A Si@SiO x Composite material, method for its production and use

Abstract

This invention provides a Si@SiO x Composite materials, their preparation methods, and applications belong to the field of lithium-ion battery materials technology. Si@SiO x The composite material consists of a core and an outer shell encapsulating the surface of the core; the core is crystalline nano-silicon; the outer shell is amorphous SiO₂. x and its hydrate SiO x • yH2O. Nano-silicon is fully dispersed in a mixed solution of deionized water and anhydrous ethanol. The resulting solution is ultrasonically stirred until homogeneous and then added to a high-pressure reactor. The high-pressure reactor is then placed in a forced-air drying oven. The composition and thickness of the coating layer are controlled by adjusting the reaction temperature and time. The coating layer formed at a lower temperature significantly improves the cycling performance of the nano-silicon; conversely, the coating layer formed at a higher temperature drastically deteriorates the cycling performance of the nano-silicon. This invention, Si@SiO... x The preparation methods for composite materials have simple and easy-to-control reaction conditions, short process flow, low cost and high yield.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery materials, in particular to a Si@SiO x composite material, a preparation method and application thereof. BACKGROUND

[0002] In recent years, due to the large use of fossil energy such as coal, oil and natural gas, serious environmental problems have been caused; at the same time, due to the non-renewable nature of fossil energy, mankind is also facing a serious energy crisis. Clean energy represented by solar energy, tidal energy and wind energy has attracted widespread attention, but as intermittent energy sources, these energy sources need suitable energy storage devices for storage. Lithium ion batteries have high specific energy density, long cycle life, no memory effect and other advantages, and have good development prospects in the fields of new energy vehicles and energy storage.

[0003] However, the current commercialized negative electrode material of lithium ion batteries is mainly graphite, and its low theoretical specific capacity (only 372 mAhg -1 ) cannot meet the requirements of the next generation of high energy density lithium ion batteries. Silicon material has the advantages of high theoretical specific capacity (3579 mAhg -1 ), moderate reaction potential (~ 0.4V), abundant resources, green environmental protection, etc., and is considered to be the most promising negative electrode material of the next generation of lithium ion batteries. However, silicon material produces a huge volume change (~ 300%) during charging and discharging, which leads to particle pulverization, active material shedding and destruction of electrode structure; at the same time, due to the volume expansion, the exposed fresh silicon continuously consumes active lithium to form a new SEI film, causing a large capacity attenuation during the cycle process, which seriously affects its large-scale application.

[0004] In order to further improve the electrochemical performance of silicon negative electrode, the most commonly used method at present is nano-treatment, preparing silicon nanowires, nanotubes, nanoparticles, etc., which can alleviate the volume expansion to a certain extent. At the same time, silicon and carbon materials are physically mixed or coated with carbon on the surface of Si to improve the conductivity and cycle stability of silicon material, but the above method has a relatively complex preparation process, high cost, and the prepared material has low capacity. SUMMARY

[0005] The present application provides a Si@SiO x composite material, a preparation method and application thereof, and aims to solve the above problems in the background art.

[0006] In order to achieve the above purpose, the embodiments of the present application provide a Si@SiO x composite material, and further provide the Si@SiO xThe preparation method and application of the composite material are described. Lithium-ion batteries using this composite material as the negative electrode have high specific capacity and excellent cycle performance.

[0007] This invention provides a Si@SiO x The composite material includes a core and a shell encapsulating the surface of the core; the core is crystalline nano-silicon; the shell is amorphous SiO₂. x and its hydrate SiO x ·yH2O.

[0008] Preferably, the size of the core is 20–500 nm.

[0009] Preferably, the thickness of the outer shell is 2 to 20 nm.

[0010] Preferably, the oxygen content of the outer shell is 0-20 wt%, and the hydrogen content is 0-1 wt%.

[0011] Based on a general inventive concept, the present invention also provides the above-mentioned Si@SiO x The method for preparing composite materials includes the following steps:

[0012] S1: Pre-treat the nano-silicon in a prepared HF solution to remove the oxide layer formed on the surface during storage;

[0013] S2: Add the pretreated nano-silicon to deionized water, and mix evenly after ultrasonic dispersion and mechanical stirring to obtain a mixed solution;

[0014] S3: Add the mixed solution to a high-pressure reactor and heat to react;

[0015] S4: After the reactor has completely cooled, the mixed solution is removed, filtered, and the solid is dried to obtain Si@SiO. x Composite materials.

[0016] Preferably, the concentration of the HF solution prepared in step S1 is 10-20 wt%, and the reaction time is 6-12 h.

[0017] Preferably, the volume ratio of anhydrous ethanol to deionized water in step S2 is 1:5.

[0018] Preferably, in step S2, the ultrasonic dispersion time is 0.5 to 1 hour, and the mechanical stirring time is 15 to 30 minutes.

[0019] Preferably, in step S3, the heating temperature is 90–180°C and the heating time is 0.5–3 hours.

[0020] Preferably, the drying equipment in step S4 is a vacuum oven, with a drying temperature of 50-80°C and a drying time of 5-10 hours.

[0021] The present invention also provides the above-mentioned Si@SiO x Application of composite materials in lithium-ion battery anode materials.

[0022] This invention pretreats nano-silicon in an HF solution to remove the original oxide layer on the surface, obtaining pure nano-silicon. The pretreated nano-silicon material is then reacted with deionized water in a high-pressure reactor to yield Si@SiO. x Composite materials. Pretreated nano-silicon materials exhibit higher surface reactivity, and the resulting composite material forms a uniform coating layer, which can effectively alleviate volume expansion during lithium insertion / extraction and improve the cycle stability of nano-silicon.

[0023] The above-described solution of the present invention has the following beneficial effects:

[0024] (1) Preparation of Si@SiO in this invention x The reaction conditions in the composite material process are simple and easy to control, with a short process flow, low cost, and high yield.

[0025] (2) The present invention applies the above-mentioned Si@SiO x Lithium-ion batteries using composite materials as the negative electrode exhibit high specific capacity and excellent cycle performance. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The Si@SiO prepared in Examples 1-3 of this invention x XRD patterns of the composite material and the comparative Si-HF material;

[0028] Figure 2 The Si@SiO prepared in Examples 1-3 of this invention x TEM image of the composite material;

[0029] Figure 3 The Si@SiO prepared in Examples 1-3 of this invention x Elemental analysis results of O and H in the composite material and the comparative Si-HF material;

[0030] Figure 4The Si@SiO prepared in Examples 1-3 of this invention x Cyclic performance graphs of the composite material and the comparative Si-HF material. Detailed Implementation

[0031] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0032] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0034] This invention addresses the existing problems by providing a Si@SiO x Composite materials, their preparation methods, and applications.

[0035] The silicon raw materials used in the embodiments and comparative examples of this invention were purchased from Shanghai Shuitian Materials Technology Co., Ltd.

[0036] In the following examples and comparative examples, when testing the electrochemical performance of the target material, the target material was first assembled into a coin cell as follows: The target material, conductive agent Super P, and binder sodium alginate were mixed in a mass ratio of 60:20:20 to form a slurry. The slurry was uniformly coated onto a copper foil current collector to obtain an electrode sheet, which was then vacuum dried at 70°C for 12 hours. The electrode sheet was cut into small round pieces with a diameter of 12 mm. A lithium metal sheet (14 mm in diameter) was used as the counter electrode, glass fiber (GF / A) as the separator, and an organic solution of LiPF6 / EC+DEC (volume ratio 1:1) / FEC (mass fraction 10%) was used as the electrolyte. The battery assembly was carried out in an argon-filled glove box. The positive electrode shell, electrode sheet, separator, electrolyte, lithium sheet, gasket, spring, and negative electrode shell were placed in the following order from bottom to top. The assembled battery was then sealed using a coin cell sealing machine.

[0037] The electrochemical performance of the coin cells was tested using a constant current charge-discharge mode with a voltage range of 0.01–2.0V.

[0038] Example 1

[0039] Step S1: 2g of 100nm silicon particles were dispersed in 40mL of ethanol and 120mL of deionized water and ultrasonically dispersed for 30min to obtain a mixed solution. A prepared 10wt% hydrofluoric acid solution was added, and the mixture was mechanically stirred for 8h. The mixture was then filtered and separated. The resulting material was vacuum dried at 50℃ for 12h to obtain Si-HF.

[0040] Step S2: Weigh 0.5g of Si-HF and place it in a glass beaker. Add 10mL of anhydrous ethanol and 50mL of deionized water. Place the beaker in an ultrasonic cleaner and ultrasonically disperse for 30min. Remove the beaker and mechanically stir for 20min to ensure thorough mixing.

[0041] Step S3: Add the well-mixed solution into the high-pressure reactor and seal it. Place the high-pressure reactor in a forced-air drying oven. Heat the reactor to 90°C with the oven and keep it at that temperature for 1 hour. Allow it to cool naturally to room temperature.

[0042] Step S4: Remove the solution from the reactor, filter and separate it, and dry the obtained solid in a vacuum oven at 50°C for 8 hours to obtain Si@SiO. x Material.

[0043] Example 2

[0044] Steps S1, S2 and S4 are the same as in Example 1.

[0045] Step S3: Add the well-mixed solution into the high-pressure reactor and seal it. Place the high-pressure reactor in a forced-air drying oven. Heat the reactor to 120°C with the oven and keep it at that temperature for 1 hour. Allow it to cool naturally to room temperature.

[0046] Example 3

[0047] Steps S1, S2 and S4 are the same as in Example 1.

[0048] Step S3: Add the well-mixed solution into the high-pressure reactor and seal it. Place the high-pressure reactor in a forced-air drying oven. After the reactor is heated to 150°C by the oven, keep it at that temperature for 1 hour and then let it cool naturally to room temperature.

[0049] Comparative Example

[0050] Si-HF material was used as a comparative example.

[0051] Figure 1 Si@SiO prepared in Examples 1-3 x The XRD patterns of the composite material and the comparative Si-HF material are shown. The comparative material only shows the crystalline diffraction peaks of silicon. In Examples 1-3, in addition to the crystalline diffraction peaks of silicon, an amorphous peak appears after 21°, and the peak intensity increases continuously from Example 1 to Example 3. This peak is the amorphous coating layer generated by the hydrothermal reaction of nano-silicon, mainly composed of amorphous SiO. x and SiOx Composed of ·yH2O.

[0052] Figure 2 Si@SiO prepared in Examples 1-3 x TEM images of the composite material show a crystalline silicon core coated with an amorphous material. From Example 1 to Example 3, the thickness of the amorphous coating layer continuously increases, and the reaction rate increases with increasing temperature, resulting in the formation of more amorphous SiO₂. x and SiO x ·yH2O.

[0053] Figure 3 Si@SiO prepared in Examples 1-3 x Analysis of the O and H elemental contents in the composite material and the comparative Si-HF material shows that the O and H contents increase linearly with increasing reaction temperature. However, calculation of the molar ratio (O / H) reveals that the O / H molar ratio in the comparative example is 4.4, and the H content is extremely low and negligible. The O / H molar ratios in Examples 1-3 are 1.54, 1.76, and 2.15, respectively; the O / H molar ratio gradually increases with increasing reaction temperature, while the H element mainly originates from the SiO in the coating layer. x ·yH2O indicates that the SiO in the coating layer increases with temperature. x ·yH2O decomposes into SiO x SiO in the coating layer at different temperatures x and SiO x ·yH2O is different.

[0054] Figure 4 Si@SiO prepared in Examples 1-3 x Cycling performance graphs of the composite material and the comparative Si-HF material show that, compared to the comparative example, the initial reversible specific capacity of Examples 1-3 is significantly reduced, and the thicker the coating layer, the lower the initial reversible specific capacity. However, the cycling performance of Examples 1 and 2 is significantly improved. After 100 charge-discharge cycles at a current of 1000 mA / g, the capacity retention rate of Example 1 reaches 79%, and that of Example 2 reaches 82%, which is a significant improvement compared to the comparative example (54%). However, with further increases in the coating layer, Example 3 contains excessive amorphous SiO₂. x However, its poor conductivity leads to Li + The inability to properly insert and remove material leads to a sharp deterioration in the material's cycling performance.

[0055] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A Si@SiO x Composite material, characterized in that, It includes a core and a shell enclosing the surface of the core; the core is crystalline nano-silicon; the size of the core is 20~500 nm; The outer shell is amorphous SiO₂. x and its hydrate SiO x ·yH2O; The Si@SiO x The method for preparing composite materials includes the following steps: S1: Pre-treat the nano-silicon in a prepared HF solution to remove the oxide layer formed on the surface during storage; S2: The pretreated nano-silicon is added to a mixed solution of anhydrous ethanol and deionized water, and then mixed evenly after ultrasonic dispersion and mechanical stirring to obtain a mixed solution; S3: Add the mixed solution to a high-pressure reactor and heat it for reaction; the heating temperature is 90-120℃, and the heating time is 0.5-3 h; S4: After the reactor has completely cooled, the mixed solution is removed, filtered, and the solid is dried to obtain Si@SiO. x Composite materials; As the reaction temperature increases, the O / H molar ratio gradually increases; SiO in the coating layer at different reaction temperatures x and SiO x ·yH2O is different.

2. The Si@SiO according to claim 1 x Composite material, characterized in that, The thickness of the outer shell is 2~20 nm.

3. The Si@SiO according to claim 1 x Composite material, characterized in that, The outer shell has an oxygen content of 0-20 wt% and a hydrogen content of 0-1 wt%.

4. A Si@SiO according to any one of claims 1 to 3 x A method for preparing composite materials, characterized in that, Includes the following steps: S1: Pre-treat the nano-silicon in a prepared HF solution to remove the oxide layer formed on the surface during storage; S2: The pretreated nano-silicon is added to a mixed solution of anhydrous ethanol and deionized water, and then mixed evenly after ultrasonic dispersion and mechanical stirring to obtain a mixed solution; S3: Add the mixed solution to a high-pressure reactor and heat to react; S4: After the reactor has completely cooled, the mixed solution is removed, filtered, and the solid is dried to obtain Si@SiO. x Composite materials.

5. The preparation method according to claim 4, characterized in that, The concentration of the HF solution prepared in step S1 is 10~20 wt%, and the reaction time is 6~12 h.

6. The preparation method according to claim 4, characterized in that, In step S2, the volume ratio of anhydrous ethanol to deionized water is 1:5; the ultrasonic dispersion time is 0.5~1 h, and the mechanical stirring time is 15~30 min.

7. The preparation method according to claim 4, characterized in that, In step S4, the drying equipment is a vacuum oven, the drying temperature is 50~80 ℃, and the drying time is 5~10 h.

8. The Si@SiO according to any one of claims 1 to 3 x The composite material or the Si@SiO prepared by the preparation method according to any one of claims 4 to 7 x Application of composite materials in lithium-ion battery anode materials.

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