WO2024082273A1 - 二次电池、用电装置和制备方法 - Google Patents

二次电池、用电装置和制备方法 Download PDF

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WO2024082273A1
WO2024082273A1 PCT/CN2022/126730 CN2022126730W WO2024082273A1 WO 2024082273 A1 WO2024082273 A1 WO 2024082273A1 CN 2022126730 W CN2022126730 W CN 2022126730W WO 2024082273 A1 WO2024082273 A1 WO 2024082273A1
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carbon
negative electrode
particle
active material
optionally
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PCT/CN2022/126730
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English (en)
French (fr)
Inventor
陶晓林
王建矿
王星会
王宁
魏志婷
木赛男
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宁德时代新能源科技股份有限公司
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Priority to PCT/CN2022/126730 priority Critical patent/WO2024082273A1/zh
Publication of WO2024082273A1 publication Critical patent/WO2024082273A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids

Definitions

  • the present application relates to the technical field of secondary batteries, and in particular to secondary batteries, electrical devices and preparation methods.
  • the present application provides a secondary battery, an electrical device and a preparation method.
  • the negative electrode active material layer included in the secondary battery has a lower tortuosity, which can accelerate the discharge of gas production and is conducive to maintaining good battery cycle performance.
  • a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet;
  • the negative electrode plate comprises a negative electrode active material layer, the negative electrode active material layer comprises carbon-based particles, the carbon-based particles comprise single carbon particles and secondary carbon particles, wherein the D v 50 of the single carbon particles is greater than the D v 50 of the secondary carbon particles;
  • D v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%.
  • single-particle carbon with a larger particle size and secondary-particle carbon with a smaller particle size are compounded.
  • the secondary-particle carbon is beneficial to reducing the tortuosity and facilitating the discharge of gas production.
  • the single-particle carbon is beneficial to maintaining good battery cell cycle performance and extending the battery life.
  • the negative electrode slurry needs to be compacted after coating and drying to adjust the thickness, density, energy density and other parameters. During the compaction (cold pressing can be used), certain pores will be formed between the particles, and these pores are interconnected, so that there is a pore connection path between the two sides of the negative electrode active material layer.
  • the ratio between the path of the pore connection path and the thickness of the negative electrode active material layer is the tortuosity of the negative electrode active material layer.
  • the addition of secondary-particle carbon with a smaller particle size can make it easier to form a pore connection path between the pores, thereby reducing the tortuosity.
  • the time required for the gas produced during formation and battery use to be discharged along the pore connection path is shorter, which is conducive to forming a more homogeneous interface, and the stability of the interface is better.
  • lower tortuosity can also improve the wetting effect of the electrolyte on the electrode.
  • the tortuosity ⁇ of the negative electrode active material layer is numerically equal to a value calculated according to the following formula: ⁇ k ⁇ Rion ⁇ A/d; wherein ⁇ is the porosity of the negative electrode active material layer at 25°C; k is the ionic conductivity of the electrolyte at 25°C, in units of ms/cm; Rion is the ionic resistance of the negative electrode sheet at 25°C, in units of ⁇ ; A is the effective area when testing Rion, in units of cm 2 ; d is the thickness of the negative electrode active material layer, in units of ⁇ m;
  • the tortuosity ⁇ of the negative electrode active material layer is ⁇ 4.75.
  • the tortuosity ⁇ of the negative electrode active material layer is ⁇ 4.70;
  • the tortuosity of the negative electrode active material layer ⁇ 4.70, and optionally, ⁇ is selected from 3.40 to 4.70;
  • the tortuosity of the negative electrode active material layer ⁇ 4.65, and optionally, ⁇ is selected from 3.40 to 4.65;
  • the tortuosity of the negative electrode active material layer ⁇ 4.62, and optionally, ⁇ is selected from 3.42 to 4.62;
  • the tortuosity of the negative electrode active material layer ⁇ 4.05, and optionally, ⁇ is selected from 3.42 to 4.05;
  • the tortuosity of the negative electrode active material layer ⁇ 3.95, and optionally, ⁇ is selected from 3.42 to 3.95;
  • the tortuosity of the negative electrode active material layer ⁇ 3.85, and optionally, ⁇ is selected from 3.45 to 3.85;
  • the tortuosity ⁇ of the negative electrode active material layer is ⁇ 3.82, and optionally, ⁇ is selected from 3.45 to 3.82.
  • the tortuosity of the negative electrode active material layer may change; as the battery is used for a longer time, the volume of the pole piece may change, thereby causing a change in tortuosity.
  • the porosity of the negative electrode active material layer is selected from 30.6% to 37.5%;
  • the porosity of the negative electrode active material layer is selected from 32.2% to 37.5%;
  • the porosity of the negative electrode active material layer is selected from 33.8% to 37.5%;
  • the porosity of the negative electrode active material layer is selected from 34.8% to 37.5%;
  • the porosity of the negative electrode active material layer is selected from 35.5% to 37.5%.
  • the porosity of the negative electrode active material layer By controlling the porosity of the negative electrode active material layer within a suitable range, it is beneficial to control the appropriate tortuosity while ensuring that the electrolyte has appropriate wettability, thereby accelerating gas production while achieving better battery cell kinetic performance.
  • the compaction density of the negative electrode active material layer is selected from 1.30 g/cc to 1.80 g/cc;
  • the compaction density of the negative electrode active material layer is selected from 1.30 g/cc to 1.70 g/cc;
  • the compaction density of the negative electrode active material layer is selected from 1.50 ⁇ 0.02 g/cc.
  • the compaction density By controlling the compaction density within a suitable range, it is beneficial to provide better energy density while accelerating gas production, and achieve good cycle performance.
  • the higher the compaction density the more beneficial it is to improve energy density.
  • an increase in compaction density will lead to a decrease in porosity, which may be detrimental to the infiltration of the electrolyte and affect the battery power.
  • the greater the compaction density the smaller the porosity, which may be detrimental to the infiltration of the electrolyte, resulting in increased difficulty in embedding active ions (such as lithium ions) and worse battery kinetic performance.
  • the mass proportion of the secondary particle carbon in the carbon-based particles is selected from 10% to 90%;
  • the mass proportion of the secondary particle carbon in the carbon-based particles is selected from 20% to 80%;
  • the mass proportion of the secondary particle carbon in the carbon-based particles is selected from 30% to 70%;
  • the mass proportion of the secondary particle carbon in the carbon-based particles is selected from 30% to 50%.
  • the inventor of the present application has found through research that in the secondary battery of the present application, as the proportion of secondary particle carbon increases, the tortuosity of the negative electrode sheet gradually decreases, and the porosity tends to increase.
  • the tortuosity and porosity can be controlled within a suitable range.
  • the mass ratio of single particle carbon and secondary particle carbon is controlled at 7:3, and the SOC at the end of gas production after formation is 26% earlier than the SOC at the end of gas production after 100% pure single particle carbon (without secondary particle carbon), and the cycle performance is improved by 1.7% (taking 400 cycles as an example) compared to 100% pure secondary particle carbon (without single particle carbon).
  • the carbon-based particles account for more than 50% by mass of the negative electrode active material in the negative electrode active material layer.
  • the mass proportion of the carbon-based particles in the negative electrode active material of the negative electrode active material layer is selected from 80% to 100%;
  • the mass proportion of the carbon-based particles in the negative electrode active material of the negative electrode active material layer is selected from 90% to 100%;
  • the mass proportion of the carbon-based particles in the negative electrode active material of the negative electrode active material layer is selected from 95% to 100%;
  • the mass proportion of the carbon-based particles in the negative electrode active material of the negative electrode active material layer is 100%;
  • the carbon-based particles contain graphite material accounting for more than 50% by mass;
  • the carbon-based particles contain graphite material in an amount selected from 80% to 100% by mass;
  • the carbon-based particles contain a graphite material selected from 90% to 100% by mass;
  • the carbon-based particles contain a graphite material selected from 95% to 100% by mass;
  • the carbon-based particles contain 100% by mass of graphite material
  • the negative electrode active material of the negative electrode active material layer contains graphite material accounting for more than 50% by mass;
  • the negative electrode active material of the negative electrode active material layer contains a graphite material selected from 80% to 100% by mass;
  • the negative electrode active material of the negative electrode active material layer contains a graphite material selected from 90% to 100% by mass;
  • the negative electrode active material of the negative electrode active material layer contains a graphite material selected from 95% to 100% by mass;
  • the negative electrode active material of the negative electrode active material layer contains 100% by mass of graphite material.
  • the carbon-based particles are graphite particles
  • the single carbon particles are single graphite particles
  • the secondary particles are secondary graphite particles
  • the negative electrode sheet When carbon-based materials are used as the main negative electrode active material in the negative electrode active material layer, compared with other types of negative electrode sheets with high silicon content, the negative electrode sheet has lower expansion, a more stable solid electrolyte interface (SEI) film, and better battery safety.
  • SEI solid electrolyte interface
  • the carbon-based particles are mainly graphite particles
  • the single-particle carbon is mainly single-particle graphite
  • the secondary particles are mainly secondary-particle graphite.
  • the negative electrode active material layer has one or more of the following characteristics:
  • the D v 50 of the single carbon particle is selected from 13 ⁇ m to 14 ⁇ m;
  • the D v 50 of the secondary carbon particles is selected from 9.5 ⁇ m to 10.5 ⁇ m.
  • the difference between D v 50 of the single carbon particle and D v 50 of the secondary carbon particle is selected from 3 ⁇ m to 4 ⁇ m.
  • the D v 99 of the single carbon particle is greater than the D v 99 of the secondary carbon particle
  • the negative electrode active material layer further has one or more of the following characteristics:
  • the D v 99 of the single carbon particle is selected from 37 ⁇ m to 44 ⁇ m;
  • the D v 99 of the secondary carbon particles is selected from 31 ⁇ m to 38 ⁇ m.
  • the difference between D v 99 of the single carbon particle and D v 99 of the secondary carbon particle is selected from 4 ⁇ m to 6 ⁇ m.
  • the D v 10 of the single carbon particle is greater than the D v 10 of the secondary carbon particle
  • the negative electrode active material layer further has one or more of the following characteristics:
  • the D v 10 of the single carbon particle is selected from 5 ⁇ m to 7 ⁇ m;
  • the D v 10 of the secondary carbon particles is selected from 3.5 ⁇ m to 5.5 ⁇ m.
  • the difference between D v 10 of the single carbon particle and D v 99 of the secondary carbon particle is selected from 1 ⁇ m to 2 ⁇ m.
  • the multi-dimensional performance of tortuosity, porosity and compaction degree can be better balanced, thereby accelerating gas production and discharge while achieving better cycle performance and power performance.
  • controlling the difference in particle size between single-particle carbon and secondary-particle carbon is more conducive to fully leveraging the compounding advantages of the two, which is beneficial for reducing tortuosity and gas emission, maintaining good battery cell cycle performance, and extending battery life.
  • the secondary granular carbon includes a plurality of micro-granular carbons and also includes a binder; wherein the number of primary particles in the micro-granular carbon is one or more;
  • the micro carbon particles are micro graphite particles
  • micro-particle carbon has one or more of the following characteristics:
  • the D v 99 of the micro-particle carbon is selected from 20 ⁇ m to 24 ⁇ m;
  • the D v 90 of the micro-particle carbon is selected from 12 ⁇ m to 15 ⁇ m;
  • the D v 50 of the microparticle carbon is selected from 5 ⁇ m to 7 ⁇ m.
  • the D v 10 of the micro-particle carbon is selected from 2 ⁇ m to 3 ⁇ m;
  • the binder is asphalt
  • the mass ratio of the binder to the plurality of carbon microparticles is selected from 1:8.5 to 1:9.5;
  • the secondary carbon particles are formed by agglomerating the plurality of carbon particles and the binder.
  • the particle size and distribution of the micro-particle carbon within a suitable range, it is beneficial to stably control the particle size of the secondary particle carbon. Further, by controlling the amount of the binder (such as asphalt), the preset particle size and distribution of the secondary particle carbon can be better achieved.
  • the secondary particulate carbon comprises a carbon-based core and an amorphous carbon layer located at least partially on a surface of the carbon-based core;
  • the thickness of the amorphous carbon layer on the surface of the secondary carbon particles is ⁇ 500nm;
  • the thickness of the amorphous carbon layer on the surface of the secondary carbon particles is selected from 200nm to 500nm;
  • the mass content of the amorphous carbon layer in the secondary carbon particles is ⁇ 3.3%.
  • the mass content of the amorphous carbon layer in the secondary carbon particles is selected from 1.3% to 3.3%;
  • the carbon-based core contains a negative electrode active material, and the negative electrode active material is graphite.
  • the inventors of the present application found that by coating at least a portion of the surface of the secondary carbon particles with amorphous carbon, the fast charging performance of the battery can be improved; further, by reasonably controlling the content of amorphous carbon, the fast charging performance of the battery can be improved while ensuring good battery cycle performance.
  • the inventors also unexpectedly discovered that when amorphous carbon is coated on the surface of secondary carbon particles, the cycle life of the battery cell may decrease as the proportion of secondary carbon particles increases.
  • the inventors speculate that this may be due to the high surface activity of amorphous carbon relative to the surface activity of the carbon-based core (such as graphite), which may reduce the stability of the negative electrode during the cycle.
  • the mass ratio of secondary carbon particles in carbon-based particles can be reasonably controlled (such as controlled at 30% to 50%) to better balance the requirements for gas removal, capacity and battery cycle stability, while achieving low tortuosity and high capacity retention.
  • an electrical device which includes the secondary battery described in the first aspect of the present application.
  • a method for preparing a negative electrode sheet comprising the following steps:
  • Preparation of single particle carbon wherein the steps of preparing the single particle carbon include: crushing, grading, pre-carbonizing, graphitizing and screening the raw materials;
  • micro-particle carbon Prepare micro-particle carbon, mix the micro-particle carbon and a binder, granulate the binder in a molten state, pre-carbonize, graphitize, optionally coat, and screen to prepare secondary particle carbon; wherein the steps of preparing micro-particle carbon include: crushing, grading, and screening the raw materials;
  • the single particle carbon and the secondary particle carbon are as defined in the first aspect of the present application; the microparticle carbon is as defined in the first aspect of the present application.
  • the non-graphite carbon-based material When preparing single-grain carbon and secondary-grain carbon, the non-graphite carbon-based material is pre-carbonized under relatively low temperature conditions (such as 1100 ⁇ 50°C), and the carbon-based particles shrink and the structure becomes more compact. After the non-graphite carbon-based material is graphitized, the hexagonal carbon atom plane network changes from a disordered arrangement in two-dimensional space (such as a chaotic layer structure or amorphous carbon) to an ordered arrangement of graphite structure in three-dimensional space.
  • relatively low temperature conditions such as 1100 ⁇ 50°C
  • the hexagonal carbon atom plane network changes from a disordered arrangement in two-dimensional space (such as a chaotic layer structure or amorphous carbon) to an ordered arrangement of graphite structure in three-dimensional space.
  • the binder (such as asphalt) plays the role of a binder on the one hand, and on the other hand, the free carbon ⁇ , asphaltene ⁇ and other carbon substances in the binder are filled on the surface of the micro-grain carbon in a flowing state.
  • the granulation step often also includes a crushing sub-step to depolymerize the aggregated particles, so as to better control the particle size and distribution of the secondary-grain carbon.
  • the method for preparing the negative electrode sheet may have one or more of the following features:
  • Each occurrence of the pre-carbonization independently comprises the following steps: heating treatment at 1050°C to 1150°C, optionally, the heating time is 24h to 72h; optionally, the pre-carbonization is carried out under inert gas conditions;
  • Each occurrence of the graphitization independently comprises the following steps: heating treatment at a temperature of >2800°C, optionally, the heating temperature is 2850°C to 3100°C; optionally, the heating time is 30h to 96h; optionally, the graphitization is carried out under inert gas conditions;
  • the granulation in the molten state of the binder includes: heating the binder in the molten state and crushing; optionally, the heating temperature is selected from 500°C to 600°C; optionally, the heating time is 4h to 6h, and optionally, the heating treatment is carried out under inert gas conditions;
  • the coating comprises the following steps: mixing the material with the organic carbon material, and heating the mixture at 1100°C to 1200°C to prepare secondary particles comprising a coating layer, and optionally, the heating time is 12h to 24h; optionally, the coating is performed under inert gas conditions; optionally, the coating layer in the secondary particles comprising the coating layer comprises amorphous carbon;
  • the single particle carbon is prepared by a method comprising the following steps in sequence: crushing the raw material, grading, pre-carbonizing at 1050°C to 1150°C, graphitizing at a temperature of >2800°C, and screening to obtain the single particle carbon;
  • the secondary particles are prepared by a method comprising the following steps in sequence: preparing the micro-particle carbon, mixing the micro-particle carbon and the binder, granulating at 500°C to 600°C, pre-carbonizing at 1050°C to 1150°C, graphitizing at a temperature of >2800°C, optionally coating at 1100°C to 1200°C, and sieving to obtain the secondary particle carbon;
  • the single carbon particle is single graphite particle; the micro carbon particle is micro graphite particle;
  • the binder is asphalt
  • the mass ratio of the binder to the plurality of the micro-particle carbons is selected from 1:8.5 to 1:9.5;
  • the organic carbon material includes one or more of asphalt, phenolic resin, furfural resin and epoxy resin;
  • the inert gas conditions each occur independently selected from conditions comprising one or more gases of nitrogen, helium, argon and neon.
  • the compounding of single-particle carbon and secondary-particle carbon can be better controlled, so that the tortuosity can be controlled within a more appropriate range, which is conducive to gas production and discharge while maintaining good battery cell cycle performance and extending battery life.
  • the amount of amorphous carbon coating can be better controlled by controlling the amount of asphalt and the temperature curve, thereby improving the fast charging performance of the battery while maintaining good cycle performance.
  • FIG1 is a SEM morphology of single-particle graphite and secondary-particle graphite in some embodiments of the present application, wherein (A) and (B) are SEM morphology of single-particle graphite at different magnifications, and (C) and (D) are SEM morphology of secondary-particle graphite at different magnifications; wherein the arrow in (B) points to the single-particle graphite, and the arrow in (D) points to the secondary-particle graphite; SEM test parameters include: working voltage (EHT) of 10.00 kV, InLens detector, working distance of 4.6 mm, and magnification of 1000X;
  • EHT working voltage
  • FIG2 is a SEM morphology image (A) of a cross section of a negative electrode sheet formed by a single particle of graphite in a comparison of the present application and a schematic diagram of a corresponding formation exhaust path (B), as well as a SEM morphology image (C) of a cross section of a negative electrode sheet formed by a single particle of graphite and a secondary particle of graphite in an embodiment of the present application and a schematic diagram of a corresponding formation exhaust path (D);
  • SEM test parameters include: an operating voltage (EHT) of 10.00 kV, an InLens detector, a working distance of 4.6 mm, and a magnification of 1000X;
  • FIG3 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG4 is an exploded view of the secondary battery of one embodiment of the present application shown in FIG3 ;
  • FIG. 5 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.
  • “Scope” disclosed in the present application is defined in the form of lower limit and upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range.
  • the scope defined in this way can include or exclude end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range.
  • the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.
  • the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following range can be fully expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.
  • the numerical range "a-b” represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers.
  • the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is just the abbreviation of these numerical combinations.
  • a parameter is expressed as an integer ⁇ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • the method may further include step (c), which means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.
  • the “include” and “comprising” mentioned in this application are open-ended or closed-ended.
  • the “include” and “comprising” may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B”.
  • any of the following conditions satisfies the condition "A or B”: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).
  • first”, “second”, “third”, etc. in “the first aspect”, “the second aspect”, “the third aspect”, etc. are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features.
  • first”, “second”, “third”, etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.
  • room temperature generally refers to 4°C to 35°C, preferably 20°C ⁇ 5°C. In some embodiments of the present application, room temperature refers to 20°C to 30°C.
  • the weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Furthermore, the weight described in the embodiment description of the present application can be a mass unit known in the chemical industry such as ⁇ g, mg, g, kg, etc.
  • Some existing technologies use the following methods to improve exhaust conditions: (1) Improve the design of the gas discharge structure in the battery to avoid excessive pressure on the battery cell; (2) Improve the physical adsorption of the electrode or electrolyte to the gas production to reduce the pressure of the battery cell; (3) Use chemical reactions to convert the gas production into a non-gaseous state to reduce the pressure; (4) Inhibit the occurrence of gas production from the source, etc.
  • a device comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet;
  • the negative electrode plate comprises a negative electrode active material layer, the negative electrode active material layer comprises carbon-based particles, the carbon-based particles comprise single carbon particles and secondary carbon particles, wherein the D v 50 of the single carbon particles is greater than the D v 50 of the secondary carbon particles;
  • D v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%.
  • the secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.
  • active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet, and the electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.
  • the separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, and at the same time to allow active ions to pass through.
  • the active ions can be lithium ions (corresponding to lithium-ion secondary batteries).
  • the "carbon-based particles" in the negative electrode active material layer refer to negative electrode active particles containing carbon, wherein the carbon has the ability to embed and de-embed active ions (such as lithium ions), that is, the carbon therein serves as a negative electrode active material.
  • the electrode plate can be a positive electrode plate or a negative electrode plate
  • the "active material” in the electrode plate refers to a substance that can reversibly embed and release active ions.
  • negative electrode active material refers to a substance used for negative electrode plates that can reversibly embed and release active ions
  • positive electrode active material refers to a substance used for positive electrode plates that can reversibly release and embed active ions.
  • active material and “active substance” have the same meaning and can be used interchangeably;
  • positive electrode active substance and “positive electrode active material” have the same meaning and can be used interchangeably;
  • negative electrode active substance and “negative electrode active material” have the same meaning and can be used interchangeably.
  • the "active material layer” includes the positive active material layer of the positive electrode sheet and the negative active material layer of the negative electrode sheet, and may refer to the positive active material layer or the negative active material layer depending on the detailed circumstances.
  • secondary particle carbon as the negative electrode active particle is a carbon-containing particle in the form of secondary particles, and the negative electrode active material therein is partially or wholly carbon.
  • Single particle carbon refers to granular carbon in the form of primary particles relative to “secondary particle carbon”. It can be understood that the negative electrode active material in the single particle carbon is carbon.
  • Primary particles and “secondary particles” are terms well known in the art.
  • Primary particles refer to single crystals or quasi-single crystal grains.
  • Secondary particles refer to agglomerated particles formed by the aggregation of two or more primary particles, and the aggregation of primary particles can be achieved by additives (such as adhesives).
  • Figure 1 is the SEM morphology images of single graphite particles and secondary graphite particles in some embodiments of the present application, wherein (A) and (B) are SEM morphology images of single graphite particles at different magnifications, (C) and (D) are SEM morphology images of secondary graphite particles at different magnifications; SEM test parameters include: working voltage (EHT) of 10.00 kV, InLens detector, working distance of 4.6 mm, and magnification of 1000X.
  • EHT working voltage
  • the volume cumulative distribution particle size D v N (wherein N represents any value selected from 0 to 100) can be used to characterize the particle size of the material, which refers to the particle size corresponding to the cumulative volume distribution percentage of the material reaching N%, and the volume proportion of the particle size less than or equal to D v N is N%.
  • D v N can be obtained from the volume cumulative distribution curve of the material particle size. If there is no other explanation, the volume cumulative distribution curve starts from zero from the small particle size side.
  • D v 99 refers to the particle size corresponding to the cumulative volume distribution percentage of the material reaching 99%
  • D v 50 refers to the particle size corresponding to the cumulative volume distribution percentage of the material reaching 50%
  • D v 10 refers to the particle size corresponding to the cumulative volume distribution percentage of the material reaching 10%.
  • D v 50 it means that the particle size of particles accounting for 50% of the volume of the material is less than or equal to D v 50, and the particle size of particles accounting for 50% of the volume of the material is greater than D v 50.
  • D v 99 it means that the particle size of particles accounting for 99% of the volume of the material is less than or equal to D v 90, and the particle size of particles accounting for 1% of the volume of the material is greater than D v 90.
  • D v 10 it means that the particle size of particles accounting for 10% of the volume of the material is less than or equal to D v 10, and the particle size of particles accounting for 90% of the volume of the material is greater than D v 10.
  • D v 99, D v 90, D v 50, and D v 10 can be measured using instruments and methods known in the art.
  • GB/T19077-2016 particle size distribution laser diffraction method can refer to GB/T19077-2016 particle size distribution laser diffraction method, and it can be conveniently measured using a laser particle size analyzer, such as Mastersizer 2000E laser particle size analyzer and LS-909 laser particle size analyzer (Europe and America) of Malvern Instrument Co., Ltd., UK.
  • a laser particle size analyzer such as Mastersizer 2000E laser particle size analyzer and LS-909 laser particle size analyzer (Europe and America) of Malvern Instrument Co., Ltd., UK.
  • single-particle carbon with a larger particle size and secondary-particle carbon with a smaller particle size are compounded.
  • the secondary-particle carbon is beneficial to reducing the tortuosity and facilitating the discharge of gas production.
  • the single-particle carbon is beneficial to maintaining good battery cell cycle performance and extending the battery life.
  • the negative electrode slurry needs to be compacted after coating and drying to adjust the thickness, density, energy density and other parameters. During the compaction (cold pressing can be used), certain pores will be formed between the particles, and these pores are interconnected, so that there is a pore connection path between the two sides of the negative electrode active material layer.
  • the ratio between the path of the pore connection path and the thickness of the negative electrode active material layer is the tortuosity of the negative electrode active material layer.
  • the addition of secondary-particle carbon with a smaller particle size can make it easier to form a pore connection path between the pores, thereby reducing the tortuosity.
  • the time required for the gas produced during formation and battery use to be discharged along the pore connection path is shorter, which is conducive to forming a more homogeneous interface, and the stability of the interface is better.
  • lower tortuosity can also improve the wetting effect of the electrolyte on the electrode.
  • the term "tortuosity of the negative electrode sheet” refers to the tortuosity of the negative electrode active material layer, unless otherwise specified. Tortuosity reflects the degree of tortuosity of the path of the pore communication passage through a certain thickness of the negative electrode active material layer. Numerically, the tortuosity ⁇ of the negative electrode active material layer can be equal to the ratio of the actual path length of the pore communication passage between the two side surfaces of the negative electrode active material layer to the thickness of the negative electrode active material layer. The theoretical minimum value of tortuosity is 1.
  • the pore communication passage is a straight through hole, and the corresponding actual path is the shortest, which is numerically consistent with the thickness of the negative electrode active material layer.
  • the greater the tortuosity the higher the degree of tortuosity of the path of the pore communication passage. Conversely, the smaller the tortuosity, the lower the degree of tortuosity of the path of the pore communication passage.
  • the value of tortuosity is related to factors such as the composition and distribution of carbon-based particles, porosity, and degree of compaction. Please refer to Figure 2 to understand the concept of "tortuosity".
  • FIG2 is a SEM morphology image (A) of the cross section of the negative electrode sheet formed by a single particle of graphite in a comparison of the present application and a corresponding schematic diagram of the formation exhaust path (B), as well as a SEM morphology image (C) of the cross section of the negative electrode sheet formed by a single particle of graphite and a secondary particle of graphite in an embodiment of the present application and a corresponding schematic diagram of the formation exhaust path (D); SEM test parameters include: working voltage (EHT) of 10.00 kV, InLens detector, working distance of 4.6 mm, magnification of 1000X.
  • EHT working voltage
  • the ratio (Lt/L) between the actual length Lt of the pore connection path shown by a single line in (B) and (D) of FIG2 and the thickness L of the negative electrode active material layer through which the line passes in the longitudinal direction can be understood as the tortuosity of the negative electrode active material layer. It can be seen that "tortuosity" is a dimensionless parameter.
  • the value of the tortuosity of the negative electrode sheet or its negative electrode active material layer can be measured by the following test and analysis method.
  • the negative electrode sheet to be tested can be a sample at any stage after being compacted (for example, processed by cold pressing) to a preset thickness and compaction density.
  • it can be a negative electrode sheet sample before formation, or it can be a negative electrode sheet sample after formation, or it can be a negative electrode sheet sample assembled into a battery cell and disassembled after a period of use.
  • the negative electrode sheet sample disassembled from the battery cell it is necessary to clean and remove the residual electrolyte in advance, for example, the negative electrode sheet sample can be washed with anhydrous ethanol.
  • the tortuosity value may be obtained by a test analysis method including the following steps, but not limited thereto:
  • a negative electrode sheet is selected, and the thickness of the negative electrode active material layer is measured as d.
  • the thickness can be tested by methods known in the art, such as comparing the surface of the substrate with and without the negative electrode active material layer, for example, by a step profiler test method.
  • the stylus of the step profiler gently rubs across the sample surface with a very small force, and the micron or even nanometer level ups and downs of the sample surface are amplified millions of times by the sensor connected to the stylus, and then converted into electronic signals, input into computer software, and finally displayed in the form of digital and graphical data.
  • the thickness of the negative electrode active material layer can also be obtained by statistically analyzing the results of multiple positions of a scanning electron microscope (SEM) photograph of a cross section of the electrode sheet in the thickness direction.
  • SEM scanning electron microscope
  • the porosity of the active material layer has a well-known meaning in the art and can be measured by instruments and methods well-known in the art.
  • the AccuPyc II 1340 fully automatic true density tester of Micromeritics of the United States can be used to test the apparent density, true density and porosity of iron ore with reference to the national standard GB/T 24586-2009.
  • the method includes cutting 30 small discs with a diameter of 14 mm from the pole piece, and based on the principle of gas adsorption, using an inert gas such as helium or nitrogen as a medium, testing the true volume of 30 small discs with a diameter of 14 mm, and then calculating the relationship between the apparent volume and the true volume of the pole piece based on the area, thickness and number of the small discs to calculate the porosity of the active material layer of the pole piece.
  • an inert gas such as helium or nitrogen
  • the following method can also be used to obtain the porosity ⁇ test value of the negative electrode active material layer.
  • the value of the tortuosity ⁇ is calculated by the following formula: ⁇ k ⁇ Rion ⁇ A/d, in which each parameter is in a specific unit.
  • the tortuosity ⁇ of the negative electrode active material layer is numerically equal to the value calculated by the following formula: ⁇ k ⁇ Rion ⁇ A/d; wherein ⁇ is the porosity of the negative electrode active material layer at 25°C; k is the ionic conductivity of the electrolyte at 25°C, in units of ms/cm; Rion is the ionic resistance of the negative electrode sheet at 25°C, in units of ⁇ ; A is the effective area when testing Rion, in units of cm 2 ; d is the thickness of the negative electrode active material layer, in units of ⁇ m.
  • porosity, ionic resistance Rion, ionic conductivity, electrode effective area and thickness of negative electrode active material layer all have well-known meanings in the art.
  • Those skilled in the art can use conventional methods in the art to test and obtain the relevant parameters ⁇ , k, Rion, A and d of the secondary battery of the present application, and the methods described above can be used preferentially.
  • test temperature of ⁇ , k, and Rion can be carried out at room temperature, and unless otherwise specified, can be carried out at 20°C to 30°C (such as 25°C), and further, can be carried out at 25°C.
  • the tortuosity ⁇ of the negative electrode active material layer is numerically equal to a value calculated according to the following formula: ⁇ k ⁇ Rion ⁇ A/d; wherein ⁇ is the porosity of the negative electrode active material layer at 25°C; k is the ionic conductivity of the electrolyte at 25°C, in ms/cm; Rion is the ionic resistance of the negative electrode sheet at 25°C, in ⁇ ; A is the effective area when testing Rion, in cm2 ; d is the thickness of the negative electrode active material layer, in ⁇ m.
  • the tortuosity ⁇ of the negative electrode active material layer is ⁇ 4.75.
  • the tortuosity ⁇ of the negative electrode active material layer may satisfy ⁇ 4.70.
  • the tortuosity ⁇ of the negative electrode active material layer may satisfy ⁇ 4.70, optionally, ⁇ may be selected from 3.40 to 4.70. In some embodiments, the tortuosity ⁇ of the negative electrode active material layer ⁇ 4.65, optionally, ⁇ may be selected from 3.40 to 4.65. In some embodiments, the tortuosity ⁇ of the negative electrode active material layer ⁇ 4.62, optionally, ⁇ may be selected from 3.42 to 4.62. In some embodiments, the tortuosity ⁇ of the negative electrode active material layer ⁇ 4.05, optionally, ⁇ may be selected from 3.42 to 4.05.
  • the tortuosity ⁇ of the negative electrode active material layer ⁇ 3.95, optionally, ⁇ may be selected from 3.42 to 3.95. In some embodiments, the tortuosity ⁇ of the negative electrode active material layer ⁇ 3.85, optionally, ⁇ may be selected from 3.45 to 3.85. In some embodiments, the tortuosity ⁇ of the negative electrode active material layer is ⁇ 3.82, and optionally, ⁇ may be selected from 3.45 to 3.82.
  • the tortuosity ⁇ of the negative electrode active material layer can also be selected from any one of the following values or a numerical range consisting of any two of the following values: 3.40, 3.42, 3.44, 3.45, 3.46, 3.48, 3.50, 3.52, 3.54, 3.55, 3.56, 3.58, 3.60, 3.62, 3.64, 3.65, 3.66, 3.68, 3.70, 3.71, 3.72, 3.73, 3.74, 3.75, 3.76, 3.77, 3.78, 3.79, 3.80, 3.81, 3.82, 3.83, 3.84, 3.85, 3.86, 3.87, 3.88, 3.89, 3.90, 3.91, 3.92, 3.93, 3.94, 3.95, 3.96, 3.97, 3.98, 3.99, 3.10 72, 3.74, 3.75, 3.76, 3.78, 3.80, 3.82, 3.84, 3.85, 3.86, 3.88, 3.90, 3.92, 3.94, 3.95, 3.96, 3.98, 4.00, 4.05, 4.1, 4.15,
  • the tortuosity of the negative electrode active material layer may change; as the battery is used for a longer time, the volume of the pole piece may change, thereby causing a change in tortuosity.
  • the porosity of the negative electrode active material layer is selected from 30.6% to 37.5%.
  • the porosity of the negative electrode active material layer is selected from 32.2% to 37.5%. In some embodiments, the porosity of the negative electrode active material layer is selected from 33.8% to 37.5%. In some embodiments, the porosity of the negative electrode active material layer is selected from 34.8% to 37.5%. In some embodiments, the porosity of the negative electrode active material layer is selected from 35.5% to 37.5%.
  • the porosity of the negative electrode active material layer can also be selected from any one of the following percentages or a numerical range consisting of any two of the following percentages: 30.6%, 31%, 31.5%, 32%, 32.2%, 32.5%, 33%, 33.5%, 33.8%, 34%, 34.5%, 34.8%, 35%, 35.5%, 36%, 36.5%, 37%, 37.5%, etc.
  • the porosity of the negative electrode active material layer can be measured by referring to the aforementioned method, such as the small molecule inert gas (such as He) replacement method.
  • the porosity of the negative electrode active material layer By controlling the porosity of the negative electrode active material layer within a suitable range, it is beneficial to control the appropriate tortuosity while ensuring that the electrolyte has appropriate wettability, thereby accelerating gas production while achieving better battery cell kinetic performance.
  • the compaction density of the negative electrode active material layer is selected from 1.30 g/cc to 1.80 g/cc. In some embodiments, the compaction density of the negative electrode active material layer is selected from 1.30 g/cc to 1.70 g/cc. In some embodiments, the compaction density of the negative electrode active material layer is selected from 1.50 ⁇ 0.02 g/cc.
  • the compaction density of the negative electrode active material layer can also be selected from any one of the following values or a numerical range consisting of any two of the following values: 1.30, 1.32, 1.34, 1.35, 1.36, 1.38, 1.40, 1.42, 1.44, 1.45, 1.46, 1.48, 1.50, 1.52, 1.54, 1.55, 1.56, 1.58, 1.60, 1.62, 1.64, 1.66, 1.68, 1.70, 1.72, 1.74, 1.75, 1.76, 1.78, 1.80, etc.
  • the "compacted density” used in this application has a well-known meaning in the art, and refers to the ratio of the mass to volume of the active material in the active material layer of the pole piece.
  • the compacted density of the pole piece can be tested in the following way: select a certain pole piece coating surface density, and after the pole piece is dried and cold pressed, use a vernier caliper to measure the total thickness of the pole piece, and the coating thickness can be calculated by deducting the thickness of the current collector. Based on the two parameters of coating surface density and coating thickness, the compacted density of the pole piece can be calculated.
  • the compaction density By controlling the compaction density within a suitable range, it is beneficial to provide better energy density while accelerating gas production, and achieve good cycle performance.
  • the higher the compaction density the more beneficial it is to improve energy density.
  • an increase in compaction density will lead to a decrease in porosity, which may be detrimental to the infiltration of the electrolyte and affect the battery power.
  • the greater the compaction density the smaller the porosity, which may be detrimental to the infiltration of the electrolyte, resulting in increased difficulty in embedding active ions (such as lithium ions) and worse battery kinetic performance.
  • the mass proportion of the secondary particle carbon in the carbon-based particles is selected from 10% to 90%. In some embodiments, the mass proportion of the secondary particle carbon in the carbon-based particles is selected from 20% to 80%. In some embodiments, the mass proportion of the secondary particle carbon in the carbon-based particles is selected from 30% to 70%. In some embodiments, the mass proportion of the secondary particle carbon in the carbon-based particles is selected from 30% to 50%.
  • the mass proportion of the secondary particulate carbon in the carbon-based particles can also be selected from any one of the following percentages or a numerical range consisting of any two of the following percentages: 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc.
  • the inventor of the present application has found through research that in the secondary battery of the present application, as the proportion of secondary particle carbon increases, the tortuosity of the negative electrode sheet gradually decreases, and the porosity tends to increase.
  • the tortuosity and porosity can be controlled within a suitable range.
  • the mass ratio of single particle carbon and secondary particle carbon is controlled at 7:3, and the SOC at the end of gas production after formation is 26% earlier than that of 100% pure single particle carbon (without secondary particle carbon), and the cycle performance is improved by 1.7% (taking 400 cycles as an example) compared with 100% pure secondary particle carbon (without single particle carbon).
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector. Further, at least one of the negative electrode film layers includes the aforementioned negative electrode active material layer, and any of the negative electrode active material layers contains a negative electrode active substance.
  • the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and further, the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode film layers on both sides may be the same or different.
  • the negative electrode active material layers on both sides may be the same or different.
  • disposed on at least one side surface of the current collector means disposed on at least one side of the current collector in the thickness direction of the current collector, and either side may be independently in direct contact with the current collector or not in direct contact with the current collector.
  • the aforementioned negative electrode active material layer is disposed on at least one side of the negative electrode current collector.
  • the negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector, and may be disposed on one surface of the negative electrode current collector, or may be disposed on both surfaces of the negative electrode current collector.
  • at least one of the negative electrode active material layers is in direct contact with the negative electrode current collector, in which case the negative electrode active material layer is in direct contact with at least one side surface (one or two surfaces) of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the metal foil copper foil may be used.
  • 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 formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode active material may adopt a negative electrode active material for a battery known in the art.
  • 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.
  • the silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.
  • the tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.
  • the present application is not limited to these substances or materials, and other traditional substances or 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.
  • the carbon-based particles are primarily carbon materials.
  • the carbon-based particles can be carbon materials, and further, the carbon materials can include but are not limited to one or more of artificial graphite, natural graphite, soft carbon and hard carbon. In some non-limiting examples thereof, the carbon material is selected from one or more of artificial graphite, natural graphite, soft carbon and hard carbon.
  • the carbon material may include but is not limited to graphite.
  • graphite may be artificial graphite, natural graphite, or a combination thereof.
  • the carbon material is graphite.
  • the negative electrode active material of the negative electrode active material layer is mainly carbon-based particles. In some embodiments, the mass proportion of the carbon-based particles in the negative electrode active material of the negative electrode active material layer is greater than 50%. In some embodiments, the mass proportion of the carbon-based particles in the negative electrode active material of the negative electrode active material layer is selected from 80% to 100%. In some embodiments, the mass proportion of the carbon-based particles in the negative electrode active material of the negative electrode active material layer is selected from 90% to 100%. In some embodiments, the mass proportion of the carbon-based particles in the negative electrode active material of the negative electrode active material layer is selected from 95% to 100%.
  • the mass proportion of the carbon-based particles in the negative electrode active material of the negative electrode active material layer is 100%.
  • the mass proportion of the carbon-based particles in the negative electrode active material of the negative electrode active material layer can also be selected from any one of the following percentages or a numerical range consisting of any two of the following percentages: 60%, 70%, 75%, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.
  • the carbon-based particles are mainly graphite materials.
  • the carbon-based particles contain a graphite material with a mass ratio of greater than 50%.
  • the carbon-based particles contain a graphite material selected from 80% to 100% by mass.
  • the carbon-based particles contain a graphite material selected from 90% to 100% by mass.
  • the carbon-based particles contain a graphite material selected from 95% to 100% by mass.
  • the carbon-based particles contain a graphite material with a mass ratio of 100%.
  • the mass ratio of graphite material in the carbon-based particles can also be selected from any of the following percentages or from the numerical interval consisting of any two of the following percentages: 60%, 70%, 75%, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.
  • the negative active material of the negative active material layer is mainly a graphite material. In some embodiments, the negative active material of the negative active material layer contains a graphite material with a mass percentage greater than 50%. In some embodiments, the negative active material of the negative active material layer contains a graphite material with a mass percentage selected from 80% to 100%. In some embodiments, the negative active material of the negative active material layer contains a graphite material with a mass percentage selected from 90% to 100%. In some embodiments, the negative active material of the negative active material layer contains a graphite material with a mass percentage selected from 95% to 100%.
  • the mass proportion of the graphite material in the negative electrode active material of the negative electrode active material layer can also be selected from any one of the following percentages or from a numerical range consisting of any two of the following percentages: 60%, 70%, 75%, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.
  • the negative active material of the negative active material layer contains 100% by mass of graphite material.
  • the carbon-based particles are graphite particles
  • the single carbon particles are single graphite particles
  • the secondary particles are secondary graphite particles.
  • single-particle graphite refers to graphite in single-particle form (i.e., primary particle form)
  • secondary-particle graphite refers to graphite in secondary particle form
  • the negative electrode active material in single-particle graphite and secondary-particle graphite is graphite.
  • the negative electrode sheet When carbon-based materials are used as the main negative electrode active material in the negative electrode active material layer, compared with other types of negative electrode sheets with high silicon content, the negative electrode sheet has lower expansion, a more stable solid electrolyte interface (SEI) film, and better battery safety.
  • SEI solid electrolyte interface
  • the carbon-based particles are mainly graphite particles
  • the single-particle carbon is mainly single-particle graphite
  • the secondary particles are mainly secondary-particle graphite.
  • the morphology and particle size consistency of the negative electrode active particles can be better controlled, thereby making the battery performance more stable.
  • the content percentage is greater than 50%, and can also be selected from ⁇ 60%, ⁇ 70%, ⁇ 80%, ⁇ 90%, ⁇ 95%, ⁇ 96%, ⁇ 98%, ⁇ 99%, 60%-100%, 70%-100%, 80%-100%, 90%-100%, 90%-100%, 95%-100%, 96%-100%, 98%-100%, 10 0%, 99% to 100%, etc., and can also be selected from any of the following percentages or from the numerical interval consisting of any two of the following percentages: 60%, 65%, 70%, 75%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.
  • the aforementioned description of the composition of the carbon-based particles and the description of the composition of the negative active material can all be applied to the definition here, such as “the carbon-based particles are mainly graphite materials”, “the negative active material of the negative active material layer is mainly carbon-based particles”, “the negative active material of the negative active material layer is mainly graphite materials”, etc.
  • the negative electrode active material layer has one or more of the following characteristics (one, two or three characteristics):
  • the D v 50 of the single carbon particle is selected from 13 ⁇ m to 14 ⁇ m
  • a non-limiting example of the D v 5 of the single carbon particle is any one of the following values or a numerical interval consisting of any two of the following values: 13 ⁇ m, 13.1 ⁇ m, 13.2 ⁇ m, 13.3 ⁇ m, 13.4 ⁇ m, 13.5 ⁇ m, 13.6 ⁇ m, 13.7 ⁇ m, 13.8 ⁇ m, 13.9 ⁇ m, 14 ⁇ m, etc.);
  • the D v 50 of the secondary carbon particles is selected from 9.5 ⁇ m to 10.5 ⁇ m (a non-limiting example of the D v 50 of the secondary carbon particles is any one of the following values or a numerical range consisting of any two of the following values: 9.5 ⁇ m, 9.6 ⁇ m, 9.7 ⁇ m, 9.8 ⁇ m, 9.9 ⁇ m, 10.0 ⁇ m, 10.1 ⁇ m, 10.2 ⁇ m, 10.3 ⁇ m, 10.4 ⁇ m, 10.5 ⁇ m, etc.); and
  • the difference between the D v 50 of the single carbon particle and the D v 50 of the secondary carbon particle is selected from 3 ⁇ m to 4 ⁇ m
  • a non-limiting example of the difference between the D v 50 of the single carbon particle and the D v 50 of the secondary carbon particle is any one of the following values or a numerical range consisting of any two of the following values: 3 ⁇ m, 3.1 ⁇ m, 3.2 ⁇ m, 3.3 ⁇ m, 3.4 ⁇ m, 3.5 ⁇ m, 3.6 ⁇ m, 3.7 ⁇ m, 3.8 ⁇ m, 3.9 ⁇ m, 4 ⁇ m, etc.).
  • the D v 99 of the single carbon particle is greater than the D v 99 of the secondary carbon particle.
  • the negative electrode active material layer further has one or more of the following characteristics (one, two or three characteristics):
  • the D v 99 of the single carbon particle is selected from 37 ⁇ m to 44 ⁇ m (a non-limiting example of the D v 99 of the single carbon particle is any one of the following values or a numerical range consisting of any two of the following values: 37 ⁇ m, 37.5 ⁇ m, 38 ⁇ m, 38.5 ⁇ m, 39 ⁇ m, 39.5 ⁇ m, 40 ⁇ m, 40.5 ⁇ m, 41 ⁇ m, 41.5 ⁇ m, 42 ⁇ m, 42.5 ⁇ m, 43 ⁇ m, 43.5 ⁇ m, 44 ⁇ m, etc.);
  • D v 99 of the secondary carbon particles is selected from 31 ⁇ m to 38 ⁇ m (non-limiting examples of D v 99 of the secondary carbon particles include any one or two of the following values: 31 ⁇ m, 31.5 ⁇ m, 32 ⁇ m, 32.5 ⁇ m, 33 ⁇ m, 33.5 ⁇ m, 34 ⁇ m, 34.5 ⁇ m, 35 ⁇ m, 35.5 ⁇ m, 36 ⁇ m, 36.5 ⁇ m, 37 ⁇ m, 37.5 ⁇ m, 38 ⁇ m, etc.); and
  • the difference between D v 99 of the single carbon particle and D v 99 of the secondary carbon particle is selected from 4 ⁇ m to 6 ⁇ m (a non-limiting example of the difference between D v 99 of the single carbon particle and D v 99 of the secondary carbon particle is any one of the following values or a numerical range consisting of any two of the following values: 4 ⁇ m, 4.2 ⁇ m, 4.4 ⁇ m, 4.5 ⁇ m, 4.6 ⁇ m, 4.8 ⁇ m, 5 ⁇ m, 5.2 ⁇ m, 5.4 ⁇ m, 5.5 ⁇ m, 5.6 ⁇ m, 5.8 ⁇ m, 6 ⁇ m, etc.).
  • the D v 10 of the single carbon particle is greater than the D v 10 of the secondary carbon particle.
  • the negative electrode active material layer further has one or more of the following characteristics (one, two or three characteristics):
  • the D v 10 of the single carbon particle is selected from 5 ⁇ m to 7 ⁇ m (a non-limiting example of the D v 10 of the single carbon particle is any one of the following values or a numerical range consisting of any two of the following values: 5 ⁇ m, 5.2 ⁇ m, 5.4 ⁇ m, 5.5 ⁇ m, 5.6 ⁇ m, 5.8 ⁇ m, 6 ⁇ m, 6.2 ⁇ m, 6.4 ⁇ m, 6.5 ⁇ m, 6.6 ⁇ m, 6.8 ⁇ m, 7 ⁇ m, etc.);
  • D v 10 of the secondary particulate carbon is selected from 3.5 ⁇ m to 5.5 ⁇ m
  • D v 100 of the secondary particulate carbon are any one of the following values or a numerical range consisting of any two of the following values: 3.5 ⁇ m, 3.6 ⁇ m, 3.8 ⁇ m, 4 ⁇ m, 4.2 ⁇ m, 4.4 ⁇ m, 4.5 ⁇ m, 4.6 ⁇ m, 4.8 ⁇ m, 5 ⁇ m, 5.2 ⁇ m, 5.4 ⁇ m, 5.5 ⁇ m, etc.); and
  • the difference between D v 10 of the single carbon particle and D v 99 of the secondary carbon particle is selected from 1 ⁇ m to 2 ⁇ m (a non-limiting example of the difference between D v 10 of the single carbon particle and D v 99 of the secondary carbon particle is any one of the following values or a numerical range consisting of any two of the following values: 1 ⁇ m, 1.1 ⁇ m, 1.2 ⁇ m, 1.3 ⁇ m, 1.4 ⁇ m, 1.5 ⁇ m, 1.6 ⁇ m, 1.7 ⁇ m, 1.8 ⁇ m, 1.9 ⁇ m, 2 ⁇ m, etc.).
  • the D v 50 of the single carbon particle is selected from 13 ⁇ m to 14 ⁇ m, and the D v 50 of the secondary carbon particle is about 10 ⁇ m; further, in some embodiments, the D v 99 of the single carbon particle is about 40.5 ⁇ m, and the D v 99 of the secondary carbon particle is about 34 ⁇ m; further, in some embodiments, the D v 10 of the single carbon particle is about 6.3 ⁇ m, and the D v 10 of the secondary carbon particle is about 4.5 ⁇ m.
  • the multi-dimensional performance of tortuosity, porosity and compaction degree can be better balanced, thereby accelerating gas production and discharge while achieving better cycle performance and power performance.
  • controlling the difference in particle size between single-particle carbon and secondary-particle carbon is more conducive to fully leveraging the compounding advantages of the two, which is beneficial for reducing tortuosity and gas emission, maintaining good battery cell cycle performance, and extending battery life.
  • the secondary particulate carbon includes a plurality of micro-particle carbons and a binder.
  • the binder can be used to aggregate the micro-particle carbons into secondary particles.
  • the number of primary particles in the micro-particle carbon is one or more.
  • micro-particle carbon is the active material in the secondary particle carbon
  • the micro-particle carbon can be regarded as carbon in the form of primary particles in the secondary particle carbon. It can be understood that the negative electrode active material in the micro-particle carbon is carbon.
  • single particle carbon is an independent carbon particle in the form of primary particles
  • micro-particle carbon corresponds to the primary particle unit that is agglomerated into secondary particles.
  • the secondary carbon particles are secondary graphite particles, and the micro carbon particles are all micro graphite particles.
  • micro-particle graphite is a primary particle of graphite of microscopic size, which is a constituent unit of secondary particle graphite.
  • Single particle graphite is an independent primary particle of graphite.
  • the micro-particle carbon has one or more of the following characteristics (may be one, two, three or four characteristics):
  • the D v 99 of the microparticle carbon is selected from 20 ⁇ m to 24 ⁇ m (non-limiting examples include any one or two of the following numerical values: 20 ⁇ m, 20.5 ⁇ m, 21 ⁇ m, 21.5 ⁇ m, 22 ⁇ m, 22.5 ⁇ m, 23 ⁇ m, 23.5 ⁇ m, 24 ⁇ m, etc.);
  • D v 90 of the microparticle carbon is selected from 12 ⁇ m to 15 ⁇ m (non-limiting examples include any one or two of the following numerical ranges: 12 ⁇ m, 12.5 ⁇ m, 13 ⁇ m, 13.5 ⁇ m, 14 ⁇ m, 14.5 ⁇ m, 15 ⁇ m, etc.);
  • the D v 50 of the microparticulate carbon is selected from 5 ⁇ m to 7 ⁇ m (non-limiting examples include any one or two of the following numerical values: 5 ⁇ m, 5.2 ⁇ m, 5.4 ⁇ m, 5.5 ⁇ m, 5.6 ⁇ m, 5.8 ⁇ m, 6 ⁇ m, 6.2 ⁇ m, 6.4 ⁇ m, 6.5 ⁇ m, 6.6 ⁇ m, 6.8 ⁇ m, 7 ⁇ m, etc.); and
  • the D v 10 of the microparticulate carbon is selected from 2 ⁇ m to 3 ⁇ m (non-limiting examples are any one or two of the following numerical values: 2 ⁇ m, 2.1 ⁇ m, 2.2 ⁇ m, 2.3 ⁇ m, 2.4 ⁇ m, 2.5 ⁇ m, 2.6 ⁇ m, 2.7 ⁇ m, 2.8 ⁇ m, 2.9 ⁇ m, 3 ⁇ m, etc.).
  • the adhesive includes asphalt. Further, the adhesive may be mainly asphalt. Furthermore, in some embodiments, the adhesive is asphalt, which has good bonding effect and is not easy to introduce adverse impurities.
  • the mass ratio of the binder to the plurality of micro-particle carbons is selected from 1:8.5 to 1:9.5, that is, selected from 1:(8.5-9.5).
  • the mass ratio of the binder to the plurality of micro-particle carbons can also be selected from any of the following ratios or from an interval consisting of any two of the following ratios: 1:8.5, 1:8.6, 1:8.7, 1:8.8, 1:8.9, 1:9.0, 1:9.1, 1:9.2, 1:9.3, 1:9.4, 1:9.5, etc.
  • the amount of the binder such as asphalt
  • the preset particle size and distribution of the secondary particle carbon can be better achieved.
  • the secondary particles are formed by agglomerating the plurality of micro-particle carbons and the binder.
  • the raw materials are few and the preparation is convenient.
  • the surface of the secondary particulate carbon comprises amorphous carbon.
  • the secondary particulate carbon comprises a carbon-based core and an amorphous carbon layer located at least a portion of the surface of the carbon-based core. It can be obtained by introducing an organic carbon material (asphalt) on the surface and then heat-treating it at a suitable temperature. The heat treatment can be performed above the melting point of the organic carbon material (such as asphalt) and below the graphitization temperature. Further, the heat treatment can be performed near the pre-carbonization temperature (which can be slightly higher than the pre-carbonization temperature). For example, the heat treatment can be performed at 1100°C to 1200°C.
  • the heat treatment time can be flexibly controlled according to the degree of conversion to amorphous carbon, for example, it can be 4h to 6h.
  • the surface-coated organic carbon material (asphalt) can be converted into amorphous carbon.
  • the aforementioned "carbon-based core” contains a negative electrode active material.
  • the carbon-based core is composed of a negative electrode active material. It should be understood that the negative electrode active material of the carbon-based core contains carbon that enables active ions (such as lithium ions) to be embedded and extracted.
  • the thickness of the amorphous carbon layer on the surface of the secondary carbon particles is ⁇ 500nm. In some embodiments, the thickness of the amorphous carbon layer on the surface of the secondary carbon particles is selected from 200nm to 500nm. The thickness of the amorphous carbon layer on the surface of the secondary carbon particles can also be selected from any one or two of the following intervals: 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 260nm, 270nm, 280nm, 290nm, 300nm, 320nm, 350nm, 360nm, 380nm, 400nm, 420nm, 450nm, 480nm, 500nm, etc.
  • the mass content of the amorphous carbon layer in the secondary carbon particles is ⁇ 3.3%. In some embodiments, the mass content of the amorphous carbon layer in the secondary carbon particles is selected from 1.3% to 3.3%.
  • the mass content of the amorphous carbon layer in the secondary carbon particles can also be selected from any one of the following percentages or any two percentage intervals: 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, etc.
  • the volume proportion of the amorphous carbon layer in the secondary carbon particles is ⁇ 3.3%. In some embodiments, the volume proportion of the amorphous carbon layer in the secondary carbon particles is selected from 1.3% to 3.3%.
  • the volume proportion of the amorphous carbon layer in the secondary carbon particles can also be selected from any one of the following percentages or any two percentage intervals: 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, etc.
  • the surface of the single carbon particle may also be coated with an amorphous carbon layer; the thickness of the amorphous carbon layer is ⁇ 500nm. In some embodiments, the thickness of the amorphous carbon layer on the surface of the single carbon particle is selected from 200nm to 500nm.
  • the thickness of the amorphous carbon layer on the surface of the single carbon particle may also be selected from any one or two of the following intervals: 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 260nm, 270nm, 280nm, 290nm, 300nm, 320nm, 350nm, 360nm, 380nm, 400nm, 420nm, 450nm, 480nm, 500nm, etc.
  • the mass content of the amorphous carbon layer in the single carbon particle is ⁇ 3.3%. In some embodiments, the mass content of the amorphous carbon layer in the single carbon particle is selected from 1.3% to 3.3%.
  • the mass content of the amorphous carbon layer in the single carbon particle can also be selected from any one of the following percentages or any two percentage intervals: 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, etc.
  • the volume proportion of the amorphous carbon layer in the single carbon particle is ⁇ 3.3%. In some embodiments, the volume proportion of the amorphous carbon layer in the single carbon particle is selected from 1.3% to 3.3%.
  • the volume proportion of the amorphous carbon layer in the single carbon particle can also be selected from any one of the following percentages or any two percentages: 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, etc.
  • the surface of at least a portion of the carbon-based particles is coated with an amorphous carbon layer, and the thickness of the amorphous carbon layer, its mass content in the carbon-based particles, and its volume share in the carbon-based particles can refer to the definition of the aforementioned amorphous carbon layer coated on the surface of secondary particle carbon or the surface of single particle carbon.
  • the confirmation of the amorphous carbon layer can be obtained by testing the conventional method of testing the crystal form of carbon materials in the art, such as Raman spectroscopy test and analysis, and the formation of the amorphous carbon layer can be analyzed based on the characteristic peak information of the carbon component in the spectrum (such as the intensity ratio of the D peak/G peak, ID/G ).
  • the D peak and the G peak are both Raman characteristic peaks of the carbon atom crystal.
  • the D peak represents the defects of the carbon atom crystal. The more defects there are, the greater the D peak intensity.
  • the D peak intensity can reflect the content of the amorphous (turbostratified stacking) region, and the G peak represents the in-plane stretching vibration of the sp2 hybridization of the carbon atom.
  • the G peak intensity can reflect the content of the graphitized (layered structure) region; as the degree of disorder of the carbon atoms increases, the intensity ratio of the D peak to the G peak also increases.
  • Whether an amorphous carbon layer is formed can be determined based on whether the ID/G (D peak/G peak intensity ratio) of the particle surface components before and after coating constitutes a statistically significant difference (e.g., p ⁇ 0.05, p ⁇ 0.01, etc.), that is, based on the degree of deviation between the turbostratic structure introduced after coating and the ID/G before coating, which is easy for those skilled in the art to judge. It is also possible to compare the difference between the Raman spectrum ID/G of the specific structural layer of the particle to be tested and the standard Raman spectrum ID/G of graphite to determine whether it is an amorphous carbon layer.
  • a statistically significant difference e.g., p ⁇ 0.05, p ⁇ 0.01, etc.
  • the volume proportion of the "amorphous carbon layer" in the carbon-based particles can be obtained by transmission electron microscopy (TEM) morphology observation combined with data analysis.
  • TEM transmission electron microscopy
  • the negative electrode sheet is cut, and a powder sample is scraped from the cross section.
  • a TEM test is performed to compare the carbon-based particles coated with an amorphous carbon layer and those not coated with an amorphous carbon layer.
  • An obvious interface can be observed on the surface of the carbon-based particles coated with an amorphous carbon layer, so that the thickness of the amorphous carbon layer at that position can be estimated from the TEM photo.
  • the analysis can be performed from multiple different cross-sectional positions, and the average value is taken as the thickness of the amorphous carbon layer.
  • the volume proportion of the amorphous carbon layer in the carbon-based particles can be estimated based on the volume of the carbon-based particles and the volume of the carbon-based core; further, based on the average mass of a single carbon-based particle, the volume of the carbon-based core (which can be calculated or obtained based on TEM test photos) and the density of the carbon-based core, the mass content of the amorphous carbon layer in the carbon-based particles can be estimated.
  • the carbon-based core contains a negative electrode active material, and the negative electrode active material is graphite. That is, the negative electrode active material in the carbon-based core is graphite.
  • the fast charging performance of the battery can be improved (for example, comparing the following Example 10 and Example 4, the fast charging performance of Example 4 is improved).
  • coating at least a portion of the surface of the single carbon particle with amorphous carbon can also improve the fast charging performance of the battery. By reasonably controlling the content of amorphous carbon, the fast charging performance of the battery can be improved while ensuring good battery cycle performance.
  • the inventors also unexpectedly discovered that when amorphous carbon is coated on the surface of carbon-based particles, taking secondary carbon particles as an example, as the proportion of secondary carbon particles increases, the cycle life of the battery cell may decrease.
  • the inventors speculate that this may be due to the high surface activity of amorphous carbon relative to the surface activity of the carbon-based core (such as graphite), which may reduce the stability of the negative electrode during the cycle; at this time, the mass ratio of secondary carbon particles in the carbon-based particles can be reasonably controlled (such as controlled at 30% to 50%, and any suitable mass ratio described above can also be referred to), so as to better balance the needs for gas production removal, capacity and battery cycle stability, while achieving low tortuosity and high capacity retention rate.
  • the negative electrode film layer may further include a binder.
  • the binder may be selected from 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).
  • the negative electrode film layer may further include a conductive agent, which may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • a conductive agent which may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).
  • a thickener eg, sodium carboxymethyl cellulose (CMC-Na)
  • the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side surface of the negative electrode collector (it can be on a single surface or on two surfaces), and after drying, compacting (cold pressing can be used), etc., the negative electrode sheet can be obtained.
  • a solvent such as deionized water
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, at least one of the positive electrode film layers includes a positive electrode active material layer, and any of the positive electrode active material layers contains a positive electrode active substance.
  • the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and further, the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • the metal foil aluminum foil may be used.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the secondary battery may be a lithium ion battery, wherein the positive electrode active material comprises a lithium ion material (non-limiting examples include lithium phosphate, lithium transition metal oxide, and any modified product of the foregoing).
  • the positive electrode active material comprises a lithium ion material (non-limiting examples include lithium phosphate, lithium transition metal oxide, and any modified product of the foregoing).
  • the positive electrode active material may be a positive electrode active material for a battery known in the art.
  • 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.
  • the present application is not limited to these materials, and other traditional materials or substances 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.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1/3 Co 1/3 Mn 1/3 O 2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM 811 ), and the like.
  • lithium cobalt oxide such as LiCoO 2
  • lithium nickel oxide such as LiNiO
  • lithium phosphates containing an olivine structure may include, but are not limited to, one or more of lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.
  • lithium iron phosphate such as LiFePO 4 (also referred to as LFP)
  • LiMnPO 4 lithium manganese phosphate
  • LiMnPO 4 lithium manganese phosphate
  • LiMnPO 4 lithium manganese phosphate and carbon
  • the positive electrode film layer may also optionally include a binder.
  • the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-tetrafluoroethylene-propylene terpolymer vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer
  • the positive electrode film layer may further optionally include a conductive agent.
  • 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.
  • the positive electrode sheet can be prepared in the following manner: 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 (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on at least one side surface of the positive electrode collector (it can be on a single surface or on two surfaces), and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.
  • a solvent such as N-methylpyrrolidone
  • the electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate.
  • the present application adopts a liquid electrolyte, that is, an electrolyte.
  • the electrolyte includes an electrolyte salt and a solvent.
  • the electrolyte salt may include an electrolyte lithium salt.
  • the electrolyte lithium salt may include one or more of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate (LiBOB), lithium difluorobisoxalatophosphate, and lithium tetrafluorooxalatophosphate.
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium perchlorate
  • LiAsF 6 lithium bisfluorosulfonyl imide
  • the solvent in the electrolyte is an organic solvent.
  • the organic solvent in the electrolyte may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • EC ethylene carbonate
  • PC propylene carbonate
  • EMC diethyl
  • the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • additives such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • the secondary battery further includes a separator.
  • the present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation.
  • the materials of each layer can be the same or different, without particular limitation.
  • Electrode assembly secondary battery
  • the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.
  • the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.
  • 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 package, such as a bag-type soft package.
  • the material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.
  • FIG3 is a secondary battery 5 of a square structure as an example.
  • the outer package may include a shell 51 and a cover plate 53.
  • the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity.
  • the positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to actual needs.
  • an electric device which includes the secondary battery described in the first aspect of the present application, and can take into account the safety and service life of the electric device.
  • the secondary battery described in the first aspect of the present application can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device.
  • the electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.
  • the mobile device may be, for example, a mobile phone, a laptop computer, etc.;
  • the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.
  • a secondary battery can be selected according to its usage requirements.
  • Fig. 5 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.
  • a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.
  • a method for preparing a negative electrode plate is provided, which can be used to prepare the negative electrode plate used in the secondary battery described in the first aspect of the present application.
  • a method for preparing a negative electrode sheet which comprises the following steps:
  • S100 preparing single-particle carbon; wherein the step of preparing the single-particle carbon comprises: crushing, grading, pre-carbonizing, graphitizing and screening the raw material (such as raw coke raw material, further such as petroleum coke);
  • S200 preparing micro-particle carbon, mixing the micro-particle carbon and a binder, granulating, pre-carbonizing, graphitizing, optionally coating, and screening in a molten state of the binder to prepare secondary particle carbon; wherein the step of preparing micro-particle carbon includes: crushing, grading, and screening raw materials (such as raw coke raw materials, further such as petroleum coke);
  • the single particle carbon and the secondary particle carbon are as defined in the first aspect of the present application; the microparticle carbon is as defined in the first aspect of the present application.
  • S100 is used to prepare single particle carbon
  • S200 is used to prepare secondary particle carbon.
  • the raw coke material may include one or more of raw petroleum coke, raw asphalt coke, metallurgical coke, etc.
  • the raw coke material includes raw petroleum coke.
  • the raw coke material is non-needle coke.
  • the non-needle coke may include one or more of non-needle raw petroleum coke and non-needle raw asphalt coke.
  • the non-needle coke includes non-needle raw petroleum coke.
  • pre-carbonization is the process of heat treating non-graphite carbon-based materials under relatively low temperature conditions (such as 1100 ⁇ 50°C). After the pre-carbonization treatment, the carbon-based particles shrink and the structure becomes denser.
  • Non-graphite carbon-based materials refer to carbon in which the carbon is not entirely graphite and may not contain any graphite components.
  • graphitization refers to the process of heat treating non-graphite carbon-based raw materials (such as carbon-based materials obtained after pre-carbonization) under relatively high temperature conditions (such as greater than 2800°C). After graphitization treatment, the hexagonal carbon atom planar network is transformed from a disordered arrangement in two-dimensional space (such as a chaotic layer structure or amorphous carbon) to an ordered arrangement of graphite structure in three-dimensional space.
  • Non-graphite carbon can be pre-carbonized at relatively low temperature conditions (such as 1100 ⁇ 50 ° C), and the carbon particles shrink and the structure becomes more compact.
  • Non-graphite (such as carbon obtained after pre-carbonization) can be graphitized, and the hexagonal carbon atom plane network is transformed from a disordered arrangement in two-dimensional space (such as a chaotic layer structure or amorphous carbon) to an ordered arrangement of graphite structure in three-dimensional space.
  • the binder (such as asphalt) plays the role of a binder on the one hand, and on the other hand, the free carbon ⁇ , asphaltene ⁇ and other carbon substances in the binder are filled on the surface of the micro-particle carbon in a flowing state.
  • the granulation step often also includes a crushing sub-step to depolymerize the polymerized particles, so as to better control the particle size and distribution of the secondary carbon particles.
  • In the molten state of the binder is a low temperature condition relative to pre-carbonization, such as 500°C to 600°C, and non-limiting examples are 500°C, 550°C, 600°C, etc. It can be understood that granulation is carried out at a temperature higher than the softening point of the binder, and the required time is such as 2h to 10h. In some non-limiting examples, the temperature can be raised to a preset temperature at a heating rate of, for example, 1°C/min to 5°C/min and then kept warm.
  • Non-limiting examples of the heating rate include 1°C/min, 1.2°C/min, 1.25°C/min, 1.3°C/min, 1.35°C/min, 1.4°C/min, 1.5°C/min, 2°C/min, 2.5°C/min, 3°C/min, 3.5°C/min, 4°C/min, 4.5°C/min, 5°C/min, etc.
  • each occurrence of the pre-carbonization independently includes the following steps: heating treatment (insulation treatment) at 1050°C to 1150°C (such as 1100°C).
  • the heating time (insulation time) is 24h to 72h (such as 24h, 36h, 40h, 48h, etc., and also 36h to 40h); in some embodiments, the pre-carbonization is carried out under inert gas conditions.
  • the temperature before the insulation step of pre-carbonization, the temperature can be raised to a preset temperature at a heating rate of, for example, 1°C/min to 10°C/min, and then the temperature is kept warm.
  • Non-limiting examples of the heating rate are 1°C/min, 1.3°C/min, 1.4°C/min, 1.5°C/min, 1.6°C/min, 1.8°C/min, 2°C/min, 3°C/min, 4°C/min, 5°C/min, 6°C/min, 8°C/min, 10°C/min, etc.
  • each occurrence of the graphitization independently comprises the following steps: heating treatment at a temperature of >2800°C.
  • the heating temperature is 2850°C to 3100°C (such as 3000°C).
  • the heating time is 30h to 96h (such as 36h, 40h, 48h, 60h, 72h, etc., and also such as 36h to 48h).
  • the graphitization is carried out under inert gas conditions.
  • the temperature before the graphitization heat preservation step, the temperature can be raised to a preset temperature at a heating rate of, for example, 1°C/min to 15°C/min, and then the temperature can be kept warm.
  • Non-limiting examples of the heating rate include 1°C/min, 1.5°C/min, 2°C/min, 2.5°C/min, 3°C/min, 3.5°C/min, 4°C/min, 4.5°C/min, 5°C/min, 6°C/min, 8°C/min, 10°C/min, 12°C/min, 15°C/min, etc.
  • the corresponding heating rate can be 1.3°C/min to 2.5°C/min, and further can be 1.5°C/min to 2°C/min.
  • the coating comprises the following steps: mixing the material with an organic carbon material (such as asphalt) in a certain mass ratio, and heating at a suitable temperature (insulation temperature, such as 1100°C to 1200°C, further such as 1150°C) to prepare secondary particles comprising a coating layer.
  • a suitable temperature such as 1100°C to 1200°C, further such as 1150°C
  • the heating time is 12h to 24h (such as 12h, 15h, 16h, 18h, 20h, etc., also such as 12h to 16h).
  • the coating is carried out under inert gas conditions.
  • the coating layer in the secondary particles comprising the coating layer contains amorphous carbon.
  • the temperature before the heat preservation step of coating, can be raised to a preset temperature at a heating rate of, for example, 1°C/min to 10°C/min, and then the temperature can be kept warm.
  • a heating rate for example, 1°C/min to 10°C/min
  • the heating rate are 1°C/min, 1.3°C/min, 1.4°C/min, 1.5°C/min, 1.6°C/min, 1.8°C/min, 2°C/min, 3°C/min, 4°C/min, 5°C/min, 6°C/min, 8°C/min, 10°C/min, etc.
  • the heating rate from room temperature (such as 20°C to 30°C, further such as 25°C) to a preset temperature (such as 1100°C to 1200°C) can be 1.3°C/min to 2.5°C/min, and further such as 1.5°C/min to 1.8°C/min.
  • a relatively low temperature 500°C to 600°C
  • a preset temperature such as 1100°C to 1200°C, further such as 1150°C
  • the temperature can be raised to a preset temperature at a heating rate of 1°C/min to 5°C/min (further such as 1.3°C/min to 2°C/min) and then preheated (500°C to 600°C insulation), and non-limiting examples of the heating rate are 1°C/min, 1.5°C/min, 2°C/min, 2.5°C/min, 3°C/min, 3.5°C/min, 4°C/min, 4.5°C/min, 5°C/min, etc.
  • the heating rate needs to be reasonably controlled. If the heating rate is too fast, it will easily lead to more defects in the coating layer carbon. When there are more defects on the surface of the carbon particles, it will be detrimental to the battery cycle performance.
  • the organic carbon material may include one or more of asphalt, phenolic resin, furfural resin, and epoxy resin. In some embodiments, the organic carbon material includes asphalt.
  • the mass of the organic carbon material (such as asphalt) accounts for the total mass of the material and the organic carbon material (such as asphalt)
  • the proportion of the mass of the amorphous carbon layer in the secondary particulate carbon in the first aspect mentioned above can refer to the mass proportion of the amorphous carbon layer in the secondary particulate carbon in the first aspect.
  • the mass of the organic carbon material accounts for ⁇ 3.3% of the total mass of the material and the organic carbon material (such as asphalt), and can further be 1.3% to 3.3%, and can also be selected from any of the following percentages or any two percentage intervals: 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, etc.
  • the "inert gas” involved when preparing single-grain carbon and secondary-grain carbon, can be used as long as it can avoid side reactions of the gas, including oxygen-free conditions to avoid oxidation of chemical components in the raw materials under high temperature conditions.
  • the inert gas includes one or more of nitrogen, helium, argon, neon, etc. In some non-limiting examples, the inert gas includes nitrogen.
  • the single carbon particle is single graphite particle; and the micro carbon particle is micro graphite particle.
  • the binder is asphalt.
  • the mass ratio of the binder to the plurality of micro-particle carbons is selected from 1:8.5 to 1:9.5, non-limiting examples of which are 1:8.5, 1:8.6, 1:8.7, 1:8.8, 1:8.9, 1:9.0, 1:9.1, 1:9.2, 1:9.3, 1:9.4, 1:9.5, etc., and can also be selected from the interval consisting of any two of the above ratios. Reference can be made to the mass ratio of micro-particle carbon to binder in the secondary particles above.
  • each occurrence of the inert gas condition is independently a nitrogen condition.
  • the compounding of single-particle carbon and secondary-particle carbon can be better controlled, so that the tortuosity can be controlled within a more appropriate range, which is conducive to gas production and discharge while maintaining good battery cell cycle performance and extending battery life.
  • the amount of amorphous carbon coating can be better controlled by controlling the amount of organic carbon material (such as asphalt) and the temperature curve, thereby improving the fast charging performance of the battery while maintaining good cycle performance.
  • the single particle carbon is prepared by a method comprising the following steps in sequence: crushing the raw material, grading, pre-carbonizing at 1050° C. to 1150° C., graphitizing at a temperature of >2800° C., and screening to obtain the single particle carbon. Before pre-carbonizing the graded material, a mixing step may be added to obtain a material with a preset particle size and distribution.
  • the steps of preparing single-particle graphite include: crushing and classifying raw materials (such as raw coke raw materials, further such as petroleum coke) ⁇ mixing ⁇ pre-carbonization ⁇ graphitization.
  • raw materials such as raw coke raw materials, further such as petroleum coke
  • the temperature and time conditions of the pre-carbonization and graphitization can be selected from any suitable temperature conditions mentioned above independently or in combination.
  • the secondary particles are prepared by a method comprising the following steps in sequence: preparing the micro-particle carbon, mixing the micro-particle carbon and the binder, granulating at 500°C to 600°C, pre-carbonizing at 1050°C to 1150°C, graphitizing at a temperature of >2800°C, optionally coating at 1100°C to 1200°C, and screening to obtain the secondary particle carbon.
  • the steps of preparing secondary graphite particles include: crushing and grading raw materials (such as raw coke raw materials, further such as petroleum coke) ⁇ mixing (mixing raw materials and binders (such as asphalt)) ⁇ granulation (low-temperature heat treatment) ⁇ crushing (deagglomerating agglomerated particles) ⁇ pre-carbonization ⁇ graphitization ⁇ coating with an amorphous carbon layer (optional step).
  • raw materials such as raw coke raw materials, further such as petroleum coke
  • mixing mixing raw materials and binders (such as asphalt)
  • granulation low-temperature heat treatment
  • crushing deagglomerating agglomerated particles
  • pre-carbonization ⁇ graphitization
  • graphitization coating with an amorphous carbon layer
  • the temperature and time conditions of granulation, pre-carbonization, graphitization and coating can be selected from any suitable temperature conditions mentioned above independently or in combination in any suitable manner.
  • room temperature refers to 20°C to 30°C
  • wt% refers to weight percentage
  • the “inert gas condition” refers to a nitrogen gas condition.
  • the heating program when preparing single-particle carbon (such as single-particle graphite), the heating program is involved. If not specifically limited, the heating rate can be selected from 0.5°C/min to 15°C/min. When it comes to the cooling program, if not specifically limited, the temperature can be cooled by furnace cooling or the like. For example, the heating rate before pre-carbonization can be 1°C/min to 10°C/min, and the heating rate before graphitization can be 1°C/min to 15°C/min.
  • the heating rate can be selected from 0.5°C/min to 15°C/min.
  • the temperature can be cooled by furnace cooling or the like.
  • the heating rate before bonding granulation can be 1°C/min to 5°C/min
  • the heating rate before pre-carbonization can be 1°C/min to 10°C/min
  • the heating rate before graphitization can be 1°C/min to 15°C/min
  • the heating rate before coating amorphous carbon can be 1°C/min to 10°C/min.
  • a preheating program such as 500 to 600°C
  • a heating rate of 1°C/min to 5°C/min can be used.
  • the heating rate from room temperature to the preset temperature (500°C to 600°C) is 1.3°C/min to 2.4°C/min, which takes 4h to 6h; when performing pre-carbonization, the heating rate from room temperature to the preset temperature (1100°C) is 1.5°C/min to 1.8°C/min, which takes 10h to 12h; when performing graphitization, the heating rate from room temperature to the preset temperature (3000°C) is 1.5°C/min to 2°C/min; when coating amorphous carbon, the heating rate from room temperature to the preset temperature (1150°C) is 1.5°C/min to 1.8°C/min.
  • Raw material crushing and classification The raw coke (petroleum coke) is crushed and classified under a mechanical mill (impact mill equipment), and D v 10, D v 50 and D v 99 are monitored and controlled at a relatively large preset size, and the particle size distribution reaches a preset distribution range, and then enters the pre-carbonization process.
  • Pre-carbonization Heat treatment is performed at 1100°C in an inert gas environment for 48 hours (including the heating time from room temperature) to further expel volatiles, further shrink and densify, which is beneficial to improve material strength and increase the subsequent graphitization bulk density.
  • step (3) The material obtained in step (3) is screened and demagnetized to obtain single-grain graphite with a preset particle size requirement.
  • the particle sizes of the prepared single-particle graphite are as follows: D v 10 is 6.3 microns, D v 50 is 13.5 microns, and D v 99 is 40.5 microns.
  • Raw material crushing and classification The raw coke (petroleum coke) is crushed and classified under a mechanical mill (impact mill equipment), and the particle size distribution is made to reach a preset distribution range.
  • the D v 10, D v 50, D v 90 and D v 99 are monitored and controlled within the preset size to obtain primary carbon particles, which then enter the bonding granulation process.
  • the particle sizes of the prepared micro-particle graphite are: D v 10 is 2 to 3 microns, D v 50 is 5 to 7 microns, D v 50 is 12 to 15 microns, and D v 99 is 20 to 24 microns.
  • step (2) Adhesive granulation: Under inert gas conditions, the dispersed carbon particles prepared in step (1) are mixed with the adhesive asphalt in a mass ratio of 9:1, and the temperature is raised to 500°C to 600°C for heat treatment for 4 to 6 hours. The particle size is controlled by adjusting the temperature rise curve, and D v 10, D v 50 and D v 99 are monitored and controlled within the preset size. The agglomerated particles are crushed using a powder deagglomeration machine to deagglomerate the agglomerated particles.
  • step (3) Pre-carbonization: After the low-temperature heat treatment in step (2), heat treatment is carried out in an inert gas environment at 1100°C for 48 hours (including the heating time from room temperature) to further expel volatiles, further shrink and densify, which is beneficial to improve material strength and increase the subsequent graphitization bulk density.
  • step (4) The graphitized secondary particles prepared in step (4) are fully mixed with asphalt in a certain mass ratio (see Table 1), and heated in an inert gas environment at 1150°C for 20 hours (including the heating time from room temperature).
  • step (6) Screening: Screening the material obtained in step (4) or step (5) to remove magnetism and obtain secondary graphite particles that meet the preset particle size requirements.
  • the particle sizes of the prepared secondary graphite particles are as follows: D v 10 is 4.5 microns, D v 50 is 10.5 microns, and D v 99 is 34 microns.
  • the intensity ratio of the D peak/G peak of graphite is analyzed by Raman spectroscopy, and the degree of deviation of the ID/G of the surface layer of the carbon-based particles before and after the amorphous carbon layer is coated is tested to determine whether there is an amorphous layer on the surface of the carbon-based particles to be tested.
  • the ID/G changes significantly in a statistical sense (p ⁇ 0.01), and those skilled in the art can make an accurate judgment on whether an amorphous carbon layer is formed.
  • the D peak intensity can reflect the content of the amorphous (turbostratic stacking) region
  • the G peak intensity can reflect the content of the graphitized (layered structure) region.
  • Thickness of amorphous carbon layer Transmission electron microscopy (TEM) analysis was performed on the carbon-based particles at multiple locations of the cross section of the negative electrode active material layer. Based on the obvious dividing line formed between the amorphous carbon layer and the carbon-based core indicated in the TEM photograph, the average value of the coating layer was statistically estimated as the thickness of the amorphous carbon layer in this application.
  • TEM Transmission electron microscopy
  • the volume proportion of the amorphous carbon layer in the carbon-based particles can be estimated based on the volume of the carbon-based particles and the volume of the carbon-based core; further, based on the average mass of a single carbon-based particle, the volume of the carbon-based core (which can be calculated or obtained based on statistics from TEM test photos) and the density of the carbon-based core, the mass proportion of the amorphous carbon layer in the carbon-based particles can be estimated.
  • the thickness of the amorphous carbon layer is controlled within the range of 200nm to 500nm, and the mass proportion of the amorphous carbon layer in the secondary carbon particles is controlled within the range of 1.3% to 3.3%.
  • Treatment of the sample to be tested Take a clean 50mL beaker, add an appropriate amount of the particle sample to be tested (about 0.5g), add 1 to 2 drops of hand sanitizer (Blue Moon brand, containing surfactants such as sodium dodecyl sulfate), and then add 20mL of deionized water. Ultrasonic treatment for 5 minutes, the ultrasonic power is 120W, so that the sample is fully dispersed.
  • hand sanitizer Blue Moon brand, containing surfactants such as sodium dodecyl sulfate
  • Particle size types D v 10, D v 50, D v 90, D v 99 tests.
  • Equipment model Malvern 2000 (MasterSizer 2000) laser particle size analyzer, reference standard process: GB/T19077-2016/ISO 13320:2009, detailed test process: Take an appropriate amount of the sample to be tested (the sample concentration is guaranteed to be 8% to 12% shading), add 20mL of anhydrous ethanol, and ultrasonically treat for 5min (53KHz/120W) to disperse the sample, and then measure the sample according to GB/T19077-2016/ISO 13320:2009 standard.
  • the negative electrode active material artificial graphite (single-grain graphite and secondary-grain graphite, see Table 1) and the conductive agent (conductive carbon SP) were dry mixed in a stirring tank for 5 minutes, and then a dispersant (sodium carboxymethyl cellulose) was added and dry mixed for 20 minutes, and then deionized water was added and stirred, keeping the solid content at about 60wt%, stirring for 120 minutes, and finally a binder (aqueous binder styrene-butadiene rubber latex) and deionized water were added, keeping the solid content at about 50wt%, and the vacuum degree was kept ⁇ -0.05MPa, and the temperature of the entire processing and stirring process was kept at 5°C to 50°C.
  • the negative electrode slurry was prepared.
  • the mass parts of single-particle graphite, secondary-particle graphite, conductive carbon SP, styrene-butadiene rubber emulsion, and sodium carboxymethyl cellulose are 84.6 parts, 9.4 parts, 2 parts, 2.5 parts, and 1.5 parts, respectively, that is, the mass ratio is 84.6:9.4:2:2.5:1.5.
  • the negative electrode slurry prepared in step (1) is uniformly coated on both sides of a current collector copper foil with a thickness of 6 ⁇ m, with a coating amount of about 9.74 mg/cm 2 on one side.
  • the negative electrode sheet is obtained after drying, cold pressing, trimming, cutting and stripping.
  • the positive electrode active material lithium iron phosphate, the conductive agent SP, and the binder polyvinylidene fluoride were fully stirred and mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:1.5:2.5 to obtain a positive electrode slurry.
  • the positive electrode slurry was evenly coated on both sides of a current collector aluminum foil with a thickness of 13 ⁇ m, with a coating amount of about 20.13 mg/cm 2 on one side.
  • the positive electrode sheet was obtained after drying, cold pressing, trimming, cutting and striping.
  • ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed evenly in a volume ratio of 3:7, lithium salt LiPF 6 is added, and stirred evenly to prepare an electrolyte.
  • the mass percentage concentration of lithium salt LiPF 6 in the electrolyte is 12.5%.
  • a polyethylene (PE) porous polymer film is used as the isolation membrane.
  • the negative electrode sheet (prepared in step (2)), the isolation film and the positive electrode sheet (prepared in step (3)) are stacked in order, with the isolation film placed between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare cell, which is then inserted into a battery casing.
  • a lithium-ion battery is prepared, which is a lithium-ion secondary battery.
  • Examples 2 to 7 respectively adopt methods substantially the same as Example 1, except that the mass ratios of single-particle graphite to secondary-particle graphite in the negative electrode active material are different, as shown in Table 1. The other steps of Examples 2 to 7 are respectively the same as Example 1.
  • Example 8 A method basically the same as Example 1 is adopted, except that: the particle size of single graphite particles, the particle size of secondary graphite particles, and the particle size of microparticles in the secondary graphite particles in the negative electrode active material are different, and the mass ratio of single graphite particles to secondary graphite particles is 6:4, as can be seen in Table 1.
  • the other steps of Example 8 are the same as those of Example 1.
  • Example 9 A method basically the same as Example 1 is adopted, except that: the particle size of single graphite particles, the particle size of secondary graphite particles, and the particle size of microparticles in the secondary graphite particles in the negative electrode active material are different, and the mass ratio of single graphite particles to secondary graphite particles is 5:5, as can be seen in Table 1.
  • the other steps of Example 9 are the same as those of Example 1.
  • Example 10 A method substantially the same as that of Example 4 is adopted, except that the secondary carbon particles used are not coated with an amorphous carbon layer.
  • Comparative Example 1 No secondary graphite particles were used. The method was basically the same as that of Example 1, except that the negative electrode active material was replaced by single-grain graphite particles of equal mass instead of secondary graphite particles, wherein the mass ratio of single-grain artificial graphite, conductive carbon SP, styrene-butadiene rubber emulsion, and sodium carboxymethyl cellulose in the negative electrode material was 94:2:2.5:1.5. See Table 1, the other steps of Comparative Example 1 were the same as those of Example 1.
  • Comparative Example 2 Single-grain graphite was not used. Comparative Example 2 used a method substantially the same as that of Example 1, except that the negative electrode active material was replaced with a single-grain graphite with an equal mass of secondary-grain graphite, wherein the mass ratio of secondary-grain artificial graphite, conductive carbon SP, styrene-butadiene rubber emulsion, and sodium carboxymethyl cellulose in the negative electrode material was 94:2:2.5:1.5. As shown in Table 1, the other steps of Comparative Example 2 were the same as those of Example 1.
  • Comparative Example 3 The method is substantially the same as that of Example 1, except that single-particle graphite with substantially the same particle size distribution is used instead of secondary particle graphite. In this case, single-particle graphite with two groups of particle sizes is used, and the mass ratio of the two groups of single-particle graphite is 5:5. See Table 1. The other steps of Comparative Example 3 are respectively the same as those of Example 1.
  • Comparative Example 4 A method substantially the same as that of Example 1 is used, except that the particle size of the single graphite particle is smaller than that of the secondary graphite particle, and the mass ratio of the single graphite particle to the secondary graphite particle is 5:5. As shown in Table 1, the other steps of Comparative Example 4 are respectively the same as those of Example 1.
  • Comparative Example 5 A method substantially the same as that of Example 1 is used, except that the particle size of the single graphite particle is close to that of the secondary graphite particle, and the mass ratio of the single graphite particle to the secondary graphite particle is 5:5. As shown in Table 1, the other steps of Comparative Example 5 are respectively the same as those of Example 1.
  • Comparative Example 6 Using a method basically the same as that in Example 4, with the same particle composition as that in Example 4 (the particle size distribution and mass ratio are the same), in the step of coating the secondary particulate carbon with an amorphous carbon layer, the heat treatment temperature is the same as that in Example 4, that is, 1150°C for 20 hours. The difference is that the heating rate of Comparative Example 6 is 25°C/min.
  • the cold pressed pole piece was cut into 6cm ⁇ 6cm samples with scissors, and then polished with IB-19500CP ion cross section polisher to obtain polished samples with cut surfaces. Then, the samples were tested with ZEISS sigma 300 equipment according to standard JY/T010-1996. The cross-sectional morphology of the pole piece was observed at a random position in the test sample.
  • ⁇ is the porosity of the negative electrode active material layer at 25°C
  • k is the ionic conductivity of the electrolyte at 25°C, in ms/cm
  • Rion is the ionic resistance of the negative electrode sheet at 25°C, in ⁇
  • A is the effective area of the electrode when testing Rion, in cm 2
  • d is the thickness of the negative electrode active material layer, in ⁇ m.
  • Electrode sample to be tested Use scissors to cut the cold pressed electrode into a square sample of 6 cm ⁇ 6 cm to test the ionic resistance Rion of the negative electrode. The square area of 36 cm2 is recorded as the electrode effective area A in formula I.
  • Battery cells to be tested lithium-ion batteries prepared in various embodiments and comparative examples.
  • FIG1 is a SEM morphology of the single graphite particle and the secondary graphite particle in Example 1. It can be seen that the single graphite particle is a single particle, while the secondary graphite particle is composed of a plurality of microparticles.
  • Comparative Example 1 no secondary graphite particles are used. Compared with Example 1, Comparative Example 1 has a high degree of tortuosity, which is not conducive to the discharge of the formed gas.
  • Comparative Example 2 single-particle graphite was not used. Compared with Example 1, the SOC of Comparative Example 2 was significantly reduced after the gas production was completed, and the cycle capacity retention rate was low.
  • Comparative Example 3 single-particle graphite with substantially the same particle size distribution is used to replace the secondary graphite particles. At this time, single-particle graphite with two groups of large and small particle sizes is used. Compared with Example 1, the SOC of Comparative Example 3 at the end of gas production is reduced.
  • Comparative Example 4 the particle size of the single-particle graphite is smaller than that of the secondary-particle graphite, the SOC decreases significantly after the gas production is completed, and the capacity retention rate P400 after 400 cycles is also significantly deteriorated.
  • Comparative Example 5 the particle size of the single-particle graphite is close to that of the secondary-particle graphite, the SOC decreases significantly after the gas production is completed, and the capacity retention rate P400 after 400 cycles is deteriorated.
  • Example 4 the fast charging performance of Example 4 is improved relative to that of Example 10.
  • both Example 4 and Example 10 have moderate tortuosity, better SOC at the end of exhaust gas production and good cycle capacity retention rate P 400 , and good cell cycle performance.
  • the present application is not limited to the above-mentioned embodiments.
  • the above-mentioned embodiments are only examples.
  • the embodiments that have the same structure as the technical idea and play the same effect are all included in the technical scope of the present application.
  • the above-mentioned embodiments only express several embodiments of the present application, and the description is relatively detailed, but it cannot be understood as a limitation on the scope of the patent.
  • various deformations that can be thought of by those skilled in the art are applied to the embodiments, and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

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Abstract

本申请公开了二次电池、用电装置和制备方法，该二次电池包括负极极片，负极极片中的负极活性材料层包括碳基颗粒，碳基颗粒包括单颗粒碳和二次颗粒碳，其中，单颗粒碳的Dv50大于二次颗粒碳的Dv50；Dv50表示材料的累计体积分布百分数达到50％时对应的粒径。

Description

二次电池、用电装置和制备方法 技术领域
本申请涉及二次电池技术领域，特别涉及二次电池、用电装置和制备方法。
背景技术
这里的陈述仅提供与本申请有关的背景信息，而不必然构成现有技术。
目前，智能手机、平板电脑等电子产品的普及，智能穿戴、电动工具和电动汽车等电子产品的快速发展，电子产品在日常生活中发挥折越来越不可或缺的作用，各类电子产品功能的发展趋势愈加多功能化、智能化趋势，电子产品长时间运行下的安全问题越发不容忽视，因此，对锂离子电池的快速排气要求越来越高。
发明内容
鉴于上述情况，本申请提供了一种二次电池、用电装置和制备方法，该二次电池中包括的负极活性材料层具有较低的迂曲度，可加快产气的排出，并有利于保持良好的电池循环性能。
在本申请的第一方面，提供一种二次电池，其包括正极极片、负极极片、隔离膜和电解液，所述隔离膜设置于所述正极极片和所述负极极片之间；
所述负极极片包括负极活性材料层，所述负极活性材料层包括碳基颗粒，所述碳基颗粒包括单颗粒碳和二次颗粒碳，其中，所述单颗粒碳的D v50大于所述二次颗粒碳的D v50；
其中，D v50表示材料的累计体积分布百分数达到50％时对应的粒径。
在该二次电池的负极活性材料层中，利用较大粒径的单颗粒碳和较小粒径的二次颗粒碳进行复配，二次颗粒碳有利于降低迂曲度，有利于产气的排出，单颗粒碳有利于保持良好的电芯循环性能，延长电池使用寿命。制备包括该负极活性材料层的负极极片的过程中，负极浆料经涂布、干燥后，还需进行压实以便调节厚度、密度、能量密度等参数，在压实(可采用冷压方式)过程中，颗粒与颗粒之间会形成一定的孔隙，这些孔隙之间相互连通，使得负极活性材料层的两侧表面之间存在孔隙连通通路，该孔隙连通通路的路径与负极活性材料层厚度之间的比值即为负极活性材料层的迂曲度。较小粒径的二次颗粒碳的加入能够使孔隙之间更容易形成孔隙连通通路，从而降低迂曲度。对于较低的迂曲度，化成及电池使用过程中的产气沿孔隙连通通路被排出所需时间更短，有利于形成更均质的界面，且界面的稳定性更好。进一步地，较低的迂曲度还可以改善电解液对极片的浸润效果。
在本申请的一些实施方式中，所述负极活性材料层的迂曲度τ在数值上等于根据以下公式计算得到的数值：ε×k×Rion×A/d；其中，ε为25℃时所述负极活性材料层的孔隙率；k为25℃时所述电解液的离子电导率，单位为ms/cm；Rion为25℃时所述负极极片的离子电阻，单位为Ω；A为测试Rion时的有效面积，单位为cm 2；d为所述负极活性材料层的厚度，单位为μm；
所述负极活性材料层的迂曲度τ≤4.75。
在本申请的一些实施方式中，所述负极活性材料层的迂曲度τ≤4.70；
可选地，所述负极活性材料层的迂曲度τ≤4.70，可选地，τ选自3.40～4.70；
可选地，所述负极活性材料层的迂曲度τ≤4.65，可选地，τ选自3.40～4.65；
可选地，所述负极活性材料层的迂曲度τ≤4.62，可选地，τ选自3.42～4.62；
可选地，所述负极活性材料层的迂曲度τ≤4.05，可选地，τ选自3.42～4.05；
可选地，所述负极活性材料层的迂曲度τ≤3.95，可选地，τ选自3.42～3.95；
可选地，所述负极活性材料层的迂曲度τ≤3.85，可选地，τ选自3.45～3.85；
可选地，所述负极活性材料层的迂曲度τ≤3.82，可选地，τ选自3.45～3.82。
通过将负极活性材料层的迂曲度控制在合适的范围内，有利于在加快产气排出的同时还保持良好的电池循环性能。二次电池经使用一段时间后，负极活性材料层的迂曲度可能发生一些变化；随着电池的使用时间增加，可能导致极片体积变化，由此导致迂曲度的变化。
在本申请的一些实施方式中，所述负极活性材料层的孔隙率选自30.6％～37.5％；
可选地，所述负极活性材料层的孔隙率选自32.2％～37.5％；
可选地，所述负极活性材料层的孔隙率选自33.8％～37.5％；
可选地，所述负极活性材料层的孔隙率选自34.8％～37.5％；
可选地，所述负极活性材料层的孔隙率选自35.5％～37.5％。
通过将负极活性材料层的孔隙率控制在合适的范围内，有利于在控制合适迂曲度的同时还保证电解液具有合适的浸润性，从而在加快产气的同时还实现较好的电芯动力学性能。
在本申请的一些实施方式中，所述负极活性材料层的压实密度选自1.30g/cc～1.80g/cc；
可选地，所述负极活性材料层的压实密度选自1.30g/cc～1.70g/cc；
可选地，所述负极活性材料层的压实密度选自1.50±0.02g/cc。
通过控制压实密度在合适的范围内，有利于在加快产气的同时还提供较好的能量密度，实现良好的循环性能。压实密度越高，对能量密度的提升越有利。但压实密度提高，会导致孔隙率降低，有可能不利于电解液的浸润，影响电池功率的发挥，压实密度越大，孔隙率越小，有可能不利于电解液浸润，导致活性离子(如锂离子)的嵌入难度增加，电池动力学性能变差。
在本申请的一些实施方式中，所述二次颗粒碳在所述碳基颗粒中的质量占比选自10％～90％；
可选地，所述二次颗粒碳在所述碳基颗粒中的质量占比选自20％～80％；
可选地，所述二次颗粒碳在所述碳基颗粒中的质量占比选自30％～70％；
可选地，所述二次颗粒碳在所述碳基颗粒中的质量占比选自30％～50％。
本申请的发明人经研究发现，在本申请的二次电池中，随着二次颗粒碳的比例增加，负极极片的迂曲度逐渐降低，孔隙率倾向于增大，通过合理控制二次颗粒碳的含量，可以将迂曲度、孔隙率控制在合适的范围内。在一些非限制性示例中，将单颗粒碳和二次颗粒碳的质量比例控制在7：3，化成排产气结束SOC相对于100％纯单颗粒碳(无二次颗粒碳)排产气结束SOC提前了26％，相对于100％纯二次颗粒碳(无单颗粒碳)循环性能提高了1.7％(以循环400圈为例)。
在本申请的一些实施方式中，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比大于50％，
所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比选自80％～100％；
可选地，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比选自90％～100％；
可选地，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比选自95％～100％；
可选地，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比为100％；
可选地，所述碳基颗粒中含有质量占比大于50％的石墨材料；
可选地，所述碳基颗粒中含有质量占比选自80％～100％的石墨材料；
可选地，所述碳基颗粒中含有质量占比选自90％～100％的石墨材料；
可选地，所述碳基颗粒中含有质量占比选自95％～100％的石墨材料；
可选地，所述碳基颗粒中含有质量占比为100％的石墨材料；
可选地，所述负极活性材料层的负极活性物质中含有质量占比大于50％的石墨材料；
可选地，所述负极活性材料层的负极活性物质中含有质量占比选自80％～100％的石墨材料；
可选地，所述负极活性材料层的负极活性物质中含有质量占比选自90％～100％的石墨材料；
可选地，所述负极活性材料层的负极活性物质中含有质量占比选自95％～100％的石墨材料；
可选地，所述负极活性材料层的负极活性物质中含有质量占比为100％的石墨材料。
在本申请的一些实施方式中，所述碳基颗粒为石墨颗粒，所述单颗粒碳为单颗粒石墨，所述二次颗粒为二次颗粒石墨。
采用碳基材料作为负极活性材料层中的主要负极活性物质时，相对于高硅含量等其他种类的负极极片，负极极片的膨胀性更低，固体电解质界面(SEI)膜更稳定，电池安全性更好。
采用石墨作为负极活性材料层中的主要负极活性物质时，在负极活性材料层中，碳基颗粒主要为石墨颗粒，单颗粒碳主要为单颗粒石墨，二次颗粒主要为二次颗粒石墨，此时，可充分利用石墨的导电性好，首效高，来源广等优点。
在本申请的一些实施方式中，所述负极活性材料层具备如下的一个或多个特征：
所述单颗粒碳的D v50选自13μm～14μm；
所述二次颗粒碳的D v50选自9.5μm～10.5μm；和
所述单颗粒碳的D v50与所述二次颗粒碳的D v50的差值选自3μm～4μm。
在本申请的一些实施方式中，所述单颗粒碳的D v99大于所述二次颗粒碳的D v99；
可选地，所述负极活性材料层还具备如下的一个或多个特征：
所述单颗粒碳的D v99选自37μm～44μm；
所述二次颗粒碳的D v99选自31μm～38μm；和
所述单颗粒碳的D v99与所述二次颗粒碳的D v99的差值选自4μm～6μm。
在本申请的一些实施方式中，所述单颗粒碳的D v10大于所述二次颗粒碳的D v10；
可选地，所述负极活性材料层还具备如下的一个或多个特征：
所述单颗粒碳的D v10选自5μm～7μm；
所述二次颗粒碳的D v10选自3.5μm～5.5μm；和
所述单颗粒碳的D v10与所述二次颗粒碳的D v99的差值选自1μm～2μm。
可以通过控制单颗粒碳及二次颗粒碳的粒径尺寸及分布，从而更好平衡迂曲度、孔隙率及压实程度的多维度性能，从而在加快产气排出的同时，还实现较好的循环性能和功率性能。
进一步地，控制单颗粒碳和二次颗粒碳之间的粒径之差，更有利于充分发挥两者的复配优势，既有利于降低迂曲度及产气的排出，还有利于保持良好的电芯循环性能，延长电池使用寿命。
在本申请的一些实施方式中，所述二次颗粒碳包括多个微颗粒碳，还包括粘合剂；其中，所述微颗粒碳中一次颗粒的数量为一个或多个；
当所述二次颗粒碳为二次颗粒石墨时，所述微颗粒碳为微颗粒石墨；
可选地，所述微颗粒碳具备如下的一个或多个特征：
所述微颗粒碳的D v99选自20μm～24μm；
所述微颗粒碳的D v90选自12μm～15μm；
所述微颗粒碳的D v50选自5μm～7μm；和
所述微颗粒碳的D v10选自2μm～3μm；
可选地，所述粘合剂为沥青；
可选地，所述粘合剂相对于所述多个微颗粒碳的质量比选自1:8.5至1:9.5；
可选地，所述二次颗粒碳是由所述多个微颗粒碳和所述粘合剂粘聚而成。
通过控制微颗粒碳的粒径及分布在合适的范围内，有利于稳定控制二次颗粒碳的粒径大小。进一步地，通过控制粘合剂(如沥青)的用量，可以较好地实现二次颗粒碳的预设粒径及分布。
在本申请的一些实施方式中，所述二次颗粒碳包含碳基芯和位于所述碳基芯表面至少一部分的无定形碳层；
可选地，所述无定形碳层在所述二次颗粒碳表面的厚度≤500nm；可选地，所述无定形碳层在所述二次颗粒碳表面的厚度选自200nm～500nm；
可选地，所述无定形碳层在所述二次颗粒碳中的质量含量≤3.3％，可选地，所述无定形碳层在所述二次颗粒碳中的质量含量选自1.3％～3.3％；
可选地，所述碳基芯包含负极活性物质，所述负极活性物质为石墨。
本申请的发明人经过研究和探索发现，通过在二次颗粒碳表面的至少一部分包覆无定形碳，可以改善电池的快充性能；进一步地，通过合理控制无定形碳的含量，可以在确保良好的电池循环性能的情况下改善电池快充性能。
发明人还意外发现，在二次颗粒碳表面包覆了无定形碳时，随着二次颗粒碳比例的增加，电芯的循环寿命可能会降低，发明人推测可能是由于无定形碳表面活性相对于碳基芯(如石墨)的表面活性高，从而可能降低负极在循环过程中的稳定性。此时，可以通过合理控制二次颗粒碳在碳基颗粒中的质量比(如控制在30％～50％)，从而更好地平衡对产气排除、容量和电池循环稳定性的需求，同时实现低迂曲度和高容量保持率。
在本申请的第二方面，提供一种用电装置，其包括本申请第一方面所述二次电池。
在本申请的第三方面，提供一种负极极片的制备方法，其包括如下步骤：
制备单颗粒碳；其中，所述制备单颗粒碳的步骤包括：将原料破碎，分级，预碳 化，石墨化和筛分；
制备微颗粒碳，将所述微颗粒碳和粘合剂混合，于所述粘合剂熔融状态下造粒，预碳化，石墨化，可选地包覆，筛分，制备二次颗粒碳；其中，所述制备微颗粒碳的步骤包括：将原料破碎、分级、筛分；
将所述单颗粒碳、所述二次颗粒碳、助剂和溶剂混合，制备负极浆料；
将所述负极浆料涂布于负极集流体的至少一侧表面，干燥，压实，制备得到所述负极极片；
其中，所述单颗粒碳和所述二次颗粒碳如本申请第一方面中所定义；所述微颗粒碳如本申请第一方面中所定义。
制备单颗粒碳及二次颗粒碳时，对非石墨的碳基材料在相对低温条件下(如1100±50℃)进行预碳化处理后，碳基颗粒收缩，结构变得更为致密。对非石墨的碳基材料进行石墨化处理后，六角碳原子平面网络从二维空间的无序排列(如乱层结构或无定形碳)转变为三维空间的有序排列的石墨结构。制备二次颗粒碳时，“粘合剂熔融状态下造粒”的过程中，粘合剂(如沥青)一方面起到粘合剂的作用，另一方面粘合剂中的游离碳α、沥青质β等碳物质流动状态下填充在微颗粒碳表面，经后续的预碳化、石墨化等工序处理后，可以得到预设粒径、表面更均匀的二次颗粒碳；此外，造粒步骤往往还包括粉碎子步骤，将发生聚合的颗粒解聚，从而更好地控制二次颗粒碳的粒径及分布。
在本申请的一些实施方式中，所述负极极片的制备方法可以具备如下一个或多个特征：
所述预碳化每次出现，独立地包括如下步骤：于1050℃～1150℃加热处理，可选地，加热时间为24h～72h；可选地，所述预碳化在惰性气体条件下进行；
所述石墨化每次出现，独立地包括如下步骤：于>2800℃的温度条件下加热处理，可选地，加热温度为2850℃～3100℃；可选地，加热时间为30h～96h；可选地，所述石墨化在惰性气体条件下进行；
所述于所述粘合剂熔融状态下造粒包括；于所述粘合剂熔融状态下加热处理，粉碎；可选地，加热温度选自500℃～600℃；可选地，加热时间为4h～6h，可选地，所述加热处理在惰性气体条件下进行；
所述包覆包括如下步骤：将物料与有机碳材料混合，于1100℃～1200℃加热处理制备包含包覆层的二次颗粒，可选地，加热时间为12h～24h；可选地，所述包覆在惰性气体条件下进行；可选地，所述包含包覆层的二次颗粒中的包覆层中包含无定形碳；
所述单颗粒碳采用依次包括如下步骤的方法制得：将原料破碎，分级，于1050℃～1150℃预碳化，于>2800℃的温度条件下石墨化，筛分，制得所述单颗粒碳；
所述二次颗粒采用依次包括如下步骤的方法制得：制备所述微颗粒碳，将所述微颗粒碳和所述粘合剂混合，于500℃～600℃下造粒，于1050℃～1150℃预碳化，于>2800℃的温度条件下石墨化，可选地于1100℃～1200℃下包覆，筛分，制得所述二次颗粒碳；
所述单颗粒碳为单颗粒石墨；所述微颗粒碳为微颗粒石墨；
所述粘合剂为沥青；
所述粘合剂相对于多个所述微颗粒碳的质量比选自1:8.5至1:9.5；
所述有机碳材料包括沥青、酚醛树脂、糠醛树脂和环氧树脂中的一种或多种；
所述惰性气体条件每次出现，独立地选自包括氮气、氦气、氩气和氖气中的一种或多种气体的条件。
通过控制预碳化、石墨化、造粒、包覆等步骤的相关参数，各参数之间相互协同配合，可以更好地控制单颗粒碳、二次颗粒碳的复配，从而将迂曲度控制在较为合适的范围内，在有利于产气排出的同时，还保持良好的电芯循环性能，延长电池使用寿命。比如，在二次颗粒表面包覆无定形碳的过程中，可以通过控制沥青用量、温度曲线从而较好地控制无定形碳的包覆量，从而在保持良好循环性能的情况下还改善电池的快充性能。
本申请的一个或多个实施例的细节在下面的附图和描述中提出。本申请的其他特征、目的和优点将从说明书、附图以及权利要求书变得明显。
附图说明
为了更好地描述和说明这里公开的那些申请的实施例或示例，可以参考一幅或多幅附图。用于描述附图的附加细节或示例不应当被认为是对所公开的申请、目前描述的实施例或示例以及目前理解的这些申请的最佳模式中的任何一者的范围的限制。而且在全部附图中，用相同的附图标号表示相同的部件。在附图中：
图1是本申请一些实施例中的单颗粒石墨与二次颗粒石墨的SEM形貌图，其中，(A)和(B)均为单颗粒石墨的不同放大倍数的SEM形貌图，(C)和(D)均为二次颗粒石墨不同放大倍数的SEM形貌图；其中，(B)中箭头指向单颗粒石墨，(D)中箭头指向二次颗粒石墨；SEM测试参数包括：工作电压(EHT)为10.00kV，采用InLens探测器，工作距离为4.6mm，放大倍数为1000X；
图2为本申请一对比例中单颗粒石墨形成的负极极片截面的SEM形貌图(A)及相应的化成排气路径示意图(B)，以及本申请一实施例中由单颗粒石墨与二次颗粒石墨形成的负极极片截面的SEM形貌图(C)及相应的化成排气路径示意图(D)；SEM测试参数包括：工作电压(EHT)为10.00kV，采用InLens探测器，工作距离为4.6mm，放大倍数为1000X；
图3是本申请一实施例的二次电池的示意图；
图4是图3所示的本申请一实施例的二次电池的分解图；
图5是本申请一实施例的二次电池用作电源的用电装置的示意图。
附图标记说明：
5，二次电池；51，壳体；52，电极组件；53，盖板；6，用电装置。
具体实施方式
以下，适当地参照附图详细说明公开了本申请的二次电池、用电装置和制备方法的一些实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下 限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。此外，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
本申请中涉及“多个”、“多种”、“多次”等，如无特别限定，指在数量上大于2或等于2。例如，“一种或多种”表示一种或大于等于两种。
本文中所使用的“其组合”、“其任意组合”、“其任意组合方式”等中包括所列项目中任两个或任两个以上项目的所有合适的组合方式。
本文中，“合适的组合方式”、“合适的方式”、“任意合适的方式”等中所述“合适”，以能够实施本申请的技术方案为准。
本文中，“优选”、“更好”、“更佳”、“为宜”仅为描述效果更好的实施方式或实施例，应当理解，并不构成对本申请保护范围的限制。如果一个技术方案中出现多处“优选”，如无特别说明，且无矛盾之处或相互制约关系，则每项“优选”各自独立。
本申请中，“进一步”、“更进一步”、“特别”等用于描述目的，表示内容上的差异，但并不应理解为对本申请保护范围的限制。
本申请中，“第一方面”、“第二方面”、“第三方面”等中，术语“第一”、“第二”、“第三”等仅用于描述目的，不能理解为指示或暗示相对重要性或数量，也不能理解为隐含指明所指示的技术特征的重要性或数量。而且“第一”、“第二”、“第三”等仅起到非穷举式的列举描述目的，应当理解并不构成对数量的封闭式限定。
本申请中，术语“室温”一般指4℃～35℃，较佳地指20℃±5℃。在本申 请的一些实施例中，室温是指20℃～30℃。
在本申请中，涉及数据范围的单位，如果仅在右端点后带有单位，则表示左端点和右端点的单位是相同的。比如，3～5h或3-5h均表示左端点“3”和右端点“5”的单位都是h(小时)。
本申请实施例说明书中所提到的相关成分的重量不仅仅可以指代各组分的含量，也可以表示各组分间重量的比例关系，因此，只要是按照本申请实施例说明书相关组分的含量按比例放大或缩小均在本申请实施例说明书公开的范围之内。进一步地，本申请实施例说明书中所述的重量可以是μg、mg、g、kg等化工领域公知的质量单位。
随着各类电子产品功能的发展趋势愈加多功能化、智能化趋势，电子产品长时间运行下的安全问题越发不容忽视，对锂离子电池的快速排气要求越来越高。一些已有技术采用如下的方式改善排气情况：(1)改善电池中的产气排出结构设计，避免电芯压力过高；(2)改善极片或电解液对产气的物理吸附性，降低电芯压力；(3)利用化学反应将产气转化成非气态从而降低压力；(4)从源头将抑制产气的发生，等等。然而上述各种手段均需引入较复杂的原料或工艺，不利于成本控制，或者还需要向极片中引入特殊添加剂，容易损害极片的克容量，或者特殊构件的引入可能会限制注液系数的调整。
基于此，在本申请的第一方面，提供一种其包括正极极片、负极极片、隔离膜和电解液，所述隔离膜设置于所述正极极片和所述负极极片之间；
所述负极极片包括负极活性材料层，所述负极活性材料层包括碳基颗粒，所述碳基颗粒包括单颗粒碳和二次颗粒碳，其中，所述单颗粒碳的D v50大于所述二次颗粒碳的D v50；
其中，D v50表示材料的累计体积分布百分数达到50％时对应的粒径。
在本申请中，二次电池包括正极极片、负极极片、电解液和隔离膜。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出，电解液在正极极片和负极极片之间起到传导离子的作用，隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使活性离子通过。活性离子可以为锂离子(可对应锂离子二次电池)。
在本申请的上下文中，如无其他说明，负极活性材料层中的“碳基颗粒”指含有碳的负极活性颗粒，其中的碳具有嵌入和脱出活性离子(如锂离子)的能力，也即其中的碳作为负极活性物质。
在本申请中，如无其他说明，电极极片可以为正极极片或负极极片，电极极片中的“活性物质”指能够可逆地嵌入与脱出活性离子能力的物质。如无其他说明，“负极活性物质”指用于负极极片的、能够可逆地嵌入与脱出活性离子能力的物质；“正极活性物质”指用于正极极片的、能够可逆地脱出与嵌入活性离子能力的物质。二次电池充电时，活性离子从正极脱出，经过电解液嵌入负极；而二次电池放电时，活性离子则从负极脱出，嵌入正极。在本申请中，“活性材料”和“活性物质”，具有相同含义，可以互换使用；“正极活性物质”与“正极活性材料”具有相同含义，可以互换使用；“负极活性物质”与“负极活性材料”具有相同含义，可以互换使用。
在本申请中，如无特别说明，“活性材料层”包括正极极片的正极活性材料层以及负极极片的负极活性材料层，根据详细的情形，可以指正极活性材料层或负极活性材料层。
在本申请中，作为负极活性颗粒的“二次颗粒碳”，是二次颗粒形式的含碳颗粒，且其中的负极活性物质部分或全部地为碳。“单颗粒碳”是相对于“二次颗粒碳”而言，指一次颗粒形式的颗粒状碳，可以理解，单颗粒碳中的负极活性物质为碳。“一次颗粒”和“二次颗粒”为本领域所熟知的术语。“一次颗粒”指单晶或类单晶晶粒。“二次颗粒”指由两个或两个以上的一次颗粒聚集而成的团聚态的颗粒，可以利用助剂(如粘合剂)实现一次颗粒的聚集。一次颗粒和二次颗粒可以通过实验手段(如使用扫描电子显微镜拍摄SEM图像)容易地区分。可参阅图1理解本申请中“单颗粒碳”和“二次颗粒碳”。图1是本申请一些实施例中的单颗粒石墨与二次颗粒石墨的SEM形貌图，其中，(A)和(B)均为单颗粒石墨的不同放大倍数的SEM形貌图，(C)和(D)均为二次颗粒石墨不同放大倍数的SEM形貌图；SEM测试参数包括：工作电压(EHT)为10.00kV，采用InLens探测器，工作距离为4.6mm，放大倍数为1000X。
在本申请的上下文中，可采用体积累计分布粒径D vN(其中，N表示选自0～100的任意数值)来表征材料的粒径尺寸，指材料的累计体积分布百分数达到N％时所对应的粒径，粒径小于等于D vN的体积占比为N％。D vN可以从材料粒径的体积累积分布曲线上获得，如无其他说明，体积累积分布曲线自小粒径侧从零开始累计。以D v99、D v90、D v50、D v10为例，D v99是指材料的累计体积分布百分数达到99％时所对应的粒径；D v50是指材料的累计体积分布百分数达到50％时所对应的粒径；D v10是指材料的累计体积分布百分数达到10％时所对应的粒径。以D v50为例，表示占材料体积50％的颗粒粒径小于等于D v50，且占材料体积50％的颗粒粒径大于D v50。以D v99为例，表示占材料体积99％的颗粒粒径小于等于D v90，且占材料体积1％的颗粒粒径大于D v90。以D v10为例，表示占材料体积10％的颗粒粒径小于等于D v10，且占材料体积90％的颗粒粒径大于D v10。本领域技术人员可以理解D v99、D v90、D v50、D v10的含义，而且可以采用本领域公知的仪器及方法进行测定。例如可以参照GB/T19077-2016粒度分布激光衍射法，采用激光粒度分析仪方便地测定，如英国马尔文仪器有限公司的Mastersizer 2000E型激光粒度分析仪、LS-909激光粒度仪(欧美克)。
在该二次电池的负极活性材料层中，利用较大粒径的单颗粒碳和较小粒径的二次颗粒碳进行复配，二次颗粒碳有利于降低迂曲度，有利于产气的排出，单颗粒碳有利于保持良好的电芯循环性能，延长电池使用寿命。制备包括该负极活性材料层的负极极片的过程中，负极浆料经涂布、干燥后，还需进行压实以便调节厚度、密度、能量密度等参数，在压实(可采用冷压方式)过程中，颗粒与颗粒之间会形成一定的孔隙，这些孔隙之间相互连通，使得负极活性材料层的两侧表面之间存在孔隙连通通路，该孔隙连通通路的路径与负极活性材料层厚度之间的比值即为负极活性材料层的迂曲度。较小粒径的二次颗粒碳的加入能够使孔隙之间更容易形成孔隙连通通路，从而降低迂曲度。对于较低的迂曲度，化成及电池使用过程中的产气沿孔隙连通通路被排出所需时间更短，有利于形成更均质的界面，且界面的稳定性更好。进一步地，较低的迂曲度还可以改善电解液对极片的浸润效果。
在本申请中，涉及“负极极片的迂曲度”，如无其他说明，指负极活性材料层的迂曲度。迂曲度反映了通过一定厚度的负极活性材料层时所通过的孔隙连通通路的路径曲折程度。在数值上，负极活性材料层的迂曲度τ可以等于负极活性材料层的两侧表面之间的孔隙连通通路的实际路径长度与负极活性材料层的厚度之比。迂曲度的理论最低值为1，此时，孔隙连通通路为直通孔，相应的实际路径最短，数值上与负极 活性材料层的厚度一致。迂曲度越大，表明孔隙连通通路的路径曲折程度越高，反之，迂曲度越小，孔隙连通通路的路径曲折程度越低。迂曲度的数值与碳基颗粒的组成及分布、孔隙率、压实程度等因素有关。可参阅图2理解“迂曲度”的概念。图2为本申请一对比例中单颗粒石墨形成的负极极片截面的SEM形貌图(A)及相应的化成排气路径示意图(B)，以及本申请一实施例中由单颗粒石墨与二次颗粒石墨形成的负极极片截面的SEM形貌图(C)及相应的化成排气路径示意图(D)；SEM测试参数包括：工作电压(EHT)为10.00kV，采用InLens探测器，工作距离为4.6mm，放大倍数为1000X。图2中(B)和(D)中单个线条所示孔隙连通通路的实际长度Lt与该线条在纵向上通过的负极活性材料层的厚度L之间的比值(Lt/L)，即可理解为该负极活性材料层的迂曲度。可见，“迂曲度”是一个无量纲参数。
在本申请中，可以通过如下的测试分析方法测算负极极片或其负极活性材料层的迂曲度的数值。待测的负极极片可以为经压实处理(例如采用冷压方式处理)至预设厚度及压实密度之后任意阶段的样品，比如，可以为化成之前的负极极片样品，也可以为化成之后的负极极片样品，还可以为组装成电芯使用一段时间后拆解得到的负极极片样品。对于从电芯中拆解得到的负极极片样品，需要预先将残余电解液清洗去除，比如可以采用无水乙醇洗涤负极极片样品。
可采用包括如下步骤的测试分析方法获取迂曲度数值，但不限于此：
(S10)选取负极极片，其负极活性材料层厚度测定为d。
可以选用本领域已知的方法测试厚度，比如可以比较设置有负极活性材料层及未设置负极活性材料层的基材表面，例如，可以通过台阶仪测试方法进行测试。台阶仪的测针以十分微小的力轻轻划过样品表面，样品表面微米甚至纳米级别的高低起伏通过与测针连接的传感器得到千百万倍的放大，然后被转换成电子信号，输入到电脑软件中，最终以数字和图形的数据形式展现出来。
还可以根据极片厚度方向断面的扫描电镜(SEM)照片的多个位置结果统计得出负极活性材料层的厚度。
(S20)测试负极活性材料层的孔隙率ε：
在本申请中，活性材料层的孔隙率为本领域公知的含义，可以用本领域公知的仪器及方法进行测定，例如可以用美国Micromeritics公司的AccuPyc II 1340型全自动真密度测试仪，参考国标GB/T 24586-2009对铁矿石表观密度、真密度和孔隙率的测定方法进行测试。该方法包括，对极片裁取30片直径为14mm的小圆片，基于气体吸附的原理，使用惰性气体比如氦气或者氮气作为介质，测试30片直径为14mm的小圆片的真体积，然后根据小圆片的面积、厚度和数量计算得到的极片表观体积与真体积的关系，计算得到极片的活性材料层的孔隙率。
还可以采用如下方法获得负极活性材料层的孔隙率ε测试值。利用小分子惰性气体(如He)置换法，结合阿基米德原理和波尔定律，精确测量材料的真实体积V 1，再通过测试计算样品的表观体积得到V 2(根据极片面积乘以负极活性材料层厚度d计算得到V 2)，则孔隙率＝(V 2-V 1)/V 2。
(S30)测试负极极片的离子阻抗Rion：裁取一定面积A的负极极片样品(也即电极有效面积为A)，通过对称电池的方式测试出极片孔隙内部的离子扩散阻抗Rion，可通过测试极片的EIS阻抗得到。
(S40)测试二次电池中电解液的离子电导率k：将相互平行且距离固定的两块极 板(可以使用本申请二次电池中的正极极片和负极极片)，放到电解液中，在极板两端加上一定电势，通过电导仪测量极板之间的电导得到电解液的离子电导率。
(S50)采用如下公式计算迂曲度τ的数值：ε×k×Rion×A/d，该公式中各参数均采用特定单位。所述负极活性材料层的迂曲度τ在数值上等于根据以下公式计算得到的数值：ε×k×Rion×A/d；其中，ε为25℃时所述负极活性材料层的孔隙率；k为25℃时所述电解液的离子电导率，单位为ms/cm；Rion为25℃时所述负极极片的离子电阻，单位为Ω；A为测试Rion时的有效面积，单位为cm 2；d为所述负极活性材料层的厚度，单位为μm。
在本申请中，孔隙率、离子阻抗Rion、离子电导率、电极有效面积和负极活性材料层厚度均具有本领域的公知含义，本领域技术人员能够利用本领域常规方法测试得到本申请二次电池相关参数ε、k、Rion、A和d，可以优先采用前述描述的方法。
在本申请中，ε、k、Rion的测试温度可以在室温下进行，如无其他说明，可以在20℃～30℃(如25℃)条件下进行，进一步地，可以在25℃条件下进行。
在本申请的一些实施方式中，所述负极活性材料层的迂曲度τ在数值上等于根据以下公式计算得到的数值：ε×k×Rion×A/d；其中，ε为25℃时所述负极活性材料层的孔隙率；k为25℃时所述电解液的离子电导率，单位为ms/cm；Rion为25℃时所述负极极片的离子电阻，单位为Ω；A为测试Rion时的有效面积，单位为cm 2；d为所述负极活性材料层的厚度，单位为μm。
所述负极活性材料层的迂曲度τ≤4.75。
在一些实施方式中，所述负极活性材料层的迂曲度τ可以满足τ≤4.70。
在一些实施方式中，所述负极活性材料层的迂曲度τ可以满足τ≤4.70，可选地，τ可以选自3.40～4.70。在一些实施方式中，所述负极活性材料层的迂曲度τ≤4.65，可选地，τ可以选自3.40～4.65。在一些实施方式中，所述负极活性材料层的迂曲度τ≤4.62，可选地，τ可以选自3.42～4.62。在一些实施方式中，所述负极活性材料层的迂曲度τ≤4.05，可选地，τ可以选自3.42～4.05。在一些实施方式中，所述负极活性材料层的迂曲度τ≤3.95，可选地，τ可以选自3.42～3.95。在一些实施方式中，所述负极活性材料层的迂曲度τ≤3.85，可选地，τ可以选自3.45～3.85。在一些实施方式中，所述负极活性材料层的迂曲度τ≤3.82，可选地，τ可以选自3.45～3.82。
在一些实施方式中，所述负极活性材料层的迂曲度τ还可以选自如下任一个数值或者选自如下任两个数值构成的数值区间：3.40、3.42、3.44、3.45、3.46、3.48、3.50、3.52、3.54、3.55、3.56、3.58、3.60、3.62、3.64、3.65、3.66、3.68、3.70、3.72、3.74、3.75、3.76、3.78、3.80、3.82、3.84、3.85、3.86、3.88、3.90、3.92、3.94、3.95、3.96、3.98、4.00、4.05、4.1、4.15、4.2、4.25、4.3、4.35、4.4、4.45、4.5、4.55、4.6、4.65、4.7等。
通过将负极活性材料层的迂曲度控制在合适的范围内，有利于在加快产气排出的同时还保持良好的电池循环性能。二次电池经使用一段时间后，负极活性材料层的迂曲度可能发生一些变化；随着电池的使用时间增加，可能导致极片体积变化，由此导致迂曲度的变化。
在本申请的一些实施方式中，所述负极活性材料层的孔隙率选自30.6％～37.5％。
在一些实施方式中，所述负极活性材料层的孔隙率选自32.2％～37.5％。在一些实施方式中，所述负极活性材料层的孔隙率选自33.8％～37.5％。在一些实施方式中，所 述负极活性材料层的孔隙率选自34.8％～37.5％。在一些实施方式中，所述负极活性材料层的孔隙率选自35.5％～37.5％。
在一些实施方式中，所述负极活性材料层的孔隙率还可以选自如下任一个百分数或者选自如下任两个百分数构成的数值区间：30.6％、31％、31.5％、32％、32.2％、32.5％、33％、33.5％、33.8％、34％、34.5％、34.8％、35％、35.5％、36％、36.5％、37％、37.5％等。
在本申请中，多孔材料的孔隙率为本领域公知的含义，可以采用本领域已知的方法测试。孔隙率由以下等式定义：孔隙率＝(1-(多孔材料的质量[g]/(多孔材料的体积[cm 3]×材料密度)))×100[％]。在本申请中，负极活性材料层的孔隙率可以参考前述的方法，如小分子惰性气体(如He)置换法测试得到。
通过将负极活性材料层的孔隙率控制在合适的范围内，有利于在控制合适迂曲度的同时还保证电解液具有合适的浸润性，从而在加快产气的同时还实现较好的电芯动力学性能。
在本申请的一些实施方式中，所述负极活性材料层的压实密度选自1.30g/cc～1.80g/cc。在一些实施方式中，所述负极活性材料层的压实密度选自1.30g/cc～1.70g/cc。在一些实施方式中，所述负极活性材料层的压实密度选自1.50±0.02g/cc。
所述负极活性材料层的压实密度还可以选自如下任一个数值或者选自如下任两个数值构成的数值区间：1.30、1.32、1.34、1.35、1.36、1.38、1.40、1.42、1.44、1.45、1.46、1.48、1.50、1.52、1.54、1.55、1.56、1.58、1.60、1.62、1.64、1.66、1.68、1.70、1.72、1.74、1.75、1.76、1.78、1.80等。
本申请所使用的“压实密度”具有本领域公知的含义，指的是极片的活性材料层中活性物质的质量与体积的比值。非限制性地，极片的压实密度可采用如下方式测试得到：选择一定的极片涂布面密度，待极片烘干冷压之后，使用游标卡尺测量极片的总厚度，扣除集流体的厚度就可以计算出涂布的厚度。根据涂布面密度及涂布厚度两个参数，就可以计算极片的压实密度。
通过控制压实密度在合适的范围内，有利于在加快产气的同时还提供较好的能量密度，实现良好的循环性能。压实密度越高，对能量密度的提升越有利。但压实密度提高，会导致孔隙率降低，有可能不利于电解液的浸润，影响电池功率的发挥，压实密度越大，孔隙率越小，有可能不利于电解液浸润，导致活性离子(如锂离子)的嵌入难度增加，电池动力学性能变差。
在本申请的一些实施方式中，所述二次颗粒碳在所述碳基颗粒中的质量占比选自10％～90％。在一些实施方式中，所述二次颗粒碳在所述碳基颗粒中的质量占比选自20％～80％。在一些实施方式中，所述二次颗粒碳在所述碳基颗粒中的质量占比选自30％～70％。在一些实施方式中，所述二次颗粒碳在所述碳基颗粒中的质量占比选自30％～50％。
所述二次颗粒碳在所述碳基颗粒中的质量占比还可以选自如下任一个百分数或者选自如下任两个百分数构成的数值区间：10％、15％、20％、25％、30％、35％、40％、45％、50％、55％、60％、65％、70％、75％、80％、85％、90％等。
本申请的发明人经研究发现，在本申请的二次电池中，随着二次颗粒碳的比例增加，负极极片的迂曲度逐渐降低，孔隙率倾向于增大，通过合理控制二次颗粒碳的含量，可以将迂曲度、孔隙率控制在合适的范围内。在一些非限制性示例中，将单颗粒 碳和二次颗粒碳的质量比例控制在7：3，化成排产气结束SOC相对于100％纯单颗粒碳(无二次颗粒碳)排产气结束SOC提前了26％，相对于100％纯二次颗粒碳(无单颗粒碳)循环性能提高了1.7％(以循环400圈为例)。
负极极片
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极膜层，进一步地，至少一个所述负极膜层包括前述的负极活性材料层，任一个所述负极活性材料层含有负极活性物质。
作为非限制性示例，所述负极集流体具有在其自身厚度方向相对的两个表面，进一步地，所述负极膜层设置在所述负极集流体相对的两个表面中的任意一者或两者上。
作为非限制性示例，当在负极集流体的两侧均设置有负极膜层时，两侧的负极膜层可以相同或不同。
作为非限制性示例，当在负极集流体的两侧均设置有负极活性材料层时，两侧的负极活性材料层可以相同或不同。
在本申请中，如无其他说明，“设置于集流体的至少一侧表面上”表示在集流体的厚度方向上，设置在集流体的至少一侧，任一侧可以独立地与集流体直接接触或不直接接触。
作为非限制性示例，前述的负极活性材料层设置在所述负极集流体的至少一侧。在一些实施例中，所述负极活性材料层设置在所述负极集流体的至少一侧表面上，可以设置在负极集流体的一个表面上，也可以设置在负极集流体的两个表面上。在一些实施例中，至少一个所述负极活性材料层与负极集流体直接接触，此时，所述负极活性材料层与所述负极集流体的至少一侧表面(一个或两个表面)直接接触。
在一些实施方式中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，负极活性物质可采用本领域公知的用于电池的负极活性物质。作为非限制性示例，负极活性物质可包括以下材料中的一种或多种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的一种或多种。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的一种或多种。但本申请并不限定于这些物质或材料，还可以使用其他可被用作电池负极活性物质的传统物质或材料。这些负极活性物质可以仅单独使用一种，也可以将两种以上组合使用。
在一些非限制性示例中，所述碳基颗粒主要为碳材料。
在一些非限制性示例中，所述碳基颗粒可以为碳材料，进一步地，所述碳材料可以包括但不限于人造石墨、天然石墨、软炭和硬炭中的一种或多种。在其中的一些非限制性示例中，所述碳材料选自人造石墨、天然石墨、软炭和硬炭中的一种或多种。
在一些实施例中，所述碳材料可以包括但不限于石墨。如本申请中所用的石墨，可以为人造石墨、天然石墨或者其组合。在其中的一些非限制性示例中，所述碳材料为石墨。
在本申请的一些实施方式中，所述负极活性材料层的负极活性物质主要为碳基颗粒。一些实施方式中，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比大于50％。在一些实施方式中，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比选自选自80％～100％。在一些实施方式中，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比选自90％～100％。在一些实施方式中，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比选自95％～100％。在一些实施方式中，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比为100％。所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比还可以选自如下任一个百分数或者选自如下任两个百分数构成的数值区间：60％、70％、75％、80％、82％、84％、85％、86％、88％、90％、92％、94％、95％、96％、97％、98％、99％、100％等。
在本申请的一些实施方式中，所述碳基颗粒主要为石墨材料。在一些实施方式中，所述碳基颗粒中含有质量占比大于50％的石墨材料。在一些实施方式中，所述碳基颗粒中含有质量占比选自80％～100％的石墨材料。在一些实施方式中，所述碳基颗粒中含有质量占比选自90％～100％的石墨材料。在一些实施方式中，所述碳基颗粒中含有质量占比选自95％～100％的石墨材料。在一些实施方式中，所述碳基颗粒中含有质量占比为100％的石墨材料。石墨材料在所述碳基颗粒中的质量占比还可以选自如下任一个百分数或者选自如下任两个百分数构成的数值区间：60％、70％、75％、80％、82％、84％、85％、86％、88％、90％、92％、94％、95％、96％、97％、98％、99％、100％等。
在本申请的一些实施方式中，所述负极活性材料层的负极活性物质主要为石墨材料。在一些实施方式中，所述负极活性材料层的负极活性物质中含有质量占比大于50％的石墨材料。在一些实施方式中，所述负极活性材料层的负极活性物质中含有质量占比选自80％～100％的石墨材料。在一些实施方式中，所述负极活性材料层的负极活性物质中含有质量占比选自90％～100％的石墨材料。在一些实施方式中，所述负极活性材料层的负极活性物质中含有质量占比选自95％～100％的石墨材料。石墨材料在所述负极活性材料层的负极活性物质中的质量占比还可以选自如下任一个百分数或者选自如下任两个百分数构成的数值区间：60％、70％、75％、80％、82％、84％、85％、86％、88％、90％、92％、94％、95％、96％、97％、98％、99％、100％等。
在一些实施方式中，所述负极活性材料层的负极活性物质中含有质量占比为100％的石墨材料。此时，所述碳基颗粒为石墨颗粒，所述单颗粒碳为单颗粒石墨，所述二次颗粒为二次颗粒石墨。
在本申请中，如无其他说明，“单颗粒石墨”指单颗粒形式(也即一次颗粒形式)的石墨，“二次颗粒石墨”指二次颗粒形式的石墨；如无其他说明，单颗粒石墨和二次颗粒石墨中的负极活性物质均为石墨。
采用碳基材料作为负极活性材料层中的主要负极活性物质时，相对于高硅含量等其他种类的负极极片，负极极片的膨胀性更低，固体电解质界面(SEI)膜更稳定，电池安全性更好。
采用石墨作为负极活性材料层中的主要负极活性物质时，在负极活性材料层中，碳基颗粒主要为石墨颗粒，单颗粒碳主要为单颗粒石墨，二次颗粒主要为二次颗粒石墨，此时，可充分利用石墨的导电性好，首效高，来源广等优点。
人造石墨作为负极活性物质时，可以更好地控制负极活性颗粒的形貌及粒径的一 致性，从而使电池性能更加稳定。
在本申请中，采用“主要”表示物质含量时，如无其他说明，含量百分比大于50％，还可以选自≥60％、≥70％、≥80％、≥90％、≥95％、≥96％、≥98％、≥99％、60％～100％、70％～100％、80％～100％、90％～100％、90％～100％、95％～100％、96％～100％、98％～100％、99％～100％等任一种范围，还可以选自如下任一种百分数或者选自如下任两种百分数构成的数值区间：60％、65％、70％、75％、80％、81％、82％、83％、84％、85％、86％、87％、88％、89％、90％、91％、92％、93％、94％、95％、96％、97％、98％、99％、100％等。前述的碳基颗粒的成分描述，负极活性物质的成分描述时涉及的“主要”均可适用这里的定义，比如“碳基颗粒主要为石墨材料”，“负极活性材料层的负极活性物质主要为碳基颗粒”，“负极活性材料层的负极活性物质主要为石墨材料”等。
在本申请的一些实施方式中，所述负极活性材料层具备如下的一个或多个特征(一个、两个或三个特征)：
(ta1)所述单颗粒碳的D v50选自13μm～14μm(所述单颗粒碳的D v5的非限制性示例如下述任一种数值或任两种数值构成的数值区间：13μm、13.1μm、13.2μm、13.3μm、13.4μm、13.5μm、13.6μm、13.7μm、13.8μm、13.9μm、14μm等)；
(ta2)所述二次颗粒碳的D v50选自9.5μm～10.5μm(所述二次颗粒碳的D v50的非限制性示例如下述任一种数值或任两种数值构成的数值区间：9.5μm、9.6μm、9.7μm、9.8μm、9.9μm、10.0μm、10.1μm、10.2μm、10.3μm、10.4μm、10.5μm等)；和
(ta3)所述单颗粒碳的D v50与所述二次颗粒碳的D v50的差值选自3μm～4μm(所述单颗粒碳的D v50与所述二次颗粒碳的D v50的差值的非限制性示例如下述任一种数值或任两种数值构成的数值区间：3μm、3.1μm、3.2μm、3.3μm、3.4μm、3.5μm、3.6μm、3.7μm、3.8μm、3.9μm、4μm等)。
在本申请的一些实施方式中，所述单颗粒碳的D v99大于所述二次颗粒碳的D v99。
在本申请的一些实施方式中，所述负极活性材料层还具备如下的一个或多个特征(一个、两个或三个特征)：
(tb1)所述单颗粒碳的D v99选自37μm～44μm(所述单颗粒碳的D v99的非限制性示例如下述任一种数值或任两种数值构成的数值区间：37μm、37.5μm、38μm、38.5μm、39μm、39.5μm、40μm、40.5μm、41μm、41.5μm、42μm、42.5μm、43μm、43.5μm、44μm等)；
(tb2)所述二次颗粒碳的D v99选自31μm～38μm(所述二次颗粒碳的D v99的非限制性示例如下述任一种数值或任两种数值构成的数值区间：31μm、31.5μm、32μm、32.5μm、33μm、33.5μm、34μm、34.5μm、35μm、35.5μm、36μm、36.5μm、37μm、37.5μm、38μm等)；和
(tb3)所述单颗粒碳的D v99与所述二次颗粒碳的D v99的差值选自4μm～6μm(所述单颗粒碳的D v99与所述二次颗粒碳的D v99的差值的非限制性示例如下述任一种数值或任两种数值构成的数值区间：4μm、4.2μm、4.4μm、4.5μm、4.6μm、4.8μm、5μm、5.2μm、5.4μm、5.5μm、5.6μm、5.8μm、6μm等)。
在本申请的一些实施方式中，所述单颗粒碳的D v10大于所述二次颗粒碳的D v10。
在本申请的一些实施方式中，所述负极活性材料层还具备如下的一个或多个特征(一个、两个或三个特征)：
(tc1)所述单颗粒碳的D v10选自5μm～7μm(所述单颗粒碳的D v10的非限制性示例如下述任一种数值或任两种数值构成的数值区间：5μm、5.2μm、5.4μm、5.5μm、5.6μm、5.8μm、6μm、6.2μm、6.4μm、6.5μm、6.6μm、6.8μm、7μm等)；
(tc2)所述二次颗粒碳的D v10选自3.5μm～5.5μm(所述二次颗粒碳的D v100的非限制性示例如下述任一种数值或任两种数值构成的数值区间：3.5μm、3.6μm、3.8μm、4μm、4.2μm、4.4μm、4.5μm、4.6μm、4.8μm、5μm、5.2μm、5.4μm、5.5μm等)；和
(tc3)所述单颗粒碳的D v10与所述二次颗粒碳的D v99的差值选自1μm～2μm(所述单颗粒碳的D v10与所述二次颗粒碳的D v99的差值的非限制性示例如下述任一种数值或任两种数值构成的数值区间：1μm、1.1μm、1.2μm、1.3μm、1.4μm、1.5μm、1.6μm、1.7μm、1.8μm、1.9μm、2μm等)。
在一些实施例中，所述单颗粒碳的D v50选自13μm～14μm，所述二次颗粒碳的D v50约为10μm；进一步地，在其中的一些实施例中，所述单颗粒碳的D v99约为40.5μm，所述二次颗粒碳的D v99约为34μm；更进一步地，在一些实施例中，所述单颗粒碳的D v10约为6.3μm，所述二次颗粒碳的D v10约为4.5μm。此处涉及的几处“约数”，各自独立地可以表示允许基于10μm具有如±0.01μm、±0.02μm、±0.05μm、±0.1μm等所示的浮动幅度。可参阅下文的实施例1～9，可参见表1。
可以通过控制单颗粒碳及二次颗粒碳的粒径尺寸及分布，从而更好平衡迂曲度、孔隙率及压实程度的多维度性能，从而在加快产气排出的同时，还实现较好的循环性能和功率性能。
进一步地，控制单颗粒碳和二次颗粒碳之间的粒径之差，更有利于充分发挥两者的复配优势，既有利于降低迂曲度及产气的排出，还有利于保持良好的电芯循环性能，延长电池使用寿命。
在本申请的一些实施方式中，所述二次颗粒碳包括多个微颗粒碳，还包括粘合剂，此时，利用粘合剂可以将这些微颗粒碳粘聚成二次颗粒；进一步地，所述微颗粒碳中一次颗粒的数量为一个或多个。
在本申请中，如无其他说明，“微颗粒碳”是二次颗粒碳中的活性物质，微颗粒碳可以视为二次颗粒碳中的一次颗粒形式的碳，可以理解，微颗粒碳中的负极活性物质为碳。在本申请中，“单颗粒碳”是独立的一次颗粒形式的碳颗粒，“微颗粒碳”对应于被粘聚成二次颗粒的一次颗粒单元。
在一些实施方式中，所述二次颗粒碳为二次颗粒石墨，所述微颗粒碳均为微颗粒石墨。
如无其他说明，“微颗粒石墨”一种微小尺寸的一次颗粒形式的石墨，是二次颗粒石墨的组成单元。而“单颗粒石墨”则是独立的一次颗粒形式的石墨。
进一步地，在一些实施方式中，所述微颗粒碳具备如下的一个或多个特征(可以为一个、两个、三个或四个特征)：
(td1)所述微颗粒碳的D v99选自20μm～24μm(非限制性示例如下述任一种数值或任两种数值构成的数值区间：20μm、20.5μm、21μm、21.5μm、22μm、22.5μm、23μm、23.5μm、24μm等)；
(td2)所述微颗粒碳的D v90选自12μm～15μm(非限制性示例如下述任一种数值或任两种数值构成的数值区间：12μm、12.5μm、13μm、13.5μm、14μm、14.5μm、 15μm等)；
(td3)所述微颗粒碳的D v50选自5μm～7μm(非限制性示例如下述任一种数值或任两种数值构成的数值区间：5μm、5.2μm、5.4μm、5.5μm、5.6μm、5.8μm、6μm、6.2μm、6.4μm、6.5μm、6.6μm、6.8μm、7μm等)；和
(td4)所述微颗粒碳的D v10选自2μm～3μm(非限制性示例如下述任一种数值或任两种数值构成的数值区间：2μm、2.1μm、2.2μm、2.3μm、2.4μm、2.5μm、2.6μm、2.7μm、2.8μm、2.9μm、3μm等)。
通过精细地控制微颗粒碳的粒径及分布在合适的范围内，更有利于稳定地控制二次颗粒粒径大小及其分布。
在一些实施方式中，所述粘合剂包括沥青。进一步，所述粘合剂可以主要为沥青。更进一步，在一些实施例中，所述粘合剂为沥青，粘合效果好，且不易引入不利杂质。
在一些实施方式中，所述粘合剂相对于所述多个微颗粒碳的质量比选自1:8.5至1:9.5，也即选自1:(8.5～9.5)。所述粘合剂相对于所述多个微颗粒碳的质量比还可以选自如下任一种比例或者选自如下任两种比例构成的区间：1:8.5、1:8.6、1:8.7、1:8.8、1:8.9、1:9.0、1:9.1、1:9.2、1:9.3、1:9.4、1:9.5等。进一步地，通过控制粘合剂(如沥青)的用量，可以较好地实现二次颗粒碳的预设粒径及分布。
在一些实施方式中，所述二次颗粒是由所述多个微颗粒碳和所述粘合剂粘聚而成。原料少，制备方便。
在本申请的一些实施方式中，所述二次颗粒碳的表面包含无定形碳。在一些实施方式中，所述二次颗粒碳包含碳基芯和位于所述碳基芯表面至少一部分的无定形碳层。可以通过在表面引入有机碳材料(沥青)后于适合温度下进行热处理得到，可以在有机碳材料(如沥青)熔点以上、石墨化温度以下进行热处理，进一步地，可以在预碳化温度附近(可以稍高于预碳化温度)进行热处理，例如可以在1100℃～1200℃下进行热处理，热处理时间可以根据向无定形碳的转化程度进行灵活控制，例如可以为4h～6h。经过热处理，可以将表面包覆的有机碳材料(沥青)转化为无定形碳。还可以参考本申请的第二方面中所描述的包覆无定形碳层的方法。
在本申请中，前述“碳基芯”包含负极活性物质。在一些非限制性示例中，该碳基芯由负极活性物质组成。应当理解，碳基芯的负极活性物质中含有能够使活性离子(如锂离子)嵌入与脱出的碳。
在一些实施方式中，所述无定形碳层在所述二次颗粒碳表面的厚度≤500nm。在一些实施方式中，所述无定形碳层在所述二次颗粒碳表面的厚度选自200nm～500nm。所述无定形碳层在所述二次颗粒碳表面的厚度还可以选自如下任一种或者任两种构成的区间：200nm、210nm、220nm、230nm、240nm、250nm、260nm、270nm、280nm、290nm、300nm、320nm、350nm、360nm、380nm、400nm、420nm、450nm、480nm、500nm等。
在一些实施方式中，所述无定形碳层在所述二次颗粒碳中的质量含量≤3.3％。在一些实施方式中，所述无定形碳层在所述二次颗粒碳中的质量含量选自1.3％～3.3％。所述无定形碳层在所述二次颗粒碳中的质量含量还可以选自如下任一种百分数或者任两种百分数构成的区间：1.3％、1.4％、1.5％、1.6％、1.7％、1.8％、1.9％、2.0％、2.1％、2.2％、2.3％、2.4％、2.5％、2.6％、2.7％、2.8％、2.9％、3.0％、3.1％、3.2％、3.3％等。
在一些实施方式中，所述无定形碳层在所述二次颗粒碳中的体积占比≤3.3％。在 一些实施方式中，所述无定形碳层在所述二次颗粒碳中的体积占比选自1.3％～3.3％。所述无定形碳层在所述二次颗粒碳中的体积占比还可以选自如下任一种百分数或者任两种百分数构成的区间：1.3％、1.4％、1.5％、1.6％、1.7％、1.8％、1.9％、2.0％、2.1％、2.2％、2.3％、2.4％、2.5％、2.6％、2.7％、2.8％、2.9％、3.0％、3.1％、3.2％、3.3％等。
在一些实施方式中，所述单颗粒碳表面也可以包覆无定形碳层；该无定形碳层的厚度≤500nm。在一些实施方式中，所述无定形碳层在所述单颗粒碳表面的厚度选自200nm～500nm。所述无定形碳层在所述单颗粒碳表面的厚度还可以选自如下任一种或者任两种构成的区间：200nm、210nm、220nm、230nm、240nm、250nm、260nm、270nm、280nm、290nm、300nm、320nm、350nm、360nm、380nm、400nm、420nm、450nm、480nm、500nm等。
进一步地，在一些实施方式中，所述无定形碳层在所述单颗粒碳中的质量含量≤3.3％。在一些实施方式中，所述无定形碳层在所述单颗粒碳中的质量含量选自1.3％～3.3％。所述无定形碳层在所述单颗粒碳中的质量含量还可以选自如下任一种百分数或者任两种百分数构成的区间：1.3％、1.4％、1.5％、1.6％、1.7％、1.8％、1.9％、2.0％、2.1％、2.2％、2.3％、2.4％、2.5％、2.6％、2.7％、2.8％、2.9％、3.0％、3.1％、3.2％、3.3％等。
进一步地，在一些实施方式中，所述无定形碳层在所述单颗粒碳中的体积占比≤3.3％。在一些实施方式中，所述无定形碳层在所述单颗粒碳中的体积占比选自1.3％～3.3％。所述无定形碳层在所述单颗粒碳中的体积占比还可以选自如下任一种百分数或者任两种百分数构成的区间：1.3％、1.4％、1.5％、1.6％、1.7％、1.8％、1.9％、2.0％、2.1％、2.2％、2.3％、2.4％、2.5％、2.6％、2.7％、2.8％、2.9％、3.0％、3.1％、3.2％、3.3％等。
在本申请的一些实施方案中，至少一部分碳基颗粒的表面包覆有无定形碳层，该无定形碳层的厚度、其在碳基颗粒中的质量含量、其在碳基颗粒中的体积占比可以参考前述无定形碳层包覆于二次颗粒碳表面或单颗粒碳表面时的定义。
在本申请中，无定形碳层的确认可以采用本领域中测试碳物质结晶形态的常规方法测试得到，比如可以采用拉曼(Raman)光谱法测试分析，可根据图谱中碳成分的特征峰信息(如D峰/G峰的强度比，I D/G)对无定形碳层的形成与否进行分析。其中，D峰、G峰均是碳原子晶体的Raman特征峰，D峰代表碳原子晶的缺陷，缺陷越多，D峰强度越大，D峰强度可反映无定形(乱层堆叠)区域的含量，G峰代表碳原子sp2杂化的面内伸缩振动，G峰强度可反映石墨化(层状结构)区域的含量；随着碳原子的无序化程度的增加，D峰与G峰的强度比也随之增加。可根据包覆前后颗粒表面成分的I D/G(D峰/G峰的强度比)是否构成具有统计学意义上显著性差异的变化(例如p<0.05、p<0.01等)，也即根据包覆后引入的乱层结构与未包覆之前的I D/G偏离程度来确定是否形成了无定形碳层，这对本领域技术人员来说是容易判断的。还可以比较待测颗粒特定结构层的拉曼图谱I D/G与石墨的标准拉曼图谱I D/G之间的差异性来判断是否为无定形碳层。
还可以根据判断是否形成了无定形碳层。石墨化度可以采用本领域已知的方法测试，石墨化度越高，表明无序化程度越低。例如石墨化度可以使用X射线衍射仪(如Bruker D8Discover)测试，测试可参考JIS K 0131-1996、JB/T 4220-2011，测出d 002的大小，然后根据公式G＝(0.344-d 002)/(0.344-0.3354)计算得出石墨化度，其中d 002是以 纳米(nm)表示的人造石墨晶体结构中的层间距。
在本申请中，关于“无定形碳层”在碳基颗粒(如二次颗粒碳或单颗粒碳)中的体积占比，可以通过透射电镜(TEM)形貌观察结合数据分析得到。对负极极片进行裁剪，从断面处刮取粉末样品，进行TEM测试，比较包覆有无定形碳层及未包覆无定形碳层的碳基颗粒，在包覆无定形碳层的碳基颗粒表面，可以观测到明显的界面，从而可从TEM照片上估算出该位置无定形碳层的厚度，可以从多个不同的断面位置进行分析，取平均值作为无定形碳层的厚度。假定碳基颗粒为球状，根据无定形碳层的厚度，结合碳基颗粒的粒径统计数据，可以根据碳基颗粒的体积、碳基芯的体积估算出无定形碳层在碳基颗粒中的体积占比；进一步地，根据单个碳基颗粒的平均质量，碳基芯的体积(可推算得到，亦可根据TEM测试照片统计得到)、碳基芯的密度，可以估算出无定形碳层在碳基颗粒中的质量含量。
在一些实施方式中，所述碳基芯包含负极活性物质，所述负极活性物质为石墨。也即，此时碳基芯中的负极活性物质为石墨。
本申请的发明人经过研究和探索发现，通过在二次颗粒碳表面的至少一部分包覆无定形碳，可以改善电池的快充性能(比如，比较下述的实施例10和实施例4，实施例4的快充性能有所改善)。此外，在单颗粒碳表明的至少一部分包覆无定形碳也可以改善电池的快充性能。通过合理控制无定形碳的含量，可以在确保良好的电池循环性能的情况下改善电池快充性能。
发明人还意外发现，在碳基颗粒表面包覆了无定形碳时，以二次颗粒碳为例，随着二次颗粒碳比例的增加，电芯的循环寿命可能会降低，发明人推测可能是由于无定形碳表面活性相对于碳基芯(如石墨)的表面活性高，从而可能降低负极在循环过程中的稳定性；此时，可以通过合理控制二次颗粒碳在碳基颗粒中的质量比(如控制在30％～50％，还可参考前文所描述的任意合适的质量比)，从而更好地平衡对产气排除、容量和电池循环稳定性的需求，同时实现低迂曲度和高容量保持率。
在一些实施方式中，负极膜层还可选地包括粘结剂。所述粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的一种或多种。
在一些实施方式中，负极膜层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种或多种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体的至少一侧表面上(可以为单个表面上，也可以为两个表面上)，经烘干、压实(可采用冷压方式)等工序后，即可得到负极极片。
正极极片
正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，至少一个所述正极膜层包括正极活性材料层，任一个所述正极活性材料层含有正极活性物质。
作为非限制性示例，所述正极集流体具有在其自身厚度方向相对的两个表面，进一步地，所述正极膜层设置在所述正极集流体相对的两个表面的其中任意一者或两者上。
在一些实施方式中，所述正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在本申请中，所述二次电池可以为锂离子电池。其中，所述正极活性物质包括锂离子材料(非限制性示例如锂磷酸盐、锂过渡金属氧化物及前述任一种的改性物等)。
在一些实施方式中，正极活性材料可采用本领域公知的用于电池的正极活性物质。作为非限制性示例，正极活性物质可包括以下材料中的一种或多种：橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。但本申请并不限定于这些材料，还可以使用其他可被用作电池正极活性物质的传统材料或物质。这些正极活性物质可以仅单独使用一种，也可以将两种以上组合使用。其中，锂过渡金属氧化物的非限制性示例可包括但不限于锂钴氧化物(如LiCoO 2)、锂镍氧化物(如LiNiO 2)、锂锰氧化物(如LiMnO 2、LiMn 2O 4)、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物(如LiNi 1/3Co 1/3Mn 1/3O 2(也可以简称为NCM 333)、LiNi 0.5Co 0.2Mn 0.3O 2(也可以简称为NCM 523)、LiNi 0.5Co 0.25Mn 0.25O 2(也可以简称为NCM 211)、LiNi 0.6Co 0.2Mn 0.2O 2(也可以简称为NCM 622)、LiNi 0.8Co 0.1Mn 0.1O 2(也可以简称为NCM 811)、锂镍钴铝氧化物(如LiNi 0.85Co 0.15Al 0.05O 2)及其改性化合物等中的一种或多种。橄榄石结构的含锂磷酸盐的非限制性示例可包括但不限于磷酸铁锂(如LiFePO 4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、磷酸锰锂(如LiMnPO 4)、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料中的一种或多种。
在一些实施方式中，正极膜层还可选地包括粘结剂。作为非限制性示例，所述粘结剂可以包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物及含氟丙烯酸酯树脂中的一种或多种。
在一些实施方式中，正极膜层还可选地包括导电剂。作为非限制性示例，所述导电剂可以包括超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种或多种。
在一些实施方式中，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如正极活性物质、导电剂、粘结剂和任意其他的组分分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体的至少一侧表面上(可以为单个表面上，也可以为两个表面上)，经烘干、冷压等工序后，即可得到正极极片。
电解质
电解质在正极极片和负极极片之间起到传导离子的作用。本申请采用液态电解质，也即采用电解液。所述电解液包括电解质盐和溶剂。在锂离子二次电池中，电解质盐可以包括电解质锂盐。
在一些实施方式中，电解质锂盐可以包括六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiCF 3SO 3)、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂(LiBOB)、二氟二草酸磷酸锂及四氟草酸磷酸锂中的一种或多种。
在一些实施方式中，电解液中的溶剂为有机溶剂。在一些实施方式中，电解液中的有机溶剂可以包括碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的一种或多种。
在一些实施方式中，所述电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
隔离膜
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
电极组件、二次电池
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图3是作为一个示例的方形结构的二次电池5。
在一些实施方式中，参照图4，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据实际需求进行选择。
在本申请的第二方面，提供一种用电装置，其包括本申请第一方面所述二次电池。可以兼顾用电装置的安全性及使用寿命等性能。
本申请第一方面所述二次电池可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以包括移动设备、电动车辆、电气列车、船舶及卫星、储能系统等，但不限于此。其中，移动设备例如可以是手机、笔记本电脑 等；电动车辆例如可以是纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等，但不限于此。
作为所述用电装置，可以根据其使用需求来选择二次电池。
图5是作为一个示例的用电装置6。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
在本申请的第三方面，提供一种负极极片的制备方法，可用于制备本申请第一方面所述二次电池中使用的负极极片。
在本申请的一些实施方式中，提供一种负极极片的制备方法，其包括如下步骤：
S100：制备单颗粒碳；其中，所述制备单颗粒碳的步骤包括：将原料(如生焦原料，进一步如石油焦)破碎，分级，预碳化，石墨化和筛分；
S200：制备微颗粒碳，将所述微颗粒碳和粘合剂混合，于所述粘合剂熔融状态下造粒，预碳化，石墨化，可选地包覆，筛分，制备二次颗粒碳；其中，所述制备微颗粒碳的步骤包括：将原料(如生焦原料，进一步如石油焦)破碎、分级、筛分；
S300：将所述单颗粒碳、所述二次颗粒碳、助剂和溶剂混合，制备负极浆料；
S400：将所述负极浆料涂布于负极集流体的至少一侧表面，干燥，压实，制备得到所述负极极片；
其中，所述单颗粒碳和所述二次颗粒碳如本申请第一方面中所定义；所述微颗粒碳如本申请第一方面中所定义。
其中，S100用于制备单颗粒碳，S200用于制备二次颗粒碳。
在一些实施方式中，所述生焦原料可以包括生石油焦、生沥青焦、冶金焦等中的一种或多种，在其中的一些优选例中，所述生焦原料包括生石油焦。在一些实施方式中，所述生焦原料为非针状焦。所述非针状焦可以包括非针状生石油焦和非针状生沥青焦中的一种或多种。在其中的一些优选例中，所述非针状焦包括非针状生石油焦。
在本申请中，如无其他说明，“预碳化”是在相对低温条件下(如1100±50℃)对非石墨的碳基材料进行热处理的过程，经预碳化处理后，碳基颗粒收缩，结构变得更为致密。“非石墨的碳基材料”指其中的碳不完全为石墨，可以不含任何石墨成分。
在本申请中，如无其他说明，“石墨化”是指在相对高温条件下(如大于2800℃)对非石墨的碳基原料(如经预碳化后得到的碳基材料)进行热处理的过程，经石墨化处理后，六角碳原子平面网络从二维空间的无序排列(如乱层结构或无定形碳)转变为三维空间的有序排列的石墨结构。
制备单颗粒石墨及二次颗粒石墨时，均涉及预碳化和石墨化的步骤。可以对非石墨的碳在相对低温条件下(如1100±50℃)进行预碳化处理后，碳颗粒收缩，结构变得更为致密。可以对非石墨的(如经预碳化后得到的碳)进行石墨化处理后，六角碳原子平面网络从二维空间的无序排列(如乱层结构或无定形碳)转变为三维空间的有序排列的石墨结构。
制备二次颗粒碳时，“粘合剂熔融状态下造粒”的过程中，粘合剂(如沥青)一方面起到粘合剂的作用，另一方面粘合剂中的游离碳α、沥青质β等碳物质流动状态下填充在微颗粒碳表面，经后续的预碳化、石墨化等工序处理后，可以得到预设粒径、表面更均匀的二次颗粒碳。此外，造粒步骤往往还包括粉碎子步骤，将发生聚合的颗 粒解聚，从而更好地控制二次颗粒碳的粒径及分布。“于所述粘合剂熔融状态下”相对于预碳化而言为低温条件，例如500℃～600℃，非限制性示例如500℃、550℃、600℃等。可以理解，造粒在高于粘合剂软化点的温度条件下进行，所需时间如2h～10h。一些非限制性示例中，可以采用例如1℃/min～5℃/min的升温速率将温度升至预设温度后进行保温，升温速率的非限制性示例如1℃/min、1.2℃/min、1.25℃/min、1.3℃/min、1.35℃/min、1.4℃/min、1.5℃/min、2℃/min、2.5℃/min、3℃/min、3.5℃/min、4℃/min、4.5℃/min、5℃/min等。一些非限制性示例中，自室温(如20℃～30℃，进一步如25℃)至预设温度(如500℃～600℃)需要4h～6h，升温速率可以为1.3℃/min～2.5℃/min，进一步可以为1.3℃/min～2.4℃/min。
在一些实施方式中，所述预碳化每次出现，独立地包括如下步骤：于1050℃～1150℃(如1100℃)加热处理(保温处理)。在一些实施例中，加热时间(保温时间)为24h～72h(如24h、36h、40h、48h等，还如36h～40h)；在一些实施例中，所述预碳化在惰性气体条件下进行。在一些非限制性示例中，进行预碳化的保温步骤之前，可以采用例如1℃/min～10℃/min的升温速率将温度升至预设温度后进行保温，升温速率的非限制性示例如1℃/min、1.3℃/min、1.4℃/min、1.5℃/min、1.6℃/min、1.8℃/min、2℃/min、3℃/min、4℃/min、5℃/min、6℃/min、8℃/min、10℃/min等。一些非限制性示例中，自室温(如20℃～30℃，进一步如25℃)至预设温度(如1050℃～1150℃)需要10h～12h，升温速率可以为1.3℃/min～2.5℃/min，进一步可以为1.4℃/min～2℃/min，进一步可以为1.5℃/min～1.8℃/min。
在一些实施方式中，所述石墨化每次出现，独立地包括如下步骤：于>2800℃的温度条件下加热处理。在一些实施例中，加热温度(保温温度)为2850℃～3100℃(如3000℃)。在一些实施例中，加热时间(保温时间)为30h～96h(如36h、40h、48h、60h、72h等，还如36h～48h)。在一些实施例中，所述石墨化在惰性气体条件下进行。在一些非限制性示例中，进行石墨化的保温步骤之前，可以采用例如1℃/min～15℃/min的升温速率将温度升至预设温度后进行保温，升温速率的非限制性示例如1℃/min、1.5℃/min、2℃/min、2.5℃/min、3℃/min、3.5℃/min、4℃/min、4.5℃/min、5℃/min、6℃/min、8℃/min、10℃/min、12℃/min、15℃/min等。一些非限制性示例中，自室温(如20℃～30℃，进一步如25℃)至预设温度(如2850℃～3100℃)需要24h～36h，相应的升温速率可以为1.3℃/min～2.5℃/min，进一步可以为1.5℃/min～2℃/min。
在一些实施方式中，所述包覆包括如下步骤：将物料与有机碳材料(如沥青)按照一定质量比例混合，于合适温度下(保温温度，如1100℃～1200℃，进一步如1150℃)加热处理制备包含包覆层的二次颗粒。在一些实施例中，加热时间(保温时间)为12h～24h(如12h、15h、16h、18h、20h等，还如12h～16h)。在一些实施例中，所述包覆在惰性气体条件下进行。在一些实施例中，所述包含包覆层的二次颗粒中的包覆层中包含无定形碳。在一些非限制性示例中，进行包覆的保温步骤之前，可以采用例如1℃/min～10℃/min的升温速率将温度升至预设温度后进行保温，升温速率的非限制性示例如1℃/min、1.3℃/min、1.4℃/min、1.5℃/min、1.6℃/min、1.8℃/min、2℃/min、3℃/min、4℃/min、5℃/min、6℃/min、8℃/min、10℃/min等。一些非限制性示例中，自室温(如20℃～30℃，进一步如25℃)至预设温度(如 1100℃～1200℃)的升温速率可以为1.3℃/min～2.5℃/min，更进一步如1.5℃/min～1.8℃/min。在一些实施例中，在包覆步骤中，将物料与有机碳材料(如沥青)混合后，还可以先在相对低温条件下(500℃～600℃)预热处理，使有机碳材料(如沥青)充分熔融，然后再升温至预设温度(如1100℃～1200℃，进一步如1150℃)进行预碳化处理。可以采用如1℃/min～5℃/min(进一步如1.3℃/min～2℃/min)的升温速率将温度升至预设温度后进行预热(500℃～600℃保温)，升温速率的非限制性示例如1℃/min、1.5℃/min、2℃/min、2.5℃/min、3℃/min、3.5℃/min、4℃/min、4.5℃/min、5℃/min等。还需要注意的是，包覆无定形碳层时，需要合理控制升温速率，如果升温速率较快，容易导致包覆层碳的缺陷较多，而碳颗粒表面的缺陷较多时会不利于电池循环性能。
在一些实施方式中，有机碳材料可以包括沥青、酚醛树脂、糠醛树脂和环氧树脂中的一种或多种。在一些实施方式中，有机碳材料包括沥青。
向物料表面包覆无定形碳层的步骤中，有机碳材料(如沥青)质量在物料和有机碳材料(如沥青)的质量总和中的占比可以参考前述第一方面中无定形碳层在二次颗粒碳中的质量占比。在一些实施例中，有机碳材料(如沥青)质量在物料和有机碳材料(如沥青)的质量总和中的占比≤3.3％，进一步可以为1.3％～3.3％，还可以选自如下任一种百分数或者任两种百分数构成的区间：1.3％、1.4％、1.5％、1.6％、1.7％、1.8％、1.9％、2.0％、2.1％、2.2％、2.3％、2.4％、2.5％、2.6％、2.7％、2.8％、2.9％、3.0％、3.1％、3.2％、3.3％等。
在本申请中，制备单颗粒碳和二次颗粒碳时，所述涉及的“惰性气体”只要能够避免气体发生副反应即可，包括无氧条件以避免原料中的化学成分在高温条件下发生氧化。在一些非限制性示例中，惰性气体包括氮气、氦气、氩气、氖气等中的一种或多种。在一些非限制性示例中，惰性气体包括氮气。
在一些实施方式中，所述单颗粒碳为单颗粒石墨；所述微颗粒碳为微颗粒石墨。
在一些实施方式中，所述粘合剂为沥青。在一些实施方式中，所述粘合剂相对于多个所述微颗粒碳的质量比选自1:8.5至1:9.5，非限制性示例如1:8.5、1:8.6、1:8.7、1:8.8、1:8.9、1:9.0、1:9.1、1:9.2、1:9.3、1:9.4、1:9.5等，还可以选自上述任两个比例构成的区间。可以参考前文的二次颗粒中微颗粒碳和粘合剂的质量比。
在一些实施方式中，所述惰性气体条件每次出现，独立地为氮气条件。
通过控制预碳化、石墨化、造粒、包覆等步骤的相关参数，各参数之间相互协同配合，可以更好地控制单颗粒碳、二次颗粒碳的复配，从而将迂曲度控制在较为合适的范围内，在有利于产气排出的同时，还保持良好的电芯循环性能，延长电池使用寿命。比如，在二次颗粒表面包覆无定形碳的过程中，可以通过控制有机碳材料(如沥青)用量、温度曲线从而较好地控制无定形碳的包覆量，从而在保持良好循环性能的情况下还改善电池的快充性能。
在一些实施方式中，所述单颗粒碳采用依次包括如下步骤的方法制得：将原料破碎，分级，于1050℃～1150℃)预碳化，于>2800℃的温度条件下石墨化，筛分，制得所述单颗粒碳。对分级后的物料进行预碳化之前，还可以增加混料步骤，以便得到预设粒径及分布的物料。
在一些实施方式中，制备单颗粒石墨的步骤包括：将原料(如生焦原料，进一步如石油焦)破碎、分级→混料→预碳化→石墨化。
制备单颗粒石墨的过程中，所述预碳化和石墨化的温度及时间条件可以各自独立地或者相组合地选自前述任意合适的温度条件。
在一些实施方式中，所述二次颗粒采用依次包括如下步骤的方法制得：制备所述微颗粒碳，将所述微颗粒碳和所述粘合剂混合，于500℃～600℃下造粒，于1050℃～1150℃预碳化，于>2800℃的温度条件下石墨化，可选地于1100℃～1200℃下包覆，筛分，制得所述二次颗粒碳。
在一些实施方式中，制备二次颗粒石墨的步骤包括：将原料(如生焦原料，进一步如石油焦)破碎、分级→混料(混合原料和粘合剂(如沥青))→造粒(低温热处理)→粉碎(将团聚的颗粒解聚)→预碳化→石墨化→包覆无定形碳层(可选步骤)。
制备二次颗粒石墨的过程中，所述造粒、预碳化、石墨化和包覆的温度及时间条件可以各自独立地或者任意合适方式组合地选自前述任意合适的温度条件。
以下，说明本申请的一些实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明技术或条件的，按照上文中的描述进行，或者按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品，或者可通过市购产品按照常规方式合成。
下面的实施例中，“室温”是指20℃～30℃，“wt％”表示质量占比。
以下各例中，如无特别说明，“惰性气体条件”为氮气条件。
人造石墨活性材料的制备
本申请中，制备单颗粒碳(如单颗粒石墨)时，涉及升温程序，如无特别限定，升温速率可以选自0.5℃/min～15℃/min。涉及降温程序时，如无特别限定，可以采用随炉冷却等方式降温。例如，进行预碳化前的升温速率可以为1℃/min～10℃/min，进行石墨化前的升温速率可以为1℃/min～15℃/min。
制备二次颗粒碳(如二次颗粒石墨)的过程中，涉及升温程序，如无特别限定，升温速率可以选自0.5℃/min～15℃/min。涉及降温程序时，如无特别限定，可以采用随炉冷却等方式降温。例如，粘合造粒前的升温速率可以为1℃/min～5℃/min，进行预碳化前的升温速率可以为1℃/min～10℃/min，进行石墨化前的升温速率可以为1℃/min～15℃/min，包覆无定形碳前的升温速率可以为1℃/min～10℃/min，如果在包覆前还设置预热程序(如500～600℃)可以采用1℃/min～5℃/min的升温速率。
以下的各制备例中，如无特别说明，进行粘合造粒时，自室温升温至预设温度(500℃～600℃)的升温速率为1.3℃/min～2.4℃/min，需4h～6h；进行预碳化时，自室温升温至预设温度(1100℃)的升温速率为1.5℃/min～1.8℃/min，需要10h～12h；进行石墨化时，自室温升温至预设温度(3000℃)的升温速率为1.5℃/min～2℃/min；包覆无定形碳时，自室温升温至预设温度(1150℃)的升温速率为1.5℃/min～1.8℃/min。
制备例1.单颗粒石墨的制备
(1)原料粉碎、分级：将原料焦(石油焦)在机械磨(冲击磨设备)下进行粉碎，分级，监测D v10、D v50和D v99，控制在相对较大的预设尺寸，并使颗粒粒径分布达到预设分布范围，然后进入预碳化工序。
(2)预碳化：在1100℃惰性气体环境下进行加热处理48h(包括自室温的升温时间)，进一步排出挥发分，进一步收缩和致密化，有利于提高材料强度和提高后续 石墨化松装密度。
(3)石墨化：预碳化结束后，直接在3000℃(大于2800℃)的惰性气体环境下进行石墨化处理72h(包括自室温的升温时间)。
(4)筛分：将第(3)步得到的物料进行筛分，除磁，得到预设粒径要求的单颗粒石墨。
本例中，制备得到的单颗粒石墨的粒径如下：D v10为6.3微米，D v50为13.5微米，D v99为40.5微米。
制备例2.二次颗粒石墨的制备
(1)原料粉碎、分级：将原料焦(石油焦)在机械磨(冲击磨设备)下进行粉碎，分级，并使颗粒粒径分布达到预设分布范围，监测D v10、D v50、D v90和D v99，控制在预设尺寸，得到一次碳颗粒，然后进入粘合造粒工序。
本例中，制备得到的微颗粒石墨的粒径：D v10为2～3微米，D v50为5～7微米，D v50为12～15微米D v99为20～24微米。
(2)粘合造粒：在惰性气体条件下，将第(1)制备的分散碳颗粒与粘合剂沥青按照质量比9:1混合，升温至500℃～600℃进行热处理4～6h，通过调节升温曲线控制颗粒粒径，监测D v10、D v50和D v99，控制在预设尺寸。采用粉体解聚打散机进行粉碎，使团聚的颗粒解聚。
(3)预碳化：第(2)步的低温热处理结束后，在1100℃惰性气体环境下进行加热处理48h(包括自室温的升温时间)，进一步排出挥发分，进一步收缩和致密化，有有利于提高材料强度和提高后续石墨化松装密度。
(4)石墨化：预碳化结束后，直接在3000℃(大于2800℃)的惰性气体环境下进行石墨化处理72h(包括自室温的升温时间)，得到石墨化二次颗粒。
(5)包覆(可选步骤)：将第(4)步制备得到的石墨化二次颗粒与沥青按照一定质量比(参照表1)充分混合，在1150℃惰性气体环境下进行加热处理20h(包括自室温的升温时间)。
(6)筛分：将第(4)步或第(5)步得到的物料进行筛分，除磁，得到符合预设粒径要求的二次颗粒石墨。
本例中，制备得到的二次颗粒石墨的粒径如下：D v10为4.5微米，D v50为10.5微米，D v99为34微米。
二次颗粒的表面层表征
1、无定形碳的表征
利用拉曼光谱测试分析石墨的D峰/G峰的强度比(I D/G)，再测试碳基颗粒表面层在无定形碳层包覆前后的I D/G偏离程度，从而判断待检测的碳基颗粒表面是否存在无定形层。形成无定形碳层后，I D/G发生统计学意义上的显著变化(p<0.01)，本领域技术人员可以判断做出是否形成了无定形碳层的准确判断。
其中，如前文所描述，石墨的拉曼图谱中，D峰强度可反映无定形(乱层堆叠)区域的含量，G峰强度可反映石墨化(层状结构)区域的含量。
2、无定形碳层的厚度、质量表征
无定形碳层厚度：透射电镜(TEM)分析，对负极活性材料层多个位置的断面处的碳基颗粒进行测试，根据TEM照片中指示的无定形碳层与碳基芯之间形成的明显分界线，统计估算出包覆层的平均值，作为本申请中无定形碳层的厚度。
无定形碳层的质量占比分析：假定碳基颗粒为球状，根据无定形碳层的厚度，结合碳基颗粒的粒径统计数据，可以根据碳基颗粒的体积、碳基芯的体积估算出无定形碳层在碳基颗粒中的体积占比；进一步地，根据单个碳基颗粒的平均质量，碳基芯的体积(可推算得到，亦可根据TEM测试照片统计得到)、碳基芯的密度，可以估算出无定形碳层在碳基颗粒中的质量占比。
根据测试结果，各实施例制备的包覆有无定形碳层的二次颗粒碳中，无定形碳层的厚度均控制在200nm～500nm范围内，无定形碳层在二次颗粒碳中的质量占比均控制在1.3％～3.3％范围内。
3、粒径测试
待测样品处理：取一洁净50mL烧杯，加入适量待测颗粒样品0.5g左右，滴加1～2滴洗手液(蓝月亮牌，含有十二烷基磺酸钠等表面活性剂)，再加入20mL去离子水，超声处理5min，超声功率为120W，使样品充分分散。
粒径尺寸类型：D v10、D v50、D v90、D v99测试。
设备型号：马尔文2000(MasterSizer 2000)激光粒度仪，参考标准流程：GB/T19077-2016/ISO 13320:2009，详细测试流程：取待测样品适量(样品浓度保证8％～12％遮光度即可)，加入20mL无水乙醇，超声处理5min(53KHz/120W)，使样品从犯分散，之后按照GB/T19077-2016/ISO 13320:2009标准对样品进行测定。
实施例1.
(1)负极浆料制备
将负极活性材料人造石墨(单颗粒石墨和二次颗粒石墨，参阅表1)和导电剂(导电碳SP)在搅拌罐中干混5min，然后加入分散剂(羧甲基纤维素钠)干混20min，再加入去离子水搅拌，保持固含量在60wt％左右，搅拌120min，最后加入粘结剂(水性粘结剂丁苯橡胶乳液)和去离子水，保持固含量在50wt％左右，并且保持真空度≤-0.05MPa，整个加工搅拌过程温度保持在5℃～50℃。制备得到负极浆料。
其中，单颗粒石墨、二次颗粒石墨、导电碳SP、丁苯橡胶乳液、羧甲基纤维素钠的质量份数分别为84.6份、9.4份、2份、2.5份和1.5份，也即质量比为84.6:9.4:2:2.5:1.5。
(2)负极极片的制备
将第(1)步制备得到的负极浆料均匀涂覆于厚度为6μm的集流体铜箔的双侧表面上，单侧涂覆量约为9.74mg/cm 2，烘干、冷压，然后进行切边、裁片、分条后，得到负极极片。
(3)正极极片的制备
将正极活性材料磷酸铁锂、导电剂SP、粘结剂聚偏二氟乙烯按质量比96:1.5:2.5在N-甲基吡咯烷酮溶剂体系中充分搅拌混合均匀后，得到正极浆料。
将正极浆料均匀涂覆于厚度为13μm的集流体铝箔的双侧表面上，单侧涂覆量约为20.13mg/cm 2，烘干、冷压，然后进行切边、裁片、分条后，得到正极极片。
(4)电解液的制备
在氩气气氛手套箱中(H 2O含量低于0.1ppm，O 2含量低于0.1ppm，其中ppm表示百万分之一体积比)，将碳酸乙烯酯(EC)和碳酸甲乙酯(EMC)按照体积比3:7混合均匀，加入锂盐LiPF 6，搅拌均匀，制备得到电解液。锂盐LiPF 6在电解液中的质量百分浓度为12.5％。
(5)隔离膜
以聚乙烯(PE)多孔聚合薄膜作为隔离膜。
(6)锂离子电池的制备
将负极极片(第(2)步制备)、隔离膜和正极极片(第(3)步制备)按顺序叠好，使隔离膜处于正负极极片中间起到隔离的作用，并卷绕得到裸电芯，之后插入电池壳体，经烘烤、注液、静置、封装、化成、分容等工序，制备得到锂离子电池，此为锂离子二次电池。
实施例2～7.改变单颗粒石墨和二次颗粒石墨的用量比
实施例2～7分别采用与实施例1基本相同的方法，区别在于：负极活性材料中的单颗粒石墨与二次颗粒石墨的质量比不同，可参见表1，实施例2～7的其他步骤分别与实施例1相同。
实施例8.采用与实施例1基本相同的方法，区别在于：负极活性材料中的单颗粒石墨粒径、二次颗粒石墨粒径、二次颗粒石墨中的微颗粒粒径不同，且单颗粒石墨与二次颗粒石墨的质量比为6:4，可参见表1，实施例8的其他步骤分别与实施例1相同。
实施例9.采用与实施例1基本相同的方法，区别在于：负极活性材料中的单颗粒石墨粒径、二次颗粒石墨粒径、二次颗粒石墨中的微颗粒粒径不同，且单颗粒石墨与二次颗粒石墨的质量比为5:5，可参见表1，实施例9的其他步骤分别与实施例1相同。
实施例10.采用与实施例4基本相同的方法，区别在于：所使用的二次颗粒碳未包覆无定形碳层。
对比例1.未使用二次颗粒石墨。采用与实施例1基本相同的方法，区别在于，负极活性材料以等质量的单颗粒石墨代替二次颗粒石墨，其中，负极材料中，单颗粒人造石墨、导电碳SP、丁苯橡胶乳液、羧甲基纤维素钠的质量比为94:2:2.5:1.5。可参见表1，对比例1的其他步骤分别与实施例1相同。
对比例2.未使用单颗粒石墨。对比例2采用与实施例1基本相同的方法，区别在于，负极活性材料以等质量的二次颗粒石墨代替单颗粒石墨，其中，负极材料中，二次颗粒人造石墨、导电碳SP、丁苯橡胶乳液、羧甲基纤维素钠的质量比为94:2:2.5:1.5。可参见表1，对比例2的其他步骤分别与实施例1相同。
对比例3.采用与实施例1基本相同的方法，区别在于，以基本相同粒径分布的单颗粒石墨代替二次颗粒石墨，此时使用大小两组粒径的单颗粒石墨，两组单颗粒石墨的质量比为5:5。可参见表1，对比例3的其他步骤分别与实施例1相同。
对比例4.采用与实施例1基本相同的方法，区别在于，单颗粒石墨的粒径小于二次颗粒石墨的粒径，且单颗粒石墨与二次颗粒石墨的质量比为5:5。可参见表1，对比例4的其他步骤分别与实施例1相同。
对比例5.采用与实施例1基本相同的方法，区别在于，单颗粒石墨的粒径与二次颗粒石墨的粒径相接近，且单颗粒石墨与二次颗粒石墨的质量比为5:5。可参见表1，对比例5的其他步骤分别与实施例1相同。
对比例6.采用与实施例4基本相同的方法，采用与实施例4相同的颗粒组成(粒径分布和质量比均相同)，向二次颗粒碳中包覆无定形碳层的步骤中，热处理温度与实施例4相同，均为1150℃热处理20h，区别在于：对比例6的升温速率为25℃/min。
表1.
Figure PCTCN2022126730-appb-000001
Figure PCTCN2022126730-appb-000002
表1中，
“ a”：实施例1-9及对比例1-6中，单颗粒碳表面均未包覆无定形碳层。
测试例
1、形貌测试：
用剪刀将冷压后的极片剪成6cm×6cm大小的样品，再用IB-19500CP离子截面抛光仪进行抛光处理，得到抛光后的带切割面的样品。之后参照标准JY/T010-1996用ZEISS sigma 300设备对样品进行测试。在所述测试样品中随机选取位置观察极片的横截面处形貌。
2、极片迂曲度测试
根据下述公式计算极片迂曲度τ＝ε×k×Rion×A/d(式I)。
其中，ε为25℃时所述负极活性材料层的孔隙率；k为25℃时所述电解液的离子电导率，单位为ms/cm；Rion为25℃时所述负极极片的离子电阻，单位为Ω；A为测试Rion时的电极有效面积，单位为cm 2；d为所述负极活性材料层的厚度，单位为μm。
式I中的各参数分别通过如下的测试分析方法获得。
(1)选取待测负极极片，测试负极活性材料层的厚度d。然后根据需求裁取一定面积的样品后分别进行离子电阻Rion、孔隙率ε的测试。
(2)测试负极极片的离子电阻Rion。
待测极片样品：用剪刀将冷压后的极片裁出6cm×6cm大小的方形样品测试负极极片的离子电阻Rion。该方形面积36cm 2记为式I中的电极有效面积A。
Rion测试方法：用设备VMP3配合高低温箱，通过对称电池的方式测试出极片孔隙内部的离子扩散阻抗Rion，可通过测试极片的交流阻抗谱(EIS)得到。
(3)测试负极极片样品的孔隙率ε：利用小分子惰性气体(He)置换法，结合阿基米德原理和波尔定律，精确测量材料的真实体积V 1，再通过测试计算样品的表观体积得到V 2(根据极片面积乘以极片厚度d计算得到V 2)，则孔隙率＝(V 2-V 1)/V 2。
(4)测试二次电池中电解液的离子电导率k：将相互平行且距离固定的两块极板(各二次电池样品中的正极极片和负极极片)，放到电解液中，在极板两端加上一定电势，通过电导仪测量极板之间的电导得到电解液的离子电导率。
3、极片压实密度的测试
裁剪一定面积A 1的负极极片小圆片，称取重量W 1，然后测量小圆片厚度d 1，用重量除以小圆片面积和厚度W/(A 1×d 1)，计算得到极片压实密度。
如无其他说明，实施例1-10及对比例1-6中的压实密度都控制在1.50g/cc。
4、电池性能测试
(1)化成产气测试
待测电芯：各实施例及对比例制备的锂离子电池。
在通过气密性检验的情况下，将电芯带夹具放入化成设备，待电芯与夹具达到化成温度(45℃)后开始化成实验，记录不同化成时间对应的排水体积，待排水体积稳定后停止实验。化成产气结束后，对应的充电电池容量C除以首次容量C 0得到SOC值：SOC＝C/C 0×100％，也记为“排产气结束SOC”。其中，C 0可根据测试流程测完后读出设备输出的容量值，C可根据化成产气结束后读出设备输出的容量值。
(2)循环性能测试
电池容量保持率测试过程如下：在25℃下，将各实施例以及对比例制备的二次电池，以1/3C恒流充电至4.3V，再以4.3V恒定电压充电至电流为0.05C，搁置5min，再以1/3C放电至2.8V，所得容量记为初始容量C d0。对上述同一个电池重复以上步骤，并同时记录循环第400次后电池的放电容量C d400，则每次循环后电池容量保持率P 400＝C d400/C d0×100％。
测试结果：
图1为实施例1中的单颗粒石墨与二次颗粒石墨的SEM形貌图，可以看出单颗粒石墨为单个颗粒，而二次颗粒石墨由多个微颗粒组成。
表2.
Figure PCTCN2022126730-appb-000003
Figure PCTCN2022126730-appb-000004
对比例1中，未使用二次颗粒石墨，相对于实施例1，对比例1迂曲度高，不利于化成产气的排出。
对比例2中，未使用单颗粒石墨，相对于实施例1，对比例2排产气结束SOC显著降低，循环容量保持率低。
对比例3中，以基本相同粒径分布的单颗粒石墨代替二次颗粒石墨，此时使用大小两组粒径的单颗粒石墨，相对于实施例1，对比例3排产气结束SOC有所降低。
对比例4中，单颗粒石墨的粒径小于二次颗粒石墨的粒径，排产气结束SOC下降明显，且循环400圈后的容量保持率P 400也明显变差。对比例5中，单颗粒石墨的粒径与二次颗粒石墨的粒径相接近，排产气结束SOC下降明显，且循环400圈后的容量保持率P 400变差。
对比例6中，无定形碳层的包覆步骤中，升温速率较快，导致包覆层碳的缺陷较多，显著恶化了循环性能，排产气结束SOC也下降明显。
此外，本申请的发明人还发现，实施例4相对于实施例10的快充性能有所改善，不过，实施例4和实施例10均具有适中的迂曲度，较优的排产气结束SOC及良好的循环容量保持率P 400，电芯循环性能好。
以上所述实施例的各技术特征可以进行任意的组合，为使描述简洁，未对上述实施例中的各个技术特征所有可能的组合都进行描述，然而，只要这些技术特征的组合不存在矛盾，都应当认为是本说明书记载的范围。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。以上所述实施例仅表达了本申请的几种实施方式，其描述较为详细，但并不能因此而理解为对专利范围的限制。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。应当指出的是，对于本领域的普通技术人员来说，在不脱离本申请构思的前提下，还可以做出若干变形和改进，这些都属于本申请的保护范围。因此，本申请的保护范围应以所附权利要求为准，说明书及附图可用于解释权利要求的内容。

Claims (16)

  1. 一种二次电池，其包括正极极片、负极极片、隔离膜和电解液，所述隔离膜设置于所述正极极片和所述负极极片之间；
    所述负极极片包括负极活性材料层，所述负极活性材料层包括碳基颗粒，所述碳基颗粒包括单颗粒碳和二次颗粒碳，其中，所述单颗粒碳的D v50大于所述二次颗粒碳的D v50；
    其中，D v50表示材料的累计体积分布百分数达到50％时对应的粒径。
  2. 根据权利要求1所述的二次电池，其中，所述负极活性材料层的迂曲度τ在数值上等于根据以下公式计算得到的数值：ε×k×Rion×A/d；其中，ε为25℃时所述负极活性材料层的孔隙率；k为25℃时所述电解液的离子电导率，单位为ms/cm；Rion为25℃时所述负极极片的离子电阻，单位为Ω；A为测试Rion时的有效面积，单位为cm 2；d为所述负极活性材料层的厚度，单位为μm；
    所述负极活性材料层的迂曲度τ≤4.75。
  3. 根据权利要求2所述的二次电池，其中，所述负极活性材料层的迂曲度τ≤4.70；
    可选地，所述负极活性材料层的迂曲度τ≤4.70，可选地，τ选自3.40～4.70；
    可选地，所述负极活性材料层的迂曲度τ≤4.65，可选地，τ选自3.40～4.65；
    可选地，所述负极活性材料层的迂曲度τ≤4.62，可选地，τ选自3.42～4.62；
    可选地，所述负极活性材料层的迂曲度τ≤4.05，可选地，τ选自3.42～4.05；
    可选地，所述负极活性材料层的迂曲度τ≤3.95，可选地，τ选自3.42～3.95；
    可选地，所述负极活性材料层的迂曲度τ≤3.85，可选地，τ选自3.45～3.85；
    可选地，所述负极活性材料层的迂曲度τ≤3.82，可选地，τ选自3.45～3.82。
  4. 根据权利要1～3中任一项所述的二次电池，其中，所述负极活性材料层的孔隙率选自30.6％～37.5％；
    可选地，所述负极活性材料层的孔隙率选自32.2％～37.5％；
    可选地，所述负极活性材料层的孔隙率选自33.8％～37.5％；
    可选地，所述负极活性材料层的孔隙率选自34.8％～37.5％；
    可选地，所述负极活性材料层的孔隙率选自35.5％～37.5％。
  5. 根据权利要求1～4中任一项所述的二次电池，其中，所述负极活性材料层的压实密度选自1.30g/cc～1.80g/cc；
    可选地，所述负极活性材料层的压实密度选自1.30g/cc～1.70g/cc；
    可选地，所述负极活性材料层的压实密度选自1.50±0.02g/cc。
  6. 根据权利要求1～5中任一项所述的二次电池，其中，所述二次颗粒碳在所述碳基颗粒中的质量占比选自10％～90％；
    可选地，所述二次颗粒碳在所述碳基颗粒中的质量占比选自20％～80％；
    可选地，所述二次颗粒碳在所述碳基颗粒中的质量占比选自30％～70％；
    可选地，所述二次颗粒碳在所述碳基颗粒中的质量占比选自30％～50％。
  7. 根据权利要求1～6中任一项所述的二次电池，其中，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比大于50％，
    所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比选自80％～100％；
    可选地，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比选自 90％～100％；
    可选地，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比选自95％～100％；
    可选地，所述碳基颗粒在所述负极活性材料层的负极活性物质中的质量占比为100％；
    可选地，所述碳基颗粒中含有质量占比大于50％的石墨材料；
    可选地，所述碳基颗粒中含有质量占比选自80％～100％的石墨材料；
    可选地，所述碳基颗粒中含有质量占比选自90％～100％的石墨材料；
    可选地，所述碳基颗粒中含有质量占比选自95％～100％的石墨材料；
    可选地，所述碳基颗粒中含有质量占比为100％的石墨材料；
    可选地，所述负极活性材料层的负极活性物质中含有质量占比大于50％的石墨材料；
    可选地，所述负极活性材料层的负极活性物质中含有质量占比选自80％～100％的石墨材料；
    可选地，所述负极活性材料层的负极活性物质中含有质量占比选自90％～100％的石墨材料；
    可选地，所述负极活性材料层的负极活性物质中含有质量占比选自95％～100％的石墨材料；
    可选地，所述负极活性材料层的负极活性物质中含有质量占比为100％的石墨材料。
  8. 根据权利要求1～7中任一项所述的二次电池，其中，所述碳基颗粒为石墨颗粒，所述单颗粒碳为单颗粒石墨，所述二次颗粒为二次颗粒石墨。
  9. 根据权利要求1～8中任一项所述的二次电池，其中，所述负极活性材料层具备如下的一个或多个特征：
    所述单颗粒碳的D v50选自13μm～14μm；
    所述二次颗粒碳的D v50选自9.5μm～10.5μm；和
    所述单颗粒碳的D v50与所述二次颗粒碳的D v50的差值选自3μm～4μm。
  10. 根据权利要求1～9中任一项所述的二次电池，其中，所述单颗粒碳的D v99大于所述二次颗粒碳的D v99；
    可选地，所述负极活性材料层还具备如下的一个或多个特征：
    所述单颗粒碳的D v99选自37μm～44μm；
    所述二次颗粒碳的D v99选自31μm～38μm；和
    所述单颗粒碳的D v99与所述二次颗粒碳的D v99的差值选自4μm～6μm。
  11. 根据权利要求1～10中任一项所述的二次电池，其中，所述单颗粒碳的D v10大于所述二次颗粒碳的D v10；
    可选地，所述负极活性材料层还具备如下的一个或多个特征：
    所述单颗粒碳的D v10选自5μm～7μm；
    所述二次颗粒碳的D v10选自3.5μm～5.5μm；和
    所述单颗粒碳的D v10与所述二次颗粒碳的D v99的差值选自1μm～2μm。
  12. 根据权利要求1～11中任一项所述的二次电池，其中，所述二次颗粒碳包括多个微颗粒碳，还包括粘合剂；其中，所述微颗粒碳中一次颗粒的数量为一个或多个；
    当所述二次颗粒碳为二次颗粒石墨时，所述微颗粒碳为微颗粒石墨；
    可选地，所述微颗粒碳具备如下的一个或多个特征：
    所述微颗粒碳的D v99选自20μm～24μm；
    所述微颗粒碳的D v90选自12μm～15μm；
    所述微颗粒碳的D v50选自5μm～7μm；和
    所述微颗粒碳的D v10选自2μm～3μm；
    可选地，所述粘合剂为沥青；
    可选地，所述粘合剂相对于所述多个微颗粒碳的质量比选自1:8.5至1:9.5；
    可选地，所述二次颗粒碳是由所述多个微颗粒碳和所述粘合剂粘聚而成。
  13. 根据权利要求1～12中任一项所述的二次电池，其中，所述二次颗粒碳包含碳基芯和位于所述碳基芯表面至少一部分的无定形碳层；
    可选地，所述无定形碳层在所述二次颗粒碳表面的厚度≤500nm；可选地，所述无定形碳层在所述二次颗粒碳表面的厚度选自200nm～500nm；
    可选地，所述无定形碳层在所述二次颗粒碳中的质量含量≤3.3％，可选地，所述无定形碳层在所述二次颗粒碳中的质量含量选自1.3％～3.3％；
    可选地，所述碳基芯包含负极活性物质，所述负极活性物质为石墨。
  14. 一种用电装置，其包括权利要求1～13中任一项所述二次电池。
  15. 一种负极极片的制备方法，其包括如下步骤：
    制备单颗粒碳；其中，所述制备单颗粒碳的步骤包括：将原料破碎，分级，预碳化，石墨化和筛分；
    制备微颗粒碳，将所述微颗粒碳和粘合剂混合，于所述粘合剂熔融状态下造粒，预碳化，石墨化，可选地包覆，筛分，制得二次颗粒碳；其中，所述制备微颗粒碳的步骤包括：将原料破碎、分级、筛分；
    将所述单颗粒碳、所述二次颗粒碳、助剂和溶剂混合，制备负极浆料；
    将所述负极浆料涂布于负极集流体的至少一侧表面，干燥，压实，制备得到所述负极极片；
    其中，所述单颗粒碳和所述二次颗粒碳如权利要求1～13任一项中所定义；所述微颗粒碳如权利要求10中所定义。
  16. 根据权利要求15所述的制备方法，其中，具备如下一个或多个特征：
    所述预碳化每次出现，独立地包括如下步骤：于1050℃～1150℃加热处理，可选地，加热时间为24h～72h；可选地，所述预碳化在惰性气体条件下进行；
    所述石墨化每次出现，独立地包括如下步骤：于>2800℃的温度条件下加热处理，可选地，加热温度为2850℃～3100℃；可选地，加热时间为30h～96h；可选地，所述石墨化在惰性气体条件下进行；
    所述于所述粘合剂熔融状态下造粒包括；于所述粘合剂熔融状态下加热处理，粉碎；可选地，加热温度选自500℃～600℃；可选地，加热时间为4h～6h，可选地，所述加热处理在惰性气体条件下进行；
    所述包覆包括如下步骤：将物料与有机碳材料混合，于1100℃～1200℃加热处理制备包含包覆层的二次颗粒，可选地，加热时间为12h～24h；可选地，所述包覆在惰性气体条件下进行；可选地，所述包含包覆层的二次颗粒中的包覆层中包含无定形碳；
    所述单颗粒碳采用依次包括如下步骤的方法制得：将原料破碎，分级，于1050℃～1150℃预碳化，于>2800℃的温度条件下石墨化，筛分，制得所述单颗粒碳；
    所述二次颗粒采用依次包括如下步骤的方法制得：制备所述微颗粒碳，将所述微颗粒碳和所述粘合剂混合，于500℃～600℃下造粒，于1050℃～1150℃预碳化，于>2800℃的温度条件下石墨化，可选地于1100℃～1200℃下包覆，筛分，制得所述二次颗粒碳；
    所述单颗粒碳为单颗粒石墨；所述微颗粒碳为微颗粒石墨；
    所述粘合剂为沥青；
    所述粘合剂相对于多个所述微颗粒碳的质量比选自1:8.5至1:9.5；
    所述有机碳材料包括沥青、酚醛树脂、糠醛树脂和环氧树脂中的一种或多种；
    所述惰性气体条件每次出现，独立地选自包括氮气、氦气、氩气和氖气中的一种或多种气体的条件。
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