Double carbon covalently encapsulated silicon oxide negative electrode material, preparation method and lithium ion battery using the negative electrode material

Abstract

A double-carbon covalently encapsulated silicon dioxide negative electrode material, a preparation method, and a lithium-ion battery using the negative electrode material belong to the technical field of lithium-ion batteries. The present invention adopts a "dissolution-capture" method, that is, utilizing the difference in polymerization degree inside and outside the 3-aminophenol-formaldehyde resin ball, using low-cost anhydrous ethanol as a chemical "scissors" to cut the low-molecular-weight fragments of the internal low polymerization degree to dissolve them, and at the same time introducing a silicon source to capture the small molecular weight fragments, achieving bidirectional coating inside and outside the silica, and preparing a double-carbon covalently encapsulated silicon dioxide negative electrode material. This process does not require the secondary introduction of a carbon source, thereby achieving bidirectional double-carbon covalent coating inside and outside the silica ball and effectively suppressing the huge volume expansion generated during the insertion and extraction of lithium ions. When the prepared negative electrode material is used as a lithium-ion battery negative electrode, the lithium-ion battery has a high initial coulombic efficiency (76.8%), fast charging capability, and good structural stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a silicon monoxide negative electrode material with dual-carbon covalent encapsulation, a preparation method thereof, and a lithium-ion battery using the negative electrode material. Background Art

[0002] Rechargeable lithium-ion batteries have been recognized as the most important power sources for portable electronic products and electric vehicles. The growing energy storage demand has gradually put forward higher requirements for energy density, lifespan, and rate performance, exceeding the theoretical limits of current lithium-ion batteries based on traditional graphite negative electrodes. Silicon monoxide (SiOx, 0 < x < 2) has advantages such as high theoretical capacity (1695~4200 mAh g -1 ), low equilibrium potential (0.2~0.4 V vs. Li / Li + ), and rich resources, and is one of the most promising negative electrode materials for high-energy-density lithium-ion batteries. However, in the process of promoting the practical application of silicon monoxide negative electrode materials, some challenges still need to be urgently solved: for example, the large volume change (118~300%) caused by the insertion and extraction of lithium ions during charge and discharge, and the low electron / ion conductivity. Especially in the case of fast charge and discharge, the severe volume change is the most fatal, which will lead to the decline of the stability of the solid electrolyte interphase film, serious pulverization of the electrode and loss of electrical contact, ultimately resulting in rapid attenuation of the battery capacity and even possible safety problems. The carbon coating strategy has been proposed to alleviate the volume expansion of the silicon monoxide negative electrode and improve the conductivity of the material at the same time. However, the current one-way covalent point contact between silicon monoxide and the carbon coating is difficult to maintain the huge volume expansion, seriously affecting its cycle stability and high-rate capacity. In addition, the carbon coating synthesis of these materials usually involves complex methods such as chemical vapor deposition, which requires expensive equipment and is difficult to produce on a large scale.

[0003] Therefore, considering all these conflicting requirements comprehensively, for silicon monoxide negative electrode materials with large volume changes, covalent bonding with a carbon coating seems to be the preferred method, but a simple and economical new covalent method needs to be developed to improve the performance of silicon monoxide negative electrode materials. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a silicon monoxide negative electrode material with dual-carbon covalent encapsulation, a preparation method thereof, and a lithium-ion battery using the negative electrode material.

[0005] The dual-carbon covalently encapsulated silicon dioxide anode material described in this invention features structural stability and rapid charging. This method employs a "dissolve-and-capture" approach, utilizing the difference in the degree of polymerization (DOP) inside and outside 3-aminophenol-formaldehyde resin spheres. Low-cost anhydrous ethanol is used as a chemical "scissor" to dissolve out low-molecular-weight fragments of the internal low-DOP. Simultaneously, a silicon source is introduced to capture these fragments, achieving bidirectional dual-carbon covalent coating of the silica inside and outside. This results in the preparation of a dual-carbon covalently encapsulated silicon dioxide anode material. When used as the negative electrode in lithium-ion batteries, this material exhibits a high initial coulombic efficiency (76.8%), rapid charging capability, and good structural stability.

[0006] The preparation method of the double-carbon covalently encapsulated silicon oxide negative electrode material of the present invention comprises the following steps:

[0007] (1) 0.05-0.2 g of 3-aminophenol (3-AP), 0.1-0.3 mL of formaldehyde aqueous solution (mass fraction of 35-37%) and 0.1-0.2 mL of ammonia water were added to 30-50 mL of deionized water in sequence, and magnetic stirring was carried out at room temperature for 30-60 minutes to synthesize 3-aminophenol-formaldehyde resin spheres; since the polymerization degree inside and outside the 3-aminophenol-formaldehyde resin spheres was different, 30-50 mL of anhydrous ethanol solution was added as a chemical "scissors" to react for 60-90 minutes to selectively remove the small molecular weight fragments with low internal polymerization degree, thereby forming hollow structure 3-aminophenol-formaldehyde resin spheres; then 0.3-0.6 g of hexadecyltrimethylammonium bromide (CTAB) and 0.5-0.8 mL of 3-aminopropyltrimonium bromide were added to the above solution in sequence. The ethoxysilane (APTES) was stirred at room temperature overnight, and 3-aminopropyltriethoxysilane (APTES) uniformly coated the surface of the hollow 3-aminophenol-formaldehyde resin spheres. At the same time, the small molecular weight fragments dissolved from the 3-aminophenol-formaldehyde resin spheres formed another layer of 3-aminophenol-formaldehyde resin on the surface of the 3-aminopropyltriethoxysilane (APTES) coating due to electrostatic interactions. After the reaction, the mixture was centrifuged at 10,000-12,000 rpm for 3-5 minutes, the supernatant was removed, and the precipitate was retained. The resulting precipitate was washed with anhydrous ethanol solution and vacuum-dried at 50-70°C for 5-10 hours, thereby obtaining hollow "sandwich" structured 3-aminophenol-formaldehyde resin@silica@3-aminophenol-formaldehyde resin spheres (APF@SiO2@APF).

[0008] (2) The hollow "sandwich" structure of 3-aminophenol-formaldehyde resin@silica@3-aminophenol-formaldehyde resin balls obtained in step (1) are placed in high-purity nitrogen with a volume fraction of 98-99%, and calcined at 600-1000°C for 2-3 hours to obtain the double-carbon covalently encapsulated silicon dioxide anode material, namely, carbon@silicon dioxide@carbon (C@SiOx@C) anode material.

[0009] Preferably, in step (1), the mass fraction of the anhydrous ethanol solution is 99.0-99.8%, and the mass fraction of the ammonia water is 27-29%;

[0010] Preferably, in step (1), the obtained precipitate is washed with anhydrous ethanol solution by adding 10-20 mL of anhydrous ethanol solution with a mass fraction of 99.0-99.8% to the obtained precipitate, ultrasonically dispersing it uniformly, and centrifuging it at a speed of 10000-12000 rpm for 3-5 minutes, removing the supernatant, and retaining the precipitate; then repeating the operation step of "adding 10-20 mL of anhydrous ethanol solution with a mass fraction of 99.0-99.8% to the obtained precipitate, ultrasonically dispersing it uniformly, and centrifuging it at a speed of 10000-12000 rpm for 3-5 minutes, removing the supernatant, and retaining the precipitate" 2-3 times;

[0011] Preferably, the heating rate during calcination in step (2) is 5-10°C / min.

[0012] The double-carbon covalently encapsulated silicon dioxide negative electrode material prepared by the present invention is a hollow nano-spherical material with a particle size of about 320 nm.

[0013] The double-carbon covalently encapsulated silicon monoxide negative electrode material of the present invention is prepared by the above method.

[0014] The present invention also provides a lithium ion battery, wherein the negative electrode material used in the lithium ion battery is the double-carbon covalently encapsulated silicon dioxide negative electrode material prepared by the present invention.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The present invention utilizes the different degrees of polymerization inside and outside the 3-aminophenol-formaldehyde resin spheres, and uses low-cost anhydrous ethanol as a chemical "scissors" to cut the low-molecular-weight fragments with low polymerization degree inside the 3-aminophenol-formaldehyde resin spheres to dissolve them. At the same time, by utilizing electrostatic interaction, silane APTES is introduced to capture the small molecular-weight fragments and obtain another layer of 3-aminophenol-formaldehyde resin coating, thereby obtaining a hollow "sandwich" structure of 3-aminophenol-formaldehyde resin@silica@3-aminophenol-formaldehyde resin spheres. This process does not require the secondary introduction of a carbon source, thereby achieving bidirectional coating inside and outside the silica spheres.

[0017] (2) After carbonization, silicon oxide is covalently connected to the inner and outer carbon layers in a Si-OC manner to form a double-carbon covalently encapsulated silicon oxide negative electrode material. This double-carbon covalent encapsulation not only greatly improves the ionic / electronic conductivity of silicon oxide, but also effectively suppresses the huge volume expansion generated during the insertion and extraction of lithium ions, thereby achieving stable cycling of the silicon oxide negative electrode material at high rates. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 : A scanning electron microscope photograph of the hollow "sandwich" structure of 3-aminophenol-formaldehyde resin@silica@3-aminophenol-formaldehyde resin spheres prepared in Example 1;

[0019] Figure 2 : Transmission electron micrograph of the double carbon covalently encapsulated silicon oxide negative electrode material prepared in Example 1, the left image is a low-magnification image, and the right image is a high-magnification image;

[0020] Figure 3 : Thermogravimetric curves of the negative electrode materials prepared in Example 1 and Comparative Example 1;

[0021] Figure 4 : Mapping element analysis diagram of the double carbon covalently encapsulated silicon oxide negative electrode material prepared in Example 1;

[0022] Figure 5 : Infrared spectrum analysis of the double carbon covalently encapsulated silicon oxide negative electrode material prepared in Example 1;

[0023] Figure 6 : X-ray photoelectron spectroscopy analysis of the double carbon covalently encapsulated silicon oxide negative electrode material prepared in Example 1;

[0024] Figure 7 : The first charge-discharge curve of the double-carbon covalently encapsulated silicon oxide negative electrode material prepared in Example 1;

[0025] Figure 8 : The rate performance curve of the double carbon covalently encapsulated silicon oxide negative electrode material prepared in Example 1;

[0026] Figure 9 : Cyclic performance curve of the double-carbon covalently encapsulated silicon oxide negative electrode material prepared in Example 1;

[0027] Figure 10 : Cross-sectional scanning electron microscope photos of the double-carbon covalently encapsulated silicon oxide negative electrode material prepared in Example 1 before cycling (left) and after cycling (right). DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme, effect advantage of the embodiments of the present invention clearer, the embodiments will be described in more detail below, and it should be noted that the embodiments described below are not all embodiments, but only embodiments of the preferred invention conditions of the present invention. The reagents and instruments used in the embodiments can be purchased through normal commercial channels. Based on the embodiments of the present invention, those of ordinary skill in the art directly obtain the present embodiments without creative activities, and belong to the scope of protection of the present invention.

[0029] Example 1:

[0030] (1) 0.1 g of 3-aminophenol (3-AP), 0.2 mL of formaldehyde aqueous solution (mass fraction 37%) and 0.15 mL of ammonia water (mass fraction 28%) were added to 30 mL of deionized water in sequence, and magnetic stirring was carried out at room temperature for 30 minutes to synthesize 3-aminophenol-formaldehyde resin spheres. Since the polymerization degree inside and outside the 3-aminophenol-formaldehyde resin spheres was different, 40 mL of anhydrous ethanol solution (mass fraction 99.5%) was added as a chemical "scissors" to react for 60 minutes to selectively remove the small molecular weight fragments with low internal polymerization degree, thereby forming hollow structure 3-aminophenol-formaldehyde resin spheres. Then, 0.5 g of hexadecyltrimethylammonium bromide (CTAB) and 0.6 mL of 3-aminopropyltriethoxysilane (APTES) were added to the above solution in sequence, and stirred at room temperature overnight. During this process, APTES uniformly coats the surface of the hollow 3-aminophenol-formaldehyde resin spheres. Simultaneously, low-molecular-weight fragments dissolved from the 3-aminophenol-formaldehyde resin spheres re-form a 3-aminophenol-formaldehyde resin coating on the surface of the silane (APTES) coating due to electrostatic interactions. After the reaction is complete, the mixture is centrifuged at 11,000 rpm for 4 minutes, the supernatant removed, and the precipitate retained. The resulting precipitate is washed with ethanol and dried at 60°C under vacuum for 8 hours, yielding approximately 0.18 g of an orange-yellow precipitate, the hollow "sandwich" structure of 3-aminophenol-formaldehyde resin@silica@3-aminophenol-formaldehyde resin spheres (APF@SiO2@APF). Figure 1 As shown, the hollow structure of APF@SiO2@APF is well-dispersed nanospheres with a particle size of about 320 nm;

[0031] The precipitate was washed with anhydrous ethanol solution by adding 20 mL of anhydrous ethanol solution with a mass fraction of 99.5% to the precipitate, then ultrasonically dispersing the precipitate, and centrifuging it at a speed of 11,000 rpm for 4 minutes, then removing the supernatant and retaining the precipitate. This step was performed 3 times in total.

[0032] (2) The hollow "sandwich" structure of 3-aminophenol-formaldehyde resin@silica@3-aminophenol-formaldehyde resin balls obtained in step (1) were calcined in a tube furnace with a gas atmosphere of 99% by volume of high-purity nitrogen at a heating rate of 5°C / min and calcined at 800°C for 2 hours to obtain about 0.12g of black powder, i.e., a double carbon covalently encapsulated silicon dioxide anode material (carbon@silicon dioxide@carbon (C@SiOx@C) anode material); Figure 2 As shown, the double carbon covalently encapsulated silicon oxide negative electrode material is a hollow "sandwich" structure nanosphere, which consists of a carbon layer, silicon oxide, and a carbon layer from the inside out. In addition, the weight loss curve of the double carbon covalently encapsulated silicon oxide negative electrode material in air atmosphere ( Figure 3 ) analysis showed that the mass fraction of the inner carbon layer in the sample was 13.81%, and the mass fraction of the outer carbon layer was 10.15%.

[0033] The double carbon covalently encapsulated silicon oxide negative electrode material prepared in this embodiment was subjected to mapping element analysis, as shown in FIG. Figure 4 As shown, the results show that the three elements silicon, oxygen and carbon are evenly distributed in the material.

[0034] The double carbon covalently encapsulated silicon oxide negative electrode material prepared in this embodiment was analyzed by infrared spectroscopy (FTIR). Figure 5 As shown in the figure, it can be concluded that silicon 2 Oxide is covalently connected to the inner and outer carbon layers in the Si-OC manner.

[0035] The double carbon covalently encapsulated silicon oxide negative electrode material prepared in this embodiment was subjected to X-ray photoelectron spectroscopy (XPS) analysis. Figure 6 As shown in Figure 3, the XPS results further prove that silicon oxide and the inner and outer carbon layers are covalently connected in a Si-OC manner. At the same time, it can be concluded that the Si-OC covalent bond content in the double-carbon covalently encapsulated silicon oxide negative electrode material is about 48%.

[0036] Comparative Example 1:

[0037] (1) 0.1 g of 3-aminophenol (3-AP), 0.2 mL of formaldehyde aqueous solution (mass fraction 37%) and 0.15 mL of ammonia water (mass fraction 28%) were added to 30 mL of deionized water in sequence and magnetically stirred at room temperature for 30 minutes to synthesize 3-aminophenol-formaldehyde resin spheres. Since the internal and external polymerization degrees of 3-aminophenol-formaldehyde resin spheres were different, 40 mL of anhydrous ethanol solution (mass fraction 99.5%) was added as a chemical "scissors" to react for 60 minutes to selectively remove the small molecular weight fragments with low internal polymerization degrees, thereby forming hollow structure 3-aminophenol-formaldehyde resin spheres. The precipitate was then washed and centrifuged three times with anhydrous ethanol. After washing and centrifuging three times, the precipitate was redispersed in 30 mL of deionized water. 0.15 mL of ammonia water and 0.6 mL of 3-aminopropyltriethoxysilane (APTES) were added dropwise to the above solution respectively and stirred at room temperature overnight. In this process, APTES was evenly coated on the surface of the hollow structure 3-aminophenol-formaldehyde resin spheres. After the reaction, the mixture was washed with anhydrous ethanol and centrifuged three times. The resulting precipitate was vacuum-dried at 60°C for 8 hours to obtain approximately 0.16 g of an orange-yellow precipitate, namely, 3-aminophenol-formaldehyde resin@silica (APF@SiO2) with a hollow "core-shell" structure.

[0038] The precipitate was washed with anhydrous ethanol solution by adding 20 mL of anhydrous ethanol solution with a mass fraction of 99.5% to the precipitate, then ultrasonically dispersing the precipitate, and centrifuging it at a speed of 11,000 rpm for 4 minutes, then removing the supernatant and retaining the precipitate. This step was performed 3 times in total.

[0039] (2) The hollow "core-shell" structure of 3-aminophenol-formaldehyde resin@silica obtained in step (1) was calcined in a tubular furnace with a gas atmosphere of 99% by volume of high-purity nitrogen at a heating rate of 5°C / min and calcined at 800°C for 2h to obtain about 0.11g of black powder, i.e., a silicon oxide negative electrode material with internal carbon unidirectional covalent encapsulation (carbon@silicon oxide (C@SiOx) negative electrode material).

[0040] Comparative Example 2:

[0041] (1) The hollow "core-shell" structure of 3-aminophenol-formaldehyde resin @ silica sample obtained in step (1) of comparative example 1 was placed in a muffle furnace for air calcination at a heating rate of 5°C / min, and the temperature was raised to 600°C and kept constant for 3 hours to obtain hollow silica nanospheres. The obtained hollow silica nanospheres were then redispersed in 30 mL of deionized water, and 0.15 mL of ammonia water, 0.1 g of 3-aminophenol (3-AP) and 0.2 mL of formaldehyde aqueous solution (mass fraction of 37%) were added to the above solution in sequence, and stirred at room temperature overnight. In this process, 3-aminophenol-formaldehyde resin spheres were uniformly coated on the surface of the hollow silica spheres. After the reaction was completed, the mixture was washed with anhydrous ethanol and centrifuged three times; the resulting precipitate was dried at 60°C and vacuum-dried for 8 hours to obtain about 0.15 g of orange-yellow precipitate, i.e., hollow "core-shell" structure of silica @ 3-aminophenol-formaldehyde resin spheres (SiO2@APF);

[0042] The precipitate was washed with anhydrous ethanol solution by adding 20 mL of anhydrous ethanol solution with a mass fraction of 99.5% to the precipitate, then ultrasonically dispersing the precipitate, and centrifuging it at a speed of 11,000 rpm for 4 minutes, then removing the supernatant and retaining the precipitate. This step was performed 3 times in total.

[0043] (2) The hollow "core-shell" structured silica@3-aminophenol-formaldehyde resin balls obtained in step (1) were calcined in a tubular furnace with a gas atmosphere of 99% by volume of high-purity nitrogen at a heating rate of 5°C / min and calcined at 800°C for 2 h. Finally, about 0.10 g of black powder was obtained, namely, silicon dioxide anode material with external carbon unidirectional covalent encapsulation (silicon dioxide@carbon (SiOx@C) anode material).

[0044] The anode materials prepared in Example 1 and Comparative Examples 1 and 2 were assembled into button cells. The specific steps were as follows: The electrode materials were prepared by mixing 80% by mass of the active material (i.e., the C@SiOx@C negative electrode material prepared in Example 1, the C@SiOx negative electrode material prepared in Comparative Example 1, and the SiOx@C negative electrode material prepared in Comparative Example 2), 10% by mass of sodium alginate as a binder, and 10% by mass of acetylene black as a conductive material with deionized water. Copper foil was used as the current collector and dried at 100°C for 12 hours to form the electrode sheet. Lithium foil was then used as the counter electrode, and a commercial solution of lithium hexafluorophosphate in ethylene carbonate and dimethyl carbonate was used as the electrolyte. Additives included 10% by volume of fluoroethylene carbonate and 2% by volume of vinylene carbonate. The entire battery assembly process was performed in an argon-filled glove box.

[0045] Table 1: Performance test data of examples and comparative examples

[0046]

[0047] The assembled batteries were tested for electrochemical performance at room temperature, and the results showed that the electrochemical performance of each sample in Table 1 was 0.2Ag. -1 The first reversible charge capacity and the first initial coulombic efficiency at the current density. Through data comparison, we found that the double carbon covalently encapsulated silicon oxide negative electrode material prepared in Example 1 has the best lithium storage performance, specifically as follows Figures 7-10 As shown. Figure 7 As shown, at 0.2Ag -1 At a current density of 1.5 , the reversible charge capacity of the double carbon covalently encapsulated silicon oxide negative electrode material obtained in Example 1 can reach 1065.1 mAh g -1 The coulombic efficiency was as high as 76.8% for the first time, proving that the prepared double carbon covalently encapsulated silicon oxide negative electrode material has excellent reversible charge and discharge capabilities. Figure 8 As shown, even at 5Ag -1 At high current density, its reversible specific capacity is still as high as 906 mAh g -1 , and when the current density returns to 0.2A -1 After that, the specific capacity recovered to 1055.8 mAh g -1 , highlighting its excellent charging rate and reversibility. Figure 9 As shown, in 2Ag -1 At a high current density, after 1200 cycles, its reversible capacity can still reach 874.2 mAh g -1 , the capacity retention rate reaches 88.3%. Figure 10 As shown, the silicon monoxide negative electrode material exhibits a lower volume expansion rate (about 27.8%) due to the covalent encapsulation with the bidirectional carbon layer.

[0048] In summary, the double-carbon covalently encapsulated silicon dioxide negative electrode material prepared by the present invention has the ability of long-term stability and rapid charging.

Claims

1. A method for preparing a double-carbon covalently encapsulated silicon oxide negative electrode material, characterized by: The steps are as follows: (1) 0.05-0.2 g of 3-aminophenol, 0.1-0.3 mL of 35-37% formaldehyde aqueous solution, and 0.1-0.2 mL of ammonia water were sequentially added to 30-50 mL of deionized water, and magnetically stirred at room temperature for 30-60 minutes to synthesize 3-aminophenol-formaldehyde resin spheres; 30-50 mL of anhydrous ethanol solution was added as a chemical "scissors" to react for 60-90 minutes to form hollow structure 3-aminophenol-formaldehyde resin spheres; then 0.3-0.6 g of hexadecyltrimethylammonium bromide and 0.5-0.8 mL of 3-aminopropyltriethoxysilane were sequentially added to the above solution, and stirred at room temperature overnight; after the reaction, the mixture was centrifuged at 10,000-12,000 rpm for 3-5 minutes, the supernatant was removed, and the precipitate was retained; The resulting precipitate was washed with anhydrous ethanol solution and then dried under vacuum at 50-70°C for 5-10 hours, thereby obtaining hollow "sandwich" structured 3-aminophenol-formaldehyde resin@silica@3-aminophenol-formaldehyde resin spheres. (2) The hollow "sandwich" structure of 3-aminophenol-formaldehyde resin@silica@3-aminophenol-formaldehyde resin balls obtained in step (1) are placed in high-purity nitrogen with a volume fraction of 98-99%, and calcined at 600-1000°C for 2-3 hours to obtain the double-carbon covalently encapsulated silicon dioxide negative electrode material.

2. The method for preparing a double-carbon covalently encapsulated silicon oxide negative electrode material according to claim 1, characterized in that: The mass fraction of the anhydrous ethanol solution is 99.0~99.8%, and the mass fraction of the ammonia water is 27~29%.

3. The method for preparing a double-carbon covalently encapsulated silicon oxide negative electrode material according to claim 1, characterized in that: The heating rate during calcination in step (2) is 5-10°C / min.

4. A double carbon covalently encapsulated silicon oxide negative electrode material, characterized by: The invention is prepared by the preparation method according to any one of claims 1 to 3.

5. A lithium-ion battery, characterized in that: The negative electrode material used in the lithium-ion battery is the double-carbon covalently encapsulated silicon dioxide negative electrode material according to claim 4.

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