Sodium supplementing agent, sodium ion battery and preparation method of sodium supplementing agent

Abstract

The invention provides a sodium supplementing agent, a sodium ion battery and a preparation method of the sodium supplementing agent, and belongs to the technical field of secondary batteries, and the sodium supplementing agent comprises an inner core and a coating layer. Wherein the inner core comprises NaxLi3-xBO3, and x is more than or equal to 1.5 and less than 3; the coating layer is positioned on the outer side of the inner core and comprises a carbon material. The sodium supplementing agent provided by the invention effectively improves the gram volume development and cycle life of the sodium ion battery.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a sodium supplement, a sodium-ion battery, and a method for preparing the sodium supplement. Background Technology

[0002] Energy storage technology has developed rapidly in recent years, with lithium-ion batteries being the most representative. Lithium-ion batteries are characterized by long cycle life and high energy density, and are widely used in consumer electronics, new energy vehicles, and aerospace.

[0003] The rapid development of the lithium battery industry has also driven up the price of lithium salts, leading to a sharp increase in raw material costs. This has limited the further development and application of lithium-ion batteries. Sodium-ion batteries, due to their highly competitive cost advantages and sustainable resource supply, have attracted attention and are expected to become a substitute for lithium-ion batteries.

[0004] Similar to lithium-ion batteries, sodium-ion batteries also suffer from the loss of active sodium due to irreversible reactions such as the formation of the SEI film on the negative electrode surface. This results in low charge / discharge specific capacity and poor cycle performance in actual charge / discharge processes, which seriously affects the commercialization of sodium-ion batteries.

[0005] Therefore, it is necessary to design a sodium supplement, a sodium-ion battery, and a method for preparing the sodium supplement in order to improve the above-mentioned problems. Summary of the Invention

[0006] This invention provides a sodium supplement, a sodium-ion battery, and a method for preparing the sodium supplement, in order to improve the technical problems of low charge-discharge capacity and poor cycle performance of sodium-ion batteries.

[0007] In a first aspect, the present invention provides a sodium supplement comprising a core and a coating layer.

[0008] The kernel includes Na x Li 3-x BO3, 1.5≤x<3; the coating layer is located outside the core and includes carbon materials.

[0009] In one example of the present invention, the coating layer is doped with non-metallic heteroatoms, which include at least one of N, B, S, and P.

[0010] In one example of the present invention, the mass content of the non-metallic heteroatoms in the coating layer is 1% to 10%.

[0011] In one example of the present invention, in the Na x Li 3-x In BO3, 1.6 ≤ x ≤ 2.8.

[0012] In one example of the present invention, the D50 particle size of the kernel is 0.5~10μm.

[0013] In one example of the present invention, the core has a mass content of 85% to 96% in the sodium supplement, and the coating layer has a mass content of 4% to 15% in the sodium supplement.

[0014] In one example of the present invention, the carbon material includes at least one of graphene, carbon nanotubes, hard carbon, soft carbon, carbon fiber, and conductive carbon.

[0015] In a second aspect, the present invention also provides a method for preparing a sodium supplement, the method comprising: The lithium source, sodium source, and boron source are mixed and sintered in stoichiometric ratio to obtain the core material; The core material and the coating material are mixed and ground to obtain a sodium supplement, wherein the coating material includes carbon material.

[0016] In one example of the present invention, the preparation method further includes a preparation step of the coating material, the preparation step including: mixing and sintering carbon material with non-metallic element raw materials to obtain the coating material; the coating material includes carbon material doped with non-metallic atoms.

[0017] In a third aspect, the present invention also provides a sodium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises a positive current collector and a positive active material layer, and the positive active material layer comprises a sodium supplement agent as described in any of the preceding examples, or a sodium supplement agent prepared by the preparation method described in any of the preceding examples.

[0018] In one example of the present invention, when the sodium-ion battery is in a 100% charged state, the surface of the negative electrode of the sodium-ion battery has a solid electrolyte interface film, and the solid electrolyte interface film contains lithium.

[0019] The sodium supplement provided by this invention includes core Na x Li 3-xThe sodium-ion battery consists of BO3 and a carbon coating layer located outside the core. During the initial formation of the sodium-ion battery, the core material preferentially releases lithium ions before releasing sodium ions. The lithium ions that dissolve in the electrolyte first participate in the formation of a lithium-containing SEI film on the negative electrode surface, reducing the loss of active sodium ions in the sodium replenishment agent due to participation in SEI film formation. Furthermore, the resulting more stable SEI film reduces the loss of active sodium ions due to repeated dissolution and regeneration during charge and discharge, thus effectively improving the specific capacity and cycle life of the sodium-ion battery. Additionally, after releasing sodium ions, the sodium replenishment agent forms a solid-phase product within the positive electrode, effectively preventing its own decomposition from increasing battery gas production. The product remaining in the positive electrode also exhibits good chemical stability, ensuring that the sodium replenishment agent does not undergo side reactions with the electrolyte or active materials after decomposition, thereby effectively mitigating the problems of battery gas production and deterioration of cycle stability caused by the introduction of the sodium replenishment agent. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other embodiments based on these drawings without inventive effort.

[0021] In the attached diagram: Figure 1 This is a schematic diagram of the structure of the sodium supplement in one embodiment of the present invention; Figure 2 This is a schematic flowchart of a sodium supplement preparation method according to an embodiment of the present invention.

[0022] The attached figures are labeled as follows: 10. Core; 20. Coating layer; 21. Carbon material; 22. Non-metallic heteroatoms. Detailed Implementation

[0023] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. It should also be understood that the terminology used in the embodiments of the present invention is for describing specific implementation schemes and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0024] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" used in this specification are only for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as part of the scope of the invention.

[0025] In this specification, the median particle size (D50) can be defined as the equivalent diameter of the particle corresponding to the cumulative particle size distribution curve reaching 50%. The median particle size (D50) can be measured, for example, by laser diffraction. D50 can be obtained using a HELOS-RODOS type dry laser particle size analyzer. Laser diffraction can typically measure particle sizes from the submicron range to several millimeters, thus providing highly reproducible and high-resolution results.

[0026] The applicant's research found that during the charging and discharging process of sodium-ion batteries, the SEI film (Solid Electrolyte Interface) formed on the negative electrode surface is mainly composed of sodium-containing organic and inorganic compounds. Compared to the SEI film in lithium-ion batteries, this SEI film has stronger solubility in the electrolyte and poorer stability at high temperatures. The unstable SEI film in sodium-ion batteries continuously dissolves and regenerates during charging and discharging, thus continuously consuming active sodium ions in the battery. This makes it difficult for sodium-ion batteries to meet energy storage requirements in practical applications in terms of charge / discharge capacity and cycle life.

[0027] Currently, while the industry uses sodium-replenishing materials to replenish active sodium in sodium-ion batteries to reduce the adverse effects of active sodium loss, these methods, though effective in compensating for the energy density deficiency caused by sodium deficiency in the cathode material, cannot prevent the unstable SEI film on the anode surface from continuously consuming active sodium ions. This results in suboptimal sodium replenishment and fails to effectively improve the charge / discharge capacity and cycle life of sodium-ion batteries.

[0028] While some sodium-rich supplemental materials can achieve efficient sodium replenishment in batteries with low decomposition potentials, these materials release gases during decomposition to release sodium. For example, Na₂CO₃ releases O₂ or CO₂, and Na₂O₂ releases O₂. Furthermore, the decomposition products of these materials are highly reactive and can easily catalyze the electrolyte, thus exacerbating the battery's gas production problem during storage. Specifically, commonly used sodium supplements such as sodium-rich ternary sodium salts release active sodium during the initial charge of sodium-ion batteries, which still participates in the formation of the SEI film on the negative electrode surface. This fails to address the poor stability of the SEI film on the negative electrode surface, making it difficult to effectively improve the charge / discharge capacity and cycle life of sodium-ion batteries. In addition, sodium-rich ternary sodium salts, containing transition metal elements, have high chemical activity. When releasing sodium ions, they easily release active oxygen, and the decomposition of residual transition metal oxides in the positive electrode not only reduces the battery's specific capacity but also catalyzes the electrolyte, further worsening gas production during subsequent charge / discharge cycles.

[0029] To address the aforementioned problems, this application provides a sodium supplement containing a core material, Na. x Li 3-x BO3. During the initial charge formation process, the core material of this sodium replenisher can preferentially release lithium ions before releasing sodium ions. This allows the preferentially released lithium ions to participate in the formation of the SEI film on the negative electrode surface, thereby reducing the amount of sodium ions released by the sodium replenisher participating in the formation of the SEI film. At the same time, by introducing lithium elements into the SEI film, the stability of the SEI film is improved, reducing the risk of dissolution of the SEI film during charge and discharge, and reducing the loss of active sodium caused by repeated dissolution and regeneration of the SEI film during charge and discharge. This effectively improves the specific capacity and cycle life of the sodium-ion battery.

[0030] like Figure 1 As shown, in a first aspect, the sodium supplement provided in this application includes a core 10 and a coating layer 20. The core 10 includes Na... x Li 3-x BO3, where 1.5 < x < 3, for example, the core 10 material can be Na. 1.6 Li 1.4 BO3, Na 1.8 Li 1.2 BO3, Na2LiBO3, Na 2.2 Li 0.8 BO3, Na 2.4 Li 0.6 BO3, Na 2.5 Li 0.5 BO3, Na 2.6 Li 0.4 BO3, Na 2.8 Li 0.2BO3. The coating layer 20 covers the outside of the core 10, and the coating layer 20 includes carbon material 21.

[0031] Based on the characteristic that lithium ions have a smaller radius than sodium ions and therefore lower extraction resistance, the core 10 material Na... x Li 3-x Introducing lithium ions into BO3 to replace some sodium ions can, on the one hand, reduce the decomposition potential of the sodium replenisher and increase its specific capacity during the first charge; on the other hand, it allows lithium ions in the sodium replenisher to be released into the electrolyte before sodium ions during the first charge formation process. The lithium ions dissolved in the electrolyte will participate in the formation of the SEI film on the negative electrode surface before sodium ions, thereby reducing the amount of sodium ions lost in the sodium replenisher due to participating in the formation of the SEI film, and further improving the charging specific capacity of the sodium replenisher.

[0032] Furthermore, compared to SEI films formed solely by sodium ions, SEI films formed by lithium ions exhibit better electrochemical stability. The resulting SEI film is less likely to dissolve in the electrolyte during charge and discharge, reducing the amount of active sodium ions consumed by repeated dissolution and regeneration during charge and discharge, thereby effectively improving the charge and discharge capacity and cycle life of sodium-ion batteries.

[0033] Furthermore, compared to the drawbacks of sodium-rich ternary sodium salts, which are prone to transition metal dissolution and catalytic electrolyte gas generation after sodium removal, the sodium replenishing agent in this application uses Na as the core material. x Li 3-x BO3 uses borate groups to support active sodium ions, which can further improve the energy density of the sodium supplement. On the other hand, compared with transition metal sodium salts, the desodium decomposition products of this sodium supplement are mostly solid products, which can reduce the gas production of the sodium supplement itself and make the desodium products of the sodium supplement have relatively good stability, avoiding catalytic effects on the electrolyte, thereby further reducing the gas production of sodium-ion batteries during charge-discharge cycles.

[0034] The coating layer 20, based on the high conductivity of the carbon material 21, can effectively reduce the migration resistance of electrons in the sodium supplement, lower the decomposition potential of the sodium supplement, and thus improve the sodium supplementation efficiency. At the same time, the coating layer 20 can also effectively reduce the direct contact between the core 10 and the external environment, improving the air stability of the sodium supplement.

[0035] In some embodiments, the mass content of the core 10 in the sodium supplement is any value in the range of 85% to 96%, for example, the mass content of the core 10 can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% or 96%.

[0036] In some embodiments, the mass content of the coating layer 20 in the sodium supplement is any value in the range of 4% to 15%, for example, the mass content of the coating layer 20 can be 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

[0037] In some embodiments, the core 10 material is Na. x Li 3-x BO3, where 1.6 ≤ x ≤ 2.8, for example, the core 10 material could be Na. 1.6 Li 1.4 BO3, Na 1.7 Li 1.3 BO3, Na 1.8 Li 1.2 BO3, Na 1.9 Li 1.1 BO3, Na2LiBO3, Na 2.1 Li 0.9 BO3, Na 2.2 Li 0.8 BO3, Na 2.3 Li 0.7 BO3, Na 2.4 Li 0.6 BO3, Na 2.5 Li 0.5 BO3, Na 2.6 Li 0.4 BO3, Na 2.7 Li 0.3 BO3 or Na 2.8 Li 0.2 BO3 In some embodiments, the D50 particle size of the core 10 is any value within the range of 0.5~10μm. For example, the D50 particle size of the core 10 can be 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, or 10μm. When the D50 particle size of the core 10 is within the above-mentioned particle size range, the diffusion distance of lithium ions and sodium ions in the sodium replenishing agent can be effectively shortened, the decomposition potential of the sodium replenishing agent can be reduced, the polarization of the sodium replenishing agent during the first charge formation process can be reduced, and the specific capacity of the sodium replenishing agent during the first charge process of the battery can be further improved.

[0038] Furthermore, it should be noted that the specific form of the carbon material 21 in the coating layer 20 is not limited and may include morphological carbon and amorphous carbon. In some embodiments, the carbon material 21 in the coating layer 20 may be selected from at least one of graphene, carbon nanotubes, hard carbon, soft carbon, carbon fiber, and conductive carbon. That is, the carbon material 21 can be any one of the materials listed above, such as graphene, carbon nanotubes, hard carbon, soft carbon, carbon fiber, or conductive carbon; the carbon material 21 can also be any combination of two or more of the materials listed above, for example, a combination of graphene and carbon nanotubes, or a combination of graphene and carbon fiber, or a combination of conductive carbon and carbon nanotubes, or a combination of hard carbon and conductive carbon, or a combination of graphene, carbon nanotubes, and conductive carbon, or a combination of hard carbon, graphene, and conductive carbon, etc., which will not be listed here. When the carbon material 21 is a combination of two or more materials, the proportion of each material within the combination is not limited and can be mixed in any proportion. In other embodiments, the carbon material 21 may also be a material not listed above.

[0039] like Figure 1 As shown, in some embodiments, the coating layer 20 is doped with non-metallic heteroatoms 22. These non-metallic heteroatoms 22 are chemically bonded to carbon atoms in the carbon material 21, thereby breaking the electronic symmetry of the carbon material 21 and introducing more active groups into the coating layer 20. Based on their electron-deficient structure, the active groups introduced by the non-metallic heteroatoms 21 into the carbon material 21 can effectively adsorb the gas produced by the decomposition of sodium supplementation agents, including reactive oxygen species. Furthermore, they can further promote electron transfer in the sodium supplementation agent based on the highly conductive carbon material 21, improving the decomposition ability of the sodium supplementation agent under low voltage and reducing its decomposition potential.

[0040] Although the carbon material 21 in the coating layer 20 can promote electron transfer in the sodium replenishing agent and reduce its decomposition potential, the hydrophobic properties of the carbon material 21 surface hinder the wetting of the sodium replenishing agent by the electrolyte. This makes it difficult for the lower ion conductivity of the sodium replenishing agent surface to match its higher electron conductivity, thereby exacerbating the polarization risk of the sodium replenishing agent and affecting its sodium replenishment efficiency. The sodium replenishing agent of this application forms hydrophilic groups on the surface of the carbon material 21 by doping non-metallic heteroatoms 22 into it. These groups include pyridine nitrogen, graphitic nitrogen, and quaternary nitrogen introduced by nitrogen doping; CPO, COP, and C3-P=O formed by phosphorus doping; and thiophene and SO formed by sulfur doping. y (0 < y < 6), etc. Hydrophilic groups introduced by doping non-metallic heteroatoms 22. The hydrophilic groups introduced on the carbon material 21 can effectively improve the wettability of the coating layer 20 to the electrolyte, accelerate the extraction rate of sodium ions from the sodium supplement, inhibit the polarization of the sodium supplement during the decomposition process, and further improve the specific capacity of the sodium supplement.

[0041] Furthermore, carbon materials 21 doped with non-metallic heteroatoms 22 also exhibit better mechanical properties. For example, boron-doped carbon nanotubes are harder, tougher, and have higher compressive strength than pure carbon nanotubes; sulfur-doped carbon nanotubes have good toughness and flexural modulus; and nitrogen-doped carbon nanotubes have high mechanical strength and heat resistance.

[0042] It should be noted that heteroatom-doped carbon materials 21 can be prepared by various methods, such as physical grinding and mixing, chemical vapor deposition, arc discharge, laser evaporation, etc.

[0043] In some embodiments, the mass content of non-metallic heteroatoms 22 in the coating layer 20 is 1% to 10%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. When the mass content of non-metallic heteroatoms 22 in the coating layer 20 is within the above range, it ensures the modification and improvement effect of doping on the conductivity of the sodium supplement, and also avoids excessive doping that could damage the carbon layer excessively, thereby affecting the protective effect of the coating layer 20 on the core 10.

[0044] In some embodiments, the non-metallic heteroatom 22 includes at least one of N, B, S, and P. That is, the non-metallic heteroatom 22 doped in the coating layer 20 can be any of the materials listed above, such as N, B, S, or P; the non-metallic heteroatom 22 doped in the coating layer 20 can also be any combination of two or more of the materials listed above. For example, the non-metallic heteroatom 22 can be a combination of N and S, or a combination of N and P, or a combination of B and P, or a combination of S and B, or a combination of N, B, and P, or a combination of N, B, S, and P, etc., and will not be listed exhaustively here. When the non-metallic heteroatom 22 is a combination of two or more materials, the proportion of each material within the combination is not limited, and they can be mixed in any proportion. In other embodiments, the non-metallic heteroatom 22 can also be a material not listed above.

[0045] In a second aspect, the present invention also provides a method for preparing the sodium supplement in any of the above embodiments, such as... Figure 2 As shown, the preparation method of this sodium supplement includes the following steps: S1. Lithium source, sodium source and boron source are mixed and sintered according to stoichiometric ratio to obtain core material; S2. The core material and the coating material are mixed and ground to obtain a sodium supplement, wherein the coating material includes carbon material.

[0046] In step S1, lithium source, sodium source, and boron source are mixed and sintered according to a stoichiometric ratio of Li:Na:B of x:3-x:1 to prepare the core material Na. x Li 3-xBO3, where 1.5 < x < 3. For example, in one instance, lithium, sodium, and boron sources are dissolved in a solvent according to stoichiometric ratios, thoroughly mixed, and then spray-dried to obtain a composite powder. Subsequently, under a protective atmosphere, the composite powder is sintered at a temperature above 600°C for 4 to 6 hours to obtain the core material Na. x Li 3-x BO3.

[0047] In some embodiments, the lithium source may include any type of water-soluble lithium-containing material, and may include, for example, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxyoxides. Specifically, the lithium source may include at least one of Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, Li₂SO₄, or Li₃C₆H₅O₇; preferably, LiOH may be selected as the lithium source.

[0048] In some embodiments, the sodium source may include any type of water-soluble sodium-containing material, and may include, for example, sodium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxyoxides. Specifically, the lithium source may include at least one of Na₂CO₃, NaNO₃, NaNO₂, NaOH, NaOH·H₂O, NaH, NaF, NaCl, NaBr, NaI, CH₃COONa, Na₂O, Na₂SO₄, or Na₃C₆H₅O₇; preferably, NaOH may be selected as the lithium source.

[0049] In some embodiments, the boron source may be selected from at least one of boric acid (H2BO3), boron trioxide (B2O3), and boron hydroxide (B(OH)3).

[0050] In step S2, the coating material and the core material are mixed according to a preset mass ratio, and then thoroughly ground to coat the core surface with the coating material, thereby producing a sodium supplement. The mass ratio of the core material to the coating material is (85~96):(4~15). For example, in one example, the core material is first ball-milled for 12 to 24 hours to adjust the particle size of the core material to a preset particle size range; then, the core material and the coating material are mixed according to the preset mass ratio, and ball-milling is continued for 12 to 48 hours to obtain the sodium supplement.

[0051] In some embodiments, step S2 further includes a coating material preparation step, which includes mixing and sintering carbon material with non-metallic element raw materials to dope non-metallic heteroatoms into the carbon material to obtain the coating material. For example, in one example, carbon material and non-metallic element raw materials are mixed and ball-milled for 12 to 48 hours to obtain a mixed powder; then, under a protective atmosphere, the mixed powder is sintered at a temperature of 600°C to 1200°C for 4 to 6 hours to obtain a carbon material doped with non-metallic heteroatoms.

[0052] In some embodiments, the carbon material is selected from at least one of graphene, carbon nanotubes, hard carbon, soft carbon, carbon fiber, and conductive carbon.

[0053] In some embodiments, the non-metallic element raw material is a precursor material containing a non-metallic element, which is at least one of N, B, S, and P. For example, the nitrogen source in the non-metallic element raw material can be selected from at least one of urea, polyacrylonitrile, melamine, or aminomethylphosphonic acid; the boron source in the non-metallic element raw material can be selected from at least one of boric acid, boron oxide, or sodium tetraborate; the sulfur source in the non-metallic element can be selected from at least one of sulfur powder, ferrous sulfate, or potassium sulfate; and the phosphorus source in the non-metallic element raw material can be selected from at least one of red phosphorus, sodium dihydrogen phosphate, or tripotassium phosphate.

[0054] In a third aspect, the present invention also provides a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive electrode material, a positive electrode conductive agent, a positive electrode binder, and a sodium supplement agent as described in any of the above embodiments, or a sodium supplement agent prepared by the preparation method described in any of the above embodiments. The negative electrode includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer includes a negative electrode material, a negative electrode conductive agent, a thickener, and a negative electrode binder. The positive and negative electrode materials can intercalate and deintercalate sodium ions to achieve energy storage and release. The electrolyte is the carrier for sodium ion transport between the positive and negative electrodes. The separator is permeable to sodium ions but non-conductive, thereby separating the positive and negative electrodes to prevent short circuits.

[0055] Because the sodium-ion battery incorporates the aforementioned sodium replenishing agent into its positive electrode, lithium ions from the sodium replenishing agent participate in the formation of the SEI film on the surface of the negative electrode when the sodium-ion battery is at 100% charge after initial charging. The lithium-containing SEI film has higher electrochemical stability and is less likely to undergo side reactions with the electrolyte, thus consuming the active sodium in the electrolyte. This effectively improves the high-temperature storage life and cycle life of the sodium-ion battery.

[0056] It should be noted that the preparation of the positive electrode, negative electrode, separator, electrolyte, and assembly of the electrochemical device in a sodium-ion battery can be carried out using conventional methods in this field. The following is an example description of the preparation method for a sodium-ion battery: Preparation of positive electrode sheet: The positive electrode material, a composite material containing sodium supplement (the sodium supplement has a mass content of 0.5%~10% in the composite material), a positive electrode conductive agent, and a positive electrode binder are mixed in a weight ratio of (90~98):(1~4):(1~4), optionally 95:2.5:2.5. N-methylpyrrolidone (NMP) solvent is added, and the mixture is stirred under vacuum until the system is homogeneous and transparent to obtain a positive electrode slurry. This positive electrode slurry is uniformly coated onto a positive electrode current collector aluminum foil, which is then air-dried at room temperature and transferred to an oven for further drying. Finally, the foil is cold-pressed and slit to obtain the positive electrode sheet.

[0057] The cathode material includes sodium-containing compounds, specifically NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaMn2O4, NaNi 1 / 2Mn 3 / 2 O2, NaFePO4, Na4Fe3(PO4)2P2O7 (NFPP for short), NaMnPO4, NaCoPO4, Na2FePO4F, Na2MnPO4F, Na2CoPO4F, Na3PS4, P2-Na 2 / 3 [Ni 1 / 3 Mn 2 / 3 The cathode material can be one or at least two of the materials listed above, such as NaFeO2 or Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, or Na2FePO4F, etc.; or any combination of two or more of the materials listed above, such as a combination of NaFeO2 and NaCoO2, or a combination of NaCrO2, NaMnO2 and NaNiO2, or a combination of Na2FePO4F and Na2MnPO4F, or NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn1 / 2 O2 and Na 2 / 3 Fe 1 / 3 Mn 2 / 3 Compositions of O2, etc., will not be listed here. It should be noted that the positive electrode material can also be any positive electrode active material not listed above. When the positive material is a combination of two or more, there is no restriction on the ratio between the components in the composition, and they can be mixed in any proportion.

[0058] The positive electrode conductive agent can be selected from at least one of conductive materials such as carbon black (Super P), acetylene black, nano metal powder, carbon nanotubes (CNT), graphene, and carbon nanofibers (VGCF); the positive electrode binder can be selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR), for example, PVDF can be selected as the positive electrode binder.

[0059] Negative electrode preparation: Negative electrode material, negative electrode conductive agent, negative electrode binder, and negative electrode dispersant are mixed in a mass ratio of (93~98):(0.2~1.5):(1~3):(0.01~1.5). N-methylpyrrolidone or deionized water is added as a solvent, and the mixture is thoroughly stirred under vacuum to obtain a negative electrode slurry. This negative electrode slurry is uniformly coated onto a negative electrode current collector, which is then air-dried at room temperature and transferred to an oven for further drying. Finally, the negative electrode is cold-pressed and slit to obtain the negative electrode sheet.

[0060] The negative electrode material can be hard carbon. The negative electrode conductive agent can be selected from at least one conductive material such as carbon black (Super P), acetylene black carbon nanotubes (CNT), nano-silver powder, graphene, and carbon nanofiber (VGCF). The negative electrode binder is selected from at least one binder such as polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), and styrene-butadiene rubber (SBR). The thickener is selected from carboxymethyl cellulose, which can be sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li).

[0061] Electrolyte preparation: In this application, the electrolyte can be any conventional type of electrolyte in the art. For example, in an argon atmosphere glove box with a water content of <10 ppm, ethylene carbonate (EC) and dimethyl carbonate (DMC) are uniformly mixed at a volume ratio of 1:1 to obtain an organic solvent. Then, fluoroethylene carbonate (FEC) additives accounting for 5% of the mass fraction of ethylene carbonate (EC) and dimethyl carbonate (DMC) are added to the organic solvent. Next, fully dried sodium salt NaClO4 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0062] Membrane preparation: The membrane is selected from conventional porous polymer membranes in the art. For example, the membrane material can be selected from one or more combinations of polyvinylidene fluoride, polystyrene, polyarylether sulfone, polyvinyl chloride, polypropylene, polyethylene, polyamide, polyimide, polyacrylic acid, polyacetal, polycarbonate, polyester, polyetherimide, polyimide, polyketone, polyphenylene ether, polyphenylene sulfide, polymethylpentene, polysulfone nonwoven glass, glass fiber materials, ceramics, metal oxides, and composites of organic and inorganic substances. For example, in one instance, the diaphragm is a porous polyethylene (PE) or polypropylene (PP) membrane, optionally a PP / PE / PP porous membrane, with a thickness of 9 μm to 18 μm, such as 9 μm, 12 μm, 16 μm or 18 μm; an air permeability of 180 s / 100 mL to 380 s / 100 mL, such as 180 s / 100 mL, 280 s / 100 mL or 380 s / 100 mL; and a porosity of 30% to 50%, such as 30%, 40% or 50%.

[0063] Battery Assembly: Battery assembly is carried out according to conventional methods. For example, after preparation, the negative electrode, separator, and positive electrode are stacked in sequence and placed in an aluminum-plastic film to obtain a bare cell. The bare cell is then placed in a casing and thoroughly baked to ensure that its water content is below 450 ppm. The prepared electrolyte is injected into the dry cell and sealed. After formation, venting, and aging, a sodium-ion battery with the preset capacity is obtained.

[0064] The conditions for formation, venting, and aging are as follows: charging to the cutoff voltage at a rate of 0.1 to 0.33 C, venting vacuum of -40 to -98 kPa, and venting time of more than 10 seconds; aging temperature of 40 to 50 °C and aging time of 24 to 72 hours.

[0065] The technical solution of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available products or can be prepared by conventional methods in the art.

[0066] Example 1 This embodiment provides a sodium-ion battery in which a sodium-replenishing agent is assembled in the positive electrode. The sodium-replenishing agent comprises a core and a coating layer surrounding the core. The core comprises 95% by mass in the sodium-replenishing agent, and the core material is sodium (Na). 2.5 Li 0.5 BO3, with a core D50 particle size of 1.5 μm; the coating layer contains 5% of the sodium supplement by mass, and the carbon material in the coating layer is carbon nanotubes.

[0067] The preparation process of this sodium supplement is as follows: (1) Lithium source LiOH, sodium source NaOH and boron source boric acid are dispersed in deionized water according to stoichiometric ratio and thoroughly mixed to obtain a mixed solution; the mixed solution is transferred to a spray drying device for spray drying treatment, the mixed solution is sprayed onto a plane to form closely arranged droplets, the droplets on the plane are placed at 250°C for heating and drying to obtain composite powder; the composite powder is placed in a furnace, and under a nitrogen atmosphere, the furnace environment is heated to 600°C at a rate of 5°C / min, and heated at 600°C for 5 hours, and then cooled to obtain the core material.

[0068] (2) The core material is ball-milled to make the D50 particle size of the core material 1.5 μm; the core material and the coating material carbon nanotubes are mixed according to a preset mass ratio and ball-milled for 24 hours to obtain the required sodium supplement.

[0069] The preparation process of this sodium-ion battery is as follows: A composite material of positive electrode material NFPP and sodium supplement (sodium supplement content in the composite material is 2% by mass), positive electrode conductive agent, and positive electrode binder are mixed at a weight ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) solvent is added, and the mixture is stirred under vacuum until the system is homogeneous. The solid content of the slurry is adjusted to 55% to obtain the positive electrode slurry. The positive electrode slurry is coated onto carbon aluminum foil, dried, and cold-pressed to form the positive electrode sheet.

[0070] The negative electrode material, hard carbon, negative electrode conductive agent, carbon black (Super P), thickener, sodium carboxymethyl cellulose (CMC-Na), and negative electrode binder, styrene-butadiene rubber (SBR), are mixed in a mass ratio of 96.6:0.8:1.2:1.4. Deionized water is added to adjust the slurry solid content to 55%. The mixture is then thoroughly stirred under vacuum to obtain the negative electrode slurry. The negative electrode slurry is uniformly coated onto the negative electrode current collector copper foil, dried, and cold-pressed to form the negative electrode sheet.

[0071] Using a 12μm thick porous PP membrane as the separator, the prepared positive electrode, separator, and negative electrode were stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. Then, an aluminum-plastic film was wrapped around the separator, and the mixture was dried in a vacuum oven at 120 °C. After injecting 5.0 g / Ah of electrolyte, the mixture was sealed. Following processes such as settling, hot and cold pressing, formation, clamping, and capacity testing, a 1 Ah soft-pack sodium-ion battery was finally obtained.

[0072] Example 2 This embodiment provides a sodium-ion battery with the same system as in Example 1. The difference between this embodiment and Example 1 is that the coating layer of the sodium replenishing agent is doped with non-metallic atoms, specifically nitrogen atoms, and the mass content of non-metallic atoms in the coating layer is 6%. The preparation process of this sodium replenishing agent is as follows: (1) Lithium source LiOH, sodium source NaOH and boron source boric acid are dispersed in deionized water according to stoichiometric ratio and thoroughly mixed to obtain a mixed solution; the mixed solution is transferred to a spray drying device for spray drying treatment, the mixed solution is sprayed onto a plane to form closely arranged droplets, the droplets on the plane are placed at 250°C for heating and drying to obtain composite powder; the composite powder is placed in a furnace, and under a nitrogen atmosphere, the furnace environment is heated to 600°C at a rate of 5°C / min, and heated at 600°C for 5 hours, and then cooled to obtain the core material.

[0073] (2) The carbon material and the nitrogen source urea are mixed evenly and ball milled for 24 hours after mixing to obtain a mixed powder. Then the mixed powder is placed in a furnace and heated to 900°C at a rate of 5°C / min under a nitrogen atmosphere. The furnace environment is heated to 900°C for 5 hours and cooled to obtain a coating material. The coating material is a carbon material doped with nitrogen atoms.

[0074] (3) The core material is ball-milled to make the D50 particle size of the core material 1.5μm; the core material and the coating material are mixed according to the preset mass ratio and ball-milled for 24 hours to obtain the required sodium supplement.

[0075] Example 3 This embodiment provides a sodium supplement agent with the same system as in Example 2. The difference between this embodiment and Example 2 is that in step (1), the stoichiometric ratio of the lithium source, sodium source, and boron source is adjusted to make the core material Na. 2.8 Li 0.2 BO3.

[0076] Example 4 This embodiment provides a sodium supplement agent with the same system as in Example 2. The difference between this embodiment and Example 2 is that in step (1), the stoichiometric ratio of the lithium source, sodium source, and boron source is adjusted to make the core material Na. 1.6 Li 1.4 BO3.

[0077] Example 5 This embodiment provides a sodium-ion battery with the same system as in embodiment 2. The difference between this embodiment and embodiment 2 is that the non-metallic atoms doped in the carbon material in the coating layer of the sodium supplement are sulfur atoms. In step (2), the mass ratio of carbon material to sulfur source sulfur powder is controlled so that the mass content of sulfur atoms in the coating layer is 0.5%.

[0078] Example 6 This embodiment provides a sodium-ion battery with the same system as in embodiment 5. The difference between this embodiment and embodiment 5 is that in step (2), the mass ratio of carbon material to sulfur source sulfur powder is controlled so that the mass content of sulfur atoms in the sodium supplement coating layer is 1%.

[0079] Example 7 This embodiment provides a sodium-ion battery with the same system as in embodiment 2. The difference between this embodiment and embodiment 2 is that the non-metallic atoms doped in the carbon material in the sodium supplement coating layer are nitrogen atoms and phosphorus atoms. In step (2), by controlling the mass ratio of carbon material, nitrogen source urea and phosphorus source red phosphorus, the mass content of nitrogen atoms doped in the coating layer is 6% and the mass content of phosphorus atoms is 2%.

[0080] Example 8 This embodiment provides a sodium-ion battery with the same system as in embodiment 2. The difference between this embodiment and embodiment 2 is that in step (1), the stoichiometric ratio of lithium source, sodium source and boron source is adjusted to make the core material Na2LiBO3; in step (2), the mass ratio of carbon material, nitrogen source urea and boron source boric acid is controlled to make the mass content of nitrogen atoms in the coating layer 6% and the mass content of boron atoms 3%.

[0081] Example 9 This embodiment provides a sodium-ion battery with the same system as that in Embodiment 2. The difference between this embodiment and Embodiment 2 is that in step (2), the mass ratio of carbon material to nitrogen source urea is controlled so that the mass content of nitrogen atoms in the sodium supplement coating layer is 11%.

[0082] Example 10 This embodiment provides a sodium-ion battery with the same system as that in Embodiment 2. The difference between this embodiment and Embodiment 2 is that in step (3), the mass ratio of the core material to the coating material is controlled so that the mass content of the core material in the sodium supplement is 80% and the mass content of the coating layer is 20%.

[0083] Example 11 This embodiment provides a sodium-ion battery with the same system as that in Embodiment 2. The difference between this embodiment and Embodiment 2 is that in step (3), the mass ratio of the core material to the coating material is controlled so that the mass content of the core material in the sodium supplement is 85% and the mass content of the coating layer is 15%.

[0084] Example 12 This embodiment provides a sodium-ion battery with the same system as in Example 2. The difference between this embodiment and Example 2 is that the D50 particle size of the core material in the sodium supplement is 0.5 μm.

[0085] Example 13 This embodiment provides a sodium-ion battery with the same system as in Embodiment 2. The difference between this embodiment and Embodiment 2 is that the D50 particle size of the core material is 10 μm.

[0086] Comparative Example 1 This comparative example provides a sodium-ion battery with the same system as Example 1. The difference between this comparative example and Example 1 is that no sodium supplement is introduced into the positive electrode.

[0087] Comparative Example 2 This comparative example provides a sodium-ion battery with the same system as Example 1. The difference between this comparative example and Example 1 is that the sodium supplement is Na3BO3 without a carbon coating layer.

[0088] Comparative Example 3 This comparative example provides a sodium-ion battery with the same system as Example 1. The difference between this comparative example and Example 1 is that the sodium supplement is Na without a carbon coating layer. 2.5 Li 0.5 BO3.

[0089] Comparative Example 4 This comparative example provides a sodium-ion battery with the same system as Example 2. The difference between this comparative example and Example 2 is that the core material in the sodium supplement is Na3BO3.

[0090] Comparative Example 5 This comparative example provides a sodium-ion battery with the same system as Example 2. The difference between this comparative example and Example 2 is that the core material in the sodium supplement is Na. 4.5 Li 0.5 FeO4.

[0091] The sodium supplements prepared in Examples 1 to 13 and Comparative Examples 1 to 5 were subjected to decomposition potential and specific capacity tests. The sodium-ion batteries provided in Examples 1 to 13 and Comparative Examples 1 to 5 were subjected to charge-discharge tests and storage gas generation tests to verify the efficacy of the present invention. The test results are shown in Table 1.

[0092] Sodium supplement capacity and decomposition potential test: The sodium supplement prepared above was mixed with conductive agent Super P and binder polyvinylidene fluoride (PVDF) in a weight ratio of 90:5:5. N-methylpyrrolidone (NMP) solvent was added and the mixture was stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry was coated onto the positive electrode current collector aluminum foil and prepared by drying, cold pressing and slitting. Sodium metal was used as the negative electrode and assembled in the following order: positive electrode shell - electrode sheet - electrolyte - separator - electrolyte - sodium sheet - gasket - spring sheet - negative electrode shell. The battery was then sealed using a sealing machine to obtain a 2032 button half cell.

[0093] At 25°C, the coin cell was charged to 4.25V with a constant current of 1mA, and the initial charge capacity and initial charge energy of the coin cell were measured. The initial charge capacity of the sodium supplement was obtained by dividing the initial charge capacity by the mass of the sodium supplement. The decomposition potential of the sodium supplement was obtained by dividing the initial charge energy by the initial charge capacity.

[0094] Sodium-ion battery gas production test: The prepared sodium-ion battery is placed in the test equipment, the equipment temperature is set to 25℃, and it is charged at a constant current and constant voltage of 0.33C to 3.65V (1C is the nominal capacity of the battery). After full charging, the initial volume V1 of the battery is measured. Then the sodium-ion battery is placed in a hot box at 60℃, and the volume change is measured every 30 days (using the "water displacement method"). The volume V2 of the battery taken out on the 60th day is recorded, and the gas production growth of the battery can be obtained as (V2-V1) / V1.

[0095] Sodium-ion battery cycle capacity retention test: The prepared battery was placed in a constant temperature testing device and charged to 3.65V at a 1C current rate using a constant current and constant voltage method at a constant temperature of 45℃. After resting for 30 minutes, the battery was discharged to 1.5V at a 1C current rate using a constant current method, obtaining the first discharge capacity C1. This charge-discharge cycle process was repeated 500 times, and the discharge capacity C500 of the 500th cycle was measured. The capacity retention rate after 500 charge-discharge cycles was calculated as C500 / C1.

[0096] Table 1: Parameters of sodium supplements prepared in Examples 1 to 13 and Comparative Examples 1 to 5, and results of battery performance tests.

[0097] Comparing the test results of Examples 1 to 5 and Comparative Example 1, it can be seen that the sodium supplement provided in this application embodiment can not only replenish active sodium in sodium-ion batteries and improve the specific capacity of sodium-ion batteries, but also effectively improve the electrochemical stability of sodium-ion batteries, effectively improve the cycle life of sodium-ion batteries, and reduce gas generation during high-temperature storage of sodium-ion batteries.

[0098] Comparing the test results of Examples 2 to 5 and Comparative Example 4, it can be seen that the sodium replenishing agent material in the comparative example, which does not introduce lithium ions, although having a higher specific charging capacity, cannot improve the poor stability of the SEI film on the negative electrode of sodium-ion batteries. This results in low sodium replenishment efficiency for sodium-ion batteries and no improvement on the gas generation problem during high-temperature storage. In contrast, the sodium replenishing agent provided in this application utilizes introduced lithium ions to participate in SEI film formation, thereby reducing the active sodium consumed in the battery during SEI film formation, improving the stability of SEI film formation, reducing the gas generation rate during high-temperature storage, and effectively improving the cycle life of sodium-ion batteries.

[0099] Comparing the test results of Examples 2 to 5 and Comparative Example 5, it can be seen that, compared with the defects of the sodium-rich ternary sodium salt decomposition products of the sodium replenishment agent being unstable and easily causing side reactions in the electrolyte, resulting in deterioration of battery gas production, the sodium replenishment agent of this application has the advantages of high energy density and high electrochemical stability. The decomposition products of the sodium replenishment agent of this application are difficult to react with the electrolyte, and the SEI film formed is also not easy to react with the electrolyte, thereby effectively reducing the storage gas production of the battery and further improving the cycle life of the battery.

[0100] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A sodium supplement, characterized in that, include: The kernel, the kernel comprising Na x Li 3-x BO3, where 1.5 < x < 3; A coating layer located outside the core, the coating layer comprising a carbon material.

2. The sodium supplement according to claim 1, characterized in that, The coating layer is doped with non-metallic heteroatoms, which include at least one of N, B, S, and P.

3. The sodium supplement according to claim 2, characterized in that, The non-metallic heteroatoms in the coating layer have a mass content of 1% to 10%.

4. The sodium supplement according to claim 1, characterized in that, In the Na x Li 3-x In BO3, 1.6 ≤ x ≤ 2.

8.

5. The sodium supplement according to claim 1, characterized in that, The core has a D50 particle size of 0.5~10μm.

6. The sodium supplement according to claim 1, characterized in that, The core has a mass content of 85% to 96% in the sodium supplement, and the coating layer has a mass content of 4% to 15% in the sodium supplement.

7. The sodium supplement according to claim 1, characterized in that, The carbon material includes at least one of graphene, carbon nanotubes, hard carbon, soft carbon, carbon fiber, and conductive carbon.

8. A method for preparing the sodium supplement according to any one of claims 1 to 7, characterized in that, include: The lithium source, sodium source, and boron source are mixed and sintered in stoichiometric ratio to obtain the core material; The core material and the coating material are mixed and ground to obtain a sodium supplement, wherein the coating material includes carbon material.

9. The method for preparing the sodium supplement according to claim 8, characterized in that, It also includes a preparation step of the coating material, the preparation step comprising: Carbon materials are mixed with non-metallic raw materials and sintered to obtain a coating material; the coating material includes carbon materials doped with non-metallic atoms.

10. A sodium-ion battery, characterized in that, The invention includes a positive electrode sheet, which comprises a positive current collector and a positive active material layer, wherein the positive active material layer comprises the sodium supplement agent as described in any one of claims 1 to 7, or the sodium supplement agent prepared by the preparation method described in claim 8 or 9.

11. The sodium-ion battery according to claim 10, characterized in that, When the sodium-ion battery is in a 100% charged state, the surface of the negative electrode of the sodium-ion battery has a solid electrolyte interface film, and the solid electrolyte interface film contains lithium.

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