In-situ carbonized zirconium-coated silicon negative electrode material, and preparation method and application thereof

Abstract

This invention discloses an in-situ zirconium carbide-coated silicon anode material, its preparation method, and its application, belonging to the field of lithium-ion battery anode materials. The preparation method of the in-situ zirconium carbide-coated silicon anode material of this invention includes the following steps: S1, mixing and granulating a precursor and silicon powder, followed by a high-temperature solid-state reaction to prepare SiO₂. x Material, wherein 0 < x ≤ 2; S2, the SiO x Materials, carbon source, magnesium source, zirconium source, and molten salt are mixed and subjected to a magnesothermic reduction reaction to obtain SiO. x The Mg-ZrC composite material is the in-situ zirconium carbide-coated silicon anode material. The in-situ zirconium carbide-coated silicon anode material prepared by the method of the present invention has high initial efficiency, excellent conductivity and stable cycle rate performance; at the same time, the in-situ one-step reaction of pre-magnesium and coating can not only reduce costs, but also avoid the introduction of impurities.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode materials, specifically to an in-situ zirconium carbide-coated silicon anode material, its preparation method, and its application. Background Technology

[0002] With the rapid depletion of non-renewable energy sources such as oil and natural gas, and the increasing deterioration of the ecological environment, energy efficiency is becoming increasingly important, and people are placing higher demands on energy storage and release. Compared with traditional secondary batteries such as lead-acid batteries and nickel-cadmium batteries, lithium-ion batteries have outstanding advantages such as high single-cell voltage, high specific energy, long cycle life, and environmental friendliness, making them an indispensable part of people's daily lives.

[0003] Silicon is the anode material with the highest theoretical specific capacity to date. It combines with lithium to form Li. 4.4 Si, with a theoretical specific capacity of 4200 mAh / g, is approximately 11 times that of graphite. Simultaneously, silicon has a higher voltage plateau than graphite, making it less prone to surface lithium plating during charging and offering better safety performance. However, as an anode material, crystalline silicon exhibits a volume expansion rate as high as 400% and amorphous silicon as high as 280% when fully lithium-intercalated. This results in continuous expansion and contraction of silicon volume during electrochemical cycling due to lithium-ion insertion and extraction. The resulting stress causes silicon to gradually pulverize during charge and discharge, ultimately leading to a loss of electrical contact between internal silicon particles and between silicon and the current collector, significantly degrading cycle performance.

[0004] Based on the above, silicon suboxide (SiO) x The introduction of oxygen into the negative electrode causes the formation of some inert components, such as Li₂O and lithium silicates, during the initial lithium insertion / extraction process. This helps to reduce the absolute volume change (SiO₂) during lithiation. x The volume of the anode material expands by about 150% after lithiation. However, the formation of inactive products such as Li2O and lithium silicate also leads to the loss of activity of some Li, further reducing the initial coulombic efficiency.

[0005] Pre-lithiation technology can compensate for the decrease in initial coulombic efficiency caused by the deactivation of Li. However, Li is reactive and easily combines with water and oxygen during the reaction to form LiOH. This leads to the deactivation of some Li and excessive LiOH can easily generate bubbles during slurry mixing, affecting the coating quality. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides an in-situ zirconium carbide-coated silicon anode material, its preparation method, and its applications. The in-situ zirconium carbide-coated silicon anode material prepared by the method of this invention possesses high initial efficiency, excellent conductivity, and stable cycle rate performance; simultaneously, the in-situ one-step reaction of pre-magnesiumization and coating not only reduces costs but also avoids the introduction of impurities.

[0007] This invention first provides a method for preparing in-situ zirconium carbide-coated silicon anode material, comprising the following steps:

[0008] S1. After mixing and granulating the precursor and silicon powder, a high-temperature solid-state reaction is carried out to prepare SiO2. x Materials, where 0 < x ≤ 2;

[0009] S2, the SiO x Materials, carbon source, magnesium source, zirconium source, and molten salt are mixed and subjected to a magnesothermic reduction reaction to obtain SiO. x -Mg-ZrC composite material, namely the in-situ zirconium carbide-coated silicon anode material.

[0010] In the above-mentioned method for preparing in-situ zirconium carbide-coated silicon anode material, in S1, the particle size of the granulated material is 1-15 mm.

[0011] The specific steps for mixing and granulating the precursor and silicon powder are as follows: the precursor and silicon powder are dry-mixed and then extruded and granulated; more specifically, the stirring frequency of the dry mixing is 5-15 Hz and the cutting frequency is 15-25 Hz.

[0012] The method further includes a drying step after granulation; specifically, the drying temperature is 140–180°C and the drying time is 3–5 hours.

[0013] In the above-mentioned method for preparing in-situ zirconium carbide-coated silicon anode material, the precursor is silicon dioxide and / or a silicon dioxide-containing natural mineral; specifically, the silicon dioxide-containing natural mineral is selected from at least one of kaolinite, diatomite, dickite, montmorillonite, halloysite, and illite.

[0014] The high-temperature solid-state reaction is performed as follows: under vacuum conditions, the temperature is first raised to 1200–1300°C and maintained for 0.5–1 hour. Then, the temperature is raised to 1400–1500°C, and the temperature is lowered to 500–850°C to collect the product, thus obtaining the SiO₂. x Material;

[0015] The mass ratio of the precursor to silicon powder is (1-3):1; specifically, it can be 2:1.

[0016] In the above-mentioned method for preparing in-situ zirconium carbide-coated silicon anode material, the heating rate is 1-5 °C / min.

[0017] In the above-mentioned method for preparing in-situ zirconium carbide-coated silicon anode material, the carbon source is at least one of sucrose, carbon black, pitch and phenolic resin;

[0018] The magnesium source is metallic magnesium powder; specifically, the chemical purity of the magnesium powder is >99%.

[0019] The zirconium source is at least one of zirconium dioxide, zirconium oxychloride, and calcium-stabilized zirconium oxide; specifically, the analytical purity of the zirconium dioxide is >99%; the analytical purity of the zirconium oxychloride is >99%; and the industrial-grade purity of the calcium-stabilized zirconium oxide is >98%.

[0020] The molten salt is potassium chloride and / or sodium chloride. The chemical purity of both the potassium chloride and sodium chloride is >99%.

[0021] In the above-mentioned method for preparing in-situ zirconium carbide-coated silicon anode material, the SiO x The mass ratio of the material, carbon source, magnesium source and zirconium source is 25:(1~2):(2~4):(1~2);

[0022] The molten salt and SiO x The mass ratio of the materials is 0.8 to 1.2:1;

[0023] Both the magnesium source and the zirconium source are 200-240 mesh powders.

[0024] In the above-mentioned method for preparing in-situ zirconium carbide-coated silicon anode material, the temperature of the magnesium thermal reduction reaction is 900–1100 °C, and the time is 2–6 h.

[0025] In the magnesium thermoelectric reduction reaction, the heating rate is 1 to 5 °C / min; specifically, it can be 3 °C / min.

[0026] The magnesium thermal reduction reaction is carried out in an inert atmosphere; specifically, the inert atmosphere is an argon atmosphere.

[0027] Specifically, the magnesium thermoelectric reduction reaction is followed by natural cooling.

[0028] In the above-mentioned method for preparing in-situ zirconium carbide-coated silicon anode material, the preparation method further includes processing SiO₂. x The steps for acid washing and drying of Mg-ZrC composite materials;

[0029] Specifically, the pickling and drying steps are as follows: SiO x The Mg-ZrC composite material was placed in distilled water and washed with stirring. Then, hydrochloric acid was added to the water and the mixture was stirred and washed with acid. After filtration, it was dried.

[0030] Specifically, the concentration of the hydrochloric acid is 0.05–1 mol / L. This invention also provides an in-situ zirconium carbide-coated silicon anode material prepared by the above method.

[0031] The application of the aforementioned in-situ zirconium carbide-coated silicon anode material in the preparation of lithium-ion battery anodes also falls within the scope of protection of this invention.

[0032] Finally, the present invention provides a lithium-ion battery, wherein the negative electrode of the lithium-ion battery is prepared from the above-mentioned in-situ zirconium carbide-coated silicon negative electrode material.

[0033] In the preparation method of this invention, a large amount of heat is generated during the magnesium thermal reduction reaction. The participation of molten salt can lower the synthesis temperature, effectively control the grain size and morphology, reduce particle agglomeration, and generate fewer impurities. Two raw material systems (SiO2, SiO2, and SiO2) are used. x In-situ zirconium carbide-coated silicon anode materials are synthesized using both the -Mg system and the Zr-Mg-C system. Pre-magnesium coating of silicon suboxide can adjust the oxygen content in silicon suboxide, reducing the formation of inactive substances and improving the initial coulombic efficiency. Zirconium carbide possesses excellent properties such as high melting point, high strength, excellent conductivity, and high chemical stability. In-situ zirconium carbide coating can alleviate the volume expansion of silicon anode materials during lithium insertion / extraction processes. Simultaneously, the one-step pre-magnesium-coating reaction avoids impurity contamination during the reaction process, saving costs. The in-situ zirconium carbide-coated silicon anode material prepared by this method exhibits high initial efficiency, excellent conductivity, and stable cycle rate performance. Attached Figure Description

[0034] Figure 1 The XRD pattern of the material prepared for Comparative Example 1.

[0035] Figure 2 The images show the XRD patterns of the composite materials prepared in Examples 1-3.

[0036] Figure 3 The image shows a relatively pure porous SiOx-Mg-ZrC composite material prepared in Example 3, as an SEM image.

[0037] Figure 4 Charge-discharge curves of button batteries made from the composite materials prepared in Examples 1-3. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0039] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0040] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0041] The magnesium powder used in the following examples has a chemical purity >99%; the zirconium dioxide has an analytical purity >99%; and the potassium chloride and sodium chloride both have a chemical purity >99%.

[0042] Example 1

[0043] S1. Take 5 kg of commercial silica and 2.5 kg of silicon powder, mix them using a dry method, stirring at 5 Hz and cutting at 15 Hz, granulate by extrusion to obtain particles with a diameter of 10-15 mm, dry at 140℃ for 5 h, place the resulting mixture in a reaction apparatus, evacuate the apparatus, first heat to 100℃ at a heating rate of 1℃ / min, then heat to 1200℃ at a heating rate of 2℃ / min, hold at that temperature for 30 min, then heat to 1400℃ at a heating rate of 2℃ / min, then cool the apparatus until the temperature drops to 500℃, remove the product, and obtain SiO2. x (0<x≤2) material.

[0044] S2, take SiO x (0<x≤2) 100g of material, 10g of magnesium powder with a particle size of 200 mesh, 4g of zirconium dioxide, 4g of pitch, and 80g of sodium chloride were mixed and placed in a tube furnace. Under argon protection, the temperature was increased to 1100℃ at a heating rate of 3℃ / min and held for 2 hours for reaction. After natural cooling, the product was removed to obtain SiO₂. x -Mg-ZrC composite material;

[0045] S3, Take the SiO obtained in S2 x 200g of Mg-ZrC composite material was first added to distilled water and washed with stirring for 1 hour. Then, 600g of 0.05mol / L hydrochloric acid was added to the distilled water and washed with stirring for 2 hours. After filtration, the product was dried in an oven at 120℃ for 5 hours. The resulting product was then ground and sieved to obtain relatively pure porous SiO2. x -Mg-ZrC composite material.

[0046] Example 2

[0047] S1. Take 5 kg of diatomaceous earth and 2.5 kg of silicon powder, mix them using a dry method, stirring at 10 Hz and cutting at 20 Hz, granulate by extrusion to obtain particles with a diameter of 5-10 mm, dry at 140℃ for 5 h, place the resulting mixture in a reaction apparatus, evacuate the apparatus, first heat to 100℃ at a heating rate of 1℃ / min, then heat to 1300℃ at a heating rate of 5℃ / min, hold at that temperature for 1 h, then heat to 1500℃ at a heating rate of 5℃ / min, then cool the apparatus until the temperature drops to 850℃, remove the product, and obtain SiO2. x (0<x≤2) material.

[0048] S2, take SiO x (0<x≤2) 100g of material, 16g of magnesium powder with a particle size of 240 mesh, 5g of zirconium dioxide, 5g of pitch, and 50g of sodium chloride and potassium chloride were mixed and placed in a tube furnace. Under argon protection, the temperature was increased to 1000℃ at a heating rate of 3℃ / min and held for 4 hours for reaction. After natural cooling, the product was removed to obtain SiO₂. x -Mg-ZrC composite material;

[0049] S3, Take the SiO obtained in S2 x 100g of Mg-ZrC composite material was first added to distilled water and washed with stirring for 1 hour. Then, 600g of 1mol / L hydrochloric acid was added to the distilled water and washed with stirring for 0.5 hours. After filtration, the product was dried in an oven at 100℃ for 8 hours. The resulting product was then ground and sieved to obtain relatively pure porous SiO2. x -Mg-ZrC composite material.

[0050] Example 3

[0051] S1. Take 4 kg of kaolin and 2 kg of silicon powder, mix them using a dry method, stirring at 15 Hz and cutting at 25 Hz, granulate by extrusion to obtain particles with a diameter of 1-5 mm, dry at 180℃ for 3 h, place the resulting mixture in a reaction apparatus, evacuate the apparatus, first heat to 100℃ at a heating rate of 1℃ / min, then heat to 1250℃ at a heating rate of 3℃ / min, hold at that temperature for 45 min, then heat to 1450℃ at a heating rate of 3℃ / min, then cool the apparatus until the temperature drops to 750℃, remove the product, and obtain SiO2. x (0<x≤2) material.

[0052] S2, take SiO x(0<x≤2) 100g of material, 14g of magnesium powder with a particle size of 220 mesh, 8g of zirconium dioxide, 8g of pitch, and 120g of potassium chloride were mixed and placed in a tube furnace. Under argon protection, the temperature was increased to 900℃ at a heating rate of 3℃ / min and held for 6 hours for reaction. After natural cooling, the product was removed to obtain SiO₂. x -Mg-ZrC composite material;

[0053] S3, Take the SiO obtained in S2 x 200g of Mg-ZrC composite material was first added to distilled water and washed with stirring for 0.5h. Then, 600g of 0.5mol / L hydrochloric acid was added to the distilled water and washed with stirring for 1h. After filtration, the product was dried in an oven at 60℃ for 10h. The resulting product was then ground and sieved to obtain relatively pure porous SiO2. x -Mg-ZrC composite material.

[0054] Comparative Example 1

[0055] The traditional method for pre-magnesium oxide silica involves high-temperature solid-state sintering. The steps are as follows:

[0056] S1. Take 4 kg of kaolin and 2 kg of silicon powder, mix them using a dry method, stirring at 15 Hz and cutting at 25 Hz, granulate by extrusion to obtain 1-5 mm particles, dry at 180℃ for 3 h, place the resulting mixture in a reaction apparatus, evacuate the apparatus, first heat to 100℃ at a heating rate of 1℃ / min, then heat to 1250℃ at a heating rate of 3℃ / min, hold at that temperature for 45 min, then heat to 1450℃ at a heating rate of 3℃ / min, then cool the apparatus until the temperature drops to 750℃, remove the product, and obtain SiO2. x (0<x≤2) material.

[0057] S2, take SiO x (0<x≤2) 100g of material and 14g of magnesium powder with a particle size of 220 mesh were placed in a tube furnace and heated to 900℃ at a heating rate of 3℃ / min under argon protection. The temperature was held for 6 hours to carry out the reaction. After natural cooling, the product was removed to obtain SiO. x -Mg composite materials;

[0058] The product characterization test results are shown in Table 1.

[0059] Table 1. Characterization test results of the product of Comparative Example 1

[0060]

[0061] XRD test results are shown below. Figure 1 .like Figure 1As shown, the traditional solid-phase pre-magnesium reaction product is a mixture of silicon and magnesium silicates. The grain size of silicon in the material is obtained by calculating the silicon peak. Since silicon-carbon anode materials form silicon-lithium alloys through an alloying reaction during charging and discharging, the volume expansion of this alloy during charging and discharging affects the battery's cycle performance. Therefore, the cycle performance of the battery can be inferred from the size of the silicon grains. The smaller the silicon grain size, the lower the volume expansion during charging and discharging, and the better the cycle performance.

[0062] Characterization tests of products from Examples 4 and 1-3

[0063] 1. The products prepared in Examples 1-3 above were tested respectively, and the specific results are shown in Table 2.

[0064] Table 2. Characterization test results of Examples 1-3

[0065]

[0066] The XRD test results of the products in Examples 1-3 are shown below. Figure 2 .like Figure 2 As shown, the products prepared in Examples 1-3 have the same peak shape. The silicon grain size was calculated using the Scherrer formula, and the calculation results are shown in Table 2. The silicon grain size in the products is relatively small, resulting in low volume expansion. The SEM image test results of the product in Example 3 are shown in Table 2. Figure 3 .like Figure 3 As shown, the product prepared in Example 3 has a well-coated surface.

[0067] 2. Performance Testing

[0068] The product of Comparative Example 1 and the zirconium carbide-coated silicon anode materials prepared in Examples 1-3 were respectively taken. The materials, super-P (superconducting carbon black) conductive agent, and PVDF (polyvinylidene fluoride) binder were mixed in a mass ratio of 8:1:1 and coated onto an 8μm copper foil to obtain the battery anode. A CR2016 coin cell was assembled using a lithium sheet as the positive electrode. The electrolyte was a 1 mol / L LiPF6 EC (ethylene carbonate) + DMC (dimethyl carbonate) solution with an EC:DMC mass ratio of 1:1, and the separator was a PP (polypropylene) separator. Electrochemical performance tests were performed. The first-cycle charge-discharge test was conducted at 0.05C, and the charge-discharge capacity and first-cycle efficiency are shown in Table 3. The charge-discharge curves of Examples 1-3 are shown below. Figure 4 As shown.

[0069] Table 3. Electrochemical performance test results

[0070]

[0071] 3. Expansion Test

[0072] The negative electrode sheets of Examples 1-3 were measured using a micrometer, with measurement points at the center, middle ring, and outer ring. After the first week of charge-discharge testing, the coin cell was disassembled for in-situ measurements. The electrode sheet thickness before and after the first week of charge-discharge is shown in Table 4.

[0073] Table 4. Expansion Test Results

[0074]

[0075] As shown in Table 4, the expansion rate of the negative electrode sheets prepared in Examples 1-3 after the first week of charge and discharge is significantly improved compared with that of Comparative Example 1.

[0076] From Table 3, Table 4 and Figure 4 It can be seen that the zirconium carbide-coated silicon anode materials prepared in Examples 1-3 have the advantages of low expansion, high initial efficiency, and high capacity.

[0077] In summary, this invention provides a method for preparing in-situ zirconium carbide-coated silicon anode materials by magnesothermic reduction, firstly by preparing SiO2 through a high-temperature solid-state reaction. x (0<x≤2), after mixing a certain amount of carbon source, magnesium source, zirconium source and molten salt, a magnesothermic reaction is carried out. After natural cooling, impurities are removed by acid washing to obtain relatively pure zirconium carbide-coated SiO. x / C (0<x≤2) composite material. The magnesium thermal reduction reaction generates a large amount of heat; the participation of molten salt can lower the synthesis temperature, effectively control grain size and morphology, reduce particle agglomeration, and produce fewer impurities. Two raw material systems (SiO2, C2O2, and C2C2) are used. x Zirconium carbide-coated silicon anode pre-magnesium materials were synthesized using both Zr-Mg-C and Zr-Mg-C systems. Pre-magnesium coating of silicon suboxide can adjust the oxygen content in silicon suboxide, reduce the formation of inactive substances, and improve the initial coulombic efficiency. Zirconium carbide possesses excellent properties such as high melting point, high strength, excellent conductivity, and high chemical stability. In-situ coating of zirconium carbide can alleviate the volume expansion of silicon anode materials during lithium insertion / extraction processes. Simultaneously, the one-step pre-magnesium-coating reaction avoids impurity contamination during the reaction process, saving costs. The in-situ zirconium carbide-coated silicon anode material prepared by this method exhibits high initial efficiency, excellent conductivity, and stable rate performance.

Claims

1. A method for preparing an in-situ zirconium carbide-coated silicon anode material, characterized in that, Includes the following steps: S1. After mixing and granulating the precursor and silicon powder, a high-temperature solid-state reaction is carried out to prepare SiO2. x Materials, where 0 < x ≤ 2; S2, the SiO x Materials, carbon source, magnesium source, zirconium source, and molten salt are mixed and subjected to a magnesothermic reduction reaction to obtain SiO. x -Mg-ZrC composite material; The preparation method further includes processing SiO₂ x The steps for acid washing and drying of Mg-ZrC composite materials; The acid washing and drying steps are as follows: SiO x The Mg-ZrC composite material was placed in distilled water and washed with stirring. Then, hydrochloric acid was added to the water and the mixture was washed with stirring. After filtration, it was dried. The SiO x The mass ratio of the material, carbon source, magnesium source and zirconium source is 25:(1~2):(2~4):(1~2).

2. The method for preparing in-situ zirconium carbide-coated silicon anode material according to claim 1, characterized in that, The precursor is silicon dioxide and / or natural minerals containing silicon dioxide; The high-temperature solid-state reaction steps are as follows: Under vacuum conditions, the temperature is first raised to 1200~1300℃ and held for 0.5~1h. Then, the temperature is raised to 1400~1500℃, and the temperature is lowered until 500~850℃, at which point the product is collected to obtain the SiO₂. x Material; The mass ratio of the precursor to silicon powder is (1~3):

1.

3. The method for preparing in-situ zirconium carbide-coated silicon anode material according to claim 2, characterized in that, The heating rate is 1~5℃ / min.

4. The method for preparing in-situ zirconium carbide-coated silicon anode material according to claim 1, characterized in that, The carbon source is at least one of sucrose, carbon black, pitch and phenolic resin; The magnesium source is metallic magnesium powder; The zirconium source is at least one of zirconium dioxide, zirconium oxychloride, and calcium-stabilized zirconium oxide; The molten salt is potassium chloride and / or sodium chloride.

5. The method for preparing in-situ zirconium carbide-coated silicon anode material according to claim 1, characterized in that, The molten salt and SiO x The mass ratio of the materials is 0.8~1.2:

1.

6. The method for preparing in-situ zirconium carbide-coated silicon anode material according to claim 1, characterized in that, The temperature of the magnesium thermal reduction reaction is 900~1100℃, and the time is 2~6h.

7. The method for preparing in-situ zirconium carbide-coated silicon anode material according to claim 1, characterized in that, The magnesium thermal reduction reaction is carried out in an inert atmosphere.

8. The in-situ zirconium carbide-coated silicon anode material prepared by the preparation method according to any one of claims 1-7.

9. The application of the in-situ zirconium carbide-coated silicon anode material according to claim 8 in the preparation of lithium-ion battery anodes.

10. A lithium-ion battery, characterized in that, The negative electrode of the lithium-ion battery is prepared from the in-situ zirconium carbide-coated silicon negative electrode material as described in claim 8.

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