A silicon oxide negative electrode material and a preparation method thereof

Abstract

The present invention discloses a silicon oxide negative electrode material and a preparation method thereof, belonging to the technical field of lithium-ion batteries. The negative electrode material includes a silicon-carbon composite, a binder, and conductive carbon black. The weight ratio of the silicon-carbon composite, the binder, and the conductive carbon black is 23:1:1, and the binder is a polyacrylic acid polymer formed by free radical polymerization. By compounding silicon dioxide with carbon to form a porous structure in which granular silicon dioxide adheres to the graphite sheet layer, the present invention can improve the conductivity of the negative electrode material and improve the volume expansion effect of silicon oxide; by using a polyacrylic acid polymer as the binder of the negative electrode material, a silane soft segment, a sulfonic acid group, and a fluorine-containing group are introduced into the polyacrylic acid molecular chain. The silane soft segment can effectively improve the flexibility of the binder, and thus can play an elastic buffering role in the volume change of silicon. The introduction of the sulfonic acid group and the fluorine-containing group can both improve the liquid absorption rate of the electrolyte, thereby improving the cycle performance of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and specifically relates to a silicon oxide negative electrode material and a preparation method thereof. Background Art

[0002] The negative electrode of a lithium-ion battery is made by uniformly applying a paste adhesive, which is a mixture of a negative electrode active material, a carbon material or a non-carbon material, a binder and an additive, on both sides of a copper foil, and then drying and rolling. The negative electrode material is the main body for storing lithium in the lithium-ion battery, enabling lithium ions to be inserted and extracted during charge and discharge. The negative electrode material mainly affects the energy density, first efficiency, cycle performance, etc. of the lithium battery, and the performance of the negative electrode material also directly affects the performance of the lithium battery.

[0003] Among lithium-ion battery negative electrode materials, when graphite is used as the negative electrode, the theoretical capacitance is 372 mAh / g, while when silicon is used as the negative electrode, the theoretical capacitance is 4200 mAh / g. Although the theoretical capacitance of silicon is large, during the process of inserting and extracting lithium ions, silicon will undergo volume expansion, resulting in stress and cracks in the material itself, and even material pulverization, which leads to an increase in the irreversible reaction between the lithium-ion negative electrode interface and the electrolyte. Currently, while improving the energy density of lithium-ion batteries, silicon-carbon composite materials are mostly prepared by combining graphite and silicon.

[0004] Silicon oxides not only have a high specific capacitance, but also have a much smaller volume effect than pure silicon, and have good stability and cycle life. Currently, small-scale commercial applications have emerged in the fields of digital and power batteries. However, although the cycle stability of silicon oxides is improved compared with that of elemental Si, silicon oxides themselves still have a certain expansion effect, resulting in the same problems as pure Si during charge and discharge, and the first-cycle capacity and cycle performance will both deteriorate to a certain extent. Therefore, effectively improving the volume expansion problem of silicon oxides is of great significance. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide an electrolyte for a secondary lithium battery and a preparation method thereof.

[0006] In the present invention, by compounding silicon dioxide and carbon to form a porous structure with granular silicon dioxide attached to graphite lamellae, the conductivity of the negative electrode material can be improved and the volume expansion effect of silicon oxides can be improved; by preparing a polyacrylic acid polymer as a binder for the negative electrode material, a silane soft segment, a sulfonic acid group and a fluorine-containing group are introduced into the polypropylene molecular chain. The silane soft segment can effectively improve the flexibility of the binder, and thus can play an elastic buffering role in the volume change of silicon. The introduction of the sulfonic acid group and the fluorine-containing group can both increase the liquid absorption rate of the negative electrode for the electrolyte, thereby improving the cycle performance of the battery.

[0007] The object of the present invention can be achieved by the following technical solutions:

[0008] A silicon oxide negative electrode material, comprising a silicon-carbon composite, a binder, and conductive carbon black, and the weight ratio of the silicon-carbon composite, the binder, and the conductive carbon black is 23:1:1.

[0009] A preparation method of a silicon oxide negative electrode material is as follows:

[0010] First step, after mixing the silicon-carbon composite, the binder, and the conductive carbon black in proportion, disperse them in N-methyl-2-pyrrolidone, and continuously stir for 24 h to obtain a uniformly mixed slurry;

[0011] Second step, coat the slurry on a copper foil, dry it at 100 °C for 8 h, and then transfer it to a vacuum dryer at 80 °C for 24 h to obtain a lithium-ion negative electrode material.

[0012] Further, the silicon-carbon composite is prepared by the following steps:

[0013] 1) Dissolve CTAB (cetyltrimethylammonium bromide) in deionized water, and vigorously stir at room temperature for 10 min. After adding ammonia water (concentration 1 mol / L), continue to stir for 10 min, then add n-octane to the above solution, stir for 30 min, and then add glucose. After dissolution, a mixed solution is obtained;

[0014] 2) Dropwise add tetraethyl orthosilicate to the mixed solution, continuously stir for 1 h, transfer it to an autoclave, and perform heat treatment at 100 °C for 24 h. Wash the obtained solid with ethanol / water 3-4 times, filter and separate it, dry it at 80 °C for 12 h, and finally calcine it at 800 °C for 4 h to carbonize it to obtain a silicon-carbon composite.

[0015] The dosage ratio of CTAB, deionized water, ammonia water, n-octane, glucose, and tetraethyl orthosilicate is 1.6 g:80 mL:7.2 mL:24 mL:0.9 g:4.2 g.

[0016] Using tetraethyl orthosilicate as the silicon source, n-octane and glucose as the carbon sources, and CTAB as the template, a silicon-carbon composite material of SiO2 / C is obtained through hydrothermal synthesis and calcination treatment; the silicon-carbon composite material is a porous material, and its porous structure is beneficial to the rapid transfer of lithium ions and electrons, and also provides a large number of active sites for lithium storage, resulting in a high reversible capacity; in the silicon-carbon composite, granular SiO2 is distributed on lamellar graphite flakes, and such a unique structure enables lithium ions to contact silicon dioxide over a larger area under the action of C, thereby enhancing the conductivity of silicon dioxide; after compounding silicon dioxide with carbon, the addition of C enhances the conductivity of the electrode material and improves the problem of low conductivity of SiO2. At the same time, the addition of C can also alleviate the volume change problem of SiO2.

[0017] Further, the binder is prepared through the following steps:

[0018] S1. Add acrylic acid and dichloromethane into a flask, then add EDCI (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, a condensing agent), stir evenly, add sodium 2-(ethylamino)ethanesulfonate, stir and react at room temperature for 2 h. After removing the solvent by rotary evaporation, extract with ethyl acetate. Finally, dry the product under vacuum at 60 °C for more than 3 h to obtain a sulfonic acid derivative; the dosage ratio of acrylic acid, dichloromethane, EDCI, and sodium 2-(ethylamino)ethanesulfonate is 7.2 g: 300 mL: 21 g: 19 g;

[0019] The -COOH on acrylic acid and the -NH2 on the molecule of sodium 2-(ethylamino)ethanesulfonate have relatively high reactivity. Under the action of the condensing agent, a polycondensation reaction occurs at room temperature to generate a sulfonic acid derivative. The specific reaction equation is as follows:

[0020]

[0021] S2. Add acrylic acid, vinyltri(lactate ethyl)silane, and the sulfonic acid derivative into a four-necked flask filled with argon, and introduce trifluoroethylene. Heat to 75 °C. Subsequently, use a constant-pressure dropping funnel to dropwise add an ethyl acetate solution of AIBN (the concentration of the ethyl acetate solution of AIBN is 5.2 mg / mL, and the dropping rate is controlled at 0.125 mL / min) into the reactor. After the dropping is completed, react at a constant temperature of 75 °C for 8 hours. Cool the product to room temperature, then remove the unreacted monomers and excess solvent by rotary evaporation. Finally, dry under vacuum at 70 °C to obtain the binder; the dosage ratio of acrylic acid, vinyltri(lactate ethyl)silane, the sulfonic acid derivative, and trifluoroethylene is 30 g: 15.5 - 16.5 g: 8.5 - 9 g: 2.0 g; the added mass of AIBN is 0.2% of the total mass of the monomers;

[0022] Using acrylic acid, vinyltri(lactate ethyl)silane, the sulfonic acid derivative, and trifluoroethylene as monomers, a binder is synthesized by free radical polymerization. The reaction equation is as follows:

[0023]

[0024] In the formula,

[0025] The binder belongs to polyacrylic polymers. Because it contains carboxyl groups with high concentration and uniform distribution, strong hydrogen bond interactions can be formed between the binder-binder and binder-silicon particles, thereby providing strong adhesion. In addition, through the incorporation of vinyltriethoxylsilane, soft segments are introduced into the polyacrylic molecular chain, thus improving the flexibility of the polymer. The enhanced flexibility can not only improve the bonding strength of the polymer, but also play an elastic buffering role against the volume change of the silicon negative electrode, thereby enhancing the electrochemical performance of the negative electrode. By introducing sulfonic acid derivatives, sulfonic acid groups are introduced onto the molecular side chain of the binder. Compared with carboxylic acid groups, they have greater polarity and are more easily solvated, resulting in a higher liquid absorption rate. The higher the liquid absorption rate, the more conducive it is to improving the diffusion of lithium ions in the electrode, thereby improving the rate performance of the battery. In addition, fluorine-containing groups are also introduced into the binder molecule. The C-F bond has a large bond energy and good thermal stability, which can improve the thermal performance. The introduced fluorine-containing groups have a higher affinity with the components in the electrolyte (such as LiPF6, ethylene carbonate, dimethyl carbonate, etc.), resulting in a certain increase in the liquid absorption rate of the electrolyte, which can provide more carriers, thereby enhancing the rate performance of the battery.

[0026] Advantages of the present invention:

[0027] In the present invention, by compounding silicon dioxide with carbon to form a porous structure with granular silicon dioxide attached to the graphite lamellae, the conductivity of the negative electrode material can be improved and the volume expansion effect of silicon oxide can be improved. By preparing a polyacrylic acid polymer as the binder of the negative electrode material, silane soft segments, sulfonic acid groups and fluorine-containing groups are introduced into the polypropylene molecular chain. The silane soft segments can effectively improve the flexibility of the binder, and thus can play an elastic buffering role against the silicon volume change. The introduction of sulfonic acid groups and fluorine-containing groups can both increase the liquid absorption rate of the electrolyte, thereby improving the cycle performance of the battery. Under the action of the above two reasons, the negative electrode material of the lithium-ion battery prepared by the above method not only has a high capacitance, but also has good rate performance. Specific embodiments

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present invention.

[0029] Example 1

[0030] Prepare a silicon-carbon composite:

[0031] 1) Dissolve 1.6 g of CTAB (cetyltrimethylammonium bromide) in 80 mL of deionized water, and stir vigorously at room temperature for 10 min. After adding 7.2 mL of ammonia water (concentration: 1 mol / L), continue stirring for 10 min. Then add 24 mL of n-octane to the above solution, stir for 30 min, and add 0.9 g of glucose. After dissolution, a mixed solution is obtained;

[0032] 2) Slowly add 4.2 g of tetraethyl orthosilicate dropwise to the mixed solution, continuously stir for 1 h, transfer it to an autoclave, and perform heat treatment at 100 °C for 24 h. Wash the obtained solid with ethanol / water 3 times, filter and separate it, dry it at 80 °C for 12 h, and finally calcine it at 800 °C for 4 h to carbonize it, obtaining a silicon-carbon composite.

[0033] Example 2

[0034] Preparation of silicon-carbon composite:

[0035] 1) Dissolve 3.2 g of CTAB (cetyltrimethylammonium bromide) in 160 mL of deionized water, and stir vigorously at room temperature for 10 min. After adding 14.4 mL of ammonia water (concentration: 1 mol / L), continue stirring for 10 min. Then add 48 mL of n-octane to the above solution, stir for 30 min, and add 1.8 g of glucose. After dissolution, a mixed solution is obtained;

[0036] 2) Slowly add 8.4 g of tetraethyl orthosilicate dropwise to the mixed solution, continuously stir for 1 h, transfer it to an autoclave, and perform heat treatment at 100 °C for 24 h. Wash the obtained solid with ethanol / water 4 times, filter and separate it, dry it at 80 °C for 12 h, and finally calcine it at 800 °C for 4 h to carbonize it, obtaining a silicon-carbon composite.

[0037] Example 3

[0038] Preparation of binder:

[0039] S1. Add 7.2 g of acrylic acid and 300 mL of dichloromethane to a flask, then add 21 g of EDCI (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, condensing agent), stir evenly, add 19 g of sodium ethylenediaminoethanesulfonate, stir and react at room temperature for 2 h. After rotary evaporation to remove the solvent, extract with ethyl acetate, and finally vacuum dry the product at 60 °C for more than 3 h to obtain a sulfonic acid derivative;

[0040] S2. Add 30 g of acrylic acid, 15.5 g of vinyltriethyl lactate silane, and 8.5 g of sulfonic acid derivative into a four-necked flask filled with argon, and introduce 2.0 g of trifluoroethylene. Heat the mixture to 75 °C. Subsequently, use a constant-pressure dropping funnel to add 21.5 mL of an ethyl acetate solution of AIBN (the concentration of the ethyl acetate solution of AIBN is 5.2 mg / mL, and the dropping rate is controlled at 0.125 mL / min) into the reactor. After the addition is completed, react at a constant temperature of 75 °C for 8 hours. Cool the product to room temperature, then rotary evaporate to remove the unreacted monomers and excess solvent, and finally dry under vacuum at 70 °C to obtain the binder.

[0041] Example 4

[0042] Preparation of binder:

[0043] S1. Add 7.2 g of acrylic acid and 300 mL of dichloromethane into a flask, then add 21 g of EDCI (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, condensing agent). After stirring evenly, add 19 g of sodium 2-aminoethanesulfonate, and stir at room temperature for 2 h. After rotary evaporating to remove the solvent, extract with ethyl acetate. Finally, dry the product under vacuum at 60 °C for more than 3 h to obtain the sulfonic acid derivative.

[0044] S2. Add 30 g of acrylic acid, 16.5 g of vinyltriethyl lactate silane, and 9 g of sulfonic acid derivative into a four-necked flask filled with argon, and introduce 2.0 g of trifluoroethylene. Heat the mixture to 75 °C. Subsequently, use a constant-pressure dropping funnel to add 22.1 mL of an ethyl acetate solution of AIBN (the concentration of the ethyl acetate solution of AIBN is 5.2 mg / mL, and the dropping rate is controlled at 0.125 mL / min) into the reactor. After the addition is completed, react at a constant temperature of 75 °C for 8 hours. Cool the product to room temperature, then rotary evaporate to remove the unreacted monomers and excess solvent, and finally dry under vacuum at 70 °C to obtain the binder.

[0045] Example 5

[0046] Preparation of silicon oxide-based lithium-ion negative electrode material:

[0047] First step. Mix 230 g of the silicon-carbon composite prepared in Example 1, 10 g of the binder prepared in Example 3, and 10 g of conductive carbon black, and disperse them in 80 mL of N-methyl-2-pyrrolidone. Continuously stir for 24 h to obtain a uniformly mixed slurry.

[0048] Second step. Coat the slurry on a copper foil, dry at 100 °C for 8 h, and then transfer to vacuum drying at 80 °C for 24 h to obtain the lithium-ion negative electrode material.

[0049] Example 6

[0050] Preparation of a silicon oxide-based lithium-ion negative electrode material:

[0051] First step: After mixing 230 g of the silicon-carbon composite prepared in Example 2, 10 g of the binder prepared in Example 4, and 10 g of conductive carbon black, disperse them in 80 mL of N-methyl-2-pyrrolidone, and continuously stir for 24 h to obtain a uniformly mixed slurry;

[0052] Second step: Coat the slurry on a copper foil, dry it at 100 °C for 8 h, and then transfer it to vacuum dry at 80 °C for 24 h to obtain the lithium-ion negative electrode material.

[0053] Comparative example

[0054] Replace the binder in Example 5 with a polyacrylic acid polymer, and keep the other raw materials and the preparation process unchanged.

[0055] For the negative electrode materials obtained in Examples 5-6 and the comparative example, assemble button lithium-ion batteries, and the measured performance parameters are shown in the following table:

[0056]

[0057] It can be seen from the data in the above table that the lithium-ion battery negative electrode material prepared by the present invention not only has a high capacitance, but also has good rate performance; combined with the data of the comparative example, it can be known that by modifying polyacrylic acid and introducing soft segments, sulfonic acid groups, and fluorine-containing groups into the polymer chain, the effect of the binder on improving the performance of the battery can be effectively enhanced.

[0058] In the description of the specification, the description with reference to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0059] The above content is only an example and explanation of the present invention. Those skilled in the art of the present technology can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, as long as they do not deviate from the invention or exceed the scope defined by the claims of the present invention, they should fall within the protection scope of the present invention.

Claims

1. A lithium-ion negative electrode material based on silicon oxide, comprising a silicon-carbon composite, a binder, and conductive carbon black. The weight ratio of the silicon-carbon composite, the binder, and the conductive carbon black is 23:1:1, and it is characterized in that, The silicon-carbon composite is prepared through the following steps: 1) Dissolve CTAB in deionized water, and vigorously stir for 10 min at room temperature. After adding ammonia water, continue to stir for 10 min. Then add n-octane to the solution, stir for 30 min, and then add glucose. After dissolution, a mixed solution is obtained; 2) Dropwise add tetraethyl orthosilicate to the mixed solution, continuously stir for 1 h, transfer it to an autoclave, and perform heat treatment at 100 °C for 24 h. Wash the obtained solid with ethanol / water 3-4 times, filter and separate, dry at 80 °C for 12 h, and finally calcine at 800 °C for 4 h to carbonize it, obtaining the silicon-carbon composite; The binder is prepared through the following steps: S1. Add acrylic acid and dichloromethane to a flask, then add EDCI. After stirring evenly, add sodium 2-(ethylenediamino)ethanesulfonate, stir and react at room temperature for 2 h. After rotary evaporation to remove the solvent, extract with ethyl acetate. Finally, vacuum-dry the product at 60 °C for more than 3 h to obtain the sulfonic acid derivative; S2. Add acrylic acid, vinyltriethoxysilane, and the sulfonic acid derivative to a four-necked flask filled with argon, and introduce trifluoroethylene. Heat to 75 °C. Subsequently, use a constant-pressure dropping funnel to dropwise add an ethyl acetate solution of AIBN to the reactor. After the dropping is completed, react at a constant temperature of 75 °C for 8 h. Cool the product to room temperature, then rotary evaporate to remove the unreacted monomers and excess solvent, and finally vacuum-dry at 70 °C to obtain the binder.

2. The lithium-ion negative electrode material based on silicon oxide according to claim 1, characterized in that, The concentration of ammonia water is 1 mol / L; the dosage ratio of CTAB, deionized water, ammonia water, n-octane, glucose, and tetraethyl orthosilicate is 1.6 g:80 mL:7.2 mL:24 mL:0.9 g:4.2 g.

3. The lithium-ion negative electrode material based on silicon oxide according to claim 1, characterized in that, In step S1, the dosage ratio of acrylic acid, dichloromethane, EDCI, and sodium 2-(ethylenediamino)ethanesulfonate is 7.2 g:300 mL:21 g:19 g.

4. The lithium-ion negative electrode material based on silicon oxide according to claim 1, characterized in that, In step S2, the concentration of the ethyl acetate solution of AIBN is 5.2 mg / mL, and the dropping rate is controlled at 0.125 mL / min.

5. The lithium-ion negative electrode material based on silicon oxide according to claim 1, characterized in that, In step S2, the dosage ratio of acrylic acid, vinyltriethoxysilane, the sulfonic acid derivative, and trifluoroethylene is 30 g:15.5 - 16.5 g:8.5 - 9 g:2.0 g; the added mass of AIBN is 0.2% of the total mass of the monomers.

6. The preparation method of the lithium-ion negative electrode material based on silicon oxide according to claim 1, characterized in that, Specifically as follows: The first step: After mixing the silicon-carbon composite, the binder, and conductive carbon black in proportion, disperse them in N-methyl-2-pyrrolidone, and continuously stir for 24 h to prepare a uniformly mixed slurry; The second step: Coat the slurry on a copper foil, dry at 100 °C for 8 h, and then transfer it to vacuum-dry at 80 °C for 24 h to obtain the lithium-ion negative electrode material.

Images