Iron trioxide coated hard carbon composite negative electrode material and preparation method and application thereof

Abstract

The invention provides a ferric oxide coated hard carbon composite negative electrode material and a preparation method and application thereof, the composite negative electrode material comprises a core part and a shell which is coated on the surface of the core part and is less than 50nm in thickness, the core part is hard carbon particles, and the particle size of the hard carbon particles is less than 20mu m; the shell is composed of a plurality of ferric oxide particles formed through in-situ deposition, the average particle size of the ferric oxide particles is 6 nm, and the synergistic effect between ferric oxide and hard carbon particles is achieved. The thickness of the ferric oxide shell is very thin, the size of ferric oxide particles in the shell is small, and a void space is formed around any ferric oxide particle, so that the volume change of ferric oxide in the sodium charging and discharging process is buffered, and the cycling stability of ferric oxide is improved. And the hard carbon has high conductivity, and meanwhile, the hard carbon provides an adhesion substrate for the ferric oxide and has the effect of increasing the conductivity. Therefore, the composite negative electrode material has high specific capacity and relatively high cycling stability.

Description

Technical Field

[0001] The invention relates to the field of negative electrode materials for sodium ion batteries, and in particular to a ferric oxide-coated hard carbon composite negative electrode material and a preparation method and application thereof. Background Art

[0002] The working principle of sodium-ion batteries is very similar to that of lithium-ion batteries, but sodium-ion batteries are lower in cost and safer, which makes them an effective supplement to lithium-ion batteries and can avoid development problems caused by resource shortages. Therefore, sodium-ion batteries are considered to be secondary batteries with great potential in the development of new energy and large-scale energy storage. Electrode materials are the key to sodium-ion battery energy storage technology, and the development of excellent electrode materials is the current research focus.

[0003] Hard carbon is an industrialized sodium ion negative electrode material with high specific capacity and stable cycle performance. How to further improve the specific capacity of hard carbon and thus improve the energy density of sodium ion batteries has become a technical difficulty. In terms of storage mechanism, hard carbon mainly relies on embedding sodium ions to store energy, and its sodium ion storage capacity is relatively low. Ferric oxide relies on a conversion mechanism to store sodium, and its sodium storage capacity is higher than that of hard carbon, but its electrical conductivity is low, and the volume change during the sodium storage process can easily lead to the breakage of ferric oxide. The research direction is to obtain high-performance sodium storage composite negative electrode materials by combining ferric oxide with hard carbon. However, the preparation method of the composite materials currently obtained is complicated, and the structure of the composite materials makes it difficult to achieve both high capacity and high cycle stability at the same time.

[0004] In view of the defects of the prior art, the present invention proposes a composite technical solution of ferric oxide and hard carbon to solve the technical problems of the prior art. Summary of the invention

[0005] In order to address the deficiencies in the prior art, the present invention provides a ferric oxide (Fe2O3) coated hard carbon composite negative electrode material and a preparation method and application thereof. The composite negative electrode material has hard carbon particles as the core, and a layer of ferric oxide shell is coated on the surface of the hard carbon particles. There is a good synergistic effect between the ferric oxide and the hard carbon particles, so that the composite negative electrode material has a high specific capacity and high cycle stability.

[0006] In order to achieve the above object, the specific scheme adopted by the present invention is: On the one hand, the present invention provides a ferric oxide-coated hard carbon composite negative electrode material, comprising a core portion and a shell with a thickness of less than 50 nm coated on the surface of the core portion, wherein the core portion is a hard carbon particle, and the particle size of the hard carbon particle is less than 20 μm; the shell is composed of a plurality of ferric oxide particles deposited in situ, and the average particle size of the ferric oxide particles is 6 nm; there is void space around any ferric oxide particle.

[0007] Furthermore, the hard carbon particles are commercial hard carbon particles.

[0008] On the other hand, the present invention provides a method for preparing a ferric oxide coated hard carbon composite negative electrode material, which mainly comprises the following steps: (1) taking DMF and deionized water in a volume ratio of 8:2, and mixing them uniformly to obtain solution A; (2) adding hard carbon particles to solution A, wherein the concentration of hard carbon relative to solution A is 6 mg to 12 mg / mL; (3) Add ferrous chloride hexahydrate and anhydrous sodium acetate to solution A, and stir evenly with a magnetic stirrer at room temperature to obtain solution B; (4) Solution B was placed in a water bath at 90° C., magnetically stirred, and then cleaned and dried to obtain a ferric oxide-coated hard carbon composite negative electrode material.

[0009] The mechanism of preparing the composite negative electrode material of the present invention is as follows: DMF (Chinese name, N, N-dimethylformamide) slowly decomposes at the reaction temperature and releases hydroxide, which produces heterogeneous nucleation on the surface of hard carbon particles, deposits to generate iron hydroxide, and gradually loses water molecules during the reaction to obtain iron oxide particles. Subsequent nucleation and growth allow the iron oxide to form an iron oxide shell on the surface of the hard carbon particles. DMF and acetate have an inhibitory effect on the growth of iron oxide, preventing the iron oxide particles from growing, so that the particle diameter is about 6nm.

[0010] Furthermore, in step (3), the concentration of ferrous chloride hexahydrate relative to solution A is 8 to 12 mg / mL, and the concentration of anhydrous sodium acetate relative to solution A is 15 to 25 mg / mL.

[0011] Furthermore, in step (4), the specific parameters of the magnetic stirring are: stirring speed 400 r / min, stirring time 4 h.

[0012] Furthermore, in step (4), the filter paper is filtered and cleaned with water and alcohol, and after cleaning, it is placed in an oven at 70° C. and dried for 24 hours.

[0013] On the other hand, the present invention provides the use of ferric oxide-coated hard carbon composite negative electrode material in sodium ion batteries.

[0014] Beneficial effects:

[0015] (1) Both ferric oxide and hard carbon particles have the ability to store sodium, but their sodium storage mechanisms are different. Hard carbon mainly relies on embedding or extracting sodium ions to store sodium, while ferric oxide mainly relies on the redox reaction of ferric oxide to store sodium. Although hard carbon has a low sodium storage capacity, it has high cycle stability. Ferrous oxide has a high sodium storage capacity, but its stability is low. The composite negative electrode material in the present invention uses hard carbon particles as the core, and a layer of ferric oxide shell is coated on the surface of the hard carbon particles, thereby achieving a synergistic effect between ferric oxide and hard carbon particles. The thickness of the ferric oxide shell is very thin, and the size of the ferric oxide particles in the shell is small. There is a void space around any ferric oxide particle, so that the volume change of ferric oxide during the process of charging and discharging sodium is buffered, thereby improving the cycle stability of ferric oxide. The hard carbon itself has a high electrical conductivity, and at the same time, it provides an attachment base for ferric oxide and increases the electrical conductivity. Therefore, the composite negative electrode material has a high specific capacity and a high cycle stability.

[0016] (2) The preparation method of the present invention is simple, has low preparation cost, and is suitable for large-scale commercial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the structure of the composite negative electrode material in the present invention.

[0018] Figure 2 Flow chart of the composite negative electrode material in the present invention.

[0019] Figure 3 This is a SEM image of the product obtained in Example 1 of the present invention.

[0020] Figure 4 The XRD diagrams of the products obtained in Example 1 and Comparative Example 1 of the present invention are shown in FIG. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0022] The present invention discloses a ferric oxide (Fe2O3) coated hard carbon composite negative electrode material and its preparation method and application. The composite negative electrode material comprises a core and a shell with a thickness of less than 50nm coated on the surface of the core. The core is a hard carbon particle with a particle size of less than 20μm. The shell is composed of a plurality of ferric oxide particles deposited in situ, and the average particle size of the ferric oxide particles is 6nm. There is a void space around any ferric oxide particle. The composite negative electrode material is applied to the field of sodium ion batteries.

[0023] Please refer to Figure 2 The method for preparing the iron oxide coated hard carbon composite negative electrode material proposed in the present invention comprises the following steps: (1) taking DMF and deionized water in a volume ratio of 8:2, and mixing them uniformly to obtain solution A; (2) adding commercial hard carbon particles to solution A, wherein the concentration of the commercial hard carbon particles relative to solution A is 6 mg to 12 mg / mL; (3) adding ferrous chloride hexahydrate and anhydrous sodium acetate to solution A, wherein the concentration of ferrous chloride hexahydrate relative to the mixed solvent is 8 to 12 mg / mL, and the concentration of anhydrous sodium acetate relative to the mixed solvent is 15 mg to 25 mg / mL, and magnetic stirring is performed at room temperature to obtain solution B; (4) Place solution B in a 90°C water bath, stir with magnetic force, stir at a speed of 400 r / min, stir for 4 hours, filter with water and alcohol, and dry in an oven at 70°C for 24 hours after cleaning. After drying, obtain nano-iron oxide-coated hard carbon composite negative electrode material.

[0024] The technical solution of the present invention is described in detail below in conjunction with specific embodiments and comparative examples. It should be noted that, unless otherwise specified, the materials used in the present invention are all commercially available materials.

[0025] Example 1 A method for preparing a ferric oxide coated hard carbon composite negative electrode material, characterized in that it mainly comprises the following steps: Step 1: Measure 8 mL of DMF and 2 mL of deionized water, mix well to obtain solution A; Step 2: Add 60 mg of commercial hard carbon into solution A; Step 3, add 100 mg of ferrous chloride hexahydrate and 200 mg of anhydrous sodium acetate to solution A, and stir magnetically at room temperature for 15 minutes to obtain solution B; Step 4: Place solution B in a 90°C water bath for magnetic stirring reaction at a speed of 400 rpm for 4 hours. After the reaction, filter and clean the solution with water and alcohol. After cleaning, dry the solution in an oven at 70°C for 24 hours to obtain a ferric oxide-coated hard carbon composite negative electrode material.

[0026] Figure 3 The SEM image of the composite negative electrode material synthesized in this example is shown. It can be seen that the hard carbon surface is coated with a layer of ferric oxide shell, and the diameter of the ferric oxide particles is about 6nm.

[0027] Example 2

[0028] The difference between Example 2 and Example 1 is only that: Step 3, 80 mg of ferrous chloride hexahydrate and 150 mg of anhydrous sodium acetate are added to Solution A.

[0029] Example 3

[0030] The only difference between Example 3 and Example 1 is that: (1) in step 2, 120 mg of commercial hard carbon is added to solution A; (2) in step 3, 120 mg of ferrous chloride hexahydrate and 250 mg of anhydrous sodium acetate are added to solution A.

[0031] Example 4

[0032] The only difference between Example 4 and Example 1 is that: (1) in step 2, 80 mg of commercial hard carbon is added to solution A; (2) in step 3, 80 mg of ferrous chloride hexahydrate and 150 mg of anhydrous sodium acetate are added to solution A.

[0033] Comparative Example 1

[0034] The difference between Comparative Example 1 and Example 1 is that step 3 is not included.

[0035] The products obtained in Example 1 and Comparative Example 1 were subjected to XRD test, and the results are as follows: Figure 4 As shown, the wide diffraction peak around 22° indicates that the hard carbon has a suitable interplanar spacing for sodium storage. The ferric oxide-coated hard carbon composite negative electrode material has a weaker diffraction peak intensity of the hard carbon due to the coating of ferric oxide, and a wider diffraction peak of ferric oxide, indicating that the ferric oxide grains are very small. Since the ferric oxide particle size is consistent with the grain size, the ferric oxide particles are relatively small.

[0036] Weigh the iron oxide-coated hard carbon composite negative electrode material, acetylene black and PVDF binder (according to the mass ratio of 8:1:1), use NMP as solvent, stir evenly to obtain a slurry of suitable viscosity. The slurry is applied to the surface of the copper sheet and placed in a vacuum oven at 100°C for 12 hours. After taking it out, it is pressed with a tablet press at a pressure of 10Mpa. After pressing, a composite electrode sheet is obtained. The prepared electrode sheet is used as the working electrode, glass fiber (Whatman GF / C) is used as the diaphragm, 1.0M sodium hexafluorophosphate (NaPF6) is dissolved in a mixed solution of diethylene glycol dimethyl ether as the electrolyte, and a metal sodium sheet is used as the counter electrode and reference electrode, and assembled into a button cell for testing. At a charge and discharge current density of 100mA / g, the cycle performance of the products obtained in Examples 1-4 and Comparative Example 1 is tested, and the results are shown in Table 1.

[0037] Table 1 Cyclic performance test results of the products obtained from Examples 1-4 and Comparative Example 1 First discharge specific capacity / mAh / g Discharge capacity after 100 cycles / mAh / g Example 1 401.7 348.8 Example 2 396.7 351.2 Example 3 367.4 348.9 Example 4 369.6 347.7 Comparative Example 1 301.1 223

[0038] As shown in Table 1, at a charge and discharge current density of 100 mA / g, the first discharge specific capacity of the products obtained in Examples 1-4 is not less than 360 mAh / g, and the discharge specific capacity after 100 cycles is not less than 340 mAh / g, which has good cycle performance. However, the first discharge specific capacity of the product obtained in Comparative Example 1 is only 301.1 mAh / g, and the capacity after 100 cycles is only 223 mAh / g. It can be seen that the composite negative electrode material prepared by the present invention significantly improves the specific capacity of the material and maintains high cycle stability.

[0039] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any equivalent changes or modifications made according to the essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A ferric oxide coated hard carbon composite negative electrode material, characterized in that: It includes a core and a shell with a thickness of less than 50nm and covering the surface of the core, wherein the core is a hard carbon particle with a particle size of less than 20μm; the shell is composed of a number of ferric oxide particles deposited in situ, and the average particle size of the ferric oxide particles is 6nm; there is a void space around any ferric oxide particle.

2. The iron oxide coated hard carbon composite negative electrode material according to claim 1, characterized in that: The hard carbon particles are commercial hard carbon particles.

3. A method for preparing a ferric oxide-coated hard carbon composite negative electrode material, characterized in that: The main steps are as follows: (1) Take DMF and deionized water in a volume ratio of 8:2 and mix them evenly to obtain solution A; (2) Add hard carbon particles to solution A, and the concentration of hard carbon relative to solution A is 6 mg~12 mg / mL; (3) Add ferrous chloride hexahydrate and anhydrous sodium acetate to solution A and stir evenly with a magnetic stirrer at room temperature to obtain solution B; (4) Place solution B in a 90°C water bath, stir magnetically, and then wash and dry to obtain a ferric oxide-coated hard carbon composite negative electrode material.

4. The method for preparing a ferric oxide-coated hard carbon composite negative electrode material according to claim 3, characterized in that: In step (3), the concentration of ferrous chloride hexahydrate relative to solution A is 8-12 mg / mL, and the concentration of anhydrous sodium acetate relative to solution A is 15 mg-25 mg / mL.

5. The method for preparing a ferric oxide coated hard carbon composite negative electrode material according to claim 3, characterized in that: In step (4), the specific parameters of the magnetic stirring are: stirring speed of 400 r / min and stirring time of 4 h.

6. The method for preparing a ferric oxide-coated hard carbon composite negative electrode material according to claim 3, characterized in that: In step (4), the filter paper is filtered and cleaned with water and alcohol, and after cleaning, it is placed in an oven at 70° C. and dried for 24 hours.

7. Use of the iron oxide coated hard carbon composite negative electrode material as described in any one of claims 1 to 2 in a sodium ion battery.

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