Preparation method of negative electrode material, negative electrode material, negative electrode sheet and battery

Abstract

The application relates to a preparation method of a negative electrode material, the negative electrode material, a negative electrode sheet and a battery. The preparation method of the negative electrode material comprises the following steps: S1, pre-carbonization treatment is conducted on a hard carbon precursor under a first inert gas atmosphere, and a pre-carbonization product is obtained; S2, the pre-carbonization product is crushed, and a crushed pre-carbonization material is obtained; S3, activation gas is introduced, the crushed pre-carbonization material is placed in a fluidized state, activation pore-forming treatment is conducted on the crushed pre-carbonization material, and a porous activation material is obtained; the activation gas comprises carbon dioxide and hydrogen; and S4, high-temperature carbonization treatment is conducted on the porous activation material under a second inert gas atmosphere, and a negative electrode material is obtained. In this way, the reversible capacity and the cycle performance of the prepared negative electrode material can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a preparation method of a negative electrode material, the negative electrode material, a negative electrode sheet and a battery. BACKGROUND

[0002] Sodium-ion batteries have similar working principles as lithium-ion batteries, and have advantages of low cost and high safety over lithium-ion batteries. Therefore, sodium-ion batteries are increasingly widely applied in the field of new energy.

[0003] In the development of sodium-ion battery systems, hard carbon materials have become a suitable choice for sodium-ion battery negative electrode materials due to their advantages of abundant resources and suitable cost. However, the hard carbon negative electrode materials prepared at present generally have problems of low reversible capacity and poor cycle performance. SUMMARY

[0004] Therefore, the embodiments of the present application provide a preparation method of a negative electrode material, the negative electrode material, a negative electrode sheet and a battery to solve at least one problem in the background art.

[0005] In a first aspect, the embodiments of the present application provide a preparation method of a negative electrode material, which comprises the following steps:

[0006] S1: performing pre-carbonization treatment on a hard carbon precursor under a first inert gas atmosphere to obtain a pre-carbonization product;

[0007] S2: performing crushing treatment on the pre-carbonization product to obtain a crushed pre-carbonization material;

[0008] S3: introducing an activation gas, placing the crushed pre-carbonization material in a fluidized state, performing activation and pore-forming treatment on the crushed pre-carbonization material to obtain a porous activation material; the activation gas comprises carbon dioxide and hydrogen;

[0009] S4: performing high-temperature carbonization treatment on the porous activation material under a second inert gas atmosphere to obtain the negative electrode material.

[0010] In combination with the first aspect of the present application, in an optional embodiment, step S1 satisfies at least one of the following characteristics:

[0011] (1) the oxygen concentration in the first inert gas atmosphere is less than or equal to 50 ppm;

[0012] (2) the pre-carbonization treatment has a heating rate of 1 ℃ / min to 5 ℃ / min;

[0013] (3) the pre-carbonization treatment comprises a first pre-carbonization treatment and a second pre-carbonization treatment, the temperature of the first pre-carbonization treatment is 150-250°C, and the time of the first pre-carbonization treatment is 1-4 hours; the temperature of the second pre-carbonization treatment is 500-700°C, and the time of the second pre-carbonization treatment is 1-10 hours;

[0014] (4) the hard carbon precursor comprises natural resin and / or synthetic resin; optionally, the natural resin comprises rosin resin and / or amber resin; the synthetic resin comprises at least one of phenolic resin, epoxy resin, and phenolic epoxy resin;

[0015] (5) the pre-carbonization product comprises oxygen-containing functional groups.

[0016] In combination with the first aspect of the present application, in an optional implementation, the particle size D50 of the crushed pre-carbonization material is 5-10 μm.

[0017] In combination with the first aspect of the present application, in an optional implementation, step S3 satisfies at least one of the following features:

[0018] (1) the volume ratio of the hydrogen in the activation gas is 20-30%;

[0019] (2) the temperature of the activation pore-forming treatment is 800-1000°C;

[0020] (3) the time of the activation pore-forming treatment is 0.5-2 hours.

[0021] In combination with the first aspect of the present application, in an optional implementation, step S4 satisfies at least one of the following features:

[0022] (1) the oxygen concentration in the second inert gas atmosphere is less than or equal to 50 ppm;

[0023] (2) the heating rate of the high-temperature carbonization treatment is 1-5°C / min;

[0024] (3) the temperature of the high-temperature carbonization treatment is 1200-1600°C;

[0025] (4) the holding time of the high-temperature carbonization treatment is 1-8 hours.

[0026] In combination with the first aspect of the present application, in an optional implementation, the passage of the activation gas to place the crushed pre-carbonization material in a fluidized state comprises:

[0027] The activated gas with a flow rate of 1.5 m / s to 3 m / s is introduced to transport the crushed pre-carbonized material into the fluidized reactor; and the activated gas with a flow rate of 0.3 m / s to 1.3 m / s is introduced to place the crushed pre-carbonized material in a fluidized state.

[0028] In a second aspect, the embodiments of the present application provide a negative electrode material, which is prepared by the preparation method of the negative electrode material according to any one of the first aspect.

[0029] In combination with the second aspect of the present application, in an optional implementation manner, the true density of the negative electrode material is less than or equal to 1.7 g / cm 3 ; and / or, the closed pore volume of the negative electrode material is greater than or equal to 0.14 cm 3 / g.

[0030] In a third aspect, the embodiments of the present application provide a negative electrode sheet, which comprises the negative electrode material according to the second aspect.

[0031] In a fourth aspect, the embodiments of the present application provide a battery, which comprises the negative electrode sheet according to the third aspect.

[0032] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0033] In the preparation method of the negative electrode material provided by the embodiments of the present application, the crushed pre-carbonized material is activated and pore-forming processed by using the mixed gas of carbon dioxide and hydrogen as the activated gas in a fluidized state. The carbon dioxide molecules are large in size and difficult to enter the small channels in the material, and mainly perform etching activation on the surface and the large channels inside the material to form micropores. The hydrogen molecules are small in size and can perform secondary activation by etching on the surface and the small channels inside the material to further promote the formation of micropores. In this way, by the synergistic activation and pore-forming effect of carbon dioxide and hydrogen, the amount of micropores in the processed porous activated material can be significantly increased. These micropores are converted into closed pores in the subsequent high-temperature carbonization process, which can provide more effective sodium storage space. Moreover, the activation and pore-forming processing is performed in a fluidized state, which can significantly improve the uniformity and efficiency of the activation and pore-forming processing, thereby improving the reversible capacity and cycle performance of the prepared negative electrode material.

[0034] Additional aspects and advantages of the present application will be made apparent by the following description and the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings, which are included to provide a further understanding of the present application, constitute a part of the present application and illustrate the illustrative embodiments of the present application and its description, which serve to explain the present application, and do not constitute improper limitations on the present application. In the drawings:

[0036] Figure 1 A flowchart of a preparation method of a negative electrode material according to an embodiment of the present application is shown in FIG. 1.

[0037] Figure 2 A scanning electron microscope image of the negative electrode material prepared in Example 1 of the present application is shown in FIG. 2.

[0038] Figure 3 A Raman spectrum of the negative electrode material prepared in Example 1 of the present application is shown in FIG. 3. DETAILED DESCRIPTION

[0039] In order to make the technical solutions and beneficial effects of the present application more obvious and easy to understand, the following will be described in detail by combining the drawings and listing specific examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application. The experimental methods not specified in the following examples are generally carried out according to the conventional experimental conditions. The reagents and raw materials used in the present application are commercially available unless otherwise specified.

[0040] In the following description, a large number of specific details are given in order to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid obscuring the present application, some technical features known in the art are not described; that is, not all features of the actual examples are described here, and well-known functions and steps are not described in detail.

[0041] The terms used herein are only for the purpose of describing specific embodiments and not as a limitation of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the terms "comprise" and / or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of the associated listed items.

[0042] In order to thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description in order to explain the technical solutions of the present application. The preferred embodiments of the present application are described in detail as follows, however, in addition to these detailed descriptions, the present application can also have other implementation manners.

[0043] Unless otherwise defined, the technical and scientific terms used in the present application have the same meaning as the technical and scientific terms in the technical field to which the present application belongs.

[0044] Unless otherwise indicated, conventional techniques or conditions for carrying out the following examples are described in the literature in the field of synthetic organic chemistry. Unless otherwise indicated, numerical ranges are inclusive of the endpoints.

[0045] The activation pore-forming treatment is a way to improve the reversible capacity of hard carbon materials. The activation pore-forming treatment specifically etches the carbon layer of the pre-carbonized material at a certain temperature to form a large number of micropores, and then the micropores are transformed into closed pores through high-temperature carbonization, so as to improve the sodium storage capacity and thus improve the reversible capacity of the negative electrode material. At present, the commonly used activation pore-forming method is to etch the hard carbon precursor by passing carbon dioxide or water vapor in the furnace body, but due to the stacking of the materials, the etching is often uneven, so that the cycle performance of the finally prepared hard carbon material is unstable, and the improvement effect of the reversible capacity is not good.

[0046] Based on this, the embodiment of the present application provides a preparation method of a negative electrode material. Please refer to Figure 1 The preparation method of the negative electrode material provided by the embodiment of the present application comprises the following steps:

[0047] S1: pre-carbonization treatment is performed on the hard carbon precursor in a first inert gas atmosphere to obtain a pre-carbonized product;

[0048] S2: the pre-carbonized product is subjected to a crushing treatment to obtain a crushed pre-carbonized material;

[0049] S3: the crushed pre-carbonized material is placed in a fluidized state by introducing an activation gas, and the crushed pre-carbonized material is subjected to an activation pore-forming treatment to obtain a porous activated material; the activation gas comprises carbon dioxide and hydrogen;

[0050] S4: high-temperature carbonization treatment is performed on the porous activated material in a second inert gas atmosphere to obtain a negative electrode material.

[0051] In the embodiment of the present application, the mixed gas comprising carbon dioxide and hydrogen is used as the activation gas to perform the activation pore-forming treatment on the crushed pre-carbonized material in the fluidized state. The carbon dioxide molecules are difficult to enter the small channels in the material due to their large size, and mainly etch and activate on the surface and large channels of the material to form micropores. The hydrogen molecules have a small size and can etch and form secondary activation on the surface and small channels of the material to further promote the formation of micropores. In this way, through the synergistic activation pore-forming effect of carbon dioxide and hydrogen, the amount of micropores in the treated porous activated material can be significantly improved. These micropores are transformed into closed pores in the subsequent high-temperature carbonization treatment, which can provide more effective sodium storage space. Moreover, the activation pore-forming treatment is performed in the fluidized state, which can significantly improve the uniformity and efficiency of the activation pore-forming treatment, thereby improving the reversible capacity and cycle performance of the prepared negative electrode material.

[0052] It should be noted that the reversible capacity and cycle performance of the negative electrode material can be understood as the reversible capacity and cycle performance that can be exerted when the negative electrode material is applied to the battery, and therefore, the application can improve the reversible capacity and cycle performance of the negative electrode material, which can also be understood as the application can improve the reversible capacity and cycle performance of the battery.

[0053] In step S1, first, the hard carbon precursor is pre-carbonized at a suitable temperature range, which can promote the escape of small molecules in the hard carbon precursor and the development of graphite crystallites, and the development of graphite crystallites lays a foundation for the formation of closed pores in the subsequent high-temperature carbonization process.

[0054] In step S1, when the oxygen concentration in the first inert gas atmosphere is too high, excessive oxygen will hinder the ordered rearrangement of carbon atoms, and a large number of defects and amorphous regions may be formed in the material, which will reduce the electronic conductivity of the prepared hard carbon material and deteriorate the electrical performance of the finally prepared negative electrode material. Moreover, when the oxygen concentration is too high, there is a risk of combustion of the hard carbon precursor. Therefore, in some embodiments, the oxygen concentration in the first inert gas atmosphere in step S1 is less than or equal to 50 ppm. In this way, the adverse effects of oxygen on the structure and performance of the material during the pre-carbonization process can be better avoided; at the same time, the safety of the process can be ensured.

[0055] Exemplarily, the first inert gas can include at least one of helium, nitrogen, argon, and xenon.

[0056] When the heating rate of the pre-carbonization process is too low, the processing efficiency will be reduced, the process cycle will be prolonged, and the energy consumption and cost will be increased; when the heating rate of the pre-carbonization process is too high, it is easy to cause a large temperature difference between the surface and the interior of the hard carbon precursor, resulting in uneven pre-carbonization. Therefore, in some embodiments, the heating rate of the pre-carbonization process is 1 ℃ / min to 5 ℃ / min, for example, it can be 1 ℃ / min, 2 ℃ / min, 3 ℃ / min, 4 ℃ / min, 5 ℃ / min, or any value within a range between any two of the above values.

[0057] In some specific embodiments, the pre-carbonization process can include a first pre-carbonization process and a second pre-carbonization process.

[0058] Specifically, the temperature of the first pre-carbonization process can be 150 ℃ to 250 ℃, for example, it can be 150 ℃, 200 ℃, 250 ℃, or any value within a range between any two of the above values, and the time of the first pre-carbonization process can be 1 h to 4 h, for example, it can be 1 h, 2 h, 3 h, 4 h, or any value within a range between any two of the above values.

[0059] In the embodiments of the present application, the first pre-carbonization treatment is first performed at a relatively low temperature, which can promote the cross-linking of the molecular chains of the hard carbon precursor (specifically, for example, resin), form a three-dimensional network structure, and improve the thermal stability of the material. If the temperature of the first pre-carbonization treatment is too low and / or the time is too short, the cross-linking of the molecular chains is slow and insufficient, and the three-dimensional network structure formed is not complete enough. If the temperature of the first pre-carbonization treatment is too high and / or the time is too long, the molecular chains of the hard carbon precursor are prone to excessive cross-linking, forming a three-dimensional network structure that is too dense, which increases the difficulty of etching in the subsequent activation process and is not conducive to the subsequent activation and pore formation. Therefore, controlling at least one of the temperature and the time of the first pre-carbonization treatment in the above range is beneficial to improving the effect of the first pre-carbonization treatment, thereby improving the quality and performance of the final prepared negative electrode material.

[0060] Specifically, the temperature of the second pre-carbonization treatment can be 500°C to 700°C, for example, can be 500°C, 550°C, 600°C, 650°C, 700°C, or any value within any two of the above value ranges. The time of the second pre-carbonization treatment can be 1h to 10h, for example, can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, or any value within any two of the above value ranges.

[0061] In the embodiments of the present application, after the first pre-carbonization treatment, the temperature is continued to be raised, and the second pre-carbonization treatment is performed at a relatively high temperature. The temperature of the second pre-carbonization treatment can be determined according to the rapid weight loss rate temperature range of the hard carbon precursor thermogravimetric curve. Controlling the temperature of the second pre-carbonization treatment in the above temperature range is beneficial to promoting the sufficient release of small molecules to form a more stable three-dimensional network structure. The hard carbon precursor is usually a high molecular polymer, and the pre-carbonization process is a chain breaking and cross-linking process. Controlling the time of the second pre-carbonization treatment in the above range can ensure the sufficiency of the pre-carbonization treatment while avoiding increasing energy consumption and cost. Preferably, the time of the second pre-carbonization treatment is 5h.

[0062] Through the combination of the first pre-carbonization treatment and the second pre-carbonization treatment, the effect of the pre-carbonization treatment can be improved, thereby improving the quality of the obtained pre-carbonization product.

[0063] In some embodiments, the hard carbon precursor includes natural resin and / or synthetic resin. Because, as a hard carbon precursor, resin can be synthesized on a large scale by fine chemical industry, and has the advantages of high batch stability, stable product structure, large output, high carbon yield, etc.

[0064] Optionally, the natural resin includes rosin resin and / or amber resin; the synthetic resin includes at least one of phenolic resin, epoxy resin, and phenolic epoxy resin.

[0065] In some embodiments, the pre-carbonized product comprises oxygen-containing functional groups. Since the oxygen-containing functional groups are usually included in various types of hard carbon precursors, the pre-carbonized product obtained by pre-carbonizing the hard carbon precursor comprises oxygen-containing functional groups. Since the presence of oxygen hinders the ordered rearrangement of carbon atoms, more defects and amorphous regions can be formed in the material, which reduces the electronic conductivity of the prepared hard carbon material and deteriorates the electrical performance of the finally prepared negative electrode material. In the embodiments of the present application, hydrogen is included in the activation gas, so that in the activation and pore-forming process, the hydrogen can also reduce the oxygen-containing functional groups in the pre-carbonized product (for example, pre-carbonized resin), thereby reducing the influence of oxygen elements in the material on the finally prepared negative electrode material.

[0066] When the particle size of the crushed pre-carbonized material after the crushing treatment in step S2 is too small, the specific surface area of the crushed pre-carbonized material will be too large, which will in turn cause the finally prepared negative electrode material to be more prone to more side reactions with the electrolyte, thereby reducing the first coulombic efficiency of the battery; when the particle size of the crushed pre-carbonized material after the crushing treatment in step S2 is too large, the migration rate of active ions (such as lithium ions or sodium ions) is hindered, thereby reducing the rate performance of the battery. In some embodiments, the particle size D50 of the crushed pre-carbonized material after the crushing treatment in step S2 is 5 μm to 10 μm. This is conducive to more uniform, sufficient and efficient activation and pore-forming treatment of the crushed pre-carbonized material in the subsequent process, thereby further improving the reversible capacity and cycle performance of the finally prepared negative electrode material.

[0067] In actual preparation processes, the crushing treatment can be performed using a device such as an air flow crusher, and the crushed pre-carbonized material can be obtained by sieving the crushed material and collecting the undersize. The air source of the air flow crusher can be compressed air, and the pressure can be 0.5 MPa to 1.0 MPa; the crushed material can be sieved through a 400-mesh sieve.

[0068] In step S3, the crushed pre-carbonized material is placed in a fluidized state, and the crushed pre-carbonized material is subjected to activation and pore-forming treatment. Fluidization refers to a state in which solid particles are suspended by the action of a gas flow. In this state, the introduction of activation gas can ensure sufficient contact between the activation gas and the solid particles, and micropores can be generated by etching the solid particles, thereby significantly improving the uniformity of the activation treatment. At the same time, the solid particles are in a suspended state, which can achieve good activation and pore-forming effect in a short time and reduce the amount of activation gas used.

[0069] In actual preparation processes, the crushed pre-carbonized material can be subjected to fluidized activation and pore-forming treatment in a fluidized reactor. The fluidized reactor cavity is heated by an electric heating body, which can be heated to a wide temperature range (50°C to 1200°C), and the temperature can be measured in real time online by an infrared pyrometer, which facilitates the control of process parameters.

[0070] Specifically, the compressed activation gas with a flow rate of 1.5 m / s to 3 m / s can be introduced to transport the crushed pre-carbonized material into the fluidized reactor, so as to ensure that the material is stably transported into the fluidized reactor and avoid flying out of the cavity of the fluidized reactor. After the crushed pre-carbonized material is completely introduced into the fluidized reactor, the flow rate of the activation gas is adjusted to 0.3 m / s to 1.3 m / s to ensure that the crushed pre-carbonized material is in a fluidized state. Then, the heating system of the fluidized bed device is started, and the activation pore-forming treatment is performed at a set temperature. Finally, after the reaction is completed, the heating is stopped, and the activated material is collected through the material collection port to obtain the porous activated material.

[0071] When the volume ratio of hydrogen in the activation gas is too low, the synergistic activation pore-forming effect of carbon dioxide and hydrogen is limited, so that the amount of micropores formed in the treated porous activated material is limited. When the volume ratio of hydrogen in the activation gas is too high, the volume ratio of carbon dioxide in the activation gas is too low, and because the reaction rate of hydrogen and carbon to generate methane is slow, the activation pore-forming effect and efficiency are reduced. Therefore, in some embodiments, the volume ratio of hydrogen in the activation gas is 20% to 30%, for example, it can be 20%, 25%, 30% or any value within the range of any two of the above values. In this way, the overall activation pore-forming effect and efficiency can be ensured.

[0072] When the temperature of the activation pore-forming treatment is too low, the activation gas is difficult to react with the carbon layer, and the pore-forming effect is not easy to achieve. When the temperature of the activation pore-forming treatment is too high, the carbon skeleton of the hard carbon material is easily etched too much, which destroys the stability of the original structure of the material and reduces the mechanical strength of the material. Therefore, in some embodiments, the temperature of the activation pore-forming treatment is 800°C to 1000°C, for example, it can be 800°C, 850°C, 900°C, 950°C, 1000°C or any value within the range of any two of the above values.

[0073] When the time of the activation pore-forming treatment is too short, the activation pore-forming treatment is insufficient, which affects the pore-forming effect. When the time of the activation pore-forming treatment is too long, the carbon material is etched too much, which destroys the stability of the original structure of the material and reduces the mechanical strength of the material. Therefore, in some embodiments, the time of the activation pore-forming treatment is 0.5 h to 2 h, for example, it can be 0.5 h, 1 h, 1.5 h, 2 h or any value within the range of any two of the above values.

[0074] Controlling at least one of the temperature and the time of the activation pore-forming treatment within the above range can ensure uniform and sufficient activation pore-forming treatment of the crushed pre-carbonized material, thereby improving the quality of the obtained porous activated material and further improving the reversible capacity and cycle performance of the finally prepared negative electrode material.

[0075] In step S4, the porous activated material is subjected to high-temperature carbonization treatment in a second inert gas atmosphere to obtain the negative electrode material. High-temperature carbonization provides more energy to promote the migration of carbon atoms, and the micropores in the porous activated material gradually close and evolve into closed pores. The closed pores can provide more pore-filling capacity, i.e., more effective sodium storage space, thereby effectively improving the reversible capacity and cycle performance of the negative electrode material.

[0076] In step S4, when the oxygen concentration in the second inert gas atmosphere is too high, excessive oxygen will hinder the ordered rearrangement of carbon atoms, and more defects and amorphous regions may be formed in the material, which will cause the electrical performance of the prepared negative electrode material to deteriorate. Moreover, when the oxygen concentration is too high, there is a risk of combustion of the carbon material. Therefore, in some embodiments, the oxygen concentration in the second inert gas atmosphere is less than or equal to 50 ppm. In this way, the adverse effects of oxygen on the structure and performance of the material during high-temperature carbonization treatment can be effectively avoided.

[0077] When the heating rate of the high-temperature carbonization treatment is too low, the processing efficiency will be reduced, the process cycle will be prolonged, and the energy consumption and cost will be increased. When the heating rate of the high-temperature carbonization treatment is too high, it is easy to cause a large temperature difference between the surface and the interior of the porous activated material, resulting in uneven high-temperature carbonization treatment. Therefore, in some embodiments, the heating rate of the high-temperature carbonization treatment is 1 ℃ / min to 5 ℃ / min, for example, it can be 1 ℃ / min, 2 ℃ / min, 3 ℃ / min, 4 ℃ / min, 5 ℃ / min, or any value within any two of the above numerical ranges.

[0078] When the temperature of the high-temperature carbonization treatment is too low, the pyrolysis and carbonization of the porous activated material will not be sufficient, resulting in a large amount of volatile substances and organic impurities remaining, which in turn reduces the purity of the prepared negative electrode material. At the same time, the carbon layer cannot be fully rearranged, and the degree of disorder is too high, resulting in poor electrical conductivity of the material. When the temperature of the high-temperature carbonization treatment is too high, the hard carbon material will be excessively graphitized, and the carbon layer spacing will be reduced, thereby deteriorating the sodium storage performance of the prepared negative electrode material. Moreover, a too high carbonization treatment temperature will increase energy consumption and cost. Therefore, in some embodiments, the temperature of the high-temperature carbonization treatment is 1200 ℃ to 1600 ℃, for example, it can be 1200 ℃, 1300 ℃, 1400 ℃, 1500 ℃, 1600 ℃, or any value within any two of the above numerical ranges.

[0079] When the holding time of the high-temperature carbonization treatment is too short, the carbon layer rearrangement time is short, the degree of disorder is too high, and the electrical conductivity of the material is poor. When the holding time of the high-temperature carbonization treatment is too long, the energy consumption and cost will be increased. Therefore, in some embodiments, the holding time of the high-temperature carbonization treatment is 1 h to 8 h, for example, it can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, or any value within any two of the above numerical ranges.

[0080] Controlling at least one of the heating rate, the temperature, and the holding time of the high-temperature carbonization treatment in the above range is beneficial to improving the effect of the high-temperature carbonization treatment, so as to improve the reversible capacity and the cycle performance of the obtained negative electrode material.

[0081] The application also provides a negative electrode material prepared by the method for preparing a negative electrode material described in any of the above embodiments.

[0082] It should be understood that the beneficial effects of the method for preparing a negative electrode material described in the above embodiments are applicable to the negative electrode material.

[0083] In some embodiments, the true density of the negative electrode material is less than or equal to 1.7 g / cm3. 3 .

[0084] In some embodiments, the closed pore volume of the negative electrode material is greater than or equal to 0.14 cm3 / g. 3

[0085] The negative electrode material prepared by the method for preparing a negative electrode material described in the above embodiments has a large number of closed pores, and thus has a low true density and a high closed pore volume, so as to ensure that the negative electrode material has a high reversible capacity and cycle performance.

[0086] The application also provides a negative electrode sheet comprising the negative electrode material described in any of the above embodiments.

[0087] In some embodiments, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer on at least one surface of the negative electrode current collector, and the negative electrode active material layer comprises the negative electrode material described in any of the above embodiments.

[0088] The application also provides a battery comprising the negative electrode sheet described in the above embodiments.

[0089] In some embodiments, the battery can be a secondary battery, which can be a lithium ion battery or a sodium ion battery, for example. In a specific embodiment, the secondary battery is a sodium ion battery. Generally, the secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting the active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, and mainly plays a role in preventing the short circuit of the positive electrode and the negative electrode, while allowing the active ions to pass through.

[0090] ​In the actual preparation process of the battery, first, the positive electrode sheet, the separator, the negative electrode sheet, and the separator can be sequentially stacked to obtain a bare battery cell after assembly, and the assembly mode can be selected as, for example, a lamination or winding mode; then, the electrolyte is injected into the dry bare battery cell, and the secondary battery is obtained after formation and aging. The negative electrode sheet is the negative electrode sheet described in the above embodiments. The positive electrode sheet includes a positive electrode current collector (which can be, for example, an aluminum foil) and a positive electrode active material layer coated on the positive electrode current collector. Specifically, the positive electrode active material layer can include a positive electrode active material, a conductive agent, and a binder, wherein the positive electrode active material can include, for example, at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese acid, lithium nickel cobalt manganese aluminate; the conductive agent can include, for example, at least one of conductive carbon black, carbon nanotubes, acetylene black; and the binder can include, for example, polyvinylidene fluoride (PVDF). The separator can be, for example, a polyethylene film, a polypropylene film, a polyvinylidene fluoride film, or a non-woven fabric, etc. The electrolyte can include, for example, a lithium salt and a solvent or a sodium salt and a solvent, wherein the lithium salt, the sodium salt, and the type of solvent are not specifically limited and can be selected according to actual needs.

[0091] The technical solutions of the present application will be further described below in conjunction with multiple embodiments and comparative examples. Embodiment 1

[0092] The preparation method of the negative electrode material in this embodiment includes the following steps:

[0093] Step S101: Take 1000g of phenolic resin (hard carbon precursor) and place it in a pre-carbonization furnace for pre-carbonization treatment under a nitrogen (first inert gas) atmosphere. The oxygen concentration at the beginning of the pre-carbonization treatment is 36ppm. The pre-carbonization treatment includes: first, increasing the temperature to 150℃ at a rate of 5℃ / min, and maintaining the temperature for 2h (first pre-carbonization treatment); then, continuing to increase the temperature to 500℃ at a rate of 5℃ / min, and maintaining the temperature for 10h (second pre-carbonization treatment), to obtain a pre-carbonization product;

[0094] Step S102: Add the pre-carbonization product to an air jet mill, with air as the gas source and a pressure of 0.6MPa for crushing treatment. After crushing, the material is passed through a 400 mesh sieve, and the undersize material is collected to obtain a crushed pre-carbonization material;

[0095] Step S103: Add the crushed pre-carbonization material to the feed bin of the fluidized bed reactor, and use a mixture of carbon dioxide and hydrogen gas (with the volume ratio of hydrogen in the mixture being 20%) as the carrier gas source and the activation gas to pass through the feed bin at a flow rate of 1.3m / s, bringing the crushed pre-carbonization material into the reactor, and then adjusting the flow rate of the activation gas to 0.3m / s. Set the temperature in the fluidized bed reactor to 800℃, and activate the pore-forming treatment for 2h. After the treatment is completed, a porous activated material is collected.

[0096] Step S104: placing the porous activated material into a high-temperature carbonization furnace, and performing high-temperature carbonization treatment under a nitrogen (second inert gas) atmosphere, wherein the oxygen concentration at the beginning of high-temperature carbonization is 40 ppm, the temperature increasing rate of high-temperature carbonization is 1 ℃ / min, the temperature is kept at 1400 ℃ for 2 h, and after the high-temperature carbonization treatment is completed, the negative electrode material is prepared. Example 2

[0097] The preparation method of the negative electrode material in this example is basically the same as that in Example 1, except that:

[0098] 1) In step S101, the hard carbon precursor is adjusted to epoxy resin; the first inert gas is adjusted to argon; the oxygen concentration at the beginning of the pre-carbonization treatment is 45 ppm; the temperature of the first pre-carbonization treatment is adjusted to 250 ℃; the holding time is adjusted to 4 h; the temperature of the second pre-carbonization treatment is adjusted to 700 ℃; and the holding time is adjusted to 1 h;

[0099] 2) In step S102, the pressure of the gas source is adjusted to 1.0 MPa;

[0100] 3) In step S103, the volume ratio of hydrogen in the mixed gas is adjusted to 30%; the crushed pre-carbonized material is fed into the feed bin by the activation gas at a flow rate of 3.0 m / s; the flow rate of the activation gas for the activation and pore forming treatment is adjusted to 1.0 m / s; the temperature of the activation and pore forming treatment is adjusted to 1000 ℃; and the time of the activation and pore forming treatment is adjusted to 0.5 h;

[0101] 4) In step S104, the second inert gas is adjusted to argon; the oxygen concentration at the beginning of high-temperature carbonization is 20 ppm; the temperature increasing rate of high-temperature carbonization is adjusted to 3 ℃ / min; the temperature of high-temperature carbonization is adjusted to 1200 ℃; and the holding time of high-temperature carbonization is adjusted to 8 h. Example 3

[0102] The preparation method of the negative electrode material in this example is basically the same as that in Example 1, except that:

[0103] 1) In step S101, the hard carbon precursor is adjusted to phenolic epoxy resin, and the addition amount is adjusted to 1500 g; the first inert gas is adjusted to argon; the oxygen concentration at the beginning of the pre-carbonization treatment is 45 ppm; the temperature of the first pre-carbonization treatment is adjusted to 200 ℃; the holding time is adjusted to 2 h; the temperature of the second pre-carbonization treatment is adjusted to 600 ℃; and the holding time is adjusted to 5 h;

[0104] 2) In step S102, the pressure of the gas source is adjusted to 0.8 MPa;

[0105] 3) In step S103, the volume ratio of hydrogen in the mixed gas is adjusted to 25%; the crushed pre-carbonized material is passed into the feeding bin by activating gas at a flow rate of 2.1 m / s; the temperature of the activation pore-forming treatment is adjusted to 900°C, and the time of the activation pore-forming treatment is adjusted to 1 h;

[0106] 4) In step S104, the second inert gas is adjusted to argon; the oxygen concentration when starting high-temperature carbonization is 10 ppm, the temperature of high-temperature carbonization is adjusted to 1600°C, and the holding time of high-temperature carbonization is adjusted to 1 h. Example 4

[0107] The preparation method of the negative electrode material in this example is basically the same as that in Example 1, except that:

[0108] 1) In step S101, the hard carbon precursor is adjusted to rosin resin; the oxygen concentration when starting pre-carbonization treatment is 46 ppm, the temperature of the first pre-carbonization treatment is adjusted to 180°C, the holding time is adjusted to 2 h, the temperature of the second pre-carbonization treatment is adjusted to 700°C, and the holding time is adjusted to 8 h;

[0109] 2) In step S102, the pressure of the gas source is adjusted to 0.9 MPa;

[0110] 3) In step S103, the volume ratio of hydrogen in the mixed gas is adjusted to 22%; the crushed pre-carbonized material is passed into the feeding bin by activating gas at a flow rate of 2.2 m / s; the flow rate of the activation gas of the activation pore-forming treatment is adjusted to 1.1 m / s, the temperature of the activation pore-forming treatment is adjusted to 900°C, and the time of the activation pore-forming treatment is adjusted to 1.5 h;

[0111] 4) In step S104, the second inert gas is adjusted to argon; the oxygen concentration when starting high-temperature carbonization is 39 ppm, the temperature of high-temperature carbonization is adjusted to 1500°C, and the holding time of high-temperature carbonization is adjusted to 3 h.

[0112] Comparative Example 1

[0113] The main difference between the preparation method of the negative electrode material in this comparative example and that in Example 1 is that step S103 is omitted, i.e., the crushed pre-carbonized material is not subjected to activation pore-forming treatment, but is directly subjected to high-temperature carbonization treatment to obtain the negative electrode material; the other steps are the same as those in Example 1.

[0114] Comparative Example 2

[0115] The main difference between the preparation method of the negative electrode material in the present comparative example and that in Example 1 is that the fluidization activation technology is not used for pore forming treatment, and the activation pore forming treatment in step S103 is adjusted as follows: the crushed pre-carbonized material is placed in a carbonization furnace for activation, the atmosphere is a mixture of carbon dioxide and hydrogen (hydrogen volume ratio is 20%), the oxygen concentration is 30 ppm at the beginning of activation, the heating rate is 5°C / min, the activation temperature is 800°C, and the activation time is 2 h; the other steps are the same as in Example 1.

[0116] Comparative Example 3

[0117] The preparation method of the negative electrode material in the present comparative example is basically the same as that in Example 1, and the difference is that:

[0118] The activation gas in step S103 is adjusted to pure carbon dioxide gas.

[0119] Comparative Example 4

[0120] The preparation method of the negative electrode material in the present comparative example is basically the same as that in Example 1, and the difference is that:

[0121] The activation gas in step S103 is adjusted to pure hydrogen gas.

[0122] In order to verify the effect of activation pore forming, the closed pore volume of the negative electrode material prepared in each of the above examples and comparative examples is tested. The test principle is as follows: first, the true density of the negative electrode material is measured by a true density instrument, and the true volume of the negative electrode material is calculated according to the true density; the true volume of the negative electrode material is composed of the closed pore volume and the skeleton volume of the carbon layer, and the unit mass of the carbon layer skeleton volume is equivalent to that of graphite, which is 2.26 cm 3 / g, then the calculation formula of the closed pore volume is:

[0123] V 闭孔 =1 / ρ 真 -1 / 2.26

[0124] Wherein, V 闭孔 is the closed pore volume in the negative electrode material, unit: cm 3 / g, ρ 真 is the true density of the negative electrode material, unit: g / cm 3 . The larger the closed pore volume is, the more pores are obtained by the activation pore forming treatment.

[0125] The above test results are shown in Table 1.

[0126] The negative electrode materials prepared in each of the above examples and comparative examples are used to prepare batteries, and the performance of the batteries is tested.

[0127] The preparation steps of the battery are as follows: the negative electrode material prepared in the above examples and comparative examples is mixed with the conductive agent and the binder in the same mass ratio, dissolved in the same amount of deionized water to obtain a negative electrode slurry, the negative electrode slurry is coated on a negative electrode current collector, and after drying and rolling, a negative electrode sheet is obtained; a metal sodium sheet is used as a positive electrode sheet; LiPF6 is dissolved in a mixed solvent of EC (ethylene carbonate), DMC (dimethyl carbonate) and FEC (fluorinated ethylene carbonate) in a volume ratio of 4.5:4.5:1 to obtain an electrolyte of 1.0 mol / L; the negative electrode sheet, the positive electrode sheet, a polypropylene separator and the electrolyte are assembled into a CR2032 button cell in an argon glove box.

[0128] The performance of the battery is tested by using a battery test system as follows:

[0129] (1) The first discharge capacity, the first charge capacity and the first coulombic efficiency: under the constant temperature condition of 25°C, the discharge capacity at this time is recorded as the first cycle (first) discharge capacity when discharged to 0V at a rate of 0.1C; the charge capacity at this time is recorded as the first cycle (first) charge capacity when charged to 2V at a rate of 0.1C; the first coulombic efficiency = (first cycle charge specific capacity / first cycle discharge specific capacity) x 100%.

[0130] (2) The capacity retention rate after 200 cycles: under the constant temperature condition of 25°C, the charge capacity of the first cycle is recorded when discharged to 0V at a current density of 1C and then charged to 2V at a rate of 1C, which is a complete charge-discharge cycle, and the process is repeated until the cycle number is equal to 200 cycles, and the charge capacity of the 200th cycle is recorded. Then, the capacity retention rate after 200 cycles = (the charge capacity of the 200th cycle / the charge capacity of the first cycle) x 100%.

[0131] The test results are shown in Table 2.

[0132] Table 1

[0133]

[0134] Table 2

[0135]

[0136] As can be seen from the true density and closed-pore volume data of the negative electrode materials in Table 1, in Comparative Example 1, the closed-pore volume of the negative electrode material is the smallest because the activation and pore-forming treatment step of the pulverized pre-carbonized material was omitted during the preparation of the negative electrode material. Comparative Example 2 used a static activation scheme for pore-forming treatment, Comparative Example 3 used a simple carbon dioxide gas activation scheme, and Comparative Example 4 used a simple hydrogen gas activation scheme. The closed-pore volume of the negative electrode materials prepared by these three schemes showed relatively limited growth. In Examples 1 to 4, a fluidized activation scheme was used, employing a mixture of carbon dioxide and hydrogen as the activation gas. The closed-pore volume of the prepared negative electrode materials showed a significant increase, thus enabling the negative electrode material to exhibit a higher reversible specific capacity.

[0137] As can be seen from the battery performance data in Table 2, the batteries corresponding to the negative electrode materials prepared in Examples 1 to 4 all exhibit high reversible specific capacity and initial coulombic efficiency. In Comparative Example 1, because the activation and pore-forming treatment step of the pulverized pre-carbonized material was omitted during the preparation of the negative electrode material, and no activation technology was used, the corresponding battery had the lowest reversible specific capacity and the lowest initial coulombic efficiency. Comparative Example 2 used a static activation scheme for activation and pore-forming treatment, Comparative Example 3 used a simple carbon dioxide gas activation and pore-forming treatment, and Comparative Example 4 used a simple hydrogen gas activation and pore-forming treatment. Although the reversible capacity and cycle performance of the corresponding batteries were improved to some extent compared to Comparative Example 1, they were all significantly lower than the reversible capacity and cycle performance of the batteries corresponding to Examples 1 to 4, indicating that the activation and pore-forming effects of the three schemes in Comparative Examples 2 to 4 were poor. This is consistent with the test results of the closed-pore volume of the negative electrode materials mentioned above.

[0138] Furthermore, the battery performance data in Table 2 also shows that, compared to Comparative Examples 1 to 4, the batteries corresponding to the negative electrode materials prepared in Examples 1 to 4 all exhibit higher cycle capacity retention (greater than 90%), demonstrating excellent cycle stability. That is, the negative electrode material prepared in this invention has high reversible capacity and cycle performance.

[0139] Figure 2 This is a scanning electron microscope (SEM) image of the negative electrode material prepared in Example 1. Figure 2 It can be seen that the negative electrode material has a spherical morphology and a high compaction density. Figure 3 This is the Raman spectrum of the negative electrode material prepared in Example 1. (From...) Figure 3 It can be seen that the negative electrode material has a high degree of disorder, which is conducive to the insertion and extraction of active ions (such as sodium ions).

[0140] The application provides a fluidized activation pore-forming scheme using mixed gas containing carbon dioxide and hydrogen as an activation gas. Through the synergistic activation pore-forming effect of carbon dioxide and hydrogen, the activation pore-forming effect can be significantly improved, so that the material after activation pore-forming is rich in a large number of micropores, which provides a basis for the formation of closed pores in subsequent high-temperature carbonization treatment, so that the volume of closed pores in the finally prepared negative electrode material is increased, and the reversible capacity and cycle performance of the negative electrode material are significantly improved.

[0141] It should be noted that the negative electrode material embodiments, the preparation method embodiments of the negative electrode material provided in the application. The negative electrode sheet embodiments and the battery embodiments belong to the same concept; the technical features in the technical solutions recorded in each embodiment can be arbitrarily combined without conflict.

[0142] It should be understood that the above embodiments are exemplary and are not intended to include all possible implementations. Various modifications and changes can also be made to the above embodiments without departing from the scope of the present disclosure. Similarly, each technical feature of the above embodiments can be arbitrarily combined to form additional embodiments of the application that have not been explicitly described. Therefore, the above embodiments only express several implementation manners of the application, and do not limit the protection scope of the patent of the application.

Claims

1. A method for producing a negative electrode material, characterized by, The method comprises the following steps: S1: performing a pre-carbonization treatment on a hard carbon precursor in a first inert gas atmosphere to obtain a pre-carbonized product; S2: performing a crushing treatment on the pre-carbonized product to obtain a crushed pre-carbonized material; S3: introducing an activation gas, placing the crushed pre-carbonized material in a fluidized state, and performing an activation pore-forming treatment on the crushed pre-carbonized material to obtain a porous activated material; the activation gas comprises carbon dioxide and hydrogen; S4: performing a high-temperature carbonization treatment on the porous activated material in a second inert gas atmosphere to obtain the negative electrode material.

2. The method of producing a negative electrode material according to claim 1, characterized by, Step S1 meets at least one of the following characteristics: (1) the oxygen concentration in the first inert gas atmosphere is less than or equal to 50 ppm; (2) the temperature rising rate of the pre-carbonization treatment is 1 ℃ / min to 5 ℃ / min; (3) the pre-carbonization treatment comprises a first pre-carbonization treatment and a second pre-carbonization treatment, the temperature of the first pre-carbonization treatment is 150 ℃ to 250 ℃, and the time of the first pre-carbonization treatment is 1 h to 4 h; the temperature of the second pre-carbonization treatment is 500 ℃ to 700 ℃, and the time of the second pre-carbonization treatment is 1 h to 10 h; (4) the hard carbon precursor comprises natural resin and / or synthetic resin; (5) the pre-carbonized product comprises an oxygen-containing functional group.

3. The method of claim 1, wherein the method is characterized by: The hard carbon precursor comprises natural resin and / or synthetic resin; the natural resin comprises rosin resin and / or amber resin; and the synthetic resin comprises at least one of phenolic resin, epoxy resin, and phenolic epoxy resin.

4. The method of claim 1, wherein the method is characterized by: The particle size D50 of the crushed pre-carbonized material is 5 μm to 10 μm.

5. The method of claim 1, wherein the method is characterized by: Step S3 meets at least one of the following characteristics: (1) the volume ratio of hydrogen in the activation gas is 20% to 30%; (2) the temperature of the activation pore-forming treatment is 800 ℃ to 1000 ℃; (3) the time of the activation pore-forming treatment is 0.5 h to 2 h.

6. The method of claim 1, wherein the method is characterized by: Step S4 meets at least one of the following characteristics: (1) the oxygen concentration in the second inert gas atmosphere is less than or equal to 50 ppm; (2) the temperature rising rate of the high-temperature carbonization treatment is 1 ℃ / min to 5 ℃ / min; (3) the temperature of the high-temperature carbonization treatment is 1200 ℃ to 1600 ℃; (4) the holding time of the high-temperature carbonization treatment is 1 h to 8 h.

7. The method of producing a negative electrode material according to any one of claims 1 to 6, characterized by, Introducing the activation gas and placing the crushed pre-carbonized material in a fluidized state comprises: Introducing the activation gas at a flow rate of 1.5 m / s to 3 m / s to transport the crushed pre-carbonized material into a fluidized reactor; and then introducing the activation gas at a flow rate of 0.3 m / s to 1.3 m / s to place the crushed pre-carbonized material in a fluidized state.

8. A negative electrode material, characterized by, The negative electrode material is prepared by using the preparation method of any one of claims 1 to 7.

9. The negative electrode material of claim 8, wherein, The true density of the negative electrode material is less than or equal to 1.7 g / cm 3 ; and / or, the closed pore volume of the negative electrode material is greater than or equal to 0.14 cm 3 / g.

10. A negative electrode sheet characterized by comprising: The negative electrode sheet comprises the negative electrode material of claim 8 or 9.

11. A battery, characterized by The negative electrode sheet of claim 10 is provided.

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