WO2023245473A1 - 负极极片及电化学装置 - Google Patents

负极极片及电化学装置 Download PDF

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WO2023245473A1
WO2023245473A1 PCT/CN2022/100320 CN2022100320W WO2023245473A1 WO 2023245473 A1 WO2023245473 A1 WO 2023245473A1 CN 2022100320 W CN2022100320 W CN 2022100320W WO 2023245473 A1 WO2023245473 A1 WO 2023245473A1
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active material
hard carbon
negative electrode
carbon particles
negative
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PCT/CN2022/100320
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English (en)
French (fr)
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郑子桂
易政
谢远森
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宁德新能源科技有限公司
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Priority to PCT/CN2022/100320 priority Critical patent/WO2023245473A1/zh
Priority to CN202280053779.6A priority patent/CN117751467A/zh
Publication of WO2023245473A1 publication Critical patent/WO2023245473A1/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
    • H01M4/139—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
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx

Definitions

  • Electrochemical devices such as lithium-ion batteries have outstanding features such as high energy density, long cycle life, and no pollution and no memory effect.
  • the application of electrochemical device batteries has gradually spread from electronic products to large-scale device fields such as electric vehicles to adapt to the sustainable development strategy of the environment and energy. As a result, higher requirements have been placed on the energy density of electrochemical device batteries.
  • graphite has the advantages of high electrical conductivity and high stability. However, graphite not only has low theoretical specific capacity and poor kinetic conditions, but also has a high volume expansion rate under rapid charging and discharging. Therefore, graphite as a negative electrode material not only makes it difficult to further improve the energy density and cycle life of electrochemical device batteries, but also brings safety risks to electrochemical device batteries.
  • the present application provides a negative electrode piece, which has a high compaction density and can enable the electrochemical device to have high energy density, long cycle life and excellent rate performance. and fast charging performance.
  • a first aspect of the application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector.
  • the negative electrode active material layer includes a negative electrode active material
  • the negative electrode active material includes hard carbon particles and graphite. Particles, hard carbon particles have a lamellar structure, based on the number of hard carbon particles, the proportion of hard carbon particles with a diameter-to-thickness ratio of 3 to 7 is a%, 30 ⁇ a ⁇ 70.
  • the negative active material layer of hard carbon particles with a specific diameter-to-thickness ratio can achieve a higher compaction density after cold pressing, which can effectively shorten the transmission path of active ions and increase the solid-phase transfer speed of active ions inside the negative active material. This can reduce the internal impedance of the electrochemical device and improve the kinetic performance, cycle performance, rate performance and fast charging performance of the electrochemical device.
  • the proportion of hard carbon particles with a diameter-to-thickness ratio of 2 to 3 is b%, and 20 ⁇ b ⁇ 60.
  • the proportion of hard carbon particles with a diameter-to-thickness ratio of 2 to 3 within the above range can make the negative active material layer of the negative electrode plate have high compactness and appropriate porosity, improve the energy density of the electrochemical device, and improve the electrochemical performance of the electrochemical device. Cycling performance, rate performance and fast charging performance of chemical devices.
  • the electrochemical device has better cycle performance, rate performance, and fast charge performance.
  • the proportion of hard carbon particles with a diameter to thickness ratio of 3 to 7 is a%
  • the proportion of hard carbon particles with a diameter to thickness ratio of 2 to 3 is b%
  • the proportion of hard carbon particles with a diameter to thickness ratio of 2 to 3 is b%.
  • the carbon particles satisfy: a+b ⁇ 95, which can further improve the high energy density, long cycle life and excellent fast charging performance of the electrochemical device.
  • the proportion of hard carbon particles with a diameter-thickness ratio of 2 to 3 is b%, and the proportion of hard carbon particles with a diameter-thickness ratio of 1 to 2 is c%.
  • the diameter-to-thickness ratio of hard carbon is distributed within the above range, which can more fully ensure that the hard carbon has a high compaction density and a suitable specific surface area, so that the negative active material layer of the negative electrode plate has a high compaction density and suitable porosity.
  • the electrochemical device has a higher energy density, and can also shorten the transmission path of lithium ions in the negative electrode plate, improve the fast charging performance of the electrochemical device, reduce the internal resistance of the electrochemical device, and reduce the first cycle of the electrochemical device. Irreversible capacity and extended cycle life of electrochemical devices.
  • the mass of the hard carbon particles accounts for 85% to 99% of the mass of the negative active material.
  • the compaction of the negative active material layer can be further improved. Density enables electrochemical devices to have higher energy density.
  • the X-ray diffraction pattern of the negative active material includes a first diffraction peak and a second diffraction peak.
  • the first diffraction peak is located between 18° and 30°, and the half-maximum width of the first diffraction peak is 4 ° to 12°; the second diffraction peak is located between 26° and 27°, and the half-peak width of the second diffraction peak is 0.1° to 0.4°.
  • the compacted density of the negative active material layer is 1.0g/cm 3 to 1.7g/cm 3 .
  • the negative active material layer of the present application includes hard carbon particles with an appropriate diameter-to-thickness ratio. Therefore, the negative active material particles in the negative active material layer are stacked more densely and can have a high compaction density, thereby increasing the negative electrode per unit volume.
  • the content of active materials increases the energy density of electrochemical devices.
  • a second aspect of the application provides an electrochemical device, including the negative electrode plate of the first aspect.
  • a list of items connected by the terms “at least one of,” “at least one of,” “at least one of,” or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase “at least one of A and B” means only A; only B; or A and B. In another example, if the items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B and C.
  • Item A may contain a single component or multiple components.
  • Item B may contain a single component or multiple components.
  • Item C may contain a single component or multiple components.
  • Hard carbon has a high hardness. After cold pressing, not only is it difficult to increase the compaction density, but it may also crush the negative electrode current collector, thereby increasing the risk of the negative electrode active material layer falling off, eventually causing internal damage to the electrochemical device battery. The resistance increased sharply and the capacity retention rate dropped significantly. During the transportation or use of electrochemical device batteries, uncompacted hard carbon particles can easily crush the diaphragm, causing the battery voltage drop per unit time of the electrochemical device battery to increase. Therefore, the direct application of hard carbon materials in electrochemical devices will not only have a very limited improvement in the energy density of the electrochemical device battery, but will also have a negative impact on the cycle performance, capacity retention rate and safety performance of the electrochemical device.
  • the diameter-to-thickness ratio of hard carbon particles can represent the ratio of the long diameter to the thickness of hard carbon particles.
  • the long diameter is the longest diameter of the hard carbon particle cross-section on the projection plane
  • the thickness is the maximum thickness perpendicular to the long diameter direction in the hard carbon particle cross-section.
  • the inventor unexpectedly discovered that, compared to microspherical hard carbon particles and irregular-shaped hard carbon particles, the active material layer of hard carbon particles with a specific diameter-to-thickness ratio after cold pressing Can achieve higher compaction density.
  • the large diameter-to-thickness ratio of hard carbon particles means that hard carbon particles of the same volume can have a thinner lamellar structure. Therefore, as shown in Figure 1, the hard carbon particles can be arranged in a stacked manner, and can have a high compaction density after cold pressing.
  • the surface contact between the lamellar hard carbon particles can effectively shorten the transmission path of Li + and improve Li +
  • the solid-phase transfer speed inside the active material can thereby reduce the internal impedance of the lithium-ion battery, improve its mechanical properties, and improve the cycle performance, rate performance and fast charge performance of the electrochemical device.
  • a can be 70, 65, 60, 55, 50, 45, 40, 35, 30, or within the range of any of the above values.
  • the electrochemical device has better cycle performance, rate performance, and fast charge performance.
  • the proportion of hard carbon particles with a diameter-to-thickness ratio of 2 to 3 is b%, and 20 ⁇ b ⁇ 60.
  • b can be 20, 25, 30, 35, 40, 45, 50, 55, 60 or within the range of any of the above values.
  • the electrochemical device has better cycle performance, rate performance, and fast charge performance.
  • the proportion of hard carbon particles with a diameter to thickness ratio of 3 to 7 is a%
  • the proportion of hard carbon particles with a diameter to thickness ratio of 2 to 3 is b%
  • the proportion of hard carbon particles with a diameter to thickness ratio of 2 to 3 is b%.
  • Carbon particles satisfy: a+b ⁇ 90.
  • the proportion of hard carbon particles with a diameter-to-thickness ratio of 2 to 3 and hard carbon particles with a diameter-to-thickness ratio of 3 to 7 in the hard carbon is within the above range, which can increase the compaction density of the negative active material layer while making
  • the area of the SEI film formed on the surface of the negative electrode plate is appropriate. Therefore, the negative electrode sheet of the present application is used in an electrochemical device, allowing the electrochemical device to have high energy density, long cycle life and excellent fast charging performance.
  • the proportion of hard carbon particles with a diameter to thickness ratio of 3 to 7 is a%
  • the proportion of hard carbon particles with a diameter to thickness ratio of 2 to 3 is b%
  • the proportion of hard carbon particles with a diameter to thickness ratio of 2 to 3 is b%.
  • the carbon particles satisfy: a+b ⁇ 95, which can further improve the cycle performance, rate performance and fast charging performance of the electrochemical device.
  • the diameter-to-thickness ratio of hard carbon particles with conventional morphology is mainly distributed in the range of 1 to 2.
  • Hard carbon materials are highly rigid, and most of the contacts between particles are point-to-point, making it difficult to densely stack them during the cold pressing process, leaving high pores. efficiency, reducing the energy density of the electrochemical device; when the diameter-to-thickness ratio of the hard carbon particles is too large, the specific surface area of the hard carbon particles also increases accordingly, and the area of the SEI film formed on the surface of the negative electrode plate also increases accordingly. This resulted in an increase in irreversible capacity in the first week. Therefore, the proportion of particles with low diameter-thickness ratio and excessive diameter-thickness ratio in hard carbon active materials should be reduced as much as possible.
  • the proportion of hard carbon particles with a diameter-thickness ratio of 1 to 2 and hard carbon particles with a diameter-thickness ratio greater than 7 is within the above-mentioned appropriate range, allowing the negative active material layer to have high Compacted density and high porosity, and reduced first-week irreversible capacity.
  • the proportion of hard carbon particles with a diameter to thickness ratio of 3 to 7 is a%
  • the proportion of hard carbon particles with a diameter to thickness ratio of 2 to 3 is b%
  • the proportion of hard carbon particles with a diameter to thickness ratio of 2 to 3 is b%.
  • the proportion of hard carbon particles with a thickness ratio of 1 to 2 is c%
  • the proportion of hard carbon particles with a diameter-to-thickness ratio greater than 7 is d%.
  • the hard carbon particles include micropores inside, the micropore diameter is less than 2 nm, and the micropore volume measured using the carbon dioxide adsorption and desorption method is greater than or equal to 0.25cc/g. In some embodiments, the hard carbon particles have a micropore volume of 1 cc/g to 5 cc/g as measured by a carbon dioxide adsorption-desorption method. At this time, the hard carbon active material contains a larger micropore volume, which to a certain extent means that it has a higher lithium storage capacity, increases the capacity of the negative active material, and increases the energy density of the electrochemical device.
  • the mass of the hard carbon particles accounts for 85% to 99% of the mass of the negative active material
  • the mass of the graphite particles accounts for 1% to 15% of the mass of the negative active material.
  • the negative active material includes 95% hard carbon particles and 5% graphite particles. The inventor found that mixing a small amount of graphite into the negative active material, and the amount of graphite blended is within the above-mentioned appropriate range, can further increase the compaction density of the negative active material layer, thereby allowing the electrochemical device to have higher energy. density.
  • graphite has a stacked structure of graphene sheets. After being mixed with hard carbon, the hard carbon can slip through the graphite sheets during the cold pressing process. As a result, the lamellar hard carbon particles can be stacked together in a more regular orientation, thereby further increasing the compaction density of the negative active material layer and increasing the energy density of the electrochemical device.
  • the X-ray diffraction (XRD) pattern of the negative active material may include a first diffraction peak and a second diffraction peak.
  • the first diffraction peak is located between 18° and 30°, and the half-peak width of the first diffraction peak is 4° to 12°.
  • the second diffraction peak is located between 26° and 27°, and the half-maximum width of the second diffraction peak is 0.1° to 0.4°.
  • the graphite particles include natural graphite particles, artificial graphite particles, or combinations thereof.
  • the artificial graphite particles may include mesocarbon microsphere (MCMB)-based artificial graphite particles, petroleum coke-based artificial graphite particles, or combinations thereof.
  • MCMB mesocarbon microsphere
  • the particle size of the negative active material may satisfy: 1 ⁇ m ⁇ Dv10 ⁇ 5 ⁇ m, 4 ⁇ m ⁇ Dv50 ⁇ 18 ⁇ m, and Dv99 ⁇ 43 ⁇ m.
  • Dv10 can be 1 ⁇ m, 1.5 ⁇ m, 2 ⁇ m, 2.5 ⁇ m, 3 ⁇ m, 3.5 ⁇ m, 4 ⁇ m, 4.5 ⁇ m, 5 ⁇ m or within the range of any of the above values
  • Dv50 can be 4 ⁇ m, 6 ⁇ m, 8 ⁇ m, 10 ⁇ m, 12 ⁇ m, 14 ⁇ m, 16 ⁇ m, 18 ⁇ m or within the range of any of the above values
  • Dv99 can be ⁇ 43 ⁇ m, ⁇ 40 ⁇ m, ⁇ 38 ⁇ m, ⁇ 35 ⁇ m, ⁇ 32 ⁇ m or ⁇ 30 ⁇ m.
  • the negative active material layer may have a compacted density of 1.0 g/cm 3 to 1.7 g/cm 3 .
  • the compacted density of the negative active material layer may be 1.0g/cm 3 , 1.1g/cm 3 , 1.2g/cm 3 , 1.3g/cm 3 , 1.4g/cm 3 , 1.5/cm 3 , 1.6g/ cm 3 , 1.7g/cm 3 or within the range of any of the above values.
  • the negative active material may have a compacted density of 1.3 to 1.7 g/cm 3 .
  • the negative active material layer of the present application includes hard carbon particles with an appropriate diameter-to-thickness ratio. Therefore, the negative active material particles in the negative active material layer are stacked more densely and can have a high compaction density, thereby increasing the negative electrode per unit volume.
  • the content of active materials increases the energy density of electrochemical devices.
  • the porosity of the negative active material layer may be 10% to 40%.
  • the porosity of the negative active material layer may be 10%, 15%, 20%, 25%, 30%, 35%, 40%, or within the range of any of the above values.
  • the diaphragm resistance of the negative electrode plate is within the above-mentioned appropriate range, which can ensure that the electrochemical device has low ohmic polarization and reduce the heat generation during the charging and discharging process of the electrochemical device, thus improving the long-term cycle performance and safety of the electrochemical device. performance.
  • hard carbon particles of this application can be obtained in a variety of ways.
  • hard carbon particles can be prepared using the template method through the following steps: mixing a lamellar inorganic template, a pore-forming agent and a resin to obtain a mixture; the mixture is heated at a pressure of 0T to 5T and a temperature of 25°C to 200°C. Curing takes 0.1h to 120h; the cured mixture is pyrolyzed for 2h at 700 to 1300°C, crushed and screened, and then treated with acid or alkali solution to remove the template to obtain hard carbon particles.
  • the lamellar inorganic templates include but are not limited to: montmorillonite, mica stone, two-dimensional silicon, and lamellar silica;
  • the pore-forming agents include but are not limited to: magnesium oxide, magnesium chloride, magnesium gluconate, zinc oxide, Zinc chloride, zinc gluconate, zinc stearate, zinc borate, iron oxide, ferric chloride, glucose, sucrose;
  • resins include but are not limited to: phenolic resin, furan resin, epoxy resin, polyester resin, bismale Amides, thermosetting polyimides, cyanate esters.
  • the mixing method can be powder mixing or solution mixing. When the mixing method is solution mixing, the choice of solvent is determined by the resin and pore-forming agent.
  • the pyrolytic carbon is then broken and screened, and then the pyrolytic carbon is placed in 1L of 2mol/L In sodium hydroxide solution, stir for 24 hours, then suction filter, repeat twice to ensure that the lamellar silica template is removed, and finally obtain the lamellar hard carbon material.
  • Metal foil or porous metal plate may be used, for example, foil or porous plate using metals such as copper, nickel, titanium, iron or alloys thereof.
  • the negative electrode current collector is copper foil.
  • the negative active material layer optionally also includes other auxiliaries, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.
  • auxiliaries such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.
  • the negative electrode piece in this application can be prepared according to conventional methods in this field.
  • hard carbon and optional other negative active materials, conductive agents, binders and thickeners are dispersed in a solvent.
  • the solvent can be N-methylpyrrolidone.
  • NMP deionized water
  • each negative active material layer given in this application refers to the parameter range of the single-sided negative active material layer.
  • the negative active material layer is disposed on both sides of the negative current collector, if the parameters of the negative active material layer on either side meet the requirements of this application, it is deemed to fall within the protection scope of this application.
  • the negative electrode sheet in this application does not exclude other additional functional layers in addition to the negative active material layer.
  • the negative electrode sheet of the present application also includes a conductive undercoat 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. composition).
  • the negative electrode sheet of the present application further includes a protective layer covering the surface of the negative active material layer.
  • the diameter-to-thickness ratio of hard carbon particles can be determined by methods and instruments known in the art.
  • a negative electrode piece cut to a certain size can be pasted on a silicon wafer carrier with conductive glue, and a cross section of the negative electrode piece can be polished using argon ion polishing to obtain a test piece; the sample can be obtained through a scanning electron microscope (SEM).
  • SEM scanning electron microscope
  • Analyze the morphology structure and element distribution of the polished section use image processing software to screen out the images of hard carbon particles, and test the long diameter value of each hard carbon particle in the section and the maximum thickness perpendicular to the long diameter direction. , thereby obtaining the diameter-to-thickness ratio of each hard carbon particle.
  • XRD patterns can be determined by methods and instruments known in the art. For example, it can be obtained by using the Bruker D8 ADVANCE X-ray powder diffractometer for XRD testing.
  • the radiation source for the XRD test is Cu K ⁇ target.
  • the test parameters can be set as follows: tube voltage is 40kV, tube current is 40mA, and the scanning step is is 0.00836°, the scanning duration of each scanning step is 0.3s, and the 2 ⁇ range is from 5° to 80°.
  • the particle sizes Dv10, Dv50, and Dv99 of the negative active material have meanings known in the art and can be measured using methods and instruments known in the art.
  • the specific surface area of the negative active material has a meaning known in the art and can be measured using methods known in the art.
  • a specific surface area analyzer such as Tristar II 3020M
  • Tristar II 3020M can be used to measure the specific surface area of the negative active material through a nitrogen adsorption/desorption method.
  • the porosity of the negative active material layer has a meaning known in the art and can be measured using methods known in the art.
  • the negative electrode sheet coated with negative active material can be punched into disc-shaped specimens. In each specimen, the volume of the negative active material layer is determined by the area and thickness of the disc; refer to GB/T24586-2009 Iron Determination of apparent density, true density and porosity of ore Standard test the porosity of the negative active material layer.
  • the diaphragm resistance of the negative electrode plate has a meaning known in the art and can be measured using methods known in the art. For example, you can cut the negative electrode piece into a specimen with a size of 60mm ⁇ 80mm, use the BER1100 multifunctional electrode piece resistance meter to conduct a resistance test on the sample, and test the diaphragm resistance of the negative electrode piece.
  • the sample can be sampled according to the following steps S10-S30.
  • step S20 Bake the negative electrode sheet dried in step S10 at a certain temperature and time (for example, 400°C, 2 hours). Select an area in the baked negative electrode sheet to sample the negative electrode active material (you can choose blade scraper powder sampling).
  • step S30 sieve the negative active material collected in step S20 (for example, using a 200-mesh screen) to finally obtain a sample that can be used to test the parameters of each negative active material mentioned above in this application.
  • a second 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.
  • an electrochemical reaction occurs to convert chemical energy into electrical energy.
  • Specific examples thereof include but are not limited to lithium-ion batteries or sodium-ion batteries.
  • the electrochemical device of the present application includes a positive electrode piece, a negative electrode piece, a separator and an electrolyte.
  • the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through 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 packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., or a soft bag, such as a bag-type soft bag.
  • the soft bag may be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PBS polybutylene succinate
  • the negative electrode sheet used in the electrochemical device of the present application is the negative electrode sheet of the first aspect of the present application.
  • the material, composition and manufacturing method of the positive electrode piece 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 facing 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 active material layer includes a positive active material.
  • the specific type of the positive active material is not specifically limited and can be selected according to requirements.
  • the cathode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds.
  • the above-mentioned modified compounds of each positive electrode active material may be doping modification, surface coating modification, or doping and surface coating modification of the positive electrode active material.
  • lithium transition metal oxides may include 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, One or more of lithium nickel cobalt aluminum oxide and its modified compounds.
  • the lithium-containing phosphate with an olivine structure may include lithium iron phosphate, a composite of lithium iron phosphate and carbon, a lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, a lithium manganese iron phosphate, a lithium manganese iron phosphate and carbon One or more of the composite materials and their modified compounds. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination.
  • the positive active material layer optionally further includes a conductive agent.
  • 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 current collector may be a metal foil or a composite current collector.
  • a metal foil aluminum foil can be used as the positive electrode current collector.
  • 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 of the present application does not exclude other additional functional layers in addition to the positive active material layer.
  • the positive electrode sheet of the present application also includes a conductive undercoat layer (for example, 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 further 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 piece and the negative electrode piece.
  • the electrolyte solution that can be used in the electrochemical device of the present application can be an electrolyte solution known in the art.
  • the electrolyte includes an organic solvent, a lithium salt, and optional additives.
  • organic solvents, lithium salts, and additives are not specifically limited and can be selected according to needs.
  • organic solvents include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate Ester (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl 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), butyric acid Methyl ester (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), sulfolane
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows active ions to pass through.
  • isolation membrane There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.
  • 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 film may include polyethylene and/or polypropylene.
  • the isolation film can be a single-layer film or a multi-layer composite film. When the isolation film is a multi-layer composite film, the materials of each layer may be the same or different. In some embodiments, a ceramic coating or a metal oxide coating can also be provided on the isolation film.
  • the third aspect of the present application provides an electrical device, which includes the electrochemical device of the second aspect of the present application.
  • the powered device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an e-book player, a portable telephone, a portable fax machine, a portable copier, a portable printer, a stereo headset, Video recorders, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, Lighting appliances, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.
  • a negative electrode slurry with a solid content of 40wt% Dissolve the negative active material, binder styrene-butadiene rubber and sodium carboxymethylcellulose (CMC-Na) in deionized water at a mass ratio of 97:1.5:1.5 to obtain a negative electrode slurry with a solid content of 40wt%; add the negative electrode The slurry is coated on both sides of the negative electrode current collector.
  • the negative electrode current collector is a 6 ⁇ m thick copper foil, and the coating thickness on one side is 50 ⁇ m. It is dried at 85°C, cold pressed, cut into pieces, and slit. Finally, it was dried under vacuum conditions at 120°C for 12 hours to obtain the negative electrode piece.
  • the mass percentage content of lamellar hard carbon is w 1 %
  • the mass percentage content of MCMB is w 2 %
  • a, b, c, d, Dv10, Dv50, Dv99 of the negative active material is shown in Table 1, Table 2, and Table 3 respectively.
  • the negative active materials in Examples 1 to 8 are 95% hard carbon and 5% MCMB
  • the negative active materials in Examples 9 to 16 are the same as Example 1 and have the same diameter as the hard carbon in Example 1. Thickness ratio distribution, the negative electrode active materials of Examples 17 to 21 have the same diameter-to-thickness ratio distribution as the hard carbon in Example 1.
  • the positive electrode sheet, isolation film, and negative electrode sheet in order and wind them to obtain the electrode assembly. Put the electrode assembly into the outer packaging. After removing the moisture at 80°C, add the above electrolyte, package and let it stand to form , degassing, shaping and other processes, the lithium-ion battery is obtained.
  • the negative active material of Comparative Example 1 is MCMB; the negative active material of Comparative Example 2 is flake graphite; the negative active material of Comparative Example 3 is 95% conventional morphology hard carbon and 5% MCMB; the negative active material of Comparative Example 4 The active material is 95% microspherical hard carbon particles and 5% MCMB.
  • Testing instrument Scanning electron microscope JSM-6360LV and its supporting X-ray energy spectrometer
  • T 0 (T 1 -T 2 )/2 Equation 2
  • W 0 represents the mass of the single-sided negative electrode active material layer
  • T 0 represents the thickness of the single-sided negative electrode active material layer
  • the negative electrode sheet coated with negative active material is punched into disc-shaped test pieces.
  • the volume of the negative active material layer is about 0.35cm 3 ; refer to GB/T24586-2009 Iron Ore Appearance Density Determination of True Density and Porosity Standard Test the porosity of the negative active material layer.
  • Testing instrument refers to the steps in the XRD test of negative active materials to obtain negative active material powder; place the dried and degassed samples in liquid nitrogen, adjust different test pressures, and measure respectively For the amount of nitrogen adsorbed, adsorption and desorption isotherms were drawn. Determine the shape of the pores based on the shape of the hysteresis loop, calculate the pore distribution and pore volume according to different pore models, use the BJH model to fit the pore size distribution curves of mesopores and macropores, and use the DFT model to fit the pore size distribution curve of micropores.
  • CC segment capacity ratio [CC segment charging capacity/(CC segment charging capacity + CV segment charging capacity)] ⁇ 100% Equation 4
  • Capacity retention rate (%) (discharge capacity of the 400th cycle/discharge capacity of the first cycle) ⁇ 100%;
  • the self-discharge rate of lithium-ion battery (V 1 -V 2 )/48.
  • the degree of internal physical micro-short circuit is greatly reduced, and the lamellar hard carbon particles have a smoother surface.
  • the transmission path of Li + can be effectively shortened and the solid-phase transfer speed of Li + inside the active material can be increased. This can reduce the internal impedance of the lithium-ion battery and improve its mechanical properties, thereby improving the performance of the lithium-ion battery.
  • the fast charging capability has been effectively improved, giving the lithium-ion battery excellent cycle performance and rate performance, and the energy density of the lithium-ion battery has been further improved.
  • the negative electrode sheet can have both a higher hard carbon content and a higher compacted density, which corresponds to The energy density of lithium-ion batteries is also relatively higher. Since hard carbon not only has a low volume expansion rate during the delithiation and lithium insertion processes, but also can limit the volume expansion of graphite during the charge and discharge process, the corresponding lithium-ion battery in the embodiment with high hard carbon content after 400 cycles The smaller the thickness expansion rate, the better the capacity retention rate after 400 cycles.

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Abstract

本申请公开了一种负极极片及电化学装置。负极极片内的片层硬碳活性材料通过面面接触取代常规形貌的硬碳活性材料的点对点接触，有效的降低负极活性材料层的内阻、同时可有效提升负极活性材料层的压实密度和降低孔隙率，进而提升锂离子电池的能量密度；锂离子在片层状硬碳负极活性材料内扩散具备更优异的动力学，有利于提升锂离子电池的快充能力；同时，低膨胀的硬碳活性材料赋予锂离子电池更佳的循环性能。此外，本申请涉及的制备方法简单，易于操作和控制，成本较为低廉，适用于工业化生产。

Description

负极极片及电化学装置 技术领域
本申请属于二次电池技术领域，具体涉及一种负极极片及电化学装置。
背景技术
诸如锂离子电池的电化学装置具有能量密度高、循环寿命长，以及无污染、无记忆效应等突出特点。作为清洁能源，电化学装置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，也对电化学装置电池的能量密度提出了更高的要求。
目前，商业化的锂离子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，石墨不仅理论比容量低、动力学条件差，而且在快速充电和放电的情况下具有高体积膨胀率。由此，石墨作为负极材料不仅难以进一步提升电化学装置电池的能量密度和循环寿命，还会给电化学装置电池带来安全隐患。
发明内容
鉴于现有技术存在的上述问题，本申请提供一种提供了一种负极极片，该负极极片具有高压实密度，能够使得电化学装置具备高能量密度、长循环寿命和优异的倍率性能及快速充电性能。
本申请的第一方面提供了一种负极极片，包括负极集流体以及位于负极集流体至少一个侧面的负极活性材料层，负极活性材料层包括负极活性材料，负极活性材料包括硬碳颗粒和石墨颗粒，硬碳颗粒具有片层状结构，基于硬碳颗粒的数量，径厚比为3至7的硬碳颗粒的占比为a％，30≤a≤70。具有特定径厚比的硬碳颗粒的负极活性材料层经冷压后能取得更高压实密度，能够有效缩短活性离子的传输路径，提升活性离子在负极活性材料内部的固相传递速度，由此能够降低电化学装置的内部阻抗，提升电化学装置的动力学性能、循环性能、倍率性能和快充性能。
在一些实施方式中，30≤a≤50，径厚比为3至7的硬碳颗粒的占比在此范围内时，电化学装置具有更优的循环性能、倍率性能和快充性能
在本申请任意实施方式中，基于硬碳颗粒的数量，径厚比为2至3的硬碳颗粒的占比为b％，20≤b≤60。径厚比为2至3的硬碳颗粒的占比在上述范围内，能够使得负极极片的负极活性材料层具备高压实度和合适的孔隙率，提高电化学装置的能量密度，提升电化学装置的循环性能、倍率性能和快充性能。
在一些实施方式中，20≤b≤50，径厚比为2至3的硬碳颗粒的占比在此范围内时，电化学装置具有更优的循环性能、倍率性能和快充性能。
在本申请任意实施方式中，硬碳颗粒满足：a+b≥90，径厚比为2至3的硬碳颗粒 以及径厚比为3至7的硬碳颗粒在硬碳中的占比在上述范围内，能够使电化学装置具备高能量密度、长循环寿命和优异的快速充电性能。
在一些实施方式中，基于硬碳颗粒的数量，径厚比为3至7的硬碳颗粒的占比为a％，径厚比为2至3的硬碳颗粒的占比为b％，硬碳颗粒满足：a+b≥95，此时可进一步提升电化学装置的高能量密度、长循环寿命和优异的快速充电性能。
在本申请任意实施方式中，基于硬碳颗粒的数量，径厚比为1至2的硬碳颗粒的占比为c％，径厚比大于7的硬碳颗粒的占比为d％，0.1≤c≤10，0.1≤d≤1。径厚比为1至2的硬碳颗粒及径厚比大于7的硬碳颗粒的占比在上述合适的范围内，能够允许负极活性材料层具备高压实密度和高孔隙率，并降低首周不可逆容量，提升电化学装置的循环性能、倍率性能和快充性能。
在本申请任意实施方式中，基于硬碳颗粒的数量，径厚比为2至3的硬碳颗粒的占比为b％，径厚比为1至2的硬碳颗粒的占比为c％，径厚比大于7的硬碳颗粒的占比为d％，硬碳颗粒满足：a+b+c+d＝100。硬碳的径厚比分布在上述范围内，能够更充分地保证硬碳具有高压实密度和合适的比表面积，从而使得负极极片的负极活性材料层具备高压实密度和合适的孔隙率，使电化学装置具备更高的能量密度，还能缩短锂离子在负极极片中的传输路径，提升电化学装置的快速充电性能、降低电化学装置的内阻，降低电化学装置的首圈不可逆容量和延长电化学装置的循环寿命。
在本申请任意实施方式中，所述硬碳颗粒的质量占所述负极活性材料质量的85％至99％，硬碳颗粒的质量在上述范围内时，能够进一步提升负极活性材料层的压实密度，使电化学装置具备较高的能量密度。
在本申请任意实施方式中，负极活性材料的X射线衍射图谱包含第一衍射峰和第二衍射峰，第一衍射峰位于18°至30°之间，第一衍射峰的半峰宽为4°至12°；第二衍射峰位于26°至27°之间，第二衍射峰的半峰宽为0.1°至0.4°。
在本申请任意实施方式中，硬碳颗粒包括微孔，采用氮气二氧化碳吸附-脱附法测得的微孔孔体积大于或等于0.25cc/g。硬碳活性材料含有更大的微孔孔体积，说明其具备更高的储锂能力，可提高负极活性材料的容量及提高电化学装置的能量密度。
在本申请任意实施方式中，负极活性材料的粒径满足：1μm≤Dv10≤5μm，4μm≤Dv50≤18μm，Dv99≤43μm；负极活性材料的粒径在上述合适的范围内，不同粒径活性材料的搭配使活性材料层在冷压后具有更加密实的堆积，以获得更高的压实密度，能够进一步提升电化学装置的能量密度和循环性能。
在本申请任意实施方式中，负极活性材料的比表面积为1m 2/g至30m 2/g。负极活性材料的比表面积在上述合适的范围内，能够使得负极活性材料颗粒具备合适的比表面积，并使得负极极片表面形成的SEI膜的面积适当，减少首次充电过程的不可逆锂的消耗，能够使得电化学装置兼具良好的动力学性能和高能量密度。
在本申请任意实施方式中，负极活性材料层的压实密度为1.0g/cm 3至1.7g/cm 3。本申请的负极活性材料层中包括径厚比适当的硬碳颗粒，因此，负极活性材料层中的负极活性材料颗粒的堆叠更为密实，能够具有高压实密度，从而能提高单位体积内负极活性材料的含量，由此提升电化学装置具备更高的能量密度。
在本申请任意实施方式中，负极活性材料层的孔隙率为10％至40％；片层硬碳活 性材料的颗粒与颗粒间有更多面面接触，更加密实的堆叠使负极活性材料层的孔隙率更低。负极活性材料层的孔隙率在上述合适的范围内，不仅能够降低负极极片的内阻，还能保证负极极片的电解液浸润性能，从而提升电化学装置的动力学性能。
本申请的第二方面提供了一种电化学装置，包括第一方面的负极极片。
本申请在负极活性材料加入硬碳颗粒和石墨颗粒，硬碳颗粒具有片层状结构，限定径厚比为3至7的硬碳颗粒的占比，能够有效缩短活性离子的传输路径，提升活性离子在负极活性材料内部的固相传递速度，能够降低电化学装置的内部阻抗，负极活性材料层经冷压后能取得更高压实密度，提升电化学装置的动力学性能、循环性能、倍率性能和快充性能。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将简要说明本申请实施例中所需要使用的附图；显而易见地，下面所描述的附图仅仅涉及本申请的一些实施方式。
图1是本申请一实施例的负极极片的截面的示意图。
图2是本申请一实施例的负极活性材料颗粒截面的扫描电子显微镜图(SEM图)。
图3是本申请实施例1的负极活性材料中硬碳颗粒的孔径分布图。
具体实施方式
为了使本申请的发明目的、技术方案和有益技术效果更加清晰，以下结合实施例对本申请进行进一步详细说明。应当理解的是，本说明书中描述的实施例仅仅是为了解释本申请，并非为了限定本申请。
为了简便，本文仅明确地公开了一些数值范围。然而，任意下限可以与任何上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，尽管未明确记载，但是范围端点间的每个点或单个数值都包含在该范围内。因而，每个点或单个数值可以作为自身的下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包含本数，“一种或几种”中“几种”的含义是两种或两种以上。
除非另有说明，本申请中使用的术语具有本领域技术人员通常所理解的公知含义。除非另有说明，本申请中提到的各参数的数值可以用本领域常用的各种测量方法进行测量(例如，可以按照在本申请的实施例中给出的方法进行测试)。
术语“中的至少一者”、“中的至少一个”、“中的至少一种”或其他相似术语所连接的项目的列表可意味着所列项目的任何组合。例如，如果列出项目A及B，那么短语“A及B中的至少一者”意味着仅A；仅B；或A及B。在另一实例中，如果列出项目A、B及C，那么短语“A、B及C中的至少一者”意味着仅A；或仅B；仅C；A及B(排除C)；A及C(排除B)；B及C(排除A)；或A、B及C的全部。项目A可包含单个组分或多个组分。项目B可包含单个组分或多个组分。项目C可包含单个组分或 多个组分。
本申请的上述发明内容并不意欲描述本申请中的每个公开的实施方式或每种实现方式。如下描述更具体地举例说明示例性实施方式。在整篇申请中的多处，通过一系列实施例提供了指导，这些实施例可以以各种组合形式使用。在各个实例中，列举仅作为代表性组，不应解释为穷举。
硬碳的硬度较高，经冷压后，不仅压实密度很难得到提升，还有可能压伤负极集流体，从而增大负极活性材料材料层脱落的风险，最终导致电化学装置电池的内阻剧增、容量保持率大幅下降。在电化学装置电池的运输或使用过程中，未被压实的硬碳颗粒也极易压伤隔膜，导致电化学装置电池单位时间内的电池的电压降提升。因此，硬碳材料直接应用于电化学装置，不仅对电化学装置电池的能量密度的提升十分有限，还会对电化学装置的循环性能、容量保持率和安全性能造成负面影响。
负极极片
本申请提出了一种负极极片，其包括负极集流体以及位于负极集流体至少一个侧面的负极活性材料层，负极活性材料层包括负极活性材料，负极活性材料包括硬碳颗粒和石墨颗粒，硬碳颗粒具有片层状结构，基于硬碳颗粒的数量，径厚比为3至7的硬碳颗粒的占比为a％，30≤a≤70。
硬碳颗粒的径厚比可表示硬碳颗粒的长径与厚度之比。其中，长径为硬碳颗粒剖面图在投影平面上的最长径，厚度为硬碳颗粒剖面内垂直于长径方向上的最大厚度。
并非意在受限于任何理论或解释，发明人意外地发现，相对于微球状硬碳颗粒和不规则形状的硬碳颗粒，具有特定径厚比的硬碳颗粒的活性材料层经冷压后能取得更高压实密度。硬碳颗粒的径厚比大，意味着同体积的硬碳颗粒能够具有更薄的片层结构。由此，如图1所示，硬碳颗粒能够层叠排列，经冷压后能够具备高压实密度，片层状硬碳颗粒间通过面面接触，能够有效缩短Li +的传输路径，提升Li +在活性材料内部的固相传递速度，由此能够降低锂离子电池的内部阻抗，提升动其力学性能，提升电化学装置的循环性能、倍率性能和快充性能。
在一些实施方式中，a可以为70、65、60、55、50、45、40、35、30或者处于上述任意数值所组成的范围内。
在一些实施方式中，30≤a≤50，径厚比为3至7的硬碳颗粒的占比在此范围内时，电化学装置具有更优的循环性能、倍率性能和快充性能。
在一些实施方式中，基于硬碳颗粒的数量，径厚比为2至3的硬碳颗粒的占比为b％，20≤b≤60。例如，b可以为20、25、30、35、40、45、50、55、60或者处于上述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，径厚比为2至3的硬碳颗粒的占比在上述范围内，能够在保证硬碳颗粒经冷压后具备高压实密度的同时，保证硬碳颗粒具备合适的比表面积。因此，这样的硬碳材料应用于负极极片，能够使得负极极片的负极活性材料层具备高压实度和合适的孔隙率，提升电化学装置的循环性能、倍率性能和快充性能。
在一些实施方式中，20≤b≤50，径厚比为2至3的硬碳颗粒的占比在此范围内时，电化学装置具有更优的循环性能、倍率性能和快充性能。
在一些实施方式中，基于硬碳颗粒的数量，径厚比为3至7的硬碳颗粒的占比为 a％，径厚比为2至3的硬碳颗粒的占比为b％，硬碳颗粒满足：a+b≥90。径厚比为2至3的硬碳颗粒以及径厚比为3至7的硬碳颗粒在硬碳中的占比在上述范围内，能够在提高负极活性材料层的压实密度的同时，使得负极极片表面形成的SEI膜面积适当。由此，本申请的负极极片应用于电化学装置，能够允许电化学装置具备高能量密度、长循环寿命和优异的快速充电性能。
在一些实施方式中，基于硬碳颗粒的数量，径厚比为3至7的硬碳颗粒的占比为a％，径厚比为2至3的硬碳颗粒的占比为b％，硬碳颗粒满足：a+b≥95，可进一步提升电化学装置的循环性能、倍率性能和快充性能。
在一些实施方式中，基于硬碳颗粒的数量，径厚比为1至2的硬碳颗粒的占比为c％，径厚比大于7的硬碳颗粒的占比为d％，0.1≤c≤10，0.1≤d≤1。
常规形貌的硬碳颗粒的径厚比主要分布范围为1至2，硬碳材料的刚性较强，颗粒间的接触以点对点居多，导致其在冷压过程难以密实堆叠，留下较高孔隙率，降低电化学装置能量密度；硬碳颗粒的径厚比过大时，相应地，硬碳颗粒的比表面积也随之增大，负极极片表面形成的SEI膜的面积也相应增大，由此导致了首周不可逆容量的增高。由此，应尽可能减少硬碳活性材料中径厚比低及径厚比过大的颗粒含量占比。并非意在受限于任何理论或解释，径厚比为1至2的硬碳颗粒及径厚比大于7的硬碳颗粒的占比在上述合适的范围内，能够允许负极活性材料层具备高压实密度和高孔隙率，并降低首周不可逆容量。
在一些实施方式中，基于硬碳颗粒的数量，径厚比为3至7的硬碳颗粒的占比为a％，径厚比为2至3的硬碳颗粒的占比为b％，径厚比为1至2的硬碳颗粒的占比为c％，径厚比大于7的硬碳颗粒的占比为d％，硬碳颗粒满足：0.1≤c≤10，0.1≤d≤1，a+b+c+d＝100。
硬碳的径厚比分布在上述范围内，能够更充分地保证硬碳具有高压实密度和合适的比表面积，从而使得负极极片的负极活性材料层具备高压实密度和合适的孔隙率。具备高压实密度的负极极片不仅能够允许电化学装置具备更高的能量密度，还能缩短锂离子在负极极片中的传输路径，由此能够提升电化学装置的快速充电性能、降低电化学装置的内阻。负极极片的适当孔隙率还能够使得负极极片表面形成的SEI膜具有合适的面积，从而降低电化学装置的首圈不可逆容量。由此，负极极片应用于电化学装置，能够显著提高电化学装置的能量密度、延长电化学装置的循环寿命，并使得电化学装置具备优异的快速充电性能。
在一些实施方式中，硬碳颗粒内部包括微孔，微孔孔径＜2nm；采用二氧化碳吸附测-脱附法测得的微孔孔体积大于或等于0.25cc/g。在一些实施方式中，用二氧化碳吸附测-脱附法测得的硬碳颗粒的微孔孔体积为1cc/g至5cc/g。此时硬碳活性材料含有更大的微孔孔体积，一定程度上意味着其具备更高的储锂能力，提高负极活性材料的容量，提高电化学装置的能量密度。
在一些实施方式中，所述硬碳颗粒的质量占所述负极活性材料质量的85％至99％，所述石墨颗粒的质量占所述负极活性材料质量的1％至15％。负极活性材料包括95％的硬碳颗粒以及5％的石墨颗粒。发明人发现，在负极活性材料中掺混少量石墨，且掺混的石墨的量在上述合适的范围内，能够进一步提升负极活性材料层的压实密度，从而允许电 化学装置具备较高的能量密度。具体地，石墨为石墨烯片堆叠结构，与硬碳混合后，在冷压过程中，硬碳可借助石墨片层产生滑移。由此，片层状的硬碳颗粒能够以更规整的取向堆叠在一起，从而进一步提高负极活性材料层的压实密度，提高电化学装置的能量密度。
在一些实施方式中，负极活性材料的X射线衍射(XRD)图谱可包含第一衍射峰和第二衍射峰。第一衍射峰位于18°至30°之间，第一衍射峰的半峰宽为4°至12°。第二衍射峰位于26°至27°之间，第二衍射峰的半峰宽为0.1°至0.4°。当负极活性材料的XRD图满足上述条件时，能够保证负极活性材料具有合适的碳微晶结构和组成成分。
在一些实施方式中，石墨颗粒包括天然石墨颗粒、人造石墨颗粒或其组合。
可选的，人造石墨颗粒可包括中间相炭微球(MCMB)类人造石墨颗粒、石油焦类人造石墨颗粒或其组合。
在一些实施方式中，负极活性材料的粒径可满足：1μm≤Dv10≤5μm，4μm≤Dv50≤18μm，Dv99≤43μm。例如，Dv10可以为1μm、1.5μm、2μm、2.5μm、3μm、3.5μm、4μm、4.5μm、5μm或者处于上述任意数值所组成的范围内；Dv50可以为4μm、6μm、8μm、10μm、12μm、14μm、16μm、18μm或者处于上述任意数值所组成的范围内；Dv99可以为≤43μm、≤40μm、≤38μm、≤35μm、≤32μm或者≤30μm。负极活性材料的粒径在上述合适的范围内，不同粒径活性材料的搭配使活性材料层在冷压后具有更加密实的堆积，以获得更高的压实密度，能够进一步提升电化学装置的能量密度和循环性能。
在一些实施方式中，负极活性材料的比表面积可为1m 2/g至30m 2/g。例如，负极活性材料的比表面积可为1m 2/g、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、15m 2/g、20m 2/g、30m 2/g或者处于上述任意数值所组成的范围内。负极活性材料的比表面积在上述合适的范围内，能够使得负极活性材料颗粒具备合适的比表面积，并使得负极极片表面形成的SEI膜的面积适当，减少首次充电过程的不可逆锂的消耗。由此，能够使得电化学装置兼具良好的动力学性能和高能量密度。
在一些实施方式中，负极活性材料层的压实密度可为1.0g/cm 3至1.7g/cm 3。例如，负极活性材料层的压实密度可为1.0g/cm 3、1.1g/cm 3、1.2g/cm 3、1.3g/cm 3、1.4g/cm 3、1.5/cm 3、1.6g/cm 3、1.7g/cm 3或者处于上述任意数值所组成的范围内。可选地，负极活性材料的压实密度可为1.3g/cm 3至1.7g/cm 3。本申请的负极活性材料层中包括径厚比适当的硬碳颗粒，因此，负极活性材料层中的负极活性材料颗粒的堆叠更为密实，能够具有高压实密度，从而能提高单位体积内负极活性材料的含量，由此提升电化学装置具备更高的能量密度。
在一些实施方式中，负极活性材料层的孔隙率可为10％至40％。例如，负极活性材料层的孔隙率可为10％、15％、20％、25％、30％、35％、40％或者处于上述任意数值所组成的范围内。
可选地，负极活性材料的孔隙率可为15％至25％。
并非意在受限于任何理论或解释，与常规形貌硬碳材料相比，片层硬碳活性材料的颗粒与颗粒间有更多面面接触，更加密实的堆叠使负极活性材料层的孔隙率更低。负极活性材料层的孔隙率在上述合适的范围内，不仅能够降低负极极片的内阻，还能保证负极极片的电解液浸润性能，从而提升电化学装置的动力学性能。
在一些实施方式中，负极极片的膜片电阻可为2mΩ至50mΩ。例如，负极极片的膜片电阻可为2mΩ、5mΩ、8mΩ、10mΩ、15mΩ、20mΩ、25mΩ、30mΩ、35mΩ、40mΩ、45mΩ、50mΩ或者处于上述任意数值所组成的范围内。
负极极片的膜片电阻在上述合适的范围内，能够保证电化学装置的具备低的欧姆极化，电化学装置充放电过程中的产热降低，从而提升电化学装置的长期循环性能和安全性能。
本申请的硬碳颗粒可以通过多种方式获得。作为一个示例，硬碳颗粒可以采用模板法、通过如下步骤制备得到：将片层状无机物模板、造孔剂与树脂混合，得到混合物；将混合物在0T至5T压力、25℃至200℃下固化0.1h至120h；将固化后的混合物在700化至1300后下热解2h，破碎筛分，之后用酸或碱溶液处理除去模板以获得硬碳颗粒。其中，片层状无机物模板包括但不限于：蒙脱土、云母石、二维硅、片层二氧化硅；造孔剂包括但不限于：氧化镁、氯化镁、葡萄酸镁、氧化锌、氯化锌、葡萄酸锌、硬脂酸锌、硼酸锌、氧化铁、氯化铁、葡萄糖、蔗糖；树脂包括但不限于：酚醛树脂、呋喃树脂、环氧树脂、聚酯树脂，双马来酰胺、热固性聚酰亚胺、氰酸酯。混合的方式可以是粉末互混，也可以是溶液混合。当混合的方式为溶液混合时，溶剂的选择由树脂及造孔剂决定，溶剂可以包括但不限于：去离子水、甲醇、乙醇、丙酮、二氯甲烷、苯、甲苯、乙酸乙酯、四氢呋喃。溶液混合之后、进行固化之前，可以除去溶剂，也可以不除去溶剂。作为一个具体的示例，硬碳颗粒可通过如下步骤制备得到：将100g热固性酚醛树脂完全溶于200mL乙醇，然后加入100g的微米级片层二氧化硅，开放环境下搅拌24使乙醇挥发，得到粘液状混合物；之后将粘液状混合物导入模压板内，设置模压压力0.5T、模压温度200℃、模压时间1h，模压结束得到前驱体材料；将前驱体材料置于管式炉中，在氩气气氛下，以3℃/min升温速率升温至1100℃，并保温2h，将前驱体热解得到热解碳，之后将热解碳破碎并筛分，然后将热解碳置于2mol/L的1L氢氧化钠溶液中，搅拌24h后抽滤，重复两次以确保除净片层二氧化硅模板，最后获得片层的硬碳材料。
本申请对负极极片的负极集流体不作限定。可以使用金属箔材或多孔金属板，例如使用铜、镍、钛、铁等金属或它们的合金的箔材或多孔板。作为示例，负极集流体为铜箔。
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侧面，负极活性材料层可以设置在负极集流体的一个侧面，也可以同时设置在负极集流体的两个侧面。例如，负极集流体具有在其自身厚度方向相对的两个侧面，负极活性材料层设置在负极集流体相对的两侧中的任意一侧或两侧上。
在一些实施方式中，负极活性材料层中并不排除除了硬碳外的其他负极活性材料。其他负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。作为示例，其他负极活性材料包括但不限于软碳、硅、硅-碳复合物、SiO、Li-Sn合金、Li-Sn-O合金、Sn、SnO、SnO 2、尖晶石结构的Li 4Ti 5O 12、Li-Al合金中的至少一种。
在一些实施方式中，负极活性材料层还可选地包括粘结剂。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，硬碳颗粒的径厚比可通过本领域已知的方法和仪器测定。例如，可以用导电胶将裁剪为一定大小的负极极片粘贴在硅片载体上，使用氩离子抛光对负极极片的一个截面进行抛光处理，得到试件；通过扫描式电子显微镜(SEM)对经抛光的截面的形貌结构和元素分布进行分析，用图像处理软件筛选出硬碳颗粒的图像，并测试截面中每一硬碳颗粒的长径的值与垂直于长径方向上的最大厚度，从而得到每一硬碳颗粒的径厚比。
在本申请中，XRD图可通过本领域已知的方法和仪器测定。例如，可以利用Bruker D8 ADVANCE X射线粉末衍射仪进行XRD测试得到，其中，XRD测试的辐射源为Cu Kα靶材，测试的参数可设置为：管电压为40kV，管电流为40mA，扫描步长为0.00836°，每一扫描步长的扫描时长为0.3s，2θ范围为5°至80°。
在本申请中负极活性材料的粒径Dv10、Dv50、Dv99具有本领域公知的含义，可采用本领域已知的方法和仪器测定。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。
在本申请中，负极活性材料的比表面积具有本领域公知的含义，可以用本领域已知的方法测定。例如可使用比表面积分析仪(例如TristarⅡ3020M)，通过氮吸附/脱附法测量负极活性材料的比表面积。
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，负极极片冷压后，用冲片机分别冲出面积为S的完全涂布有浆料的圆片和未涂布有浆料的圆片若干，分别进行称重得到平均质量W 2、W 1，分别进行测厚得到平均厚度T 2、T 1，负极极片的压实密度＝(W 2-W 1)/(T 2-T 1)/S。
在本申请中，负极活性材料层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。例如可将涂覆有负极活性材料的负极极片冲切成圆片状的试件，每一试件中，负极活性材料层的体积由圆片面积和厚度确定；参照GB/T24586-2009铁矿石表观密度真密度和孔隙率的测定标准测试负极活性材料层的孔隙率。
在本申请中，负极极片的膜片电阻具有本领域公知的含义，可以用本领域已知的方法测定。例如可以将负极极片裁切得到尺寸为60mm×80mm大小的试件，使用BER1100多功能极片电阻仪对样品进行电阻测试，测试得到负极极片的膜片电阻。
需要说明的是，上述针对负极活性材料层或负极活性材料颗粒的各种参数测试，可以在如锂离子电池制备过程中取样测试，也可以从制备好的锂离子电池中取样测试。
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S10-S30进行取样。
S10，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2-10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。
S20，将步骤S10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)。
S30，将步骤S20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
本申请第二方面提供一种电化学装置，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，其具体实例包括但不限于锂离子电池或钠离子电池。
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。
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。
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。
[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一方面的负极极片。
[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物质层。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，正极活性物质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，正极活性物质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。例如，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，正极活性物质层还可选的包括导电剂。作为示例，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，正极活性物质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，正极活性物质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物质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物质层之间、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物质层表面的保护层。
[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，电解液包括有机溶剂、锂盐和可选的添加剂，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，作为示例，锂盐包括但不限于LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiClO 4(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)、LiPO 2F 2(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，作为示例，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，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，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、锂盐、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，将锂盐、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，先将锂盐加入有机溶剂中，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。
虽然在上面关于负极极片的实施例的描述中，主要以锂离子电池为具体示例说明了根据本申请的负极极片能够实现的有益效果，但是本领域技术人员容易理解，根据本申请的负极极片的负极活性材料层具备高压实密度和合适的孔隙率，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
本申请第三方面提供了一种用电装置，其包括本申请第二方面的电化学装置。
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用电装置。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。
实施例
下述实施例更具体地描述了本发明公开的内容，这些实施例仅仅用于阐述性说明，因为在本发明公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比、和比值都是基于质量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
实施例1至21
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)按质量比97:1.5:1.5溶于去离子水中，得到固含量为40wt％的负极浆料；将负极浆料涂布于负极集流体的两个侧面上，其中，负极集流体为6μm厚的铜箔，单面涂布厚度为50μm；在85℃下烘干，经冷压、裁片、分切后，在120℃的真空条件下干燥12小时，得到负极极片。其中，基于负极活性材料的质量，片层状硬碳的质量百分含量w 1％、MCMB的质量百分含量w 2％、a、b、c、d、负极活性材料的Dv10、Dv50、Dv99、负极活性材料的比表面积、负极活性材料层的压实密度、负极活性材料层的孔隙率、负极极片的膜片电阻分别如表1、表2、表3所示。其中，实施例1至8中的负极活性材料为95％的硬碳和5％的MCMB，实施例9至16的负极活性材料与实施例1相同且具有与实施例1中硬碳相同的径厚比分布，实施例17至21的负极活性材料与具有与实施例1中硬碳相同的径厚比分布。
正极极片的制备
将正极活性材料钴酸锂、导电剂炭黑、粘结剂PVDF按照质量比97:1.4:1.6进行混合，加入适量的溶剂NMP，搅拌均匀获得固含量为72wt％的正极浆料；将正极浆料均匀涂覆在正极集流体铝箔的两个侧面上，其中，单面涂布厚度为80μm；在85℃下烘干，经冷压、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
在干燥的氩气气氛手套箱中，将碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二乙酯(DEC)按照质量比为EC：PC：DEC＝1：1：1进行混合；充分搅拌后加入锂盐LiPF 6，混合均匀得到电解液，基于电解液的质量，LiPF 6的质量含量为12.5％，向电解液中加入质量含量为2％的1,3-丙烷磺内酯、质量含量为2％的氟代碳酸乙烯酯和质量含量为2％的丁二腈。
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，在80℃下脱去水分后，加入上述电解液，经封装、静置化成、脱气、整形等工序后，得到锂离子电池。
对比例1至4
调整负极活性材料的种类，基于实施例1至21中负极极片、正极极片、电解液、隔离膜与锂离子电池的制备过程，制备对比例1至5的负极极片、正极极片、电解液、隔离膜及锂离子电池。
其中，对比例1的负极活性材料为MCMB；对比例2的负极活性材料为鳞片石墨；对比例3的负极活性材料为95％的常规形貌硬碳和5％的MCMB；对比例4的负极活性材料为95％的微球状硬碳颗粒和5％的MCMB。
对比例5至6
基于实施例1至21中负极极片、正极极片、电解液、隔离膜与锂离子电池的制备过程，根据表1中所示调整硬碳材料的a、b、c、d的值，制备对比例5、6的负极极片、正极极片、电解液、隔离膜以及锂离子电池。
测试部分
负极极片的测试
(1)硬碳颗粒的径厚比测试
测试仪器：扫描电子显微镜JSM-6360LV其配套的X射线能谱仪
取满放后的锂离子电池，拆解后取出负极极片；用DMC浸泡20min，依次用DMC、丙酮清洗后，置于烘箱内，于80于烘干12h；将烘干后的负极极片裁剪为0.5cm极，负极的试件，用导电胶将试件粘贴在1cm电胶将，负极的硅片载体上；使用氩离子抛光(工作参数：加速电压8kV，抛光时长4h)对负极极片一端的截面进行抛光处理，得到试件；通过扫描电子显微镜对经抛光的截面形貌结构和元素分布进行分析，用图像处理软件(Multiphase)筛选硬碳颗粒的图像，并测试截面中每一硬碳颗粒的长径的值与垂直于长径方向上的最大厚度，从而得到每一硬碳颗粒的径厚比。对于每一实施例或对比例中的负极极片，分别对10张SEM图像进行处理(参见图2)，统计得到a、b、c、d的值。
(2)负极活性材料的XRD测试
测试仪器：Bruker D8 ADVANCE X射线粉末衍射仪
取完全放电的锂离子电池，拆解出负极极片；经清洗并烘干后，用刮刀对负极活性材料层进行处理得到负极活性材料层粉末；将负极活性材料层粉末置于管式炉中，在400℃、氩气气氛下保温4h，以除去负极活性材料层粉末表面黏附的粘结剂，从而得到负极活性材料粉末；用X射线粉末衍射仪测试负极活性材料粉末，得到负极活性材料的XRD测试图。其中，XRD测试的辐射源为Cu Kα靶材，测试的参数可设置为：管电压为40kV，管电流为40mA，扫描步长为0.00836°，每一扫描步长的扫描时长为0.3s，2θ范围为5°至80°。
(3)负极活性材料颗粒的粒径测试
测试仪器：Bruker D8 Advance
参照负极活性材料的XRD测试中的步骤，获得负极活性材料粉末；将负极活性材料粉末分散在乙醇中，超声30分钟后，得到负极活性材料的乙醇分散液；将负极活性材料的乙醇分散液加入马尔文粒度测试仪内，测试负极活性材料颗粒的Dv10、Dv50和Dv99。
(4)负极活性材料的比表面积测试
测试仪器：比表面积分析仪TristarⅡ3020M
参照负极活性材料的XRD测试中的步骤，获得负极活性材料粉末；将负极活性材料粉末置于真空干燥箱中烘干；用比表面积分析仪测量负极活性材料的比表面积。
(5)负极活性材料层的压实密度测试
取完全放电的锂离子电池，拆解出负极极片；经清洗并烘干后，测量单面负极活性材料层的面积S、负极极片的质量W 1以及负极极片的厚度T 1；用溶剂洗掉负极活性材料层后，烘干并测量负极集流体的质量W 2以及负极集流体的厚度T 2。通过如下式1至式3计算得到负极活性材料层的压实密度。
W 0＝(W 1-W 2)/2      式1
T 0＝(T 1-T 2)/2      式2
压实密度＝W 0/(T 0×S)   式3
其中，W 0表示单面负极活性材料层的质量，T 0表示单面负极活性材料层的厚度。
(6)负极活性材料层的孔隙率测试
测试仪器：真密度测试仪(AccuPycⅡ1340)
将涂覆有负极活性材料的负极极片冲切成圆片状的试件，每一试件中，负极活性材料层的体积约为0.35cm 3；参照GB/T24586-2009铁矿石表观密度真密度和孔隙率的测定标准测试负极活性材料层的孔隙率。
(7)负极活性材料的克容量测试
将负极极片和正极极片锂片组装成扣式电池；以0.05C放电至5.0mV，以50μA放电至5.0mV，以10μA放电至5.0mV，以0.1C充电至2.0V，记录此时扣式电池的首次充电容量。负极活性材料的克容量＝首次充电容量(mAh)/负极活性材料的质量(g)。
(8)负极活性材料孔径分布测试
测试仪器：ASAP2460-物理吸附分析仪，参照负极活性材料的XRD测试中的步骤，获得负极活性材料粉末；将烘干脱气处理后的样品置于液氮中，调节不同试验压力，分别测出对氮气的吸附量，绘出吸附和脱附等温线。根据滞后环的形状确定孔的形状，按不同的孔模型计算孔分布、孔容积，使用BJH模型拟合介孔及大孔的孔径分布曲线，使用DFT模型拟合微孔的孔径分布曲线。
锂离子电池的测试
(1)锂离子电池的能量密度测试
对于每一实施例或对比例，各取5支锂离子电池进行能量密度测试。具体测试步骤如下。
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，直到上限电压为4.48V，然后在0.2C的放电电流下进行恒流放电，直至放电截止电压(3V)，计算各实施例和对比例的锂离子电池的能量密度M i相对于对比例1的能量密 度M 1的百分比A％，作为各实施例和对比例中锂离子电池的能量密度参数A，其中，A＝M i/M 1。
(2)锂离子电池的倍率性能测试
对于每一实施例或对比例，各取5支锂离子电池进行倍率性能测试。具体测试步骤为：将锂离子电池置于25℃环境中搁置1小时；以I＝1C的充电倍率对电池进行恒流充电(CC段)，充至4.48V后转为恒压充电(CV段)，充电电流低于0.05C时停止充电，搁置5分钟，再以0.2C的倍率将电池流放电至3V，搁置5分钟，此为第1次充放电循环。统计充电各阶段的充电容量(平均值)，计算CC段容量占比。依次调整I为0.2C、0.5C、1C、2C、3C，按照第1次充放电循环的流程进行第2至6次充放电循环。按照式4计算3C的充电倍率下CC段容量占比。
CC段容量占比＝[CC段充电容量/(CC段充电容量+CV段充电容量)]×100％式4
(3)锂离子电池的循环性能测试
对于每一实施例或对比例，各取5支锂离子电池进行循环性能测试。具体测试步骤如下。
在25℃下，将锂离子电池以1C倍率充电至4.48V，继续恒压充电至充电截止电流；以1C倍率放电至3V，此为一个充放电循环。记录首次充电容量、首次放电容量和首次循环的满充锂离子电池厚度。而后继续进行充放电循环，记录第400次循环的放电容量和满充锂离子电池厚度。
首次库伦效率(％)＝(首次放电容量/首次充电容量)×100％；
首周不可逆容量占比(％)＝[(首次充电容量-首次放电容量)/首次充电容量]×100％
容量保持率(％)＝(第400次循环的放电容量/首次循环的放电容量)×100％；
厚度膨胀率(％)＝[(第400次循环的满充锂离子电池厚度-首次循环的满充锂离子电池厚度)/首次循环的满充锂离子电池厚度]×100％。
(4)锂离子电池的自放电率测试
对于每一实施例或对比例，各取5支锂离子电池进行自放电率测试。具体测试步骤如下。
取80％荷电状态(state of charge，SOC)的锂离子电池，测试锂离子电池的初始开路电压，记录为V 1；在25℃下静置48小时后再次测试锂离子电池的开路电压，记录为V 2。
锂离子电池的自放电率＝(V 1-V 2)/48。
(5)锂离子电池的直流阻抗DCR测试
在25℃的环境下，将锂离子离子电池用0.5C电流进行充电至电压为4.4V，之后转为恒压充电，至电流为0.05C。然后用0.1C电流放电2小时，静置1h后，用0.1C电流(I 1)放电10s，记录最后1s放电电压V 3，然后用1C电流(I 2)放电1s，记录最后1s放电电压V 4，则DCR＝(V 3-V 4)/(I 2-I 1)。
实施例及对比例的设置及测试结果详见表1至表3。
Figure PCTCN2022100320-appb-000001
表2
Figure PCTCN2022100320-appb-000002
3
Figure PCTCN2022100320-appb-000003
通过表1可以看出，对比例1及对比例5的负极活性材料均为球状或类球状碳材料颗粒，其径厚比分布较为集中；在相似的冷压工艺下，硬碳类负极活性材料的压实密度均低于石墨类负极活性材料的压实密度。采用本申请中的片层状硬碳，由于该硬碳颗粒经冷压后堆积得更加密实，负极活性材料层具有更高的压实密度与更低的孔隙率，锂离子电池具有较高的的自放电率，说明具有合适径厚比分布的片层硬碳，经冷压后活性材料层表面更加平整，不易损伤隔膜，内部物理微短路的程度大幅降低，且片层状硬碳颗粒间通过面面接触，能够有效缩短Li +的传输路径，提升Li +在活性材料内部的固相传递速度，由此能够降低锂离子电池的内部阻抗，提升动其力学性能，由此锂离子电池的快速充电能力得到有效提升，使锂离子电池具有较优的循环性能和倍率性能，且锂离子电池的能量密度得到进一步提高。
通过实施例1、实施例9至16可以看出，负极活性材料的粒径较大时，会增加锂离子电池的首周不可逆容量，影响锂离子电池的循环性能。
通过实施例1、实施例17至21可以看出，当石墨颗粒与硬碳颗粒的质量占比适当时，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。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，硬碳含量高的实施例，其对应的锂离子电池在循环400圈后的厚度膨胀率越小，循环400圈的容量保持率也更加优异。
以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可容易想到各种等效的修改或替换，这些修改或替换都应被涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。

Claims (11)

  1. 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侧面的负极活性材料层，所述负极活性材料层包括负极活性材料，所述负极活性材料包括硬碳颗粒和石墨颗粒，所述硬碳颗粒具有片层状结构，基于所述硬碳颗粒的数量，径厚比为3至7的所述硬碳颗粒的占比为a％，30≤a≤70。
  2. 根据权利要求1所述的负极极片，其中，基于所述硬碳颗粒的数量，径厚比为2至3的所述硬碳颗粒的占比为b％，20≤b≤60。
  3. 根据权利要求2所述的负极极片，其中，所述硬碳颗粒满足：a+b≥90。
  4. 根据权利要求1所述的负极极片，其中，基于所述硬碳颗粒的数量，径厚比为1至2的所述硬碳颗粒的占比为c％，径厚比大于7的所述硬碳颗粒的占比为d％，0.1≤c≤10，0.1≤d≤1。
  5. 根据权利要求1所述的负极极片，其中，所述硬碳颗粒的质量占所述负极活性材料质量的85％至99％。
  6. 根据权利要求1所述的负极极片，其中，所述负极活性材料的X射线衍射图谱包含第一衍射峰和第二衍射峰，所述第一衍射峰位于18°至30°之间，所述第一衍射峰的半峰宽为4°至12°；所述第二衍射峰位于26°至27°之间，所述第二衍射峰的半峰宽为0.1°至0.4°。
  7. 根据权利要求1所述的负极极片，其中，所述硬碳颗粒包括微孔，采用氮气二氧化碳吸附-脱附法测得的微孔孔体积大于或等于0.25cc/g。
  8. 根据权利要求1所述的负极极片，其中，所述负极活性材料满足如下至少一者：
    (1)所述负极活性材料的粒径满足：1μm≤Dv10≤5μm，4μm≤Dv50≤18μm，Dv99≤43μm；
    (2)所述负极活性材料的比表面积为1m 2/g至30m 2/g。
  9. 根据权利要求1所述的负极极片，其中，所述负极活性材料层满足如下至少一者：
    (3)所述负极活性材料层的压实密度为1.0g/cm 3至1.7g/cm 3；
    (4)所述负极活性材料层的孔隙率为10％至40％；
  10. 根据权利要求1至9中任一项所述的负极极片，其中，所述负极极片满足以下条件至少一者：
    (5)基于所述硬碳颗粒的数量，径厚比为3至7的所述硬碳颗粒的占比为a％，30≤a≤50；
    (6)基于所述硬碳颗粒的数量，径厚比为2至3的所述硬碳颗粒的占比为b％，20≤b≤50；
    (7)基于所述硬碳颗粒的数量，径厚比为3至7的所述硬碳颗粒的占比为a％，径厚比为2至3的所述硬碳颗粒的占比为b％，所述硬碳颗粒满足：a+b≥95；
    (8)采用氮气二氧化碳吸附-脱附法测得的所述硬碳颗粒的微孔孔体积为1cc/g至5cc/g。
  11. 一种电化学装置，包括根据权利要求1至10中任一项所述的负极极片。
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