A self-supporting film negative electrode material and preparation method thereof and sodium ion battery

Abstract

The application provides a self-supporting film negative material, a preparation method thereof and a sodium ion battery, and belongs to the technical field of battery materials. The preparation method comprises the following steps: mixing coal powder and one-dimensional nanocellulose solution to obtain a mixed solution; performing suction filtration on the mixed solution to obtain a composite film; and sequentially performing pre-carbonization and secondary carbonization on the composite film to obtain the self-supporting film negative material. The one-dimensional nanocellulose and zero-dimensional coal powder are matched with each other, so that the self-supporting film negative material can be directly prepared, without the need of forming a powder, and the compounding processes such as homogenization, coating, drying and the like are avoided, so that the method is simple and easy to implement, the use of a binder is saved, and the preparation cost is greatly reduced. Moreover, the structure that the one-dimensional nanocellulose surrounds the zero-dimensional coal powder particles formed by the process is helpful to improving the wettability of the electrolyte to the negative material, improving the diffusion and migration of sodium ions, so that the sodium ion battery has high specific capacity, a first coulomb efficiency and a rate performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a self-supporting film negative electrode material, a preparation method thereof and a sodium ion battery. BACKGROUND

[0002] Sodium element is rich in reserves, so that the sodium ion battery has a great advantage in cost, is expected to reduce the battery cost, and improve market competitiveness. In the sodium ion battery, the conventional prepared sodium battery negative electrode material is a powder material, and after the powder material is prepared into a negative electrode material, the powder material still needs to be uniformly grinded, coated, dried and the like to prepare a negative electrode sheet. This preparation method is relatively complex, the cost is high, and the capacity performance and rate performance of the sodium ion battery prepared based on this need to be further improved.

[0003] Therefore, how to solve the problem of the complex preparation process, save the use of the binder in the process of preparing the sheet from the powder negative electrode material, greatly reduce the preparation cost, and further improve the capacity performance and rate performance of the sodium ion battery is the key research direction at present. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a self-supporting film negative electrode material, a preparation method thereof and a sodium ion battery. The present application utilizes one-dimensional nanocellulose and zero-dimensional coal powder to cooperate with each other, so that the self-supporting film negative electrode material can be directly prepared without forming a powder, avoiding the composite processes such as uniform gridding, coating and drying, which is simple and easy to operate, saves the use of the binder, and greatly reduces the preparation cost. Moreover, the structure of the one-dimensional nanocellulose surrounding the zero-dimensional coal powder particles formed by the process helps to improve the wettability of the electrolyte to the negative electrode material, improve the diffusion and migration of sodium ions, so that the sodium ion battery has high specific capacity, first coulombic efficiency and rate performance.

[0005] To achieve the purpose of the present application, the following technical scheme is adopted:

[0006] In a first aspect, the present application provides a preparation method of a self-supporting film negative electrode material, which comprises the following steps:

[0007] Mixing coal powder and one-dimensional nanocellulose solution to obtain a mixed solution.

[0008] Performing suction filtration on the mixed solution to obtain a composite film.

[0009] Performing pre-carbonization and secondary carbonization on the composite film in sequence to obtain the self-supporting film negative electrode material.

[0010] The application utilizes one-dimensional nanocellulose and zero-dimensional coal powder to directly prepare a self-supporting film negative electrode material without forming a powder, avoiding the compounding process such as homogenization, coating, drying and the like, being simple and easy to operate, saving the use of a binder, and greatly reducing the preparation cost. Moreover, the structure of the one-dimensional nanocellulose surrounding the zero-dimensional coal powder particles formed by the process helps to improve the wettability of the electrolyte to the negative electrode material, improve the diffusion and migration of sodium ions, so that the sodium ion battery has a high specific capacity, a first coulombic efficiency and a rate performance.

[0011] Preferably, the coal powder is ultra-micro coal powder.

[0012] Preferably, the particle size D50 of the ultra-micro coal powder is 0.2-2 μm, for example, can be 0.2 μm, 0.5 μm, 1 μm, 1.5 μm or 2 μm, etc.

[0013] Preferably, the type of the coal powder includes any one or a combination of at least two of anthracite, lean coal, lean coal, coking coal, fat coal, gas coal, weakly caking coal, non-caking coal, long flame coal or lignite, preferably long flame coal.

[0014] Preferably, the concentration of the one-dimensional nanocellulose solution is 2-20 mg / mL, for example, can be 2 mg / mL, 4 mg / mL, 6 mg / mL, 8 mg / mL, 10 mg / mL, 12 mg / mL, 14 mg / mL, 16 mg / mL, 18 mg / mL or 20 mg / mL, etc.

[0015] Preferably, in the one-dimensional nanocellulose solution, the aspect ratio of the one-dimensional nanocellulose is (100-1000):1, for example, can be 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1 or 1000:1, etc.

[0016] In the application, the one-dimensional nanocellulose with a suitable aspect ratio helps the nanocellulose to form a two-dimensional planar multi-aperture network structure and has the function of firmly holding the zero-dimensional coal powder particles.

[0017] Preferably, the weight ratio of the coal powder and the one-dimensional nanocellulose solution is (1-10):100, for example, can be 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100 or 10:100, etc., preferably (3-7):100.

[0018] In the application, the coal powder and the one-dimensional nanocellulose solution with a suitable weight ratio synergistically cooperate to form a cage-like structure of one-dimensional nanocellulose surrounding zero-dimensional ultra-micro coal powder particles.

[0019] Preferably, the mixing is accompanied by stirring.

[0020] Preferably, the stirring is at a speed of 100-500 rpm, for example, 100 rpm, 200 rpm, 300 rpm, 400 rpm or 500 rpm, etc.

[0021] Preferably, the stirring is for 1-5 h, for example, 1 h, 2 h, 3 h, 4 h or 5 h, etc.

[0022] Preferably, the filtration is vacuum filtration.

[0023] Preferably, the vacuum filtration is at a vacuum degree of 10-100 Pa, for example, 10 Pa, 20 Pa, 30 Pa, 40 Pa, 50 Pa, 60 Pa, 70 Pa, 80 Pa, 90 Pa or 100 Pa, etc., preferably 20-60 Pa.

[0024] Preferably, between the pre-carbonization and the secondary carbonization, electroplating is further performed, and the electroplating specifically comprises:

[0025] The pre-carbonized composite film is placed in an electroplating solution to perform electroplating, thereby depositing a metal conductive layer on the surface of the composite film.

[0026] In the present application, the surface of the composite film is modified by electroplating, which can solve the problem of poor conductivity of conventional hard carbon negative electrode materials, effectively improve the transmission characteristics of electrons, and improve the rate properties of sodium ion batteries.

[0027] Preferably, the electroplating solution comprises an aluminum-based solution and / or a copper-based solution. For example, it can be a copper sulfate solution, a cuprous hydride solution or an aluminum sulfate solution, etc.

[0028] Preferably, the electroplating is for 2-60 min, for example, 2 min, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min or 60 min, etc., preferably 2-20 min.

[0029] In the present application, a suitable electroplating time can obtain a metal conductive layer with a suitable thickness. If the time is too long, the thickness of the metal conductive layer will be too thick, which will seriously affect the performance of the negative electrode material. If the time is too short, the purpose of improving the conductivity of the negative electrode material cannot be achieved.

[0030] Preferably, the working temperature of the electroplating is 40-60℃, for example, 40℃, 45℃, 50℃, 55℃ or 60℃, etc.

[0031] Preferably, the thickness of the metal conductive layer is 0.1-5 μm, for example, it can be 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc.

[0032] Preferably, the temperature of the pre-carbonization is 1200-1400℃, for example, it can be 1200℃, 1300℃ or 1400℃, etc.

[0033] In the present application, the purpose of pre-carbonization is to cause the transformation of microcrystalline structure inside the self-supporting film formed by the coal powder and nanofibers, forming a "card house" microcrystalline structure that is easy to store sodium.

[0034] Preferably, the time of the pre-carbonization is 1-5 h, for example, it can be 1 h, 2 h, 3 h, 4 h or 5 h, etc.

[0035] Preferably, the heating rate of the pre-carbonization is 1-5℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, etc.

[0036] In the present application, if the heating rate of the pre-carbonization is too fast, it will cause the rapid shrinkage of the composite film, resulting in a large number of cracks, so that the self-supporting film negative material cannot be formed, and it cannot be used in the later battery process.

[0037] Preferably, the temperature of the secondary carbonization is 600-800℃, for example, it can be 600℃, 700℃ or 800℃, etc.

[0038] In the present application, the purpose of the secondary carbonization is to cause the liquefaction of the surface electroplating layer, increase the bonding force between the material surface and the metal layer, and at the same time, cause the liquid metal to penetrate into the film, filling part of the large pore structure.

[0039] Preferably, the time of the secondary carbonization is 0.5-3 h, for example, it can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, etc.

[0040] Preferably, the heating rate of the secondary carbonization is 1-5℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, etc.

[0041] In the present application, if the heating rate of the secondary carbonization is too fast, it will cause the rapid shrinkage of the composite film, resulting in a large number of cracks, so that the surface metal electroplating layer and the internal film carbon layer will move out of position, and in severe cases, the metal electroplating layer will be dissociated.

[0042] Preferably, the preparation method comprises the following steps:

[0043] (1) Coarse crushing and granulation of raw coal to a particle size D50 of 100-200 μm (for example, it can be 100 μm, 150 μm or 200 μm, etc.), and then fine grinding to a particle size D50 of 0.2-2 μm to obtain ultrafine coal powder.

[0044] (2) The ultrafine coal powder is added to a one-dimensional nanocellulose solution with a concentration of 2-20 mg / mL, and stirred and mixed at a speed of 100-500 rpm for 1-5 h to obtain a mixed solution.

[0045] The weight ratio of the ultrafine coal powder to the one-dimensional nanocellulose solution is (1-10):100; and the aspect ratio of the one-dimensional nanocellulose in the one-dimensional nanocellulose solution is (100-1000):1.

[0046] (3) Vacuum filtration of the mixed solution at a vacuum degree of 10-100 Pa for 0.5-2 h to obtain a composite film after filtration.

[0047] (4) The composite film is fixed by a graphite plate clamp, and then pre-carbonization of the composite film is carried out in a protective atmosphere (for example, it can be a nitrogen atmosphere or an argon atmosphere, etc.) to obtain a pre-carbonized composite film.

[0048] The pre-carbonization temperature is 1200-1400℃, the heating rate is 1-5℃ / min, and the time is 1-5 h.

[0049] (5) The pre-carbonized composite film is placed in an electroplating solution for electroplating, so as to deposit a metal conductive layer on the surface of the composite film to obtain an electroplated composite film.

[0050] The electroplating solution includes an aluminum-based solution and / or a copper-based solution, the electroplating time is 2-60 min, the working temperature of electroplating is 40-60℃, and the thickness of the metal conductive layer is 0.1-5 μm.

[0051] (6) The electroplated composite film is fixed by a graphite plate clamp, and then secondary carbonization of the electroplated composite film is carried out in an inert atmosphere (for example, it can be a nitrogen atmosphere or an argon atmosphere, etc.) to obtain a self-supporting film negative material.

[0052] The secondary carbonization temperature is 600-800℃, the heating rate is 1-5℃ / min, and the time is 0.5-3 h.

[0053] It should be noted that the purpose of fixing and pressing the composite film by the graphite plate clamp is to prevent the composite film from swelling and breaking at high temperature.

[0054] In the second aspect, the application provides a self-supporting film negative material prepared by the preparation method of the first aspect.

[0055] In a third aspect, the present application provides a sodium ion battery, wherein a self-supporting film negative electrode material as described in the second aspect is included in the negative electrode of the sodium ion battery.

[0056] The numerical ranges recited herein are inclusive of the endpoints and of any range that would be formed in between the recited ranges, and are presented essentially for clarity. The present application does not restrict the specific point values included in the ranges recited herein.

[0057] Compared with the prior art, the present application has the following beneficial effects:

[0058] The present application can directly prepare a self-supporting film negative electrode material by using one-dimensional nanocellulose and zero-dimensional coal powder in cooperation, without forming a powder, avoiding the compounding processes such as homogenization, coating, and drying, and being simple and easy to operate, thereby saving the use of a binder and greatly reducing the preparation cost. Moreover, the structure of the one-dimensional nanocellulose surrounding the zero-dimensional coal powder particles formed by the process helps to improve the wettability of the electrolyte to the negative electrode material, improve the diffusion and migration of sodium ions, and make the sodium ion battery have a high specific capacity (≥280 mAh / g), a first coulombic efficiency (≥88%), and a rate performance (5C / 1C≥90%). BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 SEM image of the self-supporting film negative electrode material provided for Example 1 in the present application.

[0060] Figure 2 Capacity performance chart of the button-type sodium ion battery prepared based on the self-supporting film negative electrode material provided for Example 1 in the present application at different rates. DETAILED DESCRIPTION

[0061] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0062] Example 1

[0063] The present embodiment provides a preparation method of a self-supporting film negative electrode material, which comprises the following steps:

[0064] (1) Coarsely crushing raw coal to a particle size D50 of 150 μm, and then finely grinding the coal to a particle size D50 of 1 μm to obtain ultrafine coal powder.

[0065] (2) Adding the ultrafine coal powder into a one-dimensional nanocellulose solution with a concentration of 2 mg / mL, and stirring and mixing at a speed of 300 rpm for 3 h to obtain a mixed solution.

[0066] The weight ratio of the ultrafine coal powder and the one-dimensional nanocellulose solution is 5:100; and the length-diameter ratio of the one-dimensional nanocellulose in the one-dimensional nanocellulose solution is 500:1.

[0067] (3) The mixed solution is subjected to vacuum filtration, the vacuum degree is 50 Pa, the filtration time is 1 h, and the composite film is obtained after filtration.

[0068] (4) The composite film is fixed by using a graphite plate clamp, and then the composite film is subjected to pre-carbonization in a nitrogen atmosphere, to obtain a pre-carbonized composite film.

[0069] The pre-carbonization temperature is 1300℃, the heating rate is 3℃ / min, and the time is 3 h.

[0070] (5) The pre-carbonized composite film is placed in an electroplating solution, and electroplating is performed, so as to deposit a metal conductive layer on the surface of the composite film, to obtain an electroplated composite film.

[0071] The electroplating solution is a copper sulfate solution, the electroplating time is 2 min, the electroplating working temperature is 40℃, and the thickness of the metal conductive layer is 0.1 μm.

[0072] (6) The electroplated composite film is fixed by using a graphite plate clamp, and then the electroplated composite film is subjected to secondary carbonization in a nitrogen atmosphere, to obtain a self-supporting film negative electrode material.

[0073] The secondary carbonization temperature is 700℃, the heating rate is 3℃ / min, and the time is 1.5 h.

[0074] Figure 1 An SEM image of a self-supporting film negative electrode material provided in the embodiment is shown, and it can be known from the image that the surface of the self-supporting film presents many one-dimensional nanocellulose structures.

[0075] Figure 2 A capacity performance diagram of a button-type sodium ion battery prepared based on the self-supporting film negative electrode material provided in the embodiment under different rates is shown, and it can be known from the diagram that the button-type sodium ion battery exhibits excellent rate performance and capacity performance.

[0076] Embodiment 2

[0077] The embodiment provides a preparation method of a self-supporting film negative electrode material.

[0078] (1) The raw coal is coarsely crushed to obtain an ultrafine coal powder with a particle size D50 of 100 μm, and then finely ground to a particle size D50 of 0.2 μm.

[0079] (2) The ultrafine coal powder is added to a one-dimensional nanocellulose solution with a concentration of 10 mg / mL, and stirred and mixed at a rotating speed of 100 rpm for 5 h to obtain a mixed solution.

[0080] The weight ratio of the ultrafine coal powder to the one-dimensional nanocellulose solution is 1:100; and the length-diameter ratio of the one-dimensional nanocellulose in the one-dimensional nanocellulose solution is 1000:1.

[0081] (3) The mixed solution is subjected to vacuum filtration, the vacuum degree is 10 Pa, and the filtration time is 0.5 h, to obtain a composite film after filtration.

[0082] (4) The composite film is fixed by using a graphite plate clamp, and then the composite film is subjected to pre-carbonization in a nitrogen atmosphere to obtain a pre-carbonized composite film.

[0083] The pre-carbonization temperature is 1200℃, the heating rate is 1℃ / min, and the time is 5 h.

[0084] (5) The pre-carbonized composite film is placed in an electroplating solution to perform electroplating, so as to deposit a metal conductive layer on the surface of the composite film, to obtain an electroplated composite film.

[0085] The electroplating solution comprises a cuprous hydride solution, the electroplating time is 10 min, the electroplating working temperature is 45℃, and the thickness of the metal conductive layer is 0.5μm.

[0086] (6) The electroplated composite film is fixed by using a graphite plate clamp, and then the electroplated composite film is subjected to secondary carbonization in a nitrogen atmosphere to obtain a self-supporting film negative electrode material.

[0087] The secondary carbonization temperature is 600℃, the heating rate is 1℃ / min, and the time is 3 h.

[0088] Example 3

[0089] The embodiment provides a preparation method of a self-supporting film negative electrode material, and the preparation method comprises the following steps:

[0090] (1) A raw coal is coarsely crushed to a particle size D50 of 200μm, and then finely ground to a particle size D50 of 2μm to obtain an ultrafine coal powder.

[0091] (2) The ultrafine coal powder is added to a one-dimensional nanocellulose solution with a concentration of 20 mg / mL, and stirred and mixed at a rotating speed of 500 rpm for 1 h to obtain a mixed solution.

[0092] The weight ratio of the ultrafine coal powder to the one-dimensional nanocellulose solution is 10:100; and the length-diameter ratio of the one-dimensional nanocellulose in the one-dimensional nanocellulose solution is 100:1.

[0093] (3) vacuum filtration is performed on the mixed solution, a vacuum degree is 100 Pa, a filtration time is 2 h, and a composite film is obtained after filtration.

[0094] (4) the composite film is fixed by using a graphite plate clamp, and pre-carbonization is performed on the composite film in a nitrogen atmosphere to obtain a pre-carbonized composite film.

[0095] The pre-carbonization temperature is 1400 ℃, the heating rate is 5 ℃ / min, and the time is 1 h.

[0096] (5) the pre-carbonized composite film is placed in an electroplating solution, electroplating is performed, a metal conductive layer is deposited on the surface of the composite film, and an electroplated composite film is obtained.

[0097] The electroplating solution includes an aluminum sulfate solution, the electroplating time is 60 min, the working temperature of electroplating is 60 ℃, and the thickness of the metal conductive layer is 4 μm.

[0098] (6) the electroplated composite film is fixed by using a graphite plate clamp, and secondary carbonization is performed on the electroplated composite film in a nitrogen atmosphere to obtain a self-supporting film negative electrode material.

[0099] The secondary carbonization temperature is 800 ℃, the heating rate is 5 ℃ / min, and the time is 0.5 h.

[0100] Example 4

[0101] The difference between this embodiment and example 1 is that the weight ratio of the ultrafine coal powder and the one-dimensional nanocellulose solution is 0.5:100.

[0102] The rest of the preparation method and parameters remain the same as those in example 1.

[0103] Example 5

[0104] The difference between this embodiment and example 1 is that the weight ratio of the ultrafine coal powder and the one-dimensional nanocellulose solution is 12:100.

[0105] The rest of the preparation method and parameters remain the same as those in example 1.

[0106] Example 6

[0107] The difference between this embodiment and example 1 is that the vacuum degree of the vacuum filtration is 200 Pa.

[0108] The rest of the preparation method and parameters remain the same as those in example 1.

[0109] Example 7

[0110] The difference between this embodiment and example 1 is that the pre-carbonization temperature is 1100 ℃.

[0111] The remaining preparation method and parameters are consistent with Example 1.

[0112] Example 8

[0113] The difference between this example and Example 1 is that the temperature of pre-carbonization is 1500℃.

[0114] The remaining preparation method and parameters are consistent with Example 1.

[0115] Example 9

[0116] The difference between this example and Example 1 is that the heating rate of pre-carbonization is 8℃ / min.

[0117] The remaining preparation method and parameters are consistent with Example 1.

[0118] Example 10

[0119] The difference between this example and Example 1 is that step (5) is not performed.

[0120] The remaining preparation method and parameters are consistent with Example 1.

[0121] Example 11

[0122] The difference between this example and Example 1 is that the temperature of secondary carbonization is 500℃.

[0123] The remaining preparation method and parameters are consistent with Example 1.

[0124] Example 12

[0125] The difference between this example and Example 1 is that the temperature of secondary carbonization is 1000℃.

[0126] The remaining preparation method and parameters are consistent with Example 1.

[0127] Comparative Example 1

[0128] This comparative example provides a preparation method of a self-supporting soft / hard carbon film negative electrode material, comprising the following steps:

[0129] (1) 10 g of cellulose nanofiber is dissolved in 100 mL of a compound solvent system (water / isopropyl alcohol volume ratio = 5:95), and after stirring uniformly; 2 g of ammonium dihydrogen phosphate is added to the above solution, vacuum impregnation, interfacial self-assembly at room temperature, drying at a temperature of -20℃ for 12 h, to obtain an impregnated nanocellulose film;

[0130] (2) The impregnated nanocellulose film is laid in a graphite clamp, and a crosslinked nanocellulose film is prepared by heat pressing at 150°C for 15h under an argon atmosphere;

[0131] (3) Bitumen with a softening point of 200°C and a particle size of 18μm is selected as a soft carbon source, and n-hexane is added to the bitumen, with a mass ratio of n-hexane to bitumen of 1:1; then the crosslinked nanocellulose film is laid in a bitumen solution pre-impregnated, and a nanocellulose / bitumen-based composite film is prepared by vacuum filtration;

[0132] (4) The nanocellulose / bitumen-based composite film is placed in a graphite plate clamp, and then placed in a tube furnace for heat pressing and carbonization under an argon atmosphere, with a carbonization temperature of 1600°C, a heating rate of 10°C / min, and a carbonization time of 0.5h, to obtain a self-supporting soft / hard carbon film negative electrode material.

[0133] Performance test

[0134] The negative electrode material provided in the above examples and comparative examples is directly used as a negative electrode, metal sodium is used as a counter electrode, a carbonate electrolyte (solute: NaPF6, solvent: ethylene carbonate and diethyl carbonate in a volume ratio of 1:1) is used as an electrolyte, and a polyethylene separator is used as a separator, to assemble a button sodium ion battery. The button sodium ion battery is tested for specific capacity, initial coulombic efficiency, and rate performance.

[0135] The test conditions for specific capacity and initial coulombic efficiency include: a voltage range of 0-2V, a current density of 30mA·g -1 , and a charge / discharge test is performed to obtain reversible capacity and initial efficiency. The test conditions for rate performance include: a voltage range of 0-2V, the assembled button battery is cycled for three cycles at a charge / discharge rate of 1C (i.e. a current density of 30mA·g -1 ), and then cycled for three cycles at a charge / discharge rate of 5C (i.e. a current density of 150mA·g -1 ). The reversible capacity at 5C is divided by the reversible capacity at 1C to obtain the negative electrode rate performance of the self-supporting film negative electrode material.

[0136] The test results are shown in Table 1.

[0137] Table 1

[0138]

[0139] Analysis:

[0140] The application can directly prepare a self-supporting film negative electrode material by cooperation of one-dimensional nanocellulose and zero-dimensional coal powder, without forming a powder, avoiding the composite process such as homogenization, coating, drying and the like, being simple and easy to operate, saving the use of a binder, and greatly reducing the preparation cost. Moreover, the structure of one-dimensional nanocellulose surrounding zero-dimensional coal powder particles formed by the process helps to improve the wettability of the electrolyte to the negative electrode material, improve the diffusion and migration of sodium ions, so that the sodium ion battery has high specific capacity, first coulombic efficiency and rate performance.

[0141] As can be seen from Example 1 and Examples 4-5, if the weight ratio of the ultra-fine coal powder and the one-dimensional nanocellulose solution is too small, i.e. the amount of the ultra-fine coal powder used is too small, there are too many one-dimensional nanofibers in the self-supporting film, and the formed cage structure is less, which is not conducive to the rate performance of the film negative electrode material; if the weight ratio of the ultra-fine coal powder and the one-dimensional nanocellulose solution is too large, i.e. the amount of the ultra-fine coal powder used is too large, it is not conducive to the formation of the self-supporting film, and too many coal particles cause the film surface to have uneven properties, and the particles attached to the surface are easy to fall off, and the increase of the ultra-fine coal powder also reduces the capacity properties of the film negative electrode material.

[0142] As can be seen from Example 1 and Example 6, if the vacuum degree of vacuum filtration is too large, it is not conducive to the assembly of the self-supporting film, and under a large vacuum degree, the bonding force between the one-dimensional nanocellulose and the ultra-fine coal powder is insufficient, and the film itself is easy to dissociate in the later carbonization process.

[0143] As can be seen from Example 1 and Examples 7-8, if the pre-carbonization temperature is too small, it is not conducive to the formation of the microcrystalline structure in the film negative electrode material, and the defects and functional groups on the surface of the film negative electrode material cannot be repaired, affecting the initial efficiency properties of the negative electrode material; if the pre-carbonization temperature is too large, the interlayer spacing of the microcrystalline structure layer of the film negative electrode material is small, and the transmission of sodium ions is not easy.

[0144] As can be seen from Example 1 and Example 9, if the pre-carbonization heating rate is too large, the film is easy to crack due to internal stress.

[0145] As can be seen from Example 1 and Example 10, if step (5) is not performed, i.e. the deposition of the metal conductive layer is not performed, the surface conductivity of the film is affected, and then the transmission of electrons in the film negative electrode material is affected, causing the rate performance of the negative electrode material to decrease.

[0146] As can be seen from Example 1 and Examples 11-12, if the secondary carbonization temperature is too small, the surface electroplating layer cannot be micro-liquefied at high temperature, the bonding force between the film negative electrode material and the electroplating layer cannot be enhanced, and then the transmission properties of the electrons are affected; if the secondary carbonization temperature is too large, the surface electroplating coating layer is volatilized at high temperature, and does not play a role in increasing the conductivity.

[0147] From the example 1 and the comparative example 1, it can be seen that the preparation method adopted by the prior art can realize the preparation of the high-capacity film negative material, and the application can improve the microcrystal and pore structure in the film negative by means of the combination of one-dimensional material and zero-dimensional material, and increase the conductivity of the material by assisting the electroplating process, thereby improving the rate property of the material.

[0148] The applicant declares that the process of the present application is illustrated by the above examples, but the present application is not limited to the above process steps, that is, it does not mean that the present application must rely on the above process steps to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the raw materials selected by the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing a self-supporting film negative electrode material, characterized in that: The preparation method comprises the following steps: mixing the coal powder and the one-dimensional nanocellulose solution to obtain a mixed solution; The weight ratio of the coal powder and the one-dimensional nanocellulose solution is (1-10):100; The coal powder is ultrafine coal powder; the particle size D50 of the ultrafine coal powder is 0.2-2 μm; in the one-dimensional nanocellulose solution, the aspect ratio of the one-dimensional nanocellulose is (100-1000):1; filtering the mixed solution to obtain a composite film; The filtration method is vacuum filtration; wherein the vacuum degree of the vacuum filtration is 10-100 Pa; Pre-carbonizing and secondary carbonizing the composite film in sequence to obtain the self-supporting film negative electrode material; The temperature of the pre-carbonization is 1200-1400°C; electroplating is also carried out between the pre-carbonization and the secondary carbonization, and the specific steps of the electroplating include: placing the pre-carbonized composite film in an electroplating solution and electroplating, thereby depositing a metal conductive layer on the surface of the composite film; the temperature of the secondary carbonization is 600-800°C.

2. The preparation method according to claim 1, characterized in that The types of the pulverized coal include any one of anthracite, lean coal, lean coal, coking coal, fat coal, gas coal, slightly sticky coal, non-sticky coal, long flame coal or lignite, or a combination of at least two of them.

3. The preparation method according to claim 1, characterized in that The concentration of the one-dimensional nanocellulose solution is 2-20 mg / mL.

4. The preparation method according to claim 1, characterized in that The mixing process is accompanied by stirring; wherein the stirring speed is 100-500 rpm; and the stirring time is 1-5 hours.

5. The preparation method according to claim 1, characterized in that The electroplating solution includes an aluminum-based solution and / or a copper-based solution; And / or, the electroplating time is 2-60 min; And / or, the electroplating operating temperature is 40-60°C; And / or, the thickness of the metal conductive layer is 0.1-5 μm.

6. The preparation method according to claim 1, characterized in that The pre-carbonization time is 1-5h; And / or, the heating rate of the pre-carbonization is 1-5°C / min.

7. The preparation method according to claim 1, characterized in that The secondary carbonization time is 0.5-3h; And / or, the heating rate of the secondary carbonization is 1-5°C / min.

8. The preparation method according to claim 1, characterized in that The preparation method comprises the following steps: (1) The raw coal is coarsely crushed to a particle size D50 of 100-200 μm, and then finely ground to a particle size D50 of 0.2-2 μm to obtain ultrafine coal powder; (2) adding the ultrafine coal powder to a one-dimensional nanocellulose solution having a concentration of 2-20 mg / mL, and stirring the mixture at a speed of 100-500 rpm for 1-5 hours to obtain a mixed solution; The weight ratio of the ultrafine coal powder to the one-dimensional nanocellulose solution is (1-10):100; the aspect ratio of the one-dimensional nanocellulose in the one-dimensional nanocellulose solution is (100-1000):1; (3) vacuum filtering the mixed solution at a vacuum degree of 10-100 Pa for 0.5-2 h to obtain a composite film; (4) fixing the composite film with a graphite plate fixture, and then pre-carbonizing the composite film in a protective atmosphere to obtain a pre-carbonized composite film; The pre-carbonization temperature is 1200-1400°C, the heating rate is 1-5°C / min, and the time is 1-5h; (5) placing the pre-carbonized composite film in an electroplating solution for electroplating, thereby depositing a metal conductive layer on the surface of the composite film to obtain an electroplated composite film; The electroplating solution includes an aluminum-based solution and / or a copper-based solution, the electroplating time is 2-60 minutes, the electroplating working temperature is 40-60° C., and the thickness of the metal conductive layer is 0.1-5 μm; (6) Fixing the electroplated composite film with a graphite plate fixture, and performing secondary carbonization on the electroplated composite film in an inert atmosphere to obtain a self-supporting film negative electrode material; The secondary carbonization temperature is 600-800° C., the heating rate is 1-5° C. / min, and the time is 0.5-3 h.

9. A self-supporting film negative electrode material, characterized in that: The self-supporting film negative electrode material is prepared by the preparation method according to any one of claims 1 to 8.

10. A sodium ion battery, characterized in that: The negative electrode of the sodium ion battery comprises the self-supporting film negative electrode material according to claim 9.

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