Composite silicon-based negative electrode material and preparation method thereof, and secondary battery

Abstract

The present invention provides a composite silicon-based anode material, a preparation method thereof, and a secondary battery. The composite silicon-based anode material is a composite material of SiS x Se 2‑x and graphite, where the value of x ranges from 0.2 to 1.5. The composite silicon-based anode material is spherical secondary particles aggregated by nanosheets. In this composite silicon anode material, the two-dimensional nanosheet structure can provide a stable and fast channel for the rapid diffusion of Li + . Moreover, S and Se can act as supporting elements to inhibit the volume expansion of the Si-based material during the reaction. Introducing S and Se can effectively improve the conductivity of the Si material while ensuring the structural stability of the material, thereby improving the structural stability and electrical performance of the silicon anode material. When this material is applied to a secondary battery, the battery has excellent cycle reversibility, structural stability, and a high discharge specific capacity.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary battery materials, and in particular relates to a composite silicon-based negative electrode material and a preparation method and application thereof. Background Art

[0002] With the rapid development of electric vehicles, the theoretical capacity of conventional graphite anodes is less than 400mAh / g, which can no longer meet the current long-range requirements. Therefore, the research focus of the new generation of electrode materials must be on higher energy density and high specific capacity. Silicon anodes have become the most promising lithium battery anode materials due to their ultra-high theoretical capacity (4200mAh / g); however, silicon anodes themselves face problems such as volume expansion, particle crushing, and poor intrinsic conductivity, which results in poor cycle reversibility of silicon anodes, affecting their further application.

[0003] Usually, researchers improve the conductivity of silicon-based negative electrodes by combining them with graphite materials, and suppress the volume expansion of silicon negative electrodes by preparing silicon negative electrodes with special morphology. x There are several types of silicon-based negative electrode materials, such as silicon-metal alloys and silicon alone, which all have serious volume effects. Therefore, exploring new silicon-based materials and studying their electrochemical properties are the current research focuses of silicon-based negative electrode materials. Summary of the invention

[0004] In response to the above technical problems, the present application provides a composite silicon-based negative electrode material and a preparation method thereof, and a secondary battery.

[0005] To achieve the above objectives, this application proposes the following technical solutions:

[0006] In a first aspect, a composite silicon-based negative electrode material is provided, wherein the composite silicon-based negative electrode material is SiS x Se 1-x A composite material of silicon and graphite, wherein the value of x is 0.2≤x≤1.5, and the composite silicon-based negative electrode material is a spherical secondary particle formed by the agglomeration of nanosheets.

[0007] Furthermore, the spherical secondary particles are porous spherical structures.

[0008] In a second aspect, a method for preparing a composite silicon-based negative electrode material is provided, comprising:

[0009] Mechanically mixing the graphite and the nano-silicon solid phase to obtain a mixture;

[0010] The mixture is mixed evenly with sulfur powder and selenium powder, and then molded into blocks;

[0011] The block is placed in the cavity of a high temperature and high pressure synthesis device and subjected to high temperature and high pressure treatment to obtain SiS x Se 2-xA composite negative electrode material with graphite, wherein the value of x is 0.2≤x≤1.5.

[0012] Furthermore, the molar ratio of the nano-silicon, sulfur powder and selenium powder is 1:1-3:1-3.

[0013] Furthermore, the mass ratio of the graphite to nano-silicon is 1:1-2.

[0014] Furthermore, the graphite is one or more of artificial graphite, commercial graphite, domestic mesocarbon microbeads (MCMB), and flake graphite.

[0015] Furthermore, the average particle size of the nano-silicon is 50-100 nm.

[0016] Furthermore, the pressure of the high temperature and high pressure treatment is 0.5~1.5GPa; the temperature of the high temperature and high pressure treatment is 500~800℃; the time of the high temperature and high pressure treatment is 0.5~5h; the atmosphere of the high temperature and high pressure treatment is nitrogen atmosphere and / or inert gas atmosphere.

[0017] Furthermore, the solid phase mechanical mixing time is 1 to 6 hours.

[0018] Furthermore, the solid phase mechanical mixing is ball milling.

[0019] In a third aspect, a secondary battery is provided, comprising the aforementioned composite silicon-based negative electrode material or the composite silicon-based negative electrode material prepared by the aforementioned preparation method.

[0020] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0021] Provide composite silicon-based negative electrode material SiS x Se 2-x The composite material of graphite is a spherical secondary particle formed by the aggregation of nanosheets. Its two-dimensional nanosheet structure can be Li + The rapid diffusion of SiS provides a stable and fast channel. S and Se can also act as supporting elements to inhibit the volume expansion of Si-based materials during the reaction. Si-based materials themselves have poor electronic conductivity. x Se 2-x The compound, introducing S and Se, can effectively improve the conductivity of the material while ensuring structural stability. When the composite silicon-based negative electrode material is used in a secondary battery, the battery has excellent cycle reversibility and structural stability, as well as a high discharge specific capacity.

[0022] The present invention synthesizes a spherical composite negative electrode material with two-dimensional flaky particles cross-linked in one step by a high-temperature and high-pressure synthesis method. The prepared silicon-based negative electrode material has high conductivity and structural stability. When used in secondary batteries, the battery has excellent cycle reversibility and structural stability, as well as high discharge specific capacity.

[0023] The preparation method is simple to operate, and the prepared negative electrode material can significantly improve the electrochemical performance of silicon-based materials and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 This is a SEM image of the composite silicon-based negative electrode material prepared in Example 1.

[0026] Figure 2 The transmission electron microscope images of the composite silicon-based negative electrode material prepared in Example 1 at different magnifications, wherein (a) is a TEM image of the composite silicon-based negative electrode material, and (b) is a HRTEM image of the composite silicon-based negative electrode material.

[0027] Figure 3 The electrical performance diagram of the battery assembled with the negative electrode materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0028] The present invention provides a composite silicon-based negative electrode material, wherein the composite silicon-based negative electrode material is SiS x Se 2-x A composite material of silicon and graphite, wherein the value of x is 0.2≤x≤1.5, and the composite silicon-based negative electrode material is a spherical secondary particle formed by the agglomeration of nanosheets.

[0029] In some preferred embodiments, the spherical secondary particles are porous spherical structures.

[0030] The present invention provides a method for preparing a composite silicon-based negative electrode material, comprising:

[0031] Mechanically mixing the graphite and the nano-silicon solid phase to obtain a mixture;

[0032] The mixture is mixed evenly with sulfur powder and selenium powder, and then molded into blocks;

[0033] The block is placed in a cavity of a high temperature and high pressure synthesis device and subjected to high temperature and high pressure treatment to perform sulfurization and selenization reactions to obtain SiSx Se 2-x A composite negative electrode material with graphite, wherein the value of x is 0.2≤x≤1.5, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, etc.

[0034] In the preparation method, in the block of graphite, nano-silicon, sulfur powder and selenium powder, the contact area between nano-silicon and sulfur and selenium is relatively high, and sulfur and selenium react with nano-silicon to form SiS x Se 2-x , SiS x Se 2-x The composite negative electrode material with graphite is a spherical secondary particle formed by cross-linking nanosheets, and the two-dimensional sheet morphology framework (nanosheet) is Li + The rapid diffusion of SiS provides a stable and fast channel. S and Se can also act as supporting elements to inhibit the volume expansion of Si-based materials during the reaction. Si-based materials themselves have poor electronic conductivity. x Se 2-x Compounds, the introduction of S and Se can effectively improve the conductivity of the material while ensuring the stability of the material structure.

[0035] In the preparation method, after the high temperature and high pressure treatment is completed, the pressure of the high temperature and high pressure synthesis equipment is first released, and then the temperature is lowered to room temperature to ensure that the impurities are volatilized into gas and discharged.

[0036] In some preferred embodiments, the molar ratio of the nano-silicon, sulfur powder and selenium powder is 1:1~3:1~3, wherein the molar ratio of nano-silicon to sulfur powder is 1:1~3, for example, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.2, 1:2.5, 1:2.8, 1:3, etc., and the molar ratio of nano-silicon to selenium powder is 1:1~3, for example, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.2, 1:2.5, 1:2.8, 1:3, etc.

[0037] In some preferred embodiments, the mass ratio of graphite to nano-silicon is 1:1-2, for example, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, etc.

[0038] In some preferred embodiments, the graphite is one or more of artificial graphite, commercial graphite, domestic mesocarbon microbeads (MCMB), and flake graphite.

[0039] In some preferred embodiments, the average particle size of the nano-silicon is 50-100 nm, for example, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc.

[0040] In some preferred embodiments, the pressure of the high temperature and high pressure treatment is 0.5~1.5 GPa, for example, 0.5 GPa, 0.6 GPa, 0.7 GPa, 0.8 GPa, 0.9 GPa, 1.0 GPa, 1.1 GPa, 1.2 GPa, 1.3 GPa, 1.4 GPa, 1.5 GPa, etc.

[0041] In some preferred embodiments, the temperature of the high temperature and high pressure treatment is 500~800℃, more preferably 600~800℃, for example, 600℃, 650℃, 700℃, 750℃, 800℃, etc.; the time of the high temperature and high pressure treatment is 0.5~5h, for example, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, etc.

[0042] In some preferred embodiments, the atmosphere for the high temperature and high pressure treatment is a nitrogen atmosphere and / or an inert gas atmosphere.

[0043] The purpose of solid-phase mechanical mixing is to ensure uniform compounding of nano-silicon and graphite. In order to obtain better results, in some preferred embodiments, the solid-phase mechanical mixing time is 1 to 6 hours; the solid-phase mechanical mixing is ball milling.

[0044] The present invention also provides a secondary battery, comprising the aforementioned composite silicon-based negative electrode material or the composite silicon-based negative electrode material prepared by the aforementioned preparation method.

[0045] In order to facilitate the understanding of the present invention, the present invention will be described in more comprehensive and detailed manner below in conjunction with the accompanying drawings and preferred embodiments of the specification, but the protection scope of the present invention is not limited to the following specific embodiments.

[0046] Example 1

[0047] 10g of artificial graphite and 15g of nano-silicon (average particle size 80nm) were ball-milled for 3h, and then the mixed material was evenly mixed with 24g of sulfur powder and 60g of selenium powder, and then molded into a block material. The block was placed in the cavity of a high-temperature and high-pressure synthesis device for sulfurization and selenization reactions. The synthesis pressure was 1GPa, the synthesis temperature was 700℃, and the synthesis time was 2h. Finally, a composite negative electrode material was obtained. The SEM image of the composite negative electrode material is shown in the figure below. Figure 1 As shown, from Figure 1It can be seen that the composite negative electrode material is a spherical morphology formed by cross-linking and polymerization of two-dimensional nanosheets, and has a porous structure. Transmission electron microscopy images of the composite negative electrode material at different magnifications are shown in Figure 2. Figure 2 As shown in Table 1, combined with ICP analysis and HRTEM images, it is inferred that the main phase of the product is SiS based on the lattice spacing. 0.98 Se 1.02 , and the thin and soft substance in the TEM image is graphite, so the obtained negative electrode material is SiS 0.98 Se 1.02 Composite negative electrode materials with graphite, and SiS 0.98 Se 1.02 It is entangled and cross-linked with graphite, showing a stable morphology and structure.

[0048] Comparative Example 1

[0049] 10 g of artificial graphite and 15 g of nano-silicon (average particle size 80 nm) were ball-milled and mixed for 3 h to obtain a two-dimensional layered Si@C negative electrode material.

[0050] Comparative Example 2

[0051] 10g of artificial graphite and 15g of nano-silicon (average particle size 80nm) were ball-milled for 3h, and the mixed material was evenly mixed with 48g of sulfur powder. The mixed material was molded into a block material, and the block was placed in the cavity of a high-temperature and high-pressure synthesis equipment for sulfurization reaction. The synthesis pressure was 1GPa, the synthesis temperature was 700℃, and the synthesis time was 2h to synthesize a SiS2@C composite material.

[0052] Comparative Example 3

[0053] 10g of artificial graphite and 15g of nano-silicon (average particle size 80nm) were ball-milled and mixed for 3h, and then the mixed material was evenly mixed with 117g of selenium powder and molded into a block material. The block was placed in the cavity of a high-temperature and high-pressure synthesis equipment for selenization reaction. The synthesis pressure was 1GPa, the synthesis temperature was 700℃, and the synthesis time was 2h to synthesize a SiSe2@C composite material.

[0054] Example 2

[0055] 10g of artificial graphite and 15g of nano-silicon (average particle size 80nm) were ball-milled for 3h, and then the mixed material was evenly mixed with 22g of sulfur powder and 78g of selenium powder, and then molded into a block material. The block was placed in the cavity of a high-temperature and high-pressure synthesis equipment for sulfurization and selenization reactions. The synthesis pressure was 0.5GPa, the synthesis temperature was 800℃, and the synthesis time was 0.5h. Finally, a two-dimensional layered SiS 0.78 Se 1.22 @C negative electrode material.

[0056] Example 3

[0057] 10g of artificial graphite and 20g of nano-silicon (average particle size 100nm) were ball-milled for 3h, and then the mixed material was evenly mixed with 50g of sulfur powder and 55g of selenium powder, and then molded into a block material. The block was placed in the cavity of a high-temperature and high-pressure synthesis equipment for sulfurization and selenization reactions. The synthesis pressure was 1.5GPa, the synthesis temperature was 700℃, and the synthesis time was 2h. Finally, a two-dimensional layered SiS 1.19 Se 0.81 @C negative electrode material.

[0058] Example 4

[0059] 10g of artificial graphite and 10g of nano-silicon (average particle size 80nm) were ball-milled for 3h, and then the mixed material was evenly mixed with 25g of sulfur powder and 63g of selenium powder, and then molded into a block material. The assembled block was placed in the cavity of a high-temperature and high-pressure synthesis device for sulfurization and selenization reactions. The synthesis pressure was 0.5GPa, the synthesis temperature was 700℃, and the synthesis time was 5h. Finally, a two-dimensional layered SiS 0.99 Se 1.01 @C negative electrode material.

[0060] The composite negative electrode materials prepared in Examples 1 to 4 were tested for ICP element content, and the results are shown in Table 1.

[0061] Table 1

[0062]

[0063] The new silicon-based negative electrode material powder obtained in Examples 1 to 4 and Comparative Examples 1 to 3 was used as the active material, and the conductive agent acetylene black (AB) and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 7:2:1, and N-methylpyrrolidone (NMP) was used as the solvent. The mixture was placed in a small beaker and stirred at a speed of 800 r / min for 2 hours to obtain a slurry. The slurry was coated on the current collector aluminum foil using an automatic coating machine, placed flat on tempered glass and transferred to a vacuum drying oven at 85°C for 4 hours, and then punched into a pole piece with a diameter of 14 mm, and then dried at 105°C in a vacuum drying oven for 4 hours, and placed in a glove box filled with argon atmosphere with a water content and oxygen content of less than 0.1 ppm for 4 hours to reduce the moisture adsorbed by the pole piece during the transfer process, and then assembled into a CR2032 button battery in the glove box. The separator used in the battery is a porous polyethylene film of model Celgard2300 with a diameter of 18 mm, and a lithium sheet is used as the counter electrode.

[0064] After the battery is assembled and aged for 12 hours, it is activated at a rate of 0.5C in the voltage range of 0.1~3.0V, and then charged and discharged at a rate of 2C. The cycle performance diagram is as follows Figure 3 shown.

[0065] from Figure 3 It can be seen that compared with the battery assembled with the carbon-silicon composite negative electrode material in Comparative Example 1, the cycle performance and discharge specific capacity of the batteries assembled with the modified silicon-based composite materials prepared in Comparative Example 2, Comparative Example 3 and Example 1 are improved. After analysis, this is because Si itself has a large volume effect, and after modification, compounds of Si and S and Se are formed. S and Se can serve as supporting elements to inhibit the volume expansion of Si-based materials in the reaction and alleviate the volume effect. In addition, the introduction of S and Se can effectively improve the conductivity of the material and achieve structural stability and electronic conductivity.

[0066] from Figure 3 It can also be seen that the battery assembled with the SiS2@C composite material prepared in Comparative Example 2 has a better initial capacity than the battery assembled with the SiSe2@C composite material prepared in Comparative Example 3, but a worse cycle performance; and compared with the battery assembled with the SiS2@C composite material prepared in Comparative Example 2 and the battery assembled with the SiSe2@C composite material prepared in Comparative Example 3, the SiS2@C composite material prepared in Examples 1 to 4 has a better initial capacity than the battery assembled with the SiS2@C composite material prepared in Comparative Example 2 and the battery assembled with the SiSe2@C composite material prepared in Comparative Example 3. x Se 2-x The capacity and cycle performance of batteries assembled with graphite composite materials are significantly improved.

[0067] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A composite silicon-based negative electrode material, characterized in that: The composite silicon-based negative electrode material is SiS x Se 2-x A composite material of silicon and graphite, wherein the value of x is 0.2≤x≤1.5, and the composite silicon-based negative electrode material is a spherical secondary particle formed by the agglomeration of nanosheets, and the spherical secondary particle is a porous ball structure.

2. The method for preparing the composite silicon-based negative electrode material according to claim 1, characterized in that: include: Mechanically mixing the graphite and the nano-silicon solid phase to obtain a mixture; The mixture is mixed evenly with sulfur powder and selenium powder, and then molded into blocks; The block is placed in the cavity of a high temperature and high pressure synthesis device and subjected to high temperature and high pressure treatment to obtain SiS x Se 2-x A composite negative electrode material with graphite, wherein the value of x is 0.2≤x≤1.

5.

3. The method for preparing the composite silicon-based negative electrode material according to claim 2, characterized in that: The molar ratio of the nano silicon, sulfur powder and selenium powder is 1:1-3:1-3.

4. The method for preparing the composite silicon-based negative electrode material according to claim 2, characterized in that: The mass ratio of the graphite to the nano-silicon is 1:1-2.

5. The method for preparing the composite silicon-based negative electrode material according to claim 2, characterized in that: The graphite is one or both of artificial graphite and flake graphite.

6. The method for preparing the composite silicon-based negative electrode material according to claim 2, characterized in that: The average particle size of the nano-silicon is 50-100 nm.

7. The method for preparing the composite silicon-based negative electrode material according to claim 2, characterized in that: The pressure of the high temperature and high pressure treatment is 0.5~1.5GPa; the temperature of the high temperature and high pressure treatment is 500~800℃; the time of the high temperature and high pressure treatment is 0.5~5h; the atmosphere of the high temperature and high pressure treatment is nitrogen atmosphere and / or inert gas atmosphere.

8. The method for preparing the composite silicon-based negative electrode material according to claim 2, characterized in that: The solid phase mechanical mixing time is 1 to 6 hours; The solid phase mechanical mixing is ball milling.

9. A secondary battery, characterized in that: It includes the composite silicon-based negative electrode material as claimed in claim 1 or the composite silicon-based negative electrode material prepared by the preparation method as claimed in any one of claims 2 to 8.

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