A material for protecting a lithium metal negative electrode, and a preparation method and use thereof

Abstract

The application discloses a material for protecting a lithium metal negative electrode and a preparation method and application thereof. ‑1 and a capacity of 500 mAh g ‑1 Under the condition of a current density of 100 mA g and the capacity of 500 mAh g , the lithium-oxygen battery can be stably cycled for 160 cycles, and the service life reaches 1600 h. The preparation method is simple, low in cost, and low in investment, and is suitable for batch production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a material for protecting a lithium metal negative electrode and a preparation method and application thereof. BACKGROUND

[0002] More than 70% of global energy demand is supported by fossil energy such as oil and natural gas, and overconsumption of fossil energy will cause serious global warming and air pollution problems. The continuation of the earth's scientific civilization requires our efforts now, and new energy research and development have become an urgent demand worldwide. Lithium-ion batteries have been accepted by people through a theoretical energy density of 400 Wh kg -1 and safe and stable performance, and have walked into the commercialization of lithium-ion batteries, which is leading the rise of the electric vehicle industry, but the energy density of lithium-ion batteries cannot meet all human needs. In the pursuit of higher energy density and longer service life than lithium-ion batteries, people have found that non-aqueous lithium-oxygen batteries have an unimaginable theoretical specific energy of 3500 Wh kg -1 , have the advantages of low cost and environmental friendliness. Humans have a beautiful dream for the commercialization of lithium-oxygen batteries, but the production of lithium peroxide (Li2O2) as the reaction product of the cathode of the battery will hinder electron transfer and ion diffusion, and will further exacerbate the increase in overvoltage, which is a problem that cannot be ignored in the research of lithium-oxygen batteries. People first proposed solid catalysts, including carbon-based materials, transition metal compounds and noble metals. However, traditional solid catalysts have some challenging problems, such as high cost of raw materials, complex synthesis, heavy metal pollution, and poor solid-solid contact between the catalyst itself and lithium peroxide, and electrolyte degradation.

[0003] In order to realize the reversible generation / decomposition of Li2O2 and eliminate unnecessary side reactions, in recent years, soluble redox mediators (RMs) have shown excellent performance in improving reaction dynamics and improving battery capacity, such as lithium iodide, tetrahexathiamine, 2,2,6,6, -tetramethylpiperidyl oxy, and methylphenothiazine, which are preferentially electrochemically oxidized to RM + on the surface of the cathode during the charging process, and then the RM +Contact with Li2O2, providing electron holes to oxidize and decompose it, this process can greatly reduce the charging potential, 2,2,6,6,-tetramethylpiperidinyl oxy (TEMPO) provides a significant reduction of 500mV charging potential, the cycle performance is doubled. Reducing overpotential can increase battery capacity and life, however, the researchers to solve the decomposition of lithium peroxide, an insulator, introduced a soluble redox medium will cause another problem, the electrolyte will infiltrate the inside of the battery, and the RM in the electrolyte will reach the lithium metal anode with the electrolyte wet, which means that RMs will participate in the Li2O2 reaction in the cathode, and the electrolyte will also shuttle through the separator to the lithium metal anode, and the electrolyte will spontaneously react with the lithium metal anode to cause corrosion on the surface of the lithium sheet. The irreversible reaction with lithium metal also causes the RMs reaching the anode side to lose their ORR or OER performance, thus losing the performance they should have after adding RMs. Currently, the process for inhibiting the shuttle of redox mediators to protect the lithium metal negative electrode is complex and not suitable for large-scale production. SUMMARY

[0004] The technical problem solved by the present application is to provide a material for protecting lithium metal negative electrode and its preparation method and use, which has low technical cost, simple process and is suitable for large-scale production.

[0005] The technical solution adopted by the present application to solve the above technical problem is: a preparation method of a material for protecting lithium metal negative electrode, specifically comprising the following steps:

[0006] 1) A certain amount of melamine and cobalt acetate is added to dimethyl sulfoxide, stirred, centrifuged to remove the supernatant, and the solid is washed with alcohol and water three times and then vacuum freeze-dried to obtain a yellow solid;

[0007] 2) The above yellow solid is transferred to a tube furnace and sintered at 650-800℃ under nitrogen environment at a heating rate of 4℃ / min for 4 hours; then the obtained yellow solid is ground into fine powder and added to 1.0mol / L hydrochloric acid to form a suspension, then centrifuged three times to remove free cobalt ions, and then washed with water until the pH of the washing liquid is 7. The washed powder is dried to obtain a yellow cobalt-doped carbon nitride powder;

[0008] 3) The cobalt-doped carbon nitride powder obtained above is added to N-methyl pyrrolidone reagent in a mass ratio of 9:1 to form a suspension, and ultrasonic is performed for 1h, 5-10mL of the suspension is taken each time, vacuum filtration is performed on a glass fiber separator, and vacuum drying is performed at 70℃ for 12h; finally, the separator loaded with cobalt-doped carbon nitride is cut into a diameter of 19mm, which is the material for protecting lithium metal negative electrode.

[0009] Further, the present application also provides the use of the material as a lithium-oxygen battery separator to prevent corrosion of the lithium metal anode, under the condition of current density of 100mA g -1 and capacity of 500mAh g -1 , the lithium-oxygen battery can be stably cycled for 160 cycles, and the service life reaches 1600h.

[0010] Compared with the prior art, the present application has the following characteristics:

[0011] In the present application, carbon nitride has a similar structure to graphite, which is composed of continuous three-s-triazine units and amino groups in each layer. The high degree of nitrogen doping can provide a unique band gap with sufficient active sites. The nitrogen atoms in the structural framework can activate the catalysis with metal sites, and cobalt elements can be incorporated into the carbon nitride framework without damaging the carbon nitride host. In the cobalt-doped carbon nitride compound, the bond length of Co-C bond is 1.97 and 1.98. The specific bond length makes the compound have specific stability and specific electrochemical performance. The carbon nitride prepared at 650℃ has the highest current density, repeatability and super stability, and has a large specific surface area. The packing density of carbon nitride makes the interlayer combination more compact, and has a more satisfactory vertical plane charge transfer rate. In summary, by doping of cobalt and the unique two-dimensional network structure of carbon nitride, the parasitic reaction of redox mediator TEMPO is greatly inhibited, and TEMPO is ensured to have a full and persistent reaction with Li2O2 on the cathode side; the prepared material is used as a separator of a lithium-oxygen battery to prevent corrosion of the lithium metal anode, under the condition of current density of 100mA g -1 , the lithium-oxygen battery can be stably cycled for 160 cycles, and the service life reaches 1600h. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The microstructure diagram of cobalt-doped carbon nitride prepared in Example 1 of the present application is shown in the figure;

[0013] Figure 2 The XRD diagram of cobalt-doped carbon nitride powder prepared in Example 1 of the present application is shown in the figure;

[0014] Figure 3 The SEM diagram of cobalt-doped carbon nitride powder prepared in Example 1 of the present application is shown in the figure;

[0015] Figure 4 The separator prepared in Example 1 of the present application is used as a separator of a lithium-oxygen battery, and the charge-discharge cycle diagram of the lithium-oxygen battery under the condition of current density of 100mA g -1 and capacity of 500mAh g -1 is shown in the figure. DETAILED DESCRIPTION

[0016] The application will be further described in detail in connection with the following examples.

[0017] Example 1

[0018] The 11 g of melamine and 0.15 g of cobalt acetate were added to 250 mL of dimethyl sulfoxide reagent, and after stirring vigorously for 24 h, the supernatant was removed by centrifugation, and the solid was washed with alcohol and water three times and then vacuum freeze-dried to obtain a yellow solid; the yellow solid was transferred to a tube furnace, and high-temperature sintering was performed at 650°C at a heating rate of 4°C / min under N2, and the temperature was kept for 4 h; then the yellow solid was ground into fine powder and added to 1.0 mol / L hydrochloric acid to form a suspension, and then the suspension was centrifuged and washed three times to remove free cobalt ions; then water was added for continuous washing until the pH of the washing liquid was 7, and the washed powder was dried at 60°C to obtain a yellow cobalt-doped carbon nitride powder (as shown in Figure 1 the microstructure of the cobalt-doped carbon nitride, the cobalt ions are embedded in the structure of the carbon nitride to form a stable cobalt-doped carbon nitride compound). The cobalt-doped carbon nitride powder prepared above and polyvinylidene fluoride were added to N-methylpyrrolidone at a mass ratio of 9:1 to form a suspension, and ultrasonic treatment was performed for 1 h, 5 mL of the suspension was vacuum filtered onto a glass fiber separator, and vacuum drying was performed at 70°C for 12 h; finally, the separator loaded with cobalt-doped carbon nitride was cut into a diameter of 19 mm, which was the material for protecting the lithium metal negative electrode.

[0019] The cobalt-doped carbon nitride powder obtained was subjected to X-ray diffraction analysis (XRD) to test the composition structure of the material Figure 2 ; the morphology of the material was observed by scanning electron microscopy (SEM), and the material had a tight layered structure Figure 3 ; the separator material loaded with cobalt-doped carbon nitride prepared was used as a separator of a lithium-oxygen battery to prevent corrosion of the lithium metal negative electrode, and under the conditions of a current density of 100 mAg -1 and a capacity of 500 mAh g -1 , the lithium-oxygen battery could be stably cycled for 160 cycles, and the service life reached 1600 h Figure 4 .

[0020] Example 2

[0021] The 12 g of melamine and 0.2 g of cobalt acetate were added to 250 mL of dimethyl sulfoxide reagent, after stirring vigorously for 24 h, the supernatant was removed by centrifugation, the solid was washed with alcohol and water for three times and then vacuum freeze-dried to obtain a yellow solid; the yellow solid was transferred to a tube furnace, and sintered at 700℃ under nitrogen environment at a heating rate of 4℃ per minute, and kept for 4 h; then the yellow solid was ground into fine powder and added to 1.0 mol / L hydrochloric acid to form a suspension, and then centrifuged and washed three times to remove free cobalt ions; then water was added for continuous washing until the pH of the washing liquid was 7, and the washed powder was dried at 60℃ to obtain a yellow cobalt-doped carbon nitride powder. The above prepared cobalt-doped carbon nitride powder and polyvinylidene fluoride were added to N-methyl pyrrolidone reagent in a mass ratio of 9:1 to form a suspension, and ultrasonic was performed for 1 h, 10 mL of the suspension was vacuum filtered onto a glass fiber separator, and vacuum dried at 70℃ for 12 h; finally, the separator loaded with cobalt-doped carbon nitride was cut into a diameter of 19 mm, which was the material for protecting the lithium metal negative electrode.

[0022] The obtained cobalt-doped carbon nitride powder was analyzed by X-ray diffraction to test the material composition structure; the morphology of the material was observed by scanning electron microscope; the prepared separator material loaded with cobalt-doped carbon nitride was used as a lithium-oxygen battery separator to prevent corrosion of the lithium metal negative electrode, and the charge-discharge cycle performance of the lithium-oxygen battery was tested under a current density of 100 mAg -1 .

[0023] Example 3

[0024] The 12 g of melamine and 0.2 g of cobalt acetate were added to 250 mL of dimethyl sulfoxide reagent, after stirring vigorously for 24 h, the supernatant was removed by centrifugation, the solid was washed with alcohol and water for three times and then vacuum freeze-dried to obtain a yellow solid; the yellow solid was transferred to a tube furnace, and sintered at 700℃ under nitrogen environment at a heating rate of 4℃ per minute, and kept for 4 h; then the yellow solid was ground into fine powder and added to 1.0 mol / L hydrochloric acid to form a suspension, and then centrifuged and washed three times to remove free cobalt ions; then water was added for continuous washing until the pH of the washing liquid was 7, and the washed powder was dried at 60℃ to obtain a yellow cobalt-doped carbon nitride powder. The above prepared cobalt-doped carbon nitride powder and polyvinylidene fluoride were added to N-methyl pyrrolidone reagent in a mass ratio of 9:1 to form a suspension, and ultrasonic was performed for 1 h, 10 mL of the suspension was vacuum filtered onto a glass fiber separator, and vacuum dried at 70℃ for 12 h; finally, the separator loaded with cobalt-doped carbon nitride was cut into a diameter of 19 mm, which was the material for protecting the lithium metal negative electrode.

[0025] The obtained cobalt-doped carbon nitride powder is subjected to X-ray diffraction analysis to test the material composition structure; the morphology of the material is observed by scanning electron microscope; the prepared cobalt-doped carbon nitride loaded separator material is used as a lithium-oxygen battery separator to prevent corrosion of the lithium metal negative electrode, and the charge-discharge cycle performance of the lithium-oxygen battery is tested under the condition of a current density of 100 mAg -1 .

Claims

1. A method of preparing a lithium-oxygen battery separator, characterized by, The lithium-oxygen battery diaphragm as a material for protecting a lithium metal negative electrode, the preparation method comprising the following steps: 1) A certain amount of melamine and cobalt acetate is weighed and added to dimethyl sulfoxide, stirred, centrifuged to remove supernatant, and the solid is washed with alcohol and water three times and then vacuum freeze-dried to obtain a yellow solid; 2) The yellow solid is transferred to a tube furnace, sintered at a temperature rising rate of 4 ℃ per minute to 650-800 ℃ under a nitrogen environment, and kept for 4 h; then the obtained yellow solid is ground into fine powder, added with 1.0 mol / L hydrochloric acid to form a suspension, centrifuged three times to remove free cobalt ions, then washed with water until the pH of the washing liquid is 7, and the washed powder is dried to obtain a yellow cobalt-doped carbon nitride powder; 3) The cobalt-doped carbon nitride powder prepared above is added to N-methyl pyrrolidone reagent in a mass ratio of 9:1 to prepare a suspension, ultrasonically treated for 1 h, 5-10 mL of the suspension is taken each time, vacuum filtered onto a glass fiber diaphragm, and vacuum dried at 70 ℃ for 12 h; finally, the diaphragm loaded with cobalt-doped carbon nitride is cut into a diameter of 19 mm, which is the material for protecting a lithium metal negative electrode.

2. The lithium-oxygen battery diaphragm prepared by the preparation method of claim 1.

3. A lithium-oxygen battery, characterized by, A lithium-oxygen battery separator as claimed in claim 2, under a current density of 100 mA g -1 and a capacity of 500 mAh g -1 The lithium-oxygen battery can be stably cycled for 160 cycles, with a service life of 1600 h.

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