A bimetallic negative electrode material, a preparation method and application thereof

Abstract

The application discloses a bimetal negative material and a preparation method and application thereof. The preparation method of the bimetal negative material comprises the following steps: 1) dissolving a soluble cobalt salt, ammonium metavanadate and sodium citrate in water to obtain a cobalt salt solution; 2) adding the cobalt salt solution in step 1) into a potassium cobalt cyanide solution drop by drop, mixing by stirring, and performing hydrothermal reaction to obtain a cobalt-vanadium precursor; and 3) calcining the cobalt-vanadium precursor in step 2) in a protective atmosphere to obtain the bimetal negative material. The method is simple in operation process, can prepare a precursor with good stability and good coordination of vanadium and cobalt by using Prussian blue derivatives as organic ligands, can maintain a good structure of the precursor in the calcination process, form spherical particles assembled by fine nanoparticles, and also can prepare the bimetal negative material with a heterojunction structure composed of Co and Co2VO4, good conductivity, excellent electrochemical performance and good stability.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to a bimetallic negative electrode material and a preparation method and application thereof. Background Art

[0002] In recent years, much research has been devoted to reducing the environmental impact of fossil fuels. A great deal of work has been done to build energy storage devices to enhance the effectiveness of renewable energy. Lithium-ion batteries have good development prospects in energy storage in the electronics market due to their high density, long cycle life and environmental friendliness. Conventional commercial lithium-ion batteries are composed of graphite as the negative electrode material and a combination of liquid alkyl carbonate and lithium salt as the electrolyte. However, the theoretical capacity of graphite is low (372 mAh g -1 ), limited cycle life, unsatisfactory rate performance, and lithiation voltage (~0.1V vs.Li + / Li) is close to Li + Potential (0V vs.Li + / Li), which accelerates the formation of lithium dendrites and hinders practical applications. Alloyed silicon-based anode materials have high theoretical capacity, but poor conductivity. Furthermore, during lithium alloying, they experience excessive volume expansion (>300%), leading to a significant decrease in specific capacity and thickening of the SEI film. Consequently, significant attention is being paid to the development of high-capacity anode materials.

[0003] Transition metal oxides (TMOs) have become ideal anode materials for lithium-ion batteries due to their environmental friendliness and weak voltage hysteresis (<0.7 V). However, their rate performance and cycling durability are limited by poor ionic conductivity, insufficient ion diffusion kinetics, and volume changes, which are also the most serious problems currently encountered by transition metal oxides.

[0004] During the cycle, Co and V in cobalt vanadate can react with multiple Li + In addition, Co and VO X The synergistic effect of the created invisible array can enhance rate performance. Co2VO4 has attracted considerable attention due to its low raw material cost and advantageous electronic properties. However, it still suffers from poor electrochemical kinetics, severe volume expansion (poor stability), and complex preparation processes, hindering its practical application.

[0005] Therefore, there is an urgent need to develop a method that is simple to prepare and can enhance the structural stability, conductivity, electrochemical power, rate performance and cycle durability of cobalt vanadates. Summary of the Invention

[0006] In order to overcome the problems existing in the prior art and stimulate the lithium storage capacity of high-performance negative electrode materials, the purpose of the present invention is to provide a bimetallic negative electrode material and its preparation method and application.

[0007] The inventive concept of the present invention: The present invention provides a heterostructured bimetallic negative electrode material with high reversible capacity and excellent cycle stability and a preparation method thereof. The present invention first uses a Prussian blue derivative (PBA) as a ligand, sodium citrate as a morphology regulator and a specific preparation method to prepare a Co-V-PBA precursor with a specific structure; then, the Co-V-PBA precursor is used as a sacrificial template for calcination, thereby achieving the purpose of "optimizing the stacking structure and metal Co crystals to obtain a bimetallic negative electrode material comprising a heterojunction of Co2VO4 and Co". In addition, density functional theory (DFT) calculations have verified that the Co2VO4 / Co heterostructure on the bimetallic negative electrode material can reduce Li + The migration energy barrier for diffusion is reduced, thereby enhancing the electrochemical kinetics.

[0008] This shows that this preparation method can not only basically maintain the structure of the precursor, but also the Co and V in the precursor can form coordination bonds with the Prussian blue derivative PBA well, so that the optimized stacking structure and metal Co crystals can be obtained by calcining the precursor alone. It can improve the electronic conductivity of Co2VO4 / Co and maintain strong structural stability, and can also effectively improve its electrochemical performance (including kinetics and rate stability).

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] In a first aspect, the present invention provides a method for preparing a bimetallic negative electrode material, comprising the following steps:

[0011] 1) dissolving a soluble cobalt salt, ammonium metavanadate and sodium citrate in water to obtain a cobalt salt solution;

[0012] 2) adding the cobalt salt solution in step 1) dropwise to the potassium cobalt cyanide solution, stirring and mixing, and hydrothermally reacting to obtain a cobalt vanadium precursor;

[0013] 3) calcining the cobalt-vanadium precursor in step 2) in a protective atmosphere to obtain a bimetallic negative electrode material;

[0014] Wherein, the bimetallic negative electrode material includes a heterojunction structure composed of Co2VO4 and Co.

[0015] Preferably, the hydrothermal reaction temperature in step 2) is 100° C. to 140° C., and the hydrothermal reaction time is 20 to 36 hours.

[0016] Preferably, the stirring and mixing time in step 2) is 1.5 to 3 hours.

[0017] Preferably, the temperature of the stirring and mixing in step 2) is 15-30°C.

[0018] Preferably, the hydrothermal reaction temperature in step 2) is 110° C. to 130° C., and the hydrothermal reaction time is 22 to 26 hours.

[0019] Specifically, considering that metal V is difficult to coordinate and not fully soluble in water at room temperature, and to avoid structural damage, this work first stirred the reaction at room temperature for 2 hours to ensure that all substances could be better dissolved in water, and then reacted at 120°C for 24 hours to achieve better coordination between Co and V. If the hydrothermal reaction time is shorter than 24 hours and the reaction temperature is lower than 120°C, the reaction will be incomplete and the metal and organic ligands will not be fully coordinated, which will affect the morphology of the product heterostructure and affect the electrochemical performance.

[0020] Compared to many PBA precursors prepared at room temperature, the Co-V-PBA precursor prepared by the hydrothermal method of the present invention has a smaller particle size, and the final product after calcination can better inherit the morphology of the precursor without collapse. In addition, the present invention directly prepares the bimetallic MOF (i.e., precursor) through a one-step process, which can simplify the preparation process and improve practical application.

[0021] Preferably, the soluble cobalt salt in step 1) is selected from at least one of cobalt nitrate and cobalt nitrate hexahydrate.

[0022] Preferably, in step 1), the molar ratio of the soluble cobalt salt, ammonium metavanadate and sodium citrate is 1:(4-6):(1.2-1.8).

[0023] Further preferably, in step 1), the molar ratio of the soluble cobalt salt, ammonium metavanadate and sodium citrate is 1:5:1.5.

[0024] Preferably, the concentration of the soluble cobalt salt in the cobalt salt solution in step 1) is 0.01 to 0.03 mol / L.

[0025] Preferably, the molar ratio of potassium cobalt cyanide to soluble cobalt salt in the potassium cobalt cyanide solution in step 2) is (0.5-0.8): 1. Further preferably, the molar ratio of potassium cobalt cyanide to soluble cobalt salt in the potassium cobalt cyanide solution in step 2) is (0.6-0.7): 1.

[0026] Preferably, step 2) further comprises the steps of cooling, washing the precipitate with ethanol and water, and drying.

[0027] Preferably, the cobalt-vanadium precursor in step 2) is nanoparticles, and the particle size of the nanoparticles is 400-500 nm.

[0028] Specifically, the cobalt-vanadium precursor is a spherical nanoparticle with an optimized stacking feature.

[0029] Preferably, the protective atmosphere in step 3) is nitrogen.

[0030] Preferably, the temperature of the calcination in step 3) is 550-700℃.

[0031] Preferably, the time of the calcination in step 3) is 2-5 hours.

[0032] Preferably, the heating rate of the calcination in step 3) is 3-6℃ / min -1 . Further preferably, the heating rate of the calcination in step 3) is 5℃ / min -1 .

[0033] In a second aspect, the present application provides a bimetallic negative electrode material prepared by the above method.

[0034] Preferably, the bimetallic negative electrode material comprises a plurality of Co2VO4nanoparticles and Co nanoparticles stacked in a carbon layer; the Co nanoparticles are located between the plurality of Co2VO4nanoparticles and form a heterostructure with the Co2VO4nanoparticles.

[0035] Specifically, the heterostructure is formed by two or more materials adhering together in a physical or chemical manner, forming a blurred junction interface. The reason for forming a heterostructure to improve the electrochemical performance is as follows: electrons will be redeployed around the heterostructure interface, so that the internal electrically neutral components in the part close to the boundary will be ionized to become active points of electrochemical reaction, and easily adsorb opposite charged carriers. Therefore, positively charged ions can be adsorbed on negatively charged ions near the heterostructure interface, storing more electrical energy; the built-in electric field of the heterostructure may also be the reason for enhancing the lithium storage performance, which can accelerate the diffusion ability of metal ions and provide more active sites. Cobalt has high electrical conductivity and has the function of catalyzing reversible reactions. The heterostructure constructed by cobalt and cobalt vanadate can improve the transport capacity of Li + and enhance the electrochemical performance.

[0036] Preferably, the particle size of the Co nanoparticles is 50-100 nm.

[0037] Preferably, the bimetallic negative electrode material is in the form of spherical particles, and the particle size of the bimetallic negative electrode material is 100-200 nm.

[0038] Specifically, the plurality of Co2VO4nanoparticles and Co nanoparticles are assembled (or stacked) into larger bimetallic negative electrode material particles; and the carbon is located in the outer layer of the heterostructure.

[0039] In a third aspect, the present application provides a battery comprising the bimetallic negative electrode material described above.

[0040] Preferably, the positive electrode of the battery is an alkali metal. In particular, the alkali metal is selected from at least one of lithium, sodium and potassium.

[0041] The bimetallic negative electrode material of the present application has the following advantages: the preparation method of the bimetallic negative electrode material of the present application is simple in operation process, and can prepare a precursor with good stability and good coordination of vanadium and cobalt by using Prussian blue derivative as an organic ligand; the structure of the precursor can be maintained well during calcination, and a spherical particle assembled by fine nanoparticles can be formed; and a bimetallic negative electrode material with a heterojunction structure composed of Co and Co2VO4, good electrical conductivity, excellent electrochemical performance and good stability can be prepared. Specifically, the bimetallic negative electrode material has the following advantages:

[0042] The present application synthesizes a composite material (including a Co2VO4 / Co heterojunction structure) by designing a Co-V-PBA precursor as a sacrificial template to promote the performance of a lithium ion battery.

[0043] Moreover, due to the optimized packing configuration and the presence of metallic cobalt, the formation of radical ions is catalyzed, thereby having higher electrical conductivity, shorter Li + transport paths and more active sites. Electrochemical performance shows that the discharge capacity reaches 1497.5 mAh g -1 after 300 cycles at a current density of 0.1 Ag -1 .

[0044] At the same time, density functional theory (DFT) calculations emphasize the key role of Co2VO4 / Co in improving the electrical conductivity of the electrode, reducing the Li + migration energy barrier and thus strengthening the electrochemical performance. This in-situ heterostructure construction technology provides another way to develop high-performance lithium ion battery negative electrode materials. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 Figure 4 is an XRD spectrum of the bimetallic negative electrode material CVOC-P in Example 1.

[0046] Figure 2 Figure 5 is an SEM image of the Co-V-PBA precursor in Example 1.

[0047] Figure 3 Figure 6 is an SEM image of the bimetallic negative electrode material CVOC-P in Example 1.

[0048] Figure 4 Figure 7 is a transmission electron microscope image, a high-resolution transmission electron microscope image and a selected area electron diffraction image of the bimetallic negative electrode material CVOC-P in Example 1.

[0049] Figure 5 HAADF-SEM images and elemental mapping images of Co, V, O, and C in the bimetallic negative electrode material CVOC-P in Example 1.

[0050] Figure 6 This is the full XPS spectrum of the bimetallic negative electrode material CVOC-P in Example 1.

[0051] Figure 7 This is the Co 2p high-resolution XPS spectrum of the bimetallic negative electrode material CVOC-P in Example 1.

[0052] Figure 8 This is the O1s high-resolution XPS spectrum of the bimetallic negative electrode material CVOC-P in Example 1.

[0053] Figure 9 This is the V 2p high-resolution XPS spectrum of the bimetallic negative electrode material CVOC-P in Example 1.

[0054] Figure 10 1 and 2 are the nitrogen adsorption / desorption curves and pore size distribution diagrams of the bimetallic negative electrode material CVOC-P in Example 1.

[0055] Figure 11 This is the cyclic voltammogram of the first three cycles of the bimetallic negative electrode material CVOC-P in Example 1 at 0.1 mV / s.

[0056] Figure 12 The XRD pattern and lithium storage mechanism diagram of the bimetallic negative electrode material CVOC-P in Example 1 measured under lithium desorption / lithiation conditions.

[0057] Figure 13 The bimetallic negative electrode material CVOC-P in Example 1 is used at a current density of 0.1A. -1 , the charge / discharge curves of the first three cycles under the voltage condition of 0~3V.

[0058] Figure 14 The bimetallic negative electrode materials of Example 1 and Comparative Examples 1-2 are subjected to a current density of 0.1A at an ambient temperature of 25°C. -1 , Cyclic stability test diagram under voltage conditions of 0~3V.

[0059] Figure 15 The bimetallic negative electrode material of Example 1 and the bimetallic negative electrode material of Comparative Examples 1 and 2 are subjected to an ambient temperature of 25°C and a current density of 1A. -1 , Cyclic stability test diagram under voltage conditions of 0~3V.

[0060] Figure 16The bimetallic negative electrode material of Example 1 and the bimetallic negative electrode material of Comparative Examples 1 and 2 were subjected to different current densities (0.1-2.0Ag -1 ) is the rate performance result graph measured under .

[0061] Figure 17 The bimetallic negative electrode material in Example 1 was subjected to different scanning rates (0.2-1.0 mV s -1 ) under CV curves and analysis results; (a) is the CV curve of CVOC-P at different scan rates, (b) is a comparison of the pseudocapacitance contribution rate measured at different scan rates of CVOC-P, and (c) is the CV curve of CVOC-P at a scan rate of 1.0 mV s -1 (d) is the pseudocapacitance contribution diagram, and the b-value calculation result diagram of the redox peak obtained after processing the data in (a).

[0062] Figure 18 Figures 1 and 2 show the results of the CVOC-P test using the electrostatic intermittent titration procedure (GITT) in Example 1; (a) shows the voltage response curve, (b) shows the change in the lithium ion diffusion coefficient of the CVOC-P during the charge and discharge process, (c) shows the relationship between the discharge capacity percentage and voltage during the lithium removal and insertion processes of the CVOC-P, and (d) shows the single-step titration spectrum.

[0063] Figure 19 The Li of the metal negative electrode material in Example 1 and the bimetallic negative electrode material in Comparative Example 1 during charge / discharge + Schematic diagram of migration pathway and changes in diffusion energy curve.

[0064] Figure 20 This is the XRD spectrum of the bimetallic negative electrode material CVO-P in Comparative Example 1.

[0065] Figure 21 This is the XRD spectrum of the bimetallic negative electrode material CVOC-B in Comparative Example 2. DETAILED DESCRIPTION

[0066] The present invention is further described in detail below through specific examples.

[0067] Unless otherwise specified, in the present invention, the data of different samples in the same figure are measured using the same test method and conditions; in the present invention, "CVO" represents Co2VO4; "CVOC" represents Co2VO4 / Co composite material; the P in CVO-P of Comparative Example 1 and CVOC-P of Example 1 both represent that the ligand is K3[Co(CN)6], abbreviated as PBA; the B in CVOC-B of Comparative Example 2 represents that the ligand is terephthalic acid, abbreviated as BDC.

[0068] Example 1

[0069] The present example provides a preparation method of a bimetallic negative material (CVOC-P), comprising the following steps:

[0070] 1) Dissolve 1 mmol of cobalt nitrate hexahydrate, 5 mmol of ammonium metavanadate and 1.5 mmol of sodium citrate in 60 mL of deionized water to obtain solution A;

[0071] 2) Dissolve 0.67 mmol of potassium cobalt cyanide (abbreviated as PBA, chemical formula: K3[Co(CN)6]) in 40 mL of deionized water, and stir vigorously until dissolved to obtain solution B;

[0072] 3) Slowly drop solution A into solution B and stir at room temperature (20-25℃) for 2 hours, and then transfer the mixed solution into a high-pressure reaction kettle and place it in an oven at 120℃ for hydrothermal reaction for 24 hours;

[0073] After the temperature drops to room temperature, pour the precipitate into a centrifuge tube, wash it with ethanol and water several times, and then dry the precipitate at 60℃ for 12 hours to obtain a Co-V-PBA precursor;

[0074] 4) Calcine the Co-V-PBA precursor under the condition of nitrogen atmosphere and 600℃ for 3 hours to obtain a bimetallic negative material (denoted as CVOC-P);

[0075] The heating rate of calcination in step 4) is 5℃ / min -1 .

[0076] Comparative Example 1

[0077] The present comparative example provides a preparation method of a bimetallic negative material (CVO-P), which is different from Example 1 only in that the calcination temperature is changed from 600℃ to 350℃, and the finally prepared bimetallic negative material is denoted as CVO-P.

[0078] Analysis shows that the morphology of the precursor and the bimetallic negative material obtained in the present comparative example is similar to that of Example 1.

[0079] Comparative Example 2

[0080] The present comparative example mainly controls the molar ratio of cobalt nitrate hexahydrate to ammonium metavanadate to be the same as that of Example 1, and explores the influence of different ligands on the negative material.

[0081] The present comparative example provides a preparation method of a bimetallic negative material (CVOC-B), comprising the following steps:

[0082] 1) Dissolve 0.6 mmol of cobalt nitrate hexahydrate, 3 mmol of ammonium metavanadate, and 0.5 g of polypyrrolidone (PVP) (average molecular weight: 16,000) in 50 mL of deionized water to obtain solution A;

[0083] 2) Dissolve 1.2 mmol of terephthalic acid (BDC) in 50 mL of N,N-dimethylformamide (DMF) to obtain solution B;

[0084] 3) Solutions A and B were mixed together, stirred for 2 hours, and then transferred to an autoclave and heated to 120°C for 24 hours;

[0085] When the temperature dropped to room temperature, the precipitate was poured into a centrifuge tube, washed with ethanol and water several times, and dried at 60 °C for 12 h to obtain the Co-V-BDC precursor;

[0086] 4) The Co-V-BDC precursor was placed in a nitrogen atmosphere and calcined at 600°C for 3 hours to obtain Co2VO4 / Co (labeled as CVOC-B);

[0087] The heating rate of the calcination in step 4) is 5°C min -1 .

[0088] After analysis, the morphology of the precursor and bimetallic negative electrode material obtained in this comparative example are both nano-particles, which have certain similarities with the morphology and composition of the precursor and bimetallic negative electrode material in Example 1.

[0089] Application Example 1

[0090] Negative electrode active materials: CVOC-P of Example 1, CVO-P of Comparative Example 1, and CVOC-B of Comparative Example 2.

[0091] Battery assembly method:

[0092] The negative electrode active material, acetylene black and polyvinylidene fluoride were mixed and ground in a mass ratio of 8:1:1, and 2 to 3 mL of N-methylpyrrolidone (NMP) were added to form a slurry; then, the slurry was coated on copper foil with a scraper with a length of 100 microns and transferred to a vacuum drying oven at 100°C for 12 hours; finally, a cutting device with a mold with a radius of 6 mm was used to cut the copper foil covered with the active ingredient to obtain the negative electrode.

[0093] LiPF6 was dissolved in a mixed solvent (the volume ratio of ethylene carbonate EC, diethyl carbonate DC and methylene carbonate EMC was 1:1:1) to prepare a LiPF6 electrolyte with a concentration of 1 mol / L.

[0094] In an argon-filled glove box, a lithium sheet (positive electrode), a polypropylene (PP) microporous separator, the aforementioned negative electrode, and the aforementioned electrolyte were assembled into CR2032 button cells, and their electrochemical performance was tested. Unless otherwise specified, the electrochemical performance test results reported herein are based on the aforementioned method for assembling the negative electrode material into the cell.

[0095] Characterization and performance test results:

[0096] 1. The X-ray diffraction (XRD) spectrum of the bimetallic negative electrode material CVOC-P in Example 1 is as follows: Figure 1 The XRD spectrum of the bimetallic negative electrode material CVO-P in Comparative Example 1 is shown as Figure 20 The XRD spectrum of the bimetallic negative electrode material CVOC-B in Comparative Example 2 is shown as follows. Figure 21 shown.

[0097] Depend on Figure 1 、 Figure 20 and Figure 21 The XRD spectrum of CVOC-P shows distinct diffraction peaks at 2θ = 18.48°, 30.18°, 35.56°, 56.94°, and 62.54°, attributed to Co₂VO₄ (PDF#73-1633). Also, distinct diffraction peaks at 2θ = 44.32° and 50.88° are attributed to Co (PDF#89-4307). No other impurity peaks are observed. This indicates that the bimetallic anode material CVOC-P is composed of both Co₂VO₄ and Co.

[0098] The XRD spectrum of CVO-P shows a distinct 2θ peak between 20 and 80°, indicating poor crystallinity. Significant diffraction peaks at 2θ of 29.98°, 35.42°, 42.98°, 57.14°, and 62.96° are attributed to Co₂VO₄ (PDF#73-1633). This suggests that the bimetallic anode material CVO-P contains poorly crystalline Co₂VO₄.

[0099] The XRD spectrum of CVOC-B shows distinct diffraction peaks at 18.35°, 30.28°, 35.58°, 56.96°, and 62.63° (2θ), attributed to Co₂VO₄ (PDF#73-1633). Furthermore, distinct diffraction peaks at 44.33° and 50.82° (2θ), attributed to Co (PDF#89-4307), were observed. No other impurity peaks were observed. This indicates that the bimetallic anode material CVOC-B is composed of both Co₂VO₄ and Co.

[0100] 2. Scanning Electron Microscope (SEM) image of the Co-V-PBA precursor in Example 1, as shown Figure 2 The SEM image of the bimetallic negative electrode material CVOC-P in Example 1 is shown as follows. Figure 3 shown.

[0101] Depend on Figure 2 and Figure 3 It can be seen that the Co-V-PBA precursor and the bimetallic negative electrode material CVOC-P in Example 1 have a stacked spherical structure and can maintain nano-spherical particles before and after calcination; among them, the Co-V-PBA precursor is a relatively smooth spherical particle with a particle size of 400-500nm; the bimetallic negative electrode material CVOC-P is a spherical particle stacked (or composed of) many fine Co2VO4 and Co nanoparticles (the particle size of Co nanoparticles is 50-100nm), and the particle size of the CVOC-P spherical particles is 100-200nm.

[0102] The bimetallic negative electrode material in Example 1 was ultrasonically crushed and dispersed in an ethanol solution, and then the transmission electron microscopy (TEM) image, high-resolution transmission electron microscopy (HRTEM) image and selected area electron diffraction image of CVOC-P were tested. Figure 4 shown; among them; Figure 4 (a) and (b) are TEM images of CVOC-P. Figure 4 (c) is the HRTEM image of CVOC-P. Figure 4 (d) is about Figure 4 The selected area electron diffraction pattern of (c). The HAADF-SEM image and element mapping of Co, V, O and C of the bimetallic negative electrode material CVOC-P in Example 1 are as follows: Figure 5 shown.

[0103] Depend on Figure 4 and Figure 5 It can be seen that: the transmission electron microscopy image describes the internal microstructure of the CVOC-P material, confirming that the material is composed of many nanoparticles; the high-resolution transmission electron microscopy image shows a clear heterogeneous interface (marked with a dotted line, see Figure 4 In (c)), the (311) crystal plane of Co2VO4 and the (111) crystal plane of Co can be observed at the same time.

[0104] Figure 4 (d) shows the diffraction rings of the (111)(211)(311)(400)(440) crystal planes of Co2VO4 and the (111) crystal plane of Co. Combined with the elemental mapping analysis results, it shows that Co, V, O, and C elements are uniformly distributed in the CVOC-P material.

[0105] 3. The X-ray photoelectron spectroscopy (XPS) survey spectrum, Co 2p high resolution XPS spectrum, O 1s high resolution XPS spectrum and V 2p high resolution XPS spectrum of the bimetallic negative material CVOC-P in Example 1 are shown in FIGS. Figure 6 、 Figure 7 、 Figure 8 and Figure 9 respectively.

[0106] It can be seen from Figure 6 、 Figure 7 、 Figure 8 and Figure 9 that: according to the XPS survey spectrum of the bimetallic negative material CVOC-P, it can be seen that Co, V, O and C elements coexist in the CVOC-P material. The signal peaks with binding energy of 801.88 eV and 786.18 eV are attributed to the satellite peaks (Satellict Co) of Co, the signal peaks located at 797.58 eV and 782.38 eV are attributed to Co 2+ , the signal peaks located at 795.88 eV and 780.08 eV are attributed to Co 3+ , and the signal peaks located at 793.78 eV and 778.88 eV are attributed to elemental Co, which indicates that Co 2+ , Co 3+ and elemental Co coexist.

[0107] The O 1s spectrum has signal peaks at 532.48, 530.88 and 528.78 eV, which correspond to O-H bond, C=O bond and Co / V-O bond respectively; the V 2p spectrum in FIG. c has peaks at 515.08 eV and 522.38 eV, which represent V 2p 3 / 2 and V 2p 1 / 2 respectively.

[0108] 4. The nitrogen adsorption-desorption curve (large figure) and pore size distribution graph (internal insert) of the bimetallic negative material CVOC-P in Example 1 are shown in FIG. Figure 10 .

[0109] It can be seen from Figure 10 that: the BET specific surface area of CVOC-P measured by the multipoint method is 110.18 m 2 g -1 , and the pore size distribution is 1.75-49.5 nm (the pore size is mainly 2-20 nm). This indicates that the bimetallic negative material CVOC-P has a large surface area, which can alleviate the volume change during the cycle process, accelerate the charge transfer, and is beneficial to improve the electrochemical performance.

[0110] 5. The cyclic voltammetry curve of the bimetallic negative electrode material CVOC-P in Example 1 at 0.1 mV / s for the first three cycles is as follows: Figure 11 shown.

[0111] Depend on Figure 11 It can be seen that after the CVOC-P in Example 1 was assembled into a battery, a cyclic voltammetry curve test was performed: during the first cycle of lithium insertion (charging), the peaks of 1.72V, 0.73V and 0.19V correspond to the decomposition of Co2VO4 into CoO, Li x The formation of VO2 and the reduction reaction process of CoO to Co. Moreover, compared with the second and third cycle cyclic voltammograms, the first cycle cyclic voltammogram shows a difference because the irreversible formation of SEI film and the decomposition of Co2VO4 to CoO only occur in the first scan.

[0112] In the second cycle, the reduction peaks at 1.35 V, 0.74 V, and 0.31 V can be explained as the reduction reaction of CoO to Co, the formation of Li2O, and the formation of Li x+y The formation of VO2. During the delithiation process (discharge), the peaks of 1.30V and 2.10V are related to the formation of CoO and the transfer of Li from Li x+ y The second and third curves have a high degree of overlap, indicating that the material has good cycle reversibility during the charge and discharge process.

[0113] 5. The XRD pattern of the bimetallic negative electrode material CVOC-P measured under lithium removal conditions, the XRD pattern measured under lithium insertion conditions and the lithium storage mechanism diagram are shown in Figure 5. Figure 12 (a) Figure 12 (b) and Figure 12 As shown in (c) in .

[0114] In order to further verify the lithium storage mechanism of the negative electrode material, its electrochemical mechanism was explored. Figure 12 Shown is the XRD analysis of the negative electrode after 20 cycles; during the delithiation (discharge) process, Li2O (PDF#77-2144), CoO (PDF#75-0393), and LiVO2 (PDF#84-1545) are generated at the negative electrode; during the lithium insertion (charge) process, Co (PDF#89-4307), Li2O (PDF#77-2144), and LiVO2 (PDF#84-1545) are detected by XRD analysis.

[0115] According to the above results, the electrochemical mechanism was verified and described through the lithium storage mechanism process analysis, such as Figure 12 Specifically, the reaction process is shown in formulas (1) to (3).

[0116] Co2VO4 / Co + xLi + +xe - → CoO + Li x VO2 (1)

[0117]

[0118]

[0119] 6. The bimetallic negative electrode material CVOC-P in Example 1 is subjected to a current density of 0.1Ag. -1 , the charge / discharge curve of the first three cycles under the voltage of 0~3V, as shown in Figure 13 shown.

[0120] Depend on Figure 13 It can be seen that the bimetallic negative electrode material CVOC-P has a current density of 0.1Ag -1 The charge-discharge curves of the first three cycles of CVOC-P at a voltage of 0-3 V show that the specific capacity of the negative electrode material is 1183.8 mAh g in the first cycle. -1 , and decreases in the second and third cycles due to the formation of SEI film and the decomposition of electrolyte.

[0121] The bimetallic negative electrode materials of Example 1 and Comparative Examples 1 and 2 were subjected to a current density of 0.1 Ag at an ambient temperature of 25°C. -1 , Cyclic stability test diagram under voltage of 0~3V, such as Figure 14 The bimetallic negative electrode material of Example 1 and the bimetallic negative electrode material of Comparative Examples 1-2 are subjected to an ambient temperature of 25°C and a current density of 1A. -1 , Cyclic stability test diagram under voltage of 0~3V, such as Figure 15 shown.

[0122] 7. The bimetallic negative electrode material of Example 1 and the bimetallic negative electrode material of Comparative Examples 1-2 were tested at different current densities (0.1-2.0Ag -1 ) is the rate performance result diagram measured under Figure 16 shown.

[0123] Depend on Figure 14 、 Figure 15 and Figure 16 It can be seen that CVOC-P, CVO-P and CVOC-B have the same current density of 0.1Ag -1 When the voltage is 3V, the discharge capacity after 300 cycles is 1497.5mAh g -1 , 799.4mAh g -1 and 1259.8mAh g-1 This indicates that CVOC-P shows excellent cycle stability. Meanwhile, the coulombic efficiency remains stable after the second cycle, which is due to the side reaction only occurring in the first cycle. At this time, the coulombic efficiency of CVOC-P can basically maintain about 100%.

[0124] When the current density reaches 1.0 Ag -1 , the specific capacity of CVOC-P, CVO-P and CVOC-B can still maintain at 766.6 mAh g -1 , 397.9 mAh g -1 and 672.4 mAh g -1 after 300 cycles, which further indicates that the high-conductivity metal Co and the construction of the heterostructure of CVOC-P can promote the transport of Li + . Moreover, the capacity of CVOC-P prepared only when PBA is the ligand is higher, which is because of the particularity of the PBA ligand, which not only coordinates more easily than BDC, but also forms a more stable precursor structure, thereby having good conductivity, higher specific capacity, better structural stability and better coulombic efficiency (the coulombic efficiency of CVOC-P can basically maintain about 100%).

[0125] Figure 16 The rate performance of the three negative electrode materials under different current densities is shown. When the voltage is 0-3 V and the current density is 0.1 Ag -1 , 0.2 Ag -1 , 0.3 Ag -1 , 0.4 Ag -1 , 0.5 Ag -1 , 1.0 Ag -1 and 2.0 Ag -1 , the discharge specific capacity of CVOC-P is 1292.7 mAh g -1 , 1254.8 mAh g -1 , 1148.3 mAh g -1 , 1028.8 mAh g -1 , 884.7 mAh g -1 , 797.7 mAh g -1 , 722.0 mAh g -1 , respectively. In addition, when the current density returns to 0.1 Ag -1 , the capacity returns to the initial capacity, indicating that the negative electrode material has good cycle reversibility.

[0126] Compared with CVO-P and CVOC-B, CVOC-P not only has good cycle reversibility and good rate performance, but also has higher specific capacity.

[0127] 8. Figure 17 CV curves of the bimetallic negative material in Example 1 at different scan rates (0.2-1.0 mV s -1 ) and their analysis results; wherein (a) is the CV curve of CVOC-P at different scan rates, (b) is the comparison chart of the pseudo-capacitance contribution rate measured at different scan rates of CVOC-P, (c) is the pseudo-capacitance contribution chart of CVOC-P at a scan rate of 1.0 mV s -1 , and (d) is the b value calculation results chart of the redox peaks obtained after data processing of (a).

[0128] It can be seen that: Figure 17 Figure 17 (a) of which shows the cyclic voltammetry curves at different scan rates to further explore the electrochemical dynamics, and the contribution rate of the pseudo-capacitance can be calculated according to the following formulas (4)-(5):

[0129] i = av b (4)

[0130] i(V) = k1v + k2v 1 / 2 (5)

[0131] wherein a and b are fixed values. When the b value is close to 0.5, the process is mainly diffusion, and when the b value is close to 1.0, it represents a process dominated by capacitance. In formula (5), k1v represents the pseudo-capacitance characteristics, and k2v 1 / 2 corresponds to the diffusion characteristics.

[0132] Figure 17 (b) of which shows that the pseudo-capacitance contribution gradually increases with the increase of the scan rate of the cyclic voltammetry curve; Figure 17 (c) of which shows that the pseudo-capacitance contribution rate is 90.91% at a scan rate of 0.1 mV s -1 ; Figure 17 The b value in (d) is between 0.7 and 0.9, indicating that the material is dominated by capacitance. This is because the in-situ growth of Co nanoparticles and its strong conductivity provides more active sites, enhancing the storage of Li + .

[0133] 9. GITT test method and conditions: the GITT of the static intermittent titration procedure (GITT) of the Blue Electric Test (CT 2001A, China) was used to set the voltage range to 0-3V, the interval standing time between each charge / discharge was 1h, and the measured results are shown in Figure 18 .

[0134] Figure 18 ​The results of the electrostatic intermittent titration procedure (GITT) test for CVOC-P in Example 1; wherein, (a) is a voltage response curve, (b) is a plot of the lithium ion diffusion coefficient of CVOC-P during the charging and discharging process, (c) is a plot of the relationship between the percentage of discharge capacity and voltage of CVOC-P during the delithiation and lithiation process, and (d) is a single-step titration spectrum.

[0135] In order to study the advantage of CVOC-P anode material in storing lithium, the electrochemical kinetics of CVOC-P was studied by using the electrostatic intermittent titration procedure (GITT). Figure 18 (a) of FIG. 1 illustrates the voltage response of the electrode; Figure 18 (b) of FIG. 1 illustrates that CVOC-P has a good lithium ion diffusion coefficient; Figure 18 (c) of FIG. 1 shows the relationship between the percentage of discharge capacity and voltage during the delithiation and lithiation process; in order to avoid the influence of the formation of SEI layer and the chemical change of electrolyte, Figure 18 (d) of FIG. 1 shows the curve of the second round of single-step GITT titration. These results prove that the heterogeneous structure anode material has superior electrochemical kinetics, because more additional active sites can accelerate electron transmission and improve reaction kinetics.

[0136] 10. Figure 19 The material pathway schematic diagram and diffusion energy curve change diagram of the metal anode material in Example 1 and the bimetallic anode material in Comparative Example 1 during charging / discharging; wherein, Figure 19 (a) of FIG. 2 is a model of lithium ion in different states when passing through the large pores of the material (i.e. the tetrahedral structure of Co2VO4); Figure 19 (b) of FIG. 2 is a model of lithium ion in different states when passing through the surface of the material; Figure 19 (c) of FIG. 2 is a model of lithium ion in different states when passing through the small pores of the material (i.e. the octahedral structure of Co2VO4), Figure 19 (d-f) of FIG. 2 represents the anode material in Comparative Example 1, and Co2VO4 / Co represents the anode material in Example 1.

[0137] In order to further understand the energy change in the diffusion process, we provide the diffusion energy curves of various migration pathways including site 1 (Li + passing through the large pores), site 2 (Li + passing through the surface of the 311 crystal plane of the material), and site 3 (Li + passing through the small pores). The relative energy all rises from 0 eV to the highest point, and then begins to decline, which is related to the adsorption of Li + It is obvious that when Li +The energy barrier is lowest when passing through the 311 surface, and the minimum energy barrier of CVO is higher than that of CVOC in heterostructure. These findings indicate that the introduction of metallic cobalt to construct heterostructure reduces the Li + energy barrier, which leads to strong conductivity and fast Li + Shuttle rate.

[0138] The present invention prepares a Co2VO4 / Co composite material (CVOC-P) derived from MOF with a heterogeneous structure, which can significantly improve the fast charging capability of lithium-ion batteries. Compared with pure Co2VO4, due to the unique composition and perfect structure of Co2VO4 / Co, the negative electrode material exhibits better electrochemical performance, higher rate capacity and good cycle stability. These results can be explained by the following points: (1) The heterogeneous structure and metal Co can alleviate the volume change, which is the main reason for the rapid charging of Li-ion batteries. + Provide more active sites. (2) Metal Co can catalyze electron transfer to form free radical ions, thereby improving the rate capacity of the battery. (3) The Co2VO4 / Co negative electrode material with a high specific surface area and porous structure can prevent the occurrence of side reactions, alleviate volume changes, and thus enhance cycle stability. The present invention proposes another idea for controlled synthesis using MOFs as sacrificial templates, and makes it possible to use heterostructured materials as advanced lithium-ion battery negative electrode materials.

[0139] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a bimetallic negative electrode material, characterized in that: The following steps are involved: 1) dissolving a soluble cobalt salt, ammonium metavanadate and sodium citrate in water to obtain a cobalt salt solution; 2) adding the cobalt salt solution in step 1) dropwise to the potassium cobalt cyanide solution, stirring and mixing, and performing a hydrothermal reaction to obtain a cobalt vanadium precursor; the hydrothermal reaction temperature is 100° C. to 140° C., and the hydrothermal reaction time is 20 to 36 hours; the stirring and mixing time is 1.5 to 3 hours; 3) The cobalt-vanadium precursor in step 2) is calcined in a protective atmosphere to obtain a bimetallic negative electrode material; the protective atmosphere is nitrogen; the calcination temperature is 550°C to 700°C; the calcination time is 2 to 5 hours; the calcination heating rate is 3 to 6°C min -1 ; Wherein, the bimetallic negative electrode material includes a heterojunction structure composed of Co2VO4 and Co.

2. The preparation method according to claim 1, wherein: Step 1) The molar ratio of the soluble cobalt salt, ammonium metavanadate and sodium citrate is 1:(4-6):(1.2-1.8); And / or, the molar ratio of potassium cobalt cyanide to soluble cobalt salt in the potassium cobalt cyanide solution in step 2) is (0.5-0.8):

1.

3. The preparation method according to claim 1, wherein: In step 1), the soluble cobalt salt is cobalt nitrate.

4. The preparation method according to claim 1, wherein: Step 1) The concentration of the soluble cobalt salt in the cobalt salt solution is 0.01-0.03 mol / L.

5. A bimetallic negative electrode material prepared by the preparation method according to any one of claims 1 to 4.

6. The bimetallic negative electrode material according to claim 5, characterized in that: The bimetallic negative electrode material includes a plurality of Co2VO4 nanoparticles and Co nanoparticles stacked in a carbon layer; the Co nanoparticles are located between the plurality of Co2VO4 nanoparticles and form a heterogeneous structure with the Co2VO4 nanoparticles.

7. The bimetallic negative electrode material according to claim 5, characterized in that: The bimetallic negative electrode material is in the form of spherical particles, and the particle size of the bimetallic negative electrode material is 100-200 nm.

8. A battery, characterized in that: Comprising the bimetallic negative electrode material according to any one of claims 5 to 7.

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