Sodium ion battery, preparation method for sodium ion battery, electrical device and hard carbon material

Abstract

Provided in the present disclosure are a sodium ion battery, a preparation method for the sodium ion battery, an electrical device and a hard carbon material. The sodium ion battery comprises a negative electrode sheet; the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector; the negative electrode film layer comprises a hard carbon material. On the basis of measurement using the nitrogen adsorption method, the hard carbon material comprises a porous structure, and the porous structure comprises pores having a pore size of 2 nm-8 nm; on the basis of measurement using the nitrogen adsorption method, the pore volume of the pores having a pore size of 2 nm-8 nm is 0.0004 cm3 / g-0.0040 cm3 / g.

Description

Sodium-ion battery, sodium-ion battery preparation method, electric device and hard carbon material

[0001] Cross-reference to Related Applications

[0002] The present disclosure is based on and claims priority to Chinese Patent Application No. 202410718131.7, filed on June 4, 2024, entitled “Negative electrode sheet, secondary battery, electric device and hard carbon material”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of secondary batteries, and in particular to a sodium-ion battery, a sodium-ion battery preparation method, an electric device and a hard carbon material. BACKGROUND

[0004] In recent years, with the continuous development and expansion of the new energy industry, the demand for lithium-ion batteries has been increasing year by year. Under this background, the consumption of lithium resources leads to a rapid increase in the cost of lithium-ion batteries, which is not conducive to the long-term development of the new energy industry. Sodium-ion batteries can share part of the supply and demand pressure. Due to the advantages of sodium in resources and cost, sodium-ion batteries have become an important development direction of energy storage batteries. Hard carbon is one of the mainstream negative active materials in this field due to its excellent overall performance, wide applicability and relatively low price. However, there is still a lot of room for improvement in the gravimetric capacity and kinetic performance of hard carbon materials. SUMMARY

[0005] The present disclosure is made in view of the above-mentioned problems, and aims to provide a sodium-ion battery, a sodium-ion battery preparation method, an electric device and a hard carbon material. The negative electrode sheet provided by the present disclosure has improved kinetic performance under the premise of providing better capacity.

[0006] To achieve the above-mentioned purpose, the present disclosure provides a sodium-ion battery. The sodium-ion battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer on at least one surface of the negative electrode current collector, and the negative electrode film layer comprises a hard carbon material. The hard carbon material comprises a porous structure, the porous structure comprises pores with a pore size of 2-8 nm, and the pore volume of the pores with a pore size of 2-8 nm is 0.0004 cm 3 / g-0.0040 cm 3 / g.

[0007] The hard carbon material included in the negative electrode film layer of the negative electrode sheet of the sodium-ion battery provided by the present disclosure has an optimized pore structure. Specifically, the pore volume of the pores with a pore size of 2-8 nm of the hard carbon material is 0.0004 cm 3 / g-0.0040 cm3 / g, thereby improving the kinetic performance of the hard carbon material while taking into account the specific capacity.

[0008] In some embodiments, the pore volume of the pores with a pore size of 2-8 nm of the hard carbon material is 0.0010 cm 3 / g-0.0040 cm 3 / g. Thereby, the kinetic performance of the hard carbon material is more favorable while taking into account the specific capacity.

[0009] In some embodiments, the pore volume of the pores with a pore size of 2-8 nm of the hard carbon material accounts for 3.5%-30% of the total pore volume of the hard carbon material. Thereby, the balance between the kinetic performance and the specific capacity is favorable, and suitable structural stability is maintained.

[0010] In some embodiments, the pore volume of the pores with a pore size of less than or equal to 1 nm of the hard carbon material is denoted as VI, and the pore volume of the pores with a pore size of 1-2 nm of the hard carbon material is denoted as V2, as determined by the carbon dioxide adsorption method, then VI+V2 is in the range of 0.0006 cm 3 / g to 0.0050 cm 3 / g. The pore volume of the pores with a pore size of less than 2 nm of the hard carbon material is in the above range, which is more favorable for the hard carbon material to have a suitable specific capacity.

[0011] In some embodiments, VI+V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g, thereby improving the kinetic performance of the hard carbon material while taking into account the specific capacity. 3 / g to 0.0035 cm 3 / g.

[0012] In some embodiments, the proportion of VI+V2 to the total pore volume of the hard carbon material is in the range of 18%-30%. The proportion of the pore volume of the pores with a pore size of less than 2 nm to the total pore volume of the hard carbon material is in the above range, which is more favorable for improving the specific capacity of the hard carbon material.

[0013] In some embodiments, the hard carbon material comprises pores with a pore size in the range of 1.0-1.5 nm, and the maximum value of the derivative dV / d(logD) of the cumulative pore volume V of the pores with a pore size of 1.0-1.5 nm with respect to the logarithm of the pore size D, as determined by the nitrogen adsorption method, is in the range of 0.001 cm 3(g·log(nm)) - 0.009 cm 3 (g·log(nm)) - 0.006 cm. This is further conducive to reducing the gas bubble phenomenon in the slurry process.

[0014] In some embodiments, the maximum value of the derivative dV / d(logD) of the cumulative pore volume V of the pores with a pore diameter of 1.0 nm-1.5 nm with respect to the logarithm of the pore diameter D, measured by nitrogen adsorption method, is 0.001 cm 3 (g·log(nm)) - 0.006 cm. This is further conducive to reducing the gas bubble phenomenon in the slurry process. 3 (g·log(nm)) - 0.006 cm. This is further conducive to reducing the gas bubble phenomenon in the slurry process.

[0015] In some embodiments, the pore volume of the pores with a pore diameter of 1.0 nm-1.5 nm of the hard carbon material accounts for 6% to 14% of the total pore volume of the hard carbon material.

[0016] In some embodiments, the negative electrode film layer comprises at least one of the first water-based binder, the water-based dispersant, and the first conductive agent.

[0017] In some embodiments, the water-based binder comprises one or more of styrene-butadiene rubber, acrylate rubber; the water-based dispersant comprises one or more of sodium carboxymethyl cellulose, sodium alginate, xanthan gum, carrageenan; and the conductive agent comprises one or more of Super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers.

[0018] In some embodiments, the mass content of the hard carbon material in the negative electrode film layer is above 80%.

[0019] In some embodiments, the mass content of the hard carbon material in the negative electrode film layer is above 85%, the mass content of the water-based binder is 0% to 5%, the mass content of the water-based dispersant is 0% to 5%, and the mass content of the conductive agent is 0% to 5%.

[0020] In some embodiments, the negative electrode film layer further comprises an intercalation-type sodium storage material, and the intercalation-type sodium storage material has a crystal face spacing d 002 satisfies: 0.24 nm≤d 002 ≤0.8 nm. Thus, the intercalation-type sodium storage material with the crystal face spacing within the above range can slide between layers in the microstructure, which helps to increase the powder compaction density of the negative electrode sheet when applied in a sodium ion battery, thereby helping to improve the energy density of the sodium ion battery. The mass content of the intercalation-type sodium storage material in the negative electrode film layer is less than or equal to 10%. Alternatively, the mass content of the intercalation-type sodium storage material is between 0.5% and 5%.

[0021] In some embodiments, the intercalation type sodium storage material includes at least one of a carbon-based intercalation type sodium storage material, a sulfur-based intercalation type sodium storage material, and a titanium-based intercalation type sodium storage material; the carbon-based intercalation type sodium storage material includes at least one of soft carbon and modified graphite; the soft carbon has I D / I G satisfies: 0.9≤I D / I G ≤1.6, where I D represents the D peak intensity of the Raman spectrum at 1350±50 cm -1 , I G represents the G peak intensity of the Raman spectrum at 1580±50 cm -1 .

[0022] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer arranged in a stacked manner, the first negative electrode film layer is arranged between the negative electrode current collector and the second negative electrode film layer, the first negative electrode film layer includes a first active material, and 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 intercalation type sodium storage material, and at least one of the first active material and the second active material includes the hard carbon material. The intercalation type sodium storage material can affect the sodium storage mechanism of the negative electrode active material, reduce the deposition of sodium ions in the hard carbon to form metal-like sodium, and thus reduce the risk of thermal runaway of sodium ions.

[0023] In some embodiments, the first active material includes a hard carbon material, and the second active material includes a soft carbon material. Thus, the kinetic performance is more favorable.

[0024] In some embodiments, the negative electrode tab further includes a primer layer; the thickness of the primer layer is 0.5-3 μm. Thus, the risk of missing coating is reduced, and the coating quality of the tab is improved.

[0025] Since the slurry for preparing the tab of the hard carbon material is an aqueous slurry, the difference in zeta potential with the surface of the metal current collector is large, missing coating is prone to occur, and there is a safety risk.

[0026] In some embodiments, the primer layer includes inorganic oxide and aqueous binder. The primer layer is water-resistant and has strong adhesion to the metal current collector, the inorganic oxide can enhance the anchoring effect between the primer layer and the active layer to meet the water resistance requirement and has strong surface affinity to the metal current collector, which is more favorable for reducing the risk of missing coating and improving the coating quality of the tab, and can also improve the tab adhesion strength, reduce the elongation rate of the tab during cold pressing, and effectively control the resistance of the current collector, while taking into account the electrochemical performance of the battery.

[0027] In some embodiments, the primer layer includes inorganic oxide, dispersant, second aqueous binder, and second conductive agent.

[0028] In some embodiments, in the primer layer, the inorganic oxide includes one or more of aluminum oxide, boehmite, magnesium oxide, iron oxide, silicon oxide, zirconium oxide; the mass ratio of the inorganic oxide is 30%-60%. The primer layer containing the inorganic oxide in the above mass range can enhance the adhesion to the metal current collector, further reduce the risk of coating leakage, and improve the coating quality of the pole piece.

[0029] In some embodiments, the primer layer includes 30%-60% inorganic oxide, 1%-8% dispersant, 10%-40% second water-based binder, and 10%-40% second conductive agent.

[0030] In some embodiments, the primer layer further includes a thickening agent and / or a wetting agent; the wetting agent includes one or more of polyethoxy ether surfactant, polyether silicone surfactant, non-ionic fluorocarbon polymer surfactant, acetylene surfactant; the thickening agent includes one or more of sodium carboxymethyl cellulose, sodium alginate, xanthan gum, carrageenan.

[0031] In some embodiments, the negative electrode 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.

[0032] In some embodiments, the total content of metal ions in the hard carbon material is ≤800ppm, and the content of metal ions with valence of two or more is ≤20ppm. The total content of metal ions and the content of metal ions with valence of two or more in the hard carbon material in the above range are conducive to maintaining a suitable slurry viscosity, thereby facilitating the coating of the slurry to obtain a negative pole piece with a uniform negative electrode film layer.

[0033] In some embodiments, the total content of metal ions in the hard carbon material is 20ppm-800ppm, and the content of metal ions with valence of two or more is 0.1ppm-20ppm. The total content of metal ions and the content of metal ions with valence of two or more in the hard carbon material in the above range are conducive to increasing the inorganic content of the SEM film, thereby reducing the generation of sodium dendrites or the precipitation of sodium on the surface of the hard carbon material, and thereby improving the cycle performance.

[0034] In some embodiments, the metal ions include at least one of Na + , K + , Ca 2+ , Mg 2+ , Mn 2+ , Ba 2+ , Al 3+ .

[0035] In some embodiments, the metal ions with valence of two or more are Ca 2+The content of calcium ions in the hard carbon material has a greater influence on the viscosity of the negative electrode slurry. The content of calcium ions in the hard carbon material within the above range is conducive to obtaining a suitable viscosity of the negative electrode slurry, thereby facilitating the coating of the slurry and avoiding the edge void and slurry flow, and obtaining a negative electrode sheet with a uniform negative electrode film layer.

[0036] In some embodiments, the surface oxygen element content of the hard carbon material is 6%-14%. The surface oxygen element content of the hard carbon material within the above range is conducive to maintaining a suitable interaction force between the dispersant and the hard carbon material, uniformly dispersing the slurry during the mixing process, and having good fluidity, thereby preventing the gelling phenomenon during the slurry preparation, and facilitating the coating of the slurry.

[0037] In some embodiments, the surface oxygen element content of the hard carbon material is 8%-12%. The surface oxygen element content of the hard carbon material within the above range is more conducive to the coating process of the slurry.

[0038] In some embodiments, the solvent in the electrolyte includes a carbonate solvent, and the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. In this way, the high-pressure resistance of the electrolyte can be improved.

[0039] In some embodiments, the volume ratio of propylene carbonate to the volume of the solvent is 15%-55%. In this way, not only the oxidation resistance of the electrolyte can be improved, but also the dissociation of sodium salt can improve the electrical conductivity.

[0040] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes at least one of a sodium-containing layered oxide, a polyanion sodium ion compound, and a Prussian blue sodium ion compound.

[0041] In some embodiments, the sodium-containing layered oxide is an iron-manganese-based layered oxide, and the iron-manganese-based layered oxide is at least one of a nickel-iron-manganese-based layered oxide and a copper-iron-manganese-based layered oxide.

[0042] The present disclosure also provides a preparation method of a sodium-ion battery, including preparing a negative electrode sheet, wherein the preparation of the negative electrode sheet includes: mixing negative electrode components and a solvent to obtain a negative electrode slurry, wherein the negative electrode components include a hard carbon material, the hard carbon material includes a porous structure, the porous structure includes pores with a pore size of 2nm-8nm, and the pore volume of the pores with a pore size of 2nm-8nm is 0.0004cm 3 / g-0.0040cm 3 / g; and coating the negative electrode slurry on the negative electrode current collector. The pores with a pore size of 2 nm-8 nm and a suitable pore volume can improve the kinetic performance of the hard carbon material, and the pores with this part of the pore size can also contribute to part of the capacity, so that the negative electrode sheet can have improved kinetic performance and take into account the capacity.

[0043] In some embodiments, the pore volume of the pores with a pore size of 2 nm-8 nm of the hard carbon material is 0.0010 cm 3 / g-0.0040 cm 3 / g. Thus, it is more beneficial to improve the kinetic performance of the hard carbon material and take into account the capacity.

[0044] In some embodiments, the pore volume of the pores with a pore size of 2 nm-8 nm of the hard carbon material accounts for 3.5%-30% of the total pore volume of the hard carbon material. Thus, it is further beneficial to balance the kinetic performance and capacity of the hard carbon material, and to maintain suitable structural stability.

[0045] In some embodiments, the pore volume of the pores with a pore size of less than or equal to 1 nm of the hard carbon material is denoted as V1, and the pore volume of the pores with a pore size of 1 nm-2 nm of the hard carbon material is denoted as V2, as measured by the nitrogen adsorption method, and V1+V2 is in the range of 0.0006 cm 3 / g to 0.0050 cm 3 / g. By further limiting V1+V2 in the above range, it is more beneficial to make the hard carbon material have a suitable capacity.

[0046] In some embodiments, V1+V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g. The pore volume of the pores with a pore size of 2 nm or less is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g, it is also beneficial to reduce the gas bubble phenomenon in the slurry production process while making the hard carbon material have a suitable capacity, improve the processability of the hard carbon material, and improve the uniformity of the negative electrode sheet, reduce the risk of negative electrode slurry leakage, and improve the performance of the sodium ion battery.

[0047] In some embodiments, V1+V2 is in the range of 0.0020 cm 3 / g to 0.0035 cm 3 / g.

[0048] In some embodiments, V1+V2 is 18% to 30% of the pore volume of the hard carbon material. The proportion of the pore volume of the hard carbon material in the pores having a pore diameter of 2 nm or less to the total pore volume is in the above range, which is more favorable to improving the gravimetric capacity of the hard carbon material.

[0049] In some embodiments, the hard carbon material comprises pores having a pore diameter in the range of 1.0 nm to 1.5 nm, and the maximum value of the derivative dV / d(logD) of the cumulative pore volume V of the pores having a pore diameter of 1.0 nm to 1.5 nm with respect to the logarithm of the pore diameter D, as determined by the nitrogen adsorption method, is in the range of 0.001 cm 3 / (g·log(nm)) to 0.009 cm 3 / (g·log(nm)). This is more favorable to reducing the gas evolution bubbling phenomenon in the slurry preparation process.

[0050] In some embodiments, the hard carbon material comprises pores having a pore diameter in the range of 1.0 nm to 1.5 nm, and the maximum value of the derivative dV / d(logD) of the cumulative pore volume V of the pores having a pore diameter of 1.0 nm to 1.5 nm with respect to the logarithm of the pore diameter D, as determined by the nitrogen adsorption method, is in the range of 0.001 cm 3 / (g·log(nm)) to 0.006 cm 3 / (g·log(nm)). This is further favorable to reducing the gas evolution bubbling phenomenon in the slurry preparation process.

[0051] In some embodiments, the pore volume of the pores having a pore diameter of 1.0 nm to 1.5 nm of the hard carbon material is 6% to 14% of the total pore volume of the hard carbon material.

[0052] In some embodiments, the mass percentage of the negative electrode component is 50% to 60% with respect to the mass of the negative electrode slurry. Thus, the uniformity and stability of the slurry are improved.

[0053] In some embodiments, the mass percentage of the hard carbon is 80% to 95% with respect to the mass of the negative electrode component. Thus, the energy density of the battery is improved.

[0054] In some embodiments, the negative electrode component further comprises one or more of a conductive agent, a binder, and a dispersant. The conductive agent can effectively accelerate the electron transmission rate and improve the charge and discharge efficiency of the battery. The binder is favorable to maintaining the integrity of the electrode structure during the charge and discharge of the battery. The dispersant can improve the dispersibility of the particles of the negative electrode component in the solvent, so that the slurry is easy to coat.

[0055] In some embodiments, the mixing of the negative electrode component and the solvent comprises vacuum stirring at 0°C to 30°C for 1 h to 4 h.

[0056] When the above hard carbon material is used to prepare negative electrode slurry, the bubble time can be obviously reduced, which is conducive to the smooth slurry preparation, and is also conducive to subsequent coating and cold pressing processes, thereby improving the uniformity of the negative electrode film layer and preventing the current collector from being exposed.

[0057] The present disclosure also provides a power utilization device comprising the sodium ion battery of the present disclosure or the sodium ion battery obtained by the sodium ion battery preparation method of the present disclosure.

[0058] The power utilization device of the present disclosure comprises the sodium ion battery provided by the present disclosure, and thus at least has the same advantages as the sodium ion battery.

[0059] The present disclosure also provides a hard carbon material. The hard carbon material comprises a porous structure, wherein the porous structure comprises pores with a pore size of 2 nm-8 nm, and the pore volume of the pores with a pore size of 2 nm-8 nm is 0.0004 cm 3 / g-0.0040 cm 3 / g, as determined by a nitrogen adsorption method.

[0060] The hard carbon material provided by the present disclosure has an optimized pore structure. Specifically, the pore volume of the pores with a pore size of 2 nm-8 nm of the hard carbon material is 0.0004 cm 3 / g-0.0040 cm 3 / g, so that the kinetic performance of the hard carbon material can be improved while the gram capacity is taken into account.

[0061] In some embodiments, the pore volume of the pores with a pore size of 2 nm-8 nm of the hard carbon material is 0.0010 cm 3 / g-0.0040 cm 3 / g, as determined by a nitrogen adsorption method. This is more conducive to the kinetic performance of the hard carbon material while the gram capacity is taken into account.

[0062] In some embodiments, the pore volume of the pores with a pore size of 2 nm-8 nm of the hard carbon material accounts for 3.5%-30% of the total pore volume of the hard carbon material, as determined by a nitrogen adsorption method. This is conducive to the balance of the kinetic performance and the gram capacity, and maintains suitable structural stability.

[0063] In some embodiments, the pore volume of the pores with a pore size of less than or equal to 1 nm of the hard carbon material is represented as V1, and the pore volume of the pores with a pore size of 1 nm-2 nm of the hard carbon material is represented as V2, as determined by a carbon dioxide adsorption method and a nitrogen adsorption method, respectively. Then, V1+V2 is in the range of 0.0006 cm 3 / g to 0.0050 cm 3 / g. The pore volume of the pores with a pore size of less than or equal to 2 nm of the hard carbon material is in the above range, which is more conducive to the hard carbon material having a suitable gram capacity.

[0064] In some embodiments, V1+V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g, thereby facilitating reduction of gas generation and bubbling during preparation of the negative electrode slurry while having a suitable gram capacity of the hard carbon material, so that a negative electrode tab having improved capacity and uniform negative electrode film layer can be obtained, the risk of negative electrode slurry coating failure is reduced, and the performance of the sodium ion battery is improved. Preferably, V1+V2 is in the range of 0.0020 cm 3 / g to 0.0035 cm 3 / g.

[0065] In some embodiments, the proportion of V1+V2 to the total pore volume of the hard carbon material is in the range of 18% to 30%. The proportion of the pore volume of the pores having a pore diameter of 2 nm or less to the total pore volume of the hard carbon material is in the above range, which is more advantageous for improving the gram capacity of the hard carbon material.

[0066] In some embodiments, the hard carbon material contains pores having a pore diameter in the range of 1.0 nm to 1.5 nm, and the maximum value of the derivative dV / d(logD) of the cumulative pore volume V of the pores having a pore diameter of 1.0 nm to 1.5 nm with respect to the logarithm of the pore diameter D, measured by the nitrogen adsorption method, is in the range of 0.001 cm 3 / (g·log(nm)) to 0.009 cm 3 / (g·log(nm)). This is advantageous for reducing the gas generation and bubbling during slurry preparation, further improving the performance of the negative electrode tab, reducing the risk of negative electrode slurry coating failure, and improving the performance of the secondary battery.

[0067] In some embodiments, the maximum value of the derivative dV / d(logD) of the cumulative pore volume V of the pores having a pore diameter of 1.0 nm to 1.5 nm with respect to the logarithm of the pore diameter D, measured by the nitrogen adsorption method, is in the range of 0.001 cm 3 / (g·log(nm)) to 0.006 cm 3 / (g·log(nm)). This is further advantageous for reducing the gas generation and bubbling during slurry preparation.

[0068] In some embodiments, the pore volume of the pores having a pore diameter of 1.0 nm to 1.5 nm of the hard carbon material is in the range of 6% to 14% of the total pore volume of the hard carbon material.

[0069] In some embodiments, the total content of metal ions in the hard carbon material is ≤800 ppm, and the content of metal ions having a valence of two or more is ≤20 ppm. The total content of metal ions and the content of metal ions having a valence of two or more in the hard carbon material are in the above ranges, which is advantageous for maintaining a suitable slurry viscosity, thereby facilitating coating of the slurry so that a negative electrode tab having a uniform negative electrode film layer can be obtained.

[0070] In some embodiments, the total content of metal ions in the hard carbon material is 20 ppm to 800 ppm, and the content of metal ions with valence of two or more is 0.1 ppm to 20 ppm. The total content of metal ions and the content of metal ions with valence of two or more in the hard carbon material within the above ranges is beneficial to increase the inorganic content of the SEM film, thereby reducing the generation of sodium dendrites or the precipitation of sodium on the surface of the hard carbon material, and thus improving the cycle performance.

[0071] In some embodiments, the metal ions include at least one of Na + , K + , Ca 2+ , Mg 2+ , Mn 2+ , Ba 2+ , and Al 3+ .

[0072] In some embodiments, the metal ions with valence of two or more are Ca 2+ . The content of calcium ions in the hard carbon material has a great influence on the viscosity of the negative electrode slurry, and the content within the above range is beneficial to obtain a suitable negative electrode slurry viscosity, thereby facilitating the coating of the fast slurry and avoiding the edge void and slurry flow, and obtaining a negative electrode sheet with uniform negative electrode film layer.

[0073] In some embodiments, the content of surface oxygen elements in the hard carbon material is 6% to 14%. The content of surface oxygen elements in the hard carbon material within the above range is beneficial to maintain a suitable interaction force between the dispersant and the hard carbon material, make the slurry uniformly dispersed during the mixing process, and have good fluidity, thereby facilitating the coating of the slurry without gelling phenomenon.

[0074] In some embodiments, the content of surface oxygen elements in the hard carbon material is 8% to 12%. The content of surface oxygen elements in the hard carbon material within the above range is more beneficial to the coating process of the slurry. BRIEF DESCRIPTION OF DRAWINGS

[0075] FIG. 1 is a schematic view of a battery cell according to an embodiment of the present disclosure.

[0076] FIG. 2 is an exploded view of the battery cell shown in FIG. 1 according to an embodiment of the present disclosure.

[0077] FIG. 3 is a schematic view of a battery module according to an embodiment of the present disclosure.

[0078] FIG. 4 is a schematic view of a battery pack according to an embodiment of the present disclosure.

[0079] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0080] FIG. 6 is a schematic view of an electric device using a sodium-ion battery as a power source according to an embodiment of the present disclosure.

[0081] Explanation of Reference Numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 case; 52 electrode assembly; 53 top cap assembly DETAILED DESCRIPTION

[0082] Hereinafter, embodiments of the sodium-ion battery, the sodium-ion battery manufacturing method, the electric device, and the hard carbon material of the present disclosure will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repeated description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0083] The "range" disclosed in the present disclosure is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting one lower limit and one upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way, unless otherwise specified, is inclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present disclosure, unless otherwise specified, a numerical range "a-b" represents a shorthand notation for any real combination of integers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is just a shorthand notation for these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0084] If not specifically stated, all embodiments of the present disclosure and optional embodiments can be combined with each other to form new technical solutions.

[0085] If not specifically stated, all technical features of the present disclosure and optional technical features can be combined with each other to form new technical solutions.

[0086] If not otherwise specified, all steps of the present disclosure can be performed in sequence or randomly, preferably in sequence. For example, a method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, it is mentioned that the method can further comprise step (c), which means that step (c) can be added to the method in any sequence. For example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0087] The hard carbon material has a rich pore structure. Generally, increasing the amount of micropores below 2 nm in the porous structure of the hard carbon material is beneficial for sodium storage to improve the gravimetric capacity, but a large amount of micropores is not conducive to the kinetic performance and can cause sodium precipitation risk. On the other hand, the micropores in the hard carbon can store sodium and also allow gas molecules to enter and exit, causing bubbling.

[0088] Specifically, the current theory believes that a large amount of micropores will slow down the electrolyte infiltration, increase the steric hindrance of Na intercalation at high rates, and further hinder the charge transfer, resulting in a significant deterioration of the kinetic performance. This is manifested in the reduction of part of the sodium ions to metallic Na at the interface and precipitation. At the same time, the increase in the proportion of this part of the microporous structure will increase the surface area, form more solid electrolyte interface (SEI) films and consume more active ions, further exacerbating the occurrence of sodium precipitation. In addition, too much of this part of the microporous structure will enhance the entry and exit of gas molecules, causing continuous bubbling during processing. For hard carbon materials that continuously produce gas and bubble, such as hard carbon materials that still bubble after 2 hours of pulping, processing is difficult to proceed, and the prepared negative electrode sheet has a risk of exposing the underlying negative current collector, resulting in negative electrode sheet defects, reducing the performance of the sodium ion battery. At the same time, defects in the electrode coating can also cause differences in the distribution of electrons and Na ions on the surface of the electrode sheet, increasing the risk of sodium precipitation and further causing safety hazards in the use of the battery.

[0089] Based on this, the present disclosure provides a sodium ion battery, a sodium ion battery preparation method, an electric device and a hard carbon material. The above-mentioned scheme can improve the kinetic performance, reduce the risk of negative electrode slurry leakage on the surface of the current collector, and improve the performance and safety of the sodium ion battery. The following are described in detail respectively.

[0090] Sodium ion battery

[0091] The first aspect of the present disclosure provides a sodium-ion battery comprising a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a hard carbon material, the hard carbon material comprising a porous structure, the porous structure comprising pores with a pore size of 2-8 nm, and a pore volume of the pores with a pore size of 2-8 nm determined by nitrogen adsorption method being 0.0004 cm 3 / g-0.0040 cm 3 / g.

[0092] The hard carbon material in the negative electrode sheet provided by the present disclosure has an optimized pore structure. Specifically, the pore volume of the pores with a pore size of 2-8 nm of the hard carbon material is 0.0004 cm 3 / g-0.0040 cm 3 / g. It is found through research that the pores with a pore size of 2-8 nm can improve the kinetic performance of the hard carbon material when the pore volume is appropriate, and the pores with this pore size can also contribute to part of the capacity, so that the negative electrode sheet can have improved kinetic performance and capacity.

[0093] Exemplarily, the pore volume of the pores with a pore size of 2-8 nm is 0.0004 cm 3 / g, 0.0008 cm 3 / g, 0.0010 cm 3 / g, 0.0012 cm 3 / g, 0.0014 cm 3 / g, 0.0016 cm 3 / g, 0.0018 cm 3 / g, 0.0020 cm 3 / g, 0.0022 cm 3 / g, 0.0024 cm 3 / g, 0.0026 cm 3 / g, 0.0028 cm 3 / g, 0.0030 cm 3 / g, 0.0032 cm 3 / g, 0.0035 cm 3 / g, 0.0040 cm 3 / g or a value between any two of the numerical values.

[0094] In the present disclosure, the pore volume of the hard carbon material is in the meaning known in the art and can be determined by instruments and methods known in the art. Illustratively, the method known in the art can be a gas adsorption characterization technique, mercury intrusion method, etc. Illustratively, the nitrogen adsorption method can be used to test the adsorption and desorption isotherms according to GB / T 19587-2017, and the DFT model is used to fit the distribution curve of the cumulative pore volume versus the pore size, and the pore volume of the pores with a pore size ranging from 2 nm to 8 nm is obtained. The hard carbon material can be the hard carbon material as a raw material, or can be obtained from the hard carbon material obtained by disassembling and separating the sodium-ion battery.

[0095] In some embodiments, the pore volume of the pores with a pore size ranging from 2 nm to 8 nm of the hard carbon material determined by the nitrogen adsorption method is 0.0010 cm 3 / g to 0.0040 cm 3 / g. Thus, it is more advantageous to improve the kinetic performance of the hard carbon material while taking into account the specific capacity.

[0096] In some embodiments, the pore volume of the pores with a pore size ranging from 2 nm to 8 nm of the hard carbon material determined by the nitrogen adsorption method accounts for 3.5% to 30% of the total pore volume of the hard carbon material. Thus, it is further advantageous to balance the kinetic performance and the specific capacity of the hard carbon material, and to maintain suitable structural stability. Illustratively, the proportion of the pore volume of the pores with a pore size ranging from 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 the above values.

[0097] In some embodiments, the pore volume of the pores with a pore size less than or equal to 1 nm of the hard carbon material determined by the carbon dioxide adsorption method is denoted as V1, and the pore volume of the pores with a pore size ranging from 1 nm to 2 nm of the hard carbon material determined by the nitrogen adsorption method is denoted as V2, then V1+V2 is in the range of 0.0006 cm 3 / g to 0.0050 cm 3 / g.

[0098] By further limiting V1+V2 in the above range, it is more advantageous to make the hard carbon material have a suitable specific capacity.

[0099] Illustratively, V1+V2 is 0.0006 cm 3 / g, 0.0010 cm 3 / g, 0.0013 cm 3 / g, 0.0015 cm 3 / g, 0.0018 cm 3 / g, 0.0020 cm 3 / g, 0.0023 cm 3 / g, 0.0025 cm 3 / g, 0.0028 cm 3 / g, 0.0030 cm 3 / g, 0.0033 cm 3 / g, 0.0035 cm 3 / g, 0.0038 cm 3 / g, 0.0040 cm 3 / g, 0.0043 cm 3 / g, 0.0045 cm 3 / g, 0.0048 cm 3 / g, 0.0050 cm 3 / g or a value between any two of the numerical values.

[0100] The pore volume V1 of the pores with pore size less than or equal to 1 nm of the hard carbon material can be determined by conventional methods in the art. For example, CO2adsorption / desorption pore volume pore size test. By this method, the pore volume of the pores with pore size less than or equal to 1 nm, especially in the range of 0.4 nm to 1 nm, is usually determined. Illustratively, the CO2adsorption method can be used to test the adsorption and desorption isotherms, and a DFT model is used to fit the cumulative pore volume versus pore size distribution curve, and the pore volume of the pores with specific pore size range less than or equal to 1 nm is obtained.

[0101] The pore volume V2 of the pores with pore size in the range of 1 nm to 2 nm of the hard carbon material can be determined by conventional methods in the art. For example, the above-mentioned N2adsorption / desorption pore volume pore size test.

[0102] The total pore volume of the hard carbon material can be determined by conventional methods in the art. For example, the above-mentioned N2adsorption / desorption pore volume pore size test combined with the CO2adsorption / desorption pore volume pore size test, the pore volume of the pores with pore size greater than 1 nm and the pore volume of the pores with pore size less than 1 nm are obtained respectively, and then the two are added together to obtain the total pore volume.

[0103] In some embodiments, V1+V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g. Further studies found that the pores with pore size less than 2 nm would cause a certain degree of gas bubbling during the preparation of the negative electrode slurry. For the hard carbon material that continuously produces gas bubbles, such as the hard carbon material that still bubbles after 2 hours of slurry preparation, it leads to difficult processing, and the prepared negative electrode sheet has the risk of exposing the underlying negative current collector, resulting in negative electrode sheet defects, and further affecting the performance of the sodium ion battery. The present application found that the pore volume of the pores with pore size less than 2 nm is in the range of 0.0006 cm 3 / g to 0.0035 cm 3The V1+V2 is in the range of 0.0020 cm3 / g to 0.0035 cm3 / g, which is beneficial to reduce the gas bubble phenomenon in the pulping process, improve the processability of the hard carbon material, and improve the uniformity of the negative electrode sheet, reduce the risk of negative electrode slurry leakage, and improve the performance of the sodium ion battery.

[0104] In some embodiments, the V1+V2 is in the range of 0.0020 cm3 / g to 0.0035 cm3 / g. 3 / g to 0.0035 cm3 / g. 3 / g to 0.0035 cm3 / g.

[0105] In some embodiments, the ratio of V1+V2 to the total pore volume of the hard carbon material is in the range of 18% to 30%. The ratio of the pore volume of the pores with a pore diameter of less than 2 nm to the total pore volume of the hard carbon material is in the above range, which is more beneficial to improve the gram capacity of the hard carbon material.

[0106] For example, the ratio of V1+V2 to the total pore volume is 18%, 20%, 23%, 25%, 28%, 30%, or a value between any two of the above values.

[0107] The total pore volume of the hard carbon material can be determined by conventional methods in the art. For example, the N2 adsorption-desorption pore volume pore diameter test method described above, combined with the CO2 adsorption-desorption pore volume pore diameter test method described above, respectively obtains the pore volume of pores with a pore diameter of 1 nm or more and the pore volume of pores with a pore diameter of less than 1 nm, and then adds them to obtain the total pore volume.

[0108] The dV / d(logD) mentioned in the present disclosure reflects the pore volume contributed by the unit pore diameter, which can be determined by gaseous adsorption characterization technology on the hard carbon material. For example, it can be determined by using a specific surface instrument-static capacity method. Specifically, according to the embodiments of the present disclosure, a flow method gas adsorption specific surface area measuring device (device model Micromeritics ASAP-2460) can be used to measure. The nitrogen adsorption method test adsorption and desorption isotherms are obtained, and the DFT model is used to fit the distribution curve of dV / d(logD) with respect to the pore diameter D. The maximum value is read in the range of 1.0 nm-2.0 nm.

[0109] In some embodiments, the hard carbon material comprises pores with a pore diameter in the range of 1.0 nm-1.5 nm, and the maximum value of the derivative dV / d(logD) of the cumulative pore volume V of the pores with a pore diameter of 1.0 nm-1.5 nm with respect to the logarithm of the pore diameter D is in the range of 0.001 cm3 / (g·log(nm)) to 0.009 cm3 / (g·log(nm)). 3 / (g·log(nm)) to 0.009 cm3 / (g·log(nm)). This is more beneficial to reduce the gas bubble phenomenon in the pulping process. 3 / (g·log(nm)) to 0.009 cm3 / (g·log(nm)). This is more beneficial to reduce the gas bubble phenomenon in the pulping process.

[0110] Exemplarily, the maximum value of dV / d(logD) of the pores with a pore size of 1.0 nm-1.5 nm is 0.001 cm 3 (g·log(nm)), 0.002 cm 3 (g·log(nm)), 0.003 cm 3 (g·log(nm)), 0.004 cm 3 (g·log(nm)), 0.005 cm 3 (g·log(nm)), 0.006 cm 3 (g·log(nm)), 0.007 cm 3 (g·log(nm)), 0.008 cm 3 (g·log(nm)), 0.009 cm 3 (g·log(nm)), or a value between any two of the numerical values.

[0111] In some embodiments, the maximum value of the derivative dV / d(logD) of the cumulative pore volume V with respect to the logarithm of the pore size D of the pores with a pore size of 1.0 nm-1.5 nm is 0.001 cm 3 (g·log(nm))-0.006 cm 3 (g·log(nm)). This is further conducive to reducing the gas production bubbling phenomenon in the pulping process.

[0112] In some embodiments, the pore volume of the pores with a pore size of 1.0 nm-1.5 nm of the hard carbon material accounts for 6% to 14% of the total pore volume of the hard carbon material. This is further conducive to reducing the gas production phenomenon in the pulping process. Exemplarily, the pore volume of the pores with a pore size of 1.0 nm-1.5 nm accounts for 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% of the total pore volume, or a value between any two of the numerical values.

[0113] In some embodiments, the negative electrode film layer further comprises an intercalation type sodium storage material, and the interfacial spacing d 002 of the intercalation type sodium storage material satisfies: 0.24 nm≤d 002 ≤0.8 nm. Thus, the intercalation type sodium storage material with the interfacial spacing in the above range can be interlayer slipped in the microstructure, which helps to increase the powder compaction density of the negative electrode sheet when applied in a sodium ion battery, thereby helping to improve the energy density of the sodium ion battery. The mass content of the intercalation type sodium storage material in the negative electrode film layer is less than or equal to 10%. Alternatively, the mass content of the intercalation type sodium storage material is between 0.5% and 5%.

[0114] In some embodiments, the intercalation-type sodium storage material comprises at least one of a carbon-based intercalation-type sodium storage material, a sulfur-based intercalation-type sodium storage material, and a titanium-based intercalation-type sodium storage material; the carbon-based intercalation-type sodium storage material comprises at least one of soft carbon and modified graphite; the soft carbon has a I D / I G satisfies: 0.9≤I D / I G ≤1.6, wherein I D represents the D-peak intensity of the Raman spectrum at 1350±50 cm -1 , and I G represents the G-peak intensity of the Raman spectrum at 1580±50 cm -1 .

[0115] In some embodiments, the negative electrode film layer comprises a first negative electrode film layer and a second negative electrode film layer arranged in a stacked manner, the first negative electrode film layer is arranged between the negative electrode current collector and the second negative electrode film layer, the first negative electrode film layer comprises a first active material, and the second negative electrode film layer comprises a second active material; the first active material and the second active material respectively comprise at least one of a hard carbon material and an intercalation-type sodium storage material, and at least one of the first active material and the second active material comprises a hard carbon material. The intercalation-type sodium storage material can affect the sodium storage mechanism of the negative electrode active material, reduce the deposition of sodium ions in the hard carbon to form metal-like sodium, and thus reduce the risk of thermal runaway of sodium ions.

[0116] In some embodiments, the first active material comprises a hard carbon material, and the second active material comprises a soft carbon material. In this way, the kinetic performance is more conducive to being improved.

[0117] In addition to improving the specific capacity and kinetic performance and effectively reducing the problem of gas bubble generation, the hard carbon material of the further embodiments of the present disclosure has further improved processability.

[0118] In some embodiments, the total content of metal ions in the hard carbon material is ≤800 ppm, and the content of metal ions with a valence of two or more is ≤20 ppm.

[0119] The present disclosure finds that the total content of metal ions and the content of metal ions with a valence of two or more in the above range have little effect on other ingredients in the negative electrode slurry, such as thickeners, dispersants, etc., and in particular, sodium carboxymethyl cellulose, which is conducive to maintaining a suitable viscosity of the slurry during slurry preparation, thereby facilitating uniform coating of the slurry on the negative electrode current collector.

[0120] The metal ions in the hard carbon material may, for example, be introduced by the metal elements contained in the carbon source or by doping. For the hard carbon prepared from a carbon source with a high content of metal elements such as biomass or pitch / coal, when the total amount of metal ions, in particular the total amount of metal ions with a valence of two or more, is within the above range, it is particularly advantageous for the slurry preparation and coating process.

[0121] The content of metal ions in the hard carbon can be measured by conventional methods in the art. For example, inductively coupled plasma atomic emission spectrometry, etc.

[0122] In some embodiments, the total content of metal ions in the hard carbon material is 20 ppm-800 ppm, and the content of metal ions with valence of two or more is 0.1 ppm-20 ppm. By further making the total content of metal ions and the content of metal ions with valence of two or more within the above ranges, the present disclosure can improve the processability of the hard carbon material while also increasing the inorganic content of the negative electrode SEI film, which is conducive to reducing the generation of sodium dendrites or sodium precipitation on the surface of the hard carbon material.

[0123] In some embodiments, the metal ions include at least one of Na + , K + , Ca 2+ , Mg 2+ , Mn 2+ , Ba 2+ , Al 3+ , but are not limited thereto.

[0124] In some embodiments, the metal ions with valence of two or more are Ca 2+ . Research has found that the content of calcium ions in the hard carbon material has a greater impact on the negative electrode slurry, and controlling the content of calcium ions within the above ranges is conducive to obtaining a negative electrode slurry with a suitable viscosity, which is conducive to subsequent coating processes, thereby obtaining a negative electrode tab with improved quality.

[0125] In some embodiments, the surface oxygen element content of the hard carbon material is 6%-14%. The surface of the hard carbon material often contains some oxygen-containing groups, such as -COOR, -COOH, -C=O, -OH, -C-O-C-, etc. Research has found that different surface oxygen element contents affect the viscosity of the slurry, and thus affect the processability. It is speculated that when the amount of these oxygen-containing groups is too large, they interact with components in the slurry such as binders and thickeners, affecting the uniform dispersion of the system, causing gelation, and as the standing time increases, the degree of gelation increases. This can affect subsequent processes, clog the filter, or cause the surface of the coated tab to be uneven.

[0126] For example, the surface oxygen element content of the hard carbon material is 6%, 7%, 8%, 9%, 9.5%, 10%, 10.5%, 11%, 12%, 13%, 14%, or a range formed by any two of the above values.

[0127] In some embodiments, the surface oxygen element content of the hard carbon material is 8%-12%. The surface oxygen element content of the hard carbon material within the above range is more conducive to improving the coating performance of the hard carbon material.

[0128] The hard carbon material of the present disclosure can further satisfy one or more of the following to further improve the performance of at least one aspect of the hard carbon material, such as reversible capacity, compaction density, etc.

[0129] (1) The hard carbon material has a surface coating layer. The surface coating layer can reduce surface defects.

[0130] In some embodiments, the surface coating layer is a carbon coating layer.

[0131] (2) The hard carbon material has an I D / I G ≤ 1.35; wherein I D represents the D peak intensity of the Raman spectrum at 1350 ± 50 cm -1 , and I G represents the G peak intensity of the Raman spectrum at 1580 ± 50 cm -1 . The hard carbon material has an I D / I G Within the above range, a suitable proportion of hard carbon surface disordered carbon can be maintained, and a certain amount of ordered carbon layer structure is beneficial to improving the compaction density of the hard carbon material by carbon layer sliding, and improving the energy storage density of the negative electrode.

[0132] In some embodiments, the hard carbon material has an I D / I G of 0.7-1.32. Exemplarily, the hard carbon material has an I D / I G of 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.30, or any value within a range formed by any two of the values.

[0133] (3) The hard carbon material has a number distribution particle size Dn10 of 0.5 μm-1.0 μm, which is more beneficial to the compaction density of the negative electrode sheet, and in addition, fewer low particle size particles indicate that the pore structure of the hard carbon is appropriate and the material skeleton strength is moderate.

[0134] (4) The hard carbon material has a particle size that satisfies: the volume distribution particle size Dv10 of the hard carbon material is ≤ 3.0 μm; the volume distribution particle size Dv50 of the hard carbon material is ≤ 7.9 μm; and the volume distribution particle size Dv90 of the hard carbon material is ≤ 15 μm. The particle size of the hard carbon material satisfies the above collocation, which is further beneficial to the compaction density of the negative electrode sheet.

[0135] (5) The hard carbon material has a compaction density ρ1 under 50000 N of ≥ 0.9 g / cm 3 .

[0136] (6) The hard carbon material has a specific surface area of 2 m 2 / g-12 m 2 / g. The specific surface area of the hard carbon material in the above range is conducive to obtaining a suitable pore structure and balancing the gram capacity.

[0137] In some embodiments, the specific surface area of the hard carbon material is 3 m 2 / g-8 m 2 / g. The specific surface area of the hard carbon material in the above range is more conducive to balancing the gram capacity.

[0138] (7) The tap density p2 of the hard carbon material is 0.75 g / cm 3 -0.9 g / cm 3 .

[0139] In the present disclosure, the pore volume and specific surface area of the hard carbon material are the meanings known in the art and can be measured by instruments and methods known in the art. For example, GB / T 19587-2017 can be referred to, the nitrogen adsorption method is used to test the adsorption and desorption isotherms, the specific surface area of the hard carbon material is calculated by the BET (Brunauer Emmett Teller) method, the DFT model is used to fit the cumulative pore volume distribution curve and the dV / d (logD)-D curve, and the pore volume of the pores in a specific pore size range of 1 nm or more is obtained. The testing instrument can be, for example, the ASAP-2460 specific surface area and pore size analysis tester of the Micromeritics company in the United States. The kinetic diameter of the carbon dioxide molecule is smaller than that of the nitrogen molecule, and the saturation vapor pressure is higher at 273 K, so the gas can diffuse faster into the voids below 1 nm, thereby enabling the analysis and detection of smaller microporous structures. Therefore, the carbon dioxide adsorption method is used to test the adsorption and desorption isotherms, and the DFT model is used to fit the cumulative pore volume distribution curve with respect to the pore size, and the pore volume of the pores in a specific pore size range of 0-1 nm is obtained. The testing instrument can be, for example, the ASAP-2460 specific surface area and pore size analysis tester of the Micromeritics company in the United States.

[0140] In the present disclosure, the metal elements and their contents of the hard carbon material can be measured by instruments and methods known in the art. For example, US EPA 6010D-2014 inductively coupled plasma atomic emission spectrometry can be referred to, and the testing instrument can be, for example, ICP-OES, Thermo ICAP7400.

[0141] In the present disclosure, the surface oxygen element content of the hard carbon material can be measured by instruments and methods known in the art. For example, GB / T 33502-2017 Specification for Data Recording and Reporting of Surface Chemical Analysis X-ray Photoelectron Spectroscopy (XPS) can be referred to, and the testing instrument can be, for example, Axis Supra+ X-ray photoelectron spectrometer.

[0142] In the present disclosure, I D / I G Value can be tested using a Raman spectrometer, I D represents the intensity of the D peak of the Raman spectrum of the material at 1350±50 cm -1 , corresponding to the symmetry breaking, i.e., there are disorder and lattice defects in the structure. G represents the intensity of the G peak of the Raman spectrum of the material at 1580±50 cm -1 , corresponding to the G (graphite) band of in-plane C-C vibration. The test conditions are: the excitation wavelength is 532 nm, the test wave number range is 500-2500 cm -1 , the grating is 600 lines, the objective lens is 50 times, the integration time is 10 s, the number of accumulations is 3 times, the surface scanning is obtained, and the intensity of 100 points of D peak and G peak is obtained. I D / I G , remove each 30 I D / I G , and the average value of the remaining 40 points is the I D / I G of the material. The test instrument can use Horiba LabRAM HR800 Raman spectrometer.

[0143] In the present disclosure, the compaction density of the hard carbon material is the meaning known in the art, which can be measured by instruments and methods known in the art. For example, refer to GB / T 24533-2009, and measure by electronic pressure testing machine (for example, UTM7305 type electronic pressure testing machine). The exemplary test method is as follows: weigh 1 g of sample powder, add to a mold with a bottom area of 1.327 cm 2 , press to 50000 N, keep pressure for 30 s, then release pressure, keep for 10 s, then record and calculate the powder compaction density of the material under the pressure of 50000 N.

[0144] In the present disclosure, the tap density of the hard carbon material is the meaning known in the art, which can be measured by instruments and methods known in the art. For example, refer to GB / T 5162-2006, and measure by powder tap density tester. The test instrument can use Dandong Bit BT-301, and the test parameters are as follows: vibration frequency 250±15 times / min, vibration amplitude 3±0.2 mm, vibration times 5000 times, and cylinder 25 cm 3 .

[0145] In the present disclosure, the number distribution particle size Dn10 and the volume distribution particle sizes Dv10, Dv50, Dv90 of the hard carbon material are meanings well known in the art and can be determined using instruments and methods known in the art. For example, GB / T 19077-2016 can be referred to, and a laser particle size analyzer can be used for determination. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., or the particle size of the hard carbon material can be measured and counted through a microscope image.

[0146] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is provided on either one or both of the two opposite surfaces of the negative electrode current collector.

[0147] In some embodiments, the negative electrode current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a lithium ion battery can employ a copper foil, and a sodium ion battery can employ an aluminum foil. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0148] In some embodiments, the negative electrode current collector includes at least one of a copper foil, an aluminum foil, a stainless steel foil, a titanium foil, a nickel foil, a nickel-iron foil, a nickel-copper foil, and a nickel-iron-copper foil.

[0149] In some embodiments, the negative electrode film layer can further optionally include a binder. The binder can 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).

[0150] In some embodiments, the first binder can be a first aqueous binder. The first aqueous binder can be selected from one or more of styrene butadiene rubber and acrylate rubber.

[0151] In some embodiments, the negative electrode film layer can further optionally include an aqueous dispersant. The aqueous dispersant can be selected from one or more of sodium carboxymethyl cellulose (CMC-Na), sodium alginate, xanthan gum, and carrageenan. In some embodiments, the negative electrode film layer can further optionally include a first conductive agent. The first conductive agent can be selected from at least one of Super-P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0152] In some embodiments, the negative electrode film layer further optionally comprises other additives.

[0153] In some embodiments, the negative electrode film layer comprises at least one of the first aqueous binder, the aqueous dispersant, and the first conductive agent.

[0154] In some embodiments, the mass content of the hard carbon material in the negative electrode film layer is above 80%.

[0155] In some embodiments, the mass content of the hard carbon material in the negative electrode film layer is above 85%. Illustratively, above 88%, above 90%, above 92%, above 94%, above 95%. Illustratively, the mass content of the hard carbon material in the negative electrode film layer is below 99.3%, below 99.0%, below 98.8%, below 98.5%, below 98.3%, below 98.0%.

[0156] In some embodiments, the mass content of the aqueous binder is 0% to 5%, optionally 0% to 3%, further optionally 0.5% to 2%.

[0157] In some embodiments, the mass content of the aqueous dispersant is 0% to 5%, optionally 0% to 2%, further optionally 0.1% to 1%.

[0158] In some embodiments, the mass content of the conductive agent is 0% to 5%, optionally 0% to 2%, further optionally 0.1% to 2%.

[0159] In some embodiments, the negative electrode tab further comprises a primer layer; the thickness of the primer layer is 0.5 μm to 3 μm. Thereby, the tab coating quality is improved.

[0160] In some embodiments, the primer layer comprises inorganic oxide and a second aqueous binder. The inorganic oxide has a large density and a better affinity to the metal current collector substrate, and is less likely to shrink or displace under the surface tension of the slurry compared to the hard carbon material or the conductive agent in the film layer. The aqueous slurry comprising the aqueous binder has a large surface tension, and there is often a large surface energy difference and poor coating quality when coating on the current collector substrate. The inclusion of inorganic oxide in the primer layer can particularly solve the poor compatibility of the aqueous slurry with the current collector substrate, and improve the coating quality of the aqueous slurry on the current collector substrate. Thereby, the risk of missing coating is reduced, and the tab coating quality is improved.

[0161] In some embodiments, in the base coating layer, the inorganic oxide includes one or more of alumina, boehmite, magnesia, ferric oxide, silica, and zirconia; the mass content of the inorganic oxide in the base coating layer is 30%-60%. The inclusion of the inorganic oxide in the above mass range in the base coating layer can not only improve the coating quality of the pole piece, but also improve the adhesion strength of the pole piece, reduce the elongation rate of the pole piece during cold pressing, and effectively control the resistance of the current collector, while taking into account the electrochemical performance of the battery.

[0162] The second water-based binder can also be selected from one or more of styrene-butadiene rubber and acrylate rubber. The second water-based binder can be the same as or different from the first water-based binder. The second water-based binder has water-oil amphiphilicity, and can exhibit better water resistance than a linear binder that has stronger affinity with a water solvent, so that the base coating layer can remain stable during the coating process of the upper film layer containing active substances, and further play a role in improving the coating quality of the base coating layer.

[0163] In some embodiments, the base coating layer includes inorganic oxide, a dispersant, a second water-based binder, and a second conductive agent.

[0164] The dispersant includes one or more of polyacrylic polymers. The acrylic polymer can effectively disperse the inorganic oxide and assist the inorganic oxide in fully exerting its performance. In some embodiments, the mass content of the dispersant in the base coating layer is 1%-8%, which can be selected to be 1%-5%.

[0165] 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 can be the same as or different from the first conductive agent. In some embodiments, the mass content of the second conductive agent in the base coating layer is 10%-40%.

[0166] In some embodiments, the base coating layer includes 30%-60% inorganic oxide, 1%-8% dispersant, 10%-40% second water-based binder, and 10%-40% second conductive agent.

[0167] In some embodiments, the base coating layer further includes a thickening agent and / or a wetting agent.

[0168] The wetting agent can be selected from one or more of polyethoxy ether surfactants, polyether silicone surfactants, non-ionic fluorocarbon polymer surfactants, and alkyne surfactants. The mass content of the thickening agent in the base coating layer is 0.5%-4%.

[0169] The thickening agent can be selected from one or more of sodium carboxymethyl cellulose, sodium alginate, xanthan gum, and carrageenan. The mass content of the thickening agent in the base coating layer is 0.2%-1%.

[0170] The sodium-ion battery includes a positive electrode sheet, a separator film between the negative electrode sheet and the positive electrode sheet, an electrolyte, and the negative electrode sheet in each of the above embodiments. The sodium-ion battery of the present disclosure is described below with appropriate reference to the accompanying drawings.

[0171] The term "sodium-ion battery" referred to herein means a battery cell, a battery module, or a battery pack. Each is described below.

[0172] Generally, a sodium-ion battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte (liquid), and a separator film. During charging and discharging of the battery, active ions, such as sodium ions, are intercalated and deintercalated between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator film is disposed between the positive electrode sheet and the negative electrode sheet and functions to prevent short circuiting between the positive and negative electrodes while allowing ions to pass through.

[0173] [Positive electrode sheet]

[0174] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material.

[0175] As an example, the positive electrode current collector has two opposing surfaces in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposing surfaces of the positive electrode current collector.

[0176] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0177] In some embodiments, the battery cell is a sodium-ion battery, and the positive electrode active material can be any of the positive electrode active materials known in the art for use in sodium-ion batteries. As an example, the positive electrode active material can include a sodium-containing layered oxide, a polyanion sodium-ion compound, a Prussian blue sodium-ion compound, etc., but the present disclosure is not limited to these materials and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries can also be used. For example, as an alternative technical solution of the present disclosure, in the sodium-containing layered oxide, the transition metal 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 xMO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x < 1.

[0178] In some embodiments, the positive active material comprises at least one of a sodium-containing layered oxide, a polyanionic sodium-ion compound, and a Prussian blue sodium-ion compound.

[0179] As an example, the sodium-containing layered oxide can be an iron-manganese-based layered oxide. The iron-manganese-based layered oxide comprises at least one of a nickel-iron-manganese-based layered oxide and a copper-iron-manganese-based layered oxide.

[0180] As an alternative technical means of the present disclosure, the polyanionic sodium-ion compound can be a compound having a sodium ion, a transition metal ion, and a tetrahedral (YO4) n- anion unit. 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 of (YO4) n- . The polyanionic sodium-ion compound can also be a compound having a sodium ion, a transition metal ion, a tetrahedral (YO4) n- anion unit, and a halogen anion. 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; n represents the valence of (YO4) n- ; and the halogen can be at least one of F, Cl, and Br. The polyanionic sodium-ion compound can also be a compound having a sodium ion, a tetrahedral (YO4) n- anion unit, a polyhedral (ZO y ) m+ unit, and an optional halogen anion. Y can be at least one of P, S, and Si; n represents the valence 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; and m represents the valence of (ZO y ) m+ . The polyanionic sodium-ion compound is, 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(VO y )2(PO4)2F 3-2y (0 < y < 1).

[0181] As an alternative technical means of the present disclosure, the polyanionic sodium-ion compound can be Na x-a Aa V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d wherein the A element represents an alkali metal element doped to substitute the Na element, the M element represents a metal element doped to substitute the V element, the D element represents a doping element doped to substitute the P element, the Q element represents a doping element doped to substitute the F element, the D element includes at least one of Si and S, and the Q element 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. Optionally, the A element includes at least one of K and Li; and the M element includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0182] As an optional technical manner of the present disclosure, the polyanionic sodium ion compound can be Na x R y (PO4)2P2O7, wherein x=3.5-4.5, y=2.75-3.25, and 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.

[0183] As an optional technical manner of the present disclosure, the polyanionic sodium ion compound can be Na 4+x R 3-y P 4-m O 15 / C;

[0184] wherein 0

[0185] The Prussian blue compound can be a compound having 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. The Prussian blue compound is, for example, Na a Me b Me’ c(CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a < 2, 0 < b < 1, and 0 < c < 1.

[0186] In some embodiments, the battery cell can be a lithium ion battery, and the positive electrode active material can employ a positive electrode active material for a lithium ion battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present disclosure is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material can also be used. These positive electrode active materials can be used alone only one or two or more can be used in combination. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(also can be referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(also can be referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2), and modified compounds thereof, etc. Examples of the lithium-containing phosphate of an olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon, etc.

[0187] The battery will be accompanied by the deintercalation and consumption of active ions (Li or Na) during the charging and discharging process, and the molar content of Li or Na is different when the battery is discharged to different states. In the enumeration of the positive electrode active material in the present disclosure, the molar content of Li or Na is the initial state of the material, i.e., the state before feeding, and the positive electrode active material is applied to the battery system. After charging and discharging cycles, the molar content of Li or Na will change.

[0188] In the enumeration of the positive electrode active material in the present disclosure, the molar content of oxygen is only the theoretical state value, and the release of oxygen from the crystal lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will appear to float.

[0189] In some embodiments, the positive electrode film layer also optionally includes a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene-fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene-fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic ester resin.

[0190] In some embodiments, the positive electrode film layer also optionally includes a conductive agent. As an example, the conductive agent can include at least one of Super-P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0191] [Electrolyte]

[0192] The electrolyte plays a role in conducting ions between the positive electrode tab and the negative electrode tab. The present disclosure does not have specific limitations on the type of electrolyte, which can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0193] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0194] In some embodiments, the battery cell is a sodium ion battery, and the electrolyte salt can be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bisfluorosulfonylimide, sodium bis-trifluoromethylsulfonylimide, sodium triflate, sodium difluorophosphate, sodium difluoro oxalate borate, sodium di oxalate borate, sodium difluoro di oxalate phosphate, and sodium tetrafluoro oxalate phosphate.

[0195] In some embodiments, the battery cell is a lithium ion battery, and the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium triflate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di oxalate borate, lithium difluoro di oxalate phosphate, and lithium tetrafluoro oxalate phosphate.

[0196] In some embodiments, the solvent can 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, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0197] In some embodiments, the solvent in the electrolyte solution includes a carbonate solvent, and the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. In this way, the high-pressure resistance of the electrolyte solution can be improved.

[0198] In some embodiments, the volume ratio of propylene carbonate to the volume of the solvent is 15% to 55%. In this way, not only the oxidation resistance of the electrolyte solution can be improved, but also the dissociation of sodium salt can improve the conductivity.

[0199] In some embodiments, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain performance of the battery, such as an additive for improving the overcharge performance of the battery, an additive for improving the high-temperature or low-temperature performance of the battery, and the like.

[0200] [Separator]

[0201] In some embodiments, the battery cell further includes a separator disposed between the positive electrode sheet and the negative electrode sheet. The type of the separator is not particularly limited in the present disclosure, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0202] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0203] In some embodiments, the battery cell can include an outer package. The outer package can be used to package the above-mentioned electrode assembly and electrolyte.

[0204] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, and the like. The outer package of the battery cell can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, and the like can be listed.

[0205] The shape of the battery cell is not particularly limited in the present disclosure, and can be cylindrical, square, or any other shape. For example, FIG. 1 is a battery cell 5 of a square structure as an example.

[0206] In some embodiments, referring to FIG. 2, the outer package can include a housing 51 and a top cover assembly 53. The housing 51 can include a bottom plate and side plates connected to the bottom plate, which enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be arranged on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by a person skilled in the art according to specific actual needs.

[0207] In some embodiments, the battery cell can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, which can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0208] FIG. 3 is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0209] Optionally, the battery module 4 can further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0210] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, which can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0211] FIGS. 4 and 5 are a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0212] Method for preparing sodium-ion battery

[0213] The embodiment of the present disclosure further provides a preparation method of a sodium ion battery, comprising preparing a negative electrode sheet, wherein the preparation of the negative electrode sheet comprises: mixing negative electrode components and a solvent to obtain a negative electrode slurry, wherein the negative electrode components comprise a hard carbon material, the hard carbon material comprises a porous structure, the porous structure comprises pores with a pore size of 2-8 nm, and the pore volume of the pores with a pore size of 2-8 nm is 0.0004 cm 3 / g-0.0040 cm 3 / g, as determined by a nitrogen adsorption method; and coating the negative electrode slurry on a negative electrode current collector. The pores with a pore size of 2-8 nm can improve the kinetic performance of the hard carbon material when the pore volume is appropriate, and the pores with this pore size can also contribute to part of the capacity, so that the negative electrode sheet can have improved kinetic performance and capacity.

[0214] In some embodiments, the pore volume of the pores with a pore size of 2-8 nm of the hard carbon material, as determined by a nitrogen adsorption method, is 0.0010 cm 3 / g-0.0040 cm 3 / g. Thus, it is more conducive to improving the kinetic performance of the hard carbon material and balancing the capacity.

[0215] In some embodiments, the pore volume of the pores with a pore size of 2-8 nm of the hard carbon material, as determined by a nitrogen adsorption method, accounts for 3.5%-30% of the total pore volume of the hard carbon material. Thus, it is further conducive to balancing the kinetic performance and capacity of the hard carbon material and maintaining appropriate structural stability.

[0216] In some embodiments, the pore volume of the pores with a pore size of less than or equal to 1 nm of the hard carbon material, as determined by a carbon dioxide adsorption method, is represented as V1, the pore volume of the pores with a pore size of 1-2 nm of the hard carbon material, as determined by a nitrogen adsorption method, is represented as V2, and V1+V2 is in the range of 0.0006 cm 3 / g to 0.0050 cm 3 / g. By further limiting V1+V2 in the above range, it is more conducive to making the hard carbon material have appropriate capacity.

[0217] In some embodiments, V1+V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g. The pore volume of the pores with a pore size of 2 nm or less is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g, which is also conducive to reducing the gas bubbling phenomenon in the slurry preparation process, improving the processability of the hard carbon material, improving the uniformity of the negative electrode sheet, reducing the risk of negative electrode slurry leakage, and improving the performance of the sodium ion battery.

[0218] In some embodiments, V1+V2 is in the range of 0.0020 cm3 / g to 0.0035 cm3 / g. 3 3 In some embodiments, V1+V2 is in the range of 0.0020 cm3 / g to 0.0035 cm3 / g.

[0219] In some embodiments, V1+V2 is in the range of 0.0020 cm3 / g to 0.0035 cm3 / g.

[0220] In some embodiments, the hard carbon material comprises pores with a pore size in the range of 1.0 nm-1.5 nm, and a maximum value of a derivative dV / d(logD) of a cumulative pore volume V of pores with a pore size of 1.0 nm-1.5 nm with respect to a logarithm of the pore size D, measured by nitrogen adsorption method, is in the range of 0.001 cm3 / (g·log(nm))-0.009 cm3 / (g·log(nm)). 3 3 In some embodiments, the hard carbon material comprises pores with a pore size in the range of 1.0 nm-1.5 nm, and a maximum value of a derivative dV / d(logD) of a cumulative pore volume V of pores with a pore size of 1.0 nm-1.5 nm with respect to a logarithm of the pore size D, measured by nitrogen adsorption method, is in the range of 0.001 cm3 / (g·log(nm))-0.009 cm3 / (g·log(nm)).

[0221] In some embodiments, the hard carbon material comprises pores with a pore size in the range of 1.0 nm-1.5 nm, and a maximum value of a derivative dV / d(logD) of a cumulative pore volume V of pores with a pore size of 1.0 nm-1.5 nm with respect to a logarithm of the pore size D, measured by nitrogen adsorption method, is in the range of 0.001 cm3 / (g·log(nm))-0.009 cm3 / (g·log(nm)). 3 3 In some embodiments, the hard carbon material comprises pores with a pore size in the range of 1.0 nm-1.5 nm, and a maximum value of a derivative dV / d(logD) of a cumulative pore volume V of pores with a pore size of 1.0 nm-1.5 nm with respect to a logarithm of the pore size D, measured by nitrogen adsorption method, is in the range of 0.001 cm3 / (g·log(nm))-0.009 cm3 / (g·log(nm)).

[0222] In some embodiments, the hard carbon material comprises pores with a pore size in the range of 1.0 nm-1.5 nm, and a maximum value of a derivative dV / d(logD) of a cumulative pore volume V of pores with a pore size of 1.0 nm-1.5 nm with respect to a logarithm of the pore size D, measured by nitrogen adsorption method, is in the range of 0.001 cm3 / (g·log(nm))-0.009 cm3 / (g·log(nm)).

[0223] In some embodiments, the mass percentage of the negative electrode component is 50%~60% with respect to the mass of the negative electrode slurry. Thereby, the uniformity and stability of the slurry are improved. Exemplarily, the mass percentage of the negative electrode component is 50%, 52%, 54%, 56%, 58%, 60% or a value between any two of the values with respect to the mass of the negative electrode slurry.

[0224] In some embodiments, the mass percentage of the hard carbon is 80%~95% with respect to the mass of the negative electrode component. Thereby, the energy density of the battery is improved. Exemplarily, the mass percentage of the hard carbon is 80%, 82%, 85%, 87%, 90%, 92%, 95% or a value between any two of the values with respect to the mass of the negative electrode component.

[0225] ​​​In some embodiments, the negative electrode component further comprises one or more of a conductive agent, a binder, and a dispersant. The conductive agent can effectively accelerate the electron transmission rate, improve the charge and discharge efficiency of the battery. The binder is conducive to maintaining the integrity of the electrode structure during the charging and discharging process of the battery. The dispersant can improve the dispersibility of the particles of the negative electrode component in the solvent, making the slurry easy to coat.

[0226] In some embodiments, mixing the negative electrode component and the solvent comprises vacuum stirring at 0-30°C for 1-4 hours. The present disclosure does not have specific limitations on vacuum stirring, and appropriate vacuum degree, temperature, time, stirring speed and other process conditions can be selected according to actual production needs. Generally speaking, after vacuum stirring, the slurry can be kept uniform and stable before proceeding to the next process. In some specific embodiments, the negative electrode component comprises hard carbon, dispersant, conductive agent and binder, and the negative electrode slurry is prepared by the following steps: mixing hard carbon, dispersant, conductive agent and solvent, and vacuum stirring; and further adding a binder and further stirring for 2-4 hours.

[0227] When the above-mentioned hard carbon material is used to prepare the negative electrode slurry, the bubbling time can be significantly reduced, which is conducive to the smooth progress of the slurry preparation, and also conducive to the subsequent coating and cold pressing processes, thereby improving the uniformity of the negative electrode film layer and preventing the current collector from being exposed.

[0228] In some embodiments, the preparation of the negative electrode sheet further comprises coating the negative electrode slurry on at least one surface of the negative electrode current collector and then performing processes such as drying, cold pressing, and die cutting. The present disclosure does not have specific limitations on these processes for the preparation of the negative electrode sheet, and those skilled in the art can use appropriate process methods according to actual needs.

[0229] For example, the negative electrode sheet is prepared by the following method: 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, wherein the vacuum stirring is performed at room temperature for about 1-4 hours at a speed of, for example, 1000 r / min; then, the binder (SBR) is added and the stirring is continued for about 2-4 hours to form a negative electrode slurry with good fluidity; the negative electrode slurry is coated on the current collector of Cu or Al at a coating speed of 1-3 m / min, and the surface of the sheet is good without bubbles, voids, and scratches; the coated sheet is dried at 80°C, the coating speed is adjusted to 1-3 m / min, and then the sheet is wound, and the surface of the sheet has no obvious exposed foil, pinhole, or coating leakage; the required sheet is subjected to cold pressing treatment, the sheet is cut into tabs by laser, and the negative electrode process is completed, thereby obtaining the negative electrode sheet.

[0230] In some embodiments, the method for preparing the sodium-ion battery further comprises preparing a positive electrode sheet.

[0231] The preparation of the positive electrode tab is not particularly limited in the present disclosure, and the materials used for the preparation of the positive electrode tab are as described above, and a person skilled in the art can select appropriate materials and processes according to the needs to prepare the positive electrode tab. Exemplarily, the positive electrode tab is prepared by mixing the positive electrode active material, the conductive agent and the binder in a mass ratio of 8:1:1, mixing the positive electrode active material (polyanion or layered oxygen-based positive electrode), the conductive agent (such as SP) and the binder (PVDF) with an appropriate amount of NMP (N-methyl pyrrolidone), and stirring at room temperature at a speed of 1000 r / min to form a positive electrode slurry with good fluidity; coating the positive electrode slurry on an Al current collector at a coating speed of 1-3 m / min, and the surface of the tab is good without bubbles, no virtual edge and no scratches; drying the coated tab at 80°C, adjusting the coating speed to 1-3 m / min, and then winding, and the surface of the tab is free of obvious foil exposure, pinholes or coating leakage; and the tab meeting the requirements is subjected to cold pressing treatment, laser die cutting to form tabs, and winding, to complete the preparation of the positive electrode tab.

[0232] In some embodiments, the method for preparing the sodium-ion battery further comprises: assembling the positive electrode tab, the negative electrode tab and the separator into an electrode assembly that can be prepared by a winding process or a stacking process; placing the electrode assembly in an outer package, and after filling with electrolyte, sealing to form a battery monomer. In some specific embodiments, the electrode assembly can be prepared by a winding process or a stacking process, and the present disclosure is not particularly limited in this regard. Further, the battery monomer can be further assembled into a battery module.

[0233] Similarly, the present disclosure is not particularly limited to the separator and the electrolyte, and the materials used as the separator and the components of the electrolyte are as described above, and a person skilled in the art can select appropriate separator materials and electrolyte components according to the needs.

[0234] Electric device

[0235] The present disclosure also provides an electric device, and the sodium-ion battery of the present disclosure is described below with appropriate reference to the accompanying drawings.

[0236] The electric device mentioned in the embodiments of the present disclosure includes the sodium-ion battery provided by the present disclosure or the sodium-ion battery obtained by the method for preparing the sodium-ion battery of the present disclosure. The sodium-ion battery can be used as a power source of the electric device or as an energy storage unit of the electric device. The electric device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0237] As the power consuming device, a battery cell, a battery module, or a battery pack can be selected according to the use requirement thereof.

[0238] FIG. 6 is a power consuming device as an example. The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of sodium ion batteries for the power consuming device, a battery pack or a battery module can be used.

[0239] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and a battery cell can be used as a power source.

[0240] Hard carbon material

[0241] The present disclosure also provides a hard carbon material. The hard carbon material comprises a porous structure, wherein the porous structure comprises pores with a pore size of 2-8 nm, and the pore volume of the pores with a pore size of 2-8 nm is 0.0004 cm 3 / g-0.0040 cm 3 / g, as determined by a nitrogen adsorption method.

[0242] The hard carbon material provided by the present disclosure has an optimized pore structure. Specifically, the pore volume of the pores with a pore size of 2-8 nm of the hard carbon material is 0.0004 cm 3 / g-0.0040 cm 3 / g, so that the kinetic performance of the hard carbon material can be improved while the gravimetric capacity is taken into account.

[0243] In some embodiments, the pore volume of the pores with a pore size of 2-8 nm of the hard carbon material is 0.0010 cm 3 / g-0.0040 cm 3 / g, as determined by a nitrogen adsorption method. This is more conducive to the kinetic performance of the hard carbon material while the gravimetric capacity is taken into account.

[0244] In some embodiments, the pore volume of the pores with a pore size of 2-8 nm of the hard carbon material accounts for 3.5%-30% of the total pore volume of the hard carbon material, as determined by a nitrogen adsorption method. This is conducive to the balance of kinetic performance and gravimetric capacity, and maintains suitable structural stability.

[0245] In some embodiments, the pore volume of the pores with a pore size of less than or equal to 1 nm of the hard carbon material is represented as V1, and the pore volume of the pores with a pore size of 1-2 nm of the hard carbon material is represented as V2, as determined by a carbon dioxide adsorption method and a nitrogen adsorption method, respectively. Then V1+V2 is 0.0006 cm 3 / g-0.0050 cm 3 / g. The pore volume of the pores with a pore diameter of less than 2 nm in the hard carbon material is in the above range, which is more conducive to the hard carbon material having a suitable gram capacity.

[0246] In some embodiments, V1+V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g, thereby, while making the hard carbon material have a suitable gram capacity, it is conducive to reducing the gas production bubble phenomenon in the negative electrode slurry preparation process, so as to be able to obtain a negative electrode tab with capacity improvement and uniform negative electrode film layer, reduce the risk of negative electrode slurry coating leakage, and improve the performance of the sodium ion battery. Preferably, V1+V2 is in the range of 0.0020 cm 3 / g to 0.0035 cm 3 / g.

[0247] In some embodiments, the proportion of V1+V2 in the total pore volume of the hard carbon material is in the range of 18% to 30%. The proportion of the pore volume of the pores with a pore diameter of less than 2 nm in the total pore volume is in the above range, which is more conducive to improving the gram capacity of the hard carbon material.

[0248] In some embodiments, the hard carbon material comprises pores with a pore diameter in the range of 1.0 nm-1.5 nm, and the maximum value of the derivative dV / d(logD) of the cumulative pore volume V of the pores with a pore diameter of 1.0 nm-1.5 nm with respect to the logarithm of the pore diameter D determined by the nitrogen adsorption method is in the range of 0.001 cm 3 / (g·log(nm))-0.009 cm 3 / (g·log(nm)). This is more conducive to reducing the gas production bubble phenomenon in the slurry preparation process.

[0249] Illustratively, the maximum value of dV / d(logD) of the pores with a pore diameter of 1.0 nm-1.5 nm is 0.001 cm 3 / (g·log(nm)), 0.002 cm 3 / (g·log(nm)), 0.003 cm 3 / (g·log(nm)), 0.004 cm 3 / (g·log(nm)), 0.005 cm 3 / (g·log(nm)), 0.006 cm 3 / (g·log(nm)), 0.007 cm 3 / (g·log(nm)), 0.008 cm 3 / (g·log(nm)), 0.009 cm 3 / (g·log(nm)), or a value between any two numerical values in the range.

[0250] In some embodiments, the maximum value of the derivative dV / d(logD) of the cumulative pore volume V of pores with a pore diameter of 1.0 nm-1.5 nm with respect to the logarithm of the pore diameter D, measured by nitrogen adsorption method, is 0.001 cm 3 / (g·log(nm))-0.006 cm 3 / (g·log(nm)). This is further conducive to reducing the gas bubble phenomenon during the slurry process.

[0251] In some embodiments, the pore volume of the pores with a pore diameter of 1.0 nm-1.5 nm of the hard carbon material accounts for 6% to 14% of the total pore volume of the hard carbon material.

[0252] In some embodiments, the total content of metal ions in the hard carbon material is ≤800 ppm, and the content of metal ions with a valence of two or more is ≤20 ppm. The total content of metal ions and the content of metal ions with a valence of two or more in the hard carbon material within the above ranges are conducive to maintaining a suitable slurry viscosity, thereby facilitating the coating of the slurry to obtain a negative electrode sheet with a uniform negative electrode film layer.

[0253] In some embodiments, the total content of metal ions in the hard carbon material is 20 ppm-800 ppm, and the content of metal ions with a valence of two or more is 0.1 ppm-20 ppm. The total content of metal ions and the content of metal ions with a valence of two or more in the hard carbon material within the above ranges are conducive to increasing the inorganic content of the SEM film, thereby reducing the generation of sodium dendrites or the precipitation of sodium on the surface of the hard carbon material, thereby improving the cycle performance.

[0254] In some embodiments, the metal ions include at least one of Na + , K + , Ca 2+ , Mg 2+ , Mn 2+ , Ba 2+ , and Al 3+ .

[0255] In some embodiments, the metal ions with a valence of two or more are Ca 2+ . The content of calcium ions in the hard carbon material has a greater impact on the viscosity of the negative electrode slurry, and the content within the above range is conducive to obtaining a suitable negative electrode slurry viscosity, thereby facilitating the coating of the fast slurry and avoiding the virtual edge and slurry flow, and obtaining a negative electrode sheet with a uniform negative electrode film layer.

[0256] In some embodiments, the hard carbon material has a surface oxygen element content of 6-14%. The hard carbon material having a surface oxygen element content within the above range is beneficial for maintaining a suitable interaction force between the dispersant and the hard carbon material, so that the slurry is uniformly dispersed during mixing and has good flowability, which is beneficial for preventing the slurry from gelling during slurry preparation, thereby facilitating the coating of the slurry.

[0257] In some embodiments, the hard carbon material has a surface oxygen element content of 8-12%. The hard carbon material having a surface oxygen element content within the above range is more beneficial for the coating process of the slurry.

[0258] The hard carbon material described above can be obtained by adjusting the preparation method. The carbon source is not particularly limited, and the carbon source that can be used includes pitch / coal, biomass material, and synthetic polymer material, etc. In some embodiments, different carbon sources can also be combined with each other, for example, a synthetic polymer material can be combined with other carbon sources to obtain a hard carbon material having a more beneficial internal / external structure. The hard carbon material described above can be prepared by adjusting the process conditions.

[0259] The synthetic polymer material, such as phenolic resin, epoxy resin, furan resin, etc., has a structure designability and low impurity content. By polymerizing the precursor (such as a polymerization monomer or a prepolymer) of the synthetic polymer material, or by dispersing, pore-making, or etching the synthetic polymer material, the microstructure of the carbon source can be well controlled, and thus the pore structure of the hard carbon material can be controlled.

[0260] Exemplarily, but not limited to, the preparation method of the hard carbon material using a synthetic polymer material as the carbon source includes the following steps: a solidification step of solidifying a solution comprising a polymerization monomer or a prepolymer and a solvent to obtain a carbon source; an etchant treatment step of etching the carbon source; a pre-carbonization step of pre-carbonizing the carbon source after etching at a low temperature to obtain a pre-carbonized product; a crushing step of crushing the pre-carbonized product; a deashing step; and a high-temperature carbonization step.

[0261] Exemplarily, the polymerization monomer can be a monomer of phenolic resin, epoxy resin, furan resin, etc.

[0262] Exemplarily, the prepolymer can be, for example, a resol resin.

[0263] Exemplarily, the solvent is at least one of methanol, ethanol, ethylene glycol, polyethylene glycol, glycerol, isopropyl alcohol, and other polyhydric alcohols. The solvent uniformly disperses the synthetic polymer material, which is beneficial for subsequently forming a suitable pore structure.

[0264] The temperature of the curing is not particularly limited in the present disclosure. A person skilled in the art can select a suitable temperature of the curing reaction according to the type of the specific polymerization monomer or prepolymer. Illustratively, when the prepolymer is a resol phenolic resin, the temperature of the curing is 80-150°C.

[0265] Illustratively, the etchant includes at least one of phosphoric acid, hydrogen peroxide, sulfuric acid, nitric acid, and ZnCl2.

[0266] Illustratively, the concentration of the etchant is 5-20wt%. For example, the concentration of the etchant is 5wt%, 7wt%, 9wt%, 11wt%, 13wt%, 15wt%, 17wt%, 19wt%, 20wt%, and a range between any two of them. Preferably, the concentration of the etchant is 7-13wt%.

[0267] In some embodiments, the temperature of the low-temperature pre-carbonization is 400-600°C. Illustratively, the temperature of the low-temperature pre-carbonization is 400°C, 450°C, 500°C, 550°C, 600°C, and a range between any two of them. By the low-temperature pre-carbonization treatment at the temperature, the moisture, part of the dissolved impurities, and the surface active groups can be removed, forming a pre-carbonized product with a suitable degree of compactness, while the etchant is allowed to etch the pores sufficiently, which is beneficial for adjusting the pore structure to a suitable pore structure in the subsequent high-temperature carbonization.

[0268] Illustratively, the breaking can be, for example, by a jet mill or mechanical grinding, which is not particularly limited in the present disclosure. In some embodiments, the breaking makes the Dv50 of the particles 4-8μm, which is more beneficial for adjusting the pore structure of the pre-carbonized product to a suitable pore structure in the subsequent high-temperature carbonization, dissolving the impurities sufficiently, and making the particle size distribution of the final hard carbon suitable.

[0269] Illustratively, the deashing step can be by soaking the product in an acid tank with 1-5M acid to remove the metal impurities.

[0270] In some embodiments, the temperature of the high-temperature carbonization is 1000-1300°C. This is beneficial for forming a final suitable pore structure, thereby improving the gravimetric capacity and kinetic performance. In addition, the high-temperature carbonization can also reduce a large number of defects on the surface. Illustratively, the temperature of the high-temperature carbonization is 1000°C, 1100°C, 1200°C, 1300°C, and a range between any two of them. Alternatively, the temperature of the high-temperature carbonization is 1100-1200°C.

[0271] In some embodiments, the preparation method further includes a step of forming a coating layer. This step can be performed, for example, before the high-temperature carbonization. The present disclosure does not particularly limit the specific coating process, which can be, illustratively, a conventional gas-phase coating, liquid-phase coating, or solid-phase coating in the art.

[0272] In some embodiments, the surface oxygen content of the hard carbon can be adjusted by oxidation or reduction treatment. For example, a pre-oxidation treatment can be performed before high temperature carbonization, which includes holding at 80-400 °C for 0.5-5 h in air or oxygen. Alternatively, a reduction treatment can be performed before high temperature carbonization, which includes holding at 400-800 °C for 0.5-10 h in a mixture of hydrogen and argon. By the above steps, the surface oxygen content of the hard carbon material can be adjusted to 6-14%.

[0273] In some embodiments, the preparation method further includes a classification treatment and a demagnetization treatment before obtaining the final hard carbon product, which can further optimize the problems of slurry bubbling, low slurry viscosity, and battery capacity decay.

[0274] In the above method, the porosity and pore structure can be adjusted by steps such as etchant treatment of the carbon source, temperature and time of low-temperature pre-carbonization, to obtain the above hard carbon material with improved kinetic performance and capacity.

[0275] Biomass materials are widely available, such as coconut shell, rice husk, bamboo, wheat chaff, straw, lignin, etc. Using biomass materials as carbon sources has both economic and environmental benefits.

[0276] Exemplarily, the preparation of hard carbon material using biomass material as carbon source includes the following steps. An etchant treatment step, in which the biomass material is mixed with an etchant for immersion; a pre-carbonization step, in which the product is heated at 300-500 °C, optionally 400-500 °C, for 2-6 h. The etchant treatment combined with the pre-carbonization step can remove the volatile matter in the biomass, while slightly pre-pore can be achieved. A crushing step, in which the pre-carbonized product is crushed to a particle size of Dv10≤3 μm, Dv50≤3 μm and Dv90≤3 μm. The crushing step can enable the final hard carbon material to have a suitable particle size distribution. A deashing step, in which the product is soaked in an acid washing kettle with 1-5 M acid to remove metal impurities. The deashing step can reduce the content of metal impurities, as the biomass contains a lot of metal impurities. A pre-pressing step, in which the deashed product is pressed into a cake shape with tightly packed particles, reducing the exposed area, preventing sintering volatile matter from oxidizing and damaging the carbon, and controlling the porosity. A carbonization step, in which the product is heated at 1100-1300 °C for 2-6 h to remove the remaining volatile matter. Similarly, the preparation method can further include a step of forming a coating layer, for example, which can be performed before the carbonization step.

[0277] Exemplarily, the etchant includes at least one of phosphoric acid, hydrogen peroxide, sulfuric acid, nitric acid, and ZnCl2.

[0278] Exemplarily, the concentration of the etchant is 5-20wt%. For example, the concentration of the etchant is 5wt%, 7wt%, 9wt%, 11wt%, 13wt%, 15wt%, 17wt%, 19wt%, 20wt%, and any range between any two of them. Preferably, the concentration of the etchant is 7-13wt%.

[0279] Exemplarily, the breaking can be, for example, breaking by air jet mill or mechanical mill, which is not specially limited in the present disclosure. In some embodiments, the breaking makes the Dv50 of the particles 4-8pm, which is more conducive to adjusting the pore structure of the pre-carbonized product to obtain a suitable pore structure in the subsequent high-temperature carbonization, and is also conducive to fully dissolving impurities and making the particle size distribution of the final hard carbon suitable.

[0280] Exemplarily, in the deashing step, the acid includes at least one of hydrochloric acid, sulfuric acid, nitric acid, etc. Deashing can reduce ash, which is various metals and their oxides.

[0281] In some embodiments, the amount of metal ions volatilized from the inside and remaining on the surface layer can be adjusted by further washing after carbonization. For example, taking coconut shell as the carbon source, the ion content can be further reduced by washing 3-4 times after carbonization. By combining the previous deashing step, the content of cations, especially divalent cations (such as calcium ions), in the final hard carbon material can be adjusted, thereby facilitating the preparation process of the electrode plate.

[0282] In the above method, the porosity and pore structure are adjusted by steps such as etchant treatment combined with pre-carbonization, and the temperature and time of the carbonization step, to obtain a hard carbon material with improved specific capacity and kinetic performance.

[0283] Asphalt and coal are common chemical raw materials, which are widely available and low in price, so that the preparation of hard carbon material with asphalt or coal as carbon source has lower cost.

[0284] Exemplarily, but not limited to, the preparation of hard carbon material using asphalt as carbon source includes the following steps. A pre-oxidation step, in which asphalt or modified asphalt is mixed with an oxidizing agent and heated at 200-300°C for 2-5h to form a hard carbon precursor. The oxygen content of the hard carbon precursor can be adjusted by the pre-oxidation step. Exemplarily, the oxidizing agent can be oxygen, nitric acid, or hydrogen peroxide, which are not particularly limited in the present disclosure. A pre-carbonization step, in which the hard carbon precursor is heated at 400-600°C for 2-4h. A crushing step, in which the pre-carbonized product is crushed to a particle size of Dv10≤3μm, Dv50≤3μm and Dv90≤30μm. A pre-pressing step, in which the crushed product is pressed into a cake shape with close packing of particles, reducing the exposed area, preventing sintering and oxidation damage of carbon by volatile matter, and controlling the porosity. A carbonization step, in which the product is treated at 1000-1200°C for 2-4h. Similarly, the preparation method can further include a step of forming a coating layer, for example, which can be performed before the carbonization step.

[0285] Exemplarily, the crushing can be by air jet milling or mechanical milling, which are not particularly limited in the present disclosure. In some embodiments, the crushing is such that the Dv50 of the particles is 4-8μm, which is more advantageous for adjusting the pore structure of the pre-carbonized product to a suitable pore structure in the subsequent high-temperature carbonization, for fully dissolving impurities, and for obtaining a suitable particle size distribution of the final hard carbon.

[0286] In some embodiments, the preparation method further includes a deashing step and a demagnetization step after the carbonization step. A suitable deashing step can control the content of cations, particularly divalent cations (such as calcium ions), in the final product, thereby further facilitating the preparation of hard carbon material for electrode plates.

[0287] In the above method, the porosity and pore structure are adjusted by steps such as crushing of the pre-carbonized product, temperature and pressure of the pre-pressing step, temperature and time of the carbonization step, etc., to obtain hard carbon material with improved gravimetric capacity and kinetic performance.

[0288] Examples

[0289] Hereinafter, examples of the present disclosure are described. The examples described below are exemplary and are for the purpose of explaining the present disclosure only, and are not to be construed as limiting the present disclosure. In the examples, specific techniques or conditions not noted are performed in accordance with techniques or conditions described in the literature in the field or in accordance with product instructions. Reagents or instruments not noted by the manufacturer are all conventional products that can be obtained commercially.

[0290] Example 1

[0291] Preparation of hard carbon material using biomass material as carbon source:

[0292] 1) Etching agent treatment

[0293] The lignin was mixed with ZnCl2 aqueous solution (10%wt) at a mass ratio of 1:3 and immersed for 12 h, and then taken out and dried.

[0294] 2) Pre-carbonization

[0295] The product obtained in step 1) above was treated at 400°C for 2 h in a hot-pressing furnace (TOP Industrial Technology, VHP-777) under a normal-pressure N2 atmosphere to obtain a pre-carbonized product.

[0296] 3) Crushing

[0297] The pre-carbonized product obtained in step 2) above was subjected to jet milling in a jet mill (Shengxing Environmental Protection: SX1210) to obtain a product with a Dv1 of 2 μm, a Dv50 of 5 μm, and a Dv90 of 12 μm.

[0298] 4) Deashing

[0299] The crushed product in step 3) above was immersed in a 2M aqueous hydrochloric acid solution at room temperature for 10 h in an acid pickling kettle, filtered, washed with water 3 times, and then dried at 100°C in a continuous kiln.

[0300] 5) Pre-pressing

[0301] The product obtained in step 4) above was subjected to pre-pressing in a hot-pressing furnace (TOP Industrial Technology, VHP-777) at a pressure of 50T for 1 h.

[0302] 6) Carbonization

[0303] The product obtained in step 5) above was sintered at 1400°C for 2 h at a temperature increasing rate of 2°C / min under a normal-pressure N2 atmosphere, washed with water 3 times, and then dried at 100°C in a continuous kiln to obtain the sample of Example 1.

[0304] Preparation of a negative electrode slurry:

[0305] A hard carbon material, a conductive agent, and a dispersant were mixed in deionized water at a ratio of 8:1:1, and vacuum stirring was performed at room temperature for 2.5 h (to keep the negative electrode slurry uniform without further bubbles for 4 h after vacuum stirring, and the vacuum stirring time was adjusted in the following examples and comparative examples as appropriate, but was not longer than 4 h), and a uniform negative electrode slurry was prepared, wherein the dispersant was sodium carboxymethyl cellulose, and the conductive agent was conductive carbon black.

[0306] Preparation of a negative electrode sheet:

[0307] The uniformly stirred negative electrode slurry was coated on both sides of an Al foil by a double-sided coating machine, vacuum drying at 80°C, cold pressing, slitting, and sheeting were sequentially performed after the double-sided coating was completed, and a negative electrode sheet was prepared.

[0308] Preparation of button-type half cell:

[0309] The prepared negative electrode sheet was assembled into a battery in a glove box, with a piece of metallic sodium as the counter electrode, and an electrolyte of EC: DMC (volume ratio) = 1:1 solvent with 10 v / v% FEC added and dissolved with NaPF6.

[0310] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, and the above electrolyte was added. After packaging, standing, formation, and aging, a button-type half cell was prepared.

[0311] Example 2

[0312] Preparation of hard carbon material with a synthetic polymer material as a carbon source:

[0313] 1) Curing

[0314] 25 g of anhydrous ethanol was mixed with 50 g of resol (phenol-formaldehyde resin of Model 2150, solid content 80%) and stirred to obtain a uniform solution. The solution was incubated at 80°C in an oven for 10 h to obtain a hard carbon material precursor.

[0315] 2) Etchant treatment

[0316] The hard carbon material precursor obtained in step 1) above and 10 wt% aqueous phosphoric acid solution were mixed at a mass ratio of 1:3 and immersed for 12 h.

[0317] 3) Low-temperature pre-carbonization

[0318] The hard carbon material precursor was coarsely broken, and then heated to 600°C at a heating rate of 2°C / min in a tube furnace under normal pressure in a N2 atmosphere for 5 h to obtain a pre-carbonized product.

[0319] 4) Breaking

[0320] The pre-carbonized product obtained in step 3) above was broken in a ball mill (MSK-SFM-1-1L planetary ball mill) at 300 rpm for 2 h, with zirconia as the ball mill beads and a mass ratio of material to ball mill beads of 1:3. The particle size distribution of the broken sample was measured using a Mastersizer 3000 laser particle size analyzer, and the Dv50 was 5 μm.

[0321] 5) Deashing

[0322] The pre-carbonized product broken in step 4) above was immersed in a 2M aqueous hydrochloric acid solution at room temperature for 10 h, filtered, washed with water 3 times, and dried at a temperature of 100°C in a continuous kiln.

[0323] 6) High-temperature carbonization

[0324] The product obtained in step 5) above was heated in a tube furnace under normal pressure N2atmosphere at a temperature increasing rate of 2°C / min to 1150°C for 2h.

[0325] 7) Classification

[0326] The product obtained in step 6) above was classified in a gas flow classification device (manufacturer: Jing Hua Powder, model: AB03 type), the discharge particle size was continuously monitored and tested until Dv50 reached 5pm, and the classification was completed.

[0327] 8) Demagnetization

[0328] The product obtained in step 7) above was demagnetized in a demagnetization device (manufacturer: Wan Yedai Magnetoelectric, model: GDG-250 type) until the magnetism of the product disappeared.

[0329] Preparation of negative electrode slurry, negative electrode sheet and button half-cell:

[0330] According to the similar method as in Example 1, the negative electrode slurry, negative electrode sheet were prepared using the hard carbon material of the present example, and assembled into button half-cell.

[0331] Example 3

[0332] Preparation of hard carbon material using pitch / coal as hard carbon material precursor:

[0333] 1) Pre-oxidation

[0334] The modified coal pitch (8994-94-4) was added to the oxidation reaction kettle, and normal pressure air was introduced, heated at 300°C for 3h.

[0335] 2) Pre-carbonization

[0336] The pre-oxidized pitch obtained in step 1) above was heated in a tube furnace at 450°C for 3h.

[0337] 3) Pre-pressing

[0338] The product obtained in step 2) above was pressed in a hot press (manufacturer: Dingli Technology, model: VHP-777 type) at a pressure of 30T for 1h.

[0339] 4) Carbonization

[0340] The product obtained in step 3) above was heated in a tube furnace at 1100°C under normal pressure N2atmosphere for 2h.

[0341] 5) Deashing

[0342] The product obtained in the above step 4) was soaked in a 2M aqueous hydrochloric acid solution in an acid washing kettle at room temperature for 10h, filtered, washed with water 3 times, and dried at 100°C in a continuous kiln.

[0343] 6) Demagnetization

[0344] The product obtained in the above step 5) was subjected to demagnetization in a demagnetization device (manufacturer: Wan Yedai Magnetoelectric, model: GDG-250 type) until the magnetism of the product disappeared.

[0345] Preparation of negative electrode slurry, negative electrode sheet and button half-cell:

[0346] In a similar manner to Example 1, the negative electrode slurry, negative electrode sheet and button half-cell were prepared using the hard carbon material of the present example.

[0347] Example 4

[0348] The hard carbon material was prepared in a similar manner to Example 2, except that the hard carbon material precursor was mixed and impregnated with a 20% aqueous phosphoric acid solution when preparing the hard carbon material.

[0349] Example 5

[0350] The hard carbon material was prepared in a similar manner to Example 2, except that the hard carbon material precursor was mixed and impregnated with a 10% aqueous phosphoric acid solution in a mass ratio of 1:5 when preparing the hard carbon material.

[0351] Comparative Example 1

[0352] The hard carbon material was prepared in a similar manner to Example 1, except that the precursor was not impregnated with an aqueous ZnCl2 solution when preparing the hard carbon material, and the high-temperature sintering condition was 1500°C for 10h.

[0353] Comparative Example 2

[0354] The hard carbon material was prepared in a similar manner to Example 1, except that the raw material was mixed and impregnated with a 50wt% aqueous ZnCl2 solution in a mass ratio of 1:1 when preparing the hard carbon material.

[0355] Hard carbon material related tests:

[0356] Gas adsorption test

[0357] For the hard carbon material, nitrogen and carbon dioxide adsorption method were used to test the adsorption and desorption isotherms according to GB / T 19587-2017, wherein both the nitrogen adsorption method and the carbon dioxide adsorption method used a specific surface and porosity analyzer (American Micromeritics ASAP-2460 type). For the adsorption and desorption isotherms measured by the nitrogen adsorption method, the specific surface area of the hard carbon material was calculated by the BET (Brunauer Emmett Teller) method, and the dV / d (logD) distribution curve with respect to the pore diameter D was fitted by using the DFT model, and the maximum value in the pore diameter range of 1.0-2.0 nm was read out, and the cumulative pore volume distribution curve with respect to the pore diameter was fitted, and the pore volume V2 of the pores in the pore diameter range of 1 nm-2 nm and the pore volume of the pores with a pore diameter of more than 1.0 nm were obtained. For the adsorption and desorption isotherms measured by the carbon dioxide adsorption method, the cumulative pore volume distribution curve with respect to the pore diameter was fitted by using the DFT model, and the pore volume V1 of the pores in the pore diameter range of less than 1 nm was obtained. The test results are shown in Table 1. The total pore volume of the hard carbon material is the sum of the pore volume of the pores in the pore diameter range of more than 1 nm and V1.

[0358] Hard carbon material gram capacity and average Na insertion voltage test

[0359] For the button half-cell of the above examples and comparative examples, sodium was inserted to 0V at a rate of 0.05C, and the obtained capacity was the first charge energy and charge capacity; sodium was removed to 2.5V cut-off at a rate of 0.1C, and the obtained capacity was the first discharge capacity. The mass of the hard carbon material in the negative electrode tab was calculated according to the coating weight and area of the slurry in the above tab preparation process, and the gram capacity was further calculated:

[0360] Gram capacity = first charge capacity / mass of hard carbon material.

[0361] The average Na insertion voltage V was calculated by the following formula:

[0362] Average Na insertion voltage = first charge energy / capacity.

[0363] The greater the average Na insertion voltage, the faster the cross-section charge transfer and the greater the Na insertion rate under the same conditions.

[0364] The pore characteristics, average Na insertion voltage and gram capacity test results of the hard carbon materials prepared in the above examples 1-5 and comparative examples 1-3 are shown in Table 1.

[0365] Table 1:

[0366] As can be seen from Table 1, the pore volume of the hard carbon material in the pore diameter range of 2 nm-8 nm is 0.0004 cm 3 / g-0.0040 cm 3 / g, and has improved kinetics performance under the premise of providing better capacity.

[0367] The present disclosure found in the study of the processability of the negative electrode sheet prepared by hard carbon material. Due to the rich pore structure of the hard carbon material, gas bubbles are continuously produced during the preparation of the negative electrode slurry with the hard carbon material. For example, the hard carbon material still bubbles after 2 hours of slurry preparation, the processing is difficult to proceed, and the prepared negative electrode sheet has the risk of exposing the underlying negative current collector, which can cause negative electrode sheet defects, thereby affecting the performance of the sodium ion battery. The following examples further adjust the pore structure to improve the processing performance.

[0368] Example 6

[0369] The hard carbon material was prepared according to the method similar to Example 2, except that during the preparation of the hard carbon material, the hard carbon material precursor and the phosphoric acid aqueous solution were mixed and immersed for 6h, and the high-temperature carbonization temperature was 1200℃.

[0370] Example 7

[0371] The hard carbon material was prepared according to the method similar to Example 2, except that during the preparation of the hard carbon material, the hard carbon material precursor was not subjected to phosphoric acid oxidation treatment, and the high-temperature carbonization temperature was 1300℃.

[0372] Example 8

[0373] The hard carbon material was prepared according to the method similar to Example 2, except that during the preparation of the hard carbon material, the hard carbon material precursor and the 80wt% phosphoric acid aqueous solution were mixed and immersed, and the high-temperature carbonization temperature was 1300℃.

[0374] Test of bubbling in preparation of negative electrode slurry

[0375] The hard carbon materials prepared in the above examples and comparative examples were observed for the time when bubbling stopped during the preparation of the negative electrode slurry. The situation of bubbling after 2 hours of mixing of the components of the negative electrode slurry was recorded.

[0376] In addition, 50g or more of the hard carbon materials prepared in the above examples and comparative examples were respectively added to a 500mL closed reaction kettle equipped with temperature and pressure sensors, 200mL of water was added, and then the reaction kettle was quickly closed, and stirring was started until the temperature and pressure were constant. According to the pressure change value and the ideal gas equation, the volume of gas emitted per unit mass of the hard carbon material was calculated as a measure of the amount of bubbling.

[0377] The pore characteristics, bubbling conditions, kinetic performance and specific capacity test results of the hard carbon materials prepared in Examples 2 and 6-8 above are shown in Table 2.

[0378] Table 2:

[0379] As shown in Table 2, the pore volume of hard carbon materials with pore sizes below 2 nm is 0.0006 cm³. 3 / g to 0.0035cm 3 Within the range of / g, while improving specific capacity, it is beneficial to reduce gas generation and bubbling during the pulping process. For hard carbon materials, the proportion of pore volume with a diameter less than 2nm to the total pore volume is in the range of 18% to 30%, which is beneficial for achieving suitable specific capacity in the hard carbon material.

[0380] Example 9

[0381] 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.

[0382] Example 10

[0383] 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.

[0384] The pore characteristics, bubbling behavior, kinetic properties, and specific capacity test results of the hard carbon materials prepared in Examples 9 and 10 above are shown in Table 3.

[0385] Table 3:

[0386] As shown in Table 3, when the maximum value of dV / d(logD) is between 0.001 mL / (g·nm) and 0.009 mL / (g·nm), continuous bubbling is further reduced while improving specific capacity and kinetic performance.

[0387] Example 11

[0388] 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.

[0389] Example 12

[0390] 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.

[0391] Example 13

[0392] 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.

[0393] Metal ion content test

[0394] The hard carbon materials of Examples 1 and 11-13 were used to prepare negative electrode slurries with a solid content of 20%. The slurries were stirred for 30 minutes and then filtered to obtain a clear solution, which was used to test the ion content of Ca, Mg, Na, and K.

[0395] Viscosity test of the negative electrode slurry after 24 hours of standing

[0396] The negative electrode slurries of Examples 1 and 11-13 were placed under the viscometer after standing for 24 hours. The slurry was just submerged in the scale line of the rotor. The instrument model was Shanghai Fangrui NDJ-5S, the rotor was 63# (2000-10000 mPa.s) and 64# (10000-50000 mPa.s), the rotation speed was 12 r / min, the test temperature was 25°C, and the test time was 5 minutes. The data was read when the reading was stable.

[0397] The test results of the metal ion content and the viscosity of the negative electrode slurry of the hard carbon materials prepared in Examples 1 and 11-13 are shown in Table 4.

[0398] Table 4:

[0399] As can be seen from Table 4, when the total content of metal ions is below 800 ppm and the content of metal ions with a valence of two or more is low, such as about 20 ppm or less, it is beneficial to maintain the viscosity of the slurry during slurry preparation, thereby facilitating uniform coating of the slurry on the negative electrode current collector and facilitating processing. In general, a slurry viscosity of 4000 Pa.s or more is beneficial. This can effectively reduce uneven coating, such as wavy edges. 2+ A high concentration of Ca 2+ Complexes with CMC-Na, which reduces the ability of CMC-Na to capture free water, weakening its dispersant effect, resulting in a slurry viscosity that is too low to facilitate coating of the slurry.

[0400] Example 14

[0401] The hard carbon material was prepared in a similar manner to Example 2, except that during the preparation of the hard carbon material, the etchant treatment was immersed in a 10% aqueous phosphoric acid solution for 6 hours.

[0402] Example 15

[0403] The hard carbon material was prepared in a similar manner to Example 2, except that during the preparation of the hard carbon material, the etchant treatment was immersed in a 20% aqueous phosphoric acid solution for 5 hours.

[0404] Example 16

[0405] The hard carbon material was prepared in a similar manner to Example 2, except that the hard carbon material was prepared without etchant treatment, and the pre-carbonization was reduced at 500°C for 2h under an Ar / H2(95:5) mixed atmosphere.

[0406] Example 17

[0407] The hard carbon material was prepared in a similar manner to Example 2, except that the hard carbon material was prepared with etchant treatment, and the etchant treatment was impregnated with 30% phosphoric acid aqueous solution for 6h.

[0408] Surface oxygen element content test

[0409] The surface oxygen element content of the hard carbon materials of Examples 2, 14-17 was tested by X-ray photoelectron spectroscopy (instrument model: Axis Supra / Supra+) according to GB / T 33502-2017, with three different parts of the same material being selected.

[0410] Gelation degree of negative electrode slurry

[0411] The hard carbon materials prepared in Examples 2 and 14-17 above were observed when preparing negative electrode slurry, for example by picking up the slurry with a small spoon and observing the dripping when pouring, to qualitatively determine the gelation degree.

[0412] The test results of the negative electrode slurry viscosity of the hard carbon materials prepared in Examples 2 and 14-17 and the gelation degree are shown in Table 5.

[0413] Table 5:

[0414] As can be seen from Table 5 above, the surface oxygen element of the hard carbon material is in the range of 5%-15%, which can make the viscosity of the slurry suitable and the flowability good.

[0415] It should be noted that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having substantially the same configuration and playing the same role and effect within the scope of the technical solutions of the present disclosure are all included in the technical scope of the present disclosure. In addition, within the scope of the main idea of the present disclosure, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the configuration elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A sodium-ion battery, comprising a negative electrode tab, the negative electrode tab comprising a negative electrode current collector and a negative electrode film layer on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a hard carbon material, the hard carbon material comprising a porous structure, the porous structure comprising pores with a pore size of 2 nm-8 nm. The pore volume of the pores having a pore diameter of 2 nm to 8 nm was 0.0004 cm 3 / g to 0.0040 cm 3 / g.

2. The sodium-ion battery of claim 1, wherein, The pore volume of the pores having a pore diameter of 2 nm to 8 nm of the hard carbon material was 0.0010 cm 3 / g to 0.0040 cm 3 / g.

3. The sodium-ion battery of claim 1 or 2, wherein, The pore volume of the pores with a pore size of 2 nm-8 nm of the hard carbon material accounts for 3.5%-30% of the total pore volume of the hard carbon material.

4. The sodium-ion battery of any one of claims 1-3, wherein, The pore volume of pores having a pore diameter of 1 nm or less of the hard carbon material is represented by VI, and the pore volume of pores having a pore diameter of 1 nm to 2 nm of the hard carbon material is represented by V2, and VI + V2 is in the range of 0.0006 cm3 / g to 0.0050 cm3 / g. 3 / g to 0.0050 cm 3 / g.

5. The sodium-ion battery of claim 4, wherein, V1+V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g.

6. The sodium-ion battery of claim 5, wherein, V1+V2 is in the range of 0.0020 cm 3 / g to 0.0035 cm 3 / g.

7. The sodium-ion battery of any one of claims 4-6, wherein, V1+V2 accounts for 18%-30% of the pore volume of the hard carbon material.

8. The sodium-ion battery of any one of claims 1-7, wherein, The hard carbon material contains pores having a pore diameter in the range of 1.0 nm to 1.5 nm, and a maximum value of a derivative dV / d(logD) of a cumulative pore volume V with respect to a logarithm of a pore diameter D for the pores having a pore diameter of 1.0 nm to 1.5 nm determined by the nitrogen adsorption method is in the range of 0.001 cm 3 / (g·log(nm)) to 0.009 cm 3 / (g·log(nm)) to 0.009 cm / (g·log(nm)) to 0.009 cm / (g·log(nm)) to 0.009 cm 9. The sodium-ion battery of claim 8, wherein, The maximum value of the derivative dV / d(logD) of the cumulative pore volume V of the pores having a pore diameter of 1.0 nm to 1.5 nm with respect to the logarithm of the pore diameter D is 0.001 cm 3 / (g·log(nm)) to 0.006 cm 3 / (g·log(nm)) to 0.006 cm 10. The sodium-ion battery of any one of claims 8-9, wherein, The pore volume of the pores with a pore size of 1.0 nm-1.5 nm of the hard carbon material accounts for 6%-14% of the total pore volume of the hard carbon material.

11. The sodium-ion battery of any one of claims 1-10, wherein, The negative electrode film layer comprises at least one of a first water-based binder, a water-based dispersant and a first conductive agent.

12. The sodium-ion battery of claim 11, wherein, The first water-based binder comprises one or more of styrene-butadiene rubber and acrylate rubber; the water-based dispersant comprises one or more of sodium carboxymethyl cellulose, sodium alginate, xanthan gum and carrageenan; and the first conductive agent comprises one or more of Super-P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

13. The sodium-ion battery of claim 11 or 12, wherein, The mass content of the hard carbon material in the negative electrode film layer is above 80%.

14. The sodium-ion battery of claim 13, wherein, The mass content of the hard carbon material in the negative electrode film layer is above 85%, the mass content of the first water-based binder is 0%-5%, the mass content of the water-based dispersant is 0%-5%, and the mass content of the first conductive agent is 0%-5%.

15. The sodium-ion battery of any one of claims 1-14, wherein, The negative electrode film layer further comprises an intercalation-type sodium storage material, the intercalation-type sodium storage material has a crystal face spacing d 002 satisfies: 0.24 nm ≤ d 002 ≤ 0.8 nm; the mass content of the intercalation-type sodium storage material in the negative electrode film layer is less than or equal to 10%.

16. The sodium-ion battery of claim 15, wherein, The embedded sodium storage material includes at least one of a carbon-based embedded sodium storage material, a sulfur-based embedded sodium storage material, and a titanium-based embedded sodium storage material; the carbon-based embedded sodium storage material includes at least one of soft carbon and modified graphite; the soft carbon has I D / I G satisfies: 0.9≤I D / I G ≤1.6, wherein I D represents the D peak intensity of the Raman spectrum at 1350±50cm -1 , I G represents the G peak intensity of the Raman spectrum at 1580±50cm -1 .

17. The sodium-ion battery of claim 16, wherein, The negative electrode film layer comprises a first negative electrode film layer and a second negative electrode film layer arranged in a stack, the first negative electrode film layer is arranged between the negative electrode current collector and the second negative electrode film layer, the first negative electrode film layer comprises a first active material, and the second negative electrode film layer comprises a second active material; the first active material and the second active material each comprise at least one of the hard carbon material and the intercalation-type sodium storage material, and at least one of the first active material and the second active material comprises the hard carbon material.

18. The sodium-ion battery of claim 17, wherein, The first active material comprises the hard carbon material, and the second active material comprises the soft carbon material.

19. The sodium-ion battery of any one of claims 1-18, wherein, The negative electrode tab further comprises a primer layer; the thickness of the primer layer is 0.5-3 μm.

20. The sodium-ion battery of claim 19, wherein, The primer layer comprises an inorganic oxide and a second water-based binder.

21. The sodium-ion battery of claim 19, wherein, The primer layer comprises an inorganic oxide, a dispersant, a second water-based binder and a second conductive agent.

22. The sodium-ion battery of claim 20 or 21, wherein, In the primer layer, the inorganic oxide comprises one or more of aluminum oxide, boehmite, magnesium oxide, iron oxide, silicon oxide and zirconium oxide; and the mass content of the inorganic oxide is 30%-60%.

23. The sodium-ion battery of claim 21, wherein, The primer layer comprises 30%-60% inorganic oxide, 1%-8% dispersant, 10%-40% second water-based binder and 10%-40% second conductive agent.

24. The sodium-ion battery of any one of claims 20-23, wherein, The base coat further comprises a thickening agent and / or a wetting agent; the wetting agent comprises one or more of polyethoxy ether surfactants, polyether silicone surfactants, non-ionic fluorocarbon polymer surfactants, acetylenic surfactants; the thickening agent comprises one or more of sodium carboxymethyl cellulose, sodium alginate, xanthan gum, carrageenan.

25. The sodium-ion battery of any one of claims 1-24, wherein, The negative current collector comprises 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.

26. The sodium-ion battery of any one of claims 1-25, wherein, The total content of metal ions in the hard carbon material is ≤800 ppm, and the content of metal ions with valence of two or more is ≤20 ppm.

27. The sodium-ion battery of claim 26, wherein, The total content of metal ions in the hard carbon material is 20 ppm-800 ppm, and the content of metal ions with valence of two or more is 0.1 ppm-20 ppm.

28. The sodium-ion battery of claim 26 or 27, wherein, The metal ions include at least one of Na + , K + , Ca 2+ , Mg 2+ , Mn 2+ , Ba 2+ , Al 3+ .

29. The sodium-ion battery of any one of claims 26-28, wherein, The divalent or more metal ion is Ca 2+ .

30. The sodium-ion battery of any one of claims 1-29, wherein, The surface oxygen element content of the hard carbon material is 5%-15%.

31. The sodium-ion battery of claim 30, wherein, The surface oxygen element content of the hard carbon material is 8%-12%.

32. The sodium-ion battery of any one of claims 1-31, wherein, The sodium ion battery further comprises a positive electrode sheet, a separator film between the negative electrode sheet and the positive electrode sheet, and an electrolyte, wherein the solvent in the electrolyte comprises a carbonate solvent, and the carbonate solvent comprises at least one of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

33. The sodium-ion battery of claim 32, wherein, The volume percentage of the propylene carbonate in the solvent is 15%-55%.

34. The sodium-ion battery of claim 32 or 33, wherein, The positive electrode sheet comprises a positive current collector and a positive film layer on at least one surface of the positive current collector, and the positive film layer comprises a positive active material, wherein the positive active material comprises at least one of sodium-containing layered oxide, polyanion sodium ion compound, and Prussian blue sodium ion compound.

35. The sodium-ion battery of claim 34, wherein, The sodium-containing layered oxide is an iron-manganese-based layered oxide, and the iron-manganese-based layered oxide comprises at least one of nickel-iron-manganese-based layered oxide and copper-iron-manganese-based layered oxide. 36.A method for preparing a sodium-ion battery, comprising preparing a negative electrode sheet, wherein, The preparation of the negative electrode sheet comprises: The negative electrode component and the solvent are mixed to obtain a negative electrode slurry, wherein the negative electrode component includes a hard carbon material, the hard carbon material includes a porous structure, the porous structure includes pores with a pore diameter of 2 nm to 8 nm, and the pore volume of the pores with a pore diameter of 2 nm to 8 nm is 0.0004 cm 3 / g to 0.0040 cm 3 / g; and The negative electrode slurry is coated on the negative current collector.

37. The method of manufacturing according to claim 36, wherein, The pore volume of the pores having a pore diameter of 2 nm to 8 nm of the hard carbon material was 0.0010 cm 3 / g to 0.0040 cm 3 / g.

38. The method of manufacturing according to claim 36 or 37, wherein, The pore volume of the pores with a pore size of 2 nm-8 nm in the hard carbon material is 3.5%-30% of the total pore volume of the hard carbon material.

39. The method of manufacturing according to any one of claims 36 to 38, wherein, The pore volume of the pores having a pore diameter of 1 nm or less of the hard carbon material is represented by VI, and the pore volume of the pores having a pore diameter of 1 nm to 2 nm of the hard carbon material is represented by V2, and VI + V2 is in the range of 0.0006 cm3 / g to 0.0050 cm3 / g. 3 / g to 0.0050 cm 3 / g.

40. The method of manufacturing according to claim 39, wherein, V1+V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g.

41. The method of manufacturing according to claim 40, wherein, V1+V2 is in the range of 0.0020 cm 3 / g to 0.0035 cm 3 / g.

42. The method of making according to any one of claims 39 to 41, wherein, V1+V2 accounts for 18%-30% of the pore volume of the hard carbon material.

43. The method of making according to any one of claims 36 to 42, wherein, The hard carbon material contains pores having a pore diameter in the range of 1.0 nm to 1.5 nm, and a maximum value of a derivative dV / d(logD) of a cumulative pore volume V with respect to a logarithm of a pore diameter D for the pores having a pore diameter of 1.0 nm to 1.5 nm determined by the nitrogen adsorption method is in the range of 0.001 cm 3 / (g·log(nm)) to 0.009 cm 3 / (g·log(nm)) to 0.009 cm / (g·log(nm)) to 0.009 cm / (g·log(nm)) to 0.009 cm 44. The method of manufacturing according to claim 43, wherein, The maximum value of the derivative dV / d(logD) of the cumulative pore volume V of the pores having a pore diameter of 1.0 nm to 1.5 nm with respect to the logarithm of the pore diameter D is 0.001 cm 3 / (g·log(nm)) to 0.006 cm 3 / (g·log(nm)) to 0.006 cm / (g·log(nm)) to 0.006 cm 45. The method of manufacturing according to any one of claims 36 to 44, wherein, The pore volume of the pores with a pore size of 1.0 nm-1.5 nm in the hard carbon material is 6%-14% of the total pore volume of the hard carbon material.

46. The method of making according to any one of claims 36 to 45, wherein, The mass percentage of the negative electrode components in the negative electrode slurry is 50%-60%.

47. The method of making according to any one of claims 36 to 46, wherein, The mass percentage of the hard carbon in the negative electrode components is 80%-95%.

48. The method of making according to any one of claims 36 to 47, wherein, The negative electrode components further comprise one or more of conductive agents, binders, and dispersants.

49. The method of making according to any one of claims 36 to 48, wherein, The mixing of the negative electrode components and the solvent comprises vacuum stirring at 0°C-30°C for 1 h-4 h.

50. An electric device comprising the sodium ion battery according to any one of claims 1-35 or prepared by the method according to any one of claims 36-49.

51. A hard carbon material comprising pores having a pore diameter of 2 nm to 8 nm, the pore volume of the pores having a pore diameter of 2 nm to 8 nm determined by nitrogen adsorption being 0.0004 cm 3 / g to 0.0040 cm 3 / g.

52. The hard carbon material of claim 51, wherein, The pore volume of the pores having a pore diameter of 2 nm to 8 nm of the hard carbon material was 0.0010 cm 3 / g to 0.0040 cm 3 / g.

53. The hard carbon material of claim 51 or 52, wherein, The pore volume of the pores with a pore size of 2 nm-8 nm in the hard carbon material is 3.5%-30% of the total pore volume of the hard carbon material.

54. The hard carbon material of any one of claims 51-53, wherein, The pore volume of pores having a pore diameter of 1 nm or less of the hard carbon material is represented by VI, and the pore volume of pores having a pore diameter of 1 nm to 2 nm of the hard carbon material is represented by V2, and VI + V2 is in the range of 0.0006 cm3 / g to 0.0050 cm3 / g. 3 / g to 0.0050 cm 3 / g.

55. The hard carbon material of claim 54, wherein, V1+V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g.

56. The hard carbon material of claim 55, wherein, V1+V2 is in the range of 0.0020 cm 3 / g to 0.0035 cm 3 / g.

57. The hard carbon material of any one of claims 54-56, wherein, V1+V2 is 18% to 30% of the total pore volume of the hard carbon material.

58. The hard carbon material of any one of claims 51-57, wherein, The hard carbon material contains pores having a pore diameter in the range of 1.0 nm to 1.5 nm, and a maximum value of a derivative dV / d(logD) of a cumulative pore volume V with respect to a logarithm of a pore diameter D for the pores having a pore diameter of 1.0 nm to 1.5 nm determined by the nitrogen adsorption method is in the range of 0.001 cm 3 / (g·log(nm)) to 0.009 cm 3 / (g·log(nm)) to 0.009 cm / (g·log(nm)) to 0.009 cm 59. The hard carbon material of claim 58, wherein, The maximum value of the derivative dV / d(logD) of the cumulative pore volume V of the pores having a pore diameter of 1.0 nm to 1.5 nm with respect to the logarithm of the pore diameter D is 0.001 cm 3 / (g·log(nm)) to 0.006 cm 3 / (g·log(nm)) to 0.006 cm 60. The hard carbon material of any one of claims 51-59, wherein, The pore volume of pores having a pore diameter of 1.0 nm to 1.5 nm in the hard carbon material is 6% to 14% of the total pore volume of the hard carbon material.

61. The hard carbon material of any one of claims 51-60, wherein, The total content of metal ions in the hard carbon material is ≤800 ppm, and the content of metal ions having a valence of two or more is ≤20 ppm.

62. The hard carbon material of claim 61, wherein, The total content of metal ions in the hard carbon material is 20 ppm to 800 ppm, and the content of the metal ions having a valence of two or more is 0.1 ppm to 20 ppm.

63. The hard carbon material of claim 61 or 62, wherein, The metal ions include at least one of Na + , K + , Ca 2+ , Mg 2+ , Mn 2+ , Ba 2+ , Al 3+ .

64. The hard carbon material of any one of claims 61-63, wherein, The divalent or more metal ion is Ca 2+ .

65. The hard carbon material of any one of claims 51-64, wherein, The content of surface oxygen elements in the hard carbon material is 5% to 15%.

66. The hard carbon material of claim 65, wherein, The content of surface oxygen elements in the hard carbon material is 8% to 12%.

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