Negative electrode hard carbon material, preparation method therefor, negative electrode composition, and sodium ion secondary battery and use

Abstract

A negative electrode hard carbon material, a preparation method therefor, a negative electrode composition, and a sodium ion secondary battery and a use. The negative electrode hard carbon material satisfies: the content of phosphorus being within the range of 0.001 wt%≤P≤0.300 wt%, on the basis of the total weight of the negative electrode hard carbon material; and a disorder parameter fa being within the range of 0.25≤fa≤0.75. Therefore, the negative electrode hard carbon material exhibits good comprehensive performance including capacity performance, initial coulombic efficiency, and cycle performance.

Description

Negative electrode hard carbon material, preparation method thereof, negative electrode composition, sodium ion secondary battery and use thereof

[0001] This application claims priority to Chinese patent application No. 202311840962.3 filed on December 28, 2023, and the contents of the above-mentioned Chinese patent application disclosure are hereby incorporated by reference in their entirety as a part of this application. Technical Field

[0002] The present invention generally relates to the field of energy storage technology, in particular to the field of sodium ion secondary batteries. Specifically, the present invention relates to a negative electrode hard carbon material, a preparation method thereof, a negative electrode composition comprising the negative electrode hard carbon material, a sodium ion secondary battery comprising the negative electrode composition, and uses of the sodium ion secondary battery. Background Art

[0003] In recent years, secondary batteries have played an increasingly important role in people's production and life. Compared with lithium-ion secondary batteries, sodium-ion secondary batteries are favored by the industry because of their abundant sodium reserves, low price, and many similarities with mature lithium-ion secondary batteries in terms of process routes. Similar to lithium-ion secondary batteries, sodium-ion secondary batteries generally include a positive electrode, a negative electrode, and a separator arranged between the positive electrode and the negative electrode, and work by repeatedly intercalating, transferring, and transmitting sodium ions between the positive and negative electrodes. For the negative electrode of the secondary battery, carbon-based materials such as graphite are usually used as the negative electrode. However, the interlayer spacing of the graphite negative electrode is small, the sodium storage capacity is limited, and the rate performance is poor, which makes it difficult to meet the requirements of high-performance secondary batteries. For this reason, people have begun to turn their attention to non-graphite materials.

[0004] Currently, the non-graphite negative electrode materials used in secondary batteries mainly include hard carbon and soft carbon. Soft carbon has a high degree of graphitization and a small interlayer spacing. In contrast, hard carbon is difficult to graphitize and has a large interlayer spacing, which has attracted people's attention. As a common non-graphite material, hard carbon does not have a long-range ordered structure. Some of its carbon layers are arranged randomly and stacked disorderly, forming a large number of defects and pores. With the rapid development of the battery field, people have increasingly higher requirements for battery performance, such as capacity performance, first coulombic efficiency and cycle performance. This has prompted researchers to conduct extensive research on many aspects, including hard carbon.

[0005] CN105453305A discloses a hard carbon material made from poly[(phenol glycidyl ether)-(co-formaldehyde)] and phosphoric acid, which exhibits high reversible capacity, high first coulombic efficiency, and high rate characteristics. However, the process uses polymers as raw materials, which is relatively expensive.

[0006] CN114695894A discloses a high-capacity hard carbon fast-charging negative electrode material, which uses nitrogen-phosphorus-doped hard carbon as the core and metal oxide and amorphous carbon as the shell, thereby achieving good fast-charging performance, high energy density and first coulombic efficiency. However, the preparation process is relatively complex.

[0007] CN113113601A discloses a phosphorus-doped hard carbon material. This material utilizes a phosphorus-doped hard carbon core coated with a polymer material. The material is used in lithium-ion secondary batteries, achieving high specific capacity and initial coulombic efficiency. However, the phosphorus-doped hard carbon material produced by this process contains a high phosphorus content (0.3-5% by weight of the total weight of the phosphorus-doped hard carbon material) and uses polymer as a raw material, resulting in high costs.

[0008] Damien et al. (“A SAXS outlook on disordered carbonaceous materials for electrochemical energy storage”, Damien etc., Energy Storage Materials 21(2019)162-173) established a model to study the structure of hard carbon materials prepared using different precursors. They found that the disorder parameter f derived from small-angle X-ray scattering data a It can better reflect the disorder degree of hard carbon materials. However, Damien did not study the disorder parameter f a Impact on secondary battery performance.

[0009] Given the current status of existing technologies, further research is still needed to provide hard carbon materials with better comprehensive performance, including capacity performance, first coulombic efficiency and cycle performance, so as to better meet market demand. Summary of the Invention

[0010] The present invention is made in view of the above problems existing in the prior art.

[0011] In a first aspect, the present invention relates to a negative electrode hard carbon material for a sodium ion secondary battery, which satisfies:

[0012] The phosphorus content ranges from 0.001 wt % ≤ P ≤ 0.300 wt %, such as 0.005 wt % ≤ P ≤ 0.250 wt % or 0.010 wt % ≤ P ≤ 0.160 wt % or 0.010 wt % ≤ P ≤ 0.100 wt %, based on the total weight of the negative electrode hard carbon material; and

[0013] Unordered parameter f aThe range is 0.25≤f a ≤0.75, for example 0.29≤f a ≤0.50 or 0.33≤f a ≤0.50 or 0.33≤f a ≤0.46, where f a Calculated by the following formula:

[0014] in

[0015] Wherein d is the distance between two adjacent pores in the negative electrode hard carbon material. The average spacing of the calculation, ξ is the factor that limits the long-range orderly expansion. The correlation length, d and ξ are obtained by fitting the small angle X-ray scattering data of the negative electrode hard carbon material.

[0016] In a second aspect, the present invention relates to a method for preparing the negative electrode hard carbon material according to the first aspect of the present invention, comprising:

[0017] (1) treating a carbon source in an air atmosphere at a temperature of 60-300° C., for example, 80-280° C., for 1-24 hours, for example, 2-20 hours;

[0018] (2) adding a phosphorus source to the product obtained in step (1), and then treating the resulting mixture under an inert gas atmosphere at a temperature of 60-300° C., for example, 60-260° C., for 1-12 hours, for example, 2-10 hours;

[0019] (3) pre-carbonizing the product obtained in step (2) at a temperature of 400-650° C., for example, 400-600° C., under an inert gas atmosphere for 0.5-12 hours, for example, 1-8 hours;

[0020] (4) repeatedly washing the product obtained in step (3) with deionized water until the pH of the product is in the range of 2.0-5.0, and optionally drying;

[0021] (5) uniformly mixing the product obtained in step (4) with at least one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate powder, and then sintering the mixture under an inert gas atmosphere at a temperature of 500-900° C., for example, 550-850° C., for 0.5-12 hours, for example, 2-10 hours; or

[0022] The product obtained in step (4) is stirred and soaked in at least one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate solution at a temperature of 20-100° C. for 1-12 hours, and then filtered to obtain a filter cake;

[0023] (6) repeatedly washing the product obtained in step (5) with deionized water until the pH of the product is in the range of 10.0-12.0;

[0024] (7) soaking the product obtained in step (6) in an acid solution at a temperature of 20-100° C. with stirring for 1-12 hours, filtering, and repeatedly washing the filter cake with deionized water until the pH thereof is in the range of 2.0-5.0, and then drying;

[0025] (8) Crushing the product obtained in step (7) to D v 50 Particle size in the range of 1.0-20.0 μm; and

[0026] (9) The product obtained in step (8) is subjected to high-temperature carbonization at a temperature of 1050-1600° C., for example, 1200-1500° C., for 2-8 hours, for example, 2-6 hours, under an inert gas atmosphere, and is optionally crushed.

[0027] In a third aspect, the present invention relates to a negative electrode composition, which is a negative electrode composition for a sodium ion secondary battery, comprising the negative electrode hard carbon material according to the first aspect of the present invention.

[0028] In a fourth aspect, the present invention relates to a sodium ion secondary battery comprising the negative electrode composition according to the third aspect of the present invention.

[0029] In a fifth aspect, the present invention relates to the use of the sodium ion secondary battery of the fourth aspect of the present invention in an energy storage device for solar power generation, wind power generation, smart grid peak regulation, distributed power station, backup power supply or communication base station.

[0030] The inventors unexpectedly discovered in their research that by doping a specific content of P element into the hard carbon material, the disorder parameter f of the hard carbon material can be controlled at the same time. a In a specific range, relative to P content and f a In the case of not being within the limited range, significantly improved comprehensive performance including capacity performance, first coulombic efficiency and cycle performance can be obtained. In addition, the raw materials used in the present invention are low in price, which has a cost advantage. DETAILED DESCRIPTION

[0031] In order to make the invention objectives, technical solutions and beneficial technical effects of this application clearer, this application will be described in detail below. It should be noted that the various aspects, features, implementation methods, and advantages described in this application may be compatible and / or combinable.

[0032] Unless otherwise specified, the meanings of the technical terms in this specification are the same as those generally understood by those skilled in the art.

[0033] The present invention relates to a negative electrode hard carbon material, a preparation method thereof, a negative electrode composition comprising the negative electrode hard carbon material, a sodium ion secondary battery comprising the negative electrode composition, and uses of the sodium ion secondary battery.

[0034] The present invention will be described in detail below.

[0035] Negative electrode hard carbon material

[0036] In a first aspect, the present invention relates to a negative electrode hard carbon material for a sodium ion secondary battery, which satisfies:

[0037] The phosphorus content ranges from 0.001 wt % ≤ P ≤ 0.300 wt %, such as 0.005 wt % ≤ P ≤ 0.250 wt % or 0.010 wt % ≤ P ≤ 0.160 wt % or 0.010 wt % ≤ P ≤ 0.100 wt %, based on the total weight of the negative electrode hard carbon material; and

[0038] Unordered parameter f a The range is 0.25≤f a ≤0.75, for example 0.29≤f a ≤0.50 or 0.33≤f a ≤0.50 or 0.33≤f a ≤0.46, where f a Calculated by the following formula:

[0039] in

[0040] Wherein d is the distance between two adjacent pores in the negative electrode hard carbon material. The average spacing of the calculation, ξ is the factor that limits the long-range orderly expansion. The correlation length, d and ξ are obtained by fitting the small angle X-ray scattering data of the negative electrode hard carbon material.

[0041] Unordered parameter f a This parameter was proposed by Damien et al. when they developed a model to study the structure of hard carbon materials made from different precursors. Damien found that this parameter can well reflect the degree of disorder in hard carbon materials. However, Damien did not study the factors that influence this parameter or its impact on battery performance.

[0042] The inventors unexpectedly discovered in their research that when the disorder parameter f of the hard carbon material is regulated a Within a specific range, and when the P element content in the hard carbon material is controlled within a specific range at the same time, the comprehensive performance including capacity performance, first coulombic efficiency and cycle performance is significantly improved compared to the case where either of the two is not within the scope specified by the present invention.

[0043] It should be noted that the inventors found in their research that the P content and the disorder parameter f a Affected by various factors such as the amount of added P source, pre-carbonization temperature, alkali treatment, high-temperature carbonization temperature, etc., the above parameters can be comprehensively controlled to obtain the P content and f within the range defined by the present invention. a .

[0044] In the negative electrode hard carbon material of the present invention, the doping amount of P element (i.e., the P element content in the final negative electrode hard carbon material) is 0.001 wt%≤P≤0.300 wt%, for example, 0.005 wt%≤P≤0.250 wt%, based on the total weight of the negative electrode hard carbon material. For example, based on the total weight of the negative electrode hard carbon material, the doping amount of the P element may be 0.001, 0.005, 0.010, 0.015, 0.020, 0.025, 0.030, 0.035, 0.040, 0.045, 0.050, 0.055, 0.060, 0.065, 0.070, 0.075, 0.080, 0.085, 0.090, 0.095, 0.100, 0.105, 0.110, 0.115, 0.120, 0.125, 0.130, 0.135, 0.140, 0.145 %, 0.150, 0.155, 0.160, 0.165, 0.170, 0.175, 0.180, 0.185, 0.190, 0.195, 0.200, 0.205, 0.210, 0.215, 0.220, 0.225, 0.230, 0.235, 0.240, 0.245, 0.250, 0.255, 0.260, 0.265, 0.270, 0.275, 0.280, 0.285, 0.290, 0.295, 0.300 wt %, or any two thereof. For example, the doping amount of the P element is 0.010 wt % ≤ P ≤ 0.160 wt %, based on the total weight of the negative electrode hard carbon material. When the P doping amount in the negative electrode hard carbon material is within the above range, further improved capacity performance and cycle performance can be achieved simultaneously. For another example, the P doping amount is 0.010 wt% ≤ P ≤ 0.100 wt%, based on the total weight of the negative electrode hard carbon material. When the P doping amount in the negative electrode hard carbon material is within the above range, cycle performance can be further improved.

[0045] In the negative electrode hard carbon material of the present invention, the disorder parameter f a The range is 0.25≤f a ≤0.75. For example, the disorder parameter f a0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, or any two of them. When the disorder parameter f a When it is within the above range, compared with f a When the value is outside the above range, the first coulombic efficiency, capacity performance and cycle performance are improved. For example, the disorder parameter f a The range is 0.29≤f a ≤0.50. When the disorder parameter f of the negative electrode hard carbon material a When the above range is reached, good first coulombic efficiency can be obtained while further improving the capacity performance and cycle performance. a The range is 0.33≤f a ≤0.50. When the disorder parameter f of the negative electrode hard carbon material a When the above range is reached, further improved cycle performance can be obtained. a The range is 0.33≤f a ≤0.46. When the disorder parameter f of the negative electrode hard carbon material a Within the above range, further improved capacity performance can be obtained.

[0046] In addition, further studies have found that when the negative electrode hard carbon material of the present invention meets one or more of the following conditions, further improved comprehensive performance can be obtained.

[0047] In some embodiments, the average pore diameter of the negative electrode hard carbon material of the present invention is 1.5-3.0 nm, for example, 1.5-2.5 nm. As an example, the average pore diameter of the negative electrode hard carbon material may be 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0 nm, or within the range defined by any two of them. aWhen the average pore diameter of the negative electrode hard carbon material is within the ranges defined by the present invention, further improved capacity and cycle performance can be achieved. For example, the average pore diameter of the negative electrode hard carbon material is 1.7-2.3 nm. When the average pore diameter of the negative electrode hard carbon material is within the ranges defined by the present invention, further improved capacity and cycle performance can be achieved.

[0048] The average pore diameter R of the hard carbon material can be calculated by using the parameters d and ξ obtained by fitting the small-angle X-ray scattering data of the hard carbon material and substituting them into the following formula:

[0049] in

[0050] In some embodiments, the BET specific surface area of ​​the negative electrode hard carbon material of the present invention is 1.0-35.0 m 2 / g, for example 3.0-35.0m 2 / g. As an example, the BET specific surface area of ​​the negative electrode hard carbon material can be 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0, 23.0, 24.0, 25.0, 26.0, 27.0, 28.0, 29.0, 30.0, 31.0, 32.0, 33.0, 34.0, 35.0 m 2 / g, or within the range defined by any two of them. a When the content of P is within the range defined in the present invention, when the BET specific surface area of ​​the negative electrode hard carbon material is within the above range, further improved capacity performance and cycle performance can be obtained. For example, the BET specific surface area of ​​the negative electrode hard carbon material is 4.5-14.5 m 2 When the BET specific surface area of ​​the negative electrode hard carbon material is within the above range, further improved cycle performance can be achieved. The BET specific surface area of ​​the hard carbon material can be measured by conventional methods in the art, for example, with reference to GB / T 19587-2017 "Determination of the Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method."

[0051] In some embodiments, the volume average particle size D of the negative electrode hard carbon material of the present invention is v 50 is in the range of 1.0-20.0 μm, for example 1.5-15.0 μm. aWhen the content of P in the negative electrode hard carbon material is within the range defined in the present invention, v When the particle size is within the above range, further improved capacity performance and cycle performance can be obtained. v The particle size of 50 refers to the cumulative volume distribution curve of the particle size distribution of the negative electrode hard carbon material, in which particles smaller than the particle size value and particles larger than the particle size value each account for 50% of the total volume of the negative electrode hard carbon material. v The particle size is 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 15.5, 16.0, 16.5, 17.0, 17.5, 18.0, 18.5, 19.0, 19.5, 20.0 μm, or within the range defined by any two of them. v The 50 particle size can be measured by a measurement method conventionally used in the art, for example, it can be measured by laser diffraction using a Malvern 3000 laser particle size analyzer.

[0052] Preparation method of negative electrode hard carbon material

[0053] The second aspect of the present invention provides a method for preparing the negative electrode hard carbon material according to the first aspect of the present invention, comprising the following steps:

[0054] (1) treating a carbon source in an air atmosphere at a temperature of 60-300° C., for example, 80-280° C., for 1-24 hours, for example, 2-20 hours;

[0055] (2) adding a phosphorus source to the product obtained in step (1), and then treating the resulting mixture under an inert gas atmosphere at a temperature of 60-300° C., for example, 60-260° C., for 1-12 hours, for example, 2-10 hours;

[0056] (3) pre-carbonizing the product obtained in step (2) at a temperature of 400-650° C., for example, 400-600° C., under an inert gas atmosphere for 0.5-12 hours, for example, 1-8 hours;

[0057] (4) repeatedly washing the product obtained in step (3) with deionized water until the pH of the product is in the range of 2.0-5.0, and optionally drying;

[0058] (5) uniformly mixing the product obtained in step (4) with at least one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate powder, and then sintering the mixture under an inert gas atmosphere at a temperature of 500-900° C., for example, 550-850° C., for 0.5-12 hours, for example, 2-10 hours; or

[0059] The product obtained in step (4) is stirred and soaked in at least one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate solution at a temperature of 20-100° C. for 1-12 hours, and then filtered to obtain a filter cake;

[0060] (6) repeatedly washing the product obtained in step (5) with deionized water until the pH of the product is in the range of 10.0-12.0;

[0061] (7) soaking the product obtained in step (6) in an acid solution at a temperature of 20-100° C. with stirring for 1-12 hours, filtering, and repeatedly washing the filter cake with deionized water until the pH thereof is in the range of 2.0-5.0, and then drying;

[0062] (8) Crushing the product obtained in step (7) to D v 50 Particle size in the range of 1.0-20.0 μm; and

[0063] (9) The product obtained in step (8) is subjected to high-temperature carbonization at a temperature of 1050-1600° C., for example, 1200-1500° C., for 2-8 hours, for example, 2-6 hours under an inert gas atmosphere, and is optionally crushed.

[0064] Each step of the preparation method of the present invention is described in detail below.

[0065] Step (1)

[0066] In step (1), the carbon source is treated in an air atmosphere at a temperature of 60-300° C., for example, 80-280° C., for 1-24 hours, for example, 2-20 hours (pretreatment).

[0067] The preparation method of the present invention has no particular requirements on the type of carbon source used, but preferably, in some embodiments, the carbon source is selected from one or more of coal, asphalt, and biomass;

[0068] Preferably, the coal is selected from one or more of bituminous coal and lignite;

[0069] Preferably, the asphalt is selected from one or more of medium-temperature asphalt (softening point of 70-115°C, measured according to GB2294-80) and high-temperature asphalt (softening point of 120-280°C, measured according to GB / T 4507-2014);

[0070] Preferably, the biomass is selected from one or more of coconut shells, walnut shells, apricot shells, palm shells, lignin, cellulose, starch, and bamboo. For example, the starch may be corn starch. In some embodiments, the corn starch has a particle size (particle size corresponding to the mesh size used during screening) of 5-20 μm.

[0071] It should be noted that, as Damien has discovered, hard carbon materials prepared from different types of carbon sources (precursors) may have different degrees of disorder, which will affect fa.

[0072] The purpose of step (1) is to pretreat the carbon source so as to facilitate subsequent treatment. The treatment process of step (1) can be appropriately adjusted according to the carbon source used, but preferably, the treatment temperature of step (1) is 60-300°C, such as 80-280°C, and the treatment time is 1-24 hours, such as 2-20 hours. As an example, the treatment temperature of step (1) can be 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 18, 19, 20, 21, 22, 23, 24 hours, or within the range defined by any two of them.

[0073] The above description provides examples of the carbon source type and pretreatment temperature in step (1). Those skilled in the art will readily appreciate that within the above ranges of carbon source type and pretreatment temperature, those skilled in the art can flexibly adjust the combination of the carbon source type and the pretreatment temperature to achieve a better pretreatment effect.

[0074] Step (2)

[0075] After pretreating the carbon source, a phosphorus source is added to the product obtained in step (1), and the resulting mixture is treated under an inert gas atmosphere at a temperature of 60-300° C., such as 60-260° C., for 1-12 hours, such as 2-10 hours.

[0076] The preparation method of the present invention does not particularly require the type of phosphorus source used. However, in some embodiments, the phosphorus source is preferably selected from one or more phosphoric acid or phosphates, preferably one or more of phosphoric acid, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate, and more preferably one or more of phosphoric acid and ammonium dihydrogen phosphate. When the phosphorus source is selected from the above types, especially phosphoric acid or diammonium hydrogen phosphate, the overall performance of the hard carbon material, especially its capacity, is further improved.

[0077] The preparation method of the present invention has no special requirements for the specific amount of phosphorus source, as long as the final doping amount of phosphorus element is within the range defined by the present invention, but preferably, in some embodiments, the weight ratio of the product obtained in step (1) to the phosphorus element in the phosphorus source is 100:5 to 100:45, for example, 100:5 to 100:30. For example, the weight ratio of the product obtained in step (1) to the phosphorus element in the phosphorus source is 100:5, 100:6, 100:8, 100:10, 100:15, 100:20, 100:25, 100:30, 100:35, 100:40, or within the range defined by any two of them. In some embodiments, when the phosphorus source is selected from one or more of phosphoric acid, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate, the weight ratio of the product obtained in step (1) to the phosphorus source is 100:5 to 100:100, for example, 100:30 to 100:100. As an example, the weight ratio of the product obtained in step (1) to the phosphorus source is 100:5, 100:10, 100:15, 100:20, 100:25, 100:30, 100:35, 100:40, 100:45, 100:50, 100:55, 100:60, 100:65, 100:70, 100:75, 100:80, 100:85, 100:90, 100:95, 100:100, or within the range defined by any two of them. By controlling the amount of phosphorus source added, the P content of the hard carbon material can be adjusted and the disorder parameter f can be affected. a .

[0078] After the product obtained in step (1) is uniformly mixed with a phosphorus source, the mixture is treated at a temperature of 60-300° C., for example, 60-260° C., under an inert gas atmosphere for 1-12 hours, for example, 2-10 hours. As an example, the treatment temperature may be 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650 The temperature may be 25, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, 300° C., or within the range defined by any two of them, and / or the treatment time may be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 hours, or within the range defined by any two of them. As an example, the inert gas may be an inert gas commonly used by those skilled in the art, such as nitrogen, helium, argon, etc.

[0079] Step (3)

[0080] The product obtained in step (2) is pre-carbonized under an inert gas atmosphere at a temperature of 400-650° C., for example, 400-600° C., for 0.5-12 hours, for example, 1-8 hours.

[0081] The pre-carbonization temperature also affects the P content and disorder parameter f of the final hard carbon material. a It should be noted that the pre-carbonization temperature should not be too high to avoid the P in the material from forming high polyphosphate, which becomes difficult to remove and leads to excessively high P content in the final product. In some embodiments, the pre-carbonization temperature may be 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650°C, or within the range defined by any two of them, and / or the pre-carbonization time may be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12 hours, or within the range defined by any two of them. The inert gas may be an inert gas commonly used by those skilled in the art, such as nitrogen, helium, argon, etc.

[0082] Step (4)

[0083] After the mixture of the carbon source and the phosphorus source is pre-carbonized, the product obtained in step (3) is repeatedly washed with deionized water in step (4) until the pH of the product is in the range of 2.0-5.0, and is optionally dried.

[0084] By repeatedly washing with deionized water, some impurities in the product obtained in step (3) can be removed. Preferably, in some embodiments, in step (4), the product obtained in step (3) is washed with deionized water until the pH of the product is in the range of 2.0-5.0, for example, to a pH of 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0, or within the range defined by any two thereof.

[0085] In some embodiments, preferably, after washing with deionized water, the obtained product is dried to facilitate subsequent processes. The preparation method of the present invention has no special requirements for the drying process, and the drying can be carried out using a drying method commonly used by those skilled in the art.

[0086] Step (5)

[0087] In step (5), the product obtained in step (4) is treated with sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate powder or an aqueous solution thereof. Alkali treatment plays an important role in reducing the phosphorus content, and can remove phosphorus that cannot be washed off by water in step (4) and phosphorus on the carbon skeleton. If the alkaline treatment step is not added, the phosphorus content may exceed the limit.

[0088] In step (5), the product obtained in step (4) is uniformly mixed with at least one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate powder, and then sintered at a temperature of 500-900° C., for example, 550-850° C., under an inert gas atmosphere for 0.5-12 hours, for example, 2-10 hours; or

[0089] The product obtained in step (4) is stirred and soaked in at least one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate solution at a temperature of 20-100° C. for 1-12 hours, and then filtered to obtain a filter cake.

[0090] In step (5), the product obtained in step (4) can be treated in one of the two ways described above.

[0091] In some embodiments, the product obtained in step (4) is treated by means 1. For example, at least one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate powder, or a mixture of two or more thereof, may be added to the product obtained in step (4), uniformly mixed, and then sintered at a temperature of 500-900° C., for example, 550-850° C., under an inert gas atmosphere for 0.5-12 hours, for example, 2-10 hours. As an example, the sintering temperature may be 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840 The sintering temperature may be 0, 850, 860, 870, 880, 890, 900°C, or within the range defined by any two of them, and / or the sintering time may be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12 hours, or within the range defined by any two of them. The inert gas may be an inert gas commonly used by those skilled in the art, such as nitrogen, helium, argon, etc.

[0092] The preparation method of the present invention has no particular requirements on the amount of added sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate powder, as long as it is sufficient to adjust the product obtained in step (4) to alkaline, for example, pH greater than 10.0.

[0093] In some embodiments, the amount of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate powder added on a dry weight basis is in the range of 5-50 weight %, based on 100 weight % of the product obtained in step (4). As an example, the amount of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate powder added on a dry weight basis can be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 weight %, or within the range defined by any two of them.

[0094] In some embodiments, the product obtained in step (4) is treated by method 2. For example, the product obtained in step (4) can be stirred and soaked in at least one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate solution at a temperature of 20-100° C. for 1-12 hours, and then filtered to obtain a filter cake. As an example, the temperature for the stirring and soaking treatment can be 20, 25, 30, 35, 40, 45, 50, 60, 65, 70, 75, 80, 85, 90, 95, 100° C., or within the range defined by any two of them, and / or the time for the stirring and soaking treatment can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 hours, or within the range defined by any two of them.

[0095] Similarly, the preparation method of the present invention has no particular requirements on the amount of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate solution used, as long as it is sufficient to adjust the product obtained in step (4) to alkaline, for example, pH greater than 10.0.

[0096] In some embodiments, the concentration of the sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate solution is 0.5-40% by weight. As an example, the concentration of the sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate solution can be 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 25.0, 30.0, 35.0, 40.0% by weight, or within the range defined by any two of them.

[0097] Step (6)

[0098] In step (6), the product obtained in step (5) is repeatedly washed with deionized water until the pH of the product is in the range of 10.0-12.0.

[0099] Preferably, in some embodiments, the product obtained in step (5) is washed with deionized water in step (6) until the pH of the product is in the range of 10.0-12.0, for example, washed to a pH of 10.0, 10.5, 11.0, 11.5, 12.0, or within the range defined by any two of them.

[0100] Step (7)

[0101] In step (7), the product obtained in step (6) is stirred and soaked in an acid solution at a temperature of 20-100° C. for 1-12 hours, then filtered, and the filter cake is repeatedly washed with deionized water until its pH is in the range of 2.0-5.0, and then dried.

[0102] The product obtained in step (6) can be made acidic again by treating it with an acid solution. The preparation method of the present invention has no particular requirements for the acid solution used, but preferably, the concentration of the acid solution is 0.5-30% by weight, for example, 0.5-20% by weight or 1.0-15% by weight; and / or the acid solution is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, citric acid, and acetic acid, preferably one or more of hydrochloric acid, sulfuric acid, and nitric acid. As an example, the concentration of the acid solution can be 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 25.0, 30.0% by weight, or within the range defined by any two of them.

[0103] As described above, in step (7), the product obtained in step (6) is stirred and soaked in an acid solution at a temperature of 20-100° C. for 1-12 hours, and then filtered. As an example, the temperature for the stirring and soaking treatment can be 20, 25, 30, 35, 40, 45, 50, 60, 65, 70, 75, 80, 85, 90, 95, 100° C., or within the range defined by any two thereof, and / or the stirring and soaking treatment time can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 hours, or within the range defined by any two thereof.

[0104] In some embodiments, in step (7), the filtered product after the acid solution stirring and soaking treatment is washed repeatedly with deionized water until the pH of the product is in the range of 2.0-5.0, for example, washed to a pH of 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0, or within the range defined by any two of them.

[0105] In some embodiments, preferably, after washing with deionized water, the obtained product is dried to facilitate subsequent processes. The preparation method of the present invention has no special requirements for the drying process, and the drying can be carried out using a drying method commonly used by those skilled in the art.

[0106] Step (8)

[0107] In step (8), the product obtained in step (7) is crushed to Dv 50 The particle size is in the range of 1.0-20.0 μm.

[0108] The preparation method of the present invention has no particular limitation on the crushing method, and the crushing can be carried out by the methods commonly used in the art, such as air flow mill, mechanical mill, sand mill, ball mill, etc. As an example, the product obtained in step (7) can be crushed to D v The particle size is 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0 μm, or within the range defined by any two of them.

[0109] Step (9)

[0110] In step (9), the product obtained in step (8) is subjected to high-temperature carbonization at a temperature of 1050-1600° C., for example, 1200-1500° C., for 2-8 hours, for example, 2-6 hours, under an inert gas atmosphere, and is optionally crushed.

[0111] As an example, the high temperature carbonization temperature may be 1050, 1060, 1080, 1090, 1100, 1110, 1120, 1130, 1150, 1160, 1180, 1200, 1220, 1240, 1250, 1260, 1290, 1300, 1320, 1340, 1350, 1370, 1390, 1400, 1420, 1440, 1450, 1470, 1490, 1500, 1520, 1540, 1550, 1570, 1590, 1600°C, or within the range defined by any two of them, and / or the high temperature carbonization time may be 2, 3, 4, 5, 6, 7, 8 hours, or within the range defined by any two of them. As the high temperature carbonization temperature increases, the P content and f a May decline.

[0112] In some embodiments, the high-temperature carbonization product is optionally crushed so that the volume average particle size D of the obtained hard carbon material is v 50 is in the range of 1.0-20.0 μm, for example, 1.5-15.0 μm.

[0113] Negative electrode composition

[0114] A third aspect of the present invention provides a negative electrode composition, which is a negative electrode composition for a sodium ion secondary battery, and includes the negative electrode hard carbon material according to the first aspect of the present invention.

[0115] In addition to the negative electrode hard carbon material of the present invention, the negative electrode composition (for sodium ion secondary battery) may further include a conductive agent, a binder, and any other substances that can be used by those skilled in the art as needed, such as a dispersant and additives for improving stability.

[0116] In some embodiments, based on the dry weight of the negative electrode composition (for sodium ion secondary battery), the content of the negative electrode hard carbon material may be a common amount in the art, for example, 70-95 wt %, such as 80-90 wt %.

[0117] The type of conductive agent is not particularly limited, as long as it has the properties of enhancing the negative electrode conductivity and not adversely affecting the performance of the negative electrode hard carbon material. Those skilled in the art can select the conductive agent commonly used in the art according to actual needs. As an example, the conductive agent used for the negative electrode composition (for sodium ion secondary battery) can be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0118] In some embodiments, based on the dry weight of the negative electrode composition (for sodium ion secondary batteries), the content of the conductive agent may be a commonly used amount in the art, for example, 1-10 wt %, such as 2-5 wt %.

[0119] There is no particular limitation on the binder, as long as it has the properties of enhancing the adhesion between the negative electrode hard carbon material particles and the adhesion to the current collector and does not adversely affect the performance of the negative electrode hard carbon material. Those skilled in the art can select according to actual needs. As an example, the binder for the negative electrode composition for the sodium ion secondary battery can be selected from polyfluoroolefin binders such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA) or their modified (for example, carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives and one or more of styrene-butadiene rubber, acrylic resin, carboxymethyl cellulose, polyvinyl alcohol (PVA), etc.

[0120] In some embodiments, based on the dry weight of the negative electrode composition (for a sodium ion secondary battery), the content of the binder is 1-10 wt %, for example, 2-5 wt %.

[0121] The negative electrode composition may be in the form of a slurry, ie, it may further include a solvent. The negative electrode composition may also be in a dry form, ie, it does not include a solvent, for example, it may be in the form of a negative electrode active material layer disposed on a negative electrode current collector.

[0122] Sodium ion secondary batteries

[0123] A fourth aspect of the present invention provides a sodium ion secondary battery. A sodium ion secondary battery generally includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0124] In some embodiments, the sodium ion secondary battery may further include an outer packaging for encapsulating the electrode assembly and the electrolyte. For example, the outer packaging may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., or a soft package, such as a bag-type soft package, such as a soft package made of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0125] The shape of the sodium ion secondary battery is not particularly limited, and it may be cylindrical, square, or any other shape.

[0126] Sodium ion secondary batteries can be prepared by methods commonly used in the art. For example, the positive electrode sheet, the negative electrode sheet and the separator can be made into a battery cell through a winding process or a lamination process, and then the electrolyte is injected.

[0127] positive electrode

[0128] The positive electrode (or positive electrode sheet) includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0129] The positive electrode current collector is not particularly limited, and the positive electrode current collector commonly used by those skilled in the art can be used. As an example, the positive electrode current collector can be made of a metal foil such as aluminum foil, nickel foil, or a composite current collector. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), 1,3-propane sultone (PS), polyethylene (PE), etc.), but the present invention is not limited to these materials.

[0130] The present invention has no particular limitation on the positive electrode active material, and the positive electrode active material commonly used in the art can be used. For example, the positive electrode active material can be selected from one or more of layered transition metal oxides or Prussian blue analogs. As an example, the layered transition metal oxide can have the general formula Na x M y O2, wherein M is selected from one or more of Mn, Fe, Ni, Co, Cr, Ti, Zn, V, Al, Zr, Ce and Mg, and the general formula satisfies the valence balance. In addition, the layered transition metal oxide may be doped with an element with high electronegativity, such as one or more of S, N, F, Br, Cl, I, CN, etc. As an example, the positive electrode active material may be selected from NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3One or more of O2, Na2FeP2O7, Na4Fe3(PO4)2(P2O7), Na3V2(PO4)3, NaFePO4 and NaMnFe(CN)6, etc.

[0131] In some embodiments, based on the total weight (dry weight) of the positive electrode active material layer, the content of the positive electrode material may be a common amount in the art, for example, 70-95 wt %, such as 80-90 wt %.

[0132] In addition to the positive electrode active material, the positive electrode active material layer may further include a binder, a conductive agent, and any other optional auxiliary agents such as a thickener.

[0133] There is no particular requirement for the positive electrode conductive agent. As an example, the conductive agent can be selected from one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0134] In some embodiments, the conductive agent may be present in an amount of 1-10 wt %, for example, 2-5 wt %, based on the total weight (dry weight) of the positive electrode active material layer.

[0135] There is no special requirement for the positive electrode binder. As an example, the binder is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), styrene butadiene rubber (SBR), water-based acrylic resin and carboxymethyl cellulose (CMC).

[0136] In some embodiments, the binder may be present in an amount of 1-10 wt %, for example, 2-5 wt %, based on the total weight (dry weight) of the positive electrode active material layer.

[0137] The positive electrode sheet can be prepared according to the method commonly used in the art.

[0138] For example, the positive electrode can be formed by uniformly dispersing a positive electrode active material, a conductive agent, and a binder in a solvent (eg, N-methylpyrrolidone (NMP)) to obtain a positive electrode slurry; coating the slurry on a positive electrode current collector, drying, and pressing.

[0139] Alternatively, the positive electrode can also be formed by uniformly dispersing the positive electrode active material, the conductive agent, and the binder in a solvent (e.g., N-methylpyrrolidone (NMP)) to obtain a positive electrode slurry; casting the positive electrode slurry on a separate support, drying, separating the obtained positive electrode film from the support and laminating it on a positive electrode current collector.

[0140] negative electrode

[0141] The negative electrode comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode composition of the third aspect of the present invention, for example in dry form. The negative electrode also forms an aspect of the present invention.

[0142] The negative electrode current collector is not particularly limited, and the negative electrode current collector commonly used by those skilled in the art can be used. As an example, the negative electrode current collector can be a metal foil such as copper foil, aluminum foil or a composite current collector. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector can be formed by forming a metal material (copper, aluminum, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.), but the present invention is not limited to these materials.

[0143] The negative electrode can be prepared according to a method commonly used in the art.

[0144] For example, the negative electrode can be formed by uniformly dispersing the negative electrode active material and optional conductive agent, binder and thickener in a solvent (such as N-methylpyrrolidone (NMP) or deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, drying, and pressing.

[0145] Alternatively, the negative electrode can also be formed by uniformly dispersing the negative electrode active material and optional conductive agent, binder and thickener in a solvent (such as N-methylpyrrolidone (NMP) or deionized water) to form a negative electrode slurry; casting the negative electrode slurry on a separate support, drying, separating the obtained negative electrode film from the support and laminating it on a negative electrode current collector.

[0146] electrolytes

[0147] The electrolyte conducts ions between the positive and negative electrodes. The electrolyte is not particularly limited and can be selected as needed. For example, the electrolyte can be selected from at least one of a solid electrolyte, a gel electrolyte, and a liquid electrolyte (i.e., an electrolyte solution).

[0148] In some embodiments, the electrolyte is an electrolyte solution comprising an organic aprotic solvent and an electrolyte sodium salt.

[0149] In some embodiments, the solvent can be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).

[0150] In some embodiments, the electrolyte sodium salt can be selected from one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroborate (NaBF6), sodium bis(trifluoromethylsulfonyl)imide (NaFSI), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), sodium trifluoromethylsulfonate (NaTFS), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorobis(oxalatophosphate) (NaDFOP) and sodium tetrafluorooxalatophosphate (NaTFOP).

[0151] In some embodiments, the concentration of sodium ions in the electrolyte is 0.2-2 mol / L, for example, 0.5-1.0 mol / L.

[0152] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include additives that facilitate negative electrode film formation or positive electrode film formation, or additives that improve battery performance, such as additives that improve high or low temperature performance of the battery.

[0153] diaphragm

[0154] The separator is not particularly limited, and a commonly used porous structure separator with electrochemical stability and chemical stability can be used. For example, it can be a single layer or multilayer film of one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. When a solid electrolyte is used, the separator can also be omitted.

[0155] use

[0156] The fifth aspect of the present invention provides the use of the sodium ion secondary battery according to the fourth aspect of the present invention in an energy storage device for solar power generation, wind power generation, smart grid peak regulation, distributed power station, backup power supply or communication base station.

[0157] Those skilled in the art will appreciate that the sodium ion secondary battery of the fourth aspect of the present invention may also be used for other purposes. For example, the sodium ion secondary battery may be used as a power source or energy storage unit in mobile devices (e.g., mobile phones), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, electric bicycles, electric scooters, etc.), electric trains, etc.

[0158] Example

[0159] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0160] 1. Preparation Example

[0161] Example 1

[0162] High-temperature asphalt (particle size 500 mesh, sieve mesh number, the same below) with a softening point of 250°C was selected as the carbon source, and 100g of asphalt was treated at 220°C for 20h in an air atmosphere. The treated asphalt was then evenly mixed with 60g of phosphoric acid solution (50wt%) and treated at 250°C for 4h under a nitrogen atmosphere. The resulting product was then pre-carbonized at 500°C for 2h under a nitrogen atmosphere. After cooling to room temperature, the pre-carbonized product was repeatedly washed with deionized water until the pH of the product (i.e., the pH of the washing solution, the same below) was 2.5±0.5, and then dried at 120°C. After cooling to room temperature, 400ml of sodium hydroxide solution (20wt%) was added to the dried product, stirred and soaked at 80°C for 4h, and filtered. The filtered product (filter cake, the same below) was then repeatedly washed with deionized water until the pH of the product was 11±0.5. 400 ml of hydrochloric acid solution (15 wt%) was added to the obtained product, and the mixture was stirred and soaked at 80 ° C for 4 h, and then filtered. The filtered product (filter cake, the same below) was then repeatedly washed with deionized water until the pH of the product was 2.5 ± 0.5, and then dried at 120 ° C. The dried product was ball milled using a ball mill (model: SFM-3 high-speed three-dimensional pendulum ball mill, manufacturer: Shenzhen Kejing Zhida Technology Co., Ltd., the same below) until the product D v The particle size is 10.5 μm. The ball-milled product is then carbonized at 1500°C for 3 hours in an argon atmosphere and then cooled to room temperature to obtain the final product, hard carbon. v 50The particle size is 9.3μm.

[0163] Example 2

[0164] High-temperature asphalt (500 mesh size) with a softening point of 250°C was selected as the carbon source. The experimental steps were the same as in Example 1, but the amount of phosphoric acid (50 wt%) was 100 g. The D v 50 The particle size is 9.7μm.

[0165] Example 3

[0166] High-temperature asphalt (500 mesh size) with a softening point of 250°C was selected as the carbon source. The experimental steps were the same as in Example 1, but the amount of phosphoric acid (50 wt%) was 140 g. The D v 50 The particle size is 9.8μm.

[0167] Example 4

[0168] High-temperature asphalt (500 mesh size) with a softening point of 250°C was selected as the carbon source. The experimental steps were the same as in Example 1, but the amount of phosphoric acid (50 wt%) was 180 g. The D v 50The particle size is 9.5μm.

[0169] Comparative Example 1

[0170] High-temperature asphalt (particle size 500 mesh) with a softening point of 250°C was selected as the carbon source, and 100g of asphalt was treated at 280°C for 12h in an air atmosphere. The treated asphalt was then pre-carbonized at 500°C for 2h in a nitrogen atmosphere. After cooling to room temperature, 400ml of sodium hydroxide solution (20wt%) was added to the pre-carbonized product, and stirred and soaked at 80°C for 4h, and filtered. Subsequently, deionized water was used for repeated washing until the pH of the product was 11±0.5. 400ml of hydrochloric acid solution (15wt%) was added to the resulting product, and stirred and soaked at 80°C for 4h, and filtered, and subsequently washed repeatedly with deionized water until the pH of the product was 2.5±0.5, and then dried at 120°C. The dried product was ball milled using a ball mill to obtain product D v The particle size is 10.5 μm. The ball-milled product is then carbonized at 1500°C for 3 h in an argon atmosphere and then cooled to room temperature to obtain the final product, hard carbon. v 50 The particle size is 9.8μm.

[0171] Comparative Example 2

[0172] High-temperature asphalt (500 mesh) with a softening point of 250°C was selected as the carbon source. The experimental steps were the same as in Example 1, but the amount of phosphoric acid (50 wt%) was 220 g. The D v 50 The particle size is 9.7μm.

[0173] Example 5

[0174] Coconut shell (particle size 80 mesh) was selected as the carbon source, and 100g of coconut shell was treated at 120°C for 12h under an air atmosphere. The treated coconut shell was then evenly mixed with 60g of phosphoric acid (50wt%) and treated at 150°C for 4h under a nitrogen atmosphere. The resulting product was then pre-carbonized at 400°C for 2h under a nitrogen atmosphere. After cooling to room temperature, the pre-carbonized product was repeatedly washed with deionized water until the pH was 2.5±0.5 and dried at 120°C. After cooling to room temperature, 400ml of potassium hydroxide solution (20wt%) was added to the dried product, stirred and soaked at 80°C for 4h, and filtered. The filtered product was then repeatedly washed with deionized water until the pH of the product was 11±0.5. 400 ml of nitric acid solution (10 wt%) was added to the obtained product and stirred at 80 ° C for 4 h, and filtered. The filtered product was then repeatedly washed with deionized water until the pH of the product was 2.5 ± 0.5, and then dried at 120 ° C. The dried product was ball milled using a ball mill to obtain product D v The particle size is 6.0 μm. The ball-milled product is then carbonized at 1400°C for 3 hours in an argon atmosphere and then cooled to room temperature to obtain the final product, hard carbon. v 50The particle size is 5.5μm.

[0175] Example 6

[0176] Coconut shell (80 mesh size) was selected as the carbon source. The experimental steps were the same as those in Example 5, but the pre-carbonization temperature was 500°C. The D v 50The particle size is 5.2μm.

[0177] Example 7

[0178] Coconut shell (80 mesh size) was selected as the carbon source. The experimental steps were the same as those in Example 5, but the pre-carbonization temperature was 600°C. The D v 50The particle size is 5.3μm.

[0179] Comparative Example 3

[0180] Coconut shell (80 mesh size) was selected as the carbon source. The experimental steps were the same as those in Example 5, but the pre-carbonization temperature was 700°C. The D v 50The particle size is 5.2μm.

[0181] Comparative Example 4

[0182] Coconut shell (particle size 80 mesh) was selected as the carbon source, and 100g of coconut shell was treated at 150°C for 12h under an air atmosphere. The treated coconut shell was then evenly mixed with 60g of phosphoric acid (50wt%) and treated at 200°C for 2h under a nitrogen atmosphere. The resulting product was pre-carbonized at 500°C for 2h under a nitrogen atmosphere. After cooling to room temperature, the pre-carbonized product was repeatedly washed with deionized water until the pH was 2.5±0.5, and dried at 120°C. After cooling to room temperature, 400ml of hydrochloric acid solution (15wt%) was added to the resulting product, stirred and soaked at 80°C for 4h, and filtered. The filtered product was then repeatedly washed with deionized water until the pH of the product was 2.5±0.5, and then dried at 120°C. The dried product was ball milled using a ball mill until product D v The particle size is 6.0 μm. The ball-milled product is then carbonized at 1400°C for 3 hours in an argon atmosphere and then cooled to room temperature to obtain the final product, hard carbon. v 50 The particle size is 5.4μm.

[0183] Comparative Example 5

[0184] Coconut shell (80 mesh size) was selected as the carbon source. The experimental steps were the same as those in Comparative Example 1, except that the high-temperature carbonization temperature was 1400°C and the sodium hydroxide solution (20 wt%) was replaced by potassium hydroxide solution (20 wt%). The D v 50The particle size is 5.3μm.

[0185] Comparative Example 6

[0186] Coconut shell (80 mesh size) was selected as the carbon source. The experimental steps were the same as those in Example 5, but the pre-carbonization temperature was 500°C and the high-temperature carbonization temperature was 1000°C. The D v 50The particle size is 5.5μm.

[0187] Example 8

[0188] Coconut shell (80 mesh size) was selected as the carbon source. The experimental steps were the same as those in Example 5, but the pre-carbonization temperature was 500°C and the high-temperature carbonization temperature was 1200°C. The D v 50The particle size is 5.2μm.

[0189] Example 9

[0190] Coconut shell (80 mesh size) was selected as the carbon source. The experimental steps were the same as those in Example 5, but the pre-carbonization temperature was 500°C and the high-temperature carbonization temperature was 1500°C. The D v 50The particle size is 5.3μm.

[0191] Example 10

[0192] Bituminous coal (particle size 500 mesh) was selected as the carbon source, and 100g of bituminous coal was treated at 220°C for 12h in an air atmosphere. The treated bituminous coal was then evenly mixed with 100g of phosphoric acid (50wt%) and treated at 250°C for 4h in a nitrogen atmosphere. The resulting product was pre-carbonized at 500°C for 2h in a nitrogen atmosphere. After cooling to room temperature, the pre-carbonized product was repeatedly washed with deionized water until the pH was 2.5±0.5, and dried at 120°C. After cooling to room temperature, 400ml of sodium hydroxide solution (20wt%) was added to the dried product, stirred and soaked at 80°C for 4h, and filtered. The filtered product was then repeatedly washed with deionized water until the pH of the product was 11±0.5. 400 ml of nitric acid solution (10 wt%) was added to the obtained product and stirred at 80 ° C for 4 h, and filtered. The filtered product was then repeatedly washed with deionized water until the pH of the product was 2.5 ± 0.5, and then dried at 120 ° C. The dried product was ball milled using a ball mill to obtain product D v The particle size is 8.0 μm. The ball-milled product is then carbonized at 1400°C for 3 hours in an argon atmosphere and then cooled to room temperature to obtain the final product, hard carbon. v 50The particle size is 7.2μm.

[0193] Example 11

[0194] Lignite with a particle size of 500 mesh was selected as the carbon source, and 100g of lignite was treated at 150°C for 8h in an air atmosphere. The treated lignite was then evenly mixed with 100g of phosphoric acid (50wt%) and treated at 200°C for 4h in a nitrogen atmosphere. The resulting product was then pre-carbonized at 500°C for 2h in a nitrogen atmosphere. After cooling to room temperature, the pre-carbonized product was repeatedly washed with deionized water until the pH of the product was 11±0.5, and dried at 120°C. After cooling to room temperature, 400ml of sodium hydroxide solution (20wt%) was added to the dried product, stirred and soaked at 80°C for 4h, and filtered. The resulting product was then repeatedly washed with deionized water until the pH of the product was 11±0.5. 400 ml of sulfuric acid solution (10 wt%) was added to the obtained product and stirred at 80 ° C for 4 h, filtered, and then repeatedly washed with deionized water until the pH of the product was 2.5 ± 0.5, and dried at 120 ° C. The dried product was ball milled using a ball mill to obtain product D v The particle size is 8.0 μm. The ball-milled product is then carbonized at 1400°C for 3 hours in an argon atmosphere and then cooled to room temperature to obtain the final product, hard carbon. v 50The particle size is 7.1μm.

[0195] Example 12

[0196] Corn starch (15.2 μm) was selected as the carbon source, and 100 g of starch was treated at 220 ° C for 12 h in an air atmosphere. The treated starch was then evenly mixed with 60 g of phosphoric acid (50 wt%) and treated at 150 ° C for 4 h in a nitrogen atmosphere. The resulting product was pre-carbonized at 500 ° C for 2 h in a nitrogen atmosphere. After cooling to room temperature, the pre-carbonized product was repeatedly washed with deionized water until the pH of the product was 2.5 ± 0.5, and dried at 120 ° C. After cooling to room temperature, 400 ml of sodium hydroxide solution (20 wt%) was added to the dried product, stirred and soaked at 80 ° C for 4 h, and filtered. The product was then repeatedly washed with deionized water until the pH of the product was 11 ± 0.5. 400 ml of hydrochloric acid solution (8 wt%) was added to the obtained product and stirred and soaked at 80 ° C for 4 h, filtered, and then repeatedly washed with deionized water until the pH of the product was 2.5 ± 0.5, and dried at 120 ° C. The dried product was ball milled using a ball mill to obtain product D v The particle size is 8.0 μm. The ball-milled product is then carbonized at 1400°C for 3 hours in an argon atmosphere and then cooled to room temperature to obtain the final product, hard carbon. v 50 The particle size is 7.4μm.

[0197] Example 13

[0198] Dry bamboo (80 mesh bamboo powder) was selected as the carbon source, and the experimental steps were the same as in Example 12. The D v 50The particle size is 7.1μm.

[0199] Example 14

[0200] Coconut shell (80 mesh size) was selected as the carbon source. The experimental steps were the same as those in Example 6, except that phosphoric acid (50 wt%) was replaced by ammonium dihydrogen phosphate solution (50 wt%), and potassium hydroxide solution (20 wt%) was replaced by sodium hydroxide solution (20 wt%). The D of the obtained hard carbon was v 50The particle size is 5.3μm.

[0201] Example 15

[0202] Coconut shell (80 mesh size) was selected as the carbon source. The experimental steps were the same as those in Example 6, except that phosphoric acid (50 wt%) was replaced by sodium dihydrogen phosphate solution (50 wt%), and potassium hydroxide solution (20 wt%) was replaced by sodium hydroxide solution (20 wt%). The D of the obtained hard carbon was v 50The particle size is 5.1μm.

[0203] Example 16

[0204] Coconut shell (80 mesh size) was selected as the carbon source. The experimental steps were the same as those in Example 6, except that phosphoric acid (50 wt%) was replaced by potassium dihydrogen phosphate solution (50 wt%), and potassium hydroxide solution (20 wt%) was replaced by sodium hydroxide solution (20 wt%). The D of the obtained hard carbon was v 50The particle size is 5.3μm.

[0205] Example 17

[0206] Coconut shell (80 mesh size) was selected as the carbon source, and 100g of coconut shell was treated at 120°C for 12 hours under an air atmosphere. The treated coconut shell was then evenly mixed with 60g of phosphoric acid (50wt%) and treated at 150°C for 4 hours under a nitrogen atmosphere. The resulting product was then pre-carbonized at 500°C for 2 hours under a nitrogen atmosphere. After cooling to room temperature, the pre-carbonized product was repeatedly washed with deionized water until the pH was 2.5±0.5 and dried at 120°C. 20wt% sodium hydroxide powder (based on the weight of the dried product, the same below) was added to the dried product, mixed evenly, and sintered at 550°C for 2 hours under an inert gas atmosphere. The product was then repeatedly washed with deionized water until the pH was 11±0.5. 400 ml of nitric acid solution (10 wt%) was added to the obtained product and stirred at 80 ° C for 4 h, and filtered. The filtered product was then repeatedly washed with deionized water until the pH of the product was 2.5 ± 0.5, and then dried at 120 ° C. The dried product was ball milled using a ball mill to obtain product D v The particle size is 6.0 μm. The ball-milled product is then carbonized at 1400°C for 3 hours in an argon atmosphere and then cooled to room temperature to obtain the final product, hard carbon. v 50The particle size is 5.2μm.

[0207] Example 18

[0208] Coconut shell (80 mesh size) was used as the carbon source. The experimental steps were the same as in Example 17, except that the sodium hydroxide powder was replaced with potassium hydroxide powder. v 50The particle size is 5.0μm.

[0209] Comparative Example 7

[0210] Coconut shell (80 mesh size) was used as the carbon source. The experimental steps were the same as in Example 17, except that the sodium hydroxide powder was replaced with calcium carbonate powder. v 50The particle size is 5.1μm.

[0211] Example 19

[0212] Coconut shell (particle size 80 mesh) was selected as the carbon source, and 100g of coconut shell was treated at 120°C for 12h under an air atmosphere. The treated coconut shell was then evenly mixed with 60g of phosphoric acid (50wt%) and treated at 150°C for 4h under a nitrogen atmosphere. The resulting product was then pre-carbonized at 500°C for 2h under a nitrogen atmosphere. After cooling to room temperature, the pre-carbonized product was repeatedly washed with deionized water until the pH was 2.5±0.5 and dried at 120°C. After cooling to room temperature, 400ml of potassium carbonate solution (20wt%) was added to the dried product, stirred and soaked at 100°C for 4h, and filtered. The filtered product was then repeatedly washed with deionized water until the pH of the product was 11±0.5. 400 ml of nitric acid solution (10 wt%) was added to the obtained product and stirred at 80 ° C for 4 h, and filtered. The filtered product was then repeatedly washed with deionized water until the pH of the product was 2.5 ± 0.5, and then dried at 120 ° C. The dried product was ball milled using a ball mill to obtain product D v The particle size is 6.0 μm. The ball-milled product is then carbonized at 1400°C for 3 hours in an argon atmosphere and then cooled to room temperature to obtain the final product, hard carbon. v 50 The particle size is 5.4μm.

[0213] 2. Evaluation Example

[0214] 1.BET and aperture

[0215] Refer to GB / T 19587-2017, "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method," for testing. Place a hard carbon material (30-500 mg) into a sample tube and degas. After degassing, turn off the heating power. After the sample cools to room temperature, backfill with helium and weigh the sample tube. Place the weighed sample tube into a BET surface area analyzer (Jingwei Gaobo JW-DX) and enter the sample mass into the analysis file. Click the instrument to begin the adsorption and desorption test process. The results are automatically output after the test.

[0216] 2.D v 50 Particle Size Test Method

[0217] The test was performed using a Malvern 3000 laser particle size analyzer. Carbon was selected as the standard substance, and dishwashing liquid (Liby Fresh Lemon Dishwashing Liquid (product code 06920174736779)) and water (volume ratio of dishwashing liquid: water = 1:3) were used as the dispersant. The following instrument test parameters were set: test time 10 seconds, test number 3, shading 6-15%, stirring speed 2800 r / min, ultrasonic mode on, power 50%. Click the laser particle size analyzer (Malvern 3000 laser particle size analyzer) to start the test, then add the primary sintered product or cathode material to the sample cell, controlling the amount added to adjust the sample cell shading to 6-15%. The instrument automatically repeated the test three times, and the average of the three tests was taken as the test result mean.

[0218] 3.P content

[0219] Accurately weigh approximately 0.1g of a hard carbon sample into a 50ml polytetrafluoroethylene digestion tube. Add 5ml of a 3:1 ratio of concentrated hydrochloric acid (36-38 wt%) and concentrated nitric acid (65-68 wt%) to the weighed sample digestion tube. Cover the tube and place it in a stainless steel reactor. Heat it in an oven at 180°C for approximately 10 hours, then stop heating and cool it to room temperature. Transfer the cooled solution to a 50ml volumetric flask and calibrate to volume with ultrapure water. Prepare a single element phosphorus standard solution using 1% HNO₃ as a medium. Prepare 50ml of calibration standards at concentrations of 0, 5, 10, 20, and 50mg / L. Use the calibration standards to construct a calibration curve for the standard solutions using an ICP-OES (inductively coupled plasma optical emission spectrometer). Then test the digested solutions one by one. If the upper limit of the curve is exceeded (the lower detection limit is 0.001 wt%), dilute the solution and retest. (The volume of the dilution solution used should be considered when calculating the phosphorus content.) Finally, the concentration of element P in the dilution of each sample was determined based on the measurement results of each sample and the calibration curve of the standard solution. The final content of element P was calculated based on the volume of the dilution to obtain the test results.

[0220] 4. Small-angle X-ray scattering

[0221] The Xenocs Xeuss 2.0 SAXS / WAXS system was used, with a copper X-ray source of 30W power (wavelength 0.1542nm) and an X-ray spot size of 0.8mm × 0.8mm. The virtual detector mode with three combined images was used, with a sample-camera distance of 0.55m. The corresponding scattering vector Q value was The measured intensity was calibrated for absolute intensity using glassy carbon as a standard sample, eliminating the influence of all relevant factors (including sample thickness, air, and sample holder scattering). Two-dimensional scattering data (scattering intensity data within a 2θ angle (conical) range centered on the beam axis, with different colors representing different scattering intensities) were converted to one-dimensional data (a set of data consisting of scattering vectors and corresponding scattering intensities) using Foxtrot 3.2.4 software. The one-dimensional data curves were fitted using SasView 5.0.6 software to obtain d and ξ.

[0222] The disorder parameter f of hard carbon materials a The average pore diameter can be calculated by using the parameters d and ξ obtained by fitting the small-angle X-ray scattering data of hard carbon materials and putting them into the following formula:

[0223] Some of the preparation conditions and physicochemical properties of the hard carbon materials of Examples 1-19 and Comparative Examples 1-7 are summarized in Table 1.

[0224] 5. Electrochemical performance test

[0225] Manufacturing of sodium-ion secondary batteries:

[0226] To prepare button cells, 0.45 g of hard carbon material, 0.025 g of SP (Swiss Terme high conductive carbon black SUPER-P), and 0.25 g of polyvinylidene fluoride (PVDF, purchased from SOLVAY as PVDF5130) glue (10% by mass, solvent: N-methylpyrrolidone (NMP)) were uniformly mixed, and then N-methylpyrrolidone was added to form a viscous glue. The glue was coated on aluminum foil (thickness 16 μm) and then baked in a vacuum drying oven at 120°C for 12 h to obtain a negative electrode sheet (active material mass 4 mg / cm 2 A sodium metal sheet (Aladdin) was used as the counter electrode (thickness 300±50μm). A glass fiber (Waterman) was used as the separator (thickness 675μm). A NaPF6 solution with a sodium ion concentration of 1 mol / L (the solvent was a mixture of EC and DMC, with a volume ratio of EC / DMC = 1:1) was used as the electrolyte. 2032 button cells were assembled in an Ar atmosphere protective glove box.

[0227] Manufacturing of 26700 cylindrical battery cells (26mm diameter, 70mm height):

[0228] (1) Preparation of positive electrode sheet:

[0229] The layered oxides NaCu were mixed in a mass ratio of 96.5:1.5:1.5:0.5 1 / 9 Ni 2 / 9 Fe1 / 3 Mn 1 / 3 O2, Super-P, PVDF and carbon nanotubes were then uniformly dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry; the positive electrode slurry was evenly coated on both sides of an aluminum foil (thickness of 12 μm) with a single-side surface density of 16.0 mg / cm 2 After drying and calendering (compacted density is 3.1mg / cm 3 ) and vacuum dried, and then welded with an aluminum lead wire using an ultrasonic welder to obtain a positive electrode sheet.

[0230] (2) Preparation of negative electrode sheet:

[0231] The hard carbon material of the present invention, Super-P, SBR and CMC were mixed in a mass ratio of 94.5:1.5:2.5:1.5, and then uniformly dispersed in deionized water to obtain a negative electrode slurry; the negative electrode slurry was coated on both sides of a copper foil (thickness of 8 μm) with a single-side surface density of 9 mg / cm 2 (Charge N / P ratio is 1.10), after drying and calendering (compacted density is 0.90mg / cm 3 ) and vacuum dried, and then welded with nickel lead wires using an ultrasonic welder to obtain the negative electrode sheet.

[0232] (3) Preparation of battery cells:

[0233] A double-sided ceramic-coated PE film with a thickness of 16 μm (12 μm separator, double-sided coating, 2 μm coating on each side) was placed between the positive electrode sheet and the negative electrode sheet. The sandwich structure consisting of the positive electrode sheet, the negative electrode sheet and the separator was then wound, and the wound body was placed in a 26700 cylindrical battery cell steel shell. The electrolyte was then injected (by weight percentage, the composition is: 28% EC, 28% PC, 28% DEC, 12.5% ​​NaPF6, 1% VC, 2% FEC, 0.5% PS; the injection coefficient is 4.0 g / Ah), and the battery preparation was completed after assembly.

[0234] 5.1 Charge Gram Capacity

[0235] After the button cell is assembled, place it at 25°C and discharge it at a constant current of 20 mA / g to 0 V. The battery rests for 10 minutes. Then, discharge it at a constant current of 4 mA / g to 0 V, rest for 5 minutes. The battery is then charged at a constant current of 20 mA / g to 2.0 V, and the charge specific capacity is recorded. Repeat this test three times. The average of the three charge specific capacities is the charge specific capacity test result.

[0236] 5.2 First Coulombic Efficiency

[0237] After the button battery is assembled, it is placed at a temperature of 25°C, discharged at a constant current density of 20 mA / g to 0 V, allowed to stand for 10 minutes, and then discharged at a constant current density of 4 mA / g to 0 V, and the sum of the two discharge specific capacities is recorded as the first discharge specific capacity; then allowed to stand for 5 minutes, charged at a constant current density of 20 mA / g to 2.0 V, and the charging specific capacity this time is recorded as the first charging specific capacity; the first charging specific capacity / first discharge specific capacity × 100% is the first coulombic efficiency.

[0238] 5.3 Cycle retention rate

[0239] At 25°C, charge the 26700 cylindrical battery cell at a constant current rate of 1C to 4.0V, then charge it at a constant voltage until the current is less than or equal to 0.1C, then let it stand for 10 minutes, and then discharge it at a constant current of 1C to 2.0V, then let it stand for 10 minutes. This is a charge and discharge cycle, and the discharge capacity is recorded as the discharge capacity of the first cycle of the battery. The battery is charged and discharged 100 times according to the above method, and the discharge capacity of the 100th cycle is recorded. The cycle retention rate is then calculated as the discharge capacity of the 100th cycle / the discharge capacity of the 1st cycle × 100%.

[0240] The electrochemical performance test results of the sodium ion secondary batteries prepared from the hard carbon materials of Examples 1-19 and Comparative Examples 1-7 are summarized in Table 2.

[0241] Table 2 Electrochemical performance test results of sodium ion secondary batteries

[0242] Combining Table 1 and Table 2, it can be seen that relative to the P content and f a Compared with Comparative Examples CE1 to CE7, in which any one of the values ​​is not within the specified range, Examples E1 to E19 are generally significantly better in terms of discharge capacity, first coulombic efficiency, and cycle retention.

[0243] Comparing Examples E1 and E2 with Comparative Examples CE1 and CE3 reveals that the primary difference lies in the P contents of E1 and E2 being 0.026 wt% and 0.044 wt%, respectively, while no P was detected in CE1 and the P content in CE3 was 0.310 wt%. E1 and E2 significantly outperformed CE1 and CE3 in terms of overall discharge capacity, initial coulombic efficiency, and cycle retention. Similar patterns were observed when comparing E1-E2 and CE4-CE5.

[0244] Comparing Examples E4 and E8 with Comparative Examples CE2 and CE6, it can be found that the main difference between them is that f a are 0.29 and 0.62 respectively, while in CE2 ais 0.20, f in CE6 a The discharge capacity, first coulombic efficiency and cycle retention rate of E4 and E8 are significantly better than those of CE2 and CE6 respectively.

[0245] It can be seen that the present invention regulates the P content and f a Within a limited range, the discharge capacity, first coulombic efficiency and cycle retention rate of the negative electrode hard carbon material can be effectively improved.

[0246] The above description is merely an exemplary embodiment of the present invention. It should be noted that, for those skilled in the art, improvements can be made to the present invention without departing from the inventive concept of the present invention, and these improvements all fall within the scope of protection of the present invention.

Claims

1. A negative hard carbon material for a sodium-ion secondary battery, which satisfies: The phosphorus content ranges from 0.001 wt% ≤ P ≤ 0.300 wt%, for example 0.005 wt% ≤ P ≤ 0.250 wt% or 0.010 wt% ≤ P ≤ 0.160 wt% or 0.010 wt% ≤ P ≤ 0.100 wt%, based on the total weight of the negative hard carbon material; and Disorder parameter f a has a range of 0.25 ≤ f a ≤ 0.75, for example 0.29 ≤ f a ≤ 0.50 or 0.33 ≤ f a ≤ 0.50 or 0.33 ≤ f a ≤ 0.46, where f a is calculated by the following formula: Among them where d is between two adjacent pores in the negative hard carbon material The average spacing calculated, where ξ is the one that restricts the extension of long-range order The relevant lengths, d and ξ, are obtained by fitting the small-angle X-ray scattering data of the negative hard carbon material.

2. The negative hard carbon material according to claim 1, wherein the average pore diameter of the negative hard carbon material is 1.5 - 3.0 nm, for example 1.5 - 2.5 nm or 1.7 - 2.3 nm.

3. The negative electrode hard carbon material according to any one of claims 1 or 2, wherein the BET specific surface area of the negative electrode hard carbon material is 1.0 - 35.0 m 2 / g, for example 3.0 - 35.0 m 2 / g or 4.5 - 14.5 m 2 / g.

4. The negative electrode hard carbon material according to any one of claims 1 to 3, wherein the volume average particle diameter D v 50 ranges from 1.0 to 20.0 μm, for example 1.5 to 15.0 μm.

5. A method for preparing the negative hard carbon material according to any one of claims 1 to 4, comprising: (1) Treating a carbon source in an air atmosphere at a temperature of 60 - 300 °C, for example 80 - 280 °C, for 1 - 24 hours, for example 2 - 20 hours; (2) Adding a phosphorus source to the product obtained in step (1), and then treating the resulting mixture in an inert gas atmosphere at a temperature of 60 - 300 °C, for example 60 - 260 °C, for 1 - 12 hours, for example 2 - 10 hours; (3) Pre-carbonizing the product obtained in step (2) in an inert gas atmosphere at a temperature of 400 - 650 °C, for example 400 - 600 °C, for 0.5 - 12 hours, for example 1 - 8 hours; (4) Repeatedly washing the product obtained in step (3) with deionized water until the pH of the product is in the range of 2.0 - 5.0, and optionally drying; (5) Uniformly mixing the product obtained in step (4) with at least one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate powders, and then sintering in an inert gas atmosphere at a temperature of 500 - 900 °C, for example 550 - 850 °C, for 0.5 - 12 hours, for example 2 - 10 hours; or Stirring and soaking the product obtained in step (4) with at least one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate solutions at a temperature of 20 - 100 °C for 1 - 12 h, and then filtering to obtain a filter cake; (6) Repeatedly washing the product obtained in step (5) with deionized water until the pH of the product is in the range of 10.0 - 12.0; (7) Stirring and soaking the product obtained in step (6) with an acid solution at a temperature of 20 - 100 °C for 1 - 12 h, then filtering, and repeatedly washing the filter cake with deionized water until its pH is in the range of 2.0 - 5.0, and then drying; (8) Crush the product obtained in step (7) to D v 50 with a particle size in the range of 1.0 - 20.0 μm; and (9) High-temperature carbonizing the product obtained in step (8) in an inert gas atmosphere at a temperature of 1050 - 1600 °C, for example 1200 - 1500 °C, for 2 - 8 hours, for example 2 - 6 hours, and optionally crushing.

6. The method according to claim 5, wherein the carbon source is selected from one or more of coal, pitch, and biomass; Preferably, the coal is selected from one or more of bituminous coal and lignite; Preferably, the pitch is selected from one or more of medium-temperature pitch and high-temperature pitch; Preferably, the biomass is selected from one or more of coconut shell, walnut shell, apricot shell, palm shell, lignin, cellulose, starch, and bamboo.

7. The method according to claim 5 or 6, wherein the phosphorus source is selected from one or more of phosphoric acid or phosphate, preferably selected from one or more of phosphoric acid, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate; Preferably, the weight ratio of the product obtained in step (1) to the phosphorus element in the phosphorus source is 100:5 to 100:45, such as 100:5 to 100:30; Preferably, when the phosphorus source is selected from one or more of phosphoric acid, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate, the weight ratio of the product obtained in step (1) to the phosphorus source is 100:5 to 100:100, such as 100:30 to 100:

100.

8. The method according to any one of claims 5 to 7, wherein in step (5), one or more of the following conditions are satisfied: Based on 100% by weight of the product obtained in step (4), the addition amount of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate powder in terms of dry weight is in the range of 5-50% by weight; and / or The concentration of the sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, sodium bicarbonate or potassium bicarbonate solution is 0.5-40% by weight.

9. The method according to any one of claims 5 to 8, wherein in step (7), the concentration of the acid solution is 0.5-30% by weight; and / or The acid solution is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, citric acid, and acetic acid.

10. A negative electrode composition for a sodium-ion secondary battery, which comprises the negative electrode hard carbon material according to any one of claims 1 to 4.

11. A sodium-ion secondary battery, which comprises the negative electrode composition for a sodium-ion secondary battery according to claim 10.

12. Use of the sodium-ion secondary battery according to claim 11 in an energy storage device for solar power generation, wind power generation, smart grid peak shaving, distributed power stations, backup power supplies or communication base stations.

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