A transition metal carbide-based composite material, a preparation method and applications thereof
The preparation of transition metal carbide-based composite materials by molten salt electrolysis solves the problems of few catalytic sites and small specific surface area in lithium-air battery cathode catalysts, thereby improving the cycle stability and rate performance of lithium-air batteries.
Patent Information
- Application Number
- CN202310992211.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-08-08
- Publication Date
- 2026-11-06
- Estimated Expiration
- 2043-08-08
AI Technical Summary
Existing lithium-air battery cathode catalysts suffer from a lack of catalytic sites, small specific surface area, and low reserves and high costs of precious metal materials, which affect the improvement of electrochemical dynamic performance.
Transition metal carbide-based composite materials were prepared by molten salt electrolysis. The materials were mixed with transition metal oxides, carbon sources and binders, pressed into sheets, and then subjected to molten salt electrolysis to form porous electrode sheets, which were then combined with nanoscale catalyst materials with good dispersibility.
It improves the cycle stability and rate performance of lithium-air batteries, increases the contact area between the electrode sheet and carbon, provides mesoporous channels for electron and ion transport, and optimizes electrochemical performance.
Smart Images
Figure CN116905004B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of catalytic materials technology, and in particular to a transition metal carbide-based composite material, its preparation method, and its application. Background Technology
[0002] With social development and technological advancements, people have increasingly higher demands for new energy vehicles. However, limitations in the cycle life, charge / discharge rate performance, and charge / discharge voltage gap of lithium-ion batteries restrict their performance improvement. Lithium-air batteries, on the other hand, offer advantages due to their high energy density (~3500Wh / kg). -1 This is considered a new generation of rechargeable batteries and has become a research hotspot.
[0003] The charge-discharge reactions of lithium-air batteries mainly involve oxygen evolution (OER) and oxygen reduction (ORR) reactions. The discharge reaction occurring at the positive electrode of a lithium-air battery is the ORR reaction, primarily involving the reaction of O2 with Li. + This relates to the process of Li₂O₂ formation. The charging process is an OER reaction, and the discharge product Li₂O₂ decomposes into Li. + The process of O2 and O2. Therefore, the electrochemical kinetic performance of lithium-air batteries is affected by the reaction kinetics of OER and ORR. Studies have shown that developing cathode catalysts that promote the transport of lithium ions and oxygen, and improve the decomposition efficiency of discharge products, is key to improving the electrochemical kinetic performance of lithium-air batteries.
[0004] Currently, common cathode catalysts for lithium-air batteries include precious metals, non-precious metal compounds, and carbon materials. Precious metals, as catalyst materials, possess high catalytic activity and excellent comprehensive properties such as high-temperature resistance, oxidation resistance, and corrosion resistance; however, they suffer from drawbacks such as low availability, difficulty in development, and high cost. Non-precious metal compounds include metal carbides, metal sulfides, metal oxides, and composite materials. Because they also exhibit good electrocatalytic performance, they have been proposed as potential alternatives to precious metal materials. Carbon materials possess high conductivity, low cost, low density, and the ability to easily combine with other materials to construct porous structures, making them suitable for use as electrode materials in lithium-air batteries.
[0005] The catalytic activity of transition metal carbides depends on the number of catalytic sites and the size of their effective surface area. To obtain more catalytic sites, i.e., carbides with well-formed crystals, prolonged high-temperature calcination is typically employed. However, this reduces the specific surface area due to the continuous growth and aggregation of crystals. Molten salt direct electrochemical reduction (FFC) is a novel metallurgical method initiated by the University of Cambridge and has attracted considerable attention in recent years. It involves sintering solid metal oxides to form the cathode, using graphite as the anode, and applying a voltage lower than that required for molten salt decomposition in a calcium chloride-based molten salt at a temperature below the melting point of the target product. The solid metal oxide is then directly electrolyzed in situ. This method uses oxides as raw materials and directly obtains solid metals or alloy compounds through a one-step electrolysis process, featuring a short process flow, low energy consumption, and environmental friendliness. Molten salt electrolysis for the preparation of transition metal carbides is characterized by low reaction temperature and simple process.
[0006] Therefore, the present invention provides a transition metal carbide-based composite material, its preparation method, and its application. Summary of the Invention
[0007] To address the shortcomings of the prior art, this invention provides a transition metal carbide-based composite material, its preparation method, and its applications. This invention utilizes a molten salt electrolysis method, which simplifies the required reaction conditions and allows for the preparation of nanoscale catalyst materials with good dispersibility.
[0008] The first objective of this invention is to provide a method for preparing a transition metal carbide-based composite material, comprising the following steps:
[0009] Step 1: After uniformly mixing the transition metal oxide with additives, carbon source and binder, press it into a sheet, and then sinter it to obtain the electrode sheet.
[0010] The carbon source is one or both of multi-walled carbon nanotubes and acetylene black.
[0011] Step 2: Using a graphite rod as the anode and pre-electrolysis electrode, and the electrode sheet as the cathode, perform molten salt electrolysis on the electrolytic molten salt medium for 9-10 hours;
[0012] Step 3: Using the electrode sheet from Step 2 as the anode and the graphite rod from Step 2 as the cathode, continue electrolyzing the molten salt medium from Step 2 for 4-6 hours to obtain the transition metal carbide-based composite material.
[0013] The transition metal carbide-based composite material is composed of transition metal carbides and their derived carbons.
[0014] Furthermore, the transition metal oxide is any one of tantalum oxide, titanium dioxide, and niobium oxide.
[0015] Furthermore, the additive is NH4HCO3 or CaCO3.
[0016] Furthermore, the molar ratio of the transition metal oxide to the additive is 1:1.8 to 2.2;
[0017] The ratio of the carbon source to the transition metal oxide is 0.06–1.2 g: 5 mmol.
[0018] Furthermore, the adhesive is polyvinyl alcohol with a mass concentration of 3%, and the ratio of the adhesive to the transition metal oxide is 0.08-0.12 mL: 5 mmol.
[0019] Furthermore, in step 2, the temperature of molten salt electrolysis is 750–850°C, and the electrolysis voltage is 2.8–3.2V;
[0020] In step 3, the temperature for molten salt electrolysis is 750–850℃, and the electrolysis voltage is 2.2–2.8V;
[0021] Furthermore, the electrolytic molten salt medium is a mixture of anhydrous CaCl2 and NaCl.
[0022] Furthermore, the sintering temperature is 900–1000°C, and the sintering time is 2–4 hours.
[0023] Furthermore, it also includes step 4, in which the transition metal carbide-based composite material obtained in step 3 is placed in distilled water, stirred, centrifuged and circulated at least three times, filtered and dried to obtain purified transition metal carbide-based composite material.
[0024] A second objective of this invention is to provide a transition metal carbide-based composite material prepared by the above-described preparation method.
[0025] A third objective of this invention is to provide an application of the above-mentioned transition metal carbide-based composite material in the preparation of cathode materials for lithium-air batteries.
[0026] Compared with the prior art, the present invention has the following advantages:
[0027] This invention uses transition metal oxides, additives, and multi-walled carbon nanotubes as raw materials. These are mixed with a binder and pressed into sheets. During sintering, the additives decompose to produce NH3 or CO2 gas, creating a porous structure within the cathode sheet. The multi-walled carbon nanotubes serve as a carbon source, and their inherent porous structure provides the transition metal carbide-based composite material with mesopores larger than 5 nm in diameter. This facilitates the construction of porous electrode sheets, increasing the contact area between the electrode sheet and carbon. Furthermore, intermediate products are generated during sintering, accelerating the electrolysis rate and shortening the electrolysis time. This also saves energy. The transition metal carbide-based composite material prepared by this method exhibits better dispersibility, more uniform particle size, and mesopore channels that facilitate electron and ion transport.
[0028] This invention utilizes a one-step molten salt electrolysis method to prepare transition metal carbide-based composite materials, which is simple to operate and has a short preparation time. Furthermore, the transition metal carbide-based composite materials prepared by this invention possess a macroporous structure. This porous structure is more conducive to electrolyte wetting and lithium-ion transport. The macropores formed by the accumulation of nano-transition metal carbides and their derived carbon composite materials facilitate oxygen diffusion and provide effective active space for the interconversion of O2 / Li2O2. Therefore, when used as a cathode material for lithium-air batteries, it can significantly improve the cycle stability and rate performance of lithium-oxygen batteries, thus contributing to the optimization of the electrochemical performance of lithium-air batteries.
[0029] The present invention has a simple preparation process, high electrolysis efficiency, energy saving, and the porous material structure makes it easy to optimize the electrochemical performance of lithium-air batteries. Attached Figure Description
[0030] Figure 1 The image shows a scanning electron microscope (SEM) image of the transition metal carbide-based composite material prepared in Example 1.
[0031] Figure 2 This is a magnified scanning electron microscope (SEM) image of the transition metal carbide-based composite material prepared in Example 1.
[0032] Figure 3 The first charge-discharge curve of the lithium-air battery in Example 1 at a current density of 100 mA / g is shown.
[0033] Figure 4 The stable cycling curve of the lithium-air battery in Example 1 after 100 cycles under test conditions of current density of 500mA / g and limited capacity of 1000mAh / g. Detailed Implementation
[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below.
[0035] This invention provides a transition metal carbide-based composite material, the preparation method of which is as follows:
[0036] Step 1: After uniformly mixing the transition metal oxide with additives, carbon source and binder, press it into a sheet, and then sinter it to obtain the electrode sheet.
[0037] It should be noted that the transition metal oxide used in this invention can be selected from any one of tantalum oxide, titanium dioxide, and niobium oxide.
[0038] The additives used in this invention primarily create a porous structure within the electrode sheet during its fabrication, thereby increasing the effective contact area and thus improving the electrolysis rate and shortening the electrolysis time. Preferably, NH4HCO3 or CaCO3 is used as the additive. When mixed with transition metal oxides, a carbon source, and a binder and pressed into sheets, the mixture decomposes during sintering to produce NH3 or CO2 gas, which in turn creates a porous structure within the cathode sheet. The generated NH3 or CO2 gas is then expelled with the inert argon gas.
[0039] The present invention also uses multi-walled carbon nanotubes and acetylene black as carbon sources. The porous structure of multi-walled carbon nanotubes and acetylene black themselves will provide a pore structure with a pore size greater than 5 nm for transition metal carbide-based composite materials, which is beneficial to constructing electrode sheets with porous structures.
[0040] Preferably, the present invention uses polyvinyl alcohol with a mass concentration of 3% as a binder, and the ratio of the binder to the transition metal oxide is 0.08-0.12 mL:5 mmol, more preferably 0.1 mL:5 mmol. Furthermore, the molar ratio of the transition metal oxide to the additive is 1:1.8-2.2, preferably 1:2; and the ratio of the carbon source to the transition metal oxide is 0.06-1.2 g:5 mmol.
[0041] Step 2: Using a graphite rod as the anode and pre-electrolysis electrode, and the electrode sheet as the cathode, perform molten salt electrolysis on the electrolytic molten salt medium for 9-10 hours;
[0042] It should be noted that in this step, the temperature of molten salt electrolysis is 750–850℃, the pre-electrolysis voltage is 1.4–1.6V, the electrolysis voltage is 2.8–3.2V, and the molten salt participating in the electrolysis is a mixed salt prepared by anhydrous CaCl2 and NaCl in a molar ratio of 7:3. Furthermore, during the molten salt electrolysis process in this step, transition metal oxides are electrodeoxidized at the cathode to generate transition metal carbides, and molten salt electrolysis is carried out for 9–10 hours to ensure that the transition metal oxides are completely converted into transition metal carbides on the cathode.
[0043] Step 3: Replace the cathode and anode in Step 2 above, that is, use the electrode sheet in Step 2 as the anode and the graphite rod in Step 2 as the cathode, and continue to electrolyze the molten salt medium in Step 2 for 4 to 6 hours to obtain the transition metal carbide-based composite material.
[0044] It should be noted that in this step, the temperature of molten salt electrolysis is 750-850℃, the electrolysis voltage is 2.2-2.8V, and the molten salt participating in the electrolysis is a mixed salt prepared by anhydrous CaCl2 and NaCl in a molar ratio of 7:3. In addition, during the molten salt electrolysis process in this step, the electrolysis time is controlled to be 4-6 hours so that the transition metal carbides on the anode are oxidized, thereby obtaining a transition metal carbide-based composite material.
[0045] Step 4: Place the transition metal carbide-based composite material obtained in Step 3 in distilled water, stir, centrifuge and cycle at least three times, then discard the distilled water and dry in alcohol at 60°C for 6 hours to obtain the purified transition metal carbide-based composite material.
[0046] A second objective of this invention is to provide a transition metal carbide-based composite material prepared by the above-described preparation method.
[0047] A third objective of this invention is to provide an application of the above-mentioned transition metal carbide-based composite material in the preparation of cathode materials for lithium-air batteries.
[0048] Example 1
[0049] This embodiment provides a transition metal carbide-based composite material, the preparation method of which is as follows:
[0050] Step 1, Prepare the electrode sheet:
[0051] 1) Mix 2.2094g of transition metal tantalum oxide, 0.7905g of ammonium bicarbonate, 0.12g of multi-walled CNTs and 0.1mL of 3% polyvinyl alcohol binder into an abrasive and mix for 40min to obtain a mixed powder.
[0052] 2) Take 800 mg of the mixed powder obtained above and press it into a disc under a pressure of 12 MPa for 3 min. The disc has a diameter of 14 mm and a thickness of 2 mm.
[0053] 3) The disc obtained in step 2) is sintered at 950°C for 3 hours under an argon atmosphere. The sintered disc is then drilled with a threaded drill bit with a diameter of 4 mm to facilitate its stable fixation on the graphite rod electrode, thus obtaining the electrode sheet.
[0054] Step 2, First molten salt electrolysis treatment
[0055] The electrode sheet obtained in step one above is used as the cathode;
[0056] The graphite rod was cut into a cylinder with a length of 7cm and a diameter of 1cm, and then polished to a smooth and shiny surface to prevent it from falling off during electrolysis and causing a short circuit on the molten salt surface. It was then used as the electrolysis anode and the pre-electrolysis reference electrode.
[0057] Anhydrous CaCl2 and NaCl were mixed in a molar ratio of 7:3, and 200g was used as the molten salt medium for molten salt electrolysis. Molten salt electrolysis was then carried out for 9.5h at an electrolysis temperature of 800℃ and an electrolysis voltage of 3.0V to deoxidize tantalum oxide in the cathode and generate transition metal carbides.
[0058] Step 3, Second molten salt electrolysis treatment
[0059] 1) Replace the cathode and anode, that is, use the electrode sheet formed by the transition metal carbide as the anode and the graphite rod as the cathode, and continue to electrolyze in the molten salt medium in step 2 for 5 hours under the conditions of electrolysis temperature of 800℃ and electrolysis voltage of 2.5V. After cooling to room temperature, the electrode sheet in the molten salt is electrolyzed to obtain the transition metal carbide-based composite material.
[0060] 2) After stirring and centrifuging the obtained transition metal carbide-based composite material in distilled water at least three times, the distilled water is discarded, and the material is dried in alcohol at 60°C for 6 hours to obtain a pure transition metal carbide-based composite material.
[0061] Example 2
[0062] This embodiment provides a transition metal carbide-based composite material, the preparation method of which is as follows:
[0063] Step 1, Prepare the electrode sheet:
[0064] 1) Mix 2.2094g of transition metal tantalum oxide, 0.7905g of ammonium bicarbonate, 0.06g of multi-walled CNTs, 0.06g of acetylene black and 0.1mL of 3% polyvinyl alcohol binder into an abrasive and mix for 40min to obtain a mixed powder.
[0065] 2) Take 800 mg of the mixed powder obtained above and press it into a disc under a pressure of 12 MPa for 3 min. The disc has a diameter of 14 mm and a thickness of 2 mm.
[0066] 3) The disc obtained in step 2) is sintered at 950°C for 3 hours under an argon atmosphere. The sintered disc is then drilled with a threaded drill bit with a diameter of 4 mm to facilitate its stable fixation on the graphite rod electrode, thus obtaining the electrode sheet.
[0067] Step 2, First molten salt electrolysis treatment
[0068] The electrode sheet obtained in step one above is used as the cathode;
[0069] The graphite rod was cut into a cylinder with a length of 7cm and a diameter of 1cm, and then polished to a smooth and shiny surface to prevent it from falling off during electrolysis and causing a short circuit on the molten salt surface. It was then used as the electrolysis anode and the pre-electrolysis reference electrode.
[0070] Anhydrous CaCl2 and NaCl were mixed in a molar ratio of 7:3, and 200g was used as the molten salt medium for molten salt electrolysis. Molten salt electrolysis was then carried out for 9.5h at an electrolysis temperature of 800℃ and an electrolysis voltage of 3.0V to deoxidize tantalum oxide in the cathode and generate transition metal carbides.
[0071] Step 3, Second molten salt electrolysis treatment
[0072] 1) Replace the cathode and anode, that is, use the electrode sheet formed by the transition metal carbide as the anode and the graphite rod as the cathode, and continue to electrolyze in the molten salt medium in step 2 for 5 hours under the conditions of electrolysis temperature of 800℃ and electrolysis voltage of 2.5V. After cooling to room temperature, the electrode sheet in the molten salt is electrolyzed to obtain the transition metal carbide-based composite material.
[0073] 2) After stirring and centrifuging the obtained transition metal carbide-based composite material in distilled water at least three times, the distilled water is discarded, and the material is dried in alcohol at 60°C for 6 hours to obtain a pure transition metal carbide-based composite material.
[0074] Example 3
[0075] This embodiment provides a transition metal carbide-based composite material, the preparation method of which is as follows:
[0076] Step 1, Prepare the electrode sheet:
[0077] 1) Mix 2.2094g of transition metal tantalum oxide, 0.7905g of ammonium bicarbonate, 0.36g of multi-walled CNTs, 0.84g of acetylene black and 0.1mL of 3% polyvinyl alcohol binder into an abrasive and mix for 40min to obtain a mixed powder.
[0078] 2) Take 800 mg of the mixed powder obtained above and press it into a disc under a pressure of 12 MPa for 3 min. The disc has a diameter of 14 mm and a thickness of 2 mm.
[0079] 3) The disc obtained in step 2) is sintered at 950°C for 3 hours under an argon atmosphere. The sintered disc is then drilled with a threaded drill bit with a diameter of 4 mm to facilitate its stable fixation on the graphite rod electrode, thus obtaining the electrode sheet.
[0080] Step 2, First molten salt electrolysis treatment
[0081] The electrode sheet obtained in step one above is used as the cathode;
[0082] The graphite rod was cut into a cylinder with a length of 7cm and a diameter of 1cm, and then polished to a smooth and shiny surface to prevent it from falling off during electrolysis and causing a short circuit on the molten salt surface. It was then used as the electrolysis anode and the pre-electrolysis reference electrode.
[0083] Anhydrous CaCl2 and NaCl were mixed in a molar ratio of 7:3, and 200g was used as the molten salt medium for molten salt electrolysis. Molten salt electrolysis was then carried out for 9.5h at an electrolysis temperature of 800℃ and an electrolysis voltage of 3.0V to deoxidize tantalum oxide in the cathode and generate transition metal carbides.
[0084] Step 3, Second molten salt electrolysis treatment
[0085] 1) Replace the cathode and anode, that is, use the electrode sheet formed by the transition metal carbide as the anode and the graphite rod as the cathode, and continue to electrolyze in the molten salt medium in step 2 for 5 hours under the conditions of electrolysis temperature of 800℃ and electrolysis voltage of 2.5V. After cooling to room temperature, the electrode sheet in the molten salt is electrolyzed to obtain the transition metal carbide-based composite material.
[0086] 2) After stirring and centrifuging the obtained transition metal carbide-based composite material in distilled water at least three times, the distilled water is discarded, and the material is dried in alcohol at 60°C for 6 hours to obtain a pure transition metal carbide-based composite material.
[0087] Example 4
[0088] The only difference between this embodiment and Embodiment 1 is that:
[0089] In step one of this embodiment, during the preparation of the electrode sheet:
[0090] Titanium dioxide is used as a transition metal oxide, and CaCO3 is used as an additive.
[0091] Furthermore, the molar ratio of titanium dioxide to CaCO3 is 1:1.8;
[0092] During the sintering process in step one:
[0093] The sintering temperature was 900℃ and the sintering time was 4 hours.
[0094] In step two of this embodiment, during the first molten salt electrolysis treatment:
[0095] The molten salt electrolysis temperature was 750℃, the electrolysis voltage was 3.2V, and the electrolysis time was 9h.
[0096] In step three of this embodiment, during the second molten salt electrolysis treatment:
[0097] The molten salt electrolysis temperature was 750℃, the electrolysis voltage was 2.8V, and the electrolysis time was 4h.
[0098] Example 5
[0099] The only difference between this embodiment and Embodiment 1 is that:
[0100] In step one of this embodiment, during the preparation of the electrode sheet:
[0101] Niobium oxide is used as a transition metal oxide;
[0102] Furthermore, the molar ratio of niobium oxide to NH4HCO3 is 1:2.2;
[0103] During the sintering process in step one:
[0104] The sintering temperature was 1000℃ and the sintering time was 2 hours.
[0105] In step two of this embodiment, during the first molten salt electrolysis treatment:
[0106] The molten salt electrolysis temperature was 850℃, the electrolysis voltage was 2.8V, and the electrolysis time was 10h.
[0107] In step three of this embodiment, during the second molten salt electrolysis treatment:
[0108] The molten salt electrolysis temperature was 850℃, the electrolysis voltage was 2.2V, and the electrolysis time was 6h.
[0109] Example 6
[0110] This embodiment provides a lithium-air battery, and its preparation method is as follows:
[0111] 1) Preparation of cathode materials for lithium-air batteries
[0112] The material prepared in Example 1 was mixed with 45 mg of conductive carbon (SP) and 0.1 mL of 10% PTFE at a mass ratio of 4.5:4.5:1, and stirred with 2.5 mL of NMP to obtain a mixture. The mixture was then sprayed onto a cleaned nickel foam with a diameter of 1 cm and a thickness of 1 mm. The sprayed nickel foam was then dried in an oven at 40°C for 8 hours to obtain the lithium-air battery cathode material.
[0113] 2) Equipped with lithium-air batteries
[0114] Assemble the battery in a glove box filled with argon gas:
[0115] Using the above-mentioned lithium-air battery positive electrode material as the positive electrode, lithium sheet as the negative electrode, 1M LiCF3SO3inTEGDME as the electrolyte, and glass fiber filter paper as the separator, a lithium-air battery positive electrode material is assembled.
[0116] After the battery is assembled, it is left to stand for 6 hours in an oxygen atmosphere to allow the electrolyte to fully wet the positive electrode; then oxygen is introduced and left to stand for 3 hours to allow the oxygen to dissolve in the electrolyte.
[0117] Example 7
[0118] This embodiment provides a lithium-air battery, and its preparation method is as follows:
[0119] 1) Preparation of cathode materials for lithium-air batteries
[0120] The material prepared in Example 2 was mixed with 45 mg of conductive carbon (SP) and 0.1 mL of 10% PTFE at a mass ratio of 4.5:4.5:1, and stirred with 2.5 mL of NMP to obtain a mixture. The mixture was then sprayed onto a cleaned nickel foam with a diameter of 1 cm and a thickness of 1 mm. The sprayed nickel foam was then dried in an oven at 40°C for 8 hours to obtain the lithium-air battery cathode material.
[0121] 2) Equipped with lithium-air batteries
[0122] Assemble the battery in a glove box filled with argon gas:
[0123] Using the above-mentioned lithium-air battery positive electrode material as the positive electrode, lithium sheet as the negative electrode, 1M LiCF3SO3inTEGDME as the electrolyte, and glass fiber filter paper as the separator, a lithium-air battery positive electrode material is assembled.
[0124] After the battery is assembled, it is left to stand for 6 hours in an oxygen atmosphere to allow the electrolyte to fully wet the positive electrode; then oxygen is introduced and left to stand for 3 hours to allow the oxygen to dissolve in the electrolyte.
[0125] Example 8
[0126] This embodiment provides a lithium-air battery, and its preparation method is as follows:
[0127] 1) Preparation of cathode materials for lithium-air batteries
[0128] The material prepared in Example 3 was mixed with 45 mg of conductive carbon (SP) and 0.1 mL of 10% PTFE at a mass ratio of 4.5:4.5:1, and stirred with 2.5 mL of NMP to obtain a mixture. The mixture was then sprayed onto a cleaned nickel foam with a diameter of 1 cm and a thickness of 1 mm. The sprayed nickel foam was then dried in an oven at 40°C for 8 hours to obtain the lithium-air battery cathode material.
[0129] 2) Equipped with lithium-air batteries
[0130] Assemble the battery in a glove box filled with argon gas:
[0131] Using the above-mentioned lithium-air battery positive electrode material as the positive electrode, lithium sheet as the negative electrode, 1M LiCF3SO3inTEGDME as the electrolyte, and glass fiber filter paper as the separator, a lithium-air battery positive electrode material is assembled.
[0132] After the battery is assembled, it is left to stand for 6 hours in an oxygen atmosphere to allow the electrolyte to fully wet the positive electrode; then oxygen is introduced and left to stand for 3 hours to allow the oxygen to dissolve in the electrolyte.
[0133] Experimental Section
[0134] (I) Scanning Electron Microscopy (SEM) Testing
[0135] Taking Example 1 as an example, the present invention conducted scanning electron microscopy (SEM) tests at different scales, and the structures are as follows: Figure 1 and Figure 2 As shown, where, Figure 1 The image shows a scanning electron microscope (SEM) image of the transition metal carbide-based composite material prepared in Example 1 at a scale of 200 nm. Figure 2 This is a magnified view of a scanning electron microscope (SEM) image of the transition metal carbide-based composite material prepared in Example 1 at the 100 nm scale.
[0136] And by Figure 1 and Figure 2 It can be seen that the porous structure generated by the high-temperature decomposition of additives causes the transition metal carbide-based composite material produced after electrolysis to form a macroporous structure. This structure is formed by the accumulation of nano-transition metal carbide and its derived carbon nanocomposite particles.
[0137] (II) Electrochemical Performance Testing
[0138] 1) Initial charge and discharge performance
[0139] Taking the lithium-air batteries of Examples 6-8 as examples, the present invention tested their first charge-discharge performance at a current density of 100mA / g (cutoff voltage of 2.2-4.5V), and the test results are shown in Table 1. Table 1 shows the specific capacity performance data of the lithium-air batteries of Examples 6-8 at a current density of 100mA / g during the first charge-discharge.
[0140] Table 1 Performance test results of lithium-air batteries
[0141]
[0142] Figure 3 The first charge-discharge curve of the lithium-air battery in Example 6 is shown at a current density of 100 mA / g (cutoff voltage of 2.2-4.5V). And from... Figure 3 As shown in Table 1, when the transition metal carbide-based composite material obtained in Example 6 is used as the positive electrode catalyst at a current density of 100 mA / g, its discharge plateau is at 2.7 V, its charging plateau is at 4.2 V, and its discharge capacity is 11343 mAh g. -1 The material obtained in Example 7, when used as a positive electrode catalyst, had a discharge plateau of 2.65V, a charging plateau of 4.2V, and a discharge capacity of 10157 mAh g. -1 The material obtained in Example 8, when used as a positive electrode catalyst, had a discharge plateau of 2.6V, a charging plateau of 4.2V, and a discharge capacity of 11245 mAh g. -1 The comparison showed that the material in Example 6 exhibited the best initial charge-discharge performance. This indicates that transition metal carbide-based composite materials, as positive electrode catalysts for lithium-air batteries, possess high discharge specific capacity and represent a novel type of high-performance positive electrode catalyst.
[0143] 2) Performance stability test
[0144] Taking the lithium-air battery of Example 6 as an example, this invention tests its stability at a current density of 500 mA / g and a limited capacity of 1000 mAh / g, and the test results are as follows. Figure 4 As shown.
[0145] Figure 4 The figure shows the stable cycling curve of the lithium-air battery in Example 6 after 100 cycles at a current density of 500 mA / g and a limited capacity of 1000 mAh / g. It can be seen that the charge-discharge overvoltage is only 1.08V in the first cycle and only 1.35V after 100 cycles. This demonstrates that the transition metal carbide-based composite material exhibits good cycle stability when used as the positive electrode catalyst in a lithium-air battery.
[0146] In summary, when transition metal carbide-based composite materials are used as cathode catalysts in lithium-air batteries, they reduce overvoltage and increase specific energy. Furthermore, this nanocomposite material exhibits high catalytic performance for the OER reaction, and its numerous macroporous structures provide more reactive sites for lithium-air batteries.
[0147] This demonstrates that transition metal carbides and their derived carbon nanocomposites are a novel type of high-performance cathode catalyst for lithium-air batteries.
[0148] Obviously, the above embodiments are only some embodiments of the present invention, and not all embodiments. 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.
Claims
1. A method for preparing a transition metal carbide-based composite material, characterized in that, Includes the following steps: Step 1: After uniformly mixing the transition metal oxide with additives, carbon source and binder, press it into a sheet, and then sinter it to obtain the electrode sheet. The carbon source is one or both of multi-walled carbon nanotubes and acetylene black. Step 2: Using a graphite rod as the anode and pre-electrolysis electrode, and the electrode sheet as the cathode, perform molten salt electrolysis on the electrolytic molten salt medium for 9-10 hours; Step 3: Using the electrode sheet from Step 2 as the anode and the graphite rod from Step 2 as the cathode, continue electrolyzing the molten salt medium from Step 2 for 4-6 hours to obtain the transition metal carbide-based composite material. The transition metal oxide is any one of tantalum oxide, titanium dioxide, and niobium oxide; The additive is NH4HCO3 or CaCO3; In step 2, the temperature for molten salt electrolysis is 750~850℃, and the electrolysis voltage is 2.8~3.2V; In step 3, the temperature of molten salt electrolysis is 750~850℃, the electrolysis voltage is 2.2~2.8V, and the electrolytic molten salt medium is a mixture of anhydrous CaCl2 and NaCl.
2. The preparation method according to claim 1, characterized in that, The molar ratio of the transition metal oxide to the additive is 1:1.8~2.2; The ratio of the carbon source to the transition metal oxide is 0.06~1.2g:5mmol.
3. The preparation method according to claim 1, characterized in that, The adhesive is 3% polyvinyl alcohol by mass, and the ratio of the adhesive to the transition metal oxide is 0.08~0.12mL:5mmol.
4. The preparation method according to claim 1, characterized in that, The sintering temperature is 900~1000℃, and the sintering time is 2~4h.
5. The preparation method according to claim 1, characterized in that, The process also includes step 4, in which the transition metal carbide-based composite material obtained in step 3 is placed in distilled water, stirred, centrifuged and circulated at least three times, filtered and dried to obtain a purified transition metal carbide-based composite material.
6. A transition metal carbide-based composite material prepared by the preparation method according to any one of claims 1-5.
7. The application of the transition metal carbide-based composite material according to claim 6 in the preparation of lithium-air batteries, characterized in that, The transition metal carbide-based composite material is used to prepare cathode materials for lithium-air batteries.