Composite silicon-carbon negative electrode material, negative electrode plate and preparation method of negative electrode plate

Abstract

The invention discloses a composite silicon-carbon negative electrode material, a negative electrode plate and a preparation method thereof, and belongs to the technical field of lithium batteries, and the preparation method comprises the following steps: dispersing graphene oxide and a secondary granulation silicon-carbon negative electrode material under an ice bath condition, and carrying out a spray drying method to prepare a Si / C-coated GO composite material; then adding polyethyleneimine and the like, stirring, cooling and centrifuging under an oil bath condition to obtain a Si / C-coated GO / HPEI composite material, and finally adding an adhesive ammonium polyacrylate and a conductive agent for coating and drying to obtain the composite material. According to the integrated negative electrode preparation method based on graphene oxide coating, polyethyleneimine grafting and binder in-situ cross-linking, the prepared composite silicon-carbon negative electrode material has the performance of high first efficiency and long cycle life, the obtained material is used for a lithium battery, the first charge-discharge efficiency reaches 90% or above, the first reversible capacity reaches 1550 mAh / g, and the lithium battery has a good application prospect. And after 200 cycles under the current density of 3.0 A / g, the capacity retention ratio is still 90%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, and particularly relates to a composite silicon-carbon negative electrode material, a negative electrode sheet and a preparation method thereof. BACKGROUND

[0002] In recent years, the rapid development of electric vehicles has put forward higher requirements for the energy density of lithium ion batteries. Since the current theoretical specific capacity of graphite negative electrode is close to its theoretical limit, it is necessary to develop new negative electrode materials. Since the theoretical specific capacity of silicon is ten times that of graphite (4200 mAh / g VS 372 mAh / g), it is abundant in reserves, has mature preparation technology and a suitable lithiation potential, and is therefore considered as the most potential next-generation lithium ion battery negative electrode material.

[0003] However, silicon as a negative electrode material also has many problems. The reaction of silicon and lithium is an alloying reaction, and the volume expansion rate during lithiation is close to 300%. The huge volume expansion / contraction will cause the particles to break, the electrode material to powder, and the electrode material to fall off and lose electrical contact, ultimately leading to rapid cycle performance decay. At present, many modification methods have been proposed to improve the cycle performance of silicon, such as nanocrystallization, coating, doping, binder design, and structure design. The existing technologies are all from a single method to solve the cycle problem of silicon negative electrode, such as single coating and single binder. However, there are few reports on the interface contact and volume expansion problems faced by the secondary granulated silicon-carbon negative electrode material. Completely copying the modification technology of pure silicon will cause compatibility problems, and ultimately cause both to lose. The reason is that compared with pure silicon, the secondary granulated silicon-carbon negative electrode material has a smaller volume expansion, but a more complex structure. If the composite treatment is not good, the coated material (such as graphene, graphite, and amorphous carbon) will fall off and the structure will collapse.

[0004] Research shows that when the size of silicon is <150 nm, silicon will not break, so nanocrystallization of silicon greatly improves the cycle performance of silicon. However, nanosilicon cannot be used alone in the field of negative electrode materials due to its large specific surface area. Therefore, nanosilicon needs to be secondary granulated with carbon materials to form micrometer-sized particles for better practical application prospects. However, the secondary granulated silicon-carbon micrometer material also faces the problem of volume expansion compared with the original nanosilicon material. In order to obtain a silicon-carbon negative electrode with long cycle life, a buffer structure that can effectively adapt to volume expansion / contraction needs to be designed, and a hollow, porous, core-shell, etc. complex nanostructure is usually constructed and a conductive matrix material (such as graphene) is introduced for compounding. However, the design of these complex structures and the introduction of large specific surface conductive matrix materials inevitably increase the complexity of the interface reaction of the composite material, which is not conducive to the improvement of the initial efficiency of the material.

[0005] Therefore, how to obtain a silicon-carbon-graphene composite negative electrode material with high initial efficiency and long cycle life is an urgent problem to be solved in the field of lithium ion batteries. SUMMARY

[0006] One of the purposes of the present application is to provide a preparation method of a composite silicon-carbon negative electrode material to solve the above problems.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] A preparation method of a composite silicon-carbon negative electrode material, comprising the following steps:

[0009] (1) The graphene oxide and the secondary granulated silicon-carbon negative electrode material are weighed and sequentially added to an aqueous solution, and dispersed under the condition of ice bath to obtain the dispersed graphene oxide-silicon-carbon aqueous solution; the mass percentage of the graphene oxide to the secondary granulated silicon-carbon negative electrode material is (10%-25%): (75%-90%);

[0010] (2) The graphene oxide-silicon-carbon aqueous solution obtained in step (1) is moved to a spray dryer, and a Si / C@GO composite material is prepared by using a spray drying method;

[0011] (3) The Si / C@GO composite material obtained in step (2) is dispersed into an aqueous solution or an ethanol solution, and an aqueous solution or an ethanol solution of an amino polymer is added, and stirring, cooling and centrifugation are carried out under the condition of oil bath to obtain a Si / C@GO / N composite material, and the addition amount of the amino polymer is 0.5%-3% of the mass of the Si / C@GO composite material.

[0012] As a preferred technical scheme,

[0013] In step (1), the preparation method of the secondary granulated silicon-carbon negative electrode material is as follows: first, micron silicon is nanometerized by sand milling; then, the nanometerized silicon is compounded with graphite and pitch, and granulation and secondary sintering are carried out to obtain the secondary granulated silicon-carbon negative electrode material.

[0014] As a preferred technical scheme,

[0015] In step (1), the graphene oxide is solid powder graphene oxide or graphene oxide aqueous solution.

[0016] As a preferred technical scheme,

[0017] In step (1) and step (2), when spray drying, the spray inlet temperature is 180°C, the outlet temperature is 105°C, and the flow rate is controlled to be 10 ml / min.

[0018] As a preferred technical scheme,

[0019] In step (3), the amino polymer is selected from one of polyethyleneimine, polyacrylamide, and polyallylamine.

[0020] As a preferred technical solution,

[0021] In step (3), the oil bath has a temperature of 60-90℃ and a time of 2-8h.

[0022] The second object of the present application is to provide a preparation method of a negative electrode sheet, wherein polyacrylic acid is neutralized with ammonia water to form an ammonium polyacrylate aqueous solution with viscosity, the Si / C@GO / N composite material, the conductive agent, and the ammonium polyacrylate (dry weight) are mixed in a ratio of 8:1:1, and then the mixture is subjected to blast drying at 60-80℃ for 3-8h and vacuum drying at 100-120℃ for 10-15h to obtain the electrode sheet.

[0023] As a preferred technical solution, after obtaining the electrode sheet, the electrode sheet is cut into a circular sheet, and then the circular sheet is dried at high temperature for 3h, taken out, and assembled into a battery.

[0024] The second object of the present application is to provide a composite silicon-carbon negative electrode material prepared by the above method.

[0025] By using the method of the present application, graphene oxide can be uniformly coated on the surface of the secondary granulated silicon-carbon negative electrode material, and such phenomenon can be observed very obviously by SEM.

[0026] Nitrogen-doped grafting: a modified graphene oxide modified composite material modified by, for example, polyethyleneimine can be obtained by simple solution preparation and centrifugal drying. Nitrogen elements can be observed in the composite material by EDS, and branched polyethyleneimine can be grafted to the surface of graphene oxide to form nitrogen-doped graphene oxide, which can bind the silicon-carbon material, improve the electrical conductivity, and interact with the binder to form a three-dimensional crosslinked network.

[0027] The main innovation of the present application is to construct a three-dimensional interpenetrating network structure with the functions of "conducting, buffering, and bonding" in the electrode by the synergistic design of multiple components and multiple reactions. A large number of amino groups on the polyethyleneimine chain covalently bond with the functional groups on the GO layer, which makes the GO change from isolated layers to organic-inorganic hybrid network nodes modified by polymer chains, greatly enhancing the flexibility and interface compatibility. The electrostatic complexation and hydrogen bond crosslinking of polyacrylic acid ammonia and polyethyleneimine provide a strong and tough bonding matrix for the system.

[0028] Compared with existing technologies, the advantages of this invention are as follows: This invention is based on an integrated anode preparation method using graphene oxide coating, polyethyleneimine grafting, and in-situ crosslinking with a binder. The resulting composite silicon-carbon anode material possesses both high initial efficiency and long cycle life. When used in lithium batteries, the material achieves an initial charge-discharge efficiency of over 90%, an initial reversible capacity of 1550 mAh / g, and a capacity of 790 mAh / g at a charge-discharge rate of 2 A / g. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope image of Si / C@10%GO prepared in Example 1;

[0030] Figure 2 EDS test results for Si / C@10%GO / 0.5%HPEI prepared in Example 1;

[0031] Figure 3 The graph shows the first charge-discharge efficiency test results of Si / C@10%GO / 0.5%HPEI and Si / C@10%GO prepared in Example 1.

[0032] Figure 4 The graph shows the cycle performance test results of Si / C@10%GO / 0.5%HPEI prepared in Example 1. Detailed Implementation

[0033] To explain the technical content, objectives, and effects of the present invention in detail, the following specific embodiments are provided to further illustrate the content of the present invention. However, the content of the present invention is far more than the following examples.

[0034] Unless otherwise specified, all materials used in the following examples and comparative examples are commercially available.

[0035] The graphene oxide used was commercially available 3-10μm graphene oxide powder;

[0036] The secondary granulated silicon-carbon material used (i.e., the "Si / C" material in Table 1) has a particle size of 10-16 μm, and its preparation method is as follows:

[0037] Nanoscale silicon was produced using a sand mill: the grinding media of the sand mill was zirconium balls with a particle size of 0.1-0.3 mm, the working frequency of the sand mill was 30 Hz, and the target nanoscale silicon particle size was <50 nm.

[0038] The ground silica slurry is then further dispersed and mixed with graphite and pitch in a secondary dispersion ratio of 3:Si:graphite:pitch = 3.5:1:1.

[0039] The well-dispersed slurry is spray-dried for secondary granulation, with an inlet air temperature of 150℃ and an outlet air temperature of 90℃.

[0040] The dried secondary particles are subjected to high-temperature carbonization sintering at a temperature of 1000℃, a heating rate of 5℃ / min, and a sintering time of 5h to obtain the final product.

[0041] Example 1

[0042] A composite silicon-carbon anode material, the preparation method of which is as follows:

[0043] First, take 3g of graphene oxide (GO) powder and add it to a 1000ml beaker. Then add 30g of secondary granulated silicon carbide material, making a total volume of 700ml. Under ice bath conditions, use an ultrasonic disperser to sonicate for 30 minutes and then remove it.

[0044] Then, spray drying was performed, with high-speed stirring maintained during spraying to ensure uniform dispersion of graphene oxide and silicon carbide materials. The spray inlet temperature was 180℃, the outlet temperature was 105℃, and the flow rate was controlled at 10ml / min. After spraying, the sprayed material was collected as a Si / C@10%GO composite material.

[0045] 0.05g of polyethyleneimine material was dissolved in 100ml of deionized water. After dissolution, 10g of Si / C@GO composite material was weighed and placed in a flask, which was then placed in an oil bath and stirred continuously at 90℃ for 8 hours. After the process, the mixture was centrifuged at 9000 rpm using a high-speed centrifuge. After centrifugation, the mixture was dried in a vacuum oven at 60℃ for 12 hours to obtain the composite material Si / C@10%GO / 0.5%HPEI.

[0046] Polyacrylic acid was neutralized with ammonia to form a binder with a certain viscosity. A Si / C@10%GO / 0.5%HPEI composite material and a conductive agent were then added. An electrode slurry was prepared according to an 8:1:1 ratio of active material, conductive agent, and binder. The slurry was then coated onto copper foil. The foil was dried in a forced-air environment at 60°C for 2 hours, followed by vacuum drying at 105°C for 12 hours.

[0047] Example 2

[0048] A composite silicon-carbon anode material, the preparation method of which is as follows:

[0049] First, take 3g of graphene oxide (GO) powder and add it to a 1000ml beaker. Then add 30g of secondary granulated silicon carbide material, making a total volume of 700ml. Under ice bath conditions, use an ultrasonic disperser to sonicate for 30 minutes and then remove it.

[0050] Then, spray drying was performed, with high-speed stirring maintained during spraying to ensure uniform dispersion of graphene oxide and silicon carbide materials. The spray inlet temperature was 180℃, the outlet temperature was 105℃, and the flow rate was controlled at 10ml / min. After spraying, the sprayed material was collected as a Si / C@GO composite material.

[0051] 0.3g of polyethyleneimine material was dissolved in 100ml of deionized water. After dissolution, 10g of Si / C@GO composite material was weighed and placed in a flask, which was then placed in an oil bath and stirred continuously at 90℃ for 8 hours. After the process, the mixture was centrifuged at 9000 rpm. After centrifugation, the mixture was dried in a vacuum oven at 60℃ for 12 hours to obtain the Si / C@GO / HPEI composite material, which is Si / C@10%GO / 3%HPEI.

[0052] Polyacrylic acid was neutralized with ammonia to form a binder with a certain viscosity. A Si / C@10%GO / 3%HPEI composite material and a conductive agent were then added. An electrode paste was prepared according to an 8 / 1 / 1 ratio of active material, conductive agent, and binder. The paste was then coated onto copper foil. The foil was dried in a forced-air environment at 60°C for 2 hours, followed by vacuum drying at 105°C for 12 hours.

[0053] Example 3

[0054] A composite silicon-carbon anode material, the preparation method of which is as follows:

[0055] First, take 3g of graphene oxide (GO) powder and add it to a 1000ml beaker. Then add 12g of secondary granulated silicon carbide material, making a total volume of 700ml. Under ice bath conditions, use an ultrasonic disperser to sonicate for 30 minutes and then remove it.

[0056] Then, spray drying was performed, with high-speed stirring maintained during spraying to ensure uniform dispersion of graphene oxide and silicon carbide materials. The spray inlet temperature was 180℃, the outlet temperature was 105℃, and the flow rate was controlled at 10ml / min. After spraying, the sprayed material was collected as a Si / C@GO composite material.

[0057] 0.3g of polyethyleneimine material was weighed and dissolved in 100ml of deionized water. After dissolution, 10g of Si / C@GO composite material was weighed and placed in a flask, which was then placed in an oil bath and stirred continuously at 90℃ for 8 hours. After the process, the mixture was centrifuged at 9000 rpm using a high-speed centrifuge. After centrifugation, the mixture was dried in a vacuum oven at 60℃ for 12 hours to obtain the Si / C@GO / HPEI composite material, which is Si / C@25%GO / 3%HPEI.

[0058] Polyacrylic acid was neutralized with ammonia to form a binder with a certain viscosity. A Si / C@25%GO / 3%HPEI composite material and a conductive agent were then added. An electrode paste was prepared according to an 8 / 1 / 1 ratio of active material, conductive agent, and binder. The paste was then coated onto copper foil. The foil was dried in a forced-air environment at 60°C for 2 hours, followed by vacuum drying at 105°C for 12 hours.

[0059] Example 4

[0060] A composite silicon-carbon anode material, the preparation method of which is as follows:

[0061] First, take 3g of graphene oxide (GO) powder and add it to a 1000ml beaker. Then add 10g of secondary granulated silicon carbide material, making the total volume 700ml. Under ice bath conditions, use an ultrasonic disperser to sonicate for 30 minutes and then remove it.

[0062] Then, spray drying was performed, with high-speed stirring maintained during spraying to ensure uniform dispersion of graphene oxide and silicon carbide materials. The spray inlet temperature was 180℃, the outlet temperature was 105℃, and the flow rate was controlled at 10ml / min. After spraying, the sprayed material was collected as a Si / C@GO composite material.

[0063] 0.05 g of polyethyleneimine material was weighed and dissolved in 100 ml of deionized water. After dissolution, 10 g of Si / C@GO composite material was weighed and placed in a flask, which was then placed in an oil bath and stirred continuously at 90 °C for 8 hours. After the reaction, the mixture was centrifuged at 9000 r / min using a high-speed centrifuge. After centrifugation, the mixture was dried in a vacuum oven at 60 °C for 12 hours to obtain the Si / C@GO / HPEI composite material, which is Si / C@30%GO / 0.5%HPEI.

[0064] Polyacrylic acid was neutralized with ammonia to form a binder with a certain viscosity. A Si / C@30%GO / 0.5%HPEI composite material and a conductive agent were then added. An electrode paste was prepared according to an 8 / 1 / 1 ratio of active material, conductive agent, and binder. The paste was then coated onto copper foil. The foil was dried in a forced-air environment at 60°C for 2 hours, followed by vacuum drying at 105°C for 12 hours.

[0065] Comparative Example 1

[0066] A composite silicon-carbon anode material, the preparation method of which is as follows:

[0067] First, take 3g of graphene oxide (GO) powder and add it to a 1000ml beaker. Then add 30g of secondary granulated silicon carbide material, making a total volume of 700ml. Under ice bath conditions, use an ultrasonic disperser to sonicate for 30 minutes and then remove it.

[0068] Then, spray drying was performed, with high-speed stirring maintained during spraying to ensure uniform dispersion of graphene oxide and silicon carbide materials. The spray inlet temperature was 180℃, the outlet temperature was 105℃, and the flow rate was controlled at 10ml / min. After spraying, the sprayed material was collected as a Si / C@GO composite material.

[0069] Polyacrylic acid was neutralized with ammonia to form a binder with a certain viscosity. A Si / C@10%GO composite material and a conductive agent were then added. An electrode paste was prepared according to an 8 / 1 / 1 ratio of active material, conductive agent, and binder. The paste was then coated onto copper foil. The foil was dried in a forced-air environment at 60°C for 2 hours, followed by vacuum drying at 105°C for 12 hours.

[0070] The Si / C@10%GO prepared in Example 1 was subjected to scanning electron microscopy for morphological observation. The results are as follows: Figure 1 .from Figure 1 As can be seen, graphene oxide can cover the surface of micron-sized silicon-carbon secondary particles to form a uniform graphene coating layer.

[0071] The Si / C@10%GO / 0.5%HPEI prepared in Example 1 was subjected to EDS elemental distribution testing, such as... Figure 2 The EDS analysis shows that the composite material contains nitrogen, which comes from polyethyleneimine, indicating that polyethyleneimine is grafted onto the surface of Si / C@10%GO.

[0072] The batteries prepared in each embodiment and comparative example were subjected to charge-discharge tests at a current density of 0.1 A / g. The specific data are shown in Table 1. Figure 3 The composite material prepared in Example 1 retained 90% capacity after 200 cycles of initial charge-discharge and charge-discharge current density of 3.0 A / g.

[0073] Table 1 Materials prepared under different composite ratios

[0074]

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a composite silicon-carbon anode material, characterized in that, Includes the following steps: (1) Weigh graphene oxide and secondary granulated silicon-carbon anode material, add them sequentially to an aqueous solution, and disperse them under ice bath conditions to obtain a dispersed graphene oxide-silicon-carbon aqueous solution; the mass percentage of graphene oxide to secondary granulated silicon-carbon anode material is (10%~25%): (75%~90%). (2) The graphene oxide-silicon carbon aqueous solution obtained in step (1) was transferred to a spray dryer and Si / C@GO composite material was prepared by spray drying. (3) Take the Si / C@GO composite material obtained in step (2), disperse it in an aqueous solution or ethanol solution, and then add an aqueous solution or ethanol solution of amino polymer. Stir, cool and centrifuge under oil bath conditions to obtain Si / C@GO / N composite silicon-carbon anode material. The amount of amino polymer added is 0.5% to 3% of the mass of Si / C@GO.

2. The method according to claim 1, characterized in that, In step (1), the preparation method of the secondary granulation composite silicon-carbon anode material is as follows: first, the micron-sized silicon is nano-sized by sand milling; then it is compounded with graphite and pitch, and obtained by granulation and secondary sintering.

3. The method according to claim 1, characterized in that, In step (1), the graphene oxide is graphene oxide or an aqueous solution of graphene oxide, and the particle size of the graphene oxide is 3-10 μm.

4. The method according to claim 1, characterized in that, In step (1) and step (2), during spray drying, the spray inlet temperature is 180℃, the outlet temperature is 105℃, and the flow rate is controlled at 10ml / min.

5. The method according to claim 1, characterized in that, In step (3), the amino polymer is selected from one of polyethyleneimine, polyacrylamide, and polyallylamine.

6. The method according to claim 1, characterized in that, In step (3), the temperature of the oil bath is 60℃-90℃ and the time is 2-8h.

7. The composite silicon-carbon anode material prepared by the method of any one of claims 1-6.

8. A method for preparing a negative electrode sheet, characterized in that, Polyacrylic acid is neutralized with ammonia water to form a viscous ammonium polyacrylate aqueous solution. The Si / C@GO / N composite silicon-carbon anode material prepared according to claim 7, the conductive agent, and the ammonium polyacrylate on a dry weight basis are mixed in proportion. The mixture is dried at 60-80℃ for 3-8 hours by forced air drying and at 100-120℃ for 10-15 hours by vacuum drying to obtain the electrode sheet.

9. The negative electrode sheet prepared by the method of claim 8.

10. The method according to claim 8, characterized in that, After obtaining the electrode, cut it into 12mm diameter round pieces, dry it at high temperature for 3 hours, take it out, and assemble the battery.

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