Silicon / graphene composite fiber and preparation method and application thereof

Abstract

The invention provides a silicon / graphene composite fiber and a preparation method and application thereof. The preparation method of the silicon / graphene composite fiber comprises the following steps: uniformly mixing graphene oxide and silicon powder in a dispersion liquid to obtain a spinning solution; the preparation method comprises the following steps: preparing a silicon / graphene oxide composite fiber through wet spinning, carrying out first reduction treatment on the silicon / graphene oxide composite fiber, cleaning, drying, and carrying out second reduction treatment to obtain the silicon / graphene composite fiber. The battery prepared from the silicon / graphene composite fiber provided by the invention is excellent in electrochemical performance, slow in performance attenuation, excellent in capacity retention rate, long in cycle life and good in electrochemical stability, and volume expansion of silicon is effectively inhibited; and the method is very suitable for high-energy-density power battery systems.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy materials, in particular to a silicon / graphene composite fiber and a preparation method and application thereof. BACKGROUND

[0002] In the prior art, commercial lithium ion batteries mainly use graphite-based negative electrode materials, but the theoretical specific capacity has approached the limit value (372 mAh / g), which is difficult to meet the demand for high-energy-density batteries in the fields of new energy vehicles, energy storage, etc. Silicon-based negative electrodes are considered as the core direction of the next generation of negative electrode materials due to their advantages of ultra-high theoretical specific capacity (4200 mAh / g, about 10 times that of graphite), low lithium extraction potential (which is conducive to improving the fast charging safety), and abundant resources. However, when silicon is used as a negative electrode material for lithium ion batteries, there is a serious volume expansion (~300 %) during the lithium intercalation / deintercalation process, which leads to particle pulverization of the silicon-based battery negative electrode, collapse of the electrode structure, and separation of the active material and the current collector, thereby causing problems of battery capacity attenuation and cycle life reduction, which seriously restricts its industrial application.

[0003] To overcome the above-mentioned defects, the industry has proposed a "silicon-carbon composite" technical route. Among them, nano-silicon (such as nano-silicon particles, silicon nanowires, etc.) is used to replace micrometer silicon, thereby significantly reducing the absolute expansion stress during the lithium intercalation / deintercalation process, and the shorter ion / electron transport path under nanoscale is used to improve the reaction kinetics. On this basis, carbon materials (such as porous carbon, carbon nanotubes, graphene, etc.) with high electrical conductivity and mechanical toughness are introduced as a skeleton to construct a three-dimensional continuous conductive network throughout the electrode. Thus, the electronic transport efficiency is effectively improved, and the volume change of silicon is provided with elastic buffer space.

[0004] Graphene is an ideal carrier for optimizing silicon negative electrodes due to its ultra-high electrical conductivity, mechanical flexibility, and two-dimensional confinement effect. However, nano-silicon / graphene composite materials still face severe challenges. For example, there are problems of poor structural uniformity, limited volume expansion inhibition capability, and high cost of large-scale preparation. SUMMARY

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a silicon / graphene composite fiber and a preparation method and application thereof, which are used to solve the problems in the prior art.

[0006] To achieve the above-mentioned purposes and other related purposes, the present application is obtained by the following technical solutions.

[0007] The first aspect of this invention provides a method for preparing silicon / graphene composite fibers as a negative electrode material for lithium batteries, comprising the following steps: uniformly mixing graphene oxide and silicon powder in a dispersion to obtain a spinning solution; preparing silicon / graphene oxide composite fibers by wet spinning; subjecting the silicon / graphene oxide composite fibers to a first reduction treatment; and after cleaning and drying, subjecting them to a second reduction treatment to obtain the silicon / graphene composite fibers.

[0008] Preferably, the graphene oxide has a particle size of 1~5 μm.

[0009] The 1-5 μm graphene oxide in this application is obtained by oxidizing graphite via the Hummers method, which can be prepared on a large scale at low cost, thus facilitating industrialization.

[0010] Furthermore, this particle size parameter cannot be set arbitrarily. If the size of the graphene oxide used is too small, the spinnability will be poor and the strength will be low, which is not conducive to wet spinning. If the size of the graphene oxide used is too large, it will easily clog the equipment and the risk of fiber breakage will be high.

[0011] Preferably, the particle size of the silicon powder is 20~60 μm.

[0012] The particle size parameter of silicon powder cannot be set arbitrarily. If the particle size of the silicon powder is too large, it will easily cause the needles to clog during wet spinning, making it difficult to continue spinning. If the particle size of the silicon powder is too small, the silicon powder will easily agglomerate and settle, making it impossible to disperse evenly, and the cost will be higher.

[0013] Preferably, the mass ratio of silicon powder to graphene oxide is 1:3 to 9. For example, it can be 1:4 to 8, or 1:4, 1:5, 1:6, 1:7, or 1:8.

[0014] This technical feature is a very important parameter feature, and the technical effects described in this application can only be achieved within the specific range specified in this application. If too much silicon powder is added, the resulting composite fiber, when applied to the negative electrode of a battery, will not be able to effectively suppress the volume expansion of silicon during the cycle charge and discharge process, resulting in battery capacity decay and reduced cycle life; while if the silicon powder content is too low, the energy density of the battery cannot be effectively improved.

[0015] Preferably, the concentration of graphene oxide in the dispersion is 10-25 mg / mL. For example, it can be 13-20 mg / mL, or 13 mg / mL, 14 mg / mL, 15 mg / mL, 16 mg / mL, 17 mg / mL, 18 mg / mL, 19 mg / mL, or 20 mg / mL.

[0016] Preferably, the dispersion is selected from one or more of N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0017] Preferably, the wet spinning process includes one or more of the following technical features:

[0018] The diameter of the spinning needle is 100~300 μm;

[0019] The propulsion speed is 0.05~1 cm / min;

[0020] The coagulation bath used is one or more of ethyl acetate, dichloromethane, and petroleum ether;

[0021] The temperature of the coagulation bath is 20~28℃.

[0022] The diameter of the spinning needle can be 120~200 μm or 130~180 μm; the feed speed can be 0.05~0.5 cm / min, 0.05~0.3 cm / min or 0.08~0.15 cm / min; and the temperature of the coagulation bath can be 22~28 ℃, specifically 23 ℃, 24 ℃, 25 ℃, 26 ℃ or 27 ℃.

[0023] Preferably, prior to the first reduction treatment, the silicon / graphene oxide composite fibers are collected by filtration and then dried.

[0024] Preferably, the silicon / graphene oxide composite fiber is completely immersed in a reducing acid to perform the first reduction treatment.

[0025] Preferably, the reducing acid is selected from one or more of hydroiodic acid, ascorbic acid, and cysteine. The selection of the reducing acid in this application is a very specific technical approach. Only by using the reducing agent described above can the original graphene fiber structure be maintained while removing oxygen-containing groups, without the release of gases such as carbon dioxide. If other reducing agents, such as alkaline reducing agents like hydrazine hydrate, are used, they will damage the fiber structure during the reduction process, making it impossible to obtain dense silicon / graphene fibers.

[0026] Preferably, the concentration of the reducing acid is 55-58 wt%. For example, it can be 55 wt%, 56 wt%, 57 wt%, or 58 wt%.

[0027] Preferably, the first reduction treatment takes 2 to 6 hours and the temperature is 20 to 60 ℃. For example, the temperature can be 20 to 30 ℃, 20 to 28 ℃, 22 to 28 ℃, 23 ℃, 24 ℃, 25 ℃, 26 ℃, or 27 ℃.

[0028] Preferably, the cleaning is performed using water and ethanol in sequence.

[0029] Preferably, the temperature of the second reduction treatment is 600~1000 ℃; the time is 2~4 hours.

[0030] The temperature of the second reduction treatment can be 750~850 ℃, 800 ℃, 900 ℃, 700~900 ℃, 650~950 ℃, or 1000 ℃; the time can be 4 hours, 3 hours, or 2 hours.

[0031] The temperature of the second reduction process in this application is not arbitrarily set. Only within the temperature range described in this application can carbon atoms obtain sufficient energy to migrate and rearrange, thereby effectively repairing lattice defects caused by the oxidation process and completely removing oxygen-containing functional groups from the composite fiber. If the temperature of the second reduction process is too low, the carbon atoms cannot obtain enough energy, failing to achieve the reduction effect of this application; if the temperature of the second reduction process is too high, the requirements for the reduction equipment are extremely high, and the energy consumption is also large.

[0032] Preferably, the second reduction treatment is carried out under an inert gas, which includes nitrogen.

[0033] A second aspect of the present invention provides a silicon / graphene composite fiber as a negative electrode material for lithium batteries, which is prepared by the preparation method described above.

[0034] Preferably, the diameter of the composite fiber is 30-40 μm. For example, it can be 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, or 39 μm.

[0035] Preferably, the silicon content in the composite fiber ranges from 20 to 40 wt%. For example, it can be 23.6 to 37.5 wt%, or 21 to 38 wt%.

[0036] A third aspect of the present invention provides an application of the silicon / graphene composite fiber as described above as a negative electrode material for lithium batteries.

[0037] A fourth aspect of the present invention provides a lithium battery anode slurry, wherein the raw material components of the lithium battery anode slurry include the silicon / graphene composite fiber as described above; the raw material components of the lithium battery anode slurry further include carbon black, binder, and polar solvent.

[0038] Preferably, the silicon / graphene composite fibers are ground before use, and the particle size after grinding is 5~10 μm. For example, the particle size can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0039] Preferably, the binder is selected from one or both of sodium carboxymethyl cellulose and sodium alginate. More preferably, the sodium carboxymethyl cellulose has a viscosity of 3000~5000 mPa·s at 25 °C. For example, it can be 3000 mPa·s, 4000 mPa·s, or 5000 mPa·s.

[0040] Preferably, the polar solvent is selected from N-methylpyrrolidone.

[0041] Preferably, in the raw material components of the lithium battery negative electrode slurry, the silicon / graphene composite fiber is 7-9 parts by weight, the carbon black is 0.5-2 parts by weight, the binder is 0.5-1.5 parts by weight, and the polar solvent is 25-55 parts by weight.

[0042] The weight parts of the silicon / graphene composite fiber can be 7 parts, 8 parts, or 9 parts; the weight parts of the carbon black can be 0.5 parts, 1 part, 1.5 parts, or 2 parts; the weight parts of the binder can be 0.5 parts, 1 part, or 1.5 parts; and the weight parts of the polar solvent can be 45-55 parts, 30-50 parts, or 35-55 parts.

[0043] A fourth aspect of the present invention provides a lithium battery negative electrode, which is formed by coating a current collector with a lithium battery negative electrode slurry as described above.

[0044] The fifth aspect of the present invention provides a lithium-ion battery employing a lithium battery negative electrode as described above.

[0045] The silicon / graphene composite fiber in this application is obtained by wet spinning and reduction of silicon powder and graphene oxide. The reason for not directly using silicon and graphene for spinning is that graphene itself does not have the molecular structure required to form continuous, spinnable fibers, and its dispersibility is poor, making it difficult to form a uniform, spinnable solution. Graphene oxide, on the other hand, has a completely different structure. Its surface is rich in oxygen-containing functional groups (such as hydroxyl, epoxy, and carboxyl groups). These groups make it hydrophilic, allowing it to be uniformly dispersed in water or organic solvents to form a stable, highly concentrated solution, thus possessing spinnability.

[0046] Beneficial effects:

[0047] The battery made using the silicon / graphene composite fiber provided in this application as the negative electrode exhibits excellent electrochemical performance, with high initial coulombic efficiency, high specific capacity, and high energy utilization. Furthermore, after 100 charge-discharge cycles, the battery shows slow performance degradation, excellent capacity retention, long cycle life, and good electrochemical stability, effectively suppressing silicon volume expansion. It is highly suitable for high-energy-density power battery systems.

[0048] Furthermore, the preparation method of silicon / graphene composite fibers provided in this application is simple and easy to operate. Attached Figure Description

[0049] Figure 1 The image shown is a scanning electron microscope (SEM) image of the silicon / graphene composite fiber prepared in Example 1 of this invention.

[0050] Figure 2 The image shown is an SEM image of the cross-section of the silicon / graphene composite fiber prepared in Example 1 of this invention.

[0051] Figure 3 The image shown is a transmission electron microscope (TEM) bright-field image and corresponding elemental plane distribution map of the silicon / graphene composite fiber prepared in Example 1 of this invention.

[0052] Figure 4 The diagram shows the thermogravimetric analysis of pure silicon in this invention and the silicon / graphene composite fiber prepared in Example 3.

[0053] Figure 5 The diagram shows the voltage-capacity curves of the battery made from the silicon / graphene composite fiber prepared in Example 3 of this invention during the first charge and discharge at current densities of 0.5 A / g, 1 A / g, and 5 A / g.

[0054] Figure 6 The graph shows the charge-discharge cycle performance of batteries made from silicon / graphene composite fibers prepared in the various embodiments and comparative examples of this invention at a current density of 0.5 A / g.

[0055] Figure 7 The image shown is of the product made from the silicon / graphene composite fiber prepared in Example 1 of this invention. Detailed Implementation

[0056] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0057] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0058] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0059] In the following examples and comparative examples of this application, the average particle size of the graphene oxide used was 3 μm; the average particle size of the silicon powder used was 40 μm; and the hydroiodic acid used was a 55 wt% aqueous solution of hydroiodic acid.

[0060] Example 1

[0061] This embodiment 1 provides a specific silicon / graphene composite fiber and its preparation method, including the following steps:

[0062] 1) Add 37.5 mg of silicon powder to 20 mL of 15 mg / mL graphene oxide DMF dispersion (to make the mass ratio of silicon powder to graphene oxide 1:8), and stir magnetically overnight to ensure uniform dispersion between silicon powder and graphene oxide.

[0063] Using a spinning needle with an inner diameter of 160 μm, the spinning solution was injected into a coagulation bath of ethyl acetate at a feed rate of 0.1 cm / min and a coagulation bath temperature of 25 °C to obtain silicon / graphene oxide fibers. The silicon / graphene oxide fibers were collected by vacuum filtration and then naturally dried for later use.

[0064] 2) The silicon / graphene oxide composite fiber obtained in step 1 is subjected to a first reduction treatment: it is completely immersed in hydroiodic acid solution for 2 hours, then washed with deionized water and ethanol in sequence, and dried at 60 °C; then a second reduction treatment is performed: the dried fiber is carbonized in a tube furnace at 800 °C under nitrogen protection for 2 hours to prepare the silicon / graphene fiber.

[0065] The applicant used SEM and TEM to observe the structure of the silicon / graphene composite fiber prepared in Example 1. Specific results are shown in [link to example]. Figures 1-3 .

[0066] Figure 1 Here is a SEM image of silicon / graphene composite fibers, from... Figure 1 It can be seen that the silicon / graphene composite fiber was prepared in this embodiment, and its diameter is 30~40μm.

[0067] Figure 2 SEM image of the cross-section of silicon / graphene composite fibers, by Figure 2 It can be seen that silicon nanoparticles are encapsulated inside graphene fibers.

[0068] Figure 3 This is a bright-field TEM image of silicon / graphene composite fibers and the corresponding elemental plane distribution. In the left image, black particles are silicon nanoparticles, and gray particles are graphene. Figure 3 As shown in the left image, the black particles are completely encapsulated inside by light gray graphene.

[0069] Therefore, it can be seen that in the silicon / graphene composite fiber prepared in the embodiments of this application, silicon nanoparticles are loaded on a graphene carrier and coated by the graphene carrier.

[0070] Example 2

[0071] Except for step 1), in which the mass ratio of silicon powder to graphene oxide is changed to 1:6, the rest of the steps are exactly the same as in Example 1.

[0072] Example 3

[0073] Except for step 1), in which the mass ratio of silicon powder to graphene oxide is changed to 1:4, the rest of the steps are exactly the same as in Example 1.

[0074] Comparative Example 1

[0075] Except for step 1), in which silicon powder is not added, the other steps are exactly the same as in Example 1.

[0076] Comparative Example 2

[0077] Except for step 2), where only the first restoration process is performed and the second restoration process is not performed, the remaining steps are exactly the same as in Example 1.

[0078] Comparative Example 3

[0079] Except for step 2), where only the second restoration process is performed and the first restoration process is not performed, the other steps are exactly the same as in Example 1.

[0080] Comparative Example 4

[0081] Except for step 1), where the mass ratio of silicon powder to graphene oxide is changed to 1:2, the rest of the steps are exactly the same as in Example 1.

[0082] Application Example 1: Silicon Content Detection

[0083] The applicant performed thermogravimetric analysis on the silicon / graphene composite fibers prepared in the examples to determine the silicon content in the silicon / graphene fibers. The specific test method is as follows:

[0084] The composite fibers provided in each embodiment were placed in oxygen and continuously heated at 500 °C (>450 °C). During the process, the carbon element in the composite fiber was continuously converted into carbon dioxide and released, while the silicon element was continuously converted into silicon dioxide, until the mass remained constant. The mass m1 of the silicon dioxide remaining after heating was weighed, in which the mass of Si accounted for 46.8% of the silicon dioxide mass. The mass m2 of silicon element in the composite fiber was calculated. The silicon content in each embodiment was obtained by dividing m2 by the mass m0 of the silicon / graphene fiber before heating.

[0085] The principle is as follows:

[0086] The applicant performed thermogravimetric analysis on pure silicon and the silicon / graphene composite fiber prepared in Example 3, see [link to analysis]. Figure 4 Thermogravimetric analysis was performed in an oxygen-rich environment.

[0087] Depend on Figure 4 It can be seen that when thermogravimetric analysis is performed on pure silicon, the TGA curve of pure silicon rises when the temperature reaches about 450 ℃, indicating that silicon begins to oxidize and transform into silicon dioxide, thus increasing its quality.

[0088] When thermogravimetric analysis was performed on the silicon / graphene fibers prepared in Example 3, it was found that when the temperature reached about 450°C, the TGA curve of the silicon / graphene fibers showed a slow decrease, indicating that the graphene in the composite fiber began to oxidize and continuously release carbon dioxide, resulting in a lighter weight. When the temperature reached about 620°C, the graphene was completely oxidized. Since the silicon was not completely oxidized at this time, the total mass gradually increased and turned into silicon dioxide.

[0089] Therefore, the composite fibers provided in each embodiment are placed in oxygen and continuously heated at 500 °C (>450 °C) until their mass remains constant. The mass m1 of the silicon dioxide remaining after heating is weighed, and the mass m2 of silicon in the composite fiber can be calculated. The silicon content in each embodiment is obtained by dividing m2 by the mass m0 of the silicon / graphene fiber before heating.

[0090] The specific results are shown in Table 1 below.

[0091] Table 1

[0092] Silicon content (wt%) Example 1 23.6 Example 2 29.1 Example 3 37.5 Comparative Example 1 0 Comparative Example 2 21.3 Comparative Example 3 40.6 Comparative Example 4 49.5

[0093] Application Example 2: Electrochemical Performance Testing

[0094] The applicant used the silicon / graphene composite fibers prepared in Examples 1-3 and Comparative Examples 1-4 as negative electrode materials for lithium-ion batteries and assembled the batteries, specifically including the following steps:

[0095] The silicon / graphene composite fibers provided in each embodiment and comparative example were ground to obtain silicon / graphene powder (particle size 5~10 μm). The silicon / graphene powder, carbon black, and CMC (25 ℃, 4000 mPa.s) were mixed evenly in 500 mg N-methylpyrrolidone at a mass ratio of 80 mg:10 mg:10 mg to prepare a lithium battery negative electrode slurry. This slurry was coated onto a copper foil surface and vacuum dried at 60 ℃ to prepare a lithium battery negative electrode sheet with an active material loading of 1 mg / cm³. 2 Button-type half-cells were assembled in an argon-filled glove box (H₂O < 0.01 ppm, O₂ < 0.01 ppm), with a lithium electrode used as the counter electrode and a polypropylene membrane (Celgard 2400) used as the separator. The electrolyte was a 1 M LiPF₆ solution of dimethyl carbonate (DMC) / ethylene carbonate (EC) / diethylene carbonate (DEC) (volume ratio 1:1:1), with 5 vol% fluoroethylene carbonate (FEC) as an additive.

[0096] The applicant conducted constant current charge-discharge tests on the batteries prepared in Examples 1-3 and Comparative Examples 1-4 at current densities of 0.5 A / g, 1 A / g, and 5 A / g to detect their electrochemical performance. The specific test method was as follows: in the Blue Electric testing system, after the batteries were allowed to rest for 12 hours, cyclic charge-discharge tests were started. The charge-discharge current densities were set to 0.5 A / g, 1 A / g, and 5 A / g, respectively, with a 30-second rest period between each charge-discharge cycle. The voltage protection range was set to -5 to 5 V.

[0097] The voltage-capacity curves of the battery prepared in Example 3 at current densities of 0.5 A / g, 1 A / g, and 5 A / g during its first charge-discharge cycle are shown below. Figure 5 .

[0098] Depend on Figure 5 It can be seen that when the current density is 1 A / g, the charge and discharge voltage plateau is obvious, and the capacity is still 600 mAh / g. This indicates that the battery prepared in Example 3 of this application still has good rate performance and excellent electrochemical performance when the current density is 1 A / g.

[0099] The specific test structures for the first-cycle coulombic efficiency, second-cycle charge specific capacity, and charge specific capacity after 100 cycles for each embodiment and comparative example are shown in Table 2 below; the charge-discharge cycle performance curves for each embodiment and comparative example at a current density of 0.5 A / g are shown in... Figure 6 .

[0100] Table 2

[0101] Mass content of silicon in silicon / graphene (%) Coulombic efficiency of the first cycle (%) Specific charge capacity after the 2nd cycle (mAh / g) Specific charge capacity after 100 cycles (mAh / g) Capacity retention rate after 100 cycles (%) Example 1 23.6 65 631 622 98.6 Example 2 29.1 71 751 726 96.6 Example 3 37.5 77 949 892 93.9 Comparative Example 1 0 42 173 171 99 Comparative Example 2 21.3 43 540 250 46 Comparative Example 3 40.6 72 991 804 81 Comparative Example 4 49.5 78 1170 319 27

[0102] The first-cycle coulombic efficiency is the value of the discharge capacity / charge capacity × 100% during the first complete charge-discharge cycle of a battery. It is used to measure the degree of charge loss in the first cycle. A high coulombic efficiency means that the electrochemical reactions that occur during the charge and discharge process are highly reversible, indicating that the battery's electrode materials have good reversibility, high energy utilization, and usually slow degradation in subsequent cycles and a longer cycle life.

[0103] From Table 1 and Figure 6 It is known that the batteries prepared in Examples 1 to 3 of this application have high coulombic efficiency of 65-77% in the first cycle and high charge specific capacity of 622-949 mAh / g. The batteries have good electrochemical performance and high energy utilization. Compared with the charge specific capacity in the second cycle, the batteries provided by this application have excellent capacity retention of 93.9-98.6% after 100 charge-discharge cycles, with slow performance degradation and good electrochemical stability.

[0104] As can be seen from Example 1 and Comparative Example 1, compared with Example 1, when only pure graphene is used as the negative electrode of the battery, its first-cycle coulombic efficiency and charge specific capacity are significantly lower than those of the embodiments of this application. This indicates that only when the specific silicon / graphene composite fiber provided in this application is used as the negative electrode material of the battery can the technical effect of this application be achieved.

[0105] As can be seen from Example 1 and Comparative Examples 2-3, the two reduction treatment techniques in this application are both essential. Only by performing two reduction treatments as described in this application can the technical effect of this application be achieved, which combines high first-cycle coulombic efficiency and charge specific capacity, while maintaining stable electrochemical performance.

[0106] As can be seen from Examples 1-3 and Comparative Example 4, the amount of silicon powder added in this application is very important, and its mass ratio with graphene is a very specific parameter. Only within the range described in this application can the technical effect of this application be achieved. Furthermore, with the increase of silicon powder added (i.e., the increase of silicon content in the battery negative electrode, Examples 1-3), the battery's first-cycle coulombic efficiency and specific charging capacity increase, and the electrochemical performance improves. However, if the silicon content in the negative electrode is too high (Comparative Example 4), although the first-cycle coulombic efficiency and the second-cycle specific charging capacity are high, the electrochemical performance of the battery is extremely unstable. After 100 cycles, the 100-cycle specific charging capacity decays rapidly, has a low retention rate, and cannot continue to effectively suppress the volume expansion problem during silicon charging and discharging.

[0107] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing silicon / graphene composite fibers as a negative electrode material for lithium batteries, characterized in that, The process includes the following steps: uniformly mixing graphene oxide and silicon powder in a dispersion to obtain a spinning solution; preparing silicon / graphene oxide composite fibers by wet spinning; subjecting the silicon / graphene oxide composite fibers to a first reduction treatment; cleaning and drying, followed by a second reduction treatment to obtain the silicon / graphene composite fibers.

2. The preparation method according to claim 1, characterized in that, The particle size of the graphene oxide is 1~5 μm; And / or, the particle size of the silicon powder is 20~60 μm; And / or, the mass ratio of the silicon powder to graphene oxide is 1:3~9; And / or, in the dispersion, the concentration of the graphene oxide is 10~25 mg / mL; And / or, the dispersion is selected from one or more of N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide; And / or, the wet spinning process includes one or more of the following technical features: The diameter of the spinning needle is 100~300 μm; The propulsion speed is 0.05~1 cm / min; The coagulation bath used is one or more of ethyl acetate, dichloromethane, and petroleum ether; The temperature of the coagulation bath is 20~28℃.

3. The preparation method according to claim 1, characterized in that, Before the first reduction treatment, the silicon / graphene oxide composite fibers are collected by vacuum filtration and then dried. And / or, the silicon / graphene oxide composite fiber is completely immersed in a reducing acid to perform the first reduction treatment; And / or, the temperature of the first reduction treatment is 20~60 °C; And / or, the cleaning is performed sequentially using water and ethanol; And / or, the second reduction treatment is a high-temperature treatment, with a high temperature of 600~1000 ℃; And / or, a second reduction treatment is performed under an inert gas, including nitrogen.

4. The preparation method according to claim 3, characterized in that, The reducing acid is selected from one or more of hydroiodic acid, ascorbic acid, and cysteine; And / or, the concentration of the reducing acid is 55-58 wt%.

5. A silicon / graphene composite fiber as a negative electrode material for lithium batteries, characterized in that, The composite fiber is prepared by any one of the preparation methods described in claims 1 to 4; preferably, the diameter of the composite fiber is 30 to 40 μm; preferably, the silicon content in the composite fiber is in the range of 20 to 40 wt%.

6. The application of the silicon / graphene composite fiber as described in claim 5 as a negative electrode material for lithium batteries.

7. A lithium battery negative electrode slurry, characterized in that, The raw material components of the lithium battery negative electrode slurry include the silicon / graphene composite fiber as described above; the raw material components of the lithium battery negative electrode slurry also include carbon black, binder, and polar solvent.

8. The negative electrode slurry according to claim 7, characterized in that, Before use, the silicon / graphene composite fibers are ground to a particle size of 5-10 μm. And / or, the adhesive is selected from one or two of sodium carboxymethyl cellulose and sodium alginate; And / or, the polar solvent is selected from N-methylpyrrolidone; And / or, in the raw material components of the lithium battery negative electrode slurry, the silicon / graphene composite fiber is 7-9 parts by weight, the carbon black is 0.5-2 parts by weight, the binder is 0.5-1.5 parts by weight, and the polar solvent is 25-55 parts by weight.

9. A lithium battery negative electrode, characterized in that, It is formed by coating the current collector with the lithium battery negative electrode slurry as described in claim 7 or 8.

10. A lithium-ion battery employing the lithium battery negative electrode as described in claim 9.

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