Nitrogen-doped transition metal carbide catalyst for decomposing positive electrode material sodium supplement and preparation method and application of nitrogen-doped transition metal carbide catalyst

Abstract

The invention relates to the technical field of positive electrode materials of sodium ion batteries, in particular to a nitrogen-doped transition metal carbide catalyst for decomposing a sodium supplementing agent of a positive electrode material as well as a preparation method and application of the nitrogen-doped transition metal carbide catalyst. The transition metal comprises at least one of chromium, tungsten, molybdenum, vanadium, titanium, manganese and zirconium. According to the nitrogen-doped transition metal carbide catalyst for decomposing the sodium supplementing agent of the positive electrode material, the decomposition voltage of the sodium supplementing agent can be reduced, so that the sodium supplementing requirement of a conventional positive electrode system is met.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode materials for sodium ion batteries, and in particular to a nitrogen-doped transition metal carbide catalyst for decomposing a positive electrode material sodium supplement, and a preparation method and application thereof. Background Art

[0002] At present, the most studied positive electrode sodium supplements include sodium azide (NaN3), sodium peroxide (Na2O2), sodium nickelate (NaNiO2), sodium chromate (NaCrO2), sodium carbonate (Na2CO3), sodium oxalate (Na2C2O4), etc. However, in terms of industrial application, they all have certain shortcomings, such as NaN3 is highly toxic and explosive; NaNiO2 and NaCrO2 have low capacity release efficiency, which not only cannot significantly increase the capacity, but also contain heavy metals that pollute the environment. Therefore, green and safe sodium supplement additives such as sodium carbonate, sodium oxalate and sodium peroxide are more practical, but the decomposition voltage of sodium oxalate is too high, so the decomposition process is often accompanied by various side reactions, including the decomposition of the electrolyte.

[0003] Therefore, how to reduce the decomposition voltage of sodium supplements is a technical problem to be solved urgently in this field. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a nitrogen-doped transition metal carbide catalyst for decomposing a sodium supplement for a positive electrode material, and a preparation method and application thereof. The nitrogen-doped transition metal carbide catalyst for decomposing a sodium supplement for a positive electrode material provided by the present invention can reduce the decomposition voltage of the sodium supplement to meet the sodium supplement demand of a conventional positive electrode system.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a nitrogen-doped transition metal carbide catalyst for decomposing a positive electrode material sodium supplement, wherein the transition metal loading in the nitrogen-doped transition metal carbide catalyst is 30 to 60 wt %.

[0007] The nitrogen-doped transition metal carbide catalyst for decomposing the sodium supplement agent of the positive electrode material provided by the present invention can reduce the decomposition voltage of the sodium supplement agent to meet the sodium supplement demand of the conventional positive electrode system.

[0008] Furthermore, the transition metal includes at least one of chromium, tungsten, molybdenum, vanadium, titanium, manganese and zirconium.

[0009] In a second aspect, the present invention provides a method for preparing a nitrogen-doped transition metal carbide catalyst for decomposing a positive electrode material sodium supplement as described in the first aspect, the preparation method comprising the following steps:

[0010] The nitrogen-doped transition metal carbide catalyst is obtained by mixing a nitrogen source, a transition metal source and a carbon source and calcining them at high temperature.

[0011] Further, the nitrogen source includes at least one of urea, melamine and dicyandiamide;

[0012] And / or, the transition metal source comprises a transition metal oxide, and the transition metal oxide comprises at least one of chromium oxide, tungsten oxide, molybdenum oxide, vanadium oxide, titanium oxide, manganese oxide, and zirconium oxide;

[0013] And / or, the carbon source includes conductive carbon, and the conductive carbon includes at least one of graphene, carbon nanotubes, conductive carbon black, and Ketjen black;

[0014] And / or, the mass ratio of the nitrogen source, the transition metal source and the carbon source is (5-10): (1-5): 1;

[0015] and / or, the mixing comprises ball milling mixing;

[0016] And / or, the atmosphere of the high-temperature calcination is an inert gas atmosphere, the calcination temperature is 500-900° C., and the calcination time is 3-6 hours.

[0017] In a third aspect, the present invention provides a composite sodium supplement, characterized in that the composite sodium supplement comprises a sodium salt and the nitrogen-doped transition metal carbide catalyst described in the first aspect or the nitrogen-doped transition metal carbide catalyst prepared by the preparation method described in the second aspect.

[0018] Furthermore, the sodium salt includes at least one of sodium oxalate, sodium citrate, sodium squarate, and disodium rose palmitate;

[0019] And / or, the mass ratio of the sodium salt to the nitrogen-doped transition metal carbide catalyst is (90-99.9):(0.1-10).

[0020] In a fourth aspect, the present invention provides a method for preparing the composite sodium supplement according to the third aspect, the preparation method comprising the following steps:

[0021] The sodium salt and the nitrogen-doped transition metal carbide catalyst are mixed in a solvent and then freeze-dried to obtain the composite sodium supplement.

[0022] Further, the solvent includes water;

[0023] And / or, the mass ratio of the solvent to the sodium salt is (50-100):1;

[0024] And / or, the freeze-drying process is freezing and drying in sequence, the freezing temperature is -80 to -90°C, the drying temperature is 50 to 70°C, and the drying vacuum degree is -70 to -90 kPa.

[0025] In a fifth aspect, the present invention provides a positive electrode material, which includes the composite sodium supplement described in the third aspect or the composite sodium supplement prepared by the preparation method described in the fourth aspect.

[0026] In a sixth aspect, the present invention provides a secondary battery, wherein the secondary battery comprises the positive electrode material described in the fifth aspect.

[0027] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0028] (1) The nitrogen-doped transition metal carbide catalyst for decomposing the sodium supplement agent of the positive electrode material provided by the present invention can reduce the decomposition voltage of the sodium supplement agent to meet the sodium supplement demand of the conventional positive electrode system.

[0029] (2) By using a nitrogen-doped transition metal carbide catalyst and a sodium supplement, the transition metal carbide catalyst changes the electron cloud distribution around the sodium supplement, greatly reducing the activation energy of the decomposition of the sodium supplement, thereby significantly accelerating the release of sodium ions from the sodium supplement. The nitrogen-doped transition metal carbide synthesized by the present invention has a high specific surface area and a strong adsorption capacity. It can effectively adsorb the nano sodium supplement prepared by freeze drying during the catalytic process, showing excellent ion and electron conduction properties. Thanks to the synergistic effect of the sodium supplement and the nitrogen-doped transition metal carbide, the decomposition voltage of the sodium supplement is reduced and the decomposition efficiency is improved.

[0030] (3) The nitrogen-doped transition metal carbide prepared by the present invention not only has good electrical conductivity, but also has a large specific surface area, which can provide more active sites for the electrochemical oxidation decomposition reaction of the sodium supplement, which is beneficial to improving the reaction kinetics of the oxidation decomposition reaction of the sodium supplement, while optimizing the electron transfer path and reducing the decomposition voltage of the sodium supplement.

[0031] (4) The freeze-drying method provided by the present invention realizes uniform loading of the sodium supplement and the catalyst, and the size of the composite sodium supplement is relatively small, which can effectively improve the electron transport of the sodium supplement.

[0032] (5) The transition metal oxides used in the present invention are natural substances, are cheap and readily available, have simple synthesis methods, and can be produced in large quantities. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 Schematic diagram of the preparation process of nitrogen-doped tungsten carbide provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0036] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0037] In a first aspect, the present invention provides a nitrogen-doped transition metal carbide catalyst for decomposing a positive electrode material sodium supplement, wherein the transition metal loading in the nitrogen-doped transition metal carbide catalyst is 30 to 60 wt%, for example, 30 wt%, 40 wt%, 50 wt% or 60 wt%.

[0038] The nitrogen-doped transition metal carbide catalyst for decomposing the sodium supplement agent of the positive electrode material provided by the present invention can reduce the decomposition voltage of the sodium supplement agent to meet the sodium supplement demand of the conventional positive electrode system.

[0039] In the above-mentioned nitrogen-doped transition metal carbide catalyst for decomposing the positive electrode material sodium supplement, as an optional implementation, the positive electrode material sodium supplement includes at least one of sodium oxalate, sodium citrate, sodium squarate, and disodium rose palmitate (Na2C6O6).

[0040] In the above-mentioned nitrogen-doped transition metal carbide catalyst for decomposing the positive electrode material sodium supplement, as an optional implementation, the transition metal includes at least one of chromium, tungsten, molybdenum, vanadium, titanium, manganese, and zirconium.

[0041] In a second aspect, the present invention provides a method for preparing a nitrogen-doped transition metal carbide catalyst for decomposing a positive electrode material sodium supplement as described in the first aspect, the preparation method comprising the following steps:

[0042] The nitrogen-doped transition metal carbide catalyst is obtained by mixing a nitrogen source, a transition metal source and a carbon source and calcining them at high temperature.

[0043] In the preparation method of the nitrogen-doped transition metal carbide catalyst for decomposing the positive electrode material sodium supplement, as an optional implementation, the nitrogen source includes at least one of urea, melamine, and dicyandiamide.

[0044] In the preparation method of the above-mentioned nitrogen-doped transition metal carbide catalyst for decomposing the positive electrode material sodium supplement, as an optional embodiment, the transition metal source includes a transition metal oxide, and the transition metal oxide includes at least one of chromium oxide, tungsten oxide, molybdenum oxide, vanadium oxide, titanium oxide, manganese oxide, and zirconium oxide.

[0045] In the preparation method of the above-mentioned nitrogen-doped transition metal carbide catalyst for decomposing the positive electrode material sodium supplement, as an optional implementation, the carbon source includes conductive carbon, and the conductive carbon includes at least one of graphene, carbon nanotubes, conductive carbon black, and Ketjen black.

[0046] In the preparation method of the nitrogen-doped transition metal carbide catalyst for decomposing the positive electrode material sodium supplement, as an optional implementation, the mass ratio of the nitrogen source, the transition metal source and the carbon source is (5-10): (1-5):1.

[0047] In the above-mentioned method for preparing the nitrogen-doped transition metal carbide catalyst for decomposing the positive electrode material sodium supplement, as an optional implementation, the mixing includes ball milling mixing.

[0048] In the preparation method of the above-mentioned nitrogen-doped transition metal carbide catalyst for decomposing the positive electrode material sodium supplement, as an optional embodiment, the atmosphere of the high-temperature calcination is an inert gas atmosphere, the calcination temperature is 500-900°C (for example, it can be 500°C, 600°C, 700°C, 800°C or 900°C), preferably 800°C; the calcination time is 3-6h, preferably 5h.

[0049] In a third aspect, the present invention provides a composite sodium supplement, comprising a sodium salt and the nitrogen-doped transition metal carbide catalyst described in the first aspect or the nitrogen-doped transition metal carbide catalyst prepared by the preparation method described in the second aspect.

[0050] In the above-mentioned composite sodium supplement, as an optional embodiment, the sodium salt includes at least one of sodium oxalate, sodium citrate, sodium squarate, and disodium rosinase (Na2C6O6).

[0051] In the above-mentioned composite sodium supplement, as an optional embodiment, the mass ratio of the sodium salt to the nitrogen-doped transition metal carbide catalyst is (90-99.9): (0.1-10), for example, it can be 90:10, 92:8, 93:7, 94:6, 98:2, 99.9:0.1.

[0052] In the above-mentioned composite sodium supplement, as an optional embodiment, the nitrogen-doped transition metal carbide catalyst accounts for 0.1% to 10% of the mass of the composite sodium supplement, for example, 0.1%, 2%, 4%, 6%, 8% or 10%. If the amount of catalyst is low, the sodium salt decomposition voltage is high; conversely, the overall energy density of the battery is reduced if the amount of catalyst is high.

[0053] In a fourth aspect, the present invention provides a method for preparing the composite sodium supplement as described in the third aspect, the preparation method comprising the following steps:

[0054] The sodium salt and the nitrogen-doped transition metal carbide catalyst are mixed in a solvent and then freeze-dried to obtain the composite sodium supplement.

[0055] In the preparation method of the above-mentioned composite sodium supplement, as an optional implementation, the solvent includes water.

[0056] In the preparation method of the above-mentioned composite sodium supplement, as an optional embodiment, the mass ratio of the solvent to the sodium salt is (50-100):1, for example, it can be 50:1, 60:1, 70:1, 80:1, 90:1 or 100:1.

[0057] In the preparation method of the above-mentioned composite sodium supplement, as an optional implementation, the freeze-drying process is freezing and drying in sequence, the freezing temperature is -80 to -90°C, the drying temperature is 50 to 70°C, and the drying vacuum degree is -70 to -90 kPa.

[0058] In a fifth aspect, the present invention provides a positive electrode material, which includes the composite sodium supplement described in the third aspect or the composite sodium supplement prepared by the preparation method described in the fourth aspect.

[0059] In the above-mentioned positive electrode material, as an optional embodiment, the positive electrode material also includes a positive electrode active material, and the positive electrode active material includes but is not limited to at least one of a sodium transition metal oxide, a polyanionic compound and a Prussian blue compound. The present invention is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries can also be used.

[0060] In the above positive electrode material, as an optional implementation, the mass ratio of the composite sodium supplement to the positive electrode active material is (2-5): (92-95).

[0061] In the above-mentioned positive electrode material, as an optional embodiment, in the sodium transition metal oxide, the transition metal may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Non-limiting examples of sodium transition metal oxides may include Na x MO2, wherein M may include one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0<x≤1.

[0062] In the above-mentioned positive electrode material, as an optional embodiment, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y may be one or more of P, S and Si; n represents (YO4) n- valence state.

[0063] Polyanionic compounds can also be those with sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen anions. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y may be one or more of P, S and Si, and n represents (YO4) n- valence state; the halogen can be one or more of F, Cl and Br.

[0064] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedral unit (ZO y ) m+ and an optional halogen anion. Y can be one or more of P, S and Si, and n represents (YO4) n-valence state; Z represents a transition metal, which may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; m represents (ZO y ) m+ valence state; the halogen can be one or more of F, Cl and Br.

[0065] Polyanionic compounds may include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), Na3V2(PO4)2F3 and Na3(VO y )2(PO4)2F 3-2y One or more of (0≤y≤1).

[0066] In the above positive electrode material, as an optional embodiment, the Prussian blue compound can be a compound having sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Non-limiting examples of Prussian blue compounds may include Na a Me b Me c (CN)6, wherein Me and Me' can be independently one or more of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0067] In a sixth aspect, the present invention provides a positive electrode plate, wherein the positive electrode plate comprises the positive electrode material described in the fifth aspect.

[0068] The present invention does not particularly limit the preparation method of the positive electrode sheet, and it can be prepared by referring to the existing method. For example, the positive electrode slurry is coated on the positive electrode current collector, dried, and cold pressed to form the positive electrode sheet. The positive electrode slurry can be formed by dispersing the components such as the positive electrode material of the sodium ion battery, the optional conductive agent, and the optional binder in a solvent (such as N-methylpyrrolidone) and stirring them evenly.

[0069] In a seventh aspect, the present invention provides a secondary battery, comprising the positive electrode sheet described in the sixth aspect.

[0070] It is understandable that the secondary battery can be a sodium ion battery. In the above-mentioned secondary battery, as an optional embodiment, the secondary battery also includes a negative electrode plate, a separator and an electrolyte. During the battery charging and discharging process, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays the role of conducting ions between the positive electrode plate and the negative electrode plate. The separator is arranged between the positive electrode plate and the negative electrode plate, which can prevent the positive and negative electrodes from short-circuiting, and at the same time allow ions to pass through.

[0071] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0072] Comparative Example 1

[0073] Preparation of sodium oxalate: Weigh 4 g of commercial sodium oxalate and dissolve it in 200 g of water. Freeze the sodium oxalate aqueous solution in a freeze dryer at -85°C for 1 h, and then dry it in a sample drying chamber for 24 h. The drying temperature is 60°C and the drying vacuum is -80 kPa to obtain sodium oxalate.

[0074] Example 1

[0075] Figure 1 The schematic diagram of the preparation process of nitrogen-doped tungsten carbide provided in this embodiment is as follows: Figure 1 As shown, the preparation method of nitrogen-doped tungsten carbide provided in this embodiment comprises the following steps: melamine, WO3, and CNT are placed in a constant temperature blast drying oven for 8 hours. 8g of dried melamine, 3.28g of dried WO3, and 0.8g of dried CNT are placed in a ball mill for ball milling; the ball-milled mixture is calcined in a muffle furnace filled with argon gas, and kept at 800°C for 5 hours to obtain nano-scale nitrogen-doped tungsten carbide, and the tungsten loading in the nitrogen-doped tungsten carbide is 50wt%.

[0076] The preparation method of the composite sodium supplement provided in this embodiment comprises the following steps: dissolving 4 g of sodium oxalate and 0.04 g of nitrogen-doped tungsten carbide in 200 g of water, ultrasonicating for 30 min to obtain a uniformly dispersed mixed solution, and then placing the mixed solution in a vacuum freeze dryer for freezing and drying, freezing in a freezing chamber at -85°C for 1 h, and drying in a sample drying chamber for 24 h, the drying temperature is 60°C, and the drying vacuum is -80 kPa, to obtain a composite sodium supplement.

[0077] Example 2

[0078] The preparation method of nitrogen-doped tungsten carbide provided in this embodiment comprises the following steps: placing melamine, WO3, and CNT in a constant temperature forced air drying oven for drying for 8 hours. Taking 8g of dried melamine, 3.28g of dried WO3, and 0.8g of dried CNT and placing them in a ball mill for ball milling; calcining the ball-milled mixture in a muffle furnace filled with argon gas, and keeping the temperature at 800°C for 5 hours to obtain nano-scale nitrogen-doped tungsten carbide.

[0079] The preparation method of the composite sodium supplement provided in this embodiment comprises the following steps: dissolving 4 g of sodium oxalate and 0.082 g of nitrogen-doped tungsten carbide in 200 g of water, ultrasonicating for 30 min to obtain a uniformly dispersed mixed solution, and then placing the mixed solution in a freeze dryer for freezing and drying, freezing in a freezing chamber at -85°C for 1 h, and drying in a sample drying chamber for 24 h, the drying temperature is 60°C, and the drying vacuum is -80 kPa, to obtain a composite sodium supplement.

[0080] Example 3

[0081] The preparation method of nitrogen-doped tungsten carbide provided in this embodiment comprises the following steps: placing melamine, WO3, and CNT in a constant temperature forced air drying oven for drying for 8 hours. Taking 8g of dried melamine, 3.28g of dried WO3, and 0.8g of dried CNT and placing them in a ball mill for ball milling; calcining the ball-milled mixture in a muffle furnace filled with argon gas, and keeping the temperature at 800°C for 5 hours to obtain nano-scale nitrogen-doped tungsten carbide.

[0082] The preparation method of the composite sodium supplement provided in this embodiment comprises the following steps: dissolving 4 g of sodium oxalate and 0.12 g of nitrogen-doped tungsten carbide in 200 g of water, ultrasonicating for 30 min to obtain a uniformly dispersed mixed solution, and then placing the mixed solution in a freeze dryer for freezing and drying, freezing in a freezing chamber at -85°C for 1 h, and drying in a sample drying chamber for 24 h, the drying temperature is 60°C, and the drying vacuum is -80 kPa, to obtain a composite sodium supplement.

[0083] Example 4

[0084] The preparation method of nitrogen-doped molybdenum carbide provided in this embodiment comprises the following steps: melamine, MoO3 and CNT are placed in a constant temperature blast drying oven for drying for 8 hours. 6g of dried melamine, 2.32g of dried MoO3 and 0.8g of dried CNT are placed in a ball mill for ball milling; the ball milled mixture is calcined in a muffle furnace filled with argon and kept at 800°C for 5 hours to obtain nano-scale nitrogen-doped molybdenum carbide, in which the molybdenum loading in the nitrogen-doped molybdenum carbide is 50wt%.

[0085] The preparation method of the composite sodium supplement provided in this embodiment comprises the following steps: dissolving 4 g of sodium oxalate and 0.04 g of nitrogen-doped molybdenum carbide in 200 g of water, ultrasonicating for 30 min to obtain a uniformly dispersed mixed solution, and then placing the mixed solution in a freeze dryer for freezing and drying, freezing in a freezing chamber at -85°C for 1 h, and drying in a sample drying chamber for 24 h, the drying temperature is 60°C, and the drying vacuum is -80 kPa, to obtain a composite sodium supplement.

[0086] Example 5

[0087] The preparation method of nitrogen-doped tungsten carbide provided in this embodiment is basically the same as that in Embodiment 3, except that the calcination temperature is 500° C. and the calcination time is 6 h.

[0088] The composite sodium supplement was prepared by referring to the preparation method of the composite sodium supplement provided in Example 3.

[0089] Comparative Example 2

[0090] The preparation method of the catalyst provided in this comparative example is basically the same as that of Example 3, except that WO3 is not added during the preparation process.

[0091] The composite sodium supplement was prepared by referring to the preparation method of the composite sodium supplement provided in Example 3.

[0092] Comparative Example 3

[0093] The preparation method of nitrogen-doped cobalt carbide provided in this comparative example is basically the same as the preparation method of nitrogen-doped tungsten carbide in Example 3, except that WO3 is replaced by transition metal Co2O3, and the loading amount of cobalt in the nitrogen-doped cobalt carbide is 50wt%.

[0094] The composite sodium supplement was prepared by referring to the preparation method of the composite sodium supplement provided in Example 3.

[0095] Comparative Example 4

[0096] The preparation method of nitrogen-doped copper carbide provided in this comparative example is basically the same as the preparation method of nitrogen-doped tungsten carbide in Example 3, except that WO3 is replaced by transition metal CuO, and the copper loading in the nitrogen-doped copper carbide is 50wt%.

[0097] The composite sodium supplement was prepared by referring to the preparation method of the composite sodium supplement provided in Example 3.

[0098] Comparative Example 5

[0099] The preparation method of nitrogen-doped tungsten carbide provided in this comparative example is exactly the same as that of Example 3.

[0100] The preparation method of the composite sodium supplement provided in this comparative example comprises the following steps: dissolving 4 g of sodium oxalate and 0.12 g of nitrogen-doped tungsten carbide in 200 g of water, ultrasonicating for 30 min to obtain a uniformly dispersed mixed solution, and then evaporating the mixed solution at 110° C.

[0101] Performance Testing

[0102] The sodium supplement in each embodiment and comparative example was respectively prepared into a mixed slurry in NMP according to the mass ratio of positive electrode active material (Na3V2(PO4)2F3): sodium supplement: conductive agent (Ketjen black): binder (PVDF) = 94:3:1:2, and then the slurry was evenly coated on a carbon-coated aluminum foil, vacuum dried at 120°C for 8h, and cut into Φ12mm positive electrode sheets after drying, matched with Φ14mm metal sodium sheets, and the electrolyte was NaPF6+EC+PC+EMC system. The battery was assembled into a sodium ion battery, and charged and discharged at a current of 50mA / g between 2.0 and 4.7V, and the decomposition voltage and first cycle charge specific capacity of the sodium supplement were recorded. The results are shown in Table 1.

[0103] Table 1

[0104]

[0105] From Table 1, we can see at least the following points:

[0106] (1) By comparing the embodiment with comparative example 1, it can be seen that the nitrogen-doped transition metal carbide catalyst for decomposing the positive electrode material sodium supplement provided by the present invention can reduce the decomposition voltage of the sodium supplement.

[0107] (2) By comparing Example 3 with Comparative Example 2, it can be seen that when the catalyst does not include a transition metal, the decomposition voltage of the sodium supplement increases.

[0108] (3) Comparing Example 3 and Example 4 with Comparative Examples 3 and 4, the catalyst prepared by the transition metal selected in the present invention can significantly reduce the decomposition voltage of the sodium supplement compared with conventional transition metals.

[0109] (4) By comparing Example 3 with Comparative Example 5, it can be seen that in the preparation process of the composite sodium supplement, when freeze drying is replaced by direct drying at high temperature, the decomposition voltage of the sodium supplement increases.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A nitrogen-doped transition metal carbide catalyst for decomposing a positive electrode material sodium supplement, characterized in that: The transition metal loading in the nitrogen-doped transition metal carbide catalyst is 30-60 wt %.

2. The nitrogen-doped transition metal carbide catalyst for decomposing the positive electrode material sodium supplement according to claim 1, characterized in that: The transition metal includes at least one of chromium, tungsten, molybdenum, vanadium, titanium, manganese and zirconium.

3. A method for preparing a nitrogen-doped transition metal carbide catalyst for decomposing a positive electrode material sodium supplement as claimed in claim 1 or 2, characterized in that: The preparation method comprises the following steps: The nitrogen-doped transition metal carbide catalyst is obtained by mixing a nitrogen source, a transition metal source and a carbon source and calcining them at high temperature.

4. The method for preparing the nitrogen-doped transition metal carbide catalyst for decomposing the positive electrode material sodium supplement according to claim 3, characterized in that: The nitrogen source includes at least one of urea, melamine and dicyandiamide; And / or, the transition metal source comprises a transition metal oxide, and the transition metal oxide comprises at least one of chromium oxide, tungsten oxide, molybdenum oxide, vanadium oxide, titanium oxide, manganese oxide, and zirconium oxide; And / or, the carbon source includes conductive carbon, and the conductive carbon includes at least one of graphene, carbon nanotubes, conductive carbon black, and Ketjen black; And / or, the mass ratio of the nitrogen source, the transition metal source and the carbon source is (5-10): (1-5): 1; And / or, the mixing comprises ball milling mixing; And / or, the atmosphere of the high-temperature calcination is an inert gas atmosphere, the calcination temperature is 500-900° C., and the calcination time is 3-6 hours.

5. A composite sodium supplement, characterized in that: The composite sodium supplement comprises a sodium salt and the nitrogen-doped transition metal carbide catalyst according to claim 1 or 2 or the nitrogen-doped transition metal carbide catalyst prepared by the preparation method according to claim 3 or 4.

6. The composite sodium supplement according to claim 5, characterized in that The sodium salt includes at least one of sodium oxalate, sodium citrate, sodium squarate, and disodium rosehip salt; And / or, the mass ratio of the sodium salt to the nitrogen-doped transition metal carbide catalyst is (90-99.9):(0.1-10).

7. A method for preparing the composite sodium supplement as claimed in claim 5 or 6, characterized in that: The preparation method comprises the following steps: The sodium salt and the nitrogen-doped transition metal carbide catalyst are mixed in a solvent and then freeze-dried to obtain the composite sodium supplement.

8. The method for preparing the composite sodium supplement according to claim 7, characterized in that: The solvent includes water; And / or, the mass ratio of the solvent to the sodium salt is (50-100):1; And / or, the freeze-drying process is freezing and drying in sequence, the freezing temperature is -80 to -90°C, the drying temperature is 50 to 70°C, and the drying vacuum degree is -70 to -90 kPa.

9. A positive electrode material, characterized in that: The positive electrode material includes the composite sodium supplement agent according to claim 5 or 6 or the composite sodium supplement agent prepared by the preparation method according to claim 7 or 8.

10. A secondary battery, characterized in that: The secondary battery comprises the positive electrode material according to claim 9.

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