Okra-shaped microstructure carbon layer loaded SnO2 nanoparticle composite material as well as preparation method and application thereof

Abstract

The invention discloses a carbon layer-loaded SnO2 nano-particle composite material with an okra-shaped microstructure as well as a preparation method and application of the carbon layer-loaded SnO2 nano-particle composite material. In the composite material, a large number of SnO2 nanoparticles are loaded on a hollow porous rod-like carbon layer framework to form a microstructure similar to okra. The SnO2 / C composite material effectively overcomes the problems of low theoretical capacity of a traditional anode material and low conductivity, violent volume change and the like of a traditional tin-based block material by virtue of a hollow porous structural framework, highly-nanocrystallized tin dioxide particles and multi-stage point-surface compounding of the highly-nanocrystallized tin dioxide particles and a carbon layer, and shows excellent capacity, efficiency and cycle performance.

Description

Technical Field

[0001] The invention discloses an okra-shaped microstructured carbon layer-loaded nano-tin dioxide composite material for a lithium ion battery anode, belonging to the technical field of lithium batteries. Background Art

[0002] At present, lithium-ion batteries are still the most stable, safest and most cost-effective power battery option due to their high specific energy, long cycle life, light weight, small size, mature raw material development and rapid industrialization. However, in recent years, graphite as a commercial anode material for lithium-ion batteries has become increasingly difficult to meet the needs of further development of battery technology due to its low theoretical specific capacity (372mAh / g), poor energy power density and the formation of lithium dendrites on the electrode surface. Therefore, researchers have begun to focus on developing metal oxides with higher electrochemical activity and higher theoretical energy density as a new generation of lithium-ion battery anode materials, such as SnO 2 、MnO 2 、TiO 2 As a promising anode candidate for the next generation of high-performance lithium-ion batteries, SnO 2 The material has advantages such as high theoretical capacity (782 mAh / g) and low discharge potential (1.5 V). However, there are still many key obstacles that are difficult to overcome in the process of industrial development of tin-based materials: (1) SnO 2 The material has low conductivity. Using it as an electrode material will result in weak and unstable current conduction, causing poor cycle performance, increasing the internal impedance of the battery, and reducing the battery discharge capacity. (2) SnO 2 As anode material for lithium-ion batteries, Li + During the insertion / extraction process, a huge volume change will occur, causing the electrode to pulverize, which in turn causes the electrode to collapse and fall off the current collector. This process will also cause battery safety issues; (3) Li + The embedding involves SnO 2 The process of conversion into Sn single substance, during which the Sn single substance will aggregate, resulting in a rapid decrease in the capacity of the battery, accompanied by lower coulombic efficiency.

[0003] For SnO 2 There are a series of problems. Researchers have tried to solve the problem of SnO by various means. 2 Materials can be modified and improved, such as building heterojunction structures, alloying structures, element doping, and carbon coating. 2 The nanosize effect is considered to be a feasible and efficient means to enhance the conductivity of materials and buffer volume changes. Summary of the invention

[0004] The present invention provides a carbon layer-supported SnO with okra-like microstructure 2 nanoparticle composite material, its preparation method, and its application as an anode material for lithium-ion batteries. The present invention combines wet chemical means to prepare a precursor material of nanorod-shaped tin-based metal-organic framework (Sn-MOF) with uniform size and high purity under mild conditions, and further prepares a SnO 2 / C composite material with a unique okra-like microstructure through high-temperature carbonization, and uses it as an anode active material for lithium-ion batteries, obtaining excellent electrochemical performance.

[0005] The specific implementation of the technical solution of the present invention is as follows:

[0006] A carbon layer-supported SnO with okra-like microstructure 2 nanoparticle composite material and its preparation method, including the following steps:

[0007] (1) Slowly inject a stannous sulfate solution into a mixed solution of phthalic acid and sodium hydroxide, react in a water bath at a certain temperature for a period of time, then transfer to room temperature and continue stirring for a period of time to obtain a milky white liquid, and obtain Sn-MOF material after centrifugation, washing, and drying;

[0008] (2) Place the obtained Sn-MOF material under an argon atmosphere for pyrolytic carbonization, the carbonization temperature is 600 °C, and the carbonization time is 6 hours to obtain a SnO 2 / C nanoparticle composite material.

[0009] Preferably, react in a water bath at 60 °C for 1 h.

[0010] Preferably, continue stirring at room temperature for 5 h.

[0011] Preferably, the molar ratio of stannous sulfate to phthalic acid is 1:1.

[0012] Preferably, the molar ratio of phthalic acid to sodium hydroxide is 1:1.

[0013] Preferably, the okra-like microstructure refers to that a large number of SnO 2 nanoparticles in the SnO 2 / C nanoparticle composite material are loaded on a hollow and porous rod-shaped carbon layer framework, forming a microstructure similar to okra.

[0014] The present invention also provides the application of the above carbon layer-supported SnO with okra-like microstructure 2 nanoparticle composite material as an anode material for lithium-ion batteries.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] (1) The present invention prepares a composite material of SnO nanoparticles loaded on an okra-shaped microstructure carbon layer by a simple, mild and low-cost method, and uses it as an anode material for lithium-ion batteries, showing good electrochemical lithium storage performance. In the present invention, a tin-based metal-organic framework material (Sn-MOF) is first synthesized using phthalic acid and stannous sulfate, and the selling prices of both phthalic acid ligand and stannous sulfate are below 50 yuan per 100 g (the industrial-grade price is even lower). However, the ligand raw materials used in Patent CN111342019A are expensive, and the selling price of 5 g of the reagent reaches 3661 yuan, which is more than 70 times the cost of the present invention; at the same time, this method can obtain high-quality precursor materials at room temperature and normal pressure by liquid-phase reaction, and the target product can be obtained by one-step carbonization. Therefore, in terms of raw materials and preparation process, the present invention has good economy and scalability. 2 (2) The present invention prepares Sn-MOF materials by a relatively mild method through wet chemistry. In this process, the yield of the materials is close to 100%. Compared with the Sn-MOF materials reported in the literature Nanotechnology 32(2021)485403, the materials have uniform size, higher purity, and require lower temperature. The present invention not only has a more excellent material structure, but also the preparation process is safer. In addition, the SnO

[0017] / C composite material can be obtained by one-step carbonization treatment using Sn-MOF as the precursor, and the material structure can be well preserved. Compared with past studies, the present invention has higher yield and safety reliability. 2 (3) The obtained materials have a unique okra-shaped microstructure and a hollow and porous micro-nano structure framework. Among them, the carbon framework not only enhances the electrical conductivity of the tin-based oxide, provides a large number of channels for the insertion and extraction and transport of Li

[0018] , but also effectively buffers the volume change during charge and discharge, improves the electrochemical reversibility, and realizes high capacity and high stability. + (4) BRIEF DESCRIPTION OF THE DRAWINGS (5) FIG.

[0019] Figure 1 is the SEM pattern of the SnO 2 / C materials prepared in the examples and comparative examples of the present invention.

[0020] Figure 2 FIG. 2 is the XRD pattern of the SnO

[0021] Figure 3 FIG. 2 is the AC impedance curve of the SnO 2 / C electrode and the traditional SnO

[0022] Figure 4 FIG.2 / C electrode and traditional SnO 2 Comparison of the cycling performance of nanoparticle electrodes at a rate of 0.5C. Detailed implementation manners

[0023] The present invention discloses a carbon-layer-supported nano-SnO 2 particle composite material with a unique okra-like microstructure and a preparation method thereof. The unique okra-like microstructure means that the SnO 2 / C material of the present invention has a tubular-like outer shape, is hollow inside and has dispersed particles, and its structure is similar to that of an okra. The present invention applies it to the anode of a lithium-ion battery and obtains good capacity, efficiency and cycling performance.

[0024] A preparation method of a carbon-layer-supported nano-SnO 2 particle composite material with a unique okra-like microstructure, an electrode preparation method based on the composite material, a battery assembly process, and material testing and electrochemical testing are as follows:

[0025] Material preparation: Phthalic acid and sodium hydroxide are fully dissolved in deionized water in a water bath at 60°C according to a molar ratio of 1:1 to obtain solution A. Stannous sulfate with a molar ratio of 1:0.5 - 2 relative to phthalic acid is weighed and ultrasonically dissolved in deionized water to obtain solution B. Solution B is slowly injected into solution A, and after stirring and reacting in a water bath at 60°C for 1 h, it is transferred to room temperature and stirred for another 5 h to obtain a milky white liquid. After centrifugation, washing and drying, Sn-MOF material can be obtained. The obtained Sn-MOF material is placed in a crucible and pyrolytically carbonized in a tubular furnace under an argon atmosphere. The carbonization temperature is 500 - 700°C and the carbonization time is 6 hours to obtain SnO 2 / C.

[0026] Electrode preparation: The obtained SnO 2 / C active material, conductive agent SP, and binder PVDF are uniformly mixed in a mass ratio of 6:3:1, and NMP solvent is added and ground continuously to obtain a uniform electrode paste; the electrode paste is coated on a copper foil current collector and vacuum dried at 60°C for 8 h; the obtained dried electrode sheet is cut into a circular electrode sheet for use.

[0027] Battery assembly: Using the obtained SnO 2 / C as the working electrode to assemble a CR2025 button cell for electrochemical testing. The battery assembly sequence is negative electrode case, shrapnel, gasket, counter electrode, separator, SnO 2 / C electrode, positive electrode case. The electrolyte is a mixed solution of 1M lithium hexafluorophosphate (LiPF 6 ) dissolved in EC + DMC + EMC (volume ratio 1:1:1).

[0028] Material testing and electrochemical testing:

[0029] 1. Perform scanning electron microscopy (SEM) tests on the prepared SnO 2 / C materials.

[0030] 2. Perform X-ray diffraction (XRD) tests on the prepared SnO 2 / C materials.

[0031] 3. Perform electrochemical tests such as cycling and impedance on the prepared SnO 2 / C batteries.

[0032] Example 1

[0033] Weigh 0.84 g of phthalic acid and 0.41 g of sodium hydroxide according to a molar ratio of 1:1 and transfer them to a round-bottom flask. Measure 100 mL of deionized water with a measuring cylinder and pour it into the round-bottom flask. Stir and dissolve it fully in a 60 °C water bath to obtain solution A. Weigh stannous sulfate with a molar ratio of 1:1 to phthalic acid and ultrasonically dissolve it in 30 mL of deionized water to obtain solution B. Slowly inject solution B into solution A to obtain a milky liquid, and continuously stir and react it in a 60 °C water bath for 1 hour, then transfer it to room temperature and continue stirring for 5 h. The obtained milky suspension is subjected to solid-liquid separation under a centrifuge at 3000 revolutions per minute, washed repeatedly with water 3 times, and then vacuum dried for 8 hours to obtain Sn-MOF powder. The obtained Sn-MOF has a uniform structure and a smooth surface.

[0034] Comparative Example 1

[0035] Weigh 0.42 g of phthalic acid and 0.41 g of sodium hydroxide according to a molar ratio of 1:2 and transfer them to a round-bottom flask. Measure 100 mL of deionized water with a measuring cylinder and pour it into the round-bottom flask. Stir and dissolve it fully in a 60 °C water bath to obtain solution A. Weigh stannous sulfate with a molar ratio of 1:1 to phthalic acid and ultrasonically dissolve it in 30 mL of deionized water to obtain solution B. Slowly inject solution B into solution A to obtain a milky liquid, and continuously stir and react it in a 60 °C water bath for 1 hour, then transfer it to room temperature and continue stirring for 5 h. The obtained milky suspension is subjected to solid-liquid separation under a centrifuge at 3000 revolutions per minute, washed repeatedly with water 3 times, and then vacuum dried for 8 hours to obtain Sn-MOF powder. The Sn-MOF material obtained by this method has a non-uniform structure and a large number of fracture phenomena. This is related to the excessive sodium hydroxide.

[0036] Comparative Example 2

[0037] Weigh 0.84 g of phthalic acid and 0.21 g of sodium hydroxide according to a molar ratio of 2:1 and transfer them to a round-bottom flask. Measure 100 mL of deionized water with a measuring cylinder and pour it into the round-bottom flask. Stir and dissolve it fully in a 60 °C water bath to obtain solution A. Weigh stannous sulfate in a molar ratio of 1:1 relative to phthalic acid and ultrasonically dissolve it in 30 mL of deionized water to obtain solution B. Slowly inject solution B into solution A to obtain a milky white liquid, and continuously stir and react it in a 60 °C water bath for 1 hour, then transfer it to room temperature and continue stirring for 5 h. The obtained milky white suspension is subjected to solid-liquid separation under a centrifuge at 3000 revolutions per minute, washed repeatedly with water 3 times, and then vacuum dried for 8 hours to obtain Sn-MOF powder. The Sn-MOF material obtained by this method has a non-uniform structure and a large amount of impurities. This is related to the excessive phthalic acid.

[0038] Example 2

[0039] Place the Sn-MOF powder obtained in Example 1 in a square crucible and carry out high-temperature pyrolysis carbonization under argon protection in a tubular furnace. The carbonization temperature is 600 °C, the heating rate is 5 °C / min, the carbonization time is 6 h, and after the carbonization is completed, the cooling rate is 10 °C / min. Thus, a composite material of carbon layer loaded with SnO 2 nanoparticles (SnO 2 / C) is obtained. The obtained SnO 2 / C structure is intact and is a pure phase of SnO 2 . Morphologically, it can be seen that it has a microstructure similar to okra ( Figure 1 ).

[0040] Comparative Example 3

[0041] Taking the carbonization temperature as a control group experiment, place the Sn-MOF powder obtained in Example 1 in a square crucible and carry out high-temperature pyrolysis carbonization under argon atmosphere protection in a tubular furnace. The carbonization temperature is 500 °C, the heating rate is 5 °C / min, the carbonization time is 6 h, and after the carbonization is completed, the cooling rate is 10 °C / min, thereby obtaining the corresponding composite material. Through the XRD test results ([[]] Figure 2 ), it is found that there is an impurity phase of SnO in the obtained material, which is related to the incomplete oxidation of Sn-MOF at low temperature; in addition, morphologically ( Figure 1 ), compared with the results of carbonization at 600 °C, Sn-MOF fails to carbonize completely at a lower temperature, and there is still an obvious solid rod-like structure.

[0042] Comparative Example 4

[0043] Taking the carbonization temperature as the control group experiment, the Sn-MOF powder obtained in Example 1 was placed in a square crucible and pyrolytically carbonized at a high temperature under the protection of an argon atmosphere in a tube furnace. The carbonization temperature was 700 °C, the heating rate was 5 °C / min, the carbonization time was 6 h, and after the carbonization was completed, the cooling rate was 10 °C / min, thereby obtaining the corresponding composite material. The obtained material still had an okra-like microstructure, but there was a mixed-phase elemental Sn( Figure 2 ), which was related to the reduction of some SnO 2 at high temperature; in addition, a large amount of precipitation and aggregation of elemental Sn could be seen in the morphology( Figure 1 ), and the okra-like microstructure was also damaged to a certain extent.

[0044] The SnO 2 / C material obtained in Example 2, conductive carbon SP, and binder PVDF were weighed separately on an analytical balance at a mass ratio of 6:3:1, 60 mg, 30 mg, and 10 mg respectively, and placed in a crucible and ground for 30 min to make them uniformly mixed. Then NMP solvent was added and ground continuously to obtain a uniform electrode slurry. The electrode slurry was coated on a copper foil current collector with a coating thickness of 250 μm. It was transferred to a vacuum drying oven at 60 °C and dried for 8 h, and the obtained dried electrode was cut into a circular electrode sheet for use. The loading of the active material of the electrode sheet was 0.7 - 1.0 mg. Using the obtained SnO 2 / C as the working electrode to assemble a CR2025 coin cell for electrochemical testing. The battery assembly sequence was negative electrode case, shrapnel, gasket, counter electrode, separator, SnO 2 / C electrode, positive electrode case. The electrolyte was a mixed solution of 1 M lithium hexafluorophosphate (LiPF 6 ) dissolved in EC + DMC + EMC (volume ratio 1:1:1).

[0045] 1. The phase and crystal characteristics of the materials were studied by X-ray diffractometer (XRD). The instrument model was Bruker-AXSD8 Advances, and the target used was Cu. During the test, the scanning range of the sample was 2θ = 10° - 80°. The morphology and microstructure of the materials were collected by scanning electron microscope (SEM, JSM-7800F PRIME) to analyze the size and surface morphology of the materials.

[0046] 2. The electrochemical impedance spectra of the assembled coin cells were collected by an electrochemical workstation (CHI660E, Shanghai Chenhua) with an amplitude of 5 mV in the frequency range of 0.1 - 100 kHz. The constant current charge / discharge was tested by a blue electrochemical system (LAND, CT3002A), and the applied current was calculated according to the mass of SnO 2 / C (1C = 782 mA g -1 ).

[0047] Figure 1 Taking the Sn-MOF obtained in Example 1 as a precursor, SnO 2 / C materials were obtained at different carbonization temperatures. From Figure 1 it can be seen that the obtained SnO 2 / C composite material (Example 2) consists of a large number of SnO 2 nanoparticles supported on a hollow and porous rod-shaped carbon layer framework, forming a microstructure similar to okra, with clear structure, uniform overall morphology and size, and few impurities. Among them, the hollow and porous carbon layer framework not only provides a path for the transmission of Li + ions, but also can provide good electrical conductivity. At the same time, the carbon layer framework can effectively buffer the volume change of SnO 2 during the cycling process, alleviate the electrode pulverization and structure collapse phenomena, and improve the cycling performance and Coulomb efficiency of the battery. Figure 1 In [Figure], Comparative Example 3 is the composite material obtained by carbonization at 500 °C. It can be clearly seen from the figure that there are some solid rod-shaped morphologies, rather than the expected hollow and porous tubular shapes, which is related to the incomplete carbonization of Sn-MOF at low temperatures. Figure 1 In [Figure], Comparative Example 4 is the composite material obtained by carbonization at 700 °C. It can be seen that the okra-like hollow and porous structure is damaged to a certain extent, and there are a large number of particle aggregations. This indicates that part of the SnO 2 generated during the high-temperature reaction of Sn-MOF is further reduced to Sn metal, accompanied by agglomeration phenomena; in addition, high temperature will also damage the morphology of the sample and cause structure collapse.

[0048] Figure 2 Taking the Sn-MOF obtained in Example 1 as a precursor, SnO 2 / C materials were obtained by carbonization at different temperatures. Figure 2 In [Figure], Example 2 is the XRD pattern of the composite material obtained at 600 °C. Comparing with the standard card, it can be seen that at 2θ of 26.6°, 33.8°, 37.8°, 51.7°, 61.7°, and 65.7°, they correspond to the (110), (101), (200), (211), (310), and (301) planes of SnO 2 (PDF#41-1445) respectively. The diffraction peaks of the obtained SnO 2 / C have a good correspondence with the standard card, indicating that the obtained material has a uniform phase structure, high purity, and no impurity phase. Figure 2 In [Figure], Comparative Example 3 is the composite material obtained at 500 °C, and its peak positions are the same as those of SnO 2The standard card corresponds one by one, but there is an obvious impurity peak at 29.9°, which corresponds to the SnO standard peak (PDF#06-0395), indicating the incomplete oxidation of Sn-MOF at low temperature. Figure 2 In Comparative Example 4, the composite material obtained at 700 °C has its main peak position corresponding well to that of SnO 2 The standard card, but there are obvious impurity peaks at 30.6°, 32.0°, and 44.9°, and they correspond to the XRD standard card of Sn metal (PDF#04-0673), indicating the presence of Sn metal phase in the composite, which is related to the reduction of part of SnO 2 to Sn metal at high temperature.

[0049] Figure 3 is based on the obtained SnO 2 / C and traditional SnO 2 nanoparticles as the anode material of the lithium-ion battery impedance diagram. It can be seen from the impedance curve that the obtained SnO 2 / C electrode has lower charge transfer resistance and ion diffusion resistance compared to the traditional SnO 2 nanoparticle electrode. This is closely related to the designed hollow porous okra-like SnO 2 / C composite structure, where the carbon layer accelerates charge transfer and the hollow structure promotes ion diffusion.

[0050] Figure 4 Shown is the cycling performance of the SnO 2 / C electrode and the traditional SnO 2 nanoparticle electrode. The obtained SnO 2 / C electrode was tested for charge and discharge at a rate of 0.5C. After 50 cycles, it still maintained a high specific capacity of 879.5 mAh g -1 and a Coulomb efficiency of over 98%, significantly superior to the electrode based on traditional SnO 2 nanoparticles, showing good cycling performance. This is the optimization effect of the electrochemical performance brought by the excellent material structure design.

[0051] In summary, due to the hollow porous structure framework, highly nano-sized tin dioxide particles and their multi-level "point-plane" composite with the carbon layer, the obtained SnO 2 / C composite material of the present invention effectively overcomes the problems of low theoretical capacity of traditional anode materials and low conductivity and large volume change of traditional tin-based bulk materials, and exhibits excellent capacity, efficiency and cycling performance.

Claims

1. Preparation method of carbon layer supported SnO nanoparticle composite material with okra-like microstructure 2 ​ It is characterized in that It includes the following steps: (1) Slowly inject the stannous sulfate solution into the mixed solution of phthalic acid and sodium hydroxide. After reacting in a water bath at a certain temperature for a period of time, transfer it to room temperature and continue stirring for a period of time to obtain a milky white liquid. The Sn-MOF material can be obtained after centrifugation, washing, and drying; (2)The obtained Sn-MOF material was pyrolytically carbonized under an argon atmosphere at a carbonization temperature of 600 °C for 6 hours to obtain SnO 2 / C nanoparticle composite material.

2. The method according to claim 1, It is characterized in that React in a water bath at 60 °C for 1 h.

3. The method according to claim 1, It is characterized in that Continue stirring at room temperature for 5 h.

4. The method according to claim 1, It is characterized in that The molar ratio of stannous sulfate to phthalic acid is 1:

1.

5. The method according to claim 1, It is characterized in that The molar ratio of phthalic acid to sodium hydroxide is 1:

1.

6. The composite material of SnO nanoparticles supported on the okra-shaped microstructured carbon layer prepared by the method according to any one of claims 1-5 2 nanoparticles 7. The composite material according to claim 6, It is characterized in that The okra-like microstructure refers to a large number of SnO 2 nanoparticles in the composite material being loaded on a hollow and porous rod-shaped carbon layer framework, forming a microstructure similar to okra.

8. Use of the composite material of carbon layer supported SnO nanoparticles with okra-like microstructure prepared by the method according to any one of claims 1-5 2 as an anode material for lithium ion batteries.

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