CN106207137A - A kind of composite negative electrode material of lithium ion battery and preparation method thereof - Google Patents

Abstract

The invention discloses a composite negative electrode material for a lithium ion battery and a preparation method thereof, wherein the composite material includes a carbon coating layer and an inner core wrapped by the carbon coating layer, wherein the inner core includes Fe ₃ O ₄ , FeO and Fe three-component Fe ₃ O ₄ /FeO/Fe composite core. The present invention improves the key preparation process of the composite material, directly uses micronano-sized α-Fe ₂ O ₃ particles as a precursor, uses organic compounds or polymer compounds as dispersants, reducing agents and carbon sources, and adopts a heat treatment method preparation, which effectively simplifies the preparation process and is very suitable for large-scale mass production; and, when the composite material is used as a negative electrode, it can effectively buffer the damage to the structure caused by the volume change in the charging/discharging process, improve the conductivity of the electrode material, and improve The specific capacity, cycle stability and rate performance of the material during charge/discharge.

Description

A kind of composite negative electrode material for lithium ion battery and preparation method thereof

technical field

The invention belongs to the technical field of chemical power sources, and more specifically relates to a negative electrode composite material for lithium ion batteries and a preparation method thereof. The composite material is specifically a Fe ₃ O ₄ /FeO/Fe/C composite material, which is especially suitable as a negative electrode material For lithium-ion batteries.

Background technique

In the past two decades, lithium-ion batteries have been widely used as energy devices for portable electronic devices due to their excellent properties such as high energy density and high output voltage. Although a large number of new energy storage technologies, such as lithium-sulfur batteries, lithium-air batteries, and sodium-ion batteries, pose challenges for their applications, lithium-ion batteries are still the preferred choice for powering next-generation electric vehicles and plug-in hybrid electric vehicles. Great efforts have been made to develop new electrode materials with high energy density, high power density, long service life, and high current charge-discharge performance to meet the ever-increasing performance demands. Studies have found that transition metal oxides (MOx, M:Fe, Co, Ni, etc.) have a higher specific capacity (600-1000mAh/g) than current commercial anode materials (graphite), and are a class of promising materials. Lithium-ion battery anode materials have recently attracted enormous research interest. Among these materials, magnetite (Fe ₃ O ₄ ) is the most promising material for lithium ion due to its high theoretical specific capacity (926mAh/g), low cost, non-toxic, eco-friendly, and abundant natural reserves. A negative electrode material for batteries. However, the huge volume change during lithium ion intercalation destroys the crystal particles, weakens the electrical contact between the anode material and the current collector, and makes the cycle performance of unprocessed _Fe3O4 material poor, which seriously hinders this development _. Commercial applications of materials. Moreover, the continuous rupture of active material particles will also destroy the SEI film on the surface of the active material, reducing the reversibility of the charge-discharge reaction and causing rapid capacity decay.

Many methods have been used to overcome these problems, two of which are commonly used. One is to synthesize nano-Fe ₃ O ₄ materials with various structures, such as nanoparticles, nanosheets, nanowires, nanotubes, and hollow nanostructures, which can absorb the mechanical tension generated during lithium ion intercalation and extraction, shorten the lithium ion transport path. However, the vast majority of these nanomaterials cannot be produced on a large scale, hindering practical applications. Moreover, nanonization cannot solve the poor conductivity of electrode materials. Another approach is to composite _Fe3O4 with carbon materials, including graphite, carbon nanotubes ₍ CNTs), and amorphous carbon. These carbon materials not only improve the electronic conductivity of active materials, but also act as substrate materials to inhibit particle agglomeration and buffer the damage to the structure caused by volume changes, thereby enhancing the cycle stability of composite materials. Amorphous carbon can be obtained by carbonizing organic matter. However, coating amorphous carbon on the surface of pre-synthesized electroactive materials usually requires additional synthesis steps, which makes the preparation process more complicated. Therefore, it is urgent to develop a simple method to coat amorphous carbon on the surface of electroactive nano-Fe ₃ O ₄ materials, so that the composite materials have more conductive centers.

Contents of the invention

In view of the above defects or improvement needs of the prior art, the object of the present invention is to provide a composite negative electrode material for lithium ion batteries and a preparation method thereof, wherein by improving the key preparation process of the composite material, the nanometer-sized α- Fe ₂ O ₃ particles are used as precursors, organic compounds or polymer compounds are used as dispersants, reducing agents and carbon sources, and they are prepared by heat treatment, which effectively simplifies the preparation process and is very suitable for large-scale batch production; and, in organic During the carbonization process of compound or polymer compound, amorphous carbon is tightly wrapped on the outer layer of iron oxide particles to form a carbon coating layer, and at the same time Fe ₂ O ₃ is reduced to Fe ₃ O ₄ , FeO and Fe online, which can be used in carbon and oxidation A close intermolecular contact is formed between the iron particles; since the coated carbon layer establishes a connection between each Fe ₃ O ₄ /FeO/Fe nanoparticle, when the composite material is used as a negative electrode of a lithium-ion battery, it can not only improve The electronic conductivity of the material can also effectively buffer the damage to the structure caused by the volume change during the charging/discharging process, improve the specific capacity, cycle stability and rate performance of the material during the charging/discharging process, and greatly improve the electrochemical performance of the electrode material.

In order to achieve the above object, according to one aspect of the present invention, a composite negative electrode material for lithium ion batteries is provided, wherein the composite material includes a carbon coating layer and an inner core wrapped by the carbon coating layer, wherein the The inner core is Fe ₃ O ₄ /FeO/Fe composite inner core including three components of Fe ₃ O ₄ , FeO and Fe.

According to another aspect of the present invention, the present invention provides the preparation method of above-mentioned composite negative electrode material for lithium ion battery, is characterized in that, comprises the following steps:

(1) Mix the α-Fe ₂ O ₃ raw material and the carbon source raw material by ball milling to obtain a uniformly mixed precursor; the particle size of the α-Fe ₂ O ₃ raw material is nanoscale or micron, and the carbon source raw material is at least one of organic compounds and polymer compounds;

(2) The precursor obtained in the step (1) is heat-treated in a controlled atmosphere to carbonize the carbon source material in the precursor to form a carbon coating layer, and at the same time Fe ₂ O ₃ is reduced to form Fe ₃ O ₄ /FeO/Fe composite nanoparticles, so as to finally obtain composite negative electrode materials for lithium-ion batteries;

The controlled atmosphere is at least one of inert gas, nitrogen and air; the inert gas is preferably argon.

As a further preference of the present invention, in the step (2), the heat treatment is at a temperature of 600° C. to 800° C. for 1 h to 10 h.

As a further preference of the present invention, in the step (1), the carbon source raw materials are sugars, polyacrylic acid polymers, polyacrylate polymers, polyolefin polymers and their respective derivatives at least one of .

As a further preference of the present invention, in the step (1), the mass ratio of the α-Fe ₂ O ₃ raw material to the carbon source raw material is 1:0.2˜1:10.

As a further preference of the present invention, before the heat treatment in the step (2), the precursor is also subjected to drying treatment; preferably, the drying temperature of the drying treatment is 60°C to 120°C.

Through the above technical scheme conceived by the present invention, compared with the prior art, since the large-scale production of micro-nano size α-Fe ₂ O ₃ particles is directly used as a precursor, and then an organic compound or a polymer compound is used as a dispersant, The reducing agent and the carbon source are prepared by heat treatment. During the carbonization process of organic compounds or polymer compounds, amorphous carbon is tightly wrapped in the outer layer of iron oxide particles. At the same time, Fe ₂ O ₃ is reduced to Fe ₃ O ₄ , _{FeO and Fe on-line, so that carbon (corresponding to the carbon coating layer) and iron oxide particles (that is, Fe 3 O 4 /} FeO/Fe nanoparticles, that is, Fe ₃ O ₄ /FeO/Fe core) form a tight intermolecular contact. The coated carbon layer establishes the connection between the particles, which not only improves the electronic conductivity of the material, but also buffers the structural damage caused by the volume change during the charging/discharging process. Furthermore, the presence of a small amount of Fe in this complex can greatly enhance the electrical conductivity. When used as a negative electrode material for lithium-ion batteries, the Fe ₃ O ₄ /FeO/Fe/C composite material prepared by the above method shows excellent lithium storage characteristics such as high specific capacity, excellent cycle stability, and good rate capability, demonstrating This material has great potential as a high-rate anode material for lithium-ion batteries.

The composite negative electrode material for lithium ion batteries in the present invention (ie Fe ₃ O ₄ /FeO/Fe/C composite material) is a carbon-coated Fe ₃ O ₄ /FeO/Fe composite material (ie includes Fe ₃ O ₄ /FeO/ Fe inner core, and carbon coating layer); Correspondingly, the preparation method of the composite negative electrode material for lithium ion battery in the present invention is an online solid-phase synthesis method of a kind of composite material.

The invention can overcome the defects of poor material conductivity and complex synthesis method in the prior art, and provides a simple and operable on-line solid-phase synthesis method to prepare iron oxide nanoparticles coated with amorphous carbon. The synthesized amorphous carbon is tightly wrapped on the outer layer of iron oxide particles, and Fe ₂ O ₃ is reduced to Fe ₃ O ₄ , FeO and Fe in situ and online, forming a close contact between carbon and iron oxide particles. The coated carbon layer establishes connections between particles, which not only provides material conductivity, but also buffers the damage to the structure due to volume changes during charging/discharging. The existence of a small amount of Fe in the composite can also greatly improve the conductivity of the material.

Description of drawings

Fig. 1 is the synthesizing method synoptic diagram of lithium-ion battery composite negative electrode material of the present invention;

Figure 2(a) is the XRD diffraction pattern of Fe ₃ O ₄ /FeO/Fe/C composite material, Figure 2(b) is the Raman spectrum, Figure 2(c) is the complete XPS spectrum, and Figure 2(d) is XPS fine map of Fe2p;

Figure 3(a) and Figure 3(b) are the field emission scanning electron microscope (FESEM) images of Fe ₃ O ₄ /FeO/Fe/C composites, and Figure 3(c) is the transmission electron microscope (TEM) image, Fig. 3(d) is a high-resolution transmission electron microscope (HRTEM) image;

Figure 4 is the charge and discharge curves of the Fe ₃ O ₄ /FeO/Fe/C composite electrode in the first two weeks;

Fig. 5 is the curve of the charge-discharge specific capacity of the Fe ₃ O ₄ /FeO/Fe/C composite electrode relative to the number of cycles under various rate conditions;

Figure 6 is the charge-discharge curve of the Fe ₃ O ₄ /FeO/Fe/C composite electrode in the first cycle;

Fig. 7 is the charge-discharge curve of the Fe ₃ O ₄ /FeO/Fe/C composite electrode in the first cycle.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

Example 1

In this example, a ball milling method was used to uniformly mix 1 g of nanometer α-Fe ₂ O ₃ and 0.60 g of glucose to prepare a precursor. The above precursor was dried in a furnace at 80°C, and then heat-treated at 650°C for 4 h under an argon atmosphere to carbonize glucose to form an amorphous carbon coating, and at the same time, partially reduce Fe ₂ O ₃ to form Fe ₃ O ₄ /FeO/ Fe nanoparticles. Finally, Fe ₃ O ₄ /FeO/Fe/C composite material is obtained. The synthesis process is shown in Figure 1.

The composition and phase structure of Fe ₃ O ₄ /FeO/Fe/C composites were detected by XRD method, as shown in Figure 2a. Obviously, all the identifiable diffraction peaks in the XRD pattern can be found in the face-centered magnetite (Fe ₃ O ₄ -JCDPS 19-0629), iron oxide (FeO-JCDPS 75-1550) and iron (Fe-JCDPS 87 -0721) in the diffraction pattern to find the corresponding peak. No other additional impurity diffraction peaks were observed. The results of further observation of the product by Raman spectroscopy are shown in Figure 2b. The D band at 1338 cm ^-1 and the G band at 1591 cm ^-1 confirm the presence of an amorphous carbon structure in the material.

Figure 2c shows the complete XPS spectrum of the Fe ₃ O ₄ /FeO/Fe/C composite, indicating that the samples contain Fe, C and O elements. Two characteristic peaks, Fe 2p3/2 and Fe 2p1/2, are fine spectral peaks of Fe 2p, located at 711eV and 725eV, respectively (see Figure 2d), proving that Fe ₃ O ₄ and FeO were formed in the material. No satellite peak of Fe ₂ O ₃ was observed at ~719eV, indicating that there was no γ-Fe ₂ O ₃ , and the XRD pattern was similar to that of Fe ₃ O ₄ .

The morphology and structure of the prepared Fe ₃ O ₄ /FeO/Fe/C composites were detected by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Figures 3a and 3b represent a panoramic view of the as-prepared material, showing an extremely close-packed structure formed by ~30 nm diameter nanoparticles. In the TEM image of Figure 3c, it can be clearly observed that the surface of the nanoparticles is coated with amorphous carbon, which is obtained from the online carbonization of glucose in the precursor. The carbon nanocoating not only reduced the Fe ₂ O ₃ in the precursor to Fe ₃ O ₄ , FeO and Fe online, but also acted as a substrate and a binder in the whole close-packed structure. In the HRTEM image (see Fig. 3d), at the boundary between carbon and iron oxide particles, the lattice boundary orientation can be clearly observed. The measured interplanar distances are 0.253nm, 0.296nm and 0.203nm, which correspond to the (311) and (220) crystal planes of the Fe ₃ O ₄ phase and the (110) crystal plane of the Fe phase, respectively, further revealing that the Fe ₃ Presence of O ₄ , FeO and Fe.

Figure 4 is the charge and discharge curves of the first two weeks of the Fe ₃ O ₄ /FeO/Fe/C composite electrode with a potential window of 0.01V to 3.0V and a current density of 100mA/g. The discharge specific capacity of the material in the first week reaches more than 1000mAh/g .

Figure 5 is the curve of the charge-discharge specific capacity of the Fe ₃ O ₄ /FeO/Fe/C composite electrode relative to the number of cycles under various rate conditions. It can be seen from the figure that under the potential window of 0.01-3.0V, the Fe ₃ O ₄ /FeO/Fe/C composite electrodes are charged and discharged in the range of 0.1-10A/g current density. Even at a current density of up to 10A/g, the sample can still release a reversible specific capacity of about 400mAh/g. When the current density returns to the initial 0.1A/g, the sample can still release a specific capacity value close to the original initial capacity of 1200mAh/g, showing excellent rate performance.

Example 2

In this example, a ball milling method was used to uniformly mix 1 g of nanometer α-Fe ₂ O ₃ and 0.9 g of polyvinylidene fluoride to prepare a precursor. The above precursor was dried in a furnace at 80°C, and then heat-treated at 700°C for 10 h under a nitrogen atmosphere to carbonize polyvinylidene fluoride to form an amorphous carbon coating layer, and at the same time, partially reduce Fe ₂ O ₃ to form Fe ₃ O ₄ / FeO/Fe nanoparticles. Finally, Fe ₃ O ₄ /FeO/Fe/C composite material is obtained. The synthesis process is shown in Figure 1.

Figure 6 is the first-cycle charge-discharge curve of the Fe ₃ O ₄ /FeO/Fe/C composite electrode with a potential window of 0.01-3.0V and a current density of 100mA/g. The discharge specific capacity of the material reaches nearly 1000mAh/g.

Example 3

In this example, a precursor was prepared by uniformly mixing 1 g of nanometer α-Fe ₂ O ₃ and 2 g of polyvinylidene fluoride by ball milling. Dry the above precursor in an oven at 80°C, put the precursor in a crucible with a lid and embed it in carbon powder, and heat-treat the whole device at 800°C for 1 hour in an air atmosphere to carbonize polyvinylidene fluoride to form amorphous carbon coating layer, meanwhile, Fe ₂ O ₃ is partially reduced to form Fe ₃ O ₄ /FeO/Fe nanoparticles. Finally, Fe ₃ O ₄ /FeO/Fe/C composite material is obtained. The synthesis process is shown in Figure 1.

Figure 7 is the first-cycle charge and discharge curves of the Fe ₃ O ₄ /FeO/Fe/C composite electrode with a potential window of 0.01-3.0V and a current density of 100mA/g. The discharge specific capacity of the material reaches nearly 600mAh/g.

_{The Fe3O4} /FeO/Fe composite inner core in the present invention has a particle size of nanoscale (i.e. _Fe3O4 /FeO/Fe composite nanoparticles ₎ , and the particle size of the α _{- Fe2O3} raw material is also nanoscale (Because the α-Fe ₂ O ₃ raw material is processed by ball milling, the ball milling process will further reduce the particle size of the raw material, so the particle size of the α-Fe ₂ O ₃ raw material can also be micron, as long as the final Fe ₃ The particle size of the O ₄ /FeO/Fe composite core can be controlled to be nanoscale).

The carbon sources in the above examples, such as glucose and polyvinylidene fluoride, can also be replaced by other sugars, polyacrylic acid polymers, polyacrylate polymers, polyolefin polymers and their corresponding derivatives; Correspondingly, the temperature of the heat treatment can be controlled at 600° C. to 800° C., and the time of the heat treatment can be controlled at 1 h to 10 h, so as to ensure the carbonization of these carbon sources. The ratio of α-Fe ₂ O ₃ raw materials to carbon source raw materials can be distributed in 1:0.2～1:10 in addition to the specific ratios in the above examples to ensure that the Fe ₃ O ₄ /FeO/Fe composite nanoparticles The thickness of the carbon coating on the surface. The polymer in the present invention may be a homopolymer or a copolymer. In the ball milling mixing step in the present invention, both dry ball milling and wet ball milling can be used. In the wet ball milling, absolute ethanol can be added before ball milling.

Those skilled in the art can easily understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (6)

1. A composite negative electrode material for a lithium ion battery, characterized in that the composite material comprises a carbon coating and an inner core wrapped by the carbon coating, wherein the inner core comprises Fe ₃ O ₄ , FeO and Fe Three-component Fe ₃ O ₄ /FeO/Fe composite core. 2. prepare the method for lithium-ion battery composite negative electrode material as claimed in claim 1, it is characterized in that, comprise the following steps: (1) Mix the α-Fe ₂ O ₃ raw material and the carbon source raw material by ball milling to obtain a uniformly mixed precursor; the particle size of the α-Fe ₂ O ₃ raw material is nanoscale or micron, and the carbon source raw material is at least one of organic compounds and polymer compounds; (2) The precursor obtained in the step (1) is heat-treated in a controlled atmosphere to carbonize the carbon source material in the precursor to form a carbon coating layer, and at the same time Fe ₂ O ₃ is reduced to form Fe ₃ O ₄ /FeO/Fe composite nanoparticles, so as to finally obtain composite negative electrode materials for lithium-ion batteries; The controlled atmosphere is at least one of inert gas, nitrogen and air; the inert gas is preferably argon. 3 . The method for preparing a composite negative electrode material for lithium ion batteries according to claim 2 , wherein, in the step (2), the heat treatment is performed at a temperature of 600° C. to 800° C. for 1 h to 10 h. 4 . 4. the preparation method of composite negative electrode material for lithium ion battery as claimed in claim 2, is characterized in that, in described step (1), described carbon source raw material is carbohydrate, polyacrylic acid polymer, polyacrylic acid ester Polymers, at least one of polyolefin polymers and their respective derivatives. 5. as claimed in claim 2, the preparation method of composite negative electrode material for lithium ion batteries is characterized in that, in the described step (1), the α-Fe ₂ O ₃ raw materials and the quality of both the carbon source raw materials The ratio is 1:0.2～1:10. 6. the preparation method of composite negative electrode material for lithium ion battery as claimed in claim 2, is characterized in that, before carrying out the described heat treatment in described step (2), described precursor has also been through drying treatment; Preferred , the drying temperature of the drying treatment is 60°C to 120°C.