Microrod-like iron-based bimetallic oxide and preparation method and application thereof

Abstract

The invention relates to the technical field of electrode materials, in particular to a micron rod-shaped iron-based bimetallic oxide and a preparation method and application thereof. The method comprises the following steps: mixing 1, 5-pentanediol, water and ethylenediamine to obtain a mixed solvent; soluble iron salt and soluble metal salt are jointly dissolved in a mixed solvent, a hydrothermal reaction is carried out, and the micron rod-shaped iron-based bimetallic oxide is obtained; wherein the soluble metal salt is selected from soluble zinc salt, soluble nickel salt, soluble copper salt or soluble cobalt salt. The micron rod-shaped iron-based bimetallic oxide prepared by one-step reaction through a solvothermal method is of a fusiform solid structure and is high in structural stability, and the solid micron rod structure of the micron rod-shaped iron-based bimetallic oxide negative electrode prepared by taking the micron rod-shaped iron-based bimetallic oxide as a raw material is effectively maintained and is not easy to pulverize in the charge-discharge cycle process, so that the service life of the micron rod-shaped iron-based bimetallic oxide negative electrode is prolonged, and the service life of the micron rod-shaped iron-based bimetallic oxide negative electrode is prolonged. Furthermore, the specific capacity and the cycling stability of the lithium ion battery under high current density are improved, and the defects in the prior art are overcome.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrode materials, in particular to a microrod-shaped iron-based double metal oxide and a preparation method and application thereof. BACKGROUND

[0002] Since lithium ion batteries entered the market in 1991, they have developed from power sources for small appliances to driving power sources for electric vehicles. Currently, the theoretical specific capacity of commercialized graphite-based carbon negative electrode materials is only 372 mAh / g, and lithium dendrites are easily formed during rapid charging, causing short circuits in the battery and safety problems. Therefore, developing negative electrode materials with higher specific capacity, good safety and long cycle life has become a hot topic in the research of lithium ion batteries. In recent years, iron-based double metal oxide (MFe2O4, M=Co, Zn, Ni, Cu) negative electrode materials have attracted widespread attention due to their high theoretical specific capacity (>900 mAh / g). However, due to the "conversion type" lithium storage mechanism of iron-based double metal oxides, the phase transition and large volume change of the material during the cycle process easily cause material pulverization, and there are still defects such as low charge-discharge capacity and poor cycle stability at high current density.

[0003] Researchers often use methods such as constructing porous micro-nano hierarchical structures or nanosizing materials to buffer the large volume change to solve the above problems. However, the tap density of porous materials and nanosized materials is not high, which is not conducive to improving the energy density of the battery. In addition, nanosized materials are difficult to mix and require more conductive agents and binders when making electrode sheets. In contrast, solid micrometer-sized negative electrode materials are more ideal. How to simply prepare micrometer-sized negative electrode materials with high activity and long cycle life is an important topic for the development of lithium ion batteries.

[0004] Currently, the existing methods for preparing iron-based double metal oxides reported mainly include hydrothermal method, solvothermal method, electrospinning method and template method. Among them, the hydrothermal method and the solvothermal method often use surfactants to control the morphology and size of the material, increasing the cost and making it difficult to recycle and treat the waste liquid. The material prepared by the electrospinning method is nanofibrous, and the preparation cost is high. The microstructure of the material determines its low tap density, which is difficult to improve the energy density of the battery. The template method has a complicated preparation process, and the use of templates increases the steps and the synthesis cost. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a kind of microrod-shaped iron-based double metal oxide and its preparation method and application, the present application uses 1,5-pentanediol, water and ethylenediamine as solvent medium, uses soluble iron salt and soluble metal salt (soluble zinc salt, soluble nickel salt, soluble copper salt or soluble cobalt salt) as raw material, without additional surfactant and template agent, by solvothermal method one-step reaction is prepared microrod-shaped iron-based double metal oxide (MFe2O4, M=Co or Zn or Ni or Cu), and microrod-shaped iron-based double metal oxide presents solid structure, its structure stability is strong, in the process of charge and discharge cycle, the morphology of microrod can be effectively maintained and is not prone to powder phenomenon, overcome the defects of prior art.

[0006] In order to achieve the above object, the technical scheme adopted by the present application is: The first object of the present application is to provide a preparation method of microrod-shaped iron-based double metal oxide, comprising the following steps: S1, 1,5-pentanediol and water are used as solvents, ethylenediamine is used as alkali source, the solvent and alkali source are mixed to obtain a mixed solvent. Among them, ethylenediamine is used as alkali source to provide alkaline reaction conditions, and non-alkaline conditions cannot react to generate microrod-shaped iron-based double metal oxide. In addition, 1,5-pentanediol, water and ethylenediamine are reaction solvent medium, and ethylenediamine together controls the morphology and size of microrod-shaped iron-based double metal oxide. If other alkali sources are used, although the reaction can be carried out, solid microrod product cannot be obtained.

[0007] S2, soluble iron salt and soluble metal salt are dissolved in the mixed solvent to carry out hydrothermal reaction. During the hydrothermal reaction, ethylenediamine in the mixed solvent ionizes to generate hydroxyl ions, and Fe 3+ , metal salt ions and hydroxyl ions react to form double metal oxide to obtain microrod-shaped iron-based double metal oxide.

[0008] Among them, the soluble metal salt is selected from soluble zinc salt, soluble nickel salt, soluble copper salt or soluble cobalt salt. Taking soluble cobalt salt as an example, the mechanism is as follows: H2NCH2CH2NH2+2H2O⇌H3NCH2CH2NH3 2+ +2OH - 、Co 2+ +2Fe 3+ +8OH − →CoFe2O4+4H2O.

[0009] Preferably, the molar ratio of Fe 3+ in the soluble iron salt to the metal ion in the soluble metal salt is 2:1. The microrod-shaped iron-based double metal oxide of the present application is a single-phase substance, such as CoFe2O4, with a fixed elemental composition ratio.

[0010] Preferably, the volume ratio of 1,5-pentanediol, ethylenediamine and water in the mixed solvent is 4-6:5-10:1.

[0011] Preferably, the hydrothermal reaction is carried out at 150-180℃ for 4-7h.

[0012] Preferably, the prepared microrod-shaped iron-based bimetallic oxide is further subjected to washing and drying treatment, and the drying treatment is carried out at 70-90℃.

[0013] The second object of the present application is to provide the microrod-shaped iron-based bimetallic oxide prepared by the above preparation method.

[0014] Preferably, the microrod-shaped iron-based bimetallic oxide has a spindle-shaped solid structure.

[0015] Preferably, the microrod-shaped iron-based bimetallic oxide has monodispersity, the length of the microrod-shaped iron-based bimetallic oxide is 0.6-2.0μm, the maximum diameter of the middle part is 0.2-0.4μm, and the specific surface area is 5-10m 2 2 / g.

[0016] The third object of the present application is to provide a microrod-shaped iron-based bimetallic oxide negative electrode, which is prepared by using the above microrod-shaped iron-based bimetallic oxide, a conductive agent, a binder, a solvent and a current collector, dissolving the microrod-shaped iron-based bimetallic oxide, the conductive agent and the binder in the solvent to obtain a slurry; and loading the slurry on the current collector to obtain the microrod-shaped iron-based bimetallic oxide negative electrode.

[0017] Preferably, the mass ratio of the microrod-shaped iron-based bimetallic oxide, the conductive agent and the binder is 75-80:10-15:10.

[0018] Preferably, the conductive agent is selected from Super P or conductive carbon black, acetylene black.

[0019] Preferably, the binder is polyvinylidene fluoride.

[0020] Preferably, the solvent is N-methylpyrrolidone.

[0021] Preferably, the current collector is copper foil.

[0022] The fourth object of the present application is to provide a lithium ion battery, which is prepared by using the microrod-shaped iron-based bimetallic oxide negative electrode, a positive electrode, a separator and an electrolyte.

[0023] Compared with the prior art, the present application has the following beneficial effects: ​1. The application provides a preparation method of microrod-shaped iron-based bimetallic oxide, wherein 1,5-pentanediol and water are used as solvents, ethylenediamine is used as an alkali source, the solvent and the alkali source are mixed to obtain a mixed solvent, a soluble iron salt and a soluble metal salt are dissolved in the mixed solvent to perform a hydrothermal reaction, during the hydrothermal reaction, the ethylenediamine in the mixed solvent is ionized to generate hydroxyl ions, and the hydroxyl ions and the metal salt ions react to form a bimetallic oxide, thereby obtaining the microrod-shaped iron-based bimetallic oxide; wherein the soluble metal salt is selected from a soluble zinc salt, a soluble nickel salt, a soluble copper salt or a soluble cobalt salt. 3+ The microrod-shaped iron-based bimetallic oxide prepared by the method has a solid microrod structure and excellent stability, and can maintain structural stability during the charging and discharging process of a battery, thereby achieving a long cycle life.

[0024] 2. Compared with the prior art, the preparation method has the advantages of simple process flow, strong operability, mild reaction conditions and no need for an additional calcination treatment process, thereby effectively saving energy and significantly reducing the stringent requirements for the safety performance of equipment. Meanwhile, the preparation method can realize controllable size of the microrod-shaped iron-based bimetallic oxide with good reproducibility. In addition, the solvent medium used in the application has low cost and is easy to recycle and reuse, and no pollutants are generated during the preparation process, which is green and environmentally friendly.

[0025] 3. The microrod-shaped iron-based bimetallic oxide negative electrode prepared from the microrod-shaped iron-based bimetallic oxide prepared by the method has excellent large-current charging and discharging performance and excellent cycle stability. Specifically, the discharge capacity is as high as 412 mAh / g at a current of 4 A / g. After 1400 charging and discharging cycles at a current density of 0.5 A / g, the discharge capacity can still reach 688 mAh / g, and therefore, the microrod-shaped iron-based bimetallic oxide negative electrode can be used as an ideal choice for lithium ion power battery and lithium ion energy storage battery negative electrode materials. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The XRD pattern of CoFe2O4 prepared in Example 1.

[0027] Figure 2 The SEM pattern of CoFe2O4 prepared in Example 1.

[0028] Figure 3 The TEM pattern of CoFe2O4 prepared in Example 1.

[0029] Figure 4 Rate capability plot of the coin cell made with CoFe2O4 of Example 1.

[0030] Figure 5 Long cycle capability plot of the coin cell made with CoFe2O4 of Example 1.

[0031] Figure 6 SEM image of the electrode sheet made with CoFe2O4 of Example 1 after 400 cycles.

[0032] Figure 7 SEM image of ZnFe2O4 made of Example 2.

[0033] Figure 8 SEM image of NiFe2O4 made of Example 3.

[0034] Figure 9 SEM image of CuFe2O4 made of Example 4. DETAILED DESCRIPTION

[0035] The technical solutions of the present application will be described clearly and completely below in combination with the data in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0036] It should be noted that the professional terms used in the present application are only for the purpose of describing the specific embodiments and are not intended to limit the scope of protection of the present application. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present application can be purchased from the market or prepared by the existing method.

[0037] In the prior art, the reported existing methods for preparing iron-based bimetallic oxides mainly include hydrothermal method, solvothermal method, electrospinning method and template method. Among them, the hydrothermal method and the solvothermal method use surfactants to control the material morphology size, which increases the cost and the waste liquid is not easy to recover and process. The material prepared by electrospinning is nanofiber, which has high preparation cost, and the microstructure of the material determines that the compaction density is low, which is difficult to improve the energy density of the battery. The template method has a complicated preparation process, and the use of templates increases the steps and the synthesis cost.

[0038] In view of the problems in the prior art, the application provides a preparation method of a microrod-shaped iron-based double metal oxide, which comprises the following steps: mixing 1, 5-pentanediol, water and ethylenediamine to obtain a mixed solvent; dissolving a soluble iron salt and a soluble metal salt in the mixed solvent to perform a hydrothermal reaction, wherein, in the hydrothermal reaction process, the ethylenediamine in the mixed solvent is ionized to generate hydroxyl ions, and the hydroxyl ions react with metal salt ions to form a double metal oxide, so that a microrod-shaped iron-based double metal oxide is obtained; and the soluble metal salt is selected from a soluble zinc salt, a soluble nickel salt, a soluble copper salt or a soluble cobalt salt. 3+

[0039] In view of the problems that the iron-based double metal oxide is pulverized due to a large volume change in a cycle process, has low charge-discharge capacity under a high current density and has poor cycle stability, the microrod-shaped iron-based double metal oxide (MFe2O4) with a shuttle-shaped solid structure is prepared by using a specific solvent system (1, 5-pentanediol / water / ethylenediamine) through one-step solvothermal method, so that the problems are overcome.

[0040] In view of the problems that the materials prepared by the existing methods (hydrothermal method, solvothermal method needing to add a surfactant, electrospinning method obtaining nanofibers and template method having a complicated process) have low tap density or cause electrode processing difficulty (nanomaterials needing more conductive agents and binders, slurry mixing difficulty), the target product is obtained through one-step solvothermal reaction by using only 1, 5-pentanediol, water and ethylenediamine as a mixed solvent medium without additional addition of a surfactant and a template agent, so that the problems are overcome.

[0041] In order to enable those skilled in the art to more clearly understand the technical solutions of the application, the technical solutions of the application will be described in detail below with reference to specific embodiments: Embodiment 1 A preparation method of a microrod-shaped iron-based double metal oxide comprises the following steps: S1, 2mmol of cobalt nitrate hexahydrate and 4mmol of iron nitrate nonahydrate are dissolved in a mixed solvent composed of 25mL of 1, 5-pentanediol, 5mL of deionized water and 5mL of ethylenediamine to obtain a clear solution.

[0042] S2, the clear solution is transferred to a hydrothermal reaction kettle, heated to 170 DEG C and kept at a constant temperature for 6h, after the reaction kettle is cooled to room temperature, the precipitate is collected by filtration and repeatedly washed with deionized water, and dried at 80 DEG C to obtain a microrod-shaped iron-based double metal oxide, which is denoted as CoFe2O4.

[0043] Embodiment 2 A preparation method of a microrod-shaped iron-based double metal oxide comprises the following steps:​ S1. Dissolve 2 mmol of zinc nitrate hexahydrate and 4 mmol of ferric nitrate nonahydrate in a mixed solvent consisting of 20 mL of 1,5-pentanediol, 5 mL of deionized water, and 4 mL of ethylenediamine, and stir to obtain a clear solution.

[0044] S2. Transfer the clarified solution to a hydrothermal reactor, heat it to 170°C and maintain the temperature for 6 hours. After the reactor cools to room temperature, filter and collect the precipitate, wash it repeatedly with deionized water, and dry it at 80°C to obtain micron-rod-shaped iron-based bimetallic oxide, which is recorded as ZnFe2O4.

[0045] Example 3 A method for preparing micron-rod-shaped iron-based bimetallic oxides comprises the following steps: S1. Dissolve 2 mmol of nickel nitrate hexahydrate and 4 mmol of ferric nitrate nonahydrate in a mixed solvent consisting of 25 mL of 1,5-pentanediol, 10 mL of deionized water, and 3 mL of ethylenediamine, and stir to obtain a clear solution.

[0046] S2. Transfer the clarified solution to a hydrothermal reactor, heat it to 160°C and maintain the temperature for 5 hours. After the reactor cools to room temperature, filter and collect the precipitate, wash it repeatedly with deionized water, and dry it at 80°C to obtain a micron-rod-shaped iron-based bimetallic oxide, which is recorded as NiFe2O4.

[0047] Example 4 A method for preparing micron-rod-shaped iron-based bimetallic oxides comprises the following steps: S1. Dissolve 2 mmol of copper nitrate trihydrate and 4 mmol of ferric nitrate nonahydrate in a mixed solvent consisting of 20 mL of 1,5-pentanediol, 8 mL of deionized water, and 6 mL of ethylenediamine, and stir well to obtain a clear solution.

[0048] S2. Transfer the clarified solution to a hydrothermal reactor, heat it to 180°C and maintain the temperature for 5 hours. After the reactor cools to room temperature, filter and collect the precipitate, wash it repeatedly with deionized water, and dry it at 80°C to obtain a micron-rod-shaped iron-based bimetallic oxide, which is recorded as CuFe2O4.

[0049] Depend on Figure 1 It was found that the micron-rod-shaped iron-based bimetallic oxide prepared in Example 1 of the present invention has a CoFe2O4 spinel phase structure and high crystallinity.

[0050] Depend on Figure 2 The results show that the CoFe2O4 prepared in Example 1 of the present invention has a spindle-shaped solid microrod morphology and is monodisperse. The length of the spindle-shaped microrod is 1.2μm~2.0μm, and the maximum diameter of the spindle-shaped microrod in the middle is about 0.38μm. Figure 3It is further proved that the CoFe2O4 solid microrod has a structure feature.

[0051] It is obtained that the ZnFe2O4 prepared in the embodiment 2 of the present application has a shuttle-shaped microrod morphology. Figure 7 It is obtained that the ZnFe2O4 prepared in the embodiment 2 of the present application has a shuttle-shaped microrod morphology.

[0052] It is obtained that the ZnFe2O4 prepared in the embodiment 2 of the present application has a shuttle-shaped microrod morphology. Figure 8 It is obtained that the ZnFe2O4 prepared in the embodiment 2 of the present application has a shuttle-shaped microrod morphology.

[0053] It is obtained that the ZnFe2O4 prepared in the embodiment 2 of the present application has a shuttle-shaped microrod morphology. Figure 9 It is obtained that the ZnFe2O4 prepared in the embodiment 2 of the present application has a shuttle-shaped microrod morphology.

[0054] The microrod-shaped iron-based double metal oxides are prepared in the embodiments 1 to 4 of the present application, and the effects are parallel, and the microrod-shaped iron-based double metal oxide prepared in the embodiment 1 is taken as an example, and the microrod-shaped iron-based double metal oxide negative electrode is prepared by the following method: CoFe2O4, Super P conductive carbon and polyvinylidene fluoride binder are mixed in a mass ratio of 75:15:10, N-methyl pyrrolidone solvent is added and stirred uniformly to prepare a slurry; the slurry is coated on a copper foil and vacuum dried at 70 DEG C to obtain the microrod-shaped iron-based double metal oxide negative electrode.

[0055] The microrod-shaped iron-based double metal oxide negative electrode is assembled into a button cell, a metal lithium sheet is used as a counter electrode, a polypropylene porous film is used as a separator, 1 mol of lithium hexafluorophosphate is dissolved in 1L of a mixed solvent composed of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate to prepare an electrolyte, and a CR2016 button cell is assembled.

[0056] The electrochemical performance of the microrod-shaped iron-based double metal oxide negative electrode is studied, and the constant current charge and discharge test is carried out on a CT2001A battery test system, and the voltage range is 0.01V~3V, and the specific conditions are as follows: It is obtained that the average discharge capacity under the current density of 0.2A / g is as high as 800mAh / g, and the average discharge capacity under the large current density of 4A / g is still 412mAh / g, and excellent high rate performance is shown. Figure 4 It is obtained that the average discharge capacity under the current density of 0.2A / g is as high as 800mAh / g, and the average discharge capacity under the large current density of 4A / g is still 412mAh / g, and excellent high rate performance is shown.

[0057] It is obtained that the average discharge capacity under the current density of 0.2A / g is as high as 800mAh / g, and the average discharge capacity under the large current density of 4A / g is still 412mAh / g, and excellent high rate performance is shown. Figure 5It is concluded that the discharge capacity is 688 mAh / g after 1400 cycles at a current density of 0.5 A / g, indicating that the micron rod-shaped iron-based double metal oxide negative electrode prepared by the application has excellent cycle stability.

[0058] By Figure 6 It is concluded that the CoFe2O4 still maintains the original shuttle-shaped micron rod morphology after 400 repeated charge-discharge cycles, without breaking or pulverization, indicating that it has excellent structural stability, thereby making the micron rod-shaped iron-based double metal oxide negative electrode have a long cycle life. This is because the solid micron rod structure prepared by the application has a significant structural advantage, which is strong in structural stability, and the morphology of the micron rod can be effectively maintained and is not prone to pulverization during the charge-discharge cycle process. This feature is beneficial to improve the tap density of the micron rod-shaped iron-based double metal oxide negative electrode, thereby improving the energy density of the lithium ion battery, so that more mass of electrode material can be loaded on the electrode sheet of the same volume. In addition, the rod-shaped structure provides a favorable channel for the diffusion of lithium ions in the electrode material, which can accelerate the diffusion speed of lithium ions, thereby ensuring higher capacity performance under large current charge-discharge conditions.

[0059] It should be noted that when numerical ranges are involved in the present application, both endpoints of each numerical range and any number between the two endpoints can be selected. Since the same steps and examples are used, in order to prevent repetition, the preferred embodiments of the present application are described. Although the preferred embodiments of the present application have been described, those skilled in the art can make further changes and modifications to these embodiments once they know the basic inventive concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

Claims

1. A method for preparing micron-rod-shaped iron-based bimetallic oxide, characterized in that: The steps include: 1,5-pentanediol and water are used as solvents, ethylenediamine is used as an alkali source, and the solvent and the alkali source are mixed to obtain a mixed solvent; Soluble iron salt and soluble metal salt are dissolved in a mixed solvent and subjected to a hydrothermal reaction. During the hydrothermal reaction, ethylenediamine in the mixed solvent is ionized to generate hydroxide ions, and Fe 3+ , metal salt ions react with hydroxide ions to form bimetallic oxides, thereby obtaining micron-rod-shaped iron-based bimetallic oxides; Wherein, the soluble metal salt is selected from soluble zinc salt, soluble nickel salt, soluble copper salt or soluble cobalt salt.

2. The method for preparing micron-rod-shaped iron-based bimetallic oxide according to claim 1, characterized in that: Fe in soluble iron salts 3+ The molar ratio of the metal ions to the soluble metal salt is 2:

1.

3. The method for preparing micron-rod-shaped iron-based bimetallic oxide according to claim 1, characterized in that: In the mixed solvent, the volume ratio of 1,5-pentanediol, ethylenediamine and water is 4~6:5~10:

1.

4. The method for preparing micron-rod-shaped iron-based bimetallic oxide according to claim 1, characterized in that: The conditions of the hydrothermal reaction are: reaction at 150°C~180°C for 4h~7h.

5. A micron rod-shaped iron-based bimetallic oxide, characterized in that: The micron-rod-shaped iron-based bimetallic oxide is prepared by the preparation method according to any one of claims 1 to 4.

6. The micron-rod-shaped iron-based bimetallic oxide according to claim 5, characterized in that: The micron-rod-shaped iron-based bimetallic oxides present a spindle-shaped solid structure.

7. The micron-rod-shaped iron-based bimetallic oxide according to claim 6, characterized in that: The micron rod-shaped iron-based bimetallic oxide is monodisperse. The length of the micron rod-shaped iron-based bimetallic oxide is 0.6μm~2.0μm, the maximum diameter in the middle is 0.2μm~0.4μm, and the specific surface area is 5m 2 / g~10m 2 / g.

8. A micron rod-shaped iron-based bimetallic oxide negative electrode, characterized in that: The micron-rod-shaped iron-based bimetallic oxide negative electrode is prepared from the micron-rod-shaped iron-based bimetallic oxide according to claim 5, a conductive agent, a binder, a solvent and a current collector. The micron-rod-shaped iron-based bimetallic oxide, the conductive agent and the binder are dissolved in a solvent to prepare a slurry; the slurry is loaded on a current collector and dried to obtain a micron-rod-shaped iron-based bimetallic oxide negative electrode.

9. The micron rod-shaped iron-based bimetallic oxide negative electrode according to claim 8, characterized in that: The mass ratio of the micron rod-shaped iron-based bimetallic oxide, the conductive agent and the binder is 75-80:10-15:

10.

10. A lithium ion battery, characterized in that: The lithium-ion battery is made of the micron-rod-shaped iron-based bimetallic oxide negative electrode, positive electrode, separator and electrolyte described in claim 8.

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