CN102637879A - Micro-nano-structure anode material for Li-air battery and preparation method of micro-nano-structure anode material - Google Patents

Abstract

The invention relates to a positive electrode material with a micro-nano structure for a lithium-air battery and a preparation method thereof. The preparation method includes blending metal nitride catalyst precursors and high-carbon polymers in organic solvents by electrospinning to prepare hollow composite precursors, pretreatment of precursor materials, nitriding of composite fibers, and activation of pore-forming and expanding pores. steps. The process method of the invention is simple and easy to operate, and the preparation method can easily realize the uniform distribution of nanoscale catalyst particles in the hollow carbon fiber. The prepared positive electrode material is hollow inside the tube and the tube wall is porous, and the metal nitride catalyst is evenly distributed in the three-dimensional pores of the tube wall. It has good ion transport ability and conductivity. It can effectively improve the charge and discharge capacity of lithium-air batteries, improve the high-rate performance and power density of lithium-air batteries, and reduce the internal resistance of batteries. The uniform dispersion of nano-scale metal nitrides can reduce charge-discharge polarization, and the industrialization prospect is good.

Description

A kind of micro-nano structure positive electrode material for lithium-air battery and preparation method thereof

technical field

The invention belongs to the field of new energy, and relates to a cathode material for a lithium-air battery and a preparation method thereof.

Background technique

With the development of human society, problems such as energy shortage and environmental pollution have become increasingly prominent, and people's understanding and requirements for chemical power sources have become higher and higher, prompting people to continuously explore new energy storage systems based on chemical power sources. Lithium metal-based batteries have led the development of high-performance chemical power sources in recent decades. With the successful commercialization of lithium-ion batteries, countries around the world are stepping up research on lithium-ion power batteries for vehicles. However, due to factors such as energy density, safety, and price, conventional lithium-ion batteries cannot meet the requirements of electric vehicles as a power source.

A lithium-air battery is a battery that uses lithium metal as the negative electrode and air (oxygen) as the positive electrode active material. Discharge process: Lithium in the negative electrode releases electrons and becomes lithium cations, lithium ions pass through the electrolyte, combine with oxygen and electrons flowing from the external circuit at the positive electrode to form lithium oxide or lithium peroxide, and stay at the positive electrode. Charging process: Electrons are provided through the external circuit wire, lithium ions pass through the electrolyte from the positive electrode to the surface of the negative electrode, and react on the surface of the negative electrode to form lithium metal, oxygen ions react to generate oxygen, and the generated electrons are supplied to the wire. Oxidation of 1 kg of metal lithium in lithium-air batteries can release 11680Wh of energy, eight times that of zinc-air batteries, comparable to 13000Wh/Kg of petroleum, and the positive reactant oxygen is obtained from the environment without storage. Therefore, lithium-air batteries have become an energy conversion system that has attracted much attention due to their high specific capacity and specific energy, environmental friendliness, easy miniaturization and light weight, and are also considered to be the preferred power source for next-generation power vehicles. .

At present, the main problems restricting the development of lithium-air batteries are: the product is insoluble in the organic electrolyte during the discharge process, easy to deposit on the positive electrode, blocking the oxygen transmission channel and serious polarization problems during the charge and discharge process.

Theoretically, the overall capacity and energy density of lithium-air batteries are only limited by the amount of metallic lithium. However, due to the low solubility of the discharge product lithium peroxide in the organic electrolyte, it is deposited on the surface of the air electrode, blocking the pores of the carrier material and blocking the contact between oxygen and the electrolyte, so that the discharge is terminated and the capacity of the battery is greatly reduced. Although the catalyst does not participate in the battery reaction, it determines the charge and discharge voltage and charge and discharge efficiency of the battery, and also affects the reversibility of the battery. The development and design of new air cathode support materials and high-efficiency composite catalysts have far-reaching significance for the development of lithium-air batteries.

At present, carbon materials are generally used as catalyst supports for the positive electrode of lithium-air batteries. In order to increase the specific surface area and utilization rate of the positive electrode of the lithium-air battery and improve the capacity of the battery, researchers selected carbon materials with different structures and added catalysts in different loading methods to carry out research on lithium-air batteries. Wu Xu ("Journal of The Electrochemical Society" 157(2010) A294-A297), etc. used KB carbon as the catalyst carrier, mixed the catalyst MnO ₂ with activated carbon ball milling to make the positive electrode, and the voltage polarization of the material was improved to a certain extent. , but the pores are easily blocked during the discharge process, and the capacity is very small; Li Jiaxin et al. (Electrochemical Communications "Electrochemistry Communications" 13 (2011) 698-700) used carbon nanotubes as a carrier to support MnO ₂ catalysts by impregnation method, and the discharge capacity was improved To 1768mAh/g, the charging platform has been reduced. Due to the severe agglomeration and winding of carbon tubes, the catalyst and carbon tubes cannot be uniformly recombined, and the catalyst particle size is large, which cannot exert good electrochemical performance; Taek Han Yong (Nanoscale Research Newsletter "Nanoscale Research Letters”7(2012) etc. used the hydrothermal method to compound Co ₃ O ₄ to the surface of carbon tubes as the positive electrode material, which showed good discharge capacity and low overpotential, but when charging and discharging at a large rate, the battery The capacity performance decreased sharply; Zhou Haoshen (American Chemical Society "ACS Nano" 5 (2011) 3020-3026) used graphene as a carrier, not only the discharge capacity was greatly improved, but also due to the specific microstructure of graphene. Higher reactivity shows a good catalytic effect, but the complex synthesis process and expensive cost of graphene hinder its promotion and application in lithium-air batteries.

Chinese patent CN 102240574A discloses a catalyst composed of a transition metal complex and a carbon black carrier. The lithium-air battery prepared by using the catalyst exhibits good catalytic activity and stability, but the charging and discharging of the battery under high current density The behavior is not ideal, and the hydrothermal method adopted cannot control the morphology of the catalyst; Chinese patent CN 102306808A discloses a catalyst for air electrodes that uses manganese salts and silver salts as raw materials, carbon materials as carriers, and ball milling. The preparation method and The process is simple and easy to operate, but the catalyst is not evenly distributed on the carrier, resulting in insignificant catalytic effect.

In summary, there is an urgent need in this field to develop an air cathode material with high-efficiency catalyst loading, which can effectively improve the discharge product blockage of oxygen diffusion channels while ensuring high specific capacity, improve the rate performance of the battery, have high reactivity, and reduce the electrode charge. change.

Contents of the invention

The purpose of the present invention is to provide a micro-nano structure positive electrode material for lithium-air batteries. The prepared material not only has a high specific surface area to provide sufficient reaction sites, but also the catalyst can be evenly distributed in the carbon fiber tube wall, which can effectively improve the performance of the material. Reactivity, the material can effectively ensure the diffusion of oxygen, improve the rate performance of the battery, have high reactivity, and reduce electrode polarization.

Another object of the present invention is to provide a simple and convenient preparation process for the above materials.

A micro-nano structure positive electrode material for a lithium-air battery of the present invention is a hollow porous composite fiber, which is composed of metal nitride catalyst nanoparticles and a hollow carbon fiber carrier with a micron-scale length; the carbon fiber tube wall It is composed of a plurality of nano-holes, and the plurality of nano-holes are connected to each other; the metal nitride is dispersed and loaded on the surface of the carbon fiber tube wall and in the nano-holes.

The hollow structure of the present invention is a hollow channel running through the entire carbon fiber length direction. Therefore, the material of the present invention is a kind of porous tube wall, hollow inside the tube, in-situ composite nanoscale metal nitride catalyst particles on the surface of the tube wall and in the holes. The prepared material not only has a high specific surface area to provide sufficient reaction sites, but also the uniform distribution of nano-scale metal nitride catalysts in the carbon fiber tube wall can effectively improve the reactivity of the material, and the hollow tube structure can ensure the diffusion of oxygen , with excellent electrical conductivity, can effectively increase the electrode discharge capacity, improve charge and discharge polarization, and the rate performance and power density of the battery.

The preparation method of the present invention comprises the following steps:

Step 1: In situ spinning preparation of carbon/catalyst precursor hollow fiber precursors

1. Mix high-carbon polymer with organic solvent, heat and stir to form polymer colloid solution;

2. Add catalyst precursor to polymer colloid solution, heat and stir to form spinning stock solution;

3. The spinning dope is electrostatically spun to obtain the carbon/catalyst precursor hollow fiber precursor.

The second step: pretreatment of fiber precursors

The product obtained in the first step is subjected to low-temperature heating pretreatment under an inert gas to form a trapezoidal polymer with good thermal stability, and the low-temperature heating pretreatment temperature is 100-300°C;

The third step: Nitriding the metal precursor in the composite fiber with the product obtained in the second step under a nitrogen-containing atmosphere to obtain a carbon fiber/metal nitride hollow composite fiber, and then further activating to obtain a micro-nano structure carbon fiber/metal nitride Hollow porous composite fiber.

The present invention—a method for preparing anode materials with micro-nano structures for lithium-air batteries. The material tubes are hollow inside, and the tube walls contain abundant nano-scale pores. The nano-pores communicate with each other and open on the surface of carbon fibers. Nano-scale metal nitride catalysts Particles are highly dispersed in the carbon fiber tube wall and its pores.

The outer diameter of the material of the present invention is 20 nm to 10 μm, and the inner and outer diameter ratio is 1/4 to 1/10. The length of the carbon fiber is 1 μm to 1000 μm. The nanoholes in the carbon fiber tube wall have a pore diameter of 2-50 nm, and the mesopores account for 20% to 60% of the entire distribution of nanoholes.

Since the material of the present invention has a plurality of abundant three-dimensional nano-holes, the specific surface area of the carbon fiber is 300m ² /g-2000m ² /g.

The particle size of the catalyst is between 10nm and 100nm.

In the first step of the present invention, the weight concentration of the high-carbon polymer in the polymer colloid solution is 0.1%-60%; the specific gravity of the catalyst or its metal salt precursor and the high-carbon polymer is 1/100-100/1.

In the first step 1 of the present invention, the high-carbon polymer is polyacrylonitrile, polyaniline, polyethylene oxide, dimethyl sulfoxide, polybendizole, polyethylene, polyethylene oxide, polystyrene, One or more of polymers such as polyphenylene terephthalate, asphalt, and styrene-butadiene rubber (the weight-average molecular weight of the high-carbon polymer is 60,000-300,000). The solvent is one or more of volatile dichloromethane, chloroform, and acetone, and non-volatile formic acid, dimethylformamide, and dimethylformamide.

The metal nitride catalyst described in the present invention includes one or more of molybdenum nitride, iron nitride, vanadium nitride, titanium nitride, cobalt nitride and nickel nitride.

The precursor of the metal nitride includes one or more of metal nitrates, ammonium salts, carbonates, sulfates, chloride salts, and metal organic polymers.

In the third step of the present invention, in the nitriding process of the metal oxide, the nitriding temperature is 500°C-1000°C. The heating rate to reach the required nitriding temperature is 1°C/min to 10°C/min, the holding time is 1h to 5h, and the protective atmosphere is a mixed gas of ammonia or nitrogen + hydrogen.

The activation method includes physical activation of water vapor and carbon dioxide, chemical activation of KOH, H ₃ PO ₄ , ZnCl ₂ , or physical-chemical combined activation.

The micro-nano structure positive electrode material prepared by the preparation method of the micro-nano structure positive electrode material for a lithium-air battery has the following advantages:

(1) The in-situ composite of the catalyst and the carrier carbon material enables the catalyst to be efficiently dispersed on the carrier, and at the same time the shape and size of the catalyst are controllable, which can provide better battery electrochemical performance;

(2) Metal nitride has a catalytic ability similar to that of platinum, which can have an excellent catalytic effect on the reduction of oxygen, the positive active material of lithium-air batteries, significantly improve the discharge platform of the battery, and reduce the polarization of the battery;

(3) During the nitriding process of metal oxides, the carbon fiber will also be nitrided in the ammonia atmosphere, and part of the carbon on the surface of the carbon fiber will be replaced by nitrogen, and the carbon fiber can show higher activity after nitrogen doping;

(4) The tube wall of the carbon fiber three-dimensional pore structure provides a place for the battery reaction, and has more three-phase reaction interfaces. The three-dimensional nanopores of the tube wall are used as the storage space for the catalyst, which can realize the nanometerization of the catalyst particles, and the interior runs through the entire carbon fiber. The hollow channel has no product accumulation during discharge, which can always ensure the smooth transport of oxygen; the hollow cavity and the through three-dimensional hole provide a short-distance and convenient transmission channel for ion transmission, which is conducive to the lithium ion in the composite material. Efficient transport, good electrochemical performance, especially high rate performance;

(5) The preparation process is simple and feasible, and is suitable for industrialized production;

(6) Wide range of sources of raw materials.

In summary, the process method of the present invention is simple and easy to operate. The preparation method realizes the in-situ composite of nano-scale metal nitride catalyst particles evenly distributed on the hollow carbon fiber, and the prepared material tube is hollow and the tube wall is porous. , and the catalyst is evenly distributed in the three-dimensional pores of the tube wall, which can not only provide enough space for the battery reaction, but also ensure the smooth flow of oxygen diffusion channels, and have good ion transport capacity and electrical conductivity. It can effectively improve the charge and discharge capacity of lithium-air batteries, reduce charge and discharge polarization, improve the rate performance and power density of lithium-air batteries, reduce the internal resistance of batteries, and have good industrialization prospects.

Description of drawings

Fig. 1 is the nitrogen adsorption curve of the positive electrode material obtained according to Example 1.

Fig. 2 is the rate curve diagram of the lithium-air battery obtained according to Example 1.

3 is an SEM image of the positive electrode material prepared according to Example 2.

FIG. 4 is a TEM image of the positive electrode material prepared according to Example 2.

Detailed ways

Below in conjunction with embodiment, the present invention will be described in further detail, but not limited to the scope of protection of the invention.

Example 1

Weigh 1.8g polyacrylonitrile (PAN), add 15mL N,N-dimethylformamide (DMF), stir in a 60°C water bath for 3h, then add 5g ammonium molybdate, stir for 1h, control voltage 11kV, indirect The collection distance is 15cm, the liquid flow rate is 30μl/min, and the PAN/ammonium molybdate hollow fiber is obtained through the electrospinning process. The obtained composite fibers were put into a tube furnace and pretreated at 250°C for 1 h. Under an ammonia atmosphere, the nitriding temperature is 800°C, and the heating rate is 3°C/min, the hollow composite fiber is nitrided to obtain the hollow carbon/molybdenum nitride composite fiber. The obtained material was mixed with potassium hydroxide in a ratio of 1:4, chemically activated at 800°C for 2 hours under the protection of argon, and then physically activated by _CO2 gas, and kept for 1 hour to obtain porous hollow carbon/molybdenum nitride fibers.

Electrode preparation, battery assembly and testing are as follows: layered porous hollow carbon fiber, conductive carbon and binder are mixed at a ratio of 80:10:10 to make a positive electrode, and the electrode sheet is punched into an electrode sheet with a diameter of 10mm, and a metal lithium sheet is used as the negative electrode , in an electrolyte of 1M LiTFSI/PC:EC (1:1), assembled into a CR2025 button cell in an argon-filled glove box. At room temperature (25°C), a constant current charge and discharge test was performed in a pure oxygen environment at 0.1mA/cm ² , and the charge and discharge cut-off voltage was 2 to 4.5V. As shown in Fig. 1, the specific surface area of the obtained composite fiber cathode material reaches 550m ² /g. As shown in Figure 2, at a current density of 0.1mA/cm ² , the discharge specific capacity is 4526mAh/g, and the discharge voltage plateau increases to 3.0V; when the current density increases to 0.5mA/cm ² , the discharge capacity still reaches 2750mAh /g.

Example 2

Weigh 1.8g polyacrylonitrile (PAN), add 15mL N,N-dimethylformamide (DMF), stir in a 60°C water bath for 3h, then add 1g ammonium molybdate, stir for 1h, control voltage 11kV, indirect The collection distance is 15cm, the liquid flow rate is 30μl/min, and the PAN/ammonium molybdate hollow fiber is obtained through the electrospinning process. The obtained composite fibers were put into a tube furnace and pretreated at 250°C for 1 h. Under an ammonia atmosphere, the nitriding temperature is 800°C, and the heating rate is 3°C/min, the hollow composite fiber is nitrided to obtain the hollow carbon/molybdenum nitride composite fiber. The obtained material was mixed with potassium hydroxide in a ratio of 1:4, chemically activated at 800°C for 2 hours under the protection of argon, and then physically activated by _CO2 gas, and kept for 1 hour to obtain porous hollow carbon/molybdenum nitride fibers.

Pole sheet preparation and battery assembly are the same as the test and Example 1. With the decrease of the catalyst load, the discharge capacity of the battery decreased to a certain extent, the first discharge capacity was 3800mAh/g, and the conductivity of the pole piece increased. The SEM and TEM images of the prepared cathode composite material are shown in Fig. 3 and Fig. 4 . From the SEM images, it can be seen that the morphology of the composite material is fibrous, and the length is in the order of microns. It can be seen from the TEM image that the composite material is a hollow structure with nanoscale catalyst particles loaded on the surface.

Example 3

Weigh 1.8g polyacrylonitrile (PAN), add 15mL N,N-dimethylformamide (DMF), stir in a water bath at 60°C for 3h, then add 5g ammonium molybdate, stir for 1h, control voltage 11kV, indirect The collection distance is 15cm, the liquid flow rate is 30μl/min, and the PAN/ammonium molybdate hollow fiber is obtained through the electrospinning process. The obtained composite fibers were put into a tube furnace and pretreated at 250°C for 1 h. Under an ammonia atmosphere, the nitriding temperature is 800°C, and the heating rate is 3°C/min, the hollow composite fiber is nitrided to obtain the hollow carbon/molybdenum nitride composite fiber. The obtained material was mixed with KOH in a ratio of 1:4, and chemically activated at 800° C. for 2 hours under the protection of argon to obtain porous hollow carbon/molybdenum nitride fibers.

Pole sheet preparation and battery assembly are the same as the test and Example 1. The specific surface area of the obtained positive electrode material is smaller than that of the material in Example 1, which is 480m ² /g, and the pore volume of the mesopores is reduced. The pore volume of the material after chemical activation is lower than that of the material obtained by physical-chemical combined activation in Example 1.

Example 4

Weigh 1.8g polyacrylonitrile (PAN), add 15mL N,N-dimethylformamide (DMF), stir in a water bath at 60°C for 3h, then add ferric chloride (accounting for 0.5wt% of the mass of PAN) and continue stirring for 1h , the control voltage is 11kV, the receiving distance between the two electrodes is 15cm, the liquid flow rate is 30μl/min, and the PAN/ferric chloride hollow fiber is obtained through the electrospinning process. The obtained composite fibers were put into a tube furnace and pretreated at 300 °C for 1 h. Under an ammonia atmosphere, the nitriding temperature is 800°C, and the heating rate is 3°C/min, the hollow carbon/iron chloride fiber is nitrided to obtain the hollow carbon/iron nitride composite fiber. The obtained material was mixed with KOH in a ratio of 1:4, and chemically activated at 800° C. for 2 hours under the protection of argon to obtain porous hollow carbon/iron nitride fibers.

Pole sheet preparation and battery assembly are the same as the test and Example 1. Nano-scale iron nitride is effectively dispersed on the surface of carbon fiber, and the catalytic effect is good.

Example 5

Weigh 1.8g polyacrylonitrile (PAN), add 15mL N,N-dimethylformamide (DMF), stir in a water bath at 60°C for 3h, then add cobalt nitrate and ammonium molybdate according to the cobalt-molybdenum molar ratio of 0.8, continue Stir for 1 hour, control voltage 11kV, receiving distance between two electrodes 15cm, liquid flow rate 30μl/min, and obtain PAN/cobalt molybdenum salt hollow fiber through electrospinning process. The obtained composite fibers were put into a tube furnace and pretreated at 300 °C for 1 h. Under an ammonia atmosphere, the nitriding temperature is 800°C, and the heating rate is 3°C/min, the hollow composite fiber is nitrided to obtain the hollow carbon/cobalt-molybdenum bimetal nitride composite fiber. The obtained material was mixed with KOH in a ratio of 1:4, and chemically activated at 800° C. for 2 hours under the protection of argon to obtain porous hollow carbon/cobalt-molybdenum bimetal nitride fibers.

Pole sheet preparation and battery assembly are the same as the test and Example 1. After loading cobalt molybdenum nitride in situ, the charging and discharging voltage platform of the battery is improved, and the polarization is reduced.

Claims (14)

1. A lithium-air battery with a micro-nano structure positive electrode material, characterized in that: the positive electrode material is a hollow porous composite fiber, which is composed of metal nitride catalyst nanoparticles and a micron-scale carbon fiber carrier with a hollow structure length The carbon fiber tube wall is composed of a plurality of nano-holes, and the multiple nano-holes are connected to each other; the metal nitride is dispersed and loaded on the surface of the carbon fiber tube wall and the nano-holes. 2 . The positive electrode material according to claim 1 , wherein the carbon fiber has an outer diameter of 20 nm˜10 μm, and a ratio of inner and outer diameters of 1/4˜1/10. 3 . The positive electrode material according to claim 1 , wherein the specific surface area of the carbon fiber is 300 m ² /g˜2000 m ² /g. 4. The positive electrode material according to claim 3, characterized in that: the nanopores with a pore size distribution of 2nm-50nm in the carbon fiber tube wall account for 20% to 60% of the total nanopores, and the catalyst particle size is between 10nm and 100nm . 5. The positive electrode material according to claim 1, wherein the metal nitride catalyst comprises one of molybdenum nitride, iron nitride, vanadium nitride, titanium nitride, cobalt nitride, and nickel nitride or several. 6. The preparation method of a lithium-air battery with a micro-nano structure positive electrode material according to claim 1, characterized in that: the preparation method comprises the following steps: (1) dissolving the high-carbon polymer in an organic solvent, heating and stirring to form a polymer colloid solution; adding a precursor of a metal nitride catalyst to the solution, stirring evenly, and obtaining a spinning stock solution; (2) The spinning dope is obtained through electrospinning to obtain a hollow composite precursor; (3) The hollow composite precursor is pretreated at low temperature to prepare a thermally stable carbon fiber/catalyst precursor hollow composite fiber; (4) Nitriding the metal oxide in the composite fiber at high temperature under a nitrogen-containing atmosphere to obtain a carbon fiber/metal nitride hollow composite fiber, and then further activating to obtain a micro-nano structured carbon fiber/metal nitride hollow porous composite fiber. 7. The preparation method of a micro-nano structure positive electrode material for a lithium-air battery according to claim 6, wherein the metal nitride catalyst comprises molybdenum nitride, iron nitride, vanadium nitride, nitride One or more of titanium, cobalt nitride and nickel nitride. 8. The preparation method of a micro-nano structure positive electrode material for a lithium-air battery according to claim 6, characterized in that: the precursor of the metal nitride comprises metal nitrates, ammonium salts, carbonates, One or more of sulfate, chloride, and metal organic polymers. 9 . The preparation method of a micro-nano structured cathode material for lithium-air batteries according to claim 6 , wherein the temperature of the low-temperature pretreatment is 100° C. to 300° C. 9 . 10. The preparation method of a micro-nano structure cathode material for a lithium-air battery according to claim 6 or 9, characterized in that: the nitriding temperature in the high-temperature nitriding process of the metal oxide is 500°C to 1000°C . 11. The preparation method of a micro-nano structure cathode material for a lithium-air battery according to claim 10, characterized in that: the heating rate to reach the required nitriding temperature is 1°C/min-10°C/min, and the holding time is 1h ~5h, the protective atmosphere is a mixture of ammonia or nitrogen + hydrogen. 12. The preparation method of a micro-nano structure cathode material for lithium-air batteries according to claim 6, characterized in that: the activation method includes physical activation of water vapor and carbon dioxide, KOH, H ₃ PO ₄ , ZnCl ₂ for chemical activation, or combined physical-chemical activation, the protective atmosphere is at least one of nitrogen and argon. 13. A method for preparing a positive electrode material with a micro-nano structure for a lithium-air battery according to claim 6, characterized in that: the high-carbon polymer weight concentration in the polymer colloid solution is 0.1% to 60%; the metal The specific gravity of the nitride catalyst precursor salt and the high carbon polymer is 1/100-100/1. 14. The preparation method of a micro-nano structure cathode material for a lithium-air battery according to claim 6, characterized in that: the high-carbon polymer is polyacrylonitrile, polyaniline, polyethylene oxide, dimethyl One or more of high molecular polymers such as sulfoxide, polybenzimidazole, polyethylene, polyethylene oxide, polystyrene, polyphenylene terephthalate, asphalt, and styrene-butadiene rubber; the solvent One or more of volatile dichloromethane, chloroform, acetone, non-volatile formic acid, dimethylformamide, and dimethylformamide. the

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