WO2024044963A1 - 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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WO2024044963A1
WO2024044963A1 PCT/CN2022/115828 CN2022115828W WO2024044963A1 WO 2024044963 A1 WO2024044963 A1 WO 2024044963A1 CN 2022115828 W CN2022115828 W CN 2022115828W WO 2024044963 A1 WO2024044963 A1 WO 2024044963A1
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negative electrode
active material
negative
particles
secondary battery
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PCT/CN2022/115828
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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 CN202280055204.8A priority Critical patent/CN117859212A/zh
Priority to PCT/CN2022/115828 priority patent/WO2024044963A1/zh
Publication of WO2024044963A1 publication Critical patent/WO2024044963A1/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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids

Definitions

  • This application relates to the field of energy storage, specifically to a negative electrode plate, a secondary battery and an electronic device.
  • the present application provides a negative electrode sheet and a secondary battery including the negative electrode sheet.
  • the negative active material in the negative electrode sheet of the present application has both high compaction density and high porosity, and thus This makes the negative electrode plate have excellent electrolyte wettability, which can effectively improve the impedance and discharge temperature rise of the secondary battery.
  • 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 a third electrode having holes.
  • One particle and a second particle other than the first particle wherein the first particle satisfies: 0.10 ⁇ a/b ⁇ 0.85 and 0.89 ⁇ 0.98 ⁇ C- within a 200 ⁇ m ⁇ 200 ⁇ m area of the cross section of the negative active material layer (a/b) 2 ⁇ 1.86; where, a ⁇ m represents the average maximum Feret diameter of the pores in the first particle; b ⁇ m represents the average maximum Feret diameter of the first particle; C g/cm 3 represents the negative active material Compacted density under 5t pressure, where 1.65 ⁇ C ⁇ 1.95.
  • the pores of the negative active material particles can increase the contact area between the active material and the electrolyte.
  • the pores of the negative active material will also increase the capillary absorption effect of the negative electrode plate on the electrolyte, which is beneficial to the infiltration and storage of the electrolyte.
  • the wettability of the electrolyte in the negative electrode sheet is improved, which is conducive to the diffusion of active ions.
  • the presence of pores in the negative active material in the negative electrode sheet will also reduce the distance for active ions to migrate into the negative active material. , which is conducive to the rapid deintercalation of active ions. Both will reduce the diffusion resistance of active ions in the secondary battery, thereby improving the temperature rise performance of the secondary battery under high-rate discharge conditions.
  • the size of the pores in the negative active material is too large, the mechanical strength of the negative active material will be reduced, and it will be easily damaged during the pressing process of the negative electrode sheet.
  • the size is too large, the amount of electrolyte required will increase, resulting in secondary
  • the cost of the battery is additionally increased; if the size of the pores in the negative active material is too small, the wettability of the electrolyte in the negative electrode sheet is poor, the diffusion of active ions is difficult, and the discharge temperature rise of the secondary battery is not improved.
  • This application controls the average maximum Feret diameter of the pores in the cross section of the negative active material, the average maximum Feret diameter of the first particle where the hole is located, and the 5t compaction density of the negative active material within the above range.
  • the compacted density of the active material has a good match with the pore structure.
  • the negative active material has the characteristics of both high compacted density and high porosity, which makes the negative electrode sheet containing the negative active material have excellent electrolyte wettability. It can effectively reduce the migration resistance of solvated active ions and improve the high-rate temperature rise performance of secondary batteries.
  • the size of the pores in the negative active material is too large, the mechanical strength of the negative active material will be reduced, and it will be easily damaged during the pressing process of the negative electrode sheet. At the same time, if the size is too large, the amount of electrolyte required will increase, resulting in secondary battery failure. additional cost. If the size of the pores in the negative active material is too small, the wettability of the electrolyte in the negative electrode sheet will be poor, and the diffusion of active ions will be difficult, resulting in poor improvement in the discharge temperature rise of the secondary battery.
  • 0.5 ⁇ a ⁇ 13 When the size of the pores in the negative active material is too large, the mechanical strength of the negative active material is low, and the negative electrode piece is easily damaged during the pressing process. If the size of the pores in the negative active material is too small, the wettability of the electrolyte in the negative electrode sheet will be poor, and the diffusion of active ions will be difficult, resulting in poor improvement in the discharge temperature rise of the secondary battery. In some embodiments, 1 ⁇ a ⁇ 10.
  • the particle size of the active particles with holes is within this range, the infiltration of the electrolyte can be ensured, the compaction density of the negative electrode sheet can be increased, the diffusion of active ions can be improved, and the high-rate discharge performance of the secondary battery can be improved. In some embodiments, 4.5 ⁇ b ⁇ 16.
  • the average maximum Feret diameter of the pores in the cross section of the negative active material, the average maximum Feret diameter of the first particle where the hole is located, and the 5t compacted density of the negative active material are within the above range, which can further improve the secondary battery. Large rate temperature rise performance.
  • the compacted density of the negative active material is related to the energy density and dynamics of the secondary battery. When the compacted density of the negative active material is low, the compacted density of the pole piece is also low, and the corresponding energy density of the secondary battery will also be reduced. . When the compaction density of the negative active material is too high, the kinetics of the secondary battery will deteriorate, affecting the battery performance at high rates. In some embodiments, 1.7 ⁇ C ⁇ 1.9.
  • the number of first particles having holes accounts for 35% to 95% of the sum of the number of first particles and second particles within a 200 ⁇ m ⁇ 200 ⁇ m area of the cross section of the negative active material layer.
  • the proportion of active material particles with holes is too small, the negative electrode sheet has less pore structure and has poor absorption capacity of electrolyte, which makes it difficult for active ions to diffuse, and the discharge temperature rise of the secondary battery is not improved effectively.
  • the proportion of active material particles with holes is too large, the mechanical strength of the negative active material is insufficient. When the negative electrode sheet is pressed, the negative active material particles are easily destroyed, resulting in loss of performance.
  • the number of first particles accounts for 50% to 80% of the sum of the number of first particles and second particles.
  • the negative active material layer satisfies: 0.1 ⁇ ID/IG ⁇ 0.5, where ID is the 1350 cm -1 peak in the Raman spectrum
  • the intensity of IG is the intensity of the peak at 1580cm -1 in the Raman spectrum.
  • the ID/IG ratio can characterize the defectiveness of the negative active material layer. The greater the ID/IG ratio, the higher the defectiveness.
  • the negative active material layer has a high degree of defects, its internal atomic arrangement is highly disordered and there are many lattice defects, which is conducive to increasing the deintercalation channels of active ions, increasing the deintercalation speed of active ions, and the dynamics of the negative active material will be significantly improved. However, too many defects will affect the first efficiency, cycle, storage and other performance of secondary batteries. In some embodiments, 0.2 ⁇ ID/IG ⁇ 0.45.
  • the orientation degree OI of the negative electrode piece satisfies: OI ⁇ 35.
  • the OI value of the negative electrode piece is a parameter that reflects the orientation of the grain crystals in the electrode piece. The larger the OI value, the higher the crystal orientation, and the more localized the surface where active ions can be deintercalated on the active material in the pole piece. The smaller the OI value, the lower the crystal orientation, and active ions can be deintercalated from multiple directions on the active material in the pole piece.
  • active ions can be quickly deintercalated in the negative electrode piece, which can further improve the impedance and discharge temperature rise performance of the secondary battery.
  • the porosity K of the negative electrode sheet satisfies: 15% ⁇ K ⁇ 50%. If the porosity is too small, the diffusion resistance of active ions will be large, and the effect of improving the discharge temperature rise of the secondary battery will be poor. When the porosity is too large, the compacted density of the pole pieces is too low, and the energy density of the secondary battery is too low. At the same time, the amount of electrolyte required will increase, resulting in an additional increase in the cost of the secondary battery. In some embodiments, 20% ⁇ K ⁇ 40%.
  • the thickness H of the negative electrode plate satisfies: H ⁇ 220 ⁇ m.
  • H ⁇ 220 ⁇ m the thickness of the negative electrode active material layer is too high, which will increase the distance for active ions to diffuse from the electrolyte to the active material particles inside the negative electrode sheet, making the secondary battery prone to lithium precipitation under high-rate charging. , at the same time, increasing the distance will also increase the charge transfer resistance, affecting the discharge temperature rise of the secondary battery.
  • the graphitization degree G of the negative active material satisfies: 92% ⁇ G ⁇ 98%.
  • the negative active material with high graphitization degree has high capacity and high compaction density.
  • the gram capacity Cap of the negative active material satisfies: Cap ⁇ 330 mAh/g.
  • the specific surface area BET of the negative active material satisfies: 1.0 m 2 /g ⁇ BET ⁇ 4.5 m 2 /g.
  • 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 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 impedance DCR of the secondary battery when discharged to 50% SOC at 0° C. 1C satisfies: DCR ⁇ 55.0 m ⁇ .
  • the temperature rise T satisfies: T ⁇ 8.0°C.
  • the present application provides an electronic device including the secondary battery of the second aspect.
  • the negative active material in the negative electrode sheet provided by this application has both high compaction density and high porosity, so that the negative electrode sheet containing the negative active material has excellent electrolyte wettability and can effectively reduce the migration of solvated active ions. impedance to improve the high-rate temperature rise performance of secondary batteries.
  • Figure 1 shows the DCR values of the secondary batteries of Example 2 and Comparative Example 1 of the present application, where 1 - Example 2 and 2 - Comparative Example 1.
  • Figure 2 shows the temperature rise of the secondary batteries of Example 2 and Comparative Example 1 of the present application, where 1 - Example 2 and 2 - Comparative Example 1.
  • 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 a third electrode having holes.
  • the pores of the negative active material particles can increase the contact area between the active material and the electrolyte.
  • the pores of the negative active material will also increase the capillary absorption effect of the negative electrode plate on the electrolyte, which is beneficial to the infiltration and storage of the electrolyte.
  • the wettability of the electrolyte in the negative electrode sheet is improved, which is conducive to the diffusion of active ions.
  • the presence of pores in the negative active material in the negative electrode sheet will also reduce the distance for active ions to migrate into the negative active material. , which is conducive to the rapid deintercalation of active ions.
  • Both will reduce the diffusion resistance of active ions in the secondary battery, thereby improving the temperature rise performance of the secondary battery under high-rate discharge conditions.
  • the size of the pores in the negative active material is too large, the mechanical strength of the negative active material will be reduced, and it will be easily damaged during the pressing process of the negative electrode sheet.
  • the size is too large, the amount of electrolyte required will increase, resulting in secondary Batteries cost extra. If the size of the pores in the negative active material is too small, the wettability of the electrolyte in the negative electrode sheet will be poor, and the diffusion of active ions will be difficult, resulting in poor improvement in the discharge temperature rise of the secondary battery.
  • This application controls the average maximum Feret diameter a of the pores in the cross section of the negative active material, the average maximum Feret diameter b of the first particle where the hole is located, and the 5t compacted density C of the negative active material within the above range.
  • the compacted density of the negative active material has a good match with the pore structure.
  • the negative active material has the characteristics of both high compacted density and high porosity, which makes the negative electrode sheet containing the negative active material have excellent electrolyte Wettability can effectively reduce the migration resistance of solvated active ions and improve the high-rate temperature rise performance of secondary batteries.
  • the "cross section of the negative active material layer” may be a cross section along the thickness direction of the negative active material layer.
  • a/b is 0.13, 0.17, 0.19, 0.21, 0.23, 0.25, 0.27, 0.3, 0.33, 0.35, 0.37, 0.4, 0.43, 0.45, 0.57, 0.5, 0.53, 0.55, 0.57, 0.59, 0.63, 0.65, 0.67, 0.69, 0.73, 0.75, 0.77, 0.8, 0.83, or a range consisting of any two of these values.
  • 0.2 ⁇ a/b ⁇ 0.6 When the size of the pores in the negative active material is too large, the mechanical strength of the negative active material will be reduced, and it will be easily damaged during the pressing process of the negative electrode sheet.
  • the size is too large, the amount of electrolyte required will increase, resulting in secondary battery failure. additional cost. If the size of the pores in the negative active material is too small, the wettability of the electrolyte in the negative electrode sheet will be poor, and the diffusion of active ions will be difficult, resulting in poor improvement in the discharge temperature rise of the secondary battery.
  • a is 0.7, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, A range of 11.5, 12.0, 12.5, or any two of these values.
  • the size of the pores in the negative active material is too small, the wettability of the electrolyte in the negative electrode sheet will be poor, and the diffusion of active ions will be difficult, resulting in poor improvement in the discharge temperature rise of the secondary battery.
  • b is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or these values A range consisting of any two of them. In some embodiments, 4 ⁇ b ⁇ 18. In some embodiments, 4.5 ⁇ b ⁇ 16.
  • 0.98 ⁇ C-(a/b) 2 is 0.9, 0.93, 0.95, 0.97, 1.0, 1.03, 1.05, 1.07, 1.1, 1.13, 1.15, 1.17, 1.2, 1.23, 1.25, 1.27, 1.3 , 1.33, 1.35, 1.37, 1.4, 1.43, 1.45, 1.47, 1.5, 1.53, 1.55, 1.57, 1.6, 1.63, 1.65, 1.67, 1.7, 1.73, 1.75, 1.77, 1.8, 1.83, 1.85 or any two of these values range of persons.
  • 1.3 ⁇ 0.98 ⁇ C-(a/b) 2 ⁇ 1.8 is 0.9, 0.93, 0.95, 0.97, 1.0, 1.03, 1.05, 1.07, 1.1, 1.13, 1.15, 1.17, 1.2, 1.23, 1.25, 1.27, 1.3 , 1.33, 1.35, 1.37, 1.4, 1.43, 1.45, 1.47, 1.5, 1.53, 1.55,
  • the average maximum Feret diameter of the pores in the cross section of the negative active material, the average maximum Feret diameter of the first particle where the hole is located, and the 5t compacted density of the negative active material are within the above range, which can further improve the secondary battery. Large rate temperature rise performance.
  • C is a range consisting of 1.67, 1.7, 1.73, 1.75, 1.77, 1.8, 1.83, 1.85, 1.87, 1.9, 1.93, or any two of these values.
  • the compacted density of the negative active material is related to the energy density and dynamics of the secondary battery. When the compacted density of the negative active material is low, the compacted density of the pole piece is also low, and the corresponding energy density of the secondary battery will also be reduced. . When the compaction density of the negative active material is too high, the kinetics of the secondary battery will deteriorate, affecting the battery performance at high rates.
  • the number of first particles with holes accounts for 35% to 95% of the sum of the number of first particles and second particles, for example, 40%, 43%, 45%, 47%, 49%, 53%, 55%, 57%, 60%, 63%, 65%, 67%, 70%, 73%, 75%, 77%, 79%, 83% , 85%, 87%, 90%, 93%, or a range consisting of any two of these values.
  • the proportion of active material particles with holes When the proportion of active material particles with holes is too small, the negative electrode sheet has less pore structure and has poor absorption capacity of electrolyte, which makes it difficult for active ions to diffuse, and the discharge temperature rise of the secondary battery is not improved effectively.
  • the proportion of active material particles with holes is too large, the mechanical strength of the negative active material is insufficient.
  • the negative electrode sheet is pressed, the negative active material particles are easily destroyed, resulting in loss of performance.
  • the proportion if the proportion is too large, the side reactions between the negative active material and the electrolyte will also increase significantly, which will affect the storage and cycle performance of the secondary battery.
  • the number of first particles accounts for 50% to 80% of the sum of the number of first particles and second particles.
  • the negative active material layer satisfies: 0.1 ⁇ ID/IG ⁇ 0.5, where ID is the 1350 cm -1 peak in the Raman spectrum
  • the intensity of IG is the intensity of the peak at 1580cm -1 in the Raman spectrum.
  • the ID/IG ratio can characterize the defectiveness of the negative active material layer. The greater the ID/IG ratio, the higher the defectiveness.
  • ID/IG is a range consisting of 0.15, 0.17, 0.23, 0.25, 0.3, 0.33, 0.35, 0.37, 0.4, 0.43, 0.47, or any two of these values. In some embodiments, 0.2 ⁇ ID/IG ⁇ 0.45.
  • the orientation degree OI of the negative electrode piece satisfies: OI ⁇ 35.
  • the OI value of the negative electrode piece is a parameter that reflects the orientation of the grain crystals in the electrode piece. The larger the OI value, the higher the crystal orientation, and the more localized the surface where active ions can be deintercalated on the active material in the pole piece. The smaller the OI value, the lower the crystal orientation, and active ions can be deintercalated from multiple directions on the active material in the pole piece. In this application, by limiting the OI value of the negative electrode piece to the above range, active ions can be quickly deintercalated in the negative electrode piece, which can further improve the impedance and discharge temperature rise performance of the secondary battery.
  • the OI is a range of 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, or any two of these values. In some embodiments, OI ⁇ 25. In some embodiments, 15 ⁇ OI ⁇ 25.
  • the porosity K of the negative electrode sheet satisfies: 15% ⁇ K ⁇ 50%. If the porosity is too small, the diffusion resistance of active ions will be large, and the effect of improving the discharge temperature rise of the secondary battery will be poor. When the porosity is too large, the compacted density of the pole pieces is too low, and the energy density of the secondary battery is too low. At the same time, the amount of electrolyte required will increase, resulting in an additional increase in the cost of the secondary battery.
  • K is 17%, 19%, 23%, 25%, 27%, 30%, 33%, 35%, 37%, 39%, 43%, 45%, 47%, 49%, or A range consisting of any two of these values. In some embodiments, 20% ⁇ K ⁇ 40%.
  • the thickness H of the negative electrode plate satisfies: H ⁇ 220 ⁇ m.
  • H ⁇ 220 ⁇ m the thickness of the negative electrode active material layer is too high, which will increase the distance for active ions to diffuse from the electrolyte to the active material particles inside the negative electrode sheet, making the secondary battery prone to lithium precipitation under high-rate charging.
  • increasing the distance will also increase the charge transfer resistance, affecting the discharge temperature rise of the secondary battery.
  • H is a range of 30 ⁇ m, 60 ⁇ m, 70 ⁇ m, 80 ⁇ m, 90 ⁇ m, 100 ⁇ m, 110 ⁇ m, 120 ⁇ m, 130 ⁇ m, 140 ⁇ m, 150 ⁇ m, 160 ⁇ m, 170 ⁇ m, 180 ⁇ m, 190 ⁇ m, 210 ⁇ m, or any two thereof. In some embodiments, 50 ⁇ m ⁇ H ⁇ 200 ⁇ m.
  • the graphitization degree G of the negative active material satisfies: 92% ⁇ G ⁇ 98%, for example, G is 93%, 94%, 95%, 96% or 97%.
  • the negative active material with high graphitization degree has high capacity and high compaction density.
  • the gram capacity Cap of the negative active material satisfies: Cap ⁇ 330 mAh/g. In some embodiments, 330mAh/g ⁇ Cap ⁇ 500mAh/g. In some embodiments, 330mAh/g ⁇ Cap ⁇ 450mAh/g. In some embodiments, 330mAh/g ⁇ Cap ⁇ 400mAh/g.
  • the specific surface area BET of the negative active material satisfies: 1.0 m 2 /g ⁇ BET ⁇ 4.5 m 2 /g.
  • the BET is 1.3m 2 /g, 1.5m 2 /g, 1.7m 2 /g, 2.0m 2 /g, 2.3m 2 /g, 2.5m 2 /g, 2.7m 2 / g, 3.0m 2 /g, 3.3m 2 /g, 3.5m 2 /g, 3.7m 2 /g , 4.0m 2 /g, 4.3m 2 /g or any two ranges between them.
  • 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 negative active material includes graphite. In some embodiments, the negative active material includes natural graphite.
  • the graphite preparation process includes: selecting artificial graphite with a graphitization degree of 92.0% to 95.0% and mixing it with flake graphite, where the flake graphite mass accounts for 10% to 80%, and then mixing 2% of the graphite mass. to 6% of the pore-forming agent such as sodium carbonate, and finally add asphalt in a ratio of 10% to 20% by mass of the mixture to the above mixture for coating treatment.
  • the above treated mixture is ball milled to aggregate and spheroidize the particles. After spheroidization, the pore-forming agent has been distributed inside the particles.
  • the mixture After ball milling, the mixture is subjected to carbonization of pitch and decomposition of the pore-forming agent at a high temperature of 800°C to 1200°C. At high temperatures, the pore-forming agent decomposes and generates gas expansion, causing the particles to deform and form pores inside.
  • the present application provides a secondary battery, which includes the negative electrode plate of the first aspect.
  • the impedance DCR of the secondary battery when discharged to 50% SOC at 0° C. 1C satisfies: DCR ⁇ 55.0 m ⁇ .
  • the temperature rise T satisfies: T ⁇ 8.0°C.
  • 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.
  • the base material layer is made of at least one material selected from the group consisting 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 polymethylmethacrylate, 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.
  • 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 with a thickness of 9 ⁇ m was 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 Example 1, except that the corresponding negative active material is prepared by adjusting parameters such as the proportion of flake graphite, the amount of pore-forming agent, the spheroidization time and the temperature of the high-temperature treatment, and the asphalt quality is maintained. At one-fifth of the mass of artificial graphite, the holding time remains unchanged for 2 hours.
  • the specific preparation parameters are shown in Table a:
  • the preparation process of the negative active material is similar to that of Example 5, except that the quantity proportion of the first particles is adjusted by adjusting the amount of pore-forming agent.
  • the amount of pore-forming agent is respectively It is 4.2kg, 4.3kg, 4.4kg, 4.5kg, 4.6kg, 4.7kg, 4.8kg, 5.0kg.
  • the preparation of the negative electrode, positive electrode, separator, electrolyte and lithium-ion battery is the same as in Example 5.
  • the preparation process of the negative active material is similar to that of Example 14, except that the ID/IG value of the negative active material layer is adjusted by adjusting the high-temperature treatment temperature.
  • the high-temperature treatment temperature is 990°C respectively. °C, 980°C, 970°C, 960°C, 950°C.
  • 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 that of Example 21. The difference is that the OI value and porosity of the negative electrode piece are adjusted by adjusting the spheroidization time.
  • the spheroidization times in the preparation process of Examples 24 to 39 are respectively It is 5.3h, 5.4h, 5.5h, 5.6h, 5.7h, 5.8h, 5.9h, 6.0h, 6.1h, 6.2h, 6.3h, 6.4h, 6.5h, 6.6h, 6.7h, 6.8h.
  • 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 38, except that the mass of the artificial graphite remains unchanged at 90 kg.
  • the gram capacity and specific surface area of the negative active material are adjusted by adjusting the quality of the flake graphite.
  • the results from Example 40 to Example 50 The masses of flake graphite during the preparation process were 53kg, 60kg, 51kg, 65kg, 52kg, 54kg, 55kg, 56kg, 57kg, 58kg, and 59kg respectively.
  • the preparation of the negative electrode, positive electrode, separator, electrolyte and lithium-ion battery is the same as in Example 38.
  • Negative electrode plate argon ion polishing (CP) sample preparation process disassemble the lithium-ion battery to obtain the negative electrode plate, cut the negative electrode plate into a size of 6.0mm ⁇ 6mm, then fix it on the sample stage, and use argon ion polishing (parameter: 6KV Accelerating voltage, 3h for each sample), process one end of the negative active material layer to obtain the negative active material layer CP sample.
  • CP Negative electrode plate argon ion polishing
  • the negative active material layer CP sample is prepared, it is analyzed using a scanning electron microscope (SEM).
  • the scanning electron microscope used in this application is the JSM-6360LV model of JEOL Company.
  • Maximum Feret diameter of the cross-section of the pore structure Observing the negative active material layer CP sample, in the 200um ⁇ 200um area on the cross-section in the thickness direction of the negative active material layer, there are some particles with a pore structure, and the pore cross-sections of the particles are irregular. Shape, Feret diameter refers to the distance between two boundary parallel lines of the particle hole cross-section measured along a certain direction, and the maximum distance is the maximum Feret diameter of the hole cross-section. For the hole cross-section in a particle, two parallel lines are rotated along the outer tangent line of the hole cross-section. The dimension with the largest distance between the parallel lines at a certain position is the maximum Feret diameter of the hole structure cross-section. Test the maximum Feret diameter of all particle pore cross sections in the 200 ⁇ m value a.
  • the maximum Feret diameter of the active material particle cross-section with holes Observe the negative active material layer CP sample. In the 200 ⁇ m ⁇ 200 ⁇ m area on the cross section in the thickness direction of the negative active material layer, there are cross sections of a certain number of particles. These cross sections are in the form of For irregular shapes, the Feret diameter refers to the distance between the two boundary parallel lines of the particle cross section measured along a certain direction. The maximum distance is the maximum Feret diameter of the particle cross section. 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. Test the maximum Feret diameter of all particles in the 200um ⁇ 200um area of the negative active material layer in sequence, and then calculate the average value to obtain the maximum Feret diameter b of the active particle cross section in the thickness direction of the negative active material layer.
  • the proportion of the number of first particles to the sum of the number of first particles and second particles Select a 200 ⁇ m ⁇ 200 ⁇ m area of the cross section of the negative active material layer, and count the total number of particles in this area, which is the first particles and second particles. The sum of the quantities. Count the number of active material particles with holes in this area, which is the number of first particles.
  • test standard for powder compaction density refers to GB/T 24533-2009 "Graphite Anode Materials for Lithium-Ion Batteries”.
  • specific test methods are:
  • test equipment is Sansi Zongheng UTM7305 test tonnage 0.3t, 0.5t, 0.75t, 1.0t, 1.5t, 2.0t, 2.5t, 3.0t, 4.0t, 5.0t, pressure increase rate is 10mm/min, pressure increase holding time is 30s, pressure relief rate is 30mm/min, pressure relief holding time is 10s .
  • the compacted density of the powder is the compacted density measured after 5t of pressure relief.
  • 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 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 electrode piece, which is the OI value of the negative electrode piece.
  • the protection voltage is set to 2.0V
  • Table 1 shows the average maximum Feret diameter a ⁇ m of the pores in the first particle with holes and the average maximum Feret diameter of the first particle where the hole is located in the 200 ⁇ m ⁇ 200 ⁇ m area of the cross section of the negative active material layer. Effect of value b ⁇ m and 5t compacted density C g/ m of negative active material on lithium-ion battery performance.
  • the average maximum Feret diameter of the hole in the first particle is a ⁇ m
  • the average maximum Feret diameter of the first particle where the hole is located is b
  • the 5t compacted density of the negative active material When C satisfies 0.10 ⁇ a/b ⁇ 0.85, 1.65 ⁇ C ⁇ 1.95, and 0.89 ⁇ 0.98 ⁇ C-(a/b) 2 ⁇ 1.86, the lithium-ion battery has low impedance DCR and discharge temperature rise T.
  • Table 2 shows the influence of the ratio of the number of first particles with holes to the sum of the number of first particles and second particles in the 200 ⁇ m ⁇ 200 ⁇ m area of the cross section of the negative active material layer on the performance of the lithium ion battery. Except for the parameters listed in Table 2, the remaining parameters of Examples 11 to 18 are the same as those of Example 5.
  • Table 3 shows the effect of the ID/IG ratio on the performance of the lithium ion battery within the 200 ⁇ m ⁇ 200 ⁇ m area of the cross section of the negative active material layer. Except for the parameters listed in Table 3, the remaining parameters of Examples 19 to 23 are the same as those of Example 14.
  • Table 4 shows the influence of the OI value, porosity K and thickness H of the negative electrode sheet on the performance of lithium-ion batteries. Except for the parameters listed in Table 4, the remaining parameters of Embodiment 24 to 39 are the same as those of Embodiment 21.
  • the negative electrode plate meets the condition of OI value ⁇ 25, and lithium ions can be quickly deintercalated in the negative electrode plate, thereby improving the impedance and discharge temperature rise performance of the lithium-ion battery.
  • the porosity K of the negative electrode piece is in the range of 15% to 50%, the diffusion resistance of lithium ions is low, the compaction density of the electrode piece is high, and the discharge performance of the lithium-ion battery is effectively improved.
  • Table 5 shows the effects of the graphitization degree G, gram capacity Cap, and specific surface area BET of the negative 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 38.

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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具有孔的第一颗粒和除第一颗粒外的第二颗粒，其中，在所述负极活性材料层的截面的200μm×200μm区域内，所述第一颗粒满足：0.10≤a/b≤0.85且0.89≤0.98×C-(a/b) 2≤1.86；其中，aμm表示所述第一颗粒中孔的最大费雷特直径平均值；bμm表示所述第一颗粒的最大费雷特直径平均值；C g/cm 3表示负极活性材料在5t压力下的压实密度，其中，1.65≤C≤1.95。本申请的负极极片兼具高压实密度与高孔隙率，进而能够在保证二次电池高能量密度的基础上，有效改善二次电池的阻抗及放电温升。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
随着二次电池应用市场的不断扩大，对其各项性能的要求也逐渐增高。例如在电动工具与无人机领域中，都需要二次电池具备大倍率下放电的能力，使电动工具与无人机能发挥较大功率。但由于二次电池本身的内阻，在大倍率放电过程中，其内部温度上升非常块，进而使得二次电池在高温环境下产生较大的损伤。现有技术主要是通过降低极片的涂布厚度并减小活性材料的粒度来改善二次电池的阻抗与放电温升，但这种方式会明显的降低二次电池的能量密度，而且成本也较高。
发明内容
鉴于现有技术存在的上述问题，本申请提供一种负极极片及包括该负极极片的二次电池，本申请的负极极片中负极活性材料兼具高压实密度与高孔隙率，进而使得负极极片具有优异的电解液浸润性，能够有效改善二次电池的阻抗及放电温升。
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具有孔的第一颗粒和除第一颗粒外的第二颗粒，其中，在负极活性材料层的截面的200μm×200μm区域内，所述第一颗粒满足：0.10≤a/b≤0.85且0.89≤0.98×C-(a/b) 2≤1.86；其中，aμm表示第一颗粒中孔的最大费雷特直径平均值；bμm表示第一颗粒的最大费雷特直径平均值；C g/cm 3表示负极活性材料在5t压力下的压实密度，其中，1.65≤C≤1.95。负极活性材料颗粒具有孔可以增大活性材料与电解液的接触面积，同时负极活性材料的孔也会增大负极极片对电解液的毛细吸收效应，有利于电解液的浸润与存储。一方面，电解液在负极极片内的浸润性提高，有利于活性离子的扩散，另一方面，负极极片中负极活性材料存在孔，也会减小活性离子迁移到负极活性材料中的距离，有利于活性离子的快速脱嵌，两者都会降低活性离子在二次电池中的扩散阻抗，从而改善大倍率放电条件下，二次电池的温升性 能。但是负极活性材料中孔的尺寸过大时，会降低负极活性材料的机械强度，进而易在负极极片压制过程时中被破坏，同时尺寸过大，需要的电解液量会增加，致使二次电池的成本额外增加；负极活性材料中孔的尺寸过小时，电解液在负极极片内的浸润性差，活性离子扩散较困难，二次电池的放电温升改善效果不佳。本申请通过将负极活性材料截面中孔的最大费雷特直径平均值、该孔所在的第一颗粒的最大费雷特直径平均值以及负极活性材料的5t压实密度控制在上述范围内，负极活性材料的压实密度与孔结构具有良好的匹配性，负极活性材料兼具高压实密度与高孔隙率的特征，进而使得包含该负极活性材料的负极极片具有优异的电解液浸润性，能够有效降低溶剂化活性离子的迁移阻抗，提升二次电池的大倍率温升性能。
在一些实施方式中，0.15≤a/b≤0.7。在一些实施方式中，0.2≤a/b≤0.6。负极活性材料中孔的尺寸过大时，会降低负极活性材料的机械强度，进而易在负极极片压制过程时中被破坏，同时尺寸过大，需要的电解液量会增加，致使二次电池的成本额外增加。负极活性材料中孔的尺寸过小时，电解液在负极极片内的浸润性差，活性离子扩散较困难，二次电池的放电温升改善效果不佳。
在一些实施方式中，0.5≤a≤13。负极活性材料中孔的尺寸过大时，负极活性材料的机械强度低，负极极片压制过程时中易被破坏。负极活性材料中孔的尺寸过小时，电解液在负极极片内的浸润性差，活性离子扩散较困难，二次电池的放电温升改善效果不佳。在一些实施方式中，1≤a≤10。
在一些实施方式中，4≤b≤25。当具有孔的活性颗粒的粒径在此范围内时，可保证电解液的浸润，提高负极极片的压实密度，改善活性离子的扩散，提升二次电池的大倍率放电性能。在一些实施方式中，4.5≤b≤16。
在一些实施方式中，1.2≤0.98×C-(a/b) 2≤1.86。在一些实施方式中，1.3≤0.98×C-(a/b) 2≤1.8。负极活性材料截面中孔的最大费雷特直径平均值、该孔所在的第一颗粒的最大费雷特直径平均值以及负极活性材料的5t压实密度在上述范围内，可进一步提升二次电池的大倍率温升性能。
在一些实施方式中，1.65≤C≤1.95。负极活性材料的压实密度与二次电池的能量密度和动力学有关，负极活性材料压实密度较低时，极片的压实密度也较低，相应的二次电池的能量密度也会降低。负极活性材料的压密密度过高时，二次电池的动力学会恶化，影响大倍率下的电池性能。在一些实施方式中，1.7≤C≤1.9。
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，具有孔的第 一颗粒数量占第一颗粒和第二颗粒数量之和的35％至95％。具有孔的活性材料颗粒占比太少时，负极极片的孔隙结构较少，其对电解液的吸收能力差，进而使得活性离子扩散较困难，二次电池的放电温升改善效果不佳。具有孔的活性材料颗粒占比太大时，负极活性材料的机械强度不够，负极极片在压制时，负极活性材料颗粒容易被破坏，造成其性能损失。同时占比太大，负极活性材料与电解液的副反应也会明显增加，进而会影响二次电池的存储与循环性能。在一些实施方式中，第一颗粒的数量占第一颗粒和第二颗粒数量之和的50％至80％。
在一些实施方式中，负极活性材料层的截面的200μm×200μm区域内，通过拉曼测试，负极活性材料层满足：0.1≤ID/IG≤0.5，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。ID/IG比值可以表征负极活性材料层的缺陷度，ID/IG比值越大，表明缺陷度越高。负极活性材料层缺陷度高时，其内部原子排列无序度高，晶格缺陷较多，有利于增加活性离子的脱嵌通道，提高活性离子脱嵌速度，负极活性材料的动力学会明显提升。但过多的缺陷会影响二次电池的首效、循环、存储等性能。在一些实施方式中，0.2≤ID/IG≤0.45。
在一些实施方式中，负极极片的取向度OI满足：OI≤35。负极极片OI值是反映极片中颗粒晶体取向度的一个参数。OI值越大，晶体取向度越高，活性离子在极片中活性材料上脱嵌的面就越局限。OI值越小，晶体取向度越低，活性离子可以在极片中活性材料上从多个方向脱嵌。本申请通过将负极极片的OI值限定在上述范围内，活性离子可以快速在负极极片中脱嵌，能够进一步改善二次电池的阻抗及放电温升性能。在一些实施方式中，15≤OI≤25。
在一些实施方式中，负极极片的孔隙率K满足：15％≤K≤50％。孔隙率太小时，活性离子的扩散阻抗较大，二次电池的放电温升改善效果不佳。孔隙率太大时，极片的压实密度太低，二次电池的能量密度太低，同时需要的电解液量会增加，致使二次电池的成本额外增加。在一些实施方式中，20％≤K≤40％。
在一些实施方式中，负极极片的厚度H满足：H≤220μm。负极极片的厚度过高时，负极活性材料层的厚度过高，进而会增加活性离子从电解液扩散到负极极片内部活性材料颗粒的距离，使得二次电池容易在大倍率充电下析锂，同时距离增加也会增大电荷转移阻抗，影响二次电池的放电温升。在一些实施方式中，50μm≤H≤200μm。
在一些实施方式中，负极活性材料的石墨化度G满足：92％≤G≤98％。高石墨化度的负极活性材料具有高容量和高压实密度。
在一些实施方式中，负极活性材料的克容量Cap满足：Cap≥330mAh/g。
在一些实施方式中，负极活性材料的比表面积BET满足：1.0m 2/g≤BET≤4.5m 2/g。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，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℃1C放电至50％SOC时的阻抗DCR满足：DCR≤55.0mΩ。在一些实施方式中，二次电池在25℃3C放电时，温升T满足：T≤8.0℃。
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。
本申请提供的负极极片中负极活性材料兼具高压实密度与高孔隙率，进而使得包含该负极活性材料的负极极片具有优异的电解液浸润性，能够有效降低溶剂化活性离子的迁移阻抗，提升二次电池的大倍率温升性能。
附图说明
图1示出了本申请实施例2和对比例1的二次电池的DCR值，其中，1—实施例2，2—对比例1。
图2示出了本申请实施例2和对比例1的二次电池的温升，其中，1—实施例2，2—对比例1。
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具有孔的第一颗粒和除第一颗粒外的第二颗粒，其中，在负极活性材料层的截面的200μm×200μm区域内，该第一颗粒满足：0.10≤a/b≤0.85且0.89≤0.98×C-(a/b) 2≤1.86；其中，aμm表示第一颗粒中孔的最大费雷特直径平均值；bμm表示第一颗粒的最大费雷特直径平均值；C g/cm 3表示负极活性材料在5t压力下的压实密度，其中，1.65≤C≤1.95。负极活性材料颗粒具有孔可以增大活性材料与电解液的接触面积，同时负极活性材料的孔也会增大负极极片对电解液的毛细吸收效应，有利于电解液的浸润与存储。一方面，电解液在负极极片内的浸润性提高，有利于活性离子的扩散，另一方面，负极极片中负极活性材料存在孔，也会减小活性离子迁移到负极活性材料中的距离，有利于活性离子的快速脱嵌，两者都会降低活性离子在二次电池中的扩散阻抗，从而改善大倍率放电条件下，二次电池的温升性能。但是负极活性材料中孔的尺寸过大时，会降低负极活性材料的机械强度，进而易在负极极片压制过程时中被破坏，同时尺寸过大，需要的电解液量会增加，致使二次电池的成本额外增加。负极活性材料中孔的尺寸过小时，电解液在负极极片内的浸润性差，活性离子扩散较困难，二次电池的放电温升改善效果不佳。本申请通过将负极活性材料截面中孔的最大费雷特直径平均值a、该孔所在的第一颗粒的最大费雷特直径平均值b以及负极活性材料的5t压实密度C控制在上述范围内，负极活性材料的压实密度与孔结构具有良好的匹配性，负极活性材料兼具高压实密度与高孔隙率的特征，进而使得包含该负极活性材料的负极极片具有优异的电解液浸润性，能够有效降低溶剂化活性离子的迁移阻抗，提升二次电池的大倍率温升性能。
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，a/b为0.13、0.17、0.19、0.21、0.23、0.25、0.27、0.3、0.33、0.35、0.37、0.4、0.43、0.45、0.57、0.5、0.53、0.55、0.57、0.59、0.63、0.65、0.67、0.69、0.73、0.75、0.77、0.8、0.83或这些值中任意两者组成的范围。在一些实施方式中，0.15≤a/b≤0.7。在一些实施方式中，0.2≤a/b≤0.6。负极活性材料中孔的尺寸过大时，会降低负极活性材料的机械强度，进而易在负极极片压制过程时中被破坏，同时尺寸过大，需要的电解液量会增加，致使二次电池的成本额外增加。负极活性材料中孔的尺寸过小时，电解液在负极极片内的浸润性差，活性离子扩散较困难，二次电池的放电温升改善效果不佳。
在一些实施方式中，0.5≤a≤13。在一些实施方式中，a为0.7、1.5、2.0、2.5、3.0、3.5、4.0、4.5、5.0、5.5、6.0、6.5、7.0、7.5、8.0、8.5、9.0、9.5、10.0、10.5、11.0、11.5、12.0、12.5或这些值中任意两者组成的范围。负极活性材料中孔的尺寸过大时，负极活性材料的机械强度低，负极极片压制过程时中易被破坏。负极活性材料中孔的尺寸过小时，电解液在负极极片内的浸润性差，活性离子扩散较困难，二次电池的放电温升改善效果不佳。在一些实施方式中，1≤a≤10。
在一些实施方式中，4≤b≤25。在一些实施方式中，b为5、6、7、8、9、10、11、12、13、14、15、16、17、18、19、20、21、22、23、24或这些值中任意两者组成的范围。在一些实施方式中，4≤b≤18。在一些实施方式中，4.5≤b≤16。
在一些实施方式中，0.98×C-(a/b) 2为0.9、0.93、0.95、0.97、1.0、1.03、1.05、1.07、1.1、1.13、1.15、1.17、1.2、1.23、1.25、1.27、1.3、1.33、1.35、1.37、1.4、1.43、1.45、1.47、1.5、1.53、1.55、1.57、1.6、1.63、1.65、1.67、1.7、1.73、1.75、1.77、1.8、1.83、1.85或这些值中任意两者组成的范围。在一些实施方式中，1.2≤0.98×C-(a/b) 2≤1.86。在一些实施方式中，1.3≤0.98×C-(a/b) 2≤1.8。负极活性材料截面中孔的最大费雷特直径平均值、该孔所在的第一颗粒的最大费雷特直径平均值以及负极活性材料的5t压实密度在上述范围内，可进一步提升二次电池的大倍率温升性能。
在一些实施方式中，C为1.67、1.7、1.73、1.75、1.77、1.8、1.83、1.85、1.87、1.9、1.93或这些值中任意两者组成的范围。在一些实施方式中，1.65≤C≤1.95。在一些实施方式中，1.7≤C≤1.9。负极活性材料的压实密度与二次电池的能量密度和动力学有关，负极活性材料压实密度较低时，极片的压实密度也较低，相应的二次电池的能量密度也会降低。负极活性材料的压密密度过高时，二次电池的动力学会恶化，影响大倍率下的电池性能。
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，具有孔的第 一颗粒数量占第一颗粒和第二颗粒数量之和的35％至95％，例如为40％、43％、45％、47％、49％、53％、55％、57％、60％、63％、65％、67％、70％、73％、75％、77％、79％、83％、85％、87％、90％、93％或这些值中任意两者组成的范围。具有孔的活性材料颗粒占比太少时，负极极片的孔隙结构较少，其对电解液的吸收能力差，进而使得活性离子扩散较困难，二次电池的放电温升改善效果不佳。具有孔的活性材料颗粒占比太大时，负极活性材料的机械强度不够，负极极片在压制时，负极活性材料颗粒容易被破坏，造成其性能损失。同时占比太大，负极活性材料与电解液的副反应也会明显增加，进而会影响二次电池的存储与循环性能。在一些实施方式中，第一颗粒的数量占第一颗粒和第二颗粒数量之和的50％至80％。
在一些实施方式中，负极活性材料层的截面的200μm×200μm区域内，通过拉曼测试，负极活性材料层满足：0.1≤ID/IG≤0.5，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。ID/IG比值可以表征负极活性材料层的缺陷度，ID/IG比值越大，表明缺陷度越高。负极活性材料层缺陷度高时，其内部原子排列无序度高，晶格缺陷较多，有利于增加活性离子的脱嵌通道，提高活性离子脱嵌速度，负极活性材料的动力学会明显提升。但过多的缺陷会影响二次电池的首效、循环、存储等性能。在一些实施方式中，ID/IG为0.15、0.17、0.23、0.25、0.3、0.33、0.35、0.37、0.4、0.43、0.47或这些值中任意两者组成的范围。在一些实施方式中，0.2≤ID/IG≤0.45。
在一些实施方式中，负极极片的取向度OI满足：OI≤35。负极极片OI值是反映极片中颗粒晶体取向度的一个参数。OI值越大，晶体取向度越高，活性离子在极片中活性材料上脱嵌的面就越局限。OI值越小，晶体取向度越低，活性离子可以在极片中活性材料上从多个方向脱嵌。本申请通过将负极极片的OI值限定在上述范围内，活性离子可以快速在负极极片中脱嵌，能够进一步改善二次电池的阻抗及放电温升性能。在一些实施方式中，OI为10、12、14、16、18、20、22、24、26、28、30、32、34或这些值中任意两者组成的范围。在一些实施方式中，OI≤25。在一些实施方式中，15≤OI≤25。
在一些实施方式中，负极极片的孔隙率K满足：15％≤K≤50％。孔隙率太小时，活性离子的扩散阻抗较大，二次电池的放电温升改善效果不佳。孔隙率太大时，极片的压实密度太低，二次电池的能量密度太低，同时需要的电解液量会增加，致使二次电池的成本额外增加。在一些实施方式中，K为17％、19％、23％、25％、27％、30％、33％、35％、37％、39％、43％、45％、47％、49％或这些值中任意两者组成的范围。在一些实施方式中，20％≤K≤40％。
在一些实施方式中，负极极片的厚度H满足：H≤220μm。负极极片的厚度过高时，负极活性材料层的厚度过高，进而会增加活性离子从电解液扩散到负极极片内部活性材料颗粒的距离，使得二次电池容易在大倍率充电下析锂，同时距离增加也会增大电荷转移阻抗，影响二次电池的放电温升。在一些实施方式中，H为30μm、60μm、70μm、80μm、90μm、100μm、110μm、120μm、130μm、140μm、150μm、160μm、170μm、180μm、190μm、210μm或它们之间任意两者组成的范围。在一些实施方式中，50μm≤H≤200μm。
在一些实施方式中，负极活性材料的石墨化度G满足：92％≤G≤98％，例如G为93％、94％、95％、96％或97％。高石墨化度的负极活性材料具有高容量和高压实密度。
在一些实施方式中，负极活性材料的克容量Cap满足：Cap≥330mAh/g。在一些实施方式中，330mAh/g≤Cap≤500mAh/g。在一些实施方式中，330mAh/g≤Cap≤450mAh/g。在一些实施方式中，330mAh/g≤Cap≤400mAh/g。
在一些实施方式中，负极活性材料的比表面积BET满足：1.0m 2/g≤BET≤4.5m 2/g。在一些实施方式中，BET为1.3m 2/g、1.5m 2/g、1.7m 2/g、2.0m 2/g、2.3m 2/g、2.5m 2/g、2.7m 2/g、3.0m 2/g、3.3m 2/g、3.5m 2/g、3.7m 2/g、4.0m 2/g、4.3m 2/g或它们之间任意两者组成的范围。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，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：选取石墨化度在92.0％至95.0％的人造石墨混合鳞片石墨，其中鳞片石墨质量占比为10％至80％，然后再混合石墨质量的2％至6％的造孔剂例如碳酸钠，在上述混合物中最后加混合物质量的例如10％至20％比例的沥青进行包覆处理。将上述处理后的混合物进行球磨使颗粒聚合并球形化，球形化后造孔剂已经分布在颗粒内部。球磨结束后将其混合物在高温800℃至1200℃条件下进行沥青的碳化及造孔剂的分解，在高温下造孔剂分解并产生气体膨胀，颗粒发生变形并内部形成孔隙。
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℃1C放电至50％SOC时的阻抗DCR满足：DCR≤55.0mΩ。在一些实施方式中，二次电池在25℃3C放电时，温升T满足：T≤8.0℃。
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
选取石墨化度在93.5％的人造石墨100kg，混合50kg的鳞片石墨，然后再混合石墨质量的4kg的造孔剂碳酸钠，将混合物搅拌2h，搅拌均匀后加入20kg的沥青进行混合并进行球形化处理，即球磨6h，使颗粒聚合成球形。然后讲混合物置于1000℃高温下进行碳化及造孔剂分解处理，1000℃下保温时间为2h，完成后自然冷却到室温，即可得到实施例1的负极活性材料。
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，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
以厚度9μm的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5
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整鳞片石墨的比例、造孔剂的量、球形化时间及高温处理的温度等参数来制备相应的负极活性材料，沥青质量维持在人造石墨质量的五分之一，保温时间2h保持不变。具体制备参数如表a所示：
表a
Figure PCTCN2022115828-appb-000001
Figure PCTCN2022115828-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18
负极活性材料制备
负极活性材料的制备过程与实施例5类似，不同之处在于通过调整造孔剂的量来调整第一颗粒的数量占比，实施例11至实施例18的制备过程中造孔剂的量分别为4.2kg、4.3kg、4.4kg、4.5kg、4.6kg、4.7kg、4.8kg、5.0kg。
负极、正极、隔离膜、电解液以及锂离子电池的制备同实施例5。
实施例19至实施例23
负极活性材料制备
负极活性材料的制备过程与实施例14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层的ID/IG值,实施例19至实施例23的制备过程中高温处理温度分别为990℃、980℃、970℃、960℃、950℃。
负极、正极、隔离膜、电解液以及锂离子电池的制备同实施例14。
实施例24至实施例39
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球形化时间来调整负极极片的OI值以及孔隙率，实施例24至实施例39的制备过程中球形化的时间分别为5.3h、5.4h、5.5h、5.6h、5.7h、5.8h、5.9h、6.0h、6.1h、6.2h、6.3h、6.4h、6.5h、6.6h、6.7h、6.8h。
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40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38类似，不同之处在于人造石墨质量90kg保持不变，通过调整鳞片石墨的质量来调整负极活性材料的克容量和比表面积，实施例40至 实施例50的制备过程中鳞片石墨的质量分别为53kg、60kg、51kg、65kg、52kg、54kg、55kg、56kg、57kg、58kg、59kg。
负极、正极、隔离膜、电解液以及锂离子电池的制备同实施例38。
测试方法
1、最大费雷特直径以及具有孔的第一颗粒数量占比测试
负极极片氩离子抛光(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×6mm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。
孔结构截面的最大费雷特直径：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的200um×200um区域内，存在某些颗粒具有孔结构，颗粒的孔截面呈不规则形状，费雷特直径指沿一定方向测得的颗粒孔截面两边界平行线间的距离，最大距离即该孔截面的最大费雷特直径。对于一个颗粒中的孔截面，以两根平行线沿着孔截面外切线转动一周，其中在某一位置平行线距离最大的尺寸即为该孔结构截面的最大费雷特直径。依次测试负极活性材料层切面200μm×200μm区域所有颗粒孔截面的最大费雷特直径，然后计算得到平均值，即可得负极活性材料层厚度方向的截面上孔结构截面的最大费雷特直径平均值a。
具有孔的活性材料颗粒截面的最大费雷特直径：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的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，费雷特直径指沿一定方向测得的该颗粒截面两边界平行线间的距离，最大距离即该颗粒截面的最大费雷特直径。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切面200um×200um区域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厚度方向的截面上活性颗粒截面的最大费雷特直径b。
第一颗粒数量占第一颗粒和第二颗粒数量之和的占比：选取负极活性材料层的截面的200μm×200μm区域，计数该区域中总颗粒的数量，即为第一颗粒和第二颗粒数量之和。计数该区域中具有孔的活性材料颗粒的数量，即为第一颗粒的数量。
2、粉末压实密度测试
粉末压实密度的测试标准参照GB/T 24533-2009《锂离子电池石墨类负极材料》。具体测试方法为：
称量1.0000±0.0500g的负极活性材料样品置于测试模具(CARVER#3619(13mm)中，然后将样品置于测试设备中，测试设备为三思纵横UTM7305测试吨位0.3t、0.5t、0.75t、1.0t、1.5t、2.0t、2.5t、3.0t、4.0t、5.0t，升压速率为10mm/min，升压保持时间为30s，泄压速率为30mm/min，泄压保持时间为10s。
本申请中，粉末压实密度均为5t泄压后测得的压实密度。压实密度的计算公式为：压实密度＝材料质量/(材料受力面积×样品的厚度)。
3、负极活性材料层Raman测试
在负极活性材料层截面上选取一个大小为100μm×100μm的面积，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)扫描该面积内的颗粒，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/IG的频次得到正态分布图，统计这些颗粒的(ID/IG)max、(ID/IG)min，计算IDIG的平均值，即为负极活性材料层的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、负极极片的孔隙率测试
分析原理：气体置换法，应用气体驱赶的阿基米德原理(密度＝质量/体积)，利用小分子直径的惰性气体在一定条件下的波尔定律(PV＝nRT)，精确测量被测材料的真实体积，从而得到其真密度与孔隙率。
测试：极片裁切为10mm×10mm的小方块，称量样品质量。随后将其置于真密度测试仪器中(型号为AccuPycⅡ1340)，密闭测试系统，按程度通入氮气，通过检测样品室与膨胀室中气体的压力，再根据波尔定律(PV＝nRT)来计算真实体积V2。表观体积V1＝S×H(S为样品的表面积，H为样品的厚度)，然后计算孔隙率K，K＝(V1-V2)/V1×100％。
5、负极极片OI值测试
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》测试负极活性材料层的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。计算负极极片的C004/C110的比值，即为负极极片的OI值。
6、锂离子电池的DCR测试
在25℃满充，流程如下
(1)1C直流充电(DC)至2.5V；
(2)静置10min；
(3)1C恒流(CC)至3.6V,恒压(CV)至0.05C；
在0℃条件环境中放电，温度0℃
(4)静置60min
(5)0.1C DC 10s,1.5C DC 1s；
(6)静置10min；
(7)1C DC 8min；
(8)静置30min；
(9)重复步骤(5)至(8)11次；
(保护电压设为2.0V)，取50％SOC时电池的阻抗DCR，测试结束。
7、锂离子电池的放电温升测试
(1)调整炉温至25℃，静置30min；
(2)0.5C DC至2.5V；
(3)静置30min；
(4)1C CC至3.6V，CV至0.05C
(5)静置60min；
(5)测试电池表面中心位置温度T1
(6)3C DC至2.5V；
(7)静置1min；
(8)测试电池表面中心位置温度T2
(8)温升T＝T2-T1，测试结束。
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最大费雷特直径平均值aμm、该孔所在的第一颗粒的最大费雷特直径平均值bμm以及负极活性材料的5t压实密度C g/m 3对锂离子电池性能的影响。
表1
Figure PCTCN2022115828-appb-000003
从表1的数据可以看出，在第一颗粒中孔的最大费雷特直径平均值aμm，该孔所在的第一颗粒的最大费雷特直径平均值b，负极活性材料的5t压实密度C满足0.10≤a/b≤0.85、1.65≤C≤1.95，且0.89≤0.98×C-(a/b) 2≤1.86时，锂离子电池具有低的阻抗DCR和放电温升T。
表2示出了负极活性材料层的截面的200μm×200μm区域内，具有孔的第一颗粒数 量占第一颗粒和第二颗粒数量之和的比例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18的其余参数与实施例5相同。
表2
Figure PCTCN2022115828-appb-000004
从表2可以看出，第一颗粒的数量占该区域总颗粒数量的比例在40％值95％这个范围内，负极极片中孔隙结构发达且负极极片具有一定的机械强度，锂离子电池可以发挥出良好的放电温升性能。
表3示出了负极活性材料层的截面的200μm×200μm区域内，ID/IG比值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19至实施例23的其余参数与实施例14相同。
表3
Figure PCTCN2022115828-appb-000005
从表3的结果可以发现，ID/IG比值范围满足0.15至0.50时，锂离子电池的阻抗与温升性能得到了改善，相比于实施例14，实施例19至实施例23的阻抗DCR减小，放电 温升T降低，这表明合适的缺陷度有利于锂离子电池的性能发挥。
表4示出了负极极片的OI值、孔隙率K以及厚度H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24至实施例39的其余参数与实施例21相同。
表4
Figure PCTCN2022115828-appb-000006
从表4的结果可以看出，负极极片满足OI值≤25的条件，锂离子可以快速在负极极片中脱嵌，从而改善了锂离子电池的阻抗及放电温升性能。负极极片孔隙率K在15％至50％范围内时，锂离子的扩散阻抗低，极片的压实密度高，锂离子电池的放电性能得到有效改善。
表5示出了负极活性材料的石墨化度G、克容量Cap、比表面积BET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38相同。
表5
Figure PCTCN2022115828-appb-000007
如表5所示，负极活性材料的石墨化度G在93.0％至98.0％范围内，克容量Cap≥340mAh/g，同时BET≤2.5m 2/g时，锂离子电池的阻抗与温升性能得到了明显改善。
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具有孔的第一颗粒和除第一颗粒外的第二颗粒，
    其中，在所述负极活性材料层的截面的200μm×200μm区域内，所述第一颗粒满足：0.10≤a/b≤0.85且0.89≤0.98×C-(a/b) 2≤1.86；
    其中，aμm表示所述第一颗粒中孔的最大费雷特直径平均值；bμm表示第一颗粒的最大费雷特直径平均值；
    C g/cm 3表示所述负极活性材料在5t压力下的压实密度，其中，1.65≤C≤1.95。
  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(v)中的至少一者：
    (i)0.15≤a/b≤0.7；
    (ii)1.2≤0.98×C-(a/b) 2≤1.86；
    (iii)1.7≤C≤1.9；
    (iv)0.5≤a≤13；
    (v)4≤b≤25。
  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(vi)至(ix)中的至少一者：
    (vi)0.2≤a/b≤0.6；
    (vii)1.3≤0.98×C-(a/b) 2≤1.8；
    (viii)1≤a≤10；
    (ix)4.5≤b≤16。
  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，所述第一颗粒的数量占所述第一颗粒和第二颗粒数量之和的35％至95％；和/或
    在所述负极活性材料层的截面的200μm×200μm区域内，通过拉曼测试，所述负极活性材料层满足：0.1≤ID/IG≤0.5，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。
  5. 根据权利要求4所述的负极极片，其中，所述第一颗粒的数量占所述第一颗粒和第二颗粒数量之和的50％至80％；和/或，0.2≤ID/IG≤0.45。
  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(vi)至(viii)中的至少一者：
    (x)所述负极极片的取向度OI满足：OI≤35；
    (xi)所述负极极片的孔隙率K满足：15％≤K≤50％；
    (xii)所述负极极片的厚度H满足：H≤220μm。
  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(ix)至(xii)中的至少一者：
    (xiii)所述负极活性材料的石墨化度G满足：92％≤G≤98％；
    (xiv)所述负极活性材料的克容量Cap满足：Cap≥330mAh/g；
    (xv)所述负极活性材料的比表面积BET满足：1.0m 2/g≤BET≤4.5m 2/g；
    (xvi)所述负极活性材料包括石墨。
  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℃1C放电至50％SOC时的阻抗DCR满足：DCR≤55.0mΩ，和/或
    所述二次电池在25℃3C放电时，温升T满足：T≤8.0℃。
  10. 一种电子装置，包括权利要求8或9所述的二次电池。
PCT/CN2022/115828 2022-08-30 2022-08-30 负极极片、二次电池和电子装置 WO2024044963A1 (zh)

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