MXene / Cu4Mo6Se8-based composite positive electrode material and preparation method and application thereof

Abstract

The invention discloses an MXene / Cu4Mo6Se8-based composite positive electrode material, which is of a flower-shaped aggregate structure and comprises a carbon skeleton and a Cu4Mo6Se8 / MXene nanosheet self-assembled on the carbon skeleton, and CuSe nanoparticles are loaded on the surface of the nanosheet. According to the preparation method, a Cu-Mo bimetal organic framework is combined with MXene to serve as a precursor, the CMSe / MXene nanosheet supported by the carbon framework is obtained through selenylation reaction, and in-situ growth of the ultrathin nanosheet on the carbon framework and tight combination of a selenylation product and an MXene component are achieved; a unique multi-dimensional heterostructure can be formed, electrochemical active sites are effectively increased, a magnesium ion diffusion path is shortened, volume expansion of selenide is effectively buffered in the circulation process, the circulation stability of the electrode material is remarkably improved, and the service life of the electrode material is remarkably prolonged; and the related preparation method is simple, low in cost, environment-friendly and suitable for popularization and application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrode materials, and particularly relates to a MXene / Cu4Mo6Se8-based composite positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] With the increasing demand for renewable energy and portable electronic devices, lithium-ion batteries have become the mainstream energy storage technology due to their high energy density and long cycle life. However, the uneven distribution of lithium resources, the dramatic price fluctuations, and the safety hazards (such as flammable electrolyte, battery thermal runaway, etc.) have gradually exposed the limitations of their further popularization and application in large-scale energy storage. These defects have prompted researchers to seek a new generation of energy storage systems. Magnesium batteries have become an important candidate material for the next generation of high-performance batteries due to the advantages of abundant magnesium metal resources, safety and stability, low price, and high theoretical capacity of double-electron transfer. However, the divalent Mg 2+ The strong interaction between the host material and the active material leads to slow embedding / extraction during charging and discharging, and low ion diffusion rate. Therefore, finding a suitable positive electrode material is the research focus of achieving high capacity, excellent rate performance, and long life magnesium batteries.

[0003] Among the many positive electrode materials, selenides have attracted much attention due to their conversion-type material. They can provide higher capacity through chemical bond breaking and recombination. As a conversion-type material, selenides undergo chemical bond breaking and recombination during reaction, which promotes higher capacity. However, selenides still have problems such as structural changes and slow electrochemical reaction kinetics in practical applications, which limit their performance from meeting expectations; especially the slow magnesium ion transmission rate limits their development in the field of magnesium batteries.

[0004] To improve the above problems, two-dimensional transition metal selenides (MXene) can be introduced into the selenide system for modification and optimization. However, the existing MXene modification scheme still has deficiencies. For example, patent application CN114628658A discloses a magnesium battery positive electrode material with an organic-inorganic hybrid structure, and the synthesized organic quinone / Ti3C2 MXene hybrid material solves the problems of slow diffusion rate and structural collapse of the hybrid material to a certain extent, but its cycle life and conductivity are still poor; this is mainly due to the poor conductivity of the organic material itself and the insufficient support of the two-dimensional structure of MXene. Therefore, how to build a more efficient and stable composite structure between selenide and MXene, and fully exert the synergistic effect of both, has become a key technical problem for improving the conductivity and cycle life of magnesium batteries, and is also a core difficulty to be solved by the present application. SUMMARY

[0005] One of the purposes of the present application is to provide a composite positive electrode material based on MXene and Cu4Mo6Se8, composite MXene on a bimetallic organic framework, and build a MXene-selenide heterostructure, significantly improve the conductivity of the positive electrode material, provide more active sites, and significantly enhance the magnesium ion transmission rate and magnesium storage capacity. The second purpose of the present application is to provide a simple and easy preparation method of the above-mentioned MXene / Cu4Mo6Se8-based composite positive electrode material.

[0006] The third purpose of the present application is to provide a magnesium battery based on MXene / Cu4Mo6Se8-based composite positive electrode material, which significantly enhances the transmission rate of magnesium ions in the host material, improves the electrochemical performance and rate performance, and effectively solves the problems of low capacity, poor rate performance and short cycle life of bimetallic selenide positive electrode in existing magnesium batteries.

[0007] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is: A MXene / Cu4Mo6Se8-based composite positive electrode material, which presents a flower-like aggregate structure, is self-assembled based on Cu4Mo6Se8 nanosheet sheet layer, and the introduced two-dimensional MXene sheet layer is uniformly dispersed in the composite system; the Cu4Mo6Se8 sheet layer has obvious wrinkles and undulations, and the sheet layer surface is loaded with CuSe nanoparticles; they are staggered and stacked to form a three-dimensional porous structure.

[0008] Further, the particle size of the CuSe nanoparticles is 100-200 nm. The preparation method of the above-mentioned MXene / Cu4Mo6Se8-based composite positive electrode material comprises the following steps: 1) Dissolve copper salt and first organic ligand in water and mix uniformly; add molybdenum salt and mix uniformly to obtain mixed solution I; 2) Add MXene dispersion liquid to mixed solution I and mix uniformly to obtain mixed solution II; 3) Add a second organic ligand solution to mixed solution II to obtain a precursor solution; 4) Stir the obtained precursor solution, wash and dry the obtained precipitate to obtain a composite precursor; 5) Mix the obtained composite precursor with selenium powder, grind, and then perform selenization reaction under gradient temperature increase in a protective atmosphere to obtain the MXene / Cu4Mo6Se8-based composite positive electrode material.

[0009] In the above scheme, the copper salt can be selected from one or more of copper acetate, copper nitrate, copper chloride, copper oxalate, etc.

[0010] In the above scheme, the molybdenum salt can be selected from one or more of molybdenum phosphate (hydrate), ammonium molybdate, etc.

[0011] In the above scheme, the first organic ligand can be selected from one or more of L-glutamic acid, aspartic acid, etc.

[0012] In the above scheme, the molar ratio of the copper salt to the first organic ligand is 1:0.1-0.5.

[0013] In the above scheme, the molar ratio of the molybdenum salt to the copper salt is 1:5-10.

[0014] Preferably, the concentration of the MXene dispersion liquid (solvent is water) is 4-10 mg / ml.

[0015] Further, the mass ratio of the introduced MXene to the copper salt is 1:25-35.

[0016] In the above scheme, the second organic ligand can be selected from one or more of trimesic acid, pyromellitic acid, etc.

[0017] In the above scheme, the molar ratio of the copper salt to the second ligand is 1:0.5-1.

[0018] In the above scheme, the stirring treatment time in step 4) is 12-30 h.

[0019] In the above scheme, the washing step includes washing multiple times alternately with water and ethanol.

[0020] In the above scheme, the drying step uses a vacuum drying process, and the temperature used is 40-100 ℃, and the time is 6-24 h.

[0021] In the above scheme, the mass ratio of the composite precursor to the selenium powder is 1:5-10.

[0022] In the above scheme, the protective atmosphere is one or more of argon, hydrogen-argon mixed gas, nitrogen, etc.

[0023] In the above scheme, the temperature used for the selenization reaction is 500-700 ℃, and the time is 2-5 h; in the gradient heating step, the heating rate used is 1-3 ℃ / min, and when heated to 340-360 ℃, the temperature is kept for 20-40 min; then the temperature is continuously increased to the selenization reaction temperature for the temperature keeping reaction.

[0024] The application further provides a magnesium battery positive electrode based on the MXene / Cu4Mo6Se8-based composite positive electrode material, and a preparation method thereof, which comprises the following steps: mixing and grinding the MXene / Cu4Mo6Se8-based composite magnesium battery positive electrode material obtained by the preparation method, and acetylene black to obtain a mixture I; then adding a binder (polytetrafluoroethylene solution, etc.) to stir and grind to obtain a mixture II; and pressing the mixture II into an electrode sheet by a roller press, and drying at 45-70 DEG C to obtain a magnesium battery positive electrode sheet.

[0025] Further, the mass ratio of the introduced MXene / Cu4Mo6Se8-based composite magnesium battery positive electrode material, acetylene black and binder is (6-7.5):(1.5-3):1.

[0026] The application further provides a magnesium battery based on the MXene / Cu4Mo6Se8-based composite positive electrode material, which comprises a magnesium battery positive electrode sheet (positive electrode) based on the MXene / Cu4Mo6Se8-based composite positive electrode material, a metal magnesium negative electrode, a separator and an electrolyte.

[0027] Further, the separator can be a glass separator (GF / D) or the like.

[0028] Further, the electrolyte comprises phenyl magnesium chloride, aluminum chloride and tetrahydrofuran.

[0029] Compared with the prior art, the application has the following beneficial effects: 1) The application uses Cu-Mo bimetallic organic framework fixed MXene (BMOF / MXene) as a precursor, and obtains carbon skeleton supported Cu4Mo6Se8-based nanosheet (CMSe / MXene) through a selenization reaction, realizes the direct in-situ growth of ultra-thin nanosheet on the carbon skeleton, and can realize the close combination of the selenization product and the MXene sheet layer, effectively avoiding the problems of easy agglomeration and poor combination in the traditional physical compounding method; 2) The composite material can form a unique multi-dimensional heterostructure (three-dimensional carbon skeleton+two-dimensional CMSe / MXene nanosheet+selenide particles), which can effectively increase the electrochemical active sites, shorten the diffusion path of magnesium ions, and buffer the volume expansion of selenide in the cycle process, effectively improving the cycle stability and service life of the electrode material, etc.

[0030] 3) The application provides a feasible strategy for improving the conductivity and structural stability of the positive electrode material of the multivalent ion battery, and the preparation method is simple, low in cost, and environmentally friendly, and has the potential for large-scale and marketization. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1is a SEM diagram of the MXene / Cu4Mo6Se8-based composite cathode material described in Embodiment 1 of the present application; Figure 2 is a TEM diagram (left) and an EDS diagram (right) of the MXene / Cu4Mo6Se8-based composite cathode material described in Embodiment 1 of the present application; Figure 3 is a Raman spectrum comparison diagram of the MXene / Cu4Mo6Se8-based composite cathode material described in Embodiment 1 of the present application; Figure 4 is a cycle performance comparison diagram of the MXene / Cu4Mo6Se8-based composite cathode material described in Embodiment 1 of the present application and a Cu4Mo6Se8 cathode; Figure 5 is a rate performance comparison diagram of the MXene / Cu4Mo6Se8-based composite cathode material described in Embodiment 1 of the present application and a single Cu4Mo6Se8 cathode material. DETAILED DESCRIPTION

[0032] The present application will be described in greater detail by way of specific examples. The principles and features of the present application are described below in conjunction with specific examples, which are intended only to explain the present application and are not intended to limit the scope of the present application. Unless otherwise defined, all technical and scientific terms used herein have meanings commonly understood by those skilled in the art of the present application.

[0033] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The terms “comprise”, “include”, “contain”, “have” have the meaning of non-limiting, that is, other steps and other components that do not affect the results can be added.

[0034] On the basis of the above-mentioned embodiments, the preparation method of the MXene and Cu4Mo6Se8 composite cathode material combined below further illustrates the present application. It should be understood that these embodiments are only used to illustrate the present application and are not used to limit the scope of the present application. In the following examples, the experimental method is noted for specific conditions, which is usually according to the conditions recommended by the manufacturer. Unless otherwise specified, percentages and parts are calculated by mass.

[0035] In the following examples, the preparation method of the MXene / Cu4Mo6Se8-based composite cathode material includes the following steps: S1, add trimesic acid to an ethanol solution, and obtain a mixed solution A after sufficient stirring, and reserve it; S2, add copper acetate monohydrate and L-glutamic acid to deionized water respectively, and obtain a mixed solution B after sufficient stirring; add molybdenum phosphate hydrate to the mixed solution B, and obtain a mixed solution C after sufficient stirring; S3, add MXene dispersion liquid into mixed solution C, and obtain mixed solution D after fully stirring; S4, slowly add mixed solution A into mixed solution D, and obtain mixed solution E after fully stirring; S5, fully stir mixed solution E, and then wash the obtained precipitate with deionized water and ethanol alternately for multiple times, and vacuum dry to obtain a precursor F with MXene; S6, fully grind and mix the precursor F with selenium powder, heat in a tube furnace under a specific atmosphere to perform selenization, and obtain the MXene / Cu4Mo6Se8-based composite positive electrode material.

[0036] Example 1 A MXene / Cu4Mo6Se8-based composite positive electrode material, and a preparation method thereof, includes the following steps: 1) under normal temperature conditions, 120 ml of ethanol is placed in a beaker, and 420.3 mg of trimesic acid powder is weighed and poured into the beaker, and magnetic stirring is performed for 15 min to obtain a uniform mixed solution A; 2) under normal temperature conditions, 120 ml of deionized water is placed in a beaker, and 599 mg of copper acetate monohydrate powder and 220.7 mg of L-glutamic acid powder are weighed and poured into the beaker, and magnetic stirring is performed for 15 min to obtain a uniform mixed solution B; 3) 938.2 mg of molybdenum phosphate hydrate powder (molar ratio of molybdenum salt to copper salt is 1:6) is added to mixed solution B, and magnetic stirring is performed for 15 min to obtain a uniform mixed solution C; 4) 4 ml of MXene dispersion liquid (concentration is 5 mg / ml) is poured into mixed solution C, and magnetic stirring is performed for 15 min to obtain a uniform mixed solution D; 5) mixed solution A is added to mixed solution D at a flow rate of 30 ml / min, and magnetic stirring is performed for 24 h to obtain a uniform mixed solution E; 6) after fully stirring mixed solution E, the precipitate is washed with deionized water and ethanol alternately for multiple times, and is placed in a 60℃ vacuum drying oven for drying for 12 h to obtain a composite precursor F; 7) the composite precursor F is fully ground and mixed with selenium powder at a mass ratio of 1:8, and selenization is performed in a tube furnace under a hydrogen-argon mixed gas atmosphere, wherein the heating rate used is 1℃ / min, first heated to 350℃ and kept for 30 min, and then continuously heated to a selenization reaction temperature of 600℃, and kept for 4 h, to obtain the MXene / Cu4Mo6Se8-based composite positive electrode material.

[0037] The MXene / Cu4Mo6Se8-based composite positive electrode material prepared in Example 1 is subjected to performance testing, and the results are shown as follows.

[0038] Figure 1 The scanning electron microscope (SEM) image of the obtained composite cathode material. As can be seen from the figure, the product obtained in the embodiment as a whole presents a flower-like aggregate structure, which is self-assembled from a large number of flaky or layered nanosheets. The sheet layers have obvious wrinkles and undulations, which are staggered and stacked with each other to form a three-dimensional porous structure.

[0039] Figure 2 The transmission electron microscope (TEM; left) and element spectrum (Mapping; right) images of the obtained composite cathode material. As can be seen from the TEM image, the obtained composite material presents a structure characterized by stacked and interwoven layered sheets, and the overall morphology is relatively loose; in the composite material, the flaky structure is used as a substrate, the size is about 0.5-2 μm, and the surface of the sheet layer is uniformly distributed with granular selenide (CuSe nanoparticles) with a diameter of about 100-200 nm, the obtained product constitutes a multi-dimensional network structure containing copper selenide nanoparticles, two-dimensional Cu4Mo6Se8 / MXene nanosheets and three-dimensional carbon skeleton, which can effectively increase the number of electrochemically active sites and shorten the diffusion path of magnesium ions. The energy spectrum element Mapping analysis results show that the elements C, Cu, Mo, Se and Ti (introduced by MXene) are uniformly distributed in the material, indicating that the composite uniformity is good. The carbon element is widely distributed, which serves as a carbon skeleton to support the structure; Cu, Mo and Se are uniformly distributed without obvious agglomeration or separation. It is shown that the MXene component is uniformly dispersed in the composite and participates in the construction of the structure support and conductive network.

[0040] Figure 3 The Raman image of the composite cathode material obtained in the embodiment. As can be seen from the figure, the MXene material has a Ti-C bond peak at 192 cm -1 -1, and the Cu4Mo6Se8 composite material containing MXene heterostructure also has a Ti-C peak, while the peak is not found in the pure Cu4Mo6Se8 material, indicating that the surface of the obtained composite material is rich in MXene.

[0041] The composite cathode material prepared in Example 1 is directly used as a positive electrode, and a magnesium sheet is used as a negative electrode, wherein APC is used as an electrolyte, and GF / D glass fiber is used as a separator to assemble a CR2016 type button full cell. The full cell is tested, and the results are shown in Figures 4-5 .

[0042] Figure 4 The cycle performance comparison chart of the MXene / Cu4Mo6Se8 composite cathode material and the Cu4Mo6Se8 cathode. In the pure Cu4Mo6Se8 cathode (CMS), the battery capacity is only 57 mAh g -1, and only 770 cycles; while the composite cathode material (CMS / MXene) obtained in the present application has a more excellent specific capacity, which is up to 110 mAh g -1 at a current density of 500 mA g -1 , and still maintains 90.5% of the initial capacity after 1500 cycles.

[0043] Figure 5 The rate performance comparison chart of the composite cathode material (CMS / MXene) obtained in Example 1 and Cu4Mo6Se8 cathode (CMS). It can be seen that the composite cathode material obtained in the present application has achieved significant improvement in rate performance. At a current density of 50 mA g -1 , the specific capacity thereof is more than 184 mAh g -1 . Even if the current density is increased to 500 mA g -1 , the specific capacity still maintains 110 mAh g -1 . After the current density is restored to 50 mA g -1 , the specific capacity is increased to 180 mAh g -1 , which shows excellent rate performance.

[0044] The comprehensive test results show that the composite cathode material obtained in the present application has excellent electrochemical performance and can be used for high-performance magnesium ion batteries.

[0045] Example 2 A MXene / Cu4Mo6Se8-based composite cathode material, the preparation method of which is substantially the same as that of Example 1, except that in step (7), the mass ratio of the composite precursor F to selenium powder is 1:6.

[0046] Example 3 A MXene / Cu4Mo6Se8-based composite cathode material, the preparation method of which is substantially the same as that of Example 1, except that in step (7), the selenization reaction temperature in the tube furnace is 700 ℃.

[0047] Comparative Example 1 A MXene / Cu4Mo6Se8-based composite cathode material, the preparation method of which is substantially the same as that of Example 1, except that 30 ml of MXene dispersion solution (concentration of 5 mg / ml) is added to the mixed solution C, and a uniform solution D is obtained after magnetic stirring for 15 min.

[0048] The button full cell is assembled and tested according to the above method. The test results show that at a current density of 500 mA g -1 , the discharge capacity of the electrode is 71 mAh g -1The analysis shows that when the content of MXene is high (10%), the electrochemical performance of the obtained composite material is poor.

[0049] Comparative Example 2 A Cu4Mo6Se8-based composite positive electrode material was prepared by substantially the same method as in Example 1, except that 0 ml of MXene dispersion was added to the mixed solution C, and a uniform solution D was obtained after magnetic stirring for 15 min.

[0050] The positive electrode material obtained in the present comparative example was used as a positive electrode assembly, and a button-type full cell was assembled and tested according to the above method. The test results show that at a current density of 500 mA g -1 , the discharge capacity of the electrode was 62 mAh g -1 . The analysis shows that when MXene is not present in the material, the electrochemical performance of the material is poor. Further analysis suggests that due to the physical and chemical properties of metal selenides themselves, when MXene is not compounded in the material, the structure of the positive electrode material changes greatly, the electron / ion transmission rate is poor, and the Mg 2+ diffusion is slow, resulting in a performance that is not as good as the Cu4Mo6Se8 composite positive electrode material containing MXene heterostructures.

[0051] Comparative Example 3 A Cu4Mo6Se8-based composite positive electrode material was prepared by substantially the same method as in Example 1, except that Comparative Example 2 was mechanically ground and mixed with MXene powder.

[0052] In Comparative Example 3, only mechanical compounding was used, and the interface contact between MXene and selenide was limited, the electron transmission and Mg 2+ diffusion efficiency were insufficient; the dispersion of MXene was poor, and the lamellar aggregation was prone to occur, resulting in a performance that is not as good as the Cu4Mo6Se8 composite positive electrode material containing MXene heterostructures.

[0053] Comparative Example 4 A Cu4Mo6Se8-based composite positive electrode material was prepared by substantially the same method as in Example 1, except that the composite precursor F was selenized with selenium powder in a tube furnace, and the temperature was raised (at a rate of 1 ℃ / min) to 600 ℃ in one step, and the reaction was carried out for 4.5 h.

[0054] After testing, the nanosheets in the obtained composite positive electrode material were significantly thickened and aggregated, forming a relatively dense block structure. In addition, under the same test conditions, the electrochemical performance of the composite positive electrode material was lower than that of Example 1, and the rate performance was poor.

[0055] The embodiments are only used to explain the present application, and are not used to limit the present application, and any modification without creative contribution made by the person skilled in the art according to the embodiments after reading the specification is protected by the patent law as long as it is within the scope of the claims of the present application.

Claims

1. An MXene / Cu4Mo6Se8-based composite cathode material, characterized in that, It exhibits a flower-like aggregate structure, comprising a carbon skeleton and Cu4Mo6Se8 / MXene nanosheets self-assembled on the carbon skeleton; CuSe nanoparticles are loaded on the surface of the nanosheets; the nanosheets are stacked in an interlaced manner to form a three-dimensional porous structure.

2. The MXene / Cu4Mo6Se8-based composite cathode material according to claim 1, characterized in that, The CuSe nanoparticles have a particle size of 100~200 nm.

3. The method for preparing the MXene / Cu4Mo6Se8-based composite cathode material according to claim 1 or 2, characterized in that, Includes the following steps: 1) Dissolve the copper salt and the first organic ligand in water and mix thoroughly; add the molybdenum salt and mix thoroughly to obtain mixture I; 2) Add MXene dispersion to mixture I and mix thoroughly to obtain mixture II; 3) Add the second organic ligand solution to mixture II to obtain the precursor solution; 4) The obtained precursor solution was stirred, and the obtained precipitate was washed and dried to obtain the composite precursor; 5) The obtained composite precursor is mixed with selenium powder, ground, and then subjected to a selenization reaction under a gradient temperature under a protective atmosphere to obtain the MXene / Cu4Mo6Se8-based composite cathode material.

4. The preparation method according to claim 3, characterized in that, The copper salt is one or more of copper acetate, copper nitrate, copper chloride, and copper oxalate; the molybdenum salt is one or more of molybdenum phosphate and ammonium molybdate.

5. The preparation method according to claim 3, characterized in that, The first organic ligand is one or more of L-glutamic acid and aspartic acid; the molar ratio of copper salt to the first organic ligand is 1:0.1~0.

5.

6. The preparation method according to claim 3, characterized in that, The mass ratio of introduced MXene to copper salt is 1:25~35.

7. The preparation method according to claim 3, characterized in that, The second organic ligand is one or more of pyromellitic acid and pyromellitic tetracarboxylic acid; the molar ratio of copper salt to the second organic ligand is 1:0.5~1.

8. The preparation method according to claim 3, characterized in that, The mass ratio of the composite precursor to selenium powder is 1:5~10.

9. The preparation method according to claim 3, characterized in that, The selenization reaction is carried out at a temperature of 500~700℃ for 2~5 h; the heating rate is 1~3℃ / min, and the temperature is held at 340~360℃ for 20~40 min.

10. A magnesium battery based on the MXene / Cu4Mo6Se8-based composite cathode material of claim 1, characterized in that, It includes a magnesium battery positive electrode sheet based on MXene / Cu4Mo6Se8-based composite positive electrode material, a magnesium metal negative electrode, a separator, and an electrolyte.

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