A silicon-oxygen composite negative electrode material and its preparation method and application

Abstract

The present invention discloses a silicon-oxygen composite negative electrode material and its preparation method and application. First, silicon dioxide and chitosan are uniformly dispersed in an acidic solution, dried to remove the solvent, and then calcined at high temperature under an argon environment to obtain a nitrogen-doped carbon-coated silicon-oxygen composite material; the nitrogen-doped carbon-coated silicon-oxygen composite material is washed and etched with a mixed alkali solution of sodium hydroxide and lithium hydroxide, and then washed with deionized water to obtain a carbon / porous silicon-oxygen composite material; the carbon / porous silicon-oxygen composite material, carbon graphite material, and chitosan are uniformly dispersed in an acidic solution to obtain a second mixed solution, and then dried to remove the solvent to obtain a dried product, which is then calcined at high temperature to finally obtain a silicon-oxygen composite negative electrode material. The silicon-oxygen composite negative electrode material prepared by the present invention has the advantages of high initial efficiency, high capacity, low deformation, and long cycle life, and can improve the energy density and cycle life of lithium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery negative electrode materials, and in particular relates to a silicon-oxygen composite negative electrode material and a preparation method and application thereof. Background Art

[0002] Over the past few decades, lithium-ion batteries (LIBs) have been successfully used in various electronic terminal products and electric vehicles due to their excellent comprehensive performance. With the continuous improvement of energy density requirements (the energy density of commercial graphite-lithium metal oxide systems is less than 300Wh kg -1 ), new electrode materials are urgently needed in the future to break through the theoretical limits of traditional positive and negative electrodes; silicon-based negative electrodes are considered to be the most promising negative electrode materials for the next generation of lithium-ion batteries due to their high theoretical capacity.

[0003] Despite the attractive prospects of silicon-based anode materials, their research and application are still plagued by problems such as poor conductivity and volume expansion. Although the defect of poor conductivity can be effectively solved by combining silicon with carbon materials, the huge volume expansion (about 300% and 200% for silicon and silicon oxide, respectively) is a difficult challenge that hinders the commercial application of new silicon anode materials. It can lead to anode particle crushing, electrode pulverization, and instability of the solid electrolyte interface (SEI), which seriously damages the cycle life of lithium-ion batteries.

[0004] In order to solve the problem of large volume expansion of silicon materials during the charge and discharge process, a compromise solution is to use silicon oxide as a negative electrode material. Silicon oxide, also known as silicon monoxide, has no unified conclusion on its structure. Some researchers believe that it is composed of randomly distributed Si-Si bonds and Si-O, while others believe that it is a mixed structure of cubic crystal silicon and atomic crystal silicon dioxide. Currently, the industrial production route of silicon oxide is relatively mature. It is made by the anti-disproportionation reaction of high-purity silicon and silicon dioxide under high temperature and vacuum conditions: SiO2+Si→2SiO. The theoretical maximum capacity of silicon oxide is 2680mAh g -1 , its actual reversible capacity can reach 1500mAh g -1 The volume expansion of silicon oxide during lithium insertion is significantly reduced (up to approximately 200%) compared to crystalline silicon, significantly improving its cycling performance. Furthermore, by adopting a nanostructuring strategy and combining silicon oxide with carbon materials or artificial graphite, the volume expansion effect of silicon-based anodes can be effectively mitigated, significantly improving their overall performance and possessing great potential for increasing the energy density and cycle life of lithium-ion batteries.

[0005] There is also research currently on silicon dioxide-based negative electrode materials. For example, publication number CN108493438A proposes a SiOx-based composite negative electrode material for lithium-ion batteries and a preparation method thereof. The silicon dioxide raw material is ball-milled and uniformly mixed with metal salts, followed by spray drying. The material is then calcined in an inert atmosphere to produce high-temperature disproportionation and coated with a layer of silicate on the surface of the particles. The particles are then coated with an amorphous conductive carbon layer to increase conductivity, ultimately resulting in a finished SiOx-based composite negative electrode material. Although the SiOx-based composite negative electrode material prepared by this technology has a higher electrochemical capacity than general negative electrode materials, its initial coulombic efficiency and cycle life are still relatively low and need to be further improved. Summary of the Invention

[0006] In response to the above-mentioned defects in the prior art, the purpose of the present invention is to provide a silicon-oxygen composite negative electrode material and its preparation method and application, using silicon oxide as a substrate and chitosan as a coating layer, combining high-temperature carbonization and alkaline solution treatment to obtain a carbon / porous silicon-oxygen composite material; then the carbon / porous silicon-oxygen composite material is compounded with chitosan and carbon graphite material and calcined to obtain a silicon-oxygen composite negative electrode material. The silicon-oxygen composite negative electrode has the advantages of high first efficiency, high capacity, low deformation and long cycle, and can improve the energy density and cycle life of lithium-ion batteries.

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

[0008] A first aspect of the present invention provides a method for preparing a silicon-oxygen composite negative electrode material, comprising the following steps:

[0009] S1, uniformly dispersing silicon dioxide and chitosan in an acidic solution to obtain a first mixed solution, drying the first mixed solution to remove the solvent to obtain a solid phase, and then calcining the solid phase at a high temperature under an argon environment to obtain a nitrogen-doped carbon-coated silicon-oxygen composite material;

[0010] S2, washing and etching the nitrogen-doped carbon-coated silicon-oxygen composite material with a mixed alkali solution of sodium hydroxide and lithium hydroxide, and then washing with deionized water to obtain a carbon / porous silicon-oxygen composite material;

[0011] S3, uniformly dispersing the carbon / porous silicon-oxygen composite material, carbon graphite material, and chitosan in an acidic solution to obtain a second mixed solution, drying and removing the solvent to obtain a dried product, and then calcining the dried product at a high temperature to finally obtain a silicon-oxygen composite negative electrode material.

[0012] Preferably, in step S1:

[0013] The first mixed solution is prepared by dissolving the chitosan in an acidic solution to form a carbon precursor solution, then uniformly dispersing the silicon dioxide in deionized water to obtain a suspension, and then adding the suspension to the carbon precursor solution and dispersing the mixture uniformly to obtain the first mixed solution; and / or

[0014] The D50 particle size of the silicon oxide is 1 to 10 μm; and / or

[0015] The mass ratio of silicon oxide to chitosan is 5-10:1-5; and / or

[0016] The acidic solution is prepared by adding hydrochloric acid or glacial acetic acid to deionized water to adjust the pH to less than 6; and / or

[0017] In the mixed solution, the total concentration of the chitosan and the silicon oxide is 2 to 30 wt%; and / or

[0018] The drying method is spray drying or heating evaporation; and / or

[0019] During the high-temperature calcination process, the heating rate is 3-10° C. / min, the calcination temperature is 850-1000° C., and the calcination time is 1-3 hours.

[0020] Preferably, in step S1:

[0021] During the preparation of the first mixed solution and the dissolution of the chitosan, the stirring time is 1 to 6 hours; and / or

[0022] During the preparation of the suspension, ultrasonic dispersion is used with a dispersion time of 10 to 60 minutes; and / or

[0023] During the spray drying process, the inlet temperature is 100-300°C; and / or

[0024] During the heating evaporation process, the evaporation temperature is 80-120° C., the stirring rate is 200-800 Hz, and the evaporation time is 0.5-6.

[0025] Preferably, in step S2:

[0026] In the mixed alkali solution, the molar ratio of the sodium hydroxide to the lithium hydroxide is 1-3:1-3, and the total molar concentration of the sodium hydroxide and the lithium hydroxide is 0.5-2 mol / L; and / or

[0027] During the washing and etching process, the stirring rate is 20 to 100 Hz, and the stirring time is 0.5 to 6 hours.

[0028] Preferably, in step S3:

[0029] The second mixed solution is prepared by dissolving the chitosan in an acidic solution to form a carbon precursor solution, uniformly mixing the carbon / porous silicon oxide composite material and the carbon graphite material, and uniformly dispersing them in deionized water to obtain a suspension, and then pouring the suspension into the carbon precursor solution and uniformly dispersing them to obtain a mixed solution; and / or

[0030] The mass ratio of the carbon / porous silicon oxide composite material to the carbon graphite material and chitosan is 1-5:1-5:1-5; and / or

[0031] In the second mixed solution, the total mass concentration of the carbon / porous silicon oxide composite material, the carbon graphite material and the chitosan is 2 to 50 wt %; and / or

[0032] The carbon graphite material is selected from one of artificial graphite, natural graphite, hard carbon material or soft carbon material; and / or

[0033] The acidic solution is prepared by adding hydrochloric acid or glacial acetic acid to deionized water to adjust the pH to less than 6; and / or

[0034] The drying method is spray drying or heating evaporation; and / or

[0035] During the high-temperature calcination process, the heating rate is 3-10° C. / min, the calcination temperature is 850-1000° C., and the calcination time is 1-3 hours.

[0036] Preferably, in step S3:

[0037] During the preparation of the second mixed solution, the stirring time during the dissolution of the chitosan is 1 to 6 hours; and / or

[0038] During the preparation of the suspension, ultrasonic dispersion is used with a dispersion time of 10 to 60 minutes; and / or

[0039] During the spray drying process, the inlet temperature is 100-300°C; and / or

[0040] During the heating evaporation process, the evaporation temperature is 80-120° C., the stirring rate is 200-800 Hz, and the evaporation time is 0.5-6 h.

[0041] Preferably, the nitrogen-doped carbon-coated silicon-oxygen composite material is in granular form, with a D50 particle size of 1 to 10 μm and a specific surface area of ​​less than 20 m 2 / g; the nitrogen-doped carbon-coated silicon-oxygen composite material has a carbon content of 3 to 12 wt% and a nitrogen content of 0.1 to 5 wt%; and / or

[0042] The carbon / porous silicon oxide composite material is in granular form, with a D50 particle size of 1 to 10 μm and a specific surface area of ​​less than 50 m 2 / g; the carbon / porous silicon oxygen composite material, the carbon content is 3 to 15wt%, the nitrogen content is 0.1 to 5wt%; and / or

[0043] The D50 particle size of the silicon-oxygen composite negative electrode material is 5 to 20 μm, and the specific surface area is less than 50 m 2 / g, gram capacity is 1300~2000mAh / g, and first coulombic efficiency is ≥70%.

[0044] The second aspect of the present invention provides a silicon-oxygen composite negative electrode material prepared according to the preparation method of the silicon-oxygen composite negative electrode material described in the first aspect of the present invention, characterized in that the silicon-oxygen composite negative electrode material contains SiOx, the silicon element content is 5 to 40 wt%, and x in SiOx is 0.5 to 1.5.

[0045] The third aspect of the present invention provides an application of a silicon-oxygen composite negative electrode material prepared by the method for preparing a silicon-oxygen composite negative electrode material according to the first aspect of the present invention as a negative electrode material in a lithium-ion battery.

[0046] The silicon-oxygen composite negative electrode material provided by the present invention and its preparation method and application have the following beneficial effects:

[0047] 1. The silicon-oxygen composite negative electrode material provided by the present invention, as well as its preparation method and application, uses silicon oxide as a substrate and chitosan as a coating layer, and combines high-temperature carbonization and alkaline solution treatment to obtain a carbon / porous silicon-oxygen composite material; the carbon / porous silicon-oxygen composite material is then composited with chitosan and carbon graphite material and calcined to obtain a silicon-oxygen composite negative electrode material. The silicon-oxygen composite negative electrode has the advantages of high initial efficiency, high capacity, low deformation, and long cycle life, and can improve the energy density and cycle life of lithium-ion batteries;

[0048] 2. The silicon-oxygen composite negative electrode material provided by the present invention, as well as its preparation method and application, uses a silicon oxide substrate as a high-energy-density component to improve the electrochemical capacity of the composite negative electrode. The introduction of carbon graphite material and the nitrogen-doped carbon coating obtained by calcining chitosan can improve the conductivity and rate performance of the composite negative electrode and alleviate its volume expansion effect, so that the silicon-oxygen composite negative electrode material has good overall performance when used as a negative electrode for lithium-ion batteries.

[0049] 3. The silicon-oxygen composite negative electrode material provided by the present invention, as well as its preparation method and application, utilizes a mixed alkaline solution of sodium hydroxide and lithium hydroxide to etch the nitrogen-doped carbon-coated silicon-oxygen composite material to form a carbon / porous silicon-oxygen composite material, which can reserve a certain space for the volume change of the silicon-oxygen composite material. In addition, the use of lithium hydroxide can introduce some lithium elements on the surface of the silicon-oxygen material, which can replenish lithium and improve the initial coulombic efficiency.

[0050] 4. The silicon-oxygen composite negative electrode material provided by the present invention, as well as its preparation method and application, utilizes chitosan as a binder and coating layer to combine a carbon / porous silicon-oxygen composite material and a carbon graphite material to form a uniform granular material. This can increase the carbon content of the silicon-oxygen composite negative electrode material and form a more uniform and comprehensive coating on the silicon-oxygen material, thereby reducing direct contact between the silicon-oxygen material and the electrolyte, thereby improving conductivity and initial efficiency.

[0051] 5. The silicon-oxygen composite negative electrode material provided by the present invention, as well as its preparation method and application, uses a very mature silicon oxide production process. Raw materials such as chitosan and carbon graphite materials are low in cost and abundant in resources. The process technology of the present invention is simple, the conditions are easy to control, and it is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0053] Figure 1 This is a SEM image of the nitrogen-doped carbon-coated silicon-oxygen composite material prepared in Example 1 of the present invention;

[0054] Figure 2 This is a SEM photograph of the carbon / porous silicon-oxygen composite material prepared in Example 2 of the present invention;

[0055] Figure 3 This is a SEM photograph of the silicon-oxygen composite negative electrode material-1 prepared in Example 3 of the present invention.

[0056] Figure 4 This is a SEM photograph of the silicon-oxygen composite negative electrode material-2 prepared in Example 4 of the present invention.

[0057] Figure 5 This is a SEM photograph of the silicon-oxygen composite negative electrode material-3 prepared in Example 5 of the present invention. DETAILED DESCRIPTION

[0058] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below with reference to embodiments.

[0059] The method for preparing the silicon-oxygen composite negative electrode material provided by the present invention comprises the following steps:

[0060] S1, dispersing silicon dioxide and chitosan in an acidic solution to obtain a first mixed solution, drying the first mixed solution to remove the solvent to obtain a solid phase, and then calcining the solid phase at a high temperature under an argon environment to obtain a nitrogen-doped carbon-coated silicon-oxygen composite material;

[0061] The specific process is as follows: first, silicon dioxide (SiO) and chitosan are weighed in a mass ratio of 5-10:1-5. Then, an acidic solution is prepared, and hydrochloric acid or glacial acetic acid is added to deionized water to adjust the pH to <6. The weighed chitosan is then added to the prepared acidic solution and stirred for 1-6 hours until completely dissolved, thereby obtaining a carbon precursor solution. The silicon dioxide is uniformly dispersed in deionized water to obtain a suspension, wherein ultrasonic dispersion is employed for 10-60 minutes. The suspension is then slowly added to the carbon precursor solution, and after uniform dispersion, a first mixed solution is obtained. The solvent is then removed by spray drying or thermal evaporation to obtain a solid phase. During spray drying, a vacuum tube furnace is used with an inlet temperature of 100-300°C. During thermal evaporation drying, the evaporation temperature is 80-120°C, the stirring rate is 200-800Hz, and the evaporation time is 0.5-6 hours. Finally, the solid phase is calcined at high temperature in an argon atmosphere at a heating rate of 3 to 10°C / min, a calcination temperature of 850 to 1000°C, and a calcination time of 1 to 3 hours to obtain a nitrogen-doped carbon-coated silicon-oxygen composite material, which is recorded as C / SiOx. The nitrogen-doped carbon-coated silicon-oxygen composite material prepared above is in granular form, with an average D50 particle size of 1 to 10 μm and a specific surface area of ​​less than 20 m 2 / g, the interior of the particles is disproportionated silicon oxide (SiOx), and the exterior is a nitrogen-doped carbon coating layer; the carbon content in the nitrogen-doped carbon-coated silicon-oxygen composite material is 3-12wt%, and the nitrogen content is 0.1-5wt%.

[0062] S2, washing and etching the nitrogen-doped carbon-coated silicon-oxygen composite material with a mixed alkali solution of sodium hydroxide and lithium hydroxide, and then washing with deionized water to obtain a carbon / porous silicon-oxygen composite material;

[0063] The specific process is as follows: first, a mixed alkali solution is prepared using sodium hydroxide and lithium hydroxide in a molar ratio of 1 to 3: 1 to 3, wherein the total molar concentration of sodium hydroxide and lithium hydroxide is 0.5 to 2 mol / L; then, the nitrogen-doped carbon-coated silicon-oxygen composite material is washed and etched using the mixed alkali solution, and the nitrogen-doped carbon-coated silicon-oxygen composite material is immersed in the mixed alkali solution and stirred at a stirring speed of 20 to 100 Hz and a stirring time of 0.5 to 6 hours, followed by centrifugation, and then the separated powder is washed with deionized water, and centrifuged again to obtain a powder material, which is repeated 1 to 3 times to finally obtain a carbon / porous silicon-oxygen composite material, recorded as C / D-SiOx. The carbon / porous silicon-oxygen composite material prepared above is granular, with an average D50 particle size of 1 to 10 μm and a specific surface area of ​​less than 50 m 2 / g, the interior of the particles is porous disproportionated silicon oxide (SiOx), and the exterior is a nitrogen-doped carbon coating layer. The carbon content of the carbon / porous silicon oxide composite material is 3-15wt%, and the nitrogen content is 0.1-5wt%.

[0064] S3, uniformly dispersing the carbon / porous silicon-oxygen composite material, carbon graphite material, and chitosan in an acidic solution to obtain a second mixed solution, drying and removing the solvent to obtain a dried product, and then calcining the dried product at a high temperature to finally obtain a silicon-oxygen composite negative electrode material.

[0065] The specific process is as follows: first, weigh a carbon / porous silicon oxide composite material, a carbon graphite material and chitosan in a mass ratio of 1 to 5:1 to 5:1 to 5, wherein the carbon graphite material is selected from one of artificial graphite, natural graphite, hard carbon material and soft carbon material; then, prepare an acidic solution, add hydrochloric acid or glacial acetic acid to deionized water to adjust the pH to <6, then add the weighed chitosan to the prepared acidic solution, stir for 1 to 6 hours until completely dissolved, and obtain a carbon precursor solution; then, mix the carbon / porous silicon oxide composite material and the carbon graphite material evenly, add them to deionized water, and use ultrasonic dispersion for 10 to 60 minutes to obtain a suspension, and then slowly add the suspension to the carbon precursor solution to obtain a second mixed solution. Then, spray drying or heating evaporation is used to remove the solvent and obtain a dried product; during the spray drying process, a vacuum tube furnace is used, and the inlet temperature is 100-300°C; during the heating evaporation drying process, the evaporation temperature is 80-120°C, the stirring rate is 200-800Hz, and the evaporation time is 0.5-6h. Finally, the dried product is calcined at a high temperature under an argon atmosphere, with a heating rate of 3-10°C / min, a calcination temperature of 850-1000°C, and a calcination time of 1-3h to finally obtain a silicon-oxygen composite negative electrode material, which is recorded as G / C / SiOx. The silicon-oxygen composite negative electrode material prepared above has a relatively uniform particle size distribution, with an average D50 particle size of 5-20μm and a specific surface area of ​​less than 50m 2 / g, the gram capacity (nominal specific capacity) is 600-2000 mAh / g, the silicon content of the silicon-oxygen composite negative electrode material is 5-40 wt%, and the value of x in SiOx is 0.5-1.5.

[0066] The silicon-oxygen composite negative electrode material prepared above can be used as a negative electrode material in lithium batteries. When the silicon-oxygen composite negative electrode material is made into a negative electrode material, the first coulombic efficiency is not less than 70%.

[0067] The silicon-oxygen composite negative electrode material of the present invention, its preparation method and application are further introduced below with reference to specific examples.

[0068] Example 1

[0069] This embodiment adopts the nitrogen-doped carbon-coated silicon-oxygen composite material prepared by the above step S1. The specific steps are as follows:

[0070] Preparation of nitrogen-doped carbon-coated silicon-oxygen composites: First, a 2wt% acetic acid solution was prepared. Silicon oxide and chitosan powders were weighed in a mass ratio of 8:2, with the silicon oxide having a D50 particle size of 4μm. Chitosan was dissolved in the acetic acid solution by stirring for 1 hour to form a carbon precursor solution. The silicon oxide powder was then dispersed in deionized water by ultrasonication for 10 minutes to form a suspension. The silicon oxide suspension was then slowly poured into the carbon precursor solution, uniformly dispersing the suspension to form a first mixed solution. The combined mass fraction of silicon oxide and chitosan in the first mixed solution was 5wt%. After stirring for 1 hour, the first mixed solution was heated to 90°C to evaporate the solvent, and the resulting solid phase powder was ground for later use. The solid phase powder was placed in a quartz boat, placed in a vacuum tube furnace, and carbonized at normal pressure and high temperature under argon atmosphere with a heating rate of 5°C / min, a calcination temperature of 800°C, and a calcination time of 1 h. After natural cooling to room temperature, the boat was taken out and ground to obtain a nitrogen-doped carbon-coated silicon-oxygen composite material, recorded as C / SiOx. Figure 1 This is an SEM photo of the nitrogen-doped carbon-coated silicon-oxygen composite material. The carbon content was found to be approximately 6.2% by TG test (see Table 2); the specific surface area was found to be 2.1 m by BET test. 2 / g (see Table 2); EDAX test shows that the product contains C, N, O, and Si elements (see Table 1).

[0071] Performance testing of nitrogen-doped carbon-coated silicon-oxygen composites: The nitrogen-doped carbon-coated silicon-oxygen composite prepared above was used as the active material and mixed with Super P carbon black (SP), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a ratio of 92:3:2:3. Water was used as the solvent to form a slurry, which was stirred and mixed thoroughly. The slurry was then coated onto 10μm and 150μm copper foils, vacuum-dried at 60°C for 10 hours, and cut into 14mm diameter discs after cooling. A button-type lithium-ion battery was fabricated using metallic lithium as the counter electrode, lithium hexafluorophosphate dissolved in an EC / DMC solution as the electrolyte, and Celgard as the separator. Constant current charge and discharge mode testing was performed using a LAND charge-discharge instrument, with a discharge cutoff voltage of 0.005V and a charge cutoff voltage of 1.5V. The test was carried out at a current density of 200 mA. The results are shown in Table 3. The first reversible capacity was 2097 mAh / g, the initial coulombic efficiency was 69%, and the capacity retention rate was 78.7% after 100 cycles.

[0072] The nitrogen-doped carbon-coated silicon-oxygen composite material prepared in this embodiment can be used in lithium batteries with relatively high requirements for reversible capacity.

[0073] Example 2

[0074] This embodiment adopts the above steps S1 and S2 to prepare carbon / porous silicon oxide composite material (C / SiOx). The specific steps are as follows:

[0075] The same process as in Example 1 was adopted to prepare the nitrogen-doped carbon-coated silicon-oxygen composite material, and the detailed steps are not repeated here.

[0076] Preparation of a carbon / porous silica composite: C / SiOx was washed and etched with a mixture of sodium hydroxide and lithium hydroxide (1:1, total molar concentration 1 mol / L) for 2 hours. Centrifugation was then performed to obtain a powder. The powder was washed with deionized water and centrifuged three times. This washing process was repeated three times to obtain a carbon / porous silica composite (C / D-SiOx). Figure 2 This is an SEM photo of a carbon / porous silicon-oxygen composite material. A porous structure is formed on the surface of the particles, which helps to alleviate the volume change of the silicon-oxygen material during the electrochemical reaction. EDAX results show that the carbon / porous silicon-oxygen composite material contains four elements: C, N, O, and Si (see Table 1). The carbon content is approximately 11.4 wt% as determined by TG (see Table 2); the specific surface area is 20.5 m 2 / g (see Table 2).

[0077] A lithium-ion button cell was prepared using the carbon / porous silicon oxide composite material as the active material by the same steps as in step (1), and the same tests were performed. The results are shown in Table 3. The initial reversible capacitance was 1933 mAh / g, the initial coulombic efficiency was 72%, and the capacity retention rate was 80% after 100 cycles.

[0078] The nitrogen-doped carbon-coated silicon-oxygen composite material prepared in this embodiment can be used in lithium batteries with relatively high requirements for reversible capacity.

[0079] Example 3

[0080] This embodiment adopts the above steps S1, S2 and S3 to prepare silicon-oxygen composite negative electrode material-1. The specific steps are as follows:

[0081] The same process as in Example 2 was adopted to prepare the nitrogen-doped carbon-coated carbon / porous silicon-oxygen composite material, and the detailed steps are not repeated here.

[0082] Preparation of silicon-oxygen composite negative electrode material: carbon / porous silicon-oxygen composite material, artificial graphite and chitosan were weighed in a mass ratio of 4:4:1, wherein the graphitization degree of artificial graphite was 94%, the D50 particle size was 11 μm, and the specific surface area was 1.1 m 2 / g, and the first reversible capacity is 355mAh g -1 , with an initial Coulombic efficiency of 91%. A 2wt% acetic acid solution was then prepared, and chitosan was stirred for 1 hour to fully dissolve in the acetic acid solution to form a carbon precursor solution. The carbon / porous silica composite material and artificial graphite were then thoroughly mixed and dispersed in deionized water under ultrasonication for 5 minutes to obtain a suspension. The suspension was then slowly poured into the carbon precursor solution and stirred for 30 minutes to obtain a second mixed solution, in which the mass fraction of the solid phase was 3wt%. The material was then dried using a spray drying method at an inlet temperature of 120°C. Finally, the dried material was calcined under an argon atmosphere at a heating rate of 5°C / min, a calcination temperature of 850°C, and a calcination time of 1 hour, ultimately yielding silica composite anode material-1. Figure 3 The SEM photo of silicon-oxygen composite negative electrode material-1. The EDAX results (see Table 1) show that the silicon-oxygen composite negative electrode material-1 contains four elements: C, N, O, and Si. The TG test results are shown in Table 2. The carbon content is about 66.7 wt%. The specific surface area is 1.7 m 2 / g (see Table 2).

[0083] The silicon-oxygen composite negative electrode material-1 prepared above was used as the active material, and the same steps as in step (1) were taken to prepare a lithium-ion button battery, and the same test was performed. The results are shown in Table 3. The first reversible capacity was 979 mAh / g, the initial coulombic efficiency was 80%, and after 100 cycles, the capacity retention rate was 87.4%.

[0084] The silicon-oxygen composite negative electrode material-1 prepared in this embodiment can be used in lithium batteries with relatively high requirements for coulombic efficiency and cycle life.

[0085] Example 4

[0086] This example uses steps S1, S2, and S3 to prepare silicon-oxygen composite negative electrode material-2. The specific steps are essentially the same as those in Example 3, except that in step S3, the nitrogen-doped carbon-coated carbon / porous silicon-oxygen composite material, artificial graphite, and chitosan are weighed in a mass ratio of 3:6:1.

[0087] Figure 4 The SEM photo of silicon-oxygen composite negative electrode material-2. The EDAX results (see Table 1) show that the silicon-oxygen composite negative electrode material contains four elements: C, N, O, and Si. The TG test results are shown in Table 2, and the carbon content is about 70.1wt%. The specific surface area obtained by BET test is 1.6m 2 / g (see Table 2).

[0088] The silicon-oxygen composite negative electrode material-2 prepared above was used as the active material, and the same steps as in step (1) were taken to prepare a lithium-ion button battery, and the same test was performed. The results are shown in Table 3. The first reversible capacity was 812 mAh / g, the initial coulombic efficiency was 84%, and after 100 cycles, the capacity retention rate was 89.1%.

[0089] The silicon-oxygen composite negative electrode material-2 prepared in this embodiment can be used in lithium batteries with relatively high requirements for coulombic efficiency and cycle life.

[0090] Example 5

[0091] This example uses steps S1, S2, and S3 to prepare silicon-oxygen composite negative electrode material-3. The specific steps are basically the same as those in Example 3, except that in step S3, the nitrogen-doped carbon-coated carbon / porous silicon-oxygen composite material, artificial graphite, and chitosan are weighed in a mass ratio of 2:7:1.

[0092] Figure 5The SEM photo of silicon-oxygen composite negative electrode material-3. The EDAX results (see Table 1) show that the silicon-oxygen composite negative electrode material-3 contains four elements: C, N, O, and Si. The TG test results are shown in Table 2. The carbon content is about 76.9wt%. The specific surface area is 1.4m 2 / g (see Table 2).

[0093] The silicon-oxygen composite negative electrode material-3 prepared above was used as the active material, and the same steps as in step (1) were taken to prepare a lithium-ion button battery, and the same test was performed. The results are shown in Table 3. The first reversible capacity was 654 mAh / g, the initial coulombic efficiency was 88%, and after 100 cycles, the capacity retention rate was 92.4%.

[0094] The silicon-oxygen composite negative electrode material-3 prepared in this embodiment can be used in lithium batteries with relatively high requirements for coulombic efficiency and cycle life.

[0095] Table 1 EDAX elemental analysis results of the materials prepared in Examples 1-5

[0096] name element Nitrogen-doped carbon-coated silicon-oxygen composites C, N, O, Si Carbon / porous silica composites C, N, O, Si Silicon-oxygen composite negative electrode material-1 C, N, O, Si Silicon-oxygen composite negative electrode material-2 C, N, O, Si Silicon-oxygen composite negative electrode material-3 C, N, O, Si

[0097] Table 2 Carbon content and specific surface area of ​​different materials prepared in this example

[0098]

[0099] Table 3 The first reversible capacity and first coulombic efficiency of lithium-ion button batteries prepared with the materials prepared in Examples 1-5 as negative electrode active materials

[0100]

[0101] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present invention and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A method for preparing a silicon-oxygen composite negative electrode material, characterized in that: The following steps are involved: S1, uniformly dispersing silicon dioxide and chitosan in an acidic solution to obtain a first mixed solution, drying the first mixed solution to remove the solvent to obtain a solid phase, and then calcining the solid phase at a high temperature under an argon environment to obtain a nitrogen-doped carbon-coated silicon-oxygen composite material; S2, washing and etching the nitrogen-doped carbon-coated silicon-oxygen composite material with a mixed alkali solution of sodium hydroxide and lithium hydroxide, and then washing with deionized water to obtain a carbon / porous silicon-oxygen composite material; S3, uniformly dispersing the carbon / porous silicon-oxygen composite material, carbon graphite material, and chitosan in an acidic solution to obtain a second mixed solution, drying and removing the solvent to obtain a dried product, and then calcining the dried product at a high temperature to finally obtain a silicon-oxygen composite negative electrode material.

2. The method for preparing a silicon-oxygen composite negative electrode material according to claim 1, wherein: In the step S1: The first mixed solution is prepared by dissolving the chitosan in an acidic solution to form a carbon precursor solution, then uniformly dispersing the silicon dioxide in deionized water to obtain a suspension, and then adding the suspension to the carbon precursor solution and dispersing the mixture uniformly to obtain the first mixed solution; and / or The D50 particle size of the silicon oxide is 1 to 10 μm; and / or The mass ratio of silicon oxide to chitosan is 5-10:1-5; and / or The acidic solution is prepared by adding hydrochloric acid or glacial acetic acid to deionized water to adjust the pH to less than 6; and / or In the mixed solution, the total concentration of the chitosan and the silicon oxide is 2 to 30 wt%; and / or The drying method is spray drying or heating evaporation; and / or During the high-temperature calcination process, the heating rate is 3-10° C. / min, the calcination temperature is 850-1000° C., and the calcination time is 1-3 hours.

3. The method for preparing a silicon-oxygen composite negative electrode material according to claim 2, wherein: In the step S1: During the preparation of the first mixed solution and the dissolution of the chitosan, the stirring time is 1 to 6 hours; and / or During the preparation of the suspension, ultrasonic dispersion is used with a dispersion time of 10 to 60 minutes; and / or During the spray drying process, the inlet temperature is 100-300°C; and / or During the heating evaporation process, the evaporation temperature is 80-120° C., the stirring rate is 200-800 Hz, and the evaporation time is 0.5-6.

4. The method for preparing a silicon-oxygen composite negative electrode material according to claim 1, wherein: In the step S2: In the mixed alkali solution, the molar ratio of the sodium hydroxide to the lithium hydroxide is 1-3:1-3, and the total molar concentration of the sodium hydroxide and the lithium hydroxide is 0.5-2 mol / L; and / or During the washing and etching process, the stirring rate is 20 to 100 Hz, and the stirring time is 0.5 to 6 hours.

5. The method for preparing a silicon-oxygen composite negative electrode material according to claim 1, wherein: In the step S3: The second mixed solution is prepared by dissolving the chitosan in an acidic solution to form a carbon precursor solution, uniformly mixing the carbon / porous silicon oxide composite material and the carbon graphite material, and uniformly dispersing them in deionized water to obtain a suspension, and then pouring the suspension into the carbon precursor solution and uniformly dispersing them to obtain a mixed solution; and / or The mass ratio of the carbon / porous silicon oxide composite material to the carbon graphite material and chitosan is 1-5:1-5:1-5; and / or In the second mixed solution, the total mass concentration of the carbon / porous silicon oxide composite material, the carbon graphite material and the chitosan is 2 to 50 wt %; and / or The carbon graphite material is selected from one of artificial graphite, natural graphite, hard carbon material or soft carbon material; and / or The acidic solution is prepared by adding hydrochloric acid or glacial acetic acid to deionized water to adjust the pH to less than 6; and / or The drying method is spray drying or heating evaporation; and / or During the high-temperature calcination process, the heating rate is 3-10° C. / min, the calcination temperature is 850-1000° C., and the calcination time is 1-3 hours.

6. The method for preparing a silicon-oxygen composite negative electrode material according to claim 5, wherein: In the step S3: During the preparation of the second mixed solution, the stirring time during the dissolution of the chitosan is 1 to 6 hours; and / or During the preparation of the suspension, ultrasonic dispersion is used with a dispersion time of 10 to 60 minutes; and / or During the spray drying process, the inlet temperature is 100-300°C; and / or During the heating evaporation process, the evaporation temperature is 80-120° C., the stirring rate is 200-800 Hz, and the evaporation time is 0.5-6 h.

7. The method for preparing a silicon-oxygen composite negative electrode material according to claim 1, wherein: The nitrogen-doped carbon-coated silicon-oxygen composite material is in granular form, with a D50 particle size of 1 to 10 μm and a specific surface area of ​​less than 20 m 2 / g; the nitrogen-doped carbon-coated silicon-oxygen composite material has a carbon content of 3 to 12 wt% and a nitrogen content of 0.1 to 5 wt%; and / or The carbon / porous silicon oxide composite material is in granular form, with a D50 particle size of 1 to 10 μm and a specific surface area of ​​less than 50 m 2 / g; the carbon / porous silicon oxygen composite material, the carbon content is 3 to 15wt%, the nitrogen content is 0.1 to 5wt%; and / or The D50 particle size of the silicon-oxygen composite negative electrode material is 5 to 20 μm, and the specific surface area is less than 50 m 2 / g, first coulombic efficiency ≥70%.

8. A silicon-oxygen composite negative electrode material prepared according to the method for preparing a silicon-oxygen composite negative electrode material according to any one of claims 1 to 7, characterized in that: The silicon-oxygen composite negative electrode material contains SiOx, the silicon content is 5-40 wt%, and x in SiOx is 0.5-1.

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9. Use of the silicon-oxygen composite negative electrode material prepared by the method for preparing the silicon-oxygen composite negative electrode material according to any one of claims 1 to 7 as a negative electrode material in a lithium-ion battery.

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