A porous carbon material, its preparation method and application

Abstract

The present invention belongs to the technical field of battery materials, and discloses a porous carbon material, a preparation method thereof and an application. The porous carbon material of the present invention is composed of nickel, nitrogen and carbon elements. Among them, by atomic percentage, the contents of nickel and nitrogen in the porous carbon material are 1-10% and 0.1-5% respectively. It uses microwave-assisted hydrothermal method, hydrothermal method or calcination method to prepare nano-zinc oxide, and uses nano-zinc oxide as a template. Urea and nickel chloride hexahydrate are added to furfuryl alcohol, and after reaction, it is calcined to obtain a porous carbon material. The porous carbon material of the present invention has a unique three-dimensional interconnected structure. For a lithium-sulfur battery prepared with the porous carbon material as the cathode material, it reduces the diffusion barrier of Li+ at the electrochemical interface, promotes the dynamic conversion of liquid phase-solid phase in the lithium-sulfur battery, and the synergistic effect of the catalytic activities of doped N and Ni together improves the reversibility of phase conversion, thereby improving the utilization rate of sulfur and the cycle life of the cathode.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a porous carbon material, a preparation method thereof, and an application thereof. Background Art

[0002] Energy is the driving force for the progress and development of human civilization and an important material guarantee for modern industrial technology and social and economic development. The demand for energy in human society is increasing day by day, and the problem of energy shortage is becoming increasingly prominent. At present, most renewable energies are intermittent and require efficient energy storage technologies for storage and then release energy according to demand. Energy storage technology is the core driving force for the development of renewable energies, and the development of efficient energy storage technologies has become one of the research hotspots in the field of energy development.

[0003] Lithium-sulfur batteries have gradually become one of the most promising high-efficiency energy storage technologies due to their advantages such as an ultra-high theoretical specific capacity of 1675 mAh / g and an ultra-high theoretical energy density of 2600 Wh / kg. Nevertheless, lithium-sulfur batteries still face many problems as follows: (1) The low conductivity of the active material S and its discharge products Li2S2 and Li2S leads to low sulfur utilization and poor rate performance of the battery; (2) The shuttle effect caused by the dissolution and diffusion of polysulfides, that is, the soluble polysulfides (LiPSs) migrate freely between the positive and negative electrodes, resulting in rapid battery capacity decay and low Coulomb efficiency; (3) The large volume change during charge and discharge due to the different densities of S and Li2S, etc. These problems have greatly hindered the application of lithium-sulfur batteries in actual production. Summary of the Invention

[0004] In order to overcome at least one of the above problems existing in the prior art, the present invention provides a porous carbon material, a preparation method thereof, and an application thereof.

[0005] For this purpose, the present invention adopts the following technical solutions:

[0006] The first aspect of the present invention provides a porous carbon material, which is composed of nickel, nitrogen, and carbon elements; wherein, by mass percentage, the contents of nickel and nitrogen in the porous carbon material are 1-10% and 0.1-5% respectively.

[0007] Preferably, by mass percentage, the content of nickel in the porous carbon material is 2.5-5%.

[0008] According to the porous carbon material of the present invention, it has at least the following beneficial effects: In this porous carbon material, the dispersion of nickel is good, and the porous carbon material has a three-dimensional interconnected structure, which is physically beneficial to improving the sulfur loading and the lithium-ion transmission rate.

[0009] The second aspect of the present invention provides a preparation method of the porous carbon material described in the first aspect of the present invention, including the following steps:

[0010] 1) Prepare nano-zinc oxide by microwave-assisted hydrothermal method, hydrothermal method or calcination method;

[0011] 2) Using the nano-zinc oxide as a template, add urea and nickel chloride hexahydrate to furfuryl alcohol, heat for reaction, and calcine to obtain the porous carbon material.

[0012] For the preparation method of the porous carbon material described above, in step 1), the preparation method of the nano-zinc oxide includes the following steps:

[0013] Preferably, the microwave-assisted hydrothermal method is adopted. Dissolve the anode material of the zinc-manganese battery in acetic acid, heat and concentrate to crystallization to obtain zinc acetate, then add methanol, microwave heat to a temperature of 110-130 °C, the reaction time is 10-15 min, centrifuge, wash, and dry to obtain the nano-zinc oxide. Further preferably, the microwave-assisted hydrothermal method is adopted. Dissolve the anode material of the zinc-manganese battery in acetic acid, heat and concentrate to crystallization to obtain zinc acetate, then add methanol, microwave heat to a temperature of 120-130 °C, the reaction time is 10-12 min, centrifuge, wash, and dry to obtain the nano-zinc oxide. Even more preferably, the microwave-assisted hydrothermal method is adopted. Dissolve the anode material of the zinc-manganese battery in acetic acid, heat and concentrate to crystallization to obtain zinc acetate, then add methanol, microwave heat to a temperature of 120 °C, the reaction time is 10 min, centrifuge, wash, and dry to obtain the nano-zinc oxide.

[0014] Or, preferably, the hydrothermal method is adopted. Dissolve the anode material of the zinc-manganese battery in acetic acid, heat and concentrate to crystallization to obtain zinc acetate, then add methanol, set the temperature to 50-70 °C, stir for 1.5-2.5 h, then add potassium hydroxide and react for 0.5-1.5 h, centrifuge, wash, and dry to obtain the nano-zinc oxide. Or, further preferably, the hydrothermal method is adopted. Dissolve the anode material of the zinc-manganese battery in acetic acid, heat and concentrate to crystallization to obtain zinc acetate, then add methanol, set the temperature to 60-70 °C, stir for 2-2.5 h, then add potassium hydroxide and react for 0.5-1.5 h, centrifuge, wash, and dry to obtain the nano-zinc oxide. Or, even more preferably, the hydrothermal method is adopted. Dissolve the anode material of the zinc-manganese battery in acetic acid, heat and concentrate to crystallization to obtain zinc acetate, then add methanol, set the temperature to 60 °C, stir for 2 h, then add potassium hydroxide and react for 0.5-1.5 h, centrifuge, wash, and dry to obtain the nano-zinc oxide.

[0015] Alternatively, preferably, the calcination method is adopted. The anode material of the zinc-manganese battery is dissolved in acetic acid, heated and concentrated to crystallization to obtain zinc acetate, which is calcined at a temperature of 400-480 °C for 2-3 h, and then cooled to obtain the nano-zinc oxide. Or, more preferably, the calcination method is adopted. The anode material of the zinc-manganese battery is dissolved in acetic acid, heated and concentrated to crystallization to obtain zinc acetate, which is calcined at a temperature of 430-480 °C for 2-2.5 h, and then cooled to obtain the nano-zinc oxide. Or, even more preferably, the calcination method is adopted. The anode material of the zinc-manganese battery is dissolved in acetic acid, heated and concentrated to crystallization to obtain zinc acetate, which is calcined at a temperature of 440 °C for 2 h, and then cooled to obtain the nano-zinc oxide.

[0016] For the preparation method of the porous carbon material described above, preferably, in step 2), after adding urea and nickel chloride hexahydrate to the furfuryl alcohol, stir for 30-40 min, ultrasonicate for 10-20 min, and then add it to the nano-zinc oxide. Set the reaction temperature at 80-100 °C, and the reaction time at 5-8 h. Then dry, heat to 300 °C under gas protection and hold for 5 h, wash, dry, heat to 550 °C and hold for 5 h, calcine at a temperature of 900-1000 °C for 2-3 h, cool, wash, and dry to obtain the porous carbon material. More preferably, in step 2), after adding urea and nickel chloride hexahydrate to the furfuryl alcohol, stir for 30 min, ultrasonicate for 10 min, and then add it to the nano-zinc oxide. Set the reaction temperature at 90-100 °C, and the reaction time at 5-6 h. Then dry, heat to 300 °C under argon protection and hold for 5 h, wash, dry, heat to 550 °C under argon protection and hold for 5 h, calcine at a temperature of 900 °C for 2-3 h, cool, wash, and dry to obtain the porous carbon material. Even more preferably, in step 2), after adding urea and nickel chloride hexahydrate to the furfuryl alcohol, stir for 30 min, ultrasonicate for 10 min, and then add it to the nano-zinc oxide. Set the reaction temperature at 90 °C, and the reaction time at 6 h. Then dry, heat to 300 °C under argon protection and hold for 5 h, wash, dry, heat to 550 °C under argon protection and hold for 5 h, calcine at a temperature of 900-1000 °C for 2 h, cool, wash, and dry to obtain the porous carbon material.

[0017] The preparation method of the porous carbon material according to the embodiment of the present invention has at least the following beneficial effects:

[0018] The nanoparticles of zinc oxide prepared by microwave-assisted hydrothermal method and hydrothermal method are all spherical, with a particle size of 5-15 nm; the zinc oxide nanoparticles prepared by the calcination method are rod-shaped, with a rod length of 1-2 μm and a diameter of about 30 nm. Using the zinc oxide nanoparticles prepared by microwave-assisted hydrothermal method, hydrothermal method or calcination method as a template, urea and nickel chloride hexahydrate are added to furfuryl alcohol, and the prepared porous carbon material has a significantly increased pore volume and high specific surface area, and has excellent wettability to the lithium-sulfur electrolyte, thus having the space and ability to accommodate more sulfur.

[0019] The third aspect of the present invention provides a porous carbon material cathode material, which includes an electrode membrane and an electrolyte, and the electrode membrane is made of the porous carbon material provided by the first aspect of the present invention.

[0020] Preferably, in the porous carbon material cathode material, the thickness of the electrode membrane is 10-16 mm and the mass is 1.5-3.0 mg. Further preferably, in the porous carbon material cathode material, the thickness of the electrode membrane is 10-14 mm and the mass is 1.5-2.0 mg. More preferably, in the porous carbon material cathode material, the thickness of the electrode membrane is 14 mm and the mass is 2.0 mg.

[0021] The fourth aspect of the present invention provides a preparation method of the porous carbon material cathode material described in the third aspect of the present invention, including the following steps:

[0022] 1) Add the porous carbon material into an organic solvent, disperse it, filter it through an organic filter membrane and vacuum filter it, dry it, and peel it to obtain an electrode membrane;

[0023] 2) Drop the cathode electrolyte on the electrode membrane to obtain the porous carbon material cathode material.

[0024] Preferably, in step 1), the dispersion time is 1.5-2.5 h, the drying temperature is 60-80 °C, and the drying time is 12-17 h.

[0025] Preferably, in step 2), the cathode electrolyte is Li2S6 cathode electrolyte, and the sulfur loading of the electrode membrane is 0.5-13 mg / cm 2 . Further preferably, in step 2), the cathode electrolyte is Li2S6 cathode electrolyte, and the sulfur loading of the electrode membrane is 0.5-6.2 mg / cm 2 .

[0026] The fifth aspect of the present invention provides a battery, which includes the positive electrode, negative electrode, separator and electrolyte of the battery, and the positive electrode of the battery is the porous carbon material cathode material described in the third aspect of the present invention.

[0027] Preferably, the negative electrode of the battery is a lithium sheet, the separator is a polypropylene separator, and the electrolyte is a lithium-sulfur electrolyte.

[0028] The porous carbon material according to the present invention has at least the following beneficial effects:

[0029] (1) In the porous carbon material of the present invention, nickel has good dispersibility, and the porous carbon material has a three-dimensional interconnected structure, which is physically beneficial to improving the sulfur loading and the lithium-ion transport rate.

[0030] (2) Using nano-zinc oxide prepared by microwave-assisted hydrothermal method, hydrothermal method or calcination method as a template, adding urea and nickel chloride hexahydrate to furfuryl alcohol, the prepared porous carbon material has a significantly increased pore volume and a high specific surface area, and has excellent wettability to the lithium-sulfur electrolyte, thus having the space and ability to accommodate more sulfur.

[0031] (3) In the preparation method of the porous carbon material, when the calcination temperature is 900 °C, the electron transfer rate of the lithium-sulfur battery prepared from the porous carbon material is the fastest, realizing strong cycle stability and excellent rate performance of the battery.

[0032] (4) The lithium-sulfur battery prepared with the porous carbon material as the cathode material reduces the diffusion energy barrier of Li + at the electrochemical interface, promotes the dynamic conversion of liquid-solid phase in the lithium-sulfur battery, and the synergistic effect of the catalytic activities of doped N and Ni together improves the reversibility of the phase conversion, thereby improving the sulfur utilization rate and the cycle life of the cathode. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described below with reference to the drawings, examples and comparative examples, wherein:

[0034] Figure 1 is a schematic diagram of the preparation process of the porous carbon material cathode material of the present invention.

[0035] Figure 2 are the transmission electron microscope (TEM) images, X-ray diffraction (XRD) patterns, and particle size distribution diagrams of the nano-zinc oxide prepared in step 1) of Examples 1, 3, and 5.

[0036] Figure 3 are the XRD patterns, scanning electron microscope (SEM) images, spherical aberration electron microscope images, and energy-dispersive X-ray spectroscopy (EDS) images of the porous carbon materials prepared in some examples and comparative examples.

[0037] Figure 4 are the adsorption experiments and electrochemical experiment results of polysulfide by the porous carbon materials of the blank sample, Example 1, Example 3, and Example 5.

[0038] Figure 5Battery performance test results of the batteries composed of the porous carbon materials in Example 1, Example 3, and Example 5.

[0039] Figure 6 Galvanostatic discharge curves of deposited Li2S and galvanostatic charge curves of dissolved Li2S for the batteries composed of the porous carbon materials in Example 1, Example 3, and Example 5.

[0040] Figure 7 Battery test of the long - cycle performance at 0.1C rate for the batteries composed of the porous carbon materials in Comparative Example 1 - 12.

[0041] Figure 8 Electrochemical impedance (EIS) spectra and cyclic voltammetry (CV) curves for the batteries composed of the porous carbon materials in Comparative Example 5 - 12.

[0042] Figure 9 Electrochemical performance test diagrams for the batteries composed of the porous carbon materials with different Ni contents loaded in Example 1, Example 11 - 14. Specific implementation manners

[0043] The content of the present invention will be further described in detail through specific examples and comparative examples below, but it is not limited to all the discussions and data.

[0044] The Li2S6 cathode electrolyte used in the examples and comparative examples was prepared by the following method:

[0045] 1mol / L Li2S6 cathode electrolyte: 6 mmol of Li2S and 30 mmol of sublimed sulfur were added to 6 mL of a 1mol / L LiTFSI - 5wt% LiNO3 DOL / DME (volume ratio 1:1) solution, and magnetically stirred at 60 °C for 24 h to obtain 1mol / L Li2S6 cathode electrolyte. The preparation method of 2mol / L Li2S6 cathode electrolyte was the same as above, except that the addition amounts of Li2S and sublimed sulfur were both doubled.

[0046] Unless otherwise specified, the raw materials, reagents or devices used in the examples and comparative examples can be obtained from conventional commercial channels, or can be obtained by existing technical methods. Unless otherwise specified, the test or measurement methods are all conventional methods in the art.

[0047] Example 1:

[0048] 1) Preparation of nano - zinc oxide (microwave - assisted hydrothermal method):

[0049] The anode material of the zinc-manganese battery was placed in a 6.26 mol / L acetic acid solution, heated in an oil bath at 130 °C and stirred for 30 min. After filtering off the insoluble matter, heating was continued, and the solution was concentrated to crystallization to obtain zinc acetate. 15 g of zinc acetate was weighed and placed in a 250 mL three-necked flask, 150 mL of methanol was added. The upper interface of the three-necked flask was connected to the lower interface of the condenser, and the upper interface of the condenser and the other two interfaces of the three-necked flask were sealed with a sealing film. It was heated in a water bath at 60 °C and stirred at a speed of 200 rpm for 2 h to obtain a zinc acetate-methanol solution. 15 mL of the zinc acetate-methanol solution was taken and transferred to a 35 mL sealed container with a magnetic stirrer. The microwave program was set to quickly heat to 120 °C, maintained for 10 min, the container was taken out, and the suspension was collected. This process was repeated multiple times until the zinc acetate-methanol solution was all used up. After the suspension was centrifuged at a speed of 6000 rpm, it was washed three times with absolute ethanol and dried in an oven at 60 °C for 12 h to obtain nano-zinc oxide.

[0050] 2) Preparation of porous carbon material:

[0051] 185 mg of urea and 170.56 mg of nickel chloride hexahydrate were added to 2 mL of furfuryl alcohol, magnetically stirred for 30 min, ultrasonically treated for 10 min, 5 g of the nano-zinc oxide prepared in step 1) was added, heated at 90 °C for 6 h, dried, heated to 300 °C at a rate of 5 °C / min in argon, held for 5 h. The obtained powder was washed with a mixed solution of deionized water and absolute ethanol with a volume ratio of 1:1, and then dried in an oven at 80 °C for 12 h. It was heated to 550 °C at a rate of 2 °C / min in argon, held for 5 h, and then heated to 900 °C at a rate of 10 °C / min and calcined for 2 h. After cooling to room temperature, the sample was added to a 6.26 mol / L acetic acid solution, sealed, heated to 130 °C, and stirred at a speed of 500 rpm at 130 °C for 36 h. The suspension was centrifuged at 9000 rpm and washed three times with a 6.26 mol / L acetic acid solution, and then dried in an oven at 60 °C for 12 h to obtain porous carbon material.

[0052] 3) Preparation of porous carbon material positive electrode material:

[0053] 0.003 g of porous carbon material was added to absolute ethanol, ultrasonically dispersed for 2 h, the solution was passed through an organic filter membrane nylon 66 and vacuum filtered, and vacuum dried at 60 °C for 12 h. The electrode membrane was peeled off from the filter membrane, and 50 μL of 1 mol / L Li2S6 cathode electrolyte was dropped on the electrode membrane to obtain porous carbon material positive electrode material.

[0054] 4) Preparation of battery:

[0055] Using a porous carbon material as the positive electrode, a lithium sheet with a diameter of 17 mm as the negative electrode, a polypropylene separator, a 1 mol / L LiTFSI - 2 wt% LiNO3 DOL / DME (volume ratio 1:1) solution as the electrolyte, and a standard CR2032 type battery case, a button cell was assembled and denoted as Microwave C-5% Ni.

[0056] Example 2:

[0057] Except that in the preparation of the porous carbon material positive electrode in step 3), the concentration of the cathode electrolyte dropped on the electrode membrane was 2 mol / L Li2S6, and the rest of the steps, dosages, and concentrations were the same as those in Example 1, denoted as Microwave C-5% Ni (high S).

[0058] Example 3:

[0059] 1) Preparation of nano-zinc oxide (hydrothermal method):

[0060] Take the anode material of the zinc-manganese battery and place it in a 6.26 mol / L acetic acid solution. Heat it in an oil bath at 130 °C and stir for 30 min. After filtering off the insoluble matter, continue heating and concentrate the solution to crystallization to obtain zinc acetate. Weigh 15 g of zinc acetate and place it in a 250 mL three-necked flask. Add 150 mL of methanol. Connect the upper interface of the three-necked flask to the lower interface of the condenser. Seal the upper interface of the condenser and the other two interfaces of the three-necked flask with a sealing film. Heat in a water bath at 60 °C and stir at a speed of 200 rpm for 2 h to obtain a zinc acetate-methanol solution. Add 5 g of potassium hydroxide, open the sealing film for 5 min to prevent flash boiling, collect the suspension, centrifuge it at a speed of 6000 rpm, wash it three times with absolute ethanol, and dry it in an oven at 60 °C for 12 h to obtain nano-zinc oxide.

[0061] Except that in step 1), the preparation of nano-zinc oxide (hydrothermal method) was carried out by the above hydrothermal method, and the rest of the steps, dosages, and concentrations were the same as those in Example 1, denoted as Hydrothermal C-5% Ni.

[0062] Example 4:

[0063] Except that in step 1), the nano-zinc oxide was prepared by the method of preparing nano-zinc oxide (hydrothermal method) in step 1 of Example 3, and the rest of the steps, dosages, and concentrations were the same as those in Example 2, denoted as Hydrothermal C-5% Ni (high S).

[0064] Example 5:

[0065] 1) Preparation of nano-zinc oxide (calcination method):

[0066] Place the anode material of the zinc-manganese battery in a 6.26 mol / L acetic acid solution, heat it in an oil bath at 130 °C and stir for 30 min. After filtering off the insoluble matter, continue heating and concentrate the solution to crystallization to obtain zinc acetate. Weigh 1.5 g of zinc acetate and transfer it to a crucible. First, heat the muffle furnace to 440 °C, then place the crucible in the muffle furnace and calcine for 2 h, and cool to obtain nano-zinc oxide.

[0067] Except that the preparation of nano-zinc oxide (calcination method) in step 1) is prepared by the above calcination method, the remaining steps, dosages, and concentrations are the same as those in Example 1, denoted as Calcination C-5%Ni.

[0068] Example 6:

[0069] Except that the nano-zinc oxide in step 1) is prepared by the preparation of nano-zinc oxide (calcination method) in Example 5, the remaining steps, dosages, and concentrations are the same as those in Example 2, denoted as Calcination C-5%Ni(high S).

[0070] Example 7:

[0071] Except that the temperature for calcination for 2 h in the preparation of the porous carbon material in step 2) is 700 °C, the remaining steps, dosages, and concentrations are the same as those in Example 1, denoted as Microwave C-5%Ni(700 °C).

[0072] Example 8:

[0073] Except that the temperature for calcination for 2 h in the preparation of the porous carbon material in step 2) is 800 °C, the remaining steps, dosages, and concentrations are the same as those in Example 1, denoted as Microwave C-5%Ni(800 °C).

[0074] Example 9:

[0075] Except that the temperature for calcination for 2 h in the preparation of the porous carbon material in step 2) is 1000 °C, the remaining steps, dosages, and concentrations are the same as those in Example 1, denoted as Microwave C-5%Ni(1000 °C).

[0076] Example 10:

[0077] Except that in the preparation of the porous carbon material positive electrode material in step 3), the dosage of the cathode electrolyte dropped on the electrode membrane is 4 μL, the remaining steps, dosages, and concentrations are the same as those in Example 1, denoted as Microwave C-5%Ni(low S).

[0078] Example 11:

[0079] Except that in the preparation of the porous carbon material in step 2), the amount of nickel chloride hexahydrate used is 85.28 mg, the remaining steps, amounts, and concentrations are the same as those in Example 1, denoted as Microwave C-2.5% Ni.

[0080] Example 12:

[0081] Except that in the preparation of the porous carbon material in step 2), the amount of nickel chloride hexahydrate used is 341.12 mg, the remaining steps, amounts, and concentrations are the same as those in Example 1, denoted as Microwave C-10% Ni.

[0082] Example 13:

[0083] Except that in the preparation of the porous carbon material in step 2), the amount of nickel chloride hexahydrate used is 682.24 mg, the remaining steps, amounts, and concentrations are the same as those in Example 1, denoted as Microwave C-20% Ni.

[0084] Example 14:

[0085] Except that in the preparation of the porous carbon material in step 2), the amount of nickel chloride hexahydrate used is 1.36 g, the remaining steps, amounts, and concentrations are the same as those in Example 1, denoted as Microwave C-30% Ni.

[0086] Comparative Example 1:

[0087] The difference from Example 10 is that Comparative Example 1 does not go through step 1) the preparation of nano-zinc oxide (microwave-assisted hydrothermal method), and urea, nickel chloride hexahydrate, and nano-zinc oxide are not added. The other steps, amounts, and concentrations are the same as those in Example 10, denoted as Pure C (900 °C).

[0088] Comparative Example 2:

[0089] Except that in the preparation of the porous carbon material in step 2), the calcination temperature for 2 h is 700 °C, the remaining steps, amounts, and concentrations are the same as those in Comparative Example 1, denoted as Pure C (700 °C).

[0090] Comparative Example 3:

[0091] Except that in the preparation of the porous carbon material in step 2), the calcination temperature for 2 h is 800 °C, the remaining steps, amounts, and concentrations are the same as those in Comparative Example 1, denoted as Pure C (800 °C).

[0092] Comparative Example 4:

[0093] Except that in the preparation of the porous carbon material in step 2), the calcination temperature for 2 h is 1000 °C, the remaining steps, amounts, and concentrations are the same as those in Comparative Example 1, denoted as Pure C (1000 °C).

[0094] Comparative Example 5:

[0095] It is different from Example 10 in that urea and nickel chloride hexahydrate are not added in Comparative Example 5, and the other steps, dosages, and concentrations are the same as those in Example 10, denoted as HPC(900°C).

[0096] Comparative Example 6:

[0097] Except that the calcination temperature in step 2) for preparing the porous carbon material is 700°C for 2 h, the other steps, dosages, and concentrations are the same as those in Comparative Example 5, denoted as HPC(700°C).

[0098] Comparative Example 7:

[0099] Except that the calcination temperature in step 2) for preparing the porous carbon material is 800°C for 2 h, the other steps, dosages, and concentrations are the same as those in Comparative Example 5, denoted as HPC(800°C).

[0100] Comparative Example 8:

[0101] Except that the calcination temperature in step 2) for preparing the porous carbon material is 1000°C for 2 h, the other steps, dosages, and concentrations are the same as those in Comparative Example 5, denoted as HPC(1000°C).

[0102] Comparative Example 9:

[0103] It is different from Example 10 in that nickel chloride hexahydrate is not added in Comparative Example 9, and the other steps, dosages, and concentrations are the same as those in Example 10, denoted as HPNC(900°C).

[0104] Comparative Example 10:

[0105] Except that the calcination temperature in step 2) for preparing the porous carbon material is 700°C for 2 h, the other steps, dosages, and concentrations are the same as those in Comparative Example 9, denoted as HPNC(700°C).

[0106] Comparative Example 11:

[0107] Except that the calcination temperature in step 2) for preparing the porous carbon material is 800°C for 2 h, the other steps, dosages, and concentrations are the same as those in Comparative Example 9, denoted as HPNC(800°C).

[0108] Comparative Example 12:

[0109] Except that the calcination temperature in step 2) for preparing the porous carbon material is 1000°C for 2 h, the other steps, dosages, and concentrations are the same as those in Comparative Example 9, denoted as HPNC(1000°C).

[0110] Testing method:

[0111] Polysulfide (LiPSs) adsorption experiment:

[0112] In a glove box filled with argon, Li2S and S with a mass ratio of 1:5 were completely dissolved in 1,2-dimethoxyethane (DME) to prepare a 5 mmol / L Li2S6 / DME solution. Then, 10 mg of porous carbon material was added to 5 mL of 5 mmol / L Li2S6 / DME solution and left standing for 6 h.

[0113] Li2S6 symmetric battery test:

[0114] A mixed slurry of 75 wt% sublimed sulfur, 15 wt% porous carbon material, and 10 wt% polyvinylidene fluoride (PVDF) was evenly coated on aluminum foil. At the same time, a tetraethylene glycol dimethyl ether solution of 0.15 mol / L Li2S6, 0.5 mol / L LiTFSI, and 0.1 mol / L LiNO3 was prepared as the electrolyte. When assembling the symmetric battery, two or more identical electrodes were assembled into a standard 2025-coin battery, and 40 μL of the electrolyte was added to each battery. Cyclic voltammetry (CV) measurements were performed on the symmetric battery in the range of -1.0 V to 1.0 V at a scan rate of 0.2 mV s -1 and the scanning rate was used for cyclic voltammetry (CV) measurement in the range of -1.0 V to 1.0 V.

[0115] Li2S deposition experiment:

[0116] 0.4 mmol of Li2S, 2.8 mmol of S, and 2 mmol of LiTFSI were dissolved in 2 mL of tetraethylene glycol dimethyl ether solution and stirred at 50 °C for 8 h to prepare a 0.2 mol / L Li2S8 solution. 20 μL of the Li2S8 solution was dropped into the cathode side. 20 μL of blank electrolyte without Li2S8 was added to the anode side. The assembled battery was discharged with a constant current density of 0.112 mA to 2.06 V, and then maintained at a constant potential of 2.05 V until the measured current was lower than 10 -5 A, and the deposition capacity of the porous carbon material for Li2S was calculated according to the area under the curve.

[0117] Li2S dissolution experiment:

[0118] The cathode after Li2S deposition measurement was recovered and reassembled into a new test battery. The new test battery also included blank electrolyte, Celgard separator, and lithium metal foil anode. The assembled test battery was electrostatically discharged to 1.70 V at a very low current value (about 10 -5 A), and then charged at a constant potential of 2.35 V until the test current was lower than 10 -5 A, and the decomposition capacity of the porous carbon material for Li2S was calculated according to the area under the curve.

[0119] Test Example:

[0120] (1) Figure 1 This is a schematic diagram of the preparation process of the porous carbon material cathode material of the present invention. As Figure 1 shown, first dissolve the anode material of the zinc-manganese battery in acetic acid to prepare zinc acetate, and then use microwave-assisted hydrothermal method, hydrothermal method or calcination method to prepare nano-zinc oxide. Using nano-zinc oxide, add urea and nickel chloride hexahydrate to furfuryl alcohol for reaction and calcination to obtain the porous carbon material.

[0121] (2) Use transmission electron microscope (TEM) and X-ray diffractometer (XRD) to characterize the morphology and structure of the nano-zinc oxide prepared in step 1) of Examples 1, 3, and 5. The results are as Figure 2 shown, Figure 2 In (a), it is the TEM image of the nano-zinc oxide (microwave-assisted hydrothermal method) prepared in step 1) of Example 1, Figure 2 In (b), it is the TEM image of the nano-zinc oxide (hydrothermal method) prepared in step 1) of Example 3, Figure 2 In (c), it is the TEM image of the nano-zinc oxide (calcination method) prepared in step 1) of Example 5, Figure 2 In (d) and (e), they are the particle size distribution diagrams of the nano-zinc oxide prepared in Examples 1 and 3, Figure 2 In (f), it is the XRD pattern of the nano-zinc oxide prepared in Examples 1, 3, and 5. It can be seen from the figure that the nano-zinc oxide particles prepared by the microwave-assisted hydrothermal method in Example 1 and the nano-zinc oxide particles prepared by the hydrothermal method in Example 3 are both spherical. The particle size of the nano-zinc oxide in Example 1 is mainly distributed around 13 nm, and the particle size of the nano-zinc oxide in Example 3 is mainly distributed around 7 nm; the nano-zinc oxide prepared by the calcination method in Example 5 is rod-shaped, with a rod length of 1-2 μm and a diameter of about 30 nm; in Figure 2 In (f), it shows that the characteristic peaks appearing at 31.8°, 34.4°, 36.3°, 47.5°, 56.6° and 62.9° for the three samples well belong to the (100), (002), (101), (102), (110) and (103) crystal planes of zinc oxide (PDF No: 99-0111).

[0122] (3) Conduct XRD, scanning electron microscope (SEM), aberration-corrected electron microscope, and EDS image scanning analysis on some of the prepared porous carbon materials. As Figure 3 shown, Figure 3 In (a), it is the XRD pattern of the porous carbon materials prepared in Examples 1, 3, 5, and Comparative Example 1, Figure 3 In (b), it is the XRD pattern of the porous carbon materials of Examples 1 and 7-9,Figure 3 XRD patterns of the porous carbon materials of Example 1 and Examples 11 - 14 in (c); Figure 3 SEM and TEM images of the porous carbon materials of Example 1, Example 3, and Example 5 in (d), (e), and (f) respectively; Figure 3 Aberration - corrected electron microscopy images of the porous carbon material of Example 1 at different scales in (g), (h), and (i); Figure 3 Energy - dispersive X - ray spectroscopy (EDS) images of different elements of the porous carbon material of Example 1 in (j), (k), and (l); Figure 3 In (a), for Example 1, Example 3, and Example 5, characteristic diffraction peaks of carbon only appear at 23.6° and 43.4°. These two diffraction peaks are well attributed to the (002) and (101) crystal planes of carbon, indicating that there is no zinc oxide in the final porous carbon material; Figure 3 In (b), it shows that as the calcination temperature increases, the (101) peak becomes stronger; Figure 3 In (c), for Examples 12 - 14, i.e., the porous carbon materials of Microwave C - 10%Ni, Microwave C - 20%Ni, and Microwave C - 30%Ni, characteristic peaks of Ni and NiO appear in the XRD patterns (see the positions of the yellow arrow and gray arrow in the figure respectively). In the XRD patterns of the porous carbon materials of Example 1 and Example 11, i.e., Microwave C - 5%Ni and Microwave C - 2.5%Ni, no signals belonging to nickel and its oxides are found, indicating that nickel is well - dispersed in the product. In addition, inductively coupled plasma optical emission spectrometry (ICP - OES) analysis was carried out on the porous carbon materials of Example 1 and Example 11, and the results show that the nickel contents are 4.39 wt% and 1.85 wt% respectively. Figure 3 In (d), (e), and (f), high - magnification SEM and TEM images show that the porous carbon materials of Example 1, Example 3, and Example 5 have a three - dimensional interconnected structure, which is physically beneficial to improving the sulfur loading and the lithium - ion transport rate. In Figure 3 In (g) and (h), it shows that the porous carbon material of Example 1 is loaded with nickel nanocrystals with a size of about 1 - 2 nm, and the lattice spacing of 0.20 nm is in good agreement with the (111) crystal plane of nickel. Figure 3 In (h), the high - angle annular dark - field scanning transmission electron microscopy (HAADF - STEM) image shows that individual nickel atoms are atomically dispersed around the nickel nanocrystals. These individual nickel atoms are marked as bright spots by red circles, indicating that nickel single atoms and nickel nanocrystals play a synergistic catalytic role during the battery cycling process. Figure 3EDS image analysis of (j), (k), and (l) in [the relevant context] shows that C, N, and Ni elements are all present in the porous carbon material of Example 1, further confirming the successful preparation of the porous carbon material modified by dispersed nitrogen and nickel atoms.

[0123] (4) Figure 4 Figure (5) shows the adsorption experiments and electrochemical experiment results of polysulfide lithium by the porous carbon materials of the blank sample, Example 1, Example 3, and Example 5. Figure 4 In (a) of [the relevant figure], from left to right are the Li2S6 adsorption experiment diagrams of the blank sample, Example 1, Example 3, and Example 5 porous carbon materials ("Before" is before the experiment, "After" is after the experiment). Figure 4 In (b) of [the relevant figure] is the ultraviolet-visible absorption spectrum of the solution after the blank sample, Example 1, Example 3, and Example 5 porous carbon materials adsorb Li2S6. Figure 4 In (c) of [the relevant figure] are the cyclic voltammetry (CV) curves of the Li2S6 symmetric batteries assembled with the porous carbon materials of Example 1, Example 3, and Example 5 as the positive electrode. Figure 4 In (d) of [the relevant figure] are the Tafel curves of the batteries assembled with the porous carbon materials of Example 1, Example 3, and Example 5 as the positive electrode. Figure 4 In (e) and (f) of [the relevant figure] are the EIS spectra of the batteries assembled with the porous carbon materials of Example 1, Example 3, and Example 5 as the positive electrode and the corresponding relationship diagram of Z' and ω. -1 / 2 diagram. Figure 4 In (a) of [the relevant figure], the solution colors of Example 1, Example 3, and Example 5 gradually change from brown-yellow to transparent, indicating that they have good adsorption affinity for polysulfide lithium. Figure 4 From the ultraviolet-visible absorption spectrum in (b) of [the relevant figure], it can be seen that compared with the blank sample, the S6 peak intensity of the solutions of Example 1, Example 3, and Example 5 at ~425 nm 2- decreases. Figure 4 In (c) of [the relevant figure], the electrocatalytic effects of the porous carbon materials of Example 1, Example 3, and Example 5 as the cathode in the redox reaction were evaluated by cyclic voltammetry of the symmetric battery. In the range of -0.8 V to 0.8 V of the CV curve, Example 1, Example 3, and Example 5 all show redox peaks. Among them, Example 1 shows the strongest peak current density, indicating that its electrocatalytic activity is the most effective and can promote the rapid catalytic conversion of polysulfides. Figure 4 In (d) of [the relevant figure], the Tafel curve reflects that the potential and exchange current density of the porous carbon material of Example 1 are the highest, indicating that the monodispersed 5% Ni coordinated with nitrogen in the porous carbon material of Example 1 promotes the dynamic conversion of liquid-solid phases in the lithium-sulfur battery. Figure 4(e) Electrochemical impedance spectroscopy (EIS) in shows three similar semicircles, indicating that the charge transfer resistance capabilities of the porous carbon materials in Example 1, Example 3, and Example 5 are close; at the same time, infer the diffusion coefficient of lithium ions from Figure 4 Figure (e) in, as Figure 4 shown in Figure (f) in, as the slope value decreases, the conductivity of lithium ions becomes higher and higher. The slope values of Example 1, Example 3, and Example 5 are 4.09, 9.28, and 8.87 respectively, indicating that the diffusion rate of lithium ions in Example 1 is faster than that in Example 3 and Example 5.

[0124] (5) Figure 5 are the battery performance test results of the batteries composed of the porous carbon materials in Example 1, Example 3, and Example 5. Figure 5 Figures (a) to (c) in are the cyclic voltammetry (CV) curves of the porous carbon materials in Example 1, Example 3, and Example 5 at different scanning rates respectively. Figure 5 Figure (d) in is the first-cycle charge-discharge curve of the porous carbon materials in Example 1, Example 3, and Example 5 at a rate of 0.05C. Figure 5 Figure (e) in is the cycling performance diagram of the porous carbon materials in Example 1, Example 3, and Example 5 at a rate of 0.1C. Figure 5 Figure (f) in is the cycling performance diagram of the porous carbon materials in Example 1, Example 3, and Example 5 at different rates in the range of 0.1C to 3C. Figure 5 Figure (g) in is the long-term cycling performance diagram of the porous carbon materials in Example 1, Example 3, and Example 5 at a rate of 1C and a high sulfur loading. Figure 5 Figure (h) in is the long-term cycling performance diagram of the porous carbon materials in Example 1, Example 3, and Example 5 at a rate of 1C and an ultra-high sulfur loading. Figure 5 It can be seen from Figures (a) to (c) in that typical anodic peaks (A, B) and cathodic peaks (C, D) appear in Example 1, Example 3, and Example 5. The reaction processes represented by each peak are

[0125] A: 4Li2S - 6e - → S4 2- + 8Li +

[0126] B: 2S4 2- - 4e - → S8

[0127] C: S8 + 4e - → 2S4 2-

[0128] D: S4 2- + 6e - + 8Li +→4Li2S

[0129] At the same scanning rate, the maximum current densities of Example 1 at peak B and peak C are higher than those of Example 3 and Example 5, indicating that the porous carbon material of Example 1 can better promote the formation and decomposition of insulating sulfur, which is of great significance for the different phase transformation processes of sulfur and polysulfides. Moreover, the slope values of anodic peaks A and B and cathodic peaks C and D of Example 1 are higher than those of Example 3 and Example 5, indicating that Li + transport in Example 1 is the easiest. According to the Randles-Sevcik equation, the diffusion coefficient (D + ) of the equation Li Li+ is calculated. The D Li+ of the cathode in Example 1 is the highest, which explains that the porous carbon material of Example 1 has a unique three-dimensional through-connected and interconnected hierarchical pore structure, reducing the diffusion energy barrier of Li + at the electrochemical interface. The synergistic effect of the catalytic activity of doped N and Ni together improves the reversibility of phase conversion, thereby improving the sulfur utilization rate and the cycle life of the cathode. Figure 5 Figure (d) in shows the first-cycle voltage curves of the batteries of Example 1, Example 3, and Example 5 at a rate of 0.05C within a voltage window of 1.7 - 2.8V. Compared with the battery of Example 5 (1208 mA h g -1 ) and the battery of Example 3 (833 mA h g -1 ), the charge-discharge curve of the battery of Example 1 shows a lower charging overpotential and voltage hysteresis, and at the same time achieves a higher specific capacity (1261 mA h g -1 ). In the curve of Example 1, the high utilization rate and high retention rate of the high-platform discharge capacity indicate that the diffusion of polysulfides in the lithium-sulfur battery is inhibited, while the high retention rate of the low-platform discharge capacity indicates that the trapped polysulfides are more thoroughly converted. Figure 5 As can be seen from (e) in , when the sulfur loading is 6.2 mg cm -2 , at a rate of 0.1C, the initial discharge capacity of the battery of Example 1 (1095 mA h g -1 ) is higher than that of Example 3 (834 mA h g -1 ) and Example 5 (1004 mA h g -1 ) because the pores in the porous carbon material of Example 1 are larger and can accommodate more actual sulfur load. Figure 5 As can be seen from (f) in , when the sulfur loading is 6.2 mg cm -2 , at different rates from 0.1C to 3C, the battery of Example 1 shows a higher discharge capacity than the batteries of Example 3 and Example 5. Figure 5As can be seen from (g) in [reference], the batteries of Example 1, Example 3, and Example 5 can still output extraordinary capacity after 500 cycles at a 1C rate and a sulfur loading of 6.2 mg cm -2 , especially the battery of Example 1. Figure 5 As can be seen from (h) in [reference], the batteries of Example 1, Example 3, and Example 5 maintain a relatively high specific capacity after 200 cycles at a 1C rate and a sulfur loading of 12.4 mg cm -2 , especially the battery of Example 1.

[0130] (6) Figure 6 Figure [X] shows the constant potential discharge curves of Li2S deposition and the constant potential charge curves of Li2S dissolution for the batteries composed of the porous carbon materials of Example 1, Example 3, and Example 5. Among them, Figure 6 (a) - (c) in [figure] are the constant potential discharge curves, Figure 6 (d) - (f) in [figure] are the constant potential charge curves. Figure 6 Obvious Li2S deposition peaks appear in all of (a) - (c) in [figure]. Among them, Example 1 shows the highest current density and charge capacity, indicating that the reduction of polysulfides in Example 1 has been enhanced and promoted. Figure 6 As can be seen from (d) - (f) in [figure], in the reverse Li2S decomposition reaction, Example 1 also shows the highest current density and discharge capacity. The results show that Example 1 is also highly efficient in promoting the Li2S oxidation reaction. The micropores and mesopores in Example 1 can provide abundant active sites to adsorb polysulfides and a high specific surface area to enhance the contact between carbon and polysulfides. Due to the synergistic effect of multiple interactions, Example 1 exhibits extremely strong Li2S nucleation and decomposition kinetics, verifying the bidirectional catalytic activity in the redox reaction of polysulfides.

[0131] (7) Figure 7 Figure [X] shows the long - cycle performance battery tests of the batteries composed of the porous carbon materials of Comparative Examples 1 - 12 at a 0.1C rate. Among them, Figure 7 (a) in [figure] is the long - cycle performance graph of Comparative Examples 1 - 4, Figure 7 (b) in [figure] is the long - cycle performance graph of Comparative Examples 5 - 8, Figure 7 (c) in [figure] is the long - cycle performance graph of Comparative Examples 9 - 12. As can be seen from Figure 7 (a) and (b) in [figure], at a sulfur loading of 0.5 mgcm -2 and a 0.1C rate, after continuous cycling 500 times, the specific capacities of the batteries of Comparative Examples 5 - 8 are higher than those of Comparative Examples 1 - 4 at the same calcination temperature; as can be seen from Figure 7 (b) and (c) in [figure], at a sulfur loading of 0.5 mg cm -2The sulfur loading, at a rate of 0.1C, after 500 consecutive cycles, the specific capacities of the batteries of Comparative Examples 9 to 12 are generally also higher than those of Comparative Examples 5 to 8 at the same calcination temperature, and when the calcination temperature is 900 °C, the specific capacity of its battery is the largest.

[0132] (8) Figure 8 Figure (8) shows the electrochemical impedance spectroscopy (EIS) plots and CV curves of the batteries composed of the porous carbon materials of Comparative Examples 5 to 12, where Figure 8 (a) in Figure (8) is the EIS plot of Comparative Examples 5 to 8, Figure 8 (b) in Figure (8) is the EIS plot of Comparative Examples 9 to 12, Figure 8 (c) in Figure (8) is the CV curve of Comparative Examples 5 to 8, Figure 8 (d) in Figure (8) is the CV curve of Comparative Examples 9 to 12. Figure 8 Comparing (a) and (b) in Figure (8), the electrochemical impedance of Comparative Examples 9 to 12 is significantly reduced, indicating that nitrogen doping can effectively promote the rapid transfer of electrons, and when the calcination temperature is 900 °C, the electron transfer rate is the fastest. Figure 8 Comparing (c) and (d) in Figure (8), more obvious redox peaks and higher redox currents appear in Comparative Examples 9 to 12, indicating that the introduction of nitrogen can effectively promote the catalytic conversion kinetics reaction of polysulfides.

[0133] (9) Figure 9 Figure (9) shows the test charts of the electrochemical performance of the batteries composed of the porous carbon materials with different Ni content loadings of Example 1 and Examples 11 to 14. Figure 9 (a) in Figure (9) is the cycling performance chart of the batteries composed of the porous carbon materials prepared in Example 1 and Examples 11 to 14 at a rate of 0.1C, Figure 9 (b) in Figure (9) is the CV curve of the batteries composed of the porous carbon materials prepared in Example 1 and Examples 11 to 14, Figure 9 (c) in Figure (9) is the EIS plot of the batteries composed of the porous carbon materials prepared in Example 1 and Examples 11 to 14. Figure 9 As can be seen from (a) in Figure (9), the batteries of Example 1 and Examples 11 to 12 still maintain a relatively high specific capacity after 200 cycles at a rate of 0.1C and a sulfur loading of 0.5 mg cm -2 , especially the battery of Example 1, while the specific capacities of Examples 13 to 14 are relatively low. Figure 9 As can be seen from (b) in Figure (9), the charge-discharge platforms of the batteries of Example 1 and Examples 11 to 12 are obvious, while those of Examples 13 to 14 are not obvious. Figure 9 As can be seen from (c) in Figure (9), the electrochemical impedance of Example 1 and Examples 11 to 12 is relatively small, especially the battery of Example 1, while the electrochemical impedance of Examples 13 to 14 is relatively large.

Claims

1. A method for preparing a porous carbon material for a lithium-sulfur battery positive electrode, characterized in that: The porous carbon material is composed of nickel, nitrogen and carbon elements; Wherein, the contents of nickel and nitrogen in the porous carbon material are 2.5-5% and 0.1-5% respectively, in terms of mass percentage; The porous carbon material is prepared by a preparation method comprising the following steps: 1) Preparation of nano zinc oxide by microwave-assisted hydrothermal method or hydrothermal method; 2) Using nano zinc oxide as a template, adding urea and nickel chloride hexahydrate into furfuryl alcohol, heating to react, and calcining at a temperature of 900-1000° C. to obtain the porous carbon material.

2. The method for preparing a porous carbon material for a lithium-sulfur battery positive electrode according to claim 1, characterized in that: In step 1), the preparation method of nano zinc oxide comprises the following steps: The zinc-manganese battery anode material is dissolved in acetic acid by microwave-assisted hydrothermal method, and heated and concentrated to crystallize to obtain zinc acetate, and then methanol is added and microwave-heated to a temperature of 110-130° C. for a reaction time of 10-15 min, and the nano zinc oxide is obtained by centrifugation, washing, and drying. Alternatively, a hydrothermal method is used to dissolve the zinc-manganese battery anode material in acetic acid, heat and concentrate to crystallize to obtain zinc acetate, then add methanol, set the temperature to 50-70°C, stir for 1.5-2.5h, then add potassium hydroxide to react for 0.5-1.5h, centrifuge, wash, and dry to obtain the nano zinc oxide.

3. The method for preparing a porous carbon material for a positive electrode of a lithium-sulfur battery according to claim 1, characterized in that: In step 2), after adding urea and nickel chloride hexahydrate to the furfuryl alcohol, stirring for 30-40 minutes, ultrasonicating for 10-20 minutes, adding to nano zinc oxide, setting the reaction temperature to 80-100°C, the reaction time to 5-8 hours, drying, heating to 300°C under gas protection and keeping warm for 5 hours, washing, drying, heating to 550°C and keeping warm for 5 hours, calcining for 2-3 hours, cooling, washing, and drying to obtain the porous carbon material.

4. A positive electrode material for a lithium-sulfur battery, characterized in that: It comprises an electrode membrane and an electrolyte, wherein the electrode membrane is made of a porous carbon material prepared by the method for preparing a porous carbon material for a positive electrode of a lithium-sulfur battery according to claim 1.

5. The positive electrode material for lithium-sulfur battery according to claim 4, characterized in that: The electrode membrane has a thickness of 10-16 mm and a mass of 1.5-3.0 mg.

6. The method for preparing a positive electrode material for a lithium-sulfur battery according to claim 4 or 5, characterized in that: The following steps are involved: 1) adding the porous carbon material into an organic solvent, dispersing it, passing it through an organic filter membrane and vacuum filtering it, drying it, and peeling it off to obtain an electrode membrane; 2) Adding a cathode electrolyte dropwise onto the electrode membrane to obtain the positive electrode material for a lithium-sulfur battery.

7. A lithium-sulfur battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte of the battery, wherein the positive electrode of the battery is the positive electrode material for a lithium-sulfur battery according to claim 4 or 5.

8. The lithium-sulfur battery according to claim 7, characterized in that: The negative electrode of the lithium-sulfur battery is a lithium sheet, the diaphragm is a polypropylene diaphragm, and the electrolyte is a lithium-sulfur electrolyte.

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