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

Abstract

The application provides a silicon-carbon negative electrode material and a preparation method and a lithium ion battery thereof, the silicon-carbon negative electrode material is a grape-like secondary particle, the secondary particle is composed of primary particles, carbon nanotubes and graphite, the surface of the primary particle is connected with the graphite through the carbon nanotubes; the primary particle is a double-coated silicon-based material, the inner core of the primary particle is a silicon-based material, the inner coating layer is an oxide layer, and the outer coating layer is a carbon coating layer. The application effectively enhances the conductivity of the silicon-carbon negative electrode material by designing the grape-like silicon-carbon negative electrode material, solves the problems of particle separation and poor conductivity in the expansion process, and the material has a high degree of disorder, which is beneficial to improving the fast-charging performance of the material; in addition, the double-coated silicon-based material surface can improve the initial efficiency while reducing the residual of the surface alkali, and can effectively alleviate the expansion problem of the silicon-based material, reduce the erosion of the electrolyte to the surface of the silicon-based material, and further enhance the cycle performance of the material.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, specifically relating to a silicon-carbon anode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Silicon anode materials have become one of the most promising anode materials due to their high theoretical capacity and relatively high lithium intercalation potential. Commonly used silicon anodes include silicon suboxide and nano-silicon anodes. Because silicon suboxide has relatively smaller expansion than nano-silicon anodes, it was the first to be commercialized. However, due to its lower initial efficiency (≤76%) and relatively larger expansion compared to graphite anodes, the application of silicon suboxide in the power battery market has not yet been widely adopted.

[0003] In recent years, numerous methods have emerged to improve the efficiency of silicon suboxide by pre-magnesium and pre-lithiation, but these methods also bring about processing performance problems during silicon suboxide slurry coating, such as gas generation during slurry coating and material shedding during coating. To solve the problem of silicon anode expansion, expansion suppression is usually achieved by compounding with graphite and adding carbon nanotubes to the slurry. For example, CN110600704A discloses a silicon / graphite composite material and its preparation method and application, including secondary particles composed of silicon material and graphite, with carbon nanotubes (CNTs) overlapping between silicon and graphite particles in the secondary particles, and the outer surface of the secondary particles coated with pyrolytic carbon; wherein the silicon material includes silicon suboxide and / or nano-silicon. CN108807953A discloses a method for preparing a silicon-carbon composite anode material of nano-silicon suboxide for lithium-ion batteries, including modifying silicon suboxide with titanate, and then coating it with carbon nanotubes and pitch to prepare a silicon-carbon composite anode material of nano-silicon suboxide. CN115084479A discloses a lithium-ion battery anode composite material and its preparation method. The composite material includes at least: silicon suboxide particles; a first coating layer, which is a porous material and covers the surface of the silicon suboxide particles; a second coating layer, which covers the surface of the first coating layer and has carbon nanotubes embedded in it; and graphene, wherein the adjacent layers of the graphene are filled with the double-layered silicon suboxide particles. While the solutions provided by the prior art offer some overall improvement, they do not meet application requirements.

[0004] Therefore, how to effectively improve the initial efficiency of silicon-based materials and suppress their volume expansion so that they meet application requirements is an urgent technical problem to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a silicon-carbon anode material, its preparation method, and a lithium-ion battery. This invention provides a silicon-carbon anode material that, through the design of grape-like secondary particles, effectively enhances the conductivity of the silicon-carbon anode material, solving the problems of particle separation and poor conductivity during the expansion process. Furthermore, the high degree of material disorder is beneficial for improving the material's fast-charging performance. For the primary particles, the silicon-based material surface is double-coated, which can improve initial efficiency while reducing surface alkali residue, effectively alleviating the expansion problem of the silicon-based material, reducing electrolyte erosion of the silicon-based material surface, and thus enhancing the material's cycle performance.

[0006] To achieve this objective, the present invention employs the following technical solution:

[0007] In a first aspect, the present invention provides a silicon-carbon anode material, wherein the silicon-carbon anode material is a grape-like secondary particle, the secondary particle is composed of primary particles, carbon nanotubes and graphite, and the surface of the primary particles is connected to the graphite through carbon nanotubes.

[0008] The primary particle is a double-layered silicon-based material, with a silicon-based core, an inner coating layer of oxide, and an outer coating layer of carbon.

[0009] This invention provides a silicon-carbon anode material. By designing grape-like secondary particles, the conductivity of the silicon-carbon anode material is effectively enhanced, solving the problems of particle separation and poor conductivity during the expansion process. Furthermore, the high degree of material disorder is beneficial for improving the fast-charging performance of the material. For the primary particles, the silicon-based material surface is double-coated, which can improve the initial efficiency while reducing the residual alkali on the surface. It can also effectively alleviate the expansion problem of the silicon-based material, reduce the erosion of the silicon-based material surface by the electrolyte, and thus enhance the cycle performance of the material.

[0010] It should be noted that grape-like structures refer to secondary particle aggregates formed by the bonding of primary particles with graphite, resembling the structure of grapes.

[0011] Preferably, the median particle size D50 of the secondary particles is 10-15 μm, for example, it can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0012] Preferably, the median particle size D50 of the primary particles is 1 to 5 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm or 5 μm.

[0013] Preferably, the median particle size D50 of the graphite is 1 to 5 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm or 5 μm, etc.

[0014] Preferably, the median particle size D50 of the silicon-based material is less than 7 μm, and can be, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or 6 μm, etc., preferably 1-5 μm.

[0015] Preferably, the median particle size D50 of the oxide in the inner coating layer is ≤5 nm, and can be, for example, 1 nm, 2 nm, 3 nm, 4 nm, or 5 nm, etc., preferably 1-3 nm.

[0016] Preferably, the thickness of the inner coating layer is 2-10 nm, and can be, for example, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm, etc.

[0017] In the present invention, if the thickness of the inner coating layer is too small and the coating layer is too thin, there may be exposed points and it cannot play a complete protection role; if the thickness of the inner coating layer is too large, it will affect the electronic conductivity of the material.

[0018] Preferably, the thickness of the outer coating layer is 4-10 nm, and can be, for example, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm, etc.

[0019] In the present invention, if the thickness of the outer coating layer is too small, the coating layer coverage is incomplete and the cycling performance is affected; if the thickness of the outer coating layer is too large, it will affect the ionic conductivity of the material.

[0020] Second, the present invention provides a preparation method of the silicon-carbon negative electrode material as described in the first aspect, and the preparation method includes the following steps:

[0021] (1) Mix the silicon-based material and the oxide, and perform primary sintering to obtain the silicon-based material coated with the oxide;

[0022] (2) Mix the silicon-based material coated with the oxide and the carbon material, and perform secondary sintering to obtain the silicon-based material with double-layer coating;

[0023] (3) Mix the silicon-based material with double-layer coating, graphite, and carbon nanotubes, and perform tertiary sintering to obtain the silicon-carbon negative electrode material.

[0024] Preferably, the silicon-based material in step (1) includes silicon单质 and / or SiO x , 0 < x < 2, and x can be, for example, 1, 1.2, 1.4, 1.6, or 1.8, etc.

[0025] Preferably, the oxide in step (1) is a metal oxide, and the metal oxide includes any one or a combination of at least two of Al2O3, TiO2, ZrO2, or MgO2.

[0026] Preferably, the mass ratio of silicon-based material to oxide in step (1) is 100:(0.01 to 0.05), for example, it can be 100:0.01, 100:0.02, 100:0.03, 100:0.04 or 100:0.05, etc.

[0027] Preferably, the mixing process in step (1) is accompanied by stirring.

[0028] Preferably, the atmosphere for the first sintering in step (1) is an inert atmosphere, and the gas in the inert atmosphere includes nitrogen and / or argon.

[0029] Preferably, the heating rate of the first sintering in step (1) is 3 to 5 °C / min, for example, it can be 3 °C / min, 3.5 °C / min, 4 °C / min, 4.5 °C / min or 5 °C / min, etc.

[0030] Preferably, the temperature of the first sintering in step (1) is 300 to 600°C, for example, it can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C.

[0031] In this invention, if the temperature of the first sintering is too low, it will affect the carbonization process during the subsequent second sintering, resulting in a deterioration in the material's performance; if the temperature of the first sintering is too high, it will cause disproportionation of silicon suboxide, silicon cell growth, and affect cycle performance.

[0032] Preferably, the isothermal time for the first sintering in step (1) is 2 to 4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours.

[0033] Preferably, the carbon material in step (2) includes any one or a combination of at least two of the following: asphalt, phenolic resins, alkanes, or high molecular weight organic compounds. For example, phenolic resins may be phenolic epoxy resins, alkanes may be pentane, and high molecular weight organic compounds may be chitosan.

[0034] Preferably, the asphalt includes any one or a combination of at least two of coal tar pitch, petroleum asphalt, or yellow asphalt, with coal tar pitch being the most preferred.

[0035] Preferably, the mixing process in step (2) is accompanied by stirring, and the mixing method includes:

[0036] (a) A solution is obtained by mixing carbon material and an organic solvent;

[0037] (b) Mix the solution and the oxide-coated silicon-based material.

[0038] The present invention does not limit the type of organic solvent, as long as it can dissolve carbon materials. For example, it can be kerosene or tetrahydrofuran.

[0039] Preferably, the carbon content in the solution in step (a) is 0.05 to 2 wt.%, for example, it can be 0.05 wt.%, 0.1 wt.%, 0.15 wt.%, or 0.2 wt.%.

[0040] Preferably, the atmosphere for the secondary sintering in step (2) is an inert atmosphere, and the gas in the inert atmosphere includes nitrogen and / or argon.

[0041] Preferably, the heating rate of the secondary sintering in step (2) is 3 to 5 °C / min, for example, it can be 3 °C / min, 3.5 °C / min, 4 °C / min, 4.5 °C / min or 5 °C / min, etc.

[0042] Preferably, the temperature of the secondary sintering in step (2) is 500 to 800°C, for example, it can be 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C.

[0043] Preferably, the isothermal time for the secondary sintering in step (2) is 2 to 6 hours, for example, it can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours.

[0044] Preferably, the graphite in step (3) includes any one of natural graphite, artificial graphite, primary graphite particles, or secondary graphite particles.

[0045] Preferably, the carbon nanotubes in step (3) include single-walled carbon nanotubes.

[0046] Preferably, the mass ratio of the double-layer coated silicon-based material to the graphite is (1-30):(70-99), wherein the range of the double-layer coated silicon-based material “1-30” can be, for example, 1, 5, 10, 15, 20, 25 or 30, and the range of the graphite “70-99” can be, for example, 70, 75, 80, 85, 90, 95 or 99.

[0047] Preferably, based on the total mass of the double-layer coated silicon-based material and the graphite, the content of the carbon nanotubes is 0.01 to 0.06 wt.%, for example, it can be 0.01 wt.%, 0.02 wt.%, 0.03 wt.%, 0.04 wt.%, 0.05 wt.%, or 0.06 wt.%.

[0048] In this invention, if the content of carbon nanotubes is too low, there will be fewer carbon nanotubes on the surface of the internal double-layer coated silicon-based material, resulting in relatively poor cycle performance; if the content of carbon nanotubes is too high, the carbon nanotubes will not be easily dispersed and will agglomerate more, affecting the rate performance and cycle performance of the material.

[0049] Preferably, the mixing process in step (3) is accompanied by stirring, and the mixing method includes:

[0050] A double-layer coated silicon-based material is mixed with graphite to obtain a mixture, which is then mixed with carbon nanotubes.

[0051] Preferably, the atmosphere for the three sintering processes in step (3) is an inert atmosphere, and the gas in the inert atmosphere includes nitrogen and / or argon.

[0052] Preferably, the temperature of the three sintering steps in step (3) is 600-700℃, for example, 600℃, 620℃, 640℃, 660℃, 680℃ or 700℃.

[0053] Preferably, the isothermal time for the three sintering processes in step (3) is 2 to 4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours.

[0054] Preferably, the silicon-based material in step (1) is pre-lithiated before being mixed with the oxide.

[0055] Preferably, the specific steps of the pre-lithiation treatment include:

[0056] Pre-lithiated silicon-based materials are obtained by blending silicon-based materials with lithium salts and calcining them.

[0057] Preferably, the lithium salt includes any one or a combination of at least two of lithium carbonate, lithium hydride, lithium aluminum hydride, lithium amine, or lithium chloride.

[0058] Preferably, the mass ratio of the silicon-based material to the lithium salt is (85-95):(5-10), wherein the silicon-based material is selected in the range of "85-95", for example, 85, 87, 89, 91, 93 or 95, and the lithium salt is selected in the range of "5-10", for example, 5, 6, 7, 8, 9 or 10.

[0059] Preferably, the median particle size of the lithium salt is less than or equal to the median particle size of the silicon-based material.

[0060] Preferably, the ambient dew point of the blend is <-40°C, for example, it can be -42°C, -45°C, -47°C or -50°C.

[0061] Preferably, the calcination atmosphere is an inert atmosphere.

[0062] Preferably, the calcination temperature is 400–1100°C, for example, it can be 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C or 1100°C, and is preferably 400–600°C.

[0063] Preferably, the calcination time is 4 to 10 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, preferably 6 to 8 hours.

[0064] Preferably, the silicon-based material is pulverized before being mixed with the lithium salt. The present invention does not limit the pulverization method; for example, it may be mechanical pulverization, air jet pulverization, or a combination of both.

[0065] Thirdly, the present invention provides a lithium-ion battery, wherein the negative electrode of the lithium-ion battery comprises the silicon-carbon negative electrode material as described in the first aspect.

[0066] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0067] Compared with the prior art, the present invention has the following beneficial effects:

[0068] (1) This invention provides a silicon-carbon anode material. By designing grape-like secondary particles, the conductivity of the silicon-carbon anode material is effectively enhanced, solving the problems of particle separation and poor conductivity during the expansion process. Furthermore, the material has a high degree of disorder, which is beneficial to improving the fast charging performance of the material.

[0069] (2) The present invention performs double coating on the surface of silicon-based materials, which can improve the first efficiency while reducing the residual alkali on the surface, effectively alleviate the expansion problem of silicon-based materials, reduce the erosion of the surface of silicon-based materials by electrolyte, and thus enhance the cycle performance of materials. Attached Figure Description

[0070] Figure 1 This is a backscattering electron microscope (PSEM) schematic diagram of the silicon-carbon anode material provided in Embodiment 1 of the present invention.

[0071] Figure 2 This is an electron microscope schematic diagram of the silicon-carbon anode material provided in Embodiment 1 of the present invention.

[0072] Figure 3 This is a comparison chart of the charging capabilities of the silicon-carbon anode materials provided in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0073] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0074] Example 1

[0075] This embodiment provides a silicon-carbon anode material, which is a grape-like secondary particle. The secondary particle is composed of primary particles, single-walled carbon nanotubes, and graphite primary particles. The surface of the primary particles is connected to the graphite primary particles through single-walled carbon nanotubes. The primary particles are double-coated silicon suboxide, with a silicon suboxide core, an inner coating layer of Al2O3, and an outer coating layer of carbon.

[0076] The median particle size D50 of the secondary particles is 12 μm, the median particle size D50 of the primary particles is 2 μm, the median particle size D50 of the graphite is 2 μm, the median particle size D50 of the silicon suboxide is 2 μm, the median particle size D50 of the Al2O3 in the inner coating layer is 3 nm, the thickness of the inner coating layer is 6 nm, and the thickness of the outer coating layer is 7 nm.

[0077] This embodiment also provides a method for preparing a silicon-carbon anode material, the method comprising the following steps:

[0078] (1) 10g of commercially available silicon dioxide was first mechanically crushed and then air-jet milled and classified to obtain silicon dioxide powder.

[0079] (2) The above-mentioned silicon suboxide and 1g of lithium carbonate with D50 of 1μm were mixed in a mixer at a dew point of -42℃ to obtain a mixture. The mixture was placed in a corundum crucible and calcined in a tube furnace at 800℃ for 4h in a nitrogen atmosphere to obtain pre-lithiated silicon suboxide.

[0080] (3) According to the mass ratio of 100:0.02, 10g of the pre-lithiated silicon suboxide and 0.002g of Al2O3 were put into an anhydrous and oxygen-free device, mixed and stirred, and sintered at 600°C for 2h under nitrogen atmosphere at a heating rate of 4°C / min to obtain Al2O3 coated silicon suboxide.

[0081] (4) Coal tar pitch and kerosene are mixed to obtain a solution with a coal tar pitch content of 0.1 wt.%. The solution is injected into an anhydrous and oxygen-free device using a syringe. The solution is mixed with oxide-coated silica and stirred. Under a nitrogen atmosphere, the temperature is raised to 700°C at a heating rate of 4°C / min for a second sintering of 3 hours. The temperature is then lowered to room temperature, and the material is removed and sieved to obtain double-layer coated silica.

[0082] (5) The double-layer coated silicon suboxide is mixed and stirred with graphite particles, and then single-walled carbon nanotubes are added and mixed and stirred again; the anhydrous and oxygen-free device is preheated and nitrogen gas is introduced, the temperature is raised to 650°C, and the stirring mode is turned on; the peristaltic pump-thermal injection device is used for injection, the feed rate is adjusted to 0.4 μL / min, and the temperature is kept for 3 hours for three sinterings to obtain the silicon-carbon anode material;

[0083] The mass ratio of the double-layer coated silicon-based material to the primary graphite particles is 15:85, and the content of the single-walled carbon nanotubes is 0.02 wt.%.

[0084] Figure 1 A backscattered electron microscope (SEM) schematic diagram of the silicon-carbon anode material prepared in this embodiment is shown. As can be seen from the figure, the white particles are pre-lithiated silicon-oxygen primary particles with a double-layer coating, and the black particles are graphite primary particles. The silicon-oxygen and graphite primary particles are formed into grape-like secondary particles by the preparation method provided in this embodiment.

[0085] Figure 2 The figure shows an electron microscope schematic diagram of the silicon-carbon anode material prepared in this embodiment. As can be seen from the figure, the carbon nanotubes are coated on the surface of the primary particles by the preparation method provided in this embodiment, so that they are bridged and connected between the primary particles and the carbon coating layer.

[0086] Example 2

[0087] This embodiment provides a silicon-carbon anode material, which is a grape-like secondary particle. The secondary particle is composed of primary particles, single-walled carbon nanotubes, and artificial graphite. The surface of the primary particle is connected to the artificial graphite through single-walled carbon nanotubes. The primary particle is a double-layer coated silicon suboxide, with a silicon suboxide core, an inner coating layer of Al2O3, and an outer coating layer of carbon.

[0088] The median particle size D50 of the secondary particles is 12 μm, the median particle size D50 of the primary particles is 2 μm, the median particle size D50 of the artificial graphite is 2 μm, the median particle size D50 of the silicon suboxide is 2 μm, the median particle size D50 of the Al2O3 in the inner coating layer is 3 nm, the thickness of the inner coating layer is 6 nm, and the thickness of the outer coating layer is 7 nm.

[0089] This embodiment also provides a method for preparing a silicon-carbon anode material, the method comprising the following steps:

[0090] (1) 10g of commercially available silicon dioxide was first mechanically crushed and then air-jet milled and classified to obtain silicon dioxide powder.

[0091] (2) The above-mentioned silicon suboxide and 1g of lithium carbonate with D50 of 1μm are mixed in a mixer at a dew point of -42℃ to obtain a mixture. The mixture is placed in a corundum crucible and calcined in a tube furnace at 800℃ for 4h under a nitrogen atmosphere to obtain pre-lithiated silicon suboxide.

[0092] (3) According to the mass ratio of 100:0.02, 10g of the pre-lithiated silicon suboxide and 0.002g of Al2O3 were put into an anhydrous and oxygen-free device, mixed and stirred, and sintered at 600°C for 2h under nitrogen atmosphere at a heating rate of 5°C / min to obtain Al2O3 coated silicon suboxide.

[0093] (4) Coal tar pitch and kerosene are mixed to obtain a solution with a coal tar pitch content of 0.1 wt.%. The solution is injected into an anhydrous and oxygen-free device using a syringe. The solution is mixed with oxide-coated silica and stirred. Under a nitrogen atmosphere, the temperature is raised to 600°C at a heating rate of 3°C / min for a second sintering of 4 hours. The temperature is then lowered to room temperature, and the material is removed and sieved to obtain double-layer coated silica.

[0094] (5) The double-layer coated silicon suboxide is mixed and stirred with artificial graphite, and then single-walled carbon nanotubes are added and mixed and stirred again; a silicon-oxygen graphite anode material with grape structure is prepared by spray drying using a spray dryer, and then carbonized in a high-temperature tube furnace at a heating rate of 3℃ / min, heated to 700℃ and held for 2h, and then sieved to obtain the silicon-carbon anode material;

[0095] The mass ratio of the double-layer coated silicon-based material to artificial graphite is 15:85, and the content of the single-walled carbon nanotubes is 0.03 wt.%.

[0096] Example 3

[0097] This embodiment provides a silicon-carbon anode material, which is a grape-like secondary particle. The secondary particle is composed of primary particles, single-walled carbon nanotubes, and natural graphite. The surface of the primary particle is connected to the natural graphite through single-walled carbon nanotubes. The primary particle is a double-layer coated silicon suboxide, with a silicon suboxide core, an inner coating layer of TiO2, and an outer coating layer of carbon.

[0098] The median particle size D50 of the secondary particles is 10 μm, the median particle size D50 of the primary particles is 1 μm, the median particle size D50 of the natural graphite is 1 μm, the median particle size D50 of the silicon suboxide is 1 μm, the median particle size D50 of the TiO2 in the inner coating layer is 1 nm, the thickness of the inner coating layer is 2 nm, and the thickness of the outer coating layer is 4 nm.

[0099] This embodiment also provides a method for preparing a silicon-carbon anode material, the method comprising the following steps:

[0100] (1) 10g of commercially available silicon dioxide was first mechanically crushed and then air-jet milled and classified to obtain silicon dioxide powder.

[0101] (2) The above-mentioned silicon suboxide and 0.83g of lithium chloride with D50 of 0.05μm were mixed in a mixer at a dew point of -45℃ to obtain a mixture. The mixture was placed in a corundum crucible and calcined in a tube furnace at 400℃ for 10h in an argon atmosphere to obtain pre-lithiated silicon suboxide.

[0102] (3) According to the mass ratio of 100:0.03, 10g of the pre-lithiated silicon suboxide and 0.003g of TiO2 were put into an anhydrous and oxygen-free device, mixed and stirred, and sintered at 500°C for 3h under argon atmosphere at a heating rate of 4°C / min to obtain TiO2-coated silicon suboxide.

[0103] (4) Petroleum asphalt and kerosene are mixed to obtain a solution with a petroleum asphalt content of 1 wt.%. The solution is injected into an anhydrous and oxygen-free device using a syringe. The solution and oxide-coated silica are mixed and stirred. Under an argon atmosphere, the temperature is raised to 500°C at a heating rate of 4°C / min for a second sintering of 6 hours. The temperature is then lowered to room temperature, and the material is removed and sieved to obtain double-layer coated silica.

[0104] (5) The double-layer coated silicon suboxide is mixed and stirred with natural graphite, and then single-walled carbon nanotubes are added and mixed and stirred again; the anhydrous and oxygen-free device is preheated and argon gas is introduced, the temperature is raised to 600°C, and the stirring mode is turned on; the peristaltic pump-thermal injection device is used for injection, the feed rate is adjusted to 0.3 μL / min, and the temperature is maintained for 4 hours for three sinterings to obtain the silicon-carbon anode material;

[0105] The mass ratio of the double-layer coated silicon-based material to natural graphite is 1:99, and the content of the single-walled carbon nanotubes is 0.01 wt.%.

[0106] Example 4

[0107] This embodiment provides a silicon-carbon anode material, which is a grape-like secondary particle. The secondary particle is composed of primary particles, single-walled carbon nanotubes, and natural graphite. The surface of the primary particle is connected to the natural graphite through single-walled carbon nanotubes. The primary particle is a double-layer coated silicon suboxide, with a silicon suboxide core, an inner coating layer of ZrO2, and an outer coating layer of carbon.

[0108] The median particle size D50 of the secondary particles is 15 μm, the median particle size D50 of the primary particles is 5 μm, the median particle size D50 of the natural graphite is 5 μm, the median particle size D50 of the silicon suboxide is 5 μm, the median particle size D50 of the ZrO2 in the inner coating layer is 5 nm, the thickness of the inner coating layer is 10 nm, and the thickness of the outer coating layer is 10 nm.

[0109] This embodiment also provides a method for preparing a silicon-carbon anode material, the method comprising the following steps:

[0110] (1) 10g of commercially available silicon dioxide was first mechanically crushed and then air-jet milled and classified to obtain silicon dioxide powder.

[0111] (2) The above-mentioned silicon suboxide and 0.53g of lithium hydride with D50 of 3μm were mixed in a mixer at a dew point of -45℃ to obtain a mixture. The mixture was placed in a corundum crucible and calcined in a tube furnace at 600℃ for 8h in an argon atmosphere to obtain pre-lithiated silicon suboxide.

[0112] (3) According to the mass ratio of 100:0.05, 10g of the pre-lithiated silicon suboxide and 0.005 of ZrO2 were put into an anhydrous and oxygen-free device, mixed and stirred, and sintered at 300°C for 4h under argon atmosphere at a heating rate of 3°C / min to obtain ZrO2-coated silicon suboxide.

[0113] (4) Mix yellow pitch and kerosene to obtain a solution with a yellow pitch content of 2 wt.%. Inject the solution into an anhydrous and oxygen-free device using a syringe. Mix the solution with oxide-coated silica and stir. Under an argon atmosphere, heat to 800°C at a heating rate of 5°C / min for 2 hours for secondary sintering. Cool to room temperature, remove the material and sieve it to obtain double-layer coated silica.

[0114] (5) The double-layer coated silicon suboxide is mixed and stirred with natural graphite, and then single-walled carbon nanotubes are added and mixed and stirred again; the anhydrous and oxygen-free device is preheated and argon gas is introduced, the temperature is raised to 700°C, and the stirring mode is turned on; the peristaltic pump-thermal injection device is used for injection, the feed rate is adjusted to 0.5 μL / min, and the temperature is maintained for 2 hours for three sinterings to obtain the silicon-carbon anode material;

[0115] The mass ratio of the double-layer coated silicon-based material to natural graphite is 30:70, and the content of the single-walled carbon nanotubes is 0.06 wt.%.

[0116] Example 5

[0117] The difference between this embodiment and Embodiment 1 is that the thickness of the inner coating layer is 1 nm.

[0118] The remaining preparation methods and parameters are consistent with those in Example 1.

[0119] Example 6

[0120] The difference between this embodiment and Embodiment 1 is that the thickness of the inner coating layer is 11 nm.

[0121] The remaining preparation methods and parameters are consistent with those in Example 1.

[0122] Example 7

[0123] The difference between this embodiment and Embodiment 1 is that the thickness of the outer coating layer is 2nm.

[0124] The remaining preparation methods and parameters are consistent with those in Example 1.

[0125] Example 8

[0126] The difference between this embodiment and Embodiment 1 is that the thickness of the outer coating layer is 12nm.

[0127] The remaining preparation methods and parameters are consistent with those in Example 1.

[0128] Example 9

[0129] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (3) is 200°C.

[0130] The remaining preparation methods and parameters are consistent with those in Example 1.

[0131] Example 10

[0132] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (3) is 700°C.

[0133] The remaining preparation methods and parameters are consistent with those in Example 1.

[0134] Example 11

[0135] The difference between this embodiment and Embodiment 1 is that the content of single-walled carbon nanotubes in step (5) is 0.005 wt.%.

[0136] The remaining preparation methods and parameters are consistent with those in Example 1.

[0137] Example 12

[0138] The difference between this embodiment and Embodiment 1 is that the content of single-walled carbon nanotubes in step (5) is 0.08 wt.%.

[0139] The remaining preparation methods and parameters are consistent with those in Example 1.

[0140] Comparative Example 1

[0141] This comparative example uses the same commercially available silicon suboxide and graphite particles as in Example 1, i.e. steps (2), (3) and (4) are omitted, and single-walled carbon nanotubes are not added in step (5).

[0142] The remaining preparation methods and parameters are consistent with those in Example 1.

[0143] Figure 3 A comparison chart of the charging capabilities of the silicon-carbon anode materials provided in Example 1 and Comparative Example 1 is shown. As can be seen from the chart, when charged to the same state of charge, the grape-like silicon-oxygen graphite can be charged at a higher rate than the conventional mixed silicon-oxygen graphite material without causing lithium plating in the cell, thus improving charging performance and reducing charging time.

[0144] Comparative Example 2

[0145] The difference between this comparative example and Example 1 is that step (3) is not performed, that is, Al2O3 coating is not performed, and only silicon suboxide is coated with carbon.

[0146] The remaining preparation methods and parameters are consistent with those in Example 1.

[0147] Comparative Example 3

[0148] The difference between this comparative example and Example 1 is that step (4) is not performed, that is, carbon coating is not performed, and only silicon suboxide is coated with Al2O3.

[0149] The remaining preparation methods and parameters are consistent with those in Example 1.

[0150] Comparative Example 4

[0151] The difference between this comparative example and Example 1 is that single-walled carbon nanotubes are not added in step (5).

[0152] The remaining preparation methods and parameters are consistent with those in Example 1.

[0153] Performance testing

[0154] The silicon-carbon anode materials prepared in Examples 1-12 and Comparative Examples 1-4 were used to prepare anode sheets. The specific steps included: mixing conductive carbon black, silicon-carbon anode material, binder polyacrylic acid, binder carboxymethyl cellulose, and conductive carbon nanotubes; homogenizing and coating the mixture to prepare anode sheets; and then rolling and die-cutting them. The cathode material used was high-nickel material 811. The cathode material was mixed with high-nickel material 811 and binder polyvinylidene fluoride; homogenized and coated the mixture to prepare cathode sheets; and then rolling and die-cutting them. The anode sheets were stacked with the cathode sheets and a separator, followed by electrolyte injection and pre-charge formation to obtain a 5Ah pouch cell. The electrochemical performance of the 5Ah pouch cell was then tested.

[0155] Test conditions for first discharge efficiency: at 25°C, capacity test 0.33C CC to 4.2V, CV to 0.05C; 0.33C DC to 2.5V.

[0156] First discharge efficiency = (0.33C discharge capacity / 0.33C total charging capacity) × 100%.

[0157] Rate performance testing: 0.33C / 0.5C / 1C / 2C / 3C CC to 4.2V, CV to 0.05C; 0.33C DC to 2.5V. The formula for calculating 3C rate performance is: (3C constant current charging capacity / 0.33C constant current charging capacity) × 100%.

[0158] Cycle capacity retention: 1C CC to 4.2V, CV to 0.05C; 1C DC to 2.5V. 500-cycle retention = (500th discharge capacity / 1st discharge capacity) × 100%.

[0159] Fast charging performance: Total time, in minutes, to fully charge the SoC from empty to 100%.

[0160] The test results are shown in Table 1.

[0161] Table 1

[0162]

[0163]

[0164] analyze:

[0165] As shown in the table above, the grape-like silicon-carbon anode material provided by this invention has high initial efficiency, excellent cycle performance and fast charging performance. This proves that grape-like secondary particles can effectively enhance the conductivity of silicon-carbon anode materials, solve the problems of particle separation and poor conductivity during the expansion process, and also proves that double-layer coating on the surface of silicon-based materials can improve initial efficiency, reduce surface alkali residue, effectively alleviate the expansion problem of silicon-based materials, and reduce the erosion of the silicon-based material surface by the electrolyte.

[0166] A comparison of the data results from Examples 1 and 5-6 shows that if the thickness of the inner coating layer is too small, the incomplete coating will affect the rate and cycle performance and reduce efficiency; if the thickness of the inner coating layer is too large, it will affect conductivity and reduce fast charging performance.

[0167] A comparison of the data results from Examples 1 and 7-8 shows that if the thickness of the outer coating layer is too small, the coating will be incomplete, affecting conductivity and resulting in poor cycle and rate performance; if the thickness of the outer coating layer is too large, it will affect fast charging performance.

[0168] A comparison of the data results from Examples 1 and 9-10 shows that if the temperature of the first sintering is too low, it will affect the carbonization process during the subsequent second sintering, resulting in a deterioration in the material's performance; if the temperature of the first sintering is too high, it will lead to silicon-oxygen disproportionation, reduced efficiency, and poorer cycle life.

[0169] A comparison of the data results from Examples 1 and 11-12 shows that if the content of single-walled carbon nanotubes is too low, there will be fewer surface carbon nanotubes in the internal double-layer coated silicon-based material, which will lead to a decrease in the cycling and rate performance of the material; if the content of single-walled carbon nanotubes is too high, the carbon nanotubes will not be easily dispersed and will agglomerate more, which will seriously affect the rate performance of the material.

[0170] As can be seen from the comparison of the data results of Example 1 and Comparative Example 1, the material prepared by the preparation method provided by the present invention significantly improves the rate, cycle and fast charging performance compared with conventional mixed silicon-oxygen graphite materials, and its first-time efficiency is significantly improved.

[0171] A comparison of the data results from Example 1 and Comparative Example 2 shows that if carbon coating is applied only to the surface of silicon suboxide, the cycle life, rate capability, fast charging, and first-efficiency performance deteriorate.

[0172] A comparison of the data results from Example 1 and Comparative Example 3 shows that if oxide coating is applied only to the surface of silicon suboxide, the cycle life, fast charging rate, and first-efficiency performance deteriorate.

[0173] A comparison of the data results from Example 1 and Comparative Example 4 shows that without the addition of single-walled carbon nanotubes, the cycle performance is lower and the charging time is longer.

[0174] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material is a grape-like secondary particle, which is composed of primary particles, carbon nanotubes and graphite. The surface of the primary particles is connected to the graphite through carbon nanotubes. The primary particle is a double-layer coated silicon-based material, with a silicon-based core, an inner coating layer of oxide, and an outer coating layer of carbon. Based on the total mass of the double-layer coated silicon-based material and the graphite, the carbon nanotube content is 0.01~0.06 wt.%. The thickness of the inner coating layer is 2~10 nm; The thickness of the outer coating layer is 4~10nm.

2. The silicon-carbon anode material according to claim 1, characterized in that, The median particle size D50 of the secondary particles is 10~15μm.

3. The silicon-carbon anode material according to claim 1, characterized in that, The median particle size D50 of the primary particles is 1~5μm.

4. The silicon-carbon anode material according to claim 1, characterized in that, The median particle size D50 of the graphite is 1~5μm.

5. The silicon-carbon anode material according to claim 1, characterized in that, The median particle size D50 of the silicon-based material is <7 μm.

6. The silicon-carbon anode material according to claim 5, characterized in that, The median particle size D50 of the silicon-based material is 1~5μm.

7. The silicon-carbon anode material according to claim 1, characterized in that, The median particle size D50 of the oxides in the inner coating layer is ≤5nm.

8. The silicon-carbon anode material according to claim 7, characterized in that, The median particle size of the oxides in the inner coating layer is 1~3 nm.

9. A method for preparing a silicon-carbon anode material as described in any one of claims 1-8, characterized in that, The preparation method includes the following steps: (1) Mix silicon-based materials and oxides and sinter them in one step to obtain oxide-coated silicon-based materials; (2) The oxide-coated silicon-based material is mixed with carbon material and sintered twice to obtain a double-layer coated silicon-based material; (3) The double-layer coated silicon-based material is mixed with graphite and carbon nanotubes and sintered three times to obtain the silicon-carbon anode material; The temperature of the first sintering in step (1) is 300~600℃.

10. The preparation method according to claim 9, characterized in that, The silicon-based material in step (1) includes elemental silicon and / or SiO2. x 0 <x<2。 11. The preparation method according to claim 9, characterized in that, The oxide in step (1) is a metal oxide, which includes any one or a combination of at least two of Al2O3, TiO2, ZrO2 or MgO2.

12. The preparation method according to claim 9, characterized in that, The mass ratio of silicon-based material to oxide in step (1) is 100:(0.01~0.05).

13. The preparation method according to claim 9, characterized in that, The mixing process described in step (1) is accompanied by stirring.

14. The preparation method according to claim 9, characterized in that, The atmosphere for the first sintering in step (1) is an inert atmosphere, and the gas in the inert atmosphere includes nitrogen and / or argon.

15. The preparation method according to claim 9, characterized in that, The heating rate for the first sintering in step (1) is 3~5℃ / min.

16. The preparation method according to claim 9, characterized in that, The isothermal time for the first sintering in step (1) is 2-4 hours.

17. The preparation method according to claim 9, characterized in that, The carbon material in step (2) includes any one or a combination of at least two of the following: asphalt, phenolic resins, or alkanes.

18. The preparation method according to claim 17, characterized in that, The asphalt includes any one or a combination of at least two of coal tar pitch, petroleum asphalt, or yellow asphalt.

19. The preparation method according to claim 18, characterized in that, The asphalt is coal tar pitch.

20. The preparation method according to claim 9, characterized in that, The mixing process in step (2) is accompanied by stirring, and the mixing methods include: (a) A solution is obtained by mixing carbon material and an organic solvent; (b) Mix the solution and the oxide-coated silicon-based material.

21. The preparation method according to claim 20, characterized in that, The carbon content in the solution in step (a) is 0.05~2 wt.%.

22. The preparation method according to claim 9, characterized in that, The atmosphere for the secondary sintering in step (2) is an inert atmosphere, and the gas in the inert atmosphere includes nitrogen and / or argon.

23. The preparation method according to claim 9, characterized in that, The heating rate for the secondary sintering in step (2) is 3~5℃ / min.

24. The preparation method according to claim 9, characterized in that, The temperature of the secondary sintering in step (2) is 500~800℃.

25. The preparation method according to claim 9, characterized in that, The isothermal time for the secondary sintering in step (2) is 2 to 6 hours.

26. The preparation method according to claim 9, characterized in that, The graphite mentioned in step (3) includes any one of natural graphite, artificial graphite, primary graphite particles, or secondary graphite particles.

27. The preparation method according to claim 9, characterized in that, The carbon nanotubes in step (3) include single-walled carbon nanotubes.

28. The preparation method according to claim 9, characterized in that, The mass ratio of the double-layer coated silicon-based material to the graphite is (1~30):(70~99).

29. The preparation method according to claim 9, characterized in that, Based on the total mass of the double-layer coated silicon-based material and the graphite, the carbon nanotube content is 0.01~0.06 wt.%.

30. The preparation method according to claim 9, characterized in that, The mixing process in step (3) is accompanied by stirring, and the mixing methods include: A double-layer coated silicon-based material is mixed with graphite to obtain a mixture, which is then mixed with carbon nanotubes.

31. The preparation method according to claim 9, characterized in that, The atmosphere for the three sintering steps (3) is an inert atmosphere, and the gas in the inert atmosphere includes nitrogen and / or argon.

32. The preparation method according to claim 9, characterized in that, The temperature for the three sintering steps in step (3) is 600~700℃.

33. The preparation method according to claim 9, characterized in that, The isothermal time for the three sintering processes in step (3) is 2 to 4 hours.

34. The preparation method according to claim 9, characterized in that, In step (1), the silicon-based material is pre-lithiated before being mixed with the oxide.

35. The preparation method according to claim 34, characterized in that, The specific steps of the pre-lithiation treatment include: Pre-lithiated silicon-based materials are obtained by blending silicon-based materials with lithium salts and calcining them.

36. The preparation method according to claim 35, characterized in that, The lithium salt includes any one or a combination of at least two of lithium carbonate, lithium hydride, lithium aluminum hydride, lithium amine, or lithium chloride.

37. The preparation method according to claim 35, characterized in that, The mass ratio of the silicon-based material to the lithium salt is (85~95):(5~10).

38. The preparation method according to claim 35, characterized in that, The median particle size of the lithium salt is less than or equal to the median particle size of the silicon-based material.

39. The preparation method according to claim 35, characterized in that, The ambient dew point of the blend is <-40℃.

40. The preparation method according to claim 35, characterized in that, The calcination temperature is 400~1100℃.

41. The preparation method according to claim 40, characterized in that, The calcination temperature is 400~600℃.

42. The preparation method according to claim 35, characterized in that, The calcination time is 4 to 10 hours.

43. The preparation method according to claim 42, characterized in that, The calcination time is 6-8 hours.

44. The preparation method according to claim 35, characterized in that, Before being mixed with the lithium salt, the silicon-based material is first pulverized.

45. A lithium-ion battery, characterized in that, The negative electrode of the lithium-ion battery includes the silicon-carbon negative electrode material as described in any one of claims 1-8.

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