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

Abstract

The application relates to the technical field of sodium ion battery positive electrode materials, in particular to a nitrogen-doped transition metal carbide catalyst for decomposing a positive electrode material sodium supplement agent and a preparation method and application thereof, wherein the transition metal loading of the nitrogen-doped transition metal carbide catalyst is 30-60 wt%, and the transition metal includes at least one of chromium, tungsten, molybdenum, vanadium, titanium, manganese and zirconium. The nitrogen-doped transition metal carbide catalyst for decomposing the positive electrode material sodium supplement agent can reduce the decomposition voltage of the sodium supplement agent, so as to meet the sodium supplement demand of a conventional positive electrode system.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode material technology, and in particular to a nitrogen-doped transition metal carbide catalyst for the decomposition of sodium supplementation agents in cathode materials, its preparation method, and its application. Background Technology

[0002] Currently, the most researched positive electrode sodium supplements include sodium azide (NaN3), sodium peroxide (Na2O2), sodium nickelate (NaNiO2), sodium chromate (NaCrO2), sodium carbonate (Na2CO3), and sodium oxalate (Na2C2O4). However, in terms of industrial application, they all have certain shortcomings. For example, NaN3 is highly toxic and explosive; NaNiO2 and NaCrO2 have low capacity release efficiency, not only failing to significantly improve capacity but also causing environmental pollution due to their heavy metal content. Therefore, green and safe sodium supplements such as sodium carbonate, sodium oxalate, and sodium peroxide are more practical. However, sodium oxalate has an excessively high decomposition voltage, which often leads to various side reactions during the decomposition process, including electrolyte decomposition.

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

[0004] In view of the above-mentioned shortcomings in the prior art, the purpose of this invention is to provide a nitrogen-doped transition metal carbide catalyst for the decomposition of sodium supplementation agents in cathode materials, its preparation method and application. The nitrogen-doped transition metal carbide catalyst for the decomposition of sodium supplementation agents in cathode materials provided by this invention can reduce the decomposition voltage of sodium supplementation agents to meet the sodium supplementation requirements of conventional cathode systems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a nitrogen-doped transition metal carbide catalyst for the decomposition of sodium supplementation agent in cathode materials, wherein the transition metal loading in the nitrogen-doped transition metal carbide catalyst is 30-60 wt%.

[0007] The nitrogen-doped transition metal carbide catalyst for sodium replenishment decomposition in cathode materials provided by this invention can reduce the decomposition voltage of sodium replenishment agents to meet the sodium replenishment requirements of conventional cathode systems.

[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 the decomposition of sodium supplementation agent in cathode materials 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 then calcining them at high temperature.

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

[0012] And / or, the transition metal source includes a transition metal oxide, which includes 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, which includes at least one of graphene, carbon nanotubes, conductive carbon black, and Ketjen black;

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

[0015] And / or, the mixing includes ball milling mixing;

[0016] And / or, the atmosphere for high-temperature calcination is an inert gas atmosphere, the calcination temperature is 500-900℃, and the calcination time is 3-6h.

[0017] Thirdly, 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 squartzate, and disodium rosinate;

[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] Fourthly, the present invention provides a method for preparing the compound sodium supplement described in the third aspect, the 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] Furthermore, 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 consists of freezing and drying in sequence, wherein 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] Fifthly, the present invention provides a positive electrode material, the positive electrode material comprising the composite sodium supplement agent described in the third aspect or the composite sodium supplement agent prepared by the preparation method described in the fourth aspect.

[0026] In a sixth aspect, the present invention provides a secondary battery comprising 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 sodium replenishment decomposition of cathode material provided by the present invention can reduce the decomposition voltage of sodium replenishment to meet the sodium replenishment requirements of conventional cathode system.

[0029] (2) By using a nitrogen-doped transition metal carbide catalyst and a sodium supplement, the transition metal carbide catalyst alters the electron cloud distribution around the sodium supplement, significantly reducing the activation energy for sodium supplement decomposition and thus significantly accelerating the release of sodium ions from the sodium supplement. The nitrogen-doped transition metal carbide synthesized in this invention has a high specific surface area and strong adsorption capacity. During the catalytic process, it can effectively adsorb the nano-sodium supplement prepared by freeze-drying, exhibiting 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 conductivity, but also has a large specific surface area, which can provide more active sites for the electrochemical oxidation decomposition reaction of sodium supplement, which is beneficial to improve the reaction kinetics of the oxidation decomposition reaction of sodium supplement, while optimizing the electron transfer path and reducing the decomposition voltage of sodium supplement.

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

[0032] (5) The transition metal oxides used in this invention are natural materials that are cheap and readily available. The synthesis method is simple and can be mass-produced. Attached Figure Description

[0033] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the preparation process of nitrogen-doped tungsten carbide provided in Example 1 of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0036] The endpoints and any values ​​of the ranges disclosed in this 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0037] In a first aspect, the present invention provides a nitrogen-doped transition metal carbide catalyst for the decomposition of sodium supplementation agent in cathode materials, 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 sodium replenishment decomposition in cathode materials provided by this invention can reduce the decomposition voltage of sodium replenishment agents to meet the sodium replenishment requirements of conventional cathode systems.

[0039] In the above-mentioned nitrogen-doped transition metal carbide catalyst for decomposing the sodium supplementer of the cathode material, as an optional embodiment, the sodium supplementer of the cathode material includes at least one of sodium oxalate, sodium citrate, sodium squartzate, and disodium rosinate (Na2C6O6).

[0040] In the above-mentioned nitrogen-doped transition metal carbide catalyst for sodium supplementation decomposition of cathode materials, as an optional embodiment, 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 the decomposition of sodium supplementation agent in cathode materials 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 then calcining them at high temperature.

[0043] In the above-mentioned method for preparing a nitrogen-doped transition metal carbide catalyst for sodium supplementation decomposition of cathode materials, as an optional embodiment, the nitrogen source includes at least one of urea, melamine, and dicyandiamine.

[0044] In the above-mentioned method for preparing a nitrogen-doped transition metal carbide catalyst for decomposing sodium supplementation agent in cathode materials, as an optional embodiment, the transition metal source includes a transition metal oxide, which includes at least one of chromium oxide, tungsten oxide, molybdenum oxide, vanadium oxide, titanium oxide, manganese oxide, and zirconium oxide.

[0045] In the above-mentioned method for preparing nitrogen-doped transition metal carbide catalyst for sodium supplementation decomposition of cathode materials, as an optional embodiment, 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 above-mentioned method for preparing nitrogen-doped transition metal carbide catalyst for sodium supplementation decomposition of cathode material, as an optional embodiment, the mass ratio of nitrogen source, transition metal source and carbon source is (5-10):(1-5):1.

[0047] In the above-mentioned method for preparing nitrogen-doped transition metal carbide catalysts for sodium supplementation decomposition of cathode materials, as an optional embodiment, the mixing includes ball milling mixing.

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

[0049] Thirdly, the present invention provides a composite sodium supplement agent, which 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.

[0050] In the above-mentioned compound sodium supplement, as an optional embodiment, the sodium salt includes at least one of sodium oxalate, sodium citrate, sodium squartzate, and disodium rosinate (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, or 99.9:0.1.

[0052] In the aforementioned 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 catalyst dosage is low, the sodium salt decomposition voltage is high; conversely, a high catalyst dosage reduces the overall energy density of the battery.

[0053] Fourthly, the present invention provides a method for preparing the compound sodium supplement as described in the third aspect, the 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 above-mentioned method for preparing the compound sodium supplement, as an optional embodiment, the solvent includes water.

[0056] In the above-mentioned method for preparing the compound 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 above-mentioned method for preparing the compound sodium supplement, as an optional embodiment, the freeze-drying process consists of freezing and drying in sequence, wherein 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] Fifthly, the present invention provides a positive electrode material, the positive electrode material comprising the composite sodium supplement agent described in the third aspect or the composite sodium supplement agent prepared by the preparation method described in the fourth aspect.

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

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

[0061] In the aforementioned cathode material, as an optional embodiment, the transition metal in the sodium transition metal oxide may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. A non-limiting example of the sodium transition metal oxide is Na. x MO2, where M can include one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0062] In the aforementioned cathode material, as an optional embodiment, the polyanionic compound may be a compound containing 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- The price state.

[0063] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds consisting of anionic units and halide 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- The valence state; halogens can be one or more of F, Cl and Br.

[0064] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be one or more of P, S, and Si, and n represents (YO4). n-The valence state; Z represents a transition metal, which can include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents (ZO). y ) m+ The valence state; halogens can be one or more of F, Cl and Br.

[0065] Polyanionic compounds can 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 aforementioned cathode material, as an optional embodiment, the Prussian blue compound may contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds containing Prussian blue. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. A non-limiting example of Prussian blue compounds is Na. a Me b Me c (CN)6, wherein Me and Me' can each be 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 sheet, the positive electrode sheet comprising 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 can refer to existing methods. 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 sodium-ion battery positive electrode material, optional conductive agent, optional binder, etc. in a solvent (e.g., N-methylpyrrolidone) and stirring evenly.

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

[0070] It is understood that the secondary battery can be a sodium-ion battery. In one optional embodiment, the secondary battery further includes a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

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

[0072] Comparative Example 1

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

[0074] Example 1

[0075] Figure 1 This is a schematic diagram of the preparation process of nitrogen-doped tungsten carbide provided in this embodiment, as shown below. Figure 1 As shown, the method for preparing nitrogen-doped tungsten carbide provided in this embodiment includes the following steps: melamine, WO3, and CNT are dried in a constant temperature forced-air 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 and ball-milled. The uniformly mixed mixture is calcined in a muffle furnace filled with argon gas and held at 800℃ for 5 hours to obtain nano-sized nitrogen-doped tungsten carbide with a tungsten loading of 50wt%.

[0076] The preparation method of the composite sodium supplement provided in this embodiment includes the following steps: 4g of sodium oxalate and 0.04g of nitrogen-doped tungsten carbide are dissolved in 200g of water and sonicated for 30min to obtain a uniformly dispersed mixed solution. Then, the mixed solution is placed in a vacuum freeze dryer for freezing and drying treatment. The solution is frozen in a freezing chamber at -85℃ for 1h and dried in a sample drying chamber for 24h at a drying temperature of 60℃ and a vacuum degree of -80kPa to obtain the composite sodium supplement.

[0077] Example 2

[0078] The method for preparing nitrogen-doped tungsten carbide provided in this embodiment includes the following steps: Melamine, WO3, and CNT are dried in a constant temperature forced-air 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 and ball-milled. The uniformly mixed mixture is calcined in a muffle furnace filled with argon gas and held at 800℃ for 5 hours to obtain nano-sized nitrogen-doped tungsten carbide.

[0079] The method for preparing the composite sodium supplement provided in this embodiment includes the following steps: 4g of sodium oxalate and 0.082g of nitrogen-doped tungsten carbide are dissolved in 200g of water and sonicated for 30min to obtain a uniformly dispersed mixed solution. Then, the mixed solution is placed in a freeze dryer for freezing and drying. The solution is frozen in a freezer at -85℃ for 1h and dried in a sample drying chamber for 24h at a temperature of 60℃ and a vacuum degree of -80kPa to obtain the composite sodium supplement.

[0080] Example 3

[0081] The method for preparing nitrogen-doped tungsten carbide provided in this embodiment includes the following steps: Melamine, WO3, and CNT are dried in a constant temperature forced-air 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 and ball-milled. The uniformly mixed mixture is calcined in a muffle furnace filled with argon gas and held at 800℃ for 5 hours to obtain nano-sized nitrogen-doped tungsten carbide.

[0082] The preparation method of the composite sodium supplement provided in this embodiment includes the following steps: 4g of sodium oxalate and 0.12g of nitrogen-doped tungsten carbide are dissolved in 200g of water and sonicated for 30min to obtain a uniformly dispersed mixed solution. Then, the mixed solution is placed in a freeze dryer for freezing and drying treatment. The freeze treatment is carried out in a freezer at -85℃ for 1h and dried in a sample drying chamber for 24h at a drying temperature of 60℃ and a vacuum degree of -80kPa to obtain the composite sodium supplement.

[0083] Example 4

[0084] The method for preparing nitrogen-doped molybdenum carbide provided in this embodiment includes the following steps: Melamine, MoO3, and CNTs are dried in a constant temperature forced-air drying oven for 8 hours. 6g of dried melamine, 2.32g of dried MoO3, and 0.8g of dried CNTs are placed in a ball mill and ball-milled. The uniformly mixed mixture is calcined in a muffle furnace filled with argon gas and held at 800℃ for 5 hours to obtain nanoscale nitrogen-doped molybdenum carbide with a molybdenum loading of 50wt%.

[0085] The preparation method of the composite sodium supplement provided in this embodiment includes the following steps: 4g of sodium oxalate and 0.04g of nitrogen-doped molybdenum carbide are dissolved in 200g of water and sonicated for 30min to obtain a uniformly dispersed mixed solution. Then, the mixed solution is placed in a freeze dryer for freezing and drying treatment. The freeze treatment is carried out in a freezer at -85℃ for 1h and dried in a sample drying chamber for 24h at a drying temperature of 60℃ and a vacuum degree of -80kPa to obtain the 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 Example 3, except that the calcination temperature is 500℃ and the calcination time is 6h.

[0088] The compound sodium supplement was prepared according to the preparation method of the compound 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 in Example 3, except that WO3 is not added during the preparation process.

[0091] The compound sodium supplement was prepared according to the preparation method of the compound 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. The difference is that WO3 is replaced by the transition metal Co2O3, and the loading of cobalt in nitrogen-doped cobalt carbide is 50 wt%.

[0094] The compound sodium supplement was prepared according to the preparation method of the compound 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. The difference is that WO3 is replaced with CuO as a transition metal, and the copper loading in nitrogen-doped copper carbide is 50 wt%.

[0097] The compound sodium supplement was prepared according to the preparation method of the compound 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 in Example 3.

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

[0101] Performance testing

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

[0103] Table 1

[0104]

[0105] At least the following points can be observed from Table 1:

[0106] (1) Comparing the examples with Comparative Example 1, it can be seen that the nitrogen-doped transition metal carbide catalyst for sodium supplementation decomposition of positive electrode material provided by the present invention can reduce the decomposition voltage of sodium supplementation.

[0107] (2) Comparing Example 3 with Comparative Example 2, it can be seen that when the catalyst does not contain transition metals, the decomposition voltage of the sodium supplement increases.

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

[0109] (4) 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, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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 compound sodium supplement, characterized in that, The composite sodium supplement includes sodium salt and nitrogen-doped transition metal carbide catalyst; The nitrogen-doped transition metal carbide catalyst has a transition metal loading of 30–60 wt%. The preparation method of the compound sodium supplement includes the following steps: The sodium salt and the nitrogen-doped transition metal carbide catalyst were mixed in a solvent and then freeze-dried to obtain the composite sodium supplement. The transition metal is at least one of chromium, tungsten, molybdenum, vanadium, titanium, manganese, and zirconium; The sodium salt is at least one of sodium oxalate, sodium citrate, sodium squartzate, and disodium rosinate; The mass ratio of the sodium salt to the nitrogen-doped transition metal carbide catalyst is (90-99.9):(0.1-10).

2. The compound sodium supplement according to claim 1, characterized in that, The preparation method of the nitrogen-doped transition metal carbide catalyst includes 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 then calcining them at high temperature.

3. The compound sodium supplement according to claim 2, characterized in that, The nitrogen source includes at least one of urea, melamine, and dicyandiamide; And / or, the transition metal source includes a transition metal oxide, which includes 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, which includes at least one of graphene, carbon nanotubes, conductive carbon black, and Ketjen black; And / or, the mass ratio of the nitrogen source, transition metal source and carbon source is (5-10):(1-5):1; And / or, the mixing is ball milling mixing; And / or, the atmosphere for high-temperature calcination is an inert gas atmosphere, the calcination temperature is 500-900℃, and the calcination time is 3-6h.

4. The compound sodium supplement according to claim 1, 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 consists of freezing and drying in sequence, wherein 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.

5. A positive electrode material, characterized in that, The positive electrode material includes the composite sodium supplement as described in any one of claims 1-4.

6. A secondary battery, characterized in that, The secondary battery includes the positive electrode material as described in claim 5.

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