A method for preparing magnesium-tin-doped silicon-carbon anode material

Abstract

This invention discloses a method for preparing magnesium-tin-doped silicon-carbon anode material, comprising the following steps: S1, preparing SiO2... x The material is carbon-coated to obtain SiO2. x / C composite material, where 0 < x ≤ 2; S2, the SiO2 x The / C composite material is mixed with metallic magnesium and metallic tin, heated to a certain temperature in an inert atmosphere, and held at that temperature to carry out a low-temperature magnesothermic reaction, yielding magnesium-tin doped SiO. x / C composite material; S3, the magnesium-tin doped SiO x The / C composite material was sequentially washed with water, acid-washed, and then dried. The resulting product was mixed with a carbon source and heated to a certain temperature in an inert atmosphere. The mixture was then held at this temperature to allow for a carbon layer repair reaction. After cooling, a magnesium-tin-doped silicon-carbon anode material was obtained. The anode material prepared using the method of this invention exhibits high initial efficiency, excellent conductivity, and stable cycle rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, and in particular to a method for preparing a magnesium-tin-doped silicon-carbon anode material. 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 Li deactivation. However, Li is reactive and easily combines with water and oxygen during the reaction to form LiOH. This leads to partial Li deactivation, and excessive LiOH can easily generate bubbles during slurry mixing, affecting coating quality. Using silicon suboxide (SiO₂) as a pre-lithiation agent... x Using MgO as raw material, SiO2 is reduced by magnesium thermal reduction reaction. xThe reaction +xMg → xMgO + Si, adjusting the oxygen content in silicon suboxide, can reduce the formation of inactive substances and improve the initial coulombic efficiency. However, the magnesian thermal reaction is intense, and excessively high local temperatures can lead to a sharp increase in silicon crystal size, and magnesium oxide can agglomerate into larger particles, affecting the battery's cycle performance. In existing technologies, adding one or more salts to the magnesian thermal reaction can absorb the excessive heat generated during its melting process, improving reaction uniformity. However, the introduction of halogen elements can affect battery performance. Therefore, a suitable silicon suboxide (SiO) is urgently needed. x The pre-magnesium method comprehensively enhances the application value of silicon suboxide materials in lithium-ion battery anode materials. Summary of the Invention

[0006] Based on the technical problems existing in the background technology, the present invention proposes a method for preparing magnesium-tin doped silicon-carbon anode materials.

[0007] The present invention proposes a method for preparing a magnesium-tin-doped silicon-carbon anode material, comprising the following steps:

[0008] S1, for SiO x The material is carbon-coated to obtain SiO2. x / C composite material, where 0<x≤2;

[0009] S2, the SiO x The / C composite material is mixed with metallic magnesium and metallic tin, heated to a certain temperature in an inert atmosphere, and held at that temperature to carry out a low-temperature magnesothermic reaction, yielding magnesium-tin doped SiO. x / C composite materials;

[0010] S3, The magnesium-tin doped SiO x The / C composite material is washed with water, acid-washed, and then dried. The resulting product is mixed with a carbon source and heated to a certain temperature in an inert atmosphere. The carbon layer repair reaction is carried out by holding the temperature, and after cooling, magnesium-tin doped silicon-carbon anode material is obtained.

[0011] In this invention, SiO x The material can be prepared using the following methods:

[0012] SiO is prepared by mixing silicon dioxide, silicon dioxide-containing natural minerals or combinations thereof with silicon powder in a certain proportion, granulating the mixture, and then reacting it with silicon powder at high temperature. x (0 < x ≤ 2) material; preferably, the silica-containing natural mineral is selected from at least one of kaolinite, diatomite, dickite, montmorillonite, halloysite, and illite; preferably, the specific steps of the high-temperature solid-phase reaction are as follows: under vacuum conditions, first heat to 1200-1300℃, maintain the temperature for 0.5-1h, then heat to 1400-1500℃, begin cooling, cool to 500-850℃, and collect SiO2.x Materials; preferably, the heating rate is 1-5℃ / min; preferably, the mass ratio of silicon dioxide, silicon dioxide-containing natural minerals or combinations thereof to silicon powder is (1-3):1.

[0013] Preferably, in S1, the SiO x The mass of carbon in the / C composite material is SiO₂ x 2% to 10% of the quality.

[0014] Preferably, in S1, the carbon coating is performed using a liquid phase coating method or a gas phase coating method.

[0015] Preferably, in S2, SiO x The mass ratio of the C composite material, magnesium, and tin is (1-6):0.5:(0.5-2.5).

[0016] Preferably, in S2, SiO x The average particle size D50 of the / C composite material is 1-10 μm, the particle size of magnesium is 200-240 mesh, and the particle size of tin is 200-240 mesh.

[0017] Preferably, in S2, the temperature is increased to 400–500°C in an inert atmosphere and held for 4 hours to carry out a low-temperature magnesothermic reaction.

[0018] Preferably, in S3, the carbon source is magnesium-tin-doped SiO₂. x / C composite material mass 2% to 10%.

[0019] Preferably, in step S3, hydrochloric acid with a concentration of 0.05–1 mol / L is used for acid washing.

[0020] Preferably, in step S3, the carbon layer repair reaction is carried out by heating to 800–900°C in an inert atmosphere and holding at that temperature for 3–4 hours.

[0021] Preferably, in S3, the carbon source is at least one of asphalt, polyvinyl alcohol, and glucose.

[0022] A magnesium-tin-doped silicon-carbon anode material is prepared by the method described above.

[0023] The beneficial effects of this invention are as follows:

[0024] This invention relates to silicon suboxide (SiO2). xFirst, carbon coating is performed, followed by a magnesothermal reaction. This process inhibits agglomeration during magnesothermal reduction and controls the silicon crystal size after magnesothermal reduction. Furthermore, the addition of metallic tin during magnesothermal reduction not only lowers the magnesothermal reaction temperature to around 400°C, effectively controlling silicon crystal growth, but also, due to tin's high theoretical specific capacity, improves the conductivity of lithium-ion battery anode materials. The incorporated magnesium reduces the formation of inactive Li₂O and lithium silicates, thus improving the initial charge-discharge efficiency of lithium-ion battery anode materials. Using the pre-magnesification method of this invention, silicon crystal size can be well controlled during pre-magnesification, reducing magnesium oxide agglomeration and improving cycle performance. Simultaneously, it reduces the formation of inactive substances, improving the initial coulombic efficiency. This results in anode materials with high initial efficiency, excellent conductivity, and stable cycle rate performance, comprehensively enhancing their electrochemical performance. Attached Figure Description

[0025] Figure 1 The XRD characterization results are for the pre-magnesium silicate material prepared in Comparative Example 1 of this invention.

[0026] Figure 2 The XRD characterization results are those of the pre-magnesium silicate materials prepared in Examples 1-3 of this invention.

[0027] Figure 3 The charge-discharge curves are those of the pre-magnesium silicon suboxide materials prepared in Examples 1-3 of this invention. Detailed Implementation

[0028] The technical solution of the present invention will now be described in detail through specific embodiments.

[0029] Comparative Example 1

[0030] The traditional method for pre-magnesium silicate involves high-temperature solid-state sintering. Silica and magnesium powder are uniformly mixed, and then sintered at 800–900°C to obtain the pre-magnesium silicate material. The product characterization results are shown in Table 1.

[0031] Table 1. Characterization test results of Comparative Example 1

[0032]

[0033] XRD test results, see 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.

[0034] Therefore, traditional solid-phase pre-magnesium methods typically require the use of molten salts. However, the use of molten salts necessitates an additional washing process, employing strong acids to remove salt impurities from the materials. This requires companies to adhere to safety regulations and also increases process and equipment costs.

[0035] Example 1

[0036] Preparation of SiO x Material:

[0037] Take 5 kg of commercial silica 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 of 1-5 mm, and 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, and then cool the apparatus until the temperature drops to 500℃. Remove the product to obtain SiO2. x (0<x≤2) material.

[0038] Preparation of magnesium-tin-doped silicon-carbon anode materials:

[0039] S1. Mix 1L of 200g / L sucrose solution with concentrated sulfuric acid at a volume ratio of 1:0.04 to obtain a homogeneous mixture. Then, proceed according to the SiO2... x The mass ratio of the material to sucrose is 1:1. SiO₂ is added to the mixture. x The material was stirred for 3 hours, then kept at 150℃ in an oven for 10 hours. After cooling, it was ground and heated to 700℃ at a rate of 5℃ / min under argon protection, and held for 4 hours to obtain SiO2. x / C composite material, the carbon content of which is 5% and the average particle size D50 is 7.3μm;

[0040] S2, Take 50g of the SiO2 obtained in S1 xThe / C composite material was mixed with 7.5g each of magnesium powder and tin powder with a particle size of 200 mesh, and then placed in a tube furnace. Under argon protection, the temperature was increased to 400℃ at a heating rate of 3℃ / min and held for 4 hours to carry out a low-temperature magnesothermic reaction. After natural cooling, the product was removed to obtain magnesium-tin doped SiO. x / C composite materials;

[0041] S3, Take the magnesium-tin doped SiO2 obtained in S2 x 50g of the / C composite material was first added to distilled water and stirred and washed for 1 hour, then added to 0.05mol / L hydrochloric acid and stirred and washed for 2 hours. After filtration, it was placed in an oven at 120℃ and dried for 5 hours. The obtained product was ground and sieved, mixed with 2.5g of asphalt, and placed in a tube furnace. Under argon protection, the temperature was raised to 800℃ at a heating rate of 3℃ / min and held for 4 hours to carry out the carbon layer repair reaction. After natural cooling, it was taken out to obtain magnesium-tin doped silicon-carbon anode material.

[0042] Example 2

[0043] Preparation of SiO x Material:

[0044] 4 kg of kaolin and 2 kg of silicon powder were dry-mixed at a stirring frequency of 10 Hz and a cutting frequency of 20 Hz. After extrusion granulation, particles of 1–5 mm were obtained and dried at 180 °C for 3 hours. The resulting mixture was placed in a reaction apparatus under vacuum. The temperature was first increased to 100 °C at a rate of 1 °C / min, then increased to 1250 °C at a rate of 3 °C / min and held for 45 minutes. The temperature was then increased to 1450 °C at a rate of 3 °C / min. The apparatus was then cooled until the temperature dropped to 750 °C. The product was then removed to obtain SiO₂. x (0<x≤2) material.

[0045] Preparation of magnesium-tin-doped silicon-carbon anode materials:

[0046] S1. Mix 1L of 350g / L glucose solution with concentrated sulfuric acid at a volume ratio of 1:0.05 to obtain a homogeneous mixture. Then, proceed according to the SiO2... x The mass ratio of the material to glucose is 1:0.8. SiO₂ is added to the mixture. x The material was stirred for 2 hours, then kept at 200℃ in an oven for 8 hours. After cooling, it was ground and heated to 900℃ at a rate of 3℃ / min under argon protection, and held for 4 hours to obtain SiO2. x / C composite material, the carbon content of which is 7% and the average particle size D50 is 8.2μm;

[0047] S2, Take 50g of the SiO2 obtained in S1 xThe / C composite material was mixed with 7.5g of 220-mesh magnesium powder and 10g of 220-mesh tin powder, and then placed in a tube furnace. Under argon protection, the temperature was increased to 450℃ at a heating rate of 3℃ / min and held for 4 hours to carry out a low-temperature magnesothermic reaction. After natural cooling, the product was removed to obtain magnesium-tin doped SiO. x / C composite materials;

[0048] S3, Take the magnesium-tin doped SiO2 obtained in S2 x 50g of the / C composite material was first added to distilled water and stirred and washed for 0.5h, then added to 0.5mol / L hydrochloric acid and stirred and washed for 1h. After filtration, it was placed in an oven at 60℃ and dried for 10h. The obtained product was ground and sieved, mixed with 3.5g of asphalt, and placed in a tube furnace. Under argon protection, the temperature was raised to 900℃ at a heating rate of 3℃ / min and held for 3h to carry out the carbon layer repair reaction. After natural cooling, it was taken out to obtain magnesium-tin doped silicon-carbon anode material.

[0049] Example 3

[0050] Preparation of SiO x Material:

[0051] 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 of 1-5 mm, and 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, and then cool the apparatus until the temperature drops to 850℃. Remove the product to obtain SiO2. x (0<x≤2) material.

[0052] Preparation of magnesium-tin-doped silicon-carbon anode materials:

[0053] S1, Take 100g of SiO x The material was placed in a tube furnace and heated to 700℃ under argon protection. Acetylene was introduced into the tube furnace at a rate of 10 mL / min, and the temperature was maintained for 5 hours to obtain SiO2. x / C composite material, the carbon content of which is 10% and the average particle size D50 is 8.8μm;

[0054] S2, Take 50g of the SiO2 obtained in S1 x The / C composite material was mixed with 6g of 240-mesh magnesium powder and 7.5g of 240-mesh tin powder, and then placed in a tube furnace. Under argon protection, the temperature was increased to 500℃ at a heating rate of 3℃ / min and held for 4 hours to carry out a low-temperature magnesothermic reaction. After natural cooling, the product was removed to obtain magnesium-tin doped SiO₂.x / C composite materials;

[0055] S3, Take the magnesium-tin doped SiO2 obtained in S2 x 50g of the / C composite material was first added to distilled water and stirred and washed for 1h, then added to hydrochloric acid with a concentration of 1mol / L and stirred and washed for 0.5h. After filtration, it was placed in an oven at 100℃ and dried for 8h. The obtained product was ground and sieved, mixed with 5g of asphalt, and placed in a tube furnace. Under argon protection, the temperature was raised to 900℃ at a heating rate of 3℃ / min and held for 3h to carry out the carbon layer repair reaction. After natural cooling, it was taken out to obtain magnesium-tin doped silicon-carbon anode material.

[0056] The magnesium-tin doped silicon-carbon anode materials prepared in Examples 1 to 3 above were characterized and tested respectively. The specific results are shown in Table 2.

[0057] Table 2. Characterization test results of the examples

[0058]

[0059] The XRD test results of Examples 1-3 are shown in [the original text]. Figure 2 .like Figure 2 As shown, the peak shapes in Examples 1-3 are the same. 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 deposit is relatively small, resulting in low volume expansion.

[0060] The pre-magnesium silicon suboxide material of Comparative Example 1 and the magnesium-tin doped silicon-carbon anode materials of Examples 1-3 were taken separately and thoroughly mixed at a mass ratio of material:conductive agent:binder of 8:1:1. A slurry was prepared using deionized water as the solvent, and after complete dispersion, it was coated with an 8μm copper foil. The mixture was then vacuum dried at 50°C for 12 hours and cut into 14mm diameter discs to obtain the anode material. After drying, the discs were sliced ​​and packaged with lithium sheets to form a button cell. The first-week charge-discharge test was conducted at 0.05C.

[0061] Its charge / discharge capacity and initial efficiency are shown in Table 3. The charge / discharge curves of Examples 1-3 are shown in Table 3. Figure 3 As shown.

[0062] Table 3. Electrochemical performance test results of materials

[0063]

[0064]

[0065] Expansion test: 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 measurement. The electrode sheet thickness before and after the first week of charge-discharge is detailed in Table 4.

[0066] Table 4. Expansion Test Results

[0067]

[0068] As shown in Table 4, the expansion rate of the negative electrode sheets prepared in Examples 1 to 3 after the first week of charge and discharge is significantly improved compared with the comparative examples.

[0069] From Table 3, Table 4 and Figure 3 It can be seen that the pre-magnesium silicate materials prepared in Examples 1 to 3 have the advantages of low expansion, high initial efficiency, and high capacity.

[0070] In summary, this invention discloses a method for preparing magnesium-tin-doped silicon-carbon anode materials via magnesothermal reduction. The method involves first preparing SiOx (0 < x ≤ 2) through a high-temperature solid-state reaction, then coating it with a carbon source. Following this, a certain amount of metallic magnesium and metallic tin are mixed and reacted at a low temperature, followed by natural cooling. After acid washing to remove impurities, the surface is modified to obtain a relatively pure magnesium-tin-doped SiOx / C composite material. The low-temperature magnesothermal reaction significantly reduces the increase in silicon crystal size. Simultaneously, the incorporation of tin allows for the formation of a liquid alloy with magnesium at low temperatures. Magnesium dispersed atomically in the liquid alloy exhibits higher reactivity than solid magnesium particles, thus enabling the magnesothermal reduction reaction at a lower temperature. Furthermore, metallic tin itself can serve as a lithium-ion battery anode material, possessing a high theoretical specific capacity (990 mAh / g) and excellent conductivity. The magnesium-tin-doped silicon-carbon anode material prepared by this method exhibits high initial efficiency, excellent conductivity, and stable cycle rate performance.

Claims

1. A method for preparing a magnesium-tin-doped silicon-carbon anode material, characterized in that, Includes the following steps: S1, for SiO x The material is carbon-coated to obtain SiO2. x / C composite material, where 0<x≤2; S2, the SiO x The / C composite material is mixed with metallic magnesium and metallic tin, and then heated to 400–450°C in an inert atmosphere and held for 3–5 hours to carry out a low-temperature magnesothermic reaction, yielding magnesium-tin doped SiO₂. x / C composite materials; S3, doping the magnesium-tin SiO x The / C composite material is washed with water, acid-washed, and then dried. The resulting product is mixed with a carbon source and heated to 800-900℃ in an inert atmosphere. The mixture is kept at this temperature for 3-4 hours to carry out the carbon layer repair reaction. After cooling, magnesium-tin doped silicon-carbon anode material is obtained.

2. The method for preparing magnesium-tin-doped silicon-carbon anode material according to claim 1, characterized in that, In S1, the SiO x The mass of carbon in the / C composite material is SiO₂ x 2% to 10% of the mass; in S1, carbon coating is performed using either liquid phase coating or gas phase coating.

3. The method for preparing magnesium-tin-doped silicon-carbon anode material according to claim 1, characterized in that, In S2, SiO x The mass ratio of the C composite material, magnesium, and tin is (1-6):0.5:(0.5-2.5).

4. The method for preparing magnesium-tin-doped silicon-carbon anode material according to claim 1, characterized in that, In S2, SiO x The average particle size D50 of the / C composite material is 1-10 μm, the particle size of magnesium is 200-240 mesh, and the particle size of tin is 200-240 mesh.

5. The method for preparing magnesium-tin-doped silicon-carbon anode material according to claim 1, characterized in that, In S3, the carbon source has a mass of magnesium-tin-doped SiO2. x / C composite material mass of 2% to 10%.

6. The method for preparing magnesium-tin-doped silicon-carbon anode material according to claim 1, characterized in that, In S3, hydrochloric acid with a concentration of 0.05–1 mol / L is used for acid washing.

7. The method for preparing magnesium-tin-doped silicon-carbon anode material according to claim 1, characterized in that, In S3, the carbon source is at least one of asphalt, polyvinyl alcohol, and glucose.

8. A magnesium-tin-doped silicon-carbon anode material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

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