Silicon oxide compound-coated nano-silicon negative electrode material, and preparation method and application thereof

Abstract

The application provides a silicon oxide compound coated negative electrode material of nano silicon and a preparation method and application thereof, and relates to the technical field of lithium ion batteries. The application takes nano silicon as raw material, performs low-temperature thermal oxidation on the nano silicon, and then forms a silicon oxide compound coating layer on the surface of the nano silicon, so that the content of the silicon oxide compound and the valence of silicon in the silicon oxide compound are regulated by controlling the reaction temperature and the reaction time to obtain silicon particles with different contents of the silicon oxide compound. The silicon oxide compound coating layer prepared by the application has excellent electrochemical activity and mechanical properties, can effectively inhibit the crushing of the silicon particles in the charging and discharging process, and improves the cycle stability of the battery. The preparation method of the application is simple, economical and environment-friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials for lithium ion batteries, and in particular to a negative electrode material of silicon oxide-coated nano-silicon, a preparation method thereof, and an application thereof. Background Art

[0002] Entering the 21st century, the scientific and technological level of human society has developed rapidly, and the demand for energy has increased year by year. The current energy structure is still dominated by non-renewable energy sources such as coal, oil, and natural gas. Their excessive use has caused a series of problems such as energy shortages and environmental pollution. Therefore, the development of lithium-ion batteries with high energy density and long cycle life is of great significance. In the lithium-ion battery system, the positive and negative electrode materials are containers for carrying lithium ions, and therefore largely determine the energy density of the entire battery. Graphite, as the most commonly used commercial negative electrode material, has advantages such as good conductivity and long cycle life. However, its theoretical specific capacity is low (372mAh / g, LiC6), and in actual use it is close to the theoretical value. Therefore, it is difficult to prepare the next generation of high-energy-density lithium-ion batteries by modifying graphite.

[0003] Silicon is abundant in nature. At room temperature, the silicon negative electrode forms a lithium-silicon alloy (Li 3.75 Si), with a theoretical specific capacity of up to 3579 mAh / g, can be used as the negative electrode material for the next generation of high-energy-density lithium-ion batteries. However, the alloying process of the silicon negative electrode induces a dramatic volume expansion, which in severe cases leads to particle breakage, loss of electrical contact between materials, and rapid decay of battery capacity. Surface coating is an effective method to alleviate the volume expansion of silicon particles. Common coating materials include carbon sources (CN111224105A), high molecular weight organic matter (CN116130628A), and alumina (CN105958023A). The coating process of these materials usually involves complex chemical reactions and has high preparation costs.

[0004] Therefore, the present invention designs a simple preparation process, cost-effective and excellent performance of silicon oxide compound coated nano-silicon negative electrode material and its preparation method and application Summary of the Invention

[0005] The present invention provides a silicon oxide compound coated nano-silicon negative electrode material and a preparation method and application thereof, the purpose of which is to solve the above-mentioned problems existing in the background technology.

[0006] In order to achieve the above-mentioned purpose, the embodiment of the present application provides a silicon oxide compound coated nano-silicon negative electrode material and a preparation method and application thereof. The present application takes nano-silicon as raw material, performs low-temperature thermal oxidation, and then forms a silicon oxide compound coating layer on the surface of nano-silicon. The content of silicon oxide compound and the valence state of silicon in the silicon oxide compound can be controlled by controlling the reaction temperature and reaction time. The silicon oxide compound coating layer prepared by the present application has excellent electrochemical activity and mechanical properties, can effectively inhibit the crushing of silicon particles during the charging and discharging process, and improve the cycle stability of the battery. The preparation method of the present application is simple, economical and environmentally friendly.

[0007] The embodiment of the present application provides a silicon oxide compound coated nano-silicon negative electrode material, which has a two-phase composite structure.

[0008] The two-phase composite structure comprises a core composed of nano-silicon and a silicon oxide compound layer coating the core.

[0009] The chemical formula of the two-phase composite structure is x(SiO a )·(1-x)(Si); wherein 0.0275≤x≤0.0607, 1.2≤a≤1.3.

[0010] Further, the molar content of Si 2+ in the silicon oxide compound layer accounts for 40-80% of the silicon in the silicon oxide compound, and the molar content of Si 3+ accounts for 20-60% of the silicon in the silicon oxide compound.

[0011] Based on the general concept of an invention, the embodiment of the present application provides the above-mentioned preparation method of the silicon oxide compound coated nano-silicon negative electrode material, which comprises the following preparation steps:

[0012] S1. Prepare a hydrofluoric acid ethanol aqueous solution, then add nano-silicon particle raw material, and perform ultrasonic dispersion and mechanical stirring, and then perform suction filtration separation, vacuum drying to obtain nano-silicon particles, and store them in an inert atmosphere for standby use;

[0013] S2. Take the nano-silicon particles and place them in a muffle furnace to perform oxidation reaction, heat preservation, and cooling to obtain a silicon oxide compound coated nano-silicon negative electrode material.

[0014] Further, in step S1, the concentration of the hydrofluoric acid ethanol aqueous solution is 5-20wt.%, the ultrasonic dispersion time is 30-60min, the mechanical stirring time is 1-20h, the stirring rate is 300-500r / min, the drying temperature is 50-80℃, and the inert atmosphere is high-purity argon, wherein H2O≤0.1ppm, O2≤0.1ppm.

[0015] Further, in step S2, the heating temperature is 150-550 DEG C, the heating rate is 2-20 DEG C / min, and the holding time is 1 min-5 h.

[0016] The embodiment of the present application also provides a lithium ion battery comprising the silicon oxide compound coated nano-silicon negative electrode material or the silicon oxide compound coated nano-silicon negative electrode material prepared by the preparation method.

[0017] Further, the lithium ion battery comprises the silicon oxide compound coated nano-silicon negative electrode material as a working electrode, lithium sheet as a counter electrode, 1 mol / L LiPF6 as an electrolyte and Celgard 2325 as a diaphragm.

[0018] Further, the solvent in the electrolyte is a mixed solution of diethyl carbonate and ethylene carbonate in a volume ratio of 1:1 containing 10 wt% of fluoroethylene carbonate additive.

[0019] Further, the working electrode further comprises a copper foil, a conductive agent and a binder.

[0020] The above scheme of the present application has the following beneficial effects:

[0021] 1. The present application uses nano-silicon as raw material, and prepares a silicon oxide compound coating layer on the surface of nano-silicon through low-temperature thermal oxidation, the coating layer has excellent electrochemical activity and mechanical properties, can effectively alleviate the volume expansion of silicon particles during the charging and discharging process, and promotes the charge transfer between materials.

[0022] 2. The preparation method of the present application is simple, low in energy consumption, low in cost and friendly to the environment. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0024] Figure 1 The silicon element XPS spectrum of the silicon oxide compound coated nano-silicon negative electrode material prepared in the embodiment and the comparative example of the present application;

[0025] Figure 2 The cycle performance graph of the silicon oxide compound coated nano-silicon negative electrode material prepared in the embodiment and the comparative example of the present application. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0027] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0028] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0029] The present invention addresses the problems of severe volume expansion during the alloying process of existing silicon negative electrodes, which in severe cases leads to particle breakage, loss of electrical contact between battery electrode materials, and rapid attenuation of battery capacity, as well as the problems of the existing surface coating process usually involving complex chemical reactions and high preparation costs. The present invention provides a silicon oxide compound-coated nano-silicon negative electrode material, a preparation method and application thereof.

[0030] Example 1

[0031] In this embodiment, 0.0366 (SiO 1.24 )·0.9634(Si) material, SiO 1.24 Si in the layer 2+ The molar content of silicon is 43.9%, Si 3+ The molar content of silicon is 27.7%. The specific steps include:

[0032] S1: 40 ml of hydrofluoric acid (40 wt %) was added to 160 ml of deionized water and mechanically stirred for 30 min to obtain solution A;

[0033] S2: Add 1.5 g of nanosilicon to Solution A, ultrasonically disperse for 1 hour, and mechanically stir for 10 hours to obtain Solution B. Rinse the solution several times with deionized water during vacuum filtration to remove residual hydrofluoric acid on the surface of the nanosilicon. Dry the nanosilicon under vacuum at 60°C for 24 hours and store in a glove box (H2O ≤ 0.1 ppm, O2 ≤ 0.1 ppm) until use.

[0034] S3: 0.15g of nano-silicon was spread in a corundum boat, placed in a muffle furnace, and heated to 450℃ (heating rate 3℃ / min), kept at this temperature for 10min, and cooled in the furnace. 1.24 )·0.9634(Si) material, SiO 1.24 Si in the layer 2+ The molar content of silicon is 43.9%, Si 3+The molar content of silicon is 27.7%.

[0035] Example 2

[0036] In this example, 0.0411 (SiO 1.25 )·0.9589(Si) material, SiO 1.25 Si in the layer 2+ The molar content of silicon is 49.1%, Si 3+ The molar content of silicon is 22.8%. The specific steps include the following, and the other steps are the same as those in Example 1:

[0037] 0.15g of nano-silicon was spread in a corundum ark, placed in a muffle furnace, and heated to 450℃ (heating rate 3℃ / min), kept at this temperature for 20min, and cooled in the furnace. 1.25 )·0.9589(Si) material, SiO 1.25 Si in the layer 2+ The molar content of silicon is 49.1%, Si 3+ The molar content of silicon is 22.8%.

[0038] Example 3

[0039] In this embodiment, 0.0484 (SiO 1.25 )·0.9516(Si) material, SiO 1.25 Si in the layer 2+ The molar content of silicon is 41.3%, Si 3+ The molar content of silicon is 31.9%. The steps are as follows, and the other steps are the same as those in Example 1:

[0040] 0.15g of HF-Si was spread flat in a corundum boat, placed in a muffle furnace, and heated to 450℃ (heating rate 3℃ / min), kept at this temperature for 40min, and cooled in the furnace. 1.25 )·0.9516(Si) material, SiO 1.25 Si in the layer 2+ The molar content of silicon is 41.3%, Si 3+ The molar content of silicon is 31.9%.

[0041] Comparative Example 1

[0042] This comparative example was prepared according to the following conditions: 1.38 )·0.9808(Si) material, SiO 1.38 Si in the layer 2+ The molar content of silicon is 15.3%, Si3+ The molar content of silicon is 69.2%. The specific steps include the following, and the other steps are the same as those in Example 1:

[0043] 0.15g of HF-Si was spread flat in a corundum boat, placed in a muffle furnace, and heated to 350℃ (heating rate 3℃ / min), kept at this temperature for 120min, and cooled in the furnace. 0.0192(SiO 1.38 )·0.9808(Si) material, SiO 1.38 Si in the layer 2+ The molar content of silicon is 15.3%, Si 3+ The molar content of silicon is 69.2%.

[0044] Comparative Example 2

[0045] In this embodiment, 0.1021 (SiO 1.69 )·0.8979(Si) material, SiO 1.69 Si in the layer 2+ The molar content of silicon is 7.4%, Si 3+ The molar content of silicon is 39.4%. The steps are as follows, and the other steps are the same as those in Example 1:

[0046] 0.15g of HF-Si was spread flat in a corundum boat, placed in a muffle furnace, and heated to 750℃ (heating rate 3℃ / min), kept at this temperature for 60min, and cooled in the furnace. 1.69 )·0.8979(Si) material, SiO 1.69 Si in the layer 2+ The molar content of silicon is 7.4%, Si 3+ The molar content of silicon is 39.4%.

[0047] Figure 1 The XPS spectra of silicon element in Examples 1-3 and Comparative Examples 1-2 are shown. Due to the difference in holding time, the SiO a The content gradually increases, SiO a The silicon valence state in the coating layer is mainly Si 3+ and Si 2+ , and 1.2≤a≤1.3. SiO a The coating layer transforms into lithium silicate at low potential, which has excellent electrochemical activity and is conducive to charge transfer between materials; and its excellent mechanical properties can effectively inhibit the volume expansion of silicon.

[0048] application

[0049] The nano-silicon negative electrode material coated with silicon oxide prepared in Example 1-3 and Comparative Example 1-2 is used to make a negative electrode sheet, including the following steps:

[0050] First, grind the silicon oxide compound-coated nano-silicon anode material, the conductive agent (Superp), and the binder (sodium alginate) obtained by any of the preparation methods of Examples 1-3 and Comparative Examples 1-2 at a mass ratio of 7:2:1 for 20 minutes. Add 30% ethanol aqueous solution and continue grinding for 20 minutes. The mass ratio of ethanol aqueous solution to silicon material is 1:0.07. Mix thoroughly to form a slurry. Use a coater to coat the slurry on copper foil to a thickness of 100μm. Place the electrode in a vacuum drying oven and bake at 70°C for 24 hours to fully evaporate the solvent. Cut the electrode into 12mm round pieces.

[0051] A method for assembling a battery comprising the above-mentioned negative electrode sheet comprises the following steps:

[0052] The above-mentioned 12mm silicon pole piece (circular pole piece) was used as the working electrode, the 16mm metal lithium sheet was used as the counter electrode, a Celgard 2325 separator with a diameter of 20mm was used, and 1mol / L LiPF6 (the solvent was a mixed solution of diethyl carbonate and ethylene carbonate with a volume ratio of 1:1 containing 10wt% fluoroethylene carbonate additive) was used as the electrolyte. The battery was assembled in a glove box (H2O≤0.1ppm, O2≤0.1ppm). During the battery cycle performance test, the first three cycles were activated at a current of 200mAh / g, and then cycled at a current of 1000mAh / g for 100 cycles, with a voltage range of 0.05V to 1.5V.

[0053] Figure 2 The cycle performance diagram of the silicon oxide compound coated nano-silicon negative electrode material of Examples 1-3 and Comparative Examples 1-2. Examples 1-3 all showed excellent cycle stability. a With the increase of SiO content, the cycle performance of the material is improved. The retention rate of Example 3 after 100 cycles at a current density of 1000 mAh / g is as high as 98.9%. a The content is low and the volume expansion of silicon particles cannot be effectively suppressed; in Comparative Example 2, due to SiO a The content is too high and there is a lot of high-resistance SiO2, which increases the polarization of the material and limits the material capacity.

[0054] The above is 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 principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A negative electrode material of silicon oxide coated nano-silicon, characterized in that: The negative electrode material is a two-phase composite structure; wherein, The two-phase composite structure includes a core composed of nano-silicon and a silicon oxide layer covering the core; The chemical formula of the two-phase composite structure is x(SiO a )·(1-x)(Si); wherein, 0.0275≤x≤0.0607, 1.2≤a≤1.

3.

2. The negative electrode material of silicon oxide compound coated nano-silicon according to claim 1, characterized in that: Si in the silicon oxide layer 2+ The molar content of silicon in silicon oxide compounds is 40-80%, Si 3+ The molar content of silicon accounts for 20 to 60% of the silicon in the silicon oxide compound.

3. The method for preparing the negative electrode material of silicon oxide compound coated nano-silicon according to any one of claims 1 to 2, characterized in that: The method comprises the following preparation steps: S1 configuration of hydrofluoric acid ethanol aqueous solution, followed by the addition of nano-silicon particles raw materials, ultrasonic dispersion and mechanical stirring, as well as filtration separation, vacuum drying, to obtain nano-silicon particles, and placed in an inert atmosphere for storage; S2. Place the nano-silicon particles in a muffle furnace, heat to perform an oxidation reaction, keep the temperature, and cool to obtain a negative electrode material of silicon oxide-coated nano-silicon.

4. The method for preparing the negative electrode material of silicon oxide compound coated nano-silicon according to claim 3, characterized in that: In step S1, the concentration of the hydrofluoric acid ethanol aqueous solution is 5-20wt.%; the ultrasonic dispersion time is 30-60min; the mechanical stirring time is 1-20h, and the stirring rate is 300-500r / min; the drying temperature is 50-80°C; and the inert atmosphere is high-purity argon, wherein H2O≤0.1ppm and O2≤0.1ppm.

5. The method for preparing the negative electrode material of silicon oxide compound coated nano-silicon according to claim 3, characterized in that: In step S2, the heating temperature is 150-550°C, the heating rate is 2-20°C / min, and the holding time is 1 min-5 h.

6. A lithium-ion battery, characterized in that: The lithium-ion battery comprises the negative electrode material of silicon oxide compound coated nano-silicon according to any one of claims 1 to 2 or the negative electrode material of silicon oxide compound coated nano-silicon obtained by the preparation method according to any one of claims 3 to 5.

7. The lithium-ion battery according to claim 6, characterized in that The lithium-ion battery includes the silicon oxide compound-coated nano-silicon negative electrode material as a working electrode, a lithium sheet as a counter electrode, 1 mol / L LiPF6 as an electrolyte, and Celgard 2325 as a diaphragm.

8. The lithium-ion battery according to claim 7, characterized in that The solvent in the electrolyte is a mixed solution of diethyl carbonate and ethylene carbonate in a volume ratio of 1:1 containing 10 wt% of fluoroethylene carbonate additive.

9. The lithium-ion battery according to claim 8, characterized in that The working electrode further comprises copper foil, a conductive agent and a binder.

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