Silicon-mesoporous titanium dioxide composite negative electrode material, preparation method and battery

Abstract

The present invention discloses a silicon-mesoporous titanium dioxide composite negative electrode material, a preparation method and a battery, belonging to the technical field of battery materials; the material comprises mesoporous titanium dioxide, nano-silicon and an outer coated carbon layer, wherein the mesoporous titanium dioxide has a pore diameter of 2-20 nm and a pore volume of 0.2-1.0 cm 3 / g, specific surface area 80-360m 2 / g, the nano-silicon is loaded inside the pores and on the surface of the skeleton of mesoporous titanium dioxide, the nano-silicon loading is 30-70%, the carbon coating amount is 1.5-10%, and the thickness of the silicon layer loaded on the surface of the mesoporous titanium dioxide skeleton is less than 10nm; the present invention increases the loading amount of silicon on titanium dioxide through monosilane vapor deposition, and effectively removes silicon vapor-deposited outside the pores and on the surface of the titanium dioxide carrier through alkaline etching; the obtained negative electrode material has the characteristics of high capacity, small expansion rate, stable structure and good cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a silicon-mesoporous titanium dioxide composite negative electrode material, a preparation method and a battery. Background Art

[0002] Compared to traditional graphite anodes, silicon boasts an exceptionally high theoretical specific capacity (4200 mAh / g) and a low delithiation potential (<0.5 V), making it a promising alternative for upgrading carbon-based anodes in lithium-ion batteries. Given the current demand for high-energy-density batteries in portable consumer electronics and pure electric vehicles, high-capacity silicon materials have garnered widespread attention. However, silicon also has drawbacks as a lithium-ion battery anode material: as a semiconductor, it inherently has low electrical conductivity. During electrochemical cycling, the insertion and extraction of lithium ions causes the material's volume to expand and contract by more than 300%. The resulting mechanical forces can gradually pulverize the material, leading to structural collapse. This ultimately causes the electrode active material to separate from the current collector, resulting in loss of electrical contact and significantly reduced battery cycling performance. Furthermore, due to this volume effect, silicon struggles to form a stable solid electrolyte interface (SEI) film in the electrolyte. As the electrode structure deteriorates, new SEI films continuously form on the exposed silicon surface, exacerbating silicon corrosion and capacity degradation.

[0003] Therefore, it is of great significance and value to improve the electrochemical properties of silicon-based negative electrode materials, reduce their volume expansion during charging and discharging, and improve their structural stability and cycle capacity. Summary of the Invention

[0004] The present invention aims to solve the technical problems of large volume expansion, unstable structure and poor cycle performance of silicon-based negative electrode materials during charging and discharging. The purpose is to provide a silicon-mesoporous titanium dioxide composite negative electrode material, a preparation method and a battery, thereby obtaining a silicon-mesoporous titanium dioxide composite negative electrode material with high capacity, small volume change during lithium insertion and deintercalation, stable structure and good cycle performance.

[0005] The present invention is achieved through the following technical solutions:

[0006] A silicon-mesoporous titanium dioxide composite negative electrode material comprises mesoporous titanium dioxide, nano-silicon and an outer carbon coating layer. The mesoporous titanium dioxide has a pore diameter of 2-20 nm and a pore volume of 0.2-1.0 cm 3 / g, specific surface area 80-360m 2 / g, the nano-silicon is loaded inside the pores and on the surface of the skeleton of mesoporous titanium dioxide, the nano-silicon loading amount is 30-70% (the mass fraction of nano-silicon in the negative electrode material), and the thickness of the silicon layer loaded on the surface of the mesoporous titanium dioxide skeleton is less than 10nm.

[0007] TiO2 has a theoretical specific capacity of 335mAh / g and features high lithium insertion potential, strong stability, low price, and environmental friendliness. It's worth noting that titanium dioxide exhibits structural stability and minimal volume change during charge and discharge, resulting in excellent cycle performance and safety, earning it the nickname "zero-strain" material. As the negative electrode, TiO2 possesses a high charge and discharge platform potential (approximately 1.5V), effectively avoiding the risk of lithium plating during high-rate, low-temperature charging. As a carrier, TiO2 also buffers lithium ions during high-rate charging, effectively enhancing the composite's kinetic performance.

[0008] The present invention uses mesoporous titanium dioxide as a carrier, and has strong electrochemical structure stability. The inner wall of the pores can effectively restrain the expansion stress of silicon during the charging and discharging process, maintain the stability of the overall structure, and improve the cycle performance; combined with the internal porous hollow structure, through silane vapor deposition, the silicon loading capacity is increased, thereby effectively improving the specific capacity of the composite material.

[0009] Furthermore, the coated carbon layer is coated on the outer surface of the mesoporous titanium dioxide skeleton, and the carbon coating amount is 1.5-10% (the mass fraction of the carbon content in the negative electrode material).

[0010] A method for preparing a silicon-mesoporous titanium dioxide composite negative electrode material comprises the following steps:

[0011] (1) Preparation of mesoporous titanium dioxide: Tetrabutyl titanate was dissolved in anhydrous ethanol at a mass ratio of 1:(1-7), hydrolyzed with concentrated hydrochloric acid at 45-60°C for 1-4 hours, cooled to room temperature, and then a template agent accounting for 5-50% of the mass of tetrabutyl titanate was added. The mixture was sealed and allowed to stand until it formed a gel, which was then washed, dried, and subjected to high-temperature heat treatment.

[0012] (2) Vapor deposition of nano-silicon: heating the mixture to 450-750°C in a rotary kiln under an inert atmosphere, then introducing a mixed gas at a flow ratio of monosilane to inert gas of 1:(5-20) for 0.5-4 hours, turning off the monosilane gas, stopping heating, and cooling to room temperature to obtain a titanium dioxide-loaded nano-silicon composite material;

[0013] (3) Surface silicon etching: the composite material obtained in (2) was added to 0.1-0.5M alkali solution at a mass ratio of 1:(1-4), treated for 10-45 min, filtered and vacuum dried to obtain a powder material;

[0014] (4) Carbon coating: Using liquid or gaseous carbon sources, the dried powder is subjected to surface pyrolysis in a high-temperature inert atmosphere to complete the coating treatment and prepare the Si-Void / TiO2@C negative electrode material.

[0015] The present invention increases the loading amount of silicon on titanium dioxide through monosilane vapor deposition, which can effectively improve the specific capacity of the composite material. By adopting alkaline etching, the silicon vapor-deposited outside the pores and on the surface of the titanium dioxide carrier is effectively removed, and the thickness and content of the surface silicon are controlled, thereby reducing the adverse effects of silicon exposed and not bound by the pore walls on the stability of the overall structure after multiple lithium insertion and removal cycles. At the same time, the present invention optimizes the proportion, dosage and parameter design of each substance in the preparation process to ensure the deposition amount of silicon in the titanium dioxide pores and the overall silicon content, thereby preparing a silicon-mesoporous titanium dioxide composite negative electrode material with high capacity, small volume change during lithium insertion and removal, stable structure and good cycle performance.

[0016] Furthermore, the template agent is 2,2-dihydroxymethylpropionic acid, glycerol, pentaerythritol, glucose, maltose or tartaric acid derivatives.

[0017] Furthermore, the high temperature heat treatment temperature in step (1) is 500-750°C.

[0018] Furthermore, the inert gas in step (2) includes one or more of argon, nitrogen, neon, and helium.

[0019] Furthermore, the alkaline solution in step (3) includes any one of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, lithium hydroxide solution, and ammonia water.

[0020] Furthermore, in step (4), the liquid carbon source coating specifically refers to: dissolving the organic carbon source in a solvent to form a solution, then adding the powder material obtained in step (3), mixing evenly, removing the solvent, and finally subjecting it to a heat treatment at 600-900°C; the organic carbon source includes glucose, maltose, citric acid, soluble starch, phenolic resin, asphalt, and the solvent includes water, ethanol, and tetrahydrofuran.

[0021] Furthermore, in step (4), the gas phase carbon source coating is specifically: using any one of acetylene, methane, ethylene, propylene, propane or natural gas to crack at a high temperature of 600-900°C.

[0022] A battery comprises a silicon-mesoporous titanium dioxide composite negative electrode material.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] 1. The present invention uses mesoporous titanium dioxide as a carrier, which has strong electrochemical structural stability. The inner wall of the pores can effectively restrain the expansion stress of silicon during the charge and discharge process, maintain the stability of the overall structure, and improve the cycle performance. Combined with the internal porous hollow structure, the silicon loading capacity is increased through silane vapor deposition, thereby effectively improving the specific capacity of the composite material.

[0025] 2. The present invention increases the silicon loading on titanium dioxide through monosilane vapor deposition, which can effectively improve the specific capacity of the composite material. By using alkaline etching, the silicon vapor-deposited outside the pores and on the surface of the titanium dioxide carrier is effectively removed, and the thickness and content of the surface silicon are controlled, thereby reducing the adverse effects of silicon exposed outside the pore walls on the overall structural stability after multiple lithium insertion and deintercalation cycles.

[0026] 3. The present invention optimizes the proportions, dosages, and parameter designs of various substances during the preparation process to ensure the deposition amount of silicon within the pores of titanium dioxide and the overall silicon content, thereby producing a silicon-mesoporous titanium dioxide composite negative electrode material with high capacity, small volume change during lithium insertion and extraction, stable structure, and good cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the examples. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope. A person of ordinary skill in the art can also derive other relevant drawings based on these drawings without inventive effort. In the drawings:

[0028] Figure 1 This is the TEM image of the Si-Void / TiO2@C negative electrode material prepared in Example 1. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0030] The present invention provides a silicon-mesoporous titanium dioxide composite negative electrode material, comprising mesoporous titanium dioxide, nano-silicon and an outer coated carbon layer, wherein the mesoporous titanium dioxide has a pore diameter of 2-20 nm and a pore volume of 0.2-1.0 cm 3 / g, specific surface area 80-360m 2 / g, the nano-silicon is loaded inside the pores and on the surface of the skeleton of mesoporous titanium dioxide, the nano-silicon loading amount is 30-70% (the mass fraction of nano-silicon in the negative electrode material), and the thickness of the silicon layer loaded on the surface of the mesoporous titanium dioxide skeleton is less than 10nm.

[0031] The coated carbon layer is coated on the outer surface of the mesoporous titanium dioxide skeleton, and the carbon coating amount is 1.5-10% (the carbon content accounts for the mass fraction of the negative electrode material).

[0032] The present invention also provides a method for preparing a silicon-mesoporous titanium dioxide composite negative electrode material, comprising the following steps:

[0033] (1) Preparation of mesoporous titanium dioxide: Tetrabutyl titanate was dissolved in anhydrous ethanol at a mass ratio of 1:(1-7), hydrolyzed with concentrated hydrochloric acid at 45-60°C for 1-4 hours, cooled to room temperature, and then a template agent accounting for 5-50% of the mass of tetrabutyl titanate was added. The mixture was sealed and allowed to stand until it formed a gel, which was then washed, dried, and subjected to high-temperature heat treatment.

[0034] (2) Vapor deposition of nano-silicon: heating the mixture to 450-750°C in a rotary kiln under an inert atmosphere, then introducing a mixed gas at a flow ratio of monosilane to inert gas of 1:(5-20) for 0.5-4 hours, turning off the monosilane gas, stopping heating, and cooling to room temperature to obtain a titanium dioxide-loaded nano-silicon composite material;

[0035] (3) Surface silicon etching: the composite material obtained in (2) was added to 0.1-0.5M alkali solution at a mass ratio of 1:(1-4), treated for 10-45 min, filtered and vacuum dried to obtain a powder material;

[0036] (4) Carbon coating: Using liquid or gaseous carbon sources, the dried powder is subjected to surface pyrolysis in a high-temperature inert atmosphere to complete the coating treatment and prepare the Si-Void / TiO2@C negative electrode material.

[0037] Specifically, the template agent is 2,2-dihydroxymethylpropionic acid, glycerol, pentaerythritol, glucose, maltose or tartaric acid derivatives.

[0038] Among them, the amount of template added is 5-50% of the mass of tetrabutyl titanate and is carefully designed. If the template content is low, the prepared mesoporous titanium dioxide has a small specific surface area and a small pore volume, which is not conducive to the loading of nano-silicon; if the template content is too high, the pore volume is high, the titanium dioxide structure strength is low, and it cannot withstand the deformation stress of silicon, which will reduce the stability of the composite material's multiple lithium intercalation and deintercalation structure.

[0039] The high-temperature heat treatment temperature in step (1) is 500-750°C, which is carefully designed. If the heat treatment temperature is low, dehydration is insufficient, the titanium dioxide crystal structure is not fully developed, and the structural strength is low, which affects the stability of subsequent lithium insertion and extraction. If the heat treatment temperature is too high, it is converted into an inert rutile structure, and the pore volume is significantly reduced, which is not conducive to the loading of a higher amount of silicon.

[0040] The inert gas in step (2) includes one or more of argon, nitrogen, neon and helium.

[0041] The rotary heating temperature of the drum furnace is 450-700° C., which is carefully designed. If the heating temperature is low, the silane cracking efficiency is low; if the temperature is high, it is easy to cause the growth of silicon grains.

[0042] The flow ratio of monosilane to inert gas is 1:(5-20) and is carefully designed. If the ratio is too high, the monosilane will decompose quickly and easily grow and aggregate on the surface of mesoporous titanium dioxide, resulting in pore blockage and inability to further improve the pore filling rate; if the ratio is too low, the deposition speed will be slow and the preparation time will be long.

[0043] The alkali solution in step (3) includes any one of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, lithium hydroxide solution, and ammonia solution. Furthermore, the concentration of the alkali solution is 0.1-0.5 M. If the concentration is too low, the etching speed is slow and the efficiency is low; if the concentration is too high, the etching speed is fast and the etching degree is difficult to control.

[0044] In step (4), the liquid carbon source coating specifically refers to: dissolving the organic carbon source in a solvent to form a solution, then adding the powder material obtained in step (3), mixing evenly, removing the solvent, and finally subjecting it to a heat treatment at 600-900°C; the organic carbon source includes glucose, maltose, citric acid, soluble starch, phenolic resin, asphalt, and the solvent includes water, ethanol, and tetrahydrofuran.

[0045] In step (4), the gas phase carbon source coating is specifically: any one of acetylene, methane, ethylene, propylene, propane or natural gas is cracked at a high temperature of 600-900°C.

[0046] The present invention also provides a battery comprising a silicon-mesoporous titanium dioxide composite negative electrode material.

[0047] Example 1

[0048] 1. Preparation of mesoporous titanium dioxide

[0049] Tetrabutyl titanate was dissolved in anhydrous ethanol at a mass ratio of 1:3, concentrated hydrochloric acid was added at 50°C for catalytic hydrolysis, and after cooling to room temperature, 2,2-dihydroxymethylpropionic acid template solution accounting for 20% of the mass of tetrabutyl titanate was added under vigorous stirring, and the mixture was sealed and allowed to stand. After the gel dried, it was dried in a low-temperature vacuum, finally ground and washed with water, and then dried and heat-treated at 550°C for 2h to obtain a pore diameter of 5.4 nm and a pore volume of 0.566 cm 3 / g, the specific gravity is 216.4m 2 / g of porous titanium dioxide material.

[0050] 2. Vapor deposition of nano-silicon: In an argon atmosphere, a rotary furnace is used to rotate and heat to 480°C, and then a mixed gas is introduced at a gas flow ratio of 1:5 of monosilane to argon for 2 hours. The monosilane gas is turned off and argon is continued to be introduced. The heating is stopped and the mixture is cooled to room temperature to obtain a titanium dioxide-loaded nano-silicon composite material.

[0051] 3. Surface silicon etching: The porous titanium dioxide loaded with nano-silicon was added to 0.2 M sodium hydroxide solution at a mass ratio of 1:3, treated for 10 min, filtered and dried in vacuum at 80°C.

[0052] 4. Carbon coating: The etched and dried composite powder material is added to a glucose aqueous solution, stirred and dispersed evenly, and then spray-dried. It is then heat-treated at 700°C under nitrogen to finally obtain the Si-Void / TiO2@C negative electrode material.

[0053] like Figure 1 The figure shows the TEM image of the Si-Void / TiO2@C negative electrode material prepared in this embodiment, in which the white is the silicon deposition layer and the gray-black is the porous titanium dioxide skeleton.

[0054] Example 2

[0055] 1. Preparation of mesoporous titanium dioxide: Tetrabutyl titanate was dissolved in anhydrous ethanol at a mass ratio of 1:1, concentrated hydrochloric acid was added at 45°C for catalytic hydrolysis, and after cooling to room temperature, a pentaerythritol template solution accounting for 5% of the mass of tetrabutyl titanate was added under vigorous stirring, and the mixture was sealed and allowed to stand. After the gel dried, it was dried in a low-temperature vacuum, finally ground and washed with water, and then dried and heat-treated at 700°C for 2h to obtain a pore diameter of 8.2nm and a pore volume of 0.358cm 3 / g, the specific gravity is 87.8m 2 / g of porous titanium dioxide material.

[0056] 2. Vapor deposition of nano-silicon: In an argon atmosphere, a rotary furnace is used to rotate and heat to 750°C, and then a mixed gas is introduced at a gas flow ratio of silane to argon of 1:20 for 0.5 h. The silane gas is turned off and argon is continued to be introduced. At the same time, heating is stopped and cooled to room temperature to obtain a composite material of titanium dioxide loaded with nano-silicon.

[0057] 3. Surface silicon etching: The porous titanium dioxide loaded with nano-silicon was added to 0.1 M potassium hydroxide solution at a mass ratio of 1:1, treated for 45 minutes, filtered and dried at 80°C in vacuum.

[0058] 4. Carbon coating: The etched and dried composite powder material is added to a glucose aqueous solution, stirred and dispersed evenly, and then spray-dried. It is then heat-treated at 600°C under nitrogen to finally obtain the Si-Void / TiO2@C negative electrode material.

[0059] Example 3

[0060] 1. Preparation of mesoporous titanium dioxide

[0061] Tetrabutyl titanate was dissolved in anhydrous ethanol at a mass ratio of 1:6, concentrated hydrochloric acid was added at 60°C for catalytic hydrolysis, and after cooling to room temperature, a glycerol template solution accounting for 48% of the mass of tetrabutyl titanate was added under vigorous stirring, and the mixture was sealed and allowed to stand. After the gel dried, it was dried in a low-temperature vacuum, finally ground and washed with water, and then dried and heat-treated at 750°C for 1h to obtain a pore size of 6.8nm and a pore volume of 0.972cm 3 / g, the specific gravity is 348.6m 2 / g of porous titanium dioxide material.

[0062] 2. Vapor deposition of nano-silicon: In a nitrogen atmosphere, a rotary furnace is used to rotate and heat to 450°C, and then a mixed gas is introduced according to a flow ratio of monosilane to nitrogen of 1:8 for 4 hours. The monosilane gas is turned off, and the heating is stopped and cooled to room temperature to obtain a titanium dioxide-loaded nano-silicon composite material.

[0063] 3. Surface silicon etching: The porous titanium dioxide loaded with nano-silicon was added to 0.5 M sodium hydroxide solution at a mass ratio of 1:2, treated for 10 min, filtered and dried at 80 °C in vacuum.

[0064] 4. Carbon coating: The etched and dried composite powder material is placed in a rotary furnace, argon is introduced and the temperature is raised to 850°C, and then acetylene is introduced for CVD carbon deposition coating to finally obtain Si-Void / TiO2@C negative electrode material.

[0065] Comparative Example 1

[0066] 1. Preparation of titanium dioxide

[0067] Tetrabutyl titanate was dissolved in anhydrous ethanol at a mass ratio of 1:3, concentrated hydrochloric acid was added at 50°C for catalytic hydrolysis, and after cooling to room temperature, 2,2-dihydroxymethylpropionic acid template solution accounting for 4% of the mass of tetrabutyl titanate was added under vigorous stirring, and the mixture was sealed and allowed to stand. After the gel dried, it was dried in a low-temperature vacuum, finally ground and washed with water, and then dried and heat-treated at 550°C for 2h to obtain a pore diameter of 4.3nm and a pore volume of 0.086cm 3 / g, the specific gravity is 36.6m 2 / g of porous titanium dioxide material.

[0068] 2. Vapor deposition of nano-silicon: In an argon atmosphere, a rotary furnace is used to rotate and heat to 480°C, and then a mixed gas is introduced at a gas flow ratio of 1:5 of monosilane to argon for 2 hours. The monosilane gas is turned off and argon is continued to be introduced. The heating is stopped and the mixture is cooled to room temperature to obtain a titanium dioxide-loaded nano-silicon composite material.

[0069] 3. Surface silicon etching: The porous titanium dioxide loaded with nano-silicon was added to 0.2 M sodium hydroxide solution at a mass ratio of 1:3, treated for 10 min, filtered and dried in vacuum at 80°C.

[0070] 4. Carbon coating: The etched and dried composite powder material is added to a glucose aqueous solution, stirred and dispersed evenly, and then spray-dried. It is then heat-treated at 800°C under nitrogen to finally obtain the Si-Void / TiO2@C negative electrode material.

[0071] Comparative Example 2

[0072] Except that the surface silicon etching process is not performed, other conditions are the same as those in Example 1.

[0073] Comparative Example 3

[0074] Except that the flow rate ratio of monosilane to argon was 1:1, other conditions were the same as those in Example 1.

[0075] Electrochemical performance test

[0076] The materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were used as negative electrode materials, mixed with a binder (CMC+SRB) and a conductive agent (Super-P) in a mass ratio of 80:5:5:10, and an appropriate amount of deionized water was added as a dispersant to form a slurry. The slurry was then coated on a 10 μm copper foil using a coating machine and dried at 90°C under vacuum (-0.1 MPa) for 6 hours. The slurry was then compacted with a roller to control the compaction density at 1.30 g / cm 3 14mm diameter discs were then produced using a punching machine. These discs were dried at 90°C under vacuum (-0.1 MPa) for 5 hours, weighed, and the active material weight was calculated. CR2430 button cells were assembled in a glove box, using a lithium metal sheet as the counter electrode and a polypropylene microporous membrane as the separator. 1 mol / L LiPF6 (lithium hexafluorophosphate) was dissolved in a 1:1 volume ratio of EC (ethylene carbonate) and DEC (diethyl carbonate), with 5.0% FEC (fluoroethylene carbonate) added as the electrolyte. The cells were allowed to rest at room temperature for 12 hours before constant current charge and discharge tests on a BlueDian 28°C constant temperature test system.

[0077] 1. Charge to 0.005V at 0.05C, then discharge to 1.5V at 0.1C for the first charge and discharge to calibrate the first reversible specific capacity and first efficiency.

[0078] 2. Charge to 0.005V at 0.05C, then discharge to 1.5V at 0.1C for 3 times, and then charge and discharge at 0.2C to calibrate the capacity retention rate after 200 cycles. At the same time, the following method is used to test and calculate the material volume expansion rate: (pole sheet thickness after 200 cycles - pole sheet thickness before assembly) / (pole sheet thickness before assembly - copper foil thickness) * 100%.

[0079] 3. Charge to 0.005V at 0.05C, then discharge to 1.5V at 0.1C for 3 times, then charge to 0.005V at 0.2C, discharge to 1.5V at 0.1C; charge to 0.005V at 1C, discharge to 1.5V at 0.1C, record the discharge specific capacity after charging at 0.2C and 1C rates respectively, and calculate the ratio of reversible capacity at different rates based on this.

[0080] The test results are shown in Table 1.

[0081] Table 1. Test results of negative electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3

[0082]

[0083] It can be seen from the test results of the examples that the composite negative electrode material prepared by the present invention has the characteristics of high capacity, low expansion rate and good cycle stability.

[0084] From the test results of Comparative Example 1, it can be seen that since the amount of active agent used in Comparative Example 1 is reduced, the prepared mesoporous titanium dioxide has an extremely low pore volume, and most of the nano-silicon deposited by silane is deposited on the surface of titanium dioxide. After alkaline etching, the silicon content is significantly reduced, resulting in low capacity; at the same time, since most of it is concentrated on the surface of the carrier, the stress released during the charge and discharge process cannot be effectively constrained by the pore wall of the carrier, so the cycle retention rate is low, the electrode expands significantly, and even the electrode powder falls off; and because the nano-silicon is not deposited in the pores of titanium dioxide, the buffering effect of titanium dioxide as a high lithium insertion platform cannot be exerted, resulting in a decrease in the lithium insertion ability during high-rate charging.

[0085] From the test results of Comparative Example 2, it can be seen that in Comparative Example 2, since the silicon deposited on the outer surface of the pores was not etched and removed, a large amount of silicon was deposited on the outer surface of the titanium dioxide pores. It can be seen that the expansion of the electrode increased and the cycle performance retention rate decreased; this is because the silicon particles generated by the decomposition of monosilane are not only deposited in the titanium dioxide pores, but also inevitably deposited on the outer surface of the pores. If the amount deposited on the outer surface of the pores is large, the stress generated by the deintercalation of silicon and lithium cannot be restrained by the inner wall of the silicon dioxide pore, thereby causing structural damage.

[0086] From the test results of Comparative Example 3, it can be seen that during the preparation process of Comparative Example 3, the methane inlet flow rate is too large, the nucleation rate is fast during the reaction, and a large number of cracked silicon particles are produced, which easily block the mesopore entrances and make it impossible to achieve effective deposition inside the pores. Therefore, the characteristics of mesoporous titanium dioxide cannot be brought into play, resulting in a high expansion rate of the charge and discharge electrode sheets, and deterioration of the cycle and rate performance.

[0087] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-mesoporous titanium dioxide composite negative electrode material, characterized in that: The silicon-mesoporous titanium dioxide composite negative electrode material comprises mesoporous titanium dioxide, nano-silicon and an outer carbon coating layer. The mesoporous titanium dioxide has a pore diameter of 2-20 nm and a pore volume of 0.2-1.0 cm 3 / g, specific surface area 80-360m 2 / g, the nano-silicon is loaded inside the pores and on the surface of the skeleton of mesoporous titanium dioxide, the nano-silicon loading amount is 30-70%, and the thickness of the silicon layer loaded on the surface of the mesoporous titanium dioxide skeleton is less than 10nm; The preparation method of the silicon-mesoporous titanium dioxide composite negative electrode material comprises the following steps: (1) Preparation of mesoporous titanium dioxide: Tetrabutyl titanate was dissolved in anhydrous ethanol at a mass ratio of 1:(1-7), hydrolyzed with concentrated hydrochloric acid at 45-60°C for 1-4 hours, cooled to room temperature, and a template agent accounting for 5-50% of the mass of tetrabutyl titanate was added. The mixture was sealed and allowed to stand until it formed a gel, then washed, dried, and heat treated at high temperature. (2) Vapor deposition of nano-silicon: In an inert atmosphere, a rotary furnace is used to heat the mixture to 450-750°C, and then a mixed gas is introduced at a flow ratio of monosilane to inert gas of 1:(5-20) for 0.5-4 hours. The monosilane gas is then turned off, and the heating is stopped and the mixture is cooled to room temperature to obtain a titanium dioxide-loaded nano-silicon composite material. (3) Surface silicon etching: Add the composite material obtained in (2) to 0.1-0.5M alkali solution at a mass ratio of 1:(1-4), treat for 10-45 minutes, filter and vacuum dry to obtain a powder material; (4) Carbon coating: Using liquid or gaseous carbon sources, the dried powder is subjected to surface pyrolysis in a high-temperature inert atmosphere to complete the coating treatment and prepare the Si-Void / TiO2@C negative electrode material.

2. The method for preparing a silicon-mesoporous titanium dioxide composite negative electrode material according to claim 1, characterized in that: The template agent is 2,2-dihydroxymethylpropionic acid, glycerol, pentaerythritol, glucose, maltose or tartaric acid derivative.

3. The method for preparing a silicon-mesoporous titanium dioxide composite negative electrode material according to claim 1, characterized in that: The high temperature heat treatment temperature in step (1) is 500-750°C.

4. The method for preparing a silicon-mesoporous titanium dioxide composite negative electrode material according to claim 1, characterized in that: The inert gas in step (2) includes one or more of argon, nitrogen, neon, and helium.

5. The method for preparing a silicon-mesoporous titanium dioxide composite negative electrode material according to claim 1, characterized in that: The alkaline solution in step (3) includes any one of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, lithium hydroxide solution, and ammonia water.

6. The method for preparing a silicon-mesoporous titanium dioxide composite negative electrode material according to claim 1, characterized in that: In step (4), the liquid carbon source coating specifically refers to dissolving the organic carbon source in a solvent to form a solution, then adding the powder material obtained in step (3), uniformly mixing, removing the solvent, and finally subjecting the solution to a heat treatment at 600-900°C.

7. The method for preparing a silicon-mesoporous titanium dioxide composite negative electrode material according to claim 1, characterized in that: In step (4), the gas phase carbon source coating is specifically: any one of acetylene, methane, ethylene, propylene, propane or natural gas is cracked at a high temperature of 600-900°C.

8. The method for preparing a silicon-mesoporous titanium dioxide composite negative electrode material according to claim 1, characterized in that: The coated carbon layer is coated on the outer surface of the mesoporous titanium dioxide skeleton, and the carbon coating amount is 1.5-10%.

Images