Si (at) SiOx (at) CA composite material and preparation method and application thereof

Abstract

The invention discloses a Si (at) SiOx (at) CA composite material and a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The preparation method comprises the following steps: dissolving ammonium persulfate and an acid solution with the mass fraction of 98% in deionized water, fully stirring, and uniformly mixing to obtain a mixed solution; adding silicon powder, heating, stirring, uniformly mixing, and cleaning to be neutral to obtain modified silicon particles; dissolving chitosan in an acetic acid solution, adding a cross-linking agent imidoester and the modified silicon particles, and stirring to obtain a uniform suspension; performing vacuum drying to obtain a gel precursor; and heating and pyrolyzing in an inert atmosphere to obtain the Si (at) SiOx (at) CA composite material. The invention discloses a Si (at) SiOx (at) CA composite material as well as a preparation method and application thereof, and the application of the Si (at) SiOx (at) CA composite material in a lithium ion battery improves the high reversibility and long cycle stability of the lithium ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a Si@SiO x @CA composite material, its preparation method and application. Background Art

[0002] With the rapid development of electric vehicles and grid energy storage technologies, as the core power source, the performance improvement of lithium-ion batteries (LIBs) has become the focus of research. The performance of the battery anode material directly determines the energy density, cycle life and overall efficiency of lithium-ion batteries. Therefore, the development of high-performance battery anode materials has always been the main direction of lithium-ion battery research.

[0003] Silicon anode materials have shown great application potential because their theoretical lithium storage capacity is as high as 4200 mAh / g, far exceeding that of graphite, the conventional anode material of lithium-ion batteries (about 420 mAh / g). However, silicon-based anode materials face significant technical bottlenecks in practical applications, mainly reflected in their much lower cycle stability compared to commercial graphite materials. In-depth research has found that the root cause of this problem lies in the huge volume change of silicon-based anode materials during the electrochemical charge and discharge process, and its volume expansion effect can be as high as 300%. This drastic volume change will cause mechanical fracture and pulverization, resulting in the rupture of the solid electrolyte interphase (SEI). At the same time, the generated stress will cause the electrode active material to gradually fall off from the current collector and separate from the conductive agent and binder, ultimately leading to a rapid decline in battery capacity. In addition, as a semiconductor material, silicon has a low intrinsic conductivity, resulting in slow reaction kinetics, which further limits its performance in direct applications.

[0004] To solve the above problems, researchers have developed various strategies to mitigate or suppress the volume expansion and stress effects of silicon-based anodes. Such as surface coating construction on silicon particles, microstructure design, application of new binders and prelithiation and other modification schemes. However, currently, silicon-based anode materials face many challenges. Modifying silicon-based anode materials by introducing oxygen elements will cause the rearrangement of silicon and oxygen atoms to form silicon oxides as a buffer layer to inhibit volume expansion, but it will reduce the theoretical specific capacity and first Coulomb efficiency of silicon anode materials. Summary of the Invention

[0005] The present invention aims to provide a Si@SiO x @CA composite material, its preparation method and application. This method improves the structural stability and electrochemical performance of the Si@SiO x @CA composite material, and solves the problem of poor material performance in the prior art. The present invention also provides the application of the Si@SiO x @CA composite material in lithium-ion batteries, which improves the high reversibility and long cycle stability of lithium-ion batteries.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A preparation method of Si@SiO x @CA composite material, comprising the following steps:

[0008] S1. Dissolve ammonium persulfate and a 98% acid solution in deionized water, stir well, and mix evenly to obtain a mixed solution;

[0009] S2. Add silicon powder to the mixed solution obtained in S1, heat and stir, mix evenly, and wash until neutral to obtain modified silicon particles;

[0010] S3. Dissolve chitosan in an acetic acid solution, add a crosslinking agent imidoester and the modified silicon particles obtained in S2, and stir to obtain a uniform suspension;

[0011] S4. Vacuum-dry the suspension obtained in S3 to obtain a gel precursor;

[0012] S5. Heat and pyrolyze the gel precursor obtained in S4 in an inert atmosphere to obtain Si@SiO x @CA composite material.

[0013] Preferably, in S1, the 98% acid solution with a certain mass fraction is one of sulfuric acid solution or nitric acid solution.

[0014] Preferably, in S1, the addition amount of ammonium persulfate is 2 - 10 g, and the 98% acid solution is 10 - 50 mL.

[0015] Preferably, in S2, the particle size of the silicon powder is 100 nm.

[0016] Preferably, in S2, the addition amount of the silicon powder is 0.2 - 1.0 g.

[0017] Preferably, in S2, the heating and stirring temperature is 60 - 100 °C, and the heating and stirring time is 2 - 5 h.

[0018] Preferably, in S3, the addition amount of chitosan is 2 - 10 g, the addition amount of the crosslinking agent imidoester is 0.1 - 0.5 g, and at the same time, the ratio of chitosan to imidoester is 20:1.

[0019] Preferably, in S3, the stirring speed is 500 - 800 rpm, and the stirring time is 2 - 5 h.

[0020] Preferably, in S4, the vacuum drying temperature is 80 - 120 °C, the vacuum drying time is 12 - 24 h, and the vacuum degree is -0.1 MPa.

[0021] Preferably, in S5, the heating rate is 2-10 °C / min, the pyrolysis temperature is 500-700 °C, and the pyrolysis time is 2-5 h.

[0022] The present invention also provides the Si@SiO prepared by the preparation method as described above. x @CA composite material.

[0023] The present invention also provides the Si@SiO prepared by the preparation method as described above. x @CA composite material or the Si@SiO x @CA composite material is used in the preparation of the silicon-based anode electrode sheet of a lithium-ion battery.

[0024] The present invention also provides a silicon-based anode electrode sheet of a lithium-ion battery, which is characterized by comprising the Si@SiO x @CA composite material, a binder and a conductive agent.

[0025] The present invention also provides a preparation method of the silicon-based anode electrode sheet of the lithium-ion battery, comprising the following steps:

[0026] T1. Mix the Si@SiO x @CA composite material, the conductive agent and the binder, and stir well to obtain a uniform slurry;

[0027] T2. Coat the slurry obtained in T1 evenly on a copper foil and dry it in vacuum to obtain a dried electrode sheet;

[0028] T3. Roll and cut the dried electrode sheet obtained in T2 to obtain the silicon-based anode electrode sheet of the lithium-ion battery.

[0029] Preferably, in T1, the mass ratio of the Si@SiO x @CA composite material, the binder and the conductive agent is 7:1:2.

[0030] Preferably, in T1, the conductive agent is Super P and the binder is polyacrylic acid.

[0031] Preferably, in T2, the vacuum drying temperature is 80 °C, the vacuum drying time is 24 h, and the vacuum degree is -0.1 MPa.

[0032] Preferably, in T3, the diameter of the silicon-based anode electrode sheet of the lithium-ion battery is 12 mm.

[0033] Preferably, in T3, the mass of the Si@SiO in the silicon-based anode electrode sheet of the lithium-ion battery is 0.6-1.2 g / cm x @CA composite material is 0.6-1.2 g / cm 2 .

[0034] Compared with the prior art, the present invention has the following advantages and technical effects:

[0035] The present invention discloses a Si@SiO x @CA composite material and its preparation method and application. By constructing an SiO X layer on the surface of Si particles and embedding it in a carbon gel with high mechanical strength and elastic strength, a Si@SiO x @CA composite material is formed. This structural design can effectively alleviate the volume expansion effect of Si particles during the electrochemical charge and discharge process, reduce the mechanical stress caused by volume expansion, thereby reducing the pulverization of silicon particles and the damage of the electrode structure, and improving the cycle stability of the battery. After the Si@SiO X @CA composite material is assembled into a lithium-ion battery, it exhibits excellent reversibility and long cycle stability. It can maintain a high reversible capacity at different current densities and still maintain a good capacity retention rate at high current densities. In addition, the introduction of the carbon gel not only provides mechanical support but also constructs a continuous conductive network, effectively improving the conductivity of the silicon-based anode material, making up for the defect of the low intrinsic conductivity of silicon materials, accelerating the electron transfer rate, and enhancing the rate performance of the battery. At the same time, the synergistic effect of the carbon gel layer and the SiO X layer can reduce the interfacial impedance, inhibit the direct contact between the electrolyte and the silicon particles, reduce the occurrence of side reactions, and form a more stable solid electrolyte interface (SEI), thereby improving the first Coulomb efficiency and cycle life of the battery. The preparation method of the present invention is simple and efficient, easy to industrialize, and the prepared Si@SiO x @CA composite material has broad application prospects in the field of lithium-ion batteries and can meet the requirements of high-performance batteries for electric vehicles and grid energy storage.

[0036] The following is a further detailed description of the technical solution of the present invention through examples. Specific Embodiments

[0037] The following further illustrates the technical solution of the present invention through examples.

[0038] Unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meaning understood by those of ordinary skill in the field to which the present invention belongs.

[0039] In the present invention, unless otherwise specified, other test materials and instrument equipment are all conventional test materials in the art and can be obtained through commercial channels.

[0040] Example 1

[0041] A preparation method of a Si@SiO x @CA composite material, comprising the following steps:

[0042] S1. Dissolve 6 g of ammonium persulfate and 30 mL of nitric acid solution with a mass fraction of 98% in 100 mL of deionized water, stir well, mix evenly to obtain a mixed solution;

[0043] S2. Add 0.6 g of silicon powder with a particle size of 100 nm to the mixed solution obtained in S1, heat and stir at 80 °C for 3 h, mix evenly, wash repeatedly with deionized water until the pH is neutral to obtain modified silicon particles;

[0044] S3. Dissolve 6 g of chitosan in 100 mL of acetic acid solution, add 0.3 g of cross-linking agent iminoester and the modified silicon particles obtained in S2, stir at 500 rpm for 5 h to obtain a uniform suspension;

[0045] S4. Vacuum-dry the suspension obtained in S3 at 80 °C for 24 h, with a vacuum degree of -0.1 MPa, to obtain a gel precursor;

[0046] S5. Pyrolyze the gel precursor obtained in S4 in an inert atmosphere, heat up to 600 °C at a heating rate of 5 °C / min for 2 h to obtain Si@SiO x @CA composite material.

[0047] Example 2

[0048] The preparation method is the same as that of Example 1, except that the addition amount of ammonium persulfate is 2 g and the addition amount of nitric acid solution is 10 mL.

[0049] Example 3

[0050] The preparation method is the same as that of Example 1, except that the addition amount of ammonium persulfate is 4 g and the addition amount of nitric acid solution is 20 mL.

[0051] Example 4

[0052] The preparation method is the same as that of Example 1, except that the addition amount of ammonium persulfate is 8 g and the addition amount of nitric acid solution is 40 mL.

[0053] Example 5

[0054] The preparation method is the same as that of Example 1, except that the addition amount of ammonium persulfate is 10 g and the addition amount of nitric acid solution is 50 mL.

[0055] Example 6

[0056] The preparation method is the same as that of Example 1, except that the addition amount of silicon powder is 0.2 g.

[0057] Example 7

[0058] The preparation method is the same as that of Example 1, except that the addition amount of silicon powder is 0.4 g.

[0059] Example 8

[0060] The preparation method is the same as that of Example 1, except that the addition amount of silicon powder is 0.8 g.

[0061] Example 9

[0062] The preparation method is the same as that of Example 1, except that the addition amount of silicon powder is 1.0 g.

[0063] Example 10

[0064] The preparation method is the same as that of Example 1, except that the addition amount of chitosan is 2 g and the addition amount of crosslinking agent imidoester is 0.1 g.

[0065] Example 11

[0066] The preparation method is the same as that of Example 1, except that the addition amount of chitosan is 4 g and the addition amount of crosslinking agent imidoester is 0.2 g.

[0067] Example 12

[0068] The preparation method is the same as that of Example 1, except that the addition amount of chitosan is 8 g and the addition amount of crosslinking agent imidoester is 0.4 g.

[0069] Example 13

[0070] The preparation method is the same as that of Example 1, except that the addition amount of chitosan is 10 g and the addition amount of crosslinking agent imidoester is 0.5 g.

[0071] Example 14

[0072] The preparation method is the same as that of Example 1, except that in S5, the pyrolysis temperature is 500 °C.

[0073] Example 15

[0074] The preparation method is the same as that of Example 1, except that in S5, the pyrolysis temperature is 700 °C.

[0075] Comparative Example 1

[0076] Material: Silicon powder with a particle size of 100 nm, without any treatment, can be obtained through commercial channels.

[0077] Comparative Example 2

[0078] A preparation method of Si@SiO x @CA silicon-based material, comprising the following steps:

[0079] S1. Dissolve 6 g of ammonium persulfate and 30 mL of nitric acid solution with a mass fraction of 98% in 100 mL of deionized water, stir well and mix evenly to obtain a mixed solution;

[0080] S2, adding 0.6 g of silicon powder with a particle size of 100 nm to the mixed solution obtained in S1, heating and stirring at 80° C. for 3 h, mixing evenly, and repeatedly washing with deionized water until the pH is neutral to obtain modified silicon particles;

[0081] S3, the modified silicon particles obtained in S2 were dried under vacuum at 80°C for 24 h, where the vacuum degree was -0.1 MPa, to obtain Si@SiO X Silicon-based materials.

[0082] Comparative Example 3

[0083] A method for preparing Si@CA silicon-based material comprises the following steps:

[0084] S1, dissolve 6g chitosan in 100mL acetic acid solution, add 0.3g cross-linking agent imidate and 0.6g silicon powder with a particle size of 100nm, stir at 500rpm for 5h to obtain a uniform suspension;

[0085] S2, drying the suspension obtained in S1 under vacuum at 80°C for 24 hours, wherein the vacuum degree is -0.1 MPa, to obtain a gel precursor;

[0086] S3. The gel precursor obtained in S3 was pyrolyzed in an inert atmosphere at 600°C for 2 h at a heating rate of 5°C / min to obtain a Si@CA composite material.

[0087] The effects of the composite materials provided in Examples 1-15 and Comparative Examples 1-3 were verified through the following tests.

[0088] The Si@SiO x @CA composite material is used as negative electrode active material to prepare negative electrode sheet, including the following steps:

[0089] T1. Si@SiO x @CA composite material, Super P and polyacrylic acid were mixed in a mass ratio of 7:2:1 and stirred thoroughly to obtain a uniform slurry;

[0090] T2, the slurry obtained in T1 is evenly coated on the copper foil by a coating device, and vacuum dried at 80°C for 24 hours with a vacuum degree of -0.1MPa to obtain a dry electrode;

[0091] T3, rolling and cutting the dried electrode obtained in T2 to obtain a lithium-ion battery silicon-based negative electrode electrode with a diameter of 12 mm, and the negative electrode active material loading of each silicon-based negative electrode electrode is 0.7 mg cm -2 .

[0092] The materials provided in Examples 2-15 and Comparative Examples 1-3 were applied to the preparation of silicon-based anode sheets for lithium-ion batteries, and the preparation method was the same as above.

[0093] The above-mentioned silicon-based anode sheets for lithium-ion batteries were used to prepare lithium-ion button batteries, and the method was as follows:

[0094] The assembly of the button battery was completed in a glove box (with the water and oxygen content both less than 0.01 ppm).

[0095] The prepared silicon-based anode sheet for the lithium-ion battery was used as the negative electrode, the positive electrode was a lithium sheet (with a diameter of 15 mm and a thickness of 2 mm), the separator was polypropylene (PP), and the electrolyte was 1.0 M LiPF 6 in EC+DMC. The assembly was carried out in the order of the negative electrode sheet, electrolyte, separator, electrolyte, and positive electrode sheet, and then it was sealed with a hydraulic sealer to obtain a lithium-ion battery.

[0096] The above-mentioned lithium-ion batteries were subjected to electrochemical performance tests. The test results are shown in Table 1 and Table 2.

[0097] Table 1 Test results of rate performance

[0098]

[0099]

[0100] Table 2 shows the test results of long cycle stability

[0101]

[0102]

[0103] Table 1 and Table 2 are the performance tests of the Si@SiO X @CA composite material prepared into a lithium-ion battery. Comparing the examples with the comparative examples shows that the Si@SiO X @CA composite material has excellent rate performance and cycle stability. First, this is because in the present invention, by changing the amount of the oxidant, the thickness of the SiO X layer is constructed on the surface of the silicon particles, and the appropriate SiO X layer is obtained by selecting and optimizing the amount of the oxidant. Then, during the charge and discharge process, lithium silicate and lithium oxide are generated in the SiO X layer, which can buffer the volume expansion effect of the silicon particles. Then, the Si@SiO X is embedded in the carbon gel, and the nitrogen-containing carbon gel constructed by chitosan can coat the Si@SiO X to form a continuous conductive network structure, which can regulate the electronic structure and form a fast Li + transmission channel, improve the electron transmission efficiency, and make up for the SiOX The low conductivity improves the rate performance. For example, in Table 1, the rate performance of Example 1 at 0.2 A / g - 3.0 A / g is much higher than that of other examples and comparative examples. Even at a current density of 3.0 A / g, a reversible capacity of 652 mAh / g can still be provided. At the same time, the carbon gel layer and SiO X synergistically reduce the interfacial impedance, inhibit the direct contact between the electrolyte and silicon particles, reduce side reactions, and form a more stable SEI film, which improves the first Coulombic efficiency of the lithium-ion battery; at the same time, the elastic properties of the carbon gel can disperse the stress effect during the lithiation / delithiation process, prevent the silicon particles from pulverizing through physical constraints, and improve the cycle stability of the lithium-ion battery, so that it has a capacity retention rate of 95% after 800 cycles at a current density of 1.0 A / g. These data show the excellent kinetic performance of Example 1 and prove the excellent performance of the Si@SiO X @CA composite material prepared by the present invention.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A Si@SiO x A method for preparing a CA composite material, characterized in that: The following steps are involved: S1. Dissolve ammonium persulfate and a 98% acid solution by mass in deionized water, stir thoroughly, and mix well to obtain a mixed solution; S2, adding silicon powder to the mixed solution obtained in S1, heating and stirring, mixing evenly, washing until neutral, and obtaining modified silicon particles; S3, dissolving chitosan in acetic acid solution, adding a cross-linking agent imidate and the modified silicon particles obtained in S2, and stirring to obtain a uniform suspension; S4, vacuum drying the suspension obtained in S3 to obtain a gel precursor; S5, the gel precursor obtained in S4 is pyrolyzed in an inert atmosphere to obtain Si@SiO x @CA Composites.

2. The preparation method according to claim 1, characterized in that: In S1, the acid solution is one of a sulfuric acid solution or a nitric acid solution.

3. The preparation method according to claim 1, characterized in that: In S2, the heating and stirring temperature is 60-100°C, and the heating and stirring time is 2-5h.

4. The preparation method according to claim 1, characterized in that: In S3, the stirring speed is 500-800 rpm, and the stirring time is 2-5 h.

5. The preparation method according to claim 1, characterized in that: In S4, the vacuum drying temperature is 80-120° C., the vacuum drying time is 12-24 h, and the vacuum degree is -0.1 MPa.

6. The preparation method according to claim 1, characterized in that: In S5, the heating rate is 2-10°C / min, the pyrolysis temperature is 500-700°C, and the pyrolysis time is 2-5h.

7. Si@SiO prepared by the preparation method according to any one of claims 1 to 6 x @CA Composites.

8. Si@SiO prepared by the preparation method according to any one of claims 1 to 6 x @CA composite material or Si@SiO as claimed in claim 7 x @Application of CA composite materials in the preparation of silicon-based negative electrode sheets for lithium-ion batteries.

9. A lithium-ion battery silicon-based negative electrode plate, characterized in that: Comprising the Si@SiO as claimed in claim 7 x @CA composite materials, adhesives and conductive agents.

10. A method for preparing a silicon-based negative electrode sheet for a lithium-ion battery as claimed in claim 9, characterized in that: The following steps are involved: T1. Si@SiO x @CA composite material, conductive agent and binder are mixed and stirred thoroughly to obtain a uniform slurry; T2, evenly apply the slurry obtained in T1 on the copper foil, and vacuum dry it to obtain a dry electrode; T3, rolling and cutting the dried electrode obtained in T2 to obtain a silicon-based negative electrode for a lithium-ion battery.

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