal runaway of the secondary battery.

[0005] In some embodiments of this application, the intercalated ions include at least one of sulfate, nitrate, and phosphate. These intercalated ions can better passivate the positive electrode during overcharging, significantly reduce side reactions on the positive electrode side, and promote a rapid increase in the secondary battery voltage.

[0006] In some embodiments of this application, the spacing between the modified graphite (002) crystal planes is 0.336 nm to 0.340 nm. This facilitates the deposition of intercalated ions, shortens the time required for intercalated ion deposition, and enables rapid passivation of the positive electrode.

[0007] In some embodiments of this application, the modified graphite has a particle size of 0.5 μm to 30 μm. This facilitates the in-situ precipitation of intercalated ions and rapid passivation of the positive electrode.

[0008] In some embodiments of this application, the degree of graphitization of the modified graphite is 70% to 90%. A degree of graphitization within this range can promote rapid precipitation of intercalated ions.

[0009] In some embodiments of this application, the modified graphite has a BET specific surface area of ​​1 m². 2 / g~5m 2 / g. The smaller BET specific surface area helps reduce side reactions on the high-voltage positive electrode side during overcharging, which in turn helps to further reduce the risk of thermal runaway in secondary batteries.

[0010] In some embodiments of this application, the mass percentage of intercalated ions in the modified graphite is 1% to 5%. Therefore, the modified graphite contains a certain amount of intercalated ions, which can lead to the in-situ precipitation of more intercalated ions during overcharging of the secondary battery, thereby passivating the positive electrode, promoting an increase in the positive electrode voltage, and reducing the risk of thermal runaway in the secondary battery.

[0011] In some embodiments of this application, the modified graphite content is 0.1% to 5% by mass, based on the total mass of the positive electrode active material layer. Therefore, the modified graphite content described above can passivate the positive electrode during overcharging of the secondary battery, reducing side reactions on the positive electrode side, allowing the voltage of the secondary battery to rise rapidly, and reducing the risk of thermal runaway.

[0012] In another aspect of this application, a modified graphite is proposed. In some embodiments of this application, the modified graphite has intercalated ions between its layers and / or on its surface. These intercalated ions contain non-oxygen non-metallic elements and oxygen elements. The non-oxygen non-metallic elements include at least one of sulfur, phosphorus, and nitrogen. The mass percentage of the intercalated ions in the modified graphite is 1% to 5%. When the modified graphite is used in the positive electrode active material layer of a secondary battery, during overcharging, the intercalated ions in the modified graphite can be deposited in situ and gradually deposited onto the surface of the positive electrode active material under the action of an electric field. This in-situ passivates the positive electrode, reduces side reactions on the positive electrode side, promotes a rapid increase in the secondary battery voltage, and reduces the risk of thermal runaway in the secondary battery.

[0013] In some embodiments of this application, the modified graphite satisfies at least one of the following conditions: the intercalating ions include at least one of sulfate, nitrate, and phosphate; the spacing between the (002) crystal planes of the modified graphite is 0.336 nm to 0.340 nm; the particle size of the modified graphite is 0.5 μm to 30 μm; the degree of graphitization of the modified graphite is 70% to 90%; and the BET specific surface area of ​​the modified graphite is 1 m². 2 / g~5m 2 / g. This helps to further reduce the risk of thermal runaway in secondary batteries.

[0014] In another aspect of this application, a method for preparing the aforementioned modified graphite is provided. In some embodiments of this application, the method for preparing the aforementioned modified graphite includes: intercalating graphite with an intercalation solution, collecting the filter residue, and obtaining the modified graphite. The intercalation temperature is 50°C to 80°C. The intercalation solution includes at least one of an oxidant and an intercalating agent. The oxidant includes at least one of KMnO4, NaNO3, (NH4)2S2, and H2O2. The intercalating agent includes at least one of H2SO4, (NH4)2SO4, (NH4)2S2O7, HNO3, NH4NO3, H3PO4, (NH4)3PO4, HClO4, and glacial acetic acid. The modified graphite prepared by this method possesses all the characteristics and advantages of the aforementioned modified graphite, which will not be repeated here.

[0015] In some embodiments of this application, the method for preparing the modified graphite described above satisfies at least one of the following conditions: the intercalation treatment time is 24h to 48h; the filter residue is washed with deionized water until the pH of the filtrate is 5 to 6; the washed filter residue is dried to obtain the modified graphite; and the drying temperature is 100℃ to 150℃. This is beneficial for obtaining modified graphite with excellent performance.

[0016] In some embodiments of this application, graphite is intercalated using an H2SO4 solution, wherein the mass percentage of H2SO4 in the H2SO4 solution is 60%–80%. The H2SO4 solution at this concentration has a certain oxidizing effect, which can promote the entry of intercalated ions into the graphite interlayer.

[0017] In some embodiments of this application, graphite is intercalated using an HNO3 solution, wherein the mass percentage of HNO3 in the HNO3 solution is 30% to 60%. This allows the graphite surface and / or interlayer to contain intercalated nitrate ions.

[0018] In some embodiments of this application, graphite is intercalated using an H3PO4 solution, wherein the mass percentage of H3PO4 in the H3PO4 solution is 40% to 60%. This allows the graphite surface and / or interlayer to have intercalated phosphate ions.

[0019] In another aspect of this application, an electrical device is proposed. In some embodiments of this application, the electrical device includes the aforementioned secondary battery, or the positive electrode active material layer of the secondary battery used in the electrical device includes the aforementioned modified graphite or modified graphite prepared using the aforementioned method. Thus, the electrical device possesses all the features and advantages of the aforementioned secondary battery or the aforementioned modified graphite, which will not be repeated here.

[0020] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0021] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the alternative embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0022] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0023] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0024] Figure 3 This is a schematic diagram of a battery module according to an embodiment of this application;

[0025] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0026] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of this application is shown;

[0027] Figure 6 This is a schematic diagram of an electrical device according to an embodiment of this application;

[0028] Figure 7 These are scanning electron microscope images of the modified graphite in Embodiment 3 of this application;

[0029] Figure 8These are scanning electron microscope images of the modified graphite in Embodiment 16 of this application;

[0030] Figure 9 These are XRD patterns of the modified graphite of Embodiments 3, 16, and 24 of this application and Super P of Comparative Example 1;

[0031] Figure 10 These are the overcharge curves of the batteries in Embodiments 3, 16, 24 and Comparative Example 1 of this application.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1. Battery cell; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Battery module; 3. Battery pack; 31. Upper casing; 32. Lower casing. Detailed Implementation

[0034] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0035] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0036] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0037] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0038] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of the indicated feature.

[0040] In the description of this application, "multiple" means two or more.

[0041] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0043] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0044] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0045] To meet the demands for longer driving ranges in electric vehicles and other electric vehicles, as well as higher land utilization rates in energy storage systems, the energy density of battery cells is gradually increasing. This increases the risk of thermal runaway in battery cells under abuse conditions (overcharging, overheating, mechanical short circuits, etc.).

[0046] In this application, modified graphite is added to the positive electrode active material layer of the secondary battery. The interlayer and / or surface of the modified graphite contain a certain amount of intercalated ions. During battery overcharging, the intercalated ions in the modified graphite can be precipitated in situ and gradually deposited on the surface of the positive electrode active material under the action of an electric field, thereby passivating the surface of the positive electrode active material in situ, reducing side reactions on the positive electrode side, promoting a rapid increase in voltage on the positive electrode side, shortening the overcharging time of the secondary battery, reducing the total energy input during the overcharging process of the secondary battery, and thus reducing the risk of thermal runaway of the secondary battery.

[0047] The secondary batteries disclosed in this application include lithium-ion batteries, and these batteries can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys may include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0048] In one aspect of this application, a secondary battery is proposed. In some embodiments of this application, the secondary battery may include a positive electrode sheet, which includes a positive current collector and a positive active material layer located on at least one side of the positive current collector.

[0049] In some embodiments of this application, the positive electrode active material layer of the battery may include modified graphite, and the interlayer and / or surface of the modified graphite have intercalated ions. The intercalated ions contain non-oxygen non-metallic elements and oxygen elements. The non-oxygen non-metallic elements may include at least one of sulfur, phosphorus, and nitrogen. Based on the total mass of the positive electrode active material layer, the mass percentage of intercalated ions is 0.001% to 0.25%.

[0050] In some embodiments of this application, the mass percentage of intercalated ions can be 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.2%, 0.25%, etc., based on the total mass of the positive electrode active material layer. When the mass percentage of intercalated ions in the positive electrode active material layer is within the above range, during battery overcharging, the intercalated ions can be deposited in situ and gradually deposited onto the surface of the positive electrode active material under the action of an electric field, passivating the positive electrode active material in situ. This reduces side reactions on the positive electrode side during overcharging, promotes a rapid increase in the secondary battery voltage, shortens the overcharging time of the secondary battery, reduces the total energy input during overcharging, and thus reduces the risk of thermal runaway of the secondary battery.

[0051] In the embodiments of this application, the content of intercalated ions in the positive electrode active material layer can be detected by the following method: 1g of sample and 5g of deionized water are added to a beaker in sequence, stirred at 60°C for 5h, filtered and the filtrate is collected, and the concentration of the corresponding intercalated ions (at least one of sulfate, nitrate and phosphate) is detected by ion chromatography.

[0052] In some embodiments of this application, the non-oxygen nonmetallic element may include sulfur, phosphorus, or nitrogen. In some embodiments of this application, the non-oxygen nonmetallic element may include at least two of sulfur, phosphorus, and nitrogen.

[0053] In some embodiments of this application, the intercalating ion may include at least one of sulfate, nitrate, and phosphate.

[0054] In some specific embodiments of this application, the non-oxygen nonmetallic element may include sulfur, and the intercalation ions modifying the graphite interlayer and / or surface may include sulfate (SO4). 2- The intercalated ions mentioned above can be precipitated during the overcharging process of the secondary battery and gradually deposited on the surface of the positive electrode active material under the action of an electric field, effectively passivating the positive electrode active material, thereby reducing the side reactions on the positive electrode side during overcharging, promoting the rapid rise of the secondary battery voltage, shortening the overcharging time of the secondary battery, reducing the total energy input during the overcharging process of the secondary battery, and reducing the risk of thermal runaway of the secondary battery.

[0055] In some specific embodiments of this application, the non-oxygen nonmetallic element may include phosphorus, and the intercalation ions modifying the graphite interlayer and / or surface may include phosphate (PO4) ions. 3- ).

[0056] In some specific embodiments of this application, the non-oxygen nonmetallic element may include nitrogen, and the intercalation ions modifying the graphite interlayer and / or surface may include nitrate (NO3). - ).

[0057] In some embodiments of this application, intercalated ions are present in both the interlayer and surface of the modified graphite. Some of the intercalated ions are located in the interlayer of the modified graphite, while others are attached to the surface of the modified graphite.

[0058] In some embodiments of this application, the mass percentage of intercalated ions in the modified graphite can be 1% to 5%, for example, the mass percentage of intercalated ions in the modified graphite can be 1%, 2%, 3%, 4%, 5%, etc. Thus, the modified graphite contains an appropriate amount of intercalated ions, which can precipitate and deposit onto the surface of the positive electrode active material during overcharging, thereby passivating the positive electrode active material.

[0059] In some embodiments of this application, modified graphite is obtained by intercalating graphite with an intercalating agent and / or an oxidizing agent. The mass percentage of intercalated ions in the modified graphite can be calculated based on the mass change of the raw material before and after reacting with the intercalating agent and / or oxidizing agent. The increased mass can be considered as the mass of the intercalated ions, and the percentage of the increased mass to the total mass of the modified graphite is the mass percentage of intercalated ions in the modified graphite.

[0060] In some embodiments of this application, the spacing between the modified graphite (002) crystal planes (interlayer spacing of the modified graphite) can be 0.336 nm to 0.340 nm. For example, the spacing between the modified graphite (002) crystal planes can be 0.336 nm, 0.3365 nm, 0.337 nm, 0.338 nm, 0.339 nm, 0.340 nm, etc. A spacing between the modified graphite (002) crystal planes within the above range is beneficial for the rapid precipitation of intercalated ions during the overcharging process of the secondary battery, thereby facilitating the passivation of the positive electrode active material and reducing side reactions on the positive electrode side.

[0061] In some embodiments of this application, the spacing of the modified graphite (002) crystal planes can be tested using the following method: A suitable amount of sample is laid flat on a silicon wafer, and the sample is subjected to X-ray diffraction scanning to obtain the corresponding XRD pattern. Then, the spacing of the modified graphite (002) crystal planes is calculated using the Bragg equation nλ=2d sinθ, where n is the diffraction order, λ is the X-ray wavelength, θ is the diffraction angle of the (002) crystal plane, and d is the spacing of the (002) crystal planes (the interlayer spacing of the modified graphite).

[0062] In some embodiments of this application, the particle size of the modified graphite can be from 0.5 μm to 30 μm. For example, the particle size of the modified graphite can be 0.5 μm, 1 μm, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, etc. This facilitates the precipitation of intercalated ions during overcharging and passivation of the positive electrode active material.

[0063] In some embodiments of this application, the particle size of the modified graphite can be 3μm to 6μm. For example, the particle size of the modified graphite can be 3μm, 4μm, 5μm, 6μm, etc. Smaller particle size is more conducive to the rapid precipitation of intercalated ions during overcharging, which is more conducive to the rapid passivation of the positive electrode active material and reduces the side reactions on the positive electrode side.

[0064] In some embodiments of this application, the particle size of modified graphite can be tested using the following method: After preparing an appropriate amount of modified graphite sample, the sample is adhered to conductive adhesive, and corresponding SEM images are taken. The morphology of the particles is observed, and the particle size is labeled. The average value of the size test results of 10 to 20 graphite particles is taken as the particle size of the sample.

[0065] In some embodiments of this application, the degree of graphitization of the modified graphite can be 70% to 90%, for example, 70%, 75%, 80%, 85%, 90%, etc. The degree of graphitization is not particularly high, and it contains a certain amount of intercalated ions (non-oxygen non-metallic elements and oxygen elements). These intercalated ions can precipitate and passivate the positive electrode active material during overcharging, thereby helping to reduce side reactions on the positive electrode side, promoting a rapid increase in the secondary battery voltage, and thus helping to reduce the risk of thermal runaway in the secondary battery.

[0066] In some embodiments of this application, the degree of graphitization can be tested using the following method: determining the interlayer spacing d of the modified graphite crystal structure using XRD diffraction. 002 Then, using Franklin's formula G = (0.3440 - d) 002 The degree of graphitization of the material is calculated by 0.3440-0.3354)×100%.

[0067] In some embodiments of this application, the BET specific surface area of ​​the modified graphite can be 1 m². 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g etc. Modified graphite has a smaller BET specific surface area, which is beneficial to further reduce the side reactions on the high-voltage positive electrode side during overcharging, thereby further reducing the risk of thermal runaway of secondary batteries.

[0068] In this application, BET specific surface area has a well-known meaning in the art, which can be tested by nitrogen adsorption specific surface area analysis and calculated by the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed by the Tri Star II specific surface area and porosity analyzer of Micromeritics, Inc., USA.

[0069] In some embodiments of this application, the mass percentage of modified graphite can be 0.1% to 5% based on the total mass of the positive electrode active material layer. For example, the mass percentage of modified graphite can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, etc. This is beneficial for the secondary battery to maintain good cycle performance and high energy density.

[0070] In some embodiments of this application, the secondary battery may be a lithium-ion battery.

[0071] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material.

[0072] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0073] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0074] In some embodiments of this application, the positive electrode active material may include lithium iron phosphate (LiFePO4), lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2 and lithium-rich cathode active materials.

[0075] Secondary batteries will be accompanied by Li during charging and discharging. + The insertion / extraction and consumption of Li in secondary batteries at different discharge states + The molar content varies. In the list of positive electrode active materials in this application, Li... + The molar content refers to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, after charge-discharge cycles, Li... + The molar content will change.

[0076] In the examples of positive electrode active materials in this application, the molar content of oxygen is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of oxygen will fluctuate.

[0077] In some embodiments of this application, the positive electrode active material layer may optionally include a binder. As an example, the binder in the positive electrode active material layer may include at least one of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyacrylonitrile (PAN), polyacrylate (e.g., polymethyl methacrylate PMMA), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0078] In some embodiments of this application, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent in the positive electrode active material layer may include at least one of superconducting carbon, conductive carbon black (e.g., Super P, acetylene black, Ketjen black with a branched structure, etc.), carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0079] In some embodiments of this application, the positive electrode active material layer may include modified graphite, positive electrode active material, conductive agent, and binder. In some embodiments, based on the total mass of the positive electrode active material layer, the mass percentage of modified graphite may be 0.1% to 5%, the mass percentage of positive electrode active material may be 90% to 98%, the mass percentage of conductive agent may be 0.1% to 2%, and the mass percentage of binder may be 0.1% to 5%. Specifically, the mass percentage of modified graphite may be 0.1%, 0.5%, 1%, 2%, 3%, 5%, etc., the mass percentage of positive electrode active material may be 90%, 92%, 95%, 97%, 98%, etc., the mass percentage of conductive agent may be 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2%, etc., and the mass percentage of binder may be 0.1%, 0.2%, 0.5%, 2%, 5%, etc. The content of each substance in the positive electrode active material layer is within the above range, which is beneficial for the secondary battery to maintain good cycle performance and high energy density.

[0080] In some embodiments of this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0081] Typically, besides the positive electrode, a secondary battery also includes a negative electrode, an electrolyte, and a separator. During the charging and discharging process, active metal ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0082] In some embodiments of this application, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector.

[0083] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0084] 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0085] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: carbon-containing negative electrode active materials (e.g., artificial graphite, natural graphite, soft carbon, hard carbon, etc.), silicon-containing negative electrode active materials (e.g., silicon, silicon-carbon, etc.), alloy negative electrode active materials, tin-based materials, and lithium-containing negative electrode active materials (e.g., lithium titanate, etc.). The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used.

[0086] In some embodiments, the negative electrode active material layer may optionally include a negative electrode binder. The negative electrode binder in the negative electrode active material layer 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).

[0087] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent in the negative electrode active material layer may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC)).

[0089] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, negative electrode binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0090] In some embodiments of this application, the electrolyte includes an electrolyte salt and a solvent.

[0091] In some embodiments of this application, the electrolyte salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium fluorosulfonate, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0092] In some embodiments of this application, the above-mentioned electrolyte salts can be used in combination, and the molar concentration of a single electrolyte salt can be in the range of 0.5 mol / L to 1.5 mol / L.

[0093] In some embodiments of this application, the solvent may include at least one of ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate, butene carbonate, dimethyl carbonate, methyl propyl carbonate, dipropyl carbonate, ethyl propyl carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, and γ-butyrolactone.

[0094] In some embodiments of this application, the electrolyte may also include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0095] In some embodiments, the secondary battery of this application includes the form of a battery cell, a battery module, and a battery pack.

[0096] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0097] In some embodiments, the secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above. In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft pack, such as a pouch. The material of the soft pack may be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0098] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 Here is a square-structured battery cell 1 as an example.

[0099] In some embodiments, refer to Figure 2 The outer packaging may include a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The number of electrode assemblies 12 contained in a single battery cell 1 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0100] In some embodiments, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0101] Figure 3 This is battery module 2 as an example. (See reference...) Figure 3 In battery module 2, multiple battery cells 1 can be arranged sequentially along the length of battery module 2. Of course, they can also be arranged in any other way. Furthermore, these multiple battery cells 1 can be fixed in place using fasteners.

[0102] Optionally, the battery module 2 may also include a housing with a receiving space in which multiple battery cells 1 are received.

[0103] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0104] Figure 4 and Figure 5 This is battery pack 3 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 3 may include a battery box and multiple battery modules 2 disposed within the battery box. The battery box includes an upper box 31 and a lower box 32, with the upper box 31 covering the lower box 32 to form a closed space for accommodating the battery modules 2. The multiple battery modules 2 can be arranged in any manner within the battery box.

[0105] In some embodiments, the battery cell, battery module, or battery pack may be a power source for the electrical device or an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0106] Electrical devices can be equipped with individual battery cells, battery modules, or battery packs depending on their usage requirements.

[0107] Figure 6 This is an example of an electrical device. This device can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0108] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0109] In another aspect of this application, a modified graphite is proposed. In some embodiments of this application, the interlayer and / or surface of the modified graphite have intercalated ions, which contain non-oxygen non-metallic elements and oxygen elements. The non-oxygen non-metallic elements include at least one of sulfur, phosphorus, and nitrogen. The mass percentage of intercalated ions in the modified graphite can be 1% to 5%. For example, the mass percentage of intercalated ions in the modified graphite can be 1%, 2%, 3%, 4%, 5%, etc. The modified graphite having a certain amount of intercalated ions in its interlayer and / or surface, when used in the positive electrode active material layer of a battery (e.g., as a conductive material), allows the intercalated ions to precipitate in situ and gradually deposit onto the surface of the positive electrode active material during overcharging of the secondary battery, passivating the positive electrode active material, thereby reducing side reactions on the positive electrode side, causing the secondary battery voltage to rise rapidly, reducing the total energy input during overcharging, and thus reducing the risk of thermal runaway during overcharging.

[0110] In some embodiments of this application, the intercalated ions may include at least one of sulfate, nitrate, and phosphate. These intercalated ions can be deposited in situ on the surface of the positive electrode active material during overcharging of the secondary battery, passivating the positive electrode active material, thereby suppressing side reactions on the positive electrode side, causing the secondary battery voltage to rise rapidly, reducing the total energy input during overcharging, and thus reducing the risk of thermal runaway during overcharging.

[0111] In some embodiments, the intercalating ion may include sulfate, nitrate, or phosphate. In other embodiments, the intercalating ion may include two or three of sulfate, nitrate, and phosphate.

[0112] In some embodiments of this application, non-oxygen non-metallic elements may include sulfur, and intercalated ions may include sulfate, etc. In modified graphite, the mass percentage of intercalated ions may be 1% to 5%. Thus, the modified graphite contains intercalated ions such as sulfate between layers and / or on the surface. Intercalated ions can be rapidly precipitated and deposited on the surface of the positive electrode active material during the overcharging process of the secondary battery, passivating the positive electrode active material, effectively reducing side reactions on the positive electrode side, promoting a rapid increase in the secondary battery voltage, and reducing the risk of thermal runaway due to overcharging of the secondary battery.

[0113] In the embodiments of this application, the content of intercalated ions in modified graphite can be detected by the following method: 1g of sample and 5g of deionized water are added to a beaker in sequence, stirred at 60°C for 5h, filtered and the filtrate is collected, and the concentration of the corresponding intercalated ions is detected by ion chromatography.

[0114] In some embodiments of this application, the spacing between the modified graphite (002) crystal planes (interlayer spacing of the modified graphite) can be 0.336 nm to 0.340 nm. For example, the spacing between the modified graphite (002) crystal planes can be 0.336 nm, 0.337 nm, 0.338 nm, 0.339 nm, 0.340 nm, etc. A larger spacing between the modified graphite (002) crystal planes is beneficial for the rapid precipitation of intercalated ions during overcharging and for passivating the positive electrode active material.

[0115] In some embodiments of this application, the particle size of the modified graphite is 0.5 μm to 30 μm. For example, the particle size of the modified graphite can be 0.5 μm, 1 μm, 5 μm, 15 μm, 20 μm, 25 μm, 30 μm, etc. Therefore, the modified graphite has a suitable particle size, which not only maintains good conductivity but also facilitates the rapid precipitation of intercalated ions during overcharging.

[0116] In some embodiments of this application, the degree of graphitization of the modified graphite is 70% to 90%, for example, the degree of graphitization of the modified graphite can be 70%, 75%, 80%, 85%, 90%, etc. Therefore, the degree of graphitization of the modified graphite is not too high, and there is a certain amount of intercalation ions between the layers, which is beneficial to promoting the precipitation of intercalation ions during battery overcharging.

[0117] In some embodiments of this application, the BET specific surface area of ​​the modified graphite is 1 m². 2 / g~5m 2 / g, for example, the BET specific surface area of ​​modified graphite can be 1m². 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g etc. Modified graphite has a smaller BET specific surface area, which is beneficial to further reduce the side reactions on the positive electrode side during overcharging of secondary batteries, and thus further reduce the risk of thermal runaway of secondary batteries.

[0118] In another aspect of this application, a method for preparing the aforementioned modified graphite is proposed.

[0119] In some embodiments of this application, the method for preparing the modified graphite described above may include the following steps: intercalating graphite with an intercalation solution, collecting the filter residue, and obtaining modified graphite.

[0120] In some embodiments of this application, the intercalation temperature can be 50°C to 80°C. For example, the intercalation temperature can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc. When the intercalation is performed at the above temperatures, the reaction is relatively mild, which can at least avoid excessive oxidation to a certain extent and is conducive to obtaining modified graphite with appropriate intercalation ion content.

[0121] In some embodiments, the intercalation treatment time can be 24h to 48h, for example, 24h, 28h, 32h, 36h, 40h, 48h, etc. This allows the raw materials to react fully, inserting a certain amount of intercalated ions between the graphite layers and attaching some intercalated ions to the surface.

[0122] In some embodiments of this application, the intercalation solution includes at least one of an oxidizing agent and an intercalating agent. The oxidizing agent may include at least one of KMnO4, NaNO3, (NH4)2S2, and H2O2, while the intercalating agent may include at least one of H2SO4, (NH4)2SO4, (NH4)2S2O7, HNO3, NH4NO3, H3PO4, (NH4)3PO4, HClO4, and glacial acetic acid. By treating graphite with the above-mentioned intercalating agent and / or oxidizing agent, modified graphite containing intercalated ions between and / or on the surface of the graphite layers can be obtained.

[0123] In some embodiments of this application, the intercalation solution may include at least one of H2SO4, HNO3, and H3PO4.

[0124] In some embodiments of this application, graphite can be intercalated using an H2SO4 solution, wherein the mass percentage of H2SO4 in the solution is 60%–80%. For example, the mass percentage of H2SO4 in the solution can be 60%, 65%, 70%, 75%, 80%, etc. The H2SO4 solution at these concentrations can act as both an oxidant and an intercalating agent, oxidizing the edges of the graphite and promoting the entry of the intercalating agent into the graphite interlayer. Furthermore, the resulting modified graphite contains sulfate ions in its interlayer. These sulfate ions can rapidly precipitate and passivate the positive electrode active material during overcharging of the secondary battery, thereby reducing side reactions on the positive electrode side, promoting a rapid increase in the secondary battery voltage, and reducing the risk of thermal runaway in the secondary battery.

[0125] In some embodiments of this application, graphite can be intercalated using an HNO3 solution, wherein the mass percentage of HNO3 in the HNO3 solution is 30% to 60%. For example, the mass percentage of HNO3 in the HNO3 solution can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc. Intercalation of graphite using a nitric acid solution of the above concentration results in modified graphite having a certain amount of intercalated ions (nitrate ions) between its layers and / or on its surface. During overcharging of the secondary battery, these intercalated ions can be deposited in situ and passivate the positive electrode active material.

[0126] In some embodiments of this application, graphite can be intercalated using an H3PO4 solution, wherein the mass percentage of H3PO4 in the solution can be 40% to 60%. For example, the mass percentage of H3PO4 in the solution can be 40%, 45%, 50%, 55%, 60%, etc. Intercalation of graphite using a phosphoric acid solution of the above concentration results in modified graphite having a certain amount of intercalated ions (phosphate groups) between its layers and / or on its surface. During overcharging of the secondary battery, these intercalated ions can be deposited in situ and passivate the positive electrode active material.

[0127] It should be noted that the above-mentioned H2SO4 solution, HNO3 solution, and H3PO4 solution can all be aqueous solutions.

[0128] In some embodiments of this application, after the intercalation process, filtration can be performed, the filter residue can be collected, and the filter residue can be washed with deionized water until the pH of the filtrate is 5-6 to remove unreacted acidic substances. After that, drying treatment is performed to obtain modified graphite.

[0129] In some embodiments of this application, the temperature for drying the filter residue can be 100°C to 150°C. For example, the filter residue can be dried at 100°C, 110°C, 120°C, 130°C, 140°C or 150°C. This allows for the removal of moisture in a shorter time without adversely affecting the structure of the modified graphite.

[0130] In another aspect of this application, an electrical device is proposed. In some embodiments of this application, the electrical device may include the aforementioned secondary battery, or the positive electrode active material layer of the secondary battery used in the electrical device may include the aforementioned modified graphite or modified graphite prepared using the aforementioned method. Thus, the electrical device possesses all the features and advantages of the aforementioned secondary battery or the aforementioned modified graphite, which will not be repeated here.

[0131] In some embodiments of this application, the electrical device may include mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0132] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0133] Example 1

[0134] Dv50 flake graphite with a particle size of 5 μm was added to a 60% H2SO4 aqueous solution and heated to 50°C with stirring for 24 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0135] The steps for manufacturing the positive electrode sheet are as follows: 1. Dry-mix lithium iron phosphate powder, modified graphite, conductive carbon (Super P), and polyvinylidene fluoride (PVDF) at a mass ratio of 96:0.6:0.1:3.3 for 10 minutes. Then add an appropriate amount of N-methylpyrrolidone (NMP) and mix for 2 hours. After mixing, add an appropriate amount of NMP to the slurry and adjust its viscosity to 6000-8000 cp. 2. Coat the obtained slurry evenly onto the surface of aluminum foil. After drying the slurry in an oven at 110℃ and cold-pressing it, the corresponding electrode sheet with an areal density of 20 mg / cm³ is obtained. 2 .

[0136] The steps for manufacturing the negative electrode sheet are as follows: 1. Dry-mix 96 parts by weight of activated graphite and 1 part by weight of conductive carbon for 10 minutes. Then add an appropriate amount of deionized water and 3 parts by weight of sodium carboxymethyl cellulose (CMC). Stir and mix for 2 hours to obtain the corresponding negative electrode slurry. 2. Coat the slurry evenly onto copper foil. After drying the slurry in an oven at 110℃ and cold-pressing it, the corresponding electrode sheet with an areal density of 11 mg / cm³ is obtained. 2 .

[0137] Separator: The separator is made of polypropylene substrate. Aluminum oxide with a thickness of 3μm and PVDF with a thickness of 3μm are uniformly sprayed onto the substrate surface in sequence. Both surfaces are coated with aluminum oxide and PVDF.

[0138] Electrolyte: The electrolyte consists of solvents dimethyl carbonate, methyl ethyl carbonate, ethylene carbonate, ethyl acetate, ethylene carbonate, and lithium hexafluorophosphate. The mass ratio of dimethyl carbonate, methyl ethyl carbonate, ethylene carbonate, ethyl acetate, and ethylene carbonate in the solvent is 4:1:3:2:0.5, and the molar concentration of the lithium salt in the electrolyte is 1M.

[0139] Battery assembly: The positive and negative electrode sheets are wound with a separator to form a battery cell, which is then encapsulated in an aluminum-plastic film and dried until the moisture content is 200 ppm. Electrolyte is injected into the battery cell to obtain a pouch cell.

[0140] Example 2

[0141] In Example 2, flake graphite with a Dv50 particle size of 5 μm was added to a 60% H2SO4 aqueous solution as raw material, heated to 80°C and stirred for 24 h. After the reaction was completed, the filter residue was collected and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0142] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0143] Example 3

[0144] In Example 3, flake graphite with a Dv50 particle size of 5 μm was added to a 60% H2SO4 aqueous solution as raw material, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0145] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0146] Example 4

[0147] In Example 4, flake graphite with a particle size of 5 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 70%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0148] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0149] Example 5

[0150] In Example 5, flake graphite with a Dv50 particle size of 5 μm was added to an 80% H2SO4 aqueous solution as raw material, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0151] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0152] Example 6

[0153] In Example 6, flake graphite with a Dv50 particle size of 5 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 110°C for 24 h to obtain modified graphite.

[0154] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0155] Example 7

[0156] In Example 7, flake graphite with a Dv50 particle size of 5 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 150°C for 24 h to obtain modified graphite.

[0157] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0158] Example 8

[0159] In Example 8, flake graphite with a Dv50 particle size of 5 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 150°C for 36 h to obtain modified graphite.

[0160] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0161] Example 9

[0162] In Example 9, flake graphite with a Dv50 particle size of 5 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 150°C for 48 h to obtain modified graphite.

[0163] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0164] Example 10

[0165] In Example 10, flake graphite with a Dv50 particle size of 0.5 μm was added to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0166] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0167] Example 11

[0168] In Example 11, flake graphite with a Dv50 particle size of 3 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0169] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0170] Example 12

[0171] In Example 12, flake graphite with a Dv50 particle size of 6 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0172] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0173] Example 13

[0174] In Example 13, flake graphite with a Dv50 particle size of 10 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0175] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0176] Example 14

[0177] In Example 14, flake graphite with a Dv50 particle size of 20 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0178] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0179] Example 15

[0180] In Example 15, flake graphite with a Dv50 particle size of 30 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0181] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0182] Example 16

[0183] In Example 16, flake graphite with a Dv50 particle size of 20 μm was added to an 80% H2SO4 aqueous solution as raw material, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 150°C for 24 h to obtain modified graphite.

[0184] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0185] Example 17

[0186] In Example 17, flake graphite with a Dv50 particle size of 5 μm was added to an 80% H2SO4 aqueous solution as raw material, heated to 80°C and stirred for 36 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 150°C for 24 h to obtain modified graphite.

[0187] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0188] Example 18

[0189] In Example 18, flake graphite with a Dv50 particle size of 5 μm was added as raw material to an 80% H2SO4 aqueous solution. The mixture was heated to 80°C and stirred for 36 h. After the reaction was completed, the filter residue was collected and washed with deionized water until its pH was 5-6. Then it was dried at 110°C for 24 h to obtain modified graphite.

[0190] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0191] Example 19

[0192] In Example 19, flake graphite with a Dv50 particle size of 5 μm was added to an 80% H2SO4 aqueous solution as raw material, heated to 80°C and stirred for 36 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 100°C for 24 h to obtain modified graphite.

[0193] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0194] Example 20

[0195] In Example 20, flake graphite with a Dv50 particle size of 5 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 50°C and stirred for 24 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0196] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0197] Example 21

[0198] In Example 21, flake graphite with a Dv50 particle size of 5 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0199] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0200] Example 22

[0201] In Example 22, flake graphite with a Dv50 particle size of 5 μm was added as raw material to an aqueous solution of H2SO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0202] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0203] Example 23

[0204] In Example 23, flake graphite with a Dv50 particle size of 5 μm was added as raw material to an 80% H2SO4 aqueous solution. The mixture was heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then, it was dried at 130°C for 24 h to obtain modified graphite.

[0205] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0206] Example 24

[0207] In Example 24, flake graphite with a Dv50 particle size of 5 μm was added as raw material to an aqueous solution of HNO3 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0208] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0209] Example 25

[0210] In Example 25, flake graphite with a Dv50 particle size of 5 μm was added as raw material to an aqueous solution of H3PO4 with a mass concentration of 60%, heated to 80°C and stirred for 48 h. After the reaction was completed, the filter residue was collected by filtration and washed with deionized water until its pH was 5-6. Then it was dried at 130°C for 24 h to obtain modified graphite.

[0211] Other steps are performed in accordance with Example 1, and the differences from Example 1 are recorded in Table 1.

[0212] Comparative Example 1

[0213] The difference between Comparative Example 1 and Example 1 is that no modified graphite was added during the preparation of the positive electrode sheet. The positive electrode sheet was made of lithium iron phosphate powder and conductive carbon (Super P (i.e., SP), with a specific surface area of ​​60 m²). 2 Polyvinylidene fluoride (PVDF) was dry-mixed at a mass ratio of 96:0.7:3.3 for 10 min, and then an appropriate amount of N-methylpyrrolidone (NMP) was added and stirred for 2 h. Other preparation steps and parameters in Comparative Example 1 were consistent with those in Example 1.

[0214] Comparative Example 2

[0215] The difference between Comparative Example 2 and Example 1 is that, in preparing the positive electrode sheet, unintercalated Dv50 flake graphite with a particle size of 5 μm was used instead of modified graphite. Lithium iron phosphate powder, flake graphite, conductive carbon (Super P), and polyvinylidene fluoride (PVDF) were dry-mixed at a mass ratio of 96:0.6:0.1:3.3 for 10 min, followed by the addition of an appropriate amount of N-methylpyrrolidone (NMP) and mixing for 2 h. Other preparation steps and parameters in Comparative Example 2 were consistent with those in Example 1.

[0216] The parameters of the modified graphite or the unintercalated flake graphite in Comparative Example 2, the mass percentage of intercalated ions in the positive electrode active material layer, and the mass percentage of intercalated ions in the modified graphite in each embodiment were tested as follows:

[0217] The content of intercalated ions in modified graphite can be detected by the following method: 1g of sample and 5g of deionized water are added to a beaker in sequence, stirred at 60°C for 5h, filtered and collected, and the concentration of the corresponding intercalated ions (sulfate (Examples 1-23), nitrate (Example 24) or phosphate (Example 25)) is detected by ion chromatography.

[0218] The interlayer spacing of the modified graphite or the unintercalated flake graphite (002) in Comparative Example 2 can be tested using the following method: A suitable amount of sample is laid flat on a silicon wafer, and the sample is scanned by X-ray diffraction to obtain the corresponding XRD pattern. Then, the interlayer spacing of the modified graphite or the unintercalated flake graphite is calculated using the Bragg equation nλ=2d sinθ, where n is the diffraction order, λ is the X-ray wavelength, θ is the diffraction angle of the (002) crystal plane, and d is the interlayer spacing of the (002) crystal plane.

[0219] The particle size of modified graphite can be tested using the following method: After preparing an appropriate amount of modified graphite sample, the sample is adhered to conductive adhesive, and corresponding SEM images are taken. The morphology of the particles is observed, and the particle size is labeled. The average value of the size test results of 10 graphite particles is taken as the particle size of the sample.

[0220] The degree of graphitization can be tested using the following method: The interlayer spacing d of the graphite crystal structure is determined using XRD diffraction. 002 ((002) interplanar spacing), then using Franklin's formula G=(0.3440-d 002 The degree of graphitization of the material is calculated by 0.3440-0.3354)×100%.

[0221] The BET specific surface area of ​​modified graphite, unintercalated flake graphite, or conductive carbon Super P was measured using the nitrogen adsorption specific surface area analysis method and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis was performed using a Tri Star II specific surface area and porosity analyzer from Micromeritics, Inc., USA.

[0222] Table 1

[0223]

[0224]

[0225] The electrochemical performance of the cells in each embodiment and comparative example was tested, including overcharge performance, cycle performance at 25°C, and cycle performance at 60°C. The test results are recorded in Table 2.

[0226] Overcharge test conditions: 1. Constant current 1C charging to 3.65V, then constant voltage charging to a current of 0.05C; 2. Constant current 1C charging to 5.475V. The SOC value of the battery cell when overcharged to 5.475V is calculated by the following formula: T1 / 3600*C rate *100%, where T1 is the time it takes for the battery cell to overcharge to 5.475V, in seconds; C rate This is the charging rate during overcharging.

[0227] Cyclic performance test at 25℃ / 60℃:

[0228] 1. Charge to 3.65V using a constant current of 0.5C;

[0229] 2. Let it sit for 10 minutes;

[0230] 3. Discharge at a constant current of 0.5C to 2.5V;

[0231] 4. Let it sit for 10 minutes;

[0232] 5. Repeat steps 1-4 until the cycle is completed 500 times.

[0233] It should be noted that the only difference between the cycling performance test at 25°C and the cycling performance test at 60°C is the test temperature; all other steps and parameters are the same.

[0234] Table 2

[0235]

[0236] As shown in Table 2, compared with Comparative Examples 1 and 2, the addition of modified graphite to the positive electrode in each embodiment of this application can reduce the risk of thermal runaway of the battery cell; compared with Comparative Example 1, adding unintercalated graphite to the positive electrode in Comparative Example 2 does not significantly reduce the SOC value corresponding to the overcharge of the battery cell from Umax to 1.5Umax.

[0237] Figure 7 A scanning electron microscope image of the modified graphite in Example 3 is shown, with a particle size of approximately 5 μm. Figure 8 A scanning electron microscope image of the modified graphite in Example 16 is shown, the modified graphite having a particle size of approximately 20 μm.

[0238] Figure 9 In Comparative Example 1, SP refers to the conductive carbon, graphite 1, graphite 2, and graphite 3, which are the modified graphites obtained through intercalation processing in Examples 24, 3, and 16, respectively. Figure 9 The diffraction angle and corresponding diffraction intensity of the corresponding material can be obtained. The degree of graphitization and the spacing of the graphite (002) crystal plane can be calculated using the formula mentioned above.

[0239] Figure 10 The overcharge curves of the battery cell are shown. The upper curve represents the change in State of Charge (SOC) as the cell voltage is overcharged from Umax to 1.5Umax, and the lower curve represents the change in cell temperature as a function of SOC. Figure 10 As can be seen, the SOC (State of Charge, the ratio of remaining battery capacity to rated capacity) of the cells in Comparative Example 1 (SP), Example 24 (graphite 1), Example 3 (graphite 2), and Example 16 (graphite 3) after overcharging to 1.5Umax are 127%, 119%, 117%, and 125%, respectively. This indicates that adding modified graphite to the positive electrode can significantly reduce the risk of thermal runaway in the cell. When SP, SP and graphite 1, SP and graphite 2, and SP and graphite 3 are used as the positive electrode conductive materials, the temperature rise of the 3.14Ah small pouch cell during overcharging is 6℃, 5.3℃, 5.1℃, and 5.8℃, respectively. The temperature rise of the overcharged cells also demonstrates that adding modified graphite to the positive electrode can effectively reduce the risk of thermal runaway in the cell.

[0240] Furthermore, after overcharging, the cell volumes of Comparative Example 1, Example 24, Example 3, and Example 16 were 167 mL, 134 mL, 122 mL, and 152 mL, respectively, further demonstrating that the side reactions during the overcharging process of the cells in these examples were significantly suppressed.

[0241] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," and "other embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0242] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A secondary battery, characterized in that, The positive electrode includes a positive current collector and a positive active material layer located on at least one side of the positive current collector. The positive electrode active material layer includes modified graphite, and the interlayer and / or surface of the modified graphite have intercalated ions. The intercalated ions contain non-oxygen non-metallic elements and oxygen elements. The non-oxygen non-metallic elements include at least one of sulfur, phosphorus, and nitrogen elements. Based on the total mass of the positive electrode active material layer, the mass percentage of the intercalated ions is 0.001% to 0.25%.

2. The secondary battery according to claim 1, characterized in that, The intercalating ions include at least one of sulfate, nitrate, and phosphate.

3. The secondary battery according to claim 1 or 2, characterized in that, The spacing between the modified graphite (002) crystal planes is 0.336 nm to 0.340 nm.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The modified graphite has a particle size of 0.5 μm to 30 μm.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The degree of graphitization of the modified graphite is 70% to 90%.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The modified graphite has a BET specific surface area of ​​1 m². 2 / g~5m 2 / g.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, In the modified graphite, the mass percentage of the intercalated ions is 1% to 5%.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, Based on the total mass of the positive electrode active material layer, the mass percentage of the modified graphite is 0.1% to 5%.

9. A modified graphite, characterized in that, The modified graphite has intercalated ions between layers and / or on the surface. The intercalated ions contain non-oxygen non-metallic elements and oxygen elements. The non-oxygen non-metallic elements include at least one of sulfur, phosphorus, and nitrogen elements. The mass percentage of the intercalated ions in the modified graphite is 1% to 5%.

10. The modified graphite according to claim 9, characterized in that, The modified graphite satisfies at least one of the following conditions: The intercalating ion includes at least one of sulfate, nitrate, and phosphate; The spacing between the modified graphite (002) crystal planes is 0.336 nm to 0.340 nm; The modified graphite has a particle size of 0.5 μm to 30 μm; The degree of graphitization of the modified graphite is 70% to 90%; The modified graphite has a BET specific surface area of ​​1 m². 2 / g~5m 2 / g.

11. A method for preparing the modified graphite according to claim 9 or 10, characterized in that, include: Graphite was intercalated using an intercalation solution, and the filter residue was collected to obtain the modified graphite. The intercalation treatment temperature is 50℃~80℃, and the intercalation solution includes at least one of an oxidant and an intercalating agent. The oxidant includes at least one of KMnO4, NaNO3, (NH4)2S2, and H2O2, and the intercalating agent includes at least one of H2SO4, (NH4)2SO4, (NH4)2S2O7, HNO3, NH4NO3, H3PO4, (NH4)3PO4, HClO4, and glacial acetic acid.

12. The method according to claim 11, characterized in that, At least one of the following conditions must be met: The intercalation process takes 24 hours to 48 hours. The filter residue is washed with deionized water until the pH of the filtrate is 5-6. The washed filter residue is then dried to obtain the modified graphite. The drying temperature is 100℃-150℃.

13. The method according to claim 11 or 12, characterized in that, Graphite was intercalated using an H2SO4 solution, wherein the mass percentage of H2SO4 in the H2SO4 solution was 60%–80%. Alternatively, graphite can be intercalated using an HNO3 solution, wherein the mass percentage of HNO3 in the HNO3 solution is 30% to 60%. Alternatively, graphite can be intercalated using an H3PO4 solution, wherein the mass percentage of H3PO4 in the H3PO4 solution is 40% to 60%.

14. An electrical appliance, characterized in that, The device includes a secondary battery according to any one of claims 1 to 8, or the positive electrode active material layer of the secondary battery used in the electrical device includes the modified graphite according to claim 9 or 10 or the modified graphite prepared by any one of claims 11 to 13.

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