A MoSe2 composite negative electrode material for lithium-ion batteries and its preparation method

Abstract

The present invention discloses a negative electrode material for a MoSe2 composite lithium-ion battery, which comprises MoSe2, Co3O4 and reduced graphene oxide. The MoSe2 and Co3O4 particles are loaded on the reduced graphene oxide to form a heterostructure, wherein Co3O4 is obtained by calcining ZIF-67; its preparation method comprises the following steps: (1) Synthesize ZIF-67 and then calcine it to obtain Co3O4; (2) Dissolve Co3O4 in water, then add molybdate and graphene oxide to form solution c, and dissolve selenium powder in a hydrazine hydrate solution and react until the solution turns dark red-brown to form solution d; (3) Mix solution c and solution d, carry out hydrothermal reaction at 180-220 °C, and after the reaction is completed, wash and dry the precipitate to obtain the negative electrode material for the MoSe2 composite lithium-ion battery; through the introduction of rGO, the agglomeration of MoSe2 is reduced, the specific capacity decay is slowed down, and the lithium-ion diffusion length is shortened for this composite material.

Description

Technical Field

[0001] The present invention relates to a negative electrode material for a lithium battery and a preparation method thereof, and particularly relates to a MoSe2 composite lithium ion battery negative electrode material and a preparation method thereof. Background Art

[0002] Lithium ion batteries have the advantages of no memory effect, environmental protection, etc., and are widely used in wearable electronic devices and electric vehicles. Electrode materials are the main components of LIBs. However, it is still a huge challenge to study new electrode materials with a larger specific surface area, a higher lithium ion storage capacity, and shorter ion and electron transport paths.

[0003] Molybdenum diselenide, as a typical two-dimensional layered material, is considered to be a lithium ion battery negative electrode material with great application potential due to its high theoretical specific capacity. Molybdenum diselenide can form a monolayer or multilayer hierarchical nanosheet structure similar to graphene; a Mo atom is sandwiched between two selenium atom layers stacked together by van der Waals forces, and due to its excellent electrical conductivity, structural stability and mechanical flexibility, it has been widely used in the field of electrochemistry. However, due to the existence of van der Waals forces, the aggregation of MoSe2 layered nanosheets is caused, and there is a serious volume expansion effect during the charge and discharge cycle of molybdenum diselenide, which limits the application of molybdenum diselenide negative electrode materials. Summary of the Invention

[0004] Object of the Invention: The present invention aims to provide a MoSe2 composite lithium ion battery negative electrode material that improves the dispersion degree of MoSe2 and reduces particle aggregation; the second object of the present invention is to provide a preparation method of the material.

[0005] Technical Solution: A MoSe2 composite lithium ion battery negative electrode material of the present invention is characterized in that it includes MoSe2, Co3O4 and reduced graphene oxide, and MoSe2 and Co3O4 particles are loaded on the reduced graphene oxide; wherein Co3O4 is obtained by calcining ZIF-67.

[0006] The mass ratio of the MoSe2, Co3O4 and reduced graphene oxide is 25∶4~10∶5~10.

[0007] The preparation method of the material of the present invention includes the following steps:

[0008] (1) Synthesize ZIF-67, and then calcine to obtain Co3O4;

[0009] (2) Dissolve the Co3O4 obtained in step (1) in water, then add sodium molybdate and graphene oxide to form solution c, and dissolve selenium powder in hydrazine hydrate solution and react until the solution turns dark red-brown to form solution d;

[0010] (3) Mix the solution c and solution d in step (2) and conduct a hydrothermal reaction at a reaction temperature of 180 - 220 °C. After the reaction ends, wash and dry the precipitate to obtain the MoSe2 composite anode material for lithium-ion batteries.

[0011] In step (1), using ZIF-67 as the precursor, through simple high-temperature calcination, ZIFs can be easily converted into porous metal oxides. The obtained metal oxide Co3O4 retains the characteristics of the large specific surface area, appropriate voids, and adjustable structure of the ZIFs precursor, promoting electron transport.

[0012] In step (2), selenium powder reacts in hydrazine hydrate, and the reaction equation is as follows:

[0013] 2Se + 5N2H4 → 2Se 2- + 4N2H5 + + N2;

[0014] In step (3), MoSe2 is formed during the hydrothermal reaction, and the reaction equation is as follows:

[0015] 2MoO4 2- + N2H4 + 4H2O → 2Mo 4+ + N2 + 12OH -

[0016] Mo 4+ + 2Se 2- → MoSe2;

[0017] During the hydrothermal process, graphene oxide (GO) is reduced by hydrazine hydrate to form reduced graphene oxide (rGO). rGO has excellent electrical conductivity and is not only an ideal substrate for the nucleation and growth of MoSe2 but also conducive to electron transport. Co3O4 and the generated MoSe2 are loaded on the reduced graphene oxide.

[0018] The hydrazine hydrate is used as a reducing agent in steps (2) and (3), and its dosage is excessive.

[0019] The hydrothermal reaction time is 4 - 12 hours.

[0020] In step (1), the calcination temperature is 350 - 600 °C.

[0021] The preparation method of the ZIF-67 is as follows: Dissolve 1.644 g of 2-methylimidazole in 30 mL of methanol and stir for 30 minutes to form solution a; dissolve 1.455 g of cobalt nitrate hexahydrate in 30 mL of methanol for 30 minutes to form solution b; mix solution a and solution b, stir and react at room temperature for 24 h, centrifuge and separate the synthesized purple precipitate, wash it 3 times with ethanol, and dry it under vacuum to obtain ZIF-67.

[0022] Invention mechanism: In this invention, rGO and Co3O4 are introduced into MoSe2; rGO has high conductivity and high specific surface area. Through hydrothermal reaction, the generated MoSe2 is loaded on the graphene sheets to prevent particle aggregation and slow down the specific capacity decay, and shorten the lithium ion diffusion length. Co3O4 obtained by calcining ZIF-67 has a large specific surface area, appropriate voids and adjustable structure, which promotes electron transport. MoSe2 and Co3O4 particles are loaded on the reduced graphene oxide to form a heterostructure. The construction of this heterostructure can effectively increase the contact area of the electrolyte or the electrode, buffer volume changes, and has excellent cycle stability and rate performance.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: (1) By introducing rGO, the aggregation of MoSe2 is reduced, the specific capacity decay is slowed down, and the lithium ion diffusion length is shortened; (2) Co3O4 obtained by calcining ZIF-67 has porosity and good conductivity, which is beneficial to lithium ion transport and electrolyte infiltration; (3) The heterostructure constructed by MoSe2, Co3O4 and graphene sheets has rich heterointerfaces, combines the advantages of each material and acts synergistically. The material has a high discharge specific capacity, a low charging overpotential, many active sites, a stable structure, and good cycle performance; (4) The preparation method is simple, easy to operate, and the reaction conditions are mild. Description of the Drawings

[0024] Figure 1 XRD pattern of the ZIF-67 synthesized in Example 1;

[0025] Figure 2 XRD pattern of the Co3O4 synthesized in Example 1;

[0026] Figure 3 XRD pattern of the MoSe2 composite lithium-ion battery anode material synthesized in Example 1;

[0027] Figure 4 SEM image of the MoSe2 composite lithium-ion battery anode material synthesized in Example 1;

[0028] Figure 5 XRD pattern of the MoSe2 / Co3O4 composite material synthesized in Comparative Example 1;

[0029] Figure 6 SEM image of the MoSe2 / Co3O4 composite material synthesized in Comparative Example 1;

[0030] Figure 7 Cycling performance graph (left) and charge-discharge curve graph (right) of the MoSe2 composite lithium-ion battery anode material synthesized in Example 1 at a current density of 500 mA / g;

[0031] Figure 8 Cycling performance graph (left) and charge-discharge curve graph (right) of the MoSe2 composite lithium-ion battery anode material synthesized in Example 2 at a current density of 500 mA / g;

[0032] Figure 9 Cycling performance graph (left) and charge-discharge curve graph (right) of the MoSe2 composite lithium-ion battery anode material synthesized in Example 3 at a current density of 500 mA / g;

[0033] Figure 10 Cycling performance graph (left) and charge-discharge curve graph (right) of the MoSe2 composite lithium-ion battery anode material synthesized in Example 4 at a current density of 500 mA / g;

[0034] Figure 11 Cycling performance graph (left) and charge-discharge curve graph (right) of the MoSe2 / Co3O4 composite material synthesized in Comparative Example 1 at a current density of 500 mA / g. Detailed implementation manners

[0035] The technical solution of the present invention will be further described below in conjunction with the embodiments.

[0036] Example 1

[0037] For the MoSe2 composite lithium-ion battery anode material of the present invention, the mass ratio of MoSe2, Co3O4 and reduced graphene oxide is 25:4:5, and its preparation method includes the following steps:

[0038] (1) Dissolve 1.644 g of 2-methylimidazole in 30 mL of methanol, stir for 30 minutes to form solution a; dissolve 1.455 g of cobalt nitrate hexahydrate in 30 mL of methanol for 30 minutes to form solution b; mix solution a and solution b, stir and react at room temperature for 24 h, after centrifuging and separating the synthesized purple precipitate, wash it 3 times with ethanol, and dry it under vacuum to obtain ZIF-67; calcine ZIF-67 at a high temperature of 450 °C with a heating rate of 2 °C / min and anneal for 2 h to obtain Co3O4;

[0039] (2) Dissolve 0.04 g of Co3O4 in 25 mL of deionized water by ultrasound, then add 0.24 g of sodium molybdate and 0.05 g of graphene oxide, stir to form solution c. Dissolve 0.16 g of selenium powder in 5 mL of 85% by mass hydrazine hydrate and stir vigorously until the solution turns dark red-brown to form solution d;

[0040] (3) Mix solution c and solution d evenly, transfer them to a sealed reactor, react at 200 °C for 8 h. After the reaction is completed, cool it. After centrifuging the reaction solution, wash the obtained precipitate with deionized water and dry it in vacuum at 60 °C to obtain the MoSe2 composite anode material for lithium-ion batteries.

[0041] Example 2

[0042] For the MoSe2 composite anode material for lithium-ion batteries of the present invention, the mass ratio of MoSe2, Co3O4 to reduced graphene oxide is 25:6:5, and its preparation method includes the following steps:

[0043] (1) The preparation method of ZIF-67 is the same as that in Example 1; calcine ZIF-67 at a high temperature of 350 °C with a heating rate of 2 °C / min and anneal for 2 h to obtain Co3O4;

[0044] (2) Dissolve 0.06 g of Co3O4 in 25 mL of deionized water by ultrasound, then add 0.24 g of sodium molybdate and 0.05 g of graphene oxide, stir to form solution c. Dissolve 0.16 g of selenium powder in 5 mL of 85% by mass hydrazine hydrate and stir vigorously until the solution turns dark red-brown to form solution d;

[0045] (3) Mix solution c and solution d evenly, transfer them to a sealed reactor, react at 180 °C for 12 h. After the reaction is completed, cool it. After centrifuging the reaction solution, wash the obtained precipitate with deionized water and dry it in vacuum at 60 °C to obtain the MoSe2 composite anode material for lithium-ion batteries.

[0046] Example 3

[0047] For the MoSe2 composite anode material for lithium-ion batteries of the present invention, the mass ratio of MoSe2, Co3O4 to reduced graphene oxide is 25:8:5, and its preparation method includes the following steps:

[0048] (1) The preparation method of ZIF-67 is the same as that in Example 1; calcine ZIF-67 at a high temperature of 600 °C with a heating rate of 2 °C / min and anneal for 2 h to obtain Co3O4;

[0049] (2) Dissolve 0.08 g of Co3O4 in 25 mL of deionized water by ultrasound, then add 0.24 g of sodium molybdate and 0.05 g of graphene oxide, and stir to form solution c. Dissolve 0.16 g of selenium powder in 5 mL of 85% by mass hydrazine hydrate and stir vigorously until the solution turns dark red-brown to form solution d;

[0050] (3) Mix solution c and solution d evenly, transfer them to a sealed reactor, react at 220 °C for 4 h. After the reaction is completed, cool it. After centrifuging the reaction solution, wash the obtained precipitate with deionized water and dry it in vacuum at 60 °C to obtain the MoSe2 composite anode material for lithium-ion batteries.

[0051] Example 4

[0052] For the MoSe2 composite anode material for lithium-ion batteries of the present invention, the mass ratio of MoSe2, Co3O4 and reduced graphene oxide is 25:10:5, and its preparation method includes the following steps:

[0053] (1) The preparation method of ZIF-67 is the same as that in Example 1; calcine ZIF-67 at a high temperature of 450 °C with a heating rate of 2 °C / min and anneal for 2 h to obtain Co3O4;

[0054] (2) Dissolve 0.08 g of Co3O4 in 25 mL of deionized water by ultrasound, then add 0.24 g of sodium molybdate and 0.1 g of graphene oxide, and stir to form solution c. Dissolve 0.16 g of selenium powder in 5 mL of 85% by mass hydrazine hydrate and stir vigorously until the solution turns dark red-brown to form solution d;

[0055] (3) Mix solution c and solution d evenly, transfer them to a sealed reactor, react at 200 °C for 8 h. After the reaction is completed, cool it. After centrifuging the reaction solution, wash the obtained precipitate with deionized water and dry it in vacuum at 60 °C to obtain the MoSe2 composite anode material for lithium-ion batteries.

[0056] Comparative Example 1

[0057] On the basis of Example 1, without adding graphene oxide and with other conditions unchanged, the MoSe2 / Co3O4 composite material is obtained.

[0058] Structure test

[0059] The XRD patterns of the ZIF-67, Co3O4 and MoSe2 composite anode materials for lithium-ion batteries synthesized in Example 1 are as Figures 1 - 3As shown in the figure. Compared with the standard card JCPDS 42-1467, the product obtained after high-temperature calcination of ZIF-67 is Co3O4. The X-ray diffraction peaks of the composite lithium-ion battery anode material of MoSe2 can all correspond to the diffraction peaks of Co3O4 and MoSe2. Since the addition amount of graphene is very small, no diffraction peaks are shown, and there are no other impurities, indicating that the MoSe2 / Co3O4 / rGO composite material has been successfully prepared.

[0060] The SEM image of the composite lithium-ion battery anode material of MoSe2 is as Figure 4 shown. It can be seen from the figure that MoSe2 and Co3O4 particles are tightly loaded on the reduced graphene oxide sheets, there are abundant pores between the particles, the particle size of the nanoparticles is very small, and the heterostructure constructed by MoSe2, Co3O4 and graphene sheets has abundant heterointerfaces.

[0061] The XRD and SEM images of the composite lithium-ion battery anode material of the MoSe2 / Co3O4 composite material synthesized in Comparative Example 1 are as Figure 5 shown. It can be seen from the XRD pattern that the X-ray diffraction peaks of the MoSe2 / Co3O4 composite material can all correspond to the diffraction peaks of Co3O4 and MoSe2, indicating that the MoSe2 / Co3O4 composite material has been successfully prepared; the SEM image shows that MoSe2 is a flower-like composed of flakes, covering the Co3O4 particles, which is very different from the morphology of the composite material after adding graphene.

[0062] Performance Test

[0063] The electrode materials synthesized in Examples 1 to 4 and Comparative Example 1 were assembled into coin cells to test the cycling performance and charge-discharge performance at 500 mA / g. The test method is as follows:

[0064] The products in the above Examples 1 to 4 and Comparative Example 1 were respectively assembled into CR2032 coin cells, with a lithium sheet as the counter electrode, a polypropylene porous membrane as the separator, and a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (VEC:VDMC = 1:1) of LiPF6 as the electrolyte. The CR2032 battery was completed in a glove box filled with argon (water content < 0.1 ppm, oxygen content < 0.1 ppm). The slurry used for the negative electrode was a mixture of 80% (mass percentage) active material, 10% PVDF solution, 10% conductive carbon black, and 1-methyl-2-pyrrolidone (NMP). The substrate of the electrode film was a metal copper foil; the constant current charge / discharge rate and cycling performance tests were carried out on a LAND CT2001A battery test system. Figures 7 - 10The cyclic performance graphs and charge-discharge curves of the products prepared in the above Examples 1 to 4 as lithium-ion batteries at a current density of 500 mA / g are shown. In the charge-discharge curves, 1 represents the first cycle, 2 represents the second cycle, and 50 represents the 50th cycle.

[0065] It can be seen from Figure 7 that for the MoSe2 composite lithium-ion battery anode material prepared in Example 1, at a current density of 500 mA / g, the reversible specific capacity after 350 cycles is still as high as 800 mAh g -1 , and its Coulomb efficiency is also about 100%.

[0066] It can be seen from Figure 8 that for the MoSe2 composite lithium-ion battery anode material prepared in Example 2, at a current density of 500 mA / g, the reversible specific capacity after 200 cycles is still as high as 790 mAh g -1 , and its Coulomb efficiency is also about 100%.

[0067] It can be seen from Figure 9 that for the MoSe2 composite lithium-ion battery anode material prepared in Example 3, at a current density of 500 mA / g, the reversible specific capacity after 450 cycles is still as high as 900 mAh g -1 , and its Coulomb efficiency is also about 100%.

[0068] It can be seen from Figure 10 that for the MoSe2 composite lithium-ion battery anode material prepared in Example 4, at a current density of 500 mA / g, the reversible specific capacity after 200 cycles is as high as 726 mAh g -1 , with a relatively small capacity decay; its Coulomb efficiency is also about 100%.

[0069] It can be seen from Figure 11 that when the MoSe2 / Co3O4 composite material without graphene addition in Comparative Example 1 is used as the anode of a lithium-ion battery, the capacity remains at 454 mAh / g after 100 cycles, and the performance is relatively poor.

Claims

1. A negative electrode material for a MoSe2 composite lithium-ion battery, characterized in that, It includes MoSe2, Co3O4 and reduced graphene oxide. MoSe2 and Co3O4 particles are loaded on the reduced graphene oxide to form a heterostructure. Among them, Co3O4 is obtained by calcining ZIF-67. The mass ratio of MoSe2, Co3O4 and reduced graphene oxide is 25∶8∶5. The material is prepared by the following method: (1) Synthesize ZIF-67 and then calcine it to obtain Co3O4; (2) Dissolve the Co3O4 obtained in step (1) in water, then add molybdate and graphene oxide to form solution c. Dissolve selenium powder in hydrazine hydrate solution and react until the solution turns dark red-brown to form solution d; (3) Mix solution c and solution d in step (2), carry out hydrothermal reaction, the reaction temperature is 180~220 °C. After the reaction, wash and dry the precipitate to obtain the MoSe2 composite lithium-ion battery anode material.

2. A method for preparing the material according to claim 1, characterized in that, It includes the following steps: (1) Synthesize ZIF-67 and then calcine it to obtain Co3O4; (2) Dissolve the Co3O4 obtained in step (1) in water, then add molybdate and graphene oxide to form solution c. Dissolve selenium powder in hydrazine hydrate solution and react until the solution turns dark red-brown to form solution d; (3) Mix solution c and solution d in step (2), carry out hydrothermal reaction, the reaction temperature is 180~220 °C. After the reaction, wash and dry the precipitate to obtain the MoSe2 composite lithium-ion battery anode material.

3. The preparation method of the material according to claim 2, wherein The hydrothermal time is 4~12 hours.

4. The preparation method of the material according to claim 2, characterized in that, The molybdate is sodium molybdate or ammonium molybdate tetrahydrate.

5. The preparation method of the material according to claim 2, characterized in that, In step (1), the calcination temperature is 350~600 °C.

Images