A sodium-doped carbon composite supplementing additive and application thereof in sodium-ion batteries

Abstract

The application provides a sodium-doped carbon composite supplementing additive and application thereof in a sodium ion battery. The supplementing additive contains a carbon-based nonmetal catalyst and a sodium salt, and is prepared into a positive electrode of the sodium ion battery together with a positive active material, a conductive additive and a binder. The application mainly performs element doping on the carbon-based nonmetal catalyst, and then performs compounding on the sodium salt. The sodium ions generated by decomposition of the compound can effectively solve the problem of low energy density of the battery caused by irreversible consumption of sodium ions, and the supplementing additive has the advantages of high first-cycle capacity, greatly reduced degradation voltage, high utilization rate, excellent safety and chemical stability, environmental friendliness, wide source, low cost, good operability and good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of chemical power source technology, specifically relating to a carbon-doped composite sodium supplement additive and its application in sodium-ion batteries. Background Technology

[0002] Although sodium-ion batteries and lithium-ion batteries operate on similar principles, their different metal ion insertion / extraction radii lead to drastically different requirements for electrode materials. Many electrode materials widely used in lithium-ion batteries are ineffective in sodium-ion batteries. The cycle life of a battery is related to the stability of interfaces such as the electrode-electrolyte interface. Interface formation is often accompanied by irreversible sodium ion consumption, especially at the negative electrode-electrolyte interface. This consumption is particularly pronounced in full cells compared to half-cells because the SEI film formed during the initial charge / discharge cycle consumes sodium ions, and this consumption is irreversible. Therefore, the key to controlling cycle stability and energy density in full cells lies in suppressing or reducing the irreversible consumption of a limited number of sodium ions. To address this issue, research has found that introducing sodium-replenishing additives at the positive electrode can effectively compensate for this irreversible consumption.

[0003] Patent CN111653744A discloses a sodium-replenishing additive that is a compound of sodium oxide and organic sodium salt. However, the sodium oxide in this patent is unstable in air and reacts with water and oxygen, leading to impurities in the additive, poor consistency, and significant performance fluctuations in the battery, making it unsuitable for industrial production. Patent CN111834622A discloses a sodium-replenishing agent with a metal oxide catalyst. However, the limited contact area with the additive restricts sodium ion migration, resulting in low sodium replenishment efficiency. Furthermore, the catalyst's limited activity cannot guarantee long-term stability. Patent CN113113681A discloses a sodium-replenishing additive with a metal oxide carbon catalyst. This metal oxide carbon catalyst is a composite of metal oxide and a carbon substrate, effectively reducing the decomposition potential of electrochemically inert sodium salts during battery cycling. However, this decomposition potential may be due to side reactions caused by the metal oxide, and it remains unclear whether the metal oxide acts as a catalyst or a reactant.

[0004] Therefore, it is necessary to study new composite sodium supplementation additives to reduce decomposition potential and low capacity while minimizing side reactions to improve the performance of sodium-ion batteries. To this end, the present invention provides a carbon-doped composite sodium supplementation additive and its application in sodium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a carbon-doped composite sodium-supplementing additive and its application in sodium-ion batteries. By adding a sodium-supplementing additive to the cathode material, the above-mentioned problems can be solved. The additional sodium ions provided by the sodium-supplementing additive during the formation process can compensate for the irreversible sodium ion consumption caused by side reactions or interface formation in the battery system, thereby improving the actual capacity of the whole battery and effectively improving the cycle life and energy density of sodium-ion batteries.

[0006] The specific technical solution adopted by this invention is as follows: A carbon-doped composite sodium supplementation additive comprises a doped carbon-based nonmetallic catalyst and a sodium salt, wherein the mass ratio of the carbon-based nonmetallic catalyst to the sodium salt is 1:200-1:2.5.

[0007] Preferably, the doped carbon-based nonmetallic catalyst is a carbon material doped with nonmetallic elements.

[0008] Preferably, the carbon material is selected from one or more of single-walled / multi-walled carbon nanotubes (SWCNTs / MWCNTs), graphene oxide (GO), reduced graphene oxide (RGO), Ketjen black (KB), activated carbon (AC), mesoporous carbon (CMK-3), and their functionalized derivatives.

[0009] Preferably, the functionalized derivatives of the carbon material include one or more of carboxylation, hydroxylation, and amination.

[0010] Preferably, the doped nonmetallic element includes one or more of N, S, P, B, Se, O, F, Cl, and Br; wherein the nonmetallic element accounts for 0.1-20 wt% of the carbon-based nonmetallic catalyst by mass.

[0011] Preferably, the sodium salt comprises one or more of the following: inorganic sodium salt, nitrogen-containing sodium salt, azide, and organic sodium salt; Among them: Inorganic sodium salts: NaCuO, Na3CuO2, Na4FeO3, Na2CO3, NaHCO3, Na2SO4, NaHSO4, NaNO3, Na3PO4, Na2HPO4, NaH2PO4; Azides: NaN3; Nitrogen-containing sodium salts: NaNO3, NaNO2; Organic sodium salts: Na2C3O3, Na2C4O4, Na2C5O5, Na2C6O6, Na2C2O4, Na2C3O5, Na2C4O6, Na2C5O7, Na2C6O8.

[0012] Preferably, the preparation of the doped carbon-based nonmetallic catalyst is selected from solution-assisted method and pure solid-phase method.

[0013] The solution-assisted method includes the following steps: thoroughly mixing the carbon source with the acid, reacting at 40-200℃ for 1-18 hours, cooling to room temperature, removing the solvent, and drying; then thoroughly mixing the obtained precursor directly or with a reagent containing a non-metallic element, heat-treating at 350-1000℃ for 1-8 hours under an inert atmosphere, and cooling to room temperature. The acidic solution is one or more of sulfuric acid, nitric acid, and hydrochloric acid.

[0014] Preferably, the preparation of the composite sodium supplement is selected from the solution method or the solid-phase method; The solution method includes direct evaporation or recrystallization: according to the mass ratio of carbon-based non-metallic catalyst and sodium salt, 40-100 ml of secondary water is added to the doped carbon-based non-metallic catalyst and sodium salt, and the mixture is ultrasonically mixed uniformly for 0.1-6 h.

[0015] Direct evaporation: Place the above-obtained solution in a forced-air drying oven and evaporate it at a temperature of 60-150℃ for 6-72 hours. After complete evaporation, the compound sodium supplement is obtained.

[0016] Recrystallization: Place the obtained solution in a pear-shaped funnel and add it dropwise to 100-200 mL of ethanol solution at a rate of 0.5 mL / min-5 mL / min. The preferred rate is 1.5 mL / min, and the preferred volume of ethanol solution is 150 mL. Filter the solution after the addition and wash it three times with ethanol. Dry the resulting material at 230°C for 5 hours to obtain the composite sodium supplement additive.

[0017] The solid-state method includes ball milling or grinding: the doped carbon-based non-metallic catalyst and sodium salt are weighed according to the mass ratio of carbon-based non-metallic catalyst and sodium salt; Ball milling and mixing: The weighed sodium salt and carbon-based non-metallic catalyst are added to a ball mill jar, 5-50 mL of ethanol is added for wet milling, the ball milling time is 0.1-24 h, and then dried to obtain a composite sodium supplement additive. Grinding: The weighed sodium salt and carbon-based non-metallic catalyst are added to a mortar and mixed with a grinding rod for 0.1-1 hours to obtain a composite sodium supplement additive.

[0018] A method for preparing a positive electrode sheet containing a carbon-doped composite sodium-supplementing additive, wherein the carbon-doped composite sodium-supplementing additive is mixed uniformly with a positive electrode active material, a conductive additive and a binder in a solvent, and then coated onto a current collector and dried to obtain a pre-sodiumized positive electrode sheet.

[0019] Preferably, the amount of the carbon-doped composite sodium-supplementing additive added is 2-25 wt% based on the positive electrode active material, more preferably 5-20 wt%, and even more preferably 5-10 wt%. The positive electrode active material is selected from at least one of transition metal layered oxides, polyanion compounds, Prussian blue, and sodium-containing organic compounds, preferably transition metal layered oxides, Na(Ni x Mn 1-x )O2(0 < x < 1), Na 2 / 3 (Ni x Mn y Ti 1-x-y )O2(0 < x < 1, 0 < y < 1), and one or more of them. The content is 5-20 wt% based on the total, preferably 10-15 wt%.

[0020] The conductive additive is selected from one or more of conductive carbon black (SP), carbon nanotubes (CNT), acetylene black (AB), Ketjen black (KB), graphene oxide (GO), and ordered mesoporous carbon (CMK-3), preferably conductive carbon black (SP) and acetylene black (AB). The content is 70-95 wt% based on the total, preferably 80-90 wt%.

[0021] The binder is selected from one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), and polyvinyl alcohol (PVA), preferably polyvinylidene fluoride (PVDF). The content is 5-20 wt% based on the total, preferably 10-15 wt%.

[0022] The technical effects achieved by the present invention are as follows: The carbon-based catalyst doped with non-metallic elements provided by the present invention can effectively solve the electron transfer problem of electrochemically inert sodium salts. Its composite effect is to use the high specific surface area of the carbon substrate to increase the contact area with sodium salts, thereby enhancing the corresponding catalytic effect. Compared with the sodium supplement of metal-based catalysts, carbon itself is used as a catalyst, and part of it can be used as a conductive agent.

[0023] By doping carbon materials as catalysts in the present invention, the doping of some non-metallic atoms into carbon can expose more catalytic sites, and at the same time, the ability of carbon materials to absorb atoms can be improved during the doping process. For example, when nitrogen atoms are introduced into the carbon skeleton, the conductivity and catalytic stability of the carbon material can be adjusted. Nitrogen atoms are very helpful for electron transfer and the utilization of sodium ions. By using the specific surface advantage of the carrier to optimize the electron transfer path, the decomposition potential of electrochemically inert sodium salts during the battery cycle can be effectively reduced, enabling sodium ions to be quickly decomposed and released during battery charging, and effectively supplementing the consumption of sodium ions.

[0024] The carbon-doped catalyst introduced in this invention can significantly reduce the electrochemical oxidation decomposition potential of sodium salts, and can completely decompose sodium salts within a suitable voltage range in the first cycle without any side reactions; the raw materials for the sodium supplement are widely available and low in cost. Attached Figure Description

[0025] Figure 1 The XRD pattern of the composite additive containing 10 wt% KB sodium oxalate obtained in Example 4 is shown.

[0026] Figure 2 The XRD pattern of the 10 wt% nitrogen-doped sodium oxalate composite additive prepared in Example 4 is shown. Figure 3 This is a SEM image of sodium oxalate composite containing 10 wt% nitrogen-doped KB.

[0027] Figure 4 The charge-discharge curves of a sodium battery assembled with a sodium oxalate composite additive containing 10 wt% KB are shown.

[0028] Figure 5 Charge-discharge curves of sodium batteries assembled with a 10wt% nitrogen-doped sodium oxalate composite additive.

[0029] Figure 6 Charge-discharge curves of sodium batteries assembled with sodium oxalate composite additives containing 10 wt% sulfur-doped KB content.

[0030] Figure 7 Charge-discharge curves of sodium batteries assembled with a 10wt% nitrogen- and sulfur-containing sodium oxalate composite additive. Detailed Implementation

[0031] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0032] Example: Synthesis of carbon-doped nonmetallic catalysts Example 1: Synthesis of acid-treated KB Weigh 2g of KB, mix it with concentrated sulfuric acid, and hydrothermally react it at 80℃ for 8 hours to remove residual metal on the surface and roughen the surface of the carbon material. After filtration and washing of the acid-treated Ketjen black until neutral, place it in a drying oven to dry and obtain acid-treated KB.

[0033] Example 2: Synthesis of nitrogen-doped KB Accurately weigh 0.5000g of acid-treated KB and 0.5000g of melamine and place them in an agate mortar. Grind thoroughly for 20 minutes to ensure that the acid-treated KB and melamine are evenly mixed. Transfer the ground sample to a ceramic boat and place it in a tube furnace. Then, purge the tube furnace with nitrogen for 30 minutes to ensure that the air is completely removed. Set the heating rate to 5℃ / min and maintain it at 700℃ for 2 hours. After the reaction is completed, continue to purge with nitrogen until the temperature drops to room temperature to obtain N-KB.

[0034] Example 3: Synthesis of sulfur-doped KB 0.8 g of sulfur was dissolved in carbon disulfide (CS2, 10 ml), then 0.2 g of KB was added to the sulfur-CS2 solution, followed by sonication for 15 minutes. The homogenized slurry was stirred overnight at ambient temperature to evaporate the CS2. Finally, the mixture was hydrothermally reacted at 155 °C for 12 hours to obtain S-KB.

[0035] Example 4: Synthesis of nitrogen- and sulfur-doped KB Accurately weigh 0.5000g of acid-treated KB and 0.5000g of thiourea into an agate mortar and grind them thoroughly for 20 minutes to ensure uniform mixing of the acid-treated KB and thiourea. Transfer the ground sample to a porcelain boat and place it in a tube furnace. Then, purge the tube furnace with nitrogen for 30 minutes to ensure that all air is removed. Set the heating rate to 5℃ / min and maintain it at 600℃ for 2 hours. After the reaction is complete, continue to purge with nitrogen until the temperature drops to room temperature to obtain N,S-KB.

[0036] Example 5: Synthesis of Boron-Doped KB A mixture of ground KB powder (100 mg) and H3BO3 (500 mg) was dispersed in 50 mL of DIW at room temperature by sonication for 30 minutes, followed by vigorous stirring for approximately 3 hours to promote H3BO3 adsorption on the KB carbon surface. Next, the precursor solution was placed in an oven at 80 °C. Water was evaporated, and the resulting solid powder was calcined in a tube furnace at 900 °C for 4 hours. Excess unreacted material was removed with DIW (deionized water). The mixture was then dried in a drying oven to obtain B-KB.

[0037] Example 6: Synthesis of sodium oxalate containing 10 wt% KB complex Dissolve 900 mg of sodium oxalate and 100 mg of commercial KB in 50 mL of deionized water to obtain solution A. Slowly add solution A to 150 mL of ethanol solution while stirring to form a precipitate. Then filter, dry, and place in a muffle furnace at 230 °C for 5 h to obtain 10% KB composite sodium oxalate.

[0038] Example 7: Synthesis of sodium oxalate containing 10 wt% N-KB complex As in Example 6, the 100mg commercial KB was replaced with N-KB synthesized in Example 2, and the other steps were the same as in Example 6.

[0039] Example 8: Synthesis of sodium oxalate containing 10 wt% S-KB complex As in Example 6, the 100mg commercial KB was replaced with the S-KB synthesized in Example 3, and the other steps were the same as in Example 6.

[0040] Example 9: Synthesis of sodium oxalate containing 10 wt% N,S-KB complex As in Example 6, the 100mg commercial KB was replaced with N,S-KB synthesized in Example 4, and the other steps were the same as in Example 6.

[0041] Example 10: Synthesis of sodium oxalate containing 10 wt% B-KB complex As in Example 6, the 100mg commercial KB was replaced with the B-KB synthesized in Example 5, and the other steps were the same as in Example 6.

[0042] Example 11: A mixture containing 10wt% KB composite sodium oxalate, conductive additive acetylene black, and binder PVDF is mixed in 70 parts, 20 parts, and 10 parts by weight, dissolved in solvent NMP, and stirred to obtain a uniform slurry. The slurry is then coated onto aluminum foil using a grinding rod, dried, and sliced ​​to obtain a positive electrode material with sodium-added additives.

[0043] Example 12: A mixture containing 10wt% N-KB composite sodium oxalate, conductive additive acetylene black, and binder PVDF is mixed in 70 parts, 20 parts, and 10 parts by weight, dissolved in solvent NMP, and stirred to obtain a uniform slurry. The slurry is then coated onto aluminum foil using a grinding rod, dried, and sliced ​​to obtain a positive electrode material with sodium-added additives.

[0044] Example 13: A mixture containing 10wt% S-KB composite sodium oxalate, conductive additive acetylene black, and binder PVDF is mixed in 70 parts, 20 parts, and 10 parts by weight, dissolved in solvent NMP, and stirred to obtain a uniform slurry. The slurry is then coated onto aluminum foil using a grinding rod, dried, and sliced ​​to obtain a positive electrode material with sodium-added additives.

[0045] Example 14: A mixture containing 10wt% N,S-KB composite sodium oxalate, conductive additive acetylene black, and binder PVDF is mixed in 70 parts, 20 parts, and 10 parts by weight, dissolved in solvent NMP, and stirred to obtain a uniform slurry. The slurry is then coated onto aluminum foil using a grinding rod, dried, and sliced ​​to obtain a positive electrode material with sodium-added additives.

[0046] Example 15: A mixture containing 10wt% B-KB composite sodium oxalate, conductive additive acetylene black, and binder PVDF is mixed in 70 parts, 20 parts, and 10 parts by weight, dissolved in solvent NMP, and stirred to obtain a uniform slurry. The slurry is then coated onto aluminum foil using a grinding rod, dried, and sliced ​​to obtain a positive electrode material with sodium-added additives.

[0047] Example 16: The operation steps are the same as in Example 11, except that KB is replaced with single-walled carbon nanotubes.

[0048] Example 17: The operation steps are the same as in Example 11, except that KB is replaced with multi-walled carbon nanotubes.

[0049] Example 18: The operating steps are the same as in Example 11, except that KB is replaced with activated carbon.

[0050] Example 19: The operation steps are the same as in Example 11, except that KB is replaced with CMK-3.

[0051] Example 20: The operation steps are the same as in Example 11, except that KB is replaced with graphene.

[0052] Example 21: Na, the positive electrode active material 2 / 3 Ni 1 / 3 Mn 1 / 3 Ti 1 / 3 O2, conductive additive acetylene black (AB), and binder PVDF are mixed in 70 parts, 20 parts, and 10 parts by weight, respectively. Then, 10 wt% of sodium oxalate containing 10 wt% KB composite obtained in Example 6 is added and dissolved in solvent NMP. After stirring, a uniform slurry is obtained. The slurry is then coated onto aluminum foil using a grinding rod, dried, and sliced ​​to obtain the positive electrode material with sodium-added additive.

[0053] Example 22: Na, the positive electrode active material 2 / 3 Ni 1 / 3 Mn 1 / 3 Ti 1 / 3O2, conductive additive acetylene black (AB), and binder PVDF are mixed in 70 parts, 20 parts, and 10 parts by weight, respectively. Then, 10 wt% of the active material containing 10 wt% N-KB composite sodium oxalate as obtained in Example 7 is added and dissolved in solvent NMP. After stirring, a uniform slurry is obtained. The slurry is then coated onto aluminum foil using a grinding rod, dried, and sliced ​​to obtain the positive electrode material with sodium-added additive.

[0054] Example 23: Na, the positive electrode active material 2 / 3 Ni 1 / 3 Mn 1 / 3 Ti 1 / 3 O2, conductive additive acetylene black (AB), and binder PVDF are mixed in 70 parts, 20 parts, and 10 parts by weight, respectively. Then, 10 wt% of the active material containing 10 wt% S-KB composite sodium oxalate as obtained in Example 8 is added and dissolved in solvent NMP. After stirring, a uniform slurry is obtained. The slurry is then coated onto aluminum foil using a grinding rod, dried, and sliced ​​to obtain the positive electrode material with sodium-added additive.

[0055] Example 24: Na, the positive electrode active material 2 / 3 Ni 1 / 3 Mn 1 / 3 Ti 1 / 3 O2, conductive additive acetylene black (AB), and binder PVDF are mixed in 70 parts, 20 parts, and 10 parts by weight, respectively. Then, 10 wt% of sodium oxalate containing 10 wt% N,S-KB composite obtained in Example 9 is added and dissolved in solvent NMP. After stirring, a uniform slurry is obtained. The slurry is then coated onto aluminum foil using a grinding rod, dried, and sliced ​​to obtain the positive electrode material with sodium-added additive.

[0056] Comparative Example 1: Na, the positive electrode material 2 / 3 Ni 1 / 3 Mn 1 / 3 Ti 1 / 3 O2, conductive additive acetylene black (AB), and binder PVDF are mixed in a weight ratio of 70:20:10, and then sodium carbonate (10 wt% of the active material) is added and dissolved in solvent NMP. The remaining operation steps are the same as in Example 16.

[0057] Comparative Example 2: Na, the positive electrode material 2 / 3 Ni 1 / 3 Mn 1 / 3 Ti 1 / 3O2, conductive additive acetylene black (AB), and binder PVDF are mixed in a weight ratio of 70:20:10. Then, 10 wt% of the active material is added. This is the same as in Example 6, except that sodium oxalate is replaced with sodium carbonate. The other steps are the same as in Example 6. The resulting KB composite sodium carbonate is dissolved in the solvent NMP. The remaining operation steps are the same as in Example 16.

[0058] Comparative Example 3: Na, the positive electrode material 2 / 3 Ni 1 / 3 Mn 1 / 3 Ti 1 / 3 O2, conductive additive acetylene black (AB), and binder PVDF are mixed in a weight ratio of 70:20:10. Then, 10 wt% of the active material is added, which is the same as in Example 7, except that sodium oxalate is replaced with sodium carbonate. The other steps are the same as in Example 7. The resulting nitrogen-doped KB composite sodium carbonate is dissolved in the solvent NMP. The remaining operation steps are the same as in Example 16.

[0059] Application example: Testing of electrochemical performance Electrochemical performance testing: Coin cells were assembled using the electrodes obtained in Examples 11-24 and Comparative Examples 1-3 as positive electrodes, metallic sodium sheets as negative electrodes, glass fiber as separators, and 1 mol / L NaClO4 (PC + 5% FEC) as electrolyte. Charge-discharge cycles were performed at a current density of 20 mA / g within a voltage range of 2–4.6 V. The electrochemical performance of the sodium batteries from the examples and comparative examples of this invention was tested, and the results are shown in Table 1.

[0060] from Figure 1 and Figure 2 It can be seen that the synthesized material has no other impurity peaks, indicating that the synthesized material is a pure phase. Figures 3 to 5 It can be seen that KB after acid treatment ( Figure 4 ) has a certain effect on grain refinement, and the composite sodium oxalate ( Figure 5 It can be seen that sodium oxalate adheres to the acid-treated KB; the sodium-supplementing additive obtained in the preparation example provided by the present invention has a small and uniform particle size. When it is combined with KB doped with some elements and sodium oxalate to prepare a cathode material ( Figure 5This demonstrates that the sodium-replenishing additive was successfully added to the cathode material. Table 1 shows that after adding sodium to the sodium-ion battery and doping the sodium-replenishing agent with carbon composite, the first-cycle charging capacity of the sodium battery was significantly improved. In the examples, it was found that the decomposition potential of the carbon composite sodium-replenishing additive after doping was lower than that of the ordinary pure additive; the capacity of the carbon composite sodium-replenishing additive after doping was higher than that of the ordinary pure additive. Finally, applying the doped carbon composite sodium-replenishing additive to the cathode material also resulted in a decrease in decomposition potential, increased capacity, and a higher capacity than the cathode material with conventional carbon composite sodium-replenishing additive, with a lower decomposition voltage. This indicates that the doped carbon composite sodium-replenishing additive of the present invention can be applied to sodium-ion batteries for sodium ion compensation. Furthermore, the final comparative example, replacing sodium oxalate with sodium carbonate in the examples, also achieved the same effect, reducing the decomposition voltage and increasing capacity. This demonstrates that the doped carbon catalyst of the present invention is effective for sodium-replenishing additives and is not unique. From the analysis of the effects of doping elements on sodium-ion batteries in the examples, it can be seen that N and S doping have the best effect. After N and S atoms are introduced into carbon materials, they can act as unique electron acceptors on the carbon skeleton, thereby improving the overall electrochemical performance. Doping with N and S can activate the adjacent C atoms in the carbon materials and affect the valence bond orbital energy levels of C atoms. Moreover, N and S also have a certain synergistic effect, thereby improving the electrocatalytic performance.

[0061] In summary, in terms of first-cycle charging capacity and decomposition voltage, the capacity of the battery with added carbon-doped composite sodium supplementation additive in the embodiments of the present invention is improved to a certain extent, and the sodium salt decomposition voltage is reduced. This indicates that the carbon-doped composite sodium supplementation additive selected in the present invention can achieve the purpose of sodium supplementation. In contrast, the battery without the carbon-doped catalyst of the present invention and the battery without carbon composite additive are slightly worse in terms of discharge specific capacity, sodium salt decomposition voltage and stability.

[0062] This invention provides a carbon-doped composite sodium supplement additive and its application in sodium-ion batteries. Its contribution to the prior art is that it can significantly reduce the decomposition potential of electrochemically inert sodium salts, thereby achieving efficient decomposition of sodium salts within the normal charge and discharge range of the battery and improving the electrochemical performance of the battery.

[0063] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A carbon-doped composite sodium supplement additive, characterized in that: It includes doped carbon-based nonmetallic catalysts and sodium salts, wherein the mass ratio of carbon-based nonmetallic catalysts to sodium salts is 1:200-1:2.

5.

2. The carbon-doped composite sodium-supplementing additive according to claim 1, characterized in that, The doped carbon-based nonmetallic catalyst is a carbon material doped with nonmetallic elements.

3. The carbon-doped composite sodium supplementary additive according to claim 1 or 2, characterized in that, The carbon material is selected from one or more of single-walled / multi-walled carbon nanotubes (SWCNTs / MWCNTs), graphene oxide (GO), reduced graphene oxide (RGO), Ketjen black (KB), activated carbon (AC), mesoporous carbon (CMK-3), and their functionalized derivatives.

4. The carbon-doped composite sodium supplementary additive according to claim 3, characterized in that, The functionalized derivatives of the carbon material include one or more of carboxylation, hydroxylation, and amination.

5. The carbon-doped composite sodium-supplementing additive according to claim 4, characterized in that, The doped nonmetallic element includes one or more of N, S, P, B, Se, O, F, Cl, and Br; wherein the nonmetallic element accounts for 0.1-20 wt% of the carbon-based nonmetallic catalyst by mass.

6. The carbon-doped composite sodium-supplementing additive according to claim 5, characterized in that: The sodium salt includes one or more of the following: inorganic sodium salts, nitrogen-containing sodium salts, azides, and organic sodium salts; Among them: Inorganic sodium salts: NaCuO, Na3CuO2, Na4FeO3, Na2CO3, NaHCO3, Na2SO4, NaHSO4, NaNO3, Na3PO4, Na2HPO4, NaH2PO4; Azides: NaN3; Nitrogen-containing sodium salts: NaNO3, NaNO2; Organic sodium salts: Na2C3O3, Na2C4O4, Na2C5O5, Na2C6O6, Na2C2O4, Na2C3O5, Na2C4O6, Na2C5O7, Na2C6O8.

7. The carbon-doped composite sodium-supplementing additive according to claim 6, characterized in that: The preparation of the doped carbon-based nonmetallic catalyst is selected from solution-assisted method and pure solid-phase method; The solution-assisted method includes the following steps: thoroughly mixing the carbon source with the acid, reacting at 40-200℃ for 1-18h, cooling to room temperature, removing the solvent and drying; then thoroughly mixing the obtained precursor directly or with a reagent containing non-metallic elements, heat-treating at 350-1000℃ for 1-8h under an inert atmosphere, and cooling to room temperature; the acidic solution is one or more of sulfuric acid, nitric acid, and hydrochloric acid.

8. The carbon-doped composite sodium-supplementing additive according to claim 7, characterized in that: The preparation of the composite sodium supplement is selected from solution method or solid phase method; The solution method includes direct evaporation or recrystallization: according to the mass ratio of carbon-based non-metallic catalyst and sodium salt, 40-100 ml of secondary water is added to the doped carbon-based non-metallic catalyst and sodium salt, and the mixture is ultrasonically mixed uniformly for 0.1-6 h. Direct evaporation: Place the above-obtained solution in a forced-air drying oven and evaporate it at a temperature of 60-150℃ for 6-72 hours. After complete evaporation, the compound sodium supplementation additive is obtained. Recrystallization: Place the above-obtained solution into a pear-shaped funnel and add it dropwise to 100-200 mL of ethanol solution at a rate of 0.5 mL / min-5 mL / min; preferably at a rate of 1.5 mL / min, and preferably at a volume of 150 mL of ethanol solution; filter the solution after the addition and wash it three times with ethanol; dry the obtained material at 230 °C for 5 hours to obtain the composite sodium supplement additive; The solid-state method includes ball milling or grinding: the doped carbon-based non-metallic catalyst and sodium salt are weighed according to the mass ratio of the carbon-based non-metallic catalyst and sodium salt. Ball milling and mixing: The weighed sodium salt and carbon-based non-metallic catalyst are added to a ball mill jar, 5-50 mL of ethanol is added for wet milling, the ball milling time is 0.1-24 h, and then dried to obtain a composite sodium supplement additive. Grinding: The weighed sodium salt and carbon-based non-metallic catalyst are added to a mortar and mixed with a grinding rod for 0.1-1 hours to obtain a composite sodium supplement additive.

9. A method for preparing a positive electrode sheet containing a carbon-doped composite sodium-supplementing additive, characterized in that, The doped carbon composite sodium-supplementing additive as described in any one of claims 1-8 is mixed uniformly with the positive electrode active material, conductive additive and binder in a solvent, and then coated onto the current collector and dried to obtain a pre-sodiumized positive electrode sheet.

10. The method for preparing a positive electrode sheet according to claim 9, characterized in that, The amount of the carbon-doped composite sodium-supplementing additive added is 2-25 wt% based on the positive electrode active material; The positive electrode active material is selected from at least one of transition metal layered oxides, polyanionic compounds, Prussian blue, and organic compounds containing sodium. The conductive additive is selected from one or more of conductive carbon black (SP), carbon nanotubes (CNT), acetylene black (AB), Ketjen black (KB), graphene oxide (GO), and ordered mesoporous carbon (CMK-3). The adhesive is selected from one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), and polyvinyl alcohol (PVA).

Images