WO2024044974A1 - 负极极片、二次电池和电子装置 - Google Patents

负极极片、二次电池和电子装置 Download PDF

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WO2024044974A1
WO2024044974A1 PCT/CN2022/115902 CN2022115902W WO2024044974A1 WO 2024044974 A1 WO2024044974 A1 WO 2024044974A1 CN 2022115902 W CN2022115902 W CN 2022115902W WO 2024044974 A1 WO2024044974 A1 WO 2024044974A1
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active material
negative electrode
negative
negative active
cross
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PCT/CN2022/115902
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English (en)
French (fr)
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金文博
冯鹏洋
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宁德新能源科技有限公司
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Priority to PCT/CN2022/115902 priority Critical patent/WO2024044974A1/zh
Priority to CN202280058229.3A priority patent/CN118043991A/zh
Publication of WO2024044974A1 publication Critical patent/WO2024044974A1/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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • 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
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals

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  • This application relates to the field of energy storage, specifically to a negative electrode plate, a secondary battery and an electronic device.
  • this application provides a negative electrode plate and a secondary battery including the negative electrode plate.
  • the negative electrode sheet of the present application has excellent dynamic properties and can effectively improve the low-temperature charge and discharge performance of secondary batteries.
  • the present application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.
  • the negative electrode active material layer includes a negative electrode active material
  • the negative electrode active material includes negative electrode active material particles.
  • the negative active material particles include first particles with holes, wherein, within the 200 ⁇ m ⁇ 200 ⁇ m area of the cross section of the negative active material layer, the negative active material satisfies: 0.10 ⁇ TD-0.05 ⁇ (1/X) ⁇ 0.40;
  • X represents the ratio of the average cross-sectional area of the pores in the first particle to the average cross-sectional area of the first particle, 4.0% ⁇ .
  • the negative active material particles have pores, especially those inside, which can greatly increase the contact surface between the negative electrode piece and the electrolyte, significantly increasing the lithium insertion channels for active ions such as lithium ions, making it easier for active ions to diffuse, which is beneficial to activity
  • the rapid deintercalation of ions improves the rate performance of the negative electrode piece, thereby improving the low-temperature charge and discharge performance of the secondary battery.
  • the pore ratio of the negative active material particles cannot be too high. Too many pores will lead to an increase in side reactions between the active material and the electrolyte, which will affect the first Coulombic efficiency and storage performance of the secondary battery, and will also reduce the performance of the secondary battery. Low temperature rate performance.
  • the structure and distribution of the pores inside the negative active material particles will also affect its tap density. If the tap density is too high or too low, it will not be conducive to the subsequent processing of the negative electrode slurry, thereby affecting the electrical performance of the secondary battery.
  • the ratio of the average cross-sectional area of the pores in the first particles with holes in the negative active material and the average cross-sectional area of the first particles and the tap density of the negative active material are controlled within the above range.
  • the tap density has a good match with the pore structure.
  • the appropriate pore structure significantly increases the number of lithium insertion channels inside the negative electrode piece, making it easier for active ions to diffuse, which is conducive to the rapid deintercalation of active ions and improves the rate of the negative electrode piece.
  • the performance is improved, which can improve the low-temperature charge and discharge performance of the secondary battery.
  • the appropriate tap density improves the processing performance of the material and can also improve the low-temperature rate performance of the secondary battery to a certain extent.
  • the ratio of the average cross-sectional area of the pores in the first particles to the average cross-sectional area of the first particles and the tap density of the negative active material are within the above range, which can further improve the low-temperature rate performance of the secondary battery.
  • the secondary electrode has higher low-temperature rate performance.
  • the cross-sectional area ratio of the holes is within the above range, the secondary electrode has higher low-temperature rate performance.
  • the cross-sectional area ratio of the holes is too low, the wettability of the electrolyte in the negative electrode sheet is poor, the diffusion of active ions is difficult, and the low-temperature rate performance improvement effect of the secondary battery is not good.
  • the cross-sectional area ratio of the holes is too high, the side reaction between the negative active material and the electrolyte increases, which affects the first Coulombic efficiency and storage performance of the secondary battery, and also reduces the low-temperature rate performance of the secondary battery.
  • the negative electrode material satisfies: 0.40 ⁇ 2 ⁇ BET-L/D ⁇ 1.50 and L/D ⁇ 2.50; where L represents the negative active material particles The longest cross-sectional length, in ⁇ m; D represents the shortest cross-sectional length of the negative active material particles, in ⁇ m; BET represents the specific surface area of the negative active material, in m 2 /g.
  • the negative active material particles are ellipsoidal and have high mechanical strength.
  • the active ions can be deintercalated in many directions and the deintercalation path is short, which is conducive to the improvement of its dynamic performance.
  • the specific surface area of the negative active material is moderate, and the wettability of the electrolyte in the negative electrode sheet is high, which can further improve the low-temperature rate performance of the secondary battery.
  • 0.50 ⁇ 2 ⁇ BET-L/D 0.50 ⁇ 2 ⁇ BET-L/D ⁇ 1.30.
  • 1.0 ⁇ L/D ⁇ 2.2 When the L/D is too high, the negative active material particles are in the shape of long strips, which are easy to break during the pressing process and are not conducive to the deintercalation of active ions in all directions. The dynamic properties of the negative active material are poor, thereby reducing the performance of the secondary battery. Low temperature rate performance.
  • 0.5 ⁇ BET ⁇ 2.5 When the specific surface area is too large, the surface reactivity of the negative active material is high and it is easy to react with the electrolyte, which will adversely affect the storage performance of the secondary battery.
  • the average maximum Feret diameter F of the negative active material particles satisfies: 4 ⁇ m ⁇ F ⁇ 55 ⁇ m. If the size of the negative active material particles is too small, the compacted density will be low, which will reduce the compacted density of the negative electrode piece. Moreover, the reaction between the small particles and the electrolyte will be more violent, which will affect the storage and cycle performance of the secondary battery. When the size of the negative active material particles is too large, the deintercalation path of active ions in them is longer, which will affect the rate performance of the secondary battery.
  • the single-sided thickness H of the negative active material layer satisfies: H ⁇ 90 ⁇ m. In some embodiments, 25 ⁇ m ⁇ H ⁇ 60 ⁇ m.
  • H ⁇ 90 ⁇ m In some embodiments, 25 ⁇ m ⁇ H ⁇ 60 ⁇ m.
  • the single-sided energy density E of the negative active material layer satisfies: 0.01mAh/mm 2 ⁇ E ⁇ 0.07mAh/mm 2 .
  • the energy density of the negative active material layer is proportional to its packing density. When the energy density of the negative active material layer is too low, its packing density is correspondingly too low. Although a low packing density is beneficial to the rate performance of the secondary battery, it will cause too much Loss of energy density. When the energy density of the negative active material layer is too high, its stacking density is correspondingly too high. High stacking density will seriously affect the rate performance of the secondary battery, especially the low-temperature rate performance.
  • the negative active material satisfies: ID/IG ⁇ 0.6, where ID is the intensity of the peak at 1350 cm -1 in the Raman spectrum, and IG is the intensity of the peak at 1580 cm -1 in the Raman spectrum. .
  • ID/IG the intensity of the peak at 1350 cm -1 in the Raman spectrum.
  • IG the intensity of the peak at 1580 cm -1 in the Raman spectrum.
  • 0.15 ⁇ ID/IG ⁇ 0.5 0.15 ⁇ ID/IG ⁇ 0.5.
  • the ID/IG ratio can characterize the defectiveness of the negative active material. The greater the ID/IG ratio, the higher the defectiveness. The defects of the negative active material are too high, which is not conducive to the formation of the SEI film, thus affecting the rate performance of the secondary battery.
  • the orientation degree OI of the negative active material satisfies: OI ⁇ 25. In some embodiments, 5 ⁇ OI ⁇ 25.
  • the OI value indicates the orientation degree of the negative active material. If the OI value is too large, it means that the orientation of the negative active material is too high, which is not conducive to the deintercalation of active ions, which will in turn affect the rate performance of the secondary battery.
  • the negative active material includes graphite. In some embodiments, the negative active material includes natural graphite.
  • the present application provides a secondary battery, which includes the negative electrode plate of the first aspect.
  • the discharge ratio Q1/Q2 of the secondary battery at 0°C is ⁇ 0.8, where Q1 is the discharge capacity at 0°C and 1C, and Q2 is the discharge capacity at 25°C and 1C.
  • the present application provides an electronic device including the secondary battery of the second aspect.
  • the negative active material in the negative electrode sheet of the present application has appropriate tap density and porosity, so that the negative electrode sheet has excellent dynamic properties, which can effectively improve the low-temperature charge and discharge performance of the secondary battery.
  • Figure 1 shows the discharge ratios of the secondary batteries of Example 6 and Comparative Example 3 of the present application at different temperatures, where 1 - Example 6 and 2 - Comparative Example 3.
  • any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with other lower limits to form an unexpressed range, and likewise any upper limit can be combined with any other upper limit to form an unexpressed range.
  • each individually disclosed point or single value may itself serve as a lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.
  • 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.
  • the present application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.
  • the negative electrode active material layer includes a negative electrode active material
  • the negative electrode active material includes negative electrode active material particles.
  • the negative active material particles include first particles with holes, wherein, within the 200 ⁇ m ⁇ 200 ⁇ m area of the cross section of the negative active material layer, the negative active material satisfies: 0.10 ⁇ TD-0.05 ⁇ (1/X) ⁇ 0.40;
  • X represents the ratio of the average cross-sectional area of the pores in the first particle to the average cross-sectional area of the first particle, 4.0% ⁇ .
  • the negative active material particles have pores, especially those inside, which can greatly increase the contact surface between the negative electrode piece and the electrolyte, significantly increasing the lithium insertion channels for active ions such as lithium ions, making it easier for active ions to diffuse, which is beneficial to activity
  • the rapid deintercalation of ions improves the rate performance of the negative electrode piece, thereby improving the low-temperature charge and discharge performance of the secondary battery.
  • the pore ratio of the negative active material particles cannot be too high. Too many pores will lead to an increase in side reactions between the active material and the electrolyte, which will affect the first Coulombic efficiency and storage performance of the secondary battery, and will also reduce the performance of the secondary battery. Low temperature rate performance.
  • the structure and distribution of the pores inside the negative active material particles will also affect its tap density. If the tap density is too high or too low, it will not be conducive to the subsequent processing of the negative electrode slurry, thereby affecting the electrical performance of the secondary battery.
  • the ratio of the average cross-sectional area of the pores in the first particles with holes in the negative active material and the average cross-sectional area of the first particles and the tap density of the negative active material are controlled within the above range.
  • the tap density has a good match with the pore structure.
  • the appropriate pore structure significantly increases the number of lithium insertion channels inside the negative electrode piece, making it easier for active ions to diffuse, which is conducive to the rapid deintercalation of active ions and improves the rate of the negative electrode piece.
  • the performance is improved, which can improve the low-temperature charge and discharge performance of the secondary battery.
  • the appropriate tap density improves the processing performance of the material and can also improve the low-temperature rate performance of the secondary battery to a certain extent.
  • the "cross section of the negative active material layer” may be a cross section along the thickness direction of the negative active material layer.
  • TD-0.05 ⁇ (1/X) is 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, or a range consisting of any two of these values.
  • the ratio of the average cross-sectional area of the pores in the first particles to the average cross-sectional area of the first particles and the tap density of the negative active material are within the above range, which can further improve the low-temperature rate performance of the secondary battery.
  • the cross-sectional area ratio of the holes is within the above range, the secondary electrode has higher low-temperature rate performance. When the cross-sectional area ratio of the holes is too low, the wettability of the electrolyte in the negative electrode sheet is poor, the diffusion of active ions is difficult, and the low-temperature rate performance improvement effect of the secondary battery is not good.
  • the TD is 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, or any two of these values range of composition.
  • the negative electrode material satisfies: 0.40 ⁇ 2 ⁇ BET-L/D ⁇ 1.50 and L/D ⁇ 2.50; where L represents the negative active material particles The longest cross-sectional length, in ⁇ m; D represents the shortest cross-sectional length of the negative active material particles, in ⁇ m; BET represents the specific surface area of the negative active material, in m 2 /g.
  • the negative active material particles are ellipsoidal and have high mechanical strength.
  • the active ions can be deintercalated in many directions and the deintercalation path is short, which is conducive to the improvement of its dynamic performance.
  • 2 ⁇ BET-L/D is 0.45, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, A range of 1.4, 1.45, or any two of these values.
  • 0.50 ⁇ 2 ⁇ BET-L/D ⁇ 1.30.
  • L/D is 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2.0, 2.05, 2.1, 2.15, or a range consisting of any two of these values.
  • the BET is 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or any of these values The range composed of both. In some embodiments, 0.5 ⁇ BET ⁇ 2.5. When the specific surface area is too large, the surface reactivity of the negative active material is high and it is easy to react with the electrolyte, which will adversely affect the storage performance of the secondary battery.
  • the average maximum Feret diameter F of the negative active material particles satisfies: 4 ⁇ m ⁇ F ⁇ 55 ⁇ m.
  • F is a range consisting of 5 ⁇ m, 10 ⁇ m, 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, or any two of these values. If the size of the negative active material particles is too small, the compacted density will be low, which will reduce the compacted density of the negative electrode piece.
  • the reaction between the small particles and the electrolyte will be more violent, which will affect the storage and cycle performance of the secondary battery.
  • the size of the negative active material particles is too large, the deintercalation path of active ions in them is longer, which will affect the rate performance of the secondary battery.
  • the single-sided thickness H of the negative active material layer satisfies: H ⁇ 90 ⁇ m, such as 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, 55 ⁇ m, 60 ⁇ m, 65 ⁇ m, 70 ⁇ m, 75 ⁇ m, 80 ⁇ m or 85 ⁇ m. . In some embodiments, 25 ⁇ m ⁇ H ⁇ 60 ⁇ m.
  • H ⁇ 90 ⁇ m such as 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, 55 ⁇ m, 60 ⁇ m, 65 ⁇ m, 70 ⁇ m, 75 ⁇ m, 80 ⁇ m or 85 ⁇ m.
  • 25 ⁇ m ⁇ H ⁇ 60 ⁇ m When the thickness of the negative active material layer is too high, the transmission path of active ions in the negative electrode sheet is too long, and the diffusion of active ions is difficult, which increases the polarization
  • the single-sided energy density E of the negative active material layer satisfies: 0.01mAh/mm 2 ⁇ E ⁇ 0.07mAh/mm 2 .
  • E is 0.015mAh/mm 2 , 0.02mAh/mm 2 , 0.025mAh/mm 2 , 0.03mAh/ mm 2 , 0.035mAh/mm 2 , 0.04mAh/mm 2 , 0.045mAh/mm 2 , 0.05mAh/mm 2 , 0.055mAh/mm 2 , 0.06mAh/mm 2 , 0.065mAh/mm 2 or a range consisting of any two of these values.
  • 0.013mAh/mm 2 ⁇ E ⁇ 0.056mAh/mm 2 satisfies: 0.01mAh/mm 2 ⁇ E ⁇ 0.07mAh/mm 2 .
  • E is 0.015mAh/mm 2 , 0.02mAh/mm 2 , 0.025mAh/mm 2 , 0.03mAh/ mm 2 , 0.035mAh/mm 2 , 0.04mAh/mm 2 , 0.045mAh
  • the energy density of the negative active material layer is proportional to its packing density. When the energy density of the negative active material layer is too low, its packing density is correspondingly too low. Although a low packing density is beneficial to the rate performance of the secondary battery, it will cause too much Loss of energy density. When the energy density of the negative active material layer is too high, its stacking density is correspondingly too high. High stacking density will seriously affect the rate performance of the secondary battery, especially the low-temperature rate performance.
  • the negative active material satisfies: ID/IG ⁇ 0.6, where ID is the intensity of the peak at 1350 cm -1 in the Raman spectrum, and IG is the intensity of the peak at 1580 cm -1 in the Raman spectrum. .
  • ID/IG is a range consisting of 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or any two of these values.
  • the ID/IG ratio can characterize the defectiveness of the negative active material. The greater the ID/IG ratio, the higher the defectiveness. The defects of the negative active material are too high, which is not conducive to the formation of the SEI film, thus affecting the rate performance of the secondary battery.
  • the orientation degree OI of the negative active material satisfies: OI ⁇ 25.
  • OI is a range of 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, or any two of these values.
  • the OI value indicates the orientation degree of the negative active material. If the OI value is too large, it means that the orientation of the negative active material is too high, which is not conducive to the deintercalation of active ions, which will in turn affect the rate performance of the secondary battery.
  • the negative active material includes graphite. In some embodiments, the negative active material includes natural graphite.
  • the preparation process of graphite includes: selecting large flake natural graphite as raw material, first crushing it to 5 ⁇ m to 15 ⁇ m, and then subjecting it to surface oxidation treatment to increase organic groups, and then performing spheroidization treatment. After it is transformed into spherical graphite, it is then treated at high temperatures of 5000°C to 1200°C. At high temperatures, the organic groups introduced into the particles during the spheroidization process will violently decompose and rapidly generate gas, forming pores inside the graphite particles.
  • the present application provides a secondary battery, which includes the negative electrode plate of the first aspect.
  • the discharge ratio Q1/Q2 of the secondary battery at 0°C is ⁇ 0.8, where Q1 is the discharge capacity at 0°C and 1C, and Q2 is the discharge capacity at 25°C and 1C.
  • the negative electrode current collector includes: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate covered with conductive metal, or any combination thereof.
  • the negative active material layer further includes a binder and a conductive agent.
  • binders include, but are not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-containing Oxygen polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or Nylon etc.
  • conductive agents include, but are not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof.
  • the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof.
  • the metal-based material is selected from metal powders, metal fibers, copper, nickel, aluminum, or silver.
  • the conductive polymer is a polyphenylene derivative.
  • the secondary battery of the present application also includes a positive electrode.
  • the positive electrode includes a positive electrode current collector and a positive electrode active material layer.
  • the positive electrode active material layer includes a positive electrode active material, a binder and a conductive agent.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil can be used.
  • the composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.
  • the positive active material includes lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron manganese phosphate, silicon At least one of lithium iron oxide, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel type lithium manganate, spinel type lithium nickel manganate and lithium titanate.
  • the binder includes a binder polymer such as polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethylcellulose, lithium carboxymethylcellulose, modified polyvinylidene fluoride At least one of ethylene, modified SBR rubber or polyurethane.
  • the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyvinyl alcohol, or polyacrylic acid.
  • the conductive agent includes carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black or carbon fiber; metal-based materials, such as metal powder or metal of copper, nickel, aluminum, silver, etc. Fibers; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.
  • the secondary battery of the present application also includes a separator film.
  • the material and shape of the separator film used in the secondary battery of the present application are not particularly limited and can be any technology disclosed in the prior art.
  • the isolation membrane includes polymers or inorganic substances formed of materials that are stable to the electrolyte of the present application.
  • the isolation film may include a base material layer and a surface treatment layer.
  • the base material layer is a non-woven fabric, film or composite film with a porous structure, and the material of the base material layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide.
  • polypropylene porous membrane, polyethylene porous membrane, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite membrane can be used.
  • a surface treatment layer is provided on at least one surface of the base layer.
  • the surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic layer.
  • the inorganic layer includes inorganic particles and a binder.
  • the inorganic particles are selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, At least one of yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate.
  • the binder is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy , at least one of polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the polymer layer contains a polymer, and the material of the polymer is selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, At least one of poly(vinylidene fluoride-hexafluoropropylene).
  • the secondary of this application also includes electrolyte. Electrolytes useful in this application may be electrolytes known in the art.
  • the electrolyte solution includes an organic solvent, a lithium salt, and optional additives.
  • the organic solvent in the electrolyte solution of the present application can be any organic solvent known in the prior art that can be used as a solvent for the electrolyte solution.
  • the electrolyte used in the electrolyte solution according to the present application is not limited, and it can be any electrolyte known in the prior art.
  • the additives of the electrolyte according to the present application may be any additives known in the art that can be used as electrolyte additives.
  • organic solvents include, but are not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) ), propylene carbonate or ethyl propionate.
  • the organic solvent includes ether solvents, such as at least one of 1,3-dioxane (DOL) and ethylene glycol dimethyl ether (DME).
  • the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.
  • lithium salts include, but are not limited to: lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium difluorophosphate (LiPO 2 F 2 ), lithium bistrifluoromethanesulfonimide LiN (CF 3 SO 2 ) 2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO 2 F) 2 )(LiFSI), lithium bisoxalatoborate LiB(C 2 O 4 ) 2 (LiBOB) or Lithium difluorooxalate borate LiBF 2 (C 2 O 4 ) (LiDFOB).
  • the additive includes at least one of fluoroethylene carbonate and adiponitrile.
  • secondary batteries of the present application include, but are not limited to: lithium-ion batteries or sodium-ion batteries.
  • the secondary battery includes a lithium-ion battery.
  • the present application further provides an electronic device, which includes the secondary battery described in the second aspect of the present application.
  • electronic devices of the present application include, but are not limited to, notebook computers, pen-input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, and stereo headsets. , VCR, LCD TV, portable cleaner, portable CD player, mini CD, transceiver, electronic notepad, calculator, memory card, portable recorder, radio, backup power supply, motor, automobile, motorcycle, power-assisted bicycle, bicycle , lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.
  • the organic oxidative groups involved in the particles during the spheroidization process will decompose violently and rapidly generate gas. In this way, pores left by material volatilization and gas expansion will be formed inside the curled spherical graphite.
  • the ratio X of the cross-sectional area of the hole to the cross-sectional area of the particle is 5.0%
  • the TD of the active material is 1.13g/cm 3
  • the value of TD-0.05 ⁇ (1/X) is 0.13.
  • lithium iron phosphate (chemical formula: LiFePO 4 ), conductive agent acetylene black, and binder polyvinylidene fluoride (abbreviated as PVDF) in a weight ratio of 96.3:2.2:1.5 in an appropriate amount of N-methylpyrrolidone (abbreviated as NMP).
  • NMP N-methylpyrrolidone
  • a polyethylene porous polymer film is used as the isolation membrane.
  • the positive electrode, isolation film, and negative electrode in order so that the isolation film plays an isolation role between the positive electrode and the negative electrode, and then wind it to obtain the electrode assembly; after welding the electrode lug, place the electrode assembly in the outer packaging foil aluminum plastic film , inject the electrolyte prepared above into the dried electrode assembly, and go through processes such as vacuum packaging, standing, formation, shaping, and capacity testing to obtain a soft-pack lithium-ion battery.
  • the preparation process of the negative active material is similar to that in Example 1, except that the corresponding negative active material is prepared by adjusting parameters such as the ratio and concentration of the acid and the temperature of the high-temperature treatment.
  • the specific preparation parameters are shown in Table a:
  • the preparation process of the negative active material is similar to that of Example 6, except that the length-to-diameter ratio and specific surface area of the negative active material are adjusted by adjusting the crush size of the flake graphite.
  • the flake graphite The crushed size distribution is 15.2 ⁇ m, 14.5 ⁇ m, 13.5 ⁇ m, 12.0 ⁇ m, 9.5 ⁇ m, 8.2 ⁇ m.
  • the preparation process of the negative active material is similar to that of Example 13, except that the average maximum Feret diameter of the negative active material is adjusted by adjusting the ball milling time.
  • the ball milling time distribution is: 32min, 37min, 40min, 45min, 50min, 55min, 63min, 70min.
  • the preparation process of the negative active material is the same as in Example 21.
  • Negative electrode preparation the preparation process of the negative electrode is similar to Example 21, except that the thickness and energy density of the negative electrode active material layer are adjusted by adjusting the coating weight per unit area of the active material, the preparation process of Example 25 to Example 33 , the coating weights per unit area of the active material are 0.125mg/mm 2 , 0.155mg/mm 2 , 0.178mg/mm 2 , 0.165mg/mm 2 , 0.128mg/mm 2 , 0.160mg/mm 2 , 0.133 respectively. mg/mm 2 , 0.140mg/mm 2 , 0.145mg/mm 2 .
  • the preparation of the positive electrode, separator, electrolyte and lithium-ion battery is the same as in Example 21.
  • the preparation process of the negative active material is similar to that of Example 33, except that the high-temperature treatment temperature is adjusted to adjust the tap, defectivity and OI value of the negative active material.
  • the high-temperature treatment temperature is adjusted to adjust the tap, defectivity and OI value of the negative active material.
  • the high-temperature treatment The temperatures are 890°C, 950°C, 1000°C, 850°C, 860°C, 880°C, 995°C, 860°C, 885°C, 970°C, 900°C, 920°C, 930°C, 950°C, 955°C, 966°C ,980°C.
  • the preparation of the negative electrode, positive electrode, separator, electrolyte and lithium-ion battery is the same as in Example 33.
  • Negative active material layer argon ion polishing (CP) sample preparation process disassemble the lithium-ion battery to obtain the negative electrode piece, cut the negative electrode piece into a size of 6.0mm ⁇ 6.0mm, then fix it on the sample stage, and use argon ion polishing (parameters : Accelerating voltage of 6KV, 3h for each sample), process one end of the negative active material layer to obtain the negative active material layer CP sample.
  • argon ion polishing (parameters : Accelerating voltage of 6KV, 3h for each sample
  • SEM scanning electron microscope
  • the scanning electron microscope used in this application is the JSM-6360LV model of JEOL Company.
  • the average maximum Feret diameter of the cross section of the negative active material particles in the cross section of the negative electrode piece Observe the negative active material layer CP sample, and there is a cross section with a certain number of particles in the 200 ⁇ m ⁇ 200 ⁇ m area in the thickness direction of the negative active material layer. , these sections are irregularly shaped. For a particle cross-section, two parallel lines are rotated along the outer tangent line of the particle. The dimension with the largest distance between the parallel lines at a certain position is the maximum Feret diameter of the particle cross-section.
  • Cross-sectional area of negative active material particles i.e. first particles
  • the cross-section of the particle is irregular in shape, and its color contrast is different from that around the particle.
  • the cross-sectional area of the particle can be calculated based on its contrast characteristics.
  • the cross-sectional area of the first particle can be obtained by statistically calculating the average cross-sectional area of all particles with hole characteristics in a 200 ⁇ m ⁇ 200 ⁇ m area in the thickness direction of the negative active material layer.
  • Cross-sectional area of the pores in the first particle In the 200 ⁇ m ⁇ 200 ⁇ m area of the negative active material layer, there are certain particles with a pore structure. The cross-sections of the pores in these particle cross-sections have irregular shapes, and their color contrast is different from that of the active material cross-section. , calculate its area based on its contrast characteristics.
  • the cross-sectional area of the pores in the first particles can be obtained by statistically calculating the average cross-sectional area of all the pores in the first particles in the 200 ⁇ m ⁇ 200 ⁇ m area in the thickness direction of the negative active material layer.
  • Test for the ratio of the cross-sectional area of the hole to the cross-sectional area of the particle divide the cross-sectional area of the hole in the first particle calculated above by the cross-sectional area of the first particle calculated above to obtain the X value.
  • Tap density is the mass per unit volume measured after the powder in the container is tapped under specified conditions, and the unit is g/cm 3 .
  • the test method is to fix a graduated cylinder containing a certain mass of powder on a mechanical vibration device.
  • the vibration motor drives the mechanical vibration device to vibrate vertically up and down.
  • the graduated cylinder containing the powder vibrates rhythmically with the mechanical vibration device. With the vibration, As the number of times increases, the powder in the graduated cylinder gradually becomes stronger. After the number of vibrations reaches the set number, the mechanical vibration device stops vibrating and the volume of the graduated cylinder is read. According to the definition of density: mass divided by volume, the density of the powder after tapping is obtained.
  • the lithium-ion secondary battery After the lithium-ion secondary battery is discharged to 0% SOC, disassemble and take out the negative electrode piece, and then treat it at high temperature at 400°C for 2 hours (under a nitrogen atmosphere).
  • the negative active material can be peeled off from the current collector, and the negative active material is collected for testing.
  • Raman Use a laser microscopy confocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instrument Division) to scan the negative active material to obtain the D peak and G peak of all particles within the area range.
  • Use LabSpec software to process the data to obtain each
  • the peak intensities of the D peak and G peak of the particles are ID and IG respectively.
  • ID/IG counts the frequency of ID/ID with a step size of 0.02 to obtain a normal distribution diagram.
  • (ID/ID)max, (ID /ID)min calculate the average value of ID/ID, which is the ID/IG value of the negative active material.
  • the laser wavelength of a Raman spectrometer can be in the range of 532nm to 785nm.
  • D peak generally around 1350cm -1 , caused by the symmetric stretching vibration radial breathing mode of sp2 carbon atoms in the aromatic ring (structural defect);
  • G peak Appears near 1580cm -1 and is caused by the stretching vibration between sp2 carbon atoms. It corresponds to the vibration of the E2g optical phonon in the center of the Brillouin zone (in-plane vibration of the carbon atom).
  • the lithium-ion secondary battery After the lithium-ion secondary battery is discharged to 0% SOC, disassemble and take out the negative electrode piece, and then treat it at high temperature at 400°C for 2 hours (under a nitrogen atmosphere).
  • the negative active material can be peeled off from the current collector, and the negative active material is collected for testing. OI value. According to the Machinery Industry Standard of the People's Republic of China JB/T 4220-2011 "Method for Determination of Lattice Parameters of Artificial Graphite", the (004) plane diffraction pattern and (110) plane diffraction pattern in the X-ray diffraction pattern of the negative active material were tested.
  • the test conditions are as follows: X-rays use CuK ⁇ radiation, and the CuK ⁇ radiation is removed by a filter or monochromator.
  • the working voltage of the X-ray tube is (30-35) kV, and the working current is (15-20) mA.
  • the scanning speed of the counter is 1/4(°)/min.
  • the scanning range of the diffraction angle 2 ⁇ is 53°-57°.
  • the scanning range of the diffraction angle 2 ⁇ is 75°-79°.
  • the peak area obtained from the (004) plane diffraction line pattern is recorded as C004.
  • the peak area obtained from the (110) plane diffraction line pattern is designated as C110. Calculate the C004/C110 ratio of the negative active material, which is the OI value of the negative active material.
  • the 0°C discharge ratio of lithium-ion battery 0°C discharge capacity/25°C discharge capacity ⁇ 100%.
  • Table 1 shows the ratio X of the average cross-sectional area of the pores in the first particles having holes to the average cross-sectional area of the first particles in the 200 ⁇ m ⁇ 200 ⁇ m area of the cross section of the negative active material layer, and the tap density of the negative active material. Effect of TD g/m 3 on lithium-ion battery performance.
  • Table 2 shows the influence of the longest cross-sectional length L ⁇ m, the shortest cross-sectional length D ⁇ m, and the specific surface area BETm 2 /g of the negative active material particles on the performance of the lithium ion battery within the cross-sectional area of 200 ⁇ m ⁇ 200 ⁇ m of the negative active material layer. . Except for the parameters listed in Table 2, the remaining parameters of Examples 11 to 16 are the same as those of Example 6.
  • the negative active material particles are ellipsoidal, with an aspect ratio L/D ⁇ 2.50, and the value of the aspect ratio L/D and the specific surface area BET of the negative active material satisfies: 0.40 ⁇ 2 ⁇ When BET-L/D ⁇ 1.50, lithium-ion battery has good low discharge rate performance.
  • Table 3 shows the influence of the average maximum Feret diameter F ⁇ m of the negative active material particles on the performance of the lithium ion battery in the cross-sectional area of 200 ⁇ m ⁇ 200 ⁇ m of the negative active material layer. Except for the parameters listed in Table 3, the remaining parameters of Examples 17 to 24 are the same as those of Example 13.
  • Table 4 shows the influence of the single-sided thickness H of the negative active material layer and the single-sided energy density E on the performance of the lithium ion battery. Except for the parameters listed in Table 4, the remaining parameters of Embodiment 25 to 33 are the same as those of Embodiment 21.
  • the lithium-ion battery It has a high discharge ratio, indicating that by controlling the thickness and energy density of the active material layer, the deintercalation of lithium ions can be ensured and the low-temperature rate performance of lithium-ion batteries can be effectively improved.
  • Table 5 shows the effects of the tap density TD, defectiveness ID/IG, and orientation degree OI of the negative electrode active material on the performance of the lithium ion battery. Among them, except for the parameters listed in Table 5, the remaining parameters of Embodiment 40 to Embodiment 50 are the same as Embodiment 33.
  • Example 34 From the comparison between Example 34 to Example 36 and Example 33, it can be seen that when the tap density TD g/cm 3 of the negative electrode active material satisfies 0.60 ⁇ TD ⁇ 1.30, the processing performance of the negative electrode slurry is improved, and the lithium ion battery The low-temperature rate performance is improved accordingly.
  • Example 37 to Example 40 From the comparison between Example 37 to Example 40 and Example 33, it can be seen that when ID/IG ⁇ 0.6, the low-temperature rate performance of the lithium ion battery is correspondingly improved.
  • the negative active material has lower defects, which is conducive to the formation of the SEI film and can ensure the dynamic performance of the negative active material, which in turn is conducive to improving the low-temperature rate performance of lithium-ion batteries.
  • Example 41 to Example 43 From the comparison between Example 41 to Example 43 and Example 33, it can be seen that when the OI value of the negative active material is ⁇ 15, the negative active material has the same properties and can deintercalate lithium ions well in all directions, which can be further improved. Low-temperature rate performance of lithium-ion batteries.

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Abstract

提供一种负极极片，其包括负极集流体和设置于负极集流体上的负极活性材料层，负极活性材料层包括负极活性材料，该负极活性材料包括负极活性材料颗粒，该负极活性材料颗粒包括具有孔的第一颗粒，其中，在负极活性材料层的截面200μm×200μm区域内，该负极活性材料满足：0.10≤TD-0.05×(1/X)≤0.40；其中，X表示第一颗粒中孔的截面面积平均值与第一颗粒的截面面积平均值的比值，4.0％≤X≤15％；TD表示负极活性材料的振实密度，单位为g/cm 3。本申请的负极极片具有优异的动力学性能，能够有效提升二次电池的低温充放电性能。还提供包括该负极极片的二次电池。

Description

负极极片、二次电池和电子装置 技术领域
本申请涉及储能领域，具体涉及一种负极极片、二次电池和电子装置。
背景技术
随着二次电池市场不断扩大，对其性能要求也在不断提升，其中放电倍率性能就是一个重要的指标。同时，考虑到冬天部分地区气温低的特点，二次电池还需要在低温条件下具有优异性能，例如低温放电倍率。现有技术主要是通过减小活性材料粒度来缩短活性离子的嵌锂路径和包覆改性处理方式来改善低温倍率性能，但这两种方式对负极活性材料的压实密度，克容量等损失较大，而且成本也较高。
发明内容
针对现有技术的不足，本申请提供了一种负极极片及包括该负极极片的二次电池。本申请的负极极片具有优异的动力学性能，能够有效提升二次电池的低温充放电性能。
在第一方面，本申请提供一种负极极片，其包括负极集流体和设置于负极集流体上的负极活性材料层，负极活性材料层包括负极活性材料，该负极活性材料包括负极活性材料颗粒，该负极活性材料颗粒包括具有孔的第一颗粒，其中，在负极活性材料层的截面的200μm×200μm区域内，该负极活性材料满足：0.10≤TD-0.05×(1/X)≤0.40；其中，X表示第一颗粒中孔的截面面积平均值与第一颗粒的截面面积平均值的比值，4.0％≤X≤15％；TD表示负极活性材料的振实密度，单位为g/cm 3。负极活性材料颗粒具有孔，尤其是内部具有孔，能够极大地增加负极极片与电解液的接触面，使得活性离子例如锂离子的嵌锂通道明显增加，活性离子更容易扩散，进而有利于活性离子的快速脱嵌，提高负极极片的倍率性能，从而改善二次电池的低温充放电性能。但负极活性材料颗粒的孔占比也不能过高，孔过多会导致活性材料与电解液的副反应增加，进而影响二次电池的首次库伦效率与存储性能，同时也会降低二次电池的低温倍率性能。此外，负极活性材料颗粒内部的孔的结构及分布还会影响其振实密度，振实密度过高或过低都不利于后续负极浆料的加工，进而影响二次电池的电性能发挥。本申请通过将负极活性材料中具有孔的第一颗粒中孔的 截面面积平均值与第一颗粒的截面面积平均值的比值、负极活性材料的振实密度控制在上述范围内，负极活性材料的振实密度与孔结构具有良好的匹配性，一方面，合适的孔结构使得负极极片内部嵌锂通道明显增加，活性离子更容易扩散，有利于活性离子的快速脱嵌，负极极片的倍率性能得到提升，从而能够改善二次电池的低温充放电性能，另一方面，适宜的振实密度提高了材料的加工性能，也能在一定程度上提高二次电池的低温倍率性能。
在一些实施方式中，0.1≤TD-0.05×(1/X)≤0.35。在一些实施方式中，0.19≤TD-0.05×(1/X)≤0.3。第一颗粒中孔的截面面积平均值与第一颗粒的截面面积平均值的比值以及负极活性材料的振实密度在上述范围内，可进一步提升二次电池的低温倍率性能。
在一些实施方式中，5％≤X≤13％。在一些实施方式中，7％≤X≤13％。孔的截面面积占比在上述范围内，二次电极具有较高的低温倍率性能。孔的截面面积占比过低时，电解液在负极极片内的浸润性差，活性离子扩散较困难，二次电池的低温倍率性能改善效果不佳。孔的截面面积占比过高时，负极活性材料与电解液的副反应增加，进而影响二次电池的首次库伦效率与存储性能，同时也会降低二次电池的低温倍率性能。
在一些实施方式中，0.5≤TD≤1.5。在一些实施方式中，0.6≤TD≤1.3。负极活性材料的振实密度太高与太低都会影响后续负极浆料的加工性能，不利于负极浆料在集流体上的涂覆，且浆料本身的稳定性也较差，进而影响二次电池的电性能发挥。
在一些实施方式中，在负极活性材料层的截面的200μm×200μm区域内，负极材料满足：0.40≤2×BET－L/D≤1.50且L/D≤2.50；其中，L表示负极活性材料颗粒的截面最长长度，单位为μm；D表示负极活性材料颗粒的截面最短长度，单位为μm；BET表示负极活性材料的比表面积，单位为m 2/g。在上述范围内，负极活性材料颗粒呈椭球形，具有较高的机械强度，同时活性离子的脱嵌方向多，脱嵌路径短，有利于其动力学性能的提升。此外，负极活性材料的比表面积适中，电解液在负极极片内的浸润性高，可以进一步改善二次电池的低温倍率性能。在一些实施方式中，0.50≤2×BET－L/D≤1.30。
在一些实施方式中，1.0≤L/D≤2.2。L/D过高时，负极活性材料颗粒呈长条状，其在压制过程中易断裂，且不利于活性离子在各个方向的脱嵌，负极活性材料动力学性能差，进而降低二次电池的低温倍率性能。
在一些实施方式中，0.5≤BET≤2.5。比表面积过大时，负极活性材料表面反应活性较高，易与电解液发生反应，会对二次电池的存储性能等产生不利影响。
在一些实施方式中，在负极活性材料层的截面的200μm×200μm区域内，负极活性 材料颗粒的最大费雷特直径平均值F满足：4μm≤F≤55μm。负极活性材料颗粒的尺寸过小时，其压实密度较低，会降低负极极片的压实密度，且小颗粒与电解液的反应更为剧烈，会影响二次电池的存储与循环性能。负极活性材料颗粒的尺寸过大时，活性离子在其中的脱嵌路径较长，会影响二次电池的倍率性能。
在一些实施方式中，负极活性材料层的单面厚度H满足：H≤90μm。在一些实施方式中，25μm≤H≤60μm。负极活性材料层的厚度过高时，活性离子在负极极片中的传输路径过长，活性离子扩散困难，使得二次电池的极化增大，二次电池容易发生析锂且倍率性能也会降低。
在一些实施方式中，负极活性材料层的单面能量密度E满足：0.01mAh/mm 2≤E≤0.07mAh/mm 2。负极活性材料层的能量密度与其堆积密度成正比，负极活性材料层的能量密度过低时，其堆积密度相应过低，虽然低的堆积密度有利于二次电池的倍率性能，但会过多的损失能量密度。负极活性材料层的能量密度过高时，其堆积密度相应过高，高的堆积密度会严重影响二次电池的倍率性能，尤其是低温倍率性能。
在一些实施方式中，通过拉曼测试，负极活性材料满足：ID/IG≤0.6，其中，ID为拉曼光谱中1350cm -1峰的强度，IG为拉曼光谱中1580cm -1处峰的强度。在一些实施方式中，0.15≤ID/IG≤0.5。ID/IG比值可以表征负极活性材料的缺陷度，ID/IG比值越大，表明缺陷度越高。负极活性材料缺陷过高，不利于SEI膜的形成，从而影响二次电池的倍率性能。
在一些实施方式中，负极活性材料的取向度OI满足：OI≤25。在一些实施方式中，5≤OI≤25。OI值表示负极活性材料的取向度，OI值过大，表示该负极活性材料的取向度过高，不利于活性离子的脱嵌，进而会影响二次电池的倍率性能。
在一些实施方式中，负极活性材料包括石墨。在一些实施方式中，负极活性材料包括天然石墨。
在第二方面，本申请提供了一种二次电池，其包括第一方面的负极极片。
在一些实施方式中，二次电池在0℃的放电比率Q1/Q2≥0.8，其中，Q1为0℃1C时的放电容量，Q2为25℃1C时的放电容量。
在第三方面，本申请提供了一种电子装置，其包括第二方面的二次电池。
本申请的负极极片中负极活性材料具有合适的振实密度与孔隙率，使得负极极片具有优异的动力学性能，进而能够有效提升二次电池的低温充放电性能。
附图说明
图1示出了本申请实施例6和对比例3的二次电池在不同温度下的放电比率，其中，1—实施例6，2—对比例3。
具体实施方式
为了简明，本文仅具体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，每个单独公开的点或单个数值自身可以作为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，除非另有说明，“以上”、“以下”包含本数。
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。
下面结合具体实施方式，进一步阐述本申请。应理解，这些具体实施方式仅用于说明本申请而不用于限制本申请的范围。
一、负极极片
在第一方面，本申请提供一种负极极片，其包括负极集流体和设置于负极集流体上的负极活性材料层，负极活性材料层包括负极活性材料，该负极活性材料包括负极活性材料颗粒，该负极活性材料颗粒包括具有孔的第一颗粒，其中，在负极活性材料层的截面的200μm×200μm区域内，该负极活性材料满足：0.10≤TD-0.05×(1/X)≤0.40；其中，X表示第一颗粒中孔的截面面积平均值与第一颗粒的截面面积平均值的比值，4.0％≤X≤15％；TD表示负极活性材料的振实密度，单位为g/cm 3。负极活性材料颗粒具有孔，尤其是内 部具有孔，能够极大地增加负极极片与电解液的接触面，使得活性离子例如锂离子的嵌锂通道明显增加，活性离子更容易扩散，进而有利于活性离子的快速脱嵌，提高负极极片的倍率性能，从而改善二次电池的低温充放电性能。但负极活性材料颗粒的孔占比也不能过高，孔过多会导致活性材料与电解液的副反应增加，进而影响二次电池的首次库伦效率与存储性能，同时也会降低二次电池的低温倍率性能。此外，负极活性材料颗粒内部的孔的结构及分布还会影响其振实密度，振实密度过高或过低都不利于后续负极浆料的加工，进而影响二次电池的电性能发挥。本申请通过将负极活性材料中具有孔的第一颗粒中孔的截面面积平均值与第一颗粒的截面面积平均值的比值、负极活性材料的振实密度控制在上述范围内，负极活性材料的振实密度与孔结构具有良好的匹配性，一方面，合适的孔结构使得负极极片内部嵌锂通道明显增加，活性离子更容易扩散，有利于活性离子的快速脱嵌，负极极片的倍率性能得到提升，从而能够改善二次电池的低温充放电性能，另一方面，适宜的振实密度提高了材料的加工性能，也能在一定程度上提高二次电池的低温倍率性能。
本申请中，“负极活性材料层的截面”可以为沿负极活性材料层厚度方向的截面。
在一些实施方式中，TD-0.05×(1/X)为0.11、0.12、0.13、0.14、0.15、0.16、0.17、0.18、0.19、0.20、0.21、0.22、0.23、0.24、0.25、0.26、0.27、0.28、0.29、0.30、0.31、0.32、0.33、0.34、0.35、0.36、0.37、0.38、0.39或这些值中任意两者组成的范围。在一些实施方式中，0.1≤TD-0.05×(1/X)≤0.35。在一些实施方式中，0.19≤TD-0.05×(1/X)≤0.3。第一颗粒中孔的截面面积平均值与第一颗粒的截面面积平均值的比值以及负极活性材料的振实密度在上述范围内，可进一步提升二次电池的低温倍率性能。
在一些实施方式中，X为4.5％、5％、5.5％、6％、6.5％、7％、7.5％、8％、8.5％、9％、9.5％、10％、10.5％、11％、11.5％、12％、12.5％、13％、13.5％、14％、14.5％或这些值中任意两者组成的范围。在一些实施方式中，5％≤X≤13％。在一些实施方式中，7％≤X≤13％。孔的截面面积占比在上述范围内，二次电极具有较高的低温倍率性能。孔的截面面积占比过低时，电解液在负极极片内的浸润性差，活性离子扩散较困难，二次电池的低温倍率性能改善效果不佳。孔的截面面积占比过高时，负极活性材料与电解液的副反应增加，进而影响二次电池的首次库伦效率与存储性能，同时也会降低二次电池的低温倍率性能。
在一些实施方式中，TD为0.6、0.65、0.7、0.75、0.8、0.85、0.9、0.95、1.0、1.05、1.1、1.15、1.2、1.25、1.3、1.35、1.4、1.45或这些值中任意两者组成的范围。在一些实施方式中，0.5≤TD≤1.5。在一些实施方式中，0.6≤TD≤1.3。负极活性材料的振实密度太 高与太低都会影响后续负极浆料的加工性能，不利于负极浆料在集流体上的涂覆，且浆料本身的稳定性也较差，进而影响二次电池的电性能发挥。
在一些实施方式中，在负极活性材料层的截面的200μm×200μm区域内，负极材料满足：0.40≤2×BET－L/D≤1.50且L/D≤2.50；其中，L表示负极活性材料颗粒的截面最长长度，单位为μm；D表示负极活性材料颗粒的截面最短长度，单位为μm；BET表示负极活性材料的比表面积，单位为m 2/g。在上述范围内，负极活性材料颗粒呈椭球形，具有较高的机械强度，同时活性离子的脱嵌方向多，脱嵌路径短，有利于其动力学性能的提升。此外，负极活性材料的比表面积适中，电解液在负极极片内的浸润性高，可以进一步改善二次电池的低温倍率性能。在一些实施方式中，2×BET－L/D为0.45、0.5、0.6、0.65、0.7、0.75、0.8、0.85、0.9、0.95、1.0、1.05、1.1、1.15、1.2、1.25、1.3、1.35、1.4、1.45或这些值中任意两者组成的范围。在一些实施方式中，0.50≤2×BET－L/D≤1.30。
在一些实施方式中，L/D为1.1、1.15、1.2、1.25、1.3、1.35、1.4、1.45、1.5、1.55、1.6、1.65、1.7、1.75、1.8、1.85、1.9、1.95、2.0、2.05、2.1、2.15或这些值中任意两者组成的范围。在一些实施方式中，1.0≤L/D≤2.2。L/D过高时，负极活性材料颗粒呈长条状，其在压制过程中易断裂，且不利于活性离子在各个方向的脱嵌，负极活性材料动力学性能差，进而降低二次电池的低温倍率性能。
在一些实施方式中，BET为0.6、0.7、0.8、0.9、1.0、1.1、1.2、1.3、1.4、1.5、1.6、1.7、1.8、1.9、2.0、2.1、2.2、2.3、2.4或这些值中任意两者组成的范围。在一些实施方式中，0.5≤BET≤2.5。比表面积过大时，负极活性材料表面反应活性较高，易与电解液发生反应，会对二次电池的存储性能等产生不利影响。
在一些实施方式中，在负极活性材料层的截面的200μm×200μm区域内，负极活性材料颗粒的最大费雷特直径平均值F满足：4μm≤F≤55μm。在一些实施方式中，F为5μm、10μm、15μm、20μm、25μm、30μm、35μm、35μm、40μm、45μm、50μm或这些值中任意两者组成的范围。负极活性材料颗粒的尺寸过小时，其压实密度较低，会降低负极极片的压实密度，且小颗粒与电解液的反应更为剧烈，会影响二次电池的存储与循环性能。负极活性材料颗粒的尺寸过大时，活性离子在其中的脱嵌路径较长，会影响二次电池的倍率性能。
在一些实施方式中，负极活性材料层的单面厚度H满足：H≤90μm，例如为20μm、25μm、30μm、35μm、40μm、45μm、50μm、55μm、60μm、65μm、70μm、75μm、80μm或85μm。在一些实施方式中，25μm≤H≤60μm。负极活性材料层的厚度过高时，活性离 子在负极极片中的传输路径过长，活性离子扩散困难，使得二次电池的极化增大，二次电池容易发生析锂且倍率性能也会降低。
在一些实施方式中，负极活性材料层的单面能量密度E满足：0.01mAh/mm 2≤E≤0.07mAh/mm 2。在一些实施方式中，E为0.015mAh/mm 2、0.02mAh/mm 2、0.025mAh/mm 2、0.03mAh/mm 2、0.035mAh/mm 2、0.04mAh/mm 2、0.045mAh/mm 2、0.05mAh/mm 2、0.055mAh/mm 2、0.06mAh/mm 2、0.065mAh/mm 2或这些值中任意两者组成的范围。在一些实施方式中，0.013mAh/mm 2≤E≤0.056mAh/mm 2。负极活性材料层的能量密度与其堆积密度成正比，负极活性材料层的能量密度过低时，其堆积密度相应过低，虽然低的堆积密度有利于二次电池的倍率性能，但会过多的损失能量密度。负极活性材料层的能量密度过高时，其堆积密度相应过高，高的堆积密度会严重影响二次电池的倍率性能，尤其是低温倍率性能。
在一些实施方式中，通过拉曼测试，负极活性材料满足：ID/IG≤0.6，其中，ID为拉曼光谱中1350cm -1峰的强度，IG为拉曼光谱中1580cm -1处峰的强度。在一些实施方式中，ID/IG为0.2、0.25、0.3、0.35、0.4、0.45或这些值中任意两者组成的范围。在一些实施方式中，0.15≤ID/IG≤0.6。在一些实施方式中，0.15≤ID/IG≤0.5。ID/IG比值可以表征负极活性材料的缺陷度，ID/IG比值越大，表明缺陷度越高。负极活性材料缺陷过高，不利于SEI膜的形成，从而影响二次电池的倍率性能。
在一些实施方式中，负极活性材料的取向度OI满足：OI≤25。在一些实施方式中，OI为6、8、10、12、14、16、18、20、22、24或这些值中任意两者组成的范围。在一些实施方式中，5≤OI≤25。OI值表示负极活性材料的取向度，OI值过大，表示该负极活性材料的取向度过高，不利于活性离子的脱嵌，进而会影响二次电池的倍率性能。
在一些实施方式中，负极活性材料包括石墨。在一些实施方式中，负极活性材料包括天然石墨。
在一些实施方式中，石墨的制备过程包括：选取大鳞片天然石墨作为原料，先将其粉碎到5μm至15μm，然后在其经过表面氧化处理增加有机基团后，再进行球形化处理。在其转变为球形石墨后，再通过高温5000℃至1200℃处理。在高温下，球形化处理过程中引入到颗粒内部的有机基团会发生剧烈分解并快速生成气体，在石墨颗粒内部形成孔隙。
二、二次电池
在第二方面，本申请提供了一种二次电池，其包括第一方面的负极极片。
在一些实施方式中，二次电池在0℃的放电比率Q1/Q2≥0.8，其中，Q1为0℃1C时 的放电容量，Q2为25℃1C时的放电容量。
在一些实施方式中，负极集流体包括：铜箔、铝箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜、覆有导电金属的聚合物基底或其任意组合。
在一些实施方式中，负极活性材料层还包括粘结剂和导电剂。在一些实施方式中，粘结剂包括，但不限于：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、环氧树脂或尼龙等。
在一些实施方式中，导电剂包括，但不限于：基于碳的材料、基于金属的材料、导电聚合物和它们的混合物。在一些实施例中，基于碳的材料选自天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维或其任意组合。在一些实施例中，基于金属的材料选自金属粉、金属纤维、铜、镍、铝或银。在一些实施例中，导电聚合物为聚亚苯基衍生物。
本申请的二次电池还包括正极，正极包括正极集流体和正极活性材料层，正极活性材料层包括正极活性材料、粘结剂和导电剂。
根据本申请的一些实施方式，正极集流体可以采用金属箔片或复合集流体。例如，可以使用铝箔。复合集流体可以通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子基材上而形成。
根据本申请的一些实施方式，正极活性材料包括钴酸锂、镍锰钴酸锂、镍锰铝酸锂、磷酸铁锂、磷酸钒锂、磷酸钴锂、磷酸锰锂、磷酸锰铁锂、硅酸铁锂、硅酸钒锂、硅酸钴锂、硅酸锰锂、尖晶石型锰酸锂、尖晶石型镍锰酸锂和钛酸锂中的至少一种。在一些实施例中，粘结剂包括粘合剂聚合物，例如聚偏氟乙烯、聚四氟乙烯、聚烯烃类、羧甲基纤维素钠、羧甲基纤维素锂、改性聚偏氟乙烯、改性SBR橡胶或聚氨酯中的至少一种。在一些实施例中，聚烯烃类粘结剂包括聚乙烯、聚丙烯、聚烯酯、聚烯醇或聚丙烯酸中的至少一种。在一些实施例中，导电剂包括碳基材料，例如天然石墨、人造石墨、炭黑、乙炔黑、科琴黑或碳纤维；金属基材料，例如铜、镍、铝、银等的金属粉或金属纤维；导电聚合物，例如聚亚苯基衍生物；或它们的混合物。
本申请的二次还包括隔离膜，本申请的二次电池中使用的隔离膜的材料和形状没有特别限制，其可为任何现有技术中公开的技术。在一些实施例中，隔离膜包括由对本申请的电解液稳定的材料形成的聚合物或无机物等。
例如隔离膜可包括基材层和表面处理层。基材层为具有多孔结构的无纺布、膜或复合 膜，基材层的材料选自聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺中的至少一种。具体的，可选用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。
基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。无机物层包括无机颗粒和粘结剂，无机颗粒选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙和硫酸钡中的至少一种。粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯烷氧、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的至少一种。聚合物层中包含聚合物，聚合物的材料选自聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯烷氧、聚偏氟乙烯、聚(偏氟乙烯-六氟丙烯)中的至少一种。
本申请的二次还包括电解液。可用于本申请的电解液可以为现有技术中已知的电解液。
根据本申请的一些实施方式，电解液包括有机溶剂、锂盐和可选的添加剂。本申请的电解液中的有机溶剂可为现有技术中已知的任何可作为电解液的溶剂的有机溶剂。根据本申请的电解液中使用的电解质没有限制，其可为现有技术中已知的任何电解质。根据本申请的电解液的添加剂可为现有技术中已知的任何可作为电解液添加剂的添加剂。在一些实施例中，有机溶剂包括，但不限于：碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二乙酯(DEC)、碳酸甲乙酯(EMC)、碳酸二甲酯(DMC)、碳酸亚丙酯或丙酸乙酯。在一些实施例中，有机溶剂包括醚类溶剂，例如包括1，3-二氧五环(DOL)和乙二醇二甲醚(DME)中的至少一种。在一些实施例中，锂盐包括有机锂盐或无机锂盐中的至少一种。在一些实施例中，锂盐包括，但不限于：六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、二氟磷酸锂(LiPO 2F 2)、双三氟甲烷磺酰亚胺锂LiN(CF 3SO 2) 2(LiTFSI)、双(氟磺酰)亚胺锂Li(N(SO 2F) 2)(LiFSI)、双草酸硼酸锂LiB(C 2O 4) 2(LiBOB)或二氟草酸硼酸锂LiBF 2(C 2O 4)(LiDFOB)。在一些实施例中，添加剂包括氟代碳酸乙烯酯和己二腈中的至少一种。
根据本申请的一些实施方式，本申请的二次电池包括，但不限于：锂离子电池或钠离子电池。在一些实施例中，二次电池包括锂离子电池。
三、电子装置
本申请进一步提供了一种电子装置，其包括本申请第二方面所述的二次电池。
本申请的电子设备或装置没有特别限定。在一些实施例中，本申请的电子设备包括但不限于，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。
在下述实施例及对比例中，所使用到的试剂、材料以及仪器如没有特殊的说明，均可商购获得。
实施例及对比例
实施例1
负极活性材料制备
选取黑龙江省鸡西市的大鳞片天然石墨作为原料，先将其粉碎到10μm，然后配制氧化剂溶液(5mol/L的硫酸溶液与3mol/L的硝酸溶液按照质量比2：1进行混合)。将氧化剂溶液加入到粉碎好的鳞片石墨中，氧化剂溶液与鳞片石墨的质量比例为1：10，充分搅拌氧化，搅拌时间为3h。在鳞片石墨经过表面氧化处理增加有机基团后再进行球形化处理。具体为，将搅拌好的混合物进行干燥烘干，干燥后的鳞片石墨置于球磨机中进行球磨30min，在其发生卷曲转变为球形石墨后，再通过高温800℃处理，得到负极活性材料。在高温下，球形化处理过程中卷入到颗粒内部的有机氧化基团会发生剧烈分解并快速生成气体，这样在卷曲形成的球形石墨内部会形成因物质挥发及气体膨胀作用留下的孔隙。本实施例中，所述孔的截面面积占颗粒切面面积的比值X为5.0％，活性材料的TD为1.13g/cm 3，TD-0.05×(1/X)的值为0.13。
负极的制备
将上述负极活性材料、添加剂、粘结剂丁苯橡胶(简写为SBR)、增稠剂羧甲基纤维素钠(简写为CMC)按照重量比95.7∶1.5∶1.8∶1配比，再用适量的去离子水溶剂中充分搅拌混合，使其形成均匀的负极浆料；将此浆料涂覆于集流体Cu箔上，单位面积涂布重量为0.165mg/mm 2，烘干、冷压，即可得到上述所说的负极极片。
正极的制备
将磷酸铁锂(化学式：LiFePO 4)、导电剂乙炔黑、粘结剂聚偏二氟乙烯(简写为PVDF)按重量比96.3∶2.2∶1.5在适量的N-甲基吡咯烷酮(简写为NMP)溶剂中充分搅拌混合，使其形成均匀的正极浆料；将此浆料涂覆于集流体Al箔上，烘干、冷压，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)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照质量比为EC:EMC:DEC＝1:3:3:3进行混合，接着加入氟代碳酸乙烯酯和1,3-丙烷磺内酯，溶解并充分搅拌后加入锂盐LiPF 6，混合均匀后得到电解液。其中，LiPF 6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2％，1,3-丙烷磺内酯的质量百分含量为2％，各物质的质量百分含量为基于电解液的质量计算得到。
隔离膜的制备
以聚乙烯多孔聚合物薄膜作为隔离膜。
锂离子电池的制备
将正极、隔离膜、负极按顺序叠好，使隔离膜处于正极和负极之间起到隔离的作用，然后卷绕得到电极组件；焊接极耳后将电极组件置于外包装箔铝塑膜中，将上述制备好的电解液注入到干燥后的电极组件中，经过真空封装、静置、化成、整形、容量测试等工序，获得软包锂离子电池。
实施例2至实施例10、对比例1至对比例4
负极活性材料制备
负极活性材料的制备过程与实施例1类似，不同之处在于通过调酸的比例与浓度及高温处理的温度等参数来制备相应的负极活性材料。具体制备参数如表a所示：
表a
Figure PCTCN2022115902-appb-000001
Figure PCTCN2022115902-appb-000002
负极、正极、隔离膜、电解液以及锂离子电池的制备同实施例1。
实施例11至实施例16，
负极活性材料制备
负极活性材料的制备过程与实施例6类似，不同之处在于通过调整鳞片石墨的粉碎尺寸来调整负极活性材料的长径比以及比表面积，实施例11至实施例16的制备过程中，鳞片石墨的粉碎尺寸分布为15.2μm、14.5μm、13.5μm、12.0μm、9.5μm、8.2μm。
负极、正极、隔离膜、电解液以及锂离子电池的制备同实施例6。
实施例17至实施例24
负极活性材料制备
负极活性材料的制备过程与实施例13类似，不同之处在于通过调整球磨时间来调整负极活性材料的最大费雷特直径平均值，实施例17至实施例24的制备过程中，球磨时间分布为32min、37min、40min、45min、50min、55min、63min、70min。
负极、正极、隔离膜、电解液以及锂离子电池的制备同实施例13。
实施例25至实施例33
负极活性材料制备
负极活性材料的制备过程与实施例21相同。
负极制备，负极的制备过程与实施例21类似，不同之处在于通过调整活性材料的单位面积的涂布重量来调整负极活性材料层的厚度和能量密度，实施例25至实施例33的制备过程中，活性材料的单位面积的涂布重量分别为0.125mg/mm 2、0.155mg/mm 2、0.178mg/mm 2、0.165mg/mm 2、0.128mg/mm 2、0.160mg/mm 2、0.133mg/mm 2、0.140mg/mm 2、0.145mg/mm 2。
正极、隔离膜、电解液以及锂离子电池的制备同实施例21。
实施例34至实施例50
负极活性材料制备
负极活性材料的制备过程与实施例33类似，不同之处在于通过调整高温处理温度来调整负极活性材料的振实、缺陷度和OI值，实施例34至实施例50的制备过程中，高温处理温度分别为890℃、950℃、1000℃、850℃、860℃、880℃、995℃、860℃、885℃、970℃、900℃、920℃、930℃、950℃、955℃、966℃、980℃。
负极、正极、隔离膜、电解液以及锂离子电池的制备同实施例33。
测试方法
1、最大费雷特直径以及孔的截面面积占颗粒截面面积占比测试
负极活性材料层氩离子抛光(CP)样品制备流程：拆解锂离子电池得到负极极片，将负极极片裁剪为6.0mm×6.0mm大小，然后固定在样品台上，使用氩离子抛光(参数：6KV的加速电压，每个样品3h)对负极活性物质层的一端进行处理，得到负极活性材料层CP样品。
负极活性材料层CP样品制样完成后，利用扫描式电子显微镜(SEM)对其进行分析。
本申请中使用的扫描电镜为JEOL公司的JSM-6360LV型。
负极极片截面中的负极活性材料颗粒截面的最大费雷特直径平均值：观察负极活性材料层CP样品，在负极活性材料层厚度方向的截面上200μm×200μm区域内，存在一定数量颗粒的截面，这些截面呈不规则形状。对于一个颗粒截面，以两根平行线沿着颗粒外切线转动一周，其中在某一位置平行线距离最大的尺寸即为该颗粒截面的最大费雷特直径。依次测试负极活性材料层厚度方向的截面上200μm×200μm区域内所有颗粒的最大费雷特直径，然后计算得到平均值，即可得负极活性材料层截面中的负极活性材料颗粒的最大费雷特直径平均值。
具有孔的负极活性材料颗粒(即第一颗粒)截面面积：观察负极活性材料层CP样品，在上述负极活性材料层厚度方向的截面上200μm×2000μm区域内，存在某些颗粒具有孔结构，这些颗粒的截面呈不规则形状，其颜色衬度与颗粒周围不同，根据其衬度特征可以计算颗粒截面面积。统计计算得到负极活性材料层厚度方向的截面上200μm×200μm区域内所有具有孔特征颗粒的截面面积的平均值，即可得到第一颗粒截面面积。
第一颗粒中孔的截面面积：在负极活性材料层切面200μm×200μm区域，存在某些颗粒具有孔结构，这些颗粒截面中的孔的截面具有不规则形状，其颜色衬度与活性材料截面不同，根据其衬度特征计算其面积。统计计算得到负极活性材料层厚度方向的截面上 200μm×200μm区域内所有第一颗粒中孔的截面面积的平均值，即可得到第一颗粒中孔的截面面积。
孔的截面面积占该颗粒截面面积占比测试：根据上述计算的第一颗粒中孔的截面面积除以上述计算的第一颗粒截面面积，即可得到X值。
2、振实密度测试
振实密度为在规定条件下容器中的粉末经振实后所测得的单位体积的质量，单位为g/cm 3。
测试方法为将装有一定质量的粉末的刻度量筒固定在机械振动装置上，振动电机带动机械振动装置垂直上下振动，装有粉末的刻度量筒随机械振动装置而发生有节拍的振动，随着振动次数的增加，刻度量筒里的粉末逐渐振实，振动次数达到设定次数后，机械振动装置停止振动，读出刻度量筒的体积。根据密度的定义：质量除以体积，从而求出振实后的粉末密度。具体的工艺参数：振动次数：5000次；振动频率：250±15次/min；环境温度：15℃至28℃。
3、负极活性材料Raman测试
将锂离子二次电池放电到0％SOC后，拆解取出负极极片，然后在400℃下高温处理2h(氮气气氛下)，负极活性材料即可从集流体剥离下来，收集负极活性材料测试Raman。利用激光显微共聚焦拉曼光谱仪(Raman，HR Evolution，HORIBA科学仪器事业部)扫描负极活性材料，得到该面积范围内所有颗粒的D峰和G峰，采用LabSpec软件对数据进行处理得到每一个颗粒的D峰和G峰的峰强，分别为ID和IG，ID/IG以0.02为步长统计ID/ID的频次得到正态分布图，统计这些颗粒的(ID/ID)max、(ID/ID)min，计算ID/ID平均值，即为负极活性材料的ID/IG值。拉曼光谱仪的激光波长可处于532nm至785nm的范围内。
D峰：一般在1350cm -1附近，由芳香环中sp2碳原子的对称伸缩振动径向呼吸模式引起(结构缺陷)；
G峰：出现在1580cm -1附近，由sp2碳原子间的拉伸振动引起，它对应布里渊区中心的E2g光学声子的振动(碳原子面内振动)。
4、负极活性材料的OI值测试
将锂离子二次电池放电到0％SOC后，拆解取出负极极片，然后在400℃下高温处理2h(氮气气氛下)，负极活性材料即可从集流体剥离下来，收集负极活性材料测试OI值。按照中华人民共和国机械行业标准JB/T 4220-2011《人造石墨的点阵参数测定方法》测试负极活性材料的X射线衍射图谱中的(004)面衍射线图形和(110)面衍射线图形。试验条件如下：X射线采用CuKα辐射，CuKα辐射由滤波片或单色器除去。X射线管的工作电压为(30-35)kV，工作电流为(15-20)mA。计数器的扫描速度为1/4(°)/min。在记录004衍射线图形时，衍射角2θ的扫描范围为53°-57°。在记录110衍射线图形时，衍射角2θ的扫描范围为75°-79°。由(004)面衍射线图形得到的峰面积记为C004。由(110)面衍射线图形得到的峰面积记为C110。计算负极活性材料的C004/C110的比值，即为负极活性材料的OI值。
5、锂离子电池的0℃放电比率测试
(1)调整炉温至25℃，静置5min；
(2)0.5C直流充电(DC)至2.5V；
(3)静置30min；
(4)0.2C恒流(CC)至3.6V，恒压(CV)至0.025C；
(5)静置10min；
(6)1.0C DC至2.5V(25℃放电容量)；
(7)静置10min；
(8)0.2C CC至3.6V，CV至0.025C；
(9)静置10min；
(10)调节炉温至0℃，静置60min；
(11)1.0C DC至2.5V；
(12.0.2C CC至3.6V，CV至0.025C；
(13)静置10min；
(14)1.0C DC至2.5V(0℃放电容量)；
(12)调节炉温至25℃，静置60min；
(13)测试结束。
其中，锂离子电池0℃放电比率＝0℃放电容量/25℃放电容量×100％。
测试结果
表1示出了负极活性材料层的截面的200μm×200μm区域内，具有孔的第一颗粒中孔的截面面积平均值与第一颗粒截面面积平均值的比例X、负极活性材料的振实密度TD g/m 3对锂离子电池性能的影响。
表1
Figure PCTCN2022115902-appb-000003
从表1的数据可以看出，孔的截面面积平均值占颗粒截面面积平均值的比值X在4.0％至15％范围内，且X与负极活性材料振实密度TD满足特定关系式0.1≤TD-0.05×(1/X)≤0.4时，锂离子电池具有优异的低温放电倍率性能。
表2示出了负极活性材料层的截面200μm×200μm区域内，负极活性材料颗粒的截面最长长度Lμm、截面最短长度Dμm、负极活性材料的比表面积BETm 2/g对锂离子电池性能的影响。其中，除表2中列出的参数外，实施例11至实施例16的其余参数与实施例6相同。
表2
Figure PCTCN2022115902-appb-000004
从表2的数据可以看出，负极活性材料颗粒呈椭球形，其长径比L/D≤2.50，且长径比L/D与负极活性材料的比表面积BET的值满足：0.40≤2×BET－L/D≤1.50时，锂离子电池具有良好的低放电倍率性能。
表3示出了负极活性材料层的截面200μm×200μm区域内，负极活性材料颗粒的最大费雷特直径平均值Fμm对锂离子电池性能的影响。其中，除表3中列出的参数外，实施例17至实施例24的其余参数与实施例13相同。
表3
Figure PCTCN2022115902-appb-000005
从表3的数据可以看出，负极活性材料颗粒截面的最大费雷特直径平均值F满足4μm≤F≤55μm时，锂离子电池的低温放电比率得到有效改善。合适的颗粒尺寸既能保证锂 离子的快速脱嵌，又能保证与电解液的副反应较少，从而改善了锂离子电池的低温放电性能。
表4示出了负极活性材料层的单面厚度H以及单面能量密度E对锂离子电池性能的影响。其中，除表4中列出的参数外，实施例25至实施例33的其余参数与实施例21相同。
表4
Figure PCTCN2022115902-appb-000006
从表4的数据可以看出，当负极活性材料层的单面厚度H≤90μm，负极活性材料层单面能量密度E满足0.01mAh/mm 2≤E≤0.07mAh/mm 2时，锂离子电池具有高的放电比率，表明通过控制活性材料层的厚度与能量密度，可以保证锂离子的脱嵌，有效改善锂离子电池的低温倍率性能。
表5示出了负极活性材料的振实密度TD、缺陷度ID/IG、取向度OI对锂离子电池性能的影响。其中，除表5中列出的参数外，实施例40至实施例50的其余参数与实施例33相同。
表5
Figure PCTCN2022115902-appb-000007
从实施例34至实施例36与实施例33的对比可以看出，负极活性材料的振实密度TD g/cm 3满足0.60≤TD≤1.30时，负极浆料的加工性能得到改善，锂离子电池的低温倍率性能相应地提高。
从实施例37至实施例40的与实施例33的对比可以看出，ID/IG≤0.6时，锂离子电池的低温倍率性能相应地提高。在此范围内，负极活性材料具有较低的缺陷，有利于SEI膜的形成，能够保证负极活性材料的动力学性能，进而有利于锂离子电池的低温倍率性能的提升。
从实施例41至实施例43与实施例33的对比可以看出，负极活性材料OI值≤15时，负极活性材料具有各项同性，其各个方向都能良好的脱嵌锂离子，能够进一步改善锂离子电池的低温倍率性能。
尽管已经演示和描述了说明性实施例，本领域技术人员应该理解上述实施例不能被解释为对本申请的限制，并且可以在不脱离本申请的精神、原理及范围的情况下对实施例 进行改变，替代和修改。

Claims (10)

  1. 一种负极极片，包括负极集流体和设置于负极集流体上的负极活性材料层，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负极活性材料颗粒，所述负极活性材料颗粒包括具有孔的第一颗粒，
    其中，在所述负极活性材料层的截面的200μm×200μm区域内，所述负极活性材料满足：0.10≤TD-0.05×(1/X)≤0.40，
    其中，X表示所述第一颗粒中孔的截面面积平均值与所述第一颗粒的截面面积平均值的比值，4.0％≤X≤15％；TD表示所述负极活性材料的振实密度，单位为g/cm 3。
  2. 根据权利要求1所述的负极极片，其中，所述负极极片满足如下条件(i)至(iii)中的至少一者：
    (i)0.1≤TD-0.05×(1/X)≤0.35；
    (ii)5％≤X≤13％；
    (iii)0.5≤TD≤1.5。
  3. 根据权利要求1所述的负极极片，其中，所述负极极片满足如下条件(iv)至(vi)中的至少一者：
    (iv)0.19≤TD-0.05×(1/X)≤0.3；
    (v)7％≤X≤13％；
    (vi)0.6≤TD≤1.3。
  4. 根据权利要求1所述的负极极片，其中，在所述负极活性材料层的截面的200μm×200μm区域内，所述负极活性材料满足：0.40≤2×BET－L/D≤1.50且L/D≤2.50；其中，L表示所述负极活性材料颗粒的截面最长长度，单位为μm；D表示所述负极活性材料颗粒的截面最短长度，单位为μm；BET表示所述负极活性材料的比表面积，单位为m 2/g。
  5. 根据权利要求4所述的负极极片，其中，0.50≤2×BET－L/D≤1.30，和/或1.0≤L/D≤2.2，和/或0.5≤BET≤2.5。
  6. 根据权利要求1所述的负极极片，其中，所述负极极片满足如下条件(vii)至(xi)中的至少一者：
    (vii)在所述负极活性材料层的截面的200μm×200μm区域内，所述负极活性材料颗粒的最大费雷特直径平均值F满足：4μm≤F≤55μm；
    (viii)所述负极活性材料层的单面厚度H满足：H≤90μm；
    (ix)所述负极活性材料层的单面能量密度E满足：0.01mAh/mm 2≤E≤0.07mAh/mm 2；
    (x)通过拉曼测试，所述负极活性材料满足：ID/IG≤0.6，其中，ID为拉曼光谱中1350cm -1峰的强度，IG为拉曼光谱中1580cm -1处峰的强度；
    (xi)所述负极活性材料的取向度OI满足：OI≤25。
  7. 根据权利要求1所述的负极极片，其中，所述负极极片满足如下条件(xii)至(xiv)中的至少一者：
    (xii)25μm≤H≤60μm；
    (xiii)0.15≤ID/IG≤0.5；
    (xiv)5≤OI≤25。
  8. 一种二次电池，包括权利要求1至7中任一项所述的负极极片。
  9. 根据权利要求8所述的二次电池，其中，所述二次电池在0℃的放电比率Q1/Q2≥0.8，其中，Q1为0℃ 1C时的放电容量，Q2为25℃ 1C时的放电容量。
  10. 一种电子装置，包括权利要求8或9所述的二次电池。
PCT/CN2022/115902 2022-08-30 2022-08-30 负极极片、二次电池和电子装置 WO2024044974A1 (zh)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101309859A (zh) * 2005-12-14 2008-11-19 三井矿山株式会社 石墨粒子、碳-石墨复合粒子及其制造方法
JP2014229517A (ja) * 2013-05-23 2014-12-08 日立化成株式会社 リチウムイオン二次電池用負極材、リチウムイオン二次電池用負極及びリチウムイオン二次電池
JP2021097017A (ja) * 2019-12-19 2021-06-24 トヨタ自動車株式会社 負極活物質用複合粒子

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101309859A (zh) * 2005-12-14 2008-11-19 三井矿山株式会社 石墨粒子、碳-石墨复合粒子及其制造方法
JP2014229517A (ja) * 2013-05-23 2014-12-08 日立化成株式会社 リチウムイオン二次電池用負極材、リチウムイオン二次電池用負極及びリチウムイオン二次電池
JP2021097017A (ja) * 2019-12-19 2021-06-24 トヨタ自動車株式会社 負極活物質用複合粒子

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