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

Abstract

The present disclosure provides a sodium ion battery, a preparation method for the sodium ion battery, an electric 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 the hard carbon material. It is measured by means of a nitrogen adsorption method that the hard carbon material comprises pores with the pore diameters ranging from 1.0 nm to 1.5 nm, and the maximum value of a derivative value dV / d(logD) of the cumulative pore volume V relative to the logarithm of the pore diameter D is 0.001 cm3 / (g·log(nm))-0.009 cm3 / (g·log(nm)).

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. 202410649209.4, filed on May 23, 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. Carbon negative electrode materials play a role in storing sodium during the charging process of sodium-ion batteries and are an important part of sodium-ion batteries. Hard carbon has ordered carbon microcrystals, rich micro-nano pore defects and surface defects, has a large interlayer spacing and rich pore structure, and has a relatively stable structure during sodium-ion deintercalation. Hard carbon is one of the mainstream negative electrode active materials in this field due to its excellent overall performance, wide applicability and relatively low price.

[0005] However, the current research on the processing technology of hard carbon material for preparing negative electrode sheets is insufficient, and therefore it is necessary to provide a negative electrode sheet containing hard carbon material with good processability. SUMMARY

[0006] 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 sodium-ion battery includes a negative electrode sheet, the negative electrode sheet includes hard carbon material as a negative electrode active material, and the hard carbon material has good processability. When the hard carbon material is used to prepare the negative electrode sheet, the hard carbon material effectively reduces the gas bubbling phenomenon in the pulping process, so that a negative electrode sheet with uniform negative electrode film layer can be obtained.

[0007] To achieve the above object, 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, the negative electrode film layer comprises a hard carbon material, the hard carbon material contains pores with a pore size 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 with respect to the logarithm of the pore size D of the pores with a pore size in the range of 1.0 nm-1.5 nm is in the range of 0.001 cm 3 / (g·log(nm))-0.009 cm 3 / (g·log(nm))。

[0008] 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 characteristic dV / d(logD) of the pores with a pore size in the range of 1.0 nm-1.5 nm of the hard carbon material reflects the pore volume contributed per unit pore size. The maximum value of dV / d(logD) corresponding to the pores with a pore size in the range of 1.0 nm-1.5 nm is in the above range, which is beneficial to reduce the gas production and bubbling phenomenon in the slurry preparation process, and is beneficial to the stable slurry preparation process and the uniformity of the negative electrode film layer.

[0009] In some embodiments, the maximum value of dV / d(logD) of the pores with a pore size in the range of 1.0 nm-1.5 nm of the hard carbon material is in the range of 0.001 cm 3 / (g·log(nm))-0.006 cm 3 / (g·log(nm)). This is more beneficial to reduce the gas production and bubbling phenomenon in the slurry preparation process.

[0010] In some embodiments, the pore volume of the pores with a pore size in the range of 1.0 nm-1.5 nm of the hard carbon material is in the range of 0.0003 cm 3 / g-0.0017 cm 3 / g. This is further beneficial to reduce the gas production phenomenon in the slurry preparation process.

[0011] In some embodiments, the pore volume of the pores with a pore size in the range 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 beneficial to reduce the gas production phenomenon in the slurry preparation process.

[0012] In some embodiments, the pore volume of the pores with a pore size less than 1 nm of the hard carbon material is denoted as V1, and the pore volume of the pores with a pore size in the range of 1 nm-2 nm of the hard carbon material is denoted as V2, then V1+V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g. The pore volume of the pores having a pore diameter of 2 nm or less, i.e., V1+V2, is in the above range, which is more advantageous to some extent for maintaining the gram capacity while reducing the gas bubble generation phenomenon during the slurry process.

[0013] In some embodiments, V1+V2 is in the range of 0.0020 cm3 / g to 0.0030 cm3 / g. 3 / g to 0.0030 cm3 / g. 3 / g to 0.0030 cm3 / g.

[0014] In some embodiments, the proportion of V1+V2 to the total pore volume of the hard carbon material is in the range of 4.5% 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 to some extent for maintaining the gram capacity of the hard carbon material.

[0015] In some embodiments, the proportion of V1+V2 to the total pore volume of the hard carbon material is in the range of 15% to 25%. The above proportion range is further advantageous to balance the processability and the gram capacity of the hard carbon material.

[0016] In some embodiments, the gram capacity of the hard carbon material is 250 mAh / g to 350 mAh / g in the potential range of 0 V to 2.5 V of Na / Na + .

[0017] In some embodiments, the gram capacity of the hard carbon material is not less than 290 mAh / g in the potential range of 0 V to 2.5 V of Na / Na + .

[0018] 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 range, which is advantageous to maintain a suitable slurry viscosity in the slurry process, thereby facilitating the coating of the slurry to obtain a negative electrode sheet with a uniform negative electrode film layer.

[0019] 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 having a valence of two or more is 0.1 ppm-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 range, which is advantageous not only to the slurry process but also 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, thereby improving the cycle performance.

[0020] In some embodiments, the metal ions include Na + , K + , Ca 2+ , Mg 2+at least one of Li, Na, K, Mg, Ca, Sr, Ba, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Pb, Ge, In, Tl, and Bi. 2+ at least one of Li, Na, K, Mg, Ca, Sr, Ba, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Pb, Ge, In, Tl, and Bi. 2+ at least one of Li, Na, K, Mg, Ca, Sr, Ba, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Pb, Ge, In, Tl, and Bi. 3+ at least one of Li, Na, K, Mg, Ca, Sr, Ba, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Pb, Ge, In, Tl, and Bi.

[0021] In some embodiments, the metal ion with valence of two or more is 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 slurry to obtain a negative electrode film layer of the negative electrode sheet.

[0022] In some embodiments, the surface oxygen element content of the hard carbon material is 5%-15%. 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, making the slurry uniformly dispersed during the mixing process and having good fluidity, thereby facilitating the coating of the slurry.

[0023] 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.

[0024] In some embodiments, the solvent of the electrolyte in the sodium ion battery includes a carbonate solvent, and the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. In this way, it is conducive to improving the high-pressure resistance of the electrolyte.

[0025] In some embodiments, the proportion of propylene carbonate is 15%-55% with respect to the volume of the solvent of the electrolyte. In this way, it is not only conducive to improving the oxidation resistance of the electrolyte, but also can dissociate sodium salt to improve the conductivity.

[0026] In some embodiments, 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.

[0027] In some embodiments, the sodium-containing layered oxide is an iron-manganese-based layered oxide, specifically including at least one of a nickel-iron-manganese-based layered oxide and a copper-iron-manganese-based layered oxide.

[0028] 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, and the hard carbon material contains pores with a pore size 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 with respect to the logarithm of the pore size D is in the range of 0.001 cm 3 / (g·log(nm))-0.009 cm 3(g·log(nm)) and coating the negative electrode slurry on the negative electrode current collector. By using the above hard carbon material when preparing the negative electrode slurry, the gas generation and bubbling phenomenon during the slurry preparation process can be effectively reduced, thereby obtaining a uniform negative electrode film layer and improving the quality of the negative electrode sheet.

[0029] In some embodiments, the maximum value of dV / d(logD) of the pores with a pore size of 1.0 nm-1.5 nm of the hard carbon material is in the range of 0.001 cm 3 (g·log(nm))-0.006 cm 3 (g·log(nm)). This is more conducive to reducing the gas generation and bubbling phenomenon during the slurry preparation process.

[0030] 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 is in the range of 0.0003 cm 3 / g-0.0017 cm 3 / g. This is more conducive to reducing the gas generation phenomenon during the slurry preparation process while taking into account the gravimetric capacity.

[0031] 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.

[0032] In some embodiments, the pore volume of the pores with a pore size of less than 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 to 2 nm of the hard carbon material is denoted as V2, as determined by the carbon dioxide adsorption method and the nitrogen adsorption method, respectively, and V1+V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g. By further limiting the pore volume of the pores below 2 nm, i.e., V1+V2, in the above range, the balance between the gravimetric capacity and processability of the material is more conducive to further reducing the continuous bubbling.

[0033] In some embodiments, V1+V2 is in the range of 0.0020 cm 3 / g to 0.0030 cm 3 / g.

[0034] In some embodiments, the proportion of V1+V2 to the total pore volume of the hard carbon material is in the range of 4.5% to 30%. The proportion of the pore volume of the pores with a pore size below 2 nm of the hard carbon material to the total pore volume of the hard carbon material in the above range is more conducive to maintaining the gravimetric capacity of the hard carbon material.

[0035] In some embodiments, the proportion of V1+V2 to the total pore volume of the hard carbon material is in the range of 15% to 25%. The above proportion range is further conducive to balancing the processability and gravimetric capacity of the hard carbon material.

[0036] In some embodiments, the gram capacity of the hard carbon material is 250mAh / g to 350mAh / g in the potential range of 0V to 2.5V vs. Na / Na + In some embodiments, the gram capacity of the hard carbon material is not less than 290mAh / g in the potential range of 0V to 2.5V vs. Na / Na

[0037] In some embodiments, the gram capacity of the hard carbon material is not less than 290mAh / g in the potential range of 0V to 2.5V vs. Na / Na + In some embodiments, the gram capacity of the hard carbon material is not less than 290mAh / g in the potential range of 0V to 2.5V vs. Na / Na

[0038] In some embodiments, the mass percentage of the negative electrode components is 50% to 60% relative to the mass of the negative electrode slurry. In this way, the uniformity and stability of the slurry are improved.

[0039] In some embodiments, the mass percentage of the hard carbon is 80% to 95% relative to the mass of the negative electrode components. In this way, the energy density of the battery is improved.

[0040] In some embodiments, the negative electrode components further include 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 beneficial 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 components in the solvent, so that the slurry is easy to coat.

[0041] In some embodiments, the mixing of the negative electrode components and the solvent includes vacuum stirring at 0℃ to 30℃ for 1h to 4h.

[0042] When the above hard carbon material is used to prepare the negative electrode slurry, the bubbling time can be significantly reduced, which is beneficial to the smooth preparation of the slurry and 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.

[0043] The disclosure also provides a power utilization device including the sodium ion battery of the disclosure or the sodium ion battery obtained by the preparation method of the sodium ion battery of the disclosure.

[0044] The power utilization device of the disclosure includes the sodium ion battery provided by the disclosure, and thus at least has the same advantages as the sodium ion battery.

[0045] The disclosure also provides a hard carbon material, characterized in that, as determined by a nitrogen adsorption method, the hard carbon material contains pores with a pore size in the range of 1.0nm-1.5nm, and 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 is in the range of 0.001cm 3 / (g·log(nm))-0.009cm 3 / (g·log(nm)).

[0046] The hard carbon material provided by the present disclosure has an optimized pore structure. Specifically, the dV / d(logD) of the pores with a pore size of 1.0 nm-1.5 nm of the hard carbon material reflects the pore volume contributed by the unit pore size. The maximum value of the dV / d(logD) corresponding to the pores with a pore size in the range of 1.0 nm-1.5 nm is in the above range, which is conducive to reducing the gas bubble phenomenon in the slurry preparation process, and is conducive to the stable operation of the slurry preparation process and the uniformity of the negative electrode film layer.

[0047] In some embodiments, the maximum value of the dV / d(logD) of the pores with a pore size of 1.0 nm-1.5 nm of the hard carbon material is in the range of 0.001 cm 3 / (g·log(nm))-0.006 cm 3 / (g·log(nm)). This is more conducive to reducing the gas bubble phenomenon in the slurry preparation process.

[0048] 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 is in the range of 0.0003 cm 3 / g-0.0017 cm 3 / g. This is further conducive to reducing the gas phenomenon in the slurry preparation process.

[0049] 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 phenomenon in the slurry preparation process.

[0050] In some embodiments, the pore volume of the pores with a pore size of less than 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, which are determined by the carbon dioxide adsorption method and the nitrogen adsorption method respectively, and 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 less than 2 nm of the hard carbon material, i.e., V1+V2, is in the above range, which is more conducive to maintaining the gram capacity to a certain extent while reducing the gas bubble phenomenon in the slurry preparation process.

[0051] In some embodiments, V1+V2 is in the range of 0.0020 cm 3 / g to 0.0030 cm 3 / g.

[0052] In some embodiments, the proportion of V1+V2 to the total pore volume of the hard carbon material is in the range of 4.5% to 30%. The proportion of the pore volume of the pores with a pore size of less than 2 nm of the hard carbon material to the total pore volume of the hard carbon material is in the above range, which is more conducive to maintaining the gram capacity of the hard carbon material.

[0053] In some embodiments, the ratio of V1+V2 to the total pore volume of the hard carbon material is in the range of 15% to 25%. The above ratio range is further beneficial to balance the processability and the gravimetric capacity of the hard carbon material.

[0054] In some embodiments, the gravimetric capacity of the hard carbon material is 250mAh / g to 350mAh / g in the potential range of 0V to 2.5V vs. Na / Na + .

[0055] In some embodiments, the gravimetric capacity of the hard carbon material is not less than 290mAh / g in the potential range of 0V to 2.5V vs. Na / Na + .

[0056] 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 ranges are beneficial to maintain a suitable slurry viscosity in the slurry preparation process, thereby facilitating the coating of the slurry to obtain a negative electrode sheet with uniform negative electrode film layer.

[0057] 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 ranges are beneficial to not only the slurry preparation process, but also 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.

[0058] In some embodiments, the metal ions include at least one of Na + , K + , Ca 2+ , Mg 2+ , Mn 2+ , Ba 2+ , Al 3+ .

[0059] 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 thereof in the above range is beneficial to obtain a suitable negative electrode slurry viscosity, thereby facilitating the coating of the slurry to obtain a negative electrode sheet with uniform negative electrode film layer.

[0060] In some embodiments, the surface oxygen element content of the hard carbon material is 5% to 15%. The surface oxygen element content of the hard carbon material within the above range is conducive to maintaining a suitable dispersant and hard carbon material interaction force, so that the slurry is uniformly dispersed during the mixing process and has good fluidity, thereby facilitating the coating of the slurry.

[0061] In some embodiments, the surface oxygen element content of the hard carbon material is 8% to 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. BRIEF DESCRIPTION OF DRAWINGS

[0062] FIG. 1 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0063] FIG. 2 is an exploded view of the battery cell shown in FIG. 1 according to an embodiment of the present disclosure.

[0064] FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0065] FIG. 4 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0066] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0067] FIG. 6 is a schematic diagram of an electric device using a sodium-ion battery as a power source according to an embodiment of the present disclosure.

[0068] FIG. 7 is a graph of dV / d(logD) versus pore size in a specific range for a hard carbon material prepared in Example 1 of the present disclosure based on nitrogen adsorption-desorption testing.

[0069] FIG. 8 is a graph of dV / d(logD) versus pore size in a specific range for a hard carbon material prepared in Comparative Example 1 of the present disclosure based on nitrogen adsorption-desorption testing.

[0070] FIG. 9 is a graph of dV / d(logD) versus pore size in a specific range for a hard carbon material prepared in Example 2 of the present disclosure based on nitrogen adsorption-desorption testing.

[0071] FIG. 10 is a graph of dV / d(logD) versus pore size in a specific range for a hard carbon material prepared in Comparative Example 2 of the present disclosure based on nitrogen adsorption-desorption testing.

[0072] BRIEF DESCRIPTION OF DRAWINGS DETAILED DESCRIPTION

[0073] Hereinafter, specific embodiments of the sodium-ion battery, the sodium-ion battery production 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 configurations is omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, 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.

[0074] The "ranges" disclosed in the present disclosure are defined in the form of lower and upper limits, 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 the particular range. The ranges defined in this way are inclusive of the end values, unless otherwise specified, 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. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then 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 manner of describing each and every numerical value that is contained in the range between "a" and "b," wherein "a" and "b" are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed herein, and "0-5" is merely a shorthand manner of describing each and every numerical value that is contained in the range between "0" and "5." 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, and the like.

[0075] If not specifically stated, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0076] If not specifically stated, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions.

[0077] If not specifically stated, all steps of the present disclosure can be performed in sequence or randomly, and preferably in sequence. For example, a method includes steps (a) and (b) indicates that the method can include steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, it is mentioned that the method can further include step (c), which indicates that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0078] At present, the capacity density of sodium ion battery needs to be improved. From the perspective of materials, the general energy density is equal to the product of ampere-hour and voltage, and the capacity improvement of hard carbon negative electrode material has a significant impact on the energy density of the battery. Due to the abundant pore structure of hard carbon material, part of the pores can store sodium ions and also contain gas molecules. During the preparation of negative electrode slurry with hard carbon material, continuous gas generation and bubbling will occur. For hard carbon materials that continuously generate gas and bubble, such as hard carbon materials that still bubble after 2 hours of slurry preparation, processing is difficult to proceed, and the prepared negative electrode sheet has the risk of exposing the underlying negative electrode current collector, leading to negative electrode sheet defects, and thus affecting the performance of sodium ion battery. Especially for hard carbon materials that provide higher gram capacity by increasing the pore volume of micropores in the porous structure, they also bring the above-mentioned slurry bubbling problem more seriously.

[0079] Sodium ion battery

[0080] Based on this, 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, and the negative electrode film layer comprises a hard carbon material. The hard carbon material contains pores with a pore size 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 with respect to the logarithm of the pore size D is in the range of 0.001 cm 3 / (g·log(nm))-0.009 cm 3 / (g·log(nm)).

[0081] The hard carbon material has abundant pores and channels that can adsorb and store a large amount of gas. When the hard carbon material is placed in the slurry, on the one hand, the gas in it will try to escape from the hard carbon, and the gas will be hindered and dispersed into small bubbles during the escape process, and these small bubbles will slowly pass through the pores and channels, and on the other hand, the porous structure also provides multiple gasification centers for it, which can promote the generation and release of gas, thereby forming a continuous bubbling phenomenon. The present disclosure proposes that pores with a pore size of 1.0 nm-1.5 nm have a significant impact on continuous gas generation and bubbling. By adjusting the part of the specific pore size, 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 is in the range of 0.001 cm 3 / (g·log(nm))-0.009 cm 3(g·log(nm)) can significantly reduce the duration of the bubble. It is found that the pores with larger pore size (pores with a pore size greater than 1.5 nm) have less impact on processability, presumably because the duration of the bubble caused by these pores is short; the pores with smaller pore size (pores with a pore size less than 1.0 nm) may have less impact on processability because of the small gas storage capacity; and by limiting the change rate of the volume contribution of the pores with a pore size of 1.0 nm-1.5 nm, i.e., controlling the maximum value of dV / d(logD) within the above range, the gas bubble phenomenon during pulping can be effectively reduced, thereby obtaining a uniform negative electrode film layer and improving the quality of the negative electrode sheet.

[0082] 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 numerical values.

[0083] The dV / d(logD) mentioned in the present disclosure reflects the pore volume contributed by unit pore size. This value can be obtained by measuring the hard carbon material by a conventional determination method in the art. For example, the specific surface area meter-static capacity method can be used to determine, specifically, according to the embodiments of the present disclosure, the flow method gas adsorption type specific surface area measuring device (device model Micromeritics ASAP-2460) can be used to measure the nitrogen adsorption method test adsorption and desorption isotherm, and the DFT model is used to fit the dV / d(logD) distribution curve with respect to the pore size D, and the maximum value is read in the range of 1.0-1.5 nm. 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.

[0084] In some embodiments, the maximum value of dV / d(logD) of the pores with a pore size of 1.0 nm-1.5 nm of the hard carbon material is 0.001 cm 3 (g·log(nm))-0.006 cm3 (g·log(nm)). This is more conducive to reducing the gas bubble phenomenon in the pulping process.

[0085] 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 is in the range of 0.0003 cm 3 / g-0.0017 cm 3 / g. This is more conducive to reducing the gas phenomenon in the pulping process while taking into account the specific capacity. Illustratively, the pore volume of the pores with a pore size of 1.0 nm-1.5 nm is 0.0003 cm 3 / g, 0.0005 cm 3 / g, 0.0007 cm 3 / g, 0.0009 cm 3 / g, 0.0011 cm 3 / g, 0.0013 cm 3 / g, 0.0015 cm 3 / g, 0.0017 cm 3 / g or a value between any two of the numerical values. Alternatively, the total pore volume of the pores with a pore size of 1.0 nm-1.5 nm is in the range of 0.0009 cm 3 / g-0.0014 cm 3 / g.

[0086] The pore volume of the pores with a pore size of 1.0 nm-1.5 nm is also obtained by measuring the hard carbon material by a conventional method in the art, for example, N2sorption-desorption pore volume pore size test method. Illustratively, GB / T 19587-2017 can be referred to, N2adsorption method is adopted, adsorption and desorption isotherms are tested, DFT model is used to fit the cumulative pore volume versus pore size distribution curve, and the pore volume of the pores with a specific pore size range of 1.0 nm-1.5 nm is obtained.

[0087] In some embodiments, the pore volume of the pores with a pore size of less than 1 nm of the hard carbon material measured by the carbon dioxide adsorption method is represented as V1, the pore volume of the pores with a pore size of 1 nm to 2 nm of the hard carbon material measured by the nitrogen adsorption method is represented as V2, and V1+V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g.

[0088] Further research found that when preparing the negative electrode slurry, the pores with a pore size of 2 nm or less will cause a certain degree of gas bubbling. Among them, the pores with a pore size of less than 1 nm will not cause a large amount of bubbling, but too much pore volume will cause the duration of the bubbling to be longer; the pores with a pore size of 1.5 nm to 2 nm also cause a certain amount of bubbling problem, but the duration of the bubbling is relatively short. The pores with a pore size of 2 nm or less in the material can contribute to the gram capacity. By further limiting the pore volume of the pores with a pore size of 2 nm or less, i.e. V1+V2, within the above range, the duration of the continuous bubbling is further reduced, and the balance between the gram capacity and the processability of the material is more favorable.

[0089] Exemplarily, the pore volume of the pores with a pore size of 2 nm or less 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 or a value between any two of the above values. Alternatively, V1+V2 is within the range of 0.0020 cm 3 / g to 0.0030 cm 3 / g.

[0090] The pore volume V1 of the pores with a pore size of less than 1 nm of the hard carbon material can be determined by using the conventional method in the art. For example: CO2 adsorption-desorption pore volume pore size test method. By this method, the pore volume of the pores with a pore size of less than 1 nm, especially in the range of 0.4 nm to 1 nm, is usually determined. Exemplarily, the CO2 adsorption method test adsorption and desorption isotherms can be measured according to GB / T 34709-2017, the DFT model is used to fit the cumulative pore volume versus pore size distribution curve, and the pore volume V1 of the pores with a specific pore size range of less than 1 nm is obtained.

[0091] The pore volume V2 of the pores with a pore size of 1 nm-2 nm of the hard carbon material can be determined by using a method similar to the above method to determine the cumulative pore volume versus pore size distribution curve, and V2 is obtained by integrating in the specific pore size range of 1-2 nm.

[0092] In some embodiments, the proportion of V1+V2 to the total pore volume is in the range of 4.5% to 30%. By further ensuring that the proportion of the pore volume of pores smaller than 2 nm is within the above range, it is beneficial to balance the specific capacity while reducing continuous bubbling. Exemplarily, the proportion of V1+V2 to the total pore volume is 4.5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, or a value between any two of these values.

[0093] The total pore volume of hard carbon materials can be determined using conventional methods in the field. For example, the above-mentioned N2 adsorption-desorption pore volume and pore size testing method can be combined with the CO2 adsorption-desorption pore volume and pore size testing method to obtain the pore volume of pores with a diameter greater than 1 nm and the pore volume of pores with a diameter less than 1 nm, and then the two are summed to obtain the total pore volume.

[0094] In some embodiments, the pore volume of the hard carbon material with a pore size of 1.0 nm to 1.5 nm accounts for 6% to 14% of the total pore volume of the hard carbon material. This further helps to reduce gas generation during the pulping process. Exemplarily, the proportion of the pore volume of the pores with a pore size of 1.0 nm to 1.5 nm to the total pore volume is 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or a value between any two of these values.

[0095] In some implementations, Na / Na is at a voltage of 0V to 2.5V. + Within a certain potential range, the specific capacity of hard carbon materials ranges from 250 mAh / g to 350 mAh / g. For example, in the Na / Na… + Within the potential range, the specific capacity of the hard carbon material is 250mAh / g, 275mAh / g, 300mAh / g, 325mAh / g, 350mAh / g, or a range consisting of any two of these values.

[0096] In some implementations, Na / Na is at a voltage of 0V to 2.5V. + Within the potential range, the specific capacity of hard carbon materials is not less than 290 mAh / g.

[0097] In addition to effectively reducing the problem of gas generation and bubbling, this disclosure further discloses a hard carbon material in a manner that further improves its processability.

[0098] In some embodiments, the total metal ion content in the hard carbon material is ≤800ppm, and the content of divalent or higher metal ions is ≤20ppm.

[0099] It is found that 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 has little effect on other components in the negative electrode slurry, such as dispersants, thickeners, and in particular sodium carboxymethyl cellulose, and is conducive to the role of dispersants, thickeners, and the like in the preparation of the slurry, so as to maintain a suitable viscosity of the slurry, thereby facilitating uniform coating of the slurry on the negative electrode current collector.

[0100] The metal ions in the hard carbon material may, for example, be introduced by metal elements contained in the carbon source or by doping. For hard carbon prepared from a carbon source with high content of metal elements such as biomass or pitch / coal, when the total content of metal ions, in particular the total content of metal ions with valence of two or more, is in the above range, the slurry preparation and coating process are particularly advantageous.

[0101] 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 and the like.

[0102] 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. By further bringing the total content of metal ions and the content of metal ions with valence of two or more in the above range, 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.

[0103] In some embodiments, the metal ions include at least one of Na + , K + , Ca 2+ , Mg 2+ , Mn 2+ , Ba 2+ , and Al 3+ , but are not limited thereto.

[0104] In some embodiments, the metal ions with valence of two or more are Ca 2+ . It is found that the content of calcium ions in the hard carbon material has a greater effect on the negative electrode slurry, and controlling the content of calcium ions in the above range is conducive to obtaining a negative electrode slurry with a suitable viscosity, which is conducive to subsequent coating and the like processes, thereby obtaining a negative electrode sheet with improved quality.

[0105] In some embodiments, the hard carbon material has a surface oxygen element content of 6-14%. The surface of the hard carbon material usually has some oxygen-containing groups, such as -COOR, -COOH, -C=O, -OH, -C-O-C-, etc. Studies have found that different surface oxygen element contents affect the viscosity of the slurry, and in turn affect the processing performance. It is speculated that when the amount of these oxygen-containing groups is too large, it interacts with the components in the slurry such as the binder, thickener, etc., affecting the uniform dispersion of the system, causing gelling, and as the standing time increases, the degree of gelling increases. This can affect the subsequent process, clog the filter, or cause unevenness on the surface of the coated electrode plate.

[0106] For example, the hard carbon material has a surface oxygen element content of 6%, 7%, 8%, 9%, 9.5%, 10%, 10.5%, 11%, 12%, 13%, 14%, or a range between any two of the above values.

[0107] In some embodiments, the hard carbon material has a surface oxygen element content of 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.

[0108] 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 the reversible capacity, the compaction density, etc.

[0109] (1) The hard carbon material has a surface coating layer. The surface coating layer can reduce surface defects, which is conducive to improving the reversible capacity and the initial coulombic efficiency.

[0110] In some embodiments, the surface coating layer is a carbon coating layer.

[0111] (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, the appropriate proportion of disordered carbon on the surface of the hard carbon can be maintained, and the layered structure of a certain amount of ordered carbon is conducive to improving the compaction density of the hard carbon material by slipping between the carbon layers, and improving the energy storage density of the negative electrode.

[0112] In some embodiments, the hard carbon material has an I D / I G of 0.7-1.32. For example, the hard carbon material has an I D / I Gany value within a range of 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.30, 1.32, or any two numerical values.

[0113] (3) The number distribution particle size Dn10 of the hard carbon material is 0.5-1.0 μm. This is more favorable for the compaction density of the negative electrode sheet. 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.

[0114] (4) The particle size of the hard carbon material 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 favorable for the compaction density of the negative electrode sheet.

[0115] (5) The compaction density ρ1 of the hard carbon material under 50000 N is ≥0.9 g / cm 3 .

[0116] (6) The specific surface area of the hard carbon material is 2 m 2 / g-12 m 2 / g. The specific surface area of the hard carbon material within the above range is favorable for obtaining an appropriate pore structure and balancing the gram capacity.

[0117] 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 within the above range is more favorable for balancing the gram capacity.

[0118] (7) The tap density ρ2 of the hard carbon material is 0.75 g / cm 3 -0.9 g / cm 3 .

[0119] In the present disclosure, the pore volume and specific surface area of the hard carbon material are of the meanings well known in the art and can be determined using instruments and methods known in the art. For example, the specific surface area of the hard carbon material can be determined by testing the adsorption and desorption isotherms using the nitrogen adsorption method according to GB / T 19587-2017, using the BET (Brunauer Emmett Teller) method, using the DFT model to fit, for example, the cumulative pore volume versus pore size distribution curve and the dV / d(logD)-D curve, and obtaining the pore volume of the pores in the specific pore size range of 1 nm or more. The testing instrument can be, for example, an ASAP-2460 specific surface area and pore size analyzer from Micromeritics, USA. The kinetic diameter of the carbon dioxide molecule is smaller than that of the nitrogen molecule, and the saturation vapor pressure at 273 K is higher, so the gas can diffuse faster into the voids smaller than 1 nm at this temperature, thus enabling the analysis of the smaller ultramicroporous structure. Therefore, the pore volume of the pores in the pore size range of less than 1 nm can be obtained by testing the adsorption and desorption isotherms using the carbon dioxide adsorption method, using the DFT model to fit the cumulative pore volume versus pore size distribution curve. The testing instrument can be, for example, an ASAP-2460 specific surface area and pore size analyzer from Micromeritics, USA.

[0120] In the present disclosure, the metal elements and their contents of the hard carbon material can be determined using instruments and methods known in the art. For example, the contents of the metal elements can be determined by testing according to US EPA 6010D-2014 inductively coupled plasma atomic emission spectrometry, using a testing instrument such as, for example, an ICP-OES, Thermo ICAP7400.

[0121] In the present disclosure, the surface oxygen element content of the hard carbon material can be determined using instruments and methods known in the art. For example, the surface oxygen element content can be determined by testing according to GB / T 33502-2017 Specification for Data Recording and Reporting of X-ray Photoelectron Spectroscopy (XPS) Surface Chemical Analysis, using a testing instrument such as, for example, an Axis Supra+ X-ray photoelectron spectrometer.

[0122] In the present disclosure, the I D / I G value of the hard carbon material 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., the presence of disorder and lattice defects in the structure. I 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 testing conditions are: excitation wavelength of 532 nm, and testing wave number range of 500-2500 cm-1 , the grating is 600 lines, the objective lens is 50 times, the integration time is 10 s, the cumulative number is 3 times, the surface scanning is performed, the D peak and the G peak intensity of 100 points are obtained, and the I D / I G , 30 I D / I G , the average value of the remaining 40 points is the I D / I G of the material. The testing instrument can be a Horiba LabRAM HR800 Raman spectrometer.

[0123] 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, GB / T 24533-2009 can be referred to, and the tap density can be measured by an electronic pressure testing machine (for example, a UTM7305 type electronic pressure testing machine). Exemplarily, the test method is as follows: 1 g of sample powder is weighed and added into a mold with a bottom area of 1.327 cm 2 , and is pressed to 50,000 N, and is kept for 30 s, then the pressure is released, and is kept for 10 s, then the powder tap density of the material under the pressure of 50,000 N is recorded and calculated.

[0124] 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, GB / T 5162-2006 can be referred to, and the tap density can be measured by a powder tap density tester. The testing instrument can be a Dandong Baiter BT-301, and the test parameters are as follows: vibration frequency 250±15 times / minute, vibration amplitude 3±0.2 mm, vibration times 5000 times, and cylinder 25 cm 3 .

[0125] In the present disclosure, the number distribution particle size Dn10 and the volume distribution particle size Dv10, Dv50 and Dv90 of the hard carbon material are the meanings known in the art, which can be measured by instruments and methods known in the art. For example, GB / T 19077-2016 can be referred to, and the laser particle size analyzer can be used for measurement. The testing instrument can be a Mastersizer 3000 type laser particle size analyzer of Malvern Instruments Limited, UK. Alternatively, the particle size of the hard carbon material can be measured and counted by a microscope image.

[0126] 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 any one or both of the two opposite surfaces of the negative electrode current collector.

[0127] In some embodiments, the negative 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, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0128] In some embodiments, the negative active material includes the hard carbon material provided in the above embodiments.

[0129] In some embodiments, the negative film layer can further optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0130] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0131] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a dispersing agent (e.g., sodium carboxymethyl cellulose (CMC-Na)), a thickening agent, etc.

[0132] The sodium ion battery of the present disclosure is described below with appropriate reference to the accompanying drawings.

[0133] The term “sodium ion battery” referred to herein refers to a battery cell, a battery module, or a battery pack. The following are described separately.

[0134] Generally, a sodium ion battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging of the battery, active ions, such as sodium ions, are inserted and extracted 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 is disposed between the positive electrode sheet and the negative electrode sheet and mainly functions to prevent short circuiting of the positive and negative electrodes while allowing ions to pass through.

[0135] [Positive electrode sheet]

[0136] The positive electrode sheet includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector, the positive film layer including a positive active material.

[0137] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0138] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be employed. 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.).

[0139] In some embodiments, the battery cell is a sodium ion battery, and the positive electrode active material can employ a positive electrode active material known in the art for use in sodium ion batteries. As an example, the positive electrode active material can include a sodium transition metal oxide, a polyanion compound, a Prussian blue compound, etc., and other conventionally known materials that can be used as a positive electrode active material for sodium ion batteries can also be used. For example, as an alternative technical solution of the present disclosure, in the sodium transition metal 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 x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≤ 1.

[0140] As an alternative technical solution of the present disclosure, the polyanion 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 polyanion 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 polyanion compound can also be a compound having a sodium ion, a tetrahedral (YO4) n- anion unit, a polyhedral (ZOy ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- Valence state: Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl, and Br. Examples of polyanionic compounds include NaFePO4, Na3V2(PO4)3, NaM'PO4F (M' is one or more of V, Fe, Mn, and Ni), and Na3(VO4)2(PO4)3. y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0141] As an optional technical approach in this disclosure, the polyanionic compound can be Na... x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d Wherein, element A represents an alkali metal element that substitutes for element Na, element M represents a metal element that substitutes for element V, element D represents a dopant element that substitutes for element P, and element Q represents a dopant element that substitutes for element F. Element D includes at least one of Si and S, and element Q includes at least one of Cl and O; 3.5≤x≤4.5, 0≤a≤0.15x, 0.8≤y≤1.1, 0≤b≤0.3y, 0≤c≤0.15, 0.8≤z≤1.1, 0≤d≤0.2z. Optionally, element A includes at least one of K and Li; element M includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0142] As an optional technical approach in this disclosure, the polyanionic compound can be Na... x R y (PO4)2P2O7, where 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.

[0143] As an optional technical approach in this disclosure, the polyanionic compound can be Na... 4+x R 3-y P 4-mO 15 / C;

[0144] wherein 0 < x < 0.5, 0 < y < 0.5, 0 < m < 0.2, 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.

[0145] The Prussian blue type 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 type 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.

[0146] In some embodiments, the positive active material includes at least one of a sodium-containing layered oxide, a polyanionic sodium ion compound, and a Prussian blue sodium ion compound.

[0147] In some embodiments, the sodium-containing layered oxide is an iron-manganese-based layered oxide, specifically at least one of a nickel-iron-manganese-based layered oxide and a copper-iron-manganese-based layered oxide.

[0148] In some embodiments, the battery cell is a lithium ion battery, and the positive active material can employ a positive active material for a lithium ion battery known in the art. As an example, the positive 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 active material can also be used. These positive active materials can be used alone only one kind, or two or more kinds in combination. Examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to simply as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be referred to simply as NCM 523LiNi 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 LiNi 0.85 Co 0.15 Al 0.05 O2) and modified compounds thereof. Examples of lithium-containing olivine phosphate 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, and a composite of lithium manganese iron phosphate and carbon.

[0149] The battery will be accompanied by the de-intercalation 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.

[0150] 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 lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will float.

[0151] In some embodiments, the positive electrode film layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0152] In some embodiments, the positive electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0153] [Electrolyte]

[0154] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not particularly limited in the present disclosure and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0155] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0156] 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-trifluoromethanesulfonylimide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluoroboric oxalate, sodium bisoxalate borate, sodium difluorobisoxalate phosphate, and sodium tetrafluorobisoxalate phosphate.

[0157] 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-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoroboric oxalate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0158] 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, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0159] In some embodiments, the solvent of the electrolyte solution in the sodium ion battery includes a carbonate solvent, and the carbonate solvent includes at least one of vinyl carbonate, propylene carbonate, and fluoroethylene carbonate. In this way, the high-pressure resistance of the electrolyte solution can be improved.

[0160] In some embodiments, the proportion of propylene carbonate is 15% to 55% relative to the volume of the solvent of the electrolyte solution. 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.

[0161] 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 properties of the battery, such as an additive capable of improving the overcharge performance of the battery, an additive capable of improving the high-temperature or low-temperature performance of the battery, etc.

[0162] [Separator]

[0163] In some embodiments, a separator film is further included in the battery cell. The type of the separator film is not particularly limited in the present disclosure, and any publicly known porous separator film having good chemical stability and mechanical stability can be used.

[0164] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0165] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte described above.

[0166] 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, or the like. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0167] 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 having a square structure as an example.

[0168] In some embodiments, referring to FIG. 2, the outer package can include a case 51 and a top cover assembly 53. The case 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The case 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator film can be wound or stacked to form an electrode assembly 52. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of the electrode assembly 52 included in the battery cell 5 can be one or more, and a person skilled in the art can select according to the specific actual needs.

[0169] In some embodiments, the battery cell can be assembled into a battery module, and the number of the battery cell included in the battery module can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0170] 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 arrangements can also be used. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0171] Optionally, the battery module 4 can further include a housing having an accommodation space in which the plurality of battery cells 5 are accommodated.

[0172] In some embodiments, the above-described battery module can be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0173] 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 disposed 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 provided on the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0174] Method for manufacturing sodium-ion battery

[0175] The embodiment of the present disclosure further provides a method for manufacturing a sodium-ion battery, including manufacturing a negative electrode sheet, wherein the manufacturing 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 contains pores with a pore size in a range of 1.0 nm-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 size D of the pores with the pore size in the range of 1.0 nm-1.5 nm is in a range of 0.001 cm 3 / (g·log(nm))-0.009 cm 3 / (g·log(nm)); and coating the negative electrode slurry on a negative electrode current collector. By using the above-mentioned hard carbon material when manufacturing the negative electrode slurry, the gas generation and bubbling phenomenon in the slurry manufacturing process can be effectively reduced, thereby obtaining a uniform negative electrode film layer and improving the quality of the negative electrode sheet.

[0176] In some embodiments, the maximum value of dV / d(logD) of the pores with the pore size in the range of 1.0 nm-1.5 nm of the hard carbon material is in a range of 0.001 cm 3 / (g·log(nm))-0.006 cm 3 / (g·log(nm)). This is more conducive to reducing the gas generation and bubbling phenomenon in the slurry manufacturing process.

[0177] In some embodiments, the pore volume of the pores with the pore size in the range of 1.0 nm-1.5 nm of the hard carbon material is in a range of 0.0003 cm 3 / g-0.0017 cm 3 / g. This is more conducive to reducing the gas generation phenomenon in the slurry manufacturing process while taking into account the specific capacity.

[0178] In some embodiments, the pore volume of the pores having a pore diameter of 1.0 nm to 1.5 nm accounts for 6% to 14% of the total pore volume of the hard carbon material.

[0179] In some embodiments, the pore volume of the pores having a pore diameter of less than 1 nm of the hard carbon material is denoted as V1, the pore volume of the pores having a pore diameter of 1 nm to 2 nm of the hard carbon material is denoted as V2, V1+V2 is in the range of 0.0006 cm3 / g to 0.0035 cm3 / g, as determined by the carbon dioxide adsorption method. 3 3 By further limiting the pore volume of the pores having a pore diameter of less than 2 nm, i.e. V1+V2, in the above range, the balance between the gravimetric capacity and the processability of the material is more favorable while the continuous bubbling is further reduced.

[0180] In some embodiments, V1+V2 is in the range of 0.0020 cm3 / g to 0.0030 cm3 / g. 3 3 In some embodiments, V1+V2 is in the range of 0.0020 cm3 / g to 0.0030 cm3 / g.

[0181] In some embodiments, the proportion of V1+V2 to the total pore volume of the hard carbon material is in the range of 4.5% to 30%. The proportion of the pore volume of the pores having a pore diameter of less than 2 nm to the total pore volume of the hard carbon material in the above range is more favorable for maintaining the gravimetric capacity of the hard carbon material.

[0182] In some embodiments, the proportion of V1+V2 to the total pore volume of the hard carbon material is in the range of 15% to 25%. The above proportion range is further favorable for balancing the processability and the gravimetric capacity of the hard carbon material.

[0183] In some embodiments, the gravimetric capacity of the hard carbon material is 250 mAh / g to 350 mAh / g in the potential range of 0 V to 2.5 V of Na / Na+. +

[0184] In some embodiments, the gravimetric capacity of the hard carbon material is not less than 290 mAh / g in the potential range of 0 V to 2.5 V of Na / Na+. +

[0185] In some embodiments, the mass percentage of the negative electrode components is 50% to 60% relative to the mass of the negative electrode slurry. In this way, the uniformity and stability of the slurry are favorable. Exemplarily, the mass percentage of the negative electrode components is 50%, 52%, 54%, 56%, 58%, 60%, or a value between any two of the above values, relative to the mass of the negative electrode slurry.

[0186] ​​​​In some embodiments, the hard carbon has a mass percentage of 80% to 95% relative to the mass of the negative electrode component. In this way, the energy density of the battery is facilitated. Illustratively, the hard carbon has a mass percentage of 80%, 82%, 85%, 87%, 90%, 92%, 95%, or a value between any two of the aforementioned values, relative to the mass of the negative electrode component.

[0187] 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 conducive to maintaining the integrity of the electrode structure during the charge and discharge 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.

[0188] In some embodiments, mixing the negative electrode component and the solvent comprises vacuum stirring at 0°C to 30°C for 1h to 4h. The present disclosure does not have specific limitations on the vacuum stirring, and appropriate process conditions such as vacuum degree, temperature, time, stirring speed, etc. 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, a dispersant, a conductive agent, and a binder, and the negative electrode slurry is prepared by the following steps: mixing the hard carbon, the dispersant, the conductive agent, and the solvent, and vacuum stirring; and further adding the binder and further stirring for 2 to 4h.

[0189] 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.

[0190] 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.

[0191] Exemplarily, the negative electrode sheet is prepared in the following manner: the mass ratio of the hard carbon material, the conductive agent, the binder, and the dispersing agent is 93:2:3.5:1.5, the hard carbon material, the conductive agent (SP), the dispersing agent (CMC), and a proper 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 rotation 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 a current collector of Cu or Al at a coating speed of 1-3 m / min, and the surface of the electrode sheet is good without bubbles, voids, and scratches; the coated electrode sheet is dried at 80°C, the coating speed is adjusted to 1-3 m / min, and then the electrode sheet is wound, and the surface of the electrode sheet is free of obvious foil exposure, pinholes, or coating leakage; the electrode sheet meeting the requirements is subjected to cold pressing, the electrode sheet is laser die-cut to form tabs and wound, and the preparation of the negative electrode is completed, thereby obtaining the negative electrode sheet.

[0192] In some embodiments, the method for preparing the sodium ion battery further comprises: preparing a positive electrode sheet.

[0193] The preparation of the positive electrode sheet is not particularly limited in the present disclosure, and the materials used for preparing the positive electrode sheet are as described above, and a person skilled in the art can select appropriate materials and processes to prepare the positive electrode sheet according to the needs. Exemplarily, the positive electrode sheet is prepared in the following manner: the mass ratio of the positive electrode active material, the conductive agent, and the binder is, for example, 8:1:1, the positive electrode active material, the conductive agent (such as SP), and the binder (PVDF) are mixed with a proper amount of NMP (N-methyl pyrrolidone), and the mixture is stirred at room temperature at a rotation speed of, for example, 1000 r / min to form a positive electrode slurry with good fluidity; the positive electrode slurry is coated on an Al current collector at a coating speed of 1-3 m / min, and the surface of the electrode sheet is good without bubbles, voids, and scratches; the coated electrode sheet is dried at 80°C, the coating speed is adjusted to 1-3 m / min, and then the electrode sheet is wound, and the surface of the electrode sheet is free of obvious foil exposure, pinholes, or coating leakage; the electrode sheet meeting the requirements is subjected to cold pressing, and laser die-cutting is performed to form tabs and wind, and the preparation of the positive electrode sheet is completed.

[0194] In some embodiments, the method for preparing the sodium ion battery further comprises: assembling the positive electrode sheet, the negative electrode sheet, and a 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, filling the electrolyte, and then packaging 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.

[0195] Similarly, the present disclosure does not have particular restrictions on the separator and the electrolyte solution. The materials that can be used as the separator and the components of the electrolyte solution are as described above, and a person skilled in the art can select appropriate separator materials and electrolyte components according to the needs.

[0196] Electric device

[0197] The present disclosure also provides an electric device. The sodium-ion battery of the present disclosure is described below with reference to the accompanying drawings.

[0198] 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 preparation method of 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.

[0199] As the electric device, the battery cell, the battery module or the battery pack can be selected according to the needs of the electric device.

[0200] FIG. 6 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the needs of the electric device for high power and high energy density of the sodium-ion battery, the battery pack or the battery module can be used.

[0201] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the battery cell can be used as a power source.

[0202] Hard carbon material

[0203] The present disclosure also provides a hard carbon material. The hard carbon material contains pores with a pore size 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 with respect to the logarithm of the pore size D is in the range of 0.001 cm 3 / (g·log(nm))-0.009 cm 3 / (g·log(nm)).

[0204] The negative electrode film layer of the negative electrode sheet provided by the present disclosure comprises a hard carbon material with an optimized pore structure. Specifically, the dV / d(logD) of the pores with a pore size of 1.0 nm-1.5 nm of the hard carbon material reflects the pore volume contributed by the unit pore size. The maximum value of the dV / d(logD) corresponding to the pores with a pore size in the range of 1.0 nm-1.5 nm is in the above range, which is conducive to reducing the gas bubble phenomenon during the slurry preparation process, and is conducive to the stable slurry preparation process and the uniformity of the negative electrode film layer.

[0205] In some embodiments, the maximum value of the dV / d(logD) of the pores with a pore size of 1.0 nm-1.5 nm of the hard carbon material is in the range of 0.001 cm 3 / (g·log(nm))-0.006 cm 3 / (g·log(nm)). This is more conducive to reducing the gas bubble phenomenon during the slurry preparation process.

[0206] 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 is in the range of 0.0003 cm 3 / g-0.0017 cm 3 / g. This is further conducive to reducing the gas phenomenon during the slurry preparation process.

[0207] 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 phenomenon during the slurry preparation process.

[0208] In some embodiments, the pore volume of the pores with a pore size of less than 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, which are determined by the carbon dioxide adsorption method and the nitrogen adsorption method respectively, and 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 less than 2 nm of the hard carbon material, i.e., V1+V2, is in the above range, which is more conducive to maintaining the gram capacity to a certain extent while reducing the gas bubble phenomenon during the slurry preparation process.

[0209] In some embodiments, V1+V2 is in the range of 0.0020 cm 3 / g to 0.0030 cm 3 / g.

[0210] In some embodiments, the proportion of V1+V2 to the total pore volume of the hard carbon material is in the range of 4.5% to 30%. The proportion of the pore volume of the pores with a pore size of less than 2 nm of the hard carbon material to the total pore volume of the hard carbon material is in the above range, which is more conducive to maintaining the gram capacity of the hard carbon material.

[0211] In some embodiments, the ratio of V1+V2 to the total pore volume of the hard carbon material is in the range of 15% to 25%. The above ratio range is further beneficial to balance the processability and the gravimetric capacity of the hard carbon material.

[0212] In some embodiments, the gravimetric capacity of the hard carbon material is 250 mAh / g to 350 mAh / g in the potential range of 0 V to 2.5 V vs. Na / Na + .

[0213] In some embodiments, the gravimetric capacity of the hard carbon material is not less than 290 mAh / g in the potential range of 0 V to 2.5 V vs. Na / Na + .

[0214] In some embodiments, 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. 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 ranges are beneficial to maintain a suitable slurry viscosity in the slurry preparation process, thereby facilitating the coating of the slurry to obtain a negative electrode sheet with uniform negative electrode film layer.

[0215] 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 in the above ranges are beneficial to not only the slurry preparation process, but also 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.

[0216] In some embodiments, the metal ions include at least one of Na + , K + , Ca 2+ , Mg 2+ , Mn 2+ , Ba 2+ , Al 3+ .

[0217] 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 in the above range is beneficial to obtain a suitable negative electrode slurry viscosity, thereby facilitating the coating of the slurry to obtain a negative electrode sheet with uniform negative electrode film layer.

[0218] In some embodiments, the hard carbon material has a surface oxygen element content of 5% to 15%. The hard carbon material having a surface oxygen element content within the above range is advantageous for maintaining a suitable interaction force between the dispersant and the hard carbon material, for uniformly dispersing the slurry during mixing, and for providing good flowability to the slurry, thereby facilitating coating of the slurry.

[0219] In some embodiments, the hard carbon material has a surface oxygen element content of 8% to 12%. The hard carbon material having a surface oxygen element content within the above range is more advantageous for the coating process of the slurry.

[0220] The hard carbon material described above can be obtained by adjusting the preparation method. The carbon source is not particularly limited, and examples of the carbon source that can be used include pitch / coal, biomass materials, and synthetic polymer materials. 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 advantageous internal / external structure. The hard carbon material described above can be obtained by adjusting the process conditions.

[0221] Synthetic polymer materials, such as phenolic resin, epoxy resin, furan resin, etc., have designability of structure and low impurity content. By polymerizing the precursors (e.g., polymerized monomers or prepolymers) of the synthetic polymer materials, or by dispersing, making pores, or etching the synthetic polymer materials, the microstructure of the carbon source can be well controlled, and thus the pore structure of the hard carbon material can be well controlled.

[0222] Exemplarily, but not limited to, the method for preparing a hard carbon material using a synthetic polymer material as a carbon source includes the following steps: a solidification step of solidifying a solution including a precursor of a polymer material and a solvent to obtain a carbon source; a pre-carbonization step of pre-carbonizing the carbon source 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.

[0223] Exemplarily, the polymerized monomer can be a monomer of phenolic resin, epoxy resin, or furan resin, etc.

[0224] Exemplarily, the prepolymer can be, for example, a resol resin.

[0225] 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 advantageous for subsequently forming a suitable pore structure.

[0226] In some embodiments, the temperature for curing is 80-150°C. Illustratively, the temperature for curing is 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, and any range between any two of them. The temperature for curing is advantageous for a suitable rate of curing reaction, while avoiding the formation of bubbles, and allowing the uniform distribution of the synthetic polymer material.

[0227] In some embodiments, the temperature for low-temperature pre-carbonization is 600-800°C. Illustratively, the temperature for low-temperature pre-carbonization is 600°C, 650°C, 700°C, 750°C, 800°C, and any range between any two of them. By the low-temperature pre-carbonization treatment, the moisture, partially dissolved impurities, and surface active groups can be removed, and a pre-carbonized product with a suitable degree of compactness can be formed, which is advantageous for adjusting the pore structure to a suitable pore structure in the subsequent high-temperature carbonization, and for further dissolution of impurities.

[0228] Illustratively, the crushing can be, for example, by a jet mill or a mechanical mill, and the present disclosure does not make special limitations thereto. In some embodiments, the crushing is such that the Dv50 of the particles is 4-8 μιη, 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 sufficient dissolution of impurities, and for a suitable particle size distribution of the final hard carbon.

[0229] Illustratively, the deashing step can be soaking the product in an acid washing kettle with 1-5 M acid to remove metal impurities. The biomass contains a large amount of metal impurities, and the deashing step can reduce the content of metal impurities.

[0230] In some embodiments, the temperature for high-temperature carbonization is 1100-1500°C. This is advantageous for forming a final suitable pore structure, thereby reducing the sustained bubbling during pulping while maintaining the gram capacity. In addition, the high-temperature carbonization can also reduce a large number of defects on the surface. Illustratively, the temperature for high-temperature carbonization is 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, and any range between any two of them. Alternatively, the temperature for high-temperature carbonization is 1300-1400°C.

[0231] In some embodiments, the preparation method further comprises a step of forming a coating layer. This step can be performed, for example, before the high-temperature carbonization. For example, the step of forming a coating layer comprises: placing the pre-carbonized product after deashing into a vapor deposition furnace, using N2 as a protective gas, heating to 500-800°C, switching the protective gas to a carbon-containing gas source, such as methane, ethylene, or acetylene, pyrolyzing for 1-2 h, then switching to N2 protective gas, and cooling to room temperature before discharging.

[0232] 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 heating 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 heating 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%.

[0233] In some embodiments, the preparation method further includes a classification treatment and a magnetic removal treatment before obtaining the final hard carbon product, which can further optimize the problems of slurry bubbling, low slurry viscosity, and battery capacity decay.

[0234] In the above method, the porosity and pore structure can be adjusted by steps such as crushing of the pre-carbonized product and the temperature and pressure of hot pressing, carbonization temperature and time, etc. to obtain a hard carbon material with reduced or eliminated bubbling in the slurry preparation process.

[0235] Asphalt and coal are common chemical raw materials, which are widely available and low in price, so that the preparation of hard carbon materials using asphalt or coal as a carbon source has a lower cost.

[0236] Illustratively, but not limited to, the preparation of hard carbon materials using asphalt as a carbon source includes a pre-oxidation step, a pre-carbonization step, a crushing step, a pre-pressing step, and a carbonization step. In the pre-oxidation step, asphalt or modified asphalt is mixed with an oxidizing agent and heated at 200-300 °C for 2-5 h to form a hard carbon precursor. In the pre-carbonization step, the above hard carbon precursor is heated at 400-600 °C for 2-4 h. In the crushing step, the pre-carbonized product is crushed to a particle size of Dv10≤3 μm, Dv50≤8 μm, and Dv90≤30 μm. In the pre-pressing step, the crushed product is pressed into a cake shape with tightly packed particles to reduce the exposed area, prevent the oxidation damage of carbon by sintering volatiles, and control the porosity. In the carbonization step, it is treated at 1200-1500 °C for 2-6 h. Similarly, the preparation method can further include a step of forming a coating layer, for example, which can be performed before the carbonization step.

[0237] The oxygen content of the hard carbon precursor can be adjusted by the pre-oxidation step. Illustratively, the oxidizing agent can be oxygen, nitric acid, or hydrogen peroxide, which is not specifically limited in the present disclosure.

[0238] Illustratively, the crushing can be by air jet milling or mechanical milling, which is not specifically limited in the present disclosure. In some embodiments, the crushing has a Dv50 of 4-8 μm, which is more conducive to adjusting the pore structure of the pre-carbonized product to a suitable pore structure in the subsequent high temperature carbonization, fully dissolving impurities, and making the particle size distribution of the final hard carbon suitable.

[0239] In some embodiments, the preparation method further comprises a deashing step and a demagnetization step after the carbonization step. A suitable deashing step can control the content of cations, especially divalent cations (such as calcium ions) in the final product, thereby further facilitating the obtaining of hard carbon material suitable for the process of preparing pole pieces.

[0240] In the above method, the porosity and pore structure are adjusted by steps such as crushing of the pre-carbonized product and the temperature and pressure of hot pressing, the carbonization temperature and time, so as to obtain hard carbon material with reduced or eliminated bubbling in the slurry preparation process.

[0241] Biomass materials are widely available, such as coconut shells, rice husks, bamboo, wheat chaff, straw, lignin, etc. Using biomass materials as carbon sources has both economic and environmental benefits.

[0242] Illustratively, the preparation of hard carbon material using biomass material as carbon source includes a pre-carbonization step, a crushing step, a deashing step, a pre-pressing step, and a carbonization step. In the pre-carbonization step, the biomass material is heated at 300-500°C, optionally 400-500°C, for 2-6h. The pre-carbonization step can remove volatile matter in the biomass. In the crushing step, the pre-carbonized product is crushed to a particle size of Dv10≤3μm, Dv50≤8μm and Dv90≤30μm. The crushing step can enable the final hard carbon material to have a suitable particle size distribution. In the deashing step, the product is soaked in an acid washing kettle with 1-5M acid to remove metal impurities. Biomass contains a lot of metal impurities, and the deashing step can reduce the content of metal impurities. In the pre-pressing step, 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 carbon, and controlling the porosity. In the carbonization step, heating at 1300-1600°C for 2-6h removes the remaining volatile matter. Similarly, the preparation method can further comprise a step of forming a coating layer, for example, which can be performed before the carbonization step.

[0243] Illustratively, the crushing can be by air jet milling or mechanical milling, which is not specifically limited in the present disclosure. In some embodiments, the crushing makes the Dv50 of the particles 4-8μm, which is more conducive to adjusting the pore structure of the pre-carbonized product at a high temperature in the subsequent carbonization to obtain a suitable pore structure, and also conducive to fully dissolving impurities and making the particle size distribution of the final hard carbon suitable.

[0244] Illustratively, 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.

[0245] In some embodiments, the amount of metal ions volatilized from the interior that remain in the surface layer can be adjusted by further water washing after carbonization. For example, using coconut shell as the carbon source, the ion content can be further reduced by water 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.

[0246] In the above method, by adjusting the temperature and time of crushing, pre-oxidation, sintering, etc. of the pre-carbonized product, the porosity and pore structure are adjusted to obtain a hard carbon material with reduced or eliminated bubbling in the pulping process.

[0247] Examples

[0248] Hereinafter, examples of the present disclosure will be 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 mentioned are performed in accordance with techniques or conditions described in the literature in the field or in accordance with the product manual. The reagents or instruments used, for which the manufacturer is not mentioned, are all conventional products that can be obtained commercially.

[0249] Example 1

[0250] Preparation of a hard carbon material using a biomass material as a carbon source:

[0251] 1) Pre-carbonization

[0252] Using lignin as the raw material, the pre-carbonized product was obtained by treating at 400°C for 2 hours under a normal pressure N2 atmosphere in a hot press furnace (Top Laboratory Technology, VHP-777).

[0253] 2) Crushing

[0254] The pre-carbonized product obtained in step 1) above was subjected to jet milling in a jet mill (Shengxing Environmental Protection: SX1210) to obtain a product with a Dv10 of 2 μm, a Dv50 of 5 μm, and a Dv90 of 12 μm.

[0255] 3) Deashing

[0256] The product crushed in step 2) above was immersed in a 2M aqueous hydrochloric acid solution at room temperature for 10 hours in an acid washing kettle, filtered, washed with water 3 times, and then dried at 100°C in a continuous kiln.

[0257] 4) Pre-pressing

[0258] The product obtained in step 3) above was subjected to pressing at a pressure of 50T for 1 hour in a hot press furnace (Top Laboratory Technology, VHP-777).

[0259] 5) Carbonization

[0260] The product obtained in step 4) above was sintered at 1400°C for 2h at a temperature rising rate of 2°C / min under normal pressure of N2 atmosphere, washed with water for 3 times, and then dried at 100°C in a continuous kiln to obtain the hard carbon material of Example 1.

[0261] Preparation of negative electrode slurry:

[0262] The hard carbon material, conductive agent and dispersant were mixed in a ratio of 8:1:1 in deionized water, vacuum stirring at room temperature for 2.5h (to keep the uniform state of the negative electrode slurry within 4h after vacuum stirring without further bubble, the vacuum stirring time of the following examples and comparative examples is adjusted according to the situation, but the longest is not more than 4h), and dispersed to obtain a uniform negative electrode slurry, wherein the dispersant is sodium carboxymethyl cellulose, and the conductive agent is conductive carbon black.

[0263] Preparation of negative electrode sheet:

[0264] The uniformly stirred negative electrode slurry was coated on both sides of the Al foil by a double-sided coating machine, and after the double-sided coating was completed, vacuum drying at 80°C, cold pressing, slitting and sheeting were sequentially performed to prepare the negative electrode sheet.

[0265] Preparation of button-type half cell:

[0266] The prepared negative electrode sheet was assembled into a battery in a glove box, a metal sodium sheet was used as the counter electrode, and an electrolyte was a solvent of EC: DMC (volume ratio) = 1:1 containing 10v / v% FEC and dissolved with NaPF6.

[0267] The positive electrode sheet, the separator, and the negative electrode sheet were sequentially stacked, and the above-mentioned electrolyte was added, and after the packaging, standing, formation and aging processes, a button-type half cell was prepared.

[0268] Example 2

[0269] Synthesis of polymer material as carbon source for preparation of hard carbon material:

[0270] 1) Curing

[0271] 25g of anhydrous ethanol was mixed with 50g of resol (phenol formaldehyde resin of model 2150 with solid content of 80%) and stirred to obtain a uniform solution. The solution was kept at 80°C in an oven for 10h to obtain a hard carbon material precursor.

[0272] 2) Low-temperature pre-carbonization

[0273] The hard carbon material precursor was roughly broken, and was heated to 600°C at a temperature rising rate of 2°C / min under normal pressure of N2 atmosphere in a tube furnace for 10h to obtain a pre-carbonized product.

[0274] 3) Breaking

[0275] The pre-carbonized product obtained in step 2) above was crushed 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 the mass ratio of the material to the ball mill beads being 1:3. The particle size distribution of the crushed sample was measured using a Mastersizer 3000 laser particle size analyzer, and the Dv50 was 5 pm.

[0276] 4) Deashing

[0277] The pre-carbonized product crushed in step 3) above was soaked in a 2M hydrochloric acid aqueous solution in an acid pickling kettle at room temperature for 10 h, filtered, washed with water three times, and dried at 100°C in a continuous kiln.

[0278] 5) High-temperature carbonization

[0279] The product crushed in step 4) above was heated in a tube furnace under normal pressure in a N2 atmosphere at a heating rate of 2°C / min to 1300°C for 2 h.

[0280] 6) Classification

[0281] The product obtained in step 5) above was classified in an air flow classification device (Xuexuan Powder, AB03 type), and the particle size of the outflow was continuously monitored and tested until the Dv50 reached 5 pm, and the classification was completed.

[0282] 7) Demagnetization

[0283] The product obtained in step 6) above was demagnetized in a demagnetization device (Wanye Magnetic, GDG-250) until the product lost its magnetism.

[0284] Preparation of a negative electrode slurry, a negative electrode sheet, and a button half-cell:

[0285] According to a method similar to that of Example 1, a negative electrode slurry, a negative electrode sheet, and a button half-cell were prepared using the hard carbon material of this example.

[0286] Example 3

[0287] Preparation of a hard carbon material using pitch as a hard carbon material precursor:

[0288] 1) Pre-oxidation

[0289] The modified coal pitch (model: 8994-94-4) was added to an oxidation reaction kettle, normal pressure air was introduced, and heating was performed at 300°C for 3 h.

[0290] 2) Pre-carbonization

[0291] The pre-oxidized pitch obtained in step 1) above was heated in a tube furnace at 450°C for 3 h.

[0292] 3) Pre-pressing

[0293] The product obtained in step 2) above was put into a hot-pressing furnace (TOP INDUSTRY, VHP-777) and pressed at a pressure of 30T for 1h.

[0294] 4) Carbonization

[0295] The product obtained in step 3) above was heated in a tube furnace at 1400℃ under normal pressure N2atmosphere for 2h.

[0296] 5) Deliming

[0297] The product obtained in step 4) above was immersed in a 2M aqueous hydrochloric acid solution at room temperature in an acid pickling kettle for 10h, filtered, washed with water for 3 times, and dried at a temperature of 100℃ in a continuous kiln.

[0298] 6) Demagnetization

[0299] The product obtained in step 5) above was subjected to demagnetization in a demagnetization device (WANYE MAGNETIC, GDG-250) until the magnetism of the product disappeared.

[0300] Preparation of negative electrode slurry, negative electrode sheet and button half-cell:

[0301] The negative electrode slurry, negative electrode sheet and button half-cell were prepared according to the method similar to that of Example 1, using the hard carbon material of the present example.

[0302] Example 4

[0303] The hard carbon material was prepared according to the method similar to that of Example 1, except that the temperature during carbonization was 1450℃, so as to adjust the maximum value of dV / d(logD) of the obtained hard carbon material.

[0304] Example 5

[0305] The hard carbon material was prepared according to the method similar to that of Example 1, except that the temperature during carbonization was 1300℃, so as to adjust the maximum value of dV / d(logD) of the obtained hard carbon material.

[0306] Example 6

[0307] The hard carbon material was prepared according to the method similar to that of Example 1, except that after carbonization, a step of forming a coating layer was further included. Specifically, the particles to be coated were put into a vapor deposition furnace, N2was used as the protective gas, and the temperature was controlled to preheat at 560℃ for 0.5h. After 1h of heating with methane, the protective gas was switched to N2, and the product was cooled to room temperature and discharged.

[0308] Example 7

[0309] A hard carbon material was prepared in a similar manner to Example 1, except that after sintering at 1400 °C for 2 h, the material was impregnated with a 20 wt% solution of phosphoric acid for 3 h, followed by a subsequent sintering at 1200 °C for 2 h to remove impurities introduced by the impregnation.

[0310] Comparative Example 1

[0311] A hard carbon material was prepared in a similar manner to Example 1, except that during the preparation of the hard carbon material, the carbonization temperature was 1200 °C and the sintering time was 4 h.

[0312] Comparative Example 2

[0313] A hard carbon material was prepared in a similar manner to Example 2, except that during the preparation of the hard carbon material, the carbonization temperature was 1000 °C.

[0314] Comparative Example 3

[0315] A hard carbon material was prepared in a similar manner to Example 3, except that during the preparation of the hard carbon material, the pre-oxidation time was 5 h.

[0316] Comparative Example 4

[0317] A hard carbon material was prepared in a similar manner to Example 2, except that during the preparation of the hard carbon material, the low temperature pre-carbonization was in air at 300 °C and the high temperature carbonization step was 1000 °C for 2 h followed by a ramp of 10 °C / min to 1400 °C for 0.5 h.

[0318] Hard carbon material related tests:

[0319] Gas adsorption tests

[0320] For the hard carbon material, nitrogen and carbon dioxide adsorption methods were used to test the adsorption and desorption isotherms, respectively, according to GB / T 19587-2017. Both the nitrogen and carbon dioxide adsorption methods used a specific surface and porosity analyzer (Micromeritics ASAP-2460, USA). For the nitrogen adsorption method, the specific surface area of the hard carbon material was calculated using the BET (Brunauer Emmett Teller) method based on the adsorption and desorption isotherms. The dV / d(logD) distribution curve versus pore diameter D was fitted using the DFT model, and the maximum value was read in the range of 1.0-1.5 nm. The cumulative pore volume distribution curve versus pore diameter was also fitted, and the pore volume of pores with a pore diameter in the range of 1.0-1.5 nm, the pore volume of pores with a pore diameter in the range of 1-2 nm (V2), and the pore volume of pores with a pore diameter above 1 nm were obtained. For the carbon dioxide adsorption method, the cumulative pore volume distribution curve versus pore diameter was fitted using the DFT model, and the pore volume of pores with a pore diameter below 1 nm (V1) was obtained. The results are shown in Table 1. The total pore volume of the hard carbon material was the sum of the pore volume of pores with a pore diameter above 1 nm and V1. FIGS. 7 and 8 are the dV / d(logD) distribution curves versus pore diameter in a specific range for the hard carbon material prepared in Example 1 and Comparative Example 1, respectively. As shown in FIG. 7, the maximum value of dV / d(logD) of the hard carbon material prepared in Example 1 was 0.005 cm3 / (g·log(nm)) in the range of 1.0-1.5 nm. As shown in FIG. 8, the maximum value of dV / d(logD) of the hard carbon material prepared in Comparative Example 1 was 0.010 cm3 / (g·log(nm)) in the range of 1.0-1.5 nm. FIGS. 9 and 10 are the dV / d(logD) distribution curves versus pore diameter in a specific range for the hard carbon material prepared in Example 2 and Comparative Example 2, respectively. As shown in FIG. 9, the maximum value of dV / d(logD) of the hard carbon material prepared in Example 2 was 0.006 cm3 / (g·log(nm)) in the range of 1.0-1.5 nm. As shown in FIG. 10, the maximum value of dV / d(logD) of the hard carbon material prepared in Comparative Example 2 was 0.013 cm3 / (g·log(nm)) in the range of 1.0-1.5 nm. As shown in FIGS. 7-10, the maximum values of dV / d(logD) of the hard carbon materials prepared in Examples 1 and 2 were significantly different from those of the hard carbon materials prepared in Comparative Examples 1 and 2. 3 3 3 3

[0321] Test of bubbling in preparation of negative electrode slurry

[0322] ​​​​The hard carbon materials prepared in the above examples and comparative examples were observed for the time when bubbling stopped during preparation of negative electrode slurries. The cases where bubbling continued for 2 hours after mixing the components of the negative electrode slurry were recorded.

[0323] In addition, 50 g of the hard carbon materials prepared in the above examples and comparative examples were respectively added to a 500 mL closed reaction vessel equipped with temperature and pressure sensors, 200 mL of water was added, and the reaction vessel was quickly closed, and stirring was started until the temperature and pressure became constant. The volume of gas emitted per unit mass of the hard carbon material was calculated as a measure of the amount of bubbling according to the change in pressure and the ideal gas equation.

[0324] The test results of the hard carbon materials prepared in Examples 1-7 and Comparative Examples 1-4 above are shown in Table 1.

[0325] Gravimetric capacity test of hard carbon materials

[0326] The coin-type half-cells of the above examples and comparative examples were subjected to sodium intercalation to 0 V at a rate of 0.05 C, and the capacity obtained was the initial charge capacity; sodium deintercalation to 2.5 V cutoff at a rate of 0.1 C, and the capacity obtained was the initial 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 during the preparation of the tab. Gravimetric capacity Q = initial charge capacity / mass of hard carbon material.

[0327] The pore characteristics, bubbling conditions, and gravimetric capacity test results of the hard carbon materials prepared in Examples 1-7 and Comparative Examples 1-4 above are shown in Table 1.

[0328] Table 1:

[0329] As can be seen from Table 1, when the maximum value of dV / d(logD) is between 0.001 cm 3 / (g·log(nm)) and 0.009 cm 3 / (g·log(nm)), the continuous bubbling can be effectively reduced, and a good gravimetric capacity can be maintained.

[0330] Example 8

[0331] A hard carbon material was prepared in a similar manner to Example 1, except that the carbonization step was heating at 1500°C for 4 h.

[0332] Example 9

[0333] A hard carbon material was prepared in a similar manner to Example 1, except that the carbonization step was heating at 1400°C for 5 h.

[0334] Example 10

[0335] A hard carbon material was prepared in a similar manner to Example 1, except that the carbonization step was performed at 1350°C for 6h.

[0336] The pore characteristics, the amount of bubbling, and the gravimetric capacity of the hard carbon materials prepared in Examples 8-10 above were tested and the results are shown in Table 2.

[0337] Table 2:

[0338] As can be seen from Table 2, as the pore volume of pores having a pore diameter of 2nm or less, represented by V1+V2, increases, the amount of bubbling increases, while the gravimetric capacity also increases. When the pore volume of this portion is appropriate, such as in Example 9, a balance of reduced bubbling and good gravimetric capacity can be obtained.

[0339] Example 11

[0340] A hard carbon material was prepared in a similar manner to Example 1, except that the number of water washing after carbonization was 2 times.

[0341] Example 12

[0342] A hard carbon material was prepared in a similar manner to Example 1, except that the number of water washing after carbonization was 1 time.

[0343] Example 13

[0344] A hard carbon material was prepared in a similar manner to Example 1, except that the pre-carbonization temperature was 800°C and the number of water washing after carbonization was 1 time.

[0345] Example 14

[0346] A hard carbon material was prepared in a similar manner to Example 1, except that the pre-carbonization temperature was 800°C, the particle size was broken to Dv50 of 10μm, and the number of water washing after carbonization was 1 time.

[0347] Metal ion content test

[0348] The hard carbon materials of Examples 1 and 11-14 were each mixed with a negative electrode slurry having a solid content of 20%, and the mixture was stirred for 30 minutes. The slurry was then filtered to obtain a clear solution, which was used to test the ion content of water-soluble Ca, Mg, Na, and K. The results are shown in Table 3.

[0349] Viscosity test of negative electrode slurry after standing for 24h

[0350] Select the appropriate rotor, fixed good viscometer, negative electrode paste after 24 h, placed in the viscometer, paste submerged rotor scale line, instrument model: Shanghai FANGRUI NDJ-5S, rotor: 63# (2000-10000 mPa.s), 64# (10000-50000 mPa.s), speed: 12 r / min, test temperature: 25℃, test time 5 min, read data when the number is stable.

[0351] The metal ion content of the hard carbon material prepared in Example 1, Examples 11-14 and the viscosity test results of the negative electrode paste are shown in Table 3.

[0352] Table 3:

[0353] As can be seen from Table 3, when the total content of metal ions decreases, and the content of soluble metal ions with valence of two or more is low, such as ≤20 ppm, it is beneficial to maintain the viscosity of the paste during slurry preparation, thereby facilitating uniform coating of the paste on the negative electrode current collector and facilitating processing. In general, a paste viscosity of 4000 Pa.s or more is more advantageous, which can effectively reduce uneven coating phenomena such as wavy virtual edges. In Example 14, although the total amount of metal ions is low, the Ca 2+ concentration is too large. It is speculated that high valence cations such as Ca 2+ may complex with CMC-Na, making it difficult for CMC-Na to function as a dispersant, resulting in too low a viscosity of the paste, which is not conducive to the coating of the paste.

[0354] Example 15

[0355] The hard carbon material was prepared in a similar manner to Example 1, except that during the preparation of the hard carbon material, the product was transferred to an atmosphere furnace after discharging, and oxidized in air at a temperature of 300℃ for 2 h.

[0356] Example 16

[0357] The hard carbon material was prepared in a similar manner to Example 1, except that during the preparation of the hard carbon material, the product was transferred to an atmosphere furnace after discharging, and oxidized in air at a temperature of 300℃ for 5 h.

[0358] Example 17

[0359] The hard carbon material was prepared in a similar manner to Example 1, except that during the preparation of the hard carbon material, the product was transferred to an atmosphere furnace after discharging, and reduced in an Ar / H2(95:5) mixed atmosphere at a temperature of 300℃ for 2 h.

[0360] Example 18

[0361] The hard carbon material was prepared in a similar manner to Example 1, except that after the product was discharged, it was transferred to an atmosphere furnace and oxidized in air at 300°C for 7h.

[0362] Surface oxygen element content test

[0363] The surface oxygen element content of the hard carbon materials of Examples 1, 15-18 was tested using 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.

[0364] Negative electrode slurry viscosity and gelation degree test after standing for 24h

[0365] The viscosity of the negative electrode slurries prepared from the hard carbon materials of Examples 1 and 15-18 above was tested using the method described above after the slurries were sampled in a plastic cup and allowed to stand at room temperature for 24h.

[0366] The gelation degree was qualitatively determined by picking up the slurry with a small spoon and pouring it at 45° to observe the dripping. A dripping time of less than 1s was no gelation, a dripping time of 1-5s was mild gelation, and a dripping time of more than 5s was severe gelation.

[0367] Table 4:

[0368] As can be seen from Table 4 above, a surface oxygen element content of the hard carbon material in the range of 5%-15% can result in a suitable viscosity and good flowability of the slurry.

[0369] It should be noted that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration and playing the same role and effects as the technical idea within the scope of the technical solutions of the present disclosure are all included within the technical scope of the present disclosure. Furthermore, other modes obtained by applying various modifications to the embodiments that can be thought of by those skilled in the art, or by combining part of the constituent elements of the embodiments, without departing from the spirit of the present disclosure, are also included within the scope of the present disclosure.

Claims

1. A sodium-ion battery, the sodium-ion battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector, the negative electrode film layer comprising a hard carbon material, and, as determined by nitrogen adsorption, the hard carbon material comprising pores with a pore size in the range of 1.0 nm to 1.5 nm, the maximum value of the derivative of the logarithm of the cumulative pore volume V with respect to the pore size D, dV / d(logD), is 0.001 cm⁻¹. 3 / (g·log(nm))-0.009cm 3 / (g·log(nm)).

2. The sodium-ion battery of claim 1, wherein, The maximum value of dV / d(logD) of the pores having a pore diameter of 1.0 nm to 1.5 nm of the hard carbon material is 0.001 cm 3 / (g·log(nm)) - 0.006 cm 3 / (g·log(nm)) - 0.006 cm 3. The sodium-ion battery of any one of claims 1-2, wherein, The pore volume of the pores having a pore diameter of 1.0 nm to 1.5 nm of the hard carbon material is 0.0003 cm 3 / g to 0.0017 cm / g 3 / g.

4. The sodium-ion battery of any one of claims 1-3, wherein, The pore volume of pores with a pore size of 1.0 nm to 1.5 nm accounts for 6% to 14% of the total pore volume of the hard carbon material.

5. The sodium-ion battery of any one of claims 1-4, wherein, The pore volume of the pores of the hard carbon material having a pore diameter of less than 1 nm, as determined by the carbon dioxide adsorption method, is denoted as VI, and the pore volume of the pores of the hard carbon material having a pore diameter of 1 nm to 2 nm, as determined by the nitrogen adsorption method, is denoted as V2, then VI + V2 is in the range of 0.0006 cm3 / g to 0.0035 cm3 / g. 3 / g to 0.0035 cm3 / g. 3 / g to 0.0035 cm3 / g.

6. The sodium-ion battery of claim 5, wherein, V1+V2 is in the range of 0.0020 cm 3 / g to 0.0030 cm 3 / g.

7. The sodium-ion battery of any one of claims 5 or 6, wherein, V1+V2 accounts for 4.5% to 30% of the total pore volume of the hard carbon material.

8. The sodium-ion battery of any one of claims 1-7, wherein, The hard carbon material has a gravimetric capacity of 250 mAh / g to 350 mAh / g in a potential range of 0 V to 2.5 V vs. Na / Na + + 9. The sodium-ion battery of any one of claims 1-8, wherein, The hard carbon material has a gravimetric capacity of not less than 290 mAh / g in a potential range of 0 V to 2.5 V vs. Na / Na + + 10. The sodium-ion battery of any one of claims 1-9, wherein, 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.

11. The sodium-ion battery of claim 10, wherein, The total content of metal ions in the hard carbon material is 20 ppm to 800 ppm, and the content of metal ions with a valence of two or more is 0.1 ppm to 20 ppm.

12. The sodium-ion battery of any one of claims 10-11, wherein, The metal ions include at least one of Na + , K + , Ca 2+ , Mg 2+ , Mn 2+ , Ba 2+ , Al 3+ .

13. The sodium-ion battery of any one of claims 10-12, wherein, The divalent or more metal ion is Ca 2+ .

14. The sodium-ion battery of any one of claims 1-13, wherein, The surface oxygen element content of the hard carbon material is 5% to 15%.

15. The sodium-ion battery of claim 14, wherein, The surface oxygen element content of the hard carbon material is 8% to 12%.

16. The sodium-ion battery of any one of claims 1-15, wherein, The solvent of the electrolyte in the sodium ion battery includes a carbonate solvent, and the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

17. The sodium-ion battery of claim 16, wherein, The proportion of propylene carbonate accounts for 15% to 55% of the volume of the solvent of the electrolyte.

18. The sodium-ion battery of any one of claims 16-17, wherein, 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.

19. The sodium-ion battery of claim 18, wherein, The sodium-containing layered oxide is an iron-manganese-based layered oxide, and specifically includes at least one of a nickel-iron-manganese-based layered oxide and a copper-iron-manganese-based layered oxide.

20. A method of preparing a sodium-ion battery, comprising preparing a negative electrode sheet, wherein, The preparation of the negative electrode sheet includes: A negative electrode slurry is obtained by mixing the negative electrode components and solvent. The negative electrode components include a hard carbon material. As determined by nitrogen adsorption, the hard carbon material contains pores with a pore size in the range of 1.0 nm to 1.5 nm, and the maximum value of the derivative of the logarithm of the cumulative pore volume V with respect to the pore size D, dV / d(logD), is 0.001 cm⁻¹. 3 / (g·log(nm))-0.009cm 3 / (g·log(nm)); and The negative electrode slurry is coated on the negative electrode current collector.

21. The method of making according to claim 20, wherein, The maximum value of dV / d(logD) of the pores having a pore diameter of 1.0 nm to 1.5 nm of the hard carbon material is 0.001 cm 3 / (g·log(nm)) - 0.006 cm 3 / (g·log(nm)) - 0.006 cm 22. The method of manufacturing according to claim 20 or 21, wherein, The pore volume of the pores having a pore diameter of 1.0 nm to 1.5 nm of the hard carbon material is 0.0003 cm 3 / g to 0.0017 cm / g 3 / g.

23. The production method according to any one of claims 20 to 22, wherein, The pore volume of pores with a pore size of 1.0 nm to 1.5 nm accounts for 6% to 14% of the total pore volume of the hard carbon material.

24. The production method according to any one of claims 20 to 23, wherein, The pore volume of the pores of the hard carbon material having a pore diameter of less than 1 nm, as determined by the carbon dioxide adsorption method, is denoted as VI, and the pore volume of the pores of the hard carbon material having a pore diameter of 1 nm to 2 nm, as determined by the nitrogen adsorption method, is denoted as V2, then VI + V2 is in the range of 0.0006 cm 3 / g to 0.0035 cm 3 / g.

25. The method of manufacturing according to claim 24, wherein, V1+V2 is in the range of 0.0020 cm 3 / g to 0.0030 cm 3 / g.

26. The method of making according to either of claims 24 or 25, wherein, V1+V2 accounts for 4.5% to 30% of the total pore volume of the hard carbon material.

27. The production method according to any one of claims 20 to 26, wherein, The hard carbon material has a gravimetric capacity of 250 mAh / g to 350 mAh / g over a potential range of 0 V to 2.5 V vs. Na / Na + + 28. The method of making according to claim 27, wherein, The hard carbon material has a gravimetric capacity of not less than 290 mAh / g in a potential range of 0 V to 2.5 V vs. Na / Na + + 29. The production process according to any one of claims 20 to 28, wherein, The mass percentage content of the negative electrode component is 50% to 60% relative to the mass of the negative electrode slurry.

30. The production process according to any one of claims 20 to 29, wherein, The mass percentage content of the hard carbon is 80% to 95% relative to the mass of the negative electrode component.

31. The method of making according to any one of claims 20 to 30, wherein, The negative electrode component further includes one or more of a conductive agent, a binder, and a dispersant.

32. The production method according to any one of claims 20 to 31, wherein, The mixing of the negative electrode component and the solvent includes vacuum stirring at 0°C to 30°C for 1 h to 4 h.

33. An electric device comprising the sodium ion battery according to any one of claims 1 to 19 or the sodium ion battery obtained by the preparation method according to any one of claims 20 to 32.

34. A hard carbon material comprising pores having a pore diameter in the range of 1.0 nm - 1.5 nm, the maximum value of the derivative dV / d(logD) of the cumulative pore volume V versus the logarithm of the pore diameter D being in the range of 0.001 cm 3 / (g log(nm)) - 0.009 cm 3 / (g log(nm)).

34. A hard carbon material comprising pores having a pore diameter in the range of 1.0 nm - 1.5 nm, the maximum value of the derivative dV / d(logD) of the cumulative pore volume V versus the logarithm of the pore diameter D being in the range of 0.001 cm 3 / (g log(nm)) - 0.009 cm 3 / (g log(nm)).

35. The hard carbon material of claim 34, wherein, The maximum value of dV / d(logD) of the pores having a pore diameter of 1.0 nm to 1.5 nm of the hard carbon material is 0.001 cm 3 / (g·log(nm)) - 0.006 cm 3 / (g·log(nm)).

36. The hard carbon material of any one of claims 34-35, wherein, The pore volume of the pores having a pore diameter of 1.0 nm to 1.5 nm of the hard carbon material is 0.0003 cm 3 / g to 0.0017 cm / g 3 / g.

37. The hard carbon material of any one of claims 34-36, wherein, The pore volume of pores with a pore size of 1.0 nm to 1.5 nm accounts for 6% to 14% of the total pore volume of the hard carbon material.

38. The hard carbon material of any one of claims 34-37, wherein, The pore volume of the pores of the hard carbon material having a pore diameter of less than 1 nm, as determined by the carbon dioxide adsorption method, is denoted as VI, and the pore volume of the pores of the hard carbon material having a pore diameter of 1 nm to 2 nm, as determined by the nitrogen adsorption method, is denoted as V2, then VI + V2 is in the range of 0.0006 cm3 / g to 0.0035 cm3 / g. 3 / g to 0.0035 cm3 / g. 3 / g to 0.0035 cm3 / g.

39. The hard carbon material of claim 38, wherein, V1+V2 is in the range of 0.0020 cm 3 / g to 0.0030 cm 3 / g.

40. The hard carbon material of any one of claims 38 or 39, wherein, V1+V2 accounts for 4.5% to 30% of the total pore volume of the hard carbon material.

41. The hard carbon material of any one of claims 34-40, wherein, The hard carbon material has a gravimetric capacity of 250 mAh / g to 350 mAh / g over a potential range of 0 V to 2.5 V vs. Na / Na + + 42. The hard carbon material of any one of claims 34-41, wherein, The hard carbon material has a gravimetric capacity of not less than 290 mAh / g in a potential range of 0 V to 2.5 V vs. Na / Na + + 43. The hard carbon material of any one of claims 34-42, wherein, 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.

44. The hard carbon material of claim 43, wherein, The total content of metal ions in the hard carbon material is 20 ppm to 800 ppm, and the content of metal ions with a valence of two or more is 0.1 ppm to 20 ppm.

45. The hard carbon material of claim 43 or 44, wherein, The metal ions include at least one of Na + , K + , Ca 2+ , Mg 2+ , Mn 2+ , Ba 2+ , Al 3+ .

46. The hard carbon material of any one of claims 43-45, wherein, The divalent or more metal ion is Ca 2+ .

47. The hard carbon material of any one of claims 34-46, wherein, The surface oxygen element content of the hard carbon material is 5% to 15%.

48. The hard carbon material of claim 47, wherein, The surface oxygen element content of the hard carbon material is 8% to 12%.

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