CN113336802B - A kind of organosulfur molecule based on nickel-mercaptobenzimidazole coordination compound and its preparation method and application - Google Patents

Abstract

The invention discloses a polysulfide nickel-mercaptobenzimidazole complex compound and a preparation method and application thereof. The preparation method comprises the following steps: (1) respectively dissolving nickel salt and 2-mercaptobenzimidazole in a solvent, The obtained solution is mixed with an amino weak alkaline solvent, and reacted at a certain temperature to obtain a nickel-mercaptobenzimidazole coordination compound; (2) the nickel-mercaptobenzimidazole coordination compound obtained in step (1) is mixed with sulfur powder Evenly, the reaction is heated in an inert gas atmosphere, and after the reaction is completed, the product is separated to obtain a nickel polysulfide-mercaptobenzimidazole complex. The lithium-sulfur battery prepared by using the nickel polysulfide-mercaptobenzimidazole coordination compound as the positive electrode material has good cycle stability, high-rate charge-discharge performance and high-sulfur loading performance, and the first-cycle capacity is 1354.9mAh at 0.2C g ^‑1 , a capacity of 1179.5 mAh g ^‑1 remains after 100 cycles, and the Coulombic efficiency during cycling is close to 100%.

Description

A kind of organosulfur molecule based on nickel-mercaptobenzimidazole coordination compound and its preparation method and application

technical field

The invention relates to the field of energy storage devices, in particular to a polysulfide-mercaptobenzimidazole coordination compound, a preparation method thereof and an application as a positive electrode material of a lithium-sulfur battery.

Background technique

Lithium-ion batteries based on lithium iron phosphate and nickel-cobalt-manganese ternary materials are the most successfully commercialized secondary batteries, and are widely used in consumer electronics and new energy vehicles. It is increasingly difficult to meet people's needs.

Lithium-sulfur batteries use sulfur and lithium as positive and negative active materials, respectively, with a theoretical specific capacity of 1675mAh g ^-1 and an energy density of 2600Wh kg ^-1 . More importantly, sulfur resources are abundant, inexpensive, harmless and environmentally friendly. . With these advantages, lithium-sulfur batteries are expected to become the next generation of secondary batteries, but problems such as shuttle effect, slow kinetics, and low sulfur loading hinder the commercial application of lithium-sulfur batteries. At present, various carbon materials, metal oxides and sulfides are used to adsorb lithium polysulfides to inhibit the shuttle effect and accelerate the reaction kinetics, but the ideal performance has not been achieved.

Complexes have many inherent features, such as highly ordered porous structures, controllable pore size and topology, and inorganic-organic hybrid properties. Due to these properties, the complexes are able to store more charge in the same volume. This is beneficial in providing dense cation hopping sites so that the activation energy for ion transport can be minimized, thereby increasing ionic conductivity. These characteristics are used to realize the adsorption of lithium polysulfides and the acceleration of reaction kinetics, and realize the improvement of electrochemical performances such as capacity, cycle stability, rate performance, and energy density of lithium-sulfur batteries.

SUMMARY OF THE INVENTION

In order to overcome the shortcomings and deficiencies of the prior art, the present invention provides a preparation method of a polysulfide-mercaptobenzimidazole coordination compound, and its application in the cathode material of a lithium-sulfur battery.

A first aspect of the present invention provides a nickel polysulfide-mercaptobenzimidazole coordination compound, which has the following structural formula:

The second aspect of the present invention provides the preparation method of the nickel polysulfide-mercaptobenzimidazole coordination compound described in the first aspect, comprising the following steps:

(1) nickel salt and 2-mercaptobenzimidazole are dissolved in organic solvent respectively, the solution obtained is mixed with amino weak alkaline solvent, after the reaction finishes, centrifugal collection precipitation, washing, drying obtain nickel-mercaptobenzimidazole Imidazole coordination compounds;

(2) the nickel-mercaptobenzimidazole coordination compound obtained in the step (1) is uniformly mixed with the sulfur powder, and the reaction is heated, and after the reaction finishes, the product is washed, centrifuged, and dried to obtain nickel polysulfide-mercaptobenzimidazole coordination compound; the reaction atmosphere of the heating reaction is an inert gas.

There are three coordination reaction sites in 2-mercaptobenzimidazole: the sulfur atom in C-S, the nitrogen atom in C=N, the nitrogen atom in C-N, especially the sulfur atom in the mercapto group shows strong interaction with metal vacancies. Orbital coordination ability, the coordination reaction will preferentially occur on the sulfur atom in C-S, followed by the nitrogen atom in C=N.

Further, the organic solvent used for dissolving the nickel salt and 2-mercaptobenzimidazole may be one of methanol, ethanol, and N,N-dimethylformamide. Preferably, the ratio of the added amount of the organic solvent to the volume molar ratio of the nickel salt is 30 mL: 1-12 mmol.

Further, the nickel salt is one of nitrate, hydrochloride, sulfate, acetate or a hydrate thereof.

Further, described amino weak basic solvent is a kind of in triethylamine, diethylamine, ethylenediamine, n-propylamine, isopropylamine, di-n-propylamine, diisopropylamine or tripropylamine, and its addition is the same as nickel salt. The volume molar ratio is 0.4-0.8mL:1mmol.

Further, the temperature of the reaction in the above step (1) is preferably 85-120° C., and the reaction time is 12-72 hours.

Further, the drying temperature in the above step (1) is preferably 40-100°C, for example, 60°C.

Further, the mass ratio of the sulfur powder to the nickel-mercaptobenzimidazole complex in the above step (2) is greater than 35%.

Further, the temperature of the reaction in the above step (2) is preferably 155-180° C., the heating rate is 1-10° C. min ⁻¹ , and the reaction time is 4-48 hours.

Further, the solvent of the washing product is one of carbon disulfide, carbon tetrachloride, chloroform or benzene.

Further, the drying temperature in the above step (2) is 70-100°C.

The third aspect of the present invention also provides the application of the nickel polysulfide-mercaptobenzimidazole described in the first aspect as a positive electrode material for a lithium-sulfur battery.

Compared with the prior art, the beneficial effects of the present invention are:

1. the present invention will have the 2-mercaptobenzimidazoles with chemical bonds such as -S, C=N, C-N and nickel salt generation coordination reaction, obtain nickel-mercaptobenzimidazole coordination compound, then obtain polysulfide nickel with sulfur reaction - mercaptobenzimidazole coordination compounds. The coordination compound can store more charge in the same volume, which is beneficial to provide dense cation hopping sites, so that the activation energy of ion transport can be minimized, and thus the ionic conductivity can be improved. In addition, the sulfur loading was enhanced by reacting the nickel-mercaptobenzimidazole complex with sulfur to incorporate sulfur.

2. The nickel polysulfide-mercaptobenzimidazole coordination compound of the present invention, combined with the special chemical structure of the coordination compound and the incorporation of sulfur, improves the cycle stability, high-rate charge-discharge performance and sulfur loading performance of lithium-sulfur batteries. The coin battery prepared with it as the positive electrode material shows a capacity of 1354.9mAh g ^-1 in the first cycle at 0.2C, and still retains a capacity of 1179.5mAh g ^-1 after 100 cycles, and the Coulomb efficiency is close to 100% during the cycle. It can still cycle normally at 10C and the capacity can still be recovered when the rate is gradually dropped.

Description of drawings

Fig. 1 is the synthetic route map of SNM;

Figure 2a is the XRD comparison diagram of NM and SNM;

Figure 2b is the FT-IR comparison diagram of MBI, NM and SNM;

Figure 2c is a Raman comparison diagram of NM and SNM;

Figure 2d is the 13C MAC NMR spectrum of NM and SNM;

Fig. 3 is the MALDI-TOF analysis pattern of NM and SNM;

Figure 4 is the cycle performance of the SNM/S battery at 0.2C;

Figure 5 is the cycle performance of the SNM/S battery at 2C;

Figure 6 shows the cycle performance of SNM/S batteries at different rates;

Figure 7 shows the cycling performance of SNM/S batteries with different sulfur loadings at 0.2C;

Figure 8 is the SNM/S battery and the ex-situ XPS analysis pattern after the third cycle of discharge and charging;

Figure 9 shows the cycling performance of NM/S cells at 0.2C.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The experimental methods used in the following examples are conventional methods unless otherwise specified, and the materials, reagents, etc. used can be obtained from commercial sources unless otherwise specified.

Example 1: Synthesis of polysulfide nickel-mercaptobenzimidazole coordination compound

1. Preparation of Nickel-Mercaptobenzimidazole Coordination Compounds (NM)

Dissolve 6 mmol Ni(NO3) ₂ ·6H ₂ O and 6 mmol MBI in 30 mL of anhydrous methanol (MtOH), respectively. After magnetic stirring to dissolve the two solutions, mix the two solutions, and continue to stir for about 5 min to form a homogeneous solution. Add 0.6 mL triethylamine (TEA) was stirred slightly, then transferred to a 100 mL stainless steel hydrothermal reaction kettle. The reaction kettle was placed in an 85°C oven for 48 h. After the reaction was completed, the reaction kettle was cooled to room temperature, and the reaction kettle was opened. The precipitate was collected by centrifugation and washed with MtOH. After 3 times, it was dried at 60°C and ground into powder.

2. Preparation of nickel polysulfide-mercaptobenzimidazole complex (SNM)

Grind the nickel-mercaptobenzimidazole complex into powder, dry it completely, weigh it with the sulfur powder at a mass ratio of 1:1, grind and mix it evenly, put it into an ampoule tube, transfer it to a glove box and seal it with a plastic film, Make the inside of the ampoule tube in an argon atmosphere. After the ampoule tube is taken out from the glove box, use an alcohol torch to heat the narrow part in the middle and keep rotating to make the heating uniform. When the glass is hot melted, the tube is sealed. Heat the furnace to 155°C and keep it for 12h. After heating, it was cooled to room temperature. The glass tube was knocked open, and the product was taken out and ground. The product was washed 3 times with CS2 solvent and collected by centrifugation. After drying in a fume hood to volatilize the excess solvent It was transferred to a vacuum oven at 100° C. for 12 h to ensure that excess elemental sulfur was removed, and the obtained product was a nickel polysulfide-mercaptobenzimidazole complex.

Using X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman (Raman) and 13C MACNMR for nickel-mercaptobenzimidazole complexes and nickel polysulfide-mercaptobenzimidazole complexes Characterize.

Figure 2a is the XRD comparison chart of NM and SNM in this example, the XRD test pattern of the synthesized NM powder is very consistent with the XRD pattern fitted by the NM single crystal, indicating that the NM powder used in the experiment and the grown NM single crystal particles are For the same substance, the XRD pattern of SNM is different from that of NM, which preliminarily indicates that a new phase is generated after vulcanization.

Figure 2b is the FT-IR comparison chart of MBI, NM and SNM in this example. The infrared spectrum shows that the three peaks of MBI at 2569cm ^-1 , 1620cm ^-1 and 1265cm ^-1 correspond to SH, C=N and amines, respectively. CN key. The same CN bond was observed in the infrared spectrum of NM, while the SH and C=N peaks disappeared, indicating that SH and C=N were involved in the coordination with nickel. The CN bond shifted to about 1274 cm ^-1 was observed in the infrared spectrum of SNM, indicating that the CN bond changed during the vulcanization process, and it was preliminarily judged that the CNS bond was generated.

Figure 2c shows the Raman test patterns of NM and SNM in this example. The CN peak at 230 cm ^-1 was observed in NM, while the CNS peak at 217 cm ^-1 was observed in the Raman pattern of SNM.

Figure 2d is the carbon spectrum in the solid wide-cavity superconducting NMR spectra of MBI, NM and SNM in this example, showing that the chemical environment of C in NM and SNM does not change. Combined with the above characterization results, it shows that S is successfully connected in SNM to form C-N-S.

FIG. 3 is the matrix-assisted laser desorption ionization time-of-flight mass spectrometry of NM and SNM in this example, and it is proved by the nuclear-to-mass ratio (m/z) of NM and SNM that the number of intercalated sulfur in SNM is about 8.

To sum up, it can be seen from the XRD test results that NM obtains a new phase after vulcanization. According to the infrared, Raman and carbon spectrum results, it can be seen that S is connected to the N atom of C-N of NM during the vulcanization process to form C-N-S, such as The structural diagram in the upper left corner of Figure 3 shows that there are 4 C-N bonds with the same chemical environment in the NM structure, so the possibility of connecting S to the N atom of each C-N is consistent. It can be seen from the mass spectrometry results that each SNM monomer The number of external sulfurs is 8, and it can be speculated that 2 S atoms are connected to the N atom of each C-N to obtain SNM. The structure of SNM is shown in the upper right corner of Figure 3.

Example 2: Electrochemical performance experiment of nickel polysulfide-mercaptobenzimidazole coordination compound

1. Preparation of SNM/S mixture

Completely dry the NM and grind it into powder, weigh it with sulfur powder at a mass ratio of 1:4, grind and mix evenly, put it into an ampoule tube, transfer it to a glove box and seal it with plastic wrap, so that the inside of the ampoule tube is filled with argon gas. Atmosphere, after taking out the ampoule tube from the glove box, use an alcohol torch to heat the narrow part in the middle and keep rotating to make the heating evenly. When the glass is hot ^melted , the tube is sealed. The heating rate was heated to 155 °C and kept for 12 hours. After the heating was completed, it was cooled to room temperature. The glass tube was knocked open, and the product was taken out and ground. While the sulfur vulcanized NM into SNM, more sulfur still existed in the form of elemental substance, and was mixed with SNM. Mix evenly.

2. Preparation of button battery

Mix the powder prepared above with SP and PVDF in a mass ratio of 8:1:1, add an appropriate amount of N-methylpyrrolidone and mix well, coat the surface of the aluminum foil, and cut it into discs with a diameter of 10mm after drying. After drying in a vacuum oven at 60 °C for about 6 h, the dried aluminum foil was used as the positive electrode to assemble a lithium-sulfur battery. A coin cell battery was assembled using a lithium sheet as the negative electrode and a commercial Celgard separator.

3. Electrochemical performance test

The assembled button battery was tested by the blue battery test system, and the charge-discharge capacity and cycle stability at different rates were tested in the voltage range of 2.8-4.2V.

Figure 4 shows the cycle performance of the button battery in this example at 0.2C. The results show that the capacity of 1354.9mAh g ^-1 is displayed in the first cycle at 0.2C, and the capacity of 1179.5mAh g ^-1 is still retained after 100 cycles. Near 100% coulombic efficiency during cycling.

Figure 5 shows the cycle performance of the button battery in this example at 2C. The results show that the specific capacity of the first cycle is 856.0mAh g ^-1 at the 2C rate, and 547.1mAh g ^-1 remains after 1000 cycles, and the decay per cycle is about 0.036%.

Figure 6 shows the cycle performance of the button battery in this embodiment at different rates. The cycle performance of the button battery switched at different rates is tested respectively, and the sequence is 0.2C (1293.3mAh g ^-1 ), 0.5C (1094.4mAh g ^-1 ) ), 1C(980.9mAh g ^-1 ), 2C(891.8mAh g ^-1 ), 5C(773.6mAh g ^-1 ), 10C(616.9mAh g ^-1 ), 5C(813.8mAh g ^-1 ), 2C(917.5mAh g ^-1 ), 1C (1015.0mAh g ^-1 ), 0.5C (1089.3mAh g ^-1 ), 0.2C (1147.0mAh g ^-1 ). Among them, it can still cycle normally at 10C and the capacity can still be recovered when the rate gradually drops.

Figure 7 shows the cycle performance of the coin cell in this example with different sulfur loadings at 0.2C, and the capacities of 8.4 and 7.1 mAh cm ^-2 were achieved under the conditions of sulfur loadings of 8.1 and 6.83 mg cm ^-2 , and they were stable Cycle for 50 cycles and maintain near 100% coulombic efficiency.

Figure 8 shows the XPS test results of the SNM/S electrode and the electrode after the third cycle of discharge/charge. The C1s spectrum of the SNM/S cathode before cycling is the same as that of the SNM. Figure 8a shows the C1s spectra of the electrode before cycling, discharging and charging, respectively, the peaks at 284.8 eV and 285.73 eV correspond to C=C/CC and CS bonds, respectively, and the corresponding CN bonds at 287.0 eV form CN after discharge -Li is due to the cleavage of the CNSS bond during discharge, and the CN-Li bond is still retained after charging. Figure 8b shows the N1s spectra of the electrodes in the three states. In the electrode before cycling, 399.1eV, 400.3eV, and 401.2eV correspond to Ni-N, pyrrole N, and NSS bonds, respectively. The peak may come from the composition of the SEI film on the electrode surface, the Ni-N bond is retained, the pyrrole N increases by 0.4 eV due to the change of the NSS bond, and a new NS-Li bond is formed, and the pyrrole N bond can be obtained after charging. There is a slight recovery, an increase of 0.2 eV compared with the discharge, and some NS/NSS bonds are formed at the same time, but it is not completely recovered compared to the state before discharge, which is also the reason why the SNM capacity continues to decline. The S2p spectrum in Figure 8c mainly shows the disappearance/recovery of the SS peak at 164.2/165.4 eV during discharge and charge, indicating the change of elemental sulfur in the SNM/S electrode during battery cycling and the change of Ni-S It is because of the formation of Li ₂ S during discharge. Figure 8d shows the Ni 2p spectrum, it is found that Ni is reduced after discharge, the binding energy is reduced by 0.8 eV, and Ni remains in the reduced state even after charging. Unseparated Li ions can stabilize Ni in a lower chemical state, which will continue to promote Li ion transfer and enable Li-S batteries to have longer cycle life. The change of N further indicates that the N atom of CN is the site of S connection, and the change of SS bond and Li-S bond during charge and discharge explains the reason for the good cycle stability, and the chemical change of N and Ni explains that SNM can Lithium-sulfur batteries play a role in good lithium polysulfide adsorption as well as electrochemical catalysis.

From the above test results, it can be seen that the lithium-sulfur battery prepared based on SNM as the cathode material has a capacity of up to 1354.9mAh g ^-1 in the first cycle at 0.2C, with high charge-discharge capacity and good cycle stability, and at a high rate of 10C It can still cycle normally and the capacity can still be recovered when the rate is gradually reduced.

Comparative Example: Electrochemical Performance Experiment of Nickel-Mercaptobenzimidazole Coordination Compounds

1. Preparation of button battery

Physically mix NM and elemental sulfur evenly, mix the obtained powder with SP and PVDF in a mass ratio of 8:1:1, add an appropriate amount of N-methylpyrrolidone, mix well, coat on the surface of aluminum foil, and cut after drying A 10 mm diameter disc was dried in a vacuum oven at 60 °C for about 6 h. The dried aluminum foil was used as the positive electrode to assemble a lithium-sulfur battery, the lithium sheet was used as the negative electrode, and a commercial Celgard separator was used to assemble a button battery.

2. Electrochemical performance test

The assembled button battery was tested with a blue battery test system, and the cycle performance at 0.2C was tested in the voltage range of 2.8-4.2V.

Figure 9 shows the cycle performance of the coin cell in this comparative example at 0.2C. The results show that the first cycle at 0.2C shows a capacity of 1055.7mAh g ^-1 , and the capacity is only 449.9mAh g ^-1 at 20 cycles.

The lithium-sulfur battery prepared by using SNM as the cathode material showed a capacity of 1354.9mAh g ^-1 in the first cycle at 0.2C, and still retained a capacity of 1179.5mAh g ^-1 after 100 cycles, and the Coulombic efficiency was close to 100% during the cycle. , compared with the lithium-sulfur battery prepared with NM as the cathode material, it has a higher first-circle capacity and outstanding cycle stability.

In summary, the lithium-sulfur batteries prepared with nickel polysulfide-mercaptobenzimidazole complexes as cathode materials have good cycling stability, high-rate charge-discharge performance, and high sulfur loading performance.

The above-mentioned embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention is subject to the claims.

Claims (10)

1. a nickel polysulfide-mercaptobenzimidazole coordination compound, is characterized in that, has the structural formula shown below:

2. the preparation method of nickel polysulfide-mercaptobenzimidazole coordination compound according to claim 1, is characterized in that, comprises the following steps: (1) nickel salt and 2-mercaptobenzimidazole are dissolved in organic solvent respectively, the solution obtained is mixed with amino weak alkaline solvent, after the reaction finishes, centrifugal collection precipitation, washing, drying obtain nickel-mercaptobenzimidazole Imidazole coordination compound; Described amino weak basic solvent is a kind of in triethylamine, diethylamine, ethylenediamine, n-propylamine, isopropylamine, di-n-propylamine, diisopropylamine or tripropylamine; (2) the nickel-mercaptobenzimidazole coordination compound obtained in the step (1) is uniformly mixed with the sulfur powder, and the reaction is heated, and after the reaction finishes, the product is washed, centrifuged, and dried to obtain nickel polysulfide-mercaptobenzimidazole coordination compound; the reaction atmosphere of the heating reaction is an inert gas. 3. the preparation method of nickel polysulfide-mercaptobenzimidazole coordination compound according to claim 2, is characterized in that, described nickel salt is nitrate, hydrochloride, sulfate, acetate or their hydration one of them. 4. the preparation method of nickel polysulfide-mercaptobenzimidazole coordination compound according to claim 2, is characterized in that, described organic solvent is a kind of in methanol, ethanol or N,N-dimethylacetamide . 5. the preparation method of the nickel polysulfide-mercaptobenzimidazole coordination compound according to claim 2, is characterized in that, the volume molar ratio of described amino weak basic solvent and nickel salt is 0.4～0.8mL: 1mmol. 6. the preparation method of nickel polysulfide-mercaptobenzimidazole coordination compound according to claim 2, is characterized in that, the temperature of the described reaction of step (1) is 85-120 ℃, and the time of reaction is 12-72 Hour. 7. the preparation method of polysulfide nickel-mercaptobenzimidazole coordination compound according to claim 2, is characterized in that, the sulfur powder described in step (2) and nickel-mercaptobenzimidazole coordination compound mass ratio are greater than 35 %. 8. the preparation method of nickel polysulfide-mercaptobenzimidazole coordination compound according to claim 2, is characterized in that, the temperature of the described reaction of step (2) is 155-180 ℃, and the time of reaction is 4-48 Hour. 9. the preparation method of nickel polysulfide-mercaptobenzimidazole coordination compound according to claim 2, is characterized in that, the solvent of the described washing product of step (2) is carbon disulfide, carbon tetrachloride, chloroform or A kind of benzene, and the drying temperature is 70-100°C. 10. The application of the nickel polysulfide-mercaptobenzimidazole coordination compound of claim 1 in the cathode material of lithium-sulfur batteries.

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