CN112768665A

CN112768665A - Preparation method of MnO/LiF/C composite anode material

Info

Publication number: CN112768665A
Application number: CN202110132662.4A
Authority: CN
Inventors: 陈崛东; 唐安平; 梁子钦; 徐国荣; 宋海申; 陈核章
Original assignee: Hunan University of Science and Technology
Current assignee: Hunan University of Science and Technology
Priority date: 2021-01-31
Filing date: 2021-01-31
Publication date: 2021-05-07
Anticipated expiration: 2041-01-31
Also published as: CN112768665B

Abstract

The invention discloses a preparation method of a MnO/LiF/C composite anode material. The method of the invention comprises the following steps: dissolving manganese acetate, lithium acetate and ammonium fluoride in distilled water to prepare a precursor solution; dispersing high-specific-surface-area carbon such as ketjen black, acetylene black or activated carbon in the precursor solution obtained in the step, and then performing spray drying to obtain precursor powder; and finally, sintering the obtained precursor powder in an inert atmosphere to obtain the MnO/LiF/C composite anode material. Compared with the prior art, the preparation method has the advantages of simple preparation process, wide sintering temperature range, easy control of the process, high purity of the obtained product, uniform distribution of two active components, namely MnO nano-particles and LiF nano-particles generated in situ in the sintering process in the composite material, good cycle performance of the sample and the like.

Description

Preparation method of MnO/LiF/C composite anode material

Technical Field

The invention relates to preparation of a positive electrode material, in particular to a preparation method of a MnO/LiF/C composite positive electrode material.

Background

In recent years, it has been found that a nanosized metal fluoride MF_nReversible switching reactions can occur. The lithium ion battery is considered to be a very competitive positive electrode material in the future due to high electromotive force and large theoretical capacity. However, due to the strong ionic bond character of the M-F bond, the conversion reaction needs to overcome larger activation energy and extremely poor conductivity. In the course of exploring for improvements in MFn electrochemical performance, it was discovered that O is responsible for^2-And F^-The two anions have similar ionic radii and atomic numbers, and may be O^2-Substituted MF_nF in (1)^-And an M-O covalent bond is introduced, so that the conductivity of the material is greatly improved. And MF_nIn contrast, transition Metal Oxyfluoride (MO)_xF_a-x) Showing lower voltage hysteresis and better cycling stability. For example, with strongly ionic FeF₂In contrast, FeOOF contains more Fe-O covalent bonds, which makes FeOOF more conductive than FeF₂The cycle performance is also improved. Similarly, with undoped NiF₂In contrast, NiO-doped NiF₂The doping improves the electronic conductivity, so that the discharge voltage is higher and the reversibility is better. However, MO_xF_a-xThe research on positive electrode materials has been relatively rare, in part due to the lack of readily available manufacturing processes.

In view of MO_xF_a-xThe lack of easily achievable preparation methods has led to attention to the corresponding discharge state active species, i.e., metal oxide-lithium fluoride systems, such as FeO-LiF, MnO-LiF, NiO-LiF systems, and the like, especially MnO-LiF systems. In the MnO-LiF system, Mn³⁺/Mn²⁺(redox potential 2.5V) and Mn⁴⁺/Mn³⁺(redox potential-3.75V) couples all participate in electrochemical reaction, wherein Mn⁴⁺/Mn³⁺The electricity pair mainly participates in highRedox reaction in the voltage interval, Mn³⁺/Mn²⁺The couple participates in the redox reaction throughout the voltage interval. Thus, the surface conversion reaction of MnO-LiF system

The high valence oxidation-reduction reaction of transition metal can be utilized, so that higher discharge capacity and energy density can be obtained. The typical research work for the MnO-LiF system mainly includes:

in 2014, Dimov and collaborators thereof experimentally and theoretically demonstrated the feasibility of using a compound based on LiF electrochemical splitting as a positive active material. They found that the sub-micron samples obtained by mixing LiF and MnO according to the molar ratio of lithium to manganese of 3: 2 and then performing high-energy ball milling have electrochemical activity. Under a specified charge-discharge system, the first charge specific capacity of each sample is 185mAh/g (N Dimov, et al, Electrochemical partitioning of LiF: A New Aproach to Lithium-Ion Battery materials. ECS Trans.2014,58, 87).

2017 and 2018, the group of talascon topics successively reported passing LiPF in electrolyte₆The activation process induced by surface fluorination is triggered by decomposition of the surface of the Cathode polarized MnO, and a highly disordered Mn-O-F phase of Manganese-Based Oxyfluoride is prepared In Situ (L Zhang, et al, Origin of the High Capacity mangese-Based Oxyfluoride Electrodes for Rechargeable batteries. chem. Material, 2018,30, 5362; L Zhang, et al, thickening the In Situ Electrochemical Formation of High Capacity Material From MnO, adv. energy Material, 2017,7, 1602200). When the half cell taking the metal lithium as the cathode is cycled at the rate of C/10, the discharge capacity of 167mAh/g is obtained after the manganese-based oxyfluoride is cycled for 50 weeks, which is equivalent to 90 percent of the first discharge capacity, and the good cycle performance is shown, but the rate performance is not ideal, and when the rate is increased from 0.2C to 0.5C and 1C in sequence, the discharge capacity is decreased from 160mAh/g to 100 mAh/g and 50mAh/g in sequence. On the other hand, with Li₄Ti₅O₁₂The total cell as the negative electrode is 0-3.3V (vs Li)₄Ti₅O₁₂) Interval, current density 5mA/g cycle, although discharge capacity for the first timeUp to-200 mAh/g, the voltage-capacity curve is similar to that of a half cell, but the discharge capacity of the full cell shows approximately linear decay at 15 cycles. However, this production method has an inherent drawback that PF, which is a by-product unfavorable for the stability of the electrolyte, is generated during the production process₅(LiPF₆→LiF+PF₅)。

In 2017, Kang topic reported the research work of MnO-LiF system for reversible surface conversion reaction (S-K Jung, et al, Lithium-Free Transition Metal monomers for reactive electric in Lithium-Ion batteries, Nat. energy 2017,2, 16208). The MnO-LiF/graphite nano compound prepared by the high-energy ball milling method is charged and discharged at a current density of 20mA/g within a voltage range of 1.5-4.8V, the reversible capacity reaches 240mAh/g, and the average discharge voltage is 3.1V; the MnO/graphite nano-composite has almost no electrochemical activity under the same charge-discharge system. This indicates that the addition of LiF significantly affected the MnO activity.

From the above research results, it can be seen that, in the conversion reaction process of the MnO — LiF system, LiF not only has the function of providing a lithium source for the positive electrode material, but also has the function of providing a negative ion source for charge compensation when the transition metal ions undergo oxidation and reduction reactions. From the standpoint of MnO, LiF is obtained by supplying F^-The ions can be regarded as Mn in the oxidation state³⁺Or Mn⁴⁺A stabilizer for ions. In addition, MnO can be considered as a class of aids to promote LiF cleavage. However, LiF is a stable ionic compound, and the bond energy of Li-F bond is as high as 577kJ/mol, so that the Li-F bond needs to be overcome by breaking the Li-F bond during charging, i.e. LiF itself is difficult to electrochemically break. Therefore, the electrochemical splitting of LiF needs to satisfy certain key conditions. Dimov et al (N Dimov, et al. electrochemical partitioning of LiF: A New Aproach to Lithium-Ion Battery materials. ECS Trans.2014,58,87) found that manual mixing of a mixture of MnO and LiF was not sufficient to promote electrochemical Splitting of LiF, but LiF could undergo electrochemical Splitting after high energy ball milling due to the uniform dispersion of the mixture of MnO and LiF with submicron particles and amorphization of the solid phase of LiF caused by high energy ball milling. Therefore, only the submicron level of the two phases of the metal oxide MnO and LiF is realizedEven if the nano-scale particles are uniformly dispersed and closely contacted, the surface conversion reaction can occur. How to realize the nano-scale uniform dispersion and close contact of LiF and MnO and establish a nano-active micro-area suitable for the conversion reaction is a very critical problem.

In view of the technical problems existing in the preparation of the MnO/LiF composite anode material, the invention provides a preparation method of the MnO/LiF/C composite anode material. MnO nano-particles and LiF nano-particles generated in situ in the sintering process are uniformly distributed and embedded into a nano-porous carbon matrix such as Ketjen black and high specific surface carbon. The porous carbon matrix not only provides a supporting function and a high-efficiency 3D conductive network for MnO and LiF nano particles and increases a conduction path of electrons, but also can be used as an electrolyte container to provide elastic buffer for transmission and diffusion of lithium ions and fluorine ions during high-rate charge and discharge of the material. In addition, the porous carbon layer is uniformly coated on the surfaces of the nano MnO and LiF, so that the agglomeration of material particles and the segregation of LiF in the discharging process are avoided, and the uniformity of the size and the distribution of the material particles are obviously improved, so that the diffusion path of lithium ions and fluorine ions is shortened, the utilization rate and the high rate performance of active components are improved, and meanwhile, the direct contact between the material particles and electrolyte is reduced, so that the interface stability of the material is improved.

Disclosure of Invention

The invention aims to provide a preparation method of a MnO/LiF/C composite anode material.

The purpose of the invention is realized by the following technical scheme:

a preparation method of MnO/LiF/C composite anode material comprises the following steps:

(1) dissolving manganese acetate, lithium acetate and ammonium fluoride in water to prepare a precursor solution;

(2) dispersing high-specific-surface-area carbon such as ketjen black, acetylene black or activated carbon in the precursor solution obtained in the step, and performing spray drying to obtain precursor powder;

(3) sintering the precursor powder obtained in the step (2) in an inert atmosphere, and cooling to room temperature to obtain the MnO/LiF/C composite anode material.

Further, in the step (1), the mass ratio of manganese acetate to lithium acetate is 1: 1-2; the mass ratio of lithium acetate to ammonium fluoride is 1: 1.

Further, in the step (3), the sintering temperature is 350-700 ℃, and the sintering time is 5-20 minutes.

In the MnO/LiF/C composite anode material, the mass percent of carbon is 5-20%.

The invention has the beneficial effects that:

in the invention, two active components, namely MnO nano-particles and LiF nano-particles generated in situ in the sintering process are uniformly distributed in the composite material and are embedded into a porous carbon matrix with high specific surface area carbon such as Ketjen black, acetylene black or active carbon, so that the particle size and distribution uniformity of the material are improved, and the conductivity of the material is increased. In addition, the invention has the advantages of simple preparation process, low energy consumption, low sintering temperature, short time period, easy control of the process, high purity of the obtained product and the like.

Drawings

Fig. 1 is an X-ray diffraction pattern of samples obtained in examples 1, 2, 3, 4 and 5 of the present invention, wherein examples 1 to 5 correspond to elements 1 to 5, respectively.

FIG. 2 is a SEM image (a) and a power spectrum scan (b-e) of the product obtained in example 3 of the present invention, wherein b, C, d, and e correspond to the distribution of elements of O, Mn, F, and C, respectively.

FIG. 3 is a charge-discharge curve of the product obtained in example 3 of the present invention.

FIG. 4 is a graph of the cycle performance of the product obtained in example 3 of the present invention.

Detailed Description

For a better understanding of the present invention, the present invention will be further described with reference to the following examples and drawings, but the scope of the present invention is not limited to the examples shown.

Example 1

2.4509g of manganese acetate tetrahydrate is dissolved in 500ml of distilled water, magnetic stirring is carried out until the manganese acetate tetrahydrate is completely dissolved, and 2.0402g of lithium acetate dihydrate and 0.7408g of ammonium fluoride are sequentially added to prepare a precursor solution.

And adding 0.3070g of Ketjen black into the precursor solution obtained in the step, and ultrasonically dispersing for 1 hour.

Thirdly, spray drying the precursor solution after uniform ultrasonic dispersion, wherein the air inlet temperature is 250 ℃, and the air outlet temperature is 120 ℃ to obtain precursor powder.

Fourthly, sintering the precursor powder obtained in the step three at 700 ℃ for 5 minutes in an argon atmosphere, and naturally cooling to room temperature to obtain the MnO/LiF/C compound with the carbon content of 20 wt%.

The sample of example 1 was measured using an X-ray diffractometer model Brucker D8 Advance. The XRD spectrum is shown in figure 1. As can be seen from FIG. 1, the X-ray powder diffraction data of the sample of example 1 was well matched with JCPDS standard cards for MnO (card number: 89-2804) and JCPDS standard cards for LiF (card number: 72-1538), and MnO was not present in the spectrum₂、Mn₃O₄、MnF₂And waiting for impurity peaks, which indicates that the sample has high purity.

Example 2

2.4509g of manganese acetate tetrahydrate is dissolved in 500ml of distilled water, magnetic stirring is carried out until the manganese acetate tetrahydrate is completely dissolved, and 1.0201g of lithium acetate dihydrate and 0.3704g of ammonium fluoride are sequentially added to prepare a precursor solution.

And adding 0.1076g of activated carbon into the precursor solution obtained in the step, and ultrasonically dispersing for 1 hour.

Fourthly, sintering the precursor powder obtained in the step three at 650 ℃ for 10 minutes in an argon atmosphere, and naturally cooling to room temperature to obtain the MnO/LiF/C compound with the carbon content of 10 wt%.

Example 2 the samples were measured using an X-ray diffractometer model Brucker D8 Advance. The XRD spectrum is shown in figure 1. As can be seen from FIG. 1, the X-ray powder diffraction data of the sample of example 1 was well matched with JCPDS standard cards for MnO (card number: 89-2804) and JCPDS standard cards for LiF (card number: 72-1538), and MnO was not present in the spectrum₂、Mn₃O₄、MnF₂And waiting for impurity peaks, which indicates that the sample has high purity.

Example 3

And adding 0.307g of Ketjen black into the precursor solution obtained in the step, and ultrasonically dispersing for 1 hour.

Fourthly, sintering the precursor powder obtained in the step three at 550 ℃ for 5 minutes in an argon atmosphere, and naturally cooling to room temperature to obtain the MnO/LiF/C compound with the carbon content of 20 wt%.

Example 3 the samples were measured using an X-ray diffractometer model Brucker D8 Advance. The XRD spectrum is shown in figure 1. As can be seen from FIG. 1, the X-ray powder diffraction data of the sample of example 1 was well matched with JCPDS standard cards for MnO (card number: 89-2804) and JCPDS standard cards for LiF (card number: 72-1538), and MnO was not present in the spectrum₂、Mn₃O₄、MnF₂And waiting for impurity peaks, which indicates that the sample has high purity.

The scanning electron micrograph and the EDX energy spectrum profile of the sample of example 3 are shown in FIG. 2. As can be seen from FIG. 2(a), the sample particles are uniform in morphology, are all spheroidal particles, and have a diameter of about 50 nm. FIG. 2(b-e) is a spectral profile of the sample of example 3, which corresponds to the elemental distributions of O, Mn, F and C, respectively. It can be seen that the four elements of O, Mn, F and C are uniformly distributed throughout the entire region, indicating that ketjen black is dispersedly distributed in the composite without significant particle aggregation or phase separation.

Example 3 samples according to sample: acetylene black: PVDF 75: 10: 15 to obtain a positive plate, and assembling the positive plate into the button cell to perform charge and discharge tests at a multiplying power of 0.05C in a voltage range of 1.5-4.8V. The first charge and discharge curves of the samples are shown in fig. 3, and the cycle performance curves are shown in fig. 4. It can be seen that under the set charging and discharging system, the first specific discharge capacity of the sample is 188mAh/g, the specific discharge capacity after 50 cycles is kept at 139mAh/g, and the capacity retention rate is 73.9%.

Example 4

2.4509g of manganese acetate tetrahydrate is dissolved in 500ml of distilled water, magnetic stirring is carried out until no obvious particles exist, and then 1.5302g of lithium acetate dihydrate and 0.5556g of ammonium fluoride are sequentially added to prepare a precursor solution.

And adding 0.0578g of acetylene black into the precursor solution obtained in the step, and ultrasonically dispersing for 1 hour.

Fourthly, sintering the precursor powder obtained in the step three at 450 ℃ for 20 minutes in an argon atmosphere, and naturally cooling to room temperature to obtain the MnO/LiF/C compound with the carbon content of 5 wt%.

Example 4 the sample was measured using a Brucker model D8 Advance X-ray diffractometer. The XRD spectrum is shown in figure 1. As can be seen from FIG. 1, the X-ray powder diffraction data of the sample of example 1 was well matched with JCPDS standard cards for MnO (card number: 89-2804) and JCPDS standard cards for LiF (card number: 72-1538), and MnO was not present in the spectrum₂、Mn₃O₄、MnF₂And waiting for impurity peaks, which indicates that the sample has high purity.

Example 5

Fourthly, sintering the precursor powder obtained in the step three at 350 ℃ for 20 minutes in an argon atmosphere, and naturally cooling to room temperature to obtain the MnO/LiF/C compound with the carbon content of 15 wt%.

The sample of example 5 was measured using an X-ray diffractometer model Brucker D8 Advance. The XRD spectrum is shown in figure 1. As can be seen from FIG. 1, the X-ray powder diffraction data of the sample of example 1 was well matched with JCPDS standard cards for MnO (card number: 89-2804) and JCPDS standard cards for LiF (card number: 72-1538), and MnO was not present in the spectrum₂、Mn₃O₄、MnF₂And waiting for impurity peaks, which indicates that the sample has high purity.

The above is only a preferred embodiment of the present invention, and various modifications and changes can be made by those skilled in the art based on the above concept of the present invention, for example, combinations and changes of the ratio and the process conditions within the scope of the ratio and the process conditions given in the present invention, and such changes and modifications are within the spirit of the present invention.

Claims

1. A preparation method of a MnO/LiF/C composite anode material is characterized by comprising the following steps:

(1) dissolving manganese acetate, lithium acetate and ammonium fluoride in distilled water to prepare a precursor solution;

(2) dispersing ketjen black, acetylene black or activated carbon in the precursor solution obtained in the step, and performing spray drying to obtain precursor powder;

2. The method for preparing MnO/LiF/C composite positive electrode material according to claim 1, wherein: in the step (1), the mass ratio of manganese acetate to lithium acetate is 1: 1-2; the mass ratio of lithium acetate to ammonium fluoride is 1: 1.

3. The method for preparing MnO/LiF/C composite positive electrode material according to claim 1, wherein: in the step (3), the sintering temperature is 350-700 ℃, and the sintering time is 5-20 minutes.

4. The method of claim 1, wherein the MnO/LiF/C composite positive electrode material comprises carbon in an amount of 5-20% by weight.