WO2025251682A1 - 钠离子电池、钠离子电池制备方法、用电装置和硬碳材料 - Google Patents

钠离子电池、钠离子电池制备方法、用电装置和硬碳材料

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Publication number
WO2025251682A1
WO2025251682A1 PCT/CN2025/077585 CN2025077585W WO2025251682A1 WO 2025251682 A1 WO2025251682 A1 WO 2025251682A1 CN 2025077585 W CN2025077585 W CN 2025077585W WO 2025251682 A1 WO2025251682 A1 WO 2025251682A1
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WIPO (PCT)
Prior art keywords
hard carbon
sodium
carbon material
negative electrode
ion battery
Prior art date
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Pending
Application number
PCT/CN2025/077585
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English (en)
French (fr)
Inventor
吴凯
李圆
王家政
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Publication date
Application filed by Contemporary Amperex Technology Co Ltd filed Critical Contemporary Amperex Technology Co Ltd
Priority to PCT/CN2025/096810 priority Critical patent/WO2025251931A1/zh
Publication of WO2025251682A1 publication Critical patent/WO2025251682A1/zh
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • 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
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/244—Secondary casings; Racks; Suspension devices; Carrying devices; Holders characterised by their mounting method
    • 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

  • This disclosure relates to the field of secondary battery technology, and in particular to a sodium-ion battery, a method for preparing a sodium-ion battery, an electrical device, and a hard carbon material.
  • This disclosure is made in view of the aforementioned issues, and its object is to provide a sodium-ion battery, a method for preparing a sodium-ion battery, an electrical device, and a hard carbon material.
  • the negative electrode provided by this disclosure has improved kinetic performance while providing good capacity.
  • the sodium-ion battery includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector.
  • the negative electrode film layer includes a hard carbon material.
  • the hard carbon material comprises a porous structure, including pores with a pore size of 2 nm to 8 nm.
  • the pore volume of the pores with a pore size of 2 nm to 8 nm, as determined by nitrogen adsorption, is 0.0004 cm3 /g to 0.0040 cm3 /g.
  • the negative electrode film of the sodium-ion battery disclosed herein includes a hard carbon material with an optimized pore structure.
  • the hard carbon material has pores with a diameter of 2 nm to 8 nm and a pore volume of 0.0004 cm3 /g to 0.0040 cm3 /g, thereby improving the kinetic performance of the hard carbon material while maintaining specific capacity.
  • the pore volume of hard carbon materials with pore sizes of 2nm-8nm is determined to be 0.0010 cm3 /g- 0.0040 cm3 /g by nitrogen adsorption. This is more beneficial to the kinetic properties of hard carbon materials while also taking into account specific capacity.
  • the pore volume of pores with a diameter of 2 nm to 8 nm in the hard carbon material is determined by nitrogen adsorption to account for 3.5% to 30% of the total pore volume of the hard carbon material. This is beneficial for balancing kinetic properties and specific capacity, and for maintaining suitable structural stability.
  • the pore volume of hard carbon materials with a pore size of less than or equal to 1 nm, determined by carbon dioxide adsorption, is denoted as V1
  • the pore volume of hard carbon materials with a pore size of 1 nm to 2 nm, determined by nitrogen adsorption is denoted as V2 .
  • V1 + V2 falls within the range of 0.0006 cm3 /g to 0.0050 cm3 /g.
  • a pore volume of hard carbon materials with a pore size of less than 2 nm falling within this range is more advantageous for the hard carbon materials to possess suitable specific capacity.
  • V1 + V2 is in the range of 0.0006 cm3 /g to 0.0035 cm3 /g. This allows the hard carbon material to have a suitable specific capacity while reducing gas generation and bubbling during the negative electrode slurry preparation process. This results in a negative electrode sheet with improved capacity and a uniform negative electrode film, reducing the risk of negative electrode slurry leakage and improving the performance of the sodium-ion battery. Preferably, it is in the range of 0.0020 cm3 /g to 0.0035 cm3 /g.
  • the proportion of V1 + V2 to the total pore volume of the hard carbon material is in the range of 18% to 30%. Having the proportion of pore volume with a diameter of less than 2 nm to the total pore volume within the above range is more beneficial for improving the specific capacity of the hard carbon material.
  • the hard carbon material comprises pores with a diameter in the range of 1.0 nm to 1.5 nm.
  • the maximum value of the derivative of the cumulative pore volume V of the pores with a diameter in the range of 1.0 nm to 1.5 nm, dV/d(logD), with respect to the logarithm of the pore diameter D, is determined by nitrogen adsorption and is between 0.001 cm3 /(g ⁇ log(nm)) and 0.009 cm3 /(g ⁇ log(nm)). This helps to reduce gas generation and bubbling during the slurry preparation process, further improving the performance of the negative electrode sheet, reducing the risk of negative electrode slurry leakage, and improving the performance of the secondary battery.
  • the maximum value of the derivative of the cumulative pore volume V with respect to the logarithm of the pore size D, dV/d(logD), determined by nitrogen adsorption, for pores with a pore size of 1.0 nm to 1.5 nm is between 0.001 cm3 /(g ⁇ log(nm)) and 0.006 cm3 /(g ⁇ log(nm)). This further helps to reduce gas generation and bubbling during the pulping process.
  • the pore volume of the hard carbon material with a pore size of 1.0 nm to 1.5 nm accounts for 6% to 14% of the total pore volume of the hard carbon material.
  • the negative electrode film layer includes at least one of a first aqueous binder, an aqueous dispersant, and a first conductive agent.
  • the aqueous binder includes one or more of styrene-butadiene rubber and acrylate rubber; the aqueous dispersant includes one or more of sodium carboxymethyl cellulose, sodium alginate, xanthan gum, and carrageenan; and the conductive agent includes one or more of Super-P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the mass content of hard carbon material in the negative electrode film layer is above 80%.
  • the mass content of hard carbon material in the negative electrode film layer is more than 85%
  • the mass content of aqueous binder is 0% to 5%
  • the mass content of aqueous dispersant is 0% to 5%
  • the mass content of conductive agent is 0% to 5%.
  • the negative electrode film layer further includes an intercalated sodium storage material, wherein the intercalation spacing d ⁇ sub>002 ⁇ /sub> of the intercalated sodium storage material satisfies: 0.24 nm ⁇ d ⁇ sub>002 ⁇ /sub> ⁇ 0.8 nm. Therefore, the intercalated sodium storage material with an intercalation spacing within the above range can exhibit interlayer slip in its microstructure. When applied in sodium-ion batteries, this helps increase the powder compaction density of the negative electrode sheet, thereby helping to improve the energy density of the sodium-ion battery.
  • the mass content of the intercalated sodium storage material in the negative electrode film layer is less than or equal to 10%.
  • the mass content of the intercalated sodium storage material is between 0.5% and 5%.
  • the intercalated sodium storage material includes at least one of carbon-based intercalated sodium storage material, sulfur-based intercalated sodium storage material, and titanium-based intercalated sodium storage material;
  • the carbon-based intercalated sodium storage material includes at least one of soft carbon and modified graphite; the ID / IG ratio of soft carbon satisfies: 0.9 ⁇ ID / IG ⁇ 1.6, where ID represents the intensity of the D peak in the Raman spectrum at 1350 ⁇ 50 cm ⁇ 1 , and IG represents the intensity of the G peak in the Raman spectrum at 1580 ⁇ 50 cm ⁇ 1 .
  • the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer stacked together.
  • the first negative electrode film layer is disposed between the negative electrode current collector and the second negative electrode film layer.
  • the first negative electrode film layer includes a first active material
  • the second negative electrode film layer includes a second active material.
  • the first active material and the second active material each include at least one of a hard carbon material and an intercalated sodium storage material, and at least one of the first active material and the second active material includes a hard carbon material.
  • the intercalated sodium storage material can affect the sodium storage mechanism of the negative electrode active material, reducing the possibility of sodium ions depositing in the hard carbon to form metalloid sodium, thereby reducing the risk of sodium ion thermal runaway.
  • the first active material includes a hard carbon material
  • the second active material includes a soft carbon material. This is more conducive to improving kinetic performance.
  • the negative electrode also includes an undercoating layer; the thickness of the undercoating layer is 0.5 ⁇ m-3 ⁇ m. This helps to reduce the risk of incomplete coating and improve the coating quality of the electrode.
  • the slurry used in the preparation of electrodes from hard carbon materials is an aqueous slurry, the difference in dyne value between it and the surface of the metal current collector is large, which can easily lead to incomplete coating and poses a safety risk.
  • the undercoat includes an inorganic oxide and an aqueous binder.
  • This undercoat is water-resistant and has strong adhesion to the metal current collector.
  • the inorganic oxide enhances the anchoring effect between the undercoat and the active layer, meeting water resistance requirements and exhibiting strong affinity to the metal current collector surface. This helps reduce the risk of incomplete coating, improves electrode coating quality, improves electrode bonding strength, reduces elongation during cold pressing, and effectively controls current collector resistance, thus considering the battery's electrochemical performance.
  • the base coating includes an inorganic oxide, a dispersant, a second aqueous binder, and a second conductive agent.
  • the inorganic oxide in the primer coating includes one or more of aluminum oxide, boehmite, magnesium oxide, iron oxide, silicon oxide, and zirconium oxide; the inorganic oxide accounts for 30%-60% of the total mass.
  • the inclusion of inorganic oxides within the above mass range in the primer coating can enhance adhesion to the metal current collector, further reduce the risk of incomplete coating, and improve the coating quality of the electrode sheet.
  • the base coating comprises 30%-60% inorganic oxide, 1%-8% dispersant, 10%-40% second aqueous binder, and 10%-40% second conductive agent.
  • the base coating layer further includes a thickener and/or a wetting agent;
  • the wetting agent includes one or more of polyethoxy ether surfactants, polyether silicone surfactants, nonionic fluorocarbon polymer surfactants, and alkyne surfactants;
  • the thickener includes one or more of sodium carboxymethyl cellulose, sodium alginate, xanthan gum, and carrageenan.
  • the negative current collector includes at least one of copper foil, aluminum foil, stainless steel foil, titanium foil, nickel foil, nickel-iron foil, nickel-copper foil, and nickel-iron-copper foil.
  • the total metal ion content in the hard carbon material is ⁇ 800ppm, and the content of divalent or higher metal ions is ⁇ 20ppm. Having the total metal ion content and the content of divalent or higher metal ions in the hard carbon material within these ranges is beneficial for maintaining a suitable slurry viscosity, thereby facilitating slurry coating and resulting in a negative electrode sheet with a uniform negative electrode film layer.
  • the total metal ion content in the hard carbon material is 20ppm-800ppm, and the content of divalent or higher metal ions is 0.1ppm-20ppm. Having the total metal ion content and the content of divalent or higher metal ions in the hard carbon material within these ranges is beneficial for increasing the inorganic content of the SEM film, thereby reducing the formation of sodium dendrites or sodium precipitation on the surface of the hard carbon material, thus improving cycle performance.
  • the metal ion includes at least one selected from Na + , K + , Ca2 + , Mg2 + , Mn2 + , Ba2 + , and Al3 + .
  • the divalent or higher metal ions are Ca2+ .
  • the calcium ion content in the hard carbon material has a significant impact on the viscosity of the negative electrode slurry. A content within the aforementioned range is beneficial for obtaining a suitable negative electrode slurry viscosity, thereby facilitating rapid slurry coating and avoiding false edges and slurry flow, resulting in a negative electrode sheet with a uniform negative electrode film layer.
  • the surface oxygen content of the hard carbon material is 6%-14%.
  • a surface oxygen content within this range is beneficial for maintaining appropriate interaction forces between the dispersant and the hard carbon material, ensuring uniform dispersion of the slurry during mixing and providing good fluidity. This helps prevent gelation during slurry preparation, thereby facilitating slurry coating.
  • the surface oxygen content of the hard carbon material is 8%-12%. A surface oxygen content within this range is more advantageous for the slurry coating process.
  • the solvent in the electrolyte includes carbonate solvents, including at least one of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. This is beneficial for improving the high-voltage resistance of the electrolyte.
  • the volume fraction of propylene carbonate relative to the solvent is 15%-55%. This not only improves the oxidation resistance of the electrolyte but also enhances conductivity by dissociating the sodium salt.
  • the positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector.
  • the positive electrode film layer includes a positive electrode active material, which includes at least one of sodium-containing layered oxide, polyanionic sodium ion compound, and Prussian blue sodium ion compound.
  • the sodium-containing layered oxide is an iron-manganese layered oxide, at least one of an iron-manganese layered oxide, a nickel-iron-manganese layered oxide, and a copper-iron-manganese layered oxide.
  • This disclosure also provides a method for preparing a sodium-ion battery, including preparing a negative electrode sheet.
  • the preparation of the negative electrode sheet includes: mixing a negative electrode component and a solvent to obtain a negative electrode slurry, wherein the negative electrode component includes a hard carbon material, the hard carbon material comprising a porous structure including pores with a diameter of 2 nm-8 nm, and the pore volume of the pores with a diameter of 2 nm-8 nm is determined to be 0.0004 cm3 /g-0.0040 cm3 /g by nitrogen adsorption; and coating the negative electrode slurry onto a negative electrode current collector.
  • the pores with a diameter of 2 nm-8 nm have a suitable pore volume, they can improve the kinetic performance of the hard carbon material, and these pores can also contribute to the capacity, thereby enabling the negative electrode sheet to have improved kinetic performance while maintaining capacity.
  • the pore volume of hard carbon materials with pore sizes of 2nm-8nm is determined to be 0.0010 cm3 /g- 0.0040 cm3 /g by nitrogen adsorption. This is more conducive to improving the kinetic properties of hard carbon materials while taking into account specific capacity.
  • the pore volume of pores with a diameter of 2 nm to 8 nm in the hard carbon material is determined by nitrogen adsorption to account for 3.5% to 30% of the total pore volume of the hard carbon material. This further facilitates the balance between the kinetic properties and specific capacity of the hard carbon material, and maintains suitable structural stability.
  • the pore volume of hard carbon material with a pore size of less than or equal to 1 nm, determined by carbon dioxide adsorption, is denoted as V1
  • the pore volume of hard carbon material with a pore size of 1 nm to 2 nm, determined by nitrogen adsorption is denoted as V2 .
  • V1 + V2 is in the range of 0.0006 cm3 /g to 0.0050 cm3 /g. Further limiting V1 + V2 to the above range is more beneficial for achieving a suitable specific capacity in the hard carbon material.
  • V1 + V2 is in the range of 0.0006 cm3 /g to 0.0035 cm3 /g.
  • a pore volume of 0.0006 cm3 /g to 0.0035 cm3 /g for pores with a diameter of less than 2 nm is also beneficial for achieving suitable specific capacity in hard carbon materials while reducing gas generation and bubbling during the slurry preparation process, improving the processability of hard carbon materials, enhancing the uniformity of the negative electrode sheet, reducing the risk of negative electrode slurry leakage, and improving the performance of sodium-ion batteries.
  • V1 + V2 is in the range of 0.0020 cm3 /g to 0.0035 cm3 /g.
  • V1 + V2 accounts for 18% to 30% of the pore volume of the hard carbon material.
  • a proportion of the pore volume of pores with a diameter of less than 2 nm in the hard carbon material within the above range is more conducive to improving the specific capacity of the hard carbon material.
  • the hard carbon material comprises pores with a diameter in the range of 1.0 nm to 1.5 nm.
  • the maximum value of the derivative of the cumulative pore volume V of the pores with a diameter in the range of 1.0 nm to 1.5 nm with respect to the logarithm of the pore diameter D, dV/d(logD), is determined by nitrogen adsorption and is between 0.001 cm3 /(g ⁇ log(nm)) and 0.009 cm3 /(g ⁇ log(nm)). This is more conducive to reducing gas generation and bubbling during the pulping process.
  • the maximum value of the derivative of the cumulative pore volume V with respect to the logarithm of the pore size D, dV/d(logD), determined by nitrogen adsorption, for pores with a pore size of 1.0 nm to 1.5 nm is between 0.001 cm3 /(g ⁇ log(nm)) and 0.006 cm3 /(g ⁇ log(nm)). This further helps to reduce gas generation and bubbling during the pulping process.
  • the pore volume of the hard carbon material with a pore size of 1.0 nm to 1.5 nm accounts for 6% to 14% of the total pore volume of the hard carbon material.
  • the mass percentage of the negative electrode component relative to the mass of the negative electrode slurry is 50% to 60%. This is beneficial to the uniformity and stability of the slurry.
  • the mass percentage of hard carbon relative to the mass of the negative electrode components is 80% to 95%. This is beneficial to the energy density of the battery.
  • the negative electrode component further includes one or more of a conductive agent, a binder, and a dispersant.
  • the conductive agent can effectively accelerate the electron transport rate and improve the charge/discharge efficiency of the battery.
  • the binder helps maintain the integrity of the electrode structure during battery charge/discharge.
  • the dispersant can improve the dispersibility of the negative electrode component particles in the solvent, making the slurry easier to coat.
  • mixing the negative electrode components and solvent includes: vacuum stirring at 0°C to 30°C for 1 to 4 hours.
  • the bubbling time can be significantly reduced, which is conducive to the smooth progress of slurry preparation and also beneficial to subsequent coating and cold pressing processes, thereby improving the uniformity of the negative electrode film and preventing the current collector from being exposed.
  • This disclosure also provides an electrical device, including the sodium-ion battery of this disclosure or the sodium-ion battery prepared by the sodium-ion battery preparation method of this disclosure.
  • the electrical devices disclosed herein include the sodium-ion batteries provided herein, and therefore have at least the same advantages as sodium-ion batteries.
  • the hard carbon material comprises a porous structure, which includes pores with a diameter of 2 nm to 8 nm.
  • the pore volume of the pores with a diameter of 2 nm to 8 nm is determined to be 0.0004 cm3 /g to 0.0040 cm3 /g by nitrogen adsorption method.
  • the hard carbon material disclosed herein has an optimized pore structure. Specifically, the pores of the hard carbon material with a pore size of 2 nm to 8 nm have a pore volume of 0.0004 cm3 /g to 0.0040 cm3 /g, thereby improving the kinetic properties of the hard carbon material while also taking into account its specific capacity.
  • the pore volume of hard carbon materials with pore sizes of 2nm-8nm is determined to be 0.0010 cm3 /g- 0.0040 cm3 /g by nitrogen adsorption. This is more beneficial to the kinetic properties of hard carbon materials while also taking into account specific capacity.
  • the pore volume of pores with a diameter of 2 nm to 8 nm in the hard carbon material is determined by nitrogen adsorption to account for 3.5% to 30% of the total pore volume of the hard carbon material. This is beneficial for balancing kinetic properties and specific capacity, and for maintaining appropriate structural stability.
  • the pore volume of hard carbon materials with a pore size of less than or equal to 1 nm, determined by carbon dioxide adsorption, is denoted as V1
  • the pore volume of hard carbon materials with a pore size of 1 nm to 2 nm, determined by nitrogen adsorption is denoted as V2 .
  • V1 + V2 falls within the range of 0.0006 cm3 /g to 0.0050 cm3 /g.
  • a pore volume of hard carbon materials with a pore size of less than 2 nm falling within this range is more advantageous for the hard carbon materials to possess suitable specific capacity.
  • V1 + V2 is in the range of 0.0006 cm3 /g to 0.0035 cm3 /g. This allows the hard carbon material to have a suitable specific capacity while reducing gas generation and bubbling during the negative electrode slurry preparation process. This results in a negative electrode sheet with improved capacity and a uniform negative electrode film, reducing the risk of negative electrode slurry leakage and improving the performance of the sodium-ion battery. Preferably, it is in the range of 0.0020 cm3 /g to 0.0035 cm3 /g.
  • the proportion of V1 + V2 to the total pore volume of the hard carbon material is in the range of 18% to 30%. Having the proportion of pore volume with a diameter of less than 2 nm to the total pore volume within the above range is more beneficial for improving the specific capacity of the hard carbon material.
  • the hard carbon material comprises pores with a diameter in the range of 1.0 nm to 1.5 nm.
  • the maximum value of the derivative of the cumulative pore volume V of the pores with a diameter in the range of 1.0 nm to 1.5 nm, dV/d(logD), with respect to the logarithm of the pore diameter D, is determined by nitrogen adsorption and is between 0.001 cm3 /(g ⁇ log(nm)) and 0.009 cm3 /(g ⁇ log(nm)). This helps to reduce gas generation and bubbling during the slurry preparation process, further improving the performance of the negative electrode sheet, reducing the risk of negative electrode slurry leakage, and improving the performance of the secondary battery.
  • the maximum value of the derivative of the cumulative pore volume V with respect to the logarithm of the pore size D, dV/d(logD), determined by nitrogen adsorption, for pores with a pore size of 1.0 nm to 1.5 nm is between 0.001 cm3 /(g ⁇ log(nm)) and 0.006 cm3 /(g ⁇ log(nm)). This further helps to reduce gas generation and bubbling during the pulping process.
  • the pore volume of the hard carbon material with a pore size of 1.0 nm to 1.5 nm accounts for 6% to 14% of the total pore volume of the hard carbon material.
  • the total metal ion content in the hard carbon material is ⁇ 800ppm, and the content of divalent or higher metal ions is ⁇ 20ppm. Having the total metal ion content and the content of divalent or higher metal ions in the hard carbon material within these ranges is beneficial for maintaining a suitable slurry viscosity, thereby facilitating slurry coating and resulting in a negative electrode sheet with a uniform negative electrode film layer.
  • the total metal ion content in the hard carbon material is 20ppm-800ppm, and the content of divalent or higher metal ions is 0.1ppm-20ppm. Having the total metal ion content and the content of divalent or higher metal ions in the hard carbon material within these ranges is beneficial for increasing the inorganic content of the SEM film, thereby reducing the formation of sodium dendrites or sodium precipitation on the surface of the hard carbon material, thus improving cycle performance.
  • the metal ion includes at least one selected from Na + , K + , Ca2 + , Mg2 + , Mn2 + , Ba2 + , and Al3 + .
  • the divalent or higher metal ions are Ca2+ .
  • the calcium ion content in the hard carbon material has a significant impact on the viscosity of the negative electrode slurry. A content within the aforementioned range is beneficial for obtaining a suitable negative electrode slurry viscosity, thereby facilitating rapid slurry coating and avoiding false edges and slurry flow, resulting in a negative electrode sheet with a uniform negative electrode film layer.
  • the surface oxygen content of the hard carbon material is 6%-14%.
  • a surface oxygen content within this range is beneficial for maintaining appropriate interaction forces between the dispersant and the hard carbon material, ensuring uniform dispersion of the slurry during mixing and providing good fluidity. This helps prevent gelation during slurry preparation, thereby facilitating slurry coating.
  • the surface oxygen content of the hard carbon material is 8%-12%. A surface oxygen content within this range is more advantageous for the slurry coating process.
  • Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.
  • Figure 2 is an exploded view of a battery cell according to an embodiment of the present disclosure shown in Figure 1.
  • Figure 3 is a schematic diagram of a battery module according to one embodiment of the present disclosure.
  • Figure 4 is a schematic diagram of a battery pack according to one embodiment of the present disclosure.
  • FIG 5 is an exploded view of a battery pack according to an embodiment of the present disclosure, as shown in Figure 4.
  • Figure 6 is a schematic diagram of an electrical device using a sodium-ion battery as a power source according to an embodiment of the present disclosure.
  • ranges disclosed in this disclosure is defined by a lower limit and an upper limit, whereby a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range.
  • Ranges defined in this way include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.
  • the numerical range "a-b” represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers.
  • the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations.
  • a parameter is stated as an integer ⁇ 2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
  • steps of this disclosure may be performed sequentially or randomly, preferably sequentially.
  • a method includes steps (a) and (b)
  • the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially.
  • the method may also include step (c)
  • step (c) it means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.
  • micropores Small cell structure
  • These micropores are beneficial for sodium storage, thus improving specific capacity.
  • a large number of micropores is detrimental to kinetic performance and can lead to sodium precipitation.
  • the micropores in hard carbon can store sodium, they also allow gas molecules to enter and exit, causing bubbling.
  • micropores slows down electrolyte wetting, increases steric hindrance for Na embedding at high rates, further hinders charge transfer, and significantly deteriorates kinetic performance. This manifests as some sodium ions being reduced to metallic Na at the interface and precipitating out. Simultaneously, the increased proportion of these micropores increases surface area, resulting in a larger solid electrolyte interface (SEI) film, which consumes more active ions, further exacerbating sodium precipitation. Furthermore, an excessive number of micropores enhances gas molecule entry and exit, leading to continuous bubbling during processing. For hard carbon materials that continuously produce gas and bubbles, such as those still bubbling two hours after slurry preparation, processing becomes difficult.
  • SEI solid electrolyte interface
  • the prepared negative electrode may expose the underlying negative electrode current collector, leading to defects and reduced sodium-ion battery performance. Additionally, defects in the electrode coating may cause differences in electron and Na ion concentration distribution on the electrode surface, increasing the risk of sodium precipitation and posing safety hazards for battery use.
  • this disclosure provides a sodium-ion battery, a method for preparing a sodium-ion battery, a power-consuming device, and a hard carbon material.
  • the above solutions can improve kinetic performance, reduce the risk of negative electrode slurry leakage on the current collector surface, and improve the performance and safety of sodium-ion batteries. These are described in detail below.
  • a first aspect of this disclosure provides a sodium-ion battery, including a negative electrode.
  • the negative electrode includes a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector.
  • the negative electrode film layer includes a hard carbon material, the hard carbon material comprising a porous structure including pores with a pore size of 2 nm to 8 nm, and the pore volume of the pores with a pore size of 2 nm to 8 nm is determined by nitrogen adsorption to be 0.0004 cm3 /g to 0.0040 cm3 /g.
  • the hard carbon material in the negative electrode sheet disclosed in this invention has an optimized pore structure. Specifically, the pore volume of the hard carbon material with a pore size of 2nm-8nm is 0.0004cm3 /g- 0.0040cm3 /g. Research has shown that pores with a pore size of 2nm-8nm, when possessing suitable pore volumes, can improve the kinetic performance of the hard carbon material, and these pore sizes can also contribute to the capacity, thus enabling the negative electrode sheet to have improved kinetic performance while maintaining capacity.
  • the pore volume of a pore with a diameter of 2nm-8nm is 0.0004cm3 / g, 0.0008cm3 / g, 0.0010cm3/g, 0.0012cm3/ g, 0.0014cm3 / g, 0.0016cm3 / g, 0.0018cm3 / g, 0.0020cm3 / g , 0.0022cm3 / g , 0.0024cm3 / g, 0.0026cm3 / g, 0.0028cm3 / g, 0.0030cm3/ g , 0.0032cm3 /g, 0.0035cm3/g, 0.0040cm3 /g, or a value between any two of these values.
  • the pore volume of hard carbon materials has a meaning known in the art and can be measured using instruments and methods known in the art.
  • methods known in the art may include gas adsorption characterization techniques, mercury porosimetry, etc.
  • the adsorption and desorption isotherms can be tested using the nitrogen adsorption method, and the cumulative pore volume distribution curve relative to pore size can be fitted using a DFT model to obtain the pore volume in the pore size range of 2 nm-8 nm.
  • the hard carbon material can be hard carbon material used as a raw material, or it can be hard carbon material obtained from the disassembly and separation of sodium-ion batteries.
  • the pore volume of hard carbon materials with pore sizes of 2nm-8nm is determined to be 0.0010 cm3 /g- 0.0040 cm3 /g by nitrogen adsorption. This is more conducive to improving the kinetic properties of hard carbon materials while taking into account specific capacity.
  • the pore volume of pores with a diameter of 2 nm to 8 nm in the hard carbon material is determined by nitrogen adsorption to be 3.5% to 30% of the total pore volume of the hard carbon material. This further facilitates the balance between the kinetic properties and specific capacity of the hard carbon material, and maintains suitable structural stability.
  • the proportion of the pore volume of pores with a diameter of 2 nm to 8 nm to the total pore volume of the hard carbon material is 3.5%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or a value between any two of these values.
  • the pore volume of hard carbon material with a pore size of less than or equal to 1 nm, determined by carbon dioxide adsorption, is expressed as V1
  • the pore volume of hard carbon material with a pore size of 1 nm to 2 nm, determined by nitrogen adsorption is expressed as V2 .
  • V1 + V2 is in the range of 0.0006 cm3 /g to 0.0050 cm3 /g.
  • V1 + V2 By further limiting V1 + V2 within the above range, it is more beneficial to make hard carbon materials have suitable specific capacity.
  • V1 + V2 is 0.0006 cm3 /g, 0.0010 cm3 / g, 0.0013 cm3 / g, 0.0015 cm3 /g, 0.0018 cm3/g, 0.0020 cm3/g, 0.0023 cm3 / g, 0.0025 cm3 / g, 0.0028 cm3/g, 0.0030 cm3/ g, 0.0033 cm3/ g, 0.0035 cm3/ g, 0.0038 cm3 / g, 0.0040 cm3 / g, 0.0043 cm3 /g, 0.0045 cm3 /g, 0.0048 cm3/g, 0.0050 cm3 /g, or a value between any two of these values.
  • the pore volume V ⁇ sub>1 ⁇ /sub> of hard carbon materials with pore sizes less than or equal to 1 nm can be determined using conventional methods in the art.
  • the CO ⁇ sub>2 ⁇ /sub> adsorption-desorption pore volume and diameter measurement method typically measures the pore volume of pores with diameters less than 1 nm, particularly those in the range of 0.4 nm to 1 nm.
  • the CO ⁇ sub>2 ⁇ /sub> adsorption method can be used to test adsorption and desorption isotherms, and a DFT model can be used to fit the distribution curve of the cumulative pore volume relative to the pore size, thus obtaining the pore volume of pores within a specific pore size range less than or equal to 1 nm.
  • the pore volume V ⁇ sub>2 ⁇ /sub> of hard carbon materials with pore sizes of 1 nm to 2 nm can be determined using conventional methods in the field. For example, the above-mentioned method for testing the pore volume of N ⁇ sub> 2 ⁇ /sub> adsorption-desorption pores.
  • the total pore volume of hard carbon materials can be determined using conventional methods in the field.
  • the above-mentioned N2 adsorption-desorption pore volume and pore size testing method can be combined with the CO2 adsorption-desorption pore volume and pore size testing method to obtain the pore volume of pores with a diameter greater than 1 nm and the pore volume of pores with a diameter less than 1 nm, and then the two are summed to obtain the total pore volume.
  • V1 + V2 is in the range of 0.0006 cm3 /g to 0.0035 cm3 /g.
  • This invention finds that pore volumes with a diameter of less than 2 nm within the range of 0.0006 cm3 /g to 0.0035 cm3 /g are beneficial in achieving suitable specific capacity in the hard carbon material while reducing gas generation and bubbling during slurry preparation, improving the processability of the hard carbon material, enhancing the uniformity of the negative electrode sheet, reducing the risk of incomplete coating of the negative electrode slurry, and improving the performance of the sodium-ion battery.
  • V1 + V2 is in the range of 0.0020 cm3 /g to 0.0035 cm3 /g.
  • the proportion of V1 + V2 to the total pore volume of the hard carbon material is in the range of 18% to 30%. Having the proportion of pore volume with a diameter of less than 2 nm to the total pore volume within the above range is more beneficial for improving the specific capacity of the hard carbon material.
  • the proportion of V1 + V2 to the total pore volume is 18%, 20%, 23%, 25%, 28%, 30%, or a value between any two of these values.
  • the total pore volume of hard carbon materials can be determined using conventional methods in the field.
  • the above-mentioned N2 adsorption-desorption pore volume and pore size testing method combined with the above-mentioned CO2 adsorption-desorption pore volume and pore size testing method, can be used to obtain the pore volume of pores with a diameter greater than 1 nm and the pore volume of pores with a diameter less than 1 nm, and then the two are summed to obtain the final volume.
  • the dV/d(logD) mentioned in this disclosure reflects the pore volume contributed per unit pore size and can be determined by gas adsorption characterization techniques for hard carbon materials. For example, it can be determined using a surface area analyzer-static volumetric method. Specifically, according to embodiments of this disclosure, a flow-type gas adsorption surface area measurement device (device model Micromeritics ASAP-2460) can be used for measurement. Adsorption and desorption isotherms are obtained by nitrogen adsorption testing, and the distribution curve of dV/d(logD) relative to pore size D is fitted using a DFT model, with the maximum value read in the pore size range of 1.0 nm to 2.0 nm.
  • the hard carbon material comprises pores with a diameter in the range of 1.0 nm to 1.5 nm.
  • the maximum value of the derivative of the cumulative pore volume V of the pores with a diameter in the range of 1.0 nm to 1.5 nm with respect to the logarithm of the pore diameter D, dV/d(logD), is determined by nitrogen adsorption and is between 0.001 cm3 /(g ⁇ log(nm)) and 0.009 cm3 /(g ⁇ log(nm)). This is more conducive to reducing gas generation and bubbling during the pulping process.
  • the maximum value of dV/d(logD) for a pore with an aperture of 1.0nm-1.5nm is 0.001cm3/(g ⁇ log(nm)), 0.002cm3/(g ⁇ log(nm)), 0.003cm3/(g ⁇ log(nm)), 0.004cm3 / ( g ⁇ log(nm)), 0.005cm3 / ( g ⁇ log(nm)) , 0.006cm3 / (g ⁇ log(nm)), 0.007cm3 /(g ⁇ log(nm)), 0.008cm3/(g ⁇ log(nm)), 0.009cm3 /(g ⁇ log(nm)), or a value between any two of these values.
  • the maximum value of the derivative of the cumulative pore volume V with respect to the logarithm of the pore size D, dV/d(logD), determined by nitrogen adsorption, for pores with a pore size of 1.0 nm to 1.5 nm is between 0.001 cm3 /(g ⁇ log(nm)) and 0.006 cm3 /(g ⁇ log(nm)). This further helps to reduce gas generation and bubbling during the pulping process.
  • the pore volume of the hard carbon material with a pore size of 1.0 nm to 1.5 nm accounts for 6% to 14% of the total pore volume of the hard carbon material. This further helps to reduce gas generation during the pulping process.
  • the proportion of the pore volume of the pores with a pore size of 1.0 nm to 1.5 nm to the total pore volume is 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or a value between any two of these values.
  • the negative electrode film layer further includes an intercalated sodium storage material, wherein the intercalation spacing d ⁇ sub>002 ⁇ /sub> of the intercalated sodium storage material satisfies: 0.24 nm ⁇ d ⁇ sub>002 ⁇ /sub> ⁇ 0.8 nm. Therefore, the intercalated sodium storage material with an intercalation spacing within the above range can exhibit interlayer slip in its microstructure. When applied in sodium-ion batteries, this helps increase the powder compaction density of the negative electrode sheet, thereby helping to improve the energy density of the sodium-ion battery.
  • the mass content of the intercalated sodium storage material in the negative electrode film layer is less than or equal to 10%.
  • the mass content of the intercalated sodium storage material is between 0.5% and 5%.
  • the intercalated sodium storage material includes at least one of carbon-based intercalated sodium storage material, sulfur-based intercalated sodium storage material, and titanium-based intercalated sodium storage material;
  • the carbon-based intercalated sodium storage material includes at least one of soft carbon and modified graphite; the ID / IG ratio of soft carbon satisfies: 0.9 ⁇ ID / IG ⁇ 1.6, where ID represents the intensity of the D peak in the Raman spectrum at 1350 ⁇ 50 cm ⁇ 1 , and IG represents the intensity of the G peak in the Raman spectrum at 1580 ⁇ 50 cm ⁇ 1 .
  • the negative electrode film includes a first negative electrode film and a second negative electrode film stacked together.
  • the first negative electrode film is disposed between the negative electrode current collector and the second negative electrode film.
  • the first negative electrode film includes a first active material
  • the second negative electrode film includes a second active material.
  • the first active material and the second active material each include at least one of a hard carbon material and an intercalated sodium storage material, and at least one of the first active material and the second active material includes a hard carbon material.
  • the intercalated sodium storage material can affect the sodium storage mechanism of the negative electrode active material, reducing the possibility of sodium ions depositing in the hard carbon to form metalloid sodium, thereby reducing the risk of sodium ion thermal runaway.
  • the first active material includes a hard carbon material
  • the second active material includes a soft carbon material. This is more conducive to improving kinetic performance.
  • the hard carbon material of further embodiments of this disclosure has further improved processability.
  • the total metal ion content in the hard carbon material is ⁇ 800ppm, and the content of divalent or higher metal ions is ⁇ 20ppm.
  • This disclosure reveals that when the total content of metal ions and the content of divalent or higher metal ions are within the aforementioned range, the impact on other components in the negative electrode slurry, such as thickeners, dispersants, and especially sodium carboxymethyl cellulose, is minimal. This is beneficial for maintaining a suitable viscosity of the slurry during preparation, thereby facilitating the uniform coating of the slurry onto the negative electrode current collector.
  • Metal ions in hard carbon materials may be introduced, for example, through metal elements contained in the carbon source or through doping.
  • the total amount of metal ions especially the total amount of metal ions with a positive divalent or higher valence, is particularly advantageous for pulping and coating processes when it is within the aforementioned range.
  • the content of metal ions in hard carbon can be determined by conventional methods in the art, such as inductively coupled plasma atomic emission spectrometry.
  • the total metal ion content in the hard carbon material is 20ppm-800ppm, and the content of divalent or higher metal ions is 0.1ppm-20ppm.
  • This disclosure further improves the processability of the hard carbon material and increases the inorganic content of the negative electrode SEI film by keeping the total metal ion content and the content of divalent or higher metal ions within the above ranges, which is beneficial for reducing the formation of sodium dendrites or sodium deposition on the surface of the hard carbon material.
  • the metal ions include at least one of Na + , K + , Ca2 + , Mg2 + , Mn2 + , Ba2 + , and Al3 + , but are not limited thereto.
  • the divalent or higher metal ion is Ca2+ .
  • the calcium ion content in hard carbon materials has a significant impact on the negative electrode slurry. Controlling the calcium ion content within the aforementioned range is beneficial for obtaining a negative electrode slurry with suitable viscosity, which is beneficial for subsequent coating and other processes, thereby obtaining a negative electrode sheet with improved quality.
  • the surface oxygen content of the hard carbon material is 6%-14%.
  • the surface oxygen content of the hard carbon material is 6%, 7%, 8%, 9%, 9.5%, 10%, 10.5%, 11%, 12%, 13%, 14%, or a range of any two of these values.
  • the surface oxygen content of the hard carbon material is 8%-12%. A surface oxygen content within this range is more conducive to improving the coating performance of the hard carbon material.
  • the hard carbon material disclosed herein may further satisfy one or more of the following conditions to further improve at least one aspect of the performance of the hard carbon material, such as reversible capacity, compaction density, etc.
  • Hard carbon materials have a surface coating.
  • the surface coating can reduce surface defects.
  • the surface coating is a carbon coating.
  • the ID / IG ratio of hard carbon materials is ⁇ 1.35; where ID represents the intensity of the D peak in the Raman spectrum at 1350 ⁇ 50 cm ⁇ 1 , and IG represents the intensity of the G peak in the Raman spectrum at 1580 ⁇ 50 cm ⁇ 1 .
  • ID represents the intensity of the D peak in the Raman spectrum at 1350 ⁇ 50 cm ⁇ 1
  • IG represents the intensity of the G peak in the Raman spectrum at 1580 ⁇ 50 cm ⁇ 1 .
  • the ID / IG ratio of hard carbon materials maintains a suitable proportion of disordered carbon on the surface.
  • a certain amount of ordered carbon in the layered structure is beneficial for increasing the compaction density of hard carbon materials through interlayer slip, thereby improving the negative electrode energy storage density.
  • the ID /IG ratio of the hard carbon material is 0.7-1.32.
  • the ID / IG ratio of the hard carbon material is 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.30, or any value within the range of any two values.
  • the particle size Dn10 of the hard carbon material is 0.5 ⁇ m-1.0 ⁇ m, which is more conducive to the compaction density of the negative electrode sheet.
  • the fewer low-size particles indicate that the hard carbon has an appropriate pore structure and moderate material skeleton strength.
  • the particle size of the hard carbon material meets the following requirements: the volume distribution particle size Dv10 of the hard carbon material is ⁇ 3.0 ⁇ m; the volume distribution particle size Dv50 of the hard carbon material is ⁇ 7.9 ⁇ m; and the volume distribution particle size Dv90 of the hard carbon material is ⁇ 15 ⁇ m.
  • the particle size of the hard carbon material meets the above requirements, which is more conducive to the compaction density of the negative electrode sheet.
  • the compaction density of hard carbon material at 50000N is ⁇ 1 ⁇ 0.9g/ cm3 .
  • the specific surface area of hard carbon materials is 2 m2 /g-12 m2 /g.
  • the specific surface area of hard carbon materials within the above range is conducive to obtaining a suitable pore structure and to balancing the specific capacity.
  • the specific surface area of the hard carbon material is between 3 m2 /g and 8 m2 /g. A specific surface area within this range is more conducive to balancing specific capacity.
  • the tap density ⁇ 2 of hard carbon material is 0.75 g/ cm3 - 0.9 g/ cm3 .
  • the pore volume and specific surface area of hard carbon materials have meanings known in the art and can be measured using instruments and methods known in the art.
  • the adsorption and desorption isotherms can be tested using the nitrogen adsorption method
  • the specific surface area of the hard carbon material can be calculated using the BET (Brunauer Emmett Teller) method
  • the cumulative pore volume distribution curve relative to pore size and the dV/d(logD)-D curve can be fitted using a DFT model to obtain the pore volume of pores in a specific pore size range above 1 nm.
  • the testing instrument can be the ASAP-2460 specific surface area and pore size analyzer from Micromeritics, USA.
  • Carbon dioxide molecules have a smaller kinetic diameter than nitrogen molecules and a higher saturated vapor pressure at 273 K. At this temperature, the gas can diffuse more rapidly into pores smaller than 1 nm, allowing for the analysis and detection of smaller microporous structures. Therefore, the carbon dioxide adsorption method is used to test adsorption and desorption isotherms, and a DFT model is used to fit the distribution curve of cumulative pore volume relative to pore size, thus obtaining the pore volume of pores in a specific pore size range of 0-1 nm.
  • the testing instrument can be, for example, the ASAP-2460 surface area and pore size analyzer from Micromeritics, USA.
  • the metallic elements and their contents in hard carbon materials can be determined using instruments and methods known in the art.
  • ICP-OES inductively coupled plasma atomic emission spectrometry
  • the testing instrument can be, for example, an ICP-OES instrument such as the Thermo ICAP7400.
  • the surface oxygen content of hard carbon materials can be determined using instruments and methods known in the art.
  • the testing instrument can be an Axis Supra+ X-ray photoelectron spectrometer, in accordance with the requirements of GB/T 33502-2017 for recording and reporting X-ray photoelectron spectroscopy (XPS) data for surface chemical analysis.
  • XPS X-ray photoelectron spectroscopy
  • the ID / IG value of hard carbon materials can be measured using a Raman spectrometer.
  • ID represents the intensity of the D peak in the Raman spectrum of the material at 1350 ⁇ 50 cm ⁇ 1 , corresponding to symmetry destruction, i.e., the presence of disorder and lattice defects in the structure.
  • IG represents the intensity of the G peak in the Raman spectrum of the material at 1580 ⁇ 50 cm ⁇ 1 , corresponding to the G (graphite) band of the in-plane CC vibration.
  • the test conditions are: excitation wavelength of 532 nm, test wavenumber range of 500-2500 cm ⁇ 1 , grating of 600 lines, objective lens of 50x, integration time of 10 s, cumulative scan of 3 times, area scan, obtaining the D and G peak intensities of 100 points, calculating the ID / IG of the 100 points, removing the maximum and minimum ID / IG values of the 30 points each, and the average value of the remaining 40 points is the ID / IG of the material.
  • the testing instrument can be a Horiba LabRAM HR800 Raman spectrometer.
  • the compaction density of hard carbon materials has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined by referring to GB/T 24533-2009 using an electronic pressure testing machine (e.g., a UTM7305 electronic pressure testing machine).
  • An exemplary test method is as follows: Weigh 1g of sample powder, add it to a mold with a bottom area of 1.327cm2 , pressurize to 50000N, hold the pressure for 30s, then release the pressure, hold for 10s, and then record and calculate the compaction density of the material under 50000N pressure.
  • the tap density of hard carbon materials has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using a powder tap density tester according to GB/T 5162-2006.
  • the testing instrument can be Dandong Baite BT-301, with the following test parameters: vibration frequency 250 ⁇ 15 times/minute, amplitude 3 ⁇ 0.2mm, vibration frequency 5000 times, and measuring cylinder 25cm3 .
  • the number distribution particle size Dn10 and volume distribution particle sizes Dv10, Dv50, and Dv90 of hard carbon materials have meanings known in the art and can be determined using instruments and methods known in the art. For example, they can be determined using a laser particle size analyzer, referring to GB/T 19077-2016.
  • the testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.
  • the particle size of hard carbon materials can be measured and statistically analyzed using microscopic images.
  • the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • a metal foil a lithium-ion battery may use copper foil, and a sodium-ion battery may use aluminum foil.
  • the composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate.
  • the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative current collector includes at least one of copper foil, aluminum foil, stainless steel foil, titanium foil, nickel foil, nickel-iron foil, nickel-copper foil, and nickel-iron-copper foil.
  • the negative electrode film layer may optionally include a binder.
  • the binder may be selected from at least one of styrene-butadiene rubber (SBR), acrylate rubber, polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).
  • the first adhesive may be a first water-based adhesive.
  • the first water-based adhesive may be selected from one or more of styrene-butadiene rubber and acrylic rubber.
  • the negative electrode film layer may optionally include an aqueous dispersant.
  • the aqueous dispersant may be selected from one or more of sodium carboxymethyl cellulose (CMC-Na), sodium alginate, xanthan gum, and carrageenan.
  • the negative electrode film layer may optionally include a first conductive agent.
  • the first conductive agent may be selected from at least one of Super-P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the negative electrode film layer may optionally include other additives.
  • the negative electrode film layer includes at least one of a first aqueous binder, an aqueous dispersant, and a first conductive agent.
  • the mass content of hard carbon material in the negative electrode film layer is above 80%.
  • the mass content of hard carbon material in the negative electrode film layer is 85% or more. Exemplarily, it is 88% or more, 90% or more, 92% or more, 94% or more, or greater than 95% or more. Exemplarily, the mass content of hard carbon material in the negative electrode film layer is 99.3% or less, 99.0% or less, 98.8% or less, 98.5% or less, 98.3% or less, or 98.0% or less.
  • the water-based adhesive has a mass content of 0% to 5%, optionally 0% to 3%, and more preferably 0.5% to 2%.
  • the water-based dispersant has a mass content of 0% to 5%, optionally 0% to 2%, and more preferably 0.1% to 1%.
  • the mass content of the conductive agent is 0% to 5%, optionally 0% to 2%, and more preferably 0.1% to 2%.
  • the negative electrode sheet further includes an undercoating layer; the thickness of the undercoating layer is 0.5 ⁇ m-3 ⁇ m. This is beneficial for improving the coating quality of the electrode sheet.
  • the undercoat includes an inorganic oxide and a second water-based binder.
  • Inorganic oxides have a high density and better adhesion to the metal current collector substrate, making them less prone to shrinkage or displacement under the surface tension of the slurry compared to hard carbon materials or conductive agents in the film layer.
  • Water-based slurries including water-based binders have high surface tension, often resulting in large surface energy differences and poor coating quality when coated on the current collector.
  • Including inorganic oxides in the undercoat can particularly solve the problem of poor compatibility between water-based slurries and the current collector substrate, improving the coating quality of the water-based slurry on the current collector substrate. This further helps reduce the risk of incomplete coating and improves the electrode coating quality.
  • the inorganic oxide in the undercoat includes one or more of aluminum oxide, boehmite, magnesium oxide, iron oxide, silicon oxide, and zirconium oxide; the inorganic oxide accounts for 30%-60% of the mass of the undercoat.
  • the inclusion of inorganic oxides within the aforementioned mass range in the undercoat can improve the quality of the electrode coating, enhance electrode bonding strength, reduce elongation during cold pressing, and effectively control the current collector resistance, thus ensuring optimal electrochemical performance of the battery.
  • the second waterborne binder can also be selected from one or more of styrene-butadiene rubber and acrylic rubber.
  • the second waterborne binder can be the same as or different from the first waterborne binder.
  • the second waterborne binder is amphiphilic and exhibits better water resistance compared to linear binders that have a strong affinity for water solvents. This allows the base coating to remain stable during the application of the upper film containing the active material, further enhancing the role of the base coating in improving coating quality.
  • the base coating includes an inorganic oxide, a dispersant, a second aqueous binder, and a second conductive agent.
  • the dispersant includes one or more polyacrylic polymers.
  • Acrylic polymers can effectively disperse inorganic oxides, helping them to fully exert their performance.
  • the mass content of the dispersant in the primer coating is 1%-8%, optionally 1%-5%.
  • the second conductive agent can be selected from one or more of Super-P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the second conductive agent and the first conductive agent can be the same or different.
  • the mass content of the second conductive agent in the base coating is 10%-40%.
  • the base coating comprises 30%-60% inorganic oxides, 1%-8% dispersant, 10%-40% second aqueous binder, and 10%-40% second conductive agent.
  • the base coating also includes a thickener and/or a wetting agent.
  • the wetting agent can be selected from one or more of the following: polyoxyethylene ether surfactants, polyether silicone surfactants, nonionic fluorocarbon polymer surfactants, and alkyne surfactants.
  • the thickener content in the base coating is 0.5%-4% by mass.
  • the thickener can be selected from one or more of sodium carboxymethyl cellulose, sodium alginate, xanthan gum, and carrageenan. In the base coating, the thickener content is 0.2%-1% by mass.
  • a sodium-ion battery includes a positive electrode, a negative electrode, a separator between the positive and negative electrodes, an electrolyte, and the negative electrode as described in the above embodiments.
  • the sodium-ion battery of this disclosure will be described below with appropriate reference to the accompanying drawings.
  • sodium-ion battery used in this article refers to a single battery cell, a battery module, or a battery pack. These will be explained separately below.
  • a sodium-ion battery cell typically includes a positive electrode, a negative electrode, an electrolyte (liquid), and a separator.
  • active ions such as sodium ions
  • the electrolyte acts as a conductor between the positive and negative electrodes.
  • the separator positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.
  • the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.
  • the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.
  • the positive current collector may be a metal foil or a composite current collector.
  • aluminum foil may be used as the metal foil.
  • the composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate.
  • the composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the battery cell is a sodium-ion battery
  • the positive electrode active material can be a positive electrode active material known in the art for sodium-ion batteries.
  • the positive electrode active material may include sodium-containing layered oxides, polyanionic sodium compounds, Prussian blue sodium compounds, etc., but this disclosure is not limited to these materials; other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries can also be used.
  • the transition metal in the sodium-containing layered oxide, can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce.
  • the sodium transition metal oxide is, for example, Na ⁇ sub>x ⁇ /sub> MO ⁇ sub> 2 ⁇ /sub>, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 ⁇ x ⁇ 1.
  • the positive electrode active material includes at least one of sodium-containing layered oxides, polyanionic sodium compounds, and Prussian blue sodium compounds.
  • sodium-containing layered oxides can be iron-manganese layered oxides.
  • Iron-manganese layered oxides include at least one of nickel-iron-manganese layered oxides and copper-iron-manganese layered oxides.
  • the polyanionic sodium ion compound can be a class of compounds having sodium ions, transition metal ions, and tetrahedral ( YO4 ) n- anionic units.
  • the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce;
  • Y can be at least one of P, S, and Si; and
  • n represents the valence state of ( YO4 ) n- .
  • the polyanionic sodium ion compound can also be a class of compounds having sodium ions, transition metal ions, tetrahedral ( YO4 ) n- anionic units, and halide anions.
  • the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; and n represents the valence state of ( YO4 ) n- ; the halogen can be at least one of F, Cl, and Br.
  • Polyanionic sodium ion compounds can also be a class of compounds having sodium ions, tetrahedral ( YO4 ) n- anionic units, polyhedral ( ZOy ) m+ units, and optional halide anions.
  • Y can be at least one of P, S, and Si
  • n represents the valence state of ( YO4 ) n-
  • Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce
  • m represents the valence state of ( ZOy ) m+
  • the halogen can be at least one of F, Cl, and Br.
  • Polyanionic sodium ion compounds are, for example, at least one of NaFePO4 , Na3V2 ( PO4 ) 3 , NaM'PO4F (M' is one or more of V, Fe, Mn, and Ni), and Na3 ( VOy ) 2 ( PO4 ) 2F3-2y (0 ⁇ y ⁇ 1 ) .
  • the polyanionic sodium ion compound can be Na ⁇ sub>xa ⁇ /sub>A ⁇ sub> a ⁇ /sub>V ⁇ sub>yb ⁇ /sub> M ⁇ sub> b ⁇ /sub>(PO ⁇ sub> 4 ⁇ /sub>) ⁇ sub>2 ⁇ /sub>-2c (DO ⁇ sub> 4 ⁇ /sub>) ⁇ sub>2c ⁇ /sub> F ⁇ sub>zd ⁇ /sub> Q ⁇ sub> d ⁇ /sub>, wherein element A represents an alkali metal element doping to replace element Na, element M represents a metal element doping to replace element V, element D represents a dopant element doping to replace element P, and element Q represents a dopant element doping to replace element F.
  • Element D includes at least one of Si and S, and element Q includes at least one of Cl and O; 3.5 ⁇ x ⁇ 4.5, 0 ⁇ a ⁇ 0.15x, 0.8 ⁇ y ⁇ 1.1, 0 ⁇ b ⁇ 0.3y, 0 ⁇ c ⁇ 0.15, 0.8 ⁇ z ⁇ 1.1, 0 ⁇ d ⁇ 0.2z.
  • element A includes at least one of K and Li;
  • element M includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.
  • the polyanionic sodium ion compound can be Na 4+x R 3-y P 4-m O 15 /C;
  • R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.
  • Prussian blue compounds can be a class of compounds containing sodium ions, transition metal ions, and cyanide ions ( CN- ).
  • the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce.
  • Examples of Prussian blue compounds are Na a Me b Me' c (CN) 6 , where Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, with 0 ⁇ a ⁇ 2, 0 ⁇ b ⁇ 1, and 0 ⁇ c ⁇ 1.
  • the battery cell may be a lithium-ion battery
  • the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries.
  • the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds.
  • this disclosure is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more.
  • lithium transition metal oxides include, but are not limited to , lithium cobalt oxides (such as LiCoO2 ), lithium nickel oxides (such as LiNiO2 ), lithium manganese oxides (such as LiMnO2 , LiMn2O4 ), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides (such as LiNi 1/3 Co 1/3 Mn 1/3 O2 (also abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also abbreviated as NCM 622 ), and LiNi 0.8 Co 0.1 Mn 0.1 O2 (also abbreviated as NCM 811 ).
  • lithium cobalt oxides such as LiCoO2
  • lithium nickel cobalt aluminum oxides such as LiNi 0.85 Co 0.15 Al 0.05 O 2
  • lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO 4 ), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.
  • the active ions (Li or Na) undergo insertion/extraction and consumption, resulting in different molar contents of Li or Na at different discharge states.
  • the molar contents of Li or Na refer to the initial state of the material, i.e., the state before feeding.
  • the positive electrode active material is applied to the battery system, the molar contents of Li or Na will change after charge-discharge cycles.
  • the molar content of oxygen is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of oxygen will fluctuate.
  • the positive electrode film layer may optionally include a binder.
  • the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PVDF-tetrafluoroethylene-propylene terpolymer PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer
  • tetrafluoroethylene-hexafluoropropylene copolymer tetrafluoroethylene-hexafluoropropylene copolymer
  • the positive electrode film may optionally include a conductive agent.
  • the conductive agent may include at least one selected from Super-P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the electrolyte acts as a conductor of ions between the positive and negative electrodes.
  • This disclosure does not impose specific limitations on the type of electrolyte; it can be selected according to requirements.
  • the electrolyte can be liquid, gel-like, or entirely solid.
  • the electrolyte is an electrolyte solution.
  • the electrolyte solution includes an electrolyte salt and a solvent.
  • the battery cell is a sodium-ion battery
  • the electrolyte salt may be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorosulfonamide, sodium ditrifluoromethanesulfonamide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalate borate, sodium dioxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate.
  • the battery cell is a lithium-ion battery
  • the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.
  • the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.
  • the solvent in the electrolyte includes carbonate solvents, including at least one of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. This is beneficial for improving the high-voltage resistance of the electrolyte.
  • the volume fraction of propylene carbonate relative to the solvent is 15%-55%. This not only improves the oxidation resistance of the electrolyte but also enhances conductivity by dissociating the sodium salt.
  • the electrolyte may optionally include additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.
  • the battery cell also includes a separator disposed between the positive and negative electrode plates.
  • a separator disposed between the positive and negative electrode plates. This disclosure does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.
  • the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.
  • the separator can be a single-layer film or a multi-layer composite film, without particular limitation.
  • the materials of each layer can be the same or different, without particular limitation.
  • the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.
  • the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell.
  • the outer packaging of the battery cell can also be a flexible package, such as a pouch.
  • the material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.
  • FIG. 1 shows a square battery cell 5 as an example.
  • the outer packaging may include a housing 51 and a top cover assembly 53.
  • the housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity.
  • the housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity.
  • the positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process.
  • the electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52.
  • the number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.
  • individual battery cells can be assembled into a battery module.
  • the number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.
  • FIG 3 shows a battery module 4 as an example.
  • multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.
  • the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.
  • the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.
  • FIGs 4 and 5 show a battery pack 1 as an example.
  • the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box.
  • the battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4.
  • the multiple battery modules 4 can be arranged in any manner within the battery box.
  • This disclosure also provides a method for preparing a sodium-ion battery, including preparing a negative electrode sheet.
  • the preparation of the negative electrode sheet includes: mixing a negative electrode component and a solvent to obtain a negative electrode slurry.
  • the negative electrode component includes a hard carbon material, which has a porous structure comprising pores with a diameter of 2 nm to 8 nm. The pore volume of the pores with a diameter of 2 nm to 8 nm is determined to be 0.0004 cm3 /g to 0.0040 cm3 /g by nitrogen adsorption.
  • the method also involves coating the negative electrode slurry onto a negative electrode current collector.
  • the pores with a diameter of 2 nm to 8 nm have a suitable pore volume, they can improve the kinetic performance of the hard carbon material, and these pores can also contribute to the capacity, thereby enabling the negative electrode sheet to have improved kinetic performance while maintaining capacity.
  • the pore volume of hard carbon materials with pore sizes of 2nm-8nm is determined to be 0.0010 cm3 /g- 0.0040 cm3 /g by nitrogen adsorption. This is more conducive to improving the kinetic properties of hard carbon materials while taking into account specific capacity.
  • the pore volume of pores with a diameter of 2 nm to 8 nm in the hard carbon material is determined by nitrogen adsorption to account for 3.5% to 30% of the total pore volume of the hard carbon material. This further facilitates the balance between the kinetic properties and specific capacity of the hard carbon material, and maintains suitable structural stability.
  • the pore volume of hard carbon material with a pore size of less than or equal to 1 nm, determined by carbon dioxide adsorption, is denoted as V1
  • the pore volume of hard carbon material with a pore size of 1 nm to 2 nm, determined by nitrogen adsorption is denoted as V2 .
  • V1 + V2 is in the range of 0.0006 cm3 /g to 0.0050 cm3 /g. Further limiting V1 + V2 to the above range is more beneficial for achieving a suitable specific capacity in the hard carbon material.
  • V1 + V2 is in the range of 0.0006 cm3 /g to 0.0035 cm3 /g.
  • a pore volume of 0.0006 cm3 /g to 0.0035 cm3 /g for pores with a diameter of less than 2 nm is also beneficial for achieving suitable specific capacity in hard carbon materials while reducing gas generation and bubbling during the slurry preparation process, improving the processability of hard carbon materials, enhancing the uniformity of the negative electrode sheet, reducing the risk of negative electrode slurry leakage, and improving the performance of sodium-ion batteries.
  • V1 + V2 is in the range of 0.0020 cm3 /g to 0.0035 cm3 /g.
  • V1 + V2 accounts for 18% to 30% of the pore volume of the hard carbon material.
  • a proportion of the pore volume of pores with a diameter of less than 2 nm in the hard carbon material within the above range is more conducive to improving the specific capacity of the hard carbon material.
  • the hard carbon material comprises pores with a diameter in the range of 1.0 nm to 1.5 nm.
  • the maximum value of the derivative of the cumulative pore volume V of the pores with a diameter in the range of 1.0 nm to 1.5 nm with respect to the logarithm of the pore diameter D, dV/d(logD), is determined by nitrogen adsorption and is between 0.001 cm3 /(g ⁇ log(nm)) and 0.009 cm3 /(g ⁇ log(nm)). This is more conducive to reducing gas generation and bubbling during the pulping process.
  • the maximum value of the derivative of the cumulative pore volume V with respect to the logarithm of the pore size D, dV/d(logD), determined by nitrogen adsorption, for pores with a pore size of 1.0 nm to 1.5 nm is between 0.001 cm3 /(g ⁇ log(nm)) and 0.006 cm3 /(g ⁇ log(nm)). This further helps to reduce gas generation and bubbling during the pulping process.
  • the pore volume of the hard carbon material with a pore size of 1.0 nm to 1.5 nm accounts for 6% to 14% of the total pore volume of the hard carbon material. This further helps to reduce gas generation during the pulping process.
  • the mass percentage of the negative electrode component relative to the mass of the negative electrode slurry is 50% to 60%. This is beneficial for the uniformity and stability of the slurry.
  • the mass percentage of the negative electrode component relative to the mass of the negative electrode slurry is 50%, 52%, 54%, 56%, 58%, 60%, or a value between any two of these values.
  • the mass percentage of hard carbon relative to the mass of the negative electrode component is 80% to 95%. This is beneficial to the energy density of the battery.
  • the mass percentage of hard carbon relative to the mass of the negative electrode component is 80%, 82%, 85%, 87%, 90%, 92%, 95%, or a value between any two of these values.
  • the negative electrode component further includes one or more of a conductive agent, a binder, and a dispersant.
  • the conductive agent can effectively accelerate the electron transport rate and improve the charge/discharge efficiency of the battery.
  • the binder helps maintain the integrity of the electrode structure during battery charge/discharge.
  • the dispersant can improve the dispersibility of the negative electrode component particles in the solvent, making the slurry easier to coat.
  • mixing the negative electrode components and solvent includes vacuum stirring at 0°C to 30°C for 1 to 4 hours.
  • This disclosure does not impose specific limitations on vacuum stirring; appropriate vacuum levels, temperatures, times, stirring speeds, and other process conditions can be selected according to actual production needs.
  • the slurry should remain uniform and stable after vacuum stirring and before proceeding to the next step.
  • the negative electrode components include hard carbon, a dispersant, a conductive agent, and a binder.
  • the negative electrode slurry is prepared through the following steps: mixing hard carbon, a dispersant, a conductive agent, and a solvent, and performing vacuum stirring; and further adding a binder and stirring for another 2 to 4 hours.
  • the bubbling time can be significantly reduced, which is conducive to the smooth progress of slurry preparation and also beneficial to subsequent coating and cold pressing processes, thereby improving the uniformity of the negative electrode film and preventing the current collector from being exposed.
  • the preparation of the negative electrode sheet further includes: coating a negative electrode slurry onto at least one surface of the negative electrode current collector and subsequently performing processes such as drying, cold pressing, and die cutting.
  • This disclosure does not impose particular limitations on these processes for preparing the negative electrode sheet, and those skilled in the art can employ appropriate process methods according to actual needs.
  • the negative electrode sheet is prepared as follows: The mass ratio of hard carbon material, conductive agent, binder, and dispersant is 93:2:3.5:1.5.
  • the hard carbon material, conductive agent (SP), dispersant (CMC), and an appropriate amount of deionized water are mixed and vacuum stirred at room temperature for approximately 1-4 hours at a speed of 1000 r/min.
  • the binder (SBR) is added, and stirring continues for approximately 2-4 hours to achieve fluidity.
  • Good negative electrode slurry Coat the negative electrode slurry onto the Cu or Al current collector at a belt feed rate of 1-3 m/min.
  • the electrode surface should be free of bubbles, false edges, and scratches.
  • the electrode After coating, dry the electrode at 80°C, adjust the belt feed rate to 1-3 m/min, and then wind it up.
  • the electrode surface should be free of obvious exposed foil, pinholes, or missing coating.
  • the electrode that meets the requirements is then cold-pressed, and the electrode is laser-di-cut to form tabs and wound up.
  • the negative electrode process is now complete, and the negative electrode sheet is obtained.
  • the preparation method of a sodium-ion battery further includes: preparing a positive electrode sheet.
  • the positive electrode sheet is prepared by the following method: The positive electrode active material, conductive agent, and binder are mixed in a mass ratio of 8:1:1 (e.g., 8:1:1).
  • the positive electrode active material polyanionic or laminar oxide positive electrode
  • conductive agent e.g., SP
  • binder PVDF
  • NMP N-methylpyrrolidone
  • the positive electrode slurry is coated onto an Al current collector at a speed of 1-3 m/min, resulting in a good electrode surface free of bubbles, false edges, and scratches.
  • the coated electrode sheet is dried at 80°C, the speed is adjusted to 1-3 m/min, and then it is wound up, ensuring no obvious exposed foil, pinholes, or missed coating on the electrode surface.
  • the electrode sheet that meets the requirements is then cold-pressed, laser-diced to form tabs, and wound up to complete the preparation of the positive electrode sheet.
  • the method for preparing a sodium-ion battery further includes: assembling a positive electrode, a negative electrode, and a separator into an electrode assembly that can be manufactured by a winding process or a stacking process; placing the electrode assembly in an outer package, filling it with electrolyte, and then sealing it to form a battery cell.
  • the electrode assembly can be manufactured by a winding process or a stacking process, and this disclosure does not impose any particular limitation on this.
  • the battery cell can be further assembled into a battery module.
  • separator and electrolyte does not impose any particular limitations on the separator and electrolyte.
  • the materials that can be used as separators and the electrolyte components are as described above, and those skilled in the art can select appropriate separator materials and electrolyte components as needed.
  • the electrical devices mentioned in the embodiments of this disclosure include sodium-ion batteries provided in this disclosure or sodium-ion batteries prepared by the sodium-ion battery preparation method of this disclosure.
  • Sodium-ion batteries can be used as the power source of an electrical device or as the energy storage unit of an electrical device.
  • Electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • FIG. 6 shows an example of an electrical device.
  • This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or battery module can be used.
  • Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.
  • the hard carbon material comprises a porous structure, which includes pores with a diameter of 2 nm to 8 nm.
  • the pore volume of the pores with a diameter of 2 nm to 8 nm is determined to be 0.0004 cm3 /g to 0.0040 cm3 /g by nitrogen adsorption method.
  • the hard carbon material disclosed herein has an optimized pore structure. Specifically, the pores of the hard carbon material with a pore size of 2 nm to 8 nm have a pore volume of 0.0004 cm3 /g to 0.0040 cm3 /g, thereby improving the kinetic properties of the hard carbon material while also taking into account its specific capacity.
  • the pore volume of hard carbon materials with pore sizes of 2nm-8nm is determined to be 0.0010 cm3 /g- 0.0040 cm3 /g by nitrogen adsorption. This is more beneficial to the kinetic properties of hard carbon materials while also taking into account specific capacity.
  • the pore volume of pores with a diameter of 2 nm to 8 nm in the hard carbon material is determined by nitrogen adsorption to account for 3.5% to 30% of the total pore volume of the hard carbon material. This is beneficial for balancing kinetic properties and specific capacity, and for maintaining appropriate structural stability.
  • the pore volume of hard carbon materials with a pore size of less than or equal to 1 nm, determined by carbon dioxide adsorption, is denoted as V1
  • the pore volume of hard carbon materials with a pore size of 1 nm to 2 nm, determined by nitrogen adsorption is denoted as V2 .
  • V1 + V2 falls within the range of 0.0006 cm3 /g to 0.0050 cm3 /g.
  • a pore volume of hard carbon materials with a pore size of less than 2 nm falling within this range is more advantageous for the hard carbon materials to possess suitable specific capacity.
  • V1 + V2 is in the range of 0.0006 cm3 /g to 0.0035 cm3 /g. This allows the hard carbon material to have a suitable specific capacity while reducing gas generation and bubbling during the negative electrode slurry preparation process. This results in a negative electrode sheet with improved capacity and a uniform negative electrode film, reducing the risk of negative electrode slurry leakage and improving the performance of the sodium-ion battery. Preferably, it is in the range of 0.0020 cm3 /g to 0.0035 cm3 /g.
  • the proportion of V1 + V2 to the total pore volume of the hard carbon material is in the range of 18% to 30%. Having the proportion of pore volume with a diameter of less than 2 nm to the total pore volume within the above range is more beneficial for improving the specific capacity of the hard carbon material.
  • the hard carbon material comprises pores with a diameter in the range of 1.0 nm to 1.5 nm.
  • the maximum value of the derivative of the cumulative pore volume V of the pores with a diameter in the range of 1.0 nm to 1.5 nm with respect to the logarithm of the pore diameter D, dV/d(logD), is determined by nitrogen adsorption and is between 0.001 cm3 /(g ⁇ log(nm)) and 0.009 cm3 /(g ⁇ log(nm)). This is more conducive to reducing gas generation and bubbling during the pulping process.
  • the maximum value of dV/d(logD) for a pore with an aperture of 1.0nm-1.5nm is 0.001cm3/(g ⁇ log(nm)), 0.002cm3/(g ⁇ log(nm)), 0.003cm3/(g ⁇ log(nm)), 0.004cm3 / ( g ⁇ log(nm)), 0.005cm3 / ( g ⁇ log(nm)) , 0.006cm3 / (g ⁇ log(nm)), 0.007cm3 /(g ⁇ log(nm)), 0.008cm3/(g ⁇ log(nm)), 0.009cm3 /(g ⁇ log(nm)), or a value between any two of these values.
  • the maximum value of the derivative of the cumulative pore volume V with respect to the logarithm of the pore size D, dV/d(logD), determined by nitrogen adsorption, for pores with a pore size of 1.0 nm to 1.5 nm is between 0.001 cm3 /(g ⁇ log(nm)) and 0.006 cm3 /(g ⁇ log(nm)). This further helps to reduce gas generation and bubbling during the pulping process.
  • the pore volume of the hard carbon material with a pore size of 1.0 nm to 1.5 nm accounts for 6% to 14% of the total pore volume of the hard carbon material.
  • the total metal ion content in the hard carbon material is ⁇ 800ppm, and the content of divalent or higher metal ions is ⁇ 20ppm. Having the total metal ion content and the content of divalent or higher metal ions in the hard carbon material within these ranges is beneficial for maintaining a suitable slurry viscosity, thereby facilitating slurry coating and resulting in a negative electrode sheet with a uniform negative electrode film layer.
  • the total metal ion content in the hard carbon material is 20ppm-800ppm, and the content of divalent or higher metal ions is 0.1ppm-20ppm. Having the total metal ion content and the content of divalent or higher metal ions in the hard carbon material within these ranges is beneficial for increasing the inorganic content of the SEM film, thereby reducing the formation of sodium dendrites or sodium precipitation on the surface of the hard carbon material, thus improving cycle performance.
  • the metal ion includes at least one selected from Na + , K + , Ca2 + , Mg2 + , Mn2 + , Ba2 + , and Al3 + .
  • the divalent or higher metal ions are Ca2+ .
  • the calcium ion content in the hard carbon material has a significant impact on the viscosity of the negative electrode slurry. A content within the aforementioned range is beneficial for obtaining a suitable negative electrode slurry viscosity, thereby facilitating rapid slurry coating and avoiding false edges and slurry flow, resulting in a negative electrode sheet with a uniform negative electrode film layer.
  • the surface oxygen content of the hard carbon material is 6%-14%.
  • a surface oxygen content within this range is beneficial for maintaining appropriate interaction forces between the dispersant and the hard carbon material, ensuring uniform dispersion of the slurry during mixing and providing good fluidity. This helps prevent gelation during slurry preparation, thereby facilitating slurry coating.
  • the surface oxygen content of the hard carbon material is 8%-12%. A surface oxygen content within this range is more advantageous for the slurry coating process.
  • the aforementioned hard carbon material can be prepared by adjusting the preparation method.
  • the preparation method does not have particular limitations on the carbon source; suitable carbon sources include asphalt/coal, biomass materials, and synthetic polymer materials.
  • suitable carbon sources include asphalt/coal, biomass materials, and synthetic polymer materials.
  • different carbon sources can be combined; for example, synthetic polymer materials can be combined with other carbon sources to obtain hard carbon materials with more favorable internal/external structures.
  • the aforementioned hard carbon material can be prepared by adjusting the process conditions.
  • Synthetic polymer materials such as phenolic resins, epoxy resins, and furan resins, possess structural designability and low impurity content.
  • synthetic polymer materials such as monomers or prepolymers
  • dispersing, pore-forming, or etching the synthetic polymer materials the microstructure of the carbon source can be well controlled, thereby controlling the pore structure of hard carbon materials.
  • a method for preparing hard carbon material using synthetic polymer material as carbon source includes the following steps: a curing step, curing a solution including polymeric monomers or prepolymers and solvent to obtain a carbon source; an etchant treatment step, impregnating the carbon source with an etchant; a pre-carbonization step, performing low-temperature pre-carbonization on the impregnated carbon source to obtain a pre-carbonized product; a crushing step, crushing the pre-carbonized product; a deashing step; and a high-temperature carbonization step.
  • the polymerization monomer can be a monomer of phenolic resin, epoxy resin, furan resin, etc.
  • the prepolymer may be, for instance, a methyl phenolic resin.
  • the solvent is at least one selected from methanol, ethanol, ethylene glycol, polyethylene glycol, glycerol, isopropanol, and other polyols.
  • the solvent ensures uniform dispersion of the synthesized polymer material, which is beneficial for the subsequent formation of a suitable pore structure.
  • This disclosure does not impose any particular limitation on the curing temperature.
  • Those skilled in the art can select an appropriate curing reaction temperature based on the specific type of polymeric monomer or prepolymer. For example, when the prepolymer is a methyl phenolic resin, the curing temperature is 80-150°C.
  • the etching agent includes at least one of phosphoric acid, hydrogen peroxide, sulfuric acid, nitric acid, and ZnCl2 .
  • the concentration of the etchant is 5-20 wt%.
  • the concentration of the etchant is 5 wt%, 7 wt%, 9 wt%, 11 wt%, 13 wt%, 15 wt%, 17 wt%, 19 wt%, 20 wt%, and any range between both.
  • the concentration of the etchant is 7-13 wt%.
  • the low-temperature pre-carbonization temperature is 400-600°C.
  • the low-temperature pre-carbonization temperature is 400°C, 450°C, 500°C, 550°C, 600°C, or any range between these.
  • This low-temperature pre-carbonization treatment removes moisture, some dissolved impurities, and surface-active groups, forming a pre-carbonized product with suitable density. Simultaneously, it allows the etchant to fully etch the pores, facilitating the adjustment to a suitable pore structure during subsequent high-temperature carbonization.
  • crushing can be performed by, for instance, air jet milling or mechanical milling, and this disclosure does not specifically limit it.
  • crushing results in a particle Dv50 of 4-8 ⁇ m, which is more conducive to adjusting the pore structure of the pre-carbonized product to a suitable pore structure during subsequent high-temperature carbonization, allowing impurities to dissolve sufficiently and resulting in a suitable particle size distribution of the final hard carbon.
  • the deashing step can be to remove metal impurities by immersing the product in an acid pickling tank with 1-5M acid.
  • the high-temperature carbonization temperature is 1000-1300°C. This is beneficial for forming a suitable final pore structure, thereby improving specific capacity and kinetic properties. Additionally, high-temperature carbonization can reduce a large number of surface defects. Exemplarily, the high-temperature carbonization temperature is 1000°C, 1100°C, 1200°C, 1300°C, and any range between two of these. Optionally, the high-temperature carbonization temperature is 1100-1200°C.
  • the preparation method further includes a step of forming a coating layer.
  • This step may be performed, for example, before high-temperature carbonization.
  • This disclosure does not specifically limit the coating process; exemplarily, it may be conventional gas-phase coating, liquid-phase coating, or solid-phase coating.
  • the oxygen content on the surface of hard carbon can be adjusted through oxidation or reduction treatment.
  • a pre-oxidation treatment is performed before high-temperature carbonization, which includes holding at 80°C-400°C in air or oxygen for 0.5-5 hours.
  • a reduction treatment is performed before high-temperature carbonization, which includes holding at 400°C-800°C in a mixture of hydrogen and argon for 0.5-10 hours.
  • the surface oxygen content of the hard carbon material can be adjusted to 6%-14%.
  • the preparation method further includes grading and demagnetization processes before obtaining the final hard carbon product, which can further optimize the problems of slurry bubbling, low slurry viscosity, and battery capacity decay.
  • the porosity and pore structure are adjusted by steps such as etching treatment of the carbon source and temperature and time of low-temperature pre-carbonization, so as to obtain the hard carbon material with improved kinetic performance and good specific capacity.
  • Biomass materials are widely available, such as coconut shells, rice husks, bamboo, wheat husks, straw, lignin, and so on. Using biomass materials as a carbon source has both economic and environmental benefits.
  • the preparation of hard carbon materials using biomass as a carbon source includes the following steps: An etchant treatment step, in which the biomass material is mixed with an etchant and impregnated; a pre-carbonization step, in which the material is heated at 300-500°C, optionally 400-500°C, for 2-6 hours.
  • the etchant treatment combined with the pre-carbonization step can remove volatiles from the biomass and simultaneously achieve slight pre-porosity.
  • a crushing step in which the pre-carbonized product is crushed to a particle size of Dv10 ⁇ 3 ⁇ m, Dv50 ⁇ 3 ⁇ m, and Dv90 ⁇ 3 ⁇ m. The crushing step ensures that the final hard carbon material has a suitable particle size distribution.
  • a deashing step in which the product is soaked in an acid washing kettle with 1-5M acid to remove metallic impurities. Biomass contains a relatively large amount of metallic impurities, and the deashing step can reduce the content of metallic impurities.
  • a pre-compression step in which the deashed product is compressed into a tightly packed cake shape, reducing the exposed area, preventing the oxidative damage of carbon by sintering volatiles, and controlling the porosity.
  • the carbonization step involves heating at 1100-1300°C for 2-6 hours to remove residual volatiles.
  • this preparation method may further include a step of forming a coating layer, for example, which can be carried out before the carbonization step.
  • the etching agent includes at least one of phosphoric acid, hydrogen peroxide, sulfuric acid, nitric acid, and ZnCl2 .
  • the concentration of the etchant is 5-20 wt%.
  • the concentration of the etchant is 5 wt%, 7 wt%, 9 wt%, 11 wt%, 13 wt%, 15 wt%, 17 wt%, 19 wt%, 20 wt%, and any range between both.
  • the concentration of the etchant is 7-13 wt%.
  • the acid includes at least one of hydrochloric acid, sulfuric acid, nitric acid, etc.
  • Deashing can reduce ash content, which consists of various metals and their oxides.
  • the amount of metal ions volatilized from the interior remaining on the surface can be adjusted by further washing after carbonization.
  • the ion content can be further reduced by washing 3-4 times after carbonization.
  • porosity and pore structure are adjusted by steps such as etching treatment combined with pre-carbonization, and temperature and time of the carbonization step, so as to obtain hard carbon materials with improved specific capacity and kinetic properties.
  • Asphalt and coal are common chemical raw materials, widely available and inexpensive, making it cost-effective to prepare hard carbon materials using asphalt or coal as carbon sources.
  • the preparation of hard carbon materials using asphalt as a carbon source includes the following steps: A pre-oxidation step, in which asphalt or modified asphalt is mixed with an oxidant and heated at 200-300°C for 2-5 hours to form a hard carbon precursor.
  • the oxygen content of the hard carbon precursor can be adjusted through the pre-oxidation step.
  • the oxidant can be oxygen, nitric acid, or hydrogen peroxide, and this disclosure does not specifically limit it.
  • a pre-carbonization step in which the above-mentioned hard carbon precursor is heated at 400-600°C for 2-4 hours.
  • a crushing step in which the pre-carbonized product is crushed to a particle size of Dv10 ⁇ 3 ⁇ m, Dv50 ⁇ 3 ⁇ m, and Dv90 ⁇ 30 ⁇ m.
  • a pre-compression step in which the crushed product is compressed into a cake shape with tightly packed particles to reduce the exposed area, prevent the oxidative damage of carbon by sintering volatiles, and control the porosity.
  • a carbonization step in which the material is treated at 1000-1200°C for 2-4 hours.
  • the preparation method may further include a step of forming a coating layer, for example, which may be carried out before the carbonization step.
  • crushing can be performed by air jet milling or mechanical milling, and this disclosure does not specifically limit it.
  • crushing results in a particle Dv50 of 4-8 ⁇ m, which is more conducive to adjusting the pore structure of the pre-carbonized product to a suitable pore structure during subsequent high-temperature carbonization, allowing impurities to dissolve fully and resulting in a suitable particle size distribution of the final hard carbon.
  • the preparation method further includes a deashing step and a demagnetizing step after the carbonization step.
  • a suitable deashing step can control the content of cations, especially divalent cations (such as calcium ions), in the final product, thereby further facilitating the preparation of hard carbon materials for electrode fabrication processes.
  • porosity and pore structure are adjusted by steps such as crushing the pre-carbonized product, adjusting the temperature and pressure of the pre-compression step, and adjusting the temperature and time of the carbonization step, so as to obtain hard carbon materials with improved specific capacity and kinetic properties.
  • the raw material was mixed with ZnCl2 aqueous solution (10% wt) at a mass ratio of 1:3 and impregnated for 12 hours, then removed and dried.
  • step 1) above was added to a hot press (Topli Technology, VHP-777) and treated at 400°C for 2 hours under normal pressure and N2 atmosphere to obtain a pre-carbonized product.
  • step 3 The product crushed in step 3) above is soaked in a pickling kettle with 2M hydrochloric acid aqueous solution for 10 hours at room temperature, filtered, washed with water 3 times, and then dried in a continuous kiln at 100°C.
  • step 4 The product obtained in step 4) above was pressurized in a hot press furnace (manufacturer: Dingli Technology, model: VHP-777) at 50T pressure for 1 hour.
  • step 5 The product obtained in step 5) above was sintered at 1400°C for 2 hours under a normal pressure N2 atmosphere with a heating rate of 2°C/min. It was washed with water 3 times and then dried at 100°C in a continuous kiln to obtain the sample of Example 1.
  • Hard carbon material, conductive agent, and dispersant are mixed in deionized water at a ratio of 8:1:1 and vacuum stirred at room temperature for 2.5 hours (to ensure that the negative electrode slurry remains uniform within 4 hours after vacuum stirring without further bubble formation; the vacuum stirring time in the following examples and comparative examples may be adjusted as needed, but shall not exceed 4 hours) to disperse and prepare a uniform negative electrode slurry.
  • the dispersant is sodium carboxymethyl cellulose and the conductive agent is conductive carbon black.
  • the uniformly stirred negative electrode slurry is coated onto both sides of the Al foil using a double-sided coating machine. After double-sided coating is completed, the negative electrode sheet is prepared by vacuum drying at 80°C, cold pressing, slitting, and sheet forming.
  • the prepared negative electrode sheet was used to assemble the battery in a glove box.
  • the sodium metal sheet was used as the counter electrode.
  • the positive electrode, separator, and negative electrode are stacked in sequence, and the electrolyte is added. After processes such as encapsulation, standing, formation, and aging, a button cell is made.
  • the hard carbon material precursor obtained in step 1) above is mixed with 10 wt% phosphoric acid aqueous solution at a mass ratio of 1:3 and impregnated for 12 h.
  • the hard carbon material precursor was coarsely crushed and heated to 600°C in a tube furnace under atmospheric pressure and N2 atmosphere at a heating rate of 2°C/min for 5 hours to obtain the pre-carbonized product.
  • the pre-carbonized product obtained in step 3) above was crushed in a ball mill (MSK-SFM-1-1L planetary ball mill) at 300 rpm for 2 hours.
  • the grinding balls were made of zirconia, and the mass ratio of material to grinding balls was 1:3.
  • the particle size distribution of the crushed sample was measured using a Mastersizer 3000 laser particle size analyzer, and its Dv50 was 5 ⁇ m.
  • the pre-carbonized product crushed in step 4) above is soaked in a pickling kettle with 2M hydrochloric acid aqueous solution for 10 hours at room temperature, filtered, washed with water 3 times, and dried in a continuous kiln at 100°C.
  • step 5 The product obtained in step 5) above was heated to 1150°C for 2 hours in a tube furnace under atmospheric pressure and N2 atmosphere at a heating rate of 2°C/min.
  • step 6 The product obtained in step 6) above is classified in an air classifier (manufacturer: Jinghua Powder, model: AB03). The particle size of the output is continuously monitored and tested until Dv50 reaches 5 ⁇ m, and the classification is completed.
  • an air classifier manufactured by Jinghua Powder, model: AB03.
  • step 7 The product obtained in step 7) above is demagnetized in a demagnetizing device (manufacturer: Wanyeda Magnetoelectric, model: GDG-250) until the magnetism of the product disappears.
  • a demagnetizing device manufactured by Wanyeda Magnetoelectric, model: GDG-250
  • Example 2 Following a method similar to that of Example 1, the hard carbon material of this example was used to prepare the negative electrode slurry and negative electrode sheet, and assembled into a coin cell.
  • Modified coal tar pitch (8994-94-4) was added to an oxidation reactor, atmospheric air was introduced, and the reactor was heated at 300°C for 3 hours.
  • the pre-oxidized asphalt obtained in step 1) above was heated at 450°C for 3 hours in a tubular furnace.
  • step 2) above is pressurized in a hot press (manufacturer: Dingli Technology, model: VHP-777) at 30T pressure for 1 hour.
  • step 3 The product obtained in step 3) above was heated in a tube furnace at 1100°C under normal pressure N2 atmosphere for 2 hours.
  • step 4 The product obtained in step 4) above was soaked in a pickling kettle with 2M hydrochloric acid aqueous solution for 10 hours at room temperature, filtered, washed with water 3 times, and dried in a continuous kiln at 100°C.
  • step 5 The product obtained in step 5) above is demagnetized in a demagnetizing device (manufacturer: Wanyeda Magnetoelectric, model: GDG-250) until the magnetism of the product disappears.
  • a demagnetizing device manufactured by Wanyeda Magnetoelectric, model: GDG-250
  • Example 2 Following a method similar to that of Example 1, the hard carbon material of this example was used to prepare the negative electrode slurry and negative electrode sheet, and assembled into a coin cell.
  • Hard carbon materials were prepared using a method similar to that in Example 2, except that the hard carbon material precursor was mixed and impregnated with a 20% aqueous solution of phosphoric acid during the preparation of the hard carbon material.
  • Hard carbon materials were prepared using a method similar to that in Example 2, except that the hard carbon material precursor and a 10% phosphoric acid aqueous solution were mixed and impregnated at a mass ratio of 1:5.
  • Hard carbon materials were prepared using a method similar to that in Example 1, except that the precursor was not impregnated with ZnCl2 aqueous solution and the high-temperature sintering conditions were 1500°C for 10 hours.
  • Hard carbon materials were prepared using a method similar to that in Example 1, except that the raw materials were mixed and impregnated with a 50wt% ZnCl2 aqueous solution at a mass ratio of 1:1.
  • adsorption and desorption isotherms were tested using nitrogen and carbon dioxide adsorption methods, respectively, in accordance with GB/T 19587-2017. Both nitrogen and carbon dioxide adsorption methods were performed using a specific surface area and porosity analyzer (Micromeritics ASAP-2460, USA). The specific surface area of the hard carbon material was calculated using the BET (Brunauer Emmett Teller) method based on the adsorption and desorption isotherms obtained by nitrogen adsorption. A DFT model was used to fit the distribution curve of dV/d(logD) relative to the pore size D, and the maximum value was read within the pore size range of 1.0-2.0 nm.
  • BET Brunauer Emmett Teller
  • the average Na-embedding voltage V is calculated using the following formula:
  • Average Na-intercalation voltage initial charge energy / capacity.
  • the pore volume of hard carbon materials with pore sizes of 2nm-8nm is 0.0004cm3/ g- 0.0040cm3 /g, which provides good capacity and improved kinetic performance.
  • Hard carbon materials were prepared using a method similar to that in Example 2, except that the hard carbon material precursor was mixed and impregnated in a phosphoric acid aqueous solution for 6 hours, and the high-temperature carbonization temperature was 1200°C.
  • Hard carbon materials were prepared using a method similar to that in Example 2, except that the hard carbon material precursor was not subjected to phosphoric acid oxidation treatment and the high-temperature carbonization temperature was 1300°C.
  • Hard carbon materials were prepared using a method similar to that in Example 2, except that the hard carbon material precursor was mixed and impregnated with an 80 wt% phosphoric acid aqueous solution, and the high-temperature carbonization temperature was 1300°C.
  • the hard carbon material prepared in the examples and comparative examples were added to a 500mL sealed reactor equipped with temperature and pressure sensors. After adding 200mL of water, the reactor was quickly closed, and stirring was started until the temperature and pressure remained constant. Based on the pressure change and the ideal gas equation, the volume of gas emitted per unit mass of hard carbon material was calculated as a measure of the bubbling amount.
  • the pore volume of hard carbon materials with pore sizes below 2 nm ranges from 0.0006 cm3 /g to 0.0035 cm3 /g. This improves the specific capacity while reducing gas generation and bubbling during pulping.
  • the proportion of pore volume with pore sizes below 2 nm in the total pore volume of hard carbon materials ranges from 18% to 30%, which is beneficial for achieving suitable specific capacity in hard carbon materials.
  • Hard carbon materials were prepared using a method similar to that in Example 2, except that the hard carbon material precursor and phosphoric acid aqueous solution were mixed and impregnated at a mass ratio of 1:1 for 6 hours, and the high-temperature carbonization temperature was 1200°C.
  • Hard carbon materials were prepared using a method similar to that in Example 2, except that the concentration of the phosphoric acid aqueous solution was 30% and the high-temperature carbonization temperature was 1200°C.
  • Hard carbon materials were prepared using a method similar to that in Example 1, except that the carbonization and subsequent water washing were performed twice during the preparation of the hard carbon materials.
  • Hard carbon materials were prepared using a method similar to that in Example 1, except that the carbonization and subsequent water washing was performed only once during the preparation of the hard carbon materials.
  • Hard carbon materials were prepared using a method similar to that in Example 1, except that the concentration of hydrochloric acid used in the preparation of hard carbon materials was 1M.
  • a negative electrode slurry with a solid content of 20% was prepared and stirred continuously for half an hour.
  • the resulting clear liquid was then obtained by filtration and used to test the content of water-soluble Ca, Mg, Na and K ions.
  • Hard carbon materials were prepared using a method similar to that in Example 2, except that during the etching process, the materials were immersed in a 10% phosphoric acid aqueous solution for 6 hours.
  • Hard carbon materials were prepared using a method similar to that in Example 2, except that during the etching process, the materials were immersed in a 20% phosphoric acid aqueous solution for 5 hours.
  • Hard carbon materials were prepared using a method similar to that in Example 2, except that no etchant treatment was performed during the preparation of the hard carbon materials, and the pre-carbonization was carried out at 500°C in an Ar/H 2 (95:5) mixed atmosphere for 2 hours.
  • Hard carbon materials were prepared using a method similar to that in Example 2, except that during the etching process, the materials were immersed in a 30% phosphoric acid aqueous solution for 6 hours.
  • the hard carbon materials prepared in Examples 2 and 14-17 were observed during the preparation of the negative electrode slurry.
  • the degree of gelation was qualitatively judged by picking up the slurry with a small spoon and pouring it to observe the dripping situation.

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Abstract

本公开提供了一种钠离子电池、钠离子电池的制备方法、用电装置和硬碳材料。钠离子电池包括负极极片，负极极片包括负极集流体以及位于负极集流体至少一个表面上的负极膜层，负极膜层包括硬碳材料。通过氮气吸附法测定，硬碳材料包含多孔结构，多孔结构中包括孔径为2nm-8nm的孔；通过氮气吸附法测定孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g。

Description

钠离子电池、钠离子电池制备方法、用电装置和硬碳材料
相关申请的交叉引用
本公开基于申请号为202410718131.7、申请日为2024年06月04日、发明名称为“负极极片、二次电池、用电装置和硬碳材料”的中国专利申请提出，并要求该中国专利申请的优先权，该中国专利申请的全部内容在此引入本公开作为参考。
技术领域
本公开涉及二次电池技术领域，尤其涉及一种钠离子电池、钠离子电池制备方法、用电装置和硬碳材料。
背景技术
近年来，随着新能源产业的不断发展壮大，锂离子电池的需求量逐年递增，在此背景下，锂资源的消耗导致锂离子电池成本迅速升高，这不利于新能源事业的长期发展，而钠离子电池可以分担一部分供需压力。由于钠在资源和成本上的优势，钠离子电池成为储能电池的重要发展方向。硬碳因其优异的整体性能、广泛的适用性和相对较低的价格成本，是该领域内主流负极活性材料之一。然而，硬碳材料在克容量、动力学性能等方面还有较大的提升空间。
发明内容
本公开是鉴于上述课题而进行的，其目的在于，提供一种钠离子电池、钠离子电池制备方法、用电装置和硬碳材料。本公开提供的负极极片在提供较好容量的前提下，具有改善的动力学性能。
为了达到上述目的，本公开提供了钠离子电池。钠离子电池，包括负极极片，负极极片包括负极集流体以及位于负极集流体至少一个表面上的负极膜层，负极膜层包括硬碳材料。硬碳材料包含多孔结构，多孔结构中包括孔径为2nm-8nm的孔，通过氮气吸附法测定孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g。
本公开提供的钠离子电池的负极极片的负极膜层所包括的硬碳材料具有优化的孔结构。具体地，硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g，由此，能够改善硬碳材料的动力学性能并兼顾克容量。
在一些实施方式中，通过氮气吸附法测定硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0010cm3/g-0.0040cm3/g。由此，更有利于硬碳材料的动力学性能并兼顾克容量。
在一些实施方式中，通过氮气吸附法测定硬碳材料的孔径为2nm-8nm的孔的孔体积占硬碳材料的总孔体积的3.5％-30％。由此，有利于动力学性能和克容量二者的平衡，并且保持合适的结构稳定性。
在一些实施方式中，通过二氧化碳吸附法测定硬碳材料的孔径为小于等于1nm的孔的孔体积表示为V1，通过氮气吸附法测定硬碳材料的孔径为1nm-2nm的孔的孔体积表示为V2，则V1+V2在0.0006cm3/g至0.0050cm3/g范围内。硬碳材料的孔径在2nm以下的孔的孔体积在上述范围内，更有利于硬碳材料具有合适的克容量。
在一些实施方式中，V1+V2在0.0006cm3/g至0.0035cm3/g范围内，由此，在使硬碳材料具有合适的克容量的同时，有利于减少负极浆料制备过程中的产气冒泡现象，从而能够获得容量提升且负极膜层均匀的负极极片，降低负极浆料漏涂的风险，提高钠离子电池性能。优选地，在0.0020cm3/g至0.0035cm3/g的范围内。
在一些实施方式中，V1+V2占硬碳材料的总孔体积的比例在18％至30％范围内。硬碳材料的孔径在2nm以下的孔的孔体积占总孔体积的比例在上述范围内，更有利于改善硬碳材料的克容量。
在一些实施方式中，硬碳材料包含孔径在1.0nm-1.5nm范围内的孔，通过氮气吸附法测定孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.009cm3/(g·log(nm))。这有利于减少制浆过程中的产气冒泡现象，能够进一步提高负极极片的性能，降低负极浆料漏涂的风险，提高二次电池性能。
在一些实施方式中，通过氮气吸附法测定孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.006cm3/(g·log(nm))。这进一步有利于减少制浆过程中的产气冒泡现象。
在一些实施方式中，硬碳材料的孔径为1.0nm-1.5nm的孔的孔体积占硬碳材料的总孔体积的6％至14％。
在一些实施方式中，负极膜层包括第一水性粘结剂、水性分散剂和第一导电剂中至少一种。
在一些实施方式中，水性粘结剂包括丁苯橡胶、丙烯酸酯橡胶中的一种或多种；水性分散剂包括羧甲基纤维素钠、海藻酸钠、黄原胶、卡拉胶中的一种或多种；导电剂包括Super-P，乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯、碳纳米纤维中的一种或多种。
在一些实施方式中，负极膜层中硬碳材料的质量含量在80％以上。
在一些实施方式中，负极膜层中硬碳材料的质量含量在85％以上，水性粘结剂的质量含量为0％至5％，水性分散剂的质量含量为0％至5％，导电剂的质量含量为0％至5％。
在一些实施方式中，负极膜层中还包括嵌入型储钠材料，嵌入型储钠材料的晶面间距d002满足：0.24nm≤d002≤0.8nm。由此，晶面间距在上述范围内的嵌入型储钠材料在微观结构上可以层间滑移，应用于钠离子电池中时有助于增加负极极片的粉末压实密度，从而帮助提高钠离子电池的能量密度。负极膜层中嵌入型储钠材料的质量含量小于等于10％。可选地，嵌入型储钠材料的质量含量在0.5％至5％之间。
在一些实施方式中，嵌入型储钠材料包括碳基嵌入型储钠材料、硫基嵌入型储钠材料、钛基嵌入型储钠材料中的至少一种；碳基嵌入型储钠材料包括：软碳、改性石墨中的至少一种；软碳的ID/IG满足：0.9≤ID/IG≤1.6，其中ID表示拉曼光谱在1350±50cm-1处的D峰强度，IG表示拉曼光谱在1580±50cm-1处的G峰强度。
在一些实施方式中，负极膜层包括层叠设置的第一负极膜层和第二负极膜层，第一负极膜层设置在负极集流体与第二负极膜层中间，第一负极膜层包括第一活性物质，第二负极膜层包括第二活性物质；第一活性物质和第二活性物质分别包括硬碳材料和嵌入型储钠材料中的至少一种，且第一活性物质和第二活性物质中至少一者包括硬碳材料。嵌入型储钠材料能够影响负极活性材料的储钠机制，减少钠离子在硬碳中沉积形成类金属钠的情况，由此，降低钠离子热失控的风险。
在一些实施方式中，第一活性物质包括硬碳材料，第二活性物质包括软碳材料。由此，更有利于提高动力学性能。
在一些实施方式中，负极极片还包括底涂层；底涂层的厚度为0.5μm-3μm。由此，有利于降低漏涂风险，提高极片涂布质量。
由于硬碳材料制备极片时的浆料为水系浆料，与金属集流体表面达因值差异较大容易出现漏涂，存在安全风险。
在一些实施方式中，底涂层包括无机氧化物和水性粘结剂。该底涂层耐水且与金属集流体粘结力强，无机氧化物能够增强底涂层与活性层间的锚定作用满足耐水要求且与金属集流体表面亲和性强，更有利于降低漏涂风险，提高极片涂布质量，同时又能够改善极片粘结强度、降低极片冷压时的延展率，还能够实现对集流体电阻的有效控制，兼顾电池的电化学表现。
在一些实施方式中，底涂层包括无机氧化物、分散剂、第二水性粘结剂和第二导电剂。
在一些实施方式中，在底涂层中，无机氧化物包括氧化铝、勃姆石、氧化镁、氧化铁、氧化硅、氧化锆中的一种或多种；无机氧化物的质量占比为30％-60％。底涂层中包含上述质量范围内的无机氧化物能够增强与金属集流体粘结性，进一步降低漏涂风险，提高极片涂布质量。
在一些实施方式中，底涂层包括30％-60％无机氧化物、1％-8％分散剂、10％-40％第二水性粘结剂和10％-40％第二导电剂。
在一些实施方式中，底涂层还包括增稠剂和/或润湿剂；润湿剂包括聚乙氧醚类表面活性剂、聚醚有机硅类表面活性剂、非离子型氟碳聚合物类表面活性剂、炔类表面活性剂中的一种或多种；增稠剂包括羧甲基纤维素钠、海藻酸钠、黄原胶、卡拉胶中的一种或多种。
在一些实施方式中，负极集流体包括铜箔、铝箔、不锈钢箔、钛箔、镍箔、镍铁箔、镍铜箔、镍铁铜箔中的至少一种。
在一些实施方式中，硬碳材料中金属离子总含量为≤800ppm，且二价以上的金属离子的含量为≤20ppm。硬碳材料的金属离子总含量及二价以上的金属离子的含量在上述范围内，有利于保持合适的浆料粘度，从而有利于浆料的涂覆，以便获得负极膜层均匀的负极极片。
在一些实施方式中，硬碳材料中金属离子总含量为20ppm-800ppm，且二价以上的金属离子的含量为0.1ppm-20ppm。硬碳材料的金属离子总含量及二价以上的金属离子的含量在上述范围内，有利于提高SEM膜的无机物含量，从而减少钠枝晶的产生或者硬碳材料表面析钠，从而提升循环性能。
在一些实施方式中，金属离子包括Na+、K+、Ca2+、Mg2+、Mn2+、Ba2+、Al3+中的至少一种。
在一些实施方式中，二价以上的金属离子为Ca2+。硬碳材料中钙离子含量对负极浆料的粘度影响较大，其含量在上述范围内有利于获得合适的负极浆料粘度，从而有利于快速浆料的涂覆且避免虚边和浆料流动，获得负极膜层均匀的负极极片。
在一些实施方式中，硬碳材料的表面氧元素含量为6％-14％。硬碳材料的表面氧元素含量在上述范围内，有利于保持合适的分散剂与硬碳材料间作用力，使浆料在混合过程分散均匀，并具有良好的流动性，有利于制浆不发生胶凝现象，从而有利于浆料的涂覆。
在一些实施方式中，硬碳材料的表面氧元素含量为8％-12％。硬碳材料的表面氧元素含量在上述范围内，更有利于浆料的涂覆工艺。
在一些实施方式中，电解液中的溶剂包括碳酸酯类溶剂，碳酸酯类溶剂包括碳酸亚乙酯、碳酸亚丙酯、氟代碳酸亚乙酯中至少一种。由此，有利于提高电解液的耐高压能力。
在一些实施方式中，相对于溶剂的体积，碳酸亚丙酯的体积占比15％-55％。由此，不仅有利于提高电解液耐氧化能力，还可以解离钠盐提高电导率。
在一些实施方式中，正极极片包括正极集流体以及位于正极集流体至少一个表面上的正极膜层，正极膜层包括正极活性材料，正极活性材料包括含钠层状氧化物、聚阴离子钠离子化合物、普鲁士蓝钠离子化合物中的至少一种。
在一些实施方式中，含钠层状氧化物为铁锰基层状氧化物，铁锰基层状氧化物镍铁锰基层状氧化物和铜铁锰基层状氧化物中的至少一种。
本公开还提供一种钠离子电池的制备方法，包括制备负极极片，其中，制备负极极片包括：混合负极组分和溶剂，得到负极浆料，其中，负极组分包括硬碳材料，硬碳材料包含多孔结构，多孔结构中包括孔径为2nm-8nm的孔，通过氮气吸附法测定孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g；以及将负极浆料涂覆在负极集流体上。2nm-8nm孔径的孔具有合适孔容时能够改善硬碳材料的动力学性能，并且这部分孔径的孔还能够贡献部分容量，从而使负极极片能够具有提高的动力学性能并兼顾容量。
在一些实施方式中，通过氮气吸附法测定硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0010cm3/g-0.0040cm3/g。由此，更有利于能够改善硬碳材料的动力学性能并兼顾克容量。
在一些实施方式中，通过氮气吸附法测定硬碳材料的孔径为2nm-8nm的孔的孔体积占硬碳材料的总孔体积的3.5％-30％。由此，进一步有利于硬碳材料动力学性能和克容量的平衡，并且保持合适的结构稳定性。
在一些实施方式中，通过二氧化碳吸附法测定硬碳材料的孔径为小于等于1nm的孔的孔体积表示为V1，通过氮气吸附法测定硬碳材料的孔径为1nm-2nm的孔的孔体积表示为V2，则V1+V2在0.0006cm3/g至0.0050cm3/g范围内。通过进一步限制V1+V2在上述范围，更有利于使硬碳材料具有合适的克容量。
在一些实施方式中，V1+V2在0.0006cm3/g至0.0035cm3/g范围内。孔径为2nm以下的孔的孔体积在0.0006cm3/g至0.0035cm3/g范围内，还有利于在使硬碳材料具有合适的克容量的同时，减少制浆过程中的产气冒泡现象，提高硬碳材料的可加工性，并提高负极极片的均匀性，降低负极浆料漏涂的风险，提高钠离子电池性能。
在一些实施方式中，V1+V2在0.0020cm3/g至0.0035cm3/g的范围内。
在一些实施方式中，V1+V2占硬碳材料的孔体积的18％至30％。硬碳材料的孔径在2nm以下的孔的孔体积占总孔体积的比例在上述范围内，更有利于改善硬碳材料的克容量。
在一些实施方式中，硬碳材料包含孔径在1.0nm-1.5nm范围内的孔，通过氮气吸附法测定孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.009cm3/(g·log(nm))。这更有利于减少制浆过程中的产气冒泡现象。
在一些实施方式中，通过氮气吸附法测定孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.006cm3/(g·log(nm))。这进一步有利于减少制浆过程中的产气冒泡现象。
在一些实施方式中，硬碳材料的孔径为1.0nm-1.5nm的孔的孔体积占硬碳材料的总孔体积的6％至14％。
在一些实施方式中，相对于负极浆料的质量，负极组分的质量百分含量为50％～60％。由此，有利于浆料的均匀性和稳定性。
在一些实施方式中，相对于负极组分的质量，硬碳的质量百分含量为80％～95％。由此，有利于电池的能量密度。
在一些实施方式中，负极组分还包括导电剂、粘结剂和分散剂中的一种或者多种。导电剂能够有效加快电子传输速率，提高电池的充放电效率。粘结剂有利于在电池充放电过程中维持电极结构的完整性。分散剂能够改善负极组分的颗粒在溶剂中的分散性，使浆料易于涂布。
在一些实施方式中，混合负极组分和溶剂包括：在0℃～30℃下进行1h～4h的真空搅拌。
采用上述硬碳材料制备负极浆料时，可明显减少冒泡时间，有利于制浆的顺利进行，还有利于后续的涂覆及冷压等工序，从而提高负极膜层的均匀性，防止集流体被暴露。
本公开还提供一种用电装置，包括本公开的钠离子电池或本公开的钠离子电池制备方法得到的钠离子电池。
本公开的用电装置包括本公开提供的钠离子电池，因而至少具有与钠离子电池相同的优势。
本公开还提供一种硬碳材料。硬碳材料包含多孔结构，多孔结构中包括孔径为2nm-8nm的孔，通过氮气吸附法测定孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g。
本公开提供的硬碳材料具有优化的孔结构。具体地，硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g，由此，能够改善硬碳材料的动力学性能并兼顾克容量。
在一些实施方式中，通过氮气吸附法测定硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0010cm3/g-0.0040cm3/g。这更有利于硬碳材料的动力学性能并兼顾克容量。
在一些实施方式中，通过氮气吸附法测定硬碳材料的孔径为2nm-8nm的孔的孔体积占硬碳材料的总孔体积的3.5％-30％。这有利于动力学性能和克容量二者的平衡，并且保持合适的结构稳定性。
在一些实施方式中，通过二氧化碳吸附法测定硬碳材料的孔径为小于等于1nm的孔的孔体积表示为V1，通过氮气吸附法测定硬碳材料的孔径为1nm-2nm的孔的孔体积表示为V2，则V1+V2在0.0006cm3/g至0.0050cm3/g范围内。硬碳材料的孔径在2nm以下的孔的孔体积在上述范围内，更有利于硬碳材料具有合适的克容量。
在一些实施方式中，V1+V2在0.0006cm3/g至0.0035cm3/g范围内，由此，在使硬碳材料具有合适的克容量的同时，有利于减少负极浆料制备过程中的产气冒泡现象，从而能够获得容量提升且负极膜层均匀的负极极片，降低负极浆料漏涂的风险，提高钠离子电池性能。优选地，在0.0020cm3/g至0.0035cm3/g的范围内。
在一些实施方式中，V1+V2占硬碳材料的总孔体积的比例在18％至30％范围内。硬碳材料的孔径在2nm以下的孔的孔体积占总孔体积的比例在上述范围内，更有利于改善硬碳材料的克容量。
在一些实施方式中，硬碳材料包含孔径在1.0nm-1.5nm范围内的孔，通过氮气吸附法测定孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.009cm3/(g·log(nm))。这有利于减少制浆过程中的产气冒泡现象，进一步提高负极极片的性能，降低负极浆料漏涂的风险，提高二次电池性能。
在一些实施方式中，通过氮气吸附法测定孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.006cm3/(g·log(nm))。这进一步有利于减少制浆过程中的产气冒泡现象。
在一些实施方式中，硬碳材料的孔径为1.0nm-1.5nm的孔的孔体积占硬碳材料的总孔体积的6％至14％。
在一些实施方式中，硬碳材料中金属离子总含量为≤800ppm，且二价以上的金属离子的含量为≤20ppm。硬碳材料的金属离子总含量及二价以上的金属离子的含量在上述范围内，有利于保持合适的浆料粘度，从而有利于浆料的涂覆，以便获得负极膜层均匀的负极极片。
在一些实施方式中，硬碳材料中金属离子总含量为20ppm-800ppm，且二价以上的金属离子的含量为0.1ppm-20ppm。硬碳材料的金属离子总含量及二价以上的金属离子的含量在上述范围内，有利于提高SEM膜的无机物含量，从而减少钠枝晶的产生或者硬碳材料表面析钠，从而提升循环性能。
在一些实施方式中，金属离子包括Na+、K+、Ca2+、Mg2+、Mn2+、Ba2+、Al3+中的至少一种。
在一些实施方式中，二价以上的金属离子为Ca2+。硬碳材料中钙离子含量对负极浆料的粘度影响较大，其含量在上述范围内有利于获得合适的负极浆料粘度，从而有利于快速浆料的涂覆且避免虚边和浆料流动，获得负极膜层均匀的负极极片。
在一些实施方式中，硬碳材料的表面氧元素含量为6％-14％。硬碳材料的表面氧元素含量在上述范围内，有利于保持合适的分散剂与硬碳材料间作用力，使浆料在混合过程分散均匀，并具有良好的流动性，有利于制浆不发生胶凝现象，从而有利于浆料的涂覆。
在一些实施方式中，硬碳材料的表面氧元素含量为8％-12％。硬碳材料的表面氧元素含量在上述范围内，更有利于浆料的涂覆工艺。
附图说明
图1是本公开一实施方式的电池单体的示意图。
图2是图1所示的本公开一实施方式的电池单体的分解图。
图3是本公开一实施方式的电池模块的示意图。
图4是本公开一实施方式的电池包的示意图。
图5是图4所示的本公开一实施方式的电池包的分解图。
图6是本公开一实施方式的钠离子电池用作电源的用电装置的示意图。
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5电池单体；51壳体；52电极组件；53顶盖组件
具体实施方式
以下，适当地参照附图详细说明本公开的钠离子电池、钠离子电池制备方法、用电装置和硬碳材料的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本公开而提供的，并不旨在限定权利要求书所记载的主题。
本公开所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围，除非另有说明，是包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本公开中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本公开的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。
如果没有特别的说明，本公开的所有技术特征以及可选技术特征可以相互组合形成新的技术方案。
如果没有特别的说明，本公开的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，方法包括步骤(a)和(b)，表示方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，提到方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到方法，例如，方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
硬碳材料丰富的孔结构，通常，增加硬碳材料的多孔结构中2nm以下的微孔的量，这部分孔有利于储钠以提升克容量，但是大量的微孔不利于动力学性能，可带来析钠风险。另外一方面，硬碳中的微孔既能储钠同时也会有气体分子进出导致冒泡。
具体来讲，目前的理论认为大量的微孔会使得电解液浸润变慢，高倍率下嵌Na位阻较大，电荷转移进一步受阻，动力学性能显著恶化，表现为部分钠离子在界面还原为金属态Na而析出。同时这部分微孔结构占比提高会增加表面积，形成的固体电解质界面膜(Solid Electrolyte Interface，简称SEI膜)更多从而消耗更多的活性离子，进一步加剧析钠现象的发生。另外，这部分微孔结构过多会增强气体分子的进出导致加工过程持续冒泡。对于持续地产气冒泡的硬碳材料，比如开始制浆2小时后仍然冒泡的硬碳材料，加工难以进行，制备的负极极片有暴露出底层负极集流体的风险，导致负极极片缺陷，降低钠离子电池的性能，同时极片涂层缺陷也可能引发极片表面电子、Na离子浓度分布差异，提高析钠风险，进而带来电池使用的安全性隐患。
基于此，本公开提供了一种钠离子电池、钠离子电池制备方法、用电装置和硬碳材料。上述方案能够改善动力学性能，降低集流体表面负极浆料漏涂的风险，提高钠离子电池性能及安全性。以下分别进行详述。
钠离子电池
本公开的第一方面提供了钠离子电池，包括负极极片。负极极片，包括负极集流体以及位于负极集流体至少一个表面上的负极膜层，负极膜层包括硬碳材料，硬碳材料包含多孔结构，多孔结构中包括孔径为2nm-8nm的孔，通过氮气吸附法测定孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g。
本公开提供的负极极片中的硬碳材料具有优化的孔结构。具体地，硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g。通过研究发现：2nm-8nm孔径的孔具有合适孔容时能够改善硬碳材料的动力学性能，并且这部分孔径的孔还能够贡献部分容量，从而使负极极片能够具有提高的动力学性能并兼顾容量。
示例性地，孔径为2nm-8nm的孔的孔体积为0.0004cm3/g、0.0008cm3/g、0.0010cm3/g、0.0012cm3/g、0.0014cm3/g、0.0016cm3/g、0.0018cm3/g、0.0020cm3/g、0.0022cm3/g、0.0024cm3/g、0.0026cm3/g、0.0028cm3/g、0.0030cm3/g、0.0032cm3/g、0.0035cm3/g、0.0040cm3/g或为其中任意两个数值组成的范围之间的值。
在本公开中，硬碳材料的孔体积为本领域公知的含义，可以用本领域已知的仪器及方法进行测定。示例性地，本领域已知的方法可为气态吸附表征技术、压汞法等。示例性地，可以参照GB/T 19587-2017，采用氮气吸附法测试吸附和解吸等温线，使用DFT模型拟合出累积孔体积相对于孔径的分布曲线，并得出2nm-8nm的孔径范围的孔的孔体积。硬碳材料可以为作为原料的硬碳材料，或者可以来自对钠离子电池拆解和分离得到的硬碳材料。
在一些实施方式中，通过氮气吸附法测定硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0010cm3/g-0.0040cm3/g。由此，更有利于能够改善硬碳材料的动力学性能并兼顾克容量。
在一些实施方式中，通过氮气吸附法测定硬碳材料的孔径为2nm-8nm的孔的孔体积占硬碳材料的总孔体积的3.5％-30％。由此，进一步有利于硬碳材料动力学性能和克容量的平衡，并且保持合适的结构稳定性。示例性地，孔径为2nm-8nm的孔的孔体积占硬碳材料的总孔体积的比例为3.5％、5％、8％、10％、12％、15％、18％、20％、22％、25％、28％、30％或为其中任意两个数值组成的范围之间的值。
在一些实施方式中，通过二氧化碳吸附法测定硬碳材料的孔径为小于等于1nm的孔的孔体积表示为V1，通过氮气吸附法测定硬碳材料的孔径为1nm-2nm的孔的孔体积表示为V2，则V1+V2在0.0006cm3/g至0.0050cm3/g范围内。
通过进一步限制V1+V2在上述范围，更有利于使硬碳材料具有合适的克容量。
示例性地，V1+V2为0.0006cm3/g、0.0010cm3/g、0.0013cm3/g、0.0015cm3/g、0.0018cm3/g、0.0020cm3/g、0.0023cm3/g、0.0025cm3/g、0.0028cm3/g、0.0030cm3/g、0.0033cm3/g、0.0035cm3/g、0.0038cm3/g、0.0040cm3/g、0.0043cm3/g、0.0045cm3/g、0.0048cm3/g、0.0050cm3/g或为其中任意两个数值组成的范围之间的值。
对于硬碳材料的孔径为小于等于1nm的孔的孔体积V1，可采用本领域的常规方法进行测定。例如：CO2吸脱附孔容孔径测试法。通过该方法，通常测定的是孔径为1nm以下，特别是0.4nm-1nm范围内的孔的孔体积。示例性地，可以采用CO2吸附法测试吸附和解吸等温线，使用DFT模型拟合出累积孔体积相对于孔径的分布曲线，并得出小于等于1nm的特定的孔径范围的孔的孔体积。
对于硬碳材料的孔径为1nm-2nm的孔的孔体积V2，可采用本领域的常规方法进行测定。例如：上述N2吸脱附孔容孔径测试法。
对于硬碳材料的总孔体积，可采用本领域的常规方法进行测定。例如：上述N2吸脱附孔容孔径测试法结合CO2吸脱附孔容孔径测试法，分别获得1nm以上孔径的孔的孔容以及孔径小于1nm的孔的孔容，然后将二者加和得到。
在一些实施方式中，V1+V2在0.0006cm3/g至0.0035cm3/g范围内。进一步研究发现，在制备负极浆料时，孔径为2nm以下的孔会造成一定程度的产气冒泡。对于持续地产气冒泡的硬碳材料，比如开始制浆2小时后仍然冒泡的硬碳材料，导致加工难以进行，而且制备的负极极片有暴露出底层负极集流体的风险，导致负极极片缺陷，进而影响钠离子电池的性能。本发明发现，孔径为2nm以下的孔的孔体积在0.0006cm3/g至0.0035cm3/g范围内，还有利于在使硬碳材料具有合适的克容量的同时，减少制浆过程中的产气冒泡现象，提高硬碳材料的可加工性，并提高负极极片的均匀性，降低负极浆料漏涂的风险，提高钠离子电池性能。
在一些实施方式中，V1+V2在0.0020cm3/g至0.0035cm3/g的范围内。
在一些实施方式中，V1+V2占硬碳材料的总孔体积的比例在18％至30％范围内。硬碳材料的孔径在2nm以下的孔的孔体积占总孔体积的比例在上述范围内，更有利于改善硬碳材料的克容量。
示例性地，V1+V2占总孔体积的比例为18％、20％、23％、25％、28％、30％或为其中任意两个数值组成的范围之间的值。
对于硬碳材料的总孔体积，可采用本领域的常规方法进行测定。例如：上述N2吸脱附孔容孔径测试法，结合上述CO2吸脱附孔容孔径测试法，分别获得1nm以上孔径的孔的孔容以及1nm以下孔径的孔的孔体积，然后将二者加和得到。
本公开提及的dV/d(logD)反映出单位孔径所贡献的孔体积，可通过对硬碳材料进行气态吸附表征技术而确定。例如，可以采用比表面仪-静态容量法确定，具体的，根据本公开的实施例，可以采用流动法气体吸附型比表面积测量装置(设备型号Micromeritics ASAP-2460)测量。得到氮气吸附法测试吸附和解吸等温线，使用DFT模型拟合出dV/d(logD)相对于孔径D的分布曲线，在孔径为1.0nm-2.0nm的范围内读出最大值。
在一些实施方式中，硬碳材料包含孔径在1.0nm-1.5nm范围内的孔，通过氮气吸附法测定孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.009cm3/(g·log(nm))。这更有利于减少制浆过程中的产气冒泡现象。
示例性地，孔径为1.0nm-1.5nm的孔的dV/d(logD)的最大值为0.001cm3/(g·log(nm))、0.002cm3/(g·log(nm))、0.003cm3/(g·log(nm))、0.004cm3/(g·log(nm))、0.005cm3/(g·log(nm))、0.006cm3/(g·log(nm))、0.007cm3/(g·log(nm))、0.008cm3/(g·log(nm))、0.009cm3/(g·log(nm))或为其中任意两个数值组成的范围之间的值。
在一些实施方式中，通过氮气吸附法测定孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.006cm3/(g·log(nm))。这进一步有利于减少制浆过程中的产气冒泡现象。
在一些实施方式中，硬碳材料的孔径为1.0nm-1.5nm的孔的孔体积占硬碳材料的总孔体积的6％至14％。这进一步有利于减少制浆过程中的产气现象。示例性地，孔径为1.0nm-1.5nm的孔的孔体积占总孔体积的比例为6％、7％、8％、9％、10％、11％、12％、13％、14％或为其中任意两个数值组成的范围之间的值。
在一些实施方式中，负极膜层中还包括嵌入型储钠材料，嵌入型储钠材料的晶面间距d002满足：0.24nm≤d002≤0.8nm。由此，晶面间距在上述范围内的嵌入型储钠材料在微观结构上可以层间滑移，应用于钠离子电池中时有助于增加负极极片的粉末压实密度，从而帮助提高钠离子电池的能量密度。负极膜层中嵌入型储钠材料的质量含量小于等于10％。可选地，嵌入型储钠材料的质量含量在0.5％至5％之间。
在一些实施方式中，嵌入型储钠材料包括碳基嵌入型储钠材料、硫基嵌入型储钠材料、钛基嵌入型储钠材料中的至少一种；碳基嵌入型储钠材料包括：软碳、改性石墨中的至少一种；软碳的ID/IG满足：0.9≤ID/IG≤1.6，其中ID表示拉曼光谱在1350±50cm-1处的D峰强度，IG表示拉曼光谱在1580±50cm-1处的G峰强度。
在一些实施方式中，负极膜层包括层叠设置的第一负极膜层和第二负极膜层，第一负极膜层设置在负极集流体与第二负极膜层中间，第一负极膜层包括第一活性物质，第二负极膜层包括第二活性物质；第一活性物质和第二活性分别包括硬碳材料和嵌入型储钠材料中的至少一种，且第一活性物质和第二活性物质中至少一者包括硬碳材料。嵌入型储钠材料能够影响负极活性材料的储钠机制，减少钠离子在硬碳中沉积形成类金属钠的情况，由此，降低钠离子热失控的风险。
在一些实施方式中，第一活性物质包括硬碳材料，第二活性物质包括软碳材料。由此，更有利于提高动力学性能。
除了改善克容量和动力学性能以及有效减少产气冒泡的问题，本公开进一步实施方式的硬碳材料，具有进一步提高的可加工性。
在一些实施方式中，硬碳材料中金属离子总含量为≤800ppm，且二价以上的金属离子的含量为≤20ppm。
本公开发现金属离子总含量以及二价以上的金属离子的含量在上述范围内，对负极浆料中的其他成分，如增稠剂、分散剂等，特别是羧甲基纤维素钠的影响小，有利于在制浆时保持浆料合适的粘度，从而有利于浆料均匀涂覆在负极集流体上。
硬碳材料中的金属离子，例如，可能通过碳源中含有的金属元素或者通过掺入而引入。对以生物质或沥青/煤等金属元素含量较高的碳源制备的硬碳，金属离子的总量，特别是正二价以上金属离子的总量，在上述范围内时，特别有利于制浆和涂覆工艺。
硬碳中金属离子的含量可以通过本领域中的常规方法测得。例如，电感耦合等离子体原子发射光谱法等。
在一些实施方式中，硬碳材料中金属离子总含量为20ppm-800ppm，且二价以上的金属离子的含量为0.1ppm-20ppm。本公开通过进一步使金属离子总含量以及二价以上的金属离子的含量在上述范围内，在提高硬碳材料可加工性的同时，还能提高负极SEI膜的无机物含量，有利于减少钠枝晶的产生或者硬碳材料表面析钠。
在一些实施方式中，金属离子包括Na+、K+、Ca2+、Mg2+、Mn2+、Ba2+、Al3+中的至少一种，但不限于此。
在一些实施方式中，二价以上的金属离子为Ca2+。研究发现，钙离子在硬碳材料中的含量对负极浆料的影响较大，控制钙离子的含量在上述范围内，有利于获得合适粘度的负极浆料，有利于后续的涂覆等工艺，从而获得质量提高的负极极片。
在一些实施方式中，硬碳材料的表面氧元素含量为6％-14％。硬碳材料的表面通常存在一些含氧基团，例如-COOR、-COOH、-C＝O、-OH、-C-O-C-等。研究发现，不同的表面氧元素含量会影响浆料的粘度，进而影响加工性能。推测这些含氧基团的量过大时，与粘合剂、增稠剂等浆料中的组分发生相互作用，影响体系均匀分散，造成胶凝，并随放置时间的增长，胶凝程度增加。这会影响后续工序，堵塞滤芯，或者造成涂覆的极片表面不平整。
示例性的，硬碳材料的表面氧元素含量为6％、7％、8％、9％、9.5％、10％、10.5％、11％、12％、13％、14％或为其中任意两个数值组成的范围。
在一些实施方式中，硬碳材料的表面氧元素含量为8％-12％。硬碳材料的表面氧元素含量在上述范围内，更有利于改善硬碳材料的涂覆性能。
本公开的硬碳材料可进一步满足以下各项中的一项或者多项，以进一步提升硬碳材料的至少一个方面的性能，如可逆容量、压实密度等。
(1)硬碳材料具有表面包覆层。表面包覆层能降低表面缺陷。
在一些实施方式中，表面包覆层为碳包覆层。
(2)硬碳材料的ID/IG≤1.35；其中，ID表示拉曼光谱在1350±50cm-1处的D峰强度，IG表示拉曼光谱在1580±50cm-1处的G峰强度。硬碳材料的ID/IG在上述范围内，可保持合适的硬碳表面无序碳的比例，一定量的有序碳的层状结构有利于通过碳层间滑移来提高硬碳材料的压实密度，提高负极储能密度。
在一些实施方式中，硬碳材料的ID/IG为0.7-1.32。示例性的，硬碳材料的ID/IG为0.7、0.8、0.9、1.0、1.1、1.2、1.30，或任意两个数值所组成范围内的任何值。
(3)硬碳材料的数量分布粒径Dn10为0.5μm-1.0μm，这更有利于负极极片的压实密度，此外较少的低粒径颗粒说明硬碳的孔结构适当，材料骨架强度适中。
(4)硬碳材料的粒径满足：硬碳材料的体积分布粒径Dv10为≤3.0μm；硬碳材料的体积分布粒径Dv50≤7.9μm；以及硬碳材料的体积分布粒径Dv90≤15μm。硬碳材料的粒径满足上述搭配，进一步有利于负极极片的压实密度。
(5)硬碳材料在50000N下的压实密度ρ1≥0.9g/cm3。
(6)硬碳材料比表面积为2m2/g-12m2/g。硬碳材料的比表面积在上述范围内，有利于得到合适的孔结构，有利于平衡克容量。
在一些实施方式中，硬碳材料比表面积为3m2/g-8m2/g。硬碳材料的比表面积在上述范围内，更有利于平衡克容量。
(7)硬碳材料的振实密度ρ2为0.75g/cm3-0.9g/cm3。
在本公开中，硬碳材料的孔体积、比表面积为本领域公知的含义，可以用本领域已知的仪器及方法进行测定。例如，可以参照GB/T 19587-2017，采用氮气吸附法测试吸附和解吸等温线，用BET(Brunauer Emmett Teller)法计算得出硬碳材料的比表面积，使用DFT模型拟合出累积孔体积相对于孔径的分布曲线和dV/d(logD)-D的曲线，并得出1nm以上的特定的孔径范围的孔的孔体积。测试仪器例如可以为美国Micromeritics公司的ASAP-2460型比表面积孔径分析测试仪。二氧化碳分子的动力学直径小于氮气分子，在273K下饱和蒸汽压更高，在该温度下气体能够更快地扩散到1nm以下的空隙中，从而能分析探测较小的微孔结构，因此，采用二氧化碳吸附法测试吸附和解吸等温线，使用DFT模型拟合出累积孔体积相对于孔径的分布曲线，并得出0-1nm的特定的孔径范围的孔的孔体积。测试仪器例如可以为美国Micromeritics公司的ASAP-2460型比表面积孔径分析测试仪。
在本公开中，硬碳材料的金属元素及其含量，可以用本领域已知的仪器及方法进行测定。例如可以参照US EPA 6010D-2014电感耦合等离子体原子发射光谱法，测试仪器可以采用，例如，ICP-OES，Thermo ICAP7400。
在本公开中，硬碳材料的表面氧元素含量，可以用本领域已知的仪器及方法进行测定。例如可以参照GB/T 33502-2017表面化学分析X射线光电子能谱(XPS)数据记录与报告的规范要求，测试仪器可以采用Axis Supra+X射线光电子能谱仪。
在本公开中，硬碳材料的ID/IG值可使用拉曼光谱仪进行测试，ID表示材料的拉曼光谱在1350±50cm-1处的D峰强度，对应于对称性破坏，即，在结构中存在无序和晶格缺陷。IG表示材料的拉曼光谱在1580±50cm-1处的G峰强度，对应于平面内C-C振动的G(石墨)谱带。测试条件为：激发波长为532nm，测试波数范围500-2500cm-1，光栅为600刻线，物镜为50倍，积分时间为10s，累计次数为3次，面扫，得到100个点的D峰、G峰强度，计算100个点的ID/IG，去除最大与最小的各30个ID/IG，剩余40个点的平均值即为材料的ID/IG。测试仪器可以采用Horiba LabRAM HR800拉曼光谱仪。
在本公开中，硬碳材料的压实密度为本领域公知的含义，可以用本领域已知的仪器及方法进行测定。例如可以参照GB/T 24533-2009，通过电子压力试验机(例如可以为UTM7305型电子压力试验机)进行测定。示例性测试方法如下：称取1g样品粉末，加入底面积为1.327cm2的模具中，加压至50000N，保压30s，然后卸压，保持10s，然后记录并计算得到材料在50000N压力下的粉体压实密度。
在本公开中，硬碳材料的振实密度为本领域公知的含义，可以用本领域已知的仪器及方法进行测定。例如可以参照GB/T 5162-2006，使用粉体振实密度测试仪进行测定。测试仪器可以采用丹东百特BT-301，测试参数如下：振动频率250±15次/分钟，振幅3±0.2mm，振动次数5000次，量筒25cm3。
在本公开中，硬碳材料的数量分布粒径Dn10以及体积分布粒径Dv10、Dv50、Dv90为本领域公知的含义，可以用本领域已知的仪器及方法进行测定。例如可以参照GB/T 19077-2016，采用激光粒度分析仪进行测定。测试仪器可以为英国马尔文仪器有限公司的Mastersizer 3000型激光粒度分析仪，或者，通过显微镜图像，测量和统计硬碳材料的粒径。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极膜层设置在负极集流体相对的两个表面中的任意一者或两者上。
在一些实施方式中，负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，锂离子电池可以采用铜箔，钠离子电池可以采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，负极集流体包括铜箔、铝箔、不锈钢箔、钛箔、镍箔、镍铁箔、镍铜箔、镍铁铜箔中的至少一种。
在一些实施方式中，负极膜层还可选地包括粘结剂。粘结剂可选自丁苯橡胶(SBR)、丙烯酸酯橡胶、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，第一粘结剂可为第一水性粘结剂。第一水性粘结剂可选自丁苯橡胶和丙烯酸酯橡胶中的一种或多种。
在一些实施方式中，负极膜层还可选地包括水性分散剂。水性分散剂可选自羧甲基纤维素钠(CMC-Na)、海藻酸钠、黄原胶、卡拉胶中的一种或多种。在一些实施方式中，负极膜层还可选地包括第一导电剂。第一导电剂可选自Super-P、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂。
在一些实施方式中，负极膜层包括第一水性粘结剂、水性分散剂和第一导电剂中至少一种。
在一些实施方式中，负极膜层中硬碳材料的质量含量在80％以上。
在一些实施方式中，负极膜层中硬碳材料的质量含量在85％以上。示例性地，在88％以上，在90％以上，在92％以上，在94％以上，大于95％以上。示例性地，负极膜层中硬碳材料的质量含量在99.3％以下，在99.0％以下，在98.8％以下，在98.5％以下，在98.3％以下，在98.0％以下。
在一些实施方式中，水性粘结剂的质量含量为0％至5％，可选地为0％至3％，进一步可选地为0.5％至2％。
在一些实施方式中，水性分散剂的质量含量为0％至5％，可选地为0％至2％，进一步可选地为0.1％至1％。
在一些实施方式中，导电剂的质量含量为0％至5％，可选地为0％至2％，进一步可选地为0.1％至2％。
在一些实施方式中，负极极片还包括底涂层；底涂层的厚度为0.5μm-3μm。由此，有利于提高极片涂布质量。
在一些实施方式中，底涂层包括无机氧化物和第二水性粘结剂。无机氧化物的密度大，与金属集流体基材的亲附性更好，相比于膜层中硬碳材料或导电剂不容易在浆料的表面张力作用下发生收缩或者位移。包括水性粘结剂的水性浆料表面张力大，在集流体上涂布时往往存在表面能差异值大、涂覆质量差的问题。在底涂层中包括无机氧化物尤其能够解决水性浆料与集流体基材相容性差的问题，改善水性浆料在集流体基材上的涂覆质量。由此，更有利于降低漏涂风险，提高极片涂布质量。
在一些实施方式中，在底涂层中，无机氧化物包括氧化铝、勃姆石、氧化镁、氧化铁、氧化硅、氧化锆中的一种或多种；底涂层中无机氧化物的质量占比为30％-60％。底涂层中包含上述质量范围内的无机氧化物既能够实现极片涂布质量的提高，又能够改善极片粘结强度、降低极片冷压时的延展率，还能够实现对集流体电阻的有效控制，兼顾电池的电化学表现。
第二水性粘结剂同样可选自丁苯橡胶和丙烯酸酯橡胶中的一种或多种。第二水性粘结剂与第一水性粘结剂可以相同也可以不同。第二水性粘结剂具有水油两亲性，相比于与水溶剂具有较强亲附性的线性粘结剂能够表现出更好的耐水性，使得底涂层在包含活性物质的上层膜层涂布的过程中能够始终保持稳定，进一步发挥底涂层改善涂布质量的作用。
在一些实施方式中，底涂层包括无机氧化物、分散剂、第二水性粘结剂和第二导电剂。
分散剂包括聚丙烯酸类聚合物中的一种或多种。丙烯酸类聚合物能起到有效分散无机氧化物的作用，辅助无机氧化物充分发挥其效能。在一些实施方式中，底涂层中分散剂的质量含量为1％-8％，可选为1％-5％。
第二导电剂可选自Super-P，乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯、碳纳米纤维中的一种或多种。第二导电剂和第一导电剂可以相同或不同。在一些实施方式中，底涂层中第二导电剂的质量含量为10％-40％。
在一些实施方式中，底涂层包括30％-60％无机氧化物、1％-8％分散剂、10％-40％第二水性粘结剂和10％-40％第二导电剂。
在一些实施方式中，底涂层还包括增稠剂和/或润湿剂。
润湿剂可选自聚乙氧醚类表面活性剂、聚醚有机硅类表面活性剂、非离子型氟碳聚合物类表面活性剂、炔类表面活性剂中的一种或多种。底涂层中增稠剂的质量含量为0.5％-4％。
增稠剂可选自羧甲基纤维素钠、海藻酸钠、黄原胶、卡拉胶中的一种或多种。底涂层中，增稠剂的质量含量为0.2％-1％。
钠离子电池包括正极极片、位于负极极片、正极极片之间的隔离膜、电解液以及上述各实施方式中的负极极片。以下适当参照附图对本公开的钠离子电池进行说明。
本文中提及的术语“钠离子电池”指电池单体、电池模块或电池包。以下分别进行说明。
通常情况下，钠离子电池单体包括正极极片、负极极片、电解质(液)和隔离膜。在电池充放电过程中，活性离子，如钠离子，在正极极片和负极极片之间往返嵌入和脱出。电解质在正极极片和负极极片之间起到传导离子的作用。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使离子通过。
[正极极片]
正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，正极膜层包括正极活性材料。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极膜层设置在正极集流体相对的两个表面的其中任意一者或两者上。
在一些实施方式中，正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，电池单体为钠离子电池，正极活性材料可采用本领域公知的用于钠离子电池的正极活性材料。作为示例，正极活性材料可包括含钠层状氧化物、聚阴离子钠离子化合物、普鲁士蓝钠离子化合物等，但本公开并不限定于这些材料，还可以使用其他可被用作钠离子电池正极活性材料的传统公知的材料。例如作为本公开可选的技术方案，含钠层状氧化物中，过渡金属可以是Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种。钠过渡金属氧化物例如为NaxMO2，其中M为Ti、V、Mn、Co、Ni、Fe、Cr及Cu中的一种或几种，0<x≤1。
在一些实施方式中，正极活性材料包括含钠层状氧化物、聚阴离子钠离子化合物、普鲁士蓝钠离子化合物中至少一种。
作为示例，含钠层状氧化物可为铁锰基层状氧化物。铁锰基层状氧化物包括镍铁锰基层状氧化物和铜铁锰基层状氧化物中的至少一种。
作为本公开可选的技术方式，聚阴离子钠离子化合物可以是具有钠离子、过渡金属离子及四面体型(YO4)n-阴离子单元的一类化合物。过渡金属可以是Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种；Y可以是P、S及Si中的至少一种；n表示(YO4)n-的价态。聚阴离子钠离子化合物还可以是具有钠离子、过渡金属离子、四面体型(YO4)n-阴离子单元及卤素阴离子的一类化合物。过渡金属可以是Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种；Y可以是P、S及Si中的至少一种，n表示(YO4)n-的价态；卤素可以是F、Cl及Br中的至少一种。聚阴离子钠离子化合物还可以是具有钠离子、四面体型(YO4)n-阴离子单元、多面体单元(ZOy)m+及可选的卤素阴离子的一类化合物。Y可以是P、S及Si中的至少一种，n表示(YO4)n-的价态：Z表示过渡金属，可以是Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种，m表示(ZOy)m+的价态；卤素可以是F、Cl及Br中的至少一种。聚阴离子钠离子化合物例如是NaFePO4、Na3V2(PO4)3、NaM’PO4F(M’为V、Fe、Mn及Ni中的一种或几种)及Na3(VOy)2(PO4)2F3-2y(0≤y≤1)中的至少一种。
作为本公开可选的技术方式，聚阴离子钠离子化合物可以是Nax-aAaVy-bMb(PO4)2-2c(DO4)2cFz-dQd，其中，A元素代表掺杂取代Na元素的碱金属元素，M元素代表取代V元素的金属元素，D元素代表取代P元素的掺杂元素，Q元素代表取代F元素的掺杂元素，D元素包括Si和S中的至少一种，Q元素包括Cl和O中的至少一种；3.5≤x≤4.5，0≤a≤0.15x，0.8≤y≤1.1，0≤b≤0.3y，0≤c≤0.15，0.8≤z≤1.1，0≤d≤0.2z。可选地，A元素包括K和Li中的至少一种；M元素包括Fe、Cr、Al、Sc、Ga、In、Ti、Zr、Mn、Zn、Ni、Cu和Co中的至少一种。
作为本公开可选的技术方式，聚阴离子钠离子化合物可以是NaxRy(PO4)2P2O7，其中x＝3.5-4.5，y＝2.75-3.25，R包括Mg、Al、Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Zr、Cr、Nb、Mo、In、Ga、Sn、Hf、Ta、W和Pb中的至少一种。
作为本公开可选的技术方式，聚阴离子钠离子化合物可以是Na4+xR3-y P4-mO15/C；
其中，0<x<0.5、0＜y≤0.5、0＜m≤0.2，R包括Mg、Al、Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Zr、Cr、Nb、Mo、In、Ga、Sn、Hf、Ta、W和Pb中的至少一种。
普鲁士蓝类化合物可以是具有钠离子、过渡金属离子及氰根离子(CN-)的一类化合物。过渡金属可以是Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种。普鲁士蓝类化合物例如为NaaMebMe’c(CN)6，其中Me及Me’各自独立地为Ni、Cu、Fe、Mn、Co及Zn中的至少一种，0<a≤2，0<b<1，0<c<1。
在一些实施方式中，电池单体可为锂离子电池，正极活性材料可采用本领域公知的用于锂离子电池的正极活性材料。作为示例，正极活性材料可包括以下材料中的至少一种：橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。但本公开并不限定于这些材料，还可以使用其他可被用作电池正极活性材料的传统材料。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。其中，锂过渡金属氧化物的示例可包括但不限于锂钴氧化物(如LiCoO2)、锂镍氧化物(如LiNiO2)、锂锰氧化物(如LiMnO2、LiMn2O4)、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物(如LiNi1/3Co1/3Mn1/3O2(也可以简称为NCM333)、LiNi0.5Co0.2Mn0.3O2(也可以简称为NCM523)、LiNi0.5Co0.25Mn0.25O2(也可以简称为NCM211)、LiNi0.6Co0.2Mn0.2O2(也可以简称为NCM622)、LiNi0.8Co0.1Mn0.1O2(也可以简称为NCM811)、锂镍钴铝氧化物(如LiNi0.85Co0.15Al0.05O2)及其改性化合物等中的至少一种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂(如LiFePO4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、磷酸锰锂(如LiMnPO4)、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料中的至少一种。
电池在充放电过程中会伴随活性离子(Li或Na)的脱嵌及消耗，电池在放电到不同状态时Li或Na的摩尔含量不同。本公开中关于正极活性材料的列举中，Li或Na的摩尔含量为材料初始状态，即投料前状态，正极活性材料应用于电池体系中，经过充放电循环，Li或Na的摩尔含量会发生变化。
本公开中关于正极活性材料的列举中，氧的摩尔含量仅为理论状态值，晶格释氧会导致氧的摩尔含量发生变化，实际氧的摩尔含量会出现浮动。
在一些实施方式中，正极膜层还可选地包括粘结剂。作为示例，粘结剂可以包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物及含氟丙烯酸酯树脂中的至少一种。
在一些实施方式中，正极膜层还可选地包括导电剂。作为示例，导电剂可以包括Super-P、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本公开对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，电解质采用电解液。电解液包括电解质盐和溶剂。
在一些实施方式中，电池单体为钠离子电池，电解质盐可选自六氟磷酸钠、四氟硼酸钠、高氯酸钠、六氟砷酸钠、双氟磺酰亚胺钠、双三氟甲磺酰亚胺钠、三氟甲磺酸钠、二氟磷酸钠、二氟草酸硼酸钠、二草酸硼酸钠、二氟二草酸磷酸钠及四氟草酸磷酸钠中的至少一种。
在一些实施方式中，电池单体为锂离子电池，电解质盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、三氟甲磺酸锂、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂、二氟二草酸磷酸锂及四氟草酸磷酸锂中的至少一种。
在一些实施方式中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。
在一些实施方式中，电解液中的溶剂包括碳酸酯类溶剂，碳酸酯类溶剂包括碳酸亚乙酯、碳酸亚丙酯、氟代碳酸亚乙酯中至少一种。由此，有利于提高电解液的耐高压能力。
在一些实施方式中，相对于溶剂的体积，碳酸亚丙酯的体积占比15％-55％。由此，不仅有利于提高电解液耐氧化能力，还可以解离钠盐提高电导率。
在一些实施方式中，电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
[隔离膜]
在一些实施方式中，电池单体中还包括设置在正极极片和负极极片之间的隔离膜。本公开对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，电池单体可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，电池单体的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。电池单体的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本公开对电池单体的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图1是作为一个示例的方形结构的电池单体5。
在一些实施方式中，参照图2，外包装可包括壳体51和顶盖组件53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，顶盖组件53能够盖设于开口，以封闭容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于容纳腔内。电解液浸润于电极组件52中。电池单体5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，电池单体可以组装成电池模块，电池模块所含电池单体的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。
图3是作为一个示例的电池模块4。参照图3，在电池模块4中，多个电池单体5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个电池单体5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个电池单体5容纳于该容纳空间。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。
图4和图5是作为一个示例的电池包1。参照图4和图5，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
钠离子电池的制备方法
本公开实施例方式还提供一种钠离子电池的制备方法，包括制备负极极片，其中，制备负极极片包括：混合负极组分和溶剂，得到负极浆料，其中，负极组分包括硬碳材料，硬碳材料包含多孔结构，多孔结构中包括孔径为2nm-8nm的孔，通过氮气吸附法测定孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g；以及将负极浆料涂覆在负极集流体上。2nm-8nm孔径的孔具有合适孔容时能够改善硬碳材料的动力学性能，并且这部分孔径的孔还能够贡献部分容量，从而使负极极片能够具有提高的动力学性能并兼顾容量。
在一些实施方式中，通过氮气吸附法测定硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0010cm3/g-0.0040cm3/g。由此，更有利于能够改善硬碳材料的动力学性能并兼顾克容量。
在一些实施方式中，通过氮气吸附法测定硬碳材料的孔径为2nm-8nm的孔的孔体积占硬碳材料的总孔体积的3.5％-30％。由此，进一步有利于硬碳材料动力学性能和克容量的平衡，并且保持合适的结构稳定性。
在一些实施方式中，通过二氧化碳吸附法测定硬碳材料的孔径为小于等于1nm的孔的孔体积表示为V1，通过氮气吸附法测定硬碳材料的孔径为1nm-2nm的孔的孔体积表示为V2，则V1+V2在0.0006cm3/g至0.0050cm3/g范围内。通过进一步限制V1+V2在上述范围，更有利于使硬碳材料具有合适的克容量。
在一些实施方式中，V1+V2在0.0006cm3/g至0.0035cm3/g范围内。孔径为2nm以下的孔的孔体积在0.0006cm3/g至0.0035cm3/g范围内，还有利于在使硬碳材料具有合适的克容量的同时，减少制浆过程中的产气冒泡现象，提高硬碳材料的可加工性，并提高负极极片的均匀性，降低负极浆料漏涂的风险，提高钠离子电池性能。
在一些实施方式中，V1+V2在0.0020cm3/g至0.0035cm3/g的范围内。
在一些实施方式中，V1+V2占硬碳材料的孔体积的18％至30％。硬碳材料的孔径在2nm以下的孔的孔体积占总孔体积的比例在上述范围内，更有利于改善硬碳材料的克容量。
在一些实施方式中，硬碳材料包含孔径在1.0nm-1.5nm范围内的孔，通过氮气吸附法测定孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.009cm3/(g·log(nm))。这更有利于减少制浆过程中的产气冒泡现象。
在一些实施方式中，通过氮气吸附法测定孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.006cm3/(g·log(nm))。这进一步有利于减少制浆过程中的产气冒泡现象。
在一些实施方式中，硬碳材料的孔径为1.0nm-1.5nm的孔的孔体积占硬碳材料的总孔体积的6％至14％。这进一步有利于减少制浆过程中的产气现象。
在一些实施方式中，相对于负极浆料的质量，负极组分的质量百分含量为50％～60％。由此，有利于浆料的均匀性和稳定性。示例性地，相对于负极浆料的质量，负极组分的质量百分含量为50％、52％、54％、56％、58％、60％或为其中任意两个数值组成的范围之间的值。
在一些实施方式中，相对于负极组分的质量，硬碳的质量百分含量为80％～95％。由此，有利于电池的能量密度。示例性地，相对于负极组分的质量，硬碳的质量百分含量为80％、82％、85％、87％、90％、92％、95％或为其中任意两个数值组成的范围之间的值。
在一些实施方式中，负极组分还包括导电剂、粘结剂和分散剂中的一种或者多种。导电剂能够有效加快电子传输速率，提高电池的充放电效率。粘结剂有利于在电池充放电过程中维持电极结构的完整性。分散剂能够改善负极组分的颗粒在溶剂中的分散性，使浆料易于涂布。
在一些实施方式中，混合负极组分和溶剂包括：在0℃～30℃下进行1h～4h的真空搅拌。本公开对真空搅拌没有具体限制，可根据实际生产需求选择合适的真空度、温度、时间、搅拌速度等工艺条件。通常来说，在真空搅拌之后进行下一工序之前，浆料保持均匀稳定即可。在一些具体实施方式中，负极组分包括硬碳、分散剂、导电剂和粘结剂，负极浆料通过以下步骤制备：混合硬炭、分散剂、导电剂和溶剂，并进行真空搅拌；以及进一步加入粘接剂，并进一步搅拌2～4h。
采用上述硬碳材料制备负极浆料时，可明显减少冒泡时间，有利于制浆的顺利进行，还有利于后续的涂覆及冷压等工序，从而提高负极膜层的均匀性，防止集流体被暴露。
在一些实施方式中，制备负极极片还包括：将负极浆料涂覆在负极集流体的至少一个表面上并随后进行烘干、冷压、模切等工序。本公开对负极极片的制备的这些工序没有特别限制，本领域技术人员能够根据实际需要采用合适的工艺方法。
示例性地，通过以下方式制备负极极片：按质量份计，硬碳材料、导电剂、粘结剂、分散剂质量比例为93:2:3.5:1.5，将硬碳材料、导电剂(SP)、分散剂(CMC)和适量的去离子水混合，并进行真空搅拌，其中，并在常温下进行真空搅拌约1-4小时，转速如1000r/min；然后，加入粘结剂(SBR)，继续搅拌约2-4小时，形成流动性良好的负极浆料；将负极浆料涂覆在Cu或者Al的集流体上，过带速度1-3m/min，极片表面良好无气泡、无虚边及无划痕；将涂敷后的极片，经80℃烘干，调节过带速度1-3m/min，然后进行收卷，极片表面无明显露箔、针孔或者漏涂等现象；将满足要求的极片通过冷压处理，将极片通过激光模切形成极耳并收卷，负极工序完成，即可得到负极极片。
在一些实施方式中，钠离子电池的制备方法还包括：制备正极极片。
本公开对正极极片的制备没有特别限制，可用于制备正极极片的材料如前所述，本领域技术人员能够根据需要选择合适的材料和工艺来制备正极极片。示例性地，通过以下方式制备正极极片：按质量份计，正极活性材料、导电剂、粘结剂的质量比如8:1:1，将正极活性材料(聚阴离子或者层氧类正极)、导电剂(如SP)、粘结剂(PVDF)与适量NMP(N-甲基吡咯烷酮)混合，并在室温下进行搅拌，转速如1000r/min形成流动性良好的正极浆料；将正极浆料涂覆在Al集流体上，过带速度1-3m/min，极片表面良好无气泡、无虚边及无划痕；将涂敷后的极片，经80℃烘干，调节过带速度1-3m/min，然后进行收卷，极片表面无明显露箔、针孔或者漏涂等现象；将满足要求的极片通过冷压处理，并通过激光模切形成极耳并收卷，完成正极极片制备。
在一些实施方式中，钠离子电池的制备方法还包括：将正极极片、负极极片和隔离膜组装为可通过卷绕工艺或叠片工艺制成的电极组件；将电极组件置于外包装中，并灌装电解液后封装，形成电池单体。在一些具体实施方式中，可通过卷绕工艺或叠片工艺制成电极组件，本公开对此没有特别限制。进一步地，电池单体可以进一步组装为电池模块。
同样的，本公开对隔离膜和电解液也没有特别限制，可用作隔离膜的材料以及电解液组分如前所述，本领域技术人员能够根据需要选择合适的隔离膜材料和电解液组分。
用电装置
本公开实施方式还提供一种用电装置，以下适当参照附图对本公开的钠离子电池进行说明。
本公开实施方式提及的用电装置包括本公开提供的钠离子电池或本公开的钠离子电池制备方法得到的钠离子电池。钠离子电池可以用作用电装置的电源，也可以用作用电装置的能量存储单元。用电装置可以包括移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等，但不限于此。
作为用电装置，可以根据其使用需求来选择电池单体、电池模块或电池包。
图6是作为一个示例的用电装置。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对钠离子电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用电池单体作为电源。
硬碳材料
本公开还提供一种硬碳材料。硬碳材料包含多孔结构，多孔结构中包括孔径为2nm-8nm的孔，通过氮气吸附法测定孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g。
本公开提供的硬碳材料具有优化的孔结构。具体地，硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g，由此，能够改善硬碳材料的动力学性能并兼顾克容量。
在一些实施方式中，通过氮气吸附法测定硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0010cm3/g-0.0040cm3/g。这更有利于硬碳材料的动力学性能并兼顾克容量。
在一些实施方式中，通过氮气吸附法测定硬碳材料的孔径为2nm-8nm的孔的孔体积占硬碳材料的总孔体积的3.5％-30％。这有利于动力学性能和克容量二者的平衡，并且保持合适的结构稳定性。
在一些实施方式中，通过二氧化碳吸附法测定硬碳材料的孔径为小于等于1nm的孔的孔体积表示为V1，通过氮气吸附法测定硬碳材料的孔径为1nm-2nm的孔的孔体积表示为V2，则V1+V2在0.0006cm3/g至0.0050cm3/g范围内。硬碳材料的孔径在2nm以下的孔的孔体积在上述范围内，更有利于硬碳材料具有合适的克容量。
在一些实施方式中，V1+V2在0.0006cm3/g至0.0035cm3/g范围内，由此，在使硬碳材料具有合适的克容量的同时，有利于减少负极浆料制备过程中的产气冒泡现象，从而能够获得容量提升且负极膜层均匀的负极极片，降低负极浆料漏涂的风险，提高钠离子电池性能。优选地，在0.0020cm3/g至0.0035cm3/g的范围内。
在一些实施方式中，V1+V2占硬碳材料的总孔体积的比例在18％至30％范围内。硬碳材料的孔径在2nm以下的孔的孔体积占总孔体积的比例在上述范围内，更有利于改善硬碳材料的克容量。
在一些实施方式中，硬碳材料包含孔径在1.0nm-1.5nm范围内的孔，通过氮气吸附法测定孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.009cm3/(g·log(nm))。这更有利于减少制浆过程中的产气冒泡现象。
示例性地，孔径为1.0nm-1.5nm的孔的dV/d(logD)的最大值为0.001cm3/(g·log(nm))、0.002cm3/(g·log(nm))、0.003cm3/(g·log(nm))、0.004cm3/(g·log(nm))、0.005cm3/(g·log(nm))、0.006cm3/(g·log(nm))、0.007cm3/(g·log(nm))、0.008cm3/(g·log(nm))、0.009cm3/(g·log(nm))或为其中任意两个数值组成的范围之间的值。
在一些实施方式中，通过氮气吸附法测定孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.006cm3/(g·log(nm))。这进一步有利于减少制浆过程中的产气冒泡现象。
在一些实施方式中，硬碳材料的孔径为1.0nm-1.5nm的孔的孔体积占硬碳材料的总孔体积的6％至14％。
在一些实施方式中，硬碳材料中金属离子总含量为≤800ppm，且二价以上的金属离子的含量为≤20ppm。硬碳材料的金属离子总含量及二价以上的金属离子的含量在上述范围内，有利于保持合适的浆料粘度，从而有利于浆料的涂覆，以便获得负极膜层均匀的负极极片。
在一些实施方式中，硬碳材料中金属离子总含量为20ppm-800ppm，且二价以上的金属离子的含量为0.1ppm-20ppm。硬碳材料的金属离子总含量及二价以上的金属离子的含量在上述范围内，有利于提高SEM膜的无机物含量，从而减少钠枝晶的产生或者硬碳材料表面析钠，从而提升循环性能。
在一些实施方式中，金属离子包括Na+、K+、Ca2+、Mg2+、Mn2+、Ba2+、Al3+中的至少一种。
在一些实施方式中，二价以上的金属离子为Ca2+。硬碳材料中钙离子含量对负极浆料的粘度影响较大，其含量在上述范围内有利于获得合适的负极浆料粘度，从而有利于快速浆料的涂覆且避免虚边和浆料流动，获得负极膜层均匀的负极极片。
在一些实施方式中，硬碳材料的表面氧元素含量为6％-14％。硬碳材料的表面氧元素含量在上述范围内，有利于保持合适的分散剂与硬碳材料间作用力，使浆料在混合过程分散均匀，并具有良好的流动性，有利于制浆不发生胶凝现象，从而有利于浆料的涂覆。
在一些实施方式中，硬碳材料的表面氧元素含量为8％-12％。硬碳材料的表面氧元素含量在上述范围内，更有利于浆料的涂覆工艺。
上述硬碳材料的制备可通过对制备方法进行调整而获得。制备方法对碳源没有特别限制，可以采用的碳源包括：沥青/煤、生物质材料以及合成聚合物材料等。在一些实施方式中，不同的碳源也可以相互结合，例如可以通过合成聚合物材料与其他碳源结合，以获得内部/外部结构更有利的硬碳材料。通过工艺条件的调整，可制得上述硬碳材料。
合成聚合物材料，比如酚醛树脂、环氧树脂、呋喃树脂等，具有结构可设计性和低杂含量。通过对合成聚合物材料的前体(如聚合单体或预聚物)进行聚合，或对合成聚合物材料进行分散、制孔或刻蚀等处理，可以很好地控制碳源的微观结构，进而控制硬碳材料的孔隙结构。
示例性地，但不限于此，以合成聚合物材料为碳源的硬碳材料的制备方法，包括以下步骤：固化步骤，固化包括聚合单体或预聚物与溶剂的溶液，得到碳源；刻蚀剂处理步骤，对碳源进行刻蚀剂浸渍；预碳化步骤，对浸渍后碳源进行低温预碳化，得到预碳化品；破碎步骤，破碎预碳化品；脱灰步骤，以及高温碳化步骤。
示例性地，聚合单体可以是酚醛树脂、环氧树脂、呋喃树脂等的单体。
示例性地，预聚物可以是，例如，甲阶酚醛树脂。
示例性地，溶剂为甲醇、乙醇、乙二醇、聚乙二醇、丙三醇、异丙醇及其他多元醇中的至少一种。溶剂使合成聚合物材料分散均匀，有利于后续形成合适的孔结构。
本公开对固化的温度没有特别的限制。本领域技术人员可以根据具体的聚合单体或预聚物的种类选择合适的固化反应温度。示例性地，当预聚物是甲阶酚醛树脂时，固化的温度为80-150℃。
示例性地，刻蚀剂包括磷酸、过氧化氢、硫酸、硝酸、ZnCl2中的至少一种。
示例性地，刻蚀剂的浓度为5-20wt％。例如，刻蚀剂的浓度为5wt％、7wt％、9wt％、11wt％、13wt％、15wt％、17wt％、19wt％、20wt％以及任意两者之间的范围。优选地，刻蚀剂的浓度为7-13wt％。
在一些实施方式中，低温预碳化的温度为400-600℃。示例性地，低温预碳化的温度为400℃、450℃、500℃、550℃、600℃以及任意两者之间的范围。通过温度的低温预碳化处理，可以除去水分、部分的溶出杂质以及表面活性基团，形成合适的致密程度的预碳化品，同时使刻蚀剂充分刻蚀孔，有利于在后续的高温碳化中调整成合适的孔结构。
示例性的，破碎可以是，例如，通过气流磨或者机械磨破碎，本公开对此不作特殊的限定。在一些实施方式中，破碎使颗粒的Dv50为4-8μm，这更有利于预碳化品的孔结构在后续的高温碳化中调整为合适的孔结构，使杂质充分溶出，并使最终的硬碳的粒径分布合适。
示例性的，脱灰步骤可以是通过将产物在酸洗釜中用1-5M的酸浸泡，除去金属杂质。
在一些实施方式中，高温碳化的温度为1000-1300℃。这有利于形成最终合适的孔结构，从而改善克容量和动力学性能。另外，高温碳化还可减少表面的大量缺陷。示例性地，高温碳化的温度为1000℃、1100℃、1200℃、1300℃以及任意两者之间的范围。可选的，高温碳化的温度为1100-1200℃。
在一些实施方式中，制备方法进一步包括形成包覆层的步骤。该步骤例如可以在高温碳化前进行。本公开对具体包覆的工艺不作特殊限定，示例性地，可以为本领域常规的气相包覆、液相包覆或固相包覆。
在一些实施方式中，通过氧化或还原处理，可以调整硬碳表面氧元素含量。例如，在高温碳化前，进行预氧化处理，该处理包括在空气或氧气中80℃-400℃保温0.5-5h。或者，在高温碳化前，进行还原处理，该处理包括在氢气和氩气的混合气氢中400℃-800℃保温0.5-10h。通过上述步骤，可使硬碳材料的表面氧元素含量为6％-14％。
在一些实施方式中，在得到最终硬碳产品前，制备方法还包括分级处理和除磁处理，这能够进一步优化浆料冒泡、浆料粘度低以及电池容量衰减的问题。
在上述方法中，通过诸如对碳源的刻蚀剂处理、低温预碳化的温度及时间等步骤调节孔隙率及孔结构，以获得具有改善动力学性能并兼顾克容量的上述硬碳材料。
生物质材料来源广泛，比如椰壳、稻壳、毛竹、麦壳、秸秆、木质素等等。以生物质材料做为碳源有经济和环保两方面的效果。
示例性地，以生物质材料为碳源制备硬碳材料包括以下步骤。刻蚀剂处理步骤，将生物质材料与刻蚀剂混合浸渍；预碳化步骤，在300-500℃，可选地400-500℃下加热2-6h。刻蚀剂处理结合预碳化步骤可以除去生物质中的挥发分，同时可以实现略微预致孔。破碎步骤，将预碳化的产物破碎到Dv10≤3μm，Dv50≤3μm且Dv90≤3μm颗粒尺寸。通过破碎步骤能够使最终硬碳材料具有合适的粒径分布。脱灰步骤，将产物在酸洗釜中用1～5M的酸浸泡，除去金属杂质。生物质中的金属杂质较多，脱灰步骤能够降低金属杂质的含量。预压步骤，将脱灰后的产物压成颗粒紧密堆积的饼状，减少暴露面积，阻止烧结挥发分对碳的氧化破坏，控制孔隙率。碳化步骤，在1100-1300℃下加热2-6h，除去剩余挥发分。同样的，该制备方法可以进一步包括形成包覆层的步骤，例如，可以在碳化步骤前进行。
示例性地，刻蚀剂包括磷酸、过氧化氢、硫酸、硝酸、ZnCl2中的至少一种。
示例性地，刻蚀剂的浓度为5-20wt％。例如，刻蚀剂的浓度为5wt％、7wt％、9wt％、11wt％、13wt％、15wt％、17wt％、19wt％、20wt％以及任意两者之间的范围。优选地，刻蚀剂的浓度为7-13wt％。
示例性的，破碎可以是，例如，通过气流磨或者机械磨破碎，本公开对此不作特殊的限定。在一些实施方式中，破碎使颗粒的Dv50为4-8μm，这更有利于预碳化品的孔结构在后续的高温碳化中调整获得合适的孔结构，也有利于使杂质充分溶出，并使最终的硬碳的粒径分布合适。
示例性地，在脱灰步骤中，酸包括盐酸、硫酸、硝酸等中的至少一种。脱灰可以降低灰分，灰分为各类金属及其氧化物。
在一些实施方式中，可以通过碳化后进一步水洗来调整从内部挥发出的金属离子在表层残留的量。例如，以椰壳为碳源，可以通过碳化后水洗3-4次来进一步降低离子含量。通过结合前面的脱灰步骤，能够调整最终硬碳材料中的阳离子，特别是二价阳离子(如钙离子)含量，从而有利于极片的制备工艺。
在上述方法中，通过诸如刻蚀剂处理结合预碳化、以及碳化步骤的温度及时间等步骤调节孔隙率及孔结构，以获得具有改善的克容量和动力学性能的硬碳材料。
沥青和煤作为常见的化工原料，来源广泛且价格低廉，使得以沥青或煤为碳源制备硬碳材料具有较低的成本。
示例性地，但不限于此，以沥青为碳源制备硬碳材料包括以下步骤。预氧化步骤，将沥青或者改性沥青与氧化剂混合，在200-300℃下加热2-5h，形成硬碳前驱体。通过预氧化步骤可以调节硬碳前驱体的氧含量。示例性地，的氧化剂可以是氧气、硝酸、或过氧化氢，本公开对此不作特殊限定。预碳化步骤，将上述硬碳前驱体在400-600℃下加热2-4h。破碎步骤，将预碳化的产物破碎到颗粒尺寸为Dv10≤3μm，Dv50≤3μm且Dv90≤30μm。预压步骤，将破碎后产物压成颗粒紧密堆积的饼状，减少暴露面积，阻止烧结挥发分对碳的氧化破坏，控制孔隙率。碳化步骤，在1000-1200℃处理2-4h。同样的，该制备方法可以进一步包括形成包覆层的步骤，例如，可以在碳化步骤前进行。
示例性的，破碎可以是通过气流磨或者机械磨破碎，本公开对此不作特殊的限定。在一些实施方式中，破碎使颗粒的Dv50为4-8μm，这更有利于预碳化品的孔结构在后续的高温碳化中调整为合适的孔结构，使杂质充分溶出，并使最终的硬碳的粒径分布合适。
在一些实施方式中，制备方法在碳化步骤后进一步包括脱灰步骤和除磁步骤。经过合适的脱灰步骤能够控制最终产品中阳离子，特别是二价阳离子(如钙离子)的含量，从而进一步有利于获得制备极片工艺的硬碳材料。
在上述方法中，通过诸如对预碳化产物的破碎、预压步骤的温度及压力、碳化步骤的温度及时间等步骤调节孔隙率及孔结构，以获得具有改善的克容量和动力学性能的硬碳材料。
实施例
以下，说明本公开的实施例。下面描述的实施例是示例性的，仅用于解释本公开，而不能理解为对本公开的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
实施例1
生物质材料为碳源的硬碳材料的制备：
1)刻蚀剂处理
以木质素为原料，将原料与ZnCl2水溶液(10％wt)按照质量比1:3混合浸渍12h，取出干燥。
2)预碳化
对上述步骤1)得到的产物加入到在热压炉(顶立科技，VHP-777)中常压的N2气氛下400℃处理2h，得到预碳化品。
3)破碎
对上述步骤2)得到的预碳化品在气流磨(晟星环保：SX1210)中进行气流粉碎，得到Dv1为2μm，Dv50为5μm，Dv90为12μm的产物。
4)脱灰
将上述步骤3)中破碎后的产物，在酸洗釜中，在室温下用2M的盐酸水溶液浸泡10h，过滤后用水洗3次，然后在连续式窑炉内100℃下进行干燥。
5)预压
将上述步骤4)中得到的产物在热压炉(厂家：顶立科技，型号：VHP-777型)中以50T压力，加压1小时。
6)碳化
将上述步骤5)中得到的产物在常压的N2气氛下2℃/min升温速率到1400℃下烧结2h，用水洗3次，然后在连续式窑炉内100℃下进行干燥，得到实施例1样品。
负极浆料的制备：
将硬碳材料、导电剂和分散剂按8:1:1的比例在去离子水中混合，常温下进行真空搅拌2.5h(使负极浆料在真空搅拌后4h之内保持均匀状态而不进一步出现气泡为准，以下实施例和对比例根据情况调整真空搅拌时间，但最长不超过4h)，分散制成均匀的负极浆料，其中，分散剂为羧甲基纤维素钠，导电剂为导电炭黑。
负极极片的制备：
把搅拌均匀的负极浆料通过双面涂布机涂布在Al箔两面上，双面涂布完成后，依次进行真空80℃烘干、冷压、分切、制片，制备负极极片。
扣式半电池的制备：
将制得的负极电极片在手套箱内进行电池组装，金属钠片作为对电极，电解液为溶解有NaPF6的EC:DMC(体积比)＝1:1的溶剂，其中添加加有10v/v％的FEC。
将正极极片、隔离膜、负极极片按顺序叠好，加入上述电解液，经封装、静置、化成、老化等工序后，制成扣式半电池。
实施例2
合成聚合物材料为碳源的硬碳材料的制备：
1)固化
将25g无水乙醇与50g甲阶酚醛树脂(2150型号酚醛树脂，固含量80％)混合并搅拌以获得均匀的溶液。在烘箱中，将溶液在80℃保温10h，得到硬碳材料前体。
2)刻蚀剂处理
将上述步骤1)得到的硬碳材料前体和10wt％磷酸水溶液，按照质量比1:3混合浸渍12h。
3)低温预碳化
将硬碳材料前体粗破，在管式炉中常压N2气氛下以2℃/min的升温速率升温至600℃，加热5h，得到预碳化品。
4)破碎
将上述步骤3)得到的预碳化品在球磨机(MSK-SFM-1-1L行星式球磨机)中以300rpm破碎2h，球磨珠为氧化锆材质，物料和球磨珠质量比为1:3。用Mastersizer 3000型激光粒度分析仪测破碎后样品的粒度分布，其Dv50为5μm。
5)脱灰
将上述步骤4)中破碎后的预碳化品在酸洗釜中，在室温下用2M的盐酸水溶液浸泡10h，过滤后用水洗3次，在连续式窑炉内调节温度在100℃下进行干燥。
6)高温碳化
将上述步骤5)得到的产物在管式炉中常压N2气氛下以2℃/min的升温速率升温至1150℃加热2h。
7)分级
将上述步骤6)得到的产物在气流分级设备(厂家：精华粉体，型号：AB03型)中进行分级，持续监控并测试出料粒度，直到Dv50达到5μm，完成分级。
8)除磁
将上述步骤7)得到的产物在除磁设备(厂家：万业达磁电，型号：GDG-250型)中进行除磁，直至产物的磁性消失。
负极浆料、负极极片及扣式半电池的制备：
按照与实施例1类似的方法，使用本实施例的硬碳材料制备负极浆料、负极极片，并组装为扣式半电池。
实施例3
以沥青/煤为硬碳材料前体的硬碳材料的制备：
1)预氧化
将改质煤沥青(8994-94-4)加到氧化反应釜中，通入常压空气，在300℃加热3h。
2)预碳化
将上述步骤1)得到的预氧化沥青在管式炉中450℃加热3h。
3)预压
将上述步骤2)得到的产物，在热压机(厂家：顶立科技，型号：VHP-777型)中以30T压力，加压1h。
4)碳化
将上述步骤3)得到的产物，在管式炉中在常压N2气氛1100℃下加热2h。
5)脱灰
将上述步骤4)中得到的产物在酸洗釜中，在室温下用2M的盐酸水溶液浸泡10h，过滤后用水洗3次，在连续式窑炉内调节温度在100℃下进行干燥。
6)除磁
将上述步骤5)得到的产物在除磁设备(厂家：万业达磁电，型号：GDG-250型)中进行除磁，直至产物的磁性消失。
负极浆料、负极极片及扣式半电池的制备：
按照与实施例1类似的方法，使用本实施例的硬碳材料自备负极浆料、负极极片，并组装为扣式半电池。
实施例4
按照与实施例2类似的方法制备硬碳材料，区别仅在于制备硬碳材料时，将硬碳材料前体和20％磷酸水溶液混合浸渍。
实施例5
按照与实施例2类似的方法制备硬碳材料，区别仅在于制备硬碳材料时，将硬碳材料前体和10％磷酸水溶液按照质量比1:5混合浸渍。
对比例1
按照与实施例1类似的方法制备硬碳材料，区别在于制备硬碳材料时，前驱体不使用ZnCl2水溶液浸渍处理，高温烧结条件为1500℃处理10h。
对比例2
按照与实施例1类似的方法制备硬碳材料，区别在于制备硬碳材料时，将原料与50wt％的ZnCl2水溶液按照质量比1:1混合浸渍。
硬碳材料相关测试：
气体吸附测试
对硬碳材料，参照GB/T 19587-2017，采用氮气和二氧化碳吸附法分别测试吸附和解吸等温线，其中氮气吸附法和二氧化碳吸附法使用都使用比表面及孔隙度分析仪(美国Micromeritics ASAP-2460型)。对氮气吸附法测得的吸附和解吸等温线，用BET(Brunauer Emmett Teller)法计算得出硬碳材料的比表面积，使用DFT模型拟合出dV/d(logD)相对于孔径D的分布曲线，在孔径为1.0-2.0nm的范围内读出最大值，同时拟合出累积孔体积相对于孔径的分布曲线，得出1nm-2nm的孔径范围的孔的孔体积V2，以及1.0nm以上的孔的孔体积。对二氧化碳吸附法测得的吸附和解吸等温线，使用DFT模型拟合出累积孔体积相对于孔径的分布曲线，得出1nm以下的孔径范围的孔的孔体积V1。测定结果参见表1。硬碳材料的总孔体积为1nm以上的孔径范围的孔的孔体积与V1的加和。
硬碳材料的克容量和平均嵌Na电压测试
对上述实施例和对比例的扣式半电池。以0.05C倍率嵌钠到0V，所得容量为首次充电能量和充电容量；0.1C倍率脱钠到2.5V截止，所得容量为首次放电容量。根据上述极片制备过程中浆料的涂覆重量和面积计算出负极极片中的硬碳材料的质量并进一步计算克容量：
克容量＝首次充电容量/硬碳材料的质量。
平均嵌Na电压V通过下式计算：
平均嵌Na电压＝首次充电能量/容量。
平均嵌Na电压越大，说明同等条件嵌Na时，截面电荷转移快，嵌Na速率越大。
上述实施例1-5和对比例1-3制备的硬碳材料的孔隙特征、平均嵌Na电压以及克容量测试结果参见表1所示。
表1：
由表1可见，硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g，在提供较好容量的前提下，具有改善的动力学性能。
本公开在研究以硬碳材料制备负极极片的可加工性中发现，由于硬碳材料丰富的孔结构，在用硬碳材料制备负极浆料的过程中，会持续地产气冒泡，比如开始制浆2小时后仍然冒泡的硬碳材料，加工难以进行，制备的负极极片有暴露出底层负极集流体的风险，可导致负极极片缺陷，进而影响钠离子电池的性能。下述实施例进一步调整孔结构，以改善加工性能。
实施例6
按照与实施例2类似的方法制备硬碳材料，区别在于制备硬碳材料时，硬碳材料前体和磷酸水溶液里混合浸渍6h，高温碳化的温度为1200℃。
实施例7
按照与实施例2类似的方法制备硬碳材料，区别在于制备硬碳材料时，硬碳材料前体不经过磷酸氧化处理，高温碳化的温度为1300℃。
实施例8
按照与实施例2类似的方法制备硬碳材料，区别在于制备硬碳材料时，硬碳材料前体和80wt％磷酸水溶液里混合浸渍，高温碳化的温度为1300℃。
制备负极浆料中冒泡情况测试
上述各实施例和对比例制备的硬碳材料在制备负极浆料时观察停止冒泡的时间。记录将负极浆料各组分混合制浆后2小时仍冒泡的情况。
此外，将50g以上实施例和对比例制备的硬碳材料分别加入装有温度和压力传感器的容积为500mL密闭的反应釜中，加入200mL水后迅速关闭反应釜，开启搅拌至温度和压力恒定。根据压力变化值和理想气体方程，计算单位质量的硬碳材料冒出气体的体积，作为冒泡量的度量。
上述实施例2和6-8制备的硬碳材料的孔隙特征、冒泡情况、动力学性能以及克容量测试结果参见表2所示。
表2：
从表2可以看出，硬碳材料的孔径在2nm以下的孔的孔体积在0.0006cm3/g至0.0035cm3/g范围内，在改善克容量的同时，有利于减少制浆过程中的产气冒泡现象。硬碳材料的孔径在2nm以下的孔的孔体积占总孔体积的比例在18％至30％范围内，有利于使硬碳材料具有合适的克容量。
实施例9
按照与实施例2类似的方法制备硬碳材料，区别在于制备硬碳材料时，硬碳材料前体和磷酸水溶液按照质量比1:1混合浸渍6h，高温碳化的温度为1200℃
实施例10
按照与实施例2类似的方法制备硬碳材料，区别在于制备硬碳材料时，在磷酸水溶液的浓度为30％，高温碳化的温度为1200℃。
上述实施例9和10制备的硬碳材料的孔隙特征、冒泡情况、动力学性能以及克容量测试结果参见表3所示。
表3：
由表3可见，当dV/d(logD)的最大值在0.001mL/(g·nm)-0.009mL/(g·nm)时，在改善的克容量和动力学性能的同时，进一步减少持续冒泡。
实施例11
按照与实施例1类似的方法制备硬碳材料，区别在于制备硬碳材料时碳化后水洗次数为2次。
实施例12
按照与实施例1类似的方法制备硬碳材料，区别在于制备硬碳材料时碳化后水洗次数为1次。
实施例13
按照与实施例1类似的方法制备硬碳材料，区别在于制备硬碳材料时，所使用盐酸浓度为1M。
金属离子含量测试
对实施例1和11-13的硬碳材料，配成固含量位20％的负极浆料，持续搅拌半小时，后续通过过滤得到清液，用于测试水溶性Ca、Mg、Na及K的离子含量。
静置24h后负极浆料粘度测试
选取合适的转子，固定好粘度计，将对实施例1和11-13的负极浆料静置24h后，置于粘度计下方，浆料恰好淹没转子的刻度线，仪器型号：上海方瑞NDJ-5S，转子：63#(2000-10000mPa.s)、64#(10000-50000mPa.s)，转速：12r/min，测试温度：25℃，测试时间为5min，待示数稳定读取数据。
实施例1和11-13制备的硬碳材料的金属离子含量和负极浆料粘度的测试结果参见表4。
表4：
从表4可以看出，当金属离子总含量在800ppm以下，且二价以上的金属离子的含量较低，如在约20ppm或更少时，有利于在制浆时保持浆料的粘度，从而有利于浆料均匀涂覆在负极集流体上，便于加工。通常来说，浆料粘度在4000Pa·s以上较为有利。可使涂布的不均匀现象，例如波浪虚边，被有效地减少。实施例13中，虽然金属离子总量较低，但Ca2+浓度过大，Ca2+与CMC-Na发生络合，导致CMC-Na难以抓取游离水的能力，减弱其分散剂作用，导致浆料粘度过低，不利于浆料的涂覆。
实施例14
按照与实施例2类似的方法制备硬碳材料，区别在于制备硬碳材料时，刻蚀剂处理中，用10％磷酸水溶液浸渍6h。
实施例15
按照与实施例2类似的方法制备硬碳材料，区别在于制备硬碳材料时，刻蚀剂处理中，用20％磷酸水溶液浸渍5h。
实施例16
按照与实施例2类似的方法制备硬碳材料，区别在于制备硬碳材料时，不作刻蚀剂处理，预碳化在500℃下在Ar/H2(95:5)混合气氛下还原2h。
实施例17
按照与实施例2类似的方法制备硬碳材料，区别在于制备硬碳材料时，刻蚀剂处理中，用30％磷酸水溶液浸渍6h。
表面氧元素含量测试
对实施例2、14-17的硬碳材料，参考GB/T 33502-2017，在同一个材料选三个不同部位，采用X射线光电子能谱(仪器型号为Axis Supra/Supra+)测试硬碳材料表面氧元素含量。
负极浆料的凝胶化程度
对上述实施例2和实施例14-17制备的硬碳材料在制备负极浆料时进行观察，例如通过用小勺挑起浆料并倾倒观察滴落情况，定性判断凝胶化程度。
实施例2和14-17制备的硬碳材料的负极浆料粘度的测试结果以及凝胶程度，参见表5。
表5：
从上述表5可以看出，硬碳材料的表面氧元素在5％-15％范围内，可以使浆料的粘度合适，流动性良好。
需要说明的是，本公开不限定于上述实施方式。上述实施方式仅为示例，在本公开的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本公开的技术范围内。此外，在不脱离本公开主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本公开的范围内。

Claims (66)

  1. 一种钠离子电池，所述钠离子电池包括负极极片，所述负极极片包括负极集流体以及位于所述负极集流体至少一个表面上的负极膜层，所述负极膜层包括硬碳材料，所述硬碳材料包含多孔结构，所述多孔结构中包括孔径为2nm-8nm的孔；
    通过氮气吸附法测定所述孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g。
  2. 根据权利要求1所述的钠离子电池，其中，通过氮气吸附法测定所述硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0010cm3/g-0.0040cm3/g。
  3. 根据权利要求1或2所述的钠离子电池，其中，通过氮气吸附法测定所述硬碳材料的孔径为2nm-8nm的孔的孔体积占所述硬碳材料的总孔体积的3.5％-30％。
  4. 根据权利要求1至3中任一项所述的钠离子电池，其中，通过二氧化碳吸附法测定所述硬碳材料的孔径为小于等于1nm的孔的孔体积表示为V1，通过氮气吸附法测定所述硬碳材料的孔径为1nm-2nm的孔的孔体积表示为V2，则V1+V2在0.0006cm3/g至0.0050cm3/g范围内。
  5. 根据权利要求4所述的钠离子电池，其中，V1+V2在0.0006cm3/g至0.0035cm3/g范围内。
  6. 根据权利要求5所述的钠离子电池，其中，V1+V2在0.0020cm3/g至0.0035cm3/g的范围内。
  7. 根据权利要求4至6中任一项所述的钠离子电池，其中，V1+V2占所述硬碳材料的孔体积的18％至30％。
  8. 根据权利要求1至7中任一项所述的钠离子电池，其中，所述硬碳材料包含孔径在1.0nm-1.5nm范围内的孔，通过氮气吸附法测定所述孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.009cm3/(g·log(nm))。
  9. 根据权利要求8所述的钠离子电池，其中，通过氮气吸附法测定所述孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.006cm3/(g·log(nm))。
  10. 根据权利要求8至9中任一项所述的钠离子电池，其中，所述硬碳材料的孔径为1.0nm-1.5nm的孔的孔体积占所述硬碳材料的总孔体积的6％至14％。
  11. 根据权利要求1至10中任一项所述的钠离子电池，其中，所述负极膜层包括第一水性粘结剂、水性分散剂和第一导电剂中至少一种。
  12. 根据权利要求11所述的钠离子电池，其中，所述第一水性粘结剂包括丁苯橡胶和丙烯酸酯橡胶中的一种或多种；所述水性分散剂包括羧甲基纤维素钠、海藻酸钠、黄原胶、卡拉胶中的一种或多种；所述第一导电剂包括Super-P、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯、碳纳米纤维中的一种或多种。
  13. 根据权利要求11或12所述的钠离子电池，其中，所述负极膜层中硬碳材料的质量含量在80％以上。
  14. 根据权利要求13所述的钠离子电池，其中，所述负极膜层中硬碳材料的质量含量在85％以上，所述第一水性粘结剂的质量含量为0％至5％，所述水性分散剂的质量含量为0％至5％，所述第一导电剂的质量含量为0％至5％。
  15. 根据权利要求1至14中任一项所述的钠离子电池，其中，所述负极膜层中还包括嵌入型储钠材料，所述嵌入型储钠材料的晶面间距d002满足：0.24nm≤d002≤0.8nm；所述负极膜层中所述嵌入型储钠材料的质量含量小于等于10％。
  16. 根据权利要求15所述的钠离子电池，其中，所述嵌入型储钠材料包括碳基嵌入型储钠材料、硫基嵌入型储钠材料、钛基嵌入型储钠材料中的至少一种；所述碳基嵌入型储钠材料包括：软碳、改性石墨中的至少一种；所述软碳的ID/IG满足：0.9≤ID/IG≤1.6，其中ID表示拉曼光谱在1350±50cm-1处的D峰强度，IG表示拉曼光谱在1580±50cm-1处的G峰强度。
  17. 根据权利要求16所述的钠离子电池，其中，所述负极膜层包括层叠设置的第一负极膜层和第二负极膜层，所述第一负极膜层设置在所述负极集流体与所述第二负极膜层中间，所述第一负极膜层包括第一活性物质，所述第二负极膜层包括第二活性物质；所述第一活性物质和第二活性物质分别包括所述硬碳材料和所述嵌入型储钠材料中的至少一种，且所述第一活性物质和所述第二活性物质中至少一者包括所述硬碳材料。
  18. 根据权利要求17所述的钠离子电池，其中，所述第一活性物质包括所述硬碳材料，所述第二活性物质包括所述软碳材料。
  19. 根据权利要求1至18中任一项所述的钠离子电池，其中，所述负极极片还包括底涂层；所述底涂层的厚度为0.5μm-3μm。
  20. 根据权利要求19所述的钠离子电池，其中，所述底涂层包括无机氧化物和第二水性粘结剂。
  21. 根据权利要求19所述的钠离子电池，其中，所述底涂层包括无机氧化物、分散剂、第二水性粘结剂和第二导电剂。
  22. 根据权利要求20或21所述的钠离子电池，其中，在所述底涂层中，所述无机氧化物包括氧化铝、勃姆石、氧化镁、氧化铁、氧化硅、氧化锆中的一种或多种；所述无机氧化物的质量占比为30％-60％。
  23. 根据权利要求21所述的钠离子电池，其中，所述底涂层包括30％-60％无机氧化物、1％-8％分散剂、10％-40％第二水性粘结剂和10％-40％第二导电剂。
  24. 根据权利要求20至23中任一项所述的钠离子电池，其中，所述底涂层还包括增稠剂和/或润湿剂；所述润湿剂包括聚乙氧醚类表面活性剂、聚醚有机硅类表面活性剂、非离子型氟碳聚合物类表面活性剂、炔类表面活性剂中的一种或多种；所述增稠剂包括羧甲基纤维素钠、海藻酸钠、黄原胶、卡拉胶中的一种或多种。
  25. 根据权利要求1至24中任一项所述的钠离子电池，其中，所述负极集流体包括铜箔、铝箔、不锈钢箔、钛箔、镍箔、镍铁箔、镍铜箔、镍铁铜箔中的至少一种。
  26. 根据权利要求1至25中任一项所述的钠离子电池，其中，所述硬碳材料中金属离子总含量为≤800ppm，且二价以上的金属离子的含量为≤20ppm。
  27. 根据权利要求26所述的钠离子电池，其中，所述硬碳材料中所述金属离子总含量为20ppm-800ppm，且二价以上的所述金属离子的含量为0.1ppm-20ppm。
  28. 根据权利要求26或27所述的钠离子电池，其中，所述金属离子包括Na+、K+、Ca2+、Mg2+、Mn2+、Ba2+、Al3+中的至少一种。
  29. 根据权利要求26至28中任一项所述的钠离子电池，其中，所述二价以上的金属离子为Ca2+。
  30. 根据权利要求1至29至中任一项所述的钠离子电池，其中，所述硬碳材料的表面氧元素含量为5％-15％。
  31. 根据权利要求30所述的钠离子电池，其中，所述硬碳材料的表面氧元素含量为8％-12％。
  32. 根据权利要求1至31中任一项所述的钠离子电池，其中，所述钠离子电池还包括正极极片、位于所述负极极片和所述正极极片之间的隔离膜以及电解液，所述电解液中的溶剂包括碳酸酯类溶剂，所述碳酸酯类溶剂包括碳酸亚乙酯、碳酸亚丙酯、氟代碳酸亚乙酯中至少一种。
  33. 根据权利要求32所述的钠离子电池，其中，相对于所述溶剂的体积，所述碳酸亚丙酯的体积占比15％-55％。
  34. 根据权利要求32或33所述的钠离子电池，其中，所述正极极片包括正极集流体以及位于所述正极集流体至少一个表面上的正极膜层，所述正极膜层包括正极活性材料，所述正极活性材料包括含钠层状氧化物、聚阴离子钠离子化合物、普鲁士蓝钠离子化合物中的至少一种。
  35. 根据权利要求34所述的钠离子电池，其中，所述含钠层状氧化物为铁锰基层状氧化物，所述铁锰基层状氧化物包括镍铁锰基层状氧化物和铜铁锰基层状氧化物中的至少一种。
  36. 一种钠离子电池的制备方法，包括制备负极极片，其中，制备负极极片包括：
    混合负极组分和溶剂，得到负极浆料，其中，所述负极组分包括硬碳材料，所述硬碳材料包含多孔结构，所述多孔结构中包括孔径为2nm-8nm的孔，通过氮气吸附法测定所述孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g；以及
    将所述负极浆料涂覆在负极集流体上。
  37. 根据权利要求36所述的制备方法，其中，通过氮气吸附法测定所述硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0010cm3/g-0.0040cm3/g。
  38. 根据权利要求36或37所述的制备方法，其中，通过氮气吸附法测定所述硬碳材料的孔径为2nm-8nm的孔的孔体积占所述硬碳材料的总孔体积的3.5％-30％。
  39. 根据权利要求36至38中任一项所述的制备方法，其中，通过二氧化碳吸附法测定所述硬碳材料的孔径为小于等于1nm的孔的孔体积表示为V1，通过氮气吸附法测定所述硬碳材料的孔径为1nm-2nm的孔的孔体积表示为V2，则V1+V2在0.0006cm3/g至0.0050cm3/g范围内。
  40. 根据权利要求39所述的制备方法，其中，V1+V2在0.0006cm3/g至0.0035cm3/g的范围内。
  41. 根据权利要求40所述的制备方法，其中，V1+V2在0.0020cm3/g至0.0035cm3/g的范围内。
  42. 根据权利要求39至41中任一项所述的制备方法，其中，V1+V2占所述硬碳材料的孔体积的18％至30％。
  43. 根据权利要求36至42中任一项所述的制备方法，其中，所述硬碳材料包含孔径在1.0nm-1.5nm范围内的孔，通过氮气吸附法测定所述孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.009cm3/(g·log(nm))。
  44. 根据权利要求43所述的制备方法，其中，通过氮气吸附法测定所述孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.006cm3/(g·log(nm))。
  45. 根据权利要求36至44中任一项所述的制备方法，其中，所述硬碳材料的孔径为1.0nm-1.5nm的孔的孔体积占所述硬碳材料的总孔体积的6％至14％。
  46. 根据权利要求36至45中任一项所述的制备方法，其中，相对于所述负极浆料的质量，负极组分的质量百分含量为50％～60％。
  47. 根据权利要求36至46中任一项所述的制备方法，其中，相对于所述负极组分的质量，所述硬碳的质量百分含量为80％～95％。
  48. 根据权利要求36至47中任一项所述的制备方法，其中，所述负极组分还包括导电剂、粘结剂和分散剂中的一种或者多种。
  49. 根据权利要求36至48中任一项所述的制备方法，其中，所述混合负极组分和溶剂包括：在0℃～30℃下进行1h～4h的真空搅拌。
  50. 一种用电装置，包括根据权利要求1至35中任一项所述的钠离子电池或权利要求36至49中任一项所述的制备方法得到的钠离子电池。
  51. 一种硬碳材料，所述硬碳材料包含孔径为2nm-8nm的孔，通过氮气吸附法测定所述孔径为2nm-8nm的孔的孔体积为0.0004cm3/g-0.0040cm3/g。
  52. 根据权利要求51所述的硬碳材料，其中，通过氮气吸附法测定所述硬碳材料的孔径为2nm-8nm的孔的孔体积为0.0010cm3/g-0.0040cm3/g。
  53. 根据权利要求51或52所述的硬碳材料，其中，通过氮气吸附法测定所述硬碳材料的孔径为2nm-8nm的孔的孔体积占所述硬碳材料的总孔体积的3.5％-30％。
  54. 根据权利要求51至53中任一项所述的硬碳材料，其中，通过二氧化碳吸附法测定所述硬碳材料的孔径为小于等于1nm的孔的孔体积表示为V1，通过氮气吸附法测定所述硬碳材料的孔径为1nm-2nm的孔的孔体积表示为V2，则V1+V2在0.0006cm3/g至0.0050cm3/g范围内。
  55. 根据权利要求54所述的硬碳材料，其中，V1+V2在0.0006cm3/g至0.0035cm3/g的范围内。
  56. 根据权利要求55所述的硬碳材料，其中，V1+V2在0.0020cm3/g至0.0035cm3/g的范围内。
  57. 根据权利要求54至56中任一项所述的硬碳材料，其中，V1+V2占所述硬碳材料的总孔体积的18％至30％。
  58. 根据权利要求51至57中任一项所述的所述的硬碳材料，其中，所述硬碳材料包含孔径在1.0nm-1.5nm范围内的孔，通过氮气吸附法测定所述孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.009cm3/(g·log(nm))。
  59. 根据权利要求58所述的硬碳材料，其中，通过氮气吸附法测定所述孔径为1.0nm-1.5nm的孔的累积孔体积V相对于孔径D的对数的导数dV/d(logD)的最大值在0.001cm3/(g·log(nm))-0.006cm3/(g·log(nm))。
  60. 根据权利要求51至59中任一项所述的硬碳材料，其中，所述硬碳材料的孔径为1.0nm-1.5nm的孔的孔体积占所述硬碳材料的总孔体积的6％至14％。
  61. 根据权利要求51至60中任一项所述的硬碳材料，其中，所述硬碳材料中金属离子总含量为≤800ppm，且二价以上的金属离子的含量为≤20ppm。
  62. 根据权利要求61所述的硬碳材料，其中，所述硬碳材料中所述金属离子总含量为20ppm-800ppm，且二价以上的所述金属离子的含量为0.1ppm-20ppm。
  63. 根据权利要求61或62所述的硬碳材料，其中，所述金属离子包括Na+、K+、Ca2+、Mg2+、Mn2+、Ba2+、Al3+中的至少一种。
  64. 根据权利要求61至63中任一项所述的硬碳材料，其中，所述二价以上的金属离子为Ca2+。
  65. 根据权利要求51至64至中任一项所述的硬碳材料，其中，所述硬碳材料的表面氧元素含量为5％-15％。
  66. 根据权利要求65所述的硬碳材料，其中，所述硬碳材料的表面氧元素含量为8％-12％。
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