Lithium ion battery electrode of three-dimensional graphene coated nano silicon particle composite material and preparation method and application of lithium ion battery electrode

Abstract

The invention relates to a lithium ion battery electrode of a three-dimensional graphene coated nano-silicon particle composite material and a preparation method and application thereof.A stable and good-performance carbon coating layer is used for buffering the volume effect, inhibiting expansion of a silicon material and enhancing conductivity, firstly, nanoscale materials such as Si / C are prepared, the volume change is reduced, and the conductivity of the lithium ion battery electrode is improved; and the overall electrochemical performance is improved. And secondly, a shape-preserving core-shell structure, a layered structure or an interlayer structure is adopted as a buffer layer, so that silicon pulverization is prevented, and the volume change is reduced. Compared with the prior art, an additional position is provided for sedimentation of the silicon nanoparticles through the structure of the three-dimensional graphene, and in the provided configuration, comminution of the silicon-based anode is avoided through the synergistic effect of the small size of the silicon nanoparticles, the flexibility of the three-dimensional graphene, the porous 3D structure and morphological defects, so that the cycling stability is promoted, and the service life of the silicon-based anode is prolonged. And the capacity is increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysis, and in particular relates to a lithium ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material, and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are widely used in the field of energy storage devices due to their excellent electrochemical performance and environmentally friendly characteristics. Among various emerging anode materials, silicon negative electrode materials (silicon negative electrode materials are often used as anodes) have high capacity and energy density and are considered to be one of the hot spots in lithium battery research. However, silicon negative electrode materials are currently facing huge volume expansion changes, which leads to deformation caused by mutual compression between particles, affecting electrode performance.

[0003] CN105762360A discloses a graphene-coated silicon composite negative electrode material and its preparation method and application, which includes a cavity structure composed of graphene and nano-silicon particles coated in the cavity structure, wherein the particle size of the nano-silicon particles is 1 to 100 nm, and the weight percentage of the nano-silicon particles is 5 to 95%. The preparation method is: dispersing graphene oxide and silicon powder in deionized water, mixing under ultrasonic conditions and then freeze-drying; post-treating the freeze-dried product to obtain a graphene-coated silicon composite negative electrode material. The negative electrode material can be used in lithium-ion batteries. However, this preparation and coating method is relatively simple, and the electrochemical performance needs to be further improved.

[0004] Therefore, how to buffer the volume effect stably and with good performance, inhibit the expansion of silicon materials, and enhance conductivity is a problem that needs to be solved. Summary of the invention

[0005] The purpose of the present invention is to provide a lithium ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material and its preparation method and application in order to overcome the defects of the above-mentioned prior art. The present invention uses a stable and high-performance carbon coating layer to buffer the volume effect, inhibit the expansion of silicon materials, and enhance conductivity. First, nano-scale materials such as Si / C are prepared, the volume change is reduced, and the overall electrochemical performance is improved. Secondly, a conformal core-shell structure, a layered structure or a sandwich structure is used as a buffer layer to prevent silicon from pulverizing and reduce volume changes.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The first object of the present invention is to provide a method for preparing a lithium ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material, comprising the following steps:

[0008] S1. Firstly, weigh the graphene oxide material, add a surfactant, put it into a deionized water for ultrasonic vibration, and after dissolving, add nano-silicon powder, stir and centrifuge, and take out the precipitate;

[0009] S2, freezing the precipitate obtained in step S1 with liquid nitrogen, and freeze-drying it using a freeze dryer to obtain a freeze-dried mixture;

[0010] S3, placing the freeze-dried mixture obtained in step S2 into a tube furnace, burning the material to obtain an active substance;

[0011] S4, weighing a certain mass ratio of the active material, conductive agent, and binder obtained in step S3, grinding them, and then stirring and grinding them with a magnetic stirrer to form an electrode slurry;

[0012] S5, evenly coating the electrode slurry obtained in step S4 on the carbon-coated copper foil to obtain a composite electrode sheet;

[0013] S6, drying the composite electrode obtained in step S5, and obtaining a lithium-ion battery electrode after vacuum drying at a certain temperature, that is, the lithium-ion battery electrode of the three-dimensional graphene-coated nano-silicon particle composite material.

[0014] Further, after step S6, step S7 is performed:

[0015] S7, cutting the lithium-ion battery electrode obtained in step S6 into pieces, adding electrolyte, assembling into a button-type battery shell group, and pressing the pieces with a tablet press to obtain a manufactured battery, wherein the manufactured battery is a button-type battery.

[0016] Furthermore, in step S7, the electrolyte used is a ternary electrolyte (KLD-1230C).

[0017] Further, in step S1, the surfactant is polydimethyldiallylammonium chloride;

[0018] In step S1, the ultrasonic oscillation time is 12 hours; in step S1, the mass ratio of the graphene oxide material to the nano-silicon powder is 4:1;

[0019] In step S1, the stirring and centrifuging conditions are: stirring and centrifuging at a speed of 6000 rpm for three times, each time for 5 minutes.

[0020] Furthermore, in step S2, the freeze-drying time is 48 hours.

[0021] Furthermore, in step S3, the temperature and time conditions of the tube furnace are set to 800° C. and 4 h, respectively.

[0022] Furthermore, in step S4, the mass ratio of the active material: the conductive agent: the binder is 8:1:1;

[0023] In step S4, the conductive agent is Ketjen black (ECP-600JD);

[0024] In step S4, the binder is one or more of hydroxymethyl cellulose (CMC2200) and styrene-butadiene rubber (SBR307);

[0025] In step S4, the magnetic stirring time is 8 hours, and the magnetic stirring speed control scale is 6.

[0026] Furthermore, in step S5, the coating is performed using a coater with a surface area of ​​100 μm and a loading of the active substance of 1.0 mg / cm 2 .

[0027] Furthermore, in step S6, the composite electrode is vacuum dried at 85° C. for 12 hours.

[0028] The second object of the present invention is to provide a lithium ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material, wherein the lithium ion battery electrode of the three-dimensional graphene-coated nano-silicon particle composite material is prepared by the preparation method.

[0029] The third object of the present invention is to provide an application of a lithium-ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material, and to use the lithium-ion battery electrode of the three-dimensional graphene-coated nano-silicon particle composite material in an energy storage device.

[0030] Furthermore, the lithium-ion battery electrode of the three-dimensional graphene-coated nano-silicon particle composite material is used as an anode material (negative electrode material).

[0031] The technical concept of the present invention is as follows:

[0032] The amorphous carbon deposited by the vapor phase further tightly wraps the silicon particles and is embedded in the graphene sheet structure, which can greatly alleviate the volume expansion of silicon and protect the structural stability of the electrode material, thereby further improving the electrochemical performance. First, freeze-drying is used to coat the nano-silicon to keep the graphene network structure system as unaffected as possible. This process maintains the uniformity and dispersion of these materials, providing a prerequisite for improving thermal reduction efficiency and preparing highly dispersed porous silicon composite materials. The three-dimensional interconnected graphene coating structure and the high dispersion of mesoporous silicon particles can alleviate the volume change of silicon and provide an effective transmission channel for electrons and lithium ions.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] (1) The preparation method of the present invention provides additional locations for the sedimentation of silicon nanoparticles through the structure of three-dimensional graphene. In the proposed configuration, the small size of silicon nanoparticles, the flexibility of three-dimensional graphene, the porous 3D structure and morphological defects work synergistically to avoid the crushing of silicon-based anodes, thereby promoting cycle stability and increasing capacity.

[0035] (2) The lithium-ion battery electrode of the present invention as a negative electrode can maintain good cycle stability during long-term use and gradually realize an efficient charge / discharge process. The lithium-ion battery electrode of the present invention as a negative electrode has excellent capacity output and cycle stability and can maintain high-performance operation for a long time at a higher current density. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a Fourier transform infrared spectrum of 3DGr@Si in an embodiment of the present invention.

[0037] Figure 2 3DGr@Si in the embodiment of the present invention is an XRD diagram.

[0038] Figure 3 3DGr@Si in the embodiment of the present invention has a C1s and Si 2p XPS spectrum.

[0039] Figure 4 This is a Raman spectrum diagram of 3DGr@Si in an embodiment of the present invention.

[0040] Figure 5 These are SEM images of 3DGr@Si at different magnifications in the embodiments of the present invention.

[0041] Figure 6 CV curve of the 3DGr@Si battery in the embodiment of the present invention.

[0042] Figure 7 3DGr@Si battery in the embodiment of the present invention is charged and discharged at a current density of 0.2A / g.

[0043] Figure 8 3DGr@Si battery in the embodiment of the present invention has a rate performance at different current densities.

[0044] Fig. 9 The cycle performance of the 3DGr@Si battery in the embodiment of the present invention at a current density of 0.2 A / g.

[0045] Fig.10 This is the long cycle performance of the 3DGr@Si battery in the embodiment of the present invention at a current density of 0.2 A / g.

[0046] Fig.11The figure is the rate performance of the battery in the comparative example of the present invention at different current densities. DETAILED DESCRIPTION

[0047] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0048] Features such as component models, material names, connection structures, control methods, algorithms, etc. that are not clearly stated in this technical solution shall be deemed as common technical features disclosed in the prior art.

[0049] It should be noted that, in the present invention, relational terms such as first and second, etc. are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations.

[0050] A lithium-ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material and a preparation method thereof, the preparation method comprising the following specific steps:

[0051] 1) Firstly, a certain mass of graphene oxide material is weighed and placed in a surfactant for ultrasonic vibration;

[0052] 2) After fully dissolved, add nano silicon powder and stir and centrifuge;

[0053] 3) After rapid freezing with liquid nitrogen, freeze-drying using a freeze dryer;

[0054] 4) Place the material in a tube furnace and burn it;

[0055] 5) Weigh a certain mass ratio of active material: conductive agent: binder, grind them thoroughly, and then stir and grind them with a magnetic stirrer to form an electrode slurry;

[0056] 6) evenly coating the electrode slurry on the carbon-coated copper foil;

[0057] 7) Use a vacuum pump to extract the gas in the oven, and place absorbent cotton inside the oven to absorb the water vapor dried out of the electrode slurry;

[0058] 8) After the gas in the oven is evacuated, the lithium-ion battery electrode is obtained after vacuum drying at a certain temperature;

[0059] 9) Cutting the electrode sheets into pieces and adding electrolyte to assemble into a button-type battery shell group;

[0060] 10) Tablet pressing machine;

[0061] 11) Testing the manufactured battery electrodes and batteries.

[0062] In the following examples, raw materials or processing techniques, unless otherwise specified, are conventional commercially available raw materials or conventional processing techniques in the art.

[0063] In the following examples, graphene oxide was purchased from Suzhou Tanfeng Technology Co., Ltd. Nano silicon powder was purchased from Shanghai Chaowei Nano Technology Co., Ltd., model number CW-Si-001.

[0064] Example 1

[0065] The present embodiment provides a lithium ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material, a manufactured battery including the lithium ion battery electrode, and a preparation method thereof, the preparation method comprising the following steps:

[0066] S1. Firstly, weigh the graphene oxide material (3DGr), add a surfactant, put it into a deionized water for ultrasonic vibration, and after dissolution, add nano silicon powder (Si nanoparticles), stir and centrifuge, and take out the precipitate;

[0067] S2, freezing the precipitate obtained in step S1 with liquid nitrogen, and freeze-drying it using a freeze dryer to obtain a freeze-dried mixture;

[0068] S3, placing the freeze-dried mixture obtained in step S2 into a tube furnace, burning the material to obtain an active substance;

[0069] S4, weighing a certain mass ratio of the active material, conductive agent, and binder obtained in step S3, grinding them, and then stirring and grinding them with a magnetic stirrer to form an electrode slurry;

[0070] S5, evenly coating the electrode slurry obtained in step S4 on the carbon-coated copper foil to obtain a composite electrode sheet;

[0071] S6, drying the composite electrode obtained in step S5, and obtaining a lithium-ion battery electrode after vacuum drying at a certain temperature, namely, the lithium-ion battery electrode of the three-dimensional graphene-coated nano-silicon particle composite material, denoted as 3DGr@Si;

[0072] S7, cutting the lithium-ion battery electrode obtained in step S6 into pieces, adding electrolyte, assembling into a button-type battery shell group, and pressing the pieces with a tablet press to obtain a manufactured battery, which is recorded as a 3DGr@Si battery.

[0073] In step S1, 100 mg of graphene oxide is added with a small amount of active agent polydimethyldiallylammonium chloride (PDDA, CAS: 26062-79-3), and then deionized water is added (50 to 100 mL of deionized water is sufficient, and the liquid after adding water has no obvious large particles when observed by naked eye under light), and ultrasonically vibrated for 12 hours.

[0074] In step S1, after sufficient dissolution, 25 mg of 30 nm silicon powder was added and centrifuged at 6000 rpm for three times, each time for 5 min.

[0075] In step S2, the precipitate obtained in step S1 is rapidly frozen to a frozen state using liquid nitrogen, and then pre-frozen for 3 hours using a freeze dryer, and the freeze-dried sample is freeze-dried for 48 hours.

[0076] In step S3, the freeze-dried mixture sample obtained in step S2 is placed in a tube furnace for vapor deposition (CVD), with the temperature set to 800° C. and the time set to 4 hours.

[0077] In step S4, 250 mg of the active material obtained in step S3, 31.25 mg of the conductive agent Ketjen black (ECP-600JD), 1562.5 mg of the 2 wt% (solid content) binder hydroxymethyl cellulose (CMC2200), and 65.10 mg of 48 wt% (solid content) styrene-butadiene rubber (SBR307) were weighed respectively, and stirred with a magnetic stirrer for 8 h;

[0078] In step S5, the coating is performed using a coater with a surface area of ​​100 μm and a loading of the active substance of 1.0 mg / cm 2 The coating was done with a 100um surface, and the loading of active substances after cutting was 1.0 mg / cm 2 about.

[0079] In step S6, the composite electrode obtained in step S5 is placed in a vacuum drying oven and vacuum dried at 85°C for 12 hours.

[0080] In step S7, the positive electrode shell, the negative electrode sheet (the negative electrode sheet is obtained by cutting the lithium-ion battery electrode obtained in step S6), the diaphragm, the lithium sheet, the gasket, the spring sheet and the negative electrode shell are assembled in sequence, and 6-8 drops of ternary electrolyte (KLD-1230C) are added.

[0081] In step S7, the pressure of the tablet press is set to 1000 kg / cm 2 After continuing for 5 seconds, the button battery installation is completed and a finished battery is obtained.

[0082] The physical characteristics are as follows:

[0083] 1. Fourier transform infrared spectroscopy analysis

[0084] like Figure 1 As shown in the figure, it is the Fourier infrared spectrum of 3DGr@Si. From the infrared spectrum of the material, it can be seen that 3456.5cm- 1 The stretching vibration absorption peak of OH is 2820.5cm- 1 The stretching vibration absorption peak of CH is 1589cm-1 The stretching vibration absorption peak of C=C double bond in graphene is 1352cm- 1 The in-plane bending vibration absorption peak of CH is 1111.1cm- 1 and 1085cm- 1 The antisymmetric stretching vibration absorption peak of Si-O is 768cm- 1 It is the absorption peak of Si-O symmetric stretching vibration.

[0085] 2. XRD analysis

[0086] like Figure 2 The figure shows the XRD diagram of 3DGr@Si. The crystal structure and surface element composition of the 3DGr@Si composite material were deeply explored by X-ray diffraction (XRD). In the XRD test results, the sample showed good crystallinity, showing three strong peaks at 2θ=28.6°, 47.4° and 56.2°. The diffraction peaks in these places correspond to the standard diffraction peaks of Si (PDF#77-2108). The weak peaks in other places correspond to the SiC component (PDF#73-1665). The XRD results show that the 3DGr@Si composite material is composed of two objects, Si and SiC.

[0087] 3. XPS analysis

[0088] like Figure 3 The following are the C1s and Si2p XPS spectra of 3DGr@Si. Using X-ray photoelectron spectroscopy (XPS) technology to further analyze the high-resolution spectrum in the C1s region, five key surface chemical bonds were successfully identified: Si-C bond with a binding energy of 283.7 eV, CC bond at 284.8 eV, COH bond at 285.eV, COC bond at 287.1 eV, and OC=O bond at 290.6 eV. In the Si2p high-resolution spectrum, three significant peaks at 99.9 eV, 101.4 eV, and 102.4 eV were observed, which correspond to Si-C bond, Si-O bond, and Si-Ox bond, respectively, indicating that Si in the sample exists in multiple oxidation states.

[0089] 4. Raman analysis

[0090] like Figure 4 The Raman spectrum of 3DGr@Si is shown in Figure 2. -1 The peak at 1344 cm -1 and 1580cm -1 The two broad peaks at 3DGr@Si are related to the D band and G band of graphite, respectively. Overall, this Raman spectrum shows that 3DGr@Si has a mixed sp2 and sp 3 The structural characteristics of the composite material are moderately disordered, which may have a positive impact on its energy storage applications. The ID / IG ratio is 0.84, which further confirms that there is a mixture of disordered and ordered carbon in its structure. The high level of the ID / IG ratio indicates that this composite material may have high conductivity while maintaining a certain structural stability. This property is of great significance for energy storage materials, such as lithium-ion battery anode materials, because the disordered carbon structure facilitates the insertion and extraction of ions, while the ordered sp 2 The structure helps with conductivity.

[0091] 5. SEM morphology analysis

[0092] like Figure 5 As shown in the figure, the SEM images of 3DGr@Si at different magnifications are shown. According to the SEM images of 3DGr@Si at different magnifications, it can be seen that the three-dimensional graphene-coated nano-silicon particle composite material obtained after treatment presents a uniform and regular nanoflower shape. With nano-silicon as the core, graphene nanosheets grow uniformly on its surface, inhibiting the stacking of graphene nanosheets themselves while exposing more reactive sites. This may indicate that the natural morphological defects in 3DGr provide additional buffer space to compensate for the volume expansion caused by silicon lithiation. In addition, the outer layer of graphene covers the Si nanoparticle layer, which can prevent the desorption of Si nanoparticles, that is, the loss of active materials, further improve electrical continuity, and stabilize battery performance.

[0093] The role of 3DGr and Si nanoparticles in 3DGr@Si can be summarized as follows: 3DGr provides a porous, flexible three-dimensional structure for Si nanoparticles, playing the role of buffering, stabilizing support, current collection, and part of the active material; silicon nanoparticles further increase the capacity. The small size of silicon nanoparticles, the flexibility of 3DGr, the porous three-dimensional structure and morphological defects work together to avoid the crushing of silicon-based anodes and are more conducive to the electrochemical reaction.

[0094] The electrochemical performance tests are as follows:

[0095] 1. CV

[0096] The 3DGr@Si battery was subjected to cyclic voltammetry test. The CV results of the first three cycles are as follows: Figure 6As shown. In the first scan, due to the activation of the electrode material, a complex irreversible reaction occurs at the electrode-electrolyte interface, thus presenting an irreversible redox peak, indicating the activation behavior of the material in the initial stage. At this time, a lower peak current is presented, which indirectly reflects the reduced initial material reaction activity. In the second CV, a reversible reduction peak appears, and the peak current increases, indicating that after one cycle of CV activation, some active sites on the surface of the material are activated. In the third CV, because the material has been activated for two cycles, the system tends to be stable, and a reversible redox peak appears, and the peak area increases, indicating that the electrode reaction activity is enhanced, the reversibility is good, and it is more conducive to ion insertion / extraction.

[0097] 2. Charge and discharge curve

[0098] To explore the electrochemical performance of 3DGr@Si, constant current charge and discharge (GCD) tests were performed on 3DGr@Si batteries at a voltage range of 0.01-3V and a current density of 0.2A / g. Figure 7 As shown in the figure, the charge and discharge curve of the 3DGr@Si battery at a current density of 0.2A / g. The first cycle discharge capacity and charge and discharge capacity of the 3DGr@Si battery are 2226mAh / g and 1691mAh / g, respectively, and the coulombic efficiency is only 75.98%. It is worth noting that the lower coulombic efficiency in the first cycle may be due to the formation of the solid electrolyte interface (SEI) film. The formation of the SEI film usually consumes part of the current, resulting in capacity loss during the first charge and discharge process. This is because lithium ions react with the surface of the negative electrode material during the initial cycle to form a stable film layer. In the subsequent cycles, the coulombic efficiency gradually increased, reaching 93.91% (second cycle), 94.8% (third cycle), 95.72% (fourth cycle) and 95.56% (fifth cycle), respectively. The gradual increase in coulombic efficiency and its approach to 100% indicate that the charge and discharge process of the 3DGr@Si negative electrode material (3DGr@Si battery) gradually stabilizes, and after the initial SEI film is formed, the electrochemical reaction becomes more reversible, and the battery performance is gradually restored and optimized. This phenomenon shows that the 3DGr@Si negative electrode (3DGr@Si battery) can maintain good cycle stability in long-term use and gradually achieve efficient charge / discharge process.

[0099] 3. Rate performance

[0100] The rate performance of 3DGr@Si battery at different current densities is shown in Figure 2. Figure 8 As shown. At current densities of 0.1, 0.2, 0.5, 1, 2, 5.0Ag- 1 When , the 3DGr@Si battery can achieve reversible specific capacities of 1237.59, 1149.49, 987.65, 787.01, 540.23, and 256.56 mAh / g respectively.

[0101] 4. Cycle performance

[0102] The cycling performance of 3DGr@Si battery was investigated at a current density of 0.2A / g. Fig. 9 As shown in the figure, during the first cycle, the discharge capacity of the 3DGr@Si battery reached 2226.59mAh / g, and the coulombic efficiency was 75.98%. After 100 cycles of the 3DGr@Si electrode, the discharge capacity and charge capacity of the 3DGr@Si battery were 865.34mAh / g and 853.02mAh / g, respectively, and the coulombic efficiency reached 98.58%.

[0103] The long cycle performance of 3DGr@Si battery was investigated at a current density of 0.2A / g. Fig.10 As shown in the figure, during the first cycle, the discharge capacity of the 3DGr@Si battery reached 1935mAh / g and the coulombic efficiency was 71.11%. This low coulombic efficiency can also be attributed to the initial formation of the SEI film, which consumed part of the current during the initial charge and discharge process, but as the material stabilized, the coulombic efficiency began to increase. As the number of cycles increased, the discharge capacity of the 3DGr@Si battery gradually stabilized, and the coulombic efficiency was close to 100%. This phenomenon shows that the electrochemical reaction of the 3DGr@Si battery gradually became reversible, the negative electrode material showed good charge / discharge efficiency during the cycle, and the performance of the battery system was stable. After 300 cycles of charge and discharge tests, the discharge capacity and charge capacity of the 3DGr@Si battery were 364.2mAh / g and 363.5mAh / g, respectively, and the coulombic efficiency reached 99.82%. This result shows that the 3DGr@Si battery has excellent capacity output and cycle stability, and can maintain high-performance operation for a long time at a higher current density.

[0104] Comparative Example

[0105] This comparative example provides a lithium-ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material, a manufactured battery comprising the lithium-ion battery electrode, and a preparation method thereof. The difference between this comparative example and Example 1 is that step S2 is not performed, and the precipitate obtained in step S1 is directly dried conventionally (vacuum drying oven 85°C) and then placed in a tubular furnace to burn the material to obtain an active substance.

[0106] For the battery manufactured in this comparative example, in the same constant current charge and discharge test as in Example 1, the first cycle discharge specific capacity and charge and discharge specific capacity are 1064.97 mAh / g and 623.00 mAh / g respectively, and the coulombic efficiency is only 58.50%. The first cycle discharge specific capacity, charge and discharge specific capacity and coulombic efficiency are significantly lower than those in Example 1. In the subsequent cycles, the coulombic efficiency gradually increases, and the coulombic efficiency gradually improves but still hardly approaches 100%.

[0107] like Figure 8 As shown, the battery manufactured in this comparative example has a current density of 0.1, 0.2, 0.5, 1, 2, and 5.0Ag. 1 When , the reversible specific capacities can reach 548.42, 442.1, 351.82, 197.67, 106.00 and 75.44 mAh / g respectively, and the rate performance at different current densities is lower than that of Example 1.

[0108] After 20 cycles of charge and discharge tests, the discharge specific capacity, charge specific capacity and coulombic efficiency of the battery manufactured in this comparative example are much lower than those in Example 1.

[0109] The above results show that the capacity output and cycle stability of the battery manufactured in this comparative example are far inferior to those of the 3DGr@Si battery in Example 1, which means that in the preparation process, in order to further improve the performance of the battery, the freeze-drying process in step S2 is necessary.

[0110] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A lithium-ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material, characterized in that: The following steps are involved: S1. Firstly, weigh the graphene oxide material, add a surfactant, put it into a deionized water for ultrasonic vibration, and after dissolving, add nano-silicon powder, stir and centrifuge, and take out the precipitate; S2, freezing the precipitate obtained in step S1 with liquid nitrogen, and freeze-drying it using a freeze dryer to obtain a freeze-dried mixture; S3, placing the freeze-dried mixture obtained in step S2 into a tube furnace, burning the material to obtain an active substance; S4, weighing a certain mass ratio of the active material, conductive agent, and binder obtained in step S3, grinding them, and then stirring and grinding them with a magnetic stirrer to form an electrode slurry; S5, evenly coating the electrode slurry obtained in step S4 on the carbon-coated copper foil to obtain a composite electrode sheet; S6, drying the composite electrode obtained in step S5, and obtaining a lithium-ion battery electrode after vacuum drying at a certain temperature, that is, the lithium-ion battery electrode of the three-dimensional graphene-coated nano-silicon particle composite material.

2. The method for preparing a lithium-ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material according to claim 1, characterized in that: After step S6, step S7 is performed: S7, cutting the lithium-ion battery electrode obtained in step S6 into pieces, adding electrolyte, assembling into a button-type battery shell group, and pressing the pieces with a tablet press to obtain a manufactured battery.

3. The method for preparing a lithium-ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material according to claim 1, characterized in that: In step S1, the surfactant is polydimethyldiallylammonium chloride; In step S1, the ultrasonic oscillation time is 12 hours; In step S1, the mass ratio of the graphene oxide material to the nano-silicon powder is 4:1; In step S1, the stirring and centrifuging conditions are: stirring and centrifuging at a speed of 6000 rpm for three times, each time for 5 minutes.

4. The method for preparing a lithium-ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material according to claim 1, characterized in that: In step S2, the freeze-drying time is 48 hours.

5. The method for preparing a lithium-ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material according to claim 1, characterized in that: In step S3, the temperature and time conditions of the tube furnace are set to 800° C. and 4 h, respectively.

6. The method for preparing a lithium-ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material according to claim 1, characterized in that: In step S4, the mass ratio of the active material: the conductive agent: the binder is 8:1:1; In step S4, the conductive agent is Ketjen black; In step S4, the binder is one or more of hydroxymethyl cellulose and styrene-butadiene rubber; In step S4, the magnetic stirring time is 8 hours.

7. The method for preparing a lithium-ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material according to claim 1, characterized in that: In step S5, the coating is performed using a coater with a surface area of ​​100 μm and a loading of the active substance of 1.0 mg / cm 2 .

8. The method for preparing a lithium-ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material according to claim 1, characterized in that: In step S6, the composite electrode is vacuum dried at 85°C for 12 hours.

9. A lithium-ion battery electrode of a three-dimensional graphene-coated nano-silicon particle composite material, characterized in that: The lithium-ion battery electrode of the three-dimensional graphene-coated nano-silicon particle composite material is prepared by the preparation method described in any one of claims 1 to 8.

10. An application of a lithium ion battery electrode made of a three-dimensional graphene-coated nano-silicon particle composite material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The lithium ion battery electrode of the three-dimensional graphene-coated nano-silicon particle composite material is used in energy storage devices.

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