A high-capacity performance silicon-based anode material, its preparation method and application

Abstract

The present invention discloses a high-capacity silicon-based anode material and its preparation method and application, relating to the technical field of lithium-ion batteries. In this application, micron-sized silicon powder is pickled to remove the surface oxide layer and metal impurities to obtain pure silicon powder. Then, end-group formylated polythiophene and p-phenylenediamine monomers are polymerized to form a polymer containing a Schiff base structure on the surface of the micron-sized silicon powder, obtaining a composite material with silicon coated by a Schiff base polymer. By coating a layer of Schiff base polymer on the silicon surface that can both relieve volume expansion and improve the lithium-ion transport ability on the surface of the silicon anode, it can not only reduce the contact between silicon and the electrolyte, inhibit the decomposition of the electrolyte, and improve the initial efficiency, but also limit the volume expansion of silicon and improve the cycling performance of the silicon anode.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium - ion batteries, and specifically to a high - capacity silicon - based anode material and its preparation method and application. Background Art

[0002] In the composition structure of lithium batteries, as one of the four major main materials, the anode material plays a key role in the overall performance of the battery. For a long time, lithium battery manufacturers generally choose graphite as the anode material. Graphite belongs to carbon - based anode materials, including artificial graphite and natural graphite. With good cycle stability, excellent electrical conductivity, and a layered structure suitable for lithium intercalation, it occupies an important position in the field of lithium batteries. However, with the continuous increase in the demand for portable and high - performance energy storage devices, the requirements for the performance of lithium batteries are becoming increasingly stringent. Graphite anode materials have problems such as low theoretical specific capacity (only 372 mAh / g), and during long - term cycling, its layered structure is prone to peeling and falling off. These defects seriously restrict the further improvement of the specific energy and performance of lithium batteries. To break through the above - mentioned technical bottlenecks, silicon materials show great potential because they can form binary alloys with lithium. Its theoretical capacity exceeds that of graphite by more than 10 times (up to 4200 mAh / g), and at the same time, it has advantages such as a low lithium de - intercalation / insertion voltage platform, low reactivity with the electrolyte, rich reserves, and low price, making it a very promising alternative anode material for lithium batteries. However, silicon materials also have fatal defects. During the charge - discharge process, the insertion and extraction of lithium ions will cause the silicon material to expand and contract by about 300%, and repeated cycling easily leads to the pulverization of the material structure, resulting in a sharp decline in battery capacity and life.

[0003] Therefore, in this application, micron - sized silicon powder is first pickled to remove its surface oxide layer and metal impurities to obtain pure silicon powder; then, through the polymerization of terminal - formylated polythiophene and p - phenylenediamine monomers, a polymer containing a Schiff base structure is formed on the surface of the micron - sized silicon powder, forming a composite material with a Schiff base polymer - coated silicon. Through the Schiff base polymer layer, this composite material can not only effectively alleviate the volume expansion problem of silicon materials, but also improve the lithium - ion transport ability on the surface of the silicon anode, reduce the direct contact between silicon and the electrolyte, inhibit the decomposition of the electrolyte, improve the first - charge - discharge efficiency, and at the same time limit the volume change of silicon, significantly improving the cycle performance of the silicon anode. Summary of the Invention

[0004] The purpose of the present invention is to provide a high - capacity silicon - based anode material and its preparation method and application to solve the problems existing in the prior art.

[0005] To solve the above - mentioned technical problems, the present invention provides the following technical solutions:

[0006] A preparation method of a high - capacity silicon - based anode material, comprising the following preparation steps:

[0007] Step 1: Add micron silicon powder, end-group formylated polythiophene, and p-phenylenediamine to ethanol according to a mass ratio of 42 - 45:1.2 - 1.4:1. After mixing, add acetic acid. After stirring and reacting, filter, wash the filter cake, and dry it under vacuum to obtain a silicon-Schiff base polymer composite material;

[0008] Step 2: Weigh the silicon-Schiff base polymer composite material, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber according to a mass ratio of 16 - 18:2 - 3:1 - 1.5:1, and add them to an ethanol aqueous solution with a mass fraction of 16% - 18%. Stir magnetically. After stirring, uniformly coat it on the negative current collector copper sheet through a coater. For the coated negative current collector copper sheet, dry it preliminarily and then dry it under vacuum to obtain a silicon-based negative electrode material.

[0009] As an optimization, in Step 1, the addition amount of ethanol is 16 - 18 times the mass of the micron silicon powder, the addition amount of acetic acid is 1 - 1.2 times the mass of the micron silicon powder, the stirring reaction time is 12 - 14 h, and the filtered product is washed 3 - 5 times with absolute ethanol.

[0010] As an optimization, in Step 2, the magnetic stirring time is 12 - 14 h, the blade thickness is adjusted to 10 - 12 μm during the uniform coating process of the coater, the preliminary drying temperature is 80 - 85 °C, the drying time is 10 - 15 min, the vacuum drying temperature is 120 - 130 °C, and the drying time is 12 - 14 h.

[0011] As an optimization, the micron silicon powder is pre-treated by pickling with an acid solution, and the acid solution is prepared by mixing hydrochloric acid and hydrofluoric acid according to a volume ratio of 4:1.

[0012] As an optimization, the preparation steps of the end-group formylated polythiophene include: under nitrogen protection, add the polythiophene oligomer to N,N-dimethylformamide with a mass 35 - 40 times that of the polythiophene oligomer. Under the condition of a temperature of 0 - 5 °C, stir and dissolve it, then dropwise add a Vilsmeier reagent with a mass 3 - 3.2 times that of the polythiophene oligomer. After the dropping is completed, under the condition of a temperature of 65 - 70 °C, stir and react for 46 - 48 h. After the reaction ends, cool down to 0 - 5 °C, and then use a sodium hydroxide solution with a mass fraction of 40% - 50% to adjust the pH to 10 - 11. After standing for 30 - 45 min, perform rotary evaporation and vacuum filtration to obtain the end-group formylated polythiophene.

[0013] As an optimization, the preparation steps of the Vilsmeier reagent include: under the condition of a temperature of 0 - 5 °C, dropwise add phosphorus oxychloride to N,N-dimethylformamide with a mass 6 - 7 times that of the phosphorus oxychloride, stir evenly, and stand for 30 - 45 min to obtain the Vilsmeier reagent.

[0014] As an optimization, the preparation steps of the polythiophene oligomer are as follows: Add the esterification monomer into chloroform which is 32 - 36 times the mass of the esterification monomer, stir evenly to prepare an esterification monomer solution for standby; Under the protection of nitrogen, add anhydrous ferric chloride into chloroform which is 30 - 35 times the mass of anhydrous ferric chloride, stir evenly, then dropwise add the esterification monomer solution which is 15 - 18 times the mass of anhydrous ferric chloride. After the dropping is completed, react at 40 - 45 °C for 40 - 48 h, then add methanol which is 10 - 15 times the mass of anhydrous ferric chloride. After the reaction ends, centrifuge and separate, and wash the separated product with a methanol - chloroform solution 3 - 5 times, then vacuum dry. Then add the separated product into dimethyl sulfoxide which is 20 - 22 times the mass of the separated product, stir to dissolve, then add a sodium hydroxide solution with a mass fraction of 9% - 12% which is 120 - 150 times the mass of the separated product, heat to 45 - 55 °C, react for 24 - 26 h, then transfer to a dialysis bag, dialyze for 48 - 50 h, remove the solvent, and vacuum dry to obtain the polythiophene oligomer; The molecular weight cut - off of the dialysis bag is 3500 Da; The methanol - chloroform solution is prepared by mixing methanol and chloroform according to a volume ratio of 1:1.

[0015] As an optimization, the preparation steps of the esterification monomer are as follows: Under the protection of nitrogen, add 2 - thiopheneethylamine into methanol which is 18 - 22 times the mass of 2 - thiopheneethylamine, then add methyl acrylate which is 3 - 3.5 times the mass of 2 - thiopheneethylamine and a boric acid solution with a mass fraction of 0.7% - 0.9% which is 18 - 22 times the mass of 2 - thiopheneethylamine. Then heat to 35 - 40 °C and react for 22 - 26 h. After the reaction ends, distill the solvent under reduced pressure and then purify by silica gel column chromatography, and vacuum dry the purified product to obtain the esterification monomer.

[0016] A high - capacity silicon - based anode material is prepared by the preparation method described in any one of the above.

[0017] An application of the high - capacity silicon - based anode material as described above in a lithium - ion battery.

[0018] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0019] Since the silicon negative electrode has a high theoretical specific capacity and can provide a higher energy density, silicon is used as the negative electrode material in this application. First, the micron silicon powder is pickled to remove the surface oxide layer and metal impurities to obtain pure silicon powder. Then, the polymerization of terminal formylated polythiophene and p-phenylenediamine monomers is carried out to generate a polymer containing Schiff base structure on the surface of the micron silicon powder, and a composite material with silicon coated by Schiff base polymer is obtained. By coating a layer of Schiff base polymer on the silicon surface that can not only relieve volume expansion but also improve the lithium ion transport ability on the surface of the silicon negative electrode, it can not only reduce the contact between silicon and the electrolyte, inhibit the decomposition of the electrolyte, and improve the initial efficiency, but also limit the volume expansion of silicon and improve the cycle performance of the silicon negative electrode;

[0020] In this application, 2-thiopheneethylamine is graft-modified with amino groups through methyl acrylate to generate an esterified monomer. Then, the esterified monomer is polymerized to generate a polythiophene oligomer, and after the preparation is completed, sodium hydroxide is added for hydrolysis treatment to hydrolyze the grafted methyl acrylate, thereby generating a polythiophene oligomer with a large number of carboxyl groups on the side chain. On the one hand, the large number of carboxyl groups grafted on the side chain can strengthen the binding strength between the generated Schiff base polymer and the micron silicon powder by generating hydrogen bond forces with the silicon dioxide and hydroxyl groups on the silicon surface. On the other hand, it can also generate a binder network with sodium carboxymethylcellulose through the carboxyl groups on it to strengthen the structural stability of the entire electrode, thereby improving the electrochemical performance of the silicon negative electrode. Specific Embodiments

[0021] 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 fall within the protection scope of the present invention.

[0022] Example 1

[0023] S1. Under the condition of nitrogen protection, 2-thiopheneethylamine is added to methanol with a mass 18 times that of 2-thiopheneethylamine, then methyl acrylate with a mass 3 times that of 2-thiopheneethylamine and a boric acid solution with a mass fraction of 0.7% and a mass 18 times that of 2-thiopheneethylamine are added. After that, it is heated to 35 °C and reacted for 22 h. After the reaction is completed, the solvent is distilled under reduced pressure and then purified by silica gel column chromatography, and the purified product is vacuum dried to obtain the esterified monomer;

[0024] S2. Add the esterified monomer to chloroform at 32 times the mass of the esterified monomer, stir evenly to prepare an esterified monomer solution for standby. Under the protection of nitrogen, add anhydrous ferric chloride to chloroform at 30 times the mass of anhydrous ferric chloride, stir evenly, then dropwise add the esterified monomer solution at 15 times the mass of anhydrous ferric chloride. After the addition is complete, react at 40 °C for 40 h, then add methanol at 10 times the mass of anhydrous ferric chloride. After the reaction ends, centrifuge and wash the separated product 3 times with a methanol-chloroform solution, then vacuum dry. Then add the separated product to dimethyl sulfoxide at 20 times the mass of the separated product, stir to dissolve, then add a sodium hydroxide solution with a mass fraction of 9% at 120 times the mass of the separated product, heat to 45 °C, react for 24 h, transfer to a dialysis bag, dialyze for 48 h, remove the solvent, and vacuum dry to obtain a polythiophene oligomer; the molecular weight cut-off of the dialysis bag is 3500 Da; the methanol-chloroform solution is prepared by mixing methanol and chloroform according to a volume ratio of 1:1;

[0025] S3. Under the protection of nitrogen, add the polythiophene oligomer to N,N-dimethylformamide at 35 times the mass of the polythiophene oligomer, stir to dissolve at 0 °C, then dropwise add a Vilsmeier reagent at 3 times the mass of the polythiophene oligomer. After the addition is complete, stir and react at 65 °C for 46 h. After the reaction ends, cool to 0 °C, then use a sodium hydroxide solution with a mass fraction of 40% to adjust the pH to 10, let it stand for 30 min, then rotary evaporate and filter under reduced pressure to obtain an end-formylated polythiophene; at 0 °C, dropwise add phosphorus oxychloride to N,N-dimethylformamide at 6 times the mass of phosphorus oxychloride, stir evenly, let it stand for 30 min to prepare a Vilsmeier reagent;

[0026] S4. According to a mass ratio of 42:1.2:1, add micron-sized silicon powder, end-formylated polythiophene, and p-phenylenediamine to ethanol at 16 times the mass of the micron-sized silicon powder. After mixing, add acetic acid at the mass of 1 times the micron-sized silicon powder, stir and react for 12 h, then filter and wash the filtered product 3 times with anhydrous ethanol, and vacuum dry to obtain a silicon-Schiff base polymer composite material; the micron-sized silicon powder is pre-treated by pickling with an acid solution, and the acid solution is prepared by mixing hydrochloric acid and hydrofluoric acid according to a volume ratio of 4:1;

[0027] S5. Weigh the silicon-Schiff base polymer composite material, conductive carbon black, sodium carboxymethylcellulose, and styrene-butadiene rubber according to a mass ratio of 16:2:1:1, add them to an ethanol aqueous solution with a mass fraction of 16%, stir magnetically for 12 h. After stirring, evenly coat them on the negative current collector copper sheet through a coater, adjust the blade thickness to 10 μm, and dry the coated negative current collector copper sheet at 80 °C for 10 min, then vacuum dry at 120 °C for 12 h to obtain a silicon-based negative electrode material.

[0028] Example 2

[0029] S1. Under the protection of nitrogen, 2-thiopheneethylamine was added to methanol which was 20 times the mass of 2-thiopheneethylamine. Then, methyl acrylate which was 3.25 times the mass of 2-thiopheneethylamine and a boric acid solution with a mass fraction of 0.8% which was 20 times the mass of 2-thiopheneethylamine were added. After that, the mixture was heated to 38 °C and reacted for 24 h. After the reaction, the solvent was distilled under reduced pressure and then purified by silica gel column chromatography. The purified product was vacuum dried to obtain the esterified monomer.

[0030] S2. The esterified monomer was added to chloroform which was 34 times the mass of the esterified monomer and stirred evenly to prepare an esterified monomer solution for standby. Under the protection of nitrogen, anhydrous ferric chloride was added to chloroform which was 32.5 times the mass of anhydrous ferric chloride. After stirring evenly, the esterified monomer solution which was 16.5 times the mass of anhydrous ferric chloride was added dropwise. After the addition was completed, the reaction was carried out at 43 °C for 44 h, and then methanol which was 12.5 times the mass of anhydrous ferric chloride was added. After the reaction, centrifugal separation was carried out, and the separated product was washed 4 times with a methanol-chloroform solution and then vacuum dried. Then, the separated product was added to dimethyl sulfoxide which was 21 times the mass of the separated product and stirred to dissolve. Then, a sodium hydroxide solution with a mass fraction of 11% which was 135 times the mass of the separated product was added. The mixture was heated to 50 °C and reacted for 25 h, then transferred to a dialysis bag and dialyzed for 49 h. After removing the solvent, it was vacuum dried to obtain the polythiophene oligomer. The molecular weight cut-off of the dialysis bag was 3500 Da. The methanol-chloroform solution was prepared by mixing methanol and chloroform according to a volume ratio of 1:1. [[ID=Y10]]

[0031] S3. Under the protection of nitrogen, the polythiophene oligomer was added to N,N-dimethylformamide which was 37.5 times the mass of the polythiophene oligomer. At 2 °C, after stirring to dissolve, a Vilsmeier reagent which was 3.1 times the mass of the polythiophene oligomer was added dropwise. After the addition was completed, the reaction was stirred at 68 °C for 47 h. After the reaction, the temperature was lowered to 2 °C, and then a sodium hydroxide solution with a mass fraction of 45% was used to adjust the pH to 10.5. After standing for 35 min, rotary evaporation and vacuum filtration were carried out to obtain the end-group formylated polythiophene. At 2 °C, phosphorus oxychloride was added dropwise to N,N-dimethylformamide which was 6.5 times the mass of phosphorus oxychloride, stirred evenly, and left standing for 38 min to obtain the Vilsmeier reagent.

[0032] S4. According to the mass ratio of 43.5:1.3:1, add micron silicon powder, end-group formylated polythiophene, and p-phenylenediamine to ethanol with a mass 17 times that of the micron silicon powder. After mixing, add acetic acid with a mass 1.1 times that of the micron silicon powder, stir and react for 13 h, then filter and wash the filtered product 4 times with absolute ethanol. After vacuum drying, a silicon-Schiff base polymer composite material is obtained; the micron silicon powder is pre-treated by pickling with an acid solution, and the acid solution is prepared by mixing hydrochloric acid and hydrofluoric acid according to a volume ratio of 4:1;

[0033] S5. Weigh the silicon-Schiff base polymer composite material, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber according to the mass ratio of 17:2.5:1.25:1, add them to an aqueous ethanol solution with a mass fraction of 17%, magnetically stir for 13 h. After stirring, evenly coat them on the negative current collector copper sheet through a coater, adjust the blade thickness to 11 μm. For the coated negative current collector copper sheet, dry it at 82 °C for 12 min, and then vacuum dry it at 125 °C for 13 h to obtain a silicon-based negative electrode material.

[0034] Example 3

[0035] S1. Under the protection of nitrogen, add 2-thiopheneethylamine to methanol with a mass 22 times that of 2-thiopheneethylamine, then add methyl acrylate with a mass 3.5 times that of 2-thiopheneethylamine and a boric acid solution with a mass fraction of 0.9% and a mass 22 times that of 2-thiopheneethylamine. Then heat to 40 °C and react for 26 h. After the reaction ends, distill the solvent under reduced pressure and then purify it by silica gel column chromatography. Vacuum dry the purified product to obtain an esterified monomer;

[0036] S2. Add the esterified monomer to chloroform with a mass 36 times that of the esterified monomer, stir evenly to prepare an esterified monomer solution for standby; under the protection of nitrogen, add anhydrous ferric chloride to chloroform with a mass 35 times that of anhydrous ferric chloride, stir evenly, and then dropwise add an esterified monomer solution with a mass 18 times that of anhydrous ferric chloride. After dropping, react at 45 °C for 48 h, then add methanol with a mass 15 times that of anhydrous ferric chloride. After the reaction ends, perform centrifugal separation, wash the separated product 5 times with a methanol-chloroform solution, and then vacuum dry it. Then add the separated product to dimethyl sulfoxide with a mass 22 times that of the separated product, stir to dissolve it, and then add a sodium hydroxide solution with a mass fraction of 12% and a mass 150 times that of the separated product. Heat to 55 °C and react for 26 h, then transfer it to a dialysis bag and dialyze for 50 h. After removing the solvent, vacuum dry it to obtain a polythiophene oligomer; the cut-off molecular weight of the dialysis bag is 3500 Da; the methanol-chloroform solution is prepared by mixing methanol and chloroform according to a volume ratio of 1:1;

[0037] S3. Under nitrogen protection, add the polythiophene oligomer into N,N-dimethylformamide which is 40 times the mass of the polythiophene oligomer. At a temperature of 5 °C, stir to dissolve, then dropwise add the Vilsmeier reagent which is 3.2 times the mass of the polythiophene oligomer. After the addition is complete, stir and react at a temperature of 70 °C for 48 h. After the reaction ends, cool down to 5 °C, then use a sodium hydroxide solution with a mass fraction of 50% to adjust the pH to 11. Let it stand for 45 min, then perform rotary evaporation and vacuum filtration to obtain the end-group formylated polythiophene; at a temperature of 5 °C, dropwise add phosphorus oxychloride into N,N-dimethylformamide which is 7 times the mass of phosphorus oxychloride, stir evenly, and let it stand for 45 min to obtain the Vilsmeier reagent;

[0038] S4. According to the mass ratio of 45:1.4:1, add micron silicon powder, end-group formylated polythiophene, and p-phenylenediamine into ethanol which is 18 times the mass of the micron silicon powder. After mixing, add acetic acid which is 1.2 times the mass of the micron silicon powder, stir and react for 14 h, then filter and wash the filtered product with absolute ethanol 5 times, and dry it in vacuum to obtain the silicon-Schiff base polymer composite material; the micron silicon powder is pre-treated by pickling with an acid solution, and the acid solution is prepared by mixing hydrochloric acid and hydrofluoric acid according to a volume ratio of 4:1;

[0039] S5. Weigh the silicon-Schiff base polymer composite material, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber according to the mass ratio of 18:3:1.5:1, add them into an ethanol aqueous solution with a mass fraction of 18%, stir magnetically for 14 h. After the stirring is complete, evenly coat them on the negative current collector copper sheet through a coater, adjust the blade thickness to 12 μm. After coating the negative current collector copper sheet, dry it at a temperature of 85 °C for 15 min, and then vacuum dry it at a temperature of 130 °C for 14 h to obtain the silicon-based negative electrode material.

[0040] Example 4

[0041] The difference from Example 2 is only in step S2: Add 2-thiopheneethylamine monomer to chloroform that is 32 times the mass of the 2-thiopheneethylamine monomer, stir evenly to prepare a 2-thiopheneethylamine monomer solution for standby; Under the protection of nitrogen, add anhydrous ferric chloride to chloroform that is 30 times the mass of the anhydrous ferric chloride, stir evenly, then dropwise add a 2-thiopheneethylamine monomer solution that is 15 times the mass of the anhydrous ferric chloride. After the dropping is completed, react at 40 °C for 40 h, then add methanol that is 10 times the mass of the anhydrous ferric chloride. After the reaction ends, centrifuge and separate, and wash the separated product 3 times with a methanol-chloroform solution, then vacuum dry. Then add the separated product to dimethyl sulfoxide that is 20 times the mass of the separated product, stir to dissolve, then add a sodium hydroxide solution with a mass fraction of 9% that is 120 times the mass of the separated product, heat to 45 °C, react for 24 h, transfer to a dialysis bag, dialyze for 48 h, remove the solvent, and then vacuum dry to obtain a polythiophene oligomer; The molecular weight cut-off of the dialysis bag is 3500 Da; The methanol-chloroform solution is prepared by mixing methanol and chloroform according to a volume ratio of 1:1.

[0042] Example 5

[0043] The difference from Example 2 is only in step S3: Under the protection of nitrogen, add the esterification monomer to N,N-dimethylformamide that is 35 times the mass of the esterification monomer, stir and dissolve at 0 °C, then dropwise add a Vilsmeier reagent that is 3 times the mass of the esterification monomer. After the dropping is completed, stir and react at 65 °C for 46 h. After the reaction ends, cool down to 0 °C, then use a sodium hydroxide solution with a mass fraction of 40% to adjust the pH to 10, let it stand for 30 min, then rotary evaporate and filter under reduced pressure to obtain a terminal formylated esterification monomer; At 0 °C, dropwise add phosphorus oxychloride to N,N-dimethylformamide that is 6 times the mass of the phosphorus oxychloride, stir evenly, let it stand for 30 min to obtain a Vilsmeier reagent.

[0044] Example 6

[0045] The difference from Example 2 is only in step S3: Under the protection of nitrogen, add 2-thiopheneethylamine monomer to N,N-dimethylformamide that is 35 times the mass of the 2-thiopheneethylamine monomer, stir and dissolve at 0 °C, then dropwise add a Vilsmeier reagent that is 3 times the mass of the 2-thiopheneethylamine monomer. After the dropping is completed, stir and react at 65 °C for 46 h. After the reaction ends, cool down to 0 °C, then use a sodium hydroxide solution with a mass fraction of 40% to adjust the pH to 10, let it stand for 30 min, then rotary evaporate and filter under reduced pressure to obtain a terminal formylated esterification monomer; At 0 °C, dropwise add phosphorus oxychloride to N,N-dimethylformamide that is 6 times the mass of the phosphorus oxychloride, stir evenly, let it stand for 30 min to obtain a Vilsmeier reagent.

[0046] Example 7

[0047] The difference from Example 2 is only in step S4: micron silicon powder, 2-thiopheneethylamine, and p-phenylenediamine are added to ethanol 16 times the mass of the micron silicon powder according to a mass ratio of 42:1.2:1. After mixing, acetic acid 1 time the mass of the micron silicon powder is added. After stirring and reacting for 12 h, filtration is carried out, and the filtration product is washed 3 times with absolute ethanol. After vacuum drying, a silicon-Schiff base polymer composite material is obtained; the micron silicon powder is pre-treated by pickling with an acid solution, and the acid solution is prepared by mixing hydrochloric acid and hydrofluoric acid according to a volume ratio of 4:1.

[0048] Example 8

[0049] The difference from Example 2 is only in step S4: micron silicon powder, polythiophene oligomer, and p-phenylenediamine are added to ethanol 16 times the mass of the micron silicon powder according to a mass ratio of 42:1.2:1. After mixing, acetic acid 1 time the mass of the micron silicon powder is added. After stirring and reacting for 12 h, filtration is carried out, and the filtration product is washed 3 times with absolute ethanol. After vacuum drying, a silicon-Schiff base polymer composite material is obtained; the micron silicon powder is pre-treated by pickling with an acid solution, and the acid solution is prepared by mixing hydrochloric acid and hydrofluoric acid according to a volume ratio of 4:1.

[0050] Example 9

[0051] The difference from Example 2 is only in step S5: micron silicon powder, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber are weighed according to a mass ratio of 16:2:1:1 and added to an ethanol aqueous solution with a mass fraction of 16%. Magnetic stirring is carried out for 12 h. After stirring, it is uniformly coated on the negative current collector copper sheet by a coater, and the blade thickness is adjusted to 10 μm. The coated negative current collector copper sheet is dried at 80 °C for 10 min and then vacuum dried at 120 °C for 12 h to obtain a silicon-based negative electrode material.

[0052] Battery Assembly

[0053] The silicon-based negative electrode materials prepared in Examples 1-9 above are sliced into small round electrodes with a diameter of 14 mm by a slicing machine. After weighing and recording the mass of the electrodes, a metal lithium sheet with a diameter of 14 mm is used as the counter electrode and reference electrode, and the electrolyte is 1 mol / L (the volume ratio of the three is 1:1:1). The separator is of the Celgard 2500 type. A button battery is assembled in a vacuum glove box with the water and oxygen content below 0.1 ppm. After standing for 24 h, charge and discharge cycle tests are carried out on a constant current charge and discharge tester. The test voltage range is 0.01 V~1.5 V. The first cycle is activated at a current density of 84 mA / g, and then cycle tests are carried out at a current density of 420 mA / g.

[0054] The test results of the electrochemical performance are shown in Table 1 below;

[0055] Table 1

[0056] Specimen Initial discharge capacity / (mAh / g) Charge-discharge specific capacity at 0.5C rate in the second week (mAh / g) Charge-discharge specific capacity at 1C rate in the second week (mAh / g) Example 1 1539.3 1511.4 1521.7 Example 2 1617.1 1587.3 1598.2 Example 3 1580.1 1523.7 1533.4 Example 4 1223.3 1175.4 1123.6 Example 5 1124.7 834.8 737.9 Example 6 1134.8 785.6 793.2 Example 7 857.4 724.5 717.5 Example 8 816.3 758.9 758.6 Example 9 814.8 788.7 763.2

[0057] The prepared battery in the above embodiments was subjected to a cycle stability test, cycled 100 times at 0.5C and 1C, and the capacity retention rate was calculated. The specific test results are shown in Table 2 below;

[0058] Table 2

[0059]

[0060] From the comparison of the experimental data of Examples 1 to 3 in Table 1 and Table 2, it can be found that the silicon-based anode material prepared by the present invention has good electrochemical performance and still maintains good performance after multiple uses;

[0061] In Examples 5 and 6, the main reason for the decline in their electrochemical performance is that monomers are directly used for the polymerization of Schiff base polymers, and the precipitation is too fast when the surface polymer is generated, resulting in an uneven and too rigid polymer film formed on the surface of silicon powder, leading to a too fast decline in its performance after cycling, which can also be seen from the capacity retention rate of the battery in the later 100 cycles;

[0062] In Example 4, the reason for the relatively large decline may still be that there is no carboxyl group grafted on the polythiophene side chain, resulting in no bonding network formed between it and the binder;

[0063] In Examples 7 and 8, due to the lack of formylation treatment, film formation fails, resulting in a relatively large decline in their performance, which is also reflected in Example 8.

[0064] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, in any regard, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

Claims

1. A preparation method of a high-capacity performance silicon-based anode material, characterized in that, It includes the following preparation steps: Step 1: According to the mass ratio of 42-45:1.2-1.4:1, add micron silicon powder, end-formylated polythiophene and p-phenylenediamine to ethanol. After mixing, add acetic acid, stir and react, then filter, wash the filter, and dry it under vacuum to obtain a silicon-Schiff base polymer composite material; Step 2: Weigh the silicon-Schiff base polymer composite material, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber according to the mass ratio of 16-18:2-3:1-1.5:1, add them to an ethanol aqueous solution with a mass fraction of 16%-18%, stir magnetically, and after stirring, uniformly coat it on the negative current collector copper sheet through a coater. The coated negative current collector copper sheet is preliminarily dried and then dried under vacuum to prepare a silicon-based negative electrode material; Use 2-thiopheneethylamine to graft-modify the amino group on it through methyl acrylate to generate an esterified monomer, and then polymerize the esterified monomer to generate a polythiophene oligomer. After preparation, add sodium hydroxide to carry out hydrolysis treatment to hydrolyze the grafted methyl acrylate, thereby generating a polythiophene oligomer with a large number of carboxyl groups in the side chain; The preparation steps of the end-formylated polythiophene include: under nitrogen protection, add the polythiophene oligomer to N,N-dimethylformamide which is 35-40 times the mass of the polythiophene oligomer, stir and dissolve at a temperature of 0-5°C, then dropwise add a Vilsmeier reagent which is 3-3.2 times the mass of the polythiophene oligomer. After dropping, stir and react at a temperature of 65-70°C for 46-48 h. After the reaction, cool down to 0-5°C, then use a sodium hydroxide solution with a mass fraction of 40%-50% to adjust the pH to 10-11, let it stand for 30-45 min, then rotary evaporate and carry out vacuum filtration to obtain the end-formylated polythiophene.

2. The preparation method of the high-capacity performance silicon-based anode material according to claim 1, characterized in that, In Step 1, the addition amount of ethanol is 16-18 times the mass of the micron silicon powder, the addition amount of acetic acid is 1-1.2 times the mass of the micron silicon powder, the stirring reaction time is 12-14 h, and the filtered product is washed 3-5 times with absolute ethanol.

3. The preparation method of the high-capacity performance silicon-based anode material according to claim 1, characterized in that, In Step 2, the magnetic stirring time is 12-14 h, the blade thickness is adjusted to 10-12 μm during the uniform coating process by the coater, the preliminary drying temperature is 80-85°C, the drying time is 10-15 min, the vacuum drying temperature is 120-130°C, and the drying time is 12-14 h.

4. The preparation method of the high-capacity performance silicon-based anode material according to claim 1, characterized in that, The micron silicon powder is pre-treated by pickling with an acid solution, and the acid solution is prepared by mixing hydrochloric acid and hydrofluoric acid according to a volume ratio of 4:

1.

5. The preparation method of the high-capacity performance silicon-based anode material according to claim 1, characterized in that, The preparation steps of the Vilsmeier reagent include: at a temperature of 0-5°C, dropwise add phosphorus oxychloride to N,N-dimethylformamide which is 6-7 times the mass of phosphorus oxychloride, stir evenly, and let it stand for 30-45 min to obtain the Vilsmeier reagent.

6. The preparation method of the high-capacity performance silicon-based anode material according to claim 1, characterized in that, The poly(thiophene) oligomer includes the following preparation steps: adding an esterified monomer into chloroform that is 32 - 36 times the mass of the esterified monomer, stirring evenly to prepare an esterified monomer solution for standby; under the protection of nitrogen, adding anhydrous ferric chloride into chloroform that is 30 - 35 times the mass of the anhydrous ferric chloride, stirring evenly, then dropping an esterified monomer solution that is 15 - 18 times the mass of the anhydrous ferric chloride. After the dropping is completed, reacting for 40 - 48 h at a temperature of 40 - 45 °C, then adding methanol that is 10 - 15 times the mass of the anhydrous ferric chloride. After the reaction ends, centrifugally separate, and wash the separated product 3 - 5 times with a methanol-chloroform solution, then vacuum dry. Then add the separated product into dimethyl sulfoxide that is 20 - 22 times the mass of the separated product, stir to dissolve, then add a sodium hydroxide solution with a mass fraction of 9% - 12% that is 120 - 150 times the mass of the separated product, heat to 45 - 55 °C, react for 24 - 26 h, then transfer to a dialysis bag and dialyze for 48 - 50 h. After removing the solvent, vacuum dry to obtain the poly(thiophene) oligomer; the molecular weight cut-off of the dialysis bag is 3500 Da; the methanol-chloroform solution is prepared by mixing methanol and chloroform according to a volume ratio of 1:

1.

7. The preparation method of the high-capacity performance silicon-based anode material according to claim 6, characterized in that, The esterified monomer includes the following preparation steps: under the protection of nitrogen, adding 2-thiopheneethylamine into methanol that is 18 - 22 times the mass of the 2-thiopheneethylamine, then adding methyl acrylate that is 3 - 3.5 times the mass of the 2-thiopheneethylamine and a boric acid solution with a mass fraction of 0.7% - 0.9% that is 18 - 22 times the mass of the 2-thiopheneethylamine, then heating to 35 - 40 °C and reacting for 22 - 26 h. After the reaction ends, distill the solvent under reduced pressure and then purify by silica gel column chromatography, and vacuum dry the purified product to obtain the esterified monomer.

8. A high-capacity silicon-based anode material, characterized in that, Prepared by the preparation method according to any one of claims 1 - 7 above.

9. Use of a high-capacity silicon-based anode material as described in claim 8 in a lithium-ion battery.

Images