CN112794360B - A method for preparing nanometer SnO2/GC composite negative electrode material - Google Patents

Abstract

The invention relates to a method for preparing nano SnO ₂ The method for preparing the/GC composite anode material is characterized by comprising the following steps of: a) Dropwise adding the gelatin solution into the tin salt solution and uniformly stirring, then dropwise adding the ammonia water solution until a viscous white solid is generated, and stopping stirring; b) Drying at constant temperature of 80 +/-2 ℃, transferring to a tubular furnace for carbonization heat treatment to prepare a target product SnO ₂ a/GC composite material. The advantages are that: preparation of nano SnO by using gelatin and tin salt as raw materials ₂ the/GC composite negative electrode material reduces the production cost, simplifies the production process, obtains better cycle stability and rate capability, and is suitable for industrial production.

Description

A method for preparing nanometer SnO2/GC composite negative electrode material

technical field

The invention belongs to the field of lithium ion battery manufacture, and relates to a method for preparing nano SnO ₂ /GC (gelatin carbon) composite negative electrode material.

Background technique

With the improvement of people's awareness of environmental protection, renewable energy is gradually replacing traditional fossil energy. As an important energy storage device, lithium-ion batteries have the advantages of high energy density and power density, high voltage, and low cost, which greatly improves the universality of lithium-ion battery energy storage devices, and is widely used in portable electronic devices, wearable Flexible equipment, electric vehicles and energy storage grids and other fields. At present, graphite is still the most widely used anode material, but its relatively low theoretical lithium intercalation capacity (372mAh/g) and poor rate performance limit its application in commercial energy storage systems. Therefore, to improve the capacity, cycle life, and cycle stability of Li-ion batteries, it is crucial to develop new anode materials.

Due to its high theoretical specific capacity (1492mAh/g), appropriate lithium intercalation voltage platform, abundant reserves and low price, SnO ₂ can be used as an anode material for lithium-ion batteries instead of graphite. However, SnO ₂ itself undergoes a huge volume change during charge and discharge, which can cause lattice collapse material pulverization, and its conductivity is poor, which eventually leads to poor cycle performance and rate performance. In addition, when pure nano-SnO ₂ is used as the electrode material, due to the small particle size and large specific surface area, the material is easy to agglomerate into larger secondary particles, which greatly affects the electrochemical performance of the material. In order to solve this problem, many researchers prepared SnO ₂ with different nanostructures, and improved the electrochemical performance of SnO ₂ by reducing the crystal size of SnO ₂ and adjusting the framework structure. For example, Liu et al. used NaF as a morphology control agent to synthesize _SnO2 nanoparticle-shelled hollow spheres with oriented cone-like structures by a one-step hydrothermal method, which were used as anode materials and cycled 100 times at a current density of 0.1 A/g. There is still a reversible capacity of 758mAh/g. Wang et al. prepared porous microspheres self-assembled from octahedral nano-SnO ₂ structure by one-step hydrothermal reaction without surfactant, and still had a reversible capacity of 690mAh/g after 50 cycles at a current density of 0.5A/g. Although these nano-SnO ₂ with unique morphology can slow down the decline in capacity, the simple nanonization and morphology design cannot fundamentally solve the huge volume change of SnO ₂ during cycling. The mechanical stress brought about by the volume change is gradually enhanced, which eventually leads to the collapse of the structure of _SnO2 and the deterioration of its electrochemical performance. In response to this phenomenon, researchers use carbon materials with good electrical conductivity and mechanical properties, which can not only be used as the supporting framework of the negative electrode structure, but also avoid stress extrusion from destroying the integrity of the electrode structure. The transfer rate can effectively improve the electrochemical performance of SnO ₂ , so it was proposed to combine SnO ₂ with carbon materials to prepare SnO ₂ /carbon composite materials. Courtel et al. used graphite carbon as a carbon source and synthesized it using in-situ polyol microwave-assisted technology. The nano-SnO ₂ /C composite material still has a capacity of 370mAh/g after 100 cycles at a current density of 0.2A/g. This SnO ₂ -carbon composite method does improve the capacity and cycle stability of SnO ₂ as the negative electrode material of lithium-ion batteries, but there is still a tendency of capacity decline in the long-term cycle process, and due to the complex and cumbersome synthesis technology, it is difficult to Practical application in industrial production. In order to ensure the industrial production of SnO ₂ /carbon composite anode materials in Li-ion batteries, it is necessary to insist on improving the electrochemical performance of SnO ₂ at the same time of low cost and high efficiency. Therefore, there is an urgent need for a method for preparing SnO ₂ /C composite materials with low cost and simple operation.

Contents of the invention

In order to overcome the deficiencies of the prior art, the object of the present invention is to provide a method for preparing nanometer SnO ₂ /GC composite negative electrode material, which reduces production cost, simplifies the process, and improves the cycle stability and rate performance of the lithium ion battery negative electrode material.

To achieve the above object, the present invention is achieved through the following technical solutions:

A method for preparing nanometer SnO ₂ /GC composite negative electrode material, characterized in that it comprises the following steps:

a) adding the gelatin solution dropwise to the tin salt solution and stirring evenly, then adding the ammonia solution dropwise until a viscous white solid is formed and then stopping the stirring;

b) Dry at a constant temperature of 80±2°C, transfer to a tube furnace for carbonization heat treatment, and obtain the target product SnO ₂ /GC composite material.

According to step a) and step b), different volumes of gelatin solution are added to the tin salt solution, and different SnO ₂ /GC composite materials are obtained by adjusting the mass ratio of tin salt and gelatin in the precursor composite material.

The precipitating agent is ammonia solution.

Compared with prior art, the beneficial effect of the present invention is:

The invention adopts gelatin and tin salt as raw materials to prepare nano SnO ₂ /GC composite negative electrode material, reduces production cost, simplifies production process, obtains better cycle stability and rate performance, and makes it suitable for industrial production. Gelatin is a linear polypeptide compound composed of 18 kinds of amino acids, which has the characteristics of low price, good biocompatibility, and easy commercialization, and there is a strong physical and chemical interaction between gelatin and most compounds, and the synthetic material has good flexibility and mechanical properties. The present invention adopts the sol-gel method that can be scaled up in the laboratory to prepare the composite material. The process is simple and the operation is convenient. The prepared composite material with a small amount of mesoporous nano SnO ₂ /gelatin carbon has good cycle stability and rate performance , greatly improving the electrochemical performance of the material, and this Sol-Gel method of coating with gelatin as a carbon source is also applicable to other metal oxides.

Description of drawings

Fig. 1 is the process flow chart of embodiment one.

Fig. 2 is the XRD pattern of GC (gelatin carbon), SnO ₂ and SnO ₂ /GC (gelatin carbon) composite materials with different mass ratios.

(a)-(c) in Figure 3 are the TG/DTG diagrams of SnO ₂ /GC-15, SnO ₂ /GC-40 and SnO ₂ /GC-90 composite materials respectively; (d) in Figure 3 is the SnO ₂ / Summary plot of TG of GC-15, SnO ₂ /GC-40 and SnO ₂ /GC-90 composites.

(a) and (b) in Fig. 4 are SEM images of nano-SnO ₂ particles; (c) and (d) in Fig. 4 are SEM images of SnO ₂ /GC-40 composite material.

(a) in Figure 5 is the SEM image of the SnO ₂ /GC-40 composite material; (b)-(f) in Figure 5 is the EDS scan of the C, N, O, Sn elements of the SnO ₂ /GC-40 composite material and its semi-quantitative analysis of surface elements.

In Fig. 6 (a) is the XPS full spectrum of SnO ₂ /GC-40 composite material; (b) is the XPS fine spectrum of C1s; (c) is the XPS fine spectrum of Sn3d; (d) is the XPS fine spectrum of N1s ( SnO ₂ /GC-40).

Fig. 7 is the pore size distribution curve of SnO ₂ /GC-15, SnO ₂ /GC-40 and SnO ₂ /GC-90 composite material calculated by BJH method; among Fig. 7 (a) is the overall curve; among Fig. 7 (b ) is a local graph.

Figure 8(a) is the cycle capacity graph of SnO ₂ , GC, SnO ₂ /GC-15, SnO ₂ /GC-40 and SnO ₂ /GC-90 composites at a current density of 0.1A/g; SnO ₂ , SnO 2 /GC-15, SnO ₂ /GC-40 and SnO ₂ at 0.1A/g, 0.2A/g, 0.5A/g, 1A/g, _2A /g and 0.1A/g current densities The rate diagram of the SnO 2 /GC-90 composite, (c) is the long cycle capacity diagram of the SnO ₂ /GC-40 composite at a current density of 0.1A/g.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings, but it should be pointed out that the implementation of the present invention is not limited to the following embodiments.

A method for preparing nanometer SnO ₂ /GC composite negative electrode material comprises the following steps:

1. Preparation of _SnO2 Nanospheres

a, dropwise adding a precipitating agent to the pH=6 of the solution in the tin salt solution, obtain a milky white precipitate, and repeatedly centrifuge and wash to obtain the solid powder of the precursor of SnO ₂ ;

b After drying, carbonize in an air atmosphere at 500°C for 3 hours, collect samples after cooling and seal them for storage;

2. Preparation of SnO ₂ /GC composites

a. Add the gelatin solution dropwise to the tin salt solution and stir evenly, then add the ammonia solution dropwise until the viscous white solid is formed and then stop stirring;

b Dry at a constant temperature of 80±2°C, transfer to a tube furnace for carbonization heat treatment, and obtain the target product SnO ₂ /GC composite material.

c According to step a and step b, add different volumes of gelatin solution to the tin salt solution respectively, and obtain different SnO ₂ /GC composite materials by adjusting the mass ratio of tin salt and gelatin in the precursor composite material.

Embodiment one

(1) Preparation of _SnO2 nanospheres

Dissolve 10mmol SnCl ₄ ·5H ₂ O (0.3506g) in 40mL deionized water to obtain solution A, then add 4mol/L ammonia solution dropwise while stirring until the pH of the solution reaches about 6, and continue stirring for 1 hour to obtain a milky white precipitate. The SnO ₂ nanoparticles were obtained by centrifuging three times with deionized water and absolute ethanol, respectively. After drying at 80°C for 12h, carbonize in an air atmosphere at 500°C for 3h, collect _SnO2 nanoparticles and seal them for storage after cooling.

(2) Preparation of SnO ₂ /GC composites

Dissolve 10 g of gelatin in 100 ml of deionized water, stir magnetically for 1 hour to fully swell the gelatin particles, then transfer to a water bath, and stir magnetically at 80°C to obtain light yellow gelatin solution B. Then 10mmol SnCl ₄ 5H ₂ O (0.3506g) was dissolved in 40mL deionized water, and a colorless and clear tin salt solution C was obtained after 1h. 15mL, 40mL, and 90mL gelatin B were added dropwise to solution C, and stirred thoroughly After 30 minutes, add 4 mol/L ammonia solution dropwise until the pH of the solution reaches about 7, stir at 60°C until the solution turns into a milky white viscous liquid, then stop heating. After cooling, a gelatinous white solid is obtained. Take it out after drying at a constant temperature of 80°C for 16 hours, grind it into a powder, transfer it to a crucible, and heat it at a constant temperature of 500°C for 3 hours in a tube furnace under an N ₂ atmosphere. After cooling to room temperature, the SnO ₂ /GC composite material is obtained. The volumetric amounts of gelatin are named as SnO ₂ /GC-15, SnO ₂ /GC-40, and SnO ₂ /GC-90, respectively. For the convenience of comparison, the cooled gelatin solution was also subjected to the same drying and carbonization treatment, and the obtained gelatin carbon sample was named GC. Finally, it was used as the anode material of lithium-ion battery to assemble the button battery and test its electrochemical performance.

P42/mnm空间群，且在2θ＝27°、34°、38°、52°有四个强衍射峰，对应SnO₂的(110)、(101)、(200)、(211)晶面，这与四方晶相金红石结构的SnO₂标准卡一致(ICOD 01-077-0448)。但在SnO₂/GC复合材料的XRD图谱中没有观察到SnO₂的衍射峰，一种结果可能是复合材料中没有生成SnO₂，而另一种结果可能是复合材料中生成了SnO₂，但SnO₂为无定形结构所以不显示特征峰。Fig. 2 is the XRD pattern of GC (gelatin carbon), SnO ₂ and SnO ₂ /GC (gelatin carbon) composite materials with different mass ratios. The lattice parameters corresponding to the _SnO2 diffraction peaks are

P42/mnm space group, and there are four strong diffraction peaks at 2θ=27°, 34°, 38°, 52°, corresponding to (110), (101), (200), (211) crystal planes of SnO ₂ , This is consistent with the _SnO2 standard card of the tetragonal phase rutile structure (ICOD 01-077-0448). However, no diffraction peak of SnO 2 was observed in the XRD pattern _of the SnO ₂ /GC composite material. One result may be that SnO ₂ was not generated in the composite material, and the other result may be that SnO ₂ was generated in the composite material, but SnO ₂ has an amorphous structure so it does not show characteristic peaks.

It can be seen from Fig. 3(d) that the carbon contents in the SnO ₂ /GC-15, SnO ₂ /GC-40 and SnO ₂ /GC-90 composite materials are 62.0%, 68.2% and 74.2%, respectively.

From Fig. 4(a), it is known that the nanometer SnO ₂ particles magnified by 10KX obviously gather into large clusters. In order to observe the microstructure of SnO ₂ more intuitively, the SEM image of SnO ₂ magnified by 50KX shows that the nano-SnO ₂ particles are spherical, and the particle size ranges between 10-20nm. In addition, as shown in Figure 4(c) and (d), compared with the pure SnO ₂ spherical nanoparticles, the microscopic morphology of the composite material has changed greatly, and the SnO ₂ is completely wrapped by gelatin, presenting an irregular block structure and smooth surface

It can be seen from Fig. 5 that the signal of carbon element in gelatin and the signal of oxygen and tin element in tin dioxide overlap uniformly on the entire particle surface, indicating that the carbon layer is uniformly coated on the surface of SnO ₂ nanoparticles. The semi-quantitative analysis of each element is shown in Table 1.

Table 1 Semi-quantitative analysis table of each element in Map

It can be known from Fig. 6(a) that the SnO ₂ /GC-40 composite material contains four elements: Sn, O, C and N. Figure 6(b)-(d) are the XPS high-resolution fine spectra of Sn3d, C1s, and N1s respectively. From the Sn3d spectrum in Figure 6(b), it can be seen that the bond energies of Sn3d5/2 and Sn3d3/2 are 487.02eV and 495.45 eV, the binding energy difference is 8.47eV, which is consistent with the spin-orbit peak of SnO ₂ , which proves that the Sn element exists in the form of Sn ⁴⁺ ions. Figure 6(c) shows that the C1s peak is split into four types of carbons, the peak at 284.66eV belongs to ^sp2 graphitic hybrid carbon with CC single bond, and the peak at 285.65eV belongs to ^sp3 diamond-like hybrid carbon with CO single bond , the peaks at 287.8eV and 288.95eV correspond to the carbons of C=O bond and COO bond, respectively. The high-resolution N1s peak in Figure 6(d) has four components, and their binding energies are located at 398.64eV, 400.0eV, 401.07eV and 403.22eV, respectively, corresponding to 42.45wt% pyridine nitrogen, 13.77wt% nitro nitrogen, 26.72 wt% of pyrrole nitrogen and 17.06wt% of quaternary nitrogen, it can be seen that the main forms of nitrogen in the carbon layer are pyridine nitrogen and pyrrole nitrogen.

From Figure 7, the specific surface areas of SnO ₂ -GC-15, SnO ₂ -GC-40 and SnO ₂ -GC-90 samples are 4.879 ² /g, 34.567m ² /g and 2.642m ² /g respectively, and the pore size distribution Most of them are concentrated between 3-12nm, indicating that the samples obtained by mixing SnO ₂ and gelatin are mostly mesoporous, which is related to the physical and chemical properties of gelatin itself.

As shown in Figure 8(a), after 100 charge-discharge cycles, the lithium storage capacities of GC and SnO ₂ are 111.9mAh/g and 57.8mAh/g, respectively. SnO ₂ -GC-15, SnO ₂ -GC-40 and SnO ₂ - The lithium storage capacities of the GC-90 samples are 321.9mAh/g, 353.6mAh/g and 307.9mAh/g, respectively. The comparison found that the lithium storage capacity of SnO ₂ /GC composites is higher than that of pure GC and SnO ₂ , indicating that carbon coating can effectively relieve the structural stress caused by the huge volume change of SnO ₂ during charge-discharge cycles, thereby stabilizing the material. The lattice structure hinders the collapse of the lattice structure. See Figure 8(b), after 100 cycles at current densities of 0.1A/g, 0.2A/g, 0.5A/g, 1A/g, and 2A/g, the lithium storage capacity of SnO ₂ /GC-40 The performance is the best, respectively 379.2mAh/g, 298.3mAh/g, 206.8mAh/g, 135.3mAh/g, 61.1mAh/g, when the current density returns to 0.1A/g again, SnO ₂ /GC-40 There is still a lithium storage capacity of 385.3mAh/g. The lithium storage capacities of SnO ₂ , SnO ₂ /GC-15, and SnO ₂ /GC-90 are 50.5mAh/g, 274.6mAh/g, and 322.6mAh/g, respectively. These results show that SnO ₂ /GC-40 is relatively SnO ₂ , SnO ₂ /GC-15 and SnO ₂ /GC-90 have better rate performance. Figure 8(c) shows that the SnO ₂ /GC-40 sample still has a lithium storage capacity of 397mAh/g after 500 charge-discharge cycles, which further indicates that the SnO ₂ /GC-40 composite has excellent electrochemical stability . At the same time, the lithium storage capacity of the SnO ₂ /GC-40 sample first decreased and then increased with the increase of the number of cycles.

In the present invention, GC is used as a carbon source, and nano-SnO ₂ is coated with carbon by a one-pot sol-gel (Sol-Gel) method to generate a tin salt/GC composite precursor in situ, and then calcined at a high temperature to obtain a porous SnO ₂ /GC composite Material. At the same time, the electrochemical performance of the composite was further optimized by adjusting the mass ratio of tin salt and GC in the precursor composite.

Claims (1)

1. Preparation of nano SnO ₂ The method for preparing the/GC composite anode material is characterized by comprising the following steps of:

a) Respectively dropwise adding 15mL, 40mL and 90mL of 0.1 g/mL gelatin solution into 40mL of 0.25 mmol/mL tin salt solution, uniformly stirring, dropwise adding 4mol/L ammonia water solution until a viscous white solid is generated, and stopping stirring;

b) Drying at constant temperature of 80 +/-2 ℃, transferring to a tube furnace for carbonization heat treatment to prepare a target product SnO ₂ a/GC composite;

the carbonization heat treatment is carried out in N ₂ Heating at 500 deg.C for 3h; said SnO ₂ SnO in/GC composites ₂ Is an amorphous structure.

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