CN111533171A

CN111533171A - Simple calcination method for preparing porous MnO2Method (2)

Info

Publication number: CN111533171A
Application number: CN202010266243.5A
Authority: CN
Inventors: 李秀万
Original assignee: Huaqiao University
Current assignee: Huaqiao University
Priority date: 2020-04-07
Filing date: 2020-04-07
Publication date: 2020-08-14
Anticipated expiration: 2040-04-07
Also published as: CN111533171B

Abstract

The invention discloses a simple calcination method for preparing porous MnO₂The method comprises the steps of taking potassium permanganate as a manganese source, taking n-butanol as a carbon source, adopting a liquid phase synthesis method to carry out uniform reaction in a water bath, carrying out centrifugal washing and drying on the obtained product, and then carrying out annealing treatment on the dried product to obtain black powder, namely the final product. The invention designs a simple and cheap liquid phase synthesis method, which can realize large-scale preparation of MnO by combining simple calcination in air₂And (3) nano materials. Preparation to obtain MnO₂The nano-sized particles are uniformly distributed, obvious gaps are formed among the particles, the lithium ion diffusion distance is favorably shortened, the contact area with electrolyte is increased, and the MnO can be greatly improved₂Lithium storage properties of the samples.

Description

Simple calcination method for preparing porous MnO2Method (2)

Technical Field

The invention belongs to the technical field of nano material preparation, and particularly relates to a method for preparing porous MnO by a simple calcination method₂The method of (1).

Background

Nanostructured inorganic materials are receiving increasing attention because of their special electrical, optical, mechanical and thermal properties. The manganese oxide compound has rich resource, low cost, no environmental pollution, changeable composition, complicated structure,The special function shows wide application prospect in the fields of electronics, batteries, catalysis, high-temperature superconduction, giant magnetoresistance materials, ceramics and the like, so the research on the preparation method, the structural representation, the reaction mechanism and the application of the material is attracted attention. Wherein MnO is₂As an important inorganic functional material, the organic functional material has been widely applied in the fields of catalysis, electrode materials and the like.

Graphite is mostly adopted as a negative electrode material in the traditional commercial lithium ion battery, but the performance improvement of the lithium ion battery is limited due to the lower specific capacity (372mAh/g) and energy density of the graphite. Compared with the prior art, the manganese oxide has various advantages as the negative electrode material of the lithium ion battery: firstly, the manganese oxide has higher theoretical specific capacity (700-1200mAh/g) which is more than twice of that of a graphite material (which provides a space for developing a high-capacity lithium ion battery); secondly, among the currently known transition group metal oxides, manganese oxide has the lowest charge-discharge plateau (about 0.4V) (which is advantageous for increasing the voltage and power of lithium ion batteries); finally, the storage amount of manganese element in the earth crust is rich, the price of manganese oxide raw material is lower, the environmental pollution is less, and the method has wide commercial prospect. At present, the preparation methods for preparing manganese dioxide nano materials are more, and mainly comprise a sol-gel method, a hydrothermal method, a precipitation method, an electrospinning method, a gas-phase precipitation method and the like. However, these methods have the disadvantages of complicated preparation process, high production cost, low efficiency, high-end required equipment, inability of realizing large-scale production, and the like, and have little significance for commercial application.

Aiming at the problem, the design of a high-performance manganese oxide cathode material which is simple in preparation, low in cost and easy to produce in a large scale becomes a key. In the idea, the porous material is prepared by a calcination method to be the first choice. The calcination method is the most common material synthesis method in industry, and not only is the method simple and the steps simple, but also more importantly, the anode material of the lithium ion battery is mainly prepared by the calcination method at present. Therefore, the method has the advantage of equipment recycling in lithium ion battery material synthesis enterprises. However, materials prepared by an industrial calcination method are often in a micron scale, the morphology uniformity is poor, and the performance is difficult to meet the requirements of the lithium ion battery cathode. Therefore, a porous structure is designed to relieve the problem of uneven morphology of the calcining method.

Disclosure of Invention

In order to solve the problem that the porous manganese oxide material in the current lithium ion battery cathode material is difficult to prepare on a large scale, the invention provides a simple calcination method for preparing porous MnO₂The method of (1).

In order to achieve the above object, the present invention is realized by:

simple calcination method for preparing porous MnO₂The method comprises the steps of taking potassium permanganate as a manganese source, taking n-butanol as a carbon source, adopting a liquid phase synthesis method to carry out uniform reaction in a water bath, carrying out centrifugal washing and drying on the obtained product, and then carrying out annealing treatment on the dried product, wherein the obtained black powder is the final product.

Further, the annealing treatment is to transfer the dried product to a tubular furnace, heat the product to 300-500 ℃ at the speed of 2-5 ℃/min in the air atmosphere, keep the temperature for 3-6h, and then naturally cool the product.

Further, the heating rate of the annealing treatment is 2 ℃/MIN, the temperature is raised to 400 ℃, the temperature is kept for 3H, and then the temperature is naturally reduced.

Further, the ratio of the potassium permanganate to the n-butyl alcohol is 10-13:1mg/mL, the potassium permanganate is placed into a container filled with the n-butyl alcohol, water bath heating is adopted, heating is carried out to 60-80 ℃, reaction is carried out, and the reaction time is 6-12 h.

Further, the drying of the product obtained after the water bath reaction is carried out in an oven at the temperature of 60-80 ℃ for 30-60 min.

Compared with the prior art, the invention has the following beneficial effects:

the invention designs a simple and cheap liquid phase synthesis method, which can realize large-scale preparation of MnO by combining simple calcination in air₂And (3) nano materials. Preparation to obtain MnO₂The nano-sized particles are uniformly distributed, obvious gaps are formed among the particles, the lithium ion diffusion distance is favorably shortened, the contact area with electrolyte is increased, and the MnO can be greatly improved₂Lithium storage properties of the samples. First discharge capacity at a current density of 1000mA/gReach 1366.4mAh/g, and the discharge capacity can still be kept at about 850mAh/g after 250 times of circulation, and the lithium ion battery has excellent circulation stability. The lithium storage performance test result shows that ideal MnO can be prepared in a large scale by a simple method₂Anode material, which enables the commercial production of MnO₂And the graphite material can replace the traditional graphite material, and has wide market prospect.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is an XRD pattern of a sample before and after annealing according to the present invention.

FIG. 2 is SEM images of samples before and after annealing according to the present invention at different magnifications.

FIG. 3 is a graph showing the results of a charge/discharge experiment of a sample of MnO2 at a current density of 500mA/g according to the present invention₂Sample charge-discharge capacity and coulombic efficiency curve; (b) MnO at a current density of 500mA/g₂A sample charge-discharge curve; (c) is MnO₂A charge-discharge specific capacity curve of the sample under different current densities; (d) is a charge-discharge curve corresponding to the graph (c) at different current densities; (e) MnO at 1000mA/g Current Density₂Charge-discharge capacity curve for the first 250 cycles of the sample.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments that can be derived by one of ordinary skill in the art from the embodiments given herein are intended to be within the scope of the present invention.

According to the embodiment of the invention, a simple calcination method is provided for preparing porous MnO₂Method (2)The simple calcination method is used for preparing the porous MnO₂The method comprises the steps of taking potassium permanganate as a manganese source, taking n-butanol as a carbon source, adopting a liquid phase synthesis method to carry out uniform reaction in a water bath, carrying out centrifugal washing and drying on the obtained product, and then carrying out annealing treatment on the dried product, wherein the obtained black powder is the final product.

In the embodiment of the invention, the annealing treatment is to transfer the dried product into a tubular furnace, heat the dried product to 300-500 ℃ at the speed of 2-5 ℃/min in the air atmosphere, keep the temperature for 3-6h, and then naturally cool the product. As a preferable scheme of the embodiment of the present invention, the temperature increase rate of the annealing treatment is 2 ℃/min, specifically, the temperature is increased to 400 ℃ at the rate of 2 ℃/min, the temperature is maintained for 3 hours, and then the temperature is naturally reduced.

Wherein the dosage ratio of the potassium permanganate to the n-butyl alcohol is 10-13:1mg/mL, the potassium permanganate is placed into a container filled with the n-butyl alcohol, water bath heating is adopted, heating is carried out to 60-80 ℃, reaction is carried out, and the reaction time is 6-12 h.

Wherein, the drying of the product obtained after the water bath reaction is carried out in an oven at the temperature of 60-80 ℃ for 30-60 min.

The following is a detailed description of specific embodiments.

Example 1

500mg of KMnO₄40mL of n-butanol (CH) was added₃(CH₂)₂CH₂OH), stirring for 10min, and heating to 80 ℃ for reaction for 12 h. After cooling, the product was washed centrifugally and dried in an oven at 60 ℃ for 30 min. Then, transferring the dried product to a tubular furnace, heating to 400 ℃ at the speed of 2 ℃/min in the air atmosphere, keeping for 3h, and naturally cooling to finally obtain black MnO₂Powder, i.e. porous MnO as final product of the invention₂And (3) nano materials.

Example 2

400mg of KMnO₄40mL of n-butanol (CH) was added₃(CH₂)₂CH₂OH), stirring for 10min, and heating to 70 ℃ for reaction for 12 h. After cooling, the product was washed centrifugally and dried in an oven at 70 ℃ for 50 min. Subsequently, the dried product is driedTransferring to a tubular furnace, heating to 450 deg.C at a speed of 2 deg.C/min in air atmosphere, maintaining for 3 hr, and naturally cooling to obtain black MnO₂Powder, i.e. porous MnO as final product of the invention₂And (3) nano materials.

Example 3

450mg of KMnO₄40mL of n-butanol (CH) was added₃(CH₂)₂CH₂OH), stirring for 10min, and heating to 80 ℃ for reaction for 10 h. After cooling, the product was washed centrifugally and dried in an oven at 80 ℃ for 30 min. Then, transferring the dried product to a tubular furnace, heating to 460 ℃ at the speed of 2 ℃/min in the air atmosphere, keeping for 3h, and naturally cooling to finally obtain black MnO₂Powder, i.e. porous MnO as final product of the invention₂And (3) nano materials.

Example 4

500mg of KMnO₄40mL of n-butanol (CH) was added₃(CH₂)₂CH₂OH), stirring for 10min, and heating to 60 ℃ for reaction for 12 h. After cooling, the product was washed centrifugally and dried in an oven at 60 ℃ for 40 min. Then, transferring the dried product to a tubular furnace, heating to 380 ℃ at the speed of 2 ℃/min in the air atmosphere, keeping for 4h, and naturally cooling to finally obtain black MnO₂Powder, i.e. porous MnO as final product of the invention₂And (3) nano materials.

Example 5

500mg of KMnO₄40mL of n-butanol (CH) was added₃(CH₂)₂CH₂OH), stirring for 10min, and heating to 80 ℃ for reaction for 10 h. After cooling, the product was washed centrifugally and dried in an oven at 60 ℃ for 40 min. Then, transferring the dried product to a tubular furnace, heating to 420 ℃ at the speed of 2 ℃/min in the air atmosphere, keeping for 4h, and naturally cooling to finally obtain black MnO₂Powder, i.e. porous MnO as final product of the invention₂And (3) nano materials.

Results and analysis

Based on example 1, the samples before and after calcination in example 1 were used as the target,in order to study the structure and morphology of the sample before and after calcination, X-ray diffraction and scanning electron microscopy tests were performed on the sample. FIG. 1 is an XRD pattern of a sample before and after annealing. As can be seen from fig. 1 (a), the XRD pattern of the sample before annealing is relatively complicated. Wherein, the diffraction peak corresponding to the red line and the MnO of monoclinic system₂The standard cards (JCPDSCard NO.42-1317) are in one-to-one correspondence, and main 5 diffraction peaks are located at 12.5 degrees, 25.3 degrees, 35.3 degrees, 37.3 degrees and 40.0 degrees and respectively correspond to crystal faces (001), (002), (20-1), (11-1) and (201). The diffraction peak corresponding to the blue line is related to the Mn of the tetragonal system₃O₄The standard Card (JCPDS Card NO. 18-0803). Wherein, 5 main diffraction peaks at 18.0 degrees, 28.9 degrees, 32.4 degrees, 36.0 degrees and 60.0 degrees and Mn are respectively₃O₄The (102), (112), (103), (211), and (224) crystal planes of (A) and (B) correspond to each other. In addition, some weak miscellaneous peaks and other phases MnO exist₂And (7) corresponding. The above results indicate that the powder sample before annealing was MnO₂And Mn₃O₄Further demonstrates the complex phase of the product of the low temperature liquid phase synthesis. FIG. 1 (b) is the XRD pattern of the annealed sample, with the diffraction peaks at the same positions as MnO in FIG. 1 (a)₂The diffraction peak positions of the annealing sample are the same, and no other diffraction impurity peaks exist, which indicates that the sample is pure-phase MnO₂. At the same time, MnO₂The diffraction peak is more pronounced and sharp than in fig. 1 (a), indicating that the crystallinity of the sample is improved after annealing.

SEM images of the sample material before and after annealing at different magnifications are respectively obtained through a scanning electron microscope. Fig. 2 (a), (b) and (c) are scanning electron microscope images of the sample before annealing at different magnifications, and it is clear from fig. 2 (a), (b) and (c) that the particle size of the sample before annealing is small and about 50nm in size. These small particles agglomerate and agglomerate with each other to form the mass shown in the figure. FIGS. 2(d), (e) and (f) are SEM pictures of the annealed samples at different magnifications, and the MnO formed after annealing is shown in FIGS. 2(d), (e) and (f)₂The sample particles were approximately 200nm in size due to recrystallization of the small particles prior to annealing. Overall, MnO after annealing₂The particles are uniformly distributed, and obvious gaps exist among the particles. Such a cavityMore-gap and uniformly-distributed structure for MnO₂The volume expansion caused by the reaction plays a role in buffering, the contact area of the active material and the electrolyte is increased, the diffusion length of lithium ions is shortened, and the stability of the battery can be effectively improved.

Porous MnO prepared in example 1 of the present invention₂Performing MnO under a certain current density based on the nano material₂And (4) sample charge and discharge experiments. Shown in FIG. 3 (a) is MnO at a current density of 500mA/g₂Sample cycling stability curve. As shown in (a), MnO₂The first discharge capacity of the sample reaches 1548.3mAh/g, the first charge capacity is only 905.1mAh/g, and the coulomb efficiency of the first charge and discharge is only 58.4%. The irreversible capacity loss up to 643mAh/g is mainly due to two factors: on the one hand, the formation of an irreversible solid electrolyte interface film (SEI) on the electrode surface leads to a higher first charge capacity than MnO₂The theoretical capacity of (a); on the other hand, part of MnO₂The first irreversible lithium intercalation of the particles leads to lower coulombic efficiencies. MnO₂The second discharge capacity of the sample reaches 894.4 mAh/g. After 100 cycles, the discharge capacity is basically kept at about 880mAh/g, which proves that MnO₂The samples were excellent in cycling stability. Meanwhile, the coulombic efficiency of the battery is stabilized to be about 99.0% from the second cycle to the first hundred cycles, and the excellent cycle stability of the sample is further proved. FIG. 3 (b) is a charge-discharge curve corresponding to (a), and the charge-discharge voltage window is 0.02 to 3.00V. It is clear from the figure that two discharge plateaus, at 1.2V and 0.4V, respectively for Mn, appear during the first discharge⁴⁺And Mn²⁺The specific reaction equation of the reduction process is as follows:

MnO₂+2Li⁺+2e^-→MnO+Li₂O

MnO+2Li⁺+2e^-→Mn+Li₂O

likewise, two charging platforms, at 1.3V and 1.8V, corresponding to the metals Mn and Mn, respectively, were also present during the first charging process²⁺The specific reaction equation of the oxidation process is as follows:

Mn+Li₂O→MnO+2Li⁺+2e^-

MnO+Li₂O→MnO₂+2Li⁺+2e^-

after the first charge and discharge, the voltage platforms of the second charge and discharge and the third charge and discharge are the same as the first charge and discharge, and the MnO is proved₂The material has good reversibility. More importantly, the charge-discharge platform of the material is hardly changed after 50 and 100 cycles, and MnO is proved from another aspect₂The samples were excellent in cycling stability.

FIG. 3 (e) is MnO at 1000mA/g Current Density₂Cycling stability curve of the sample. As can be seen from the graph, the first discharge capacity reached 1366.4mAh/g, and the second discharge capacity reached 725.0 mAh/g. In the first 15 cycles, the capacity was slightly reduced, and the 15 th discharge capacity was 657.2 mAh/g. After this, the capacity starts to increase slowly. After 130 cycles, the discharge capacity reaches 891.6 mAh/g. This capacity increase phenomenon often occurs on transition metal oxides, the reason for which is mainly caused by activation of the active material during cycling. As is clear from the figure, MnO was present up to 250 cycles₂The sample capacity is not reduced and is basically stabilized at about 850mAh/g, which proves that MnO₂Cycling stability of the samples.

For further verification of lithium storage performance, for MnO₂The rate characteristics of the samples were tested. MnO in FIG. 3 (c)₂The multiplying power performance graph of different current densities of the sample under a voltage window of 0.02-3.00V. When the current density is respectively 500mA/g, 1000mA/g, 2000 mA/g, 5000mA/g and 10000mA/g, the corresponding specific discharge capacity is respectively 889.7 mAh/g, 714.2 mAh/g, 596.0 mAh/g, 316.7 mAh/g and 122.2 mAh/g. When the current density is recovered to 500mA/g, the specific discharge capacity is increased to 904.5mAh/g again, which indicates that MnO₂The sample has good cycling stability and rate capability. Fig. 3 (d) and fig. 3 (c) show the corresponding charge/discharge curves. It can be seen from the graph that there are two discharge plateaus in the discharge curves at the current densities of 500, 1000, 2000 and 5000mA/g, which is consistent with the results of fig. 3 (b). When the current is increased to 10000mA/g, the original 0.4V discharge is leveled due to the overpotential caused by the large currentThe table is less than 0V, and does not participate in the discharge reaction within the voltage window, resulting in the excessively low specific discharge capacity at the current density of 10000mA/g in (c) of FIG. 3.

In conclusion, the invention designs a simple and cheap liquid phase synthesis method, and the simple calcination in air can realize the large-scale preparation of MnO₂And (3) nano materials. Preparation to obtain MnO₂The nano-sized particles are uniformly distributed, obvious gaps are formed among the particles, the lithium ion diffusion distance is favorably shortened, the contact area with electrolyte is increased, and the MnO can be greatly improved₂Lithium storage properties of the samples. Under the current density of 1000mA/g, the first discharge capacity reaches 1366.4mAh/g, and the discharge capacity can still be kept at about 850mAh/g after the circulation of 250 times, so that the lithium ion battery has excellent circulation stability. The lithium storage performance test result shows that ideal MnO can be prepared in a large scale by a simple method₂Anode material, which enables the commercial production of MnO₂And the graphite material can replace the traditional graphite material, and has wide market prospect.

The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that are not thought of through the inventive work should be included in the scope of the present invention.

Claims

1. Simple calcination method for preparing porous MnO₂The method is characterized in that potassium permanganate is used as a manganese source, n-butanol is used as a carbon source, a liquid phase synthesis method is adopted to carry out uniform reaction in a water bath, the obtained product is centrifugally washed and dried, the dried product is annealed, and the obtained black powder is the final product.

2. The preparation of porous MnO according to claim 1 by a simple calcination method₂The method is characterized in that the annealing treatment is to transfer the dried product into a tube furnace, heat the product to 300-500 ℃ at the speed of 2-5 ℃/min in the air atmosphere, keep the temperature for 3-6h, and then naturally cool the product.

3. Root of herbaceous plantThe preparation of porous MnO by simple calcination method according to claim 2₂The method is characterized in that the temperature rise rate of the annealing treatment is 2 ℃/min, the temperature is raised to 400 ℃, the temperature is kept for 3h, and then the temperature is naturally reduced.

4. The simple calcination process of any one of claims 1 to 3 to produce porous MnO₂The method is characterized in that the dosage ratio of potassium permanganate to n-butyl alcohol is 10-13:1mg/mL, potassium permanganate is placed into a container filled with n-butyl alcohol, water bath heating is adopted, heating is carried out to 60-80 ℃, reaction is carried out, and the reaction time is 6-12 h.

5. The preparation of porous MnO according to claim 4 by a simple calcination method₂The method is characterized in that the drying of the product obtained after the water bath reaction is carried out in an oven at the temperature of 60-80 ℃ for 30-60 min.