A graphene-coated magnesium oxide material and derivatives and gas cells thereof

Abstract

The application provides a graphene-coated magnesium oxide material and derivatives and gas batteries, and belongs to metal-gas batteries, mainly including a graphene-coated magnesium oxide material MgO@C and a graphene-coated magnesium oxide and metal composite material MgO / M@C, and a negative electrode or negative electrode-free gas battery and / or a positive electrode-free gas battery prepared from the two materials; and a graphene nanocage material or a graphene and metal composite nanocage structure catalyst material M@C prepared from the two materials. The application directly uses MgO@C or MgO / M@C as a positive electrode material of a Mg-O2 battery or a Mg-CO2 battery, and a magnesium metal can not be used as a negative electrode; and when the MgO@C or MgO / M@C material is used as a positive electrode material of a Mg-O2 battery, oxygen in the environment is not even needed.

Description

Technical Field

[0001] This invention relates to metal-gas batteries, and more particularly to a graphene-coated magnesium oxide material MgO@C and a graphene-coated magnesium oxide and metal composite material MgO / M@C, as well as negative electrode-free gas batteries and / or positive electrode-free gas batteries prepared from these two materials; and graphene nanocage materials or graphene and metal composite nanocage structure catalyst materials M@C prepared from these two materials. Background Technology

[0002] Environmental pollution and energy shortages have severely hampered the development of human society. As a highly efficient electrochemical energy storage technology, secondary batteries are currently the most important research area for the development of new energy. High energy density, long cycle life, high safety, and low cost are the top priorities in the development of secondary batteries.

[0003] Metal-gas batteries, including metal-oxygen batteries and metal-carbon dioxide batteries, are novel rechargeable batteries proposed in recent years and have attracted much attention due to their extremely high energy density. However, the development of metal-gas batteries mainly faces three problems:

[0004] The first problem is that the slow electrochemical reaction kinetics of metal-gas batteries lead to excessively high overpotentials and severe capacity decay, requiring significant improvements in both actual capacity and cycle life. To enhance the energy density and long-term cycle stability of metal-gas batteries, researchers often employ catalytically active materials as the cathode, primarily including transition metal catalysts, noble metal catalysts, carbon, carbon nanotubes, and their composites, such as Ru / super P, Mo2C / CNTs, Ni / N-doped carbon, Cu / N-doped carbon, NiO-CNTs, and Ir nanosheets / carbon nanofibers. These materials, as cathode catalysts in metal-gas batteries, can improve battery cycle performance and reduce overpotential. However, the scarcity, high cost, and poor durability of these catalytic cathode materials hinder their practical application.

[0005] The second problem is that current metal-gas batteries do not contain active ions in their positive electrode, so only metal negative electrodes can be used. However, metal negative electrodes have high activity but poor safety performance. The third problem is that the active material of the positive electrode in gas batteries needs to be circulated with a gas, such as CO2 or O2, which is inconvenient to carry and not conducive to large-scale application.

[0006] Therefore, there is an urgent need to explore new electrochemically and chemically stable catalytic cathode materials that possess both high energy density and high cycle stability. For the commercialization of gas batteries, cathode catalyst materials need to be simple to prepare and low in cost. Furthermore, the development of metal-gas batteries without metal anodes or even without gas cathodes would open up more application possibilities for such batteries. Summary of the Invention

[0007] To address the aforementioned problems in the existing technology, this invention provides a graphene-coated magnesium oxide material, its derivatives, and a gas battery.

[0008] The technical solution of the present invention is as follows:

[0009] First, the present invention provides a graphene-coated magnesium oxide material MgO@C, wherein the preparation method of the MgO@C material includes any one of the following two methods:

[0010] (1) Ignite magnesium strips or magnesium powder in a carbon dioxide atmosphere, collect the ignition products and pass them through a 50-800 mesh sieve to remove unreacted metallic magnesium, and obtain graphene-coated magnesium oxide material MgO@C.

[0011] (2) Place magnesium strips or magnesium powder in a tube furnace, pass a carbon dioxide atmosphere, and heat to 400-1000℃. Different temperatures can yield graphene-coated magnesium oxide materials MgO@C with different particle sizes.

[0012] Second, this invention provides a graphene-coated magnesium oxide and metal composite material MgO / M@C, wherein the preparation method of the MgO / M@C material is as follows:

[0013] Magnesium strips or magnesium powder are mixed with other metal oxides M x O y They are ignited together in carbon dioxide or treated at high temperatures of 400-1000℃ to obtain a graphene-coated magnesium oxide and metal composite material MgO / M@C.

[0014] The magnesium strip or magnesium powder and M x O y The mass ratio is 1-10000:1.

[0015] Preferably, the metal oxide M x O y Including but not limited to CoO, Co3O4, NiO, MoO3, MoO2, MnO2, or Mn3O4.

[0016] Third, the present invention also provides gas batteries prepared from the two materials mentioned above, that is, when MgO@C material or MgO / M@C material is used as the positive electrode catalyst material of Mg-O2 battery or Mg-CO2 battery, magnesium metal can be used as the negative electrode; or other materials can be used to replace magnesium metal as the negative electrode.

[0017] Furthermore, when MgO@C or MgO / M@C is used as the positive electrode catalyst material for Mg-O2 or Mg-CO2 batteries, the negative electrode can be any conductor instead of magnesium metal, such as iron sheet, copper sheet, aluminum sheet, or tin sheet.

[0018] Preferably, when the gas battery is a Mg-O2 battery, the positive electrode of the battery may or may not use oxygen or other active gases.

[0019] Furthermore, the positive electrode of the Mg-O2 battery or Mg-CO2 battery does not require an additional catalyst.

[0020] Fourth, the present invention provides a graphene nanocage material or a graphene-metal composite nanocage structure catalyst material prepared from the two materials mentioned above, which directly electrochemically decomposes MgO@C material or MgO / M@C material to remove MgO, respectively obtaining graphene nanocage material or graphene-metal composite nanocage structure catalyst material M@C.

[0021] The direct electrochemical decomposition method is as follows:

[0022] The powder of MgO@C material or MgO / M@C material is pressed into a film, and an electric current is passed through both sides of the film to electrochemically decompose and remove MgO; the film is then disassembled to obtain graphene nanocage material or graphene and metal composite nanocage structure catalyst material M@C.

[0023] The electrochemical decomposition parameters are: current range 0.1uA-10A, and energizing time 0.1-1000 hours.

[0024] Preferably, the specific steps of the direct electrochemical decomposition are as follows:

[0025] (1) The powder of MgO@C material or MgO / M@C material is uniformly filled into the mold, and the powder is pressed into a film under a pressure of 0.1-300MPa using a tablet press.

[0026] (2) Take out the membrane as the positive electrode, and use a solid electrolyte membrane and a counter electrode as the negative electrode. Pass a current of 0.1uA-10A for 0.1-1000 hours to decompose MgO and obtain graphene nanocage material or graphene and metal composite nanocage structure catalyst material M@C.

[0027] Furthermore, in the direct electrochemical decomposition preparation of graphene nanocage materials, the solid electrolyte membrane can be, but is not limited to, MgZr4(PO4)6, and the counter electrode can be, but is not limited to, graphite, silicon carbon, silicon, metallic magnesium, etc. When energized, the positive and negative electrodes can be placed in a battery mold, and the battery mold can be, but is not limited to, the Swalogek battery mold.

[0028] Fifth, the present invention also provides applications of the two materials prepared by direct electrochemical decomposition, namely, the graphene nanocage material or M@C as the positive electrode material of metal-gas batteries;

[0029] The metal-gas batteries include, but are not limited to, Li-O2, Na-O2, K-O2, Al-O2, Zn-O2, Mg-O2, Ca-O2 and Li-CO2, Na-CO2, K-CO2, Al-CO2, Zn-CO2, Mg-CO2, Ca-CO2.

[0030] Sixth, this invention also provides a metal-gas battery positive electrode sheet prepared using MgO@C material or MgO / M@C material to contain graphene nanocage material or graphene and metal composite nanocage structure catalytic material. The preparation method is as follows:

[0031] First, prepare MgO@C material or MgO / M@C material into electrode sheets according to the preparation method of gas battery positive electrode sheet, and then perform in-situ electrochemical decomposition to remove MgO, respectively to obtain metal-gas battery positive electrode sheets containing graphene nanocage material or graphene and metal composite nanocage structure catalyst material.

[0032] The in-situ electrochemical decomposition refers to assembling the electrode sheets into a gas battery, energizing the positive and negative electrodes, with the following energizing parameters: current range 0.1uA-100mA, energizing time 0.1-1000 hours.

[0033] Preferably, the specific preparation steps of the above method are as follows:

[0034] (1) Prepare a mixed material by mixing MgO@C material or MgO / M@C material and conductive material at a mass ratio of 0.1-100:1;

[0035] (2) Mix the above-mentioned mixed material with a polyvinylidene fluoride solution with a concentration of 0.01-15wt% at a mass ratio of 0.01-100:1, and continue to add solvent until the slurry has a suitable consistency;

[0036] (3) Then grind it thoroughly in a mortar until uniform, and then coat it evenly on the pre-cut breathable conductor substrate. Vacuum dry at 40-180℃ for 1-100h to obtain the positive electrode material.

[0037] (4) Assemble the obtained positive electrode material into a gas battery, wherein the negative electrode includes, but is not limited to, lithium metal, graphite, silicon carbide, silicon, sodium metal or magnesium metal.

[0038] (5) Charge the MgO to decompose it, wherein the current range is 0.1uA-100mA and the charging time is 0.1-1000 hours, thereby obtaining a metal-gas battery positive electrode containing graphene nanocage material or a composite nanocage structure catalyst material of graphene and metal.

[0039] Furthermore, in the preparation of the positive electrode sheet of the metal-gas battery, the conductive materials include, but are not limited to, carbon black and Super P; the solvent of the polyvinylidene fluoride solution includes, but is not limited to, N-methylpyrrolidone and water; and the gas-permeable conductors include, but are not limited to, nickel foam and carbon paper.

[0040] The beneficial technical effects of this invention are as follows:

[0041] 1. In the process of preparing MgO@C materials, this invention may add other metal oxides M x O y For example, Co3O4, thus preparing MgO / M@C materials with catalytic properties, such as Co / MgO@C.

[0042] 2. This invention directly uses MgO@C or MgO / M@C as the positive electrode material for Mg-O2 or Mg-CO2 batteries. The negative electrode does not require magnesium metal (i.e., a negative electrode-free battery), because MgO produces Mg during charging. Furthermore, when MgO@C or MgO / M@C is used as the positive electrode material for Mg-O2 batteries, the environment does not even require oxygen (i.e., it can simultaneously be without positive electrode active gas, negative electrode, and additional catalyst), because MgO produces oxygen during charging.

[0043] 3. This invention employs an electrochemical method to remove MgO from MgO@C material, yielding graphene nanocage material. This electrochemical method can either charge the MgO@C material to decompose MgO into Mg and oxygen, leaving behind graphene nanocages; or it can directly electrolyze it in situ within a battery. The graphene nanocage material obtained by this method possesses highly active sites (I... d / I g =1.0-2.5), which can be used as the positive electrode material for different types of gas batteries, and even other battery electrode materials.

[0044] Similarly, electrochemical decomposition of MgO in MgO / M@C can yield graphene nanocage structured materials catalyzed by M metal with highly active sites.

[0045] 4. The graphene nanocage structure prepared by this invention has a larger specific surface area and more reactive sites, thus endowing the gas battery with good electrochemical performance; on the other hand, the graphene nanocage structure can enhance the conductivity of the catalyst material, which is conducive to gas diffusion, thus endowing the gas battery with good cycle life. Attached Figure Description

[0046] Figure 1 The X-ray diffraction pattern of the graphene-coated magnesium oxide material prepared in Example 1 is shown below.

[0047] Figure 2 This is a SEM image of the graphene-coated magnesium oxide material prepared in Example 1;

[0048] Figure 3 The X-ray diffraction pattern of MgO / Co@C prepared in Example 3 is shown below.

[0049] Figure 4 TEM image of MgO / Co@C prepared in Example 3;

[0050] Figure 5 Charge-discharge cycle performance was tested for Example 5;

[0051] Figure 6 Charge-discharge cycle performance was tested for Example 13;

[0052] Figure 7 This is a TEM image of the graphene nanocage material prepared in Example 15;

[0053] Figure 8 The image shows a TEM image of the graphene-Co composite nanocage structure catalyst material Co@C prepared in Example 16. Detailed Implementation

[0054] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0055] Example 1: Preparation of graphene-coated magnesium oxide material MgO@C by combustion method

[0056] A magnesium strip (0.5g) with its surface oxide layer removed was placed in a glass bottle filled with a carbon dioxide atmosphere (99% concentration) and ignited using an extended igniter. The combustion time was approximately 2 minutes. The ignition product was collected and passed through a 200-mesh sieve to remove unreacted metallic magnesium, yielding graphene-coated magnesium oxide material MgO@C.

[0057] The X-ray diffraction pattern of the prepared MgO@C is shown below. Figure 1 As shown in the figure, the diffraction peaks indicate that the product is graphene-coated magnesium oxide, and unreacted metallic magnesium has been completely removed. The SEM image of MgO@C is shown below. Figure 2 As shown in the figure, the product obtained is magnesium oxide coated with graphene.

[0058] Example 2: Preparation of graphene-coated magnesium oxide material MgO@C by high-temperature treatment method

[0059] Prepare 0.5 g of metallic magnesium powder and heat it in a 99% carbon dioxide atmosphere at a rate of 5 °C / min until it reaches 750 °C and holds for 8 hours. Then, under the protection of a carbon dioxide atmosphere, allow it to cool naturally to room temperature. Remove the powder and grind it in a mortar to a mesh size below 200 to obtain graphene-coated magnesium oxide (MgO@C). The particle size of the material obtained at this temperature is approximately 50 nm.

[0060] Example 3: Preparation of graphene-coated magnesium oxide and metal composite material MgO / M@C by combustion method

[0061] A mixture of magnesium powder (0.54 g) and Co3O4 (0.30 g) (mass ratio of magnesium powder to Co3O4 2.16:1.20) was ignited in a 99% carbon dioxide atmosphere for approximately 2 minutes. The ignition product was collected and passed through a 200-mesh sieve to remove unreacted metallic magnesium, thus preparing a graphene-coated magnesium oxide / cobalt composite material (MgO / Co@C). The XRD and TEM images of the prepared MgO / Co@C are shown below. Figure 3 , 4 As shown.

[0062] Example 4: Preparation of graphene-coated magnesium oxide and metal composite material MgO / M@C by high-temperature treatment method

[0063] A mixture of 3.3 g magnesium powder and 0.30 g Co3O4 (mass ratio of magnesium powder to Co3O4:1) was prepared and heated in a 99% carbon dioxide atmosphere at a heating rate of 5 °C / min until it reached 750 °C and held for 8 h. Then, it was allowed to cool naturally to room temperature under a carbon dioxide atmosphere. The mixture was then removed and ground in a mortar to a fineness below 200 mesh to obtain a graphene-coated magnesium oxide / cobalt composite material (MgO / Co@C).

[0064] Example 5: Preparation of a magnesium-free Mg-O2 battery with an anode from MgO@C obtained in Example 1

[0065] (1) 5 mg of MgO@C material prepared in Example 1 and 5 mg of conductive carbon black Super P were mixed to form a mixed material.

[0066] Mix 10 mg of the above-mentioned mixed material with 50 mg of a 5 wt% polyvinylidene fluoride solution (the solvent of the polyvinylidene fluoride solution is N-methylpyrrolidone), continue to add N-methylpyrrolidone solvent until the catalyst slurry has a suitable consistency, and then grind it thoroughly in an agate mortar until uniform.

[0067] The material was evenly coated onto a pre-cut nickel foam substrate with a thickness of 3 mm and a diameter of 12 mm, and then vacuum dried at 100°C for 12 hours to obtain the cathode material.

[0068] The MgO@C and conductive carbon black Super P are loaded onto sheet-like nickel foam to form a porous conductive network structure with a pore size of 0.23 mm. The open area of ​​the overall electrode accounts for 98% of the total area.

[0069] The loading of MgO@C was approximately 0.3 mg / cm³. 2 .

[0070] (2) Assemble the batteries in a glove box filled with argon atmosphere, using CR2032 button cell battery cases with a 2mm pore diameter and a pore density of 5-8 pores / cm². 2 The negative electrode is a tin sheet, the positive electrode is the positive electrode material prepared in step (1), the electrolyte is 0.5M magnesium bis(trifluoromethanesulfonyl)imide dissolved in a mixed solution of EMIMBF4 and triethylene glycol dimethyl ether (volume ratio 1:9), and the separator is a glass fiber separator.

[0071] The positive electrode material is placed on one side of the opening in the battery case, and the tin sheet is placed on the other side of the battery case. The components are assembled in the same order as a normal button cell battery. The button cell battery sealing machine presses the components together to complete the battery assembly.

[0072] (3) Place the assembled battery in a 1000ml homemade sealed container, fill it with oxygen, and seal it. Add 40µL of deionized water to the sealed container. Perform a charge-discharge test at a current density of 400mA / g and a cutoff specific capacity of 1000mAh / g. The results of the first charge-discharge cycle are as follows: Figure 5 As shown.

[0073] Comparative Example 1:

[0074] It is basically the same as Example 5, except that the positive electrode uses commercial graphene.

[0075] The test results show that the overvoltage of charge and discharge is 3.5V, which is much higher than that of the MgO@C we prepared. Therefore, it is shown that the MgO@C prepared by this invention can improve the electrochemical performance of the system.

[0076] Example 6: A Mg-O2 battery with a magnesium anode was prepared using MgO@C obtained in Example 1.

[0077] It is basically the same as Example 5, except that the negative electrode is made of magnesium.

[0078] Test results show that the battery's first-cycle overvoltage is only 0.60V. Compared to commercial graphene as a cathode material, which cycles for 30 hours, the MgO@C material of this invention can cycle for 200 hours under the same test conditions.

[0079] Example 7: Preparation of a magnesium-free Mg-CO2 battery with an anode from MgO@C obtained in Example 2

[0080] The experiment was basically the same as in Example 5, except that 5 mg of the MgO@C material prepared in Example 2 and 5 mg of conductive carbon black Super P were mixed together; and the battery test atmosphere was changed from oxygen to carbon dioxide.

[0081] Under test conditions of 400 mA / g current density and 1000 mAh / g cutoff specific capacity, the battery's first-cycle overvoltage is approximately 3V. Compared to commercial graphene as a cathode material, which cycles for 10 hours, the MgO@C material of this invention can cycle for 40 hours under the same test conditions.

[0082] Example 8: Mg-CO2 battery with magnesium anode prepared from MgO@C obtained in Example 2

[0083] It is basically the same as Example 7, except that the negative electrode is made of magnesium.

[0084] Test results show that the battery's first-cycle overvoltage is about 3V. Compared to commercial graphene as a cathode material, which cycles for 20 hours, the MgO@C material of this invention can cycle for more than 150 hours under the same test conditions.

[0085] Example 9: Preparation of a magnesium-free Mg-CO2 battery with an anode from the MgO / Co@C obtained in Example 3

[0086] It is basically the same as Example 7, except that 5 mg of the MgO / Co@C material prepared in Example 3 and 5 mg of conductive carbon black Super P are formulated into a mixed material.

[0087] Under test conditions of 400 mA / g current density and 1000 mAh / g cutoff specific capacity, the battery's first-cycle overvoltage is approximately 2.5V.

[0088] Example 10: Mg-CO2 battery with magnesium anode prepared from MgO / Co@C obtained in Example 3

[0089] It is basically the same as Example 9, except that the negative electrode is made of magnesium.

[0090] Test results show that the battery overvoltage is about 2V in the first cycle and the cycle time exceeds 180 hours.

[0091] Example 11: Preparation of a magnesium-free Mg-O2 battery with an anode from the MgO / Co@C obtained in Example 4

[0092] It is basically the same as Example 5, except that 5 mg of the MgO / Co@C material prepared in Example 4 and 5 mg of conductive carbon black Super P are mixed together.

[0093] Under test conditions of 400 mA / g current density and 1000 mAh / g cutoff specific capacity, the battery's first-cycle overvoltage is approximately 1.5V.

[0094] Example 12: Mg-O2 battery with magnesium anode prepared from MgO / Co@C obtained in Example 4

[0095] It is basically the same as Example 11, except that the negative electrode is made of magnesium.

[0096] Test results show that the battery's first-cycle overvoltage is approximately 0.6V, and it can cycle for over 250 hours.

[0097] Example 13: The Mg-O2 battery prepared from MgO@C obtained in Example 1 is basically the same as that in Example 5, except that the battery test atmosphere is changed from oxygen to argon.

[0098] Test results showed that the overvoltage during battery charging was the same as in oxygen, and the battery could be circulated in argon for 10 hours.

[0099] Example 14: Preparation of an oxygen-free, negative electrode-free Mg-O2 battery from the MgO / Co@C obtained in Example 3

[0100] The process is basically the same as in Example 13, except that 5 mg of the MgO / Co@C material prepared in Example 3 and 5 mg of conductive carbon black Super P are mixed together to form a composite material.

[0101] Test results showed that the overvoltage during battery charging was similar to that in oxygen, and the battery could be cycled in argon for 20 hours.

[0102] Example 15: Preparation of graphene nanocage materials from MgO@C obtained in Example 1

[0103] The MgO@C powder obtained in Example 1 was uniformly filled into a mold. The powder was first pressed into a film using a tablet press under a pressure of 100 MPa. The film was then removed and, along with a solid electrolyte membrane and a graphite counter electrode, was placed into a battery mold (Swalogek battery). A current of 100 mA was applied, and the charging time was 10 hours to decompose the MgO, yielding a graphene nanocage structure catalyst material. Its TEM image is shown below. Figure 7 As shown.

[0104] Example 16: Preparation of Co-catalyzed graphene nanocages (i.e., Co@C, a composite nanocage structure catalyst material of graphene and Co) from the MgO / Co@C obtained in Example 4.

[0105] The MgO / M@C powder obtained in Example 4 was uniformly filled into a mold. The powder was first pressed into a film using a tablet press under a pressure of 100 MPa. The film was then removed and, along with a solid electrolyte membrane and a graphite counter electrode, was placed into a battery mold (Swalogek battery). A current of 100 mA was applied, and the charging time was 10 hours. This decomposed the MgO, yielding the Co@C material. Its TEM image is shown below. Figure 8 As shown.

[0106] Example 17: Preparation of a magnesium-oxygen battery from the graphene nanocage material obtained in Example 15

[0107] (1) 5 mg of graphene nanocage material prepared in Example 15 and 5 mg of conductive carbon black Super P were mixed to form a mixed material.

[0108] Mix 10 mg of the above-mentioned mixed material with 50 mg of a 5 wt% polyvinylidene fluoride solution (the solvent of the polyvinylidene fluoride solution is N-methylpyrrolidone), continue to add N-methylpyrrolidone solvent until the catalyst slurry has a suitable consistency, and then grind it thoroughly in an agate mortar until uniform.

[0109] The material was evenly coated onto a pre-cut nickel foam substrate with a thickness of 3 mm and a diameter of 12 mm, and then vacuum dried at 100°C for 12 hours to obtain the cathode material.

[0110] The graphene nanocage catalyst and conductive carbon black Super P are loaded on sheet-like nickel foam to form a porous conductive network structure with a pore size of 0.23 mm. The open area of ​​the overall electrode accounts for 98% of the total area.

[0111] The graphene nanocage catalyst was loaded with approximately 0.3 mg / cm³. 2 ;

[0112] (2) Assemble the magnesium-oxygen battery in a glove box filled with argon atmosphere, using a CR2032 button cell with a 2mm pore diameter and a pore density of 5-8 pores / cm². 2 The negative electrode is a magnesium sheet, the positive electrode is the positive electrode material prepared in step (1), the electrolyte is 0.5M bis(trifluoromethanesulfonyl)imide magnesium dissolved in a mixed solution of EMIMBF4 and triethylene glycol dimethyl ether (volume ratio 1:9), and the separator is a glass fiber separator.

[0113] The positive electrode material is placed on one side of the opening in the battery casing, and the magnesium sheet is placed on the other side of the battery casing. The components are assembled in the same order as a normal button cell battery. The components are then pressed together by a button cell battery sealing machine to complete the assembly of the magnesium-oxygen battery.

[0114] (3) Place the assembled magnesium-oxygen battery in a 1000ml homemade sealed container, fill it with dry oxygen, and seal it. Perform charge-discharge cycle performance tests at a current density of 400mA / g and a cutoff specific capacity of 1000mAh / g. The test results are as follows: Figure 6 As shown.

[0115] Comparative Example 2: Control group without graphene nanocages

[0116] The method is essentially the same as in Example 17, except that 10 mg of conductive carbon black Super P is mixed with 50 mg of a 5 wt% polyvinylidene fluoride solution. Because conductive carbon black Super P does not possess the catalytic properties of graphene nanocages, the battery has a high overvoltage of approximately 4.0 V, resulting in poor cycle performance and only being able to cycle stably for one cycle.

[0117] Example 18: Preparation of lithium-oxygen batteries using the graphene-Co composite nanocage structure catalyst material Co@C obtained in Example 16.

[0118] Similar to Example 17, the difference is that "5 mg of graphene nanocage material prepared in Example 15" in Example 17 is replaced with 5 mg of Co@C material prepared in Example 16, and "sealed with dry oxygen" is replaced with 40 μL of deionized water added to the bottle. In addition, lithium metal is used as the negative electrode.

[0119] Due to the good catalytic performance of Co@C material, under test conditions of 400mA / g current density and 1000mAh / g cutoff specific capacity, the battery overvoltage is only 0.80V, which is lower than the overvoltage of most reported noble metals, and it can cycle stably for 400 hours.

[0120] Example 19: Preparation of a metal-gas battery positive electrode sheet containing a graphene nanocage structure using MgO@C obtained in Example 1.

[0121] (1) 5 mg of MgO@C material prepared in Example 1 and 5 mg of conductive carbon black Super P were mixed to form a mixed material.

[0122] (2) Mix 10 mg of the above-mentioned mixed material with 50 mg of polyvinylidene fluoride solution with a concentration of 5 wt% (the solvent of polyvinylidene fluoride solution is N-methylpyrrolidone), and continue to add N-methylpyrrolidone solvent until the catalyst slurry is of suitable consistency.

[0123] (3) Then grind it thoroughly in an agate mortar until uniform, and coat it evenly on a pre-cut nickel foam substrate with a thickness of 3 mm and a diameter of 12 mm. Dry it under vacuum at 100°C for 12 h to obtain the positive electrode material.

[0124] The graphene nanocage catalyst and conductive carbon black Super P are loaded on sheet-like nickel foam to form a porous conductive network structure with a pore size of 0.23 mm. The open area of ​​the overall electrode accounts for 98% of the total area.

[0125] The loading of MgO@C was approximately 0.3 mg / cm³. 2 .

[0126] (4) Assemble the magnesium-oxygen battery in a glove box filled with argon atmosphere, using a CR2032 button cell with a 2mm pore diameter and a pore density of 5-8 pores / cm². 2 The negative electrode is a magnesium sheet, the positive electrode is the positive electrode material prepared in step (3), the electrolyte is 0.5M bis(trifluoromethanesulfonyl)imide magnesium dissolved in a mixed solution of EMIMBF4 and triethylene glycol dimethyl ether (volume ratio 1:9), and the separator is a glass fiber separator.

[0127] The positive electrode material is placed on one side of the opening in the battery casing, and the magnesium sheet is placed on the other side of the battery casing. The components are assembled in the same order as a normal button cell battery. The components are then pressed together by a button cell battery sealing machine to complete the assembly of the magnesium-oxygen battery.

[0128] (5) First, charge the battery at a current density of 400 mA / g for 10 hours to decompose magnesium oxide and obtain a positive electrode containing graphene nanocage material. The battery containing the graphene nanocage material positive electrode was subjected to charge-discharge cycle performance tests at a current density of 400 mA / g and a cutoff specific capacity of 1000 mAh / g. The test results showed that the overvoltage was approximately 3.0V.

[0129] Example 20: Preparation of a metal-gas battery cathode material containing a composite nanocage structure catalytic material of graphene and Co using the MgO / Co@C material obtained in Example 3.

[0130] (1) 5 mg of the MgO / Co@C material prepared in Example 3 and 5 mg of conductive carbon black Super P were mixed to form a mixed material.

[0131] (2) Mix 10 mg of the above-mentioned mixed material with 50 mg of polyvinylidene fluoride solution with a concentration of 5 wt% (the solvent of polyvinylidene fluoride solution is N-methylpyrrolidone), and continue to add N-methylpyrrolidone solvent until the catalyst slurry is of suitable consistency.

[0132] (3) Then grind it thoroughly in an agate mortar until uniform, and coat it evenly on a pre-cut nickel foam substrate with a thickness of 3 mm and a diameter of 12 mm. Dry it under vacuum at 100°C for 12 h to obtain the positive electrode material.

[0133] The graphene nanocage catalyst and conductive carbon black Super P are loaded on sheet-like nickel foam to form a porous conductive network structure with a pore size of 0.23 mm. The open area of ​​the overall electrode accounts for 98% of the total area.

[0134] The loading of MgO@C was approximately 0.3 mg / cm³. 2 .

[0135] (4) Assemble the magnesium-oxygen battery in a glove box filled with argon atmosphere, using a CR2032 button cell with a 2mm pore diameter and a pore density of 5-8 pores / cm². 2 The negative electrode is a magnesium sheet, the positive electrode is the positive electrode material prepared in step (3), the electrolyte is 0.5M bis(trifluoromethanesulfonyl)imide magnesium dissolved in a mixed solution of EMIMBF4 and triethylene glycol dimethyl ether (volume ratio 1:9), and the separator is a glass fiber separator.

[0136] The positive electrode material is placed on one side of the opening in the battery casing, and the magnesium sheet is placed on the other side of the battery casing. The components are assembled in the same order as a normal button cell battery. The components are then pressed together by a button cell battery sealing machine to complete the assembly of the magnesium-oxygen battery.

[0137] (5) First, charge the battery at a current density of 400 mA / g for 10 hours to decompose magnesium oxide, thereby obtaining a positive electrode sheet containing a composite nanocage structure catalytic material (Co@C) of graphene and Co. The battery with this positive electrode sheet was subjected to charge-discharge cycle performance tests at a current density of 400 mA / g and a cutoff specific capacity of 1000 mAh / g. The test results showed an overvoltage of approximately 2.5V and stable cycling for 200 hours.

[0138] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, and for those of ordinary skill in the art, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. Therefore, the present invention is not limited to the specific details without departing from the general concept defined by the claims and their equivalents.

Claims

1. A gas battery prepared from a graphene-coated magnesium oxide and metal composite material MgO / M@C, characterized in that, The gas battery is a Mg-O2 battery or a Mg-CO2 battery. Graphene-coated magnesium oxide and the metal composite material MgO / M@C are used as the positive electrode catalyst material for the Mg-O2 battery or the Mg-CO2 battery. The gas battery has no negative electrode. When the gas battery is a Mg-O2 battery, oxygen or other active gases are not used at the positive electrode. The preparation method of the graphene-coated magnesium oxide and metal composite material MgO / M@C is as follows: Magnesium strips or magnesium powder are mixed with metal oxide M x O y The two materials are ignited together in carbon dioxide or treated at high temperatures of 750-1000℃ to obtain a graphene-coated magnesium oxide and metal composite material MgO / M@C. The magnesium strip or magnesium powder and M x O y The mass ratio is 1-11:1; the metal oxide M x O y It can be CoO, Co3O4, NiO, MoO3, MoO2, MnO2, or Mn3O4.

2. A metal-gas battery positive electrode sheet containing a composite nanocage structure catalytic material of graphene and metal, prepared from a graphene-coated magnesium oxide and metal composite material MgO / M@C, characterized in that... The preparation method is as follows: First, graphene-coated magnesium oxide and metal composite material MgO / M@C are prepared into an electrode sheet according to the preparation method of gas battery positive electrode sheet. Then, in-situ electrochemical decomposition is performed to remove MgO, and metal-gas battery positive electrode sheet containing graphene and metal composite nanocage structure catalyst material is obtained. The in-situ electrochemical decomposition refers to assembling the electrode sheets into a gas battery, energizing the positive and negative electrodes, with the following energizing parameters: current range 0.1uA-100mA, energizing time 0.1-1000 hours; The preparation method of the graphene-coated magnesium oxide and metal composite material MgO / M@C is as follows: Magnesium strips or magnesium powder are mixed with metal oxide M x O y The two materials are ignited together in carbon dioxide or treated at high temperatures of 750-1000℃ to obtain a graphene-coated magnesium oxide and metal composite material MgO / M@C. The magnesium strip or magnesium powder and M x O y The mass ratio is 1-11:1; the metal oxide M x O y It can be CoO, Co3O4, NiO, MoO3, MoO2, MnO2, or Mn3O4.

3. The metal-gas battery positive electrode sheet according to claim 2, characterized in that, The specific preparation steps are as follows: (1) A mixture of graphene-coated magnesium oxide and metal composite material MgO / M@C and conductive material is prepared in a mass ratio of 0.1-100:1; (2) Mix the above-mentioned mixed material with a polyvinylidene fluoride solution with a concentration of 0.01-15wt% at a mass ratio of 0.01-100:1, and continue to add solvent until the slurry has a suitable consistency; (3) Then grind it thoroughly in a mortar until uniform, and coat it evenly on the pre-cut breathable conductor substrate. Dry it under vacuum at 40-180℃ for 1-100 h to obtain the positive electrode material. (4) Assemble the obtained positive electrode material into a gas battery, wherein the negative electrode includes lithium metal, graphite, silicon carbide, silicon, sodium metal or magnesium metal; (5) Charge the MgO to decompose it, wherein the current range is 0.1uA-100mA and the charging time is 0.1-1000 hours, thereby obtaining the metal-gas battery positive electrode sheet containing a composite nanocage structure catalyst material of graphene and metal.

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