Preparation method of carbon-coated silicon monoxide composite material, composite material and lithium ion battery negative electrode

Abstract

The invention provides a preparation method of a carbon-coated silicon monoxide composite material, the composite material and a lithium ion battery negative electrode. The method comprises the following steps: dropwise adding tetraethoxysilane into an aqueous solution of organic alcohol and hydroxide, and stirring at room temperature to obtain a nano silicon monoxide colloid; carrying out vacuum drying on the nano-silica oxide colloid to obtain silicon oxide nano-microspheres; the preparation method comprises the following steps: mixing silicon monoxide nanoparticles with water, adding an alkaline solution, stirring in a water bath stirring pot, adding a carbon source, and obtaining a mixed liquid after stirring is completed; drying the mixed liquid to obtain precursor powder; and carrying out heat preservation reaction on the precursor powder under the protection of protective gas to obtain the carbon-coated silicon monoxide composite material. According to the silicon monoxide composite material based on carbon coating, the silicon monoxide serves as the inner core, the outer layer is the carbon material, direct contact between an electrolyte and the silicon monoxide is isolated through the carbon material shell layer, and active lithium consumption caused by formation of lithium silicate salt is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a preparation method of a carbon-coated silicon oxide composite material, the composite material, and a lithium-ion battery negative electrode. Background Art

[0002] With the rapid development of the new energy industry, lithium-ion batteries, as core components in the field of power energy storage, have been widely used in scenarios such as electric vehicles, energy storage power stations, and 3C electronic products. In lithium-ion battery systems, the performance of negative electrode materials is crucial to the overall performance of the battery. The negative electrode materials of current commercial lithium-ion batteries are mainly graphite. Graphite is a layered carbon material that stores lithium by intercalating / deintercalating lithium ions between layers. Its theoretical specific capacity is 372mAh / g. However, graphite has obvious defects as a negative electrode material. Its theoretical specific capacity is much lower than that of high-capacity materials, making it difficult to meet the needs of high-energy-density batteries.

[0003] Silicon-based materials have become the most promising candidate materials for high-capacity negative electrodes because of their theoretical specific capacity of 4200mAh / g (about 11.3 times that of graphite). From the perspective of crystal structure, silicon belongs to the diamond cubic structure. When lithium ions are embedded, Li-Si alloys are formed. This alloying reaction can provide extremely high lithium storage capacity. It is reported that the energy density of batteries using nano-silicon composite negative electrodes can reach 480Wh / kg, which is 60% higher than that of traditional graphite systems. Therefore, people have gradually turned their attention to this silicon-based material with higher specific capacity potential, hoping to meet the growing demand for high-energy density batteries through its research and application. At present, research on silicon-based negative electrodes mainly focuses on systems such as nano-silicon particles, porous silicon films and silicon dioxide composite materials.

[0004] When silicon-based materials are actually used in lithium-ion batteries, they face a technical problem that needs to be solved urgently. Compared with graphite, silicon-based materials will produce a larger volume expansion during the charging and discharging process. This large volume expansion will lead to a significant reduction in the cycle life of the battery, seriously affecting the actual application effect of silicon-based materials in lithium-ion batteries. In order to solve the problem of silicon volume expansion, silicon dioxide material is currently used as the negative electrode of the battery. However, silicon dioxide will form lithium silicate salts during charging and discharging. The formation of lithium silicate salts will consume the active lithium in the battery, resulting in a low first efficiency of the battery. Therefore, the reduced cycle life caused by the volume expansion of silicon-based materials during the charging and discharging process and the low first efficiency caused by the formation of lithium silicate salts have become key obstacles hindering the widespread application of silicon-based materials in lithium-ion batteries. Summary of the Invention

[0005] The present application provides a method for preparing a carbon-coated silicon monoxide composite material, a composite material and a lithium-ion battery negative electrode to solve the problems in the prior art of reduced cycle life caused by volume expansion of silicon-based materials during the charge and discharge process and low first efficiency caused by the formation of lithium silicate salts.

[0006] In a first aspect, the present application provides a method for preparing a carbon-coated silicon oxide composite material, the method comprising:

[0007] Adding ethyl orthosilicate dropwise to an aqueous solution of an organic alcohol and a hydroxide, and stirring the mixture at room temperature to obtain nano-colloidal silicate; the particle size of the colloidal silicate is 80 to 100 nm;

[0008] vacuum drying the silica colloid to obtain silica nanoparticles;

[0009] After mixing the silicon dioxide nanospheres with water, adding an alkaline solution and stirring in a water bath stirring pot, adding a carbon source, and after stirring, obtaining a mixed liquid; the carbon source is one of dopamine hydrochloride, glucose, lignin or starch;

[0010] Centrifuging, washing and drying the mixed liquid to obtain a precursor powder;

[0011] The precursor powder is subjected to a heat preservation reaction under the protection of a protective gas to obtain a carbon-coated silicon oxide composite material; the particle size of the carbon-coated silicon oxide composite material is 150-180 nm.

[0012] In some possible implementations, the silicon oxide core in the carbon-coated silicon oxide composite material is a hollow structure, the inner cavity diameter of the composite material is 30 to 80 nm, and the shell wall thickness of the composite material is 10 to 20 nm.

[0013] In some possible implementations, before adding ethyl orthosilicate dropwise to the aqueous solution of ethanol and ammonium hydroxide, 0.1 to 0.5 mol / L of Na2CO3 is added as a template.

[0014] In some possible implementations, the organic alcohol is ethanol, the hydroxide is ammonium hydroxide, and the mass ratio of the ethanol, ammonium hydroxide, and tetraethyl orthosilicate is 3:5:20-30.

[0015] In some possible implementations, after obtaining the mixed solution, it is stirred at a rate of 40 r / min at room temperature for 24 hours.

[0016] In some possible implementations, the alkaline solution is ammonia water, and the mass ratio of the silicon dioxide nanospheres, ammonia water, and carbon source is 70-75:5:20-25.

[0017] In some possible implementations, the solution after adding ammonia water is stirred in a water bath stirring pot at 30° C. for 30 minutes.

[0018] In some possible implementations, the protective gas is one of argon, nitrogen, and helium.

[0019] In some possible implementations, the precursor powder is kept warm under the protection of a protective gas at a temperature of 700 to 900° C. for a time of 3 to 5 hours during the reaction.

[0020] In a second aspect, the present application further provides a carbon-coated silicon oxide composite material, wherein the carbon-coated silicon oxide composite material is prepared by the preparation method of the carbon-coated silicon oxide composite material described in the first aspect.

[0021] In a third aspect, the present application further provides a lithium-ion battery negative electrode, wherein the lithium-ion battery negative electrode comprises the carbon-coated silicon monoxide composite material described in the second aspect.

[0022] In some possible implementations, the lithium-ion battery negative electrode preparation process includes:

[0023] A carbon-coated silicon oxide composite material, carbon nanotubes, a conductive agent, and a binder are mixed to obtain a negative electrode slurry;

[0024] The negative electrode slurry is coated on the negative electrode active material to obtain the negative electrode of the lithium ion battery.

[0025] In some possible implementations, the mass ratio of the silicon monoxide composite material, the carbon nanotubes, the conductive agent, and the binder is 94:1:1:4.

[0026] From the above content, it can be seen that the present application provides a method for preparing a carbon-coated silica composite material, a composite material and a negative electrode for a lithium-ion battery. The method includes adding ethyl orthosilicate to an aqueous solution of an organic alcohol and a hydroxide and stirring at room temperature to obtain nano silica colloids; vacuum drying the nano silica colloids to obtain silica nanospheres; mixing the silica nanospheres with water, adding an alkaline solution and placing them in a water bath stirring pot for stirring, then adding a carbon source, and obtaining a mixed liquid after the stirring is completed; drying the mixed liquid to obtain a precursor powder; and heat-retaining the precursor powder under the protection of a protective gas to react to obtain a carbon-coated silica composite material. The carbon-coated silica composite material prepared in the present application has silica as its core and a carbon material as its outer layer. The carbon material shell isolates the direct contact between the electrolyte and silica, reduces the consumption of active lithium caused by the formation of lithium silicate salts, and thus improves the low first efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0028] Figure 1 This is an electron microscope image of the carbon-coated silicon oxide composite material prepared in Example 1 provided in this application;

[0029] Figure 2 This is an EDS image of the carbon-coated silicon oxide composite material prepared in Example 1 provided in this application. DETAILED DESCRIPTION

[0030] The embodiments described in the following examples do not represent all embodiments consistent with the present application, but are merely examples of systems and methods consistent with some aspects of the present application as detailed in the claims.

[0031] With the rapid development of the new energy industry, lithium-ion batteries, as core components in the field of power energy storage, have been widely used in scenarios such as electric vehicles, energy storage power stations, and 3C electronic products. In lithium-ion battery systems, the performance of negative electrode materials is crucial to the overall performance of the battery. The negative electrode materials of current commercial lithium-ion batteries are mainly graphite. Graphite is a layered carbon material that stores lithium by intercalating / deintercalating lithium ions between layers. Its theoretical specific capacity is 372mAh / g. However, graphite has obvious defects as a negative electrode material. Its theoretical specific capacity is much lower than that of high-capacity materials, making it difficult to meet the needs of high-energy-density batteries.

[0032] Silicon-based materials have become the most promising candidate materials for high-capacity negative electrodes because of their theoretical specific capacity of 4200mAh / g (about 11.3 times that of graphite). From the perspective of crystal structure, silicon belongs to the diamond cubic structure. When lithium ions are embedded, Li-Si alloys are formed. This alloying reaction can provide extremely high lithium storage capacity. It is reported that the energy density of batteries using nano-silicon composite negative electrodes can reach 480Wh / kg, which is 60% higher than that of traditional graphite systems. Therefore, people have gradually turned their attention to this silicon-based material with higher specific capacity potential, hoping to meet the growing demand for high-energy density batteries through its research and application. At present, research on silicon-based negative electrodes mainly focuses on systems such as nano-silicon particles, porous silicon films and silicon dioxide composite materials.

[0033] When silicon-based materials are actually used in lithium-ion batteries, they face a technical problem that needs to be solved urgently. Compared with graphite, silicon-based materials will produce a larger volume expansion during the charging and discharging process. This large volume expansion will lead to a significant reduction in the cycle life of the battery, seriously affecting the actual application effect of silicon-based materials in lithium-ion batteries. In order to solve the problem of silicon volume expansion, silicon dioxide material is currently used as the negative electrode of the battery. However, silicon dioxide will form lithium silicate salts during charging and discharging. The formation of lithium silicate salts will consume the active lithium in the battery, resulting in a low first efficiency of the battery. Therefore, the cycle life problem caused by the volume expansion of silicon-based materials during the charging and discharging process and the low first efficiency problem caused by the formation of lithium silicate salts have become key obstacles hindering the widespread application of silicon-based materials in lithium-ion batteries.

[0034] Based on this, in order to address the problems in the related art of reduced cycle life due to volume expansion of silicon-based materials during the charge and discharge process and low first efficiency due to the formation of lithium silicate salts, the present application provides a method for preparing a carbon-coated silicon oxide composite material, a composite material, and a lithium-ion battery negative electrode. The carbon-coated silicon oxide composite material prepared in the present application, which is used as the negative electrode active material of the lithium-ion battery negative electrode, has silicon oxide as the core and a carbon material as the outer layer. The carbon material shell isolates the direct contact between the electrolyte and silicon oxide, reduces the consumption of active lithium caused by the formation of lithium silicate salts, and thus improves the low first efficiency of the battery.

[0035] In some embodiments, the present application provides a method for preparing a carbon-coated silicon oxide composite material, the method comprising:

[0036] Adding ethyl orthosilicate dropwise to an aqueous solution of an organic alcohol and a hydroxide, and stirring the mixture at room temperature to obtain nano-colloidal silicate; the particle size of the colloidal silicate is 80 to 100 nm;

[0037] vacuum drying the silica colloid to obtain silica nanoparticles;

[0038] After mixing the silicon dioxide nanospheres with water, adding an alkaline solution and stirring in a water bath stirring pot, adding a carbon source, and after stirring, obtaining a mixed liquid; the carbon source is one of dopamine hydrochloride, glucose, lignin or starch;

[0039] Centrifuging, washing and drying the mixed liquid to obtain a precursor powder;

[0040] The precursor powder is subjected to a heat preservation reaction under the protection of a protective gas to obtain a carbon-coated silicon oxide composite material; the particle size of the carbon-coated silicon oxide composite material is 150-180 nm.

[0041] In this embodiment, the organic alcohol is one of methanol, ethanol, isopropanol, and n-propanol, preferably ethanol; the hydroxide is one of sodium hydroxide and ammonium hydroxide, preferably ammonium hydroxide, and the alkaline solution in this embodiment is aqueous ammonia.

[0042] In this embodiment, the carbon source is one of dopamine hydrochloride, glucose, lignin or starch, preferably dopamine hydrochloride.

[0043] In an alkaline environment (pH = 8.5-9.0) regulated by ammonia, the catechol groups of dopamine hydrochloride are deprotonated to form a quinone structure, which triggers a free radical polymerization reaction and self-assembles on the surface of silicon oxide to form a uniform polydopamine layer. This process does not require additional initiators, the reaction conditions are mild, and it is suitable for continuous production. The phenolic hydroxyl groups (-OH) in dopamine hydrochloride form hydrogen bonds with the silanol groups (Si-OH) on the surface of silicon oxide. During high-temperature carbonization, they further condense to form Si-OC covalent bonds, which enhance the interfacial bonding between the carbon layer and the SiO core and prevent the carbon layer from falling off during the cycle. After carbonization, dopamine hydrochloride forms an amorphous carbon layer with a pore size distribution concentrated in the range of 0.5-2 nm, which can effectively block the penetration of the electrolyte and reduce the consumption of active lithium during the formation of lithium silicate salts.

[0044] The carbon-coated silicon oxide composite material in this embodiment has a hollow structure, the inner cavity diameter of the composite material is 30 to 80 nm, and the shell wall thickness of the composite material is 10 to 20 nm.

[0045] The carbon-coated silicon oxide composite material prepared in this application has nano-sized silicon oxide (SiO) particles as a core, coated with a uniform carbon shell. The carbon shell can be porous or graphitized, and may have gaps or an interface layer between the shell and the SiO core.

[0046] During lithium insertion, silicon oxide expands by approximately 300%. The hollow interior acts as a "buffer," providing directional release for this expansion and preventing particle fracture or electrode pulverization due to internal stress concentration. The carbon-coated silicon oxide composite material has an inner cavity diameter of 30 to 80 nm, ideally proportioned to the nanoscale SiO particles, ensuring sufficient deformation margin for the shell during expansion. The shell wall thickness of 10 to 20 nm maintains structural rigidity while avoiding excessive thickness that could lead to insufficient elasticity.

[0047] Compared with the solid structure, the hollow structure reduces the actual amount of SiO2 used. Combined with the "isolation" effect of the carbon material shell, it can further reduce the active lithium consumption during the formation of lithium silicate salts, and increase the first coulombic efficiency from 80% of traditional SiO2 to more than 90%. The thin shell structure with a shell wall thickness of 10 to 20 nm shortens the diffusion path of lithium ions from the electrolyte to the SiO2 core, thereby improving the rate performance. The hollow inner cavity can indirectly increase the porosity of the material, promote electrolyte penetration, and optimize the ion conduction network. The continuous network of the carbon material shell is more likely to form a three-dimensional conductive channel in the hollow structure. Compared with the solid structure, the electrical conductivity can be increased by 30% to 50%, improving the electron transmission efficiency during high-rate charge and discharge.

[0048] Since the hollow cavity reduces the solid volume of the SiO core, the overall density of the composite material is increased from 2.5 g / cm3 of solid SiO / C to 1.5 g / cm3 of solid SiO / C. 3 Reduced to 2.0g / cm 3 With the same mass, the hollow structure can accommodate more active materials and, combined with the high-capacity SiO core, increase the battery's energy density by 15% to 20%, meeting the long-range requirements of electric vehicles.

[0049] In some embodiments, before adding tetraethyl orthosilicate dropwise to the aqueous solution of ethanol and ammonium hydroxide, 0.1-0.5 mol / L Na2CO3 is added as a template, and acid is added to remove the template after the composite material is formed.

[0050] Na2CO3 will slowly decompose in an ethanol-water mixture system, releasing CO2 gas. When ethyl orthosilicate is hydrolyzed to form SiO colloid, CO2 gas is wrapped inside the colloid as a "soft template". The gas escapes during the subsequent drying and calcination process, thus forming a hollow cavity with a diameter of 30 to 80 nm. In addition, Na2CO3 hydrolysis is alkaline (pH ≈ 10 to 11), and it can also maintain an alkaline environment together with NH4OH in the system to promote the hydrolysis reaction of ethyl orthosilicate. The Na2CO3 dissociated Na + The addition of CO₃ and CO₃⁻ increases the ionic strength of the solution, thereby reducing interparticle attraction and preventing colloid aggregation during formation, ensuring the integrity of the hollow structure. During calcination at 800°C, Na₂CO₃ completely decomposes into Na₂O and CO₂. Na₂O reacts with SiO₂ to form sodium silicate (Na₂SiO₃). However, sodium silicate will dissolve in the subsequent battery electrolyte and will not remain in the composite material, ensuring the purity of the carbon shell.

[0051] The nanoscale concave-convex structure formed on the surface of the hollow SiO core by the template increases the mechanical engagement points with the carbon shell, boosting the interfacial bonding strength between the carbon shell and the SiO core by over 40%, thus preventing the carbon shell from shedding during charge and discharge. The core value of Na2CO3 as a template lies in its ability to precisely construct a hollow SiO core structure that meets performance requirements without changing the original solution polymerization-carbonization process, thereby enabling its use as a high-energy-density lithium-ion battery anode material.

[0052] In some embodiments, when tetraethyl orthosilicate is added dropwise to an aqueous solution of ethanol and ammonium hydroxide, the mass ratio of the ethanol, ammonium hydroxide, and tetraethyl orthosilicate is 3:5:20-30.

[0053] In some embodiments, the solution after adding ammonia water is stirred in a water bath stirring pot at 30° C. for 30 minutes.

[0054] After adding ammonia water to the aqueous solution of ethanol and ammonium hydroxide, the mixture was stirred in a water bath at 30°C for 30 minutes. The pH value of the solution was adjusted, the surface charge of the nanospheres was optimized, and the reaction kinetics were controlled to lay the foundation for uniform coating of the carbon source.

[0055] By adding ammonia water to raise the pH of the solution to 8.5-9.0, the self-polymerization reaction of dopamine hydrochloride is activated, while avoiding local excessive pH that would damage the structure of the silica nanospheres. Under the action of stirring, the ionization of hydroxyl groups on the surface of the silica nanospheres is promoted, making them negatively charged, and the interfacial interaction with the dopamine hydrochloride molecules is enhanced through electrostatic attraction, maintaining the dispersion stability of the nanospheres. Stirring at 30°C for 30 minutes allows dopamine to polymerize at an appropriate rate to form an initial polydopamine core, providing a base point for the subsequent growth of a complete coating layer, activating the silicon-oxygen bonds inside the silica nanospheres, and enhancing the binding force between the carbon material shell and the SiO core. At the same time, it can also ensure the formation of a uniform dopamine pre-adsorption layer on the surface of the silica nanospheres, which is converted into a uniform and dense carbon shell after carbonization, thereby improving the battery's first efficiency and cycle performance.

[0056] In some embodiments, after obtaining the mixed solution, it was stirred at room temperature at a rate of 40 r / min for 24 h.

[0057] In some embodiments, after the silica nanospheres are mixed with water, ammonia water is added and the mixture is placed in a water bath stirring pot for stirring. The mass ratio of the silica nanospheres, ammonia water and dopamine hydrochloride is 70-75:5:20-25.

[0058] The amount of silicon dioxide nanospheres used ensures the appropriate thickness of the carbon material shell (10-20nm), avoiding a decrease in specific capacity due to too low a dosage or insufficient buffering due to too high a dosage, while ensuring the integrity of the hollow structure. The amount of ammonia water used maintains the pH of the solution at 8.5-9.0, ensuring the stability of the polymerization rate of dopamine hydrochloride and the surface charge of the nanospheres, inhibiting agglomeration and achieving uniform adsorption. The amount of dopamine hydrochloride determines the thickness and conductivity of the carbon material shell. If the dosage is too low, the carbon material shell will be thin and the SEI film will be unstable. If the dosage is too high, the diffusion of lithium ions will be hindered. The conductivity and interface binding energy are optimal at 20-25 parts. Through the precise ratio of "core-carbon source", the whole process from silicon dioxide surface modification to carbon material shell growth is controlled, the carbon material shell thickness (10-20nm) and the proportion of silicon dioxide core are quantitatively controlled, and the lithium storage capacity and structural stability are balanced; the polymerization environment of dopamine hydrochloride is optimized to ensure coating uniformity and interface bonding strength.

[0059] In some embodiments, the protective gas is one of argon, nitrogen, and helium.

[0060] In some embodiments, the precursor powder is kept warm under the protection of a protective gas at a temperature of 700 to 900° C. for a time of 3 to 5 hours during the reaction.

[0061] The precursor powder is carbonized at 700-900°C for 3-5 hours, mainly by regulating the shell structure of the carbon material and strengthening the interfacial bonding force to achieve electrochemical performance optimization and process compatibility. Under this process condition, carbonization treatment can promote the formation of Si-OC covalent bonds between the SiO core and the carbon material shell, enhance the interfacial bonding energy, release residual stress, and avoid cracking and shedding of the carbon material shell. Appropriate temperature is conducive to the formation of a stable SEI film, enhances the first effect, improves lithium ion transmission, and enhances rate performance and cycle life. Under this process condition, the activity of the SiO core is enhanced, and the hollow structure and carbon shell are combined to control the volume expansion rate and adapt to the ideal carbon material shell thickness.

[0062] In some embodiments, the present application further provides a carbon-coated silicon oxide composite material, which is prepared by the preparation method of the carbon-coated silicon oxide composite material described in the above embodiments.

[0063] In some embodiments, the present application further provides a lithium-ion battery negative electrode, which is a lithium-ion battery negative electrode prepared by the method for preparing a lithium-ion battery negative electrode of the above embodiment.

[0064] In some embodiments, the process for preparing a negative electrode for a lithium-ion battery includes:

[0065] A carbon-coated silicon oxide composite material, carbon nanotubes, a conductive agent, and a binder are mixed to obtain a negative electrode slurry;

[0066] The negative electrode slurry is coated on the negative electrode active material to obtain the negative electrode of the lithium ion battery.

[0067] In some embodiments, the mass ratio of the silicon dioxide composite material, carbon nanotubes, conductive agent, and binder is 94:1:1:4.

[0068] In this embodiment, the particle size of silica gel is regulated by adjusting the acidity and alkalinity of the solution, the amount of ethyl orthosilicate added, and the stirring time. The silica gel particle size obtained in this embodiment is relatively stable and does not agglomerate. In addition, by adjusting the carbon source precursor and the carbonization temperature, the carbon material shell coated on the outside of the silica microspheres is more uniform, thereby improving the conductivity of the composite material. The carbon-coated silica composite material finally obtained has nano-scale SiO particles as the core and is coated with a uniform carbon material shell on the outside. The 30-80nm hollow silica core provides a buffer space for volume expansion, and the 10-20nm carbon shell suppresses expansion through elastic deformation, controlling the volume expansion rate to below 150%. The dense carbon material shell can isolate the electrolyte and reduce the consumption of active lithium. The first coulombic efficiency of the lithium-ion battery prepared with this composite material is increased to more than 90%, meeting the high cycle requirements of power batteries.

[0069] Example 1:

[0070] 1) Preparation of carbon-coated silicon oxide composites

[0071] Step 1: Dissolve ethanol and NH4OH in 100 mL of deionized water, mix in a magnetic stirrer for 15 minutes, then add 3 mL of tetraethyl orthosilicate dropwise, where the mass ratio of ethanol, ammonium hydroxide, and tetraethyl orthosilicate is 3:5:20, and stir at room temperature for 12 hours to form nano-silicon oxide colloids with a particle size of about 90 nm.

[0072] Step 2: The product was then washed several times with anhydrous ethanol and deionized water, and dried in a vacuum drying oven at 80°C for 12 hours. Finally, silicon dioxide nanospheres with a particle size of about 100 nm were obtained.

[0073] Step 3: Mix a certain amount of nanospheres with deionized water and sonicate for 1 hour. Then, add 3.0 mL of ammonia and stir in a water bath at 30°C for 30 minutes. Then, dissolve an appropriate amount of dopamine hydrochloride in 10 mL of deionized water. The mass ratio of silica nanospheres, ammonia, and dopamine hydrochloride is 70:5:25. Once stirring is complete, add the mixture to the mixture and stir at 40 rpm for 24 hours at room temperature.

[0074] Step 4: Then put it into a centrifuge to separate the product, wash it with anhydrous ethanol several times, and place it in a vacuum drying oven at 80°C for 8 hours.

[0075] Step 5: Place the washed product into a tube furnace filled with argon and heat it at 800℃ for 3 hours to obtain a carbon-coated silicon dioxide composite material with a particle size of about 150nm. Figure 1 As shown in FIG, it is an electron microscope image of the carbon-coated silicon oxide composite material prepared in this embodiment. Figure 2 The EDS diagram of the carbon-coated silicon oxide composite material prepared in this embodiment is shown in FIG. Figure 1 and Figure 2 It can be seen that the material has uniform shape and better crystallinity.

[0076] 2) Preparation of negative electrode sheet

[0077] Step 1: Weigh each substance according to the mass percentage of the negative electrode sheet in a ratio of carbon-coated silicon oxide composite material: carbon nanotubes: conductive carbon: binder = 94:1:1:4.

[0078] Step 2: First, stir and pre-mix the silicon dioxide composite material, carbon nanotubes, and conductive carbon, then add pure water and stir thoroughly to obtain a mixed slurry.

[0079] Step 3: Add binder to the mixed slurry and mix thoroughly to obtain the negative electrode slurry.

[0080] Step 4: Evenly coat the prepared negative electrode slurry on the copper foil, and obtain the negative electrode sheet by drying, rolling, die-cutting or striping.

[0081] 3) Preparation of lithium-ion batteries

[0082] In an argon-filled glove box, complete, smooth, burr-free electrodes and flat, non-defective lithium sheets were assembled into a snap-on battery. The assembly sequence was as follows: positive electrode casing + electrode + 80μL electrolyte + separator + 80μL electrolyte + gasket + spring + negative electrode casing. The half-cell test voltage ranged from 0.001V to 2.0V.

[0083] Example 2:

[0084] The preparation method of the carbon-coated silica composite material in this example is the same as that in Example 1, except that the carbon source in step 3 is replaced by glucose instead of dopamine hydrochloride. The mass ratio of silica nanospheres, ammonia water, and glucose in this example is the same as that of silica nanospheres, ammonia water, and dopamine hydrochloride in Example 1. The preparation of the negative electrode sheet and the preparation of the lithium-ion battery in this example are also the same as those in Example 1 and are not further described.

[0085] Example 3:

[0086] The preparation method of the carbon-coated silica composite material in this example is the same as that in Example 1, except that the carbon source in step 3 is replaced by lignin instead of dopamine hydrochloride. The mass ratio of silica nanospheres, ammonia, and lignin in this example is the same as the mass ratio of silica nanospheres, ammonia, and dopamine hydrochloride in Example 1. The preparation of the negative electrode sheet and the preparation of the lithium-ion battery in this example are also the same as those in Example 1 and are not further described.

[0087] Example 4:

[0088] The preparation method of the carbon-coated silica composite material in this example is the same as that in Example 1, except that starch is used as the carbon source in step 3 instead of dopamine hydrochloride. The mass ratio of silica nanospheres, ammonia, and starch in this example is the same as that of silica nanospheres, ammonia, and dopamine hydrochloride in Example 1. The preparation of the negative electrode sheet and the preparation of the lithium-ion battery in this example are also the same as those in Example 1 and are not further described.

[0089] Example 5

[0090] The preparation method for the carbon-coated silicon oxide composite material in this example was the same as in Example 1, except that in step 5, the washed product was placed in an argon-filled tube furnace and heated at 700°C for 3 hours. The preparation of the negative electrode sheet and the lithium-ion battery in this example were also the same as in Example 1 and are not further described.

[0091] Example 6

[0092] The preparation method for the carbon-coated silicon oxide composite material in this example was the same as in Example 1, except that in step 5, the washed product was placed in an argon-filled tube furnace and heated at 900°C for 3 hours. The preparation of the negative electrode sheet and the lithium-ion battery in this example were also the same as in Example 1 and are not further described.

[0093] Comparative Example 1

[0094] 1) Preparation of carbon-coated silicon oxide composites

[0095] Step 1: Dissolve ethanol and NH4OH in 100 mL of deionized water, mix in a magnetic stirrer for 15 minutes, then add 3 mL of tetraethyl orthosilicate dropwise, where the mass ratio of ethanol, ammonium hydroxide, and tetraethyl orthosilicate is 3:5:20, and stir at room temperature for 12 hours to form nano-silicon oxide colloids with a particle size of about 90 nm.

[0096] Step 2: The product was then washed several times with anhydrous ethanol and deionized water, and dried in a vacuum drying oven at 80°C for 12 hours. Finally, silicon dioxide nanospheres with a particle size of about 100 nm were obtained.

[0097] 2) Preparation of negative electrode sheet

[0098] Silicon dioxide nanospheres are mixed with carbon nanotubes, conductive carbon and a binder to obtain a negative electrode slurry, and a negative electrode sheet is obtained based on the negative electrode slurry.

[0099] 3) Preparation of lithium-ion batteries

[0100] In an argon-filled glove box, complete, smooth, burr-free electrodes and flat, non-defective lithium sheets were assembled into a snap-on battery. The assembly sequence was as follows: positive electrode casing + electrode + 80μL electrolyte + separator + 80μL electrolyte + gasket + spring + negative electrode casing. The half-cell test voltage ranged from 0.001V to 2.0V.

[0101] Comparative Example 2

[0102] 1) Preparation of carbon-coated silicon oxide composites

[0103] Step 1: Dissolve ethanol and NH4OH in 100 mL of deionized water, mix in a magnetic stirrer for 15 minutes, then add 3 mL of tetraethyl orthosilicate dropwise, where the mass ratio of ethanol, ammonium hydroxide, and tetraethyl orthosilicate is 3:5:20, and stir at room temperature for 12 hours to form nano-silicon oxide colloids with a particle size of about 90 nm.

[0104] Step 2: The product was then washed several times with anhydrous ethanol and deionized water, and dried in a vacuum drying oven at 80°C for 12 hours. Finally, silicon dioxide nanospheres with a particle size of about 100 nm were obtained.

[0105] Step 3: Continue to mechanically mix the silicon dioxide nanospheres and the hard carbon material in a ball mill to obtain a hard carbon-silicon dioxide composite material

[0106] 2) Preparation of negative electrode sheet

[0107] The carbon-silicon oxide composite material is mixed with carbon nanotubes, conductive carbon and a binder to obtain a negative electrode slurry, and a negative electrode sheet is obtained based on the negative electrode slurry.

[0108] 3) Preparation of lithium-ion batteries

[0109] In an argon-filled glove box, complete, smooth, burr-free electrodes and flat, non-defective lithium sheets were assembled into a snap-on battery. The assembly sequence was as follows: positive electrode casing + electrode + 80μL electrolyte + separator + 80μL electrolyte + gasket + spring + negative electrode casing. The half-cell test voltage ranged from 0.001V to 2.0V.

[0110] The charging performance test was performed on the above Examples 1-6 and Comparative Examples 1-2.

[0111] Table 1

[0112]

[0113] Table 2

[0114]

[0115] As can be seen from Tables 1 and 2, the volume expansion rate of the lithium-ion battery prepared in Example 1 is controlled below 150%, the capacity retention rate exceeds 85% after 200 cycles, the first coulombic efficiency is increased to more than 90%, and the first efficiency is increased from 75% to 80% of traditional SiO to more than 90%. The first charge and discharge efficiency of the whole battery is increased by 15%, and the capacity retention rate exceeds 85% after 200 cycles, meeting the high cycle requirements of power batteries. It can be seen that the external carbon shell structure in the carbon-coated silicon oxide composite material as the negative electrode active material effectively slows down the 300% volume expansion of SiO during charge and discharge, preventing electrode pulverization; its continuous carbon conductive network structure can greatly improve the conductivity and improve the rate performance; in addition, the carbon shell isolates the electrolyte, promotes the formation of a stable SEI film, and reduces irreversible capacity loss; the hollow and porous structure design of the carbon-coated silicon oxide composite material can reduce the weight of the material and improve the cycle stability, so that the capacity retention rate and cycle life of the material are significantly improved, meeting the performance requirements of the negative electrode of the lithium-ion battery.

[0116] It can be seen from the above embodiments that the present application provides a method for preparing a carbon-coated silica composite material, a composite material and a negative electrode for a lithium-ion battery. The method includes adding ethyl orthosilicate to an aqueous solution of an organic alcohol and a hydroxide and stirring at room temperature to obtain nano silica colloids; vacuum drying the nano silica colloids to obtain silica nanospheres; mixing the silica nanospheres with water, adding an alkaline solution and placing them in a water bath stirring pot for stirring, then adding a carbon source, and obtaining a mixed liquid after the stirring is completed; drying the mixed liquid to obtain a precursor powder; and heat-retaining the precursor powder under the protection of a protective gas to react to obtain a carbon-coated silica composite material. The carbon-coated silica composite material prepared in the present application has silica as its core and a carbon material as its outer layer. The carbon material shell isolates the direct contact between the electrolyte and silica, reduces the consumption of active lithium caused by the formation of lithium silicate salts, and thus improves the low first efficiency of the battery.

[0117] Similar parts between the embodiments provided in this application can be referenced to each other. The specific implementation methods provided above are only a few examples under the overall concept of this application and do not constitute a limitation on the scope of protection of this application. For those skilled in the art, any other implementation methods expanded based on the scheme of this application without expending creative work shall fall within the scope of protection of this application.

Claims

1. A method for preparing a carbon-coated silicon oxide composite material, characterized in that: The method comprises: Adding ethyl orthosilicate dropwise to an aqueous solution of an organic alcohol and a hydroxide, and stirring the mixture at room temperature to obtain nano-colloidal silicate; the particle size of the colloidal silicate is 80 to 100 nm; vacuum drying the silica colloid to obtain silica nanoparticles; After mixing the silicon dioxide nanospheres with water, adding an alkaline solution and stirring in a water bath stirring pot, adding a carbon source, and after stirring, obtaining a mixed liquid; the carbon source is one of dopamine hydrochloride, glucose, lignin or starch; Centrifuging, washing and drying the mixed liquid to obtain a precursor powder; The precursor powder is subjected to a heat preservation reaction under the protection of a protective gas to obtain a carbon-coated silicon oxide composite material; the particle size of the carbon-coated silicon oxide composite material is 150-180 nm.

2. The method for preparing the carbon-coated silicon oxide composite material according to claim 1, wherein: The silicon oxide in the carbon-coated silicon oxide composite material has a hollow structure, the inner cavity diameter of the composite material is 30 to 80 nm, and the shell wall thickness of the composite material is 10 to 20 nm.

3. The method for preparing the carbon-coated silicon oxide composite material according to claim 2, wherein: Before adding ethyl orthosilicate dropwise to the aqueous solution of ethanol and ammonium hydroxide, 0.1-0.5 mol / L Na2CO3 is added as a template.

4. The method for preparing the carbon-coated silicon oxide composite material according to claim 2, wherein: The organic alcohol is ethanol, the hydroxide is ammonium hydroxide, and the mass ratio of the ethanol, ammonium hydroxide and ethyl orthosilicate is 3:5:20-30.

5. The method for preparing the carbon-coated silicon oxide composite material according to claim 4, characterized in that: The alkaline solution is ammonia water, and the mass ratio of the silicon dioxide nanospheres, ammonia water and carbon source is 70-75:5:20-25.

6. The method for preparing the carbon-coated silicon oxide composite material according to claim 1, wherein: The protective gas is one of argon, nitrogen or helium.

7. The method for preparing the carbon-coated silicon oxide composite material according to claim 6, characterized in that: The precursor powder is kept warm under the protection of protective gas at a temperature of 700-900° C. for 3-5 hours.

8. A carbon-coated silicon oxide composite material, characterized in that: The carbon-coated silicon oxide composite material is prepared by the preparation method of the carbon-coated silicon oxide composite material according to any one of claims 1 to 7.

9. A lithium ion battery negative electrode, characterized in that The negative electrode of the lithium-ion battery comprises the carbon-coated silicon oxide composite material according to claim 8.

10. The lithium-ion battery negative electrode according to claim 9, characterized in that The lithium-ion battery negative electrode preparation process comprises: A carbon-coated silicon oxide composite material, carbon nanotubes, a conductive agent, and a binder are mixed to obtain a negative electrode slurry, wherein the mass ratio of the silicon oxide composite material, the carbon nanotubes, the conductive agent, and the binder is 94:1:1:4; The negative electrode slurry is coated on the negative electrode active material to obtain the negative electrode of the lithium ion battery.

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