WO2024066338A1 - 负极活性材料、包含其的负极极片、电化学装置及用电装置 - Google Patents

负极活性材料、包含其的负极极片、电化学装置及用电装置 Download PDF

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WO2024066338A1
WO2024066338A1 PCT/CN2023/091185 CN2023091185W WO2024066338A1 WO 2024066338 A1 WO2024066338 A1 WO 2024066338A1 CN 2023091185 W CN2023091185 W CN 2023091185W WO 2024066338 A1 WO2024066338 A1 WO 2024066338A1
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negative electrode
active material
electrode active
hard carbon
lithium
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PCT/CN2023/091185
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English (en)
French (fr)
Inventor
郑子桂
谭福金
易政
谢远森
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宁德新能源科技有限公司
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Publication of WO2024066338A1 publication Critical patent/WO2024066338A1/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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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
    • 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application belongs to the technical field of electrochemical batteries, and specifically relates to a negative electrode active material, a negative electrode sheet containing the negative electrode active material, an electrochemical device, and an electrical device.
  • Secondary batteries represented by lithium-ion secondary batteries have outstanding features such as high energy density, long cycle life, low pollution, and no memory effect. As a clean energy source, the application of secondary batteries has gradually spread from electronic products to large-scale devices such as electric vehicles to adapt to the sustainable development strategy of the environment and energy. Therefore, higher requirements are also placed on the energy density of secondary batteries.
  • the negative electrode material of commercial secondary batteries is still mainly graphite.
  • Graphite has advantages such as high conductivity and high stability.
  • the theoretical capacity of graphite is about 372mAh/g, and in recent years it has almost been developed to its theoretical capacity limit.
  • the energy density of lithium-ion batteries using graphite as negative electrode material is difficult to further improve.
  • the present application provides a negative electrode active material, a negative electrode plate, an electrochemical device and an electrical device containing the same.
  • the negative electrode active material has a low average delithiation potential and can improve the energy density of the negative electrode plate, the electrochemical device and the electrical device.
  • the first aspect of the present application provides a negative electrode active material, including a hard carbon material, wherein the hard carbon material has a plurality of micropores, so that the average delithiation potential of the negative electrode active material with metallic lithium as a counter electrode is 0.15V (vs Li + /Li) To 0.40V (vs Li + /Li).
  • the hard carbon material has a ratio of the average molar number of oxygen atoms to carbon atoms, O/C, of 0.01 to 0.10.
  • the O/C value of the hard carbon material is from 0.02 to 0.07.
  • the negative electrode active material satisfies: Wherein, C 1 mAh/g represents the lithium desorption capacity of the hard carbon material between 0V (vs Li + /Li) and 0.15V (vs Li + /Li) with metallic lithium as the counter electrode; C 0 mAh/g represents the total lithium desorption capacity of the hard carbon material with metallic lithium as the counter electrode.
  • the X-ray diffraction pattern of the hard carbon material has a characteristic peak located between 18° and 30°, and the half-peak width of the characteristic peak is between 4° and 12°.
  • the hard carbon material includes a core and a coating layer located on at least a portion of the surface of the core, and abundant micropores are located in the core.
  • the micropore volume V of the hard carbon material measured by a carbon dioxide gas adsorption method satisfies: 0cc/g ⁇ V ⁇ 0.05cc/g, and the diameter d nm of the micropores satisfies: d nm ⁇ 0.9nm.
  • the hard carbon material has a true density, ⁇ g/cc, measured by an n-butanol impregnation method, of 1.1 g/cc to 1.6 g/cc.
  • the hard carbon material has a D V 50 of 6 ⁇ m to 15 ⁇ m.
  • the hard carbon material has a specific surface area of 2 m 2 /g to 10 m 2 /g.
  • a second aspect of the present application provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode active material of the first aspect.
  • the negative electrode active material layer further includes artificial graphite, and a mass ratio A of the negative electrode active material to the artificial graphite satisfies: 0 ⁇ A ⁇ 1/3.
  • the compaction density PD g/cm 3 of the negative electrode active material layer is 1.0 g/cm 3 to 1.7 g/cm 3 .
  • the negative electrode active material layer has a porosity of 15% to 30%.
  • a third aspect of the present application provides an electrochemical device, comprising the negative electrode sheet according to the second aspect.
  • a fourth aspect of the present application provides an electrical device, comprising the electrochemical device of the third aspect.
  • FIG1 is a schematic diagram of an embodiment of an electrochemical device of the present application.
  • FIG2 is an exploded view of the embodiment of the electrochemical device of the present application shown in FIG1 ;
  • FIG3 is a schematic diagram of an electrical device used as a power source in an embodiment of the electrochemical device of the present application
  • FIG4 is a voltage-capacity curve diagram of a button cell corresponding to Example 4 of the present application.
  • range disclosed in the present application is defined in the form of a lower limit and an 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 boundaries of a particular range.
  • the range defined in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a specific parameter, it is understood that the range of 60-110 and 80-120 is also expected.
  • 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 term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B”. More specifically, 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).
  • hard carbon materials have received great attention due to their advantages such as high gram capacity, good rate performance, low temperature performance and good cycle performance.
  • hard carbon materials can be used as negative electrode active materials for lithium-ion batteries, but also as negative electrode active materials for sodium-ion batteries, and have broad application prospects.
  • existing hard carbon materials have defects such as high irreversible capacity and unsatisfactory capacity utilization. When used in lithium-ion batteries or sodium-ion batteries, the improvement of battery energy density is very limited, and it is difficult to meet the needs of practical applications.
  • the inventors after in-depth thinking, provide a negative electrode active material, which has a low average lithium desorption potential and is applied to a secondary battery to improve the energy density of the secondary battery.
  • the present application provides a negative electrode active material, including a hard carbon material having a plurality of micropores, so that the average delithiation potential of the hard carbon material with metallic lithium as a counter electrode is 0.15V (vs Li + /Li) to 0.40V (vs Li + /Li).
  • a hard carbon material has a plurality of micropores, lithium ions can be stored in the micropores during the lithium insertion process, thereby providing a reversible capacity.
  • the hard carbon material has a specific microporous structure so that the average delithiation potential of the hard carbon material with metallic lithium as a counter electrode is within the above-mentioned lower range, the hard carbon material can have a high reversible capacity, especially a low voltage platform capacity, on the one hand, and can have good lithium ion diffusion kinetics on the other hand. Therefore, the negative electrode active material of the present application is applied to secondary batteries, which can allow the secondary batteries to have high energy density, high first coulombic efficiency and good cycle performance.
  • the above-mentioned specific microporous structure is intended to represent any microporous structure that can make the average delithiation potential of the hard carbon material with metallic lithium as the counter electrode be 0.15V (vs Li + /Li) to 0.40V (vs Li + /Li), which may include a microporous structure with the number and volume of micropores in any suitable range, and/or a microporous structure with the morphology of the micropores and a suitable distribution position in the hard carbon material, but is not limited thereto.
  • the average delithiation potential of the negative electrode active material with metallic lithium as the counter electrode is 0.15V (vs Li + /Li) to 0.40V (vs Li + /Li), which is not limited here.
  • the O/C value of the ratio of the average molar number of oxygen atoms to carbon atoms of the hard carbon material may be 0.01 to 0.10.
  • the O/C value of the hard carbon material may be 0.01, 0.02, 0.05, 0.07, 0.10 or within a range consisting of any of the above values.
  • the O/C value of the hard carbon material may be 0.02 to 0.07.
  • the O/C value of the hard carbon material may be 0.02, 0.03, 0.04, 0.05, 0.06, 0.07 or is within the range formed by any of the above values. It is not intended to be limited by any theory or explanation.
  • the O/C value in the hard carbon material is within the above appropriate range, the presence of a small amount of oxygen atoms is beneficial to the deintercalation of lithium ions inside the micropores, which is beneficial to the capacity of the negative electrode active material.
  • the O/C value is within the above appropriate range, it will also be able to reduce the risk of irreversible capacity loss due to excessive oxygen content, thereby improving the reversible capacity of the negative electrode active material. Therefore, the negative electrode active material of the present application is applied to secondary batteries, which can further improve the energy density and first coulomb efficiency of the secondary batteries.
  • the negative electrode active material may satisfy: Wherein, C 1 mAh/g represents the lithium removal capacity of the hard carbon material between 0V (vs Li + /Li) and 0.15V (vs Li + /Li) with metallic lithium as the counter electrode; C 0 mAh/g represents the total lithium removal capacity of the hard carbon material with metallic lithium as the counter electrode. It is not intended to be limited to any theory or explanation. During the lithium removal capacity test with metallic lithium as the counter electrode, lithium ions stored in the micropores of the hard carbon material are usually released between 0V and 0.15V, so the above C 1 is highly correlated with the microporous structure in the hard carbon material.
  • the microporous structure in the hard carbon material can provide more reversible capacity, so that the lithium removal capacity of the hard carbon material under the low voltage platform has a higher proportion in the total lithium removal capacity.
  • the higher low voltage platform capacity proportion helps to further reduce the average lithium removal potential of the hard carbon material. Therefore, the negative active material of the present application is applied to secondary batteries, which can further improve the energy density of secondary batteries.
  • the X-ray diffraction (XRD) pattern of the hard carbon material may have a characteristic peak located between 18° and 30°, and the half-peak width of the characteristic peak is 4° to 12°.
  • the XRD pattern of the negative active material has the above-mentioned characteristic peak, it can indicate that the 002 interplanar spacing of the hard carbon material is between 0.37nm and 0.41nm, which is much larger than the 002 interplanar spacing of graphite.
  • the larger 002 interplanar spacing facilitates the rapid deintercalation of lithium ions inside the hard carbon material, thereby improving the reversible capacity and kinetic performance of the negative active material. Therefore, the negative active material of the present application is applied to secondary batteries, which can improve the energy density and rate performance of the secondary batteries.
  • the hard carbon material may include a core and a coating located on at least a portion of the surface of the core, wherein the micropores are located in the core.
  • the coating may be a dense coating that does not contain micropores.
  • the thickness of the coating may be less than or equal to 100 nm.
  • the coating may cover more than 50% of the surface area of the core, more than 80% of the surface area, more than 90% of the surface area, or 100% of the surface area.
  • the coating can convert the open micropores on the surface of the core into closed micropores, thereby effectively isolating the inside of the micropores from contact with the electrolyte, thereby reducing the irreversible loss of active ions caused by the formation of an SEI film by the electrolyte inside the micropores.
  • the reversible capacity of the negative electrode active material can be improved, thereby allowing a secondary battery using the negative electrode active material to have a high energy density and a high first coulombic efficiency. Rate.
  • the hard carbon material includes a core and a coating layer located on at least part of the surface of the core.
  • the micropore volume V of the hard carbon material measured by the carbon dioxide gas adsorption method can satisfy: 0cc/g ⁇ V ⁇ 0.05cc/g.
  • the coating layer can convert the open micropores on the surface of the core into closed micropores; when some micropores have a small volume, during the carbon dioxide gas absorption test, it is not only difficult for carbon dioxide molecules to enter the micropores of the core for adsorption and desorption, but also difficult to be adsorbed by some small-volume micropores, thus, the micropore volume of the hard carbon material measured by the carbon dioxide gas adsorption method is within the above-mentioned smaller range.
  • the coating layer can effectively isolate the inside of the micropores from contact with the electrolyte, thereby reducing the irreversible loss of active ions caused by the formation of SEI film by the electrolyte inside the micropores; on the other hand, small-volume micropores are conducive to the deposition of lithium ions or sodium ions with a smaller radius, thereby further improving the lithium storage capacity/sodium storage capacity of the hard carbon material. Therefore, the negative electrode active material of the present application is applied to a secondary battery, which can further improve the energy density and the first coulombic efficiency of the secondary battery.
  • the diameter d nm of the micropores may satisfy: d nm ⁇ 0.9 nm.
  • the diameter of the micropores within the above-mentioned suitable range is conducive to the smooth deposition and release of lithium ions (ion radius of about 76 pm) or sodium ions (ion radius of about 102 pm) in the micropores, thereby facilitating the improvement of the reversible capacity of the hard carbon particles.
  • the negative electrode active material of the present application can have a high reversible capacity and be applied to secondary batteries, which can allow the battery to have a higher energy density.
  • the true density ⁇ g/cc of the hard carbon material measured by the n-butanol impregnation method may be 1.1g/cc to 1.6g/cc.
  • the true density of the graphite material measured by the n-butanol impregnation method is about 2.22g/cc.
  • the hard carbon material has more micropores and a larger 002 crystal plane spacing, so that it can have a lower true density while having a high capacity. Therefore, the negative active material of the present application is applied to a secondary battery, and the mass energy density of the secondary battery can also be improved.
  • the volume average particle size D V 50 of the hard carbon material may be 6 ⁇ m to 15 ⁇ m.
  • the D V 50 of the hard carbon material may be 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m or within a range formed by any of the above values.
  • the hard carbon material may be a primary particle.
  • the hard carbon material can have good electrolyte wetting performance, and on the other hand, the hard carbon material can have a smaller specific surface area, thereby reducing the active ions consumed during the first charge due to the formation of the SEI film on the surface of the hard carbon material. Therefore, the negative electrode active material of the present application is applied to a secondary battery, which can enable the secondary battery to have both Good kinetics and high first coulombic efficiency.
  • the specific surface area of the hard carbon material may be 2m 2 /g to 10m 2 /g.
  • the specific surface area of the hard carbon material may be 2m 2 /g, 3m 2 /g, 4m 2 /g, 5m 2 /g, 6m 2 /g, 7m 2 /g, 8m 2 / g, 9m 2 /g, 10m 2 /g or within the range of any of the above values.
  • the larger the specific surface area of the negative electrode active material particles the larger the area of the SEI film formed on the surface of the negative electrode active material particles during the first charging of the secondary battery, and the more active ions are lost.
  • the specific surface area of the negative electrode active material particles the more binder is consumed to form the negative electrode active material layer, and thus, the internal resistance of the negative electrode active material layer is also higher.
  • the specific surface area of the hard carbon material is within the above-mentioned appropriate range, it is applied to the secondary battery, which can not only make the SEI film formed during the first charging process have an area of appropriate size, but also reduce the amount of binder in the negative electrode active material layer. As a result, the loss of active ions and the internal resistance of the negative electrode active material layer can be reduced, thereby improving the initial coulombic efficiency, energy density, cycle performance and safety performance of the secondary battery.
  • the hard carbon material in the negative electrode active material of the present application can be obtained through the following steps S10 to S40. It should be noted that the hard carbon material in the negative electrode active material of the present application can be obtained in many ways, and this example is only used to explain the present application, not to limit the present application.
  • the hard carbon precursor material can be selected from one or more of asphalt, biomass, and resin materials.
  • the oxygen-containing atmosphere refers to an atmosphere containing oxygen, for example, compressed air, or a mixed gas of oxygen and an inert gas, in which the mass percentage of oxygen can be 1% to 100%.
  • the gas flow rate of the oxygen-containing atmosphere can be 0.1L/min to 5L/min.
  • the reaction time of step S10 can be less than or equal to 48h.
  • the inert atmosphere may include an atmosphere that does not react with the oxygen-bearing hard carbon precursor material, for example, a nitrogen atmosphere, an argon atmosphere, or other rare gas atmosphere.
  • the gas flow rate of the inert atmosphere may be 0.1 L/min to 5 L/min.
  • the insulation time may be 1 h to 4 h.
  • the inert atmosphere may include an atmosphere that does not react with the pre-carbonized product, for example, a nitrogen atmosphere, an argon atmosphere or other rare gas atmosphere.
  • the gas flow rate of the inert atmosphere may be 0.1 L/min to 5 L/min.
  • the insulation time may be 1 h to 12 h.
  • the carbonized product may be crushed and graded to obtain a carbonized product with a particle size within a suitable range.
  • the reducing atmosphere can be selected from an atmosphere containing a reducing gas, such as an acetylene-argon mixed gas with a mass percentage of 5% acetylene, or a methane-argon mixed gas with a mass percentage of 10% methane.
  • a reducing gas such as an acetylene-argon mixed gas with a mass percentage of 5% acetylene, or a methane-argon mixed gas with a mass percentage of 10% methane.
  • the gas flow rate of the reducing atmosphere can be 0.1L/min to 3L/min.
  • the insulation time can be 0.1h to 8h.
  • the cross-linked structure inside the hard carbon precursor material can be changed.
  • the material after carbonization, the material can have a suitable microporous structure and a high micropore content.
  • a dense coating layer can be formed on the surface of the carbonized product, thereby obtaining a hard carbon material composed of a core containing multiple micropores and a coating, and on the other hand, the oxygen content of the carbonized product can be reduced, so that the O/C value of the hard carbon material is within a suitable range.
  • a hard carbon material having multiple micropores can be prepared so that the average delithiation potential of the hard carbon material with metallic lithium as the counter electrode is 0.15V (vs Li + /Li) to 0.40V (vs Li + /Li).
  • the average delithiation potential of the hard carbon material with metallic lithium as the counter electrode has a meaning known in the art and can be determined by methods known in the art.
  • the hard carbon material can be mixed evenly with an appropriate amount of a binder, a conductive agent and a solvent to obtain a negative electrode slurry; the negative electrode slurry can be applied to the surface of the negative electrode collector to obtain a negative electrode plate; a button cell is assembled with a metallic lithium plate as a positive electrode plate and the negative electrode plate; the button cell is charged and discharged to determine the charging capacity and charging energy of the button cell; the charging capacity is divided by the charging energy to obtain the average delithiation potential of the hard carbon material.
  • the O/C value of the hard carbon material has a meaning known in the art and can be measured by methods known in the art.
  • the O/C value of the hard carbon material can be tested using an element analyzer (Elementar Unicube).
  • C 1 mAh and C 0 mAh have the meanings known in the art.
  • This field can be used
  • the hard carbon material can be mixed evenly with an appropriate amount of a binder, a conductive agent and a solvent to obtain a negative electrode slurry; the negative electrode slurry can be applied to the surface of the negative electrode current collector to obtain a negative electrode plate; a button battery can be assembled with a metal lithium plate as a positive electrode plate and the negative electrode plate; the button battery can be charged and discharged in cycles; the charging capacity is divided by the charging energy to obtain the average delithiation potential of the hard carbon material; the gram capacity of the charging section 0V (vs Li + /Li) to 0.15V (vs Li + /Li) is divided by the total charging capacity to obtain
  • the volume average particle size D V 50 of the hard carbon material has a well-known meaning in the art, which means that in the volume-based particle size distribution of the hard carbon material, 50% of the particles have a particle size smaller than this value, and can be measured by methods known in the art. For example, it can be measured with a laser particle size analyzer (e.g., Mastersizer 2000E, Malvern, UK) with reference to GB/T 19077-2016 particle size distribution laser diffraction method.
  • a laser particle size analyzer e.g., Mastersizer 2000E, Malvern, UK
  • the specific surface area of the hard carbon material has a well-known meaning in the art and can be measured by methods known in the art.
  • the specific surface area of the hard carbon material can be measured by a specific surface area analyzer (TristarII3020M) by nitrogen adsorption/desorption method.
  • the micropore diameter dnm of the hard carbon material has a meaning known in the art and can be measured by methods known in the art. For example, it can be obtained by testing with an ASAP2460-physical adsorption analyzer. Specifically, after drying and degassing the negative electrode active material powder, an ASAP2460-physical adsorption analyzer is used to test the atmosphere with carbon dioxide, adjust different test pressures, measure the adsorption amount of carbon dioxide, and draw adsorption and desorption isotherms. The shape of the pores is determined according to the shape of the hysteresis loop, and the pore size distribution curve of the micropores is fitted using the DFT model to obtain the micropore diameter dnm of the hard carbon material.
  • an ASAP2460-physical adsorption analyzer is used to test the atmosphere with carbon dioxide, adjust different test pressures, measure the adsorption amount of carbon dioxide, and draw adsorption and desorption isotherms.
  • the shape of the pores is determined according to the shape of the h
  • a second aspect of the present application provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode active material of the first aspect of the present application.
  • the negative electrode plate of the present application includes the negative electrode active material of the first aspect of the present application, so as to have high reversible capacity and good lithium ion diffusion kinetics. Therefore, the negative electrode active material of the present application is applied to a secondary battery, which can allow the secondary battery to have high energy density, high first coulomb efficiency and good cycle performance.
  • the negative electrode active material layer does not exclude other negative electrode active materials except the negative electrode active material of the first aspect of the present application.
  • the negative electrode active material layer further includes artificial graphite, and the mass ratio A of the negative electrode active material to the artificial graphite may satisfy: 0 ⁇ A ⁇ 1/3.
  • the mass ratio of the negative electrode active material to the artificial graphite within the above-mentioned appropriate range can not only reduce the volume expansion rate of the negative electrode sheet in a fully charged state, but also improve The capacity of the negative electrode active material layer can be increased, thereby improving the energy density of the secondary battery.
  • the negative electrode active material layer further includes the artificial graphite, and the compaction density PD g/cm 3 of the negative electrode active material layer may be 1.0 g/cm 3 to 1.7 g/cm 3 .
  • the compaction density of the negative electrode active material layer is often not high, about 0.9g/ cm3 to 1.2g/ cm3 , resulting in large gaps in the hard carbon material after cold pressing.
  • the negative electrode active material particles in the negative electrode active material layer are stacked more densely, so that the above-mentioned higher compaction density can be achieved.
  • the content of negative electrode active material per unit volume of the negative electrode active material layer can be increased, thereby allowing the secondary battery using the negative electrode sheet of the present application to have a higher volume energy density.
  • the negative electrode active material layer further includes the above-mentioned artificial graphite, and the porosity of the negative electrode active material layer may be 15% to 30%.
  • the porosity of the negative electrode active material layer is within the above-mentioned suitable range, so that the electrolyte fully infiltrates the active material particles and improves the dynamic performance; if the cross-sectional porosity is too large, the contact points between the active material particles are reduced, the internal resistance of the secondary battery is increased, and the matrix energy density is also lost.
  • the present application does not limit the negative electrode current collector of the negative electrode plate.
  • Metal foil, porous metal plate or composite current collector can 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 substrate.
  • the composite current collector can 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 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 plate is a negative electrode plate of a lithium ion battery, and the negative electrode current collector can be copper foil.
  • the negative electrode plate is a negative electrode plate of a sodium ion battery, and the negative electrode current collector can be copper foil or aluminum foil.
  • the negative electrode current collector has two surfaces opposite to each other in the thickness direction thereof, and the negative electrode active material layer may be disposed on one surface of the negative electrode current collector or on both surfaces of the negative electrode current collector.
  • the negative electrode current collector has two surfaces opposite to each other in the thickness direction thereof, and the negative electrode active material layer is disposed on any one surface or both surfaces of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode active material layer may further include a binder.
  • the binder may be selected from at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.
  • the negative electrode active material layer may further optionally include a conductive agent.
  • the conductive agent may be selected from a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof.
  • the carbon-based material may be selected from at least one of natural graphite, artificial graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the metal-based material may be selected from metal powders and metal fibers.
  • the conductive polymer may include a polyphenylene derivative.
  • the negative electrode active material layer may further 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 in the present application can be prepared according to conventional methods in the art.
  • the hard carbon and other optional negative electrode active materials, conductive agents, binders and thickeners are dispersed in a solvent, and the solvent can be N-methylpyrrolidone (NMP) or deionized water to form a uniform negative electrode slurry, and the negative electrode slurry is coated on the negative electrode current collector, and the negative electrode sheet is obtained through drying, cold pressing and other processes.
  • NMP N-methylpyrrolidone
  • each negative electrode active material layer refers to the parameter range of a single-side negative electrode active material layer.
  • the parameters of the negative electrode active material layer on either side satisfy this application and are considered to fall within the protection scope of this application.
  • the negative electrode sheet in the present application does not exclude other additional functional layers in addition to the negative electrode active material layer.
  • the negative electrode sheet of the present application also includes a conductive primer layer (for example, composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector.
  • the negative electrode sheet of the present application also includes a protective layer covering the surface of the negative electrode active material layer.
  • the compaction density of the negative electrode active material layer has a meaning known in the art and can be measured by methods known in the art.
  • the porosity of the negative electrode active material layer has a meaning known in the art and can be measured by methods known in the art.
  • the porosity of the negative electrode active material layer can be tested by a true density meter according to the standard "GB/T24586-2009 Determination of Apparent Density, True Density and Porosity of Iron Ore".
  • various parameter tests on the negative electrode active material or the negative electrode active material layer may be conducted by sampling during the battery preparation process or by sampling from a prepared secondary battery.
  • the sampling can be performed according to the following steps (1) to (3).
  • the lithium-ion battery is discharged (for safety reasons, the battery is generally fully discharged); the negative electrode sheet is removed after the battery is disassembled, and the negative electrode sheet is soaked in dimethyl carbonate (DMC) for a certain period of time (e.g., 2 to 10 hours); then the negative electrode sheet is removed and dried at a certain temperature and time (e.g., 60°C, 4 hours), and the negative electrode sheet is removed after drying.
  • DMC dimethyl carbonate
  • step (2) The negative electrode sheet dried in step (1) is baked at a certain temperature and time (e.g., 400° C., 2 hours), and a region of the baked negative electrode sheet is selected to sample the negative electrode active material (sampling can be performed by scraping powder with a blade).
  • a certain temperature and time e.g. 400° C., 2 hours
  • step (3) The negative electrode active material collected in step (2) is sieved (for example, sieved with a 200-mesh sieve) to finally obtain a sample that can be used to test the parameters of the negative electrode active material mentioned above in the present application.
  • the third aspect of the present application provides an electrochemical device, including any device in which an electrochemical reaction occurs to convert chemical energy into electrical energy.
  • the electrochemical device can be a primary battery or a secondary battery, and specific examples thereof include all kinds of lithium primary batteries, lithium secondary batteries, sodium primary batteries or sodium secondary batteries.
  • the electrochemical device of the present application includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.
  • the negative electrode sheet used in the electrochemical device of the present application is the negative electrode sheet of the second aspect of the present application.
  • the material, composition and manufacturing method of the positive electrode sheet used in the electrochemical device of the present application may include any technology known in the prior art.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material.
  • the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode active material layer includes a positive electrode active material.
  • the specific type of the positive electrode active material is not particularly limited and can be selected according to requirements.
  • the electrochemical device is a lithium ion battery.
  • the positive electrode active material may include a lithium One or more of transition metal oxides, lithium phosphates with olivine structure and their respective modified compounds.
  • the modified compounds of each of the above-mentioned positive electrode active materials can be doping modification, surface coating modification, or doping and surface coating modification of the positive electrode active material.
  • the lithium transition metal oxide may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their modified compounds.
  • the lithium phosphate containing olivine structure may include one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon and their modified compounds.
  • These positive electrode active materials can be used alone or in combination of two or more.
  • the electrochemical device is a sodium ion battery.
  • the positive electrode active material may be a positive electrode active material for a sodium ion secondary battery known in the art.
  • the positive electrode active material may include one or more of a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound.
  • the polyanionic compounds include: A1fM3g ( PO4 ) iOjX13 -j , wherein A1 is one or more selected from H, Li, Na, K and NH4, M3 is one or more selected from Ti, Cr, Mn, Fe, Co, Ni, V, Cu and Zn, X1 is one or more selected from F , Cl and Br, 0 ⁇ f ⁇ 4, 0 ⁇ g ⁇ 2, 1 ⁇ i ⁇ 3, 0 ⁇ j ⁇ 2; NanM4PO4X2 , wherein M4 is one or more selected from Mn, Fe, Co, Ni, Cu and Zn , X2 is one or more selected from F, Cl and Br, 0 ⁇ n ⁇ 2; NapM5q ( SO4 ) 3 , wherein M5 is one or more selected from Mn, Fe, Co, Ni, Cu and Zn, 0 ⁇ p ⁇ 2 , 0 ⁇ q ⁇ 2; NasMntFe3 - t ( PO4 ) 3 ) 2 (P 2 O 7
  • the above-mentioned Prussian blue compounds can be listed as: A 2 u M 6 v [M 7 (CN) 6 ] w ⁇ xH 2 O, wherein A 2 is one or more of H + , NH 4 + , alkali metal cations and alkaline earth metal cations, M 6 and M 7 are each independently one or more of transition metal cations, 0 ⁇ u ⁇ 2, 0 ⁇ v ⁇ 1, 0 ⁇ w ⁇ 1, 0 ⁇ x ⁇ 6.
  • a 2 is one or more of H + , Li + , Na + , K + , NH 4 + , Rb + , Cs + , Fr + , Be 2+ , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ and Ra 2+ , M 6 and M 7 are each independently Ti, V, Cr, Mn, Fe, Co, Cations of one or more transition metal elements selected from Ni, Cu, Zn, Sn and W.
  • A2 is one or more selected from Li + , Na + and K +
  • M6 is one or more selected from Mn, Fe, Co, Ni and Cu
  • M7 is one or more selected from Mn, Fe, Co, Ni and Cu.
  • the positive electrode active material layer may further include a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the positive electrode active material layer may also optionally include a binder.
  • the conductive agent may be selected from a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof.
  • the carbon-based material may be selected from at least one of natural graphite, artificial graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the metal-based material may be selected from metal powders and metal fibers.
  • the conductive polymer may include a polyphenylene derivative.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • the positive electrode current collector may be an aluminum foil.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may be selected from one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.
  • the polymer material base layer may be selected from polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.
  • the positive electrode sheet in the present application can be prepared according to conventional methods in the art.
  • the positive electrode active material layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing.
  • the positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring them evenly.
  • the solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.
  • the positive electrode sheet of the present application does not exclude other additional functional layers in addition to the positive electrode active material layer.
  • the positive electrode sheet of the present application also includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the positive electrode current collector and the positive electrode active material layer and disposed on the surface of the positive electrode current collector.
  • the positive electrode sheet of the present application also includes a protective layer covering the surface of the positive electrode active material layer.
  • the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate.
  • the electrolyte that can be used in the electrochemical device of the present application can be an electrolyte known in the prior art.
  • the electrolyte may include an organic solvent, an electrolyte salt, and optional additives.
  • the types of the organic solvent, the lithium salt, and the additives are not particularly limited and may be selected according to requirements.
  • the electrochemical device is a lithium ion battery
  • the electrolyte salt may include a lithium salt.
  • the lithium salt includes, but is not limited to, at least one of LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiClO 4 (lithium perchlorate), LiFSI (lithium bisfluorosulfonyl imide), LiTFSI (lithium bistrifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorobisoxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate).
  • the electrochemical device is a sodium ion battery
  • the electrolyte salt may include a sodium salt.
  • the sodium salt may be selected from at least one of NaPF 6 , NaClO 4 , NaBCl 4 , NaSO 3 CF 3 and Na(CH 3 )C 6 H 4 SO 3 .
  • the organic solvent includes but is not limited to ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sul
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include 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 additive includes but is not limited to at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl carbonate (VEC), diethylene sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propane sultone (PS), 1,3-propylene sultone (PST), sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB).
  • FEC fluoroethylene carbonate
  • VC vinylene carbonate
  • VEC vinyl carbonate
  • DTD diethylene sulfate
  • ES vinyl sulfite
  • PS 1,3-propane sultone
  • PST 1,3-propylene sultone
  • succinic anhydride succinonit
  • the electrolyte can be prepared by conventional methods in the art. For example, an organic solvent, an electrolyte salt, The optional additives are mixed evenly to obtain an electrolyte. There is no particular restriction on the order of adding the materials, for example, the electrolyte salt and the optional additives are added to the organic solvent and mixed evenly to obtain the electrolyte; or, the electrolyte salt is first added to the organic solvent, and then the optional additives are added to the organic solvent and mixed evenly to obtain the electrolyte.
  • the separator is disposed between the positive electrode and the negative electrode, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing active ions to pass through.
  • the present application has no particular restrictions on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited to these.
  • the material of the isolation membrane may include polyethylene and/or polypropylene.
  • the isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different. In some embodiments, a ceramic coating or a metal oxide coating can also be provided on the isolation membrane.
  • 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 electrochemical device of the present application also includes an outer package for packaging the electrode assembly and the electrolyte.
  • the outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., or a soft package, such as a bag-type soft package.
  • the material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PBS polybutylene succinate
  • FIG1 is an electrochemical device 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 membrane 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 electrochemical device 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • the beneficial effects that can be achieved by the electrochemical device according to the present application are mainly described by taking the secondary battery as a specific example in the above description of the embodiments of the electrochemical device, it is easy for those skilled in the art to It is understood that in the electrochemical device according to the present application, the thickness difference between any positions in any cross-section of the positive electrode current collector is within a suitable range, so that the positive electrode current collector has high mechanical strength, and thus the electrochemical device has high safety performance. Therefore, when applied to other types of electrochemical devices, the corresponding beneficial effects can also be achieved.
  • a fourth aspect of the present application provides an electrical device, which includes the electrochemical device of the third aspect of the present application.
  • the electric device of the present application is not particularly limited, and it can be used for any electronic device known in the prior art.
  • the electric device can include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.
  • Fig. 3 is an example of an electric device, which is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • phenolic resin powder 200g was spread flat on a 25cm ⁇ 40cm stainless steel plate and placed in a vacuum oven. The oven was heated to 300°C and kept warm for 3h. During this period, compressed air was continuously introduced into the oven at a rate of 3L/min to obtain an oxygenated hard carbon precursor material; the oxygenated hard carbon precursor material was heated to 600°C at a heating rate of 1°C/min in a nitrogen atmosphere with a flow rate of 1L/min, and kept warm for 2h to obtain a pre-carbonized product; then the temperature was increased to 1100°C at a heating rate of 5°C/min in a nitrogen atmosphere with a flow rate of 1L/min, and kept warm for 2h.
  • the negative electrode active material, binder styrene-butadiene rubber and sodium carboxymethyl cellulose (CMC-Na) were dissolved in deionized water at a weight ratio of 97:1.5:1.5 to form a negative electrode slurry (solid content of 40wt%).
  • a 10 ⁇ m thick copper foil was used as the negative electrode current collector, and the negative electrode slurry was coated on the current collector of the negative electrode sheet with a coating thickness of 50 ⁇ m, dried at 85°C, and then cold pressed, cut and slit, and dried under vacuum conditions at 120°C for 12 hours to obtain a negative electrode sheet.
  • the positive electrode active materials lithium cobalt oxide, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:1.4:1.6, N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred evenly to obtain a positive electrode slurry; the positive electrode slurry (solid content is 72wt%) is evenly coated on the positive electrode collector aluminum foil with a coating thickness of 80 ⁇ m, and then dried at 85°C, and then after cold pressing, cutting and slitting, it is dried under vacuum conditions at 85°C for 4 hours to obtain a positive electrode sheet.
  • NMP N-methylpyrrolidone
  • Ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) are mixed in a mass ratio of 1:1:1 to obtain an organic solvent; LiPF 6 is dissolved in the organic solvent, and then fluoroethylene carbonate (FEC) is added and mixed uniformly to obtain an electrolyte. Based on the total mass of the electrolyte, the mass percentage of LiPF 6 is 12.5%, and the mass percentage of fluoroethylene carbonate is 5%.
  • Polyethylene (PE) with a thickness of 7 ⁇ m was used as the separator.
  • the positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in order to obtain an electrode assembly, which is then placed in an outer package, and the above-mentioned electrolyte is added. After packaging, standing, forming, shaping, and other processes, a lithium-ion battery is obtained.
  • the design potential range of a lithium-ion battery is 2.0V to 4.53V.
  • the insulation time of the phenolic resin in the oven was adjusted to 6h, 9h, 12h, 16h and 20h respectively to prepare the negative electrode active materials of Examples 2 to 6.
  • Example 2 Based on the preparation process of Example 1, the D V 50 of the hard carbon material was adjusted as shown in Table 2 to prepare negative electrode active materials, negative electrode sheets, positive electrode sheets, electrolytes, separators and lithium ion batteries of Examples 7 to 11.
  • the negative electrode active materials are hard carbon material and artificial graphite. Based on the preparation process of Example 1, the amounts of hard carbon material and artificial graphite are adjusted as shown in Table 3 (wherein the mass proportion of hard carbon is calculated based on the sum of the masses of hard carbon material and artificial graphite, and the mass proportion of artificial graphite is also calculated based on the sum of the masses of hard carbon material and artificial graphite) to prepare the negative electrode active materials, negative electrode sheets, positive electrode sheets, electrolytes, isolation membranes and lithium-ion batteries of Examples 12 to 16.
  • the negative electrode active material is adjusted to artificial graphite
  • the design potential range of the lithium ion battery is adjusted to 3.0V to 4.48V
  • the negative electrode sheet, positive electrode sheet, electrolyte, isolation membrane and lithium ion battery of Comparative Example 1 are prepared.
  • Example 2 Based on the preparation process of Example 1, the negative electrode active material was replaced with Kuraray's TZ-509R hard carbon to prepare the negative electrode plate, positive electrode plate, electrolyte, isolation membrane and lithium ion battery of Comparative Example 2.
  • Example 2 Based on the preparation process of Example 1, the phenolic resin was not subjected to oxygenation treatment, and the negative electrode active material, negative electrode plate, positive electrode plate, electrolyte, isolation membrane and lithium ion battery of Comparative Example 2 were prepared.
  • Example 2 Based on the preparation process of Example 1, the D V 50 of the hard carbon material was adjusted as shown in Table 1 to prepare negative electrode active materials, negative electrode sheets, positive electrode sheets, electrolytes, separators and lithium ion batteries of Comparative Examples 7 to 5.
  • Example 1 Based on the preparation process of Example 1, the mass ratio of the hard carbon material to the artificial graphite was adjusted as shown in Table 1 (wherein the mass ratio of the hard carbon is calculated based on the sum of the masses of the hard carbon material and the artificial graphite, and the mass ratio of the artificial graphite is also calculated based on the sum of the masses of the hard carbon material and the artificial graphite), and the negative electrode active material, negative electrode sheet, positive electrode sheet, electrolyte, isolation membrane and lithium-ion battery of Comparative Example 6 were prepared.
  • Table 1 wherein the mass ratio of the hard carbon is calculated based on the sum of the masses of the hard carbon material and the artificial graphite, and the mass ratio of the artificial graphite is also calculated based on the sum of the masses of the hard carbon material and the artificial graphite
  • the negative electrode active material, negative electrode sheet, positive electrode sheet, electrolyte, isolation membrane and lithium-ion battery of Comparative Example 6 were prepared.
  • test parameters target material is CuK ⁇ ; voltage and current are 40KV/40mA; scanning angle range is 5° to 80°; scanning step length is 0.00836°; each step time is 0.3s.
  • the negative electrode active material was dispersed in an ethanol dispersant and subjected to ultrasound for 30 minutes. The sample was then added to a Malvern particle size tester to test the D V 50 of the hard carbon material.
  • the specific surface area of the negative electrode active material was measured by the nitrogen adsorption/desorption method: the negative electrode active material was dried in a vacuum drying oven, then loaded into a sample tube and measured in an analyzer.
  • the negative electrode active material is made into a negative electrode sheet through mixing, coating and drying. Lithium sheets are used as positive electrodes and assembled into button batteries for testing.
  • the button battery is discharged to 0mV at 0.05C, discharged to 0mV at 50 ⁇ A, discharged to 0mV at 10 ⁇ A, and charged to 2.5V at 0.1C.
  • the capacity of the button battery at this time is recorded, and the capacity divided by the mass of the active material on the negative electrode sheet is recorded as the gram capacity.
  • 0.05C refers to the current value at 0.05 times the preset gram capacity
  • 0.1C refers to the current value at 0.1 times the preset gram capacity.
  • the charging capacity divided by the discharge capacity is recorded as the first efficiency.
  • the charging capacity divided by the charging energy is recorded as the average potential for delithiation.
  • the gram capacity of the charging section from 0V to 0.15V divided by the total charging capacity is recorded as the ratio of the gram capacity of delithiation from 0V to 0.15V to the total gram capacity C1 / C0 .
  • the voltage-capacity curve of the button battery corresponding to Example 4 during the above-mentioned charging and discharging process is recorded as the ratio of the gram capacity of delithiation from 0V to 0.15V to the total gram capacity C1 / C0 .
  • Test instrument ASAP2460-physical adsorption analyzer
  • the ASAP2460-physical adsorption analyzer was used for testing.
  • the test atmosphere was carbon dioxide.
  • Different test pressures were adjusted to measure the adsorption of carbon dioxide and draw adsorption and desorption isotherms.
  • the shape of the pores was determined according to the shape of the hysteresis loop, and DFT was used to calculate the adsorption capacity of carbon dioxide.
  • the model is used to fit the pore size distribution curve of the micropores, and the micropore volume V cc/g and the micropore diameter d ⁇ m of the hard carbon material are calculated.
  • Test instrument Element analyzer (Elementar Unicube)
  • the negative electrode active material layer samples were prepared into complete discs, 30 samples were tested for each embodiment or comparative example, and the volume of each sample was about 0.35 cm3; the porosity of the negative electrode active material layer was tested according to the standard "GB/T24586-2009 Determination of apparent density, true density and porosity of iron ore".
  • the negative electrode current collector is coated with a negative electrode active material layer on both sides
  • the weight is recorded as W 1
  • a micrometer to measure the thickness T 1 of the negative electrode sheet
  • W 2 the compaction density of the negative electrode active material layer arranged on one side of the negative electrode current collector
  • PD (W 1 -W 2 )/[(T 1 -T 2 ) ⁇ S].
  • the upper limit charging voltage of the lithium ion battery whose negative electrode active material includes graphite is 4.48V, and the discharge cut-off voltage is 3.0V;
  • the upper limit charging voltage of the lithium ion battery of the embodiment whose negative electrode active material is pure hard carbon is 4.53V, and the discharge cut-off voltage is 2.0V.
  • the first charge and discharge are performed, constant current charging is performed at a charging current of 1C until the upper limit voltage is reached and then constant voltage charging is performed, and then constant current discharge is performed at a discharge current of 1C until the discharge cut-off voltage is reached, and the discharge capacity and full charge thickness of the first cycle are recorded; then 800 charge and discharge cycles are performed, and the discharge capacity and full charge thickness of the lithium ion battery are recorded at the 800th cycle.
  • the upper limit voltage of the lithium ion battery in the embodiment where the negative electrode active material is graphite or blended graphite is 4.48V, and the discharge cut-off voltage is 3.0V; the upper limit voltage of the lithium ion battery in the embodiment where the negative electrode active material is pure hard carbon is 4.53V, and the discharge cut-off voltage is 2.0V.
  • Cycle capacity retention rate (discharge capacity of the 800th cycle/discharge capacity of the first cycle) ⁇ 100%;
  • Cycle thickness expansion rate (thickness of the fully charged lithium-ion battery at the 800th cycle - thickness of the fully charged lithium-ion battery at the first cycle) / thickness of the fully charged lithium-ion battery at the first cycle ⁇ 100%.
  • test data of each embodiment and comparative example are shown in Table 1 to Table 3 respectively.
  • the hard carbon material has a higher gram capacity and a ratio of 0V to 0.15V lithium delithiation capacity to the total capacity, indicating that the oxygen treatment of the precursor can effectively increase the micropore content of the hard carbon material, thereby obtaining a higher gram capacity, and the lithium-ion battery using the hard carbon material has the highest energy density.
  • Example 4 By comparing Example 4, Example 7 to Example 11, Comparative Example 4 and Comparative Example 5, it can be seen that the hard carbon active materials after three carbonizations have a specific surface area close to that of commercial graphite. Controlling the particle size of the hard carbon active material by crushing and screening can effectively adjust the Dv50 and specific surface area of the material, further improving the initial efficiency and cycle performance of the lithium-ion battery.
  • the particle size of the negative electrode active material is small, the irreversible capacity of the lithium-ion battery in the first week will increase, and the continuous consumption of lithium ions during the cycle will affect the cycle performance of the lithium-ion battery.
  • the present application is not limited to the above-mentioned embodiments.
  • the above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application.
  • other methods of applying various deformations that can be thought of by those skilled in the art to the embodiments and combining some of the constituent elements in the embodiments are also included in the scope of the present application.

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Abstract

本申请提供了一种负极活性材料、包含其的负极极片、电化学装置及用电装置。该负极活性材料包括硬碳材料，硬碳材料具有多个微孔，以使硬碳材料以金属锂为对电极的脱锂平均电位为0.15V(vs Li+/Li)至0.40V(vs Li+/Li)。

Description

负极活性材料、包含其的负极极片、电化学装置及用电装置
相关申请的交叉引用
本申请要求享有于2022年09月30日提交的名称为“负极活性材料、包含其的负极极片、电化学装置及用电装置”的中国专利申请202211206036.6的优先权，该申请的全部内容通过引用并入本文中。
技术领域
本申请属于电化学电池技术领域，具体涉及一种负极活性材料、包含其的负极极片、电化学装置及用电装置。
背景技术
以锂离子二次电池为代表的二次电池具有能量密度高、循环寿命长，以及污染小、无记忆效应等突出特点。作为清洁能源，二次电池的应用已由电子产品逐渐普及到电动汽车等大型装置领域，以适应环境和能源的可持续发展战略。由此，也对二次电池的能量密度提出了更高的要求。
目前，商业化的二次电池负极材料仍以石墨为主。石墨具有高电导率和高稳定性等优势。但是，石墨理论容量约为372mAh/g，近年来几乎已开发到其理论容量上限，以石墨为负极材料的锂离子电池的能量密度难以进一步提升。
因此，开发一种负极活性材料，以提升二次电池的能量密度，对二次电池的发展具有重要的意义。
发明内容
鉴于现有技术存在的上述问题，本申请提供一种负极活性材料、包含其的负极极片、电化学装置及用电装置，该负极活性材料具有低的脱锂平均电位，能够提升负极极片、电化学装置及用电装置的能量密度。
本申请的第一方面提供一种负极活性材料，包括硬碳材料，硬碳材料具有多个微孔，以使负极活性材料以金属锂为对电极的脱锂平均电位为0.15V(vs Li+/Li) 至0.40V(vs Li+/Li)。
在任意实施方式中，硬碳材料的氧原子与碳原子的平均摩尔数之比O/C值为0.01至0.10。
在任意实施方式中，硬碳材料的O/C值为0.02至0.07。
在任意实施方式中，负极活性材料满足：其中，C1mAh/g表示以金属锂为对电极，硬碳材料在0V(vs Li+/Li)至0.15V(vs Li+/Li)之间的脱锂容量；C0mAh/g表示以金属锂为对电极，硬碳材料的脱锂总容量。
在任意实施方式中，硬碳材料的X射线衍射图谱具有位于18°至30°之间的特征峰，特征峰的半峰宽为4°至12°。
在任意实施方式中，硬碳材料包括内核及位于内核的至少部分表面的包覆层，丰富的微孔位于内核中。
在任意实施方式中，硬碳材料通过二氧化碳气体吸附法测得的微孔孔体积V满足：0cc/g＜V≤0.05cc/g，微孔的直径d nm满足：d nm≤0.9nm。
在任意实施方式中，硬碳材料通过正丁醇浸渍法测得的真密度ρg/cc为1.1g/cc至1.6g/cc。
在任意实施方式中，硬碳材料的DV50为6μm至15μm。
在任意实施方式中，硬碳材料的比表面积为2m2/g至10m2/g。
本申请的第二方面提供一种负极极片，包括负极集流体以及位于负极集流体至少一个表面上的负极活性材料层，负极活性材料层包括第一方面的负极活性材料。
在任意实施方式中，负极活性材料层还包括人造石墨，负极活性材料与人造石墨的质量比A满足：0＜A≤1/3。
在任意实施方式中，负极活性材料层的压实密度PD g/cm3为1.0g/cm3至1.7g/cm3。
在任意实施方式中，负极活性材料层的孔隙率为15％至30％。
本申请的第三方面提供一种电化学装置，包括根据第二方面的负极极片。
本申请的第四方面提供一种用电装置，包括第三方面的电化学装置。
附图说明
图1是本申请电化学装置的实施方式的示意图；
图2是图1所示的本申请的电化学装置的实施方式的分解图；
图3是本申请的电化学装置的实施例用作电源的用电装置的示意图；
图4是本申请实施例4对应的扣式电池的电压-容量曲线图；
附图标记说明：
5电化学装置；51壳体；52电极组件；53盖板。
具体实施方式
以下，适当地参照附图具体说明本申请的电化学装置和用电装置的实施方式。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，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”。更具体地，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)。
如背景技术所述，寻找负极活性材料以提升二次电池的能量密度，对二次电池的发展具有重要的意义。在众多有待开发的负极活性材料中，硬碳材料由于其克容量高、倍率性能良好、低温性能和循环性能良好等优势，受到了极大的关注。不仅如此，硬碳材料既可以作为锂离子电池的负极活性材料，又可以作为钠离子电池的负极活性材料，具有广阔的应用前景。然而，现有的硬碳材料存在不可逆容量高、容量发挥不理想等缺陷，应用于锂离子电池或钠离子电池，对电池能量密度的提升十分有限，难以满足实际应用的需要。
鉴于此，发明人经深入思考，提供了一种负极活性材料，该负极活性材料具有低的脱锂平均电位，应用于二次电池，能够提升二次电池的能量密度。
负极活性材料
本申请第一方面提供一种负极活性材料，包括硬碳材料，该硬碳材料具有多个微孔，以使硬碳材料以金属锂为对电极的脱锂平均电位为0.15V(vs Li+/Li)至0.40V(vs Li+/Li)。并非意在受限于任何理论或解释，发明人意外地发现：当硬碳材料中具有多个微孔时，在嵌锂过程中，锂离子能够储存于微孔内，从而提供可逆容量。当硬碳材料中具有特定的微孔结构，以使得硬碳材料以金属锂为对电极的脱锂平均电位在上述较低的范围内时，硬碳材料一方面能够具有高可逆容量，尤其是低电压平台容量，另一方面能够具有良好的锂离子扩散动力学性能。由此，本申请的负极活性材料应用于二次电池，能够允许二次电池具备高能量密度、高首次库伦效率和良好的循环性能。
上述特定的微孔结构意在表示任何能够使得硬碳材料以金属锂为对电极的脱锂平均电位为0.15V(vs Li+/Li)至0.40V(vs Li+/Li)的微孔结构，其可以包括微孔的数量、体积在任意合适范围内的微孔结构，和/或微孔的形貌、在硬碳材料中的分布位置合适的微孔结构，但不限于此。本领域技术人员可以通过多种方式获得具有特定微孔结构的硬碳材料，以使得负极活性材料以金属锂为对电极的脱锂平均电位为0.15V(vs Li+/Li)至0.40V(vs Li+/Li)，在此不作限定。
在一些实施方式中，硬碳材料的氧原子与碳原子的平均摩尔数之比O/C值可为0.01至0.10。例如，硬碳材料的O/C值可以为0.01，0.02，0.05，0.07，0.10或者处于以上任意数值所组成的范围内。可选地，硬碳材料的O/C值可以为0.02至0.07。例如，硬碳材料的O/C值可以为0.02，0.03，0.04，0.05，0.06，0.07或 者处于以上任意数值所组成的范围内。并非意在受限于任何理论或解释，当硬碳材料中，O/C值在上述合适的范围内时，少量氧原子的存在有利于锂离子在微孔内部的脱嵌，从而有利于负极活性材料的容量发挥。此外，O/C值在上述合适的范围内时，还将能够降低由于氧含量过高带来不可逆容量损失的风险，从而提升负极活性材料的可逆容量。由此，本申请的负极活性材料应用于二次电池，能够进一步提升二次电池的能量密度和首次库伦效率。
在一些实施方式中，负极活性材料可满足：其中，C1mAh/g表示以金属锂为对电极，所述硬碳材料在0V(vs Li+/Li)至0.15V(vs Li+/Li)之间的脱锂容量；C0mAh/g表示以金属锂为对电极，所述硬碳材料的脱锂总容量。并非意在受限于任何理论或解释，在以金属锂为对电极的脱锂容量测试过程中，存储于硬碳材料的微孔内的锂离子通常于0V至0.15V之间脱出，故上述C1与硬碳材料内的微孔结构相关度较高。C1满足上述条件时，意味着硬碳材料内的微孔结构能够提供更多的可逆容量，以使得硬碳材料在低电压平台下的脱锂容量在脱锂总容量中具有较高的占比，较高的低电压平台容量占比有助于进一步降低硬碳材料的脱锂平均电位，由此，本申请的负极活性材料应用于二次电池，能够进一步提升二次电池的能量密度。
在一些实施方式中，硬碳材料的X射线衍射(XRD)图谱可具有位于18°至30°之间的特征峰，该特征峰的半峰宽为4°至12°。当负极活性材料的XRD图片具有上述特征峰时，可表示硬碳材料的002晶面间距在0.37nm至0.41nm之间，远大于石墨的002面间距。较大的002晶面间距有助于锂离子在硬碳材料内部的快速脱嵌，从而能够提升负极活性材料的可逆容量和动力学性能。由此，本申请的负极活性材料应用于二次电池，能够提升二次电池的能量密度和倍率性能。
在一些实施方式中，硬碳材料可包括内核及位于内核的至少部分表面的包覆层，所述微孔位于内核中。上述包覆层可以为不包含微孔的致密包覆层。在一些实施例中，包覆层的厚度可以为小于等于100nm。在一些实施例中，包覆层可以覆盖内核的50％表面积以上，80％表面积以上，90％表面积以上，或者100％表面积。当硬碳材料具有上述结构时，包覆层能够将内核表面的开口微孔转化为闭口微孔，从而有效隔绝微孔内部与电解液接触，进而减少由电解液在微孔内部形成SEI膜导致的活性离子的不可逆损失。由此，能够提升负极活性材料的可逆容量，从而允许应用该负极活性材料的二次电池具备高能量密度以及高首次库伦效 率。
在一些实施方式中，硬碳材料包括内核及位于内核的至少部分表面的包覆层。硬碳材料通过二氧化碳气体吸附法测得的微孔孔体积V可满足：0cc/g＜V≤0.05cc/g。当硬碳材料包括包覆于内核至少部分表面的包覆层时，包覆层能够将内核表面的开口微孔转化为闭孔微孔；当部分微孔具有较小的体积时，在二氧化碳气体吸测试过程中，二氧化碳分子不仅难以进入内核的微孔，以进行吸附和脱附，而且也难以被部分小体积微孔吸附，由此，硬碳材料通过二氧化碳气体吸附法测得的微孔孔体积在上述较小的范围内。当硬碳材料通过二氧化碳气体吸附法测得的微孔孔体积在上述较小的范围内时，一方面，包覆层能够有效隔绝微孔内部与电解液接触，从而减少由电解液在微孔内部形成SEI膜导致的活性离子的不可逆损失；另一方面，小体积微孔有利于半径较小的锂离子或钠离子沉积，从而能够进一步提升硬碳材料的储锂容量/储钠容量。由此，本申请的负极活性材料应用于二次电池，能够进一步提升二次电池的能量密度和首次库伦效率。
在一些实施方式中，微孔的直径d nm可满足：d nm≤0.9nm。微孔的直径在上述合适的范围内，有利于锂离子(离子半径约为76pm)或钠离子(离子半径约为102pm)在微孔内顺利地沉积和脱出，从而有利于提升硬碳颗粒的可逆容量。由此，本申请的负极活性材料能够具有高可逆容量，应用于二次电池，能够允许电池具备更高的能量密度。
在一些实施方式中，硬碳材料通过正丁醇浸渍法测得的真密度ρg/cc可为1.1g/cc至1.6g/cc。石墨材料通过正丁醇浸渍法测得的真密度约为2.22g/cc。本申请的负极活性材料中，硬碳材料具有较多的微孔以及较大的002晶面间距，从而能够在具有高容量的同时，具有更低的真密度。由此，本申请的负极活性材料应用于二次电池，还能够提升二次电池的质量能量密度。
在一些实施方式中，硬碳材料的体积平均粒径DV50可以为6μm至15μm。例如，硬碳材料的DV50可以为6μm，7μm，8μm，9μm，10μm，11μm，12μm，13μm，14μm，15μm或处于以上任意数值所组成的范围内。可选地，硬碳材料可以为一次颗粒。当硬碳材料的体积平均粒径在上述合适的范围内时，一方面能够硬碳材料具有良好的电解液浸润性能，另一方面能够使得硬碳材料具有较小的比表面积，从而减少首次充电过程中，由于在硬碳材料表面形成SEI膜而消耗的活性离子。由此，本申请的负极活性材料应用于二次电池，能够使得二次电池兼具 良好的动力学性能和高首次库伦效率。
在一些实施方式中，硬碳材料的比表面积可以为2m2/g至10m2/g。例如，硬碳材料的比表面积可以为2m2/g，3m2/g，4m2/g，5m2/g，6m2/g，7m2/g，8m2/g，9m2/g，10m2/g或处于以上任意数值所组成的范围内。一般来说，负极活性材料颗粒的比表面积越大，在二次电池首次充电的过程中，负极活性材料颗粒表面形成的SEI膜的面积也越大，损失的活性离子也越多。此外，负极活性材料颗粒的比表面积越大，形成负极活性材料层所需要消耗的粘结剂也越多，由此，负极活性材料层的内阻也越高。当硬碳材料的比表面积在上述合适的范围内时，应用于二次电池，既能够使得首次充电过程中，形成的SEI膜具有合适大小的面积，又能够减少负极活性材料层中粘结剂的用量。由此，能够降低活性离子的损失和负极活性材料层的内阻，从而提升二次电池的首次库伦效率、能量密度、循环性能以及安全性能。
作为一个示例，本申请的负极活性材料中的硬碳材料可以通过如下步骤S10至S40获得。需要说明的是，本申请的负极活性材料中的硬碳材料可以通过多种方式获得，本示例仅是用于解释本申请，而非为了限制本申请。
S10，将硬碳前驱体材料置于含氧气氛中，使反应体系温度保持在100℃至300℃，从而得到赋氧硬碳前驱体材料。
在步骤S10中，硬碳前驱体材料可以选自沥青、生物质、树脂类材料中的一种或几种。含氧气氛表示含有氧气的气氛，例如，可以为压缩空气，或者是氧气与惰性气体的混合气体，该混合气体中，氧气的质量百分含量可以为1％至100％。含氧气氛的气体流速可以为0.1L/min至5L/min。步骤S10的反应时长可以为小于等于48h。
S20，将赋氧硬碳前驱体材料置于惰性气氛中，以0.5℃/min至5℃/min的升温速率升温到450℃至650℃后，保温一段时间，以使赋氧硬碳前驱体材料预碳化，从而得到预碳化产物。
在步骤S20中，惰性气氛可以包括不与赋氧硬碳前驱体材料发生副反应的气氛，例如，可以为氮气气氛、氩气气氛或其他稀有气体气氛。惰性气氛的气体流速可以为0.1L/min至5L/min。步骤S20中，保温的时长可以为1h至4h。
S30，将预碳化产物置于惰性气氛中，以0.5℃/min至10℃/min的升温速率升温到700℃至1600℃后，保温一段时间，以使预碳化产物进一步碳化，从而得 到碳化产物。
在步骤S30中，惰性气氛可以包括不与预碳化产物发生副反应的气氛，例如，可以为氮气气氛、氩气气氛或其他稀有气体气氛。惰性气氛的气体流速可以为0.1L/min至5L/min。步骤S30中，保温的时长可以为1h至12h。在一些实施例中，得到碳化产物后，还可以对碳化产物进行破碎和粒度分级处理，从而得到粒径在合适范围内的碳化产物。
S40，将碳化产物置于还原性气氛中，以0.5℃/min至20℃/min的升温速率升温到500℃至1100℃后，保温一段时间，从而得到硬碳材料。
在步骤S40中，还原气氛可以选自含有还原性气体的气氛，例如可以为乙炔的质量百分含量为5％的乙炔-氩气混合气，或者甲烷的质量百分含量为10％的甲烷-氩气混合气。还原气氛的气体流速可以为0.1L/min至3L/min。步骤S40中，保温的时长可以为0.1h至8h。
上述示例中，通过对硬碳前驱体材料进行赋氧处理，提升硬碳前驱体材料的氧含量，能够改***碳前驱体材料内部的交联结构。由此，经碳化后，材料内部能够具有合适的微孔结构，并具有较高的微孔含量。通过对碳化产物在还原性气氛中保温处理，一方面能够在碳化产物表面形成致密的包覆层，从而得到由包含多个微孔的内核和包付出组成的硬碳材料，另一方面能够降低碳化产物的氧含量，使得硬碳材料的O/C值在合适的范围内。由此，能够制备得到具有多个微孔，以使硬碳材料以金属锂为对电极的脱锂平均电位为0.15V(vs Li+/Li)至0.40V(vs Li+/Li)的硬碳材料。
本申请中，硬碳材料以金属锂为对电极的脱锂平均电位具有本领域公知的含义，可采用本领域已知的方法测定。例如，可以将硬碳材料与适量的粘结剂、导电剂与溶剂混合均匀，得到负极浆料；将负极浆料涂布于负极集流体表面，得到负极极片；以金属锂片作正极极片，与该负极极片组装的的扣式电池；对扣式电池进行充放电循环，以确定扣式电池的充电容量和充电能量；用充电容量除以充电能量，即得到硬碳材料的脱锂平均电位。
本申请中，硬碳材料的O/C值具有本领域公知的含义，可采用本领域已知的方法测定。例如，可以采用元素分析仪(Elementar Unicube)测试硬碳材料的O/C值。
本申请中，C1mAh、C0mAh具有本领域公知的含义，可采用本领域 已知的方法测定。例如，可以将硬碳材料与适量的粘结剂、导电剂与溶剂混合均匀，得到负极浆料；将负极浆料涂布于负极集流体表面，得到负极极片；以金属锂片作正极极片，与该负极极片组装的的扣式电池；对扣式电池进行充放电循环；用充电容量除以充电能量，即得到硬碳材料的脱锂平均电位；将充电段0V(vs Li+/Li)至0.15V(vs Li+/Li)的克容量除以充电总容量，得到
本申请中，硬碳材料的体积平均粒径DV50具有本领域公知的含义，其表示硬碳材料在体积基准的粒度分布中，50％的颗粒粒径小于该值，可采用本领域已知的方法测定。例如，可以参照GB/T 19077-2016粒度分布激光衍射法，采用激光粒度分析仪(例如英国马尔文Mastersizer 2000E)测定。
本申请中，硬碳材料的比表面积具有本领域公知的含义，可采用本领域已知的方法测定。例如，可使用比表面积分析仪(TristarⅡ3020M)，通过氮吸附/脱附法测量硬碳材料的比表面积。
本申请中，硬碳材料的微孔直径dnm具有本领域公知的含义，可采用本领域已知的方法测定。例如，可以通过ASAP2460-物理吸附分析仪测试得到，具体地，取负极活性材料粉末进行烘干脱气预处理后，使用ASAP2460-物理吸附分析仪，测试气氛为的二氧化碳，调节不同试验压力，分别测出对二氧化碳的吸附量，绘出吸附和脱附等温线。根据滞后环的形状确定孔的形状，使用DFT模型拟合微孔的孔径分布曲线，从而得到硬碳材料的微孔直径dnm。
负极极片
本申请第二方面提供一种负极极片，包括负极集流体以及位于负极集流体至少一个表面上的负极活性材料层，负极活性材料层包括本申请第一方面的负极活性材料。
本申请的负极极片包括本申请第一方面的负极活性材料，从而能够具有高可逆容量和良好的锂离子扩散动力学性能。由此，本申请的负极活性材料应用于二次电池，能够允许二次电池具备高能量密度、高首次库伦效率和良好的循环性能。
本申请的负极极片中，负极活性材料层中并不排除除了本申请第一方面的负极活性材料外的其他负极活性材料。
在一些实施方式中，负极活性材料层还包括人造石墨，负极活性材料与人造石墨的质量比A可满足：0＜A≤1/3。负极活性材料与人造石墨的质量比在上述合适的范围内，不仅可以降低负极极片在满充状态下的体积膨胀率，还可以提升 负极活性材料层的容量，进而提升二次电池的能量密度。
在一些实施方式中，负极活性材料层还包括上述人造石墨，负极活性材料层的压实密度PD g/cm3可为1.0g/cm3至1.7g/cm3。
以硬碳材料作为单一负极活性材料制备的负极极片中，负极活性材料层的压实密度往往不高，约为0.9g/cm3至1.2g/cm3，导致硬碳材料在冷压后还存在较大空隙。与合适比例的人造石墨混合后，负极活性材料层中的负极活性材料颗粒的堆叠更为密实，从而能够具上述较高的压实密度。由此，能够提高单位体积的负极活性材料层内，负极活性材料的含量，从而允许应用本申请负极极片的二次电池具备更高的体积能量密度。
在一些实施方式中，负极活性材料层还包括上述人造石墨，负极活性材料层的孔隙率可为15％至30％。负极活性材料层的孔隙率在上述合适的范围内，使电解液充分浸润活性材料颗粒，提升动力学性能；截面孔隙率过大，活性材料颗粒间的接触点减少，二次电池的内阻增大且基体能量密度也有所损失。
本申请对负极极片的负极集流体不作限定。可以使用金属箔材、多孔金属板或复合集流体。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。作为一个示例，负极极片为锂离子电池的负极极片，负极集流体可以为铜箔。作为另一个示例，负极极片为钠离子电池的负极极片，负极集流体可以为铜箔或铝箔。
在一些实施方式中，负极集流体具有在自身厚度方向上相对的两个表面，负极活性材料层可以设置在负极集流体的一个表面，也可以同时设置在负极集流体的两个表面。例如，负极集流体具有在其自身厚度方向相对的两个表面，负极活性材料层设置在负极集流体相对的两表中的任意一个表面或两个表面上。
在一些实施方式中，所述负极活性材料层还可选地包括粘结剂。所述粘结剂可选自聚乙烯醇、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂或尼龙中的至少一种。
在一些实施方式中，负极活性材料层还可选地包括导电剂。导电剂可选自基于碳的材料、基于金属的材料、导电聚合物或上述物质的任意组合。作为示例，基于碳的材料可选自天然石墨、人造石墨、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至少一种。基于金属的材料可选自金属粉、金属纤维。导电聚合物可包括聚亚苯基衍生物。
在一些实施方式中，负极活性材料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。
本申请中负极极片可以按照本领域常规方法制备。例如将所述硬碳及可选的其他负极活性材料，导电剂，粘结剂和增稠剂分散于溶剂中，溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水，形成均匀的负极浆料，将负极浆料涂覆在负极集流体上，经烘干、冷压等工序得到负极极片。
需要说明的是，本申请所给的各负极活性材料层参数均指单侧负极活性材料层的参数范围。当负极活性材料层设置在负极集流体的两侧时，其中任意一侧的负极活性材料层参数满足本申请，即认为落入本申请的保护范围内。
另外，本申请中的负极极片并不排除除了负极活性材料层之外的其他附加功能层。例如，在某些实施方式中，本申请的负极极片还包括夹在负极集流体和负极活性材料层之间、设置于负极集流体表面的导电底涂层(例如由导电剂和粘结剂组成)。在另外一些实施方式中，本申请的负极极片还包括覆盖在负极活性材料层表面的保护层。
在本申请中，负极活性材料层的压实密度具有本领域公知的含义，可以用本领域已知的方法测定。例如，使用电子天平对面积为S的处理后负极极片(负极集流体的双面涂覆有负极活性材料层)进行称重，重量记为W1，并使用万分尺测得负极极片的厚度T1；使用溶剂洗掉负极活性材料层，烘干，测量负极集流体的重量，记为W2，并使用万分尺测得负极集流体的厚度T2；设置在负极集流体一侧的负极活性材料层的压实密度PD＝(W1-W2)/[(T1-T2)·S]。
在本申请中，负极活性材料层的的孔隙率具有本领域公知的含义，可以用本领域已知的方法测定。例如，可以根据《GB/T24586-2009铁矿石表观密度真密度和孔隙率的测定》标准，通过真密度仪测试负极活性材料层的孔隙率。
需要说明的是，本申请中，针对负极活性材料或负极活性材料层的各种参数测试，可以在电池制备过程中取样测试，也可以从制备好的二次电池中取样测试。
当上述测试样品是从制备好的锂离子电池中取样时，作为示例，可以按如下步骤(1)至(3)进行取样。
(1)将锂离子电池做放电处理(为了安全起见，一般使电池处于满放状态)；将电池拆卸后取出负极极片，使用碳酸二甲酯(DMC)将负极极片浸泡一定时间(例如2至10小时)；然后将负极极片取出并在一定温度和时间下干燥处理(例如60℃，4小时)，干燥后取出负极极片。此时即可以在干燥后的负极极片中取样测试本申请上述的负极活性材料层相关的各参数。
(2)将步骤(1)干燥后的负极极片在一定温度及时间下烘烤(例如400℃，2小时)，在烘烤后的负极极片中任选一区域，对负极活性材料取样(可以选用刀片刮粉取样)。
(3)将步骤(2)收集到的负极活性材料做过筛处理(例如用200目的筛网过筛)，最终得到可以用于测试本申请上述的各负极活性材料参数的样品。
电化学装置
本申请第三方面提出了一种电化学装置，包括其中发生电化学反应以将化学能与电能互相转化的任何装置。电化学装置可以是一次电池或二次电池，其具体实例包括所有种类的锂一次电池、锂二次电池、钠一次电池或钠二次电池。
在一些实施方式中，本申请的电化学装置包括正极极片、负极极片、隔离膜和电解液。
[负极极片]
本申请的电化学装置中使用的负极极片为本申请第二方面的负极极片。
[正极极片]
本申请的电化学装置中使用的正极极片的材料、构成和其制造方法可包括任何现有技术中公知的技术。
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上且包括正极活性材料的正极活性材料层。作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极活性材料层设置在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，正极活性材料层包括正极活性材料，正极活性材料的具体种类不受到具体的限制，可根据需求进行选择。
在一些实施方式中，电化学装置为锂离子电池。正极活性材料可以包括锂过 渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或几种。在本申请的电化学装置中，上述各正极活性材料的改性化合物可以是对正极活性材料进行掺杂改性、表面包覆改性、或掺杂同时表面包覆改性。作为示例，锂过渡金属氧化物可以包括锂钴氧化物、锂镍氧化物、锂锰氧化物、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、锂镍钴铝氧化物及其改性化合物中的一种或几种。作为示例，橄榄石结构的含锂磷酸盐可以包括磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、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及其改性化合物中的一种或几种。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，电化学装置为钠离子电池。正极活性材料可采用本领域公知的用于钠离子二次电池的正极活性材料。作为示例，正极活性材料可包括钠过渡金属氧化物、聚阴离子型化合物及普鲁士蓝类化合物中的一种或几种。作为示例，上述钠过渡金属氧化物例如可以列举出：Na1-xCuhFekMnlM1 mO2-y，其中M1为Li、Be、B、Mg、Al、K、Ca、Ti、Co、Ni、Zn、Ga、Sr、Y、Nb、Mo、In、Sn及Ba中的一种或几种，0<x≤0.33，0<h≤0.24，0≤k≤0.32，0<l≤0.68，0≤m<0.1，h+k+l+m＝1，0≤y<0.2；Na0.67Mn0.7NizM2 0.3-zO2，其中M2为Li、Mg、Al、Ca、Ti、Fe、Cu、Zn及Ba中的一种或几种，0<z≤0.1；NaaLibNicMndFeeO2，其中0.67<a≤1，0<b<0.2，0<c<0.3，0.67<d+e<0.8，b+c+d+e＝1。作为示例，上述聚阴离子型化合物例如可以列举出：A1 fM3 g(PO4)iOjX1 3-j，其中A1为H、Li、Na、K及NH4中的一种或几种，M3为Ti、Cr、Mn、Fe、Co、Ni、V、Cu及Zn中的一种或几种，X1为F、Cl及Br中的一种或几种，0<f≤4，0<g≤2，1≤i≤3，0≤j≤2；NanM4PO4X2，其中M4为Mn、Fe、Co、Ni、Cu及Zn中的一种或几种，X2为F、Cl及Br中的一种或几种，0<n≤2；NapM5 q(SO4)3，其中M5为Mn、Fe、Co、Ni、Cu及Zn中的一种或几种，0<p≤2，0<q≤2；NasMntFe3-t(PO4)2(P2O7)，其中0<s≤4，0≤t≤3，例如t为0、1、1.5、2或3。
作为示例，上述普鲁士蓝类化合物例如可以列举出：A2 uM6 v[M7(CN)6]w·xH2O，其中A2为H+、NH4 +、碱金属阳离子及碱土金属阳离子中的一种或几种，M6和M7各自独立地为过渡金属阳离子中的一种或几种，0<u≤2，0<v≤1，0<w≤1，0<x<6。例如A2为H+、Li+、Na+、K+、NH4 +、Rb+、Cs+、Fr+、Be2+、Mg2+、Ca2+、Sr2+、Ba2+及Ra2+中的一种或几种，M6和M7各自独立地为Ti、V、Cr、Mn、Fe、Co、 Ni、Cu、Zn、Sn及W中的一种或几种过渡金属元素的阳离子。优选地，A2为Li+、Na+及K+中的一种或几种，M6为Mn、Fe、Co、Ni及Cu中的一种或几种过渡金属元素的阳离子，M7为Mn、Fe、Co、Ni及Cu中的一种或几种过渡金属元素的阳离子。
在一些实施方式中，正极活性材料层还可选的包括导电剂。作为示例，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至少一种。
在一些实施方式中，正极活性材料层还可选的包括粘结剂。作为示例，导电剂可选自基于碳的材料、基于金属的材料、导电聚合物或上述物质的任意组合。作为示例，基于碳的材料可选自天然石墨、人造石墨、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至少一种。基于金属的材料可选自金属粉、金属纤维。导电聚合物可包括聚亚苯基衍生物。
在一些实施方式中，正极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，正极集流体可采用铝箔。复合集流体可包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层。作为示例，金属材料可选自铝、铝合金、镍、镍合金、钛、钛合金、银、银合金中的一种或几种。作为示例，高分子材料基层可选自聚丙烯、聚对苯二甲酸乙二醇酯、聚对苯二甲酸丁二醇酯、聚苯乙烯、聚乙烯等。
本申请中正极极片可以按照本领域常规方法制备。例如，正极活性材料层通常是将正极浆料涂布在正极集流体上，经干燥、冷压而成的。正极浆料通常是将正极活性材料、可选的导电剂、可选的粘结剂以及任意的其他组分分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)，但不限于此。
本申请的正极极片并不排除除了正极活性材料层之外的其他附加功能层。例如，在一些实施方式中，本申请的正极极片还包括夹在正极集流体和正极活性材料层之间、设置于正极集流体表面的导电底涂层(例如由导电剂和粘结剂组成)。在另外一些实施方式中，本申请的正极极片还包括覆盖在正极活性材料层表面的保护层。
[电解液]
电解液在正极极片和负极极片之间起到传导活性离子的作用。可用于本申请电化学装置的电解液可以为现有技术已知的电解液。
在一些实施方式中，所述电解液可包括有机溶剂、电解质盐和可选的添加剂，有机溶剂、锂盐和添加剂的种类均不受到具体的限制，可根据需求进行选择。
在一些实施方式中，电化学装置为锂离子电池，所述电解质盐可以包括锂盐。作为示例，所述锂盐包括但不限于LiPF6(六氟磷酸锂)、LiBF4(四氟硼酸锂)、LiClO4(高氯酸锂)、LiFSI(双氟磺酰亚胺锂)、LiTFSI(双三氟甲磺酰亚胺锂)、LiTFS(三氟甲磺酸锂)、LiDFOB(二氟草酸硼酸锂)、LiBOB(二草酸硼酸锂)、LiPO2F2(二氟磷酸锂)、LiDFOP(二氟二草酸磷酸锂)及LiTFOP(四氟草酸磷酸锂)中的至少一种。上述锂盐可以单独使用一种，也可以同时使用两种或两种以上。
在一些实施方式中，电化学装置为钠离子电池，所述电解质盐可以包括钠盐。作为示例，钠盐可选自NaPF6、NaClO4、NaBCl4、NaSO3CF3及Na(CH3)C6H4SO3中的至少一种。
在一些实施方式中，作为示例，所述有机溶剂包括但不限于碳酸亚乙酯(EC)、碳酸亚丙酯(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(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的至少一种。上述有机溶剂可以单独使用一种，也可以同时使用两种或两种以上。可选地，上述有机溶剂同时使用两种或两种以上。
在一些实施方式中，所述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。
作为示例，所述添加剂包括但不限于氟代碳酸乙烯酯(FEC)、碳酸亚乙烯酯(VC)、乙烯基碳酸乙烯酯(VEC)、硫酸乙烯酯(DTD)、硫酸丙烯酯、亚硫酸乙烯酯(ES)、1,3-丙磺酸内酯(PS)、1,3-丙烯磺酸内酯(PST)、磺酸酯环状季铵盐、丁二酸酐、丁二腈(SN)、己二腈(AND)、三(三甲基硅烷)磷酸酯(TMSP)、三(三甲基硅烷)硼酸酯(TMSB)中的至少一种。
电解液可以按照本领域常规的方法制备。例如，可以将有机溶剂、电解质盐、 可选的添加剂混合均匀，得到电解液。各物料的添加顺序并没有特别的限制，例如，将电解质盐、可选的添加剂加入到有机溶剂中混合均匀，得到电解液；或者，先将电解质盐加入有机溶剂中，然后再将可选的添加剂加入有机溶剂中混合均匀，得到电解液。
[隔离膜]
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。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，隔离膜的材质可以选自玻璃纤维、无纺布、聚乙烯、聚丙烯、聚偏氟乙烯中的一种或几种，但不仅限于这些。可选地，隔离膜的材质可以包括聚乙烯和/或聚丙烯。隔离膜可以是单层薄膜，也可以是多层复合薄膜。隔离膜为多层复合薄膜时，各层的材料相同或不同。在一些实施方式中，隔离膜上还可以设置陶瓷涂层、金属氧化物涂层。
在一些实施方式中，正极极片、上述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。
本申请的电化学装置还包括外包装，用于封装电极组件及电解液。在一些实施方式中，外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等，也可以是软包，例如袋式软包。软包的材质可以是塑料，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)中的至少一种。
本申请对电化学装置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1是作为一个示例的方形结构的电化学装置5。
在一些实施方式中，参照图2，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。电化学装置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具体实际需求进行选择。
虽然在上面关于电化学装置的实施例的描述中，主要以二次电池为具体示例说明了根据本申请的电化学装置能够实现的有益效果，但是本领域技术人员容易 理解，根据本申请的电化学装置中，正极集流体的任意横截面中，任意位置之间的厚度差在合适的范围内，从而使得正极集流体具备高机械强度，进而使得电化学装置具备高安全性能，因此应用于其它类型的电化学装置中时，同样能够实现相应的有益效果。
用电装置
本申请第四方面提供了一种用电装置，其包括本申请第三方面的电化学装置。
本申请的用电装置没有特别限定，其可以是用于现有技术中已知的任何电子设备。在一些实施方式中，用电装置可以包括但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
图3是作为一个示例的用电装置。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。
实施例
以下，说明本申请的实施例。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。实施例中未注明具体技术或条件的，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。
实施例1
负极活性材料的制备
将200g酚醛树脂粉末平铺于25cm×40cm的不锈钢铁盘内，置于真空烘箱内，烘箱升温至300℃，保温3h，期间以3L/min的速度不间断的向烘箱内部通入压缩空气，获得赋氧硬碳前驱体材料；将赋氧硬碳前驱体材料在1L/min流速的氮气气氛下以1℃/min的升温速度升温至600℃，保温2h，得到预碳化产物；然后在1L/min流速的氮气气氛下以5℃/min的升温速度升温至1100℃，保温2h，经破碎分级后得到碳化产物；取10g碳化产物在0.5L/min流速的5％wt的甲烷氩气混合气氛下以1℃/min的升温速度升温至600℃，保温2h，得到负极活性材料。
负极极片的制备
将负极活性材料、粘结剂丁苯橡胶和羧甲基纤维素钠(CMC-Na)按重量比97：1.5：1.5的比例溶于去离子水中，形成负极浆料(固含量为40wt％)。采用10μm厚度铜箔作为负极集流体，将负极浆料涂覆于负极极片的集流体上，涂覆厚度为50μm，在85℃下烘干，然后经过冷压、裁片、分切后，在120℃的真空条件下干燥12小时，得到负极极片。
正极极片的制备
将正极活性材料钴酸锂、导电炭黑(Super P)、聚偏二氟乙烯(PVDF)按照重量比97:1.4:1.6进行混合，加入N-甲基吡咯烷酮(NMP)作为溶剂，搅拌均匀得到正极浆料；将正极浆料(固含量为72wt％)均匀涂覆在正极集流体铝箔上，涂覆厚度为80μm，在85℃下烘干，然后经过冷压、裁片、分切后，在85℃的真空条件下干燥4小时，得到正极极片。
电解液的制备
将碳酸乙烯酯(EC)、碳酸丙烯酯(PC)及碳酸二乙酯(DEC)按照质量比为1:1:1进行混合，得到有机溶剂；将LiPF6溶解在上述有机溶剂中，再加入氟代碳酸乙烯酯(FEC)混合均匀，得到电解液。其中，基于电解液的总质量，LiPF6的质量百分含量为12.5％，氟代碳酸乙烯酯的质量百分含量为5％。
隔离膜的制备
采用厚度为7μm的聚乙烯(PE)作为隔离膜。
锂离子电池的制备
将正极极片、隔离膜、负极极片按顺序堆叠并卷绕得到电极组件，将电极组件放入外包装中，加入上述电解液，经封装、静置、化成、整形等工序后，得到锂离子电池。锂离子电池的设计电位区间为2.0V至4.53V。
实施例2至6
基于实施例1中负极活性材料的制备过程，将实施例2至实施例6的负极活性材料过程中，酚醛树脂在烘箱中的保温时间分别调整为6h、9h、12、16h、20h，制备得到实施例2至6的负极活性材料。
实施例2至6的负极极片、正极极片、电解液、隔离膜和锂离子电池的制备过程与实施例1相同。
实施例7至11
基于实施例1的制备过程，根据表2所示调整硬碳材料的DV50，制备实施例7至11的负极活性材料、负极极片、正极极片、电解液、隔离膜和锂离子电池。
实施例12至16
负极活性材料为硬碳材料和人造石墨，基于实施例1的制备过程，根据表3所示调整硬碳材料与人造石墨的用量(其中，硬碳质量占比基于硬碳材料和人造石墨的质量之和计算，人造石墨质量占比也基于硬碳材料和人造石墨的质量之和计算)制备实施例12至16的负极活性材料、负极极片、正极极片、电解液、隔离膜和锂离子电池。
对比例1
基于实施例1的制备过程，将负极活性材料调整为人造石墨，锂离子电池的设计电位区间调整为3.0V至4.48V，制备对比例1的负极极片、正极极片、电解液、隔离膜和锂离子电池。
对比例2
基于实施例1的制备过程，将负极活性材料替换为可乐丽的TZ-509R硬碳，制备对比例2的负极极片、正极极片、电解液、隔离膜和锂离子电池。
对比例3
基于实施例1的制备过程，对酚醛树脂不做赋氧处理，制备对比例2的负极活性材料、负极极片、正极极片、电解液、隔离膜和锂离子电池。
对比例4至对比例5
基于实施例1的制备过程，根据表1所示调整硬碳材料的DV50，制备对比例7至5的负极活性材料、负极极片、正极极片、电解液、隔离膜和锂离子电池。
对比例6
基于实施例1的制备过程，根据表1所示调整硬碳材料与人造石墨的质量比(其中，硬碳质量占比基于硬碳材料和人造石墨的质量之和计算，人造石墨质量占比也基于硬碳材料和人造石墨的质量之和计算)，制备对比例6的负极活性材料、负极极片、正极极片、电解液、隔离膜和锂离子电池。
测试部分
取完全放电的锂离子电池，拆解后取出负极用DMC(乙烯碳酸酯)浸泡20min后，再依次用DMC、丙酮各淋洗一遍，以去除电解液及表层SEI膜，之后将其置于烘箱内，80℃烘烤12h，获得处理后的负极极片；用刮刀刮下负极极片上的 粉末，并将刮下的粉末在氩气保护的条件下于管式炉中在400℃下热处理4h，以除去负极活性材料表面黏附的粘结剂，获得负极活性材料；对所获得的负极活性材料层及负极活性材料进行如下测试。
(1)XRD测试
测试仪器：X射线粉末衍射仪(仪器型号：Bruker D8 ADVANCE)
测试参数：靶材为CuKα；电压电流为40KV/40mA；扫描角度范围为5°至80°；扫描步长为0.00836°；每步长时间为0.3s。
(2)体积平均粒径DV50测试
测试仪器：马尔文粒度测试仪(Mastersizer 2000E)
将负极活性材料分散在乙醇分散剂中，超声30分钟后，将样品加入到马尔文粒度测试仪内，测试硬碳材料的DV50。
(3)比表面积测试
测试仪器：比表面积分析仪(TristarⅡ3020M)
通过氮吸附/脱附法测量负极活性材料的比表面积：将负极活性材料在真空干燥箱中烘干，然后装入样品管中，在分析仪中测量。
(4)克容量测试
将负极活性材料通过混料、涂布、烘干后制成负极片，使用锂片做正极，组装成扣式电池进行测试。
扣式电池以0.05C放电至0mV，以50μA放电至0mV，以10μA放电至0mV，以0.1C充电至2.5V，记录此时扣式电池的容量，该容量除以负极片上活性材料的质量记为克容量。0.05C指的是0.05倍预设克容量下的电流值，0.1C指的是0.1倍预设克容量下的电流值。将充电容量除以放电容量记为首次效率。将充电容量除以充电能量记为脱锂平均电位。将充电段0V至0.15V克容量除以充电总容量记为0V至0.15V脱锂克容量占总克容量比C1/C0。其中，实施例4对应的扣式电池在上述充放电过程中的电压-容量曲线图。
(5)负极活性材料孔径分布测试
测试仪器：ASAP2460-物理吸附分析仪
取负极活性材料粉末进行烘干脱气预处理后，使用ASAP2460-物理吸附分析仪进行测试，测试气氛为的二氧化碳，调节不同试验压力，分别测出对二氧化碳的吸附量，绘出吸附和脱附等温线。根据滞后环的形状确定孔的形状，使用DFT 模型拟合微孔的孔径分布曲线，计算得微孔孔体积V cc/g以及硬碳材料的微孔直径dμm。
(6)负极活性材料真密度测试
取负极活性材料粉末，参照《GB/T24203-2009炭素材料真密度、真气孔率测定方法煮沸法》标准，使用正丁醇为溶剂测试负极活性材料的真密度。
(7)O/C值测试
测试仪器：元素分析仪(Elementar Unicube)
使用元素分析仪的CHN模式和O模式分别测试上述方法获得的负极活性材料样品，分别测得负极活性材料的碳元素质量含量A、氧元素质量含量B，O/C值＝0.75×B/A。
(8)负极活性材料层孔隙率测试
将负极活性材料层样品制备成完整圆片，每个实施例或对比例测试30个样品，每个样品体积为约0.35cm3；根据《GB/T24586-2009铁矿石表观密度真密度和孔隙率的测定》标准进行测试负极活性材料层的孔隙率。
(9)负极活性材料层压实密度测试
使用电子天平对面积为S的处理后负极极片(负极集流体的双面涂覆有负极活性材料层)进行称重，重量记为W1，并使用万分尺测得负极极片的厚度T1；使用溶剂洗掉负极活性材料层，烘干，测量负极集流体的重量，记为W2，并使用万分尺测得负极集流体的厚度T2；设置在负极集流体一侧的负极活性材料层的压实密度PD＝(W1-W2)/[(T1-T2)·S]。
(10)锂离子电池能量密度测试
每组锂离子电池各取5支。首先，在25℃的环境中，进行第一次充电和放电，在0.5C的充电电流下进行恒流和恒压充电，直到上限电压，然后在0.2C的放电电流下进行恒流放电，放电至截止电压，计算各实施例和对比例相对于对比例1的能量密度百分比。
其中，负极活性材料包含石墨的锂离子电池充电上限电压为4.48V，放电截至电压为3.0V；负极活性材料为纯硬碳的实施例的锂离子电池充电上限电压为4.53V，放电截至电压为2.0V。
(11)锂离子电池循环性能测试
每组锂离子电池各取5支。通过以下步骤对锂离子电池重复进行充电和放电， 并计算锂离子电池的放电容量保持率和厚度膨胀。
首先，在25℃的环境中，进行第一次充电和放电，在1C的充电电流下进行恒流充电，直到达到上限电压后转为恒压充电，然后在1C的放电电流下进行恒流放电，直到放电截至电压，记录首次循环的放电容量和满充l厚度；而后进行800次的充电和放电循环，记录第800次循环的放电容量和满充锂离子电池的厚度。其中，负极活性材料为石墨或掺混石墨的实施例的锂离子电池充电上限电压为4.48V，放电截至电压为3.0V；负极活性材料为纯硬碳的实施例的锂离子电池充电上限电压为4.53V，放电截至电压为2.0V。
循环容量保持率＝(第800次循环的放电容量/首次循环的放电容量)×100％；
循环厚度膨胀率＝(第800次循环的满充锂离子电池的厚度-首次循环的满充锂离子电池的厚度)/首次循环的满充锂离子电池的厚度×100％。
各实施例及对比例的测试数据分别如表1至表3所示。
表1
通过对比实施例1～实施例6、对比例1至对比例3可以看出，通过对前驱体的赋氧处理，硬碳材料具有更高的克容量和0V至0.15V脱锂容量占总容量比，说明对前驱体的赋氧处理可以有效的提升硬碳材料的微孔含量，进而获得更高的克容量，且使用该硬碳材料的锂离子电池具备最高的能量密度。
表2
通过对比实施例4、实施例7～实施例11、对比例4、对比例5可以看出，经三次碳化后的硬碳活性材料均具有接近商用石墨的比表面积，通过破碎筛分控制硬碳活性材料的粒度能够有效调整材料的Dv50及比表面积，进一步提升锂离子电池的首次效率和循环性能，当负极活性材料的粒径较小时，会增加锂离子电池的首周不可逆容量，在循环过程中锂离子的持续消耗，影响锂离子电池的循环性能。
表3
通过实施例12～实施例16、对比例1和对比例6可以看出，随着硬碳材料质量比的提升，负极活性材料层的压实密度程下降趋势，负极活性材料层的孔隙率变大。由于硬碳不仅在脱锂和嵌锂过程中的体积膨胀率低，而且能够限制石墨在充放电过程的体积膨胀，硬碳质量占比高的实施例，其对应的锂离子电池在循环厚度膨胀率越小，循环容量保持率也更加优异。当掺混人造石墨与硬碳材料的质量占比适当时，负极极片能够兼具较高的硬碳含量和较高的压实密度，其对应的 锂离子电池的能量密度也相对更高。
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。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。

Claims (12)

  1. 一种负极活性材料，包括硬碳材料，所述硬碳材料具有多个微孔，所述硬碳材料以金属锂为对电极的脱锂平均电位为0.15V至0.40V。
  2. 根据权利要求1所述的负极活性材料，其中，所述硬碳材料的氧原子与碳原子的摩尔数之比O/C值为0.01至0.10。
  3. 根据权利要求1或2所述的负极活性材料，其中，所述硬碳材料的氧原子与碳原子的摩尔数之比O/C值为0.02至0.07。
  4. 根据权利要求1至3中任一项所述的负极活性材料，其满足： 其中，C1mAh/g表示以金属锂为对电极，所述硬碳材料在0V至0.15V之间的脱锂容量；C0mAh/g表示以金属锂为对电极，所述硬碳材料的脱锂总容量。
  5. 根据权利要求1至4中任一项所述的负极活性材料，所述硬碳材料的X射线衍射图谱具有位于18°至30°之间的特征峰，所述特征峰的半峰宽为4°至12°。
  6. 根据权利要求1至5中任一项所述的负极活性材料，其中，所述硬碳材料包括内核及位于所述内核的至少部分表面的包覆层，所述多个微孔位于所述内核中。
  7. 根据权利要求1至6中任一项所述的负极活性材料，其中，所述硬碳材料通过二氧化碳气体吸附法测得的微孔孔体积V cc/g满足：0＜Vcc/g≤0.05cc/g，所述微孔的直径d nm满足：d nm≤0.9nm。
  8. 根据权利要求1至7中任一项所述的负极活性材料，其中，所述负极活性材料满足如下至少一者：
    (1)所述硬碳材料通过正丁醇浸渍法测得的真密度ρg/cc为1.1g/cc至1.6g/cc；
    (2)所述硬碳材料的DV50为6μm至15μm；
    (3)所述硬碳材料的比表面积为2m2/g至10m2/g。
  9. 一种负极极片，包括负极集流体以及位于所述负极集流体至少一个表面上的负极活性材料层，所述负极活性材料层包括根据权利要求1至8中任一项所述的负极活性材料。
  10. 根据权利要求9所述负极极片，其中，所述负极活性材料层满足以下条件中的至少一者：
    (1)所述负极活性材料层还包括人造石墨，所述负极活性材料与所述人造石墨的质量比A满足：0＜A≤1/3；
    (2)所述负极活性材料层的压实密度PD g/cm3为1.0g/cm3至1.7g/cm3；
    (3)所述负极活性材料层的孔隙率为15％至30％。
  11. 一种电化学装置，包括根据权利要求9至10中任一项所述的负极极片。
  12. 一种用电装置，包括根据权利要求11所述的电化学装置。
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