A magnesium-doped tin dioxide composite material, a preparation method and application thereof

Abstract

The application provides a magnesium-doped tin dioxide composite material and a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The magnesium-doped tin dioxide composite material is obtained by adopting a sol-gel method to perform carbon-coating treatment on tin by using a carbon source and then performing a hydrothermal reaction with magnesium. The magnesium-doped tin dioxide composite material realizes a synergistic lithium storage effect of magnesium and tin elements in the charging and discharging process by introducing the second-phase magnesium element. On the one hand, the volume expansion of the tin-based negative electrode material can be effectively relieved, powder agglomeration can be inhibited, and the material structure can be stabilized; on the other hand, the effect of providing electrochemical active sites can be achieved, the electrochemical performance of the negative electrode material can be further improved, and more possible ideas for the wide application of the tin-based negative electrode material are provided.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a magnesium-doped tin dioxide composite material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, as an important new energy device, have advantages over lead-acid, nickel-cadmium, and nickel-metal hydride batteries, including higher energy density and longer cycle life.

[0003] With advantages such as high open-circuit voltage, low self-discharge, and no memory effect, it currently occupies the main market for power batteries in consumer electronics products.

[0004] Currently, the theoretical specific capacity of commercially available graphite anodes is 372 mAh / g; tin dioxide, due to its high theoretical specific capacity (theoretically 790 mAh / g),... -1 Tin dioxide (TI) is considered a promising anode material for lithium-ion batteries due to its low toxicity, low cost, and wide availability. However, the significant volume expansion of tin after lithium insertion and extraction, coupled with repeated lithium deintercalation, leads to gradual tin pulverization, resulting in poor electrical contact with the current collector and shortening the cycle life of lithium-ion batteries. To improve the electrochemical performance of tin dioxide anode materials, research has focused on material nanostructuring, coating treatment, mesoporous or microporous tin embedding, and the preparation of tin alloys by doping elements. The aim is to suppress its volume expansion and pulverization, improve conductivity, and ultimately enhance the electrochemical activity and stability of tin dioxide anode materials. Among these methods, nanostructuring tin-based materials can effectively accommodate volume expansion, but agglomeration may occur after a certain number of cycles; carbon coating of tin-based materials can improve conductivity, but may reduce the specific capacity; mesoporous or microporous tin embedding can provide more active sites, but may reduce the initial coulombic efficiency; appropriate cation doping can further improve electronic conductivity, ion permeability of the carbon layer, charge transfer at the interface, and the stability of the solid-electrolyte interface film. However, tin-based materials doped with cations suffer from the same problem as metallic tin anodes after a certain number of electrode reactions, mainly the agglomeration and fragmentation of nano-tin, which leads to electrode failure. Summary of the Invention

[0005] The purpose of this invention is to provide a magnesium-doped tin dioxide composite material, its preparation method and application, to alleviate the volume expansion of tin-based anode materials, inhibit powder agglomeration, and improve the electrochemical performance of tin-based anode materials.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a magnesium-doped tin dioxide composite material, comprising the following steps:

[0008] A tin salt, a water-soluble carbon source, and water are mixed to obtain a tin-carbon mixed solution.

[0009] The tin-carbon mixed solution is mixed with a magnesium salt aqueous solution, and the resulting tin-magnesium mixed solution is subjected to a hydrothermal reaction to obtain a magnesium-doped tin dioxide composite material.

[0010] Preferably, the tin salt includes stannous chloride; the water-soluble carbon source includes fructose, glucose, or sucrose.

[0011] Preferably, the molar ratio of the tin salt to the water-soluble carbon source is 1:0.05 to 0.08.

[0012] Preferably, the total concentration of metal ions in the tin-carbon mixed solution is 1–2 mol / L.

[0013] Preferably, the concentration of the magnesium salt aqueous solution is 0.03–0.1 mol / L; the molar ratio of magnesium salt in the tin salt and magnesium salt aqueous solutions is 1:0.03–0.1.

[0014] Preferably, the total concentration of metal ions in the tin-magnesium mixed solution is 1-2 mol / L.

[0015] Preferably, the tin-carbon mixed solution is mixed with the magnesium salt aqueous solution at a temperature of 40–60°C for a time of 0.5–1 h.

[0016] Preferably, the hydrothermal reaction is carried out at a temperature of 160–180°C for 18–24 hours.

[0017] The present invention provides a magnesium-doped tin dioxide composite material prepared by the preparation method described in the above technical solution.

[0018] This invention provides the application of the magnesium-doped tin dioxide composite material described above in lithium-ion batteries.

[0019] This invention employs a sol-gel method, where raw materials are uniformly mixed in the liquid phase. During the hydrothermal reaction, the tin source undergoes hydrolysis and oxidation to generate SnO2. Simultaneously, magnesium is doped into the SnO2 lattice, forming a three-dimensional network structure gel. This invention introduces a second phase of magnesium into tin dioxide, achieving a synergistic lithium storage effect between magnesium and tin during charge and discharge. On one hand, magnesium doping enables material nanostructuring, and the fine powder effectively alleviates the volume expansion of tin-based anode materials, inhibits powder agglomeration, and stabilizes the material structure. On the other hand, magnesium doping can cause more lattice distortion in the tin dioxide lattice, resulting in smaller grain sizes and exposing more electrochemical active sites, which can further improve the electrochemical performance of the anode material and provide more possible ideas for the wider application of tin-based anode materials. Moreover, the smaller grain size allows for a deeper degree of nano-scale material powdering. The finer nano-sized particles not only shorten the lithium-ion transport path, but also remain relatively small in size after the volume expansion during the electrode reaction. The secondary particles can basically maintain the structure and morphology before the charge-discharge reaction. In addition, magnesium can combine with the amorphous lithium oxide produced in the electrode reaction, allowing some lithium ions that would otherwise not participate in the reaction to return to the electrode reaction.

[0020] Furthermore, this invention employs a carbon source to encapsulate tin with carbon. After carbonization, the carbon source exists as amorphous carbon, which can provide a conductive network for the material, thereby further improving the electrochemical performance of the material.

[0021] The preparation method of this invention is simple and easy to operate. It synthesizes magnesium-doped tin dioxide composite material with uniform particles through a simple wet chemical method, avoiding the cumbersome parameter control process in the traditional ball milling doping process. At the same time, it avoids the use of organic and toxic reagents such as coprecipitants, and has the advantages of being green, environmentally friendly and easy to implement. Attached Figure Description

[0022] Figure 1 The image shows the SEM characterization of the Mg-3 anode material in Example 1.

[0023] Figure 2 The image shows the SEM characterization of the Mg-5 anode material in Example 2.

[0024] Figure 3 The image shows the SEM characterization of the Mg-10 anode material in Example 3.

[0025] Figure 4 The image shows the SEM characterization of the Mg-0 anode material in Comparative Example 1.

[0026] Figure 5 XRD characterization diagrams (a) and diffraction peaks (b) of four groups of negative electrode materials, namely Mg-3, Mg-5, Mg-10 and Mg-0;

[0027] Figure 6 The graphs show the cycle performance curves of four groups of negative electrode materials: Mg-3, Mg-5, Mg-10, and Mg-0.

[0028] Figure 7 This is a SEM image of the Mg-3 anode material in Example 1 after 100 cycles;

[0029] Figure 8 The image shows the SEM characterization of the Mg-0 anode material in Comparative Example 1 after 100 cycles.

[0030] Figure 9 The images show TEM characterizations of the four negative electrode materials in Examples 1-3 (Mg-3, Mg-5, Mg-10) and Comparative Example 1 (Mg-0). Detailed Implementation

[0031] This invention provides a method for preparing a magnesium-doped tin dioxide composite material, comprising the following steps:

[0032] A tin salt, a water-soluble carbon source, and water are mixed to obtain a tin-carbon mixed solution.

[0033] The tin-carbon mixed solution is mixed with a magnesium salt aqueous solution, and the resulting tin-magnesium mixed solution is subjected to a hydrothermal reaction to obtain a magnesium-doped tin dioxide composite material.

[0034] In this invention, unless otherwise specified, all raw materials required for preparation are commercially available products well known to those skilled in the art.

[0035] This invention involves mixing tin salt, a water-soluble carbon source, and water to obtain a tin-carbon mixed solution.

[0036] In this invention, the tin salt preferably includes stannous chloride, more preferably stannous chloride dihydrate; the stannous chloride used in this invention is hydrolyzed and oxidized to tin dioxide upon contact with oxygen, exhibiting a gel-like characteristic during the hydrolysis and oxidation process, thereby realizing the preparation of magnesium-doped tin dioxide composite materials by sol-gel method, which is simpler to operate than ball milling or sintering methods.

[0037] In this invention, the water-soluble carbon source preferably includes fructose, glucose or sucrose.

[0038] In this invention, the molar ratio of the tin salt to the water-soluble carbon source is preferably 1:0.05 to 0.08, more preferably 1:0.06 to 0.08.

[0039] In this invention, the total concentration of metal ions in the tin-carbon mixed solution is preferably 1 to 2 mol / L, more preferably 1.2 to 1.4 mol / L.

[0040] After obtaining the tin-carbon mixed solution, the present invention mixes the tin-carbon mixed solution with a magnesium salt aqueous solution, and performs a hydrothermal reaction on the resulting tin-magnesium mixed solution to obtain a magnesium-doped tin dioxide composite material.

[0041] In this invention, the magnesium salt in the magnesium salt aqueous solution is preferably magnesium chloride; the molar ratio of the magnesium salt in the tin salt and magnesium salt aqueous solution is preferably 1:0.03-0.1, more preferably 1:0.05-0.1; the concentration of the magnesium salt aqueous solution is preferably 0.03-0.1 mol / L, more preferably 0.05-0.08 mol / L.

[0042] In this invention, the total concentration of metal ions in the tin-magnesium mixed solution is preferably 1-2 mol / L, more preferably 1.02-1.05 mol / L.

[0043] In this invention, the mixing temperature of the tin-carbon mixed solution and the magnesium salt aqueous solution is preferably 40-60°C, more preferably 50°C, and the mixing time is preferably 0.5-1h, more preferably 0.75h; the stirring speed of the mixing is preferably 400-600r / min, and more preferably 500r / min.

[0044] In this invention, the hydrothermal reaction temperature is preferably 160–180°C, more preferably 165–170°C, and the reaction time is preferably 18–24 h, further preferably 19–23 h, and even more preferably 20–22 h. The relatively low hydrothermal temperature used in this invention allows the carbon source to exist in the form of amorphous carbon.

[0045] During the hydrothermal reaction, stannous chloride hydrolyzes to generate basic stannous chloride (SnCl2+H2O=Sn(OH)Cl+HCl). This component is easily oxidized after combining with oxygen to generate SnO2. In this invention, magnesium is doped during the hydrothermal process, so that the magnesium element is embedded in the lattice of the oxidation product SnO2 to form a magnesium-doped tin dioxide composite material.

[0046] After the hydrothermal reaction is completed, the present invention preferably performs sequential filtration, washing, drying, pulverizing, grinding and sieving of the obtained product system to obtain magnesium-doped tin dioxide composite material.

[0047] In this invention, the washing preferably includes sequential washing with an ethanol solution and washing with water. The mass fraction of the ethanol solution is preferably 72-78%, more preferably 73-77%, and even more preferably 75-76%. The number of times the ethanol solution is washed is preferably ≥2 times, more preferably ≥3 times, and even more preferably ≥4 times. The number of times the water is washed is preferably ≥2 times, more preferably ≥3 times, and even more preferably ≥4 times.

[0048] In this invention, the drying temperature is preferably 85-95°C, more preferably 90°C; the drying time is preferably 10-14 hours, more preferably 11-13 hours, and more preferably 12 hours.

[0049] In this invention, the mesh size of the sieve is preferably 300-500 mesh, more preferably 350-450 mesh, and even more preferably 400 mesh.

[0050] The present invention provides a magnesium-doped tin dioxide composite material prepared by the preparation method described in the above technical solution.

[0051] This invention provides the application of the magnesium-doped tin dioxide composite material described above in lithium-ion batteries. The method for this application is not particularly limited; any method well-known in the art can be used.

[0052] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0053] Example 1

[0054] Stannous chloride, fructose, and water were mixed to obtain a tin-carbon mixed solution, wherein the molar ratio of stannous chloride to fructose was 1:0.05, and the total concentration of metal ions in the tin-carbon mixed solution was 1 mol / L.

[0055] A tin-carbon mixed solution was mixed with a 0.03 mol / L magnesium chloride aqueous solution at a temperature of 40℃, a mixing speed of 400 r / min, and a mixing time of 0.5 h. The molar ratio of tin salt to magnesium salt was 1:0.03, resulting in a total metal ion concentration of 1.02 mol / L in the tin-magnesium mixed solution. After mixing, a hydrothermal reaction was carried out at 160℃ for 18 h. After the reaction, the resulting system was filtered, washed three times with a 75% ethanol solution, then washed three times with deionized water, and finally dried at 85℃ for 12 h. The resulting material was then pulverized, ground, and passed through a 400-mesh sieve to obtain a magnesium-doped tin dioxide composite material (labeled as Mg-3 anode material).

[0056] Example 2

[0057] Stannous chloride, fructose, and water were mixed to obtain a tin-carbon mixed solution, wherein the molar ratio of stannous chloride to fructose was 1:0.06, and the total concentration of metal ions in the tin-carbon mixed solution was 1.2 mol / L.

[0058] A tin chloride-carbon mixed solution was mixed with a 0.05 mol / L magnesium chloride aqueous solution at a temperature of 50°C, a mixing speed of 500 r / min, and a mixing time of 0.75 h. The molar ratio of tin salt to magnesium salt was 1:0.05. The total concentration of metal ions in the resulting tin-magnesium mixed solution was 1.03 mol / L. After mixing, a hydrothermal reaction was carried out at 170°C for 20 h. After the reaction, the resulting system was filtered, washed three times with a 75% ethanol solution, then washed three times with deionized water, and finally dried at 90°C for 12 h. The resulting material was then pulverized, ground, and passed through a 400-mesh sieve to obtain a magnesium-doped tin dioxide composite material (labeled as Mg-5 anode material).

[0059] Example 3

[0060] Stannous chloride, fructose, and water were mixed to obtain a tin-carbon mixed solution, wherein the molar ratio of stannous chloride to fructose was 1:0.08, and the total concentration of metal ions in the tin-carbon mixed solution was 1.4 mol / L.

[0061] A tin-carbon mixed solution was mixed with a 0.1 mol / L magnesium chloride aqueous solution at a temperature of 60°C, a mixing speed of 600 r / min, and a mixing time of 1 h. The molar ratio of tin salt to magnesium salt was 1:0.1. The total concentration of metal ions in the resulting tin-magnesium mixed solution was 1.05 mol / L. After mixing, a hydrothermal reaction was carried out at 180°C for 22 h. After the reaction, the resulting system was filtered, washed three times with a 75% ethanol solution, then washed three times with deionized water, and finally dried at 95°C for 12 h. The resulting product was then pulverized, ground, and passed through a 400-mesh sieve to obtain a magnesium-doped tin dioxide composite material (labeled as Mg-10 composite material).

[0062] Comparative Example 1

[0063] The only difference from Example 1 is that magnesium chloride aqueous solution is not added for mixing, and the tin dioxide particles prepared in Comparative Example 1 are used as the negative electrode material (labeled as Mg-0 negative electrode material).

[0064] Characterization and performance testing

[0065] 1) Figure 1 Here is a SEM characterization image of the Mg-3 anode material in Example 1; from Figure 1 It can be seen that the Mg-3 anode material has uniform particles and no surface defects.

[0066] 2) Figure 2 Here are the SEM characterization images of the Mg-5 anode material in Example 2; from Figure 2 It can be seen that the Mg-5 anode material has no surface defects, but agglomeration of fine particles can be observed.

[0067] 3) Figure 3 Here are the SEM characterization images of the Mg-10 anode material in Example 3; from Figure 3 It can be seen that the Mg-10 anode material has no surface defects, but the fine particles are agglomerated.

[0068] 4) Figure 4 Here are the SEM characterization images of the Mg-0 anode material in Comparative Example 1; from Figure 4 It can be seen that the surface of the Mg-0 anode material is rough and uneven, and surface defects can be clearly observed.

[0069] 5) Figure 5 (a) shows the XRD characterization diagrams (2-Theta (degree)-2θ (°), Intensity (au)-strength (au)) of four groups of negative electrode materials: Mg-0, Mg-3, Mg-5, and Mg-10. Figure 5 As shown in (a), no other impurity peaks appeared in any of the four groups of samples, which means that magnesium ions were successfully embedded into the SnO2 lattice and no diffraction peaks of MgCl2 in the raw material were observed. Figure 5 (b) shows the diffraction peaks of four groups of samples (Mg-0, Mg-3, Mg-5, and Mg-10) on the (110) crystal plane. Figure 5 As shown in (b), with the gradual increase of Mg ion doping in the four groups of samples (Mg-0, Mg-3, Mg-5, and Mg-10), the diffraction peaks broaden overall, the peak intensity decreases, and the peak plane shifts to the right. This indicates that the average particle size of SnO2 decreases accordingly. Furthermore, besides replacing a portion of Sn... 4+ In addition, Mg 2+ Doping can also create new dislocation vacancies, further increasing the surface diffusion barrier and limiting grain growth. As a result, the comparative sample with a higher doping level has smaller grains.

[0070] 6) The negative electrode materials prepared in Examples 1-3 and the Mg-O negative electrode material prepared in Comparative Example 1 were assembled into a battery. Cycle performance tests were conducted by charging and discharging within a voltage window of 0.05–3V. The results are shown in [Figure 1]. Figure 6 (Cycle number, Specific capacity (mAh / g), Columbic efficiency (%)) Figure 6As can be seen, the battery obtained with the Mg-3 anode material prepared in Example 1 has an initial discharge specific capacity of 975.2 mAh / g at 0.1C, and maintains a specific capacity of 476.6 mAh / g after 100 cycles; the battery obtained with the Mg-5 anode material prepared in Example 2 has an initial discharge specific capacity of 979.0 mAh / g at 0.1C, and maintains a specific capacity of 334.1 mAh / g after 100 cycles; the battery obtained with the Mg-10 anode material prepared in Example 3 has an initial discharge specific capacity of 1094.8 mAh / g at 0.1C, and maintains a specific capacity of 388.4 mAh / g after 100 cycles; the battery obtained with the Mg-0 anode material prepared in Comparative Example 1 has an initial discharge specific capacity of 1035.8 mAh / g at 0.1C, and maintains a specific capacity of 159.1 mAh / g after 100 cycles.

[0071] 7) The Mg-3 anode material prepared in Example 1 was cycled for 100 cycles under the conditions described in 6) above, and then characterized by SEM. The results are shown in [Figure 1]. Figure 7 ,Depend on Figure 7 It can be seen that the Mg-3 anode material has a stable structure and has not experienced structural breakage or excessive volume expansion.

[0072] The Mg-0 anode material prepared in Comparative Example 1 was cycled for 100 cycles under the conditions described in 6) above, and then characterized by SEM. The results are shown in [Figure 1]. Figure 8 ;Depend on Figure 8 It can be seen that the Mg-0 anode material not only underwent powder breakage, but the broken small particles also agglomerated together.

[0073] 8) The anode materials prepared in Examples 1-3 and the Mg-O anode material prepared in Comparative Example 1 were characterized by TEM. The results are shown in the figure. Figure 9 (Where (a) represents Mg-0, (b) represents Mg-3, (c) represents Mg-5, and (d) represents Mg-10), from Figure 9 It can be seen that as the doping amount gradually increases, the crystal grain size of the four groups of samples (Mg-0, Mg-3, Mg-5, and Mg-10) gradually decreases, and carbon layers can be observed in all four groups of samples.

[0074] As can be seen from the above embodiments, by introducing a second-phase magnesium element, this invention achieves a synergistic lithium storage effect between magnesium and tin elements during charge and discharge. On the one hand, it can effectively alleviate the volume expansion of tin-based anode materials, inhibit powder agglomeration, and stabilize the material structure. On the other hand, it also provides electrochemical active sites, which can further improve the electrochemical performance of the anode material. The presence of fructose can also provide a conductive network for the material. The preparation method of this invention is simple and easy to operate, avoiding the cumbersome parameter control process of traditional doping processes, and avoiding the use of organic and toxic reagents such as co-precipitants. It has the advantages of being green, environmentally friendly, and easy to implement.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle 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 method for preparing a magnesium-doped tin dioxide composite material for lithium-ion batteries, characterized in that, Includes the following steps: A tin salt, a water-soluble carbon source, and water are mixed to obtain a tin-carbon mixed solution. The tin-carbon mixed solution is mixed with a magnesium salt aqueous solution, and the resulting tin-magnesium mixed solution is subjected to a hydrothermal reaction to obtain a magnesium-doped tin dioxide composite material. The tin salt includes stannous chloride; The molar ratio of the tin salt to the water-soluble carbon source is 1:0.05~0.08; The molar ratio of magnesium salt in the aqueous solution of tin salt and magnesium salt is 1:0.03~0.1; The hydrothermal reaction is carried out at a temperature of 160-180℃ for 18-24 hours.

2. The preparation method according to claim 1, characterized in that, The water-soluble carbon source includes fructose, glucose, or sucrose.

3. The preparation method according to claim 1 or 2, characterized in that, The total concentration of metal ions in the tin-carbon mixed solution is 1~2 mol / L.

4. The preparation method according to claim 1, characterized in that, The concentration of the magnesium salt aqueous solution is 0.03~0.1 mol / L.

5. The preparation method according to claim 1, characterized in that, The total concentration of metal ions in the tin-magnesium mixed solution is 1~2 mol / L.

6. The preparation method according to claim 1 or 5, characterized in that, The tin-carbon mixed solution is mixed with the magnesium salt aqueous solution at a temperature of 40~60℃ for a time of 0.5~1h.

7. The magnesium-doped tin dioxide composite material prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the magnesium-doped tin dioxide composite material of claim 7 in lithium-ion batteries.

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