Silicon-carbon composite negative electrode material, and preparation method and application thereof

Abstract

The application provides a silicon-carbon composite negative electrode material, which comprises a substrate and a coating layer coated on the substrate, the substrate comprises multilayer graphite and nano silicon intercalated between the multilayer graphite, and the material of the coating layer is a conductive material polymer compound, and the application also provides a preparation method and application of the silicon-carbon composite negative electrode material; compared with the prior art, after the prepared silicon-carbon composite negative electrode material is used as a negative electrode material of a lithium ion battery, the initial efficiency is greatly improved, and the cycle stability is also improved compared with a pure silicon negative electrode material; the nano silicon particles are coated by graphite and polyaniline, so that the conductivity and cycle stability of the material are improved, the specific capacity of the material is greatly superior to that of a traditional graphite negative electrode material, the lithium ion battery assembled by the electrode material has a capacity of 1000 mAh / g under a current density of 100 mA / g, and the electrode material is a relatively ideal negative electrode material of an ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery negative electrode active material, in particular to a silicon-carbon composite negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have a wide range of applications in portable electronic devices, electric vehicles and other fields due to their high energy density, long cycle life, environmental friendliness and other advantages. Among the many components of lithium ion batteries, the negative electrode material is one of the main "culprits" that ensures the further improvement of the energy density and cycle stability of lithium ion batteries and dominates the cost of the battery. Currently, the commercial negative electrode material of lithium ion batteries is mainly graphite material. Graphite is a cheap and stable battery negative electrode material and is the most widely commercialized negative electrode material. However, the theoretical capacity of graphite is only 372 mAh·g-1, and in recent years the capacity of commercial graphite has reached 355-360 mAh·g-1, close to its theoretical specific capacity, and it is difficult to have more room for improvement. With the vigorous development of electric vehicles, batteries with graphite as the negative electrode have been difficult to meet people's endurance requirements. Therefore, silicon-based negative electrode materials have attracted widespread attention due to their high capacity.

[0003] Among the currently developed negative electrode materials of lithium ion batteries, silicon-based materials are favored due to their low potential and extremely high theoretical capacity. However, silicon-based materials undergo severe volume changes (expansion rate up to 300%) during the process of deintercalating lithium ions, causing damage to the material structure and mechanical pulverization, leading to the separation of electrode materials and the current collector, and thus losing electrical contact, resulting in rapid capacity decay. Therefore, while obtaining high capacity, how to improve the cycle performance of silicon-based negative electrode materials is a current research focus. In order to buffer the capacity decay caused by the huge volume change of silicon during the electrochemical process, various methods have been used to improve the cycle performance of silicon negative electrode materials. For example, patent 202111349182.X designs a silicon-carbon composite negative electrode material, which includes silicon-based active particles, conductive material and carbon coating layer. The addition of conductive material can enhance the conductivity of silicon-based material, and the carbon coating layer can effectively alleviate the volume expansion, thereby enhancing the electrochemical performance of silicon-based negative electrode material to a certain extent. However, the above-mentioned materials are prepared by multi-step operation, which has high experimental cost, many process variables, and is difficult to commercialize and has high cost. SUMMARY

[0004] The technical problem solved by the present application is to provide a silicon-carbon composite negative electrode material that not only improves the conductivity of the material and inhibits the volume expansion of the negative electrode material, but also improves the cycle stability of the material.

[0005] To achieve the above object, the technical scheme adopted by the present application is: a silicon-carbon composite negative electrode material, comprising a substrate and a coating layer coated outside the substrate, the substrate comprises multilayer graphite and nanosilicon intercalated between the multilayer graphite, and the material of the coating layer is a conductive material polymer compound.

[0006] Optionally, the particle size of the nanosilicon is 100-200 nm.

[0007] Optionally, the conductive material polymer compound is selected from polyaniline or polypyrrole.

[0008] Another object of the present application is to provide a preparation method of the above-mentioned silicon-carbon composite negative electrode material, which specifically comprises the following steps:

[0009] S1, graphite is combined with nanosilicon powder to obtain a substrate;

[0010] S2, the substrate prepared in step S1 is coated with an outer layer to obtain a silicon-carbon composite negative electrode material.

[0011] Optionally, in step S1, the substrate is prepared by a liquid phase mixing method, and the specific steps are as follows: graphite is ultrasonically dispersed in deionized water to obtain a graphite dispersion liquid, nanosilicon powder is then put into the graphite dispersion liquid and ultrasonically and uniformly stirred, and then the sample is freeze-dried, heated to a final temperature and kept for a certain time to obtain the substrate.

[0012] Optionally, the mass ratio of graphite to nanosilicon powder is (100-1):20.

[0013] Optionally, the heating and keeping are both carried out in a protective atmosphere of inert gas, the final temperature is 500-700℃, and the keeping time is 2-7h.

[0014] Optionally, the inert gas is selected from one or a combination of several of argon, helium and neon;

[0015] Optionally, the flow rate of the inert gas is 50-150sccm.

[0016] Optionally, in step S2, in-situ synthesis method is used for outer layer coating, and the specific steps are as follows: the substrate obtained in step S1 is ultrasonically dispersed in deionized water to obtain a suspension, an aqueous hydrochloric acid solution of aniline monomer and an aqueous hydrochloric acid solution of ammonium persulfate are then sequentially added dropwise into the suspension, stirred uniformly, filtered and washed to obtain a filter cake, the filter cake is dried, and then heated to a final temperature and kept for a certain time to obtain a silicon-carbon composite negative electrode material.

[0017] Optionally, the molar ratio of aniline monomer to hydrochloric acid is (1-2):20, and the molar ratio of aniline monomer to ammonium persulfate is (1-2):1.

[0018] Optionally, the stirring is carried out in an ice water bath, and the stirring time is 6-24h.

[0019] Optionally, the drying condition is as follows: the drying temperature is 60-80 DEG C, and the drying time is 10-14h.

[0020] Optionally, the heat preservation treatment condition is as follows: the heating and heat preservation are both carried out in an inert gas protection atmosphere, the final temperature is 600-900 DEG C, and the heat preservation time is 4-10h.

[0021] A third object of the present application is to provide the application of the above-mentioned silicon-carbon composite negative electrode material in lithium ion batteries.

[0022] Compared with the prior art, the present application has the following advantages: first, the preparation method provided by the present application uses liquid phase mixing, which is a highly competitive method for preparing electrode materials, and can effectively manufacture high-performance electrode materials to meet the growing demand for lithium battery negative electrode materials; at the same time, the preparation method has high repeatability, and can easily realize batch preparation, which is suitable for industrial production.

[0023] Second, after the silicon-carbon composite negative electrode material prepared by the present application is used as the negative electrode material of a lithium ion battery, the initial efficiency is greatly improved compared with pure silicon negative electrode material, and the cycle stability is also improved; by double-coating the nano-silicon particles with graphite and polyaniline, the conductivity and cycle stability of the material are increased, and compared with traditional graphite negative electrode materials, the specific capacity is also greatly improved; the lithium ion battery assembled by the electrode material maintains a capacity of 1000mAh / g at a current density of 100mA / g, and is a relatively ideal ion battery negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a scanning electron microscope photo of the silicon-carbon composite negative electrode material prepared in Example 1 of the present application.

[0025] Figure 2 It is a transmission electron microscope photo of the silicon-carbon composite negative electrode material prepared in Example 1 of the present application.

[0026] Figure 3 It is an X-ray diffraction pattern of the silicon-carbon composite negative electrode material prepared in Example 1 of the present application.

[0027] Figure 4 It is the charge-discharge curve of the button cell prepared in Example 6 of the present application.

[0028] Figure 5 It is the cycle performance curve of the button cell prepared in Example 6 of the present application. DETAILED DESCRIPTION

[0029] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, specific embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0030] Embodiment 1:

[0031] The embodiment provides a silicon-carbon composite negative electrode material, which comprises a substrate and a coating layer coated on the substrate, the substrate comprises multi-layer graphite and nano-silicon intercalated between the multi-layer graphite, and the coating layer is made of a conductive material polymer compound; the multi-layer graphite is graphite; the particle size of the nano-silicon is 100 nm; and the conductive material polymer compound is selected from polyaniline.

[0032] The embodiment also provides a preparation method of the silicon-carbon composite electrode material, which comprises the following specific steps:

[0033] Firstly, 1 g of graphite is dispersed in 200 mL of deionized water under the action of ultrasonic waves for 30 minutes, and is subjected to magnetic stirring for 120 minutes; then, nano-silicon powder is slowly added into the dispersion liquid under the action of ultrasonic waves for 2 hours, and is subjected to magnetic stirring for 2 hours; and then, the sample is obtained through freeze drying, and is placed into a tube furnace under the protection of an argon atmosphere with a flow rate of 150 sccm, and is heated to 650 DEG C and kept for 7 hours to obtain the substrate.

[0034] Then, the obtained substrate is ultrasonically dispersed into 200 mL of deionized water, and a hydrochloric acid solution of aniline monomer is dropped into the above suspension; then, a hydrochloric acid solution of ammonium persulfate is added dropwise, and is continuously stirred in an ice water bath for 24 hours until the solution color becomes dark green; the dark green product is filtered and washed with ethanol for three times, the obtained filter cake is dried in a vacuum oven at 60 DEG C for 12 hours, and is placed into a tube furnace after drying under the protection of an argon atmosphere with a flow rate of 150 sccm, and is heated to 700 DEG C and kept for 7 hours to obtain the silicon-carbon composite negative electrode material.

[0035] The inventors detect the performance of the prepared silicon-carbon composite negative electrode material, and the detection results are shown in Table 1. Figures 1-3 Figure 1 is a scanning electron microscope photo of the silicon-carbon composite negative electrode material, and it can be seen that the material is a multi-layer sheet structure on which some silicon nanoparticles are loaded, and some thin carbon layers can also be seen on the edge surface; Figure 2 is a TEM diagram of the silicon-carbon composite negative electrode material, and it can be seen from the diagram that there is nano-silicon in the composite material, the particle size range is 100-200 nm, and the polyaniline (carbonized) coating layer formed on the surface has a continuous and dense structure; Figure 3 is an XRD diffraction spectrum of the silicon-carbon composite negative electrode material, and it can be seen that there are obvious diffraction peaks of silicon and graphite, and no other impurity peaks.

[0036] Embodiment 2: ​

[0037] The only difference from Example 1 is that the mass ratio of nano-silicon powder to graphite in Example 2 is 1:10. The rest of the preparation methods and steps are the same as in Example 1. The resulting silicon-carbon composite anode material is labeled as Si@EG@p-PANI-1. Electrode materials prepared from Si@EG@p-PANI-1 are tested.

[0038] Example 3:

[0039] The only difference from Example 1 is that the mass ratio of nano-silicon powder to graphite in Example 3 is 3:10. The rest of the preparation methods and steps are the same as in Example 1. The resulting silicon-carbon composite anode material is labeled as Si@EG@p-PANI-3. Electrode materials prepared from Si@EG@p-PANI-3 are tested.

[0040] Example 4:

[0041] The only difference from Example 1 is that in Example 4, the mass ratio of nano-silicon powder to graphite is 1:1, and the amount of aniline monomer added is 0.5 ml. The rest of the preparation methods and steps are the same as in Example 1. The obtained silicon-carbon composite anode material is labeled as Si@EG@p-PANI-2-1. Electrode materials prepared from Si@EG@p-PANI-2-1 are tested.

[0042] Example 5:

[0043] The only difference from Example 1 is that in this Example 2, the mass ratio of nano-silicon to graphite is 1:1, and the amount of aniline monomer added is 5 ml. The rest of the preparation methods and steps are the same as in Example 1. The obtained silicon-carbon composite anode material is labeled as Si@EG@p-PANI-2-3. Electrode materials prepared from the material Si@EG@p-PANI-2-3 are tested.

[0044] Example 6:

[0045] Battery preparation: First, the silicon-carbon composite anode material obtained in Example 1 was used as the active material, and the conductive agent (super-P) and binder (CMC) were ground thoroughly at a mass ratio of 8:1:1. An appropriate amount of deionized water was added and stirred to form a uniform slurry. Next, the uniformly stirred slurry was evenly coated onto the rough surface of a copper foil using a coating machine. The copper foil was dried in a forced-air oven at 60°C, and then placed in a vacuum oven at 80°C for 12 hours. Finally, the fully dried copper foil was cut into 12mm diameter discs, weighed, and then dried and stored at room temperature. Throughout the preparation process, the surface loading of the copper foil could be maintained at 1.2 mg / cm² by adjusting the slurry concentration and the height of the scraper. -2 Approximately. In an argon-filled glove box (where the volume fractions of H2O and O2 are both less than 1 × 10⁻⁶), -7The coin-type battery was assembled by using lithium metal as a reference electrode.

[0046] Test procedure: The battery capacity test was performed by using the battery test system CT2001A battery tester from Wuhan Lantian Electronic Co., Ltd. The constant current charge-discharge capacity test was performed on the coin-type battery with the negative electrode of the material Si@EG@p-PANI obtained in Example 1, wherein the battery was discharged at a current density of 100 mA / g to 0.01 V, and then charged at the same current density to 3 V, and the cycle was repeated for 5 times. The cycle was repeated for 100 times at a current density of 1000 mA / g.

[0047] The test results are shown in Figure 4 and Figure 5 , wherein Figure 4 is the charge-discharge curve of the coin-type battery prepared, Figure 5 is the electrochemical performance diagram of the coin-type battery prepared, and it can be seen that the lithium ion battery assembled with the electrode material has a capacity of about 1000 mAh·g -1 at a current density of 100 mA·g -1 , and the specific capacity and cycle stability are greatly improved compared with the pure silicon negative electrode.

[0048] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited to this. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications shall fall within the protection scope of the present disclosure.

Claims

1. A silicon-carbon composite negative electrode material, characterized by, The silicon-carbon composite negative electrode material comprises a base and a coating layer coated outside the base, the base is composed of multi-layer graphite and nano-silicon intercalated between the multi-layer graphite, and the material of the coating layer is a conductive material polymer compound. S1, combining graphite with nano-silicon powder to obtain a base; S2, coating the base obtained in step S1 to obtain a silicon-carbon composite negative electrode material; In step S1, the base is prepared by a liquid phase mixing method, and the specific steps are as follows: graphite is ultrasonically dispersed in deionized water to obtain a graphite dispersion liquid, nano-silicon powder is then put into the graphite dispersion liquid and ultrasonically and uniformly stirred, and then the sample is freeze-dried, heated to a final temperature and kept for a certain time to obtain the base; In step S2, the outer coating is prepared by an in-situ synthesis method, and the specific steps are as follows: the base obtained in step S1 is ultrasonically dispersed in deionized water to obtain a suspension, an aqueous hydrochloric acid solution of aniline monomer and an aqueous hydrochloric acid solution of ammonium persulfate are then added dropwise into the suspension in sequence, stirred uniformly, filtered, and the precipitate is washed to obtain a filter cake, the filter cake is dried, and then the dried filter cake is heated to a final temperature and kept for a certain time to obtain the silicon-carbon composite negative electrode material.

2. The silicon-carbon composite negative electrode material of claim 1, wherein, The particle size of the nano-silicon is 100-200 nm.

3. The silicon-carbon composite negative electrode material of claim 1, wherein, The mass ratio of graphite to nano-silicon powder is (100-1):20; And / or, the heating and keeping are both carried out in an inert gas atmosphere, the final temperature is 500-700℃, and the keeping time is 2-7h.

4. The silicon-carbon composite negative electrode material of claim 1, wherein, The molar ratio of aniline monomer to hydrochloric acid is (1-2):20, and the molar ratio of aniline monomer to ammonium persulfate is (1-2):

1.

5. The method of claim 1, wherein the silicon-carbon composite negative electrode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture at a temperature of 800-1,200°C for 1-10 hours in an inert gas atmosphere. The stirring is carried out in an ice water bath, and the stirring time is 6-24h; And / or, the drying conditions are as follows: the drying temperature is 60-80℃, and the drying time is 10-14h.

6. The silicon-carbon composite negative electrode material of claim 1, wherein, The keeping conditions are as follows: the heating and keeping are both carried out in an inert gas atmosphere, the final temperature is 600-900℃, and the keeping time is 4-10h.

7. The silicon-carbon composite negative electrode material according to any one of claims 1-2 is applied in a lithium ion battery.

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