LiAlO2 fast ion conductor coated silicon-carbon composite material as well as preparation method and application thereof

Abstract

The invention discloses a LiAlO2 fast ion conductor coated silicon-carbon composite material as well as a preparation method and application thereof, and belongs to the technical field of lithium ion battery materials. The LiAlO2 fast ion conductor coated silicon carbon composite material has a core-shell structure; an inner core of the composite material is a silicon-carbon composite material, the silicon-carbon composite material is formed by coating a three-dimensional carbon material with an amorphous carbon layer and loading a nano silicon compound, a shell of the composite material is a LiAlO2 fast ion conductor layer, and the silicon-carbon composite material with a three-dimensional network structure is constructed, and the surface of the silicon-carbon composite material is coated with the LiAlO2 fast ion conductor layer, so that the composite material is obtained. According to the present invention, with the LiAlO2, the volume expansion of the nanometer silicon during the charge-discharge process can be effectively relieved, the stability of the silicon-carbon composite material structure can be improved so as to significantly improve the cycle performance of the battery, and the LiAlO2 can provide the rapid channel for the transmission of the lithium ion during the charge-discharge process so as to improve the rate performance of the battery;

Description

Technical Field

[0001] The present invention relates to a lithium ion battery negative electrode material, in particular to a LiAlO2 fast ion conductor coated silicon-carbon composite material, a preparation method thereof, and application of the LiAlO2 fast ion conductor coated silicon-carbon composite material in lithium ion batteries, belonging to the technical field of lithium battery materials. Background Art

[0002] With the rapid development of fields such as electronic products and electric vehicles, the performance requirements for lithium-ion batteries are becoming increasingly stringent. Silicon-carbon anode materials are considered highly promising next-generation lithium-ion battery anode materials due to their ultra-high theoretical specific capacity (up to 4200 mAh / g), promising to significantly increase the battery's energy density. However, silicon undergoes significant volume changes (up to 300% to 400%) during the charge and discharge process, which can lead to structural destruction of the silicon-carbon composite material, causing electrode pulverization and poor electrical contact between the active material and the current collector. This, in turn, leads to rapid battery capacity decay and poor cycling stability, severely hindering the practical application of silicon-carbon anode materials.

[0003] At present, in order to solve the above-mentioned technical problems of silicon-carbon negative electrode materials, researchers have taken a variety of measures, such as nano-sizing, alloying, composite and surface coating. Among them, surface coating is a relatively effective method. By coating the surface of the silicon-carbon material with a layer of material with good stability and ion conductivity, it can effectively alleviate the volume expansion of silicon, protect the integrity of the silicon-carbon material structure, and improve the cycle performance and rate performance of the battery. However, the existing coating materials and coating methods still have some shortcomings. For example, the bonding force between the coating layer and the silicon-carbon material is not strong enough, and the coating layer is prone to falling off after multiple charge and discharge cycles; the ion conductivity of some coating materials is poor, which affects the charge and discharge efficiency of the battery. Summary of the Invention

[0004] In response to the technical defects of the above-mentioned prior art, the first object of the present invention is to provide a LiAlO2 fast ion conductor coated silicon-carbon composite material, which constructs a three-dimensional network structure silicon-carbon composite material and coats a LiAlO2 fast ion conductor layer on the surface of the silicon-carbon composite material. It can not only effectively alleviate the volume expansion of nano-silicon during the charging and discharging process, but also improve the stability of the silicon-carbon composite material structure, thereby significantly improving the cycle performance of the battery. At the same time, LiAlO2 has good ionic conductivity and can provide a fast channel for the transmission of lithium ions during the charging and discharging process, thereby improving the rate performance of the battery.

[0005] The second object of the present invention is to provide a method for preparing a LiAlO2 fast ion conductor coated silicon-carbon composite material, which has simple process, easy operation, low cost, and is suitable for large-scale industrial production.

[0006] The third object of the present invention is to provide an application of a LiAlO2 fast ion conductor coated silicon-carbon composite material as a lithium ion negative electrode material. The resulting lithium ion battery exhibits high stability and high rate performance, which can solve the problems of large volume expansion, poor cycle stability and poor rate performance of existing silicon-carbon composite materials used in lithium ion batteries during charging and discharging.

[0007] In order to achieve the above technical objectives, the present invention provides a LiAlO2 fast ion conductor coated silicon-carbon composite material having a core-shell structure; its core is a silicon-carbon composite material; the silicon-carbon composite material is composed of an amorphous carbon layer coated with a three-dimensional carbon material loaded with nano-silicon composite, and its shell is a LiAlO2 fast ion conductor layer.

[0008] The LiAlO2 fast ion conductor coated silicon-carbon composite material of the present invention uses a three-dimensional carbon material as a matrix material, and utilizes the porous structure (such as porous carbon) and interlayer (such as graphene) of the carbon material to load nano-silicon, which can achieve high dispersion and stable loading of nano-silicon. At the same time, an amorphous carbon layer is wrapped on the outside to construct a structurally stable three-dimensional network structure silicon-carbon composite material. During the charge and discharge process, even if the silicon particles undergo volume changes, the three-dimensional network structure can maintain a certain integrity, thereby avoiding pulverization and shedding of the electrode material, thereby extending the service life of the battery. In addition, the amorphous carbon deposited on its surface has good stability. On the one hand, it can prevent the nano-silicon particles from being exposed to air or water, causing the active silicon to fail; on the other hand, it can improve the powder conductivity of the material, reduce the migration resistance of lithium ions during the charging and discharging process, greatly reduce the polarization phenomenon, and improve the discharge capacity and the first coulomb efficiency. The electrical conductivity and ion conductivity of the amorphous carbon layer are relatively weak. The LiAlO2 fast ion conductor coating layer is further coated on the surface of the amorphous carbon layer. Its good mechanical resistance can further effectively alleviate the volume expansion of silicon during the charging and discharging process, improve the stability of the silicon-carbon negative electrode material structure, and thus significantly improve the cycle performance of the battery; at the same time, its good ionic conductivity can provide a fast channel for the transmission of lithium ions during the charging and discharging process, thereby improving the rate performance of the battery.

[0009] As a preferred embodiment, the three-dimensional carbon material includes at least one of porous carbon and layered graphene. Porous carbon and layered graphene can utilize their porous structure or interlayers to stably support nano-silicon, and can also reserve space for the volume change of nano-silicon during the charge and discharge process, thereby preventing the pulverization and shedding of the negative electrode material.

[0010] As a preferred solution, the mass of the nano-silicon accounts for 45-55wt% of the mass of the silicon-carbon composite material. As an active ingredient, nano-silicon has a low content that affects the capacity of the composite material, while a high content causes agglomeration of nano-silicon particles, resulting in low utilization rate.

[0011] As a preferred embodiment, the mass of the amorphous carbon layer is 1.0-10.0% of the mass of the silicon-carbon composite material. The thickness of the amorphous carbon inner layer cannot be too small. If it is too small, it cannot form a dense coating, making it difficult to suppress the volume expansion of silicon during charge and discharge. If it is too thick, it will affect the charge and discharge capacity.

[0012] As a preferred solution, the mass of the LiAlO2 fast ion conductor layer is 0.10-1.0% of the mass of the silicon-carbon composite material. If the mass content of the LiAlO2 fast ion conductor is relatively low, a uniform and dense coating cannot be formed on the surface of the silicon-carbon composite material, resulting in a relatively poor modification effect on the silicon-carbon composite material particles. If the mass content of the LiAlO2 fast ion conductor is relatively high, the LiAlO2 fast ion conductor layer on the surface of the silicon-carbon negative electrode particles is too thick, which will increase the resistivity of the powder and directly affect the electrochemical performance of the material.

[0013] The present invention provides a method for preparing a LiAlO2 fast ion conductor coated silicon-carbon composite material, which comprises the following steps:

[0014] 1) First, nano-silicon is deposited on the surface of the three-dimensional carbon material by pyrolysis, and then an amorphous carbon layer is deposited by vapor phase to obtain a silicon-carbon composite material;

[0015] 2) dissolving the lithium source, aluminum source and complexing agent in a solvent to form a uniform solution;

[0016] 3) Ultrasonic dispersion of the silicon-carbon composite material into the uniform solution, followed by stirring reaction, solid-liquid separation, drying and calcination to obtain a LiAlO2-coated silicon-carbon composite material.

[0017] The technical solution of the present invention adopts liquid phase coating when coating the outer layer of LiAlO2 fast ion conductor. The prior art usually adopts high temperature solid phase coating method. For silicon carbon composite materials, high temperature solid phase method usually requires mechanical mixing. The surface of single particle is easily damaged by mechanical force, and there is agglomeration between particles, resulting in uneven coating layer. At the same time, high temperature solid phase coating mainly relies on physical adsorption or mechanical intercalation, and the binding force is usually weak. It is easy to fall off during subsequent treatment (such as high temperature sintering, friction, ultrasonic dispersion) or use. The liquid phase coating method of the present invention can achieve low temperature coating, which can avoid the growth of silicon grain size caused by temperature. At the same time, it is easy to achieve uniform deposition at the molecular or ionic level by controlling the reaction conditions (such as concentration, temperature, pH value, stirring speed, addition method), forming a continuous, dense and thickness controllable coating layer. In addition, in the liquid phase coating method, the precursor molecules / ions can undergo chemical adsorption, coordination or chemical reaction with the surface of the core particles to form chemical bonding or strong physical adsorption, thereby obtaining a stronger binding force, thereby improving the stability and durability of the coating layer.

[0018] As a preferred solution, the conditions for the pyrolysis deposition of nano-silicon are: the temperature is 420~700℃, and the amount of gaseous silicon source introduced is controlled to control the mass of nano-silicon to 45~55wt% of the total mass of the carbon-silicon composite material. The gaseous silicon source includes at least one of silane, silicon tetrachloride, dihydrodichlorosilane, methylsilane, dichlorodimethylsilane, etc. These small molecule gaseous silicon sources can be pyrolyzed at high temperatures to generate elemental nano-silicon. The pyrolysis deposition of nano-silicon process is carried out under a protective atmosphere, such as at least one of nitrogen, argon, and hydrogen. The protective atmosphere is provided by nitrogen and / or inert gas with a flow rate controlled at 1.0~5.0L / min. The temperature of pyrolysis deposition is further preferably 470~530℃. The amount of gaseous silicon source introduced is further preferably controlled to control the mass of nano-silicon to 48~52wt% of the total mass of the carbon-silicon composite material. The ratio of nano-silicon and carbon materials mainly affects the performance of the composite material, such as cycle and reversible capacity; if the silicon content is too much, the risk of silicon agglomeration and silicon floating on the particle surface will be greater, which will affect the cycle performance of the composite material; if the nano-silicon content is too little, the active substance (nano-silicon) will decrease, and the reversible capacity and first coulombic efficiency of the composite material will not meet expectations.

[0019] As a preferred solution, the conditions for vapor deposition of the amorphous carbon layer are: temperature of 500~900°C, flow rate of gaseous carbon source of 0.5~2.0L / min, and time of 60~300min. The temperature of vapor deposition is further preferably 520~650°C. The time of vapor deposition is further preferably 120~180min. The preferred vapor deposition conditions are to control the thickness of the amorphous carbon coating layer, that is, the amorphous carbon accounts for 1.0~10.0wt% of the mass of the silicon-carbon composite material, and further preferably in the range of 2.0~5.0wt%. If the deposition temperature is too high, it is easy to cause the silicon grain size to become larger; if the deposition temperature is too low, it will result in poor quality of the carbon layer, low powder conductivity, and unsatisfactory coating effect.

[0020] As a preferred solution, the lithium source includes at least one of lithium acetate, lithium carbonate, and lithium hydroxide.

[0021] As a preferred solution, the aluminum source includes at least one of aluminum isopropoxide, aluminum sulfate, aluminum chloride, and aluminum nitrate.

[0022] As a preferred embodiment, the complexing agent comprises at least one of ethylenediaminetetraacetic acid, triethanolamine, and citric acid. On the one hand, the complexing agent can partially dissociate or hydrolyze hydrogen ions in the solution, has a certain buffering effect, and can adjust the pH value of the solution. At the same time, the appropriate pH value also helps the complexing agent to play a complexing role, enhancing the complexing effect on metal ions. On the other hand, the complexing agent can change the activity of the metal ion and promote the reaction. By complexing with the aluminum ion, the reaction speed of the aluminum ion can be controlled, so that the compound is evenly deposited on the particle surface to form a uniform, dense coating.

[0023] As a preferred solution, the mass ratio of the lithium source to the aluminum source and the complexing agent is 4-6:7-10:2-4.

[0024] As a preferred embodiment, the stirring reaction conditions are: a stirring rate of 100-300 rpm, a reaction temperature of 80-120°C, and a reaction time of 120-480 min. Under the preferred stirring reaction conditions, the LiAlO2 precursor material can be uniformly adsorbed on the surface of the silicon-carbon composite material.

[0025] As a preferred solution, the solvent is water and / or anhydrous ethanol.

[0026] As a preferred solution, the ultrasonic dispersion time is 30 to 120 minutes.

[0027] As a preferred solution, the drying is performed by vacuum drying, the vacuum condition is ≤10 Pa, the drying temperature is 80-150° C., and the drying time is 60-360 min.

[0028] As a preferred solution, the calcination conditions are: temperature of 500-700°C and time of 120-240 minutes. Low-temperature heat treatment can further strengthen the coating bonding strength and improve the stability and durability of the coating layer.

[0029] The present invention also provides an application of a LiAlO2 fast ion conductor coated silicon-carbon composite material, which is used as a lithium ion negative electrode material.

[0030] The present invention's LiAlO2 fast ion conductor-coated silicon-carbon anode material is used to prepare a lithium-ion battery. The LiAlO2 fast ion conductor-coated silicon-carbon anode material, carbon black, carboxymethyl cellulose, and styrene-butadiene rubber are mixed uniformly in a mass ratio of 85:10:4:1, and deionized water with a solid content of 45% is added to form a slurry. The slurry is then evenly coated onto copper foil using a coater and baked in a vacuum oven at 120°C for 2 hours to form a working electrode. A button-type battery is assembled in an argon-protected glove box using a lithium sheet as the counter electrode, a 25μm PP separator, and 1 mol / L LiPF6 (a 1:1 volume ratio mixture of ethylene carbonate and dimethyl carbonate) as the electrolyte.

[0031] The preparation method of the LiAlO2 fast ion conductor coated silicon-carbon negative electrode material of the present invention comprises the following steps:

[0032] 1) Preparation of silicon-carbon composite materials: The three-dimensional carbon material is placed in a fluidized bed reactor and heated to a high temperature under a protective atmosphere. A silicon source gas is then introduced to decompose and deposit nanosilicon on the surface of the carbon matrix. After silicon deposition is completed, the temperature is continued to rise, and a carbon source gas is then introduced to perform a carbon coating operation, causing amorphous carbon to decompose and deposit on the surface of the particles to obtain a silicon-carbon composite material.

[0033] 2) Preparation of LiAlO2 coating layer: lithium source, aluminum source and complexing agent are added to the solvent in a certain mass ratio, stirred and dissolved to form a transparent solution.

[0034] 3) The silicon-carbon negative electrode material prepared above is added to the solution, ultrasonically dispersed, and then stirred for reaction under certain temperature conditions. After the reaction is completed, the product is filtered, washed, and dried to obtain a silicon-carbon negative electrode material with a lithium-aluminum complex on the surface. The silicon-carbon negative electrode material with a lithium-aluminum complex on the surface is calcined at a high temperature under a protective atmosphere to finally obtain a LiAlO2-coated silicon-carbon negative electrode material.

[0035] Compared with the existing technology, the technical solution of the present invention has the following advantages:

[0036] 1. The LiAlO2 fast ion conductor-coated silicon-carbon composite material provided by the present invention forms a three-dimensional network structure by interconnecting nano-silicon, three-dimensional carbon material and amorphous carbon coating layer. This structure can effectively improve the structural stability of the composite material. During the charge and discharge process, even if the silicon particles undergo volume changes, the three-dimensional network structure can maintain a certain integrity, avoiding the pulverization and shedding of the electrode material, thereby extending the service life of the battery.

[0037] 2. The present invention utilizes a liquid phase method to coat the surface of a carbon-silicon composite material with a dense, uniform, and stable LiAlO2 fast ion conductor coating. This effectively mitigates the volume expansion of silicon during the charge and discharge process, improves the structural stability of the silicon-carbon negative electrode material, and thus significantly enhances the battery's cycling performance. Experiments have shown that a lithium-ion battery prepared using the present invention's LiAlO2-coated silicon-carbon negative electrode material retains over 90% of its capacity after 1,000 cycles at a 1C rate. However, a lithium-ion battery prepared using an uncoated silicon-carbon negative electrode material retains only about 85% of its capacity after 1,000 cycles under the same conditions.

[0038] 3. The LiAlO2 coating of the present invention has excellent ionic conductivity, providing a fast channel for the transmission of lithium ions during the charge and discharge process, thereby improving the battery's rate performance. Lithium-ion batteries prepared using the LiAlO2-coated silicon-carbon negative electrode material of the present invention can still maintain a high specific capacity of over 1800 mAh / g when charged and discharged at a high rate of 5C. Lithium-ion batteries prepared using silicon-carbon negative electrode materials without LiAlO2 coating have a specific capacity of only about 1500 mAh / g at a 5C rate.

[0039] 4. The preparation method of the present invention is simple, easy to operate, low-cost, and suitable for large-scale industrial production. Furthermore, by precisely controlling various parameters during the preparation process, the structure and performance of the LiAlO2-coated silicon-carbon anode material can be precisely regulated to meet the performance requirements of lithium-ion batteries in different application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a process flow chart of the LiAlO2 fast ion conductor coated silicon-carbon negative electrode material prepared by the present invention.

[0041] Figure 2 This is a schematic diagram of the structure of the LiAlO2 fast ion conductor coated silicon-carbon negative electrode material prepared by the present invention.

[0042] Figure 3 The capacity-voltage curves of the silicon-carbon negative electrode prepared in Comparative Example 1 and the LiAlO2 fast ion conductor coated silicon-carbon negative electrode material prepared in Example 2 are shown.

[0043] Figure 4 This is the XRD pattern of the LiAlO2 fast ion conductor coated silicon-carbon negative electrode material prepared in Example 2.

[0044] Figure 5 These are the SEM and EDS images of the LiAlO2 fast ion conductor coated silicon-carbon negative electrode material prepared in Example 2.

[0045] Figure 6The figure is a cycle performance diagram of the silicon-carbon negative electrode prepared in comparative example 1 and the LiAlO2 fast ion conductor coated silicon-carbon negative electrode material prepared in example 2. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0047] Example 1

[0048] 1) Preparation of silicon-carbon negative electrode material: 15 kg of porous carbon was placed in a fluidized bed reactor and heated to 500 ° C under a nitrogen atmosphere. Then, monosilane gas was introduced at a gas flow rate of 1.5 L / min to decompose and deposit nanosilicon on the carbon surface. The amount of silicon deposited was 50 wt%. After the silicon deposition was completed, the temperature was continued to rise to 560 ° C, and then acetylene gas was introduced at a gas flow rate of 1.0 L / min for carbon coating. The amorphous carbon coating amount was 3.0 wt%, and a silicon-carbon negative electrode material was obtained.

[0049] 2) Preparation of the LiAlO2 coating: 5g of lithium acetate, 8g of aluminum isopropoxide, and 3g of ethylenediaminetetraacetic acid were sequentially added to 100ml of deionized water and stirred at 150rpm for 180 minutes to dissolve and form a transparent solution. 500g of the silicon-carbon anode material prepared above was added to the solution and ultrasonically dispersed for 100 minutes. The mixture was then stirred and reacted at 100°C for 180 minutes. After the reaction, the product was filtered, washed, and dried at 100°C at ≤10Pa for 120 minutes to obtain a silicon-carbon anode material with a surface complexed with a lithium-aluminum complex. The silicon-carbon anode material with a surface complexed with a lithium-aluminum complex was calcined at 600°C for 120 minutes under a nitrogen atmosphere to obtain a LiAlO2-coated silicon-carbon anode material. The LiAlO2 coating amount accounted for 0.25wt% of the mass of the silicon-carbon anode material.

[0050] Example 2

[0051] 1) Preparation of silicon-carbon negative electrode material: 15 kg of porous carbon was placed in a fluidized bed reactor and heated to 500 ° C under a nitrogen atmosphere. Then, monosilane gas was introduced at a gas flow rate of 1.5 L / min to decompose and deposit nanosilicon on the carbon surface. The amount of silicon deposited was 50 wt%. After the silicon deposition was completed, the temperature was continued to rise to 560 ° C, and then acetylene gas was introduced at a gas flow rate of 1.0 L / min for carbon coating. The amorphous carbon coating amount was 3.0 wt%, and a silicon-carbon negative electrode material was obtained.

[0052] 2) Preparation of the LiAlO2 coating: 5g of lithium acetate, 8g of aluminum isopropoxide, and 3g of ethylenediaminetetraacetic acid were sequentially added to 100ml of deionized water and stirred at 150rpm for 180 minutes to dissolve and form a transparent solution. 250g of the silicon-carbon anode material prepared above was added to the solution and ultrasonically dispersed for 100 minutes. The mixture was then stirred and reacted at 100°C for 180 minutes. After the reaction, the product was filtered, washed, and dried at 100°C at ≤10Pa for 120 minutes to obtain a silicon-carbon anode material with a surface complexed with a lithium-aluminum complex. The silicon-carbon anode material with a surface complexed with a lithium-aluminum complex was calcined at 600°C for 120 minutes under a nitrogen atmosphere to obtain a LiAlO2-coated silicon-carbon anode material. The LiAlO2 coating amount accounted for 0.50wt% of the mass of the silicon-carbon anode material.

[0053] Example 3

[0054] 1) Preparation of silicon-carbon negative electrode material: 15 kg of porous carbon was placed in a fluidized bed reactor and heated to 500 ° C under a nitrogen atmosphere. Silane gas was then introduced at a gas flow rate of 1.5 L / min to decompose and deposit nanosilicon on the carbon surface. The amount of silicon deposited was 50 wt%. After the silicon deposition was completed, the temperature was continued to rise to 560 ° C, and acetylene gas was then introduced at a gas flow rate of 1.0 L / min for carbon coating. The amorphous carbon coating amount was 3.0 wt%, and a silicon-carbon negative electrode material was obtained.

[0055] 2) Preparation of the LiAlO2 coating: 5g of lithium acetate, 8g of aluminum isopropoxide, and 3g of ethylenediaminetetraacetic acid were sequentially added to 100ml of deionized water and stirred at 150rpm for 180 minutes to dissolve and form a transparent solution. 165g of the silicon-carbon anode material prepared above was added to the solution and ultrasonically dispersed for 100 minutes. The mixture was then stirred and reacted at 100°C for 180 minutes. After the reaction, the product was filtered, washed, and dried at 100°C at ≤10Pa for 120 minutes to obtain a silicon-carbon anode material with a surface complexed with a lithium-aluminum complex. The silicon-carbon anode material with a surface complexed with a lithium-aluminum complex was calcined at 600°C for 120 minutes under a nitrogen atmosphere to obtain a LiAlO2-coated silicon-carbon anode material. The LiAlO2 coating amount accounted for 0.75wt% of the mass of the silicon-carbon anode material.

[0056] Example 4

[0057] 1) Preparation of silicon-carbon negative electrode material: 15 kg of porous carbon was placed in a fluidized bed reactor and heated to 500 ° C under a nitrogen atmosphere. Silane gas was then introduced at a gas flow rate of 1.5 L / min to decompose and deposit nanosilicon on the carbon surface. The amount of silicon deposited was 50 wt%. After the silicon deposition was completed, the temperature was continued to rise to 560 ° C, and acetylene gas was then introduced at a gas flow rate of 1.0 L / min for carbon coating. The amorphous carbon coating amount was 3.0 wt%, and a silicon-carbon negative electrode material was obtained.

[0058] 2) Preparation of the LiAlO2 coating: 5g of lithium acetate, 8g of aluminum isopropoxide, and 3g of ethylenediaminetetraacetic acid were sequentially added to 100ml of deionized water and stirred at 150 rpm for 180 minutes to dissolve and form a transparent solution. 125g of the silicon-carbon anode material prepared above was added to this solution and ultrasonically dispersed for 100 minutes. The mixture was then stirred and reacted at 100°C for 180 minutes. After the reaction, the product was filtered, washed, and dried at 100°C at ≤10Pa for 120 minutes to obtain a silicon-carbon anode material with a surface complexed with a lithium-aluminum complex. The silicon-carbon anode material with a surface complexed with a lithium-aluminum complex was calcined at 600°C for 120 minutes under a nitrogen atmosphere to obtain a LiAlO2-coated silicon-carbon anode material. The LiAlO2 coating amount accounted for 1.00 wt% of the mass of the silicon-carbon anode material.

[0059] Example 5

[0060] 1) Preparation of silicon-carbon negative electrode material: 15 kg of porous carbon was placed in a fluidized bed reactor and heated to 500 ° C under a nitrogen atmosphere. Silane gas was then introduced at a gas flow rate of 1.5 L / min to decompose and deposit nanosilicon on the carbon surface. The amount of silicon deposited was 50 wt%. After the silicon deposition was completed, the temperature was continued to rise to 560 ° C, and acetylene gas was then introduced at a gas flow rate of 1.0 L / min for carbon coating. The amorphous carbon coating amount was 3.0 wt%, and a silicon-carbon negative electrode material was obtained.

[0061] 2) Preparation of the LiAlO2 coating: 5g of lithium acetate, 8g of aluminum isopropoxide, and 3g of ethylenediaminetetraacetic acid were sequentially added to 100ml of deionized water and stirred at 150 rpm for 180 minutes to dissolve and form a transparent solution. 98g of the silicon-carbon anode material prepared above was added to this solution and ultrasonically dispersed for 100 minutes. The mixture was then stirred and reacted at 100°C for 180 minutes. After the reaction, the product was filtered, washed, and dried at 100°C at ≤10Pa for 120 minutes to obtain a silicon-carbon anode material with a surface complexed with a lithium-aluminum complex. The silicon-carbon anode material with a surface complexed with a lithium-aluminum complex was calcined at 600°C for 120 minutes under a nitrogen atmosphere to obtain a LiAlO2-coated silicon-carbon anode material. The LiAlO2 coating constituted 1.25 wt% of the total weight of the silicon-carbon anode material.

[0062] Comparative Example 1

[0063] The only difference from Example 2 is that step 2) is eliminated, that is, LiAlO2 coating is not performed, and a silicon-carbon negative electrode material not coated with LiAlO2 is prepared.

[0064] Comparative Example 2

[0065] The only difference from Example 2 is that the complexing agent in step 2) is eliminated and no complexing agent is added during the reaction to prepare the LiAlO2-coated silicon-carbon negative electrode material.

[0066] Figure 1 This is a process flow chart of the LiAlO2 fast ion conductor coated silicon-carbon negative electrode material prepared by the present invention.

[0067] Figure 2 This is a schematic diagram of the structure of the LiAlO2 fast ion conductor coated silicon-carbon negative electrode material prepared by the present invention. The results show that the structure is a core-shell structure with silicon-carbon negative electrode material as the matrix, with silicon-carbon negative electrode particles in the middle, an amorphous carbon coating layer on the outer layer, and a LiAlO2 fast ion conductor coating layer on the outermost layer.

[0068] Figure 3 The following is a capacity-voltage curve comparing the silicon-carbon anode prepared in Example 1 with the LiAlO2 fast ion conductor-coated silicon-carbon anode material prepared in Example 2. The test results show that the LiAlO2 fast ion conductor-coated silicon-carbon anode material achieves a 0.1C-1.5V reversible capacity of 1901.68 mAh / g for a button-type battery, significantly higher than that of the silicon-carbon anode material in Example 1 (0.1C-1.5V reversible capacity of 1700.91 mAh / g for a button-type battery, and an initial discharge efficiency of 93.17%).

[0069] Figure 4This is the XRD pattern of the LiAlO2 fast ion conductor coated silicon-carbon anode material prepared in Example 2. The test results show that no LiAlO2 fast ion conductor peak was found, which indicates that the introduction of a small amount of LiAlO2 fast ion conductor does not affect the structural integrity of the silicon-carbon anode material.

[0070] Figure 5 SEM and EDS images of the LiAlO2 fast ion conductor-coated silicon-carbon anode material prepared in Example 2. SEM results show uniform particle size, with the presence of nanoscale particles on the particle surface, presumably related to the LiAlO2 fast ion conductor. EDS results show no Li element, likely due to the very low energy of Li in the X-ray spectrum of only 50 eV, a normal phenomenon. Al and O elements are evenly distributed on the particle surface, indicating good uniformity of the LiAlO2 fast ion conductor coating.

[0071] Figure 6 The following is a graph comparing the cycling performance of the silicon-carbon anode prepared in Example 1 and the LiAlO2 fast ion conductor-coated silicon-carbon anode material prepared in Example 2. The test results show that the LiAlO2 fast ion conductor-coated silicon-carbon anode material has a capacity retention rate of 90.38% for a 3.5Ah-18650 cylindrical battery after 1000 cycles at room temperature and 0.5C / 1C, significantly higher than that of Comparative Example 1 (a capacity retention rate of 84.90% for a 3.5Ah-18650 cylindrical battery after 1000 cycles at room temperature and 0.5C / 1C).

[0072] Example 6 (Application Example)

[0073] The materials prepared in Examples 1-5 and Comparative Examples 1-2 were used to test the performance of button cells. The button cell fabrication steps were as follows: the negative electrode material prepared under the above conditions, carbon black, carboxymethyl cellulose, and styrene-butadiene rubber were mixed uniformly in a mass ratio of 85:10:4:1. Deionized water with a solids content of 45% was then added to form a slurry. The slurry was then evenly coated onto copper foil using a coater (the coating surface was required to be smooth, free of visible particles and copper leakage). The working electrode was then baked in a vacuum oven at 120°C for 2 hours. The button cell was assembled in an argon-protected glove box using a lithium foil as the counter electrode, a 25 μmPP separator, and 1 mol / l LiPF6 (a 1:1 volume ratio mixture of ethylene carbonate and dimethyl carbonate) as the electrolyte.

[0074] Table 1: The negative electrode materials of Examples 1 to 5 and Comparative Examples 1 to 2 prepared by the button cells at 0.1C and 5C rates

[0075] The test results show that the lithium-ion batteries assembled with the LiAlO2-coated silicon-carbon negative electrode materials prepared in Examples 1 to 5 of the present invention are significantly superior to the lithium-ion batteries assembled with the silicon-carbon negative electrode materials without LiAlO2 coating prepared in Comparative Example 1 in terms of reversible capacity and rate performance at 0.1C and 5C rates. In addition, when no complexing agent is introduced, the surface of the LiAlO2 fast ion conductor-coated silicon-carbon negative electrode material has uneven coating, resulting in relatively poor battery performance. This fully demonstrates the effectiveness and superiority of the LiAlO2-coated silicon-carbon negative electrode material and its preparation method of the present invention.

Claims

1. A LiAlO2 fast ion conductor coated silicon-carbon composite material, characterized in that: It has a core-shell structure; its core is a silicon-carbon composite material; the silicon-carbon composite material is composed of an amorphous carbon layer covering a three-dimensional carbon material loaded with nano-silicon composite, and its shell is a LiAlO2 fast ion conductor layer.

2. The method for preparing a LiAlO2 fast ion conductor coated silicon-carbon composite material according to claim 1, characterized in that: The three-dimensional carbon material includes at least one of porous carbon and layered graphene.

3. The method for preparing a LiAlO2 fast ion conductor coated silicon-carbon composite material according to claim 1 or 2, characterized in that: The mass of the nano-silicon accounts for 45-55 wt% of the mass of the silicon-carbon composite material; and / or, The mass of the amorphous carbon layer is 1.0-10.0% of the mass of the silicon-carbon composite material; and / or, The mass of the LiAlO2 fast ion conductor layer is 0.10-1.0% of the mass of the silicon-carbon composite material.

4. The method for preparing a LiAlO2 fast ion conductor coated silicon-carbon composite material according to any one of claims 1 to 3, characterized in that: The following steps are involved: 1) First, nano-silicon is deposited on the surface of the three-dimensional carbon material by pyrolysis, and then an amorphous carbon layer is deposited by vapor phase to obtain a silicon-carbon composite material; 2) dissolving the lithium source, aluminum source and complexing agent in a solvent to form a uniform solution; 3) Ultrasonic dispersion of the silicon-carbon composite material into the uniform solution, followed by stirring reaction, solid-liquid separation, drying and calcination to obtain a LiAlO2-coated silicon-carbon composite material.

5. The method for preparing a LiAlO2 fast ion conductor coated silicon-carbon composite material according to claim 4, characterized in that: The conditions for the pyrolysis deposition of nano-silicon are: a temperature of 420-700°C.

6. The method for preparing a LiAlO2 fast ion conductor coated silicon-carbon composite material according to claim 4, characterized in that: The conditions for vapor deposition of the amorphous carbon layer are: temperature of 500-900° C., flow rate of the gaseous carbon source of 0.5-2.0 L / min, and time of 60-300 min.

7. The method for preparing a LiAlO2 fast ion conductor coated silicon-carbon composite material according to claim 4, characterized in that: The lithium source includes at least one of lithium acetate, lithium carbonate, and lithium hydroxide; The aluminum source includes at least one of aluminum isopropoxide and aluminum oxide; The complexing agent includes at least one of ethylenediaminetetraacetic acid, triethanolamine, and citric acid; The mass ratio of the lithium source to the aluminum source and the complexing agent is 4-6:7-10:2-4.

8. The method for preparing a LiAlO2 fast ion conductor coated silicon-carbon composite material according to claim 4, characterized in that: The stirring reaction conditions are: stirring rate of 100-300 rpm, reaction temperature of 80-120° C., and reaction time of 120-480 min.

9. The method for preparing a LiAlO2 fast ion conductor coated silicon-carbon composite material according to claim 4, characterized in that: The calcination conditions are: temperature of 500-700° C. and time of 120-240 min.

10. Use of a LiAlO2 fast ion conductor coated silicon-carbon composite material according to any one of claims 1 to 3, characterized in that: Used as lithium-ion negative electrode material.

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