Silicon-based composite material and preparation method thereof, negative electrode material, and lithium-ion battery

Abstract

The present invention provides a silicon-based composite material and a preparation method thereof, a negative electrode material, and a lithium-ion battery. The silicon-based composite material includes a ferrosilicon alloy core layer, a first coating layer, and a second coating layer; the first coating layer is coated on the outer surface of the ferrosilicon alloy core layer; the second coating layer is coated on the outer surface of the first coating layer away from the ferrosilicon alloy core layer; wherein the material of the first coating layer includes carbon; and the material of the second coating layer includes an oxide. The present application uses ferrosilicon alloy as the core layer, which can provide a buffer matrix to alleviate the volume change of silicon. At the same time, the present invention sequentially arranges a first coating layer and a second coating layer on the outer surface of the core layer. In this way, the present application can further significantly improve the structural stability of the silicon-based composite material on the basis of ensuring that the battery meets the electrochemical performance requirements of conventional batteries (such as capacity performance and initial charge and discharge efficiency), thereby improving the cycle stability of the battery.

Description

Technical Field

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

[0002] With the rapid development of the new energy sector in recent years, the energy density and cycle life requirements of lithium-ion batteries in automobiles and 3C electronic products have become increasingly higher. The electrode materials of lithium-ion batteries are key factors in determining battery performance, among which the negative electrode materials play a key role. Currently, most commercial lithium-ion battery negative electrode materials are graphite, with a theoretical capacity of only 372mAh / g, which cannot meet the growing demand for energy density. The development of negative electrode materials with higher energy density is urgent. Silicon materials are considered to be the most promising lithium-ion battery negative electrode materials due to their high theoretical capacity (4200mAh / g). However, the rapid degradation of electrical performance caused by the volume expansion of silicon during the lithium insertion process limits its commercial application.

[0003] In response to the above problems, a large amount of modification work on silicon-based materials has been carried out at home and abroad. The main research methods are nano-sizing, compositeization, silicon-oxygen composite, etc. In addition, introducing a second phase of metal compounds into silicon materials is an effective method. Silicon and metal are composited to form a Si-M alloy system. The structure of this material is that silicon is dispersed in the alloy phase system. The good ductility and conductivity of the alloy phase improve the electrical properties of the silicon material. The ductility can buffer the volume expansion effect of the silicon matrix, and the conductivity can improve the ion mobility and give full play to the capacity. Ferrosilicon alloy material is a new type of silicon-based negative electrode material that meets this characteristic. The FeSi inside the material x It plays the role of buffering and improving conductivity. Compared with pure silicon materials, it has better electrochemical properties, but it still has a certain volume expansion effect, which leads to serious performance degradation and cannot meet actual use needs.

[0004] Currently, the primary modification method for ferrosilicon alloy anode materials is carbon coating, which can limit expansion to a certain extent. However, the carbon shell of ferrosilicon materials modified with carbon coating alone cannot maintain structural stability for a long time, and after multiple cycles, it still cracks and falls off, causing rapid capacity decay. Therefore, it is necessary to provide a new silicon-based composite material that can effectively improve this problem. Summary of the Invention

[0005] The main purpose of the present invention is to provide a silicon-based composite material and its preparation method, a negative electrode material, and a lithium-ion battery, so as to solve the problems in the prior art such as poor battery cycle stability caused by poor structural stability of the silicon-based composite material.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, there is provided a silicon-based composite material, which includes: a ferrosilicon alloy core layer; a first coating layer coated on the outer surface of the ferrosilicon alloy core layer; and a second coating layer coated on the outer surface of the first coating layer away from the ferrosilicon alloy core layer; wherein the material of the first coating layer includes carbon; and the material of the second coating layer includes oxide.

[0007] Furthermore, the second coating layer is provided with a plurality of through holes; preferably, the radial width of the through holes is 50 to 800 nm, more preferably 50 to 150 nm; preferably, the porosity of the second coating layer is 5 to 20%; preferably, the specific surface area of ​​the second coating layer is 0.5 to 2 m 2 / g.

[0008] Furthermore, the oxide is selected from one or more of boron trioxide, phosphorus pentoxide, arsenic trioxide or vanadium pentoxide.

[0009] Furthermore, the ferrosilicon alloy core layer is in powder form; preferably, the average particle size of the ferrosilicon alloy core layer is 0.5 to 2.5 μm; preferably, the weight content of iron in the ferrosilicon alloy core layer is 5 to 15 wt%; preferably, the thickness of the first coating layer is 50 to 150 nm, more preferably 50 to 80 nm; preferably, the thickness of the second coating layer is 10 to 100 nm, more preferably 50 to 80 nm.

[0010] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a method for preparing the aforementioned silicon-based composite material is provided, and the preparation method comprises the following steps: step S1, providing a ferrosilicon alloy core layer; step S2, coating a first coating layer on the outer surface of the ferrosilicon alloy core layer, and coating a second coating layer on the outer surface of the first coating layer away from the ferrosilicon alloy core layer, thereby forming a silicon-based composite material.

[0011] Furthermore, step S1 includes: ball-milling the ferrosilicon alloy and the ball-milling medium to obtain a first slurry containing a ferrosilicon alloy core layer; preferably, the ball-to-material ratio during the ball-milling process is 16 to 20:1; preferably, the raw materials during the ball-milling process also include a dispersant, and more preferably, the dispersant is selected from one or more of citric acid, sodium tripolyphosphate or sodium metasilicate; preferably, the ball-milling medium is anhydrous ethanol and / or water.

[0012] Further, step S2 includes: step S21, stirring and mixing the first slurry and the carbon source to obtain a second slurry; step S22, drying the second slurry and performing a first heat treatment under an inert gas atmosphere to obtain a first heat treatment product; step S23, mixing the first heat treatment product and the oxide, and performing a second heat treatment under an inert gas atmosphere to obtain a silicon-based composite material; wherein the carbon source includes a first carbon source and a second carbon source; the thermal decomposition temperature of the first carbon source is less than the thermal decomposition temperature of the second carbon source; the treatment temperature of the first heat treatment is greater than or equal to the thermal decomposition temperature of the first carbon source; the treatment temperature of the second heat treatment is greater than or equal to the thermal decomposition temperature of the second carbon source, and the treatment temperature of the second heat treatment is greater than or equal to the melting point of the oxide; preferably, the difference between the thermal decomposition temperature of the second carbon source and the thermal decomposition temperature of the first carbon source is between 450 and 550°C.

[0013] Furthermore, the first carbon source is one or more of asphalt, carboxymethyl cellulose, glucose, polyethylene glycol or potato starch; preferably, the second carbon source is one or more of phenolic resin, polyimide resin or bismaleimide resin; preferably, in the carbon source, the weight ratio of the first carbon source to the second carbon source is 4 to 8:1; preferably, the amount of the carbon source is 30 to 45% of the weight of the ferrosilicon alloy layer; preferably, the oxide is in powder form, and the average particle size of the oxide is 50 to 500 mm, more preferably 50 to 100 nm; preferably, the amount of the oxide is 30 to 80% of the weight of the carbon source; preferably, stirring is carried out under vacuum conditions, and the stirring speed is 800 to 2000 r / min; preferably, the treatment time of the first heat treatment is 1 to 6 hours; preferably, the treatment time of the second heat treatment is 1 to 9 hours.

[0014] Further, when the first carbon source is asphalt and the oxide is boron trioxide, the treatment temperature of the first heat treatment is 350-450°C, and the treatment temperature of the second heat treatment is 800-900°C; or, when the first carbon source is glucose and the oxide is phosphorus pentoxide, the treatment temperature of the first heat treatment is 250-500°C, and the treatment temperature of the second heat treatment is 600-1000°C; or, when the first carbon source is carboxymethyl cellulose and the oxide is vanadium pentoxide, the treatment temperature of the first heat treatment is 200-300°C, and the treatment temperature of the second heat treatment is 600-900°C.

[0015] According to another aspect of the present invention, a negative electrode material is provided. The negative electrode material includes the aforementioned silicon-based composite material; or the silicon-based composite material prepared by the aforementioned preparation method.

[0016] According to another aspect of the present invention, a lithium-ion battery is provided, wherein the lithium-ion battery has the aforementioned negative electrode material.

[0017] The present invention uses ferrosilicon alloy as the core layer. The FeSix phase core can provide a buffer matrix to alleviate the volume change of silicon. At the same time, the present invention provides a first coating layer (made of carbon) on the outer surface of the core layer, and coats the outer surface of the first coating layer with a second coating layer (made of oxide). In this way, the present application can not only enable the battery to meet the electrochemical performance of conventional batteries (such as capacity performance and initial charge and discharge efficiency), but also further significantly improve the structural stability of the silicon-based composite material, thereby improving the cycle stability of the battery and making the battery have a better capacity retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0019] Figure 1 shows an SEM image (10 μm) of the silicon-based composite material in Example 2 of the present invention;

[0020] Figure 2 shows an SEM image (1 μm) of the silicon-based composite material in Example 2 of the present invention;

[0021] Figure 3 A comparison chart of discharge cycle curves of the batteries in Example 1 of the present invention and Comparative Example 2 is shown. DETAILED DESCRIPTION

[0022] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0023] As described in the background of the present invention, existing silicon-based composite materials suffer from poor structural stability, leading to poor battery cycling stability. To address this issue, the present invention provides a silicon-based composite material comprising a ferrosilicon alloy core layer, a first coating layer, and a second coating layer; the first coating layer coating the outer surface of the ferrosilicon alloy core layer; and the second coating layer coating the outer surface of the first coating layer away from the ferrosilicon alloy core layer. The first coating layer is made of carbon, and the second coating layer is made of an oxide.

[0024] The present invention adopts ferrosilicon alloy as the core layer, FeSi xThe core of the phase can provide a buffer matrix to alleviate the volume change of silicon. At the same time, the present invention sets a first coating layer (material includes carbon) on the outer surface of the core layer, and coats a second coating layer (material includes oxide) on the outer surface of the first coating layer. In this way, the present application can not only promote the battery to meet the electrochemical performance of conventional batteries (such as capacity performance and initial charge and discharge efficiency), but also further significantly improve the structural stability of the silicon-based composite material, thereby improving the cycle stability of the battery and making the battery have a more excellent capacity retention rate. Among them, the material of the above-mentioned first coating layer includes carbon, which as an intermediate layer can not only further improve the electrical conductivity of the material, but also provide a buffer matrix for the ferrosilicon alloy core layer to further alleviate the volume change of the ferrosilicon alloy core layer, so that the electrical performance and cycle stability of the battery can be improved. The material of the above-mentioned second coating layer is selected from oxides, which have higher mechanical properties and can more effectively avoid the phenomenon of crushing and collapse of the silicon-based composite material, thereby further improving the structural stability of the silicon-based composite material, and then slowing down the negative impact of the volume change of the material in subsequent practical applications, so as to further significantly improve the cycle stability of the battery.

[0025] Further preferably, the inventors of the present invention also found in the process of designing the above-mentioned double-layer coating structure that although the oxide coating layer can effectively improve the structural stability of the material, it will also cause the electrochemical properties of the material (such as capacity performance and initial charge and discharge efficiency) to decrease slightly. Therefore, in a preferred embodiment, the present invention further provides a plurality of through-holes in the second coating layer. This through-hole structure is conducive to the immersion of the electrolyte, enhances the contact between ferrosilicon / carbon and the electrolyte, provides a transmission channel for lithium ions, and enhances the ionic conductivity of the material, thereby improving the electrochemical performance of the battery, and thus enabling the battery to simultaneously take into account very excellent electrochemical performance and cycle stability.

[0026] Specifically, the present invention uses ferrosilicon material as the core layer, and the internal FeSi xThe inner core of the phase provides a buffer matrix that can alleviate the volume change of silicon. Secondly, the use of carbon material as the first coating layer can improve the conductivity of the material, maintain structural stability, and form a conductive contact. Thirdly, the use of oxide as the second coating layer, and the second coating layer has a through-hole structure, which can further provide a transmission channel for the insertion and extraction of lithium ions while improving the stability of the material structure. Based on the synergistic effect of the above-mentioned triple modification effect, the silicon-based composite material of the present invention can simultaneously take into account excellent electrochemical properties and cycle stability. More preferably, the oxide is selected from one or more of boron trioxide, phosphorus pentoxide, arsenic trioxide or vanadium pentoxide. The radial width of the through-holes in the second coating layer is 50 to 800 nm (more preferably 50 to 150 nm, for example, 50 nm, 55 nm, 58 nm, 59 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm or 150 nm), the porosity of the second coating layer is 5 to 20% (for example, 5%, 6%, 12%, 15%, 18% or 20%), and the specific surface area is 0.5 to 2 m 2 / g (for example, it can be 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.5m 2 / g, 1.8m 2 / g or 2.0m 2 / g).

[0027] In order to further improve the structural stability of the material, in a preferred embodiment, the iron content in the ferrosilicon alloy is 5 to 15 wt% (for example, it can be 5 wt%, 10 wt% or 15 wt%). More preferably, the ferrosilicon alloy core layer is in powder form, and the average particle size of the ferrosilicon alloy core layer is 0.5 to 2.5 μm (for example, it can be 0.5 μm, 1 μm, 1.5 μm, 2 μm or 2.5 μm). Based on this, the internal stress of the material can be effectively reduced to avoid the expansion and powdering phenomenon caused by the excessive size of the particles. In order to further balance the uniformity of the above-mentioned excellent properties of the material, it is preferred that the thickness of the first coating layer is 50 to 150 nm (more preferably 50 to 80 nm, for example, it can be 50 nm, 60 nm, 65 nm, 70 nm, 77 nm, 79 nm or 80 nm), and the thickness of the second coating layer is 10 to 100 nm (more preferably 50 to 80 nm, for example, it can be 75 nm, 76 nm, 77 nm, 78 nm or 80 nm).

[0028] The present invention also provides a method for preparing the aforementioned silicon-based composite material, which comprises the following steps: step S1, providing a ferrosilicon alloy core layer; step S2, coating the outer surface of the ferrosilicon alloy core layer with a first coating layer, and coating the outer surface of the first coating layer away from the ferrosilicon alloy core layer with a second coating layer, thereby forming a silicon-based composite material.

[0029] The present invention adopts ferrosilicon alloy as the core layer, and the internal FeSi x The inner core of the phase can provide a buffer matrix to alleviate the volume change of silicon. At the same time, the present invention sets a first coating layer (the material includes carbon) on the outer surface of the core layer, and covers the outer surface of the first coating layer with a second coating layer (the material includes oxide). In this way, the structural stability of the material and the cycle stability of the battery can be further greatly improved. On the one hand, the first coating layer serves as an intermediate layer, which can improve the electrical conductivity of the material and further provide a buffer for the ferrosilicon alloy core layer. On the other hand, the material of the second coating layer is selected from oxides, which have higher mechanical properties and can effectively avoid the phenomenon of crushing and collapse of silicon-based composite materials, thereby ensuring its structural stability and mitigating the negative effects of the material due to volume changes, thereby further improving the cycle stability of the battery. In addition, the above-mentioned preparation method of the present invention is simple, has cost advantages, and can be industrialized.

[0030] In a preferred embodiment, step S1 comprises: ball-milling the ferrosilicon alloy and the ball-milling medium to obtain a first slurry containing a ferrosilicon alloy core layer. The present invention mixes the ferrosilicon alloy and the ball-milling medium by ball-milling to reduce the internal stress of the material, thereby alleviating the expansion and pulverization phenomenon caused by excessively large material particles. Preferably, tungsten carbide grinding balls are used for ball milling; more preferably, the particle size of the tungsten carbide grinding balls is 2 to 6 mm. More preferably, the ball-to-material ratio during the ball milling process is 16 to 20:1. More preferably, the ball milling medium is anhydrous ethanol and / or water. It is further preferred that the raw materials in the ball milling process also include a dispersant, and the dispersant is selected from one or more of citric acid, sodium tripolyphosphate, or sodium metasilicate.

[0031] In a preferred embodiment, step S2 includes: step S21, stirring and mixing the first slurry and the carbon source to obtain a second slurry; step S22, drying the second slurry and performing a first heat treatment under an inert gas atmosphere to obtain a first heat treatment product; step S23, mixing the first heat treatment product and the oxide, and performing a second heat treatment under an inert gas atmosphere to obtain a silicon-based composite material; wherein the carbon source includes a first carbon source and a second carbon source, the thermal decomposition temperature of the first carbon source is less than the thermal decomposition temperature of the second carbon source; the treatment temperature of the first heat treatment is ≥ the thermal decomposition temperature of the first carbon source; the treatment temperature of the second heat treatment is ≥ the thermal decomposition temperature of the second carbon source, and the treatment temperature of the second heat treatment is ≥ the melting point of the oxide.

[0032] The present invention first adds two carbon sources with different decomposition temperatures to the above-mentioned ferrosilicon alloy core layer and stirs and mixes them so that the materials are evenly mixed to improve the subsequent coating effect. Subsequently, a first heat treatment is performed under an inert gas atmosphere at a lower treatment temperature. At this time, the carbon source with a lower thermal decomposition temperature begins to decompose to form a uniform amorphous carbon coating layer on the surface of the core layer. Next, an oxide is added and a second heat treatment is performed at a higher treatment temperature. At this time, the carbon source with a higher decomposition temperature in the first heat treatment begins to decompose, releasing gas, which passes through the molten liquid oxide to form pores on its surface. After cooling to room temperature, a silicon-based composite material with the above structure is obtained. Preferably, the difference between the thermal decomposition temperature of the second carbon source and the thermal decomposition temperature of the first carbon source is between 450 and 550°C.

[0033] The material thus prepared has three beneficial effects: First, the present invention uses ferrosilicon material as the core layer, and the internal FeSi x The core provides a buffer matrix to alleviate the volume change of silicon. Secondly, the use of carbon material as the first coating layer can improve the conductivity of the material, maintain structural stability, and form a conductive contact. Thirdly, the use of oxide as the second coating layer, and the second coating layer has a through-hole structure, which can further provide a transmission channel for the insertion and extraction of lithium ions while improving the stability of the material structure. Based on the synergistic effect of the above triple modification effects, the silicon-based composite material of the present invention can simultaneously take into account excellent electrochemical performance and cycle stability.

[0034] To further improve the battery's capacity and cycle retention, in a preferred embodiment, the first carbon source is one or more of asphalt, carboxymethyl cellulose, glucose, polyethylene glycol, or potato starch. Preferably, the second carbon source is selected from one or more of phenolic resin, polyimide, or bismaleimide, more preferably phenolic resin and / or polyimide. More preferably, the weight ratio of the first carbon source to the second carbon source is 4 to 8:1 (e.g., 4:1, 5:1, 6:1, 7:1, or 8:1).

[0035] In order to further balance the electrochemical performance and cycle stability of the battery, the amount of carbon source is preferably 30-45% of the weight of the ferrosilicon alloy, for example, 30%, 40%, 43% or 45%. When the amount of carbon source is lower than this range, the coating effect will be poor, the conductivity of the material will decrease, and the battery specific capacity and rate performance will also decrease. When the amount of carbon source is higher than this range, the proportion of active material will decrease, resulting in a decrease in the battery specific capacity. More preferably, the oxide is in powder form, the average particle size of the oxide is 50-500nm (more preferably 50-100nm, for example, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm), and the amount of oxide is 30-80% of the weight of the carbon source, for example, 30%, 33%, 55% or 80%. When the amount of oxide is lower than this range, the buffering effect of the second coating layer will be weakened, thereby reducing the cycle performance of the battery. When the amount of oxide used is higher than this range, the proportion of active material will decrease and the specific capacity of the battery will decrease.

[0036] To further improve the uniformity of the material's excellent properties, in a preferred embodiment, in step S21, stirring is performed under vacuum conditions at a stirring speed of 800 to 2000 r / min. Preferably, the first heat treatment lasts for 1 to 6 hours (more preferably 1 to 3 hours); the second heat treatment lasts for 1 to 9 hours (more preferably 5 to 9 hours).

[0037] In some preferred embodiments, when the first carbon source is pitch and the oxide is boron trioxide, the treatment temperature of the first heat treatment is 350-450° C. (more preferably 400-450° C.), and the treatment temperature of the second heat treatment is 800-900° C. (more preferably 850-900° C.); or, when the first carbon source is glucose and the oxide is phosphorus pentoxide, the treatment temperature of the first heat treatment is 250-500° C., and the treatment temperature of the second heat treatment is 600-1000° C.; or, when the first carbon source is carboxymethyl cellulose and the oxide is vanadium pentoxide, the treatment temperature of the first heat treatment is 200-300° C., and the treatment temperature of the second heat treatment is 600-900° C. In these embodiments, the second carbon source can be independently selected from one or more of a phenolic resin, a polyimide resin, or a bismaleimide resin.

[0038] The present invention further provides a negative electrode material, comprising the aforementioned silicon-based composite material; or the silicon-based composite material prepared by the aforementioned preparation method. Based on the aforementioned reasons, the negative electrode material has better structural stability.

[0039] The present invention also provides a lithium-ion battery having the aforementioned negative electrode material. Based on the above reasons, the lithium-ion battery has better capacity and cycle retention rate.

[0040] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0041] Example 1

[0042] Weigh 70 g of ferrosilicon alloy powder (the iron content in the ferrosilicon alloy is 15 wt%), add 500 mL of anhydrous ethanol as a ball milling medium, the ball-to-material ratio is 18:1, and ball mill at 500 r / min for 6 h to obtain a first slurry containing a ferrosilicon alloy core layer with a particle size of 1.6 μm.

[0043] Then, 30 g of a carbon source was added to the first slurry. The carbon source was a powder mixture of asphalt and phenolic resin, with the two carbon sources being prepared in a weight ratio of asphalt to phenolic resin of 8:1. The mixture was stirred under vacuum at a stirring speed of 1000 rpm for 1 hour to obtain a second slurry.

[0044] The second slurry was filtered and dried in a vacuum drying oven for 12 hours, then placed in a box furnace for the first heat treatment in an argon atmosphere, heated to 450°C at a heating rate of 5°C / min and kept warm for 2 hours, and then cooled to room temperature in the furnace to obtain the first heat-treated product.

[0045] Then, 10 g of B2O3 (average particle size of 80 nm) was added to the product of the first heat treatment, mixed evenly and returned to the furnace. A second heat treatment was performed in an argon atmosphere, with the temperature being increased to 900°C at 5°C / min and kept at that temperature for 6 hours to obtain a silicon-based composite material.

[0046] The radial width of the through hole is 55 nm; the porosity of the second coating layer is 12%; the specific surface area of ​​the second coating layer is 0.9 m 2 The thickness of the first coating layer is 80 nm, and the thickness of the second coating layer is 75 nm.

[0047] Example 2

[0048] The only difference from Example 1 is that the carbon source is a powder mixture of asphalt and polyimide, and the two carbon sources are configured according to a weight ratio of asphalt:polyimide=8:1.

[0049] The radial width of the through hole is 60 nm; the porosity of the second coating layer is 12%; the specific surface area of ​​the second coating layer is 1.1 m 2 The thickness of the first coating layer was 79 nm, and the thickness of the second coating layer was 78 nm.

[0050] Example 3

[0051] The only difference from Example 1 is that the carbon source is a powder mixture of asphalt and bismaleimide, and the two carbon sources are configured according to a weight ratio of asphalt:bismaleimide=8:1.

[0052] The radial width of the through hole is 120 nm; the porosity of the second coating layer is 15%; the specific surface area of ​​the second coating layer is 1.5 m 2 The thickness of the first coating layer was 77 nm, and the thickness of the second coating layer was 77 nm.

[0053] Example 4

[0054] The only difference from Example 2 is that the two carbon sources are configured in a weight ratio of asphalt:polyimide=6:1.

[0055] The radial width of the through hole is 110 nm; the porosity of the second coating layer is 18%; the specific surface area of ​​the second coating layer is 1.8 m 2 The thickness of the first coating layer was 60 nm, and the thickness of the second coating layer was 79 nm.

[0056] Example 5

[0057] The only difference from Example 2 is that the two carbon sources are configured in a weight ratio of asphalt:polyimide=4:1.

[0058] The radial width of the through hole is 115 nm; the porosity of the second coating layer is 20%; the specific surface area of ​​the second coating layer is 2.0 m 2 The thickness of the first coating layer is 50 nm, and the thickness of the second coating layer is 80 nm.

[0059] Example 6

[0060] The only difference from Example 2 is that the added amount of B2O3 is 5g.

[0061] The radial width of the through hole is 60 nm; the porosity of the second coating layer is 12%; the specific surface area of ​​the second coating layer is 1.2 m 2 The thickness of the first coating layer is 80 nm, and the thickness of the second coating layer is 39 nm.

[0062] Example 7

[0063] The only difference from Example 2 is that the treatment temperature of the first heat treatment is 300°C.

[0064] The radial width of the through hole is 59 nm; the porosity of the second coating layer is 5%; the specific surface area of ​​the second coating layer is 2.0 m 2The thickness of the first cladding layer was 79 nm, and the thickness of the second cladding layer was 38 nm.

[0065] Example 8

[0066] The only difference from Example 2 is that the treatment temperature of the second heat treatment is 700°C.

[0067] The radial width of the through hole is 58 nm; the porosity of the second coating layer is 8%; the specific surface area of ​​the second coating layer is 0.8 m 2 The thickness of the first coating layer was 70 nm, and the thickness of the second coating layer was 31 nm.

[0068] Example 9

[0069] The only difference from Example 2 is that the amount of carbon source used is 14 g.

[0070] The radial width of the through hole is 50 nm; the porosity of the second coating layer is 12%; the specific surface area of ​​the second coating layer is 1.0 m 2 The thickness of the first coating layer is 30 nm, and the thickness of the second coating layer is 76 nm.

[0071] Example 10

[0072] The only difference from Example 2 is that the amount of carbon source used is 21 g.

[0073] The radial width of the through hole is 51 nm; the porosity of the second coating layer is 12%; the specific surface area of ​​the second coating layer is 1.1 m 2 The thickness of the first coating layer is 50 nm, and the thickness of the second coating layer is 75 nm.

[0074] Example 11

[0075] The only difference from Example 2 is that the amount of B2O3 added is 24 g.

[0076] The radial width of the through hole is 46 nm; the porosity of the second coating layer is 10%; the specific surface area of ​​the second coating layer is 0.9 m 2 The thickness of the first coating layer is 80 nm, and the thickness of the second coating layer is 100 nm.

[0077] Example 12

[0078] The only difference from Example 2 is that the amount of B2O3 added is 16.5 g.

[0079] The radial width of the through hole is 110 nm; the porosity of the second coating layer is 15%; the specific surface area of ​​the second coating layer is 1.3 m 2The thickness of the first coating layer was 80 nm, and the thickness of the second coating layer was 80 nm.

[0080] Example 13

[0081] The difference from Example 2 is that the first carbon source is carboxymethyl cellulose, the oxide is vanadium pentoxide, the treatment temperature of the first heat treatment is 300°C, and the treatment temperature of the second heat treatment is 900°C.

[0082] The radial width of the through hole is 105 nm; the porosity of the second coating layer is 13%; the specific surface area of ​​the second coating layer is 1.3 m 2 The thickness of the first coating layer was 65 nm, and the thickness of the second coating layer was 76 nm.

[0083] Example 14

[0084] The difference from Example 2 is that the first carbon source is glucose, the oxide is phosphorus pentoxide, the treatment temperature of the first heat treatment is 500°C, and the treatment temperature of the second heat treatment is 1000°C.

[0085] The radial width of the through hole is 100 nm; the porosity of the second coating layer is 6%; the specific surface area of ​​the second coating layer is 0.8 m 2 The thickness of the first coating layer was 50 nm, and the thickness of the second coating layer was 78 nm.

[0086] Example 15

[0087] The only difference from Example 2 is that the two carbon sources are configured according to a weight ratio of asphalt:polyimide=10:1.

[0088] The radial width of the through hole is 89 nm; the porosity of the second coating layer is 4%; the specific surface area of ​​the second coating layer is 0.4 m 2 The thickness of the first coating layer was 76 nm, and the thickness of the second coating layer was 78 nm.

[0089] Example 16

[0090] The only difference from Example 2 is that the carbon source is only asphalt.

[0091] Comparative Example 1

[0092] The only difference from Example 2 is that no B2O3 is added during the second heat treatment.

[0093] Comparative Example 2

[0094] The only difference from Example 2 is that no carbon source and boron oxide are added for sintering and coating, and only the ferrosilicon alloy core layer is ball-milled.

[0095] Performance testing:

[0096] The product obtained in Example 2 was subjected to SEM detection, and the results were as follows: Figure 1 and Figure 2 As shown in the figure, it can be seen that the silicon-based composite material includes: a ferrosilicon alloy core layer, a first coating layer coated on the outer surface of the ferrosilicon alloy core layer, and a second coating layer coated on the outer surface of the first coating layer away from the ferrosilicon alloy core layer, and the second coating layer has a plurality of through holes. The reason for the formation of this porous structure is that during the first heat treatment, the asphalt begins to pyrolyze to form amorphous carbon to coat the ferrosilicon alloy core layer, but the polyimide does not undergo a large amount of decomposition at this temperature due to its high temperature resistance. During the second heat treatment, when the temperature is heated to about 650°C, the boron oxide begins to liquefy into a liquid with high viscosity. At the same time, the polyimide also begins to decompose in large quantities at this temperature to produce gas overflow, forming a large number of pores on the boron oxide until it is completely decomposed. Then, when the temperature is lowered, the above-mentioned porous boron oxide shell structure is formed.

[0097] The negative electrode materials prepared in the embodiment and the comparative example were respectively made into 2032-type button batteries to test the electrochemical properties of the materials. The current density of all batteries was 100 mA / g and the voltage range was 0.01-1.5 V. Figure 3 The following table shows the comparison of the discharge cycle curves of the batteries in Example 1 of the present invention and Comparative Example 2. The specific test results are shown in Table 1 below:

[0098] Table 1

[0099] First discharge specific capacity mAh / g First charge and discharge efficiency% Capacity retention rate (relative to the second cycle)% Example 1 1402.3 86.3 82.6 / 100 laps Example 2 1475.4 85.9 83.4 / 100 laps Example 3 1426.5 84.6 80.4 / 100 laps Example 4 1488.6 84.1 85.6 / 100 laps Example 5 1456.4 83.7 83.6 / 100 laps Example 6 1521.7 85.1 75.5 / 100 laps Example 7 1426.5 84.1 72.3 / 100 laps Example 8 1410.9 83.2 71.6 / 100 laps Example 9 1386.7 82.0 70.4 / 100 laps Example 10 1421.3 84.9 78.6 / 100 laps Example 11 1405.3 81.0 86.4 / 100 laps Example 12 1412.3 84.6 82.1 / 100 laps Example 13 1401.4 83.1 80.4 / 100 laps Example 14 1400.8 82.6 80.1 / 100 laps Example 15 1395.6 82.4 80.3 / 100 laps Example 16 1052.6 83.4 86.4 / 100 laps Comparative Example 1 1502.9 86.5 66.3 / 100 laps Comparative Example 2 1683.4 75.3 15.1 / 20 laps

[0100] It can be found from Comparative Example 1 and Example 2 that the provision of the second coating layer mentioned above in the present application can significantly improve the cycle stability of the product on the basis of having excellent charge and discharge specific capacity and charge and discharge efficiency.

[0101] It can be found from Example 16 and Example 2 that compared with the second coating layer without a through-hole structure, the second coating layer having multiple through-holes can enable the product to have better cycle stability while also exhibiting excellent charge and discharge specific capacity and charge and discharge efficiency, thereby enabling the product to take into account better cycle stability, charge and discharge specific capacity and charge and discharge efficiency at the same time.

[0102] It can be found from Comparative Example 2 and Example 2 that the silicon-based composite material based on the above-mentioned specific structure of the present invention can significantly improve the cycle stability on the basis of excellent charge and discharge specific capacity and charge and discharge efficiency compared with conventional ferrosilicon materials.

[0103] Further, from Examples 2, 4, 5, and 15, it can be found that the preferred weight ratio of the first carbon source to the second carbon source is 4 to 8:1. By controlling the weight ratio of the first carbon source to the second carbon source within this range, the product can simultaneously achieve excellent cycle stability, charge-discharge specific capacity, and charge-discharge efficiency. When the weight ratio of the first carbon source to the second carbon source is not within this range (such as in Example 15), the porosity of the product material is poor and the charge-discharge specific capacity of the battery will be relatively low.

[0104] Further, it can be found from Examples 2, 6, 11 and 12 that the preferred amount of oxide is 30-80% of the weight of the carbon source. When the amount of oxide is outside this range (such as in Example 6), the cycle stability of the product is poor.

[0105] Further, from Examples 2, 7, and 8, it can be found that when the first carbon source is pitch and the oxide is boron trioxide, the preferred treatment temperature for the first heat treatment is 350-450°C, and the treatment temperature for the second heat treatment is 800-900°C. When the heat treatment temperature is outside this range (such as in Examples 7 and 8), the product's cyclic stability is poor.

[0106] Further, it can be found from Examples 2, 9 and 10 that the preferred amount of carbon source is 30-45% of the weight of the ferrosilicon alloy layer. When the amount of carbon source is outside this range (such as in Example 9), the cycle stability of the product is poor.

[0107] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A silicon-based composite material, characterized in that: The silicon-based composite material comprises: Ferrosilicon alloy core layer; a first coating layer, coating the outer surface of the ferrosilicon alloy core layer; and a second coating layer, coating an outer surface of the first coating layer away from the ferrosilicon alloy core layer; Wherein, the material of the first coating layer includes carbon; the material of the second coating layer includes oxide; The carbon is obtained by thermal decomposition of a first carbon source and a second carbon source at different thermal decomposition temperatures; The first carbon source is one or more of asphalt, carboxymethyl cellulose, glucose, polyethylene glycol or potato starch; the second carbon source is one or more of phenolic resin, polyimide resin or bismaleimide resin; The porosity of the second coating layer is 5-20%; The oxide is selected from one or more of boron trioxide and vanadium pentoxide.

2. The silicon-based composite material according to claim 1, characterized in that The second cladding layer is provided with a plurality of through holes.

3. The silicon-based composite material according to claim 2, characterized in that The radial width of the through hole is 50-800 nm.

4. The silicon-based composite material according to claim 2, characterized in that The radial width of the through hole is 50-150 nm.

5. The silicon-based composite material according to claim 2, characterized in that: The specific surface area of ​​the second coating layer is 0.5~2m 2 / g.

6. The silicon-based composite material according to claim 1 or 2, characterized in that: The ferrosilicon alloy core layer is in powder form.

7. The silicon-based composite material according to claim 6, characterized in that: The average particle size of the ferrosilicon alloy core layer is 0.5-2.5 μm.

8. The silicon-based composite material according to claim 6, characterized in that: The weight content of iron in the ferrosilicon alloy core layer is 5-15 wt %.

9. The silicon-based composite material according to claim 6, characterized in that: The thickness of the first coating layer is 50-150 nm.

10. The silicon-based composite material according to claim 6, characterized in that: The thickness of the first coating layer is 50-80 nm.

11. The silicon-based composite material according to claim 6, characterized in that: The thickness of the second coating layer is 10-100 nm.

12. The silicon-based composite material according to claim 6, characterized in that: The thickness of the second coating layer is 50-80 nm.

13. A method for preparing the silicon-based composite material according to any one of claims 1 to 12, characterized in that: The preparation method comprises the following steps: Step S1, providing a ferrosilicon alloy core layer; Step S2 , coating the outer surface of the ferrosilicon alloy core layer with a first coating layer, and coating the outer surface of the first coating layer away from the ferrosilicon alloy core layer with a second coating layer, thereby forming the silicon-based composite material.

14. The preparation method according to claim 13, characterized in that The step S1 includes: ball-milling the ferrosilicon alloy and the ball-milling medium to obtain a first slurry containing the ferrosilicon alloy core layer.

15. The preparation method according to claim 14, characterized in that The ball-to-material ratio in the ball milling process is 16-20:

1.

16. The preparation method according to claim 14, characterized in that The raw materials in the ball milling process also include a dispersant.

17. The preparation method according to claim 16, characterized in that The dispersant is selected from one or more of citric acid, sodium tripolyphosphate or sodium metasilicate.

18. The preparation method according to claim 14, characterized in that The ball milling medium is anhydrous ethanol and / or water.

19. The preparation method according to claim 14, characterized in that The step S2 comprises: Step S21, stirring and mixing the first slurry and the carbon source to obtain a second slurry; Step S22, drying the second slurry and then performing a first heat treatment under an inert gas atmosphere to obtain a first heat-treated product; Step S23, mixing the first heat-treated product and the oxide, and performing a second heat treatment under an inert gas atmosphere to obtain the silicon-based composite material; Wherein, the carbon source includes a first carbon source and a second carbon source; The thermal decomposition temperature of the first carbon source is less than the thermal decomposition temperature of the second carbon source; The treatment temperature of the first heat treatment is greater than or equal to the thermal decomposition temperature of the first carbon source; The treatment temperature of the second heat treatment is greater than or equal to the thermal decomposition temperature of the second carbon source, and the treatment temperature of the second heat treatment is greater than or equal to the melting point of the oxide; The first carbon source is one or more of asphalt, carboxymethyl cellulose, glucose, polyethylene glycol or potato starch; the second carbon source is one or more of phenolic resin, polyimide resin or bismaleimide resin.

20. The preparation method according to claim 19, characterized in that The difference between the thermal decomposition temperature of the second carbon source and the thermal decomposition temperature of the first carbon source is between 450° C. and 550° C.

21. The preparation method according to claim 19, characterized in that In the carbon source, the weight ratio of the first carbon source to the second carbon source is 4-8:

1.

22. The preparation method according to claim 19, characterized in that The amount of the carbon source is 30-45% of the weight of the ferrosilicon alloy layer.

23. The preparation method according to claim 19, characterized in that The oxide is in powder form, and the average particle size of the oxide is 50-500 mm.

24. The preparation method according to claim 23, characterized in that The average particle size of the oxide is 50-100 nm.

25. The preparation method according to claim 19, characterized in that The amount of the oxide is 30-80% by weight of the carbon source.

26. The preparation method according to claim 19, characterized in that The stirring is carried out under vacuum conditions at a stirring speed of 800-2000 r / min.

27. The preparation method according to claim 19, characterized in that The treatment time of the first heat treatment is 1 to 6 hours.

28. The preparation method according to claim 19, characterized in that The treatment time of the second heat treatment is 1 to 9 hours.

29. The preparation method according to claim 19, characterized in that When the first carbon source is pitch and the oxide is boron trioxide, the treatment temperature of the first heat treatment is 350-450° C., and the treatment temperature of the second heat treatment is 800-900° C.; or When the first carbon source is carboxymethyl cellulose and the oxide is vanadium pentoxide, the treatment temperature of the first heat treatment is 200-300°C, and the treatment temperature of the second heat treatment is 600-900°C.

30. A negative electrode material, characterized in that The negative electrode material comprises the silicon-based composite material according to any one of claims 1 to 12; or, the silicon-based composite material prepared by the preparation method according to any one of claims 13 to 29.

31. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode material according to claim 30.

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