Lithium ion battery and c-si material, preparation method and application thereof

Abstract

The application relates to the technical field of lithium ion batteries, and discloses a C-Si material, a preparation method and application thereof, and a lithium ion battery, wherein the material comprises graphite and double-coating layer nano silicon material distributed on the surface of the graphite; the particle size of the nano silicon material is 50-300 nm; the thickness of a first coating layer in the double-coating layer is 2-10 nm, and the first coating layer comprises carbon, oxygen and silicon; the thickness of a second coating layer in the double-coating layer is 5-20 nm, and the second coating layer mainly comprises carbon elements; and the double-coating layer nano silicon material distributed on the surface of the graphite is adhered to the graphite through the second coating layer. The nano silicon material provided by the application has large specific capacity, high initial coulomb efficiency and excellent cycle stability when applied in a lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of C-Si materials, specifically to a C-Si material, its preparation method and application, and lithium-ion batteries. Background Technology

[0002] Silicon anode materials are the most promising next-generation lithium-ion battery anode materials due to their nearly 10 times higher theoretical specific energy density (4200 mAh / g) compared to currently commercial graphite anodes (370 mAh / g), low operating voltage, abundant reserves, good biocompatibility, and environmental friendliness. However, the volume effect (300%–400%) of silicon anode materials during battery charge-discharge processes significantly reduces the cycle stability of the battery. Research has found that when silicon powder is refined to the nanoscale, the stress resistance of silicon materials to the phase interface increases, effectively preventing the fracture and pulverization of silicon anode materials. Furthermore, nanoscale silicon materials can effectively reduce the diffusion and transport paths of particles and electrons, reduce electrode polarization during charge-discharge processes, and increase the electrochemical performance of the electrode.

[0003] Currently, mainstream commercial silicon anode materials typically use nano-sized silicon particles combined with graphite-based anode materials. This involves coating the nano-silicon particles onto the surface of graphite using a polymeric carbon precursor, followed by high-temperature pyrolysis to form a silicon-carbon composite anode material entirely coated with carbon. However, the presence of a large amount of coated carbon has two main drawbacks. First, it limits the expansion space of the silicon particles; excessive expansion can easily cause the coating layer to crack and the active material to detach. Second, the inactive lithium intercalation of the coated carbon significantly reduces the material's initial coulombic efficiency. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art and provide a C-Si material, its preparation method, and its applications. The C-Si material provided by this invention, when applied in lithium-ion batteries, exhibits high initial coulombic efficiency and excellent charge-discharge cycle stability.

[0005] To achieve the aforementioned objective, the present invention provides a C-Si material comprising: graphite and a double-coated layer of nano-silicon material distributed on the surface of the graphite, wherein the particle size of the nano-silicon material is 50-300 nm.

[0006] The thickness of the first coating layer in the double coating layer is 2-10 nm, preferably 3-6 nm; the first coating layer includes carbon, oxygen, and silicon.

[0007] The thickness of the second coating layer in the double coating layer is 5–20 nm, preferably 10–18 nm; the second coating layer mainly comprises carbon elements; the double-coated nano-silicon material distributed on the graphite surface is adhered and bonded to the graphite through the second coating layer. This invention... Figure 1 A schematic diagram of the structure of the C-Si material of the present invention is provided as an example. Figure 2 This shows a schematic diagram of the structure of existing C-Si materials; by Figure 1 and Figure 2 In comparison, it can be seen that the carbon in the C-Si material of this invention is mainly coated on the surface of nano-silicon, while the graphite surface has almost no coating of pitch pyrolysis carbon; silicon-carbon materials prepared by conventional methods ( Figure 2 Graphite also has a carbon coating on its surface.

[0008] In this invention, the C-Si material mainly contains graphite. The graphite content is above 80% by weight.

[0009] In this invention, the particle size is obtained by laser particle size analyzer, and the test conditions include: using ethanol as solvent and laser shading of 4-5%.

[0010] In this invention, the coating thickness and composition were obtained by high-magnification transmission electron microscopy. The test conditions included: using a FEI Titan Cubed Themis G2 300 aberration-corrected transmission electron microscope, accelerating voltage 200KV, maximum magnification 1.1 million times, point resolution 0.25nm, and EDS detection line 0.1wt%.

[0011] In this invention, the scanning electron microscope (SEM) tests were performed using a JSM-7800F super-resolution field emission scanning electron microscope.

[0012] In this invention, the range of graphite types that can be selected is relatively wide. Commonly used graphite types 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 is one or more of artificial graphite and natural graphite.

[0013] In the first coating layer, the content of each element can be selected within a wide range. According to a preferred embodiment of the present invention, in the first coating layer, the mass fraction of oxygen element is 15-35%, preferably 25-35%; and the mass fraction of carbon element is 20-40%, preferably 21-29%.

[0014] The first coating layer may optionally include surface-modifying elements such as phosphorus. According to a preferred embodiment of the present invention, the first coating layer further includes phosphorus, wherein the mass fraction of phosphorus is 0.5-10%, preferably 1-3%.

[0015] According to a preferred embodiment of the present invention, the carbon in the second coating layer is carbon from pyrolysis of pitch. The aforementioned preferred embodiment enables uniform coating of the nano-silicon surface, alleviating stress concentration and breakage caused by volume expansion of silicon during lithiation. Furthermore, carbon material is formed in situ from the pitch between silicon and graphite during pyrolysis, increasing the stability of silicon on the graphite surface and effectively preventing electrochemical sintering of silicon during lithiation.

[0016] C-Si 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 C-Si materials is provided, comprising the following steps:

[0017] 1) The nano-silicon powder was mixed with a solvent and stirred to obtain the first suspension;

[0018] 2) Optionally, add a carbon-containing surface modifier source and continue stirring to mix evenly;

[0019] 3) After stirring, filter and wash with solvent, preferably 3 to 5 times, filter, and dry under vacuum or inert atmosphere to obtain the precursor of nano-silicon particles coated with the first coating layer;

[0020] 4) The nano-silicon particle precursor coated by the first coating layer is mixed with a solvent and stirred to obtain a second suspension;

[0021] 5) The second suspension is milled to disperse the nano-silicon particle precursor coated by the first coating layer in the solvent.

[0022] 6) Prepare an asphalt-solvent solution and add it to the second suspension dispersed in step 5), and continue to disperse by sand milling;

[0023] 7) After mixing graphite powder with solvent, add the slurry obtained in step 6), mix evenly, and then spray dry to obtain C-Si material precursor;

[0024] 8) The C-Si material precursor is calcined in an inert atmosphere in multiple stages;

[0025] The solvent in step 4) is insoluble in asphalt;

[0026] The solvent in step 6) can dissolve asphalt and is miscible with the solvent in step 4).

[0027] In this invention, the range of solvents that can be selected in step 1) is relatively wide. The following is an illustrative example, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the solvent is a mixture of water and ethanol, wherein the ethanol concentration is 0-70%, where 0 means that it is infinitely close to 0. Preferably, the ethanol concentration in the mixed solvent is 10-40 wt%. The aforementioned ranges can achieve the purpose of this invention. The examples are illustrative and cannot limit the scope of this invention.

[0028] In this invention, in step 1), the formulation of the first suspension can be selected from a wide range. Preferably, the mass fraction of nano-silicon powder in the first suspension is 2-30%, and more preferably 5-20%. All of the aforementioned ranges can achieve the purpose of this invention. The embodiments are illustrative examples and should not be construed as limiting the scope of this invention.

[0029] The types of carbon-containing surface modifier sources described in this invention are relatively wide, and commonly used carbon-containing surface modifiers can all be used in this invention. For this invention, it is preferred that the carbon-containing surface modifier source also contains other surface modification elements such as P. 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 2), the phosphorus-containing 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. Further, 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. All of the aforementioned substances can achieve the purpose of this invention. The examples are illustrative examples and do not limit the scope of this invention. In the examples of this invention, phytic acid is provided as an aqueous solution with a concentration of 40-60 wt% to illustrate the advantages of this invention, but it does not limit the scope of this invention.

[0030] In this invention, the amount of carbon-containing surface modifier source added can be selected from a wide range, and the specific amount is determined according to the required coating thickness and modification composition.

[0031] In this invention, any solvent that meets the foregoing requirements can be used in this invention. For this invention, in step 4), the solvent is preferably a C2-C6 alcohol and / or water, preferably selected from at least one of ethanol, isopropanol and butanol, and more preferably ethanol.

[0032] In this invention, in step 4), the formulation of the second suspension can be selected from a wide range. Preferably, the mass fraction of the nano-silicon particle precursor coated by the first coating layer in the second suspension is 2-20%, more preferably 5-15%, and even more preferably 5-8%. All of the above ranges can achieve the purpose of this invention. The embodiments are illustrative examples and should not be construed as limiting the scope of this invention.

[0033] In this invention, sand milling is a prior art technique, and there are no special requirements for the equipment and conditions used in it. The following is an illustrative description, but it does not limit the scope of this invention.

[0034] According to one embodiment of the present invention, the grinding conditions include: a rotation speed of 1000-3000 rpm, preferably 1500-2500 rpm; and a time of 0.25-3 h, preferably 0.5-2 h.

[0035] In this invention, in step 6), the mass fraction of asphalt in the asphalt-solvent solution can be selected within a wide range. For this invention, it is preferably 20% to 40%. All of the aforementioned ranges can achieve the purpose of this invention. The embodiments are illustrative examples and should not be construed as limiting the scope of this invention.

[0036] According to a preferred embodiment of the present invention, preferably, in step 6), the amount of asphalt added is 0.3 to 0.4 times the mass of nano-silicon. The aforementioned range can achieve the purpose of the present invention. The embodiments are exemplary and should not be construed as limiting the scope of the present invention. The aforementioned preferred embodiment can, on the one hand, combine the preferred mass fraction of asphalt in the asphalt-solvent solution to achieve the precipitation of asphalt in the nano-silicon suspension and coating the surface of nano-silicon; on the other hand, it can control the coating thickness of asphalt on the nano-silicon surface.

[0037] According to a preferred embodiment of the present invention, the solvent is preferably selected from one or more of NMP and tetrahydrofuran, preferably a mixture of NMP and tetrahydrofuran, wherein the content of any one of them is not less than 10% by weight, preferably not less than 40% by weight.

[0038] In this invention, step 7) aims to prepare a C-Si material precursor slurry. According to a preferred embodiment of the invention, preferably, in step 7), the amount of graphite added is 10 to 40 times the mass of the nano-silicon. The aforementioned range can achieve the objective of this invention. These examples are illustrative and should not be construed as limiting the scope of the invention. Using the aforementioned preferred embodiment, the specific capacity of the prepared C-Si material can be achieved in the range of 400 to 600 mAh / g. Within this range, it is more advantageous to achieve a good distribution and spacing of silicon on the graphite surface.

[0039] According to a preferred embodiment of the present invention, preferably, in step 7), a solvent is added to adjust the solid content of the slurry to 25-50%. The aforementioned range can achieve the purpose of the present invention. The embodiments are exemplary and should not be construed as limiting the scope of the present invention. The aforementioned preferred embodiment can adjust the viscosity of the slurry, which is beneficial to the spray drying process.

[0040] According to a preferred embodiment of the present invention, preferably, in step 7), the solvent is selected from C2-C6 alcohols and / or water, and more preferably from at least one of ethanol, isopropanol and butanol; the aforementioned preferred embodiment can achieve good dispersion of graphite.

[0041] In this invention, the range of selectable calcination conditions is relatively wide, and its purpose is to heat-treat the coating layer on the surface of nano-silicon. According to a preferred embodiment of this invention, preferably, in step 8), the multi-stage calcination step includes: heating at a heating rate of 10-20℃ / min for 20-40 min to 400-500℃, then heating at a heating rate of 1-10℃ / min for 50-100 min to 550-650℃, holding at the temperature for 1-3 h after the heating is completed, then heating at a heating rate of 4-8℃ / min for 20-50 min to 700-1000℃, holding at the temperature for 15-120 min after the heating is completed, and finally cooling naturally.

[0042] According to a preferred embodiment of the present invention, preferably, in step 8), the multi-stage roasting step includes: heating at a rate of 15°C / min for 20-40 minutes to 400-500°C, then heating at a rate of 2°C / min for 50-100 minutes to 550-650°C, holding at the temperature for 1-3 hours after the heating is completed, then heating at a rate of 5°C / min for 20-50 minutes to 700-1000°C, holding at the temperature for 15-120 minutes after the heating is completed, and finally cooling naturally.

[0043] This invention provides the application of the material described herein in lithium-ion batteries.

[0044] 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 C-Si material described in the present invention.

[0045] The C-Si material provided by this invention, when applied in lithium-ion batteries, exhibits high initial coulombic efficiency and excellent charge-discharge cycle stability.

[0046] The C-Si material preparation method provided by this invention is simple and conducive to large-scale industrial production.

[0047] The method of the present invention has the following advantages:

[0048] 1. By utilizing the precipitation of asphalt in a solvent, silicon is coated in situ without sintering. Graphite is then added for sintering, resulting in a more tightly bonded carbon layer formed by the in-situ sintering of graphite and asphalt. After pyrolysis, the carbonized asphalt coats the silicon surface, fixing the connection points with the graphite to the graphite surface, thus fixing the nano-silicon particles to the graphite surface. This avoids the fusion of silicon during the lithiation process.

[0049] 2. The method of the present invention significantly reduces the amount of pyrolytic carbon used for coating, and increases the material's initial efficiency and specific capacity.

[0050] 3. The first coating layer of the present invention self-assembles into bonds on the silicon surface, which is beneficial to the uniform coating of C on the silicon surface;

[0051] 4. Preferably, this invention adjusts the amount of asphalt added to completely coat the silicon surface, thereby increasing the interaction between silicon and graphite and making silicon evenly distributed on the graphite surface. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the structure of the C-Si material of the present invention;

[0053] Figure 2 This is a schematic diagram of the structure of existing C-Si materials;

[0054] Figure 3This is a TEM image of the material after pyrolysis of the first coating layer nano-silicon precursor prepared in Example 1 of this invention;

[0055] Figure 4 This is a TEM image of the material after the second coating layer coats the first coating layer nano-silicon precursor prepared in Example 1 of this invention after pyrolysis;

[0056] Figure 5 This is a SEM image of the C-Si material prepared in Example 1 of this invention;

[0057] Figure 6 This is a SEM image of the C-Si material prepared in Example 1 of this invention;

[0058] Figure 7 This is a SEM image of the C-Si material prepared in a comparative manner. Detailed Implementation

[0059] 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.

[0060] The present invention will be described in detail below through examples. In the following examples, the electrochemical performance and cycle stability of the battery were measured using a CT2001A Blue Battery Testing System; the graphite raw material was a commercially available product of Luoyang Yuexing Company with the grade G216; the silicon powder raw material was not limited, with a purity of 99% and a particle size of 100-200 nm.

[0061] Example 1

[0062] 1) Add 1.5 kg of nano-silicon powder (particle size: 100 nm ~ 200 nm) to a mixed solvent of 15 kg of ethanol and water in a mass ratio of 1:2, and stir until homogeneous.

[0063] 2) Slowly add 0.75 kg of 50% phytic acid aqueous solution and stir for 4 hours.

[0064] 3) After stirring, filter the slurry and wash the filter cake until neutral using a mixed solvent of ethanol and water in a mass ratio of 1:2. Place it in a vacuum drying oven at 80°C for more than 24 hours to obtain the nano-silicon precursor coated with the first coating layer.

[0065] 4) Take 80g of the nano-silicon precursor coated with the first coating layer and stir to mix with 1520g of ethanol solvent;

[0066] 5) After dispersing in a nano-sand mill for 30 minutes (2500 rpm), a nano-silicon precursor slurry with good dispersibility and coated with a first coating layer is obtained.

[0067] 6) Prepare a 30% solids content asphalt-NMP solution. Take 237g of the asphalt-NMP solution and add it dropwise to the nano-silicon precursor slurry coated with the first coating layer with good dispersibility. Continue to sand mill and disperse for 1 hour to obtain the nano-silicon material precursor coated with the first coating layer by the second coating layer.

[0068] 7) Add 1604g of graphite to 2000g of ethanol solvent, stir and mix evenly, then add the slurry from step 6), and stir and mix evenly. Dry and granulate by spray drying to obtain C-Si material precursor powder.

[0069] 8) The powder was placed in a nitrogen atmosphere and calcined using the following procedure: heating at a rate of 15℃ / min for 30 min, then heating at a rate of 2℃ / min for 80 min, holding at that temperature for 2 h, then heating at a rate of 5℃ / min for 36 min, holding at that temperature for 60 min, and finally cooling naturally. C-Si material was obtained after calcination.

[0070] Through high-magnification transmission electron microscopy images, such as Figure 3 The image shows the nano-silicon material coated with the first coating layer (obtained by pyrolyzing the material obtained in step 3 under the pyrolysis conditions in step 8). The results show that the thickness of the first coating layer is about 5.5 nm, with a phosphorus content of 2.7 wt%, an oxygen content of 25 wt%, and a carbon content of 29 wt%. Figure 4 The image shows a second coating layer covering a first coating layer of nano-silicon material (obtained by drying the material obtained in step 6 and then pyrolyzing it under the pyrolysis conditions in step 8). The second coating layer is about 14 nm thick, and dense amorphous carbon material can be observed.

[0071] C-Si materials were characterized using scanning electron microscopy, such as... Figure 5 and Figure 6 As shown, it can be observed that the spherical double-coated nano-silicon material is adhered to the surface of the graphite material through the second coating layer, and there is almost no graphite material coated with pitch pyrolysis carbon.

[0072] test

[0073] The electrochemical performance of the prepared C-Si material was tested using the following method:

[0074] The negative electrode was a mixture of C-Si 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.

[0075] The electrochemical performance of CR2025 button batteries at a rate of 0.1C (1C = 400 mAh / g) and their cycle stability at a rate of 0.5C were determined.

[0076] The results showed that the prepared C-Si material 1 had a delithiation capacity of 413.6 mAh / g at 0.1C rate, an initial coulombic efficiency of 90.1%, and a capacity retention of more than 90% after 300 cycles at 0.5C rate.

[0077] It can be seen that the C-Si material of the present invention exhibits high initial coulombic efficiency and excellent charge-discharge cycle stability when applied to lithium-ion batteries.

[0078] Example 2

[0079] Steps 1 to 3 are the same as in Example 1, except that 0.5 kg of phytic acid aqueous solution is added.

[0080] 4) Take 190g of the nano-silicon precursor coated with the first coating layer and stir to mix with 3610g of ethanol solvent.

[0081] 5) After dispersing in a nano-sand mill for 30 minutes (2000 rpm), a nano-silicon precursor slurry with good dispersibility and coated with a first coating layer is obtained.

[0082] 6) Prepare a 30% solids content asphalt-NMP solution. Take 316g of the asphalt-NMP solution and add it dropwise to the nano-silicon precursor slurry coated with the first coating layer with good dispersibility. Continue to disperse by sand milling for 1 hour.

[0083] 7) Add 5710g of graphite to 10000g of ethanol solvent, stir and mix evenly, then add the slurry from step 6), and stir and mix evenly. Dry and granulate by spray drying to obtain C-Si material precursor powder.

[0084] 8) The powder was placed in a nitrogen atmosphere and calcined using the following procedure: heating at a rate of 15℃ / min for 30 min, then heating at a rate of 2℃ / min for 80 min, holding at that temperature for 2 h, then heating at a rate of 5℃ / min for 36 min, holding at that temperature for 60 min, and finally cooling naturally. C-Si material 2 was obtained after calcination.

[0085] The results showed that the first coating layer was approximately 3.4 nm thick, containing 1.4 wt% phosphorus, 29 wt% oxygen, and 22 wt% carbon. The second coating layer was approximately 15 nm thick.

[0086] The test was conducted in the same manner as in Example 1.

[0087] The results showed that the prepared C-Si material 2 had a delithiation capacity of 428.5 mAh / g at 0.1C rate, an initial coulombic efficiency of 90.1%, and a capacity retention of more than 94% after 300 cycles at 0.5C rate.

[0088] Example 3

[0089] The method of Example 1 is the same, except that in step 4), 80g of the nano-silicon precursor coated with the first coating layer is taken and mixed with 760g of ethanol solvent.

[0090] The test was the same as in Example 1, and the product parameters are shown in Table 1.

[0091] The results showed that the prepared C-Si material 3 had a delithiation capacity of 404.3 mAh / g at 0.1C rate, an initial coulombic efficiency of 88.2%, and a capacity retention of more than 84% after 300 cycles at 0.5C rate.

[0092] Example 4

[0093] The method is the same as in Example 1, except that the solvent used in steps 4 and 7 is water.

[0094] The test was the same as in Example 1, and the product parameters are shown in Table 1.

[0095] The results showed that the prepared C-Si material 1 had a delithiation capacity of 387.2 mAh / g at 0.1C rate, an initial coulombic efficiency of 84%, and a capacity retention of more than 87% after 300 cycles at 0.5C rate.

[0096] Example 5

[0097] Steps 1 to 7 are the same as in Example 1.

[0098] 8) The obtained precursor powder was placed in a nitrogen atmosphere and calcined according to the following procedure: heating at a rate of 15℃ / min for 30 min, holding at that temperature for 240 min, then heating at a rate of 5℃ / min for 68 min, holding at that temperature for 60 min, and finally cooling naturally. After calcination, C-Si material 5 was obtained.

[0099] The test was the same as in Example 1, and the product parameters are shown in Table 1.

[0100] The results showed that the prepared C-Si material 5 had a delithiation capacity of 403.1 mAh / g at 0.1C rate, with an initial coulombic efficiency of only 84.2%, and the capacity retention decreased to 84% after 300 cycles at 0.5C rate.

[0101] Example 6

[0102] Same as in Example 1, except that the asphalt-NMP solution in the step is replaced with a mixture of asphalt-NMP-tetrahydrofuran, the amount of solvent remains the same, and the weight ratio of NMP:tetrahydrofuran is 1:1.

[0103] The results showed that the prepared C-Si material 5 had a delithiation capacity of 449.8 mAh / g at 0.1C rate, an initial coulombic efficiency of 90.5%, and a capacity retention of more than 95% after 300 cycles at 0.5C rate.

[0104] Table 1

[0105]

[0106] Comparative Example 1

[0107] Steps 1 to 5 are the same as in Example 1, except that NMP solvent is used to disperse the nano-silicon.

[0108] 6) Add 5.71 kg of graphite to 10 kg of NMP solvent, stir and mix evenly, then add the nano-silicon dispersion slurry from step 5), and stir and mix evenly.

[0109] 7) Prepare a 30% solids content asphalt-NMP solution. Take 632g of the asphalt-NMP solution and add it dropwise to the nano-silica precursor slurry coated with the first coating layer, which has good dispersibility. Continue stirring and dispersing for 10 hours. Dry and granulate by spray drying to obtain the comparative material precursor powder.

[0110] 8) The powder was calcined under a nitrogen atmosphere using the following procedure: heating at a rate of 15°C / min for 30 min, then heating at a rate of 2°C / min for 80 min, holding at that temperature for 2 h, then heating at a rate of 5°C / min for 36 min, holding at that temperature for 60 min, and finally cooling naturally. The comparative material was obtained after calcination.

[0111] The material of Comparative Example 1 was characterized by scanning electron microscopy, such as... Figure 7 It can be observed that a layer of pitch pyrolysis carbon coats the silicon material and graphite together.

[0112] The test was conducted in the same manner as in Example 1.

[0113] The results showed that the prepared Comparative Example 1 material had a delithiation capacity of 394.4 mAh / g at 0.1C rate, an initial coulombic efficiency of only 75.2%, and a capacity retention of 80% after 50 cycles at 0.5C rate.

[0114] It can be seen that the C-Si material of the present invention, when applied to lithium-ion batteries, exhibits higher initial coulombic efficiency and better charge-discharge cycle stability compared to the comparative example.

[0115] 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 C-Si material, characterized in that, The material comprises: graphite and double-coated nano-silicon material distributed on the surface of the graphite, the particle size of the nano-silicon material being 50-300 nm; The thickness of the first coating layer in the double coating layer is 2-10 nm; the first coating layer comprises carbon, oxygen and silicon; The thickness of the second coating layer in the double coating layer is 5-20 nm; the second coating layer comprises carbon elements; The double-coated nano-silicon material distributed on the surface of the graphite is adhered and connected to the graphite through the second coating layer.

2. The C-Si material according to claim 1, wherein, The thickness of the first coating layer in the double coating layer is 3-6 nm; The thickness of the second coating layer in the double coating layer is 10-18 nm.

3. The C-Si material according to claim 1, wherein, The graphite is one or more of artificial graphite and natural graphite; and / or In the first coating layer, the mass fraction of oxygen elements is 15-35%; the mass fraction of carbon elements is 20-40%; and / or The first coating layer further comprises phosphorus, and the mass fraction of phosphorus elements is 0.5-10%; And / or The carbon in the second coating layer is pitch pyrolytic carbon.

4. The C-Si material according to claim 3, wherein, In the first coating layer, the mass fraction of oxygen elements is 25-35%; the mass fraction of carbon elements is 21-29%; And / or The first coating layer further comprises phosphorus, and the mass fraction of phosphorus elements is 1-3%.

5. A method of producing a C-Si material, characterized by, The method comprises the following steps: 1) mixing and stirring nano-silicon powder with a solvent to obtain a first suspension; 2) adding a carbon-containing surface modifier source and continuing to stir and mix uniformly; 3) after stirring is completed, filtering and cleaning with a solvent, filtering, drying in a vacuum or inert atmosphere to obtain a first coating layer coated nano-silicon particle precursor; 4) mixing the first coating layer coated nano-silicon particle precursor with a solvent and stirring to obtain a second suspension; 5) sanding and dispersing the second suspension; 6) configuring a pitch-solvent solution and adding the dispersed second suspension of step 5) for sanding and dispersing; 7) mixing graphite powder with a solvent, adding the slurry obtained in step 6), mixing uniformly and then performing spray drying to obtain a C-Si material precursor; 8) calcining the C-Si material precursor in multiple stages in an inert atmosphere; The solvent in step 4) is insoluble in pitch; The solvent in step 6) can dissolve pitch and is miscible with the solvent of step 4).

6. The method of claim 5, wherein, In step 1), The solvent is a mixed solvent of water and ethanol, wherein the ethanol concentration is 0-70 wt%; and / or The mass fraction of nano-silicon powder in the first suspension is 2-30%.

7. The method of claim 6, wherein, In step 1), The solvent is a mixed solvent of water and ethanol, wherein the ethanol concentration is 10-40 wt%; and / or The mass fraction of nano-silicon powder in the first suspension is 5-20%.

8. The method of claim 5, wherein, In step 2), The carbon-containing surface modifier source is an organic matter containing phosphoric acid groups.

9. The method of claim 8, wherein, In step 2), The carbon-containing surface modifier source is an ester containing phosphoric acid groups and / or an organic acid containing phosphoric acid groups.

10. The method of claim 8, wherein, In step 2), The organic matter containing phosphoric acid groups is selected from at least one of phytic acid, phenylphosphonic acid, lecithin and n-dodecyl phosphoric acid.

11. The method of claim 10, wherein, In step 2), Phytic acid is provided in the form of an aqueous solution with a concentration of 40-60 wt%.

12. The method of claim 5, wherein, In step 4), the solvent is a C2-C6 alcohol and / or water; and / or The mass fraction of the first coated nano-silicon particle precursor in the second suspension is 2-20%.

13. The method of claim 12, wherein, In step 4), the solvent is at least one of ethanol, isopropanol and butanol; and / or The mass fraction of the first coated nano-silicon particle precursor in the second suspension is 5-15%.

14. The method of claim 13, wherein, In step 4), the solvent is ethanol; and / or The mass fraction of the first coated nano-silicon particle precursor in the second suspension is 5-8%.

15. The method of claim 5, wherein, In step 5), the sanding conditions include: a rotation speed of 1000-3000 rpm; and a time of 0.25-3 h.

16. The method of claim 15, wherein, In step 5), the sanding conditions include: a rotation speed of 1500-2500 rpm; and a time of 0.5-2 h.

17. The method of claim 5, wherein, In step 6), the mass fraction of the asphalt in the asphalt-solvent solution is 20-40%; and / or The amount of asphalt added is 0.3-0.9 times the mass of the nano-silicon powder; and / or The solvent is selected from one or more of NMP and tetrahydrofuran; and / or In step 7), The amount of graphite added is 10-40 times the mass of the nano-silicon powder; and / or The solvent is selected from a C2-C6 alcohol and / or water; and / or In step 8), the multi-stage calcination step includes: The multi-stage calcination step includes: heating at a rate of 10-20℃ / min for 20-40 min to 400-500℃, then heating at a rate of 1-10℃ / min for 50-100 min to 550-650℃, holding for 1-3 h after the heating is completed, then heating at a rate of 4-8℃ / min for 20-50 min to 700-1000℃, holding for 15-120 min after the heating is completed, and finally naturally cooling. In step 6), 18. The method of claim 17, wherein, The solvent is selected from a mixture of NMP and tetrahydrofuran, wherein the content of any one is not less than 10% by weight; and / or In step 7), The solvent is selected from at least one of ethanol, isopropanol and butanol. In step 6), 19. The method of claim 18, wherein, The solvent is selected from a mixture of NMP and tetrahydrofuran, wherein the content of any one is not less than 40% by weight.

20. Use of the material of any one of claims 1-4 in a lithium ion battery. A lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises the C-Si material of any one of claims 1-4.

21. A lithium-ion battery, characterized by, ​

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