Silicon-carbon materials, methods of making and using the same, and lithium-ion batteries

Abstract

The application provides a silicon-carbon material, a preparation method and application thereof, and a lithium ion battery, and the silicon-carbon material comprises multi-layer graphite sheets and nanometer silicon sheets between the graphite sheets, and the nanometer silicon sheets are mainly distributed between the graphite sheet layers; the thickness of the graphite sheet is 2-100 nm, and the average diameter of the graphite sheet is 2-20 mu m; the thickness of the nanometer silicon sheet is 10-50 nm, and the average diameter of the nanometer silicon sheet is 100-500 nm. The structure of the silicon-carbon material increases the interaction force between the nanometer silicon sheet and the graphite sheet, and increases the stability of the material. The silicon-carbon material provided by the application has large specific capacity and excellent cycle stability when applied to the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of silicon-carbon materials, specifically to a silicon-carbon material, its preparation method, and its applications. Background Technology

[0002] With increasing national policies and market demands for higher battery energy density, high-energy-density lithium-ion batteries have become a key focus for research institutions and companies. Silicon anode materials, possessing a theoretical specific energy density nearly 10 times higher than currently commercial graphite anodes (370 mAh / g) (4200 mAh / g), along with low operating voltage, abundant reserves, good biocompatibility, and environmental friendliness, are considered the most promising next-generation lithium-ion battery anode material and have attracted widespread attention. Research has shown that lithium-ion batteries assembled using silicon anode materials can achieve up to 40% higher energy density.

[0003] However, large-sized bulk silicon anodes suffer from poor electronic conductivity, low lithium-ion diffusion coefficient, and severe volume changes (300-400%) during lithium insertion and extraction, leading to increased polarization during charging and discharging, rapid capacity decay, and even safety issues such as battery structural damage. To address these problems, nano-sizing of bulk silicon materials can effectively reduce electron transport distance and lithium-ion diffusion distance, mitigating polarization and volume expansion during charging and discharging. Typically, nano-sized silicon particles combined with graphite-based anode materials are used, simultaneously solving the problems of volume expansion and poor conductivity during lithium insertion and extraction. However, given that battery manufacturing only allows a 5% volume expansion tolerance, the silicon content in commercially available silicon-carbon composite materials is generally around 5 wt%. Therefore, increasing the silicon content in silicon-based anode materials and reducing silicon volume expansion during lithiation is of great significance. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art, namely, the severe volume expansion of silicon during lithiation leading to phase separation and thus severe battery capacity decay. This invention provides a silicon-carbon material, its preparation method, and its applications. The silicon-carbon material provided by this invention, when applied to lithium-ion batteries, exhibits high specific capacity and excellent charge-discharge cycle stability.

[0005] According to a first aspect of the present invention, the present invention provides a silicon-carbon material comprising multiple layers of graphite sheets and nano-silicon wafers between the graphite sheets, the nano-silicon wafers being mainly distributed between the graphite sheet layers; the thickness of the graphite sheets is 2-100 nm, and the average diameter of the graphite sheets is 2-20 μm; the thickness of the nano-silicon wafers is 10-50 nm, and the average diameter of the nano-silicon wafers is 100-500 nm.

[0006] According to a second aspect of the present invention, the present invention provides a method for preparing a silicon-carbon material, the method comprising the following steps:

[0007] 1) Mix micron-sized silicon powder with a solvent to obtain a suspension;

[0008] 2) The suspension is transferred to a nano-sand mill for the first sand milling;

[0009] 3) Add graphite and optionally conductive carbon black for a second milling process;

[0010] 4) Optionally, a nano-silicon wafer surface modifier source is added for a third sand milling process;

[0011] 5) After sand milling, discharge the material, filter it, clean it with solvent, and dry the material under vacuum or inert atmosphere to obtain the precursor.

[0012] 6) The precursor is calcined in an inert atmosphere.

[0013] According to a third aspect of the present invention, the present invention provides the application of the nano-silicon material described herein in lithium-ion batteries.

[0014] According to a fourth aspect of the present invention, the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises the nano-silicon material described in the present invention.

[0015] The structure of the silicon-carbon material of this invention increases the interaction force between the silicon nanosheets and the graphite sheets, thereby increasing the stability of the material. The silicon-carbon material provided by this invention, when applied in lithium-ion batteries, exhibits high specific capacity and excellent cycle stability. Attached Figure Description

[0016] Figure 1 This is the XRD characterization diagram of the silicon-carbon material in Example 1 of the present invention;

[0017] Figure 2 This is a SEM image of the silicon-carbon material of Embodiment 1 of the present invention;

[0018] Figure 3 This is a SEM image of the silicon-carbon material of Embodiment 1 of the present invention;

[0019] Figure 4 This is a SEM image of the nano-silicon wafers in the silicon-carbon material of Embodiment 1 of the present invention;

[0020] Figure 5 This is a TEM image of the silicon nanosheets in the silicon-carbon material of Embodiment 1 of the present invention;

[0021] Figure 6 This is an HRTEM image of the nano-silicon wafer in the silicon-carbon material of Embodiment 1 of the present invention;

[0022] Figure 7 This is a SEM-EDS image of the nano-silicon wafers in the silicon-carbon material of Example 1 of the present invention;

[0023] Figure 8 This is a SEM image of graphene, the raw material used in Example 1 of the present invention. Detailed Implementation

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] This invention provides a silicon-carbon material comprising multiple layers of graphite sheets and silicon nanosheets between the graphite sheets, with the silicon nanosheets mainly distributed between the graphite sheets. The graphite sheets have a thickness of 2–100 nm and an average spacing of 2–20 μm; the silicon nanosheets have a thickness of 10–50 nm and an average spacing of 100–500 nm. The structure of the silicon-carbon material of this invention increases the interaction force between the silicon nanosheets and the graphite sheets, thereby increasing the material's stability. The silicon-carbon material provided by this invention, when applied in lithium-ion batteries, exhibits high specific capacity and excellent cycle stability.

[0026] In this invention, the thickness of the graphite sheet, the average diameter of the graphite sheet, the thickness of the nano-silicon wafer, and the surface element content were obtained using a JSM-7800F super-resolution field emission scanning electron microscope.

[0027] In this invention, the average diameter of the nano-silicon wafer refers to the average diameter of the irregular sheet material. The average diameter of the nano-silicon wafer and the surface coating of the nano-silicon wafer were determined using a FEI Titan Cubed Themis G2300 spherical aberration-corrected transmission electron microscope with an accelerating voltage of 200KV, a maximum magnification of 1.1 million times, a point resolution of 0.25nm, and an EDS detection line of 0.1wt%.

[0028] According to a preferred embodiment of the present invention, the silicon-carbon material comprises 30-70% graphite sheets and 30-70% silicon nanosheets by mass. In this invention, the composition of the silicon-carbon material is calculated using the amount of material fed.

[0029] According to a preferred embodiment of the present invention, the thickness of the graphite sheet is 4–12 nm.

[0030] According to a preferred embodiment of the present invention, the average diameter of the graphite sheet is 9–19 μm.

[0031] According to a preferred embodiment of the present invention, the thickness of the nano-silicon wafer is 15-40 nm.

[0032] According to a preferred embodiment of the present invention, the average diameter of the silicon nanosheet is 150–300 nm.

[0033] According to a preferred embodiment of the present invention, the spacing between adjacent stacked graphite sheets is 20–1000 nm, preferably 100–300 nm.

[0034] In this invention, the spacing between adjacent stacked graphite sheets refers to the distance between graphite sheets after inserting nano-silicon wafers, which is obtained by scanning electron microscopy.

[0035] According to a preferred embodiment of the present invention, the nano-silicon wafer includes a single silicon core and a surface modification layer, which can further improve the initial charge-discharge efficiency and cycle stability of the material.

[0036] According to a preferred embodiment of the present invention, the surface modification layer comprises carbon, oxygen, silicon, and phosphorus.

[0037] According to a preferred embodiment of the present invention, the thickness of the surface modification layer of the nano-silicon wafer is 2-10 nm, preferably 2-5 nm.

[0038] According to a preferred embodiment of the present invention, the mass fraction of phosphorus in the surface modification layer of the nano-silicon wafer is 0.5-10%, the mass fraction of oxygen is 15-35%, and the mass fraction of carbon is 20-40%.

[0039] According to a preferred embodiment of the present invention, preferably, the mass fraction of phosphorus in the surface modification layer of the nano-silicon wafer is 1-3%, the mass fraction of oxygen is 18-31%, and the mass fraction of carbon is 24-36%.

[0040] By adopting the aforementioned preferred embodiments, the initial charge-discharge efficiency and cycle stability of the material can be further improved.

[0041] According to a preferred embodiment of the present invention, the silicon-carbon material comprises stacked graphite sheets, uniformly distributed nano-silicon wafers between the graphite sheet layers, and spherical conductive carbon black distributed between the silicon wafers.

[0042] In this invention, the range of types of conductive carbon black is relatively wide. Commonly used types of conductive carbon black can be used in this invention. This is an illustrative example, but it does not limit the scope of this invention. For this invention, preferably, the conductive carbon black is one or more of acetylene black and Super P.

[0043] In this invention, the range of types of graphite sheet materials that can be selected is relatively wide. Commonly used types of graphite sheet materials can all be used in this invention. This is an illustrative example, but it does not limit the scope of this invention. For this invention, preferably, the graphite sheet material is one or more of graphene, artificial graphite, and natural graphite, and preferably graphene.

[0044] Silicon-carbon materials possessing the aforementioned features of this invention all exhibit significant advantages, and their preparation methods do not require special consideration. In accordance with this invention, a method for preparing silicon-carbon materials is provided, comprising the following steps:

[0045] 1) Mix micron-sized silicon powder with a solvent to obtain a suspension;

[0046] 2) The suspension is transferred to a nano-sand mill for the first sand milling;

[0047] 3) Add graphite and optionally conductive carbon black for a second milling process;

[0048] 4) Optionally, a nano-silicon wafer surface modifier source is added for a third sand milling process;

[0049] 5) After sand milling, discharge the material, filter it, clean it with solvent (preferably), and dry the material under vacuum or inert atmosphere to obtain the precursor.

[0050] 6) The precursor is calcined in an inert atmosphere.

[0051] The purpose of this invention can be achieved by following the methods described above. The methods of this invention are simple to operate and easy to mass-produce.

[0052] In this invention, the range of raw material quantity and conditions in step 1) is relatively wide. According to a preferred embodiment of this invention, in step 1), the mass fraction of micron-sized silicon powder in the suspension is 2-20%, preferably 5-15%.

[0053] According to a preferred embodiment of the present invention, the particle size of the micron-sized silicon powder is 1 to 20 micrometers, preferably 1 to 10 micrometers.

[0054] In this invention, the range of solvents that can be selected is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the solvent is a C2-C6 alcohol, preferably selected from at least one of ethanol, isopropanol and butanol.

[0055] In this invention, the range of selectable grinding conditions is relatively wide. The following is an illustrative description, but it does not limit the scope of this invention.

[0056] In this invention, the grinding conditions in steps 2) to 4) include: grinding is carried out in air or a protective gas atmosphere, preferably in a protective gas atmosphere.

[0057] According to a preferred embodiment of the present invention, the protective gas is preferably nitrogen and / or argon.

[0058] According to a preferred embodiment of the present invention, preferably, the amount of grinding beads in the nano-grinding mill is 70-95% of the apparent volume of the mill cavity, and more preferably 80-90%.

[0059] According to a preferred embodiment of the present invention, the diameter of the abrasive beads is preferably 0.1 to 1 mm, and more preferably 0.5 to 0.7 mm.

[0060] According to a preferred embodiment of the present invention, preferably, the sand mill is a nano-sand mill.

[0061] According to a preferred embodiment of the present invention, the grinding conditions of the first sand mill preferably include: a rotation speed of 2000 to 3000 rpm and a time of 0.25 to 1.5 h, preferably 0.5 to 1 h.

[0062] According to a preferred embodiment of the present invention, the grinding conditions of the second sand mill preferably include: a rotation speed of 2000-3000 rpm and a time of 2-8 hours, preferably 3-5 hours.

[0063] According to a preferred embodiment of the present invention, the grinding conditions of the third grinding mill preferably include: a rotation speed of 2000 to 3000 rpm; and a time of 0.25 to 1.5 h, preferably 0.5 to 1 h.

[0064] The aforementioned preferred sand milling implementation method has the advantages of high energy efficiency, simple operation, and flexibility.

[0065] The amount of graphite added in this invention can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, preferably, in step 3), the amount of graphite added is 50% to 200% of the silicon mass; more preferably, it is 50% to 100%. The aforementioned preferred embodiment has the advantage of making the nano-silicon wafers uniformly distributed in the graphite layer and on the surface without forming an excessively thick accumulation, effectively optimizing the volume expansion and cycle stability of the material.

[0066] The amount of conductive carbon black added in this invention can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, preferably, the amount of conductive carbon black added is 1% to 20% of the silicon mass; more preferably, it is 5% to 10%. The aforementioned preferred embodiment has the advantage of forming a point-to-surface conductive network with the flake graphite, effectively enhancing the conductivity of the material, and can isolate the nano-silicon wafers to a certain extent, avoiding electrochemical sintering.

[0067] The types of surface modifier sources described in this invention are relatively wide. The following is an illustrative example, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, preferably, in step 4), the surface modifier source is an organic compound containing a phosphate group, preferably an ester containing a phosphate group and / or an organic acid containing a phosphate group; more preferably, the organic compound containing a phosphate group is selected from at least one of phytic acid, phenylphosphonic acid, lecithin, and n-dodecyl phosphoric acid. Using the aforementioned preferred surface modifier sources has the advantage of forming stable chemical bonds with the surface of the silicon nanosheet, constructing a uniform, stable, dense, and inert coating layer.

[0068] In this invention, the range of optional amounts of the surface modifier source is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the amount of the surface modifier source added is preferably 2% to 10% of the mass of silicon powder based on phosphorus element, more preferably 2% to 5%. Using the aforementioned preferred amount has the advantage of obtaining an optimized coating thickness.

[0069] In this invention, the range of selectable conditions for vacuum or inert atmosphere drying is relatively wide. The purpose is to remove the solvent from the precursor material under an inert atmosphere to avoid excessive oxidation of the material during high-temperature calcination. According to a preferred embodiment of this invention, preferably, in step 5), the drying temperature is 70-120°C and the drying time is 5-24 hours.

[0070] In this invention, the range of selectable calcination conditions is relatively wide. The purpose is to carbonize the organic coating layer on the surface of the nano-silicon wafer and remove other organic matter remaining during the preparation process. According to a preferred embodiment of this invention, preferably, in step 6), the calcination conditions include: calcination is carried out under an inert atmosphere, wherein the inert atmosphere is nitrogen and / or argon.

[0071] According to a preferred embodiment of the present invention, the temperature is preferably increased to 700-1000°C at a heating rate of 2-10°C / min, and then maintained for 0.25-2 hours.

[0072] According to a preferred embodiment of the present invention, the mass fraction of micron-sized silicon powder in the suspension is 2-20%, preferably 5-15%; the particle size of the micron-sized silicon powder is 1-20 micrometers, preferably 1-10 micrometers.

[0073] According to a preferred embodiment of the present invention, the solvent is a C2-C6 alcohol, preferably selected from at least one of ethanol, isopropanol and butanol.

[0074] According to a preferred embodiment of the present invention, the ball milling is carried out in air or a protective gas atmosphere, preferably in a protective gas atmosphere;

[0075] According to a preferred embodiment of the present invention, the protective gas is preferably nitrogen and / or argon.

[0076] According to a preferred embodiment of the present invention, preferably, the sand milling is carried out in a sand mill, and the amount of grinding beads in the sand mill is 70-95% of the apparent volume of the sand mill cavity, preferably 80-90%.

[0077] According to a preferred embodiment of the present invention, the diameter of the abrasive beads is preferably 0.1 to 1 mm, and more preferably 0.1 to 0.6 mm.

[0078] According to a preferred embodiment of the present invention, preferably, the sand mill is a continuous stirring media ball mill.

[0079] According to a preferred embodiment of the present invention, the grinding conditions of the first stage of grinding preferably include: a rotation speed of 2000 to 3000 rpm; and a time of 0.25 to 1.5 h, preferably 0.5 to 1 h.

[0080] According to a preferred embodiment of the present invention, the grinding conditions of the second stage of grinding preferably include: a rotation speed of 2000-3000 rpm and a time of 2-8 hours, preferably 3-5 hours.

[0081] According to a preferred embodiment of the present invention, the grinding conditions of the third stage of grinding preferably include: a rotation speed of 2000 to 3000 rpm; and a time of 0.25 to 1.5 h, preferably 0.5 to 1 h.

[0082] According to a preferred embodiment of the present invention, the amount of graphite added is 50% to 200% of the mass of silicon; preferably 50% to 100%.

[0083] According to a preferred embodiment of the present invention, the amount of conductive carbon black added is 1% to 20% of the silicon mass; preferably 5% to 10%.

[0084] According to a preferred embodiment of the present invention, the surface modifier is an organic compound containing a phosphate group, preferably an ester containing a phosphate group and / or an organic acid containing a phosphate group; more preferably, the phosphorus-containing organic precursor is selected from at least one of phytic acid, phenylphosphonic acid, lecithin and n-dodecyl phosphoric acid.

[0085] According to a preferred embodiment of the present invention, the amount of the surface modifier added is 2% to 10% of the mass of the phosphorus element, preferably 2% to 5%, of the mass of the silicon powder.

[0086] According to a preferred embodiment of the present invention, the vacuum drying temperature is 70-120°C and the drying time is 5-24 hours.

[0087] According to a preferred embodiment of the present invention, the calcination conditions include: calcination is carried out under an inert atmosphere, wherein the inert atmosphere is nitrogen and / or argon.

[0088] According to a preferred embodiment of the present invention, preferably, the calcination temperature is 700-1000°C and the calcination time is 0.25-2h.

[0089] The aforementioned scope data of the present invention can all achieve the purpose of the present invention. The following embodiments are exemplary examples, but do not limit the scope of the present invention.

[0090] This invention provides the application of the nano-silicon material described herein in lithium-ion batteries.

[0091] The present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises the nano-silicon material described in the present invention.

[0092] The present invention will be described in detail below through embodiments. In the following embodiments, the thickness parameter of the silicon surface coating layer was measured by high-magnification transmission electron microscopy; the elemental content was measured by scanning electron microscopy-EDS; the thickness of the graphite sheet, the thickness of the nano-silicon wafer, and the spacing between adjacent stacked graphite sheets were measured by scanning electron microscopy; and the average diameter of the graphite sheet and the nano-silicon wafer was measured by X-ray diffraction.

[0093] The silicon powder raw material is from GCL New Energy's silicon furnace feedstock, with a purity of 99.999%. 50 The particle size is 5 micrometers;

[0094] The graphene was a self-made sample.

[0095] The artificial graphite is a commercially available product from Luoyang Yuexing Company, brand name GS16S.

[0096] In this invention, the thickness and average diameter of the graphite sheet, the thickness and average diameter of the nano-silicon wafer, and the thickness of the surface modification layer are obtained by observation and measurement based on SEM and TEM images.

[0097] Example 1

[0098] I: 80g of micronized silicon (d 50 Add the 5-micron diameter beads to 1520g of ethanol solvent and stir until homogeneous. Add the above suspension to a nano-mill with grinding beads of 0.5-0.7mm diameter and a filling rate of 90%. Mill at 2500rpm for 1 hour under an argon atmosphere.

[0099] II: Add 60g of graphene and 4g of conductive acetylene black to the silanol suspension, and continue to grind at 2500rpm for 3 hours.

[0100] III: Add phytic acid solution (P / Si ratio of 4.2%) and continue milling at 2500 rpm for 1 hour.

[0101] IV: After sand milling, all slurries were filtered and washed three times with ethanol. After filtration, the obtained material was dried under vacuum at 80°C for 12 hours. Finally, the dried silicon-carbon precursor was heated to 800°C at a heating rate of 5°C / min under an argon atmosphere and calcined for 30 minutes. After natural cooling, silicon-carbon material 1 was obtained. The results are shown in Table 1.

[0102] The following example provides XRD characterization of the silicon-carbon material, raw material micron-sized silicon, graphene, and nano-silicon wafers prepared according to the method of Example 1, except that graphene and conductive acetylene black are not added. Figure 1 As shown, graphite peaks and silicon diffraction peaks are clearly observed. Compared to the raw graphene, the broad diffraction peak at 18.2° in the silicon-carbon material is almost unobservable, and the peak height at 26.4° is significantly reduced, indicating that the sheet size of graphene decreases during the sand milling process, mainly due to the breakage of amorphous regions. Comparing silicon-carbon material 1 and nano-silicon wafers with micron-sized silicon, it can be found that after sand milling, the diffraction peaks of micron-sized silicon decrease at their highest points, while the full width at half maximum (FWHM) increases, indicating an increase in amorphous regions within the silicon.

[0103] Analysis of silicon nanosheets in silicon-carbon materials using scanning electron microscopy and transmission electron microscopy, such as... Figures 2-6 As shown, the thickness and elemental content of the coating layer on the surface of the nano-silicon wafer can be obtained.

[0104] Figures 2-3 The image shown is a SEM image of the silicon-carbon material of Embodiment 1 of the present invention. Compared to the tightly stacked graphite sheets of the raw material graphene used (SEM image as shown...), Figure 8 As shown), by Figure 2 and Figure 3It can be seen that the silicon nanosheets are mainly distributed between the graphene sheets, with only a small number of silicon nanosheets on the surface of large graphene sheets. The thickness of the graphene sheets is about 4 nm, the average diameter and average spacing of the graphene sheets are about 18 μm, and the spacing between adjacent stacked graphene sheets is about 150 nm. Figure 4 This is a SEM image of the silicon nanosheets in the silicon-carbon material of Example 1. As can be seen from the image, the prepared silicon particles are in sheet form, and the thickness of the silicon nanosheets is about 21 nm. Figure 5 This is a TEM image of the silicon-carbon material containing nano-silicon wafers in Example 1 of the present invention. Figure 5 It can be seen that the average diameter of the prepared silicon nanowafer is 186 nm; Figure 6 This is an HRTEM image of the nano-silicon wafer in the silicon-carbon material of Example 1 of the present invention, by... Figure 6 It can be seen that the thickness of the coating layer on the surface of the nano-silicon wafer is 6.5 nm; Figure 7 This is a SEM-EDS image of the nano-silicon wafers in the silicon-carbon material of Example 1 of this invention. Figure 7 It can be seen that C, O, and P elements are uniformly distributed on the surface of the nano-silicon wafer, with phosphorus content of 2.5 wt%, oxygen content of 24 wt%, and carbon content of 32 wt%.

[0105] test

[0106] The electrochemical performance of the prepared silicon-carbon material was tested using the following methods:

[0107] The negative electrode was a mixture of silicon carbide material, acetylene black, sodium carboxymethyl cellulose, polyacrylic acid (J&K 25% aqueous solution, MW240000, Lot: LJ60T60), and styrene-butadiene rubber (Shanghai Sixin Industrial Co., Ltd., LB-422) (mass ratio 80:10:10 / 3:10 / 3:10 / 3), the positive electrode was a lithium metal sheet, the electrolyte was a 1 mol / L LiPF6 mixed solution of ethyl carbonate, methyl ethyl carbonate, and dimethyl carbonate (volume ratio 1:1:1), and the separator was a lithium-ion battery PE separator. The CR2025 button cell was assembled and its electrochemical performance was characterized.

[0108] The electrochemical performance of CR2025 button batteries at 0.1C rate (1C = 1800 mAh / g) and their cycle stability at 0.5C rate were determined.

[0109] The results showed that the prepared silicon-carbon material 1 had a delithiation capacity of 1830 mAh / g at 0.1C rate with an initial efficiency of 82%, and the capacity retention rate was still greater than 90% after 300 cycles at 0.5C rate.

[0110] It can be seen that the silicon-carbon material of the present invention has high specific capacity and excellent charge-discharge cycle stability when applied to lithium-ion batteries.

[0111] Example 2

[0112] The method is the same as in Example 1, except that artificial graphite is used instead of graphene.

[0113] The tests were conducted in the same manner as in Example 1. The test results are similar to those in Example 1, and the results are shown in Table 1.

[0114] The results showed that the prepared silicon-carbon material 2 had a delithiation capacity of 1723 mAh / g at 0.1C rate, with an initial efficiency of 81%, and the capacity retention rate was still greater than 80% after 180 cycles at 0.5C rate.

[0115] Example 3

[0116] The method was the same as in Example 1, except that the amount of phytic acid added was 2.0% P / Si ratio. The test results were similar to those in Example 1.

[0117] The tests were conducted in the same manner as in Example 1. The test results are similar to those in Example 1, and the results are shown in Table 1.

[0118] The results showed that the prepared silicon-carbon material 3 had a delithiation capacity of 1636 mAh / g at 0.1C rate, with an initial efficiency of 76%, and a capacity retention of more than 86% after 300 cycles at 0.5C rate.

[0119] Example 4

[0120] The method is the same as in Example 1, except that after milling the micron-sized silicon slurry for 15 minutes, graphene and conductive acetylene black are added, and milling is continued for 2 hours. Phytic acid is then added and milled for another 15 minutes.

[0121] The tests were conducted in the same manner as in Example 1. The test results are similar to those in Example 1, and the results are shown in Table 1.

[0122] The results showed that the prepared silicon-carbon material 4 had a delithiation capacity of 1421 mAh / g at 0.1C rate with an initial efficiency of 71%, but the capacity retention was less than 80% after 200 cycles at 0.5C rate.

[0123] Example 5

[0124] The method is the same as in Example 1, except that after milling the micron-sized silicon slurry for 15 minutes, graphene and conductive acetylene black are added, and milling is continued for 7 hours. After adding phytic acid, milling is continued for 1.5 hours.

[0125] The tests were conducted in the same manner as in Example 1. The test results are similar to those in Example 1, and the results are shown in Table 1.

[0126] The results showed that the prepared silicon-carbon material 5 had a delithiation capacity of 1768 mAh / g at 0.1C rate with an initial efficiency of 81%, but the capacity retention was less than 80% after 150 cycles at 0.5C rate.

[0127] Example 6

[0128] The method is the same as in Example 1, except that conductive acetylene black is not added in step II.

[0129] The tests were conducted in the same manner as in Example 1. The test results are similar to those in Example 1, and the results are shown in Table 1.

[0130] The results showed that the prepared silicon-carbon material 6 had a delithiation capacity of 1742 mAh / g at 0.1C rate with an initial efficiency of 85%, and a capacity retention of 81% after 300 cycles at 0.5C rate.

[0131] Example 7

[0132] The method is the same as in Example 1, except that step III is omitted.

[0133] The tests were conducted in the same manner as in Example 1. The test results are similar to those in Example 1, and the results are shown in Table 1.

[0134] The results showed that the prepared silicon-carbon material 7 had a delithiation capacity of 1573 mAh / g at 0.1C rate with an initial efficiency of 78%, and a capacity retention of less than 80% after 120 cycles at 0.5C rate.

[0135] Comparative Example 1

[0136] 80g of micron-sized silicon (d) 50 Add the 5-micron diameter beads to 1520g of ethanol solvent and stir until homogeneous. Add the above suspension to a nano-mill with grinding beads of 0.5-0.7mm diameter and a filling rate of 90%. Mill at 2500rpm for 4 hours under an argon atmosphere.

[0137] The nano-silicon wafer ethanol suspension obtained after sand milling was transferred to a mixing tank, and 60g of graphene and 4g of conductive acetylene black were added. The mixture was then mechanically stirred for 4 hours.

[0138] Add phytic acid solution (P / Si ratio of 4.2%) and mechanically stir for 8 hours.

[0139] The obtained slurry was filtered and washed three times with ethanol. After filtration, the material was dried under vacuum at 80°C for 12 hours. Finally, the dried silicon-carbon precursor was heated to 800°C at a heating rate of 5°C / min under an argon atmosphere and calcined for 30 minutes. After natural cooling, the silicon-carbon material was obtained.

[0140] The test was conducted in the same manner as in Example 1.

[0141] The results showed that the prepared comparative silicon-carbon material had a delithiation capacity of 1041 mAh / g at 0.1C rate with an initial efficiency of 71%, but the capacity retention was less than 80% after 50 cycles at 0.5C rate.

[0142] Table 1

[0143]

[0144] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A silicon-carbon material, characterized in that, The silicon-carbon material comprises multiple layers of graphite sheets and nano-silicon wafers between the graphite sheets, with the nano-silicon wafers distributed between the graphite sheet layers; the thickness of the graphite sheets is 4~12nm, and the average diameter spacing of the graphite sheets is 9~19µm; the thickness of the nano-silicon wafers is 15~40nm, and the average diameter spacing of the nano-silicon wafers is 150~300nm; the spacing between adjacent stacked graphite sheets is 100~300nm. The nano-silicon wafer comprises a single silicon core and a surface modification layer, wherein the surface modification layer contains carbon, oxygen, silicon, and phosphorus; the mass fraction of phosphorus in the surface modification layer of the nano-silicon wafer is 2.5-3%, the mass fraction of oxygen is 24-31%, and the mass fraction of carbon is 32-36%; the thickness of the surface modification layer of the nano-silicon wafer is 6.5-7 nm. The silicon-carbon material includes stacked graphite sheets, uniformly distributed nano-silicon wafers between the graphite sheet layers, and spherical conductive carbon black distributed between the silicon wafers. The graphite sheet material is graphene.

2. The silicon-carbon material according to claim 1, wherein, In the silicon-carbon material, graphite sheets account for 30-70% by mass, and nano-silicon wafers account for 30-70% by mass.

3. The silicon-carbon material according to claim 1, wherein, The conductive carbon black is one or more of acetylene black and Super P.

4. A method for preparing the silicon-carbon material according to any one of claims 1 to 3, characterized in that, The method includes the following steps: 1) Mix micron-sized silicon powder with a solvent to obtain a suspension; 2) The suspension is transferred to a nano-sand mill for the first sand milling; 3) Add graphite and conductive carbon black for a second grinding; 4) Add a nano-silicon wafer surface modifier source for a third sand milling process; 5) After sand milling, discharge the material, filter it, clean it with solvent, and dry the material under vacuum or inert atmosphere to obtain the precursor. 6) The precursor is calcined in an inert atmosphere; The amount of the surface modifier source added is 4.2% to 5% of the mass of silicon powder, based on phosphorus element. The grinding conditions for the first sand mill include: a rotation speed of 2000~3000 rpm; and a grinding time of 0.5~1h. The grinding conditions for the second sand mill include: a rotation speed of 2000~3000 rpm; and a grinding time of 3~5 hours. The grinding conditions for the third grinding mill include: a rotation speed of 2000~3000 rpm and a grinding time of 0.5~1h.

5. The preparation method according to claim 4, wherein, In step 1), the suspension contains, The mass fraction of micron-sized silicon powder is 2-20%; and / or The particle size of micron-sized silicon powder is 1~20 microns; The solvent is a C2-C6 alcohol.

6. The preparation method according to claim 5, wherein, In step 1), the suspension contains, The mass fraction of micron-sized silicon powder is 5-15%; and / or The particle size of micron-sized silicon powder is 1~10 microns; The solvent is selected from at least one of ethanol, isopropanol, and butanol.

7. The preparation method according to claim 4, wherein, In steps 2) through 4), the respective grinding conditions include: The grinding is carried out in air or a protective gas atmosphere; The amount of abrasive beads in a nano-grinding mill is 70-95% of the apparent volume of the mill cavity; The diameter of the abrasive beads is 0.1~1mm; The sand mill is a nano sand mill.

8. The preparation method according to claim 7, wherein, In steps 2) through 4), the respective grinding conditions include: The grinding is carried out under a protective gas atmosphere; The amount of grinding beads in the nano-grinding mill is 80-90% of the apparent volume of the mill cavity; The diameter of the abrasive beads is 0.5~0.7mm.

9. The preparation method according to claim 8, wherein, The protective gas is nitrogen and / or argon.

10. The preparation method according to claim 4, wherein, In step 3), The amount of graphite added is 50% to 200% of the mass of the micron-sized silicon powder; and / or The amount of conductive carbon black added is 1% to 20% of the mass of silicon.

11. The preparation method according to claim 10, wherein, In step 3), The amount of graphite added is 50% to 100% of the mass of the micron-sized silicon powder; and / or The amount of conductive carbon black added is 5% to 10% of the mass of silicon.

12. The preparation method according to claim 4, wherein, In step 4), The surface modifier source is an organic compound containing phosphate groups; and / or In step 5), the drying temperature is 70~120℃ and the drying time is 5~24 hours; and / or In step 6), the calcination conditions include: calcination is carried out under an inert atmosphere, wherein the inert atmosphere is nitrogen and / or argon.

13. The preparation method according to claim 12, wherein, In step 4), The surface modifier source is an ester containing a phosphate group and / or an organic acid containing a phosphate group.

14. The preparation method according to claim 13, wherein, The organic compound containing a phosphate group is selected from at least one of phytic acid, phenylphosphonic acid, lecithin, and n-dodecyl phosphate.

15. The application of the silicon-carbon material according to any one of claims 1 to 3 in a lithium-ion battery.

16. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises the silicon-carbon material as described in any one of claims 1 to 3.

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