Method for preparing silicon-carbon composite negative electrode material and application thereof

Abstract

The application provides a method for preparing a silicon-carbon composite negative electrode material and application. The method comprises the following steps: firstly, mixing a carbon source, a triblock copolymer template agent, a surfactant and an alkali material with a solvent for primary mixing, and adding a silicon material for dispersion, then adding an aldehyde compound solution for secondary mixing, and adding an acid solution for tertiary mixing to obtain a silicon material coated by a polymer; secondly, calcining the obtained silicon material coated by the polymer for primary calcination to obtain a precursor material; and finally, calcining the obtained precursor material for secondary calcination to obtain the silicon-carbon composite negative electrode material. The application provides a silicon-carbon composite negative electrode material with a hollow core-shell structure, so that the first coulomb efficiency and the cycle stability of the composite material in the cycle process are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of negative electrode materials, and particularly relates to a method for preparing a silicon-carbon composite negative electrode material and application thereof. BACKGROUND

[0002] With the rapid development of electric vehicles and 3C electronic products, batteries have become the most important component. The endurance problem of electric vehicles has always been the focus of researchers, and therefore, it is necessary to develop a high-energy-density lithium ion battery system to meet the current needs of life and production.

[0003] At present, graphite is one of the commonly used negative electrode materials of lithium ion batteries, and one lithium ion can be accommodated in every 6 carbon atoms in the structure of graphite, while one silicon atom can accommodate 4 lithium ions, which makes silicon-based materials have an ultra-high theoretical specific capacity. In recent years, silicon-based negative electrode materials have attracted widespread attention due to their high theoretical specific capacity, low working potential, and abundant earth resources and environmental friendliness. However, although silicon-based negative electrode materials have high specific capacity, when used as negative electrode materials of lithium ion batteries, the large volume expansion of the active particles leads to the crushing of the active particles, the separation of the active material from the current collector, the continuous growth of the SEI film, and low coulombic efficiency, which seriously hinders the further application of lithium ion batteries.

[0004] In order to alleviate the problems of volume expansion and poor conductivity of silicon-based materials, the prior art discloses a technical solution of compounding silicon-based materials with carbon materials. Carbon materials have excellent structural stability and electrochemical activity, and do not react with electrolyte, and have good compatibility with silicon, and the two can be in close contact after compounding. At present, most methods for preparing silicon-carbon materials usually coat a carbon layer on the surface of silicon material to form a solid "core-shell" structure, which effectively improves the comprehensive performance of the silicon-carbon composite material. However, the above-mentioned solid "core-shell" structure also has defects, that is, in the cycle process, due to the large stress borne by the silicon particles in the process of lithium intercalation and lithium extraction, the carbon coating layer on the surface of silicon may crack, which cannot effectively alleviate the problem of volume expansion of silicon for a long time, resulting in the structure of the silicon-carbon composite material being broken, the cycle stability being decreased, the SEI film being continuously grown, and low coulombic efficiency.

[0005] Therefore, in the field, there is an urgent need to develop a silicon-carbon composite material with long-term structural stability, and the carbon layer will not crack, which can avoid the problem of volume expansion of silicon material. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application aims to provide a method for preparing a silicon-carbon composite negative electrode material and an application thereof. The present application provides a silicon-carbon composite negative electrode material having a hollow core-shell structure, which can provide a buffer space for the volume expansion effect of silicon particles, avoid the adverse effects of the volume expansion effect of silicon materials on the carbon shell, and thus improve the initial coulombic efficiency and cycle stability of the composite material during the cycle process.

[0007] To achieve the above object, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a method for preparing a silicon-carbon composite negative electrode material, wherein the silicon-carbon composite negative electrode material has a core-shell structure and a gap between the silicon material core and the carbon shell, and the method comprises the following steps:

[0009] (1) mixing a carbon source, a triblock copolymer template agent, a surfactant, and an alkali material with a solvent for the first time, adding a silicon material for dispersion, then adding an aldehyde compound solution for the second time, and adding an acid solution for the third time to obtain a silicon material coated with a polymer;

[0010] (2) calcining the silicon material coated with a polymer obtained in step (1) for the first time to obtain a precursor material;

[0011] (3) calcining the precursor material obtained in step (2) for the second time to obtain the silicon-carbon composite negative electrode material.

[0012] The present application prepares a silicon-carbon composite negative electrode material having a hollow core-shell structure. By using a triblock copolymer as a template agent, it begins to decompose during the first calcination, so that no other hard template needs to be introduced to form a hollow core-shell structure. At the same time, the addition of a surfactant is beneficial to the formation of a spherical structure. In the presence of an alkali material, the carbon source can undergo a polymerization reaction with an aldehyde compound, thereby coating the surface of the silicon material with a layer of polymer microspheres. In the subsequent second calcination process, high-temperature carbonization occurs to form a carbon shell, so that the silicon-carbon composite negative electrode material is beneficial to relieving the volume expansion problem of the silicon-carbon material and avoiding the structural cracking problem of the carbon shell, thereby prolonging the cycle life of the silicon-carbon material, improving its coulombic efficiency, and improving its structural stability.

[0013] Preferably, the carbon source in step (1) comprises any one or a combination of at least two of 2,6-diaminopyridine, 2,3,4-triaminopyridine, or 2,3-diaminopyridine.

[0014] In the present application, by using the carbon source with rich nitrogen atoms in the above structure, the introduction of nitrogen atoms into the carbon shell can provide more reaction sites. The doping of nitrogen elements is also conducive to building a more compact and stable interface between the silicon material core and the carbon shell, and in addition, it can improve the transport efficiency of lithium ions and enhance the electrical conductivity.

[0015] Preferably, the triblock copolymer template in step (1) comprises F127 template and / or P123 template.

[0016] It should be noted that the F127 template is polyoxyethylene polyoxypropylene ether; the P123 template is polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO).

[0017] In the present application, by using the above-mentioned triblock copolymer template, there is no need to introduce other hard templates, and it can also play the role of a surfactant.

[0018] Preferably, the surfactant in step (1) comprises any one or a combination of at least two of sodium dodecyl benzene sulfonate, sodium dodecyl sulfate or sodium dodecyl sulfonate.

[0019] In the present application, the addition of surfactant is conducive to the formation of a spherical structure.

[0020] Preferably, the alkali material in step (1) comprises any one or a combination of at least two of sodium hydroxide, ammonia or potassium hydroxide.

[0021] In the present application, the alkaline environment is conducive to the generation of carbon spheres.

[0022] Preferably, the solvent in step (1) is a mixed solvent composed of ethanol and deionized water.

[0023] Preferably, the volume ratio of ethanol to deionized water in the solvent in step (1) is (1.1-1.5):1, for example, it can be 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, etc.

[0024] In the present application, by adjusting the volume ratio of ethanol to deionized water, a carbon shell with a suitable size can be obtained, a too low ratio will not be able to generate a spherical shell, and vice versa will cause the generated spherical shell to be too large.

[0025] Preferably, the silicon material in step (1) comprises any one or a combination of at least two of silicon nanoparticles and silicon dioxide particles.

[0026] Preferably, the diameter of the silicon material in step (1) is 10-50 nm, for example, it can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, etc.

[0027] Preferably, the temperature of the dispersion in step (1) is 30-35℃, for example, it can be 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, etc.; the time is 30 min.

[0028] Preferably, the aldehyde compound solution in step (1) includes any one or a combination of at least two of formaldehyde solution, acetaldehyde solution or propyl aldehyde solution.

[0029] In the present application, under alkaline conditions, the amino functional group in the structure of the carbon source and the carbonyl group in the structure of the aldehyde compound can undergo an aminal reaction, thereby generating a polymer coating layer.

[0030] Preferably, the temperature of the secondary mixing in step (1) is 30-35℃, for example, it can be 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, etc.; the time is 8 h.

[0031] Preferably, the acid solution in step (1) is acetic acid solution.

[0032] Preferably, the temperature of the third mixing in step (1) is 30-35℃, for example, it can be 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, etc.; the time is 12 h.

[0033] Preferably, the mass ratio of the carbon source and the surfactant in step (1) is (1-1.5):1, for example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, etc.

[0034] In the present application, by adjusting the mass ratio of the carbon source and the surfactant, the raw material has a suitable surface tension, and a too low ratio will not be able to reduce the surface tension to form a spherical shape, and vice versa, an irregular structure will be generated.

[0035] Preferably, the mass ratio of the carbon source and the silicon material in step (1) is (2-4):1, for example, it can be 2:1, 2.2:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.8:1, 4:1, etc.

[0036] In the present application, by adjusting the mass ratio of the carbon source and the silicon material, the silicon material is uniformly and completely coated, a too low ratio will result in the silicon material being unable to be completely coated, and vice versa, there will be an excess of carbon material, causing waste of raw materials.

[0037] Preferably, the mass ratio of the triblock copolymer template agent and the carbon source in step (1) is (0.9-1.2):1, for example, it can be 0.9:1, 1:1, 1.12:1, 1.15:1, 1.18:1, 1.2:1, etc.

[0038] In the present application, by regulating the content of the triblock copolymer template agent, the size of the spherical shell can be regulated, too low content will result in the generated shell diameter is too small, otherwise it will generate the spherical shell is too large.

[0039] Preferably, after the third mixing in step (1), it further includes centrifugation and drying treatment in sequence.

[0040] Preferably, the drying time is 6-24h, for example, it can be 6h, 8h, 10h, 12h, 14h, 16h, 18h, 22h, 24h, etc.

[0041] Preferably, the first calcination in step (2) is carried out under an inert atmosphere.

[0042] Preferably, the inert atmosphere includes nitrogen and / or argon.

[0043] Preferably, the temperature of the first calcination in step (2) is 370-500℃, for example, it can be 370℃, 390℃, 400℃, 420℃, 450℃, 480℃, 500℃, etc.; the time is 0.5-4h, for example, it can be 0.5h, 0.8h, 1h, 2h, 3h, 4h, etc.

[0044] Preferably, the second calcination in step (3) is carried out under an inert atmosphere.

[0045] Preferably, the inert atmosphere includes nitrogen and / or argon.

[0046] Preferably, the temperature of the second calcination in step (3) is 700-1200℃, for example, it can be 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, etc.; the time is 0.5-4h, for example, it can be 0.5h, 0.8h, 1h, 2h, 3h, 4h, etc.

[0047] Preferably, the temperature of the second calcination in step (3) is 700-1200℃, for example, it can be 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, etc.; the time is 0.5-4h, for example, it can be 0.5h, 0.8h, 1h, 2h, 3h, 4h, etc.

[0048] Preferably, the temperature of the second calcination in step (3) is 700-1200℃, for example, it can be 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, etc.; the time is 0.5-4h, for example, it can be 0.5h, 0.8h, 1h, 2h, 3h, 4h, etc.

[0049] In the second aspect, the present application provides a silicon-carbon composite negative electrode material, the silicon-carbon composite negative electrode material has a core-shell structure, and there is a gap between the silicon material core and the carbon shell, the silicon-carbon composite negative electrode material is prepared by the method for preparing a silicon-carbon composite negative electrode material according to the first aspect.

[0050] Preferably, the thickness of the silicon material inner core is 10-50nm, for example, can be 10nm, 20nm, 30nm, 40nm, 50nm, etc.

[0051] Preferably, the thickness of the carbon shell is 35-45nm, for example, can be 35nm, 38nm, 40nm, 42nm, 45nm, etc.

[0052] Preferably, there is a gap of 30nm between the silicon material inner core and the carbon shell.

[0053] In a third aspect, the present application provides a secondary battery, which comprises a positive electrode, a negative electrode, an electrolyte and a separator, wherein the negative electrode comprises the silicon-carbon composite negative electrode material according to the second aspect.

[0054] Compared with the prior art, the present application has the following beneficial effects:

[0055] The present application provides a method for preparing a silicon-carbon composite negative electrode material, which uses a triblock copolymer as a template agent, which starts to decompose during the first calcination, so that no other hard template needs to be introduced, thereby forming a hollow core-shell structure. At the same time, the addition of a surfactant is beneficial to the formation of a spherical structure. In the presence of an alkali material, the carbon source can undergo a polymerization reaction with an aldehyde compound, thereby coating a layer of polymer microspheres on the surface of the silicon material, so as to undergo high-temperature carbonization to form a carbon shell during the subsequent second calcination process, so that the silicon-carbon composite negative electrode material is beneficial to relieving the volume expansion problem of the silicon-carbon material, avoiding the structure cracking problem of the carbon shell, thereby prolonging the cycle life of the silicon-carbon material, improving its coulombic efficiency and structural stability. DETAILED DESCRIPTION

[0056] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations on the present application.

[0057] Example 1

[0058] The present embodiment provides a method for preparing a silicon-carbon composite negative electrode material, which has a core-shell structure and a gap between the silicon material inner core and the carbon shell, the method comprising the following steps:

[0059] (1) mixing 2,6-diaminopyridine, F127 template agent, sodium dodecyl benzene sulfonate surfactant and sodium hydroxide with solvent (volume ratio of ethanol and deionized water is 1.4:1) for one time, adding silicon nanoparticles with a diameter of 30 nm for ultrasonic dispersion for 30 min, continuously stirring at 30℃ for 1 h, then adding formaldehyde solution, continuously stirring at 30℃ for 8 h, adding acetic acid solution, stirring at 30℃ for 12 h, centrifuging to collect the stirred product, after one centrifugation, centrifuging with deionized water and ethanol for two times respectively. The centrifuged product is dried in a vacuum drying box for 12 h, removing water in the sample to obtain a polymer-coated silicon material, wherein the mass ratio of 2,6-diaminopyridine to sodium dodecyl benzene sulfonate surfactant is 1:1, the mass ratio of 2,6-diaminopyridine to silicon nanoparticles is 2:1, and the mass ratio of 2,6-diaminopyridine to F127 template agent is 1:1.1;

[0060] (2) heating the polymer-coated silicon material obtained in step (1) to 400℃ at a rate of 2℃ / min in a nitrogen atmosphere, and then keeping the temperature for 2 h to obtain a precursor material;

[0061] (3) heating the precursor material obtained in step (2) to 800℃ at a rate of 5℃ / min in a nitrogen atmosphere, and keeping the temperature for 3 h, and then cooling to room temperature to obtain the silicon-carbon composite negative electrode material.

[0062] Example 2

[0063] The present embodiment provides a method for preparing a silicon-carbon composite negative electrode material, the silicon-carbon composite negative electrode material having a core-shell structure and a gap between the silicon material core and the carbon shell, the method comprising the following steps:

[0064] (1) mixing 2,6-diaminopyridine, F127 template agent, sodium dodecyl benzene sulfonate surfactant and sodium hydroxide with solvent (volume ratio of ethanol and deionized water is 1.2:1) for one time, adding silicon nanoparticles with a diameter of 20 nm for ultrasonic dispersion for 30 min, continuously stirring at 30℃ for 1 h, then adding formaldehyde solution, continuously stirring at 30℃ for 8 h, adding acetic acid solution, stirring at 30℃ for 12 h, centrifuging to collect the stirred product, after one centrifugation, centrifuging with deionized water and ethanol for two times respectively. The centrifuged product is dried in a vacuum drying box for 12 h, removing water in the sample to obtain a polymer-coated silicon material, wherein the mass ratio of 2,6-diaminopyridine to sodium dodecyl benzene sulfonate surfactant is 1.2:1, the mass ratio of 2,6-diaminopyridine to silicon nanoparticles is 2.5:1, and the mass ratio of 2,6-diaminopyridine to F127 template agent is 1:1;

[0065] (2) The polymer-coated silicon material obtained in step (1) is heated to 400°C at a rate of 2°C / min in a nitrogen atmosphere, and then kept for 2h to obtain a precursor material;

[0066] (3) The precursor material obtained in step (2) is heated to 800°C at a rate of 5°C / min in a nitrogen atmosphere, and kept for 3h, and then cooled to room temperature to obtain the silicon-carbon composite negative electrode material.

[0067] Example 3

[0068] The present embodiment provides a method for preparing a silicon-carbon composite negative electrode material having a core-shell structure and a gap between the silicon material core and the carbon shell, which comprises the following steps:

[0069] (1) 2,6-diaminopyridine, F127 template agent, sodium dodecyl benzene sulfonate surfactant, and sodium hydroxide are mixed with a solvent (ethanol and deionized water in a volume ratio of 1.3:1) for the first time, and 40nm-diameter silicon nanoparticles are added for ultrasonic dispersion for 30min, and then stirred at 30°C for 1h, and then formaldehyde solution is added and stirred at 30°C for 8h, and then acetic acid solution is added and stirred at 30°C for 12h, and then the stirred product is collected by centrifugation, and after one centrifugation, deionized water and ethanol are used for centrifugation twice respectively. The centrifuged product is dried in a vacuum drying box for 12h to remove the water in the sample to obtain a polymer-coated silicon material, wherein the mass ratio of 2,6-diaminopyridine to sodium dodecyl benzene sulfonate is 1.3:1, the mass ratio of 2,6-diaminopyridine to silicon nanoparticles is 3.5:1, and the mass ratio of 2,6-diaminopyridine to F127 template agent is 1:1;

[0070] (2) The polymer-coated silicon material obtained in step (1) is heated to 400°C at a rate of 2°C / min in a nitrogen atmosphere, and then kept for 2h to obtain a precursor material;

[0071] (3) The precursor material obtained in step (2) is heated to 800°C at a rate of 5°C / min in a nitrogen atmosphere, and kept for 3h, and then cooled to room temperature to obtain the silicon-carbon composite negative electrode material.

[0072] Example 4

[0073] The present embodiment provides a method for preparing a silicon-carbon composite negative electrode material having a core-shell structure and a gap between the silicon material core and the carbon shell, which comprises the following steps:

[0074] (1) 2,6-diaminopyridine, F127 template agent, sodium dodecyl benzene sulfonate surfactant and sodium hydroxide were mixed with solvent (volume ratio of ethanol and deionized water was 1.1:1) for the first time, and 10 nm diameter silicon nanoparticles were added for ultrasonic dispersion for 30 min, stirring was continued at 30°C for 1 h, then formaldehyde solution was added and stirring was continued at 30°C for 8 h, acetic acid solution was added and stirring was continued at 30°C for 12 h, the stirred product was collected by centrifugation, after one centrifugation, deionized water and ethanol were used for centrifugation twice respectively. The centrifuged product was dried in a vacuum drying oven for 6 h, the water in the sample was removed to obtain a polymer-coated silicon material, wherein the mass ratio of 2,6-diaminopyridine to sodium dodecyl benzene sulfonate surfactant was 1:1, the mass ratio of 2,6-diaminopyridine to silicon nanoparticles was 2:1, and the mass ratio of 2,6-diaminopyridine to F127 template agent was 1:0.9;

[0075] (2) The polymer-coated silicon material obtained in step (1) was heated to 370°C at a rate of 1°C / min in a nitrogen atmosphere, and then kept at 370°C for 4 h to obtain a precursor material;

[0076] (3) The precursor material obtained in step (2) was heated to 700°C at a rate of 1°C / min in a nitrogen atmosphere, and then kept at 700°C for 4 h, and cooled to room temperature to obtain the silicon-carbon composite negative electrode material.

[0077] Example 5

[0078] The present embodiment provides a method for preparing a silicon-carbon composite negative electrode material, the silicon-carbon composite negative electrode material has a core-shell structure, and there is a gap between the silicon material core and the carbon shell, the method comprises the following steps:

[0079] (1) 2,6-diaminopyridine, F127 template agent, sodium dodecyl benzene sulfonate surfactant and sodium hydroxide were mixed with solvent (volume ratio of ethanol and deionized water was 1.5:1) for the first time, and 50 nm diameter silicon nanoparticles were added for ultrasonic dispersion for 30 min, stirring was continued at 35°C for 1 h, then formaldehyde solution was added and stirring was continued at 35°C for 8 h, acetic acid solution was added and stirring was continued at 35°C for 12 h, the stirred product was collected by centrifugation, after one centrifugation, deionized water and ethanol were used for centrifugation twice respectively. The centrifuged product was dried in a vacuum drying oven for 24 h, the water in the sample was removed to obtain a polymer-coated silicon material, wherein the mass ratio of 2,6-diaminopyridine to sodium dodecyl benzene sulfonate surfactant was 1.5:1, the mass ratio of 2,6-diaminopyridine to silicon nanoparticles was 4:1, and the mass ratio of 2,6-diaminopyridine to F127 template agent was 1:1.2;

[0080] (2) The polymer-coated silicon material obtained in step (1) is heated to 500°C at a rate of 5°C / min in a nitrogen atmosphere, and then kept for 1 h to obtain a precursor material;

[0081] (3) The precursor material obtained in step (2) is heated to 1200°C at a rate of 5°C / min in a nitrogen atmosphere, and kept for 1 h, and then cooled to room temperature to obtain the silicon-carbon composite negative electrode material.

[0082] Example 6

[0083] The difference between this example and Example 1 is that the mass ratio of 2,6-diaminopyridine to sodium dodecyl benzene sulfonate surfactant in step (1) is 0.5:1, and the others are the same as those in Example 1.

[0084] Example 7

[0085] The difference between this example and Example 1 is that the mass ratio of 2,6-diaminopyridine to sodium dodecyl benzene sulfonate surfactant in step (1) is 3:1, and the others are the same as those in Example 1.

[0086] Example 8

[0087] The difference between this example and Example 1 is that the mass ratio of 2,6-diaminopyridine to silicon nanoparticles in step (1) is 1:1, and the others are the same as those in Example 1.

[0088] Example 9

[0089] The difference between this example and Example 1 is that the mass ratio of 2,6-diaminopyridine to silicon nanoparticles in step (1) is 6:1, and the others are the same as those in Example 1.

[0090] Example 10

[0091] The difference between this example and Example 1 is that the mass ratio of F127 template agent to 2,6-diaminopyridine in step (1) is 0.5:1, and the others are the same as those in Example 1.

[0092] Example 11

[0093] The difference between this example and Example 1 is that the mass ratio of F127 template agent to 2,6-diaminopyridine in step (1) is 1.5:1, and the others are the same as those in Example 1.

[0094] Example 12

[0095] The difference between this example and Example 1 is that 2,6-diaminopyridine is replaced by 2,3,4-triaminopyridine of the same content in step (1), and the others are the same as those in Example 1.

[0096] Comparative Example 1

[0097] The difference between this comparative example and Example 1 is that no F127 template agent is added in step (1), and no step (2) is performed, only step (1) and step (3) are performed, and the others are the same as Example 1.

[0098] Comparative Example 2

[0099] The difference between this comparative example and Example 1 is that no sodium dodecyl benzene sulfonate surfactant is added in step (1), and the others are the same as Example 1.

[0100] Application Examples 1-12 and Comparative Application Examples 1-2

[0101] The silicon-carbon composite negative electrode materials provided by Examples 1-12 and Comparative Examples 1-2 are assembled into CR2032 button lithium ion half batteries, and the assembly method is as follows:

[0102] The active material (silicon-carbon material of the application), conductive agent carbon black, butadiene rubber binder, and carboxymethylcellulose thickener are mixed according to the mass ratio of 95:1:2:2, deionized water is added and stirred thoroughly, a uniform negative electrode slurry is prepared, coated on a copper foil, dried and rolled to obtain a negative electrode sheet, and a small round sheet with a diameter of 12mm is made by a punching machine.

[0103] Preparation of CR2032 button lithium ion half battery: metal lithium sheet as negative electrode, the above electrode sheet as positive electrode and separator are assembled in a glove box, and appropriate amount of lithium battery electrolyte (the concentration of LiPF4 is 1 mol / L, and the solvent is composed of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1).

[0104] Test conditions

[0105] The lithium ion batteries provided by Application Examples 1-12 and Comparative Application Examples 1-2 are tested for performance, and the test method is as follows:

[0106] (1) Cycle performance test: the assembled CR2032 button battery is tested for charge and discharge on a LAND battery test system (model CT2001A), and the charge and discharge voltage range is set to 0.001-1.5V. The charge and discharge mode is set to constant current charge and discharge, the current density is 1 Ag -1 , and the cycle number is 200 cycles.

[0107] (2) The first coulombic efficiency test: the assembled CR2032 button cell was tested on the LAND battery test system (model CT2001A), and the charge-discharge voltage range was set to 0.001-1.5V. The charge-discharge mode was set to constant current charge-discharge, the current was set to 0.2C, and the cycle was 2 times.

[0108] The test results are shown in Table 1:

[0109] Table 1

[0110]

[0111]

[0112] As can be seen from Table 1, the silicon-carbon negative electrode material prepared by the method described in the application can be prepared under suitable conditions by adjusting the ratio of ethanol to water, controlling the content of surfactant and template agent, and the first coulombic efficiency of the lithium ion battery assembled by the silicon-carbon material can be as high as 91.5%. Under a current density of 1Ag -1 , the capacity retention rate after 200 cycles can be as high as 92.6%.

[0113] Compared with Application Example 1, Application Examples 6-7 are cases where the mass ratio of 2,6-diaminopyridine and sodium dodecylbenzenesulfonate surfactant exceeds the limited range, resulting in the failure to generate a spherical structure; Application Examples 8-9 are cases where the mass ratio of 2,6-diaminopyridine and silicon nanoparticles exceeds the limited range, resulting in the failure to form a good coating layer on the surface of the silicon material; Application Examples 10-11 are cases where the content of F127 template agent exceeds the limited range, resulting in the failure to form a spherical shell of suitable size; and Application Example 12 is a case where the type of carbon source is replaced, indicating that the use of 2,6-diaminopyridine has better technical effects.

[0114] The applicant declares that the process method of the application is illustrated by the above examples, but the application is not limited to the above process steps, i.e. it does not mean that the application must rely on the above process steps to be implemented. It should be understood by those skilled in the art that any improvement on the application, equivalent replacement of the materials selected by the application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the scope of protection and disclosure of the application.

Claims

1. A method for preparing a silicon-carbon composite negative electrode material, characterized by, The silicon-carbon composite negative electrode material has a core-shell structure, and has a gap between the silicon material core and the carbon shell, and the method comprises the following steps: (1) mixing a carbon source, a triblock copolymer template agent, a surfactant and an alkali material with a solvent for the first time, and adding a silicon material for dispersion, and then adding an aldehyde compound solution for the second time mixing, and then adding an acid solution for the third time mixing to obtain a polymer-coated silicon material; (2) calcining the polymer-coated silicon material obtained in step (1) for the first time to obtain a precursor material; (3) calcining the precursor material obtained in step (2) for the second time to obtain the silicon-carbon composite negative electrode material.

2. The method of claim 1, wherein, The carbon source in step (1) includes any one or a combination of at least two of 2,6-diaminopyridine, 2,3,4-triaminopyridine or 2,3-diaminopyridine.

3. The method of claim 1, wherein, The triblock copolymer template agent in step (1) includes F127 template agent and / or P123 template agent.

4. The method of claim 1, wherein, The surfactant in step (1) includes any one or a combination of at least two of sodium dodecyl benzene sulfonate, sodium dodecyl sulfate or sodium dodecyl sulfonate.

5. The method of claim 1, wherein, The alkali material in step (1) includes any one or a combination of at least two of sodium hydroxide, ammonia or potassium hydroxide.

6. The method of claim 1, wherein, The solvent in step (1) is a mixed solvent composed of ethanol and deionized water.

7. The method of claim 1, wherein, The volume ratio of ethanol to deionized water in the solvent in step (1) is (1.1-1.5):

1.

8. The method of claim 1, wherein, The silicon material in step (1) includes any one or a combination of at least two of silicon nanoparticles and silicon dioxide particles.

9. The method of claim 1, wherein, The diameter of the silicon material in step (1) is 10-50nm.

10. The method of claim 1, wherein, The temperature of the dispersion in step (1) is 30-35℃, and the time is 30min.

11. The method of claim 1, wherein, The aldehyde compound solution in step (1) includes any one or a combination of at least two of formaldehyde solution, acetaldehyde solution or propyl aldehyde solution.

12. The method of claim 1, wherein, The temperature of the second mixing in step (1) is 30-35℃, and the time is 8h.

13. The method of claim 1, wherein, The acid solution in step (1) is an acetic acid solution.

14. The method of claim 1, wherein, The temperature of the third mixing in step (1) is 30-35℃, and the time is 12h.

15. The method of claim 1, wherein, The mass ratio of the carbon source to the surfactant in step (1) is (1-1.5):

1.

16. The method of claim 1, wherein, The mass ratio of the carbon source to the silicon material in step (1) is (2-4):

1.

17. The method of claim 1, wherein, The mass ratio of the triblock copolymer template agent to the carbon source in step (1) is (0.9-1.2):

1.

18. The method of claim 1, wherein, After the third mixing in step (1), it further includes centrifugation and drying treatment in sequence.

19. The method of claim 18, wherein, The drying time is 6-24h.

20. The method of claim 1, wherein, The first calcination in step (2) is carried out in an inert atmosphere.

21. The method of claim 20, wherein, The inert atmosphere includes nitrogen and / or argon.

22. The method of claim 1, wherein, The heating rate of the first calcination in step (2) is 1-5℃ / min.

23. The method of claim 1, wherein, The temperature of the first calcination in step (2) is 370-500℃, and the time is 0.5-4h.

24. The method of claim 1, wherein, The second calcination in step (3) is carried out in an inert atmosphere.

25. The method of claim 24, wherein, The inert atmosphere includes nitrogen and / or argon.

26. The method of claim 1, wherein, The heating rate of the second calcination in step (3) is 1-5℃ / min.

27. The method of claim 1, wherein, The temperature of the secondary calcination in step (3) is 700-1200℃, and the time is 0.5-4h.

28. A silicon-carbon composite negative electrode material, characterized by, The silicon-carbon composite negative electrode material has a core-shell structure, and has a gap between the silicon material core and the carbon shell, and is prepared by the method for preparing a silicon-carbon composite negative electrode material according to any one of claims 1-27.

29. The silicon-carbon composite negative electrode material of claim 28, wherein, The thickness of the silicon material core is 10-50nm.

30. The silicon-carbon composite negative electrode material of claim 28, wherein, The thickness of the carbon shell is 35-45nm.

31. The silicon-carbon composite negative electrode material of claim 28, wherein, The gap between the silicon material core and the carbon shell is 30nm.

32. A secondary battery, characterized by comprising: The secondary battery comprises a positive electrode, a negative electrode, an electrolyte and a separator, and the negative electrode comprises the silicon-carbon composite negative electrode material according to any one of claims 28-31.

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