A lithium-oxygen battery with high rate capability and a preparation method thereof

Abstract

The application discloses a lithium-oxygen battery with high rate performance and a preparation method thereof, and relates to the technical field of lithium-oxygen batteries. The application uses carbon-based nanocage loaded with metal ruthenium (Ru) as a positive electrode catalytic composite material, and adds soluble redox medium ferrous glycinate (Fe(gly)2) in an electrolyte; the high catalytic activity of Ru is used to reduce the overpotential during the charging and discharging reaction of the lithium-oxygen battery; the large specific surface area and hierarchical pore structure of the carbon-based nanocage are used to assist the dispersion and accommodation of the discharge product Li2O2 and the transportation of oxygen, lithium ions and other materials; the Fe(gly)2 is used to effectively catalyze the formation of uniformly dispersed small-size particles of the Li2O2 discharge product and the performance of the decomposition during the charging process; in addition, the application limits the loading amount of the metal ruthenium on the positive electrode catalytic material to be 12-14 wt%, and the concentration of the Fe(gly)2 in the electrolyte to be 30-50 mM, so that the two fully play a synergistic role; under the conditions of a cutoff capacity of 1000 mAh / g and a current density of 5 A / g, the lithium-oxygen battery can be cycled for more than 150 cycles, and the rate performance and the cycle stability are obviously enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium-oxygen batteries, and particularly relates to a lithium-oxygen battery with a ruthenium-loaded carbon-based nanocage as a positive electrode composite catalytic material and with a soluble redox medium added to the electrolyte, and a specific preparation method of the lithium-oxygen battery. BACKGROUND

[0002] In recent years, in order to cope with the problems of global climate change and energy crisis, researchers in the relevant field have made unremitting efforts to find clean and renewable alternative energy. The demand for energy storage and conversion devices in society has increased, and high-performance electrochemical energy storage devices have received more and more attention. Among them, lithium-oxygen batteries (LOB) have attracted much attention due to their extremely high theoretical energy density of more than 11000 Wh / kg.

[0003] When the lithium-oxygen battery is discharged, a complex three-phase interface reaction occurs at the positive electrode. Oxygen (O2) reacts with lithium ions (Li + ) to generate lithium superoxide (LiO2) intermediate, and then through dismutation reaction to generate the final discharge product lithium peroxide (Li2O2). The product Li2O2 will gradually deposit on the surface of the positive electrode because it is difficult to dissolve in the electrolyte. Because Li2O2 has poor electrical conductivity, it is difficult to completely decompose during charging. With the increase of the number of battery cycles, the positive electrode is covered with Li2O2 or even the porous channels are blocked, which hinders the transmission of O2 and electrolyte. The oxygen reduction reaction (ORR) of the positive electrode during discharge and the oxygen evolution reaction (OER) during charging are both affected. During charging and discharging, it is difficult to maintain a stable voltage platform, and due to the polarization effect, the overpotential will also be greatly increased. The increase in voltage during the OER process makes the electrolyte more likely to decompose, forming different by-products and accumulating on the positive electrode, thereby further reducing the performance of the battery and seriously degrading the charge-discharge capacity and cycle life of the battery.

[0004] To solve the above problems, the skilled person usually starts from the aspects of positive electrode material, electrolyte components, separator, etc. The ideal positive electrode material of LOB should have good electrical conductivity, large specific surface area, good ORR / OER catalytic performance and electrochemical stability. The high-performance positive electrode materials reported so far are usually carbon materials with large specific surface area, suitable pore structure and high electrical conductivity. After loading noble metals, transition metals and their oxides with good ORR / OER catalytic activity on the carbon-based material, the performance of the positive electrode far exceeds that of a single component. In the case of high current density, it can still maintain a lower overpotential and higher cycle number. Liu et al. reported a positive electrode material in “Rationally Designed Three-Dimensional N-Doped Graphene Architecture Mounted with Ru Nanoclusters as a High-Performance Air Cathode for Lithium-Oxygen Batteries”, which is a nitrogen-doped 3D reduced graphene oxide (3D-NrGO) loaded with ruthenium (Ru). After preparing 3D-NrGO by hydrothermal method, RuCl3 is used as Ru source, and after reduction, the final product Ru / 3D-NrGO is obtained. The material has a discharge capacity of 23922 mAh / g at a current density of 0.1 A / g; and reaches 200 cycle numbers at a current density of 0.2 A / g and a cutoff capacity of 1000 mAh / g. The stability of the carbon-based positive electrode loaded with noble metals is greatly improved, but the current density is still small.

[0005] Chinese patent CN116230966A discloses “Preparation method and application of supported high-dispersion alloy nanocluster catalyst”, which simultaneously loads two metals, ruthenium and palladium, on carbon nanocage. The positive electrode material RuPd / CNCs has a discharge capacity of 30000 mAh / g at a current density of 0.1 A / g; and reaches 300 cycle numbers at a current density of 0.1 A / g and a cutoff capacity of 1000 mAh / g. Although the cycle number is higher, the current density is still low in the case of using multiple noble metals. That is, the rate performance of the existing LOB is usually limited to <0.5 A / g, which is a challenge for high energy conversion applications.

[0006] The reason why a large number of studies have used carbon-based materials loaded with high-performance metal or metal oxides as positive electrode materials, but still only use small current tests, is that the ORR / OER catalytic performance of the material will be greatly weakened under high current. Because the Li2O2 particles are large, uneven and dispersed and stacked, it is difficult for them to completely decompose during charging, and the excessive "dead" Li2O2 in the positive electrode exacerbates the polarization effect, and high current under the polarization effect leads to too high overpotential, which makes the electrolyte begin to have side reactions, so we often see that the LOB performance under high current rapidly decays, and this phenomenon mainly arises from the passivation of the positive electrode caused by the accumulation of Li2O2.

[0007] To improve the reversibility of the battery, a soluble redox medium (RM) can be added to the electrolyte. This medium shuttles between the electrode and the electrolyte during battery operation, acts as a charge shuttle between the surface of Li2O2 in the electrode and the electrolyte, and reversibly provides (ORR) or accepts (OER) electrons to achieve easy conversion between O2 and Li2O2. By gaining or losing electrons on the surface of the electrode to form a redox couple, it effectively avoids the performance decay problem caused by the coverage of the positive electrode.

[0008] Commonly used RMs reported include hemoglobin (Heme), iron porphyrin (FePro), iron phthalocyanine (FePc), etc. Chinese patent CN109193030A discloses a lithium-oxygen battery electrolyte using molybdenum pentachloride as a redox medium. The addition of molybdenum pentachloride as an RM in the electrolyte helps the formation of Li2O2 during discharge, and also plays a role in stabilizing the carbon positive electrode; Li2O2 can be effectively decomposed during charging, reducing the charging voltage and improving the cycle stability.

[0009] From the existing technology, if carbon-based positive electrode materials loaded with metal or metal oxides are combined with soluble RMs, based on the combined action of such carbon-based materials and RMs, it may be possible to further improve the cycle stability of LOB under large current density while maintaining high ORR / OER catalytic activity of the positive electrode; on this basis, if a new high-performance positive electrode catalytic composite material can be developed and used with the best proportion of soluble RMs, the two can maximize the synergistic effect, or it can further effectively improve the number of cycles of LOB under large current, and provide possibilities and new ideas for the practical application of lithium-oxygen batteries. SUMMARY

[0010] The application aims to solve the problems in the prior art, and provides a lithium-oxygen battery with high rate capability and a preparation method thereof.

[0011] A lithium-oxygen battery with high rate capability, which is composed of a positive electrode shell with holes, a positive electrode sheet, a separator, an electrolyte, a lithium sheet, a gasket, an elastic sheet and a negative electrode shell, wherein the positive electrode sheet is prepared by coating a slurry of a positive electrode catalytic composite material and a binder on a current collector, the positive electrode catalytic composite material is composed of a carbon-based nanocage carrier loaded with ruthenium (Ru), and the loading amount of the ruthenium is 12-14 wt%; and the electrolyte is added with a soluble redox medium, i.e., ferrous glycinate (Fe(gly)2), and the concentration of the Fe(gly)2 in the electrolyte is 30-50 mM.

[0012] Further, the lithium-oxygen battery can be cycled for more than 150 cycles under a cutoff capacity of 1000 mAh / g and a current density of 5 A / g.

[0013] Further, the carbon-based nanocage is a carbon nanocage (CNC) or a nitrogen-doped carbon nanocage (NCNC).

[0014] A preparation method of a lithium-oxygen battery with high rate capability, and the preparation process is as follows:

[0015] 1) uniformly mix carbon-based nanocages and ethylene glycol in a container;

[0016] 2) drop a precursor solution of ruthenium into the container and stir to mix;

[0017] 3) microwave heating in a microwave oven, and post-treatment to obtain a dry sample powder;

[0018] 4) heat reduction of the sample powder under an inert atmosphere to obtain ruthenium-loaded carbon-based nanocages;

[0019] 5) mix the ruthenium-loaded carbon-based nanocages with a binder, coat on a current collector, vacuum dry to obtain a positive electrode sheet;

[0020] 6) weigh Fe(gly)2 and lithium bis-trifluoromethylsulfonylimide (LiTFSI) and dissolve them in dimethyl sulfoxide (DMSO) as RMs and lithium salt respectively, heat and mix to prepare an electrolyte;

[0021] 7) Assembling the button cell in a glove box, the water content and oxygen content of the glove box should be less than 0.1 ppm, more preferably 0.01 ppm, the amount of electrolyte used in assembling the battery is preferably 100-200 μL, and the cover pressure is preferably 50-100 kg / cm 2 .

[0022] Further, in step (1), the carbon-based nanocage is a carbon nanocage or a nitrogen-doped carbon nanocage, the mass of the carbon-based nanocage is 50-100 mg, and the volume of the ethylene glycol is 30-50 mL.

[0023] Further, in step (2), the precursor solution of metallic ruthenium is prepared by dissolving ruthenium chloride in water, and the concentration of ruthenium chloride in the precursor solution is 20 g / L.

[0024] Further, in step (3), the microwave frequency is 2450 MHz, the microwave power is 800 W, and the microwave heating time is 30-60 s.

[0025] Further, in step (4), the heating rate of the thermal reduction process is 5-10 ℃ / min, the heat treatment temperature is 200-400 ℃, and the time for maintaining the heat treatment temperature is 120-240 min.

[0026] Further, in step (5), the vacuum degree during vacuum drying is preferably 0.1-100 Pa, the temperature is preferably 60-80 ℃, and the vacuum drying time is preferably 60-600 min.

[0027] Further, in step (6), the concentration of Fe(gly)2 in the electrolyte is 30-50 mM, the concentration of LiTFSI is 1 M, the heating temperature is 40-60 ℃, and the heating time is 12-24 h.

[0028] The beneficial effects of the present application are:

[0029] 1.The lithium-oxygen battery disclosed in the present application uses Ru-loaded carbon-based nanocage as a positive electrode catalytic composite material and dopes soluble redox medium ferrous glycinate (Fe(gly)2) in the electrolyte; the present application greatly reduces the overpotential during the charge-discharge reaction of the lithium-oxygen battery by using the high catalytic activity of Ru; the large specific surface area and hierarchical pore structure of the carrier carbon-based nanocage effectively assist the dispersion and accommodation of the discharge product Li2O2 and the transportation of oxygen, lithium ions and other materials; the performance of Fe(gly)2 in effectively catalyzing the formation of uniformly dispersed small-size particles of Li2O2 discharge product and decomposing during the charging process improves the reversibility of the battery under high current density; the present application uses the synergistic effect of the positive electrode composite catalyst Ru / NCNC and the soluble redox medium Fe(gly)2 to maintain high ORR / OER catalytic activity of the positive electrode while significantly improving the rate performance and cycle stability of the lithium-oxygen battery under high current density;

[0030] 2.The present application limits the loading of Ru on the positive electrode catalytic composite material and the concentration of Fe(gly)2 in the electrolyte in the Ru / NCNC-Fe(gly)2 lithium-oxygen battery, so that the prepared lithium-oxygen battery can exhibit the best rate performance and cycle stability, and can be cycled more than 150 times under a cutoff capacity of 1000 mAh / g and a current density of 5 A / g. The excellent performance of the battery under high current density makes it possible for the lithium-oxygen battery to be truly practical. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is the SEM picture of CNC;

[0032] Figure 2 is the nitrogen adsorption-desorption curve of NCNC used in the examples and comparative examples;

[0033] Figure 3 is the pore size distribution graph of NCNC used in the examples and comparative examples;

[0034] Figure 4 is the conductivity test graph of NCNC used in the examples and comparative examples and Ru / NCNC prepared in Example 7;

[0035] Figure 5 is the low-power electron microscope graph of Ru / NCNC prepared in Example 5;

[0036] Figure 6 is the cycle number comparison graph of different positive electrode materials;

[0037] Figure 7 is the cycle performance test graph of the lithium-oxygen batteries prepared in Comparative Examples 1-2 and Example 5 under high current density;

[0038] Figure 8is a cycle number comparison chart of Ru / NCNC-Fe(gly)2 lithium-oxygen batteries obtained after changing the Ru loading;

[0039] Figure 9 is a cycle voltage test chart of Ru / NCNC-Fe(gly)2 lithium-oxygen batteries (left) and NCNC lithium-oxygen batteries (right) prepared in Example 5 before 100 cycles;

[0040] Figure 10 is an EIS chart of Ru / NCNC-Fe(gly)2 lithium-oxygen batteries and NCNC lithium-oxygen batteries prepared in Example 5 before 50 cycles;

[0041] Figure 11 is an SEM chart of the positive electrode material of Ru / NCNC-Fe(gly)2 lithium-oxygen batteries (left) and NCNC (right) prepared in Example 5 after cycles;

[0042] Figure 12 is an XRD chart of Ru / NCNC-Fe(gly)2 lithium-oxygen batteries (left) and NCNC (right) prepared in Example 5 after cycles. DETAILED DESCRIPTION

[0043] The following examples further illustrate the content of the present application, but should not be understood as limiting the present application. Modifications and replacements to the method, steps or conditions of the present application, without departing from the essence of the present application, all belong to the scope of the present application.

[0044] In the following examples and comparative examples, the positive electrode catalytic composite material used is a nitrogen-doped carbon nanocage (NCNC) loaded with metal ruthenium (Ru), denoted as Ru / NCNC, and the loading of ruthenium refers to the mass ratio of the metal element Ru in the whole Ru / NCNC, which can be controlled by changing the amount of the precursor.

[0045] The NCNC can be replaced by carbon nanocage (CNC), and the preparation methods of NCNC and CNC are prior art. The preparation processes of the two are similar, and only the benzene used in the preparation of CNC is replaced by pyridine. The specific steps are not described here.

[0046] Figure 1 is an SEM picture of CNC, from which it can be seen that the spherical structure is composed of lamellar structure, and the carbon nanocage with a diameter of about 20 nm constitutes the lamellar structure, which is also the most basic unit. This hierarchical structure not only maintains the good electrical conductivity and high specific surface area of carbon materials, but also has a hierarchical pore structure with the coexistence of micropores, mesopores and macropores. This hierarchical pore structure helps the uniform dispersion, accommodation and material transport of the discharge product Li2O2 of lithium-oxygen batteries in the positive electrode.

[0047] The nitrogen adsorption-desorption curve and pore size distribution of the used NCNC are shown in Figures 2-3 According to the BET test, the nitrogen adsorption-desorption curve of the NCNC exhibits a H4 type hysteresis loop, and the low end of the adsorption has a sharp increase, indicating the presence of micropores; there is no obvious saturation platform in the adsorption stage, indicating the presence of both macropores and mesopores. The specific surface area is as high as 1290 m 2 / g, and the pore size distribution curve shows that the main pore structure is mesopores with a size of 2-40 nm.

[0048] The conductivity test diagram of the used NCNC is shown in Figure 4 The bulk conductivity calculation formula is: κ = IL / UA, wherein L and A are the thickness (6 mm) and area (11.8 mm 2 ), respectively, and I and U are the current and voltage, respectively; the conductivity of the NCNC is 181 S / m.

[0049] Preparation of Comparative Example 1, Ru / NCNC lithium-oxygen battery

[0050] 50 mg of NCNC was weighed into a beaker, 30 mL of ethylene glycol was added to the beaker and ultrasonic dispersion was performed for 30 min, followed by magnetic stirring for 30 min. 5 g of ruthenium chloride powder was uniformly dissolved in 250 mL of pure water to prepare a ruthenium chloride precursor aqueous solution, and 5 mL thereof was taken and dropped into the above-mentioned ethylene glycol beaker, and magnetic stirring was continued for 60 min. After the magnetic stirrer in the beaker was removed, the sample was placed in a microwave oven (frequency 2450 MHz, power 800 W) for microwave heating for 60 s. Then the sample was filtered and washed with ethanol. The dried sample powder was taken out and placed in a porcelain boat, and the porcelain boat was placed in a quartz tube, and the sample was reduced in a hydrogen atmosphere in a tube furnace, wherein the hydrogen was 10% hydrogen-argon mixed gas, the tube furnace had a heating rate of 10 ℃ / min, the room temperature was 20 ℃, the heating time was 38 min, and after the temperature was raised to 400 ℃, the temperature was kept for 2 h, and then the temperature was naturally cooled to room temperature to obtain the final sample Ru / NCNC, and the Ru loading was 12 wt% as tested by XPS.

[0051] A commercial 60% PTFE aqueous solution was diluted 500 times to be used as a binder. Ru / NCNC and PTFE binder were mixed uniformly at a mass ratio of 95:5. Specifically, 0.3 mg of Ru / NCNC was weighed into an agate mortar, 5 drops of binder were added, and 2 mL of ethanol was added as a dispersant. All the materials were mixed uniformly and the larger particles were ground with an agate rod. All the slurry was uniformly scraped onto a 1 cm diameter Hydroson 330N hydrophilic carbon cloth round piece current collector. The electrode piece was vacuum dried in a vacuum drying oven at a temperature of 70 ℃ and a vacuum degree of 10 Pa or less for 12 h to obtain a Ru / NCNC positive electrode piece, which was transferred to a glove box for use.

[0052] In a glove box, 2.87 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was weighed out as lithium salt in electrolyte and dissolved in 10 mL of dimethyl sulfoxide (DMSO). The electrolyte sample was heated and stirred at 60 °C for 24 h in the glove box to obtain the final electrolyte.

[0053] A coin cell was assembled in the glove box in the order of positive electrode shell with holes, Ru / NCNC positive electrode, glass fiber separator, LiTFSI / DMSO electrolyte, lithium sheet, stainless steel gasket, spring, negative electrode shell. Among them, the battery shell is CR2032 stainless steel battery shell, the positive electrode is a 19-hole stainless steel shell for oxygen to enter the battery, the electrolyte is 200 μL, the thickness of lithium sheet, gasket and spring is 15.6 mm, and the clamping pressure is 80 kg / cm 2 .

[0054] The material performance was tested by using a blue cell test system. The test tank was provided with a 4-way stop valve for controlling the communication between the inside and outside of the tank. Oxygen was continuously supplied into the tank during the test, and the gas flow was preferably 10-20 sccm, and the test temperature was preferably 30 °C. The battery can be cycled more than 25 times at a cutoff capacity of 1000 mAh / g and a current density of 5 A / g, and the rate performance is general.

[0055] Preparation of lithium-oxygen battery of Comparative Example 2, NCNC-Fe(gly)2

[0056] A commercially available 60% PTFE aqueous solution was diluted 500 times to serve as a binder. NCNC and PTFE binder were mixed in a mass ratio of 95:5. Specifically, 0.3 mg of NCNC was weighed out using a microbalance and poured into a marble mortar. Five drops of the binder were added, and 2 mL of ethanol was added as a dispersant. A marble rod was used to mix and grind the materials to break up larger particles. The slurry was evenly scraped onto a 1 cm diameter Hoesch 330N hydrophilic carbon cloth round sheet current collector. The electrode sheet was vacuum dried in a vacuum drying oven at a temperature of 70 °C and a vacuum degree of less than 10 Pa for 12 h to obtain an NCNC positive electrode sheet, which was transferred to a glove box for use.

[0057] In a glove box, 102 mg of ferrous glycinate (Fe(gly)2) and 2.87 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were weighed out as redox mediator and lithium salt in electrolyte, respectively, and dissolved in 10 mL of dimethyl sulfoxide (DMSO) to obtain an electrolyte with a Fe(gly)2 concentration of 50 mM. The electrolyte sample was heated and stirred at 60 °C for 24 h in the glove box to obtain the final electrolyte.

[0058] The button cell was assembled in the same way as in Comparative Example 1 and tested for performance on a Blue Electric battery test system. The cell cycled over 117 times at a cutoff capacity of 1000 mAh / g and a current density of 5 A / g, indicating that the stability of the cell was significantly improved after the addition of the redox mediator.

[0059] Example 1, Preparation of a lithium-oxygen battery with Ru / NCNC-Fe(gly)2

[0060] 50 mg of NCNC was weighed into a beaker, 30 mL of ethylene glycol was added to the beaker, and the mixture was ultrasonically dispersed for 30 min, followed by magnetic stirring for 30 min. 5 g of ruthenium chloride powder was uniformly dissolved in 250 mL of pure water to prepare a ruthenium chloride precursor aqueous solution, and 0.42 mL of the solution was added dropwise into the above-mentioned ethylene glycol beaker, and the mixture was continuously stirred magnetically for 60 min. The magnet was removed from the beaker, and the sample was placed in a microwave oven (frequency 2450 MHz, power 800 W) for microwave heating for 60 s. The sample was then filtered and washed with ethanol. The sample was vacuum dried in a vacuum drying oven at a temperature of 70°C and a vacuum degree of less than 10 Pa for 12 h. The dried sample powder was taken out and placed in a porcelain boat, which was placed in a quartz tube, and the sample was reduced in a hydrogen atmosphere in a tube furnace, wherein the hydrogen was a 10% hydrogen-argon mixture, the tube furnace had a heating rate of 10°C / min, the room temperature was 20°C, the heating time was 38 min, and after the temperature was raised to 400°C, the sample was kept at this temperature for 2 h and then naturally cooled to room temperature to obtain the final sample Ru / NCNC, and the Ru loading was 1 wt% as determined by XPS.

[0061] A commercially available 60% PTFE aqueous solution was diluted 500 times to be used as a binder. Ru / NCNC and PTFE binder were mixed uniformly at a mass ratio of 95:5. Specifically, 0.3 mg of Ru / NCNC was weighed into an agate mortar, 5 drops of the binder were added, and 2 mL of ethanol was added as a dispersant. The materials were mixed uniformly and the larger particles were ground with an agate rod. The slurry was uniformly scraped onto a 1 cm diameter Hydro-son 330N hydrophilic carbon cloth round sheet current collector. The electrode sheet was vacuum dried in a vacuum drying oven at a temperature of 70°C and a vacuum degree of less than 10 Pa for 12 h to obtain a Ru / NCNC positive electrode sheet, which was transferred to a glove box for use.

[0062] In the glove box, 10.2 mg of ferrous glycinate (Fe(gly)2) and 2.87 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were dissolved in 10 mL of dimethyl sulfoxide (DMSO) to obtain an electrolyte with a Fe(gly)2 concentration of 5 mM. The electrolyte sample was heated and stirred at 60°C in the glove box for 24 h to obtain the final electrolyte.

[0063] A button cell was assembled in the same way as in Comparative Example 1 and tested for performance on a Blue Electric battery test system. The cell cycled over 100 times at a cutoff capacity of 1000 mAh / g and a current density of 5 A / g.

[0064] Example 2, Preparation of a Ru / NCNC-Fe(gly)2 lithium-oxygen battery

[0065] A 50 mg sample of NCNC was weighed into a beaker, and 30 mL of ethylene glycol was added to the beaker. The sample was ultrasonically dispersed for 30 min, and then magnetically stirred for 30 min. 5 g of ruthenium chloride powder was dissolved in 250 mL of pure water to prepare a ruthenium chloride precursor aqueous solution. 2.08 mL of the solution was added dropwise to the ethylene glycol beaker, and the sample was magnetically stirred for another 60 min. The magnet was removed from the beaker, and the sample was placed in a microwave oven (frequency 2450 MHz, power 800 W) for microwave heating for 60 s. The sample was then filtered and washed with ethanol. The sample was vacuum dried in a vacuum drying oven at a temperature of 70 °C and a vacuum degree of less than 10 Pa for 12 h. The dried sample powder was taken out and placed in a porcelain boat, which was placed in a quartz tube. The sample was reduced in a hydrogen atmosphere in a tube furnace, with the hydrogen being a 10% hydrogen-argon mixture. The tube furnace was heated at a rate of 10 °C / min, with a room temperature of 20 °C and a heating time of 38 min. After the temperature was raised to 400 °C, the sample was held at this temperature for 2 h, and then naturally cooled to room temperature. The final sample, Ru / NCNC, was obtained, with a ruthenium loading of 5 wt% as determined by XPS.

[0066] A commercially available 60% PTFE aqueous solution was diluted 500 times to serve as a binder. The Ru / NCNC and the PTFE binder were mixed in a mass ratio of 95:5. Specifically, 0.3 mg of Ru / NCNC was weighed into an agate mortar, 5 drops of the binder were added, and 2 mL of ethanol was added as a dispersant. The materials were mixed and ground with an agate rod to break up any large particles. The slurry was uniformly coated onto a 1 cm diameter Hydro-sonic 330N hydrophilic carbon cloth round sheet current collector. The electrode sheet was vacuum dried in a vacuum drying oven at a temperature of 70 °C and a vacuum degree of less than 10 Pa for 12 h to obtain a Ru / NCNC positive electrode sheet, which was transferred to a glove box for use.

[0067] In the glove box, 20.4 mg of ferrous glycinate (Fe(gly)2) and 2.87 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were dissolved in 10 mL of dimethyl sulfoxide (DMSO) to obtain an electrolyte with a Fe(gly)2 concentration of 10 mM, as a redox mediator and a lithium salt in the electrolyte, respectively. The electrolyte sample was heated and stirred at 60 °C in the glove box for 24 h to obtain the final electrolyte.

[0068] A button cell was assembled in the same way as in Comparative Example 1 and tested for performance on a Blue Electric battery test system. The cell cycled over 100 times at a cutoff capacity of 1000 mAh / g and a current density of 5 A / g.

[0069] Example 3, Preparation of a Ru / NCNC-Fe(gly)2 lithium-oxygen battery

[0070] A 50 mg sample of NCNC was weighed into a beaker, and 30 mL of ethylene glycol was added to the beaker. The sample was ultrasonically dispersed for 30 min, and then magnetically stirred for 30 min. 5 g of ruthenium chloride powder was dissolved in 250 mL of pure water to form a ruthenium chloride precursor aqueous solution, and 4.17 mL of the solution was added dropwise to the ethylene glycol beaker. The sample was magnetically stirred for another 60 min. The magnet was removed from the beaker, and the sample was placed in a microwave oven (frequency 2450 MHz, power 800 W) for microwave heating for 60 s. The sample was then filtered and washed with ethanol. The sample was vacuum dried in a vacuum drying oven at a temperature of 70 °C and a vacuum degree of less than 10 Pa for 12 h. The dried sample powder was taken out and placed in a porcelain boat, which was placed in a quartz tube. The sample was reduced in a hydrogen atmosphere in a tube furnace, with the hydrogen being a 10% hydrogen-argon mixture. The tube furnace was heated at a rate of 10 °C / min, with a room temperature of 20 °C and a heating time of 38 min. After the temperature was raised to 400 °C, the sample was held at this temperature for 2 h, and then naturally cooled to room temperature. The final sample, Ru / NCNC, was obtained, with a ruthenium loading of 10 wt% as determined by XPS.

[0071] A commercial 60% PTFE aqueous solution was diluted 500 times to serve as a binder. The Ru / NCNC and the PTFE binder were mixed in a mass ratio of 95:5. Specifically, 0.3 mg of Ru / NCNC was weighed into an agate mortar, 5 drops of the binder were added, and 2 mL of ethanol was added as a dispersant. The materials were mixed and ground with an agate rod to break up any large particles. The slurry was uniformly coated onto a 1 cm diameter Hydro-sonic 330N hydrophilic carbon cloth round current collector. The electrode was vacuum dried in a vacuum drying oven at a temperature of 70 °C and a vacuum degree of less than 10 Pa for 12 h to obtain a Ru / NCNC positive electrode, which was transferred to a glove box for use.

[0072] In the glove box, 40.8 mg of ferrous glycinate (Fe(gly)2) and 2.87 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were dissolved in 10 mL of dimethyl sulfoxide (DMSO) to obtain an electrolyte with a Fe(gly)2 concentration of 20 mM, as a redox mediator and a lithium salt in the electrolyte, respectively. The electrolyte sample was heated and stirred at 60 °C in the glove box for 24 h to obtain a final electrolyte.

[0073] A button cell was assembled in the same way as in Comparative Example 1 and tested for performance on a Blue Electric battery test system. The cell cycled over 100 times at a cutoff capacity of 1000 mAh / g and a current density of 5 A / g.

[0074] Example 4, Preparation of a Ru / NCNC-Fe(gly)2 lithium-oxygen battery

[0075] A 50 mg sample of NCNC was weighed into a beaker, and 30 mL of ethylene glycol was added to the beaker. The sample was then ultrasonically dispersed for 30 min and magnetically stirred for 30 min. A 5 g sample of ruthenium chloride powder was dissolved in 250 mL of pure water to form a ruthenium chloride precursor aqueous solution, and 8.33 mL of the solution was added dropwise to the ethylene glycol beaker. The sample was then magnetically stirred for another 60 min. The magnet was removed from the beaker, and the sample was placed in a microwave oven (frequency 2450 MHz, power 800 W) for microwave heating for 60 s. The sample was then filtered and washed with ethanol. The sample was vacuum dried in a vacuum drying oven at a temperature of 70 °C and a vacuum degree of less than 10 Pa for 12 h. The dried sample powder was then placed in a porcelain boat, which was placed in a quartz tube, and the sample was reduced in a hydrogen atmosphere in a tube furnace. The hydrogen atmosphere was a 10% hydrogen-argon mixture, the tube furnace had a temperature ramping rate of 10 °C / min, the room temperature was 20 °C, and the temperature ramping time was 38 min. After the temperature was raised to 400 °C, the sample was held at this temperature for 2 h, and then naturally cooled to room temperature. The final sample, Ru / NCNC, was obtained, and the Ru loading was 20 wt% as determined by XPS testing.

[0076] A commercially available 60% PTFE aqueous solution was diluted 500 times to serve as a binder. The Ru / NCNC and the PTFE binder were mixed in a mass ratio of 95:5. Specifically, 0.3 mg of Ru / NCNC was weighed into an agate mortar, 5 drops of the binder were added, and 2 mL of ethanol was added as a dispersant. The materials were mixed and ground with an agate rod to break up any large particles. The slurry was uniformly scraped onto a 1 cm diameter Hydro-sonic 330N hydrophilic carbon cloth round sheet current collector. The electrode sheet was vacuum dried in a vacuum drying oven at a temperature of 70 °C and a vacuum degree of less than 10 Pa for 12 h to obtain a Ru / NCNC positive electrode sheet, which was transferred to a glove box for use.

[0077] In the glove box, 102 mg of ferrous glycinate (Fe(gly)2) and 2.87 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were dissolved in 10 mL of dimethyl sulfoxide (DMSO) to obtain an electrolyte with a Fe(gly)2 concentration of 50 mM, in which Fe(gly)2 and LiTFSI served as a redox mediator and a lithium salt, respectively. The electrolyte sample was heated and stirred at 60 °C in the glove box for 24 h to obtain a final electrolyte.

[0078] A button cell was assembled in the same way as in Comparative Example 1 and tested for performance on a Blue Electric battery test system. The cell cycled over 100 times at a cutoff capacity of 1000 mAh / g and a current density of 5 A / g

[0079] Example 5, Preparation of a Ru / NCNC-Fe(gly)2 lithium-oxygen battery

[0080] 50 mg of NCNC was weighed into a beaker, 30 mL of ethylene glycol was added to the beaker and ultrasonically dispersed for 30 min, then magnetically stirred for 30 min. 5 g of ruthenium chloride powder was uniformly dissolved in 250 mL of pure water to prepare a ruthenium chloride precursor aqueous solution, and 5 mL thereof was dropped into the above-mentioned ethylene glycol beaker, and the magnetic stirring was continued for 60 min. After the magnetic stirrer in the beaker was removed, the sample was placed in a microwave oven (frequency 2450 MHz, power 800 W) for microwave heating for 60 s. Then the sample was filtered and washed with ethanol. The dried sample powder was taken out and placed in a porcelain boat, and the porcelain boat was placed in a quartz tube, and the sample was reduced in a hydrogen atmosphere in a tube furnace, wherein the hydrogen was a 10% hydrogen-argon mixture, the tube furnace had a heating rate of 10°C / min, the room temperature was 20°C, the heating time was 38 min, and after the temperature was raised to 400°C, the temperature was kept for 2 h, and then the sample was naturally cooled to room temperature to obtain the final sample Ru / NCNC. The Ru loading was 12 wt% as tested by XPS. The conductivity test results of the Ru / NCNC obtained in this example are shown in Table 1. Figure 4 The conductivity of the Ru / NCNC was 175 S / m.

[0081] A commercially available 60% PTFE aqueous solution was diluted 500 times to be used as a binder. Ru / NCNC and PTFE binder were mixed uniformly at a mass ratio of 95:5. Specifically, 0.3 mg of Ru / NCNC was weighed into an agate mortar, 5 drops of binder were added, and 2 mL of ethanol was added as a dispersant. All the materials were mixed uniformly and the larger particles were ground with an agate rod. All the slurry was uniformly scraped onto a 1 cm diameter Hydro-sonic 330N hydrophilic carbon cloth round piece current collector. The electrode piece was vacuum dried in a vacuum drying oven at a temperature of 70°C and a vacuum degree of 10 Pa or less for 12 h to obtain a Ru / NCNC positive electrode piece, which was transferred to a glove box for use.

[0082] In the glove box, 102 mg of glycine ferrous (Fe(gly)2) and 2.87 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were dissolved in 10 mL of dimethyl sulfoxide (DMSO) to obtain an electrolyte with a Fe(gly)2 concentration of 50 mM, as a redox mediator and lithium salt in the electrolyte, respectively. The electrolyte sample was heated and stirred at 60°C in the glove box for 24 h to obtain the final electrolyte.

[0083] Button cells were assembled using the same method as in Comparative Example 1 and performance tested on a BlueDian battery testing system. The battery cycled for over 150 cycles at a cutoff capacity of 1000 mAh / g and a current density of 5 A / g. The battery achieved a full discharge capacity of 29,089 mAh / g at a current density of 0.5 A / g and 20,159 mAh / g at a current density of 1 A / g. The significantly enhanced cycling stability and discharge capacity at high rates demonstrate the material's high rate capability and cycling stability.

[0084] The relevant parameters of the lithium oxygen batteries obtained in Comparative Examples 1-2 and Examples 1-5 are as follows:

[0085]

[0086] Related tests:

[0087] The low magnification electron microscope image of Ru / NCNC prepared in Example 5 is as follows: Figure 5 As shown in the figure, it can be seen that the metal ruthenium on the surface of the nitrogen-doped carbon nanocage is uniform in size, and metal lattice fringes can be observed. The average particle size of the metal particles is 3.11nm.

[0088] Figure 6 The comparison results of the number of cycles of different positive electrode materials are shown. In the figure, Ru / NCNC is the Ru / NCNC prepared in Example 5. It can be seen from the figure that at a current density of 0.5A / g, commercial activated carbon XC72 can maintain about 50 cycles and the charge and discharge overpotential is always high. This is because its specific surface area and porosity are far inferior to those of carbon cages (CNC), and it lacks catalytic activity. Its pores are easily blocked and deactivated. Nitrogen cages (NCNC) have nearly 30 more cycles than CNC, mainly because the introduction of N changes the geometry and electronic structure of the carbon matrix, constructing more defects or active sites. After NCNC is loaded with Ru, the number of cycles far exceeds that of the unloaded sample, exceeding 200 cycles. Because metallic ruthenium itself has good OER and ORR activity, the high specific surface area and hierarchical pore structure of NCNC are used to facilitate the dispersion, retention and transport of materials, effectively enhancing the cycle stability of the battery.

[0089] Figure 7 The cycling performance of the lithium-oxygen batteries prepared in Comparative Examples 1-2 and Example 5 at high current density is shown. By comparison, it is found that the Ru / NCNC-Fe(gly)2 lithium-oxygen battery prepared in Example 5 can be cycled for more than 150 times at a current density of 5A / g, and its cycling stability at high rates is significantly higher than that of lithium-oxygen batteries with the same Fe(gly)2 concentration in the electrolyte but without Ru loading on the positive electrode carbon-based material, and is also significantly higher than that of lithium-oxygen batteries with the same Ru loading on NCNC but without Fe(gly)2 added to the electrolyte.

[0090] Figure 8 The cycle number of the lithium-oxygen battery prepared by controlling the Fe(gly)2 concentration in the electrolyte to be 50 mM and only changing the Ru loading on the NCNC positive electrode material in the preparation of Ru / NCNC-Fe(gly)2 lithium-oxygen battery. As can be seen from the figure, when the Ru loading is 12.97 wt%, the cycle number reaches the highest 203 cycles (cut-off capacity 1000 mAh / g, current density 0.5 A / g, electrolyte 1 M LiTFSI / DMSO). As can be seen from the figure, the effect of Ru loading on the positive electrode carbon cage material on the cycle number is not simply positively correlated. In the low loading stage, the cycle number of the lithium-oxygen battery generally increases with the increase of Ru loading, with small fluctuations, but the overall fluctuation is not large. The cycle number reaches the highest when the Ru loading is 12.97 wt%, but as the Ru loading further increases, the cycle number of the lithium-oxygen battery will decrease significantly, which means that the more Ru loading is not necessarily better. As a preferred, the Ru loading is controlled at 12-14 wt%.

[0091] Figure 9 The cycle voltage of the Ru / NCNC-Fe(gly)2 lithium-oxygen battery prepared in Example 5 (left) and the NCNC lithium-oxygen battery (right) (the NCNC lithium-oxygen battery refers to a lithium-oxygen battery prepared by using only NCNC material as the positive electrode composite catalytic material and without adding Fe(gly)2 in the electrolyte. Except for this, the preparation method and process of the battery are exactly the same as in Example 5, and the same below) before 100 cycles. The charge-discharge platform of Ru / NCNC-Fe(gly)2 is at least closer to the theoretical equilibrium voltage of 2.96 V before 100 cycles compared with NCNC, that is, it has a lower charge-discharge overpotential and can maintain a longer cycle number. In addition to the OER / ORR catalytic activity brought by the Ru loading, the catalysis and oxygen loading function of Fe(gly)2 increase the cycle life of the battery.

[0092] Figure 10 The EIS graph of the Ru / NCNC-Fe(gly)2 lithium-oxygen battery prepared in Example 5 and NCNC before 50 cycles. As can be seen from the figure, with the increase of cycle number, the charge transfer impedance of Ru / NCNC-Fe(gly)2 slowly increases and is always smaller than that of NCNC positive electrode, while the transfer impedance and internal resistance of NCNC positive electrode increase, proving that Li2O2 is seriously accumulated on the positive electrode. The Ru / NCNC-Fe(gly)2 battery has a higher degree of Li2O2 decomposition during charging, and the battery has good reversibility, which is the main reason for its high cycle stability.

[0093] Figure 11The SEM images of the positive electrode materials of the Ru / NCNC-Fe(gly)2 lithium-oxygen battery and the NCNC lithium-oxygen battery prepared in Example 5 after 50 cycles can be seen from the left small images, the Ru / NCNC-Fe(gly)2 surface particles are smaller and more dispersed. Small and dispersed particles mean that the catalytic decomposition performance of Ru on Li2O2 and the dispersion nucleation and ORR / OER dual catalytic performance of Fe(gly)2 on Li2O2 are effectively exerted. The degree of Li2O2 decomposition is higher, the reversibility is better, and the battery stability is higher. Looking at the right small images, the NCNC positive electrode surface attachments are larger and connected into blocks, which is not conducive to material and charge transfer, and the performance decays faster as the cycle progresses.

[0094] Figure 12 The XRD images of the positive electrode materials of the Ru / NCNC-Fe(gly)2 lithium-oxygen battery and the NCNC prepared in Example 5 after 50 cycles, the Li2O2 peak intensity of the NCNC battery after cycling is higher, indicating that the NCNC positive electrode has more Li2O2 or the Li2O2 particles are larger, and the accumulation of too much "dead" Li2O2 leads to an increase in overpotential, reducing reversibility.

[0095] The above shows and describes the basic principles, main features and advantages of the present application. However, the above description is only a specific embodiment of the present application, and the technical features of the present application are not limited to this. Any person skilled in the art who does not deviate from the technical solution of the present application should be covered in the patent range of the present application.

Claims

1. A lithium-oxygen battery with high rate capability, which is composed of a porous positive shell, a positive electrode sheet, a separator, an electrolyte, a lithium sheet, a gasket, a spring, and a negative shell, wherein the positive electrode sheet is prepared by coating a slurry of a positive catalytic composite material mixed with a binder on a current collector, and characterized in that: the positive catalytic composite material is composed of a carbon-based nanocage carrier loaded with ruthenium, and the loading amount of ruthenium is 12-14 wt%; the electrolyte is added with a soluble redox medium Fe(gly)2, and the concentration of Fe(gly)2 in the electrolyte is 30-50 mM; the lithium-oxygen battery can be cycled for more than 150 cycles at a cutoff capacity of 1000 mAh / g and a current density of 5 A / g. The carbon-based nanocage is a carbon nanocage or a nitrogen-doped carbon nanocage. The preparation process is as follows: (1) Mix the carbon-based nanocage and ethylene glycol uniformly in a container; 2. A lithium-oxygen battery with high rate capability as claimed in claim 1, wherein, (2) Add the precursor solution of ruthenium into the container and stir to mix; 3. A method for preparing a lithium-oxygen battery with high rate capability, characterized in that, (3) Microwave heating, and post-treatment to obtain a dry sample powder; (4) Heat reduction of the sample powder under an inert atmosphere to obtain a ruthenium-loaded carbon-based nanocage; (5) Mix the ruthenium-loaded carbon-based nanocage with a binder, coat it on a current collector, and vacuum dry to obtain a positive electrode sheet; (6) Weigh Fe(gly)2 and LiTFSI, dissolve them in DMSO, heat and mix to prepare an electrolyte, and the concentration of Fe(gly)2 in the electrolyte is 30-50 mM; (7) Assemble a coin cell battery in a glove box. In step (1), the carbon-based nanocage is a carbon nanocage or a nitrogen-doped carbon nanocage, the mass of the carbon-based nanocage is 50-100 mg, and the volume of ethylene glycol is 30-50 mL. In step (2), the precursor solution of ruthenium is prepared by dissolving ruthenium chloride in water, and the concentration of ruthenium chloride in the precursor solution is 20 g / L. In step (3), the microwave frequency is 2450 MHz, the microwave power is 800 W, and the microwave heating time is 30-60 s.

4. The method of claim 3, wherein the lithium-oxygen battery has a high rate capability. In step (4), the heating rate of the heat reduction process is 5-10 ℃ / min, the heat treatment temperature is 200-400 ℃, and the time for maintaining the heat treatment temperature is 120-240 min.

5. The method of claim 3, wherein the lithium-oxygen battery has a high rate capability. In step (6), the concentration of LiTFSI is 1 M, the heating temperature is 40-60 ℃, and the heating time is 12-24 h.

6. The method of claim 3, wherein the lithium-oxygen battery has a high rate capability. ​ 7. The method of claim 3, wherein the lithium-oxygen battery has a high rate capability. ​ 8. The method of claim 3, wherein the lithium-oxygen battery has a high rate capability. ​

Images