Negative electrode material and preparation method thereof, negative electrode plate and battery

Abstract

The embodiment of the invention provides a negative electrode material, and particularly relates to a composite carbon material with a gradient pore structure, which is prepared by the following steps: dissolving polycyclic aromatic hydrocarbons such as asphalt and coal as precursors in organic solvents such as pyridine and tetrahydrofuran to form a liquid phase, dipping the porous carbon material in the liquid phase of the precursors, pre-carbonizing for multiple times, and carbonizing to obtain the composite carbon material with the gradient pore structure. The composite carbon material with the gradient pore structure is obtained. According to the negative electrode material, the proportion of the secondary micropores is 25-80%, the proportion of the large micropores is 20-75%, the proportion of the mesopores is less than or equal to 10%, the graphitization degree is less than 1.3, and the structural stability and the electrochemical performance of the battery can be improved. Furthermore, a negative electrode plate and a battery can be prepared according to the negative electrode material.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a negative electrode material, a preparation method thereof, a negative electrode sheet, a battery, and an electrical device. Background Art

[0002] With the increasing aggravation of environmental pollution, the new energy industry has attracted more and more attention. In the new energy industry, battery technology is an important factor related to its development. For alkali metal ion batteries such as sodium ion batteries and lithium ion batteries, the nano - pore structure of carbon - based negative electrode materials will affect the electrochemical performance of the materials at low - potential platforms.

[0003] The performance of the negative electrode material is crucial for the performance of the battery. Therefore, how to provide a negative electrode material to improve the performance of the battery is an urgent technical problem to be solved. Summary of the Invention

[0004] This application provides a negative electrode material, a preparation method thereof, a negative electrode sheet, a battery, and an electrical device to improve the performance of the battery.

[0005] In a first aspect, this application provides a negative electrode material, which is a porous carbon material with micropores: in this negative electrode material, the proportion of sub - micropores is 25% - 80%, the proportion of macropores is 20% - 75%, and the proportion of mesopores is less than or equal to 10%; wherein, sub - micropores refer to micropores with a diameter less than 1 nm, and macropores refer to micropores with a diameter greater than or equal to 1 nm and less than 2 nm.

[0006] In the negative electrode material of this application, the quantity ratio of disordered carbon layers and ordered carbon layers is reasonable, the combination is stable, and it has a gradient pore structure, achieving a relatively balanced and stable performance among the high - rate discharge capacity, cycle performance, and energy density of the ion battery, thereby improving the performance of the battery.

[0007] In certain implementation manners of the first aspect, in this negative electrode material, the proportion of sub - micropores is 45% - 75%, the proportion of macropores is 25% - 45%, and the proportion of mesopores is less than or equal to 10%.

[0008] By adjusting the diameter and proportion of micropores, the storage form and total amount of active ions in the porous carbon material can be further adjusted.

[0009] In certain implementation manners of the first aspect, the graphitization degree of this negative electrode material is less than 1.3.

[0010] In certain implementation manners of the first aspect, the graphitization degree of this negative electrode material is less than 1.2.

[0011] Reducing the graphitization degree can further improve the high - rate discharge performance of the negative electrode material.

[0012] In a second aspect, the present application provides a negative electrode sheet, including the negative electrode material in the first aspect and any one of the possible implementation manners thereof.

[0013] In a third aspect, the present application provides a battery, including the negative electrode sheet described in the second aspect.

[0014] In a fourth aspect, the present application provides an electrical device, including the battery described in the third aspect.

[0015] In a fifth aspect, the present application provides a method for preparing a negative electrode material, the method including: dissolving a precursor in a solvent, stirring, dispersing and then centrifuging to obtain a precursor solution, wherein the precursor is a polycyclic aromatic hydrocarbon substance; impregnating and centrifuging a porous carbon material with the precursor solution to obtain an insoluble substance; drying the insoluble substance to obtain a powdery material; performing a pre-carbonization treatment on the powdery material in an inert or weakly reducing atmosphere to obtain a pre-carbonized powder, wherein the pre-carbonization temperature of the pre-carbonization treatment is 300 - 650 °C; repeating the impregnation and centrifuging treatment, the drying treatment and the pre-carbonization treatment on the pre-carbonized powder at least 2 times to obtain a carbonization precursor. Performing a carbonization treatment on the carbonization precursor in an inert or weakly reducing atmosphere, wherein the carbonization temperature of the carbonization treatment is 1100 - 1500 °C.

[0016] In some implementation manners of the fifth aspect, the concentration of the precursor solution is 30 - 120 g / L.

[0017] In some implementation manners of the fifth aspect, the concentration of the precursor solution is 30 g / L.

[0018] When the concentration of the precursor solution is 30 g / L, the prepared negative electrode material has better electrochemical performance.

[0019] In some implementation manners of the fifth aspect, the carbonization temperature is 1500 °C.

[0020] When the carbonization temperature is 1500 °C, the prepared negative electrode material has better electrochemical performance.

[0021] In some implementation manners of the fifth aspect, the pre-carbonization temperature is 450 - 550 °C.

[0022] When the pre-carbonization temperature is 450 - 550 °C, the average pore size of the negative electrode material can be reduced, and the prepared negative electrode material has better electrochemical performance.

[0023] In some implementation manners of the fifth aspect, the precursor is low-temperature pitch or high-temperature pitch.

[0024] When the precursor is low-temperature pitch or high-temperature pitch, the prepared negative electrode material has better electrochemical performance.

[0025] In some implementations of the fifth aspect, the solvent is tetrahydrofuran and the drying temperature is 70 °C; or the solvent is pyridine and the drying temperature is 115 °C.

[0026] The evaporation temperatures of tetrahydrofuran and pyridine are close to the evaporation temperature of water. Using one of them as the solvent is conducive to the convenience of industrial production.

[0027] In some implementations of the fifth aspect, the number of impregnation and centrifugation treatments, drying treatments, and pre-carbonization treatments is 5 times.

[0028] Increasing the number of impregnation and centrifugation treatments, drying treatments, and pre-carbonization treatments can increase the graphitization degree and improve the electrochemical performance. Description of the Drawings

[0029] Figure 1 It is the TEM image of Example 1 of the present application.

[0030] Figure 2 It is the nitrogen adsorption / desorption isotherm test of Example 1 of the present application.

[0031] Figure 3 It is the pore size distribution diagram of Example 1 of the present application.

[0032] Figure 4 It is the pore size distribution diagram of Example 8 of the present application.

[0033] Figure 5 It is the EIS of Example 1 of the present application.

[0034] Figure 6 It is the rate performance diagram of Example 1 of the present application.

[0035] Figure 7 It is the cycle performance diagram of Example 1 of the present application. Detailed Embodiments

[0036] Next, the technical solutions in the present application will be described in conjunction with the drawings.

[0037] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. The defined range may or may not include the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also within the protection scope of this application. In addition, if multiple minimum end values, such as 1 and 2, are listed, and multiple maximum end values, such as 3, 4, and 5, are listed at the same time, the following ranges are all within the protection scope of this application: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed in this application, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter can take any arbitrarily large value, such as integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc., or real numbers 3.6, 7.85, 14.12493, etc.

[0038] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0039] The following briefly introduces common technical terms in this field.

[0040] Impregnation method: A material treatment method in which the object to be impregnated is immersed in a solution so that the solute in the solution penetrates into the internal pores or crystal structure of the object to be impregnated. The impregnation method can also be called the liquid-phase impregnation method.

[0041] Polycyclic aromatic hydrocarbons (PAHs): Aromatic hydrocarbons containing two or more benzene rings, such as coal, asphalt, petroleum, or diphenylmethane, triphenylmethane, naphthol, etc.

[0042] Porous carbon materials refer to a class of carbon materials with a porous structure, such as porous charcoal, activated carbon, carbon molecular sieves, etc. Porous charcoal refers to a specific substance that can be prepared and used. Porous charcoal is often used as one of the raw materials for carbon-based negative electrode materials in the field of battery preparation.

[0043] Classification of pore sizes: According to the pore size classification method of the International Union of Pure and Applied Chemistry (IUPAC), micropores refer to pores with a diameter less than 2 nm, mesopores (intermediate pores) refer to pores with a diameter between 2 and 50 nm, and macropores refer to pores with a diameter greater than 50 nm, including micron-sized pores. In this application, pores with d < 1 nm are defined as sub-micropores, and pores with 1 nm ≤ d < 2 nm are defined as large micropores.

[0044] The charge-discharge platform potential refers to the potential value at which the battery potential changes within a relatively stable region during the charging and discharging processes of the battery. This region is called the charge-discharge platform, and its potential value corresponds to the stable voltage of the battery in the charging and discharging states.

[0045] Disordered carbon layer materials usually have low crystallinity and a high specific surface area. Their structure is relatively loose, with many micropores and defects, and they are also called soft carbon materials or soft carbon. Common soft carbon materials include activated carbon.

[0046] Ordered carbon layer materials usually have high crystallinity, and their structure is more ordered and dense. They are also called hard carbon materials or hard carbon. Hard carbon generally has high crystallinity and order, with a large horizontal distance (L a ) between adjacent carbon atoms and a large carbon layer spacing (L c ). Compared with soft carbon, hard carbon has a lower specific surface area. Among them, graphite is the most typical hard carbon material. In addition, hard carbon is also a hard carbon material with high crystallinity.

[0047] Taking a sodium-ion battery as an example, when the battery is at the high-potential charge-discharge platform, sodium ions are stored by adsorbing and inserting into the carbon layer; when the battery is at the low-potential charge-discharge platform, sodium ions are filled in the micropores. Therefore, the ratio and combination method of the disordered carbon layer and the ordered carbon layer have a significant impact on the comprehensive performance of the sodium-ion battery. Materials formed by the combination of the disordered carbon layer and the ordered carbon layer are usually called heterogeneous carbon materials or composite carbon materials. If the ordered carbon layer is in a strip shape and adheres to the outside of the disordered carbon layer, this material can be called a coated carbon material.

[0048] Graphitization degree: The graphitization degree refers to the degree of order of the crystal structure in carbon materials. Highly graphitized carbon materials usually have better electrical conductivity and mechanical properties. The higher the graphitization degree, the more ordered the crystal structure of the carbon material, and its properties are closer to those of hard carbon. In Raman spectroscopy analysis, I G is a parameter representing the degree of order of the structure in carbon materials. A higher I G value usually indicates a higher strength of the crystal structure; I Dis a parameter representing an amorphous or defective structure. A higher I D value usually indicates the presence of more amorphous structures or defects in the carbon material. Usually, I D :I G can be used to characterize the graphitization degree. The smaller the value of I D :I G , the higher the surface graphitization degree.

[0049] The charge-discharge rate of the battery can be expressed by the ratio of the current density to the energy density. For example, for a battery with an energy density of 300 mAh / g, the charge rate of a charging current of 300 mA / g is 1 times, simply denoted as 1C; the charge rate of a charging current of 1200 mA / g is 4C, and so on.

[0050] There is a mutually restrictive relationship among the three performance indicators of the high-rate discharge capacity, cycle performance, and energy density of the ion battery. Taking the sodium-ion battery as an example, if the micropore diameter in the disordered carbon layer is small, the surface area of the electrode is relatively high, providing more insertion sites, which helps to increase the number of inserted sodium ions, that is, the energy density. However, correspondingly, the ion insertion is relatively difficult, which may lead to a decline in the battery performance during high-rate discharge. If the micropore diameter in the disordered carbon layer is large, the sodium ion insertion and extraction rate is relatively high, and the battery performance during high-rate discharge is high. However, correspondingly, on the one hand, it will reduce the surface area of the electrode, which may limit the number of insertion sites, thus affecting the energy density of the battery; on the other hand, it will reduce the cycle performance of the ion battery. Therefore, the proportion of micropores of different sizes in the disordered carbon layer has a significant impact on the comprehensive performance of the sodium-ion battery.

[0051] Gradient pore structure: In each embodiment of the present application, the pore diameter of a specific material aggregates at specific values in the sub-micropore and macropore distribution ranges, and has a small amount of mesopores, which indicates that the material has a gradient pore structure. Specifically, the pore structure of the material can be analyzed through the pore diameter distribution diagram. The pore diameter distribution diagram of the material with a gradient pore structure shows a peak shape in both the sub-micropore distribution range and the macropore distribution range. A reasonable gradient pore structure can achieve a balance among the high-rate discharge capacity, cycle performance, and energy density of the ion battery.

[0052] Pre-carbonization: The pre-carbonization in this embodiment refers to the process of heat-treating an organic material or a carbon precursor to transform it into a carbon material. The fully pre-carbonized organic material can form a pyrolytic carbon layer with high quality during carbonization.

[0053] Carbonization: Carbonization is a chemical reaction process that involves decomposing a compound into smaller molecules or building blocks under high-temperature conditions. This process is typically carried out in the absence of oxygen or other gases to prevent oxidation reactions. During carbonization, the high temperature can trigger the breaking of bonds within the compound, causing the macromolecule to shed functional groups or release some small molecules. Specifically, the carbonization of organic matter mainly includes carbonization in an oxygen-free environment above 1100 °C, and the carbonized organic matter forms an ordered carbon layer. This ordered carbon layer formed by carbonization is also called a pyrolytic carbon layer.

[0054] In the current related technologies, when preparing the anode material, the chemical vapor deposition (CVD) method is generally used to deposit other gases such as methane on the surface of soft carbon materials such as activated carbon to form a pyrolytic carbon layer. CVD has high energy consumption and low efficiency, and it is very difficult to deposit a pyrolytic carbon layer in the internal pores of soft carbon materials. There is also a type of technology that prepares porous hard carbon materials by carbonizing natural organic materials such as wood. However, such materials have a significant number of mesopores and macropores, a low soft carbon content, and the energy density and cycling performance of battery performance are affected.

[0055] The applicant has found through research that after impregnating a soft carbon material in a polycyclic aromatic hydrocarbon precursor and then carbonizing it, hard carbon materials can be filled in the internal micropores of the soft carbon material as an ordered carbon layer, obtaining a composite carbon material with a gradient pore structure and a reasonable ratio of soft and hard carbon, which is beneficial to improving the performance of the battery. It should be understood that the batteries referred to in the embodiments of the present application all refer to alkali metal ion batteries, including lithium-ion batteries or sodium-ion batteries, and also include magnesium-ion batteries, zinc-ion batteries, etc. An embodiment described by taking a lithium-ion battery as an example can also be applied to a sodium-ion battery, and vice versa.

[0056] In view of this, the embodiments of the present application provide an anode material. Among them, polycyclic aromatic hydrocarbons such as asphalt and coal are used as precursors, dissolved in organic solvents such as pyridine and tetrahydrofuran to form a liquid phase, and a porous carbon material is placed in the precursor liquid phase for impregnation, and after multiple pre-carbonizations, carbonization is carried out to obtain a composite carbon material with a gradient pore structure. This anode material can improve the structural stability and electrochemical performance of the battery. Further, an anode electrode sheet and a battery can be prepared according to this anode material.

[0057] [Anode Material]

[0058] In this embodiment, the anode material is a porous carbon material with micropores, and the anode material is also called powder. In this anode material, the proportion of sub-micropores is 25% - 80%, the proportion of macropores is 20% - 75%, and the proportion of mesopores is less than or equal to 10%; among them, sub-micropores refer to micropores with a diameter less than 1 nanometer, and macropores refer to micropores with a diameter greater than or equal to 1 nanometer and less than 2 nanometers.

[0059] In some embodiments, in the negative electrode material, the proportion of sub-micropores is 45% to 75%, the proportion of macropores is 25% to 45%, and the proportion of mesopores is less than or equal to 10%.

[0060] In some embodiments, the graphitization degree of the negative electrode material is less than 1.3.

[0061] In some embodiments, the graphitization degree of the negative electrode material is less than 1.2.

[0062] The negative electrode material of the present application can be prepared by the following method:

[0063] Dissolve the precursor in a solvent, stir, disperse and then centrifuge to obtain a precursor solution, wherein the precursor is a polycyclic aromatic hydrocarbon substance;

[0064] Use the precursor solution to impregnate and centrifuge the porous carbon material to obtain an insoluble substance;

[0065] Dry the insoluble substance to obtain a powdery material;

[0066] Pre-carbonize the powdery material in an inert or weakly reducing atmosphere to obtain a pre-carbonized powder, wherein the pre-carbonization temperature of the pre-carbonization treatment is 300 to 650 °C;

[0067] Repeat the impregnation and centrifugation treatment, drying treatment and pre-carbonization treatment of the pre-carbonized powder at least 2 times to obtain a carbonization precursor.

[0068] Carbonize the carbonization precursor in an inert or weakly reducing atmosphere, wherein the carbonization temperature of the carbonization treatment is 1100 to 1500 °C.

[0069] It should be understood that during the pre-carbonization process, the volatilization process of small molecules in the powdery material is more likely to form sub-micropores in the powdery material; while during the carbonization process at 1100 °C, the volatilization process of small molecules in the carbonization precursor is more likely to form macropores in the carbonization precursor. Therefore, the selection of the pre-carbonization temperature has a great influence on the pore structure and pore size of the negative electrode material. Optionally, the pre-carbonization temperature is 450 to 550 °C.

[0070] It should be understood that by adjusting the diameter and proportion of micropores, the storage form and total amount of active ions such as lithium ions and sodium ions in the porous carbon material can be further adjusted. In some embodiments, repeat the impregnation and centrifugation treatment, drying treatment and pre-carbonization treatment of the pre-carbonized powder 4 times to adjust the diameter and proportion of micropores.

[0071] In some embodiments, the mass of the precursor is 1 to 20 g, and the volume of the organic solvent is 100 mL, that is, the concentration of the precursor solution is 10 to 200 g / L.

[0072] Optionally, the mass of the precursor is 3 to 12 g, and the concentration of the precursor solution is 30 to 120 g / L.

[0073] Optionally, the mass of the precursor is 3 g, and the concentration of the precursor solution is 30 g / L.

[0074] In some embodiments, the mass of the porous carbon material is 10 to 20 g, that is, the ratio of the mass of the porous carbon material to the volume of the solvent is 100 to 200 g / L. A reasonable amount of the porous carbon material can balance the impregnation efficiency and the yield of the negative electrode material.

[0075] In some embodiments, the precursor can be pitch or coal. These two types of precursors are easily obtained and have no biological toxicity, which is convenient for industrial production.

[0076] In some embodiments, the porous carbon material can be soft carbon materials such as activated carbon and porous carbon, or hard carbon materials such as graphite and hard carbon.

[0077] In some embodiments, the organic solvent can be tetrahydrofuran or pyridine. The temperature at which these organic solvents volatilize completely is close to the temperature at which water vapor evaporates. During industrial production, a common blast drying oven for drying aqueous solutions can be fully utilized. Specifically, when tetrahydrofuran is used as the solvent, the drying temperature is greater than or equal to 70 °C; when pyridine is used as the solvent, the drying temperature is greater than or equal to 115 °C. If other solvents are used, appropriate drying temperatures should be selected.

[0078] In some embodiments, the inert or weakly reducing atmosphere can be an argon atmosphere, a nitrogen atmosphere, a hydrogen atmosphere, or a carbon dioxide atmosphere. Optionally, an argon atmosphere is used during both the pre-carbonization treatment and the carbonization treatment.

[0079] Optionally, the carbonization temperature is greater than or equal to 1300 °C, which can further improve the electrochemical performance of the obtained powder.

[0080] Optionally, the carbonization temperature is 1500 °C, which can further improve the electrochemical performance of the obtained powder.

[0081] [Negative electrode plate]

[0082] An embodiment of the present application provides a negative electrode plate, including the negative electrode material in the above embodiments.

[0083] In some embodiments, the negative electrode plate includes a negative electrode current collector and a coating provided on the negative electrode current collector. The coating includes the negative electrode material in the above embodiments.

[0084] In some embodiments, the coating includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride - tetrafluoroethylene - propylene terpolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene terpolymer, tetrafluoroethylene - hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0085] In some embodiments, the coating includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0086] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum 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.).

[0087] [Battery]

[0088] An embodiment of the present application provides a battery, including the negative electrode sheet in the above - mentioned embodiment.

[0089] The embodiment of the present application does not particularly limit the shape of the battery, and it can be cylindrical, square, button - shaped battery, soft - package battery, or any other shape.

[0090] In some embodiments, the positive electrode sheet includes a lithium - containing metal oxide or a sodium - containing metal oxide coating.

[0091] Optionally, the battery includes an electrolyte. The electrolyte can be solid - state, semi - solid - state, or liquid - state, and the embodiment of the present application does not make specific limitations on this.

[0092] [Electric - using device]

[0093] An embodiment of the present application provides an electric - using device, including the battery described in the above - mentioned embodiment.

[0094] The electric - using device can be electronic products such as smartphones, smart tablet devices, watches, etc., or industrial and commercial facilities such as base stations, data centers, energy storage centers, and energy storage modules of photovoltaic power stations. The embodiment does not limit the type and use of the electric - using device.

[0095] In the following examples, where specific techniques or conditions are not indicated, they shall be in accordance with the techniques or conditions described in the literature in this field or in accordance with the product specifications. Where the manufacturers of the reagents or instruments used are not indicated, they are all conventional products that can be obtained commercially.

[0096] <Example 1>

[0097] (a) Dissolve 3 g of high-temperature pitch in 100 mL of tetrahydrofuran to obtain a suspension of 30 g / L. Stir the suspension magnetically at 600 r / min and disperse for another 1 h.

[0098] (b) Centrifuge the suspension obtained in step (a) at 8000 r / min for 10 min to remove the insoluble matter. Take the supernatant to obtain the precursor solution.

[0099] (c) Immerse 20 g of porous carbon in the solution obtained in step (b) for 12 h. Stir magnetically at 600 r / min and disperse for another 1 h.

[0100] (d) Centrifuge the suspension obtained in step (c) at 8000 r / min for 10 min, and then collect the insoluble matter.

[0101] (e) Place the insoluble matter obtained in step (d) in an oven and dry it at 70 °C for 12 h to ensure that the solvent is completely evaporated, obtaining a powdery material.

[0102] (f) Perform pre-carbonization treatment on the powdery material obtained in step (e) in an inert or weakly reducing atmosphere. Heat it at a heating rate of 2 - 5 °C / min to 550 °C and hold for 1 h.

[0103] (g) Repeat steps (c) to (f) for the powdery material obtained in step (f) 4 times.

[0104] (h) Perform carbonization treatment on the powdery material obtained in step (g) in an argon atmosphere. Heat it at a heating rate of 2 °C / min to 1300 °C and hold for 2 h. After cooling to room temperature, collect the powdery material to obtain the anode material.

[0105] <Example 2>

[0106] The preparation method of Example 2 is substantially the same as that of Example 1, except that the concentration of the precursor solution in step (a) is different. In Example 2, dissolve 12 g of low-temperature pitch in 100 mL of tetrahydrofuran to obtain a precursor solution of 120 g / L.

[0107] <Example 3>

[0108] The preparation method of Example 3 is substantially the same as that of Example 1, except that:

[0109] First, the solvents in step (a) are different. In Example 3, 3 g of high-temperature pitch was dissolved in 100 mL of pyridine.

[0110] Second, the drying temperature in step (e) was reselected according to the new solvent. In Example 3, the drying temperature was 115 °C.

[0111] <Example 4>

[0112] The preparation method of Example 4 was substantially the same as that of Example 1, except that the precursor in step (a) was different. In Example 4, 3 g of low-temperature pitch was dissolved in 100 mL of tetrahydrofuran.

[0113] <Example 5>

[0114] The preparation method of Example 5 was substantially the same as that of Example 1, except that the precursor in step (a) was different. In Example 5, 3 g of pulverized coal was dissolved in 100 mL of tetrahydrofuran.

[0115] <Example 6>

[0116] The preparation method of Example 6 was substantially the same as that of Example 1, except that the pre-carbonization temperature in step (f) was different. In Example 6, the pre-carbonization temperature was 450 °C.

[0117] <Example 7>

[0118] The preparation method of Example 7 was substantially the same as that of Example 1, except that the carbonization temperature in step (h) was different. In Example 7, the carbonization temperature was 1500 °C.

[0119] <Example 8>

[0120] The preparation method of Example 8 was substantially the same as that of Example 1, except that the number of repetitions of steps (b) to (f) in step (g) was different. In Example 8, steps (c) to (f) were repeated 2 times.

[0121] It should be understood that the settings of parameters such as the magnetic stirring speed, centrifugation speed and time, impregnation time, drying time, and protective atmosphere are related to the preparation scale of the product or the model of the equipment used, and have no direct connection with the performance of the prepared anode material. The settings of such parameters should not be construed as a limitation on the technical solution of this application.

[0122] The parameters of the above examples are shown in Table 1.

[0123] Table 1

[0124]

[0125] Mix the above-mentioned anode material, polyvinylidene fluoride binder, and carbon black conductive agent in a mass ratio of 90:5:5. Using N-methyl-pyrrolidone as the solvent, adjust the amount of solvent added to control the slurry viscosity within 100 - 20,000 mPa·s. Use a coater or sprayer to coat this slurry on the anode current collector. After drying at 85°C, perform cold pressing, then trim the edges, cut into pieces, and slit into strips. Then dry in a vacuum at 85°C for 4 hours and weld the tabs to make the anode plate of the battery meeting the requirements.

[0126] Stack and wind the above-mentioned anode plate, separator, and cathode plate in sequence to obtain an electrode assembly; place the electrode assembly into an outer package, add electrolyte, and after processes such as encapsulation, standing, formation, and aging, obtain the battery. In some embodiments, the cathode plate includes a coating of lithium-containing metal oxide or sodium-containing metal oxide.

[0127] [Measurement of energy density]

[0128] At 25°C, charge the battery at a constant current of 0.33C to 4.35V, then charge at a constant voltage of 4.35V until the current is less than 0.05C, and then discharge at 0.33C to 2.8V to obtain the discharge energy E; weigh on an electronic scale to obtain the mass m. It should be understood that the above charging voltage and discharging voltage can be adjusted according to the actual performance of the cathode material or anode material, and this embodiment does not limit this.

[0129] The energy density K = E / m.

[0130] [Measurement of rate performance]

[0131] Use a constant current charge and discharge instrument. Under the condition of 25°C, perform multiple charge and discharge tests on the battery at different current densities successively, and record the energy density of the battery after each charge and discharge process. Specifically, first perform 5 - 10 charge and discharge cycles at a current density of 30 mA / g, then perform 5 - 10 charge and discharge cycles at a current density of 50 mA / g, and so on, perform charge and discharge cycles at current densities of 100 mA / g, 300 mA / g, 500 mA / g, 1000 mA / g, and 2000 mA / g to obtain the rate performance graph. Among them, the "rate" can be expressed by the ratio of the current density to the battery energy density.

[0132] [Measurement of cycle performance]

[0133] Use a constant current charge and discharge instrument. Under the condition of 25°C, perform multiple charge and discharge tests on the battery at the same current density, and record the energy density of the battery after each charge and discharge process. The current density selected in this application is 1000 mA / g.

[0134] A half-cell is a portion of a battery that contains only one electrode (positive or negative) and its corresponding electrolyte. It should be understood that the energy density, rate capability, and cycle performance tests in this embodiment are all conducted on the negative electrode portion of the battery.

[0135] [Test of lattice constant]

[0136] The X-ray diffraction pattern of the material was measured using a D8 Advance X-ray diffractometer, and the structure and relative number of graphite crystals were analyzed using the software provided by the device. Finally, the horizontal distance between adjacent carbon atoms (L a ) and carbon interlayer spacing (L c ).

[0137] [Test of graphitization degree]

[0138] Thermo Scientific DXR3 SmartRaman spectrometer was used to test the Raman scattering intensity of the material in the G band. G and the Raman scattering intensity I in the D band D , calculate the degree of graphitization.

[0139] [Pore size test and nitrogen adsorption / desorption isotherm test]

[0140] The TriStar II 3020 high-throughput surface area and pore size analyzer and its built-in software were used to directly obtain the pore size distribution data and nitrogen adsorption / desorption isotherms of the materials. Nitrogen adsorption / desorption was used to measure the pore size distribution of materials larger than 1 nm, while carbon dioxide adsorption / desorption was used to measure the pore size distribution of materials less than or equal to 1 nm.

[0141] In addition to the above examples, this application also uses a negative electrode material and battery prepared from commercially available hard carbon as a comparative example for characterization and testing. Table 2 shows the experimental results of each example and comparative example.

[0142] Table 2

[0143]

[0144] Table 2 shows the distribution ratio of the micropore diameters of the composite carbon materials in each embodiment in the submicropore, macropore, and mesopore ranges. In the negative electrode material of this application, submicropores account for 25% to 80%, macropores account for 20% to 75%, and mesopores account for ≤10%.

[0145] In this application, the graphitization degree can be used to represent the ratio of soft carbon to hard carbon in the prepared anode material, and the energy density retention rate is the ratio of the energy density measured at a half-cell charge-discharge current density of 1000 mA / g to the energy density measured at a half-cell charge-discharge current density of 30 mA / g, which represents the high-rate discharge performance of the battery. The graphitization degree of the comparative example is 1.42, and the energy density retention rate is significantly lower than that of each example. Among the examples, the energy density retention rate of Example 8 with the highest graphitization degree is the lowest, and the energy density retention rate of Example 5 with the lowest graphitization degree is the highest. The rule of the graphitization degree and the energy density retention rate of the remaining examples conforms to the phenomenon that the lower the graphitization degree, the higher the energy density retention rate.

[0146] Among the 8 examples of this application, the graphitization degree of 6 examples is less than 1.2. Preferably, the graphitization degree of the anode material of this application is less than 1.2, and it has a higher energy density retention rate.

[0147] Combined with Table 2, it can be seen that except for Example 6, in the anode material of this application, the proportion of submicropores is higher than that of macropores. The proportion of submicropores is 45% - 75%, the proportion of macropores is 25% - 45%, and the proportion of mesopores is ≤10%. The temperature of the pre-carbonization treatment in the preparation process of Example 6 is 450 °C, which is lower than 550 °C of other examples. The proportion of macropores in Example 6 is significantly larger than that of other examples, indicating that choosing a pre-carbonization treatment temperature of 550 °C can reduce the average pore diameter. Comparing the electrochemical performances of Example 1, Example 3, and Example 6, it can be found that the electrochemical performances of Example 1 and Example 3 with smaller average pore diameters are higher than those of Example 6 with a larger average pore diameter. Therefore, reducing the average pore diameter can improve the electrochemical performance.

[0148] In the preparation process of Example 8, the number of repetitions of impregnation, centrifugation, and pre-carbonization treatment is less than that of other examples, resulting in Example 8 having the highest graphitization degree among all examples. Therefore, increasing the number of repetitions of impregnation, centrifugation, and pre-carbonization treatment can reduce the graphitization degree.

[0149] The carbonization temperature in the preparation process of Example 7 is higher than that of other examples, and the highest energy density and cyclic energy density are obtained. Therefore, the carbonization temperature is preferably 1500 °C.

[0150] In the preparation process of Example 5, pulverized coal was selected as the precursor, and its electrical properties are relatively lower than those of other examples, while the precursors selected in other examples are all pitch. Therefore, the precursor is preferably low-temperature pitch or high-temperature pitch.

[0151] The concentration of the precursor solution in the preparation process of Example 2 is 120 g / L, which is higher than 30 g / L of other examples, and its electrical properties are relatively lower than those of other examples. Therefore, the concentration of the precursor solution is preferably 30 g / L.

[0152] Figure 1 It is the transmission electron microscope (TEM) image of Example 1. Among them, Figure 1 (a) in it shows the structure where the hard carbon phase (pyrolytic carbon layer) of the composite carbon material is embedded in the soft carbon phase (porous carbon), Figure 1 (b) in it shows the structure where the hard carbon phase of the composite carbon material coats the soft carbon phase. In both of these structures, the soft carbon phase and the hard carbon phase are fully combined with each other, and the structure is stable.

[0153] Figure 2 It is the nitrogen adsorption / desorption isotherm test of Example 1. Among them, P / P0 on the abscissa represents the relative pressure of the adsorbed gas. It can be clearly seen that the specific surface area of the porous carbon after being filled with the polycyclic aromatic hydrocarbon pyrolytic carbon layer decreases, indicating that the proportion of hard carbon in the composite carbon material has been significantly increased.

[0154] Figure 3 It shows the pore size distribution diagram obtained from Example 1. Among them, d on the abscissa p represents the pore size, and V in the ordinate p represents the pore volume, is a representation method of the relative quantity commonly used in the pore size distribution diagram. From Figure 3 (a) in it, it can be seen that the pore size of this material is mainly distributed in the micropore range and the mesopore range, and the number of macropores can be ignored; from Figure 3 (b) in it, it can be seen that this material shows a peak shape in both of the two sub-ranges of 0.4 - 0.7 nm and 0.7 - 1.0 nm, and is evenly distributed in the large micropore distribution range.

[0155] Figure 4 It shows the pore size distribution diagram of Example 8. From Figure 4 (a) in it, it can be seen that the pore size of this material is mainly distributed in the micropore range and the mesopore range, and the number of macropores can be ignored; from Figure 4 (b) in it, it can be seen that this material shows a peak shape in both of the two sub-ranges of 0.4 - 0.7 nm and 0.7 - 1.0 nm, and is evenly distributed in the large micropore distribution range.

[0156] Figure 5 It is the electrochemical impedance spectroscopy (EIS) diagram of Example 1. Among them, the abscissa represents the real part of the impedance of this material, the ordinate represents the opposite number of the imaginary part of the impedance of this material, and each point on the curve represents the test results at different frequencies. Compared with the original porous carbon material, the composite carbon material with a gradient pore structure has a higher impedance slope in the low-frequency region, indicating that the impedance of the sodium ion diffusion process inside the material particles is smaller.

[0157] Figure 6The rate performance graph for Example 1 shows that when the current density is 30-1000 mA / g, the energy density of the battery is significantly greater than that of the comparative example. Combined with Table 2, it can be seen that when the charge and discharge current density is 30 mA / g, the negative electrode half-cell energy density is 326-419 mAh / g; when the charge and discharge current density is 1000 mA / g, the negative electrode half-cell energy density is 118-208 mAh / g, and the energy density retention rate is 29.3%-44.8%, showing good high-rate discharge performance. The energy density retention rate of the comparative example is 19.0%, and when the charge and discharge current density is 1000 mA / g, the negative electrode half-cell energy density is 21 mAh / g, indicating lower electrochemical performance than all the examples.

[0158] Figure 7 This is the cycle performance diagram of Example 1. 300 charge and discharge cycles were performed at a charge and discharge current density of 1000 mA / g. The energy density retention rate of the negative electrode half-cell of Example 1 exceeded 90%, and the energy density was significantly greater than that of the comparative example.

[0159] In summary, the negative electrode material of the present application has a reasonable ratio of disordered carbon layers and ordered carbon layers, a stable combination, and a gradient pore structure, achieving relatively balanced and stable performance between the high-rate discharge capability, cycle performance and energy density of the ion battery.

[0160] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A negative electrode material, characterized in that, The negative electrode material is a porous carbon material with micropores: In the negative electrode material, the proportion of sub-micropores is 25% - 80%, the proportion of macropores is 20% - 75%, and the proportion of mesopores is less than or equal to 10%; wherein, the sub-micropores refer to micropores with a diameter less than 1 nm, and the macropores refer to micropores with a diameter greater than or equal to 1 nm and less than 2 nm.

2. The negative electrode material according to claim 1, wherein, In the negative electrode material, the proportion of the sub-micropores is 45% - 75%, the proportion of the macropores is 25% - 45%, and the proportion of the mesopores is less than or equal to 10%.

3. The negative electrode material according to claim 1 or 2, characterized in that, The graphitization degree of the negative electrode material is less than 1.

3.

4. The negative electrode material according to claim 3, characterized in that, The graphitization degree of the negative electrode material is less than 1.

2.

5. A negative electrode plate, characterized in that, Comprising the negative electrode material according to any one of claims 1 to 4.

6. A battery, characterized in that, Comprising the negative electrode plate according to claim 5.

7. An electrical device, characterized in that, Comprising the battery according to claim 6.

8. A method for preparing a negative electrode material, characterized in that, Comprising: Dissolve the precursor in a solvent, stir, disperse and then centrifuge to obtain a precursor solution, wherein the precursor is a polycyclic aromatic hydrocarbon substance; Use the precursor solution to impregnate and centrifuge the porous carbon material to obtain an insoluble substance; Dry the insoluble substance to obtain a powdery material; Pre-carbonize the powdery material in an inert or weakly reducing atmosphere to obtain a pre-carbonized powder, wherein the pre-carbonization temperature of the pre-carbonization treatment is 300 - 650 °C; Repeat the impregnation and centrifugation treatment, the drying treatment and the pre-carbonization treatment on the pre-carbonized powder at least 2 times to obtain a carbonization precursor; Carry out carbonization treatment on the carbonization precursor in an inert or weakly reducing atmosphere, wherein the carbonization temperature of the carbonization treatment is 1100 - 1500 °C.

9. The method according to claim 8, characterized in that, The concentration of the precursor solution is 30 - 120 g / L.

10. The method according to claim 9, characterized in that, The concentration of the precursor solution is 30 g / L.

11. The method according to any one of claims 8 to 10, characterized in that, The carbonization temperature is 1500 °C.

12. The method according to any one of claims 8 to 11, characterized in that, The pre-carbonization temperature is 450 - 550 °C.

13. The method according to any one of claims 8 to 12, characterized in that, The precursor is low-temperature pitch or high-temperature pitch.

14. The method according to any one of claims 8 to 13, characterized in that The solvent is tetrahydrofuran, and the drying temperature is 70 °C; or the solvent is pyridine, and the drying temperature is 115 °C.

15. The method according to any one of claims 8 to 14, characterized in that, The number of times of the impregnation and centrifugation treatment, the drying treatment and the pre-carbonization treatment is 5 times.

Images