A lithium ion battery anode material of a silicon particle encapsulated by a coupled graphene structure and a preparation method thereof

Abstract

The application provides a lithium ion battery negative electrode material of a graphene structure coupled encapsulating silicon particles and a preparation method thereof, and belongs to the field of new energy materials and energy storage technology. The preparation route of the electrode material is as follows: firstly, a plane graphene layer is deposited on the surface of silicon particles by using a chemical vapor deposition method, and then vertical graphene is grown on the surface of the plane graphene layer. Subsequently, a required gap is formed in the material by partially etching the silicon core through a chemical etching method, so that the vertical graphene-plane graphene coupled structure encapsulating the silicon particles is obtained. In the application, the vertical graphene is epitaxially grown at the defects of the plane graphene, a vertical graphene-plane graphene coupled structure with seamless connection and no obvious interface separation is formed, and excellent mechanical stability is given to the material; the gap formed in the vertical graphene-plane graphene coupled structure through the chemical etching treatment can effectively relieve the volume expansion problem of silicon.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular, to a lithium ion battery negative electrode material with silicon particles encapsulated by a coupled graphene structure and a preparation method thereof. BACKGROUND

[0002] Currently, graphite is still the most commonly used negative electrode material for commercial lithium ion batteries, but its theoretical capacity (372 mAh g -1 ) is low, which has been difficult to meet the needs of high energy density and fast charging. Silicon is widely considered as an ideal candidate for the next generation of negative electrode materials due to its extremely high theoretical specific capacity (about 4200 mAh g -1 ). However, silicon expands by 300%~400% during lithiation, which easily leads to particle pulverization, repeated rupture of SEI film and electrode failure, resulting in rapid capacity decay.

[0003] Current main solutions include: (1) nano-structuring of silicon, such as nanoparticles, porous structures, etc., to alleviate volume expansion, but there are problems such as complex preparation, high cost, serious agglomeration and low volumetric energy density; (2) silicon-carbon composite structure, which improves the conductivity and buffers the volume change through carbon materials, including amorphous carbon, carbon nanotubes, graphene, etc. Such structural design improves the rate performance and cycle stability of silicon-carbon negative electrode to some extent. However, due to the lack of space for silicon expansion, such structure is difficult to maintain stability under long-term cycling. (3) Silicon-carbon composite structure with built-in space, which provides the required space for silicon volume expansion by encapsulating silicon particles in a carbon coating layer with built-in space. Such structural design further improves the cycle stability of silicon-carbon negative electrode, but the existing carbon encapsulation structure is difficult to withstand the huge stress and strain caused by silicon volume expansion due to its intrinsic defects or structural defects in the preparation process, making it difficult to ensure the stability of silicon-carbon negative electrode material during long-term cycling. SUMMARY

[0004] The present application provides a novel lithium ion battery negative electrode material, a composite material with silicon particles encapsulated by a coupled vertical graphene and planar graphene structure. First, a planar graphene layer is deposited on the surface of silicon particles using chemical vapor deposition technology, then vertical graphene is grown on the surface of the planar graphene layer by epitaxial growth, thereby constructing a vertical graphene-planar graphene composite shell layer, and finally, a gap is constructed inside the composite material by partially etching the silicon particles through chemical etching, thereby obtaining a composite material with silicon particles encapsulated by a coupled vertical graphene and planar graphene structure.

[0005] To achieve the above-mentioned application purposes, the present application develops the following technical solutions:

[0006] A preparation method of a lithium ion battery negative electrode material encapsulating silicon particles with a coupled graphene structure, comprising the following steps:

[0007] S1, depositing a planar graphene layer on the surface of the silicon particles by a chemical vapor deposition method

[0008] S2, growing vertical graphene on the surface of the planar graphene by a chemical vapor deposition method, thereby obtaining a planar graphene-vertical graphene coupled structure

[0009] S3, partially removing the silicon core using a chemical etching method, thereby introducing voids inside the negative electrode material, and obtaining the negative electrode material.

[0010] Preferably, the growth temperature of the planar graphene layer and the vertical graphene is 400-1100°C.

[0011] Preferably, the carbon source used for preparing the planar graphene or the vertical graphene coupled structure in S1 or S2 is one of acetylene, methane, and ethanol.

[0012] Preferably, the auxiliary atmosphere used for preparing the planar graphene layer or the vertical graphene in S1 or S2 is one or more of argon, nitrogen, carbon monoxide, carbon dioxide, and hydrogen.

[0013] Preferably, the chemical etching reagent in the etching process in S3 is one or more of sodium hydroxide, ammonia, and potassium hydroxide.

[0014] Preferably, the negative electrode material can be used in a liquid electrolyte-based lithium ion battery or a solid electrolyte-based lithium ion battery.

[0015] A lithium ion battery negative electrode material encapsulating silicon particles with a coupled graphene structure, characterized in that the structure of the negative electrode material sequentially from inside to outside is silicon particles, planar graphene, and vertical graphene.

[0016] Preferably, the size of the silicon particles is 50 nm-10 μm.

[0017] Preferably, the thickness of the planar graphene layer is 2-200 nm.

[0018] Preferably, the growth direction of the vertical graphene is perpendicular to the planar graphene, the height of the vertical graphene is 5-400 nm, and the number of layers decreases along the growth direction.

[0019] Preferably, the coupled structure of the vertical graphene and the planar graphene completely encapsulates the silicon particles.

[0020] The patent application has the following beneficial effects compared with the prior art:

[0021] 1. The composite material in the present application can buffer the volume expansion of silicon during silicon lithiation on one hand, avoiding the serious damage of silicon expansion to the carbon shell, and can stitch the defects of planar graphene by means of vertical graphene epitaxial growth on the other hand, enhancing the mechanical properties of planar graphene, thus endowing the vertical graphene-planar graphene composite shell with excellent mechanical stability. In addition, the excellent conductive network of vertical graphene-planar graphene can promote the rapid transmission of electrons and lithium ions, thus realizing the coordination and unity of high capacity, high rate performance and good cycle stability.

[0022] 2. The advantage of depositing planar graphene on the surface of silicon particles by CVD method is that, compared with the amorphous carbon layer obtained by pyrolyzing carbon source in argon or nitrogen gas, the graphene shell with obvious layered structure can be obtained by pyrolyzing carbon source in the weak oxidation atmosphere of carbon dioxide. In addition, the planar graphene layer obtained in the weak oxidation etching atmosphere of carbon dioxide has obvious defect sites, which is beneficial for the subsequent epitaxial growth of vertical graphene on these defects as nucleation sites, so as to stitch the planar graphene and vertical graphene into a strong and tough overall structure in the form of covalent bond.

[0023] 3. The advantage of setting the flow rate ratio of CO2 to carbon source gas (methane, acetylene and ethanol) to be less than 1 / 1 is that it is more conducive to the deposition of planar graphene when the flow rate ratio is less than 1 / 1. Once the flow rate ratio is greater than 1 / 1, on one hand, it will accelerate the oxidation of silicon by CO2 at high temperature, and on the other hand, it will make the planar graphene unable to be uniformly deposited.

[0024] 4. The advantage of setting the CVD temperature for depositing planar graphene to be above 800 degrees is that it is beneficial for the carbon source gas (methane, acetylene and ethanol, etc.) to be fully decomposed by heat, and more conducive to the efficient deposition of planar graphene under the induction of CO2.

[0025] 5. The advantage of planar graphene is that the presence of planar graphene can effectively encapsulate the internal silicon particles, and the relatively complete encapsulation structure can avoid the direct contact of electrolyte with silicon particles, thus avoiding the occurrence of interface side reactions. In addition, silicon expansion is easy to cause the rupture of amorphous carbon shell, while the interlayer slip of graphene sheet layer can alleviate the damage of silicon expansion to the shell. Furthermore, planar graphene provides a matrix for the growth of vertical graphene.

[0026] 6. The advantage of using epitaxial growth to couple planar graphene and vertical graphene is that, compared with traditional multi-level carbon coating methods, which lack strong interlayer interactions between multi-level carbon layers, epitaxial growth allows vertical graphene to use the defects of planar graphene as nucleation sites, effectively stitching the defects of planar graphene together through carbon-carbon covalent bonds, thereby enhancing the mechanical stability of the graphene capsule and thus enhancing its resistance to stress and strain during lithiation.

[0027] 7. The advantage of using alkaline reagents for the silicon particles inside graphene capsules is that, compared to traditional silicon-carbon materials, which typically use highly dangerous and corrosive HF to etch a sacrificial layer on the silicon surface when preparing internal pores, the use of low-risk alkaline reagents can effectively adjust the etching effect on silicon particles by adjusting their concentration, reaction temperature, and reaction time. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a TEM image of the planar graphene layer deposited on the surface of silicon particles in Example 1.

[0030] Figure 2 TEM image of the composite material of silicon particles encapsulated by the vertical graphene and planar graphene coupling structure in Example 1;

[0031] Figure 3 The image shows the XRD pattern of the composite material of silicon particles encapsulated by the vertical graphene and planar graphene coupling structure in Example 1.

[0032] Figure 4 The first charge-discharge curve of the silicon-carbon anode material prepared in Example 1;

[0033] Figure 5 The cycling performance of the silicon-carbon anode material prepared in Example 1;

[0034] Figure 6 Rate performance of the silicon-carbon anode material prepared in Example 1 Detailed Implementation

[0035] The embodiments of the present application will be described in detail below with examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions not noted in the examples are carried out under the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not noted by the manufacturer, which are all conventional products that can be obtained by market purchase.

[0036] Example 1:

[0037] A preparation method of a lithium ion battery anode material coupling a graphene structure to encapsulate silicon particles, comprising the following steps:

[0038] S1, depositing a planar graphene layer on the surface of silicon particles by chemical vapor deposition method

[0039] 100g of silicon particles with a size of 20 microns were placed in a tube furnace, heated to 900 °C at a heating rate of 10 °C / min under an argon atmosphere. Then the argon was turned off, CO2 was continuously introduced at a flow rate of 20 mL / min, and the temperature of the tube furnace was raised to 1000 °C within 15 minutes to pretreat the silicon particles. When the temperature of the tube furnace reached 1000 °C, CH4 was introduced at a flow rate of 50 mL / min; and when the temperature of the tube furnace reached 1000 °C, the flow rate of CO2 was increased to 40 mL / min, and the reaction was maintained for 15 minutes, thereby coating a planar graphene layer on the surface of the silicon particles.

[0040] S2, growing vertical graphene on the surface of the planar graphene by chemical vapor deposition method, thereby obtaining a planar graphene-vertical graphene coupling structure

[0041] The CO2 and CH4 were turned off, argon was introduced into the tube furnace at a flow rate of 40 mL / min, and the temperature of the tube furnace was raised to 1100 °C within 15 minutes. Then the argon was turned off, a mixed gas of CH4 and H2 was introduced into the tube furnace at a flow rate of 50 mL / min each, and the reaction was continued for 2 hours. After the reaction was completed, the mixed gas was turned off, and argon was continuously introduced into the tube furnace, and the tube furnace was naturally cooled under an argon atmosphere, thereby growing vertical graphene on the surface of the planar graphene in situ to form a planar graphene-vertical graphene coupling structure.

[0042] S3, using a chemical etching method to partially remove the silicon core, thereby introducing voids inside the anode material, to obtain an anode material.

[0043] The planar graphene-vertical graphene coupling structure obtained in S2 was immersed in a 1 M NaOH solution, heated at 70 °C for 20 minutes, then washed and dried to obtain the final anode material.

[0044] Figure 1 For the TEM image of the planar graphene layer deposited on the surface of the silicon particles, it can be seen that the graphene is uniformly deposited on the surface of the silicon particles, and the number of layers is about 5. At the same time, it can be seen that there are a large number of discontinuous defects in the deposited graphene layer. In addition, the (111) crystal plane of silicon can also be observed, and the corresponding interlayer spacing is 0.313 nm. Figure 2 For TEM characterization of the composite material of the vertical graphene and planar graphene coupling structure encapsulating the silicon particles, the structure of the silicon particles from the inside out, the internal gap, the planar graphene and the vertical graphene can be clearly seen. Figure 2 a). From Figure 2 b can be seen that the vertical graphene epitaxially grows vertically from the defects of the planar graphene, effectively filling the defects of the planar graphene. Figure 2 c shows that the vertical graphene presents a trend of decreasing number of layers along the growth direction. SAED Figure 2 d) and XRD Figure 3 characterization clearly shows the (111), (220) and (311) crystal planes of silicon. EDS images further confirm the structural characteristics of the composite material of the vertical graphene and planar graphene coupling structure encapsulating the silicon particles (e-g). Figure 2 Figure 4 For the first charge-discharge curve of the obtained composite material of the vertical graphene and planar graphene coupling structure encapsulating the silicon particles at 0.1C, it can be seen that the first charge capacity of the negative electrode material is 2077.6 mAh / g, and the first coulombic efficiency is 87%. After 500 cycles at 1C, the capacity retention rate is still as high as 78.6%, as shown in Figure 5 . Figure 6 For the rate performance of the negative electrode material, the specific capacity of the negative electrode material at 0.1, 0.2, 0.5, 1, 2, 3 and 5C is 2064.4, 1953.5, 1799.6, 1634.6, 1456.4, 1253.5, 944.0 and 692.3 mAh / g, respectively.

[0045] Example 2:

[0046] A preparation method of a lithium ion battery negative electrode material encapsulating silicon particles by a coupling graphene structure, comprising the following steps:

[0047] S1, depositing a planar graphene layer on the surface of the silicon particles by a chemical vapor deposition method

[0048] ​Put 10 g of silicon particles with a size of 50 microns into a tube furnace, heat to 800 °C at a heating rate of 10 °C / min under a nitrogen atmosphere. Then, shut off the nitrogen, continuously pass in CO2 at a flow rate of 30 mL / min, and increase the temperature of the tube furnace to 900 °C within 20 minutes to pretreat the silicon particles. When the temperature of the tube furnace reaches 900 °C, pass in CH4 at a flow rate of 60 mL / min; and when the temperature of the tube furnace reaches 900 °C, maintain the flow rate of CO2 at 30 mL / min, and maintain the reaction for 10 minutes to coat the silicon particles with a planar graphene layer.

[0049] S2, growing vertical graphene on the planar graphene surface by a chemical vapor deposition method to obtain a planar graphene-vertical graphene coupled structure

[0050] Shut off the CO2 and CH4, pass in nitrogen into the tube furnace at a flow rate of 60 mL / min, and increase the temperature of the tube furnace to 1100 °C within 30 minutes. Then, shut off the nitrogen, pass in a mixed gas of CH4 and H2 into the tube furnace, and maintain the reaction for 2 hours, wherein the flow rate of CH4 is 20 mL / min, and the flow rate of H2 is 80 mL / min; after the reaction ends, shut off the mixed gas, continue to pass in nitrogen into the tube furnace, and naturally cool the tube furnace under a nitrogen atmosphere to grow vertical graphene on the planar graphene surface in situ to form a planar graphene-vertical graphene coupled structure.

[0051] S3, partially removing the silicon core by using a chemical etching method to introduce voids into the negative electrode material, and obtaining the negative electrode material.

[0052] Immersion of the planar graphene-vertical graphene coupled structure obtained in S2 into a 1 M NaOH solution, reaction at room temperature for 5 hours, then washing and drying to obtain the final negative electrode material.

[0053] The negative electrode material of the planar graphene-vertical graphene coupled structure encapsulating the silicon particles has a first charge capacity of 1955.3 mAh / g at 0.1C, and a first coulombic efficiency of 85%. After 500 cycles at 1C, the capacity retention rate is 75.2%. The rate capacity of the negative electrode material at 0.1, 0.2, 0.5, 1, 2, 3 and 5C is 1955.4, 1902.5, 1696.3, 1592.1, 1396.8, 1193.5, 882.3 and 622.6 mAh / g, respectively.

[0054] Example 3:

[0055] A preparation method of a lithium ion battery negative electrode material of a coupled graphene structure encapsulating silicon particles, comprising the following steps:

[0056] S1, depositing a planar graphene layer on the surface of silicon particles by chemical vapor deposition method

[0057] 50 g of silicon particles with a size of 10 microns were placed in a tube furnace and heated to 900 °C at a heating rate of 10 °C / min under an argon atmosphere. Subsequently, the argon was turned off, CO2 was continuously introduced at a flow rate of 20 mL / min, and the temperature of the tube furnace was increased to 1000 °C within 15 minutes to pretreat the silicon particles. When the temperature of the tube furnace reached 1000 °C, ethanol vapor was introduced at a flow rate of 50 mL / min; and when the temperature of the tube furnace reached 1000 °C, the flow rate of CO2 was increased to 40 mL / min, and the reaction was maintained for 5 minutes, thereby coating a planar graphene layer on the surface of the silicon particles.

[0058] S2, growing vertical graphene on the surface of the planar graphene by a chemical vapor deposition method, thereby obtaining a planar graphene-vertical graphene coupled structure

[0059] The CO2 and ethanol vapor were turned off, argon was introduced into the tube furnace at a flow rate of 40 mL / min, and the temperature of the tube furnace was increased to 1100 °C within 15 minutes. Subsequently, the argon was turned off, a mixed gas of ethanol vapor and H2 was introduced into the tube furnace at a flow rate of 10 mL / min each, and the reaction was maintained for 4 hours; after the reaction was completed, the mixed gas was turned off, and argon was continuously introduced into the tube furnace, and the tube furnace was naturally cooled under an argon atmosphere, thereby growing vertical graphene on the surface of the planar graphene in situ to form a planar graphene-vertical graphene coupled structure.

[0060] S3, partially removing the silicon core using a chemical etching method, thereby introducing voids into the negative electrode material, to obtain a negative electrode material.

[0061] The planar graphene-vertical graphene coupled structure obtained in S2 was immersed in a 1 M ammonia solution and heated at 80 °C for 10 minutes, and then washed and dried to obtain a final negative electrode material.

[0062] The negative electrode material of the planar graphene-vertical graphene coupled structure encapsulating the silicon particles had a first charge capacity of 2161.5 mAh / g at 0.1C, and a first coulombic efficiency of 82%. After 500 cycles at 1C, the capacity retention rate was still as high as 72.6%. The rate capacity of this negative electrode material at 0.1, 0.2, 0.5, 1, 2, 3, and 5C was 2160.1, 1973.9, 1820.5, 1737.6, 1557.1, 1362.5, 1041.0, and 722.7 mAh / g, respectively.

[0063] Example 4:

[0064] A preparation method of a lithium ion battery anode material coupling a graphene structure to encapsulate silicon particles, comprising the following steps:

[0065] S1, depositing a planar graphene layer on the surface of silicon particles by a chemical vapor deposition method

[0066] 100g of silicon particles with a size of 50 microns were placed in a tube furnace and heated to 800 °C at a heating rate of 10 °C / min under an argon atmosphere. Then the argon was turned off, CO2 was continuously introduced at a flow rate of 20 mL / min, and the tube furnace temperature was raised to 900 °C within 15 minutes to pretreat the silicon particles. When the tube furnace temperature reached 900 °C, acetylene was introduced at a flow rate of 20 mL / min; and when the tube furnace temperature reached 900 °C, the flow rate of CO2 was mL / min, and the reaction was maintained for 20 minutes, thereby coating a planar graphene layer on the surface of the silicon particles.

[0067] S2, growing vertical graphene on the surface of the planar graphene by a chemical vapor deposition method, thereby obtaining a planar graphene-vertical graphene coupling structure

[0068] The CO2 and acetylene were turned off, argon was introduced into the tube furnace at a flow rate of 40 mL / min, and the tube furnace temperature was raised to 1100 °C within 15 minutes. Then the argon was turned off, a mixed gas of acetylene and H2 was introduced into the tube furnace at a flow rate of 50 mL / min each, and the reaction was continued for 1 hour; after the reaction was completed, the mixed gas was turned off, and argon was continuously introduced into the tube furnace, and the tube furnace was naturally cooled under an argon atmosphere, thereby growing vertical graphene on the surface of the planar graphene in situ to form a planar graphene-vertical graphene coupling structure.

[0069] S3, using a chemical etching method to partially remove the silicon core, thereby introducing voids inside the anode material, and obtaining the anode material.

[0070] The planar graphene-vertical graphene coupling structure obtained in S2 was immersed in a 1 M NaOH solution and heated at 50 °C for 60 minutes, then washed and dried to obtain the final anode material.

[0071] The first charge capacity of the negative electrode material of the vertical graphene and planar graphene coupling structure encapsulating silicon particles is 1850.5 mAh / g at 0.1C, and the first coulombic efficiency is 89%. After 500 cycles at 1C, the capacity retention rate is still as high as 77.2%. The rate capacity of the negative electrode material at 0.1, 0.2, 0.5, 1, 2, 3 and 5C is 1853.4, 1793.7, 1680.3, 1502.6, 1336.1, 1055.9, 821.7 and 580.4 mAh / g, respectively.

[0072] Example 5

[0073] A lithium ion battery negative electrode material of a coupling graphene structure encapsulating silicon particles, the structure of the negative electrode material is silicon particles, planar graphene and vertical graphene from inside to outside. Wherein, there is a certain gap between the silicon particles and the planar graphene, at the same time, the planar graphene and the vertical graphene form a seamless connection and no interface separation coupling structure.

[0074] The above is only a specific embodiment of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a lithium-ion battery anode material with a graphene-coupled structure encapsulated silicon particles, characterized in that, Includes the following steps: S1. A planar graphene layer is deposited on the surface of silicon particles using a chemical vapor deposition method; In an atmosphere containing carbon source gas and carbon dioxide, a planar graphene layer is deposited on the surface of silicon particles at a temperature of 800℃~1100℃; wherein the flow rate ratio of CO2 to carbon source gas is set to be less than 1 / 1. S2. Vertical graphene is grown on the surface of planar graphene by chemical vapor deposition, thereby obtaining a planar graphene-vertical graphene coupled structure. In an atmosphere containing carbon source gas and hydrogen, epitaxial growth is performed on the surface of the planar graphene layer at a temperature of 400℃ to 1100℃ to form vertical graphene seamlessly connected to the planar graphene layer by covalent bonds, thereby obtaining a planar graphene-vertical graphene coupled structure; the carbon source gas is selected from at least one of acetylene, methane, and ethanol. S3. Using chemical etching, the silicon core is partially removed, thereby introducing voids inside the negative electrode material to obtain the negative electrode material.

2. A lithium-ion battery anode material with a coupled graphene structure encapsulating silicon particles, wherein the anode material is prepared by the method of claim 1, characterized in that, The structure of the negative electrode material, from the inside out, consists of silicon particles, planar graphene, and vertical graphene. There are certain gaps between the silicon particles and the planar graphene, and the planar graphene and vertical graphene form a seamless connection and a coupling structure without interface separation.

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