Modified preparation method of ant nest type silicon-carbon composite electrode material

Abstract

The preparation method comprises the following steps: by taking coated asphalt as a carbon source, obtaining a pyridine soluble substance coated with the asphalt in a pyridine extraction manner, dispersing silicon-aluminum alloy powder into a pyridine solution of the pyridine soluble substance, and carrying out ultrasonic dispersion on the silicon-aluminum alloy powder to obtain a silicon-carbon composite electrode material; and after the solvent is evaporated to dryness, carbonizing, pickling and drying to obtain the ant nest type porous silicon-carbon composite electrode material. The composite electrode material is composed of an external carbon layer and internal porous silicon, the diameter of the internal porous silicon is 4-9 [mu] m, and the thickness of the carbon layer is 0.2-0.4 [mu] m; the first-circle coulombic efficiency is 70% or above, the reversible specific capacity under the 0.1 C current density reaches 800 mAh / g or above, and the specific capacity under the 3C large current density reaches 520 mAh / g or above. The internal three-dimensional porous silicon effectively relieves the volume expansion of the micron silicon, and the outer layer is coated with the asphalt carbon layer to form a continuous conductive network, so that the overall conductivity is improved, and the interface stability is enhanced. The composite electrode material has the advantages of good conductivity, high reversible specific capacity, stable cycle performance and good rate capability.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery electrode materials, and relates to an "ant nest"-type silicon-carbon composite electrode material and a modified preparation method thereof. Background Art

[0002] Silicon nanomaterials have obvious effects in improving the cycling performance and rate performance of silicon-based materials. However, due to their large specific surface area, more SEI is formed for the first time, resulting in a large irreversible capacity and a low Coulombic efficiency. In addition, the low tap density of nanomaterials also makes the actual volume energy density of the nanosilicon electrode much lower than the theoretical value, and even lower than that of commercial graphite electrodes. In recent years, many efforts have been made to further increase the tap density and loading mass of nanosilicon-based materials and improve their areal specific capacity to meet the requirements of practical applications. Reducing the size of silicon to the nanoscale can effectively improve the performance of silicon materials. Although the silicon material will not crack or pulverize due to volume expansion, the volume expansion of silicon itself still exists, which means that the SEI film will still be damaged and continuously generated, consuming a large amount of lithium ions, seriously reducing the Coulombic efficiency and the reversible specific capacity of the battery. In addition, the electrical conductivity of nanosilicon has not been improved yet. Therefore, by introducing active or inactive materials with good electrical conductivity to prepare silicon-based composites, on the one hand, the electrical conductivity of silicon-based materials can be effectively improved, and on the other hand, by replacing part of the silicon to reduce the proportion of silicon in the material, the degree of volume expansion can be reduced, and other materials can buffer the silicon volume change effect and maintain the overall stability of the material, thus significantly improving the electrochemical performance of silicon-based materials. Such materials include various carbon materials, metals, metal oxides, and conductive polymers, etc. Among them, silicon-carbon composites are important materials that are most promising as the next-generation lithium-ion battery anodes. This is because silicon-carbon composites combine the advantages of both silicon and carbon materials. Silicon provides a high specific capacity, while carbon has good electrical conductivity and mechanical strength, wide sources, and rich varieties. Moreover, the charge and discharge platforms of both are very low, belonging to the same main group, with good compatibility, many synthesis methods, and being economical and environmentally friendly. Therefore, they are regarded as the best candidates for realizing the commercialization of high-energy-density lithium-ion batteries in the industry. At the same time, research shows that the porous structure helps to significantly alleviate the severe volume expansion problem of silicon-based materials during the charge and discharge process, thereby improving their cycling stability and electrochemical performance.

[0003] CN107215874A discloses a preparation method of ant nest-like porous silicon for lithium-ion batteries. By using the ammoniation reaction of magnesium silicide, a crude product of silicon and magnesium nitride is prepared, and after washing away magnesium nitride with hydrochloric acid, ant nest-like porous silicon is obtained. CN109888232A discloses a porous nano-silicon-carbon composite anode material for lithium-ion batteries. The silicon-aluminum alloy block is reacted with dilute hydrochloric acid to remove aluminum, obtaining a porous silicon nano-material; it is calcined in the presence of a carbon source to obtain a carbon-coated porous silicon composite electrode material. CN114105145B discloses that after forming Si / Mg3N2 by nitriding micron Mg2Si, carbon is directly coated by CVD, and then Mg3N2 is washed away to obtain three-dimensional porous silicon coated with carbon on the outside. CN118248828A prepares a porous silicon-carbon electrode material for lithium batteries by forming an adjustable calcium carbonate layer as a sacrificial template and further generating a carbon-coated layer. CN106299277B proposes to coat nano-silicon with pitch, which can avoid direct contact between silicon particles and the electrolyte, slow down the capacity decay rate, and at the same time shorten the diffusion path of lithium ions, ensuring that the electronic conduction of the electrode material will not be lost, that is, improving the first charge-discharge efficiency, charge-discharge capacity and cycle performance. However, the existing silicon-carbon composite materials still have a series of problems such as uneven coating, fragile structure and poor cycle stability. Summary of the Invention

[0004] In order to solve the key problems in the prior art such as uneven carbon coating, poor continuity of the coating layer structure, and severe volume expansion of silicon-carbon composite materials, the present invention introduces the pyridine-soluble component in coated pitch as a controllable carbon source. This component has good molecular uniformity and high carbon yield after carbonization, and can form a dense and continuous coating layer on the surface of the composite material, realizing in-situ uniform coating of silicon-aluminum alloy powder. And by selectively etching the metal aluminum phase, a three-dimensional connected "ant nest" structure is constructed, effectively alleviating the volume effect of silicon-based materials, enhancing the stability and integrity of the carbon layer conductive network and the lithium-ion transport efficiency, thereby significantly improving the cycle life and rate performance of lithium-ion batteries.

[0005] The purpose of the present invention is achieved through the following technical solutions;

[0006] A modified preparation method of an "ant nest"-type silicon-carbon composite electrode material, comprising the following specific steps:

[0007] Step (1): Using coated pitch as a carbon precursor, the pyridine-soluble matter of coated pitch is obtained by pyridine extraction, and the pyridine-soluble matter is ultrasonically dissolved in anhydrous pyridine to form a homogeneous and stable pyridine solution;

[0008] Step (2): Adding silicon-aluminum alloy powder to the pyridine solution, heating and stirring at 110 °C until pyridine is completely evaporated to obtain silicon-aluminum alloy powder coated with pyridine-soluble matter;

[0009] Step (3): Place the silicon-aluminum alloy powder coated with pyridine-soluble matter in a corundum boat and perform high-temperature carbonization under an argon atmosphere to obtain carbon-coated silicon-aluminum alloy.

[0010] Step (4): Add the carbon-coated silicon-aluminum alloy to a hydrochloric acid solution, stir and soak it until no more bubbles escape, complete the selective etching of the aluminum phase in the silicon-aluminum alloy to form a three-dimensional porous structure. Centrifuge the product and wash it with ethanol and deionized water until neutral, and dry it for 24 h to obtain the "ant nest"-type porous silicon-carbon composite electrode material.

[0011] In step (1) of the present invention, the coating pitch is prepared by oxidative cross-linking of ethylene tar. The oxidative cross-linking is carried out by introducing air for oxidation at 250-280 °C for 4-8 hours until the softening point of the coating pitch is 250 °C - 280 °C, and the mass ratio of pyridine-soluble matter is 50%-70%. The pyridine-soluble matter component with a lower molecular weight and rich polar functional groups is directionally separated by pyridine extraction. The pyridine extraction refers to extraction with pyridine under reflux conditions at 130 °C using the Soxhlet extraction method. The obtained pyridine-soluble matter is mainly composed of low-molecular-weight aromatic and oxygen-containing functional group components. This component not only has good solubility and wettability but also has high molecular activity and lamellar structure flexibility, and can be fully dispersed in the liquid phase and evenly adsorbed on the surface of silicon-aluminum alloy particles. The dosage ratio of pyridine to pyridine-soluble matter is 100 ml: 1-1.5 g, and it is treated by ultrasonic for 30 min to obtain a stable and uniform pyridine solution for fine liquid-phase coating of silicon-aluminum alloy powder.

[0012] In step (2) of the present invention, the mass ratio of silicon to aluminum elements in the silicon-aluminum alloy is Al:Si = 6:1 or 4:1 or 2:1, and the final silicon content in the product is jointly controlled by the type of silicon-aluminum alloy used and the addition amount of pyridine-soluble matter in the coating pitch. The dosage ratio of pyridine-soluble matter to silicon-aluminum alloy is 1 g: (1-2) g to control the mass ratio of silicon in the final silicon-carbon composite electrode material to be 15%-35%.

[0013] In step (3) of the present invention, the conditions for high-temperature carbonization are: heating to 1000 °C at a heating rate of 5 °C / min and holding for carbonization for 2 h. This process not only realizes the in-situ curing of the carbon layer but also promotes the continuity and structural compactness of the carbon layer.

[0014] In step (4) of the present invention, the concentration of the hydrochloric acid solution is 1.5 M.

[0015] The present invention also provides an "ant nest"-type silicon-carbon composite electrode material prepared by the above method. The electrode material is composed of an external carbon layer and an internal porous silicon. The diameter of the internal porous silicon is 0.4 - 0.7 μm, and the thickness of the carbon layer is 0.2 - 0.4 μm; the first-cycle Coulombic efficiency is above 70%, the reversible specific capacity reaches above 800 mAh / g at a current density of 0.1C, and the specific capacity reaches above 520 mAh / g at a large current density of 3C.

[0016] The present invention proposes a preparation method of a novel silicon-carbon composite electrode material based on micron-scale porous silicon structure, which has the significant advantages of precise structure regulation and industrial feasibility of raw material sources. First, using ethylene tar as the raw material, the coated asphalt obtained by oxidative cross-linking is used as the carbon source. The pyridine-soluble component separated from this asphalt has characteristics such as high molecular structure activity, rich functional groups, and excellent interfacial wettability, and can form a uniform and dense precursor coating layer on the surface of the silicon-aluminum alloy. Subsequently, the silicon-aluminum alloy is coated with the pyridine-soluble substance in the coated asphalt. After high-temperature carbonization and acid etching steps, the external carbon layer is completely retained, while the metal aluminum in the internal silicon-aluminum alloy reacts with hydrochloric acid and is removed, leaving a porous silicon structure, and in-situ constructing a "ant nest"-like porous structure. The present invention successfully prepares a carbon-coated porous silicon composite material with through-hole channels inside. In this composite system, the three-dimensional porous silicon network provides a space adjustment ability for buffering volume expansion, significantly reducing the risk of structural rupture; while the outer coated asphalt carbon layer improves the overall conductivity and enhances the interfacial stability by forming a continuous conductive network. The present invention uses the pyridine-soluble substance in ethylene tar for the regulation of porous silicon coating, combining structural and functional integration and industrialization potential, and has strong technological innovation and application value.

[0017] Compared with the prior art, the present invention has the following significant beneficial effects:

[0018] 1. The present invention uses the coated asphalt prepared by oxidative cross-linking of ethylene tar as the carbon source. Ethylene tar is a by-product resource in the ethylene industry, with wide sources and low costs. Through directional oxidation and polycondensation reactions, its structure is regulated to obtain a coated asphalt with a high softening point and stable carbonization yield, realizing the high-value conversion of low-value by-products into high-performance carbon materials, and providing a green and economical new idea for the large-scale preparation of silicon-carbon composite materials.

[0019] 2. By etching the silicon-aluminum alloy with hydrochloric acid, the aluminum component is selectively removed to form a uniformly distributed micron-scale porous structure in the silicon particles. The formed pores are mostly mesopores of medium size, effectively alleviating the volume expansion problem of silicon materials during charge and discharge processes. Compared with traditional nano-silicon or high specific surface area porous silicon systems, the porous silicon structure obtained by this method significantly inhibits side reactions while improving the capacity, ensuring a high first-cycle Coulombic efficiency and cycle stability of the material.

[0020] 3. The present invention innovatively introduces the pyridine-soluble matter in the coated asphalt as the liquid-phase coating carbon source. The pyridine-soluble matter in the coated asphalt has multiple advantages in coating applications: its molecular weight is moderate, its fluidity is good, it can uniformly wet the surface of the electrode particles, and form a dense coating layer; at the same time, it has appropriate adhesiveness, which can not only enhance the bonding strength between particles, but also will not be overly hardened to affect the processing performance. During the high-temperature carbonization process, the pyridine-soluble matter can form a continuous and stable carbon layer, improving the conductivity and structural stability of the material, and its shrinkage rate is low, which can effectively reduce the cracks in the coating layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a transmission electron microscope photograph of the "ant nest"-type silicon-carbon composite electrode material prepared by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described in more detail below in conjunction with the embodiments.

[0023] Example 1:

[0024] This example provides a modified preparation method of an "ant nest"-type silicon-carbon composite material, including the following specific steps:

[0025] (1) Take a certain amount of coated asphalt with a softening point of 250 °C and place it in a Soxhlet extractor. The pyridine-soluble matter of the coated asphalt is obtained by pyridine extraction. Weigh 1.5 g of the pyridine-soluble matter and add it to 100 ml of pyridine, and ultrasonicate for 30 min until completely dissolved to obtain a pyridine solution;

[0026] (2) Weigh 1.5 g of silicon-aluminum alloy powder with a silicon-aluminum element mass ratio of 6:1 and add it to the above pyridine solution. Heat and stir in an oil bath at 110 °C until the pyridine is completely evaporated to obtain silicon-aluminum alloy powder coated with pyridine-soluble matter;

[0027] (3) Place the silicon-aluminum alloy powder coated with pyridine-soluble matter in a corundum boat, and heat it to 1000 °C at a heating rate of 5 °C / min in an argon atmosphere and carbonize for 2 h to obtain carbon-coated silicon-aluminum alloy;

[0028] (4) Add the carbon-coated silicon-aluminum alloy to 1.5 M hydrochloric acid and stir and soak until the bubbles no longer escape, completing the selective etching of the aluminum phase in the silicon-aluminum alloy to form a three-dimensional porous structure. The centrifuged product is washed three times with ethanol and deionized water until neutral, and dried for 24 h to obtain the "ant nest"-type porous silicon-carbon composite electrode material A. Among them, by mass fraction, the silicon content is 20%, the diameter of the internal porous silicon is 9 μm, and the carbon layer thickness is 0.2 μm.

[0029] Example 2:

[0030] This embodiment provides a method for preparing an "ant nest"-type silicon-carbon composite material, which includes the following specific steps:

[0031] (1) Take a certain amount of coated asphalt with a softening point of 280°C and place it in a Soxhlet extractor. Obtain the pyridine-soluble matter of the coated asphalt through pyridine extraction. Weigh 1 g of the pyridine-soluble matter and add it to 100 ml of pyridine, and ultrasonicate for 30 min until completely dissolved to obtain a pyridine solution;

[0032] (2) Weigh 1.5 g of silicon-aluminum alloy powder with a silicon-aluminum mass ratio of 4:1 and add it to the above pyridine solution. Heat and stir in an oil bath at 110°C until the pyridine is completely evaporated to obtain silicon-aluminum alloy powder coated with pyridine-soluble matter;

[0033] (3) Place the silicon-aluminum alloy powder coated with pyridine-soluble matter in a corundum boat, and heat it to 1000°C at a heating rate of 5°C / min in an argon atmosphere and carbonize for 2 h to obtain carbon-coated silicon-aluminum alloy;

[0034] (4) Add the carbon-coated silicon-aluminum alloy to 1.5 M hydrochloric acid, stir and soak until no bubbles escape, complete the selective etching of the aluminum phase in the silicon-aluminum alloy to form a three-dimensional porous structure. Centrifuge the product and wash it three times with ethanol and deionized water until neutral, and dry it for 24 h to obtain the "ant nest"-type porous silicon-carbon composite electrode material B. Among them, by mass fraction, the silicon content is 24%, the diameter of the internal porous silicon is 7 μm, and the carbon layer thickness is 0.2 μm.

[0035] Example 3:

[0036] This embodiment provides a method for preparing an "ant nest"-type silicon-carbon composite material, which includes the following specific steps:

[0037] (1) Take a certain amount of coated asphalt with a softening point of 280°C and place it in a Soxhlet extractor. Obtain the pyridine-soluble matter of the coated asphalt through pyridine extraction. Weigh 2 g of the pyridine-soluble matter and add it to 100 ml of pyridine, and ultrasonicate for 30 min until completely dissolved to obtain a pyridine solution;

[0038] (2) Weigh 3.5 g of silicon-aluminum alloy powder with a silicon-aluminum mass ratio of 4:1 and add it to the above pyridine solution. Heat and stir in an oil bath at 110°C until the pyridine is completely evaporated to obtain silicon-aluminum alloy powder coated with pyridine-soluble matter;

[0039] (3) Place the silicon-aluminum alloy powder coated with pyridine-soluble matter in a corundum boat, and heat it to 1000°C at a heating rate of 5°C / min in an argon atmosphere and carbonize for 2 h to obtain carbon-coated silicon-aluminum alloy;

[0040] (4) Add the carbon-coated silicon-aluminum alloy to 1.5 M hydrochloric acid, stir and soak it until no more bubbles escape, completing the selective etching of the aluminum phase in the silicon-aluminum alloy to form a three-dimensional porous structure. Centrifuge the product and wash it three times with ethanol and deionized water until neutral, then dry it for 24 h to obtain the "ant nest"-type porous silicon-carbon composite electrode material C. Among them, by mass fraction, the silicon content is 27%, the diameter of the internal porous silicon is 7 μm, and the thickness of the carbon layer is 0.3 μm.

[0041] Example 4:

[0042] This example provides a preparation method of an "ant nest"-type silicon-carbon composite material, including the following specific steps:

[0043] (1) Take a certain amount of coating pitch with a softening point of 280 °C and place it in a Soxhlet extractor. Obtain the pyridine-soluble matter of the coating pitch through pyridine extraction. Weigh 1 g of the pyridine-soluble matter and add it to 100 ml of pyridine, and ultrasonicate for 30 min until completely dissolved to obtain a pyridine solution.

[0044] (2) Weigh 1.5 g of silicon-aluminum alloy powder with a silicon-aluminum mass ratio of 2:1 and add it to the above pyridine solution. Heat and stir it in an oil bath at 110 °C until the pyridine completely evaporates to obtain silicon-aluminum alloy powder coated with pyridine-soluble matter.

[0045] (3) Place the silicon-aluminum alloy powder coated with pyridine-soluble matter in a corundum boat, and heat it to 1000 °C at a heating rate of 5 °C / min in an argon atmosphere and carbonize it for 2 h to obtain carbon-coated silicon-aluminum alloy.

[0046] (4) Add the carbon-coated silicon-aluminum alloy to 1.5 M hydrochloric acid, stir and soak it until no more bubbles escape, completing the selective etching of the aluminum phase in the silicon-aluminum alloy to form a three-dimensional porous structure. Centrifuge the product and wash it three times with ethanol and deionized water until neutral, then dry it for 24 h to obtain the "ant nest"-type porous silicon-carbon composite electrode material D. Among them, by mass fraction, the silicon content is 34%, the diameter of the internal porous silicon is 5 μm, and the thickness of the carbon layer is 0.2 μm.

[0047] Test example:

[0048] Use the "ant nest"-type porous silicon-carbon composite electrode materials A, B, C, and D prepared in Examples 1-4 as electrode materials:

[0049] 1. Electrode preparation: Mix the obtained material with acetylene black and polyacrylic acid according to a mass ratio of 7.5:1:1.5, use deionized water as a solvent, grind it to form a uniform slurry, and coat it on a copper foil. Vacuum dry it at 90 °C for 24 h, and roll it to obtain an electrode sheet.

[0050] 2. Battery performance test: The obtained negative electrode sheets were cut into electrode sheets with a diameter of 12 mm for battery assembly. The assembly process was carried out in a glove box filled with Ar gas, and the water and oxygen content was less than 0.01 ppm. The battery used a CR2032 type button battery, with a lithium metal sheet as the counter electrode, a polypropylene membrane as the separator, and 1 M lithium hexafluorophosphate (its solvent was a mixture of ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1, added with 5% fluoroethylene carbonate) as the electrolyte. The assembled button battery was subjected to 0.1C charge-discharge cycle performance test and 3C rate performance test at 20 °C within a voltage range of 0.05V - 2.2V. The measured initial specific capacity (mAh / g), first charge-discharge efficiency (%), and reversible cycle specific capacity (mAh / g, 300 cycles) of the battery were recorded, and the silicon content in each electrode material was also given. The results are shown in Table 1.

[0051] Table 1 Comparison of electrode material performance

[0052]

[0053] It can be seen from the data in Table 1 that compared with the existing graphite negative electrode (360 mAh / g), the "ant nest" - type porous silicon-carbon composite materials A, B, C, and D prepared by the methods described in Examples 1 - 4 of the present invention all have higher charge-discharge cycle performance. In addition, through comparison, it can be found that the initial Coulomb efficiency of the battery slightly decreases with the increase of the silicon content in the electrode material, but the overall capacity increases with the increase of the silicon content. The silicon content in the composite material is jointly determined by the addition amount of the initial coated asphalt pyridine-soluble matter and the silicon content in the silicon-aluminum alloy, while the thickness of the carbon shell mainly depends on the addition ratio of carbon and silicon-aluminum alloy, and has little relationship with the proportion of silicon in the used alloy. In electrode material D, the silicon content is as high as 34%, and the composite material shows a specific capacity of 1042 mAh / g at a current density of 0.1 mA / g.

[0054] Figure 1 This is the transmission electron microscope photograph of the "ant nest" - type silicon-carbon composite electrode material prepared in Example 1 of the present invention. Among them, by mass fraction, the silicon content is 20%, the carbon content is 80%, the diameter of the internal porous silicon is 9 μm, and the carbon layer thickness is 0.2 μm.

Claims

1. A modified preparation method of an "ant nest"-type silicon-carbon composite electrode material, characterized in that The specific steps include: Step 1: Using the coated asphalt as a carbon source, extracting the coated asphalt with pyridine to obtain a pyridine-soluble substance, and dissolving the pyridine-soluble substance in pyridine by ultrasonication to obtain a pyridine solution; Step 2: Add the silicon-aluminum alloy powder to the pyridine solution, heat and stir at 110° C. until the pyridine is completely evaporated, thereby obtaining a silicon-aluminum alloy powder coated with pyridine soluble matter; Step 3: placing the silicon-aluminum alloy powder coated with the pyridine soluble substance in a corundum porcelain boat and carbonizing it at high temperature under an argon atmosphere to obtain a carbon-coated silicon-aluminum alloy; Step 4: Add the carbon-coated silicon-aluminum alloy to a 1.5M hydrochloric acid solution and stir and soak until bubbles no longer escape, completing the selective etching of the aluminum phase in the silicon-aluminum alloy to form a three-dimensional porous structure. The centrifuged product is washed with ethanol and deionized water until neutral, and dried for 24 hours to obtain an "ant nest" type porous silicon-carbon composite material.

2. The modified preparation method of an "ant nest"-type silicon-carbon composite electrode material according to claim 1, characterized in that, The coated asphalt is prepared by oxidative cross-linking of ethylene tar, has a softening point of 250-280° C., and the mass of pyridine soluble matter in the coated asphalt accounts for 50%-70% of the total mass of the coated asphalt.

3. The modification and preparation method of an "ant nest" type silicon-carbon composite electrode material according to claim 1, characterized in that: The mass ratio of silicon to aluminum elements in the silicon aluminum alloy is Al:Si=6:1 or 4:1 or 2:

1.

4. The modified preparation method of an "ant nest"-type silicon-carbon composite electrode material according to claim 1, characterized in that, The usage ratio of pyridine to pyridine soluble matter is 100ml:1-1.5g, and the usage ratio of pyridine soluble matter to silicon-aluminum alloy is 1g:1-2g.

5. The modification and preparation method of an "ant nest" type silicon-carbon composite electrode material according to claim 1, characterized in that: The conditions for high-temperature carbonization are: heating to 1000°C at a heating rate of 5°C / min and carbonizing for 2 h.

6. A "ant nest"-type silicon-carbon composite electrode material prepared by the method according to any one of claims 1-5, characterized in that, The electrode material consists of an outer carbon layer and inner porous silicon. The diameter of the inner porous silicon is 4-9 μm, and the thickness of the carbon layer is 0.2-0.4 μm. The mass proportion of silicon in the silicon-carbon composite electrode material is 15%-35%.

7. The "ant nest" type silicon-carbon composite electrode material according to claim 6, characterized in that: The electrode material has a first-cycle coulombic efficiency of more than 70%, a reversible specific capacity of more than 800 mAh / g at a current density of 0.1C, and a specific capacity of more than 520 mAh / g at a high current density of 3C.

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