WO2024007184A1 - 二次电池和电子装置 - Google Patents

二次电池和电子装置 Download PDF

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Publication number
WO2024007184A1
WO2024007184A1 PCT/CN2022/104059 CN2022104059W WO2024007184A1 WO 2024007184 A1 WO2024007184 A1 WO 2024007184A1 CN 2022104059 W CN2022104059 W CN 2022104059W WO 2024007184 A1 WO2024007184 A1 WO 2024007184A1
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Prior art keywords
secondary battery
active material
material layer
negative electrode
graphite particles
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PCT/CN2022/104059
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English (en)
French (fr)
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冯鹏洋
唐佳
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宁德新能源科技有限公司
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Priority to CN202280057189.0A priority Critical patent/CN117916909A/zh
Priority to PCT/CN2022/104059 priority patent/WO2024007184A1/zh
Publication of WO2024007184A1 publication Critical patent/WO2024007184A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of energy storage, and specifically to a secondary battery and an electronic device.
  • secondary batteries need to have both high energy density and fast charging capabilities.
  • lithium-ion batteries natural graphite with a high gram capacity is often used as the negative electrode material.
  • natural graphite is soft and the surface porosity of the negative electrode decreases after rolling, resulting in poor ion conductivity and reduced wettability. Affects the rate performance of lithium-ion batteries, etc.
  • this application provides a secondary battery and an electronic device including the secondary battery.
  • the secondary battery of the present application has both high energy density and excellent rate performance.
  • the present application provides a secondary battery, which includes a negative electrode.
  • the negative electrode 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 graphite particles, wherein along the negative electrode active material In the thickness direction of the layer, the 10 ⁇ m area from the surface of the negative active material layer to the inside of the negative active material layer is the first area.
  • the secondary battery satisfies: 3 ⁇ m1/n1 ⁇ 18, 5% ⁇ n1 ⁇ 20%, where m1 represents the third The proportion of graphite particles in a region where the angle between the longest diameter of the graphite particles and the direction of the negative electrode current collector is 0° to 20°.
  • n1 represents the cross-sectional porosity of the first region.
  • the inventor of this application has found that during the secondary battery pressing process, the graphite particles in the first area of the negative active material layer are in direct contact with the roller that applies pressure.
  • the general natural graphite has a soft texture and is prone to occur under pressure conditions. Overpressure will in turn lead to a reduction in the porosity in the first region, affecting the infiltration of the electrolyte, thereby affecting the internal dynamic performance of the secondary battery.
  • a certain angle between the graphite particles and the current collector can ensure a short enough transmission path for active ions, which is conducive to the embedding of active ions.
  • appropriate porosity can maximize the energy density of secondary batteries.
  • the secondary battery satisfies: 5 ⁇ m1/n1 ⁇ 12 and/or 7% ⁇ n1 ⁇ 15%.
  • the negative active material can be further controlled.
  • the porosity of the layer shortens the transmission path of active ions, improves the energy density of the secondary battery and improves its rate performance.
  • 60% ⁇ m1 ⁇ 90% 60% ⁇ m1 ⁇ 90%.
  • m1 is within the above range, the transmission path of active ions can be shortened, the infiltration of the electrolyte can be improved, the rate performance of the secondary battery can be improved, and the energy density of the secondary battery can be increased.
  • 65% ⁇ m1 ⁇ 85% can further shorten the transmission path of active ions and improve the infiltration of the electrolyte, thereby improving the rate performance of the secondary battery and increasing its energy density.
  • the longest diameter of the graphite particles in the first region is 20 ⁇ m to 40 ⁇ m.
  • the longest diameter of the graphite particles in the first region is within the above range, it is beneficial to the insertion and extraction of active ions, and the active material layer has appropriate porosity, which can further improve the rate performance and energy density of the secondary battery.
  • the longest diameter of the graphite particles in the first region is 20 ⁇ m to 30 ⁇ m.
  • the longest diameter of the graphite particles in the first region is within the above range, it is more conducive to the insertion and extraction of active ions, Ensure that the active material layer has appropriate porosity, effectively improving the rate performance and energy density of the secondary battery.
  • the area outside the first area is the second area
  • the secondary battery satisfies: 1 ⁇ m2/n2 ⁇ 5, 40% ⁇ m2 ⁇ 70%
  • m2 represents the proportion of graphite particles in the second region where the angle between the longest diameter of the graphite particles and the direction of the negative electrode current collector is 0° to 20°
  • n2 represents the cross-sectional porosity of the second region.
  • the second area is less affected by rolling pressure than the first area.
  • the porosity of the second area is slightly larger than that of the first area and the graphite particles tend to be arranged more perpendicular to the direction of the current collector, which is beneficial to the infiltration of the electrolyte and the absorption of active ions. transmission, further improving the rate performance of secondary batteries and increasing their energy density.
  • the secondary battery satisfies: 2 ⁇ m2/n2 ⁇ 4 and/or 45% ⁇ m2 ⁇ 65%.
  • the negative active material layer is more It is conducive to the transmission of active ions and has appropriate porosity, reducing the internal impedance of the battery, effectively improving the rate performance of the secondary battery and increasing its energy density.
  • n2 10% ⁇ n2 ⁇ 50%.
  • n2 is within the above range, the infiltration of the electrolyte and the transmission of active ions can be improved, and the negative active material layer has appropriate porosity, improving the rate performance of the secondary battery.
  • 20% ⁇ n2 ⁇ 40% can further promote the transmission of active ions and improve the infiltration of electrolyte, improve the rate performance of the secondary battery and increase its energy density.
  • the longest diameter of the graphite particles in the second region is 5 ⁇ m to 25 ⁇ m.
  • the longest diameter of the graphite particles in the second region is within the above range, it is beneficial to the insertion and extraction of active ions, and the active material layer has appropriate porosity, which can further improve the rate performance and energy density of the secondary battery.
  • the longest diameter of the graphite particles in the second region is 5 ⁇ m to 20 ⁇ m, which is more conducive to the insertion and extraction of active ions and improves the rate performance of the secondary battery.
  • the negative electrode meets at least one of the following conditions (a) to (d): (a) the longest diameter of the graphite particles in the negative electrode active material layer is 5 ⁇ m to 40 ⁇ m; (b) the negative electrode active material layer The compacted density is 1.0g/cm 3 to 1.5g/cm 3 ; (c) the single-sided thickness of the negative active material layer is 30 ⁇ m to 80 ⁇ m; (d) the single-sided weight of the negative active material layer is 0.03 mg/mm 2 to 0.12 mg/mm 2 .
  • the longest diameter of the graphite particles in the negative active material layer is 5 ⁇ m to 40 ⁇ m.
  • the transmission path of active ions can be shortened and the electrolyte can be improved.
  • the infiltration improves the dynamic performance inside the secondary battery and ensures that the active material layer has appropriate porosity, thereby improving the rate performance and energy density of the secondary battery.
  • the longest diameter of the graphite particles in the negative active material layer is 5 ⁇ m to 30 ⁇ m.
  • the negative active material layer is more conducive to the transmission of active ions and has appropriate porosity, and the secondary battery has more High energy density and better rate performance.
  • the compacted density of the negative active material layer is 1.0g/cm 3 to 1.5g/cm 3 , and when the compacted density is within the above range, the first region and the second region have appropriate pores rate, which is beneficial to the infiltration of electrolyte and the deintercalation of active ions, making the secondary battery have high energy density and excellent rate performance.
  • the single-sided thickness of the negative active material layer is 30 ⁇ m to 80 ⁇ m.
  • the single-sided thickness of the negative active material layer is within the above range, it is beneficial to improve the fast charging performance of the secondary battery and ensure high volumetric energy density.
  • the single-sided weight of the negative active material layer is 0.03 mg/mm 2 to 0.12 mg/mm 2 .
  • the resistance during deintercalation of active ions can be reduced, the transmission path of ions can be shortened, and the active material layer has appropriate porosity, which can improve the rate performance and increase the rate of the secondary battery. its energy density.
  • the graphite includes natural graphite.
  • the natural graphite satisfies at least one of the following conditions (e) to (h) to: (e) the natural graphite includes primary particles; (f) the Dv50 of the natural graphite is 4 ⁇ m to 25 ⁇ m; (g) The powder compacted density of natural graphite is 1.7g/cm 3 to 2.05g/cm 3 ; (h) the specific surface area of natural graphite is 3m 2 /g to 6m 2 /g. According to some embodiments of the present application, natural graphite has a Dv50 of 4 ⁇ m to 25 ⁇ m. When the particle size of natural graphite is within the above range, it is beneficial to the deintercalation of active ions, improves the internal dynamic performance of the secondary battery, and enhances its rate performance.
  • the natural graphite has a powder compacted density of 1.7 to 2.05 g/cm 3 .
  • the powder compaction density is within the above range, it can not only ensure that the secondary battery has a higher energy density, but also maintain better dynamic properties and improve the rate performance of the secondary battery.
  • the specific surface area of natural graphite is 3 m 2 /g to 6 m 2 /g. Controlling the specific surface area within this range can not only reduce the consumption caused by active ions forming a film on the surface, but also maintain a good electrolyte infiltration speed, which can further improve the rate performance and energy density of the secondary battery.
  • the electrolyte infiltration time of the negative active material layer is ⁇ 70s, indicating that the electrolyte has a good infiltration effect in the negative active material layer, improves the internal dynamics of the secondary battery, and enhances its rate performance.
  • the present application provides an electronic device including the secondary battery of the first aspect.
  • the negative electrode of the secondary battery provided by this application includes a specific negative active material layer, so that the secondary battery has both high energy density and excellent rate performance.
  • Figure 1 is a schematic diagram of the angle between the longest diameter of graphite particles and the direction of the negative electrode current collector.
  • 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 secondary battery, which includes a negative electrode.
  • the negative electrode 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 graphite particles, wherein along the negative electrode active material In the thickness direction of the layer, the 10 ⁇ m area from the surface of the negative active material layer to the inside of the negative active material layer is the first area.
  • the secondary battery satisfies: 3 ⁇ m1/n1 ⁇ 18, 5% ⁇ n1 ⁇ 20%, where m1 represents the third The proportion of graphite particles in a region where the angle between the longest diameter of the graphite particles and the direction of the negative electrode current collector is 0° to 20°.
  • n1 represents the cross-sectional porosity of the first region.
  • the inventor of this application has found that during the secondary battery pressing process, the graphite particles in the first area of the negative active material layer are in direct contact with the roller that applies pressure.
  • the general natural graphite has a soft texture and is prone to occur under pressure conditions. Overpressure will in turn lead to a reduction in the porosity in the first region, affecting the infiltration of the electrolyte, thereby affecting the internal dynamic performance of the secondary battery.
  • a certain angle between the graphite particles and the current collector can ensure a short enough transmission path for active ions, which is conducive to the embedding of active ions.
  • appropriate porosity can maximize the volumetric energy density of the secondary battery. .
  • the surface of the negative electrode active material layer means the surface of the negative electrode active material layer away from the current collector.
  • m1/n1 is 3.5, 4, 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, 15, 15.5, 16, 16.5, 17, 17.5 or a range consisting of any two of these values.
  • the cross-sectional porosity value n1 of the first region is 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%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19 %, 19.5%, or a range consisting of any two of these values. According to some embodiments of the present application, 7% ⁇ n1 ⁇ 15%.
  • the transmission path of active ions can be shortened, which is conducive to the embedding of active ions and the infiltration of electrolyte, and appropriate porosity can maximize the volumetric energy density of the secondary battery.
  • cross-sectional porosity refers to the porosity of the cross-sectional area of the negative active material layer perpendicular to the direction of the negative current collector.
  • m1 refers to the quantity percentage.
  • m1 is 63%, 65%, 67%, 69%, 70%, 73%, 75%, 77%, 79%, 80%, 83%, 85%, 87%, 89%, or A range consisting of any two of these values.
  • the rate performance reduces the volumetric energy density of the secondary battery accordingly; when m1 is too low, the porosity of the first region is high, which increases the contact area between the electrolyte and the active material, causing side reactions between the electrolyte and the active material, and The electrolyte consumption increases.
  • m1 is within the above range, the secondary battery has better rate performance and higher volumetric energy density.
  • the longest diameter of the graphite particles in the first region is 20 ⁇ m to 40 ⁇ m.
  • the longest diameter of the graphite particles is 21 ⁇ m, 22 ⁇ m, 23 ⁇ m, 24 ⁇ m, 25 ⁇ m, 26 ⁇ m, 27 ⁇ m, 28 ⁇ m, 29 ⁇ m, 30 ⁇ m, 31 ⁇ m, 32 ⁇ m, 33 ⁇ m, 34 ⁇ m, 35 ⁇ m, 36 ⁇ m, 37 ⁇ m, 38 ⁇ m, 39 ⁇ m or A range consisting of any two of these values.
  • the longest diameter of the graphite particles in the first region is 20 ⁇ m to 30 ⁇ m. When the longest diameter of the graphite particles is within the above range, it is beneficial to the transmission of active ions, and the active material layer has appropriate porosity, which can further improve the rate performance and energy density of the secondary battery.
  • the "longest diameter of graphite particles” refers to the longest distance between any two points on the graphite particles in the field of view when observing the negative active material layer CP sample using a scanning electron microscope (SEM).
  • the cross-sectional porosity and the longest length of graphite particles can be adjusted by selecting graphite particle raw materials such as soft/hard raw materials, granulating/shaping the graphite particle raw materials, or controlling the cold pressing pressure during pole piece production. The angle between the diameter and the direction of the negative electrode current collector.
  • the graphite particle raw material can be selected through the selection of soft/hard raw materials.
  • the greater the cold pressing pressure the smaller the graphite particles will be.
  • the above methods can adjust the angle between the longest diameter of the graphite particles and the direction of the negative electrode current collector and the cross-sectional porosity of the negative electrode active material layer.
  • the area outside the first area is the second area
  • the secondary battery satisfies: 1 ⁇ m2/n2 ⁇ 5, 40% ⁇ m2 ⁇ 70%
  • m2 represents the proportion of graphite particles in the second region where the angle between the longest diameter of the graphite particles and the direction of the negative electrode current collector is 0° to 20°
  • n2 represents the cross-sectional porosity of the second region.
  • the second area is less affected by rolling than the first area, so the cross-sectional porosity of the second area is slightly larger than that of the first area, and the graphite particles in the second area tend to be arranged perpendicular to the direction of the current collector, which is beneficial to electrolysis.
  • the infiltration of liquid and the transmission of active ions can further improve the rate performance and energy density of secondary batteries.
  • m2/n2 is a range consisting of 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or any two of these values.
  • m2 is 43%, 45%, 47%, 49%, 50%, 53%, 55%, 57%, 59%, 60%, 63%, 65%, 67%, 69%, or A range consisting of any two of these values.
  • m2/n2 and m2 are within the above range, the infiltration of the electrolyte and the transmission of active ions can be improved, and the active material layer has appropriate porosity, improving the rate performance of the secondary battery and increasing its energy density.
  • m2 is the quantity percentage.
  • n2 is 10%, 12%, 15%, 16%, 18%, 20%, 22%, 25%, 27%, 29%, 30%, 33%, 35%, 37%, A range consisting of 39%, 40%, 43%, 45%, 47%, 49%, or any two of these values.
  • 20% ⁇ n2 ⁇ 40% When n2 is within the above range, it can further improve the infiltration of the electrolyte and facilitate the transmission of active ions, ensure that the active material layer has appropriate porosity, improve the rate performance of the secondary battery, and increase its energy density.
  • the longest diameter of the graphite particles in the second region is 5 ⁇ m to 25 ⁇ m.
  • the longest diameter of the graphite particles is 5 ⁇ m, 8 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, 17 ⁇ m, 18 ⁇ m, 19 ⁇ m, 20 ⁇ m, 21 ⁇ m, 22 ⁇ m, 23 ⁇ m, 24 ⁇ m, or these A range consisting of any two of the values.
  • the longest diameter of the graphite particles in the second region is 5 ⁇ m to 20 ⁇ m. When the longest diameter of the graphite particles is within the above range, it is more conducive to the insertion and extraction of active ions, ensuring that the active material layer has appropriate porosity, which can further improve the energy density and rate performance of the secondary battery.
  • the longest diameter of the graphite particles in the negative active material layer is 5 ⁇ m to 40 ⁇ m.
  • the major diameter of the graphite particles is 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, 17 ⁇ m, 18 ⁇ m, 19 ⁇ m, 20 ⁇ m, 21 ⁇ m, A range consisting of 22 ⁇ m, 23 ⁇ m, 24 ⁇ m, 25 ⁇ m, 26 ⁇ m, 27 ⁇ m, 28 ⁇ m, 29 ⁇ m, 30 ⁇ m, 31 ⁇ m, 32 ⁇ m, 33 ⁇ m, 34 ⁇ m, 35 ⁇ m, 36 ⁇ m, 37 ⁇ m, 38 ⁇ m, 39 ⁇ m, or any two of these values.
  • the longest diameter of the graphite particles in the negative active material layer is 5 ⁇ m to 30 ⁇ m.
  • the transmission path of active ions in the negative active material layer can be shortened, the infiltration of the electrolyte can be improved, the dynamic performance inside the secondary battery can be improved, and the active material layer can be guaranteed With appropriate porosity, it can improve the rate performance and energy density of secondary batteries.
  • the compacted density of the negative active material layer is 1.0g/cm 3 to 1.5g/cm 3 .
  • the first region and the second region have appropriate porosity, which is beneficial to the infiltration of the electrolyte and the deintercalation of active ions, so that the secondary battery has high energy density and excellent rate. performance.
  • the single-sided thickness of the negative active material layer is 30 ⁇ m to 80 ⁇ m. In some embodiments, the single-sided thickness of the negative active material layer is a range of 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, 55 ⁇ m, 60 ⁇ m, 65 ⁇ m, 70 ⁇ m, 75 ⁇ m, or any two of these values.
  • the thickness of the negative active material layer is within the above range, it is more conducive to the infiltration of the electrolyte and the transmission of active ions, and reduces the transmission impedance of active ions, which not only helps improve the fast charging performance of the secondary battery, but also ensures its High energy density.
  • the thickness of one side of the negative electrode active material layer refers to the thickness of the negative electrode active material layer on one side of the negative electrode current collector, that is, the thickness of one side of the negative electrode active material layer.
  • the double-sided thickness of the negative active material layer is 60 ⁇ m to 160 ⁇ m.
  • the single-sided weight of the negative active material layer is 0.03 mg/mm 2 to 0.12 mg/mm 2 .
  • the single-sided weight of the negative active material layer is 0.05mg/mm 2 , 0.06mg/mm 2 , 0.07mg/mm 2 , 0.08mg/mm 2 , 0.09mg/mm 2 , 0.1mg/mm 2 , 0.11 mg/mm 2 or a range consisting of any two of these values.
  • the weight of one side of the negative active material layer is too low, the thickness of one side of the negative active material layer is too small, and the pole piece is easily damaged during the pressing process; when the weight of one side of the negative active material layer is too high, the active ions The transmission path becomes longer and the intercalation and removal resistance increases, which in turn leads to lithium precipitation.
  • the single-sided weight of the negative active material layer is within the above range, the resistance during deintercalation of active ions can be reduced, the transmission path of ions can be shortened, and the active material layer has appropriate porosity, which can improve the rate performance and increase the rate of the secondary battery. its energy density.
  • the weight of one side of the negative electrode active material layer refers to the weight of the negative electrode active material layer on one side of the negative electrode current collector, that is, the weight of one side of the negative electrode active material layer.
  • the graphite includes natural graphite.
  • natural graphite includes primary particles.
  • primary natural graphite particles refer to spheroidized and coated natural graphite, which has not undergone granulation treatment.
  • the preparation process of natural graphite includes: selecting natural flake graphite for crushing, and weighing natural flake graphite powder with a mass fraction of 50% to 90% based on the total mass of natural flake graphite and binder.
  • the particle size Dv50 of natural flake graphite powder is 3 ⁇ m to 15 ⁇ m; based on the total mass of natural flake graphite and binder, weigh the binder with a mass fraction of 10% to 50%, and the binder includes a softening point of 120 At least one of asphalt, phenolic resin or epoxy resin between 120°C and 300°C, where the asphalt includes high-purity asphalt with a softening point between 120°C and 300°C.
  • Material A is mixed with a certain amount of coating agent.
  • the mixing mass ratio of material A: coating agent is 95:5.
  • the coating agent includes at least one of asphalt, kerosene, resin or graphene.
  • natural graphite has a Dv50 of 4 ⁇ m to 25 ⁇ m.
  • natural graphite has a Dv50 of 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, 17 ⁇ m, 18 ⁇ m, 19 ⁇ m, 20 ⁇ m, 21 ⁇ m, 22 ⁇ m, 23 ⁇ m, 24 ⁇ m. or a range of any two of these values.
  • the particle size of natural graphite is within the above range, it is conducive to the deintercalation of active ions, can reduce the resistance during the deintercalation of active ions, shorten the transmission path of ions and lengthen, and the active material layer has appropriate porosity, improving rate performance of secondary batteries and improve their energy density.
  • Dv50 means that in the volume-based particle size distribution of natural graphite, 50% of the particles have a particle size smaller than this value.
  • the natural graphite has a powder compacted density of 1.7 to 2.05 g/cm 3 .
  • the natural graphite has a powder compacted density of 1.75g/cm 3 , 1.8g/cm 3 , 1.85g/cm 3 , 1.9g/cm 3 , 1.95g/cm 3 , 2.00g/cm 3 or A range consisting of any two of these values.
  • the powder compaction density is within the above range, it can not only ensure a higher volume energy density, but also maintain better internal dynamic properties and improve the rate performance of the secondary battery.
  • natural graphite has a specific surface area (BET) of 3 m 2 /g to 6 m 2 /g. In some embodiments, natural graphite has a specific surface area of 3.5 m 2 /g, 4 m 2 /g, 4.5 m 2 /g, 5 m 2 /g, or 5.5 m 2 /g. Controlling the specific surface area within this range can not only reduce the consumption caused by active ions forming a film on the surface, but also maintain a good electrolyte infiltration speed, which can further improve the rate performance and energy density of the secondary battery.
  • BET specific surface area
  • the electrolyte infiltration time of the negative active material layer is ⁇ 70 s.
  • the electrolyte infiltration time of the negative active material layer is the time when 5 mL of electrolyte is dropped onto the surface of the negative active material layer with a length of 50 mm and a width of 50 mm and the electrolyte completely disappears from the surface of the active material layer.
  • the electrolyte infiltration time of the negative active material layer is ⁇ 70s, it indicates that the electrolyte has a good infiltration effect on the negative active material layer, which can improve the internal dynamics of the secondary battery and enhance its rate performance.
  • 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 first aspect of the present application.
  • the electronic equipment or device of the present application is not particularly limited.
  • 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 disc transceiver
  • calculator memory card
  • portable recorder radio
  • backup power supply motor, automobile, motorcycle, power-assisted bicycle, bicycle , lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.
  • Preparation of natural graphite Select the raw material natural flake graphite for crushing. Based on the total mass of natural flake graphite and binder pitch, weigh the natural flake graphite powder with a mass fraction of 50% to 90% and a particle size Dv50 of 3 ⁇ m to 15 ⁇ m. , based on the total mass of natural flake graphite and binder asphalt, weigh the binder asphalt powder with a mass fraction of 10% to 50%, and conduct the above weighed natural flake graphite powder and binder asphalt powder. Mix, where the asphalt selects high-purity asphalt with a softening point of 200°C. The uniformly mixed powder is placed in the reactor while heating and stirring. The heating temperature is controlled at 800°C.
  • Material A is mixed with a certain amount of coating agent.
  • the mixing mass ratio of material A: coating agent is 95:5.
  • graphene is selected as the coating agent. After mixing evenly, it is placed in a high-temperature carbonization furnace and calcined at 1150°C for 4 hours to obtain Material B is the natural graphite used in the negative active material layer of this application.
  • the natural graphite, styrene-butadiene rubber (abbreviated as SBR) and sodium carboxymethyl cellulose (abbreviated as CMC) prepared above are fully stirred and mixed in a deionized water solvent according to a weight ratio of 98:1:1 to form a uniform
  • SBR styrene-butadiene rubber
  • CMC sodium carboxymethyl cellulose
  • Examples 1 to 17 and Comparative Example 1 adjust the cross-sectional porosity of the negative active material layer and the longest length of the graphite particles by controlling the OI value of the raw material natural flake graphite, the mass fraction of the binder asphalt powder, and the cold pressing pressure of the negative electrode sheet.
  • the angle between the diameter and the direction of the negative electrode current collector is as shown in Table A below.
  • a polyethylene porous polymer film with a thickness of 7 ⁇ m was used as the isolation membrane.
  • LiPF 6 In a dry argon atmosphere, add LiPF 6 to a solvent composed of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) in a weight ratio of 1:1:1 and mix evenly.
  • concentration of LiPF 6 is 1.15 mol/L
  • fluoroethylene carbonate and adiponitrile then add fluoroethylene carbonate and adiponitrile, and mix evenly to obtain an electrolyte.
  • the weight content of fluoroethylene carbonate is 3%
  • the weight content of adiponitrile is 2%.
  • 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.
  • Negative ion grinding (CP) sample preparation process Disassemble the lithium-ion battery to obtain the negative electrode piece, scrape off the negative active material layer with a scraper, cut the negative active material layer into a size of 0.5cm ⁇ 1cm, and use conductive glue to cut the The negative active material layer is pasted on a 1cm ⁇ 1.5cm silicon wafer carrier, and then argon ion polishing (parameter: 8KV acceleration voltage, 4h for each sample) is used to process one end of the negative active material layer to obtain the negative active material.
  • Layer CP sample Disassemble the lithium-ion battery to obtain the negative electrode piece, scrape off the negative active material layer with a scraper, cut the negative active material layer into a size of 0.5cm ⁇ 1cm, and use conductive glue to cut the The negative active material layer is pasted on a 1cm ⁇ 1.5cm silicon wafer carrier, and then argon ion polishing (parameter: 8KV acceleration voltage, 4h for each sample) is used to
  • 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.
  • Use SEM negative electrode active material layer CP sample obtain 50 cross-sectional pictures, count the angles between the longest diameter of all graphite particles in the thickness section of the negative electrode active material layer and the direction of the current collector, and then use image software to process it to obtain the negative electrode active material layer
  • Second area The angle between the longest diameter of all graphite particles in the thickness section and the direction of the current collector, and then use image software to count and calculate the angle between the longest diameter of all graphite particles in the field of view in different areas and the direction of the current collector to get the average value , obtain data on the angle between the longest diameter of graphite particles in different areas and the direction of the current collector.
  • test standard for powder compaction density refers to GB/T 24533-2009 "Graphite Anode Materials for Lithium-Ion Batteries”.
  • specific test methods are:
  • the test equipment is Sansi Zongheng UTM7305 test tonnage 0.3t, 0.5t, 0.75t, 1.0 t, 1.5t, 2.0t, 2.5t, 3.0t, 4.0t, 5.0t, the pressure increase rate is 10mm/min, the pressure increase holding time is 30s, the pressure relief rate is 30mm/min, and the pressure relief holding time is 10s.
  • the compacted density of the powder is the compacted density measured after 5t of pressure relief.
  • the particle size testing method refers to GB/T 19077-2016.
  • the specific process is:
  • Particle size measurement is accomplished by measuring the intensity of scattered light when a laser beam passes through a dispersed particle sample during the test. The data are then used analytically to calculate the particle size distribution that forms this scattering spectrum. The refractive index of the particles used in the test is 1.8. One sample is tested three times, and the particle size is finally taken as the average of the three tests.
  • the lithium-ion battery was connected to the Bio-Logic VMP3B electrochemical workstation produced by the French Biolog company for testing.
  • the frequency range was 30mHz to 50kHz and the amplitude was 5mV.
  • the data is analyzed using the impedance complex plane diagram to obtain the lithium ion liquid phase transfer impedance (Rion).
  • 2C discharge capacity retention rate 2C discharge capacity/0.1C discharge capacity ⁇ 100%.
  • the DCR mentioned in this application refers to the DC resistance of the lithium-ion battery at 10% state of charge (SOC).
  • EIS test steps Connect the lithium-plated three-electrode battery to the Bio-Logic VMP3B electrochemical workstation produced by the French company Biolog for testing.
  • the frequency range for the test is 30mHz to 50kHz, and the amplitude is 5mV.
  • After collecting the data The data were analyzed using the impedance complex plane diagram to obtain the Rct data.
  • Judgment of the degree of lithium evolution Judgment based on the state of the fully charged and disassembled negative electrode.
  • the entire negative electrode is golden yellow and the gray area is ⁇ 2%, it is judged that lithium is not deposited; when most of the negative electrode is golden yellow, but there is Gray can be observed in some parts, and the gray area is between 2% and 20%, then it is judged as slight lithium precipitation; when the negative electrode part is gray, but some golden yellow can still be observed, and the gray area is between 20% and 60%, then it is considered as slight lithium precipitation. It is judged to be lithium precipitation; when most of the negative electrode appears gray and the gray area is >60%, it is judged to be severe lithium precipitation.
  • the discharge capacity of the lithium-ion battery is D mAh
  • the platform voltage of the lithium-ion battery is UV
  • the length, width and thickness of the lithium-ion battery are L mm/W mm/H mm respectively.
  • the volume energy density VED D ⁇ U/(L ⁇ W ⁇ H) ⁇ 1000.
  • Table 1 shows the impact of the cross-sectional porosity of the negative active material layer and the proportion of graphite particles whose angle between the longest diameter of the graphite particles and the direction of the negative electrode current collector is 0° to 20° on the performance of the lithium ion battery.
  • the cross-sectional porosity of the first region is n1
  • the proportion of graphite particles in the first region where the angle between the longest diameter of the graphite particles and the direction of the negative electrode current collector is 0° to 20° is m1
  • the cross-sectional porosity of the second region The rate is n2
  • the proportion of graphite particles in the second region where the angle between the longest diameter of the graphite particles and the direction of the negative electrode current collector is 0° to 20° is m2.
  • the longest diameter of the graphite particles in the first region is the same, both 31 ⁇ m; the longest diameter of the graphite particles in the second region is the same, both 31 ⁇ m.
  • the compacted density of the negative active material layer is the same, both 1.3g/cm 3 ; the single-sided thickness of the negative active material layer is the same, both 38 ⁇ m; The single-sided weight is the same, 0.05 mg/mm 2 .
  • Examples 1 to 10 and Comparative Example 1 the Dv50 of natural graphite is the same, both 22 ⁇ m. In Examples 11 to 13, the Dv50 of natural graphite is the same, both 22 ⁇ m.
  • the transmission path of lithium ions can be shortened and the internal dynamic performance of the lithium ion battery can be improved. , further improving the rate performance of lithium-ion batteries so that they have higher energy density.
  • Table 2 shows the effects of the compacted density of the active material layer, the longest diameter of the graphite particles, the thickness of one side of the negative active material layer, and the weight of one side on the performance of the lithium ion battery. Except for the parameters listed in Table 2, the remaining parameters of Examples 18 to 34 are the same as those of Example 7.
  • Table 3 shows the effects of natural graphite particle size, powder compaction density and BET on lithium-ion battery performance. Except for the parameters listed in Table 3, the remaining parameters of Examples 35 to 44 are the same as those of Example 7.
  • Example 35 to Example 44 As shown in Example 7, Example 35 to Example 44, as the particle size of graphite particles increases, the infiltration time required for the electrolyte increases, indicating that the speed of lithium ion diffusion decreases. On the other hand, as the specific surface area increases Reduced, the consumption of active lithium required for film formation is reduced, and the efficiency of lithium-ion batteries is improved for the first time. Therefore, by adjusting the graphite particle size, powder compaction density and specific surface area, the lithium-ion battery can further have lower liquid phase transmission impedance and higher first efficiency, and improve its rate performance.

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Abstract

提供一种二次电池，该二次电池包括负极，负极包括负极集流体和设置于负极集流体上的负极活性物质层，负极活性物质层包括石墨颗粒，其中，沿负极活性物质层的厚度方向，负极活性物质层表面至负极活性物质层内部10μm的区域为第一区域，二次电池满足：3≤m1/n1≤18，5％≤n1≤20％，其中，m1表示第一区域中石墨颗粒最长径与负极集流体方向的夹角为0°至20°的石墨颗粒的占比，n1表示第一区域的截面孔隙率。本申请的二次电池同时具有高的能量密度和优异的倍率性能。还提供包括该二次电池的电子装置。

Description

二次电池和电子装置 技术领域
本申请涉及储能领域，具体涉及一种二次电池和电子装置。
背景技术
近年来，随着电子产品和电动汽车的快速发展，对二次电池的要求越来越高，尤其是需要二次电池同时具备较高的能量密度以及快充能力。以锂离子电池为例，常使用具有较高克容量的天然石墨作为负极材料，但天然石墨质软，负极在经过辊压后表层孔隙率降低，导致离子传导变差的同时浸润性能降低，进而影响锂离子电池的倍率性能等。
发明内容
针对现有技术的不足，本申请提供了一种二次电池及包括该二次电池的电子装置。本申请的二次电池同时具有高的能量密度和优异的倍率性能。
在第一方面，本申请提供一种二次电池，其包括负极，负极包括负极集流体和设置于负极集流体上的负极活性物质层，负极活性物质层包括石墨颗粒，其中，沿负极活性物质层的厚度方向，负极活性物质层表面至负极活性物质层内部10μm的区域为第一区域，二次电池满足：3≤m1/n1≤18，5％≤n1≤20％，其中，m1表示第一区域中石墨颗粒最长径与负极集流体方向的夹角为0°至20°的石墨颗粒的占比，n1表示第一区域的截面孔隙率。本申请的发明人研究发现，在二次电池压制过程中，负极活性物质层第一区域内的石墨颗粒与施加压力的辊直接接触，而一般的天然石墨质地较软，在压力条件下容易发生过压，进而导致第一区域内孔隙率降低，影响电解液的浸润，从而影响二次电池内部动力学性能。一方面，石墨颗粒与集流体呈一定的夹角能够保证足够短的活性离子的传输路径，有利于活性离子的嵌入，另一方面合适的孔隙率能够最大程度地提升二次电池的能量密度。
根据本申请的一些实施方式，二次电池满足：5≤m1/n1≤12和/或7％≤n1≤15％，当m1/n1和/或n1满足上述范围时，可进一步控制负极活性物质层的孔隙率，缩短活性离子的传输路径，提高二次电池的能量密度和提升其倍率性能。
根据本申请的一些实施方式，60％≤m1≤90％。m1在上述范围内时，可缩短活性离子的传输路径，提高电解液的浸润，提升二次电池的倍率性能以及提高二次电池的能量密度。
根据本申请的一些实施方式，65％≤m1≤85％，可进一步缩短活性离子的传输路径和改善电解液的浸润，提升二次电池的倍率性能及提高其能量密度。
根据本申请的一些实施方式，第一区域中石墨颗粒最长径为20μm至40μm。当第一区域中石墨颗粒最长径在上述范围内时，有利于活性离子的嵌入和脱出，且活性物质层具有合适的孔隙率，可进一步提升二次电池的倍率性能和提高其能量密度。
根据本申请的一些实施方式，所述第一区域中石墨颗粒最长径为20μm至30μm，当第一区域中石墨颗粒最长径在上述范围内时，更有利于活性离子的嵌入和脱出，保证活性物质层具有合适的孔隙率，有效提升二次电池的倍率性能和提高其能量密度。
根据本申请的一些实施方式，沿负极活性物质层的厚度方向，第一区域之外的区域为第二区域，二次电池满足：1≤m2/n2≤5，40％≤m2≤70％，其中，m2表示第二区域中石墨颗粒最长径与负极集流体方向的夹角为0°至20°的石墨颗粒的占比，n2表示第二区域的截面孔隙率。第二区域受辊压的影响低于第一区域，因此第二区域的孔隙率稍大于第一区域且石墨颗粒更趋于垂直集流体方向排布，进而有利于电解液的浸润和活性离子的传输，进一步提升二次电池的倍率性能和提高其能量密度。
根据本申请的一些实施方式，二次电池满足：2≤m2/n2≤4和/或45％≤m2≤65％，当m2/n2和/或m2满足上述范围时，负极活性物质层更有利于活性离子传输及具有合适孔隙率，降低电池内部阻抗，有效提升二次电池的倍率性能和提高其能量密度。
根据本申请的一些实施方式，10％≤n2≤50％。n2在上述范围内时，可提高电解液的浸润和活性离子的传输，且负极活性物质层具有合适的孔隙率，提升二次电池的倍率性能。
根据本申请的一些实施方式，20％≤n2≤40％，可进一步促进活性离子传输和改善电解液的浸润，提升二次电池的倍率性能及提高其能量密度。
根据本申请的一些实施方式，第二区域中石墨颗粒最长径为5μm至25μm。当第二区域中石墨颗粒最长径在上述范围内时，有利于活性离子的嵌入和脱出，且活性物质层具有合适的孔隙率，可进一步提升二次电池的倍率性能和提高其能量密度。
根据本申请的一些实施方式，所述第二区域中石墨颗粒最长径为5μm至20μm，此时更有利于活性离子的嵌入和脱出，改善二次电池的倍率性能。
根据本申请的一些实施方式，负极满足如下条件(a)至(d)中的至少一者：(a) 负极活性物质层中石墨颗粒最长径为5μm至40μm；(b)负极活性物质层的压实密度为1.0g/cm 3至1.5g/cm 3；(c)负极活性物质层的单面厚度为30μm至80μm；(d)负极活性物质层的单面重量为0.03mg/mm 2至0.12mg/mm 2。
根据本申请的一些实施方式，负极活性物质层中石墨颗粒最长径为5μm至40μm，负极活性物质层中石墨颗粒最长径在上述范围内时，可缩短活性离子的传输路径，提高电解液的浸润，改善二次电池内部的动力学性能，且保证活性物质层具有合适的孔隙率，提升二次电池的倍率性能和提高其能量密度。
根据本申请的一些实施方式，所述负极活性物质层中石墨颗粒最长径为5μm至30μm，此时负极活性物质层更有利于活性离子的传输及具有合适的孔隙率，二次电池具有更高的能量密度和更优的倍率性能。
根据本申请的一些实施方式，负极活性物质层的压实密度为1.0g/cm 3至1.5g/cm 3，当压实密度在上述范围内时，第一区域和第二区域具有合适的孔隙率，进而有利于电解液的浸润和活性离子的脱嵌，使得二次电池具有高的能量密度和优异的倍率性能。
根据本申请的一些实施方式，负极活性物质层的单面厚度为30μm至80μm。当负极活性物质层的单面厚度在上述范围内时，既有利于提升二次电池的快充性能，又能够保证高的体积能量密度。
根据本申请的一些实施方式，负极活性物质层的单面重量为0.03mg/mm 2至0.12mg/mm 2。负极活性物质层的单面重量在上述范围内时，可减小活性离子脱嵌时的阻力，缩短离子的传输路径，且活性物质层具有合适的孔隙率，改善二次电池的倍率性能和提高其能量密度。
根据本申请的一些实施方式，石墨包括天然石墨。
根据本申请的一些实施方式，天然石墨满足如下条件(e)至(h)至的至少一者：(e)天然石墨包括一次颗粒；(f)天然石墨的Dv50为4μm至25μm；(g)天然石墨的粉末压实密度为1.7g/cm 3至2.05g/cm 3；(h)天然石墨的比表面积为3m 2/g至6m 2/g。根据本申请的一些实施方式，天然石墨的Dv50为4μm至25μm。天然石墨的颗粒粒径在上述范围内时，有利于活性离子的脱嵌，改善二次电池内部的动力学性能，提升其倍率性能。
根据本申请的一些实施方式，天然石墨的粉末压实密度为1.7g/cm 3至2.05g/cm 3。粉末压实密度在上述范围内时，既能保证二次电池具有较高的能量密度，又能保持较好的动力学性能，提升二次电池的倍率性能。
根据本申请的一些实施方式，天然石墨的比表面积为3m 2/g至6m 2/g。将比表面积控 制在该范围内，既能减少因活性离子在表面成膜带来的消耗，又能保持较好的电解液浸润速度，可以进一步提升二次电池的倍率性能和提高其能量密度。
根据本申请的一些实施方式，负极活性物质层的电解液浸润时间≤70s，说明电解液在负极活性物质层具有较好的浸润效果，改善二次电池内部动力学，提升其倍率性能。
在第二方面，本申请提供了一种电子装置，其包括第一方面的二次电池。
本申请提供的二次电池的负极包括特定的负极活性物质层，使得二次电池同时具有高的能量密度和优异的倍率性能。
附图说明
图1是石墨颗粒最长径与负极集流体方向的夹角示意图。
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、二次电池
在第一方面，本申请提供一种二次电池，其包括负极，负极包括负极集流体和设置于负极集流体上的负极活性物质层，负极活性物质层包括石墨颗粒，其中，沿负极活性物质层的厚度方向，负极活性物质层表面至负极活性物质层内部10μm的区域为第一区域，二次电池满足：3≤m1/n1≤18，5％≤n1≤20％，其中，m1表示第一区域中石墨颗粒最长径与负极集流体方向的夹角为0°至20°的石墨颗粒的占比，n1表示第一区域的截面孔隙率。本申请的发明人研究发现，在二次电池压制过程中，负极活性物质层第一区域内的石墨颗粒与施加压力的辊直接接触，而一般的天然石墨质地较软，在压力条件下容易发生过压，进而导致第一区域内孔隙率降低，影响电解液的浸润，从而影响二次电池内部动力学性能。一方面，石墨颗粒与集流体呈一定的夹角能够保证足够短的活性离子的传输路径，有利于活性离子的嵌入，另一方面合适的孔隙率能够最大程度地提升二次电池的体积能量密度。
本申请中，“负极活性物质层的表面”表示远离集流体的负极活性物质层的表面。
根据本申请的一些实施方式，m1/n1为3.5、4、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、15、15.5、16、16.5、17、17.5或这些值中任意两者组成的范围。根据本申请的一些实施方式，5≤m1/n1≤12。当m1/n1满足上述范围时，可以缩短活性离子的传输路径，有利于活性离子的嵌入和电解液的浸润，提高二次电池内部的动力学，改善二次电池的倍率性能。
根据本申请的一些实施方式，第一区域的截面孔隙率值n1为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％、15％、15.5％、16％、16.5％、17％、17.5％、18％、18.5％、19％、19.5％或这些值中任意两者组成的范围。根据本申请的一些实施方式，7％≤n1≤15％。当截面孔隙率在上述范围时，可缩短活性离子的传输路径，有利于活性离子的嵌入和电解液的浸润，且合适的孔隙率能够最大程度地提升二次电池的体积能量密度。
本申请中，“截面孔隙率”为负极活性物质层垂直负极集流体方向的切面(即截面)区域的孔隙率。
根据本申请的一些实施方式，60％≤m1≤90％。本申请中“m1”为数量百分含量。在一些实施方式中，m1为63％、65％、67％、69％、70％、73％、75％、77％、79％、80％、83％、85％、87％、89％或这些值中任意两者组成的范围。根据本申请的一些实施方式，65％≤m1≤85％。m1过高时，第一区域的孔隙率较低，使得活性离子嵌锂通道堵塞，进 而使得二次电池阻抗增大，且会加剧副反应，进而消耗较多的活性离子，影响二次电池的倍率性能，使得二次电池的体积能量密度相应降低；m1过低时，第一区域孔隙率较高，使得电解液与活性材料的接触面积增多，引起电解液与活性材料间的副反应，且电解液消耗增多，当m1在上述范围内时，二次电池具有较优的倍率性能和较高的体积能量密度。
根据本申请的一些实施方式，第一区域中石墨颗粒最长径为20μm至40μm。在一些实施方式中，石墨颗粒最长径为21μm、22μm、23μm、24μm、25μm、26μm、27μm、28μm、29μm、30μm、31μm、32μm、33μm、34μm、35μm、36μm、37μm、38μm、39μm或这些值中任意两者组成的范围。根据本申请的一些实施方式，第一区域中石墨颗粒最长径为20μm至30μm。当石墨颗粒最长径在上述范围内时，有利于活性离子的传输，且活性物质层具有合适的孔隙率，可进一步提升二次电池的倍率性能和提高其能量密度。
本申请中“石墨颗粒最长径”为采用扫描电子显微镜(SEM)观察负极活性物质层CP样品时，视野中石墨颗粒上任意两点之间的最长距离。本申请中，可通过石墨颗粒原料的选型如质软/质硬原料、对石墨颗粒原料进行造粒/整形处理或控制极片制作时的冷压压力来调整截面孔隙率与石墨颗粒最长径与负极集流体方向的夹角。具体地，可通过石墨颗粒原料的选型如质软/质硬原料，如石墨原料OI值越小，其越难以被压，表现为质硬原料，m值越小；或对石墨颗粒原料进行造粒/整形处理，如造粒用粘结剂含量越高，成品石墨颗粒较难被压，m值越小；或控制极片制作时的冷压压力，如冷压压力越大，石墨颗粒越倾向于平行于集流体排布，即m值越大；以上方式均可调整石墨颗粒最长径与负极集流体方向的夹角和负极活性物质层的截面孔隙率。
根据本申请的一些实施方式，沿负极活性物质层的厚度方向，第一区域之外的区域为第二区域，二次电池满足：1≤m2/n2≤5，40％≤m2≤70％，其中，m2表示第二区域中石墨颗粒最长径与负极集流体方向的夹角为0°至20°的石墨颗粒的占比，n2表示第二区域的截面孔隙率。第二区域受辊压的影响低于第一区域，因此第二区域的截面孔隙率稍大与第一区域，且第二区域中石墨颗粒更趋于垂直集流体方向排布，进而有利于电解液的浸润和活性离子的传输，可进一步提升二次电池的倍率性能和提升其能量密度。
根据本申请的一些实施方式，m2/n2为1.5、2、2.5、3、3.5、4、4.5或这些值中任意两者组成的范围。在一些实施方式中，m2为43％、45％、47％、49％、50％、53％、55％、57％、59％、60％、63％、65％、67％、69％或这些值中任意两者组成的范围。根据本申请的一些实施方式，2≤m2/n2≤4。根据本申请的一些实施方式，45％≤m2≤65％。当m2/n2和m2在上述范围内时，可提高电解液的浸润和活性离子的传输，且活性物质层具有合适 的孔隙率，提升二次电池的倍率性能本和提高其能量密度。本申请中，m2为数量百分含量。
根据本申请的一些实施方式，10％≤n2≤50％。在一些实施方式中，n2为10％、12％、15％、16％、18％、20％、22％、25％、27％、29％、30％、33％、35％、37％、39％、40％、43％、45％、47％、49％或这些值中任意两者组成的范围。根据本申请的一些实施方式，20％≤n2≤40％。n2在上述范围内时，可进一步提高电解液的浸润和有利于活性离子的传输，保证活性物质层具有合适的孔隙率，提升二次电池的倍率性能和提高其能量密度。
根据本申请的一些实施方式，第二区域中石墨颗粒最长径为5μm至25μm。在一些实施方式中，第二区域中，石墨颗粒最长径为5μm、8μm、11μm、12μm、13μm、14μm、15μm、16μm、17μm、18μm、19μm、20μm、21μm、22μm、23μm、24μm或这些值中任意两者组成的范围。根据本申请的一些实施方式，第二区域中石墨颗粒最长径为5μm至20μm。当石墨颗粒最长径在上述范围内时，更有利于活性离子的嵌入和脱出，保证活性物质层具有合适的孔隙率，可进一步提升二次电池的能量密度和倍率性能。
根据本申请的一些实施方式，负极活性物质层中石墨颗粒最长径为5μm至40μm。在一些实施方式中，负极活性物质层中，石墨颗粒的长径为6μm、7μm、8μm、9μm、10μm、11μm、12μm、13μm、14μm、15μm、16μm、17μm、18μm、19μm、20μm、21μm、22μm、23μm、24μm、25μm、26μm、27μm、28μm、29μm、30μm、31μm、32μm、33μm、34μm、35μm、36μm、37μm、38μm、39μm或这些值中任意两者组成的范围。根据本申请的一些实施方式，负极活性物质层中石墨颗粒最长径为5μm至30μm。负极活性物质层中石墨颗粒最长径在上述范围内时，可缩短负极活性物质层中活性离子的传输路径，提高电解液的浸润，改善二次电池内部的动力学性能，且保证活性物质层具有合适的孔隙率，提升二次电池的倍率性能和提高其能量密度。
根据本申请的一些实施方式，负极活性物质层的压实密度为1.0g/cm 3至1.5g/cm 3。当压实密度在上述范围内时，第一区域和第二区域具有合适的孔隙率，进而有利于电解液的浸润和活性离子的脱嵌，使得二次电池具有高的能量密度和优异的倍率性能。
根据本申请的一些实施方式，负极活性物质层的单面厚度为30μm至80μm。在一些实施方式中，负极活性物质层的单面厚度为35μm、40μm、45μm、50μm、55μm、60μm、65μm、70μm、75μm或这些值中任意两者组成的范围。当负极活性物质层的厚度在上述范围内时，更有利于电解液的浸润和活性离子的传输，降低活性离子的传输阻抗，既有利于提升二次电池的快充性能，又能够保证其具有高的能量密度。
本申请中，“负极活性物质层的单面厚度”为负极集流体单面的负极活性物质层的厚度，即负极活性物质层的单面厚度。根据本申请的一些实施方式，负极活性物质层的双面厚度为60μm至160μm。
根据本申请的一些实施方式，负极活性物质层的单面重量为0.03mg/mm 2至0.12mg/mm 2。在一些实施方式中，负极活性物质层的单面重量为0.05mg/mm 2、0.06mg/mm 2、0.07mg/mm 2、0.08mg/mm 2、0.09mg/mm 2、0.1mg/mm 2、0.11mg/mm 2或这些值中任意两者组成的范围。负极活性物质层的单面重量过低时，会导致负极活性物质层的单面厚度太小，在压制过程中，极片容易产生损伤；负极活性物质层的单面重量过高时，活性离子的传输路径变长，嵌脱阻力增大，进而导致析锂。负极活性物质层的单面重量在上述范围内时，可减小活性离子脱嵌时的阻力，缩短离子的传输路径，且活性物质层具有合适的孔隙率，改善二次电池的倍率性能和提高其能量密度。
本申请中，“负极活性物质层的单面重量”为负极集流体单面的负极活性物质层的重量，即负极活性物质层的单面重量。
根据本申请的一些实施方式，石墨包括天然石墨。
根据本申请的一些实施方式，天然石墨包括一次颗粒。本申请中，天然石墨一次颗粒指的是球化和包覆后的天然石墨，其不经过造粒处理。
根据本申请的一些实施方式，天然石墨的制备过程包括：选取天然鳞片石墨进行粉碎，基于天然鳞片石墨和粘结剂的总质量，称取质量分数为50％至90％的天然鳞片石墨粉体，天然鳞片石墨粉体的粒径Dv50为3μm至15μm；基于天然鳞片石墨和粘结剂的总质量，称取质量分数为10％至50％的粘结剂，粘结剂包括软化点在120℃至300℃的沥青、酚醛树脂或环氧树脂中的至少一种，其中，沥青包括软化点在120℃至300℃的高纯沥青。将上述称取的天然鳞片石墨粉体和粘结剂进行混合，将混合均匀的粉末置于反应釜中边加热边搅拌，加热温度控制在500℃至1000℃，然后对混合粉体进行石墨化，得到半成品A料。A料与一定量的包覆剂混合，A料：包覆剂的混合质量比为95：5，其中，包覆剂包括沥青、煤油、树脂或石墨烯中的至少一种，混合均匀后置于高温碳化炉中1150℃煅烧4h，得到料B，料B即为本申请中负极活性物质层中使用的天然石墨。
根据本申请的一些实施方式，天然石墨的Dv50为4μm至25μm。在一些实施方式中，天然石墨的Dv50为5μm、6μm、7μm、8μm、9μm、10μm、11μm、12μm、13μm、14μm、15μm、16μm、17μm、18μm、19μm、20μm、21μm、22μm、23μm、24μm或这些值中任意两者组成的范围。天然石墨的颗粒粒径在上述范围内时，有利于活性离子的脱嵌，可减小 活性离子脱嵌时的阻力，缩短离子的传输路径变长，且活性物质层具有合适的孔隙率，改善二次电池的倍率性能和提高其能量密度。
本申请中，Dv50表示天然石墨在体积基准的粒度分布中，50％的颗粒粒径小于该值。
根据本申请的一些实施方式，天然石墨的粉末压实密度为1.7g/cm 3至2.05g/cm 3。在一些实施方式中，天然石墨的粉末压实密度为1.75g/cm 3、1.8g/cm 3、1.85g/cm 3、1.9g/cm 3、1.95g/cm 3、2.00g/cm 3或这些值中任意两者组成的范围。粉末压实密度在上述范围内时，既能保证较高的体积能量密度，又保持较好内部的动力学性能，改善二次电池的倍率性能。
根据本申请的一些实施方式，天然石墨的比表面积(BET)为3m 2/g至6m 2/g。在一些实施方式中，天然石墨的比表面积为3.5m 2/g、4m 2/g、4.5m 2/g、5m 2/g或5.5m 2/g。将比表面积控制在该范围内，既能减少因活性离子在表面成膜带来的消耗，又能保持较好的电解液浸润速度，可以进一步提升二次电池的倍率性能和提高其能量密度。
根据本申请的一些实施方式，负极活性物质层的电解液浸润时间≤70s。本申请中，负极活性物质层的电解液浸润时间为将5mL电解液滴到长50mm、宽50mm的负极活性物质层表面，电解液在活性物质层表面完全消失时的时间。负极活性物质层的电解液浸润时间≤70s时，说明电解液在负极活性物质层具有较好的浸润效果，可改善二次电池内部动力学，提升其倍率性能。
根据本申请的一些实施方式，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。
根据本申请的一些实施方式，负极活性物质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物质层，正极活性物质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。
二、电子装置
本申请进一步提供了一种电子装置，其包括本申请第一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
正极的制备
将钴酸锂(分子式为LiCoO 2)、乙炔黑和聚偏二氟乙烯(简写为PVDF)按重量比 96:2:2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；将正极浆料涂覆于铝箔上，烘干、冷压、裁片、焊接极耳，得到正极。
负极的制备
天然石墨的制备：选取原料天然鳞片石墨进行粉碎，基于天然鳞片石墨和粘结剂沥青的总质量，称取质量分数为50％至90％的粒径Dv50为3μm至15μm的天然鳞片石墨粉体，基于天然鳞片石墨和粘结剂沥青的总质量，称取质量分数为10％至50％的粘结剂沥青粉体，将上述称取的天然鳞片石墨粉体和粘结剂沥青粉体进行混合，其中沥青选取软化点为200℃的高纯沥青，将混合均匀的粉末置于反应釜中边加热边搅拌，加热温度控制在800℃，然后对混合粉体进行石墨化，得到半成品A料。A料与一定量的包覆剂混合，A料：包覆剂的混合质量比例为95：5，其中，包覆剂选择石墨烯，混合均匀后置于高温碳化炉中1150℃煅烧4h，得到料B，料B即为本申请负极活性物质层中所用天然石墨。
将上述制备得到的天然石墨、丁苯橡胶(简写为SBR)和羧甲基纤维素钠(简写为CMC)按照重量比98:1:1在去离子水溶剂中充分搅拌混合，使其形成均匀的负极浆料；将负极浆料涂覆于预先涂覆有底涂层(炭黑)的负极集流体铜箔上，底涂层的厚度为1.5μm，烘干、采用不同辊压压力对涂布好的负极进行冷压、裁片、焊接。
实施例1至实施例17和对比例1通过控制原料天然鳞片石墨OI值、粘结剂沥青粉体质量分数和负极极片冷压压力来调整负极活性物质层的截面孔隙率及石墨颗粒最长径与负极集流体方向的夹角，具体如下表A所示。
表A
Figure PCTCN2022104059-appb-000001
Figure PCTCN2022104059-appb-000002
隔离膜的制备
以厚度7μm的聚乙烯多孔聚合物薄膜作为隔离膜。
电解液的制备
在干燥氩气环境下，在碳酸乙烯酯(EC)、碳酸丙烯酯(PC)和碳酸二乙酯(DEC)按照重量比1：1：1混合而成的溶剂中，加入LiPF 6混合均匀，其中LiPF 6的浓度为1.15mol/L，再加入氟代碳酸乙烯酯和己二腈，混合均匀得到电解液。其中，基于电解液的总重量计，氟代碳酸乙烯酯的重量含量为3％，己二腈的重量含量为2％。
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。
测试方法
1、截面孔隙率、石墨颗粒最长径、石墨颗粒最长径与集流体方向的夹角测试
负极离子研磨(CP)样品制备流程：拆解锂离子电池得到负极极片，将负极活性物质层用刮刀刮下，将负极活性物质层裁剪为0.5cm×1cm大小，使用导电胶将裁剪好的负极活性物质层黏贴在1cm×1.5cm大小的硅片载体上，然后使用氩离子抛光(参数：8KV的加速电压，每个样品4h)对负极活性物质层的一端进行处理，得到负极活性物质层CP样品。
负极活性物质层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。
负极活性物质层不同厚度截面孔隙率测试：选取测试面积1000μm×Aμm，统计A＝10μm和A>10μm厚度处截面内所有的颗粒与颗粒之间的空隙，通过maps的测试方式获得颗粒与孔隙明暗明显的照片，然后采用image软件对极片进行处理，获得截面孔隙率。
石墨颗粒最长径测试
通过SEM负极活性物质层CP样品，获取50张截面照片后，统计负极活性物质层厚度截面内所有的石墨颗粒最长径，然后采用image软件处理，获得负极活性物质层石墨颗粒最长径的统计数据和计算得到平均值；另外，对每张图片选取测试面积1000μm×Aμm，统计A＝10μm(第一区域)和A>10μm至集流体表面(第二区域)厚度截面内所有的石墨颗粒最长径，通过image软件对不同区域视野内所有石墨颗粒最长径进行统计和计算得到平均值，获得不同区域石墨颗粒最长径的数据。
石墨颗粒最长径与集流体方向的夹角测试
采用SEM负极活性物质层CP样品，获取50张截面图片后，统计负极活性物质层厚度截面内所有的石墨颗粒最长径与集流体方向的夹角，然后采用image软件处理，获得负极活性物质层石墨颗粒最长径与集流体方向的夹角和计算得到平均值；另外，对每张图片选取测试面积1000μm×Aμm，统计A＝10μm(第一区域)和A>10μm至集流体表面(第二区域)厚度截面内所有的石墨颗粒最长径与集流体方向的夹角，然后采用image软件对不同区域视野内所有石墨颗粒最长径与集流体方向的夹角进行统计和计算得到平均值，获得不同区域石墨颗粒最长径与集流体方向的夹角的数据。
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的石墨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、颗粒粒度测试
先将拆解出的负极活性物质层，置于坩埚中，加热至300℃至600℃。然后将集流体与天然石墨粉体进行分离，得到待测天然石墨粉体。
颗粒粒度测试方法参照GB/T 19077-2016。具体流程为：
称量待测天然石墨样品1g与20mL去离子水和微量分散剂混合均匀，置于超声设备中超声5min后将溶液倒入进样***Hydro 2000SM中进行测试，所用测试设备为马尔文公司生产的Mastersizer 3000。
测试过程中当激光束穿过分散的颗粒样品时，通过测量散射光的强度来完成粒度测量。然后数据用于分析计算形成该散射光谱图的颗粒粒度分布。测试所用颗粒折射率为1.8，一个样品测试三次，颗粒粒度最终取三次测试的平均值。
4、负极活性物质层的浸润时间测试
取长50mm、宽50mm的负极活性物质层样品。在干燥条件下，将5mL电解液滴在样品表面，开始计时。待样品表面电解液完全消失，停止计时。计时时间记为负极活性物质层的浸润时间。每个实施例或对比例测试30个样品，取平均值，所述电解液与锂离子电池中的电解液相同。
5、锂离子液相传递阻抗(Rion)测试
将锂离子电池接入法国比奥罗杰公司生产的Bio-Logic VMP3B电化学工作站进行测试，频率范围为30mHz至50kHz，振幅为5mV。采集数据后采用阻抗复平面图对数据进行分析，得到锂离子液相传递阻抗(Rion)。
6、锂离子电池的2C放电容量保存率的测试方法
将锂离子电池在25℃下静止5分钟后，以0.7C的电流恒流充电至4.45V，再以4.45V的恒压充电至0.05C，静置5分钟，然后以0.5C恒流放电至3.0V，静止5分钟。重复上述充放电过程，以0.1C进行放电，记录锂离子电池的0.1C放电容量，然后以2C进行放电，记录锂离子电池的2C放电容量。通过下式锂离子电池的2C放电容量保存率：
2C放电容量保存率＝2C放电容量/0.1C放电容量×100％。
7、直流电阻(DCR)测试
在25℃下，将锂离子电池以1.5C恒流充电至4.45V，再以4.45V恒压充电至0.05C，静置30分钟。以0.1C放电10秒，记录电压值为U1，以1C放电360秒，记录电压值为U2。重复充放电步骤5次。“1C”是在1小时内将锂离子电池容量完全放完的电流值。
通过下式计算锂离子电池在25℃下的直流电阻R：
R＝(U2-U1)/(1C-0.1C)。
采用上述测试锂离子电池在25°℃下的直流电阻R的方法步骤测试锂离子电池在0℃下的直流电阻，区别仅在于操作温度为0℃。
除非有特别说明，本申请所述的DCR指的是锂离子电池在10％荷电状态(SOC)下的直流电阻。
8、电化学阻抗谱(EIS)测试
a)三电极电池的制备和镀锂，如上述锂离子电池的制备方式一致，在锂离子电池的 制备过程中将铜丝接入电池作为参比电极，负极以20μA的电流分别镀锂6h，镀锂完毕后测试EIS。
b)EIS测试步骤：将镀锂的三电极电池接入由法国比奥罗杰公司生产的Bio-Logic VMP3B电化学工作站进行测试，测试用频率范围为30mHz至50kHz，振幅为5mV，采集数据后采用阻抗复平面图对数据进行分析，得到Rct的数据。
9、负极析锂程度测试
取被测锂离子电池在0℃测试温度下，静置5分钟，以0.8C的电流恒流充电至4.45V，再以4.45V的电压恒压充电至0.05C；静置5分钟，再以0.5C的电流恒流放电至3.0V，静置5分钟。重复上述充放电流程10次后，将电池满充，于干燥房内拆解，拍照记录负极的状态。
析锂程度判定：根据满充拆解负极的状态来判定，当负极整体显示为金黄色且显示为灰色的面积<2％，则判定为不析锂；当负极大部分为金黄色，但有部分位置可观察到灰色，灰色面积在2％至20％之间，则判定为轻微析锂；当负极部分为灰色，但仍可观察到部分金黄色，灰色面积在20％至60％，则判定为析锂；当负极大部分显示为灰色，灰色面积＞60％时，则判定为严重析锂。
10、体积能量密度
记锂离子电池的放电容量为D mAh，锂离子电池的平台电压为U V，锂离子电池的长宽厚尺寸分别为L mm/W mm/H mm。则体积能量密度VED＝D×U/(L×W×H)×1000。
11、首次效率测试
将组装好的锂离子电池，按照0.5C的倍率进行充电激活处理，充电至4.45V后，记录此时容量为C0，然后将电池以0.5C的倍率进行放电处理，放电至3.0V时，记录此时容量为D0，首次效率测试的公式即为D0/C0×100％。
测试结果
表1示出了负极活性物质层截面孔隙率及石墨颗粒最长径与负极集流体方向的夹角为0°至20°的石墨颗粒的占比对锂离子电池性能的影响。
其中，第一区域的截面孔隙率为n1，第一区域中石墨颗粒最长径与负极集流体方向的夹角为0°至20°的石墨颗粒的占比为m1；第二区域的截面孔隙率为n2，第二区域中石墨颗粒最长径与负极集流体方向的夹角为0°至20°的石墨颗粒的占比为m2。
实施例1至实施例17和对比例1中，第一区域中石墨颗粒最长径相同，均为31μm； 第二区域中石墨颗粒最长径相同，均为31μm。
实施例1至实施例17和对比例1中，负极活性物质层的压实密度相同，均为1.3g/cm 3；负极活性物质层的单面厚度相同，均为38μm；负极活性物质层的单面重量相同，均为0.05mg/mm 2。
实施例1至实施例17和对比例1中，石墨的粉末压实密度相同，均为2.00g/cm 3；石墨的比表面积相同，均为3.42m 2/g。
实施例1至实施例10、实施例14至实施例17以及对比例1中，天然石墨的Dv50相同，均为22μm，实施例11至实施例13中，天然石墨的Dv50相同，均为22μm。
表1
Figure PCTCN2022104059-appb-000003
从实施例1至实施例17和对比例1的数据可以看出，当负极活性物质层的第一区域截面孔隙率和石墨颗粒最长径与负极集流体方向的夹角为0°至20°的石墨颗粒的占比满足3≤m1/n1≤18，5％≤n1≤20％时，可缩短锂离子的传输距离，改善锂离子电池内部动力学，和保证负极活性物质层具有合适的孔隙率，可明显提高锂离子电池的体积能量密度和降低电化学阻抗，使得锂离子电池兼具高的能量密度和优异的倍率性能。
当m1在60％至90％、1≤m2/n2≤5、40％≤m2≤70％、10％≤n2≤50％时，可缩短锂 离子的传输路径，提升锂离子电池内部动力学性能，进一步改善锂离子电池的倍率性能，使其具有较高的能量密度。
表2示出活性材料层的压实密度、石墨颗粒最长径、负极活性物质层的单面厚度以及单面重量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18至实施例34的其余参数与实施例7相同。
表2
Figure PCTCN2022104059-appb-000004
如表2所示，当天然石墨的Dv50为4μm至25μm、负极活性物质层中石墨颗粒最长径为5μm至40μm、负极活性物质层的压实密度为1.0g/cm 3至1.5g/cm 3时，调整负极活性 物质层的单面厚度为30μm至80μm和负极活性物质层的单面重量为0.03mg/mm 2至0.12mg/mm 2时，可降低锂离子的脱嵌阻力，有利于锂离子的传输，降低锂离子电池的阻抗，进一步改善其倍率性能和改善其析锂情况。
表3示出天然石墨的颗粒粒径、粉末压实密度和BET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35至实施例44的其余参数与实施例7相同。
表3
Figure PCTCN2022104059-appb-000005
如实施例7，实施例35至实施例44所示，随着石墨颗粒粒径的增加，电解液所需的浸润时间增加，表明锂离子扩散的速度减小，另一方面随着比表面积的减小，成膜所需活性锂的消耗减小，锂离子电池的首次效率提升。故通过调节石墨颗粒粒径、粉末压实密度和比表面积，可使锂离子电池进一步具有较低的液相传输阻抗和较高的首次效率，改善其倍率性能。
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 (14)

  1. 一种二次电池，包括负极，所述负极包括负极集流体和设置于负极集流体上的负极活性物质层，所述负极活性物质层包括石墨颗粒，其中，沿所述负极活性物质层的厚度方向，所述负极活性物质层表面至所述负极活性物质层内部10μm的区域为第一区域，所述二次电池满足：3≤m1/n1≤18，5％≤n1≤20％，其中，m1表示所述第一区域中石墨颗粒最长径与所述负极集流体方向的夹角为0°至20°的石墨颗粒的占比，n1表示所述第一区域的截面孔隙率。
  2. 根据权利要求1所述的二次电池，其中，所述二次电池满足如下条件(1)至(2)中的至少一者：
    (1)5≤m1/n1≤12；
    (2)7％≤n1≤15％。
  3. 根据权利要求1或2所述的二次电池，其中，所述二次电池满足如下条件(3)至(4)中的至少一者：
    (3)60％≤m1≤90％；
    (4)所述第一区域中石墨颗粒最长径为20μm至40μm。
  4. 根据权利要求1或2所述的二次电池，其中，所述二次电池满足如下条件(5)至(6)中的至少一者：
    (5)65％≤m1≤85％。
    (6)所述第一区域中石墨颗粒最长径为20μm至30μm。
  5. 根据权利要求1所述的二次电池，其中，沿所述负极活性物质层的厚度方向，所述第一区域之外的区域为第二区域，所述二次电池满足：1≤m2/n2≤5，40％≤m2≤70％，其中，m2表示所述第二区域中石墨颗粒最长径与所述负极集流体方向的夹角为0°至20°的石墨颗粒的占比，n2表示所述第二区域的截面孔隙率。
  6. 根据权利要求5所述的二次电池，其中，所述二次电池满足如下条件(7)至(8)中的至少一者：
    (7)2≤m2/n2≤4；
    (8)45％≤m2≤65％。
  7. 根据权利要求5或6所述的二次电池，其中，所述二次电池满足如下条件(9)至(10)中的至少一者：
    (9)10％≤n2≤50％；
    (10)所述第二区域中石墨颗粒最长径为5μm至25μm。
  8. 根据权利要求5或6所述的二次电池，其中，所述二次电池满足如下条件(11)至(12)中的至少一者：
    (11)20％≤n2≤40％；
    (12)所述第二区域中石墨颗粒最长径为5μm至20μm。
  9. 根据权利要求1所述的二次电池，其中，所述二次电池满足如下条件(a)至(d)中的至少一者：
    (a)所述负极活性物质层中石墨颗粒最长径为5μm至40μm；
    (b)所述负极活性物质层的压实密度为1.0g/cm 3至1.5g/cm 3；
    (c)所述负极活性物质层的单面厚度为30μm至80μm；
    (d)所述负极活性物质层的单面重量为0.03mg/mm 2至0.12mg/mm 2。
  10. 根据权利要求1所述的二次电池，其中，所述负极活性物质层中石墨颗粒最长径为5μm至30μm。
  11. 根据权利要求1所述的二次电池，其中，所述石墨包括天然石墨。
  12. 根据权利要求11所述的二次电池，其中，所述天然石墨满足如下条件(e)至(h)中的至少一者：
    (e)所述天然石墨为一次颗粒；
    (f)所述天然石墨的Dv50为4μm至25μm；
    (g)所述天然石墨的粉末压实密度为1.7g/cm 3至2.05g/cm 3；
    (h)所述天然石墨的比表面积为3m 2/g至6m 2/g。
  13. 根据权利要求1所述的二次电池，其中，所述负极活性物质层的电解液浸润时间≤70s。
  14. 一种电子装置，包括权利要求1至13中任一项所述的二次电池。
PCT/CN2022/104059 2022-07-06 2022-07-06 二次电池和电子装置 WO2024007184A1 (zh)

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