Carbon negative electrode material and its preparation method

Abstract

The present invention relates to the technical field of carbon materials, and particularly relates to a carbon negative electrode material and a preparation method thereof. The preparation method of the carbon negative electrode material comprises the following steps: (a) preparing a wet film from a polyarylene oxadiazole stock solution, and then soaking the wet film in a solution to obtain a precursor; (b) performing carbonization treatment and graphitization treatment on the precursor to obtain the carbon negative electrode material; the solution comprises dioxane and water with a mass ratio of (2-6):1. Based on the polyarylene oxadiazole material, in the process of preparing the precursor, the precursor is washed with a specific solution to endow the precursor with a suitable pore structure. After subsequent carbonization and graphitization treatments, a carbon material with more stable micro-nano pore structures can be obtained, which is beneficial to the diffusion of lithium ions.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon materials, and particularly relates to a carbon negative electrode material and a preparation method thereof. Background Art

[0002] At present, lithium-ion batteries have become an important part of the society for storing and using electric energy. Among the numerous applications of lithium-ion batteries, electric vehicles are rapidly becoming the main source of demand for rechargeable batteries. However, the problems of short driving range and long charging time limit their further development. As a key component of electric vehicles, the energy density and power density of lithium-ion batteries determine the driving range and charging time of electric vehicles.

[0003] The main limiting factor for the difficult optimization of the charging time of electric vehicles is the negative electrode of lithium-ion batteries. The currently commercial negative electrode of lithium-ion batteries is graphite material. During the charging process, lithium ions in the electrolyte are inserted between the graphite lattices to achieve energy storage. However, the transport of lithium ions in graphite material shows a high degree of anisotropy. Lithium ions mainly enter the lattice from the edge of the graphite layer, resulting in a greatly increased transport path of lithium ions and the formation of lithium deposition. Therefore, developing a carbon negative electrode material with a high lithium ion diffusion rate is the key to optimizing the charging time of lithium-ion batteries.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] One object of the present invention is to provide a preparation method of a carbon negative electrode material. The prepared carbon negative electrode material has a certain number of pore structures, which is beneficial to the diffusion of lithium ions.

[0006] Another object of the present invention is to provide a carbon negative electrode material prepared by the above preparation method.

[0007] In order to achieve the above objects of the present invention, on the one hand, the present invention provides a preparation method of a carbon negative electrode material, including the following steps:

[0008] (a) A wet film is prepared from a polyaryleneoxadiazole stock solution, and then the wet film is soaked in a solution to obtain a precursor;

[0009] (b) The precursor is subjected to carbonization treatment and graphitization treatment to obtain a carbon negative electrode material;

[0010] The solution includes dioxane and water with a mass ratio of (2-6):1.

[0011] In a specific embodiment of the present invention, the solution includes dioxane and water with a mass ratio of (3-5):1.

[0012] In a specific embodiment of the present invention, the time of the soaking treatment is 0.5 to 2 h. Further, in the soaking treatment, the solution is replaced every 15 to 25 min.

[0013] In a specific embodiment of the present invention, the thickness of the wet film is 200 to 800 μm.

[0014] In a specific embodiment of the present invention, the preparation of the poly(arylene oxadiazole) stock solution includes: reacting nitroterephthalic acid and hydrazine salt at 80 to 90 °C for 1.5 to 2.5 h under the action of fuming sulfuric acid; then reacting at 120 to 130 °C for 0.5 to 1 h. Further, the solid content of the poly(arylene oxadiazole) stock solution is 4% to 6%.

[0015] In a specific embodiment of the present invention, the molar ratio of the nitroterephthalic acid to the hydrazine salt is 1:(1.05 to 1.1).

[0016] In a specific embodiment of the present invention, in the carbonization treatment, the temperature is 1100 to 1300 °C, and the heat preservation time is 10 to 30 min. Further, in the carbonization treatment, the heating rate from room temperature to 1100 to 1300 °C is 8 to 12 °C / min.

[0017] In a specific embodiment of the present invention, in the graphitization treatment, the temperature is 1800 to 2200 °C, and the heat preservation time is 30 to 50 min. Further, in the graphitization treatment, the heating rate from 1100 to 1300 °C to 1800 to 2200 °C is 8 to 12 °C / min.

[0018] On the other hand, the present invention provides a carbon negative electrode material, which is prepared by using the preparation method of any one of the above-mentioned carbon negative electrode materials.

[0019] In a specific embodiment of the present invention, the BET specific surface area of the carbon negative electrode material is 15 to 60 cm 2 / g.

[0020] On the other hand, the present invention provides a negative electrode plate, which includes a current collector and a negative electrode active layer; in the negative electrode active layer, any one of the above-mentioned carbon negative electrode materials is included.

[0021] On yet another aspect, the present invention provides a secondary battery, which includes a positive electrode plate, a negative electrode plate and an electrolyte; the negative electrode plate is any one of the above-mentioned negative electrode plates.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The present invention is based on poly(arylene oxadiazole) materials. During the preparation of the precursor, washing is carried out with a specific solution to endow the precursor with a suitable pore structure. After subsequent carbonization and graphitization treatments, a carbon material with more stable micro-nano pore structures can be obtained, which is beneficial to the diffusion of lithium ions.

[0024] (2) The negative electrode sheet prepared with the carbon negative electrode material of the present invention has an impedance significantly lower than that of a commercial graphite negative electrode, and the diffusion coefficient of the negative electrode sheet is significantly higher than that of the commercial graphite negative electrode.

[0025] (3) The secondary battery assembled with the negative electrode sheet of the present invention has a high capacity and excellent cycle stability, and has high practical value. Description of the Drawings

[0026] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0027] Figure 1 It is the electron micrograph of the precursor film provided in Example 1 of the present invention.

[0028] Figure 2 It is the electron micrograph of the precursor film provided in Comparative Example 1 of the present invention.

[0029] Figure 3 It is the electron micrograph of the precursor film provided in Comparative Example 2 of the present invention.

[0030] Figure 4 It is the electron micrograph of the carbon negative electrode material provided in Example 1 of the present invention.

[0031] Figure 5 It is the electron micrograph of the carbon negative electrode material provided in Comparative Example 1 of the present invention.

[0032] Figure 6 It is the electron micrograph of the carbon negative electrode material provided in Comparative Example 2 of the present invention.

[0033] Figure 7 It is the electron micrograph of the commercial graphite negative electrode of Comparative Example 3.

[0034] Figure 8 It is the adsorption isotherm curve of the carbon negative electrode material provided in Example 1 of the present invention.

[0035] Figure 9 It is the XRD pattern of the nitro poly(arylene oxadiazole) material and the p-phenylene poly(arylene oxadiazole) material prepared in Example 1 and Example 16 of the present invention.

[0036] Figure 10 The electron microscope image of the precursor film provided in Embodiment 16 of the present invention;

[0037] Figure 11 The constant current charge-discharge curve of the carbon negative electrode material provided in Embodiment 1 of the present invention;

[0038] Figure 12 The impedance test results corresponding to the carbon negative electrode material provided in Embodiment 1 of the present invention and the commercial graphite negative electrode;

[0039] Figure 13 The lithium ion diffusion coefficient corresponding to the carbon negative electrode material provided in Embodiment 1 of the present invention;

[0040] Figure 14 The lithium ion diffusion coefficient corresponding to the commercial graphite negative electrode of Comparative Example 3;

[0041] Figure 15 The charge-discharge curve of the full cell prepared from the carbon negative electrode material provided in Embodiment 1 of the present invention;

[0042] Figure 16 The cycle life curves of the full cells prepared from the carbon negative electrode material provided in Embodiment 1 of the present invention and the full cells prepared from the commercial graphite negative electrode. Detailed implementation manners

[0043] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific implementation manners. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. For those conditions not specified in the embodiments, they shall be carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0044] One aspect of the present invention provides a preparation method of a carbon negative electrode material, including the following steps:

[0045] (a) A wet film is prepared from a polyarylene oxadiazole stock solution, and then the wet film is immersed in a solution for treatment to obtain a precursor;

[0046] (b) The precursor is subjected to carbonization treatment and graphitization treatment to obtain a carbon negative electrode material;

[0047] The solution includes dioxane and water with a mass ratio of (2-6):1.

[0048] In the preparation of the carbon negative electrode material of the present invention, based on the polyarylene oxadiazole material, a polyarylene oxadiazole wet film form is first prepared from the stock solution, and then the wet film is immersed in a specific solution. By using the dissolution of a proper amount of dioxane in sulfuric acid in the solution, a porous structure is formed in the wet film. After subsequent carbonization and graphitization treatments, a carbon material with more stable micro-nano pore structures can be obtained, which is beneficial to the diffusion of lithium ions.

[0049] The present invention studies and finds that the composition of the solution for treating the wet film has a great influence on the pore structure in the precursor. Dioxane has a stronger binding ability with sulfuric acid than water, and for the same volume, dioxane can absorb more sulfuric acid than water. When washing the POD wet film with dioxane, a large amount of sulfuric acid will be quickly absorbed by dioxane, and the whole solidification time is short, which is beneficial to the formation of the pore structure. While using water to wash the POD wet film, the solidification time is long, and the heat released by the combination of water and sulfuric acid is large. Therefore, the POD molecular chains have time to move sufficiently, which easily leads to the closure of the pore structure of the POD film. When the content of dioxane in the solution is too high, a large number of pores with larger sizes will be formed in the precursor, resulting in too low strength of the precursor film, and it is difficult to maintain the pore structure during subsequent carbonization and graphitization treatments; when the water content in the solution is too high, no pore structure can be formed in the precursor. The present invention uses a solution of dioxane and water with a mass ratio of (2 - 6):1 to immerse the wet film, on the one hand, to form a precursor with a certain number of pore structures, and on the other hand, to avoid too large pore structure sizes to prevent the collapse of the pore structure during subsequent carbonization and graphitization treatments. For example, in different embodiments, the mass ratio of dioxane to water in the solution can be 2:1, 3:1, 4:1, 5:1, 6:1 or the range composed of any two of them.

[0050] Most organic solvents such as NMP, DMSO, etc. will react with sulfuric acid and cannot be used in the present invention. When using ethanol, since ethanol will also react with sulfuric acid above 140°C, the whole reaction temperature needs to be controlled not to exceed 60°C. And when using ethanol to replace the mixed solution of dioxane and water in the present invention, the surface of the whole POD film obtained is still relatively dense, and the pore structure of the POD film is less, and a carbon material with micro-nano porous structures cannot be prepared.

[0051] In a specific embodiment of the present invention, the solution comprises dioxane and water with a mass ratio of (3 - 5):1. By further optimizing and adjusting the composition of the solution, the pore structure of the prepared carbon negative electrode material can be further optimized to facilitate the diffusion of lithium ions, etc.

[0052] In a specific embodiment of the present invention, the immersion treatment time is 0.5 - 2 h. Further, during the immersion treatment, the solution is replaced every 15 - 25 min.

[0053] In actual operation, in a single immersion, the amount of the solution is 50 to 60 times the mass of the wet film. By controlling the amount of the solution within the above range, sulfuric acid can be washed out at an appropriate rate, ensuring that the POD precursor film has an appropriate and stable pore structure.

[0054] The soaking time of the treatment affects the number and size of the pore structures in the precursor obtained after soaking the wet film. If the soaking time is too long, the pore structure size is likely to be too large; while if the soaking time is insufficient, the number of pore structures is small. For example, in different embodiments, the soaking time can be 0.5 h, 1 h, 1.5 h, 2 h or the range composed of any two of them.

[0055] In actual operation, during the soaking treatment, the solution is replaced every 15 to 25 minutes, the solution is removed, and a new solution is used to continue soaking. The ratio of the new solution is the same as that of the solution before replacement. Replacing the solution at regular intervals can avoid too high acidity of the soaking solution, resulting in insufficient washing of sulfuric acid. The residual sulfuric acid in the precursor will cause poly(arylene oxadiazole) to degrade during the carbonization process, thereby reducing the conductivity of the finally obtained carbon negative electrode material.

[0056] In a specific embodiment of the present invention, the thickness of the wet film is 200 to 800 μm.

[0057] The thickness of the wet film affects the soaking process of the solution on the wet film. For example, if the thickness of the wet film is too high, the pore uniformity of different parts of the precursor along the thickness direction is poor. For example, in different embodiments, the thickness of the wet film can be 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm or the range composed of any two of them.

[0058] In actual operation, the preparation method of the wet film may include: placing the poly(arylene oxadiazole) stock solution on a substrate such as a glass plate, and using a scraper or other film scraping device to prepare a wet film with a preset thickness.

[0059] In a specific embodiment of the present invention, the preparation of the poly(arylene oxadiazole) stock solution includes: reacting nitroterephthalic acid and hydrazine salt at 80 to 90 °C for 1.5 to 2.5 h under the action of fuming sulfuric acid; then reacting at 120 to 130 °C for 0.5 to 1 h. Further, the solid content of the poly(arylene oxadiazole) stock solution is 4% to 6%.

[0060] The reaction at 80 to 90 °C is mainly to completely dissolve the raw materials in fuming sulfuric acid and carry out prepolymerization to form a prepolymer; the reaction at 120 to 130 °C is mainly for the prepolymer to further polymerize to form a high polymer.

[0061] For example, in different embodiments, the solid content of the poly(arylene oxadiazole) stock solution can be 4%, 4.5%, 5%, 5.5%, 6% or the range composed of any two of them.

[0062] In a specific embodiment of the present invention, the molar ratio of nitroterephthalic acid to hydrazine salt is 1:(1.05 - 1.1). Among them, the hydrazine salt includes but is not limited to hydrazine sulfate. In fuming sulfuric acid, the sulfur trioxide content can be 20wt% - 30wt%, such as 25wt% but not limited thereto.

[0063] In the preparation of the poly(arylene oxadiazole) stock solution of the present invention, nitroterephthalic acid is used, and its large nitro side group is utilized to reduce the crystallinity of POD, making the POD structure more transportable and more conducive to pore formation.

[0064] In a specific embodiment of the present invention, during the carbonization treatment, the temperature is 1100 - 1300 °C, and the heat preservation time is 10 - 30 min. Further, during the carbonization treatment, the heating rate from room temperature to 1100 - 1300 °C is 8 - 12 °C / min.

[0065] In different embodiments, during the carbonization treatment, the temperature can be 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C or a range composed of any two of them, and the heat preservation time can be 10 min, 15 min, 20 min, 25 min, 30 min or a range composed of any two of them.

[0066] The present invention has found through research that when the heating rate is too fast, the carbonization of poly(arylene oxadiazole) in the precursor is insufficient; when the heating rate is too slow, the integrity of the pore structure deteriorates. In the carbonization treatment of the wet film to obtain a precursor with a certain pore diameter, the heating rate from room temperature to 1100 - 1300 °C is further controlled within the range of 8 - 12 °C / min to balance ensuring the integrity of the pore structure and the sufficiency of carbonization. In different embodiments, the heating rate from room temperature to 1100 - 1300 °C can be 8 °C / min, 9 °C / min, 10 °C / min, 11 °C / min, 12 °C / min or a range composed of any two of them.

[0067] In a specific embodiment of the present invention, during the graphitization treatment, the temperature is 1800 - 2200 °C, and the heat preservation time is 30 - 50 min. Further, during the graphitization treatment, the heating rate from 1100 - 1300 °C to 1800 - 2200 °C is 8 - 12 °C / min.

[0068] In different embodiments, during the graphitization treatment, the temperature can be 1800 °C, 1900 °C, 2000 °C, 2100 °C, 2200 °C or a range composed of any two of them, and the heat preservation time can be 30 min, 35 min, 40 min, 45 min, 50 min or a range composed of any two of them.

[0069] In the graphitization treatment, when the heating rate is too fast, the degree of graphitization of the finally obtained carbon negative electrode material is insufficient; when the heating rate is too slow, the pore structure is likely to collapse. In the regulation of graphitization treatment in the present invention, the heating rate from 1100 to 1300 °C to 1800 to 2200 °C is in the range of 8 to 12 °C / min to balance and ensure the integrity of the pore structure and the degree of graphitization. For example, in different embodiments, the heating rate from 1100 to 1300 °C to 1800 to 2200 °C can be 8 °C / min, 9 °C / min, 10 °C / min, 11 °C / min, 12 °C / min or the range composed of any two of them.

[0070] In actual operation, the carbonization and graphitization treatments can be carried out in a tube furnace. During the carbonization and graphitization processes, nitrogen is continuously introduced to ensure that the entire process is carried out under the protection of a protective gas.

[0071] On the other hand, the present invention provides a carbon negative electrode material prepared by using the preparation method of any one of the above carbon negative electrode materials.

[0072] In a specific embodiment of the present invention, the BET specific surface area of the carbon negative electrode material is 15 to 60 cm 2 / g, such as 40 to 60 cm 2 / g.

[0073] For example, in different embodiments, the BET specific surface area of the carbon negative electrode material can be 15 cm 2 / g, 20 cm 2 / g, 25 cm 2 / g, 30 cm 2 / g, 35 cm 2 / g, 40 cm 2 / g, 45 cm 2 / g, 50 cm 2 / g, 55 cm 2 / g, 60 cm 2 / g or the range composed of any two of them.

[0074] On the other hand, the present invention provides a negative electrode sheet, which includes a current collector and a negative electrode active layer; in the negative electrode active layer, any one of the above carbon negative electrode materials is included.

[0075] Among them, in the negative electrode active layer, in addition to the carbon negative electrode material, a conductive agent and a binder may also be included. The dosage of each component in the negative electrode active layer can be adjusted according to the conventional ratio in the art.

[0076] In some specific embodiments of the present invention, the type of the current collector is not limited and can be conventionally adjusted according to the actual requirements of the battery.

[0077] On the other hand, the present invention provides a secondary battery, comprising a positive electrode plate, a negative electrode plate and an electrolyte; the negative electrode plate is any one of the above-mentioned negative electrode plates.

[0078] The battery of the present invention can be used in various common electrical devices, such as transportation means, electronic products, etc., but is not limited thereto.

[0079] Example 1

[0080] This example provides a method for preparing a carbon negative electrode material, comprising the following steps:

[0081] (1) Preparation of poly(arylene oxadiazole) stock solution:

[0082] Charge nitroterephthalic acid and hydrazine sulfate in a molar ratio of 1:1.05, and the reaction solvent is fuming sulfuric acid (sulfur trioxide concentration is about 25 wt%, and the solid content of the overall charge is about 5%); heat the reaction materials to 80 °C and react for 2 h, then heat to 120 °C and react for 0.5 h, stop the reaction, and cool to room temperature.

[0083] (2) Preparation of precursor film:

[0084] Coat the stock solution prepared in step (1) on a glass plate, and use a scraper to coat to form a wet film with a thickness of 500 μm; then immerse the wet film in a solution for 1 h, and replace the fresh solution every 20 min (the solution ratio remains unchanged, and in a single immersion treatment, the mass of the solution is 55 times the mass of the wet film), and take out to obtain the precursor film; wherein, the solution is dioxane and water with a mass ratio of 4:1.

[0085] (3) Carbonization and graphitization treatment:

[0086] Place the precursor film prepared in step (2) in a tubular furnace, continuously introduce nitrogen, then heat to 1200 °C at a heating rate of 10 °C / min and hold for 20 min, and then continue to heat to 2000 °C at a heating rate of 10 °C / min and hold for 40 min; cool naturally to room temperature to obtain the carbon negative electrode material.

[0087] Example 2

[0088] This example refers to the method for preparing the carbon negative electrode material in Example 1, and the difference is only that: the composition of the solution used for the immersion treatment in step (2) is different.

[0089] In step (2) of this example, the solution used for the immersion treatment is dioxane and water with a mass ratio of 2:1.

[0090] Example 3

[0091] This example refers to the method for preparing the carbon negative electrode material in Example 1, and the difference is only that: the composition of the solution used for the immersion treatment in step (2) is different.

[0092] In step (2) of this embodiment, the solution used for the soaking treatment is dioxane and water with a mass ratio of 6:1.

[0093] Example 4

[0094] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being that the composition of the solution used for the soaking treatment in step (2) is different.

[0095] In step (2) of this embodiment, the solution used for the soaking treatment is dioxane and water with a mass ratio of 3:1.

[0096] Example 5

[0097] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being that the composition of the solution used for the soaking treatment in step (2) is different.

[0098] In step (2) of this embodiment, the solution used for the soaking treatment is dioxane and water with a mass ratio of 5:1.

[0099] Example 6

[0100] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being that in the soaking treatment of step (2) of this embodiment, the solution is not replaced.

[0101] Example 7

[0102] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being that the thickness of the wet film in step (2) is different.

[0103] In this embodiment, the thickness of the wet film is 200 μm.

[0104] Example 8

[0105] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being that the thickness of the wet film in step (2) is different.

[0106] In this embodiment, the thickness of the wet film is 800 μm.

[0107] Example 9

[0108] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being that step (3) is different.

[0109] Step (3) of this embodiment includes: placing the precursor film prepared in step (2) in a tubular furnace, continuously introducing nitrogen, then heating to 1100 °C at a heating rate of 8 °C / min and holding for 30 min, and then continuing to heat to 1800 °C at a heating rate of 8 °C / min and holding for 50 min; naturally cooling to room temperature to obtain the carbon negative electrode material.

[0110] Example 10

[0111] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being: step (3) is different.

[0112] Step (3) of this embodiment includes: placing the precursor film prepared in step (2) in a tubular furnace, continuously introducing nitrogen, then heating to 1300 °C at a heating rate of 12 °C / min and holding for 10 min, and then continuing to heat to 2200 °C at a heating rate of 12 °C / min and holding for 30 min; naturally cooling to room temperature to obtain the carbon negative electrode material.

[0113] Example 11

[0114] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being: step (3) is different.

[0115] Step (3) of this embodiment includes: placing the precursor film prepared in step (2) in a tubular furnace, continuously introducing nitrogen, then heating to 1200 °C at a heating rate of 2.5 °C / min and holding for 20 min, and then continuing to heat to 2000 °C at a heating rate of 10 °C / min and holding for 40 min; naturally cooling to room temperature to obtain the carbon negative electrode material.

[0116] Example 12

[0117] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being: step (3) is different.

[0118] Step (3) of this embodiment includes: placing the precursor film prepared in step (2) in a tubular furnace, continuously introducing nitrogen, then heating to 1200 °C at a heating rate of 15 °C / min and holding for 20 min, and then continuing to heat to 2000 °C at a heating rate of 10 °C / min and holding for 40 min; naturally cooling to room temperature to obtain the carbon negative electrode material.

[0119] Example 13

[0120] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being: step (3) is different.

[0121] Step (3) of this embodiment includes: placing the precursor film obtained in step (2) in a tube furnace, continuously introducing nitrogen, then heating it to 1200 °C at a heating rate of 10 °C / min and holding for 20 min, and then continuing to heat to 2000 °C at a heating rate of 5 °C / min and holding for 40 min; naturally cooling to room temperature to obtain the carbon negative electrode material.

[0122] Example 14

[0123] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being: step (3) is different.

[0124] Step (3) of this embodiment includes: placing the precursor film obtained in step (2) in a tube furnace, continuously introducing nitrogen, then heating it to 1200 °C at a heating rate of 10 °C / min and holding for 20 min, and then continuing to heat to 2000 °C at a heating rate of 15 °C / min and holding for 40 min; naturally cooling to room temperature to obtain the carbon negative electrode material.

[0125] Example 15

[0126] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being: step (3) is different.

[0127] Step (3) of this embodiment includes: placing the precursor film obtained in step (2) in a tube furnace, continuously introducing nitrogen, then heating it to 1400 °C at a heating rate of 10 °C / min and holding for 20 min, and then continuing to heat to 2500 °C at a heating rate of 10 °C / min and holding for 40 min; naturally cooling to room temperature to obtain the carbon negative electrode material.

[0128] Example 16

[0129] This embodiment refers to the preparation method of the carbon negative electrode material in Example 1, with the only difference being: in the preparation of the poly(arylene oxadiazole) stock solution in step (1), equimolar amounts of terephthalic acid are used to replace nitroterephthalic acid in Example 1.

[0130] Comparative Example 1

[0131] Comparative Example 1 refers to the preparation method of the carbon negative electrode material in Example 1, with the difference being: the composition of the solution used for the soaking treatment in step (2) is different.

[0132] The solution used for the soaking treatment in step (2) of Comparative Example 1 is dioxane and water with a mass ratio of 1:1.

[0133] Comparative Example 2

[0134] Comparative Example 2 refers to the preparation method of the carbon negative electrode material in Example 1, with the difference being: the composition of the solution used for the soaking treatment in step (2) is different.

[0135] In step (2) of Comparative Example 2, the solution used for the immersion treatment was pure dioxane.

[0136] Comparative Example 3

[0137] Commercial graphite anode material (Supplier: Kelude; Grade: MA-EN-AN-001204).

[0138] Experimental Example 1

[0139] Figure 1 This is the electron micrograph of the precursor film provided in Example 1 of the present invention. Figure 2 and Figure 3 are the electron micrographs of the precursor films provided in Comparative Example 1 and Comparative Example 2 of the present invention respectively. It can be seen from the figures that when the wet film is immersed in the solution of the present invention, a precursor with a pore structure of appropriate size and quantity can be formed. When the water content in the solution is too high, no pore structure can be formed; when the dioxane content in the solution is too high, a large number of pores with larger sizes will be formed in the precursor, and the strength of the precursor film is too low, and the pore structure will collapse and cannot be maintained during the subsequent carbonization and graphitization treatments.

[0140] Figure 4 This is the electron micrograph of the carbon anode material provided in Example 1 of the present invention. Figure 5 and Figure 6 are the electron micrographs of the carbon anode materials provided in Comparative Example 1 and Comparative Example 2 of the present invention respectively. Figure 7 is the electron micrograph of the commercial graphite anode of Comparative Example 3. It can be seen from the figures that there are many micro-nano pore structures in the carbon anode material of the present invention, while the commercial graphite anode is in a flaky structure with a smooth surface and no obvious pore structure. In Comparative Example 1, the water content in the solution used was too high and no pore structure could be formed, and the carbonized material still had a high density; in Comparative Example 2, the dioxane content in the solution used was too high, and the pore size in the precursor was large and the quantity was large. During the carbonization and graphitization treatments, the pore structure collapsed and the porous structure could not be maintained. By comparison, it can be seen that the carbon anode material of the present invention is beneficial to the faster diffusion of lithium ions in the electrode and shortens the transmission distance of lithium ions.

[0141] The BET specific surface areas of the carbon anode materials of different examples and comparative examples were tested, and the test results are shown in Table 1. Figure 8 This is the adsorption isotherm curve of the carbon anode material (C-POD) provided in Example 1 of the present invention and the commercial graphite anode of Comparative Example 3.

[0142] Table 1 BET specific surface areas of different carbon anode materials

[0143]

[0144]

[0145] Figure 9 XRD patterns of the nitro poly(arylene oxadiazole) material and the p-phenylene poly(arylene oxadiazole) material prepared in Example 1 and Example 16 of the present invention (the preparation of the specific XRD samples includes: preparing precursor films according to the steps of Example 1 and Example 16 respectively, placing them in an oven and drying at 120 °C for 3 h to obtain XRD powder samples), Figure 10 is the electron micrograph of the precursor film provided in Example 16 of the present invention. From Figure 9 it can be seen that the crystallization peak intensity of the nitro poly(arylene oxadiazole) material in Example 1 is significantly lower than that of the p-phenylene poly(arylene oxadiazole) material in Example 16. As a result, the pore structure of the precursor film obtained in Example 1 of the present invention is more than that of the precursor film in Example 16, and the uniformity is better, which is beneficial to obtaining carbon materials with better performance after graphitization.

[0146] Experimental Example 2

[0147] In order to further prove the performance differences of different carbon negative electrode materials, the impedance and lithium ion diffusion coefficient were further tested. The specific test methods are as follows:

[0148] (1) Preparation of the lithium battery negative electrode: Mix the carbon negative electrode material, Super C65 conductive carbon black and PVDF in a mass ratio of 8:1:1, and add 10% of the NMP solution based on the solid mass, and stir evenly to form a negative electrode slurry. Then coat the slurry on the surface of the copper current collector, with the slurry coating thickness of 30 μm, and finally dry it in a vacuum oven to obtain the lithium battery negative electrode; the thickness of the battery active material is about 26 μm, the capacity of the graphite electrode is about 425 mAh / g, and the charge-discharge current density is 0.1 A / g. It is greater than the currently commercial graphite negative electrode (350 mAh / g). Figure 11 is the constant current charge-discharge curve corresponding to the carbon negative electrode material provided in Example 1 of the present invention.

[0149] (2) Assembly of the battery: Use graphite as the working electrode, and assemble a button-type half-cell with a metal lithium counter electrode. The separator is a ceramic-coated separator (provided by Kelude: MA-EN-SE-002402); among them, the electrolyte is 1 M LiPF6 + EC / DEC / DMC with a volume ratio of 1:1:1, and 5 wt% of ethylene carbonate is added;

[0150] (3) Conduct impedance and lithium ion diffusion tests on the battery, and the test results are shown in Table 2.

[0151] Figure 12The impedance test results of the carbon negative electrode material provided in Embodiment 1 of the present invention and the commercial graphite negative electrode are shown. It can be seen from the figure that in the intermediate frequency region, the R-cc of the carbon negative electrode material of the present invention is much smaller than that of the commercial negative electrode, indicating that the movement resistance of lithium ions in the electrode of the carbon negative electrode material of the present invention is small. Further, the diffusion coefficient was calculated. Figure 13 and Figure 14 are the lithium ion diffusion coefficients corresponding to the carbon negative electrode material and the commercial graphite negative electrode provided in Embodiment 1 of the present invention respectively. In the carbon negative electrode material of Embodiment 1 of the present invention, the lithium ion diffusion coefficient D Li+ is 9.8×10 -11 cm 2 / s. In the commercial graphite negative electrode of Comparative Example 3, the lithium ion diffusion coefficient D Li+ is 4.2×10 -11 cm 2 / s, further indicating that the electrode prepared from the carbon negative electrode material of Embodiment 1 of the present invention is more conducive to lithium ion transmission.

[0152] Table 2 Impedance and lithium ion diffusion coefficients of different carbon negative electrode materials

[0153]

[0154]

[0155] Furthermore, the electrochemical performance tests were carried out on the carbon negative electrode material of Embodiment 1 of the present invention and the commercial graphite negative electrode of Comparative Example 3. The negative electrode of the lithium battery, the aforementioned electrolyte and the lithium iron phosphate positive electrode (supplier: Kelude; grade: CU-EL-PL-200101) prepared according to the foregoing method were assembled into a full cell for charge and discharge tests. Figure 15 is the charge and discharge curve (charge rate 5C) of the full cell prepared from the carbon negative electrode material provided in Embodiment 1 of the present invention. It can be seen from the figure that obvious charge and discharge platforms appear during the charge and discharge processes, indicating that the energy storage behavior of the carbon negative electrode material of the present invention is the same as that of graphite and follows intercalation electrochemistry. Figure 16 is the cycle life curve of the full cell prepared from the carbon negative electrode material provided in Embodiment 1 of the present invention and the full cell prepared from the commercial graphite negative electrode. It can be seen from the figure that the capacity and cycle life of the full cell prepared from the carbon negative electrode material provided in Embodiment 1 of the present invention are significantly higher than those of the commercial graphite negative electrode at the 5C charge rate; this is also due to the rich pore structure of the carbon negative electrode material of the present invention; a large number of pore structures shorten the movement path of lithium ions in the electrode, resulting in a significant increase in both the capacity and the cycle life.

[0156] From the above test results, it can be seen that the present invention is based on poly(arylene oxadiazole) materials. During the preparation of the precursor, washing is carried out with a specific solution to endow the precursor with a suitable pore structure. After subsequent carbonization and graphitization treatments, a carbon material with more stable micro-nano pore structures can be obtained, which is beneficial to the diffusion of lithium ions. Compared with the currently commercial graphite negative electrode, the carbon negative electrode material with high lithium ion transport kinetics of the present invention can better exert the advantages of high capacity and long life in high-rate lithium batteries and has high practical value.

[0157] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a carbon negative electrode material, characterized in that: The steps include: (a) preparing a wet film using a poly(arylene oxadiazole) stock solution, and then immersing the wet film in a solution to obtain a precursor; (b) subjecting the precursor to carbonization and graphitization to obtain a carbon negative electrode material; The solution comprises dioxane and water in a mass ratio of (3-5) : 1; The preparation of the polyaromatic oxadiazole stock solution comprises: reacting nitroterephthalic acid and hydrazine salt at 80-90° C. for 1.5-2.5 hours under the action of fuming sulfuric acid; and then reacting at 120-140° C. for 0.5-1 hour.

2. The preparation method according to claim 1, characterized in that: The soaking time is 0.5 to 2 hours.

3. The preparation method according to claim 1, characterized in that: During the soaking treatment, the solution is replaced every 15 to 25 minutes.

4. The preparation method according to claim 1, characterized in that: The thickness of the wet film is 200-800 μm.

5. The preparation method according to claim 1, characterized in that: The solid content of the polyaromatic oxadiazole stock solution is 4% to 6%.

6. The preparation method according to claim 1, characterized in that: The molar ratio of the nitroterephthalic acid to the hydrazine salt is 1:(1.05-1.1).

7. The preparation method according to claim 1, characterized in that: In the carbonization treatment, the temperature is 1100-1300° C. and the insulation time is 10-30 minutes.

8. The preparation method according to claim 7, characterized in that: In the carbonization treatment, the heating rate from room temperature to 1100-1300° C. is 8-12° C. / min.

9. The preparation method according to claim 1, characterized in that: In the graphitization treatment, the temperature is 1800-2200° C. and the insulation time is 30-50 minutes.

10. The preparation method according to claim 9, characterized in that: In the graphitization treatment, the heating rate from 1100-1300° C. to 1800-2200° C. is 8-12° C. / min.

11. A carbon negative electrode material, characterized in that: The method is prepared according to any one of claims 1 to 10.

12. The carbon negative electrode material according to claim 11, characterized in that: The BET specific surface area of ​​the carbon negative electrode material is 15 to 60 cm 2 / g.

13. The carbon negative electrode material according to claim 11, characterized in that: The BET specific surface area of ​​the carbon negative electrode material is 40 to 60 cm 2 / g.

14. A negative electrode plate, characterized in that: It comprises a current collector and a negative electrode active layer; the negative electrode active layer comprises a carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 10 or a carbon negative electrode material according to any one of claims 11 to 13.

15. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, characterized in that: The negative electrode plate is the negative electrode plate according to claim 14.

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