CN113346065A - Preparation method, material and application of high-performance CoSe/C-NS composite material - Google Patents

Abstract

The invention discloses a preparation method of a high-performance CoSe/C-NS composite material, which comprises the following steps: thiourea is added as an S source in the process of preparing ZIF-67 to prepare S-doped S-ZIF-67 precursor; and fully mixing the S-ZIF-67 precursor with selenium powder, and annealing under the protection of nitrogen to obtain the CoSe/C-NS composite material. The invention also discloses the high-performance CoSe/C-NS composite material and application thereof in a lithium ion battery. The method synthesizes the S-doped S-ZIF-67 precursor in one step, does not need hydrothermal reaction, saves energy and time, and after selenylation annealing treatment, S elements are uniformly distributed on the surface of the outer layer of the composite material, and the crystal face spacing of the carbon skeleton of the outer layer of the material is widened by introducing more defects through S, so that the integral structure of the composite material is firmer, the conductivity of the material is enhanced, and the CoSe/C-NS composite material has higher energy density, better rate capability and stronger cycling stability when being used as a cathode.

Description

Preparation method, material and application of high-performance CoSe/C-NS composite material

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a preparation method, a material and application of a high-performance CoSe/C-NS composite material.

Background

The current commercial lithium ion battery cathode materials are mainly artificial graphite and natural graphite materials, and the theoretical specific capacity of the graphite material is only 372mAh g < -1 >, so that the increasing energy density requirement of the lithium ion battery cannot be met. The inquired Chinese patent application number is 201911053422.4, and the patent named as a CO-Mn-S composite material and a preparation method and application thereof discloses that the CO-Mn-S composite material is obtained by carrying out hydrothermal reaction on thiourea and soluble manganese salt after preparing ZIF-67, wherein the dosage of thiourea is about 3-50 times of that of ZIF-67, the dosage of raw materials is large, the economy is poor, and a more economical and efficient method with less dosage needs to be found, thioacetamide is adopted, and the substance is classified into a 2B type carcinogen in a carcinogen list published by international cancer research institution of world health organization international in 2017, 10, 27 days, and is required to find a substance with less carcinogenicity or no carcinogenicity to be applied to a super capacitor. The structure stability of the existing lithium battery cathode material is not strong enough, and the capacity is attenuated too fast under the heavy current density; the material has irregular shape and structure, which can affect the tap density when used as a negative electrode, and needs to be continuously improved to find a substitute material with higher performance.

In view of the above, it is desirable to develop a high-performance lithium ion battery negative electrode material having the advantages of high energy density, long cycle life, high structural stability, etc.

Disclosure of Invention

The invention aims to provide a preparation method, a material and an application of a high-performance CoSe/C-NS composite material aiming at the defects of the prior art, the composite material is a nano polyhedral composite material based on a CoSe-based outer layer with a carbon skeleton protective layer, an S-doped S-ZIF-67 precursor is synthesized in one step, a hydrothermal reaction is not needed, energy and time are saved, an S element is uniformly distributed on the surface of the outer layer of the composite material after selenylation annealing treatment, the crystal face spacing of the carbon skeleton of the outer layer of the material is widened through more defects introduced by S, the integral structure of the composite material is more stable, and the conductivity of the material is enhanced, so that the CoSe/C-NS composite material has higher energy density, better rate performance and stronger cycling stability when being used as a negative electrode.

The technical scheme adopted by the invention to achieve the aim is as follows:

a preparation method of a high-performance CoSe/C-NS composite material comprises the following steps:

s1: thiourea is added as an S source in the process of preparing ZIF-67 to prepare S-doped S-ZIF-67 precursor;

s2: and fully mixing the S-ZIF-67 precursor with selenium powder, and annealing under the protection of nitrogen to obtain the CoSe/C-NS composite material.

Preferably, in the step S2, the mass ratio of the S-ZIF-67 precursor to the selenium powder is 1 (0.8-1.2). 4. Preferably, in step S2, the S-ZIF-67 precursor and the selenium powder are fully mixed for more than 10 minutes, and the annealing conditions are as follows: annealing at 550-650 deg.C for 4-5 hr, with the temperature rise rate set at 5 deg.C/min.

Preferably, the preparation process of the S-ZIF-67 precursor in the step S1 includes: dissolving Co (NO3) 2.6H 2O in methanol to form solution A, dissolving 2-methylimidazole and thiourea in methanol to form solution B, slowly dripping the solution A into the solution B, mixing to form solution C, standing, centrifuging and drying to obtain the S-ZIF-67 precursor.

Preferably, the ratio of the dosage of Co (NO3) 2.6H 2O, 2-methylimidazole, thiourea and methanol is 5 mmol: 20 mmol: 15 mmol: 50-200 ml.

Preferably, the standing time is more than 24 hours; the centrifugation adopts methanol as a solvent, and the methanol is centrifugally washed for more than three times; the drying is carried out at 70 ℃ for 24-48 hours.

The CoSe/C-NS composite material is obtained by the preparation method of the high-performance CoSe/C-NS composite material.

The application of the CoSe/C-NS composite material is to prepare the composite material into a negative pole piece to be applied to a lithium ion battery. Preferably, the preparation process of the negative pole piece comprises the following steps: grinding the CoSe/C-NS composite material, acetylene black and PVDF in a mortar according to the weight ratio of 8:1:1 for more than 10 minutes, then fully mixing, dropwise adding a proper amount of N-methyl pyrrolidone (NMP), stirring for 10 hours at room temperature under the action of a magnetic stirrer to obtain a paste material, uniformly pouring the paste material onto a current collector copper foil, coating to obtain a negative pole piece, and drying to obtain the working electrode of the lithium ion battery.

According to the invention, selenization treatment is carried out through a coprecipitation method and annealing, so that the N, S co-doped CoSe/C composite material with a regular polyhedral morphology is successfully prepared. ZIF-67 is used as a Co source and an N source of the composite material, S doping modification is carried out on the ZIF-67, and the obtained ZIF-67(S-ZIF-67) with S doping is used as a precursor of the invention. And fully mixing the S-ZIF-67 precursor with Se powder, and then annealing in an inert gas atmosphere to obtain the CoSe/C-NS composite material which can still maintain the energy density of 1494mAh/g after being applied to the negative electrode material of the lithium ion battery under the current density of 0.2A/g and being circulated for 300 times. In addition, the CoSe/C-NS composite material still shows extremely excellent electrochemical performance under high current density; under the high current density of 2A/g, after 500 charge-discharge cycles, the CoSe/C-NS composite material can still keep stable structure and maintain the energy density of more than 513 mAh/g. The introduction of S doping brings more defects and larger crystal face spacing for the carbon skeleton of the outer layer of the composite material, so that Li & lt + & gt can be more smoothly embedded/removed in the composite material, and the integral resistance of the CoSe/C-NS composite material in the charge-discharge cycle of a battery is reduced; meanwhile, the integral structure of the material can be more stable, which is very important for improving the cycle performance, especially the rate performance, of the material.

The invention also discloses a ZIF-67 precursor based CoSe2/C composite material with two distinct crystal forms, which is successfully prepared by a very simple synthesis method, Mo can be introduced to dope the CoSe2 composite material to endow the composite material with stronger conductivity in the synthesis process, the doped composite material is applied as a negative electrode material of a potassium ion battery, and the synthesized CoSe2/C-65M60 composite material with the CoSe2(JCPDS No.65-3327) crystal form keeps the energy density of more than 328mAh/g under the current density of 0.05A/g after 60 times of charge-discharge cycles; while CoSe2/C-53M00 having a crystalline form of CoSe2(JCPDS No.53-0449) can maintain an energy density of only about 247mAh/g under the same conditions; after the crystal form transformation of the CoSe2 is promoted by Mo doping, the capacity of the material under the same condition is improved by about 33 percent, because CoSe2(JCPDS No.65-3327) has larger unit cell volume, the resistivity of the material is favorably reduced.

Compared with the prior art, the invention has the following beneficial effects:

1. the CoSe/C-NS composite material is a nano polyhedral composite material based on a CoSe base and provided with a carbon skeleton protective layer on the outer layer, an S-doped S-ZIF-67 precursor is synthesized in one step, hydrothermal reaction is not needed, energy and time are saved, the yield of the material can be increased, and the composite material has better economy; moreover, the CoSe/C-NS composite material subjected to selenization annealing treatment has a perfect hollow structure, and S elements can be seen to be uniformly distributed on the surface of the outer layer of the composite material, so that the function of stabilizing the material structure is achieved.

2. The N-doped carbon nano polyhedron subjected to selenization annealing treatment is applied to the lithium ion battery cathode material based on the ZIF-67 precursor, excellent performance is shown, the S-doped ZIF-67 is used as the precursor, the carbon skeleton on the outer layer of the S element doped composite material is introduced, N, S co-doped CoSe/C composite material is developed on the basis of the existing N-doped CoSe composite material, the crystal face spacing of the carbon skeleton on the outer layer of the material is widened through more defects introduced by S, the overall structure of the composite material is more stable, the conductivity of the material is enhanced, and the CoSe/C-NS composite material has higher energy density, better rate performance and stronger cycle stability when being used as the cathode. Under the current density of 200 mA.g < -1 >, the specific capacity of 1494 mAh.g < -1 > can be still maintained after 300 cycles; and also exhibits good cycle performance (the specific capacity of more than 513mAh g < -1 > is still maintained after 500 charge-discharge cycles) under high current density (2A g < -1 >); under the current density of 100mA · g < -1 >, the coulombic efficiency during the first charge and discharge is about 50.99%, and the residual capacity after 190 cycles is 1244mAh · g < -1 >; during which time the maximum capacity occurred at the 157 th cycle and reached 1325mA g-1.

3. The CoSe/C-NS composite material of the invention obtains more regular material appearance on the nanometer level, and enhances the structural stability of the CoSe/C material; further modification of the CoSe/C material to achieve better energy density; the structure of the CoSe/C composite material is more stable to obtain better rate performance; and the electrochemical performance of the CoSe/C composite material under high current density when the CoSe/C composite material is used as a negative electrode is improved.

The foregoing is a summary of the technical solutions of the present invention, and the present invention is further described below with reference to the accompanying drawings and detailed description.

Description of the drawings:

FIG. 1 is SEM images (a, b) of ZIF-67 and S-ZIF-67 and SEM images (C, d) of CoSe/C-NS and CoSe/C-N;

FIG. 2 is TEM images of CoSe/C-NS and CoSe/C-N (a, b) and TEM Mapping image of CoSe/C-NS (C-g);

FIG. 3 is an XRD image (a) of S-ZIF-67 and an XRD image (b) of CoSe/C-NS and CoSe/C-N;

FIG. 4 is a cyclic voltammogram of CoSe/C-NS;

FIG. 5 is a charge-discharge curve of CoSe/C-N at a current density of 0.2A/g;

FIG. 6 is graphs (a), (b) of the cyclic performance of CoSe/C-NS and CoSe/C-N at current densities of 0.2A/g and 2A/g, respectively, at a voltage range of 0.01-3.0V;

FIG. 7 is a graph of rate performance of CoSe/C-NS and CoSe/C-N;

FIG. 8 is a graph of the electrochemical impedance of CoSe/C-NS and CoSe/C-N.

The specific implementation mode is as follows:

in order to make the objects, technical solutions and advantages of the present invention more apparent, the following embodiments are described in detail. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Example 1: the preparation method, material and application of the high-performance CoSe/C-NS composite material provided by the embodiment are combined with the accompanying drawings 1-3, and comprise (1) a preparation process of an S-doped ZIF-67 precursor (S-ZIF-67): fully dissolving 5mmol of Co (NO3) 2.6H 2O in 50ml of methanol to form A solution (magenta); then 20mmol of 2-methylimidazole and 15mmol of thiourea were sufficiently co-dissolved in 50ml of methanol to form a solution B (colorless and transparent); under the strong stirring of a magnetic stirrer, the solution A is very slowly dripped into the solution B by using a rubber head dropper to form a mixed solution C (dark purple); and (3) standing the mixed solution C for 24 hours at room temperature under the same strong stirring of a magnetic stirrer, repeatedly centrifuging and washing the precipitate in the mixed solution C by using methanol, wherein the process usually needs to be continued for more than 3 times, drying the purple precipitate after centrifuging and washing in a vacuum drying oven at 70 ℃ for 24 hours, and finally collecting the substance of the S-ZIF-67 precursor of the dark purple powder.

(2) Fully mixing an S-ZIF-67 precursor and selenium powder according to a set mass ratio, then annealing under the protection of nitrogen to obtain a CoSe/C-NS composite material, adding thiourea as an S source in the process of synthesizing ZIF-67 (a porous crystal material), and synthesizing an S-doped ZIF-67(S-ZIF-67) precursor (deep purple). And fully mixing the S-ZIF-67 and the selenium powder for more than 10 minutes, then transferring the fully mixed substance (purple black) into a tube furnace, annealing for 4 hours at 600 ℃ under the protection of nitrogen, setting the heating rate to be 5 ℃/min, and collecting the final product, namely the black powder CoSe/C-NS composite material.

(3) The application comprises the following steps: the preparation process of the negative pole piece comprises the steps of grinding the active material (CoSe/C-NS), the acetylene black and the PVDF in a mortar according to the weight ratio of 8:1:1 for more than 10 minutes to fully mix the active material, the acetylene black and the PVDF, dropwise adding a proper amount of N-methyl pyrrolidone (NMP), stirring for 10 hours at room temperature under the action of a magnetic stirrer to obtain a paste material, uniformly pouring the paste material onto a current collector (copper foil), and coating the paste material into a pole piece with the thickness of about 150 mu m by using a manual coater. Drying the pole pieces for 12 hours at a temperature set to 80 ℃ by using an air drying oven, and finally transferring the pole pieces to an electric heating vacuum drying oven to dry the pole pieces for 12 hours at a temperature of 120 ℃; the circular pole pieces, cut to a diameter of about 1.2cm by a microtome, were dried at 120 ℃ in a vacuum oven, leaving them ready for assembly of the button cells.

(4) Assembling a simulated button cell: the specification of the button cell is CR2016 type, the button cell is assembled in a glove box, the protective gas in the glove box is argon, the water-oxygen partial pressure is lower than 1ppm, a positive shell, a gasket, a lithium sheet, a diaphragm, a negative pole piece and the gasket which are matched with the CR2016 are sequentially assembled, and a proper amount of electrolyte is dripped among the lithium sheet, the diaphragm and the negative pole piece, so that the diaphragm and the negative pole piece are fully infiltrated by the electrolyte; finally, sealing and compacting the assembled analog button cell under the pressure of about 4 Mpa; the assembled cell was left to stand at room temperature for 8-12 hours for testing.

(5) And (3) characterization and test: the CoSe/C-NS composite material is characterized by adopting the following methods, namely, a scanning electron microscope (equipment model: FESEM, Hitachi S-4800), a transmission electron microscope (equipment model: TEM, JEOL, JEM-2100F), X-ray diffraction analysis (test information: using an anode target Cu target Kalpha radiation source, lambda is 0.15418nm, a scanning angle is 5-80 degrees, a scanning speed is 5 DEG.min-1, a working voltage is 40kV, a working current is 40mA) and X-ray photoelectron spectroscopy analysis (equipment model: Thermo Fis K-Alpha spectrometer). The method comprises the steps of obtaining a charge-discharge curve, a cycle performance curve and a multiplying power performance curve by adopting a BTS-5V/5mA-164 type constant current charge-discharge equipment voltage range of 0.01V-3V and respectively using current densities of 50mA g-1, 100mA g-1, 200mA g-1, 500mA g-1, 1A g-1 and 2A g-1, and calculating the coulomb efficiency. The electrochemical workstation model CHI660C was used to perform cyclic voltammetry tests (0.1 mV. s-1, 0.01-3V) and alternating current impedance tests (0.01Hz-100kHz, 5mV) on the composite.

Example 2: the preparation method, the material and the application of the high-performance CoSe/C-NS composite material provided by the embodiment are basically the same as those of theembodiment 1, except that:

s1: thiourea is added as an S source in the process of preparing ZIF-67 to prepare S-doped S-ZIF-67 precursor; in the preparation process of the S-ZIF-67 precursor, the dosage ratio of Co (NO3) 2.6H 2O, 2-methylimidazole, thiourea and methanol is 5 mmol: 20 mmol: 15 mmol: 50 ml; the standing time is more than 24 hours; the drying is carried out at 70 ℃ for 24 hours.

S2: and fully mixing the S-ZIF-67 precursor with selenium powder, and annealing under the protection of nitrogen to obtain the CoSe/C-NS composite material. The mass ratio of the S-ZIF-67 precursor to the selenium powder is 1: 0.8; fully mixing the S-ZIF-67 precursor with the selenium powder for more than 10 minutes, wherein the annealing treatment conditions are as follows: annealing treatment was carried out at 550 ℃ for 4 hours, and the temperature rise rate was set to 5 ℃/min.

Example 3: the preparation method, the material and the application of the high-performance CoSe/C-NS composite material provided by the embodiment are basically the same as those of theembodiment 1, except that:

s1: thiourea is added as an S source in the process of preparing ZIF-67 to prepare S-doped S-ZIF-67 precursor; in the preparation process of the S-ZIF-67 precursor, the dosage ratio of Co (NO3) 2.6H 2O, 2-methylimidazole, thiourea and methanol is 5 mmol: 20 mmol: 15 mmol: 150 ml; the standing time is more than 24 hours; the drying is carried out at 70 ℃ for 24 hours.

S2: and fully mixing the S-ZIF-67 precursor with selenium powder, and annealing under the protection of nitrogen to obtain the CoSe/C-NS composite material. The mass ratio of the S-ZIF-67 precursor to the selenium powder is 1: 0.8; fully mixing the S-ZIF-67 precursor with the selenium powder for more than 10 minutes, wherein the annealing treatment conditions are as follows: annealing at 650 ℃ for 5 hours with a temperature rise rate of 5 ℃/min.

Example 4: the preparation method, the material and the application of the high-performance CoSe/C-NS composite material provided by the embodiment are basically the same as those of theembodiment 1, except that:

s1: thiourea is added as an S source in the process of preparing ZIF-67 to prepare S-doped S-ZIF-67 precursor; in the preparation process of the S-ZIF-67 precursor, the dosage ratio of Co (NO3) 2.6H 2O, 2-methylimidazole, thiourea and methanol is 5 mmol: 20 mmol: 15 mmol: 200 ml; the standing time is more than 24 hours; the drying is carried out at 70 ℃ for 48 hours.

S2: and fully mixing the S-ZIF-67 precursor with selenium powder, and annealing under the protection of nitrogen to obtain the CoSe/C-NS composite material. The mass ratio of the S-ZIF-67 precursor to the selenium powder is 1: 1; fully mixing the S-ZIF-67 precursor with the selenium powder for more than 10 minutes, wherein the annealing treatment conditions are as follows: annealing at 600 deg.C for 5 hr, and setting the heating rate at 5 deg.C/min.

Example 5: the preparation method, the material and the application of the high-performance CoSe/C-NS composite material provided by the embodiment are basically the same as those of theembodiment 1, except that:

s1: thiourea is added as an S source in the process of preparing ZIF-67 to prepare S-doped S-ZIF-67 precursor; in the preparation process of the S-ZIF-67 precursor, the dosage ratio of Co (NO3) 2.6H 2O, 2-methylimidazole, thiourea and methanol is 5 mmol: 20 mmol: 15 mmol: 200 ml; the standing time is more than 24 hours; the drying is carried out at 70 ℃ for 48 hours.

S2: and fully mixing the S-ZIF-67 precursor with selenium powder, and annealing under the protection of nitrogen to obtain the CoSe/C-NS composite material. The mass ratio of the S-ZIF-67 precursor to the selenium powder is 1: 1.1; fully mixing the S-ZIF-67 precursor with the selenium powder for more than 10 minutes, wherein the annealing treatment conditions are as follows: annealing treatment was carried out at 650 ℃ for 4 hours, and the temperature rise rate was set to 5 ℃/min.

And (3) performance testing: referring to FIG. 4, a Cyclic Voltammogram (CV) of CoSe/C-NS tested using a scan rate of 0.1mV can be used to analyze the redox reaction of the CoSe/C-NS anode material in the operation of a lithium ion battery. In the process of scanning from high potential to low potential for the first time, 3 obvious reduction peaks respectively positioned at 1.15V, 0.90V and 0.45V can be found; the reduction peak at 1.15V corresponds to the process of converting CoSe into lixcooe, in which Li + insertion occurs; the reduction peak at 0.90V characterizes the process of forming a solid electrolyte interface film (SEI film) on the electrode surface; the reduction peak appearing at 0.45V characterizes the formation process of transition metal simple substances Co and Li2 Se; then, in the process of scanning from low potential to high potential, 2 oxidation peaks appear at 1.38V and 2.18V respectively, and LixCoSe is converted into CoSe again in the process, and Li + is removed from the CoSe/C-NS composite material. Furthermore; CV curves of 2 nd and 3 rd scans are presented for further analysis of the reaction of the CoSe/C-NS composite material as the negative electrode material of the lithium ion battery; in the process of scanning from a high potential to a low potential, a reduction peak appearing at 0.9V in the first scanning disappears in the 2 nd and 3 rd scanning; the reduction peaks respectively positioned at 1.15V and 0.45V in the first scanning are shifted to 1.35V and 0.52V, and the first scanning also respectively corresponds to the Li < + > embedding process and the transition metal simple substance Co and Li2Se forming process; in the subsequent process of scanning from low potential to high potential, the appearance positions of oxidation peaks in the 2 nd and 3 rd scans are not shifted compared with the first scan, and the process of reconverting LixCoSe into CoSe Li + to be removed from the composite material is also characterized; the CV curve can be used to conclude that the CoSe/C-NS composite material shows good reversibility when used as the cathode of the lithium ion battery.

And (3) testing the charge and discharge performance: referring to FIG. 5, it shows the charge and discharge curves of CoSe/C-NS at the 1 st, 2 nd, 3 rd, 5 th, 10 th and 50 th cycles at a current density of 0.2A/g when used as the negative electrode material of a lithium ion battery, and the results show that the platform voltage exhibited by the CoSe/C-NS composite material during the charge and discharge processes is consistent with the results exhibited by the CV curves when used as the negative electrode material of a lithium ion battery; in the process of first charging and discharging, the discharging specific capacity of the CoSe/C-NS composite material is 1292mAh/g, the charging specific capacity is 1043mAh/g, and the first Coulombic Efficiency (CE) of the material is 80.7 percent; the irreversible capacity loss in the first charge-discharge process can be attributed to the formation of an SEI film, and meanwhile, the first coulombic efficiency of the CoSe/C-NS composite material is higher than that of the lithium ion battery cathode material of other similar systems by 80.7%.

And (3) testing the cycle performance: referring to FIG. 6, the cycle performance of the CoSe/C-NS and CoSe/C-N composite materials respectively used as the negative electrode materials of the lithium ion battery is shown; as shown in (a), the CoSe/C-NS composite material shows an energy density of 1494mAh/g after 300 charge-discharge cycles under the current density of 0.2A/g, and the CoSe/C-N negative electrode material has an energy density of 797 mAh/g; the energy density of the two materials is increased in the circulation, because CoSe nano particles in the composite material are damaged along with the insertion/extraction of Li < + >, and more reactive active sites appear; but the overall structure of the composite is maintained due to the support of the carbon skeleton of the outer layer of the composite. As shown in (b), under the high current density of 2A/g, the CoSe/C-NS composite material also shows excellent cycle performance, and after 500 charge-discharge cycles, the CoSe/C-NS composite material can still maintain the energy density of more than 513 mAh/g; and the CoSe/C-N composite material begins to rapidly drop in energy density at a high current density of 2A/g after about 384 th charge-discharge cycle, which indicates that the structure of the CoSe/C-N composite material has begun to deteriorate after about 384 th charge-discharge cycle; therefore, the doping of S brings more interlayer spacing space for the outer carbon skeleton, so that the CoSe/C-NS has a more stable structure than the CoSe/C-N composite material, and the CoSe/C-NS composite material still shows excellent cycle performance under high current density.

As shown in the following Table 1-1, it can be found that the CoSe/C-NS composite material prepared by the invention has better electrochemical performance by comparing the electrochemical performance of similar anode material and the CoSe/C-NS composite material prepared by the invention.

TABLE 1-1 comparison of Performance of similar Material systems

And (3) rate performance test: referring to FIG. 7, the rate performance of the CoSe/C-NS and CoSe/C-N composite material as the negative electrode material of the lithium ion battery is compared by testing the rate performance of the two materials with current densities of 0.05A/g, 0.1A/g, 0.2A/g, 0.5A/g, 1A/g, 2A/g and 0.05A/g, respectively. The CoSe/C-NS composite material respectively shows average energy density of 725mAh/g, 682mAh/g, 992mAh/g, 811mAh/g, 687mAh/g, 644mAh/g and 872mAh/g under the condition of the current density; as comparative CoSe/C-N lithium ion battery negative electrode materials, average capacities of 592mAh/g, 614mAh/g, 802mAh/g, 671mAh/g, 591mAh/g, 528mAh/g, and 676mAh/g were exhibited at current densities of 0.05A/g, 0.1A/g, 0.2A/g, 0.5A/g, 1A/g, 2A/g, and 0.05A/g, respectively. Therefore, the CoSe/C-NS has better rate performance than CoSe/C-N when being used as a negative electrode material of a lithium ion battery.

And (3) testing the alternating current impedance performance: referring to FIG. 8, the results of Electrochemical Impedance Spectroscopy (EIS) of the CoSe/C-NS and CoSe/C-N composite materials are used to compare the conductivity of the materials when used as the negative electrode material of lithium battery; the radius of a characteristic semicircle of an EIS curve of the CoSe/C-NS composite material is obviously smaller than that of the CoSe/C-N composite material, which shows that the charge transfer resistance and the internal resistance of the CoSe/C-NS composite material are both smaller than those of the CoSe/C-N composite material when the CoSe/C-NS composite material is used as a cathode of a lithium battery, and the S doping brings more defects and larger crystal face spacing for an outer carbon skeleton of the material, so that the charge transmission is smoother.

Variations and modifications to the above-described embodiments may occur to those skilled in the art, which fall within the scope and spirit of the above description. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and variations of the present invention should fall within the scope of the claims of the present invention.

Claims (9)

1. A preparation method of a high-performance CoSe/C-NS composite material is characterized by comprising the following steps:

s1: thiourea is added as an S source in the process of preparing ZIF-67 to prepare S-doped S-ZIF-67 precursor;

s2: and fully mixing the S-ZIF-67 precursor with selenium powder, and annealing under the protection of nitrogen to obtain the CoSe/C-NS composite material.

2. The method for preparing the high-performance CoSe/C-NS composite material according to claim 1, wherein in the step S2, the mass ratio of the S-ZIF-67 precursor to the selenium powder is 1 (0.8-1.2).

3. The method for preparing a high-performance CoSe/C-NS composite material according to claim 1, wherein in the step S2, the S-ZIF-67 precursor and the selenium powder are fully mixed for more than 10 minutes, and the annealing conditions are as follows: annealing at 550-650 deg.C for 4-5 hr, with the temperature rise rate set at 5 deg.C/min.

4. The method of preparing a high performance CoSe/C-NS composite material of claim 1, wherein the preparation of the S-ZIF-67 precursor in step S1 comprises: dissolving Co (NO3) 2.6H 2O in methanol to form solution A, dissolving 2-methylimidazole and thiourea in methanol to form solution B, slowly dripping the solution A into the solution B, mixing to form solution C, standing, centrifuging and drying to obtain the S-ZIF-67 precursor.

5. The method for preparing high performance CoSe/C-NS composite material according to claim 4, wherein the ratio of the amounts of Co (NO3) 2.6H 2O, 2-methylimidazole, thiourea and methanol is 5 mmol: 20 mmol: 15 mmol: 50-200 ml.

6. The method of claim 4, wherein the standing time is 24 hours or more; the centrifugation adopts methanol as a solvent, and the methanol is centrifugally washed for more than three times; the drying is carried out at 70 ℃ for 24-48 hours.

7. The method of preparing a high performance CoSe/C-NS composite material as claimed in any one of claims 1 to 6, resulting in a CoSe/C-NS composite material.

8. The use of the CoSe/C-NS composite material of claim 7, wherein said composite material is prepared into a negative electrode sheet for use in a lithium ion battery.

9. The use of the CoSe/C-NS composite material according to claim 8, wherein the negative electrode sheet is prepared by a process comprising: grinding the CoSe/C-NS composite material, acetylene black and PVDF in a mortar according to the weight ratio of 8:1:1 for more than 10 minutes, then fully mixing, dropwise adding a proper amount of N-methyl pyrrolidone (NMP), stirring for 10 hours at room temperature under the action of a magnetic stirrer to obtain a paste material, uniformly pouring the paste material onto a current collector copper foil, coating to obtain a negative pole piece, and drying to obtain the working electrode of the lithium ion battery.

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