A lithium battery composite anode material and its preparation method

Abstract

The present invention discloses a lithium battery composite anode material and a preparation method thereof, belonging to the technical field of lithium batteries. The lithium battery composite anode material of the present invention is prepared by high-temperature pyrolysis of Fe-Ni metal-organic framework as a substrate together with modified nano-silicon powder. This material is a porous carbon-silicon composite material with a relatively high specific surface area and porosity, which can provide more active sites, facilitating the insertion and extraction of lithium ions. At the same time, the porous structure can also alleviate the volume expansion problem of silicon materials during charge and discharge processes. The composite anode material of the present invention not only utilizes the high lithium storage capacity of silicon but also can exert the excellent electrical conductivity and structural stability of porous carbon materials, having a high specific capacity and excellent electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and particularly relates to a composite anode material for lithium batteries and a preparation method thereof. Background Art

[0002] With the rapid economic take-off of our country, the existing energy system can no longer meet the demand. The consumption of fossil fuels is irreversible and has brought incalculable environmental problems. The wide application of electric energy has promoted the development of lithium-ion batteries. Currently, the main anode used in commercial lithium-ion batteries is various graphite materials. Although the preparation technology is mature, the maximum can only reach its theoretical specific capacity value (372 mA·h / g), making it difficult to meet the high requirements for battery energy density and use stability. Therefore, the research and development of high-performance lithium-ion batteries is an urgent task.

[0003] As a new type of anode material for lithium batteries, silicon has become the focus of researchers due to its high theoretical specific capacity (4200 mAh / g). However, directly using it as the anode material cannot highlight the high-capacity advantage. This is mainly because when lithium ions are inserted / extracted into / from the silicon unit cell, it will cause serious volume expansion, and then cracks will appear on the electrode surface, resulting in rapid attenuation of battery capacity and poor cycle life.

[0004] To solve the above existing problems, silicon-carbon composite materials have attracted more and more attention from researchers. The silicon material provides high specific capacity, while the carbon material has excellent electrochemical and structural stability, good electrical conductivity, and almost no volume change during lithiation, maintaining the integrity of the electrode, which can effectively solve the problem of volume expansion of the silicon anode during the insertion and extraction of lithium ions in lithium-ion batteries. Therefore, how to prepare a high-performance composite anode material for lithium batteries and improve the electrochemical stability of the composite material is an urgent problem to be solved in this field. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite anode material for lithium batteries and a preparation method thereof. The anode material is a lithium battery anode material prepared from a metal Fe-Ni bimetallic organic framework and sodium alginate-modified nano-silica powder. The material has a loose porous structure, which can effectively solve the problem of volume expansion of the silicon anode during the insertion and extraction of lithium ions in lithium-ion batteries. The nano-silicon particles modified by sodium alginate are evenly dispersed in the pores of the iron-nickel organometallic framework-based porous carbon material, forming a stable composite material structure. This structure can not only utilize the high lithium storage capacity of silicon but also give play to the excellent electrical conductivity and structural stability of the porous carbon material, having good rate performance and cycle stability.

[0006] To achieve the above technical purpose, the technical solution adopted by the present invention is as follows:

[0007] A preparation method of a composite anode material for lithium batteries, which includes the following steps:

[0008] (1) Dissolve triethylenediamine and terephthalic acid in DMF. After stirring evenly, add FeCl2·4H2O and NiCl2·6H2O to the above homogeneous solution. After magnetic stirring for 3 h, transfer it to a polytetrafluoroethylene hydrothermal reaction kettle. After reacting at 150 °C for 24 h, naturally cool it to room temperature. Centrifuge and wash the obtained solid product with DMF and absolute ethanol for 3 - 5 times, and then put it into a vacuum drying oven to dry to obtain the Fe-Ni-MOF substrate;

[0009] (2) Take 0.5 g of sodium alginate and add it to 100 ml of 1 mol / L NaCl solution, stir to dissolve completely to obtain solution A; take 2 g of nano-silica powder and add it to 100 ml of deionized water, ultrasonically disperse it evenly and then mix it evenly with solution A. After reacting for 2 - 3 h under magnetic stirring, centrifuge to separate the solid product, wash it with deionized water for many times, and dry it in an oven to obtain the sodium alginate modified nano-silica material;

[0010] (3) Mix the Fe-Ni-MOF substrate and the sodium alginate modified nano-silica material, mechanically ball mill for 1 h, then transfer the mixture to a tubular furnace, introduce argon as the protective gas, carry out high-temperature calcination, naturally cool and grind to obtain the lithium battery composite anode material.

[0011] Preferably, in the step (1), the molar ratio of triethylenediamine, terephthalic acid, FeCl2·4H2O, and NiCl2·6H2O is: 15:15:4:1; the concentration of triethylenediamine in the DMF solution is 0.05 mol / L.

[0012] Preferably, in the step (1), the vacuum drying temperature is 80 °C and the time is 12 h.

[0013] Preferably, in the step (2), the oven drying temperature is 60 °C and the time is 10 h.

[0014] Preferably, in the step (3), the mass ratio of the Fe-Ni-MOF substrate to the sodium alginate modified nano-silica material is 0.3 - 0.8:1.

[0015] Preferably, the specific method of high-temperature calcination in the step (3) is: heat up to 200 °C at a rate of 3 °C / min, keep warm for 1 - 2 h, then adjust the heating rate to 5 °C / min and rise to 800 °C, and keep warm and react for 2 - 3 h.

[0016] The lithium battery composite anode material prepared by the above method of the present invention has the following specific usage method: After fully grinding the anode material prepared by the present invention, it is ground and stirred with conductive carbon black and binder according to a mass ratio of 8:1:1 until a uniformly dispersed slurry is formed, and then it is coated on a copper foil with an I-shaped scraper, and the thickness of the slurry is 75 μm. It is dried in a vacuum drying oven at 60 °C for 12 h, taken out, cut into circular pieces with a diameter of 12 mm on a slicing machine and pressed, and the pressure is 6 MPa to obtain a lithium battery anode sheet. The lithium battery anode material has good electrochemical performance, improving the cycle stability and rate performance of the battery. At the same time, the special porous structure of the prepared composite material is more conducive to the penetration of the electrolyte into the electrode material, shortening the transmission paths of electrons and lithium ions, and improving the diffusion rate of lithium ions and the cycle performance of the battery.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1) In the present invention, a Fe-Ni bimetallic organic framework material is rationally designed and synthesized as a carbon material, and a porous material with a higher porosity is prepared by reasonably regulating the ratio of Fe-Ni. The rich pore structure and active sites inside the material are conducive to the insertion and extraction of lithium ions, providing transmission channels for a large number of ions and electrons. The introduction of the iron-nickel bimetal further enhances this transmission performance, enabling the material to quickly respond to current changes during charge and discharge and maintaining good structural stability during charge and discharge.

[0019] 2) At the same time, the present invention uses sodium alginate-modified nano-silicon powder as the silicon-based material. The addition of sodium alginate can interact with the surface of the nano-silicon powder through the hydrophilic groups carboxyl and hydroxyl on its molecular chain, reducing the surface energy, and can significantly improve the cycle stability of the nano-silicon powder. Coated on the surface of the silicon particles, it can effectively prevent the volume expansion of silicon during charge and discharge and reduce structural damage; the sodium alginate-modified nano-silicon powder and the Fe-Ni MOFs support each other in structure, forming a more stable electrode structure. This structure helps to resist mechanical stress during charge and discharge, reducing the pulverization and shedding of the electrode material; the protective layer formed by sodium alginate on the surface of the silicon particles can also prevent direct contact between silicon and the electrolyte, reducing the occurrence of side reactions and improving the stability of the interface. The porous structure of the Fe-Ni MOFs also provides more channels for the penetration of the electrolyte, contributing to the formation of a more stable SEI film.

[0020] 3) The lithium battery composite anode material prepared by the present invention has excellent cycle stability, high specific capacity, and small capacitance loss after cyclic discharge, and has good application prospects. Description of the Drawings

[0021] Figure 1Scanning electron microscope images of the electrode materials obtained in Example 3 and Comparative Example 1 of the present invention, where a is the SEM image of Example 3, b is the partially enlarged SEM image of Example 3, and c is the SEM image of Comparative Example 1;

[0022] Figure 2 Electrochemical impedance test result diagrams of the electrode materials obtained in Example 3, Comparative Example 1, and Comparative Example 2 of the present invention. Detailed implementation manners

[0023] The technical solution of the present invention will be further described below in conjunction with specific embodiments, but not limited thereto. Example

[0024] A preparation method of a lithium battery composite anode material, which includes the following steps:

[0025] (1) Dissolve triethylenediamine and terephthalic acid in DMF, stir evenly, then add FeCl2·4H2O and NiCl2·6H2O to the above homogeneous solution, magnetically stir for 3 h, then transfer it to a polytetrafluoroethylene hydrothermal reaction kettle, react at 150 °C for 24 h, and then naturally cool to room temperature. The obtained solid product is centrifugally washed 3 times with DMF and absolute ethanol and then placed in a vacuum drying oven to dry at 80 °C for 12 h to obtain a Fe-Ni-MOF substrate; the molar ratio of triethylenediamine, terephthalic acid, FeCl2·4H2O, and NiCl2·6H2O is: 15:15:4:1; the concentration of triethylenediamine in the DMF solution is 0.05 mol / L.

[0026] (2) Take 0.5 g of sodium alginate and add it to 100 ml of 1 mol / L NaCl solution, stir to dissolve completely to obtain solution A; take 2 g of nano-silicon powder and add it to 100 ml of deionized water, ultrasonically disperse it evenly and then mix it evenly with solution A, react under magnetic stirring for 3 h, then centrifuge to separate to obtain a solid product, wash it with deionized water for many times, and dry it in an oven at 60 °C for 10 h to obtain sodium alginate modified nano-silicon material;

[0027] (3) Mix the Fe-Ni-MOF substrate with the sodium alginate modified nano-silicon material, mechanically ball mill for 1 h, then transfer the mixture to a tube furnace, introduce argon as a protective gas, carry out high-temperature calcination, naturally cool and grind to obtain the lithium battery composite anode material; the mass ratio of the Fe-Ni-MOF substrate to the sodium alginate modified nano-silicon material is 0.3:1; the specific high-temperature calcination method is: heat up to 200 °C at a rate of 3 °C / min, keep warm for 2 h, then adjust the heating rate to 5 °C / min and rise to 800 °C, and keep warm and react for 2 h. Example

[0028] A preparation method of a lithium battery composite anode material, which includes the following steps:

[0029] (1) Dissolve triethylenediamine and terephthalic acid in DMF. After stirring evenly, add FeCl₂·4H₂O and NiCl₂·6H₂O to the above homogeneous solution. After magnetic stirring for 3 h, transfer it into a polytetrafluoroethylene hydrothermal reaction kettle. After reacting at 150 °C for 24 h, naturally cool it to room temperature. Wash the obtained solid product 5 times by centrifugation with DMF and absolute ethanol, and then put it into a vacuum drying oven and dry it at 80 °C for 12 h to obtain the Fe-Ni-MOF substrate; the molar ratio of triethylenediamine, terephthalic acid, FeCl₂·4H₂O, and NiCl₂·6H₂O is: 15:15:4:1; the concentration of triethylenediamine in the DMF solution is 0.05 mol / L.

[0030] (2) Take 0.5 g of sodium alginate and add it to 100 ml of 1 mol / L NaCl solution. Stir until completely dissolved to obtain solution A; take 2 g of nano-silica powder and add it to 100 ml of deionized water. After ultrasonic dispersion evenly, mix it with solution A evenly. After reacting for 2 h under magnetic stirring, centrifuge to separate the solid product, wash it many times with deionized water, and dry it at 60 °C for 10 h in an oven to obtain the sodium alginate modified nano-silica material;

[0031] (3) Mix the Fe-Ni-MOF substrate and the sodium alginate modified nano-silica material, and mechanically ball mill for 1 h. Then transfer the mixture into a tubular furnace, introduce argon as the protective gas, and perform high-temperature calcination. After natural cooling and grinding, the lithium battery composite anode material is obtained; the mass ratio of the Fe-Ni-MOF substrate to the sodium alginate modified nano-silica material is 0.5:1; the specific high-temperature calcination method is: heat up to 200 °C at a rate of 3 °C / min, keep it warm for 1 h, then adjust the heating rate to 5 °C / min and rise to 800 °C, and keep it warm and react for 3 h. Example

[0032] A preparation method of a lithium battery composite anode material, which comprises the following steps:

[0033] (1) Dissolve triethylenediamine and terephthalic acid in DMF. After stirring evenly, add FeCl₂·4H₂O and NiCl₂·6H₂O to the above homogeneous solution. After magnetic stirring for 3 h, transfer it into a polytetrafluoroethylene hydrothermal reaction kettle. After reacting at 150 °C for 24 h, naturally cool it to room temperature. Wash the obtained solid product 5 times by centrifugation with DMF and absolute ethanol, and then put it into a vacuum drying oven and dry it at 80 °C for 12 h to obtain the Fe-Ni-MOF substrate; the molar ratio of triethylenediamine, terephthalic acid, FeCl₂·4H₂O, and NiCl₂·6H₂O is: 15:15:4:1; the concentration of triethylenediamine in the DMF solution is 0.05 mol / L.

[0034] (2) Take 0.5 g of sodium alginate and add it to 100 ml of 1 mol / L NaCl solution, stir until completely dissolved to obtain solution A; take 2 g of nano-silicon powder and add it to 100 ml of deionized water, after ultrasonic dispersion evenly, mix it with solution A evenly, react for 3 h under magnetic stirring, then centrifuge to separate to obtain a solid product, wash it with deionized water for multiple times, and dry it in an oven at 60 °C for 10 h to obtain sodium alginate modified nano-silicon material;

[0035] (3) Mix the Fe-Ni-MOF substrate with the sodium alginate modified nano-silicon material, mechanically ball mill for 1 h, then transfer the mixture into a tubular furnace, introduce argon as the protective gas, carry out high-temperature calcination, and naturally cool and grind to obtain the lithium battery composite anode material; the mass ratio of the Fe-Ni-MOF substrate to the sodium alginate modified nano-silicon material is 0.8:1; the specific high-temperature calcination method is: heat up to 200 °C at a rate of 3 °C / min, keep the temperature for 1 h, then adjust the heating rate to 5 °C / min and rise to 800 °C, and keep the temperature for reaction for 2 h.

[0036] A preparation method of a lithium battery composite anode material, which comprises the following steps:

[0037] (1) Dissolve triethylenediamine and terephthalic acid in DMF, stir evenly, then add FeCl2·4H2O to the above-mentioned homogeneous solution, stir magnetically for 3 h, then transfer it into a polytetrafluoroethylene hydrothermal reaction kettle, react at 150 °C for 24 h, naturally cool to room temperature, wash the obtained solid product with DMF and absolute ethanol by centrifugation for 3 - 5 times, and then put it into a vacuum drying oven and dry it at 80 °C for 12 h to obtain the Fe-MOF substrate; the molar ratio of triethylenediamine, terephthalic acid, and FeCl2·4H2O is: 15:15:4; the concentration of triethylenediamine in the DMF solution is 0.05 mol / L.

[0038] (2) Take 0.5 g of sodium alginate and add it to 100 ml of 1 mol / L NaCl solution, stir until completely dissolved to obtain solution A; take 2 g of nano-silicon powder and add it to 100 ml of deionized water, after ultrasonic dispersion evenly, mix it with solution A evenly, react for 3 h under magnetic stirring, then centrifuge to separate to obtain a solid product, wash it with deionized water for multiple times, and dry it in an oven at 60 °C for 10 h to obtain sodium alginate modified nano-silicon material;

[0039] (3) Mix the Fe-Ni-MOF substrate with the sodium alginate-modified nano-silicon material, and after mechanical ball milling for 1 h, transfer the mixture into a tubular furnace, introduce argon as the protective gas, and perform high-temperature calcination. After natural cooling and grinding, the lithium battery composite anode material is obtained; the mass ratio of the Fe-Ni-MOF substrate to the sodium alginate-modified nano-silicon material is 0.8:1; the specific high-temperature calcination method is as follows: heat up to 200 °C at a rate of 3 °C / min, keep the temperature for 1 h, then adjust the heating rate to 5 °C / min and rise to 800 °C, and keep the temperature for reaction for 2 h.

[0040] In this comparative example, except that NiCl2·6H2O is not added in step (1), the others are the same as in Example 3.

[0041] A preparation method of a lithium battery composite anode material, which includes the following steps:

[0042] (1) Dissolve triethylenediamine and terephthalic acid in DMF, stir evenly, then add FeCl2·4H2O and NiCl2·6H2O to the above homogeneous solution, magnetically stir for 3 h, then transfer it into a polytetrafluoroethylene hydrothermal reaction kettle, react at 150 °C for 24 h, and then naturally cool to room temperature. The obtained solid product is centrifugally washed 5 times with DMF and absolute ethanol and then placed in a vacuum drying oven at 80 °C for drying for 12 h to obtain the Fe-Ni-MOF substrate; the molar ratio of triethylenediamine, terephthalic acid, FeCl2·4H2O, and NiCl2·6H2O is: 15:15:4:1; the concentration of triethylenediamine in the DMF solution is 0.05 mol / L.

[0043] (2) Mix the Fe-Ni-MOF substrate with nano-silicon powder, and after mechanical ball milling for 1 h, transfer the mixture into a tubular furnace, introduce argon as the protective gas, and perform high-temperature calcination. After natural cooling and grinding, the lithium battery composite anode material is obtained; the mass ratio of the Fe-Ni-MOF substrate to the nano-silicon powder is 0.8:1; the specific high-temperature calcination method is as follows: heat up to 200 °C at a rate of 3 °C / min, keep the temperature for 1 h, then adjust the heating rate to 5 °C / min and rise to 800 °C, and keep the temperature for reaction for 2 h.

[0044] In this comparative example, except that unmodified nano-silicon powder is directly used, the others are the same as in Example 3.

[0045] Performance test

[0046] The electrochemical performance of the lithium battery composite anode materials prepared in Examples 1-3 and Comparative Examples 1-2 was tested. The specific steps are as follows: The anode material prepared in the present invention was thoroughly ground and then ground and stirred with acetylene black and sodium alginate according to a mass ratio of 8:1:1 until a uniformly dispersed slurry was formed. Then, it was coated on a copper foil with an I-shaped scraper, and the thickness of the slurry was 75 μm. It was dried in a vacuum drying oven at 60 °C for 12 h, taken out, cut into circular pieces with a diameter of 12 mm on a slicing machine and pressed, and the pressure was 6 MPa to obtain the lithium battery anode sheet. After weighing and marking, it was quickly transferred to a glove box under an argon atmosphere to assemble a CR-2032 type button battery. The counter electrode was a lithium metal sheet, the separator model was Celgard 2400, and the diameter was 19 mm. After assembly and standing for 12 h, various electrochemical performance tests were carried out. A battery charge and discharge test system was used to perform cyclic charge and discharge tests at a set current density, and the voltage range was 0.01~2.00 V. First, it was activated for 3 cycles at a current density of 50 mA / g, and then a long cycle test was carried out at a current density of 100 mA / g. The specific test results are shown in Table 1.

[0047] Table 1 Performance test results

[0048] ;

[0049] As can be seen from the above data, the lithium battery composite anode material prepared in the present invention has good electrochemical performance, with a high discharge specific capacity, good electrical conductivity and cycling performance. This shows that the material of the present invention has a loose porous structure, which can effectively solve the problem of volume expansion of the silicon anode during the insertion and extraction process of lithium ions. The sodium alginate-modified nano-silicon particles are uniformly dispersed in the pores of the iron-nickel metal-organic framework-based porous carbon material ( Figure 1 ), forming a stable composite material structure. This structure can not only utilize the high lithium storage capacity of silicon, but also give play to the excellent electrical conductivity and structural stability of the porous carbon material, and has good rate performance and cycling stability.

[0050] The lithium battery composite anode materials prepared in Example 3, Comparative Example 1 and Comparative Example 2 were selected, and an electrochemical impedance test was carried out using an electrochemical analyzer. The electrochemical impedance test parameters: the test frequency range was 0.1×10 -6 ~1×10 6 Hz. The EIS spectrum and the corresponding fitting circuit are as Figure 2 shown. In the fitting circuit diagram, R s , R ct are the electrolyte resistance and the charge transfer resistance respectively, CPE1 is a constant phase angle element related to the interfacial resistance, W0 is an element of the Warburg resistance, and among them, R ct can reflect the difficulty of the charge transfer process at the electrode / electrolyte interface. FromFigure 2 It can be seen that the impedance R of the lithium battery composite anode material prepared in Example 3 of the present invention ct is significantly lower than the impedance values of Comparative Example 1 and Comparative Example 2, which indicates that the introduction of the iron-nickel bimetal and the diatomite-modified nano-silicon powder in the electrode material prepared by the present invention synergistically further enhances the conductivity of the material, and the electrochemical performance of the material is good.

[0051] It should be noted that the above embodiments are only some of the embodiments of the preferred implementation manners of the present invention, rather than all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite negative electrode material for a lithium battery, characterized in that: It includes the following steps: (1) Dissolve triethylenediamine and terephthalic acid in DMF, stir evenly, add FeCl2·4H2O and NiCl2·6H2O to the uniform solution, stir magnetically for 3 h, transfer to a polytetrafluoroethylene hydrothermal reactor, react at 150°C for 24 h, cool naturally to room temperature, wash the obtained solid product with DMF and anhydrous ethanol by centrifugation for 3-5 times, and dry it in a vacuum drying oven to obtain a Fe-Ni-MOF substrate; (2) Add 0.5 g of sodium alginate to 100 ml of 1 mol / L NaCl solution, stir and dissolve completely to obtain solution A; add 2 g of nano-silicon powder to 100 ml of deionized water, disperse evenly by ultrasonication and mix evenly with solution A, react for 2-3 hours under magnetic stirring, separate by centrifugation to obtain a solid product, wash with deionized water for several times, and dry in an oven to obtain a sodium alginate modified nano-silicon material; (3) The Fe-Ni-MOF substrate is mixed with the sodium alginate modified nano-silicon material, and after mechanical ball milling for 1 hour, the mixture is transferred into a tubular furnace, argon is introduced as a protective gas, high-temperature calcination is performed, and natural cooling and grinding are performed to obtain a lithium battery composite negative electrode material.

2. The method for preparing a composite negative electrode material for a lithium battery according to claim 1, characterized in that: In the step (1), the molar ratio of triethylenediamine, terephthalic acid, FeCl2·4H2O and NiCl2·6H2O is 15:15:4:1; and the concentration of triethylenediamine in the DMF solution is 0.05 mol / L.

3. The method for preparing a composite negative electrode material for a lithium battery according to claim 1, characterized in that: The vacuum drying temperature in step (1) is 80° C. and the time is 12 h.

4. The method for preparing a composite negative electrode material for a lithium battery according to claim 1, characterized in that: In step (2), the oven drying temperature is 60° C. and the time is 10 h.

5. The method for preparing a composite negative electrode material for a lithium battery according to claim 1, characterized in that: In the step (3), the mass ratio of the Fe-Ni-MOF substrate to the sodium alginate modified nano-silicon material is 0.3-0.8:

1.

6. The method for preparing a composite negative electrode material for a lithium battery according to claim 1, characterized in that: The high temperature calcination method in step (3) is specifically as follows: heating to 200°C at a rate of 3°C / min, keeping the temperature for 1-2 hours, adjusting the heating rate to 5°C / min to 800°C, and keeping the temperature for 2-3 hours.

7. A lithium battery composite negative electrode material prepared by the preparation method according to any one of claims 1 to 6.

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