A positive electrode sodium supplement agent, its preparation method and application

Abstract

This invention proposes a positive electrode sodium supplement agent, its preparation method, and its application. The positive electrode sodium supplement agent is Na2MnO. 3‑x x is 0.1-0.3, where x is the oxygen vacancy content. This invention proposes a positive electrode sodium supplement agent, its preparation method, and its application. This agent can reduce the sodium removal potential, improve the air stability of the positive electrode sodium supplement agent, and exhibit a gentler volume change, significantly enhancing the sodium supplementation effect and improving the initial coulombic efficiency, cycle life, and safety performance of the full cell.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, specifically to a positive electrode sodium replenishing agent, its preparation method, and its application. Background Technology

[0002] In recent years, with the development of renewable energy, the energy storage market has been booming. Although lithium-ion batteries remain the mainstream technology in the industry, the scarcity and uneven distribution of lithium resources lead to high costs, limiting their widespread application in power storage. In contrast, sodium-ion batteries have rapidly emerged as a focus in the energy storage market due to their advantages such as low cost and abundant resources. However, in sodium-ion batteries, irreversible sodium loss during the first charge and discharge cycle severely restricts the improvement of the overall energy density, especially on the negative electrode side. During the first charge and discharge cycle, the formation of the solid electrolyte interface (SEI) film consumes a large amount of active sodium ions, resulting in a low initial coulombic efficiency and significantly weakening the overall energy output capacity of the battery. Summary of the Invention

[0003] This invention proposes a positive electrode sodium supplement agent, its preparation method, and its application. It can reduce the sodium removal potential of the positive electrode sodium supplement agent, improve the air stability of the positive electrode sodium supplement agent, and make the volume change of the positive electrode sodium supplement agent gradual, effectively avoiding the damage to the electrode structure caused by the severe volume shrinkage of the positive electrode sodium supplement agent, thereby ensuring the integrity of the electrode interface, significantly improving the sodium supplementation effect of the positive electrode sodium supplement agent, and improving the first coulombic efficiency, cycle life, and safety performance of the full cell.

[0004] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution.

[0005] This invention provides a positive electrode sodium supplement agent, wherein the positive electrode sodium supplement agent is Na2MnO. 3-x x is 0.1-0.3.

[0006] In one embodiment of the present invention, x represents the oxygen vacancy content.

[0007] In one embodiment of the present invention, x is 0.17-0.22.

[0008] In one embodiment of the present invention, the specific surface area of ​​the positive electrode sodium supplement is 8m². 2 / g-10m 2 / g.

[0009] In one embodiment of the present invention, the median particle size of the positive electrode sodium supplement is 4μm-5μm.

[0010] The present invention also provides a method for preparing the above-described positive electrode sodium supplement, comprising:

[0011] The sodium and manganese sources are mixed and then calcined and cooled to obtain the precursor. The ball milling speed and time are set, and the precursor is ball milled in an inert atmosphere to obtain a positive electrode sodium supplement. The ball milling speed is 500rpm-700rpm, and the ball milling time is 24h-36h.

[0012] In one embodiment of the present invention, the sodium source includes sodium carbonate, and the manganese source includes manganese hydroxide, wherein the specific surface area of ​​the manganese hydroxide is 7 m². 2 / g-11m 2 / g, wherein the median particle size of the manganese hydroxide is 3.5μm-5.5μm.

[0013] The present invention also provides a sodium-ion battery, comprising: A positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material and a positive electrode sodium supplementer, wherein the positive electrode sodium supplementer is selected from the positive electrode sodium supplementer described above or the positive electrode sodium supplementer obtained by the preparation method described above; Negative electrode sheet, including negative electrode active material; A diaphragm is disposed between the positive electrode and the negative electrode.

[0014] In one embodiment of the present invention, the positive electrode active material comprises a layered transition metal oxide, and / or the negative electrode active material comprises hard carbon.

[0015] The present invention also provides an electronic device comprising the sodium-ion battery described above.

[0016] In summary, this invention proposes a positive electrode sodium supplement agent, its preparation method, and its application. By introducing oxygen vacancies into the positive electrode sodium supplement agent, the average valence state of manganese is reduced, thereby lowering the sodium removal potential of the positive electrode sodium supplement agent and effectively exerting its sodium supplementation function. Controlling the oxygen vacancy content in the positive electrode sodium supplement agent allows for full utilization of its sodium supplementation function at a lower potential, reducing side reactions between the positive electrode sodium supplement agent and the electrolyte, and improving the cycle performance of sodium-ion batteries. It can improve the air stability of the positive electrode sodium supplement agent, reduce its sensitivity to water and carbon dioxide, and prevent deliquescence or carbonation. It can be stored, transported, and weighed and dispersed under normal dry conditions, and maintains the stability of sodium source release capacity during electrode preparation, thereby improving its operability and reliability in engineering applications. This solves the problems of strong alkaline sodium supplement agents such as sodium oxide readily reacting rapidly with moisture and carbon dioxide in the air, leading to the loss of effective sodium source, and introducing impurity phases, increasing the risk of slurry gelation, and interfacial side reactions during electrode preparation and battery assembly, thus improving the electrochemical consistency and safety of the battery. This process ensures the compatibility of the positive electrode sodium supplement with the positive electrode active material, matching its sodium removal potential with the charging potential platform of the positive electrode active material, significantly improving its compatibility and practicality as a sodium supplement. Simultaneously, the positive electrode sodium supplement fills the gaps between materials in the positive electrode sheet, constructing a good conductive network, reducing local overpotential, alleviating uneven current density distribution, and reducing the occurrence of side reactions in the positive electrode sheet, thereby improving battery cycle stability. It effectively avoids damage to the electrode structure caused by severe volume shrinkage of the positive electrode sodium supplement, thus ensuring the integrity of the electrode interface and improving the initial coulombic efficiency, cycle life, and safety performance of the full battery. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is the X-ray absorption spectrum of the positive electrode sodium supplement in Example 1 of the present invention. Detailed Implementation

[0019] 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.

[0020] It should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Unless otherwise specified, the reagents and materials used in the following embodiments were purchased from reputable chemical reagent suppliers and were of analytical purity.

[0021] The technical solution of the present invention will be further described in detail below with reference to several embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention proposes a positive electrode sodium replenishing agent, wherein the positive electrode sodium replenishing agent is Na2MnO. 3-x Where x is, for example, 0.1-0.3, and x represents the oxygen vacancy content in the positive electrode sodium supplement. Oxygen vacancies are crystal defects formed in oxygen-containing compounds such as metal oxides due to oxygen atoms detaching from the crystal lattice. In this embodiment, the value of x can be determined by X-ray absorption spectroscopy (XAS). By introducing oxygen vacancies into the positive electrode sodium supplement, the average valence state of manganese is reduced, thereby lowering the sodium removal potential of the positive electrode sodium supplement and effectively exerting its sodium supplementation function.

[0023] In one embodiment of the present invention, sodium supplementation agent Na2MnO is used at the positive electrode. 3-x In this context, x is preferably 0.17-0.22. When the oxygen vacancy content introduced into the positive electrode sodium supplement is too low, Na2MnO 3-x While retaining the electrochemical characteristics of its original layered structure, its inherent low electronic conductivity and sluggish sodium ion migration kinetics make it difficult to effectively remove sodium within the normal operating voltage window of the battery. This prevents it from fulfilling its intended sodium replenishment function, and its poor electrochemical activity can actually dilute the overall efficiency of the positive electrode active material, leading to a decrease in battery capacity. When too many oxygen vacancies are introduced into the positive electrode sodium replenisher, it may cause excessive disordering and amorphization of the material, generating electrochemically unstable phases. During sodium removal, these phases will undergo numerous irreversible side reactions with the electrolyte, consuming large amounts of active sodium and disrupting the stability of the electrode / electrolyte interface, ultimately negatively impacting the battery's cycle life. Therefore, controlling the amount of Na2MnO in the positive electrode sodium replenisher is crucial. 3-x The low oxygen vacancy content maximizes the sodium-supplementing effect of the sodium supplement while reducing side reactions.

[0024] In the positive electrode sodium supplement, sodium is stably bound within the crystal lattice framework in a lattice-occupying form. The positive electrode sodium supplement exhibits high air stability and low sensitivity to water and carbon dioxide (CO2), making it resistant to deliquescence or carbonation. It can be stored, transported, and weighed and dispersed under normal dry conditions, and maintains the stability of sodium source release capacity during electrode preparation, thereby improving its operability and reliability in engineering applications. This solves the problem of strong alkaline sodium supplements such as sodium oxide readily reacting rapidly with moisture and carbon dioxide in the air, leading to the loss of effective sodium source. It also addresses the issues of introducing impurity phases, increasing the risk of slurry gelation, and interfacial side reactions during electrode preparation and battery assembly, ultimately improving the electrochemical consistency and safety of the battery.

[0025] In one embodiment of the present invention, the specific surface area of ​​the positive electrode sodium supplement is, for example, 8 m². 2 / g-10m 2 / g, the median particle size D50 of the positive electrode sodium supplement is, for example, 4μm-5μm. The median particle size D50 refers to the particle size value corresponding to a cumulative volume distribution percentage of 50% in the volume distribution curve. When the particle size of the positive electrode sodium supplement is too large and the specific surface area is too low, the contact interface between the positive electrode sodium supplement and the electrolyte is insufficient, and the ion / charge transfer kinetics are limited. This easily leads to a high initiation potential for the sodium removal reaction or incomplete reaction, manifested as decreased sodium supplementation efficiency, incomplete release of sodium source during the first charge, and deterioration of cycle stability. When the particle size of the positive electrode sodium supplement is too small and the specific surface area is too high, it easily exacerbates the interfacial side reactions with the electrolyte, leading to the consumption of effective sodium source, the formation of insulating byproducts on the surface, or the thickening of the interfacial film. This results in risks such as increased irreversible capacity, decreased initial coulombic efficiency, and deterioration of cycle performance. Therefore, by controlling the specific surface area and median particle size of the positive electrode sodium supplement, the contact interface between the positive electrode sodium supplement and the electrolyte, ion / charge transfer kinetics, etc., can be controlled, thereby improving the battery capacity, initial coulombic efficiency reduction, and cycle performance.

[0026] This invention also proposes a method for preparing a positive electrode sodium supplement, which is used to prepare the above-mentioned positive electrode sodium supplement. The preparation method includes: mixing a sodium source and a manganese source and then calcining and cooling to obtain a precursor; setting a ball milling speed and ball milling time, and ball milling the precursor under an inert atmosphere to obtain the positive electrode sodium supplement; wherein, the ball milling speed is, for example, 500 rpm-700 rpm, and the ball milling time is, for example, 24 h-36 h.

[0027] In one embodiment of the present invention, the sodium source includes, for example, sodium carbonate, and the manganese source includes, for example, manganese hydroxide, wherein the specific surface area of ​​manganese hydroxide is, for example, 7 m². 2 / g-11m 2 / g, the median particle size of manganese hydroxide is, for example, 3.5μm-5.5μm. By controlling the specific surface area and median particle size of the reactants, the specific surface area and median particle size of the obtained precursor can be controlled.

[0028] In one embodiment of the present invention, sodium and manganese sources are weighed and mixed at a stoichiometric ratio of sodium ions to manganese ions, for example, 2:1. The mixed raw materials are placed in a muffle furnace and heated to 650°C-800°C at a heating rate of 3°C / min-8°C / min under an air atmosphere, and calcined at this temperature for 10-15 hours. The mixture is then cooled to room temperature with the furnace to obtain a precursor Na₂MnO₃ with a layered structure. In this embodiment, the reaction equation for obtaining the precursor is: 2Na₂CO₃ + 2Mn(OH)₂ + O₂ → 2Na₂MnO₃ + 2CO₂ + 2H₂O.

[0029] In one embodiment of the present invention, the precursor Na2MnO3 is ball-milled at a set ball milling speed and time to obtain a positive electrode sodium supplement. Specifically, the precursor Na2MnO3 and grinding balls are placed together in a ball milling device such as a planetary ball mill jar at a mass ratio of 1:20-1:40. The grinding balls are, for example, zirconia grinding balls. An inert gas such as argon is introduced into the ball mill jar as a protective atmosphere. The ball milling speed is set, for example, 500 rpm-700 rpm, and the ball milling time is set, for example, 24 h-36 h. After ball milling, the powder sample is taken out under argon protection, thus obtaining the positive electrode sodium supplement. During the ball milling process, mechanical force induces the layered structure of the precursor Na2MnO3 to transform into a disordered phase, and simultaneously introduces a large number of oxygen vacancies. In order to maintain charge balance, the valence state of the transition metal manganese decreases accordingly. Compared to the high-valence manganese in the precursor Na2MnO3, which has insufficient oxidizing activity, the lower-valence manganese can participate in oxidation and provide charge compensation during sodium removal, thus significantly reducing the potential required for sodium ion removal. This ensures that when the sodium replenisher is matched with the positive electrode active material, its sodium removal potential matches the charging potential plateau of the positive electrode active material. This avoids the problem of the sodium source not being effectively released within the normal operating voltage window of the battery due to an excessively high sodium removal potential, significantly improving its compatibility and practicality as a sodium replenisher.

[0030] The sodium supplement agent at the positive electrode is Na2MnO. 3-x In this process, the introduction of oxygen vacancies enhances the oxidizing activity of oxygen anions. In the precursor Na2MnO3, oxygen anions mainly coordinate with transition metals in the (Na4TM2)O configuration. However, in the positive electrode sodium supplement Na2MnO3 provided by this invention… 3-x In this study, (Na5TM)O with a higher sodium coordination number and (Na6)O with pure sodium coordination were successfully introduced. These changes in coordination environment increased the Na-O-Na coordination ratio, which is beneficial for raising the energy level of the oxygen 2p orbital, thereby enhancing the oxidation activity of the oxygen anion and making O... 2- It can be oxidized to O at a lower potential. n-This effect contributes to capacity. This effect, combined with the reduction in manganese valence caused by oxygen vacancies, synergistically promotes the sodium replenishment agent at the positive electrode to undergo a desodium reaction at a relatively low potential.

[0031] This invention also proposes a sodium-ion battery, comprising a casing and an electrode assembly disposed within the casing. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The separator is placed between the positive and negative electrodes to prevent short circuits and allow sodium ions to pass through. The positive electrode includes a positive active material and a sodium-replenishing agent, selected from the aforementioned sodium-replenishing agents or those obtained by the aforementioned preparation method. The positive electrode, separator, and negative electrode are sequentially stacked to ensure that a separator is present between any positive and negative electrode. A multi-layered stack is obtained by winding or folding and is then installed as the electrode assembly within the battery casing. Finally, electrolyte is injected into the casing once or in multiple stages to completely immerse the electrode assembly in the electrolyte, which conducts ions between the positive and negative electrodes. In one embodiment of this invention, the sodium-ion battery is, for example, a secondary battery, which may be, for example, a pouch battery, a prismatic battery, or a cylindrical battery. This invention does not specifically limit the type of sodium-ion battery.

[0032] In one embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active layer coated on at least one surface of the positive current collector. The positive current collector is, for example, a foil formed by surface treatment of materials such as nickel, titanium, aluminum, silver, stainless steel, or carbon. Besides foil, the positive current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or non-woven fabric. The thickness of the positive current collector is, for example, 8 μm-15 μm. In this embodiment, the positive current collector is, for example, an aluminum foil, and the thickness of the aluminum foil is, for example, 15 μm.

[0033] In one embodiment of the present invention, the positive electrode active layer includes a positive electrode active material, a positive electrode sodium supplement, a positive electrode binder, and a positive electrode conductive agent. The positive electrode active material may include, for example, a layered transition metal oxide, specifically, Na. 0.95 Ni 0.159 Mn 0.317 Cu 0.158 Mg 0.158 Ti 0.208 O2, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, Na 0.85 Ni 0.4 Mn 0.4 Fe 0.2 O2, Na 0.85 Ni 0.3 Mn 0.4 Fe 0.3O2, NaNi 0.34 Fe 0.33 Mn 0.33 O2, Na 0.95 Ni 0.159 Mn 0.317 Cu 0.316 Ti 0.208 At least one of O2, etc., is used to improve the energy density, cycle stability, and safety of sodium-ion batteries, while also improving the compatibility of the positive electrode sodium supplement and the positive electrode active material. The positive electrode sodium supplement Na2MnO provided by this invention... 3-x During the initial charge, sodium ions are primarily released, and the bulk material does not undergo overall decomposition. Its crystal framework remains stable, and volume change is relatively gradual during electrochemical sodium removal. Furthermore, the positive electrode sodium supplement fills the gaps between materials in the positive electrode, constructing a good conductive network, reducing local overpotential, mitigating uneven current density distribution, and minimizing side reactions in the positive electrode, thereby improving battery cycle stability. This effectively avoids damage to the electrode structure caused by severe volume shrinkage of the positive electrode sodium supplement, ensuring the integrity of the electrode interface and improving the initial coulombic efficiency, cycle life, and safety performance of the full battery.

[0034] In one embodiment of the present invention, the positive electrode binder is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer (ETFE), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), ethylene-tetrafluoropropylene-tetrafluoroethylene terpolymer (TFE-HFP-VDF), or tetrafluoroethylene-hexafluoropropylene copolymer (FEP). The positive electrode conductive agent is selected from one or more of conductive carbon black (Super P), acetylene black, or Ketjen black. In the positive electrode active layer, the mass ratio of the positive electrode active material, the positive electrode sodium supplement, the positive electrode binder, and the positive electrode conductive agent is, for example, (86-94):(2-8):(1-3):(1-3).

[0035] In one embodiment of the present invention, the positive electrode active material, positive electrode sodium supplement, positive electrode binder, and positive electrode conductive agent are mixed according to a mass ratio, and then an organic solvent is added and stirred until the system is homogeneous to obtain a positive electrode slurry. The organic solvent is, for example, selected from N-methylpyrrolidone (NMP). The mixture is first stirred at 300 rpm-500 rpm for 30 min-60 min, and then stirred at 1600 rpm-2000 rpm for 60 min-120 min to obtain a uniformly distributed positive electrode slurry with suitable viscosity. The solid content of the positive electrode slurry is, for example, 40 wt%-70 wt%. The positive electrode slurry is uniformly coated onto at least one side of the positive electrode current collector. Based on the total mass of the positive electrode active material and the positive electrode sodium supplement, the coating surface density is, for example, 18 mg / cm³. 2 -25mg / cm 2 The positive electrode sheet is obtained after drying in a vacuum dryer, followed by processes such as rolling, trimming, cutting, and slitting. In one embodiment of the present invention, after rolling, the thickness of the positive electrode active layer on one side is, for example, 51 μm-83 μm, and the compaction density of the positive electrode active layer on one side is, for example, 3 g / cm³. 3 -3.5g / cm 3 .

[0036] In one embodiment of the present invention, the negative electrode sheet includes, for example, a negative current collector and a negative active layer coated at least on one surface of the negative current collector. The negative current collector is selected from, for example, a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, or a stainless steel current collector, and the thickness of the negative current collector is, for example, 6 μm-15 μm. In this embodiment, the negative current collector is, for example, copper foil, and the thickness of the copper foil is, for example, 15 μm.

[0037] In one embodiment of the present invention, the negative electrode active layer includes a negative electrode active material, a negative electrode binder, a thickener, and a negative electrode conductive agent. The negative electrode active material includes, for example, hard carbon materials. The negative electrode binder is selected from at least one of the following: polymerized styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylic acid (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), or carboxymethyl chitosan (CMCS). The thickener is selected from, for example, sodium carboxymethyl cellulose (CMC). The negative electrode conductive agent is selected from, for example, one or a mixture of several of the following: conductive carbon black, acetylene black, nano-silver powder, carbon nanotubes, or graphene. The mass ratio of negative electrode active material, negative electrode binder, thickener and negative electrode conductive agent in negative electrode active layer is, for example, (91-97):(1-3):(1-3):(1-3).

[0038] In one embodiment of the present invention, the negative electrode active material, negative electrode binder, negative electrode dispersant, and negative electrode conductive agent are mixed according to a mass ratio, and then deionized water is added. The mixture is first stirred at 300-500 rpm for 30-60 minutes, and then stirred at 1600-2000 rpm for 60-120 minutes to obtain a uniformly distributed negative electrode slurry with suitable viscosity. The solid content of the negative electrode slurry is, for example, 35wt%-65wt%. The negative electrode slurry is uniformly coated onto at least one side of the negative electrode current collector. The coating surface density, calculated based on the mass of the negative electrode active material, is, for example, 10 mg / cm³. 2 -15mg / cm 2 The negative electrode slurry is uniformly coated onto at least one side of the negative electrode current collector, dried in a vacuum drying oven, and then subjected to processes such as rolling, edge trimming, cutting, and slitting to obtain the negative electrode sheet. In one embodiment of the present invention, after the negative electrode sheet is rolled, the thickness of one side of the negative electrode active layer is, for example, 90 μm-166 μm, and the compaction density of one side of the negative electrode active layer is, for example, 0.9 g / cm³. 3 -1.1g / cm 3 .

[0039] In one embodiment of the present invention, the electrolyte includes, for example, an organic solvent, a sodium salt, and additives. The organic solvent includes, for example, one or a combination of at least two of the following: propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), diethylene glycol dimethyl ether (DEGD), ethylene carbonate (EC), dimethyl carbonate (DMC), methyl propyl carbonate (MPC), 2,3-butylene carbonate (BC), or ethyl acrylate (EA). Sodium salts include, for example, sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluoroarsenate (NaAsF6), sodium dioxaborate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorosulfonylimide (NaFSI), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), or combinations of at least two of these. Additives include, for example, at least one of fluoroethylene carbonate (FEC), 1,3-propanesultone (1,3-PS), 1,3,2-dioxathiolane 2,2-dioxide (DTD), and 1,3-propenesulfonyl lactone (Prop-1-ene-1,3-sultone (PST).

[0040] In one embodiment of the present invention, when preparing the electrolyte, if the nitrogen content in the glove box is 99.999%, the actual oxygen content in the glove box is less than or equal to 0.1 ppm, and the moisture content is less than or equal to 0.1 ppm, an organic solvent is selected, such as ethylene carbonate and dimethyl carbonate, and the volume ratio of ethylene carbonate and dimethyl carbonate is, for example, 1:1. The sodium salt is, for example, sodium hexafluorophosphate, and the concentration of sodium hexafluorophosphate is, for example, 1 mol / L. The additive is, for example, fluoroethylene carbonate, and the content of fluoroethylene carbonate is, for example, 1 wt%-5 wt% based on the total weight of the electrolyte.

[0041] In one embodiment of the present invention, the separator is, for example, a polyethylene (PE) membrane, a polypropylene (PP) membrane, a glass fiber membrane, a polyethylene membrane, or a composite membrane. The thickness of the separator is, for example, 9μm-15μm. In this embodiment, the separator is, for example, a laminated structure of PP / PE / PP three layers. In one embodiment of the present invention, the above-mentioned positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode to act as a separator. The stacked or wound electrodes form an electrode assembly. The electrode assembly is installed in a casing, baked at 80℃-100℃ to remove moisture, injected with electrolyte, and sealed. Afterwards, it undergoes processes such as settling, formation, hot and cold pressing, and inspection to obtain a sodium-ion battery.

[0042] The present invention will be explained in more detail below by referring to embodiments, which should not be construed as limiting. Appropriate modifications can be made within the scope of the invention and all such modifications fall within the technical scope of the invention. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available or can be prepared by conventional methods in the art, and the instruments used in the embodiments are also commercially available.

[0043] Example 1 Preparation of sodium supplementation agent at the positive electrode: Analytical grade Na₂CO₃ and sodium hydroxide with a specific surface area of ​​8.92 m² were prepared. 2 Mn(OH)₂ with a median particle size D50 of 4.57 μm was weighed and mixed at a stoichiometric ratio of Na:Mn = 2:1. The mixture was placed in a muffle furnace and heated to 700 °C at a heating rate of 5 °C / min under air atmosphere, and calcined at this temperature for 12 hours. It was then cooled to room temperature with the furnace to obtain a layered precursor, Na₂MnO₃. The synthesized precursor powder was then placed in a planetary ball mill jar with zirconia grinding balls at a mass ratio of 1:30, and argon gas was introduced into the jar as a protective atmosphere. Mechanical ball milling was then performed at 500 rpm for 24 hours. After ball milling, the powder sample was removed under argon protection to obtain the positive electrode sodium supplement. The positive electrode sodium supplement was tested by X-ray absorption spectroscopy. Figure 1 As shown, the K-absorption edge energy of Mn was determined to be 6552.3 eV (calculated using the integral method). Since the K-absorption edge energy of Mn changes linearly with valence state, and considering that the K-absorption edge energies of Mn metal and MnO2 standard samples are 6539 eV and 6553 eV respectively, the valence state of Mn in this sample can be calculated to be +3.8. Because the material maintains overall charge conservation, the oxygen vacancy content x is calculated to be 0.1. Therefore, the chemical formula of the obtained positive electrode sodium supplement is Na2MnO. 2.9 .

[0044] Preparation of the positive electrode: NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, positive electrode sodium supplement Na2MnO 2.9 Polyvinylidene fluoride (PVDF) and conductive carbon black were mixed in a mass ratio of 90:6:2:2. NMP was then added, and the mixture was stirred at 400 rpm for 40 minutes, followed by stirring at 1800 rpm for 90 minutes to obtain a positive electrode slurry with a solid content of 55 wt%. The positive electrode slurry was then uniformly coated onto both sides of a 15 μm thick aluminum foil. Based on the total mass of the positive electrode active material and the positive electrode sodium supplement, the coating surface density was 20 mg / cm³. 2 The electrode sheets were then transferred to a vacuum oven at 100°C and dried for 12 hours. Following this, they underwent rolling, edge trimming, cutting, and slitting processes to obtain the positive electrode sheet. The thickness of the positive active layer on one side was 62.5 μm, and the compaction density on one side was 3.2 g / cm³. 3 .

[0045] Preparation of the negative electrode sheet: Hard carbon material, conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a mass ratio of 96:2:1:1. Deionized water was added, and the mixture was stirred at 400 rpm for 40 min, followed by stirring at 1800 rpm for 90 min to obtain a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry was uniformly coated on both sides of a 15 μm copper foil. The coating density was controlled at 10 mg / cm² based on the mass of the negative electrode active material. 2 The electrode sheets were then transferred to a vacuum oven at 100°C and dried for 12 hours. Following this, they underwent rolling, edge trimming, cutting, and slitting processes to obtain the negative electrode sheet. The thickness of the negative electrode active layer on one side was 100 μm, and the compaction density on one side was 1.0 g / cm³. 3 .

[0046] Preparation of electrolyte: In a glove box with a nitrogen atmosphere containing 0.1 ppm oxygen and 0.1 ppm moisture, ethylene carbonate and dimethyl carbonate were mixed evenly at a volume ratio of 1:1. NaPF6 and FEC were added. The concentration of NaPF6 was 1 mol / L, and the content of FEC was 2 wt% based on the total mass of the electrolyte being 100%.

[0047] Membrane selection: Select a 20μm thick glass fiber membrane.

[0048] Battery fabrication: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The stacked electrodes form the electrode assembly. The electrode assembly is then placed in an aluminum-plastic film, baked at 85°C to remove moisture, injected with the electrolyte, and sealed. After standing, formation, hot and cold pressing, and inspection processes, a soft-pack sodium-ion battery is obtained.

[0049] Example 2 In the preparation of the positive electrode sodium supplement, the precursor Na2MnO3 was ball-milled at 500 rpm for 30 h. X-ray absorption spectroscopy analysis revealed that the chemical formula of the obtained positive electrode sodium supplement was Na2MnO3. 2.87 The other steps are the same as in Example 1.

[0050] Example 3 In the preparation of the positive electrode sodium supplement, the precursor Na2MnO3 was ball-milled at 500 rpm for 36 hours. X-ray absorption spectroscopy analysis revealed that the chemical formula of the obtained positive electrode sodium supplement was Na2MnO3. 2.86 The other steps are the same as in Example 1.

[0051] Example 4 In the preparation of the positive electrode sodium supplement, the precursor Na2MnO3 was ball-milled at 600 rpm for 24 hours. X-ray absorption spectroscopy analysis revealed that the chemical formula of the obtained positive electrode sodium supplement was Na2MnO3. 2.83 The other steps are the same as in Example 1.

[0052] Example 5 In the preparation of the positive electrode sodium supplement, the precursor Na2MnO3 was ball-milled at 600 rpm for 30 h. X-ray absorption spectroscopy analysis revealed that the chemical formula of the obtained positive electrode sodium supplement was Na2MnO3. 2.8 The other steps are the same as in Example 1.

[0053] Example 6 In the preparation of the positive electrode sodium supplement, the precursor Na2MnO3 was ball-milled at 600 rpm for 36 hours. X-ray absorption spectroscopy analysis revealed that the chemical formula of the obtained positive electrode sodium supplement was Na2MnO3. 2.78 The other steps are the same as in Example 1.

[0054] Example 7 In the preparation of the positive electrode sodium supplement, the precursor Na2MnO3 was ball-milled at 700 rpm for 24 hours. X-ray absorption spectroscopy analysis revealed that the chemical formula of the obtained positive electrode sodium supplement was Na2MnO3. 2.76 The other steps are the same as in Example 1.

[0055] Example 8 In the preparation of the positive electrode sodium supplement, the precursor Na2MnO3 was ball-milled at 700 rpm for 30 h. X-ray absorption spectroscopy analysis revealed that the chemical formula of the obtained positive electrode sodium supplement was Na2MnO3. 2.72 The other steps are the same as in Example 1.

[0056] Example 9 In the preparation of the positive electrode sodium supplement, the precursor Na2MnO3 was ball-milled at 700 rpm for 36 hours. X-ray absorption spectroscopy analysis revealed that the chemical formula of the obtained positive electrode sodium supplement was Na2MnO3. 2.7 The other steps are the same as in Example 1.

[0057] Example 10 In preparing the positive electrode sodium supplement, analytical grade Na₂CO₃ and a specific surface area of ​​9.92 m² were used. 2 / g of Mn(OH)2 with a median particle size D50 of 4.06μm was weighed and mixed at a stoichiometric ratio of Na:Mn = 2:1. Other steps were the same as in Example 5.

[0058] Example 11 In preparing the positive electrode sodium supplement, analytical grade Na₂CO₃ and a specific surface area of ​​8.03 m² were used. 2 / g of Mn(OH)2 with a median particle size D50 of 5.01μm was weighed and mixed at a stoichiometric ratio of Na:Mn = 2:1. Other steps were the same as in Example 5.

[0059] Example 12 In preparing the positive electrode sodium supplement, analytical grade Na₂CO₃ and a specific surface area of ​​10.85 m² were used. 2 / g of Mn(OH)2 with a median particle size D50 of 3.76μm was weighed and mixed at a stoichiometric ratio of Na:Mn = 2:1. Other steps were the same as in Example 5.

[0060] Example 13 In preparing the positive electrode sodium supplement, analytical grade Na₂CO₃ and a specific surface area of ​​7.41 m² were used. 2 / g of Mn(OH)2 with a median particle size D50 of 5.24μm was weighed and mixed at a stoichiometric ratio of Na:Mn=2:1. Other steps were the same as in Example 5.

[0061] Comparative Example 1 When preparing the positive electrode sheet, no sodium supplement is added; instead, NaNi is used. 1 / 3 Fe 1 / 3 Mn 1 / 3 After mixing O2, polyvinylidene fluoride and conductive carbon black in a mass ratio of 96:2:2, other operations are the same as in Example 1.

[0062] Comparative Example 2 In the preparation of the positive electrode sodium supplement, the precursor Na2MnO3 was ball-milled at 400 rpm for 30 h. X-ray absorption spectroscopy analysis revealed that the chemical formula of the obtained positive electrode sodium supplement was Na2MnO3. 2.93Other operations remain the same as in Example 1.

[0063] Comparative Example 3 In the preparation of the positive electrode sodium supplement, the precursor Na2MnO3 was ball-milled at 800 rpm for 30 h. X-ray absorption spectroscopy analysis revealed that the chemical formula of the obtained positive electrode sodium supplement was Na2MnO3. 2.68 Other operations remain the same as in Example 1.

[0064] Comparative Example 4 In preparing the positive electrode sodium supplement, the precursor Na2MnO3 was not ball-milled, and Na2MnO3 was used as the positive electrode sodium supplement. Other operations were consistent with those in Example 1.

[0065] In this invention, the preparation conditions and characteristics of the positive electrode sodium supplement in Examples 1-13 and Comparative Examples 1-4 are shown in Tables 1-2, and the performance of the sodium-ion battery was tested, with the test results shown in Table 3.

[0066] Table 1. Preparation conditions and oxygen vacancy content of the positive electrode sodium supplement in Examples 1-13 and Comparative Examples 2-3.

[0067] In one embodiment of the present invention, the specific surface area of ​​the positive electrode sodium supplement is determined by gas physical adsorption, using a nitrogen (N2) adsorption-desorption isotherm and calculated based on the BET (Brunauer–Emmett–Teller) model. During the test, 0.1 g of the positive electrode sodium supplement is placed in the sample tube of the specific surface area analyzer and degassed under an inert atmosphere to remove adsorbed water and surface volatiles. After degassed, N2 adsorption is tested. The relative pressure (P / P0) range of 0.05–0.30 is selected for specific surface area calculation.

[0068] In one embodiment of the present invention, the median particle size D50 of the positive electrode sodium supplement was measured using a laser diffractometer. Before testing, 0.1 g of the positive electrode sodium supplement was dispersed in anhydrous ethanol, and ultrasonic dispersion was used to reduce agglomeration. With circulation and stirring on, the dispersed sample suspension was slowly added, and the change in opacity was observed in real time. The amount of sample added was adjusted to achieve an opacity of 8%-12%. After reaching a stable opacity, dispersion continued for 60 seconds, and the instrument's built-in ultrasonic function was activated for 30 seconds to eliminate weak agglomeration. Particle size measurement was then performed, with each measurement lasting 15 seconds. After the measurement, the median particle size D50 of the positive electrode sodium supplement was recorded.

[0069] Table 2 shows the specific surface area and median particle size of the sodium supplement agent at the positive electrode in Examples 5 and 10-13.

[0070] In one embodiment of the present invention, the initial coulombic efficiency and capacity test involves placing the sodium-ion battery in a constant temperature chamber at 25°C and charging it to 4.0V at a constant current of 0.05C, recording the specific capacity C of the first charge cycle. cha After standing for 5 minutes, discharge at a constant current of 0.33C to 2.0V, and record the discharge specific capacity C of the first cycle. dis First-week Coulomb efficiency (ICE) = (C dis / C cha )×100%.

[0071] In one embodiment of the present invention, the 25°C charge-discharge cycle test involves placing the sodium-ion battery in a constant-temperature chamber at 25°C. After completing the first charge-discharge cycle as described above, the battery is charged at a constant current of 0.33C to 4.0V, then charged at a constant voltage of 0.05C. After resting for 5 minutes, it is discharged at a constant current of 0.33C to 2.0V. This charge-discharge cycle is repeated 200 times, and the discharge specific capacity C of the 200th cycle is recorded. 200 Then the capacity retention rate = (C 200 / C dis )×100%.

[0072] In the above tests, the specific capacity was calculated as the total mass of the positive electrode active material and the sodium supplement material.

[0073] Table 3. Performance of sodium-ion batteries in Examples 1-13 and Comparative Examples 1-4

[0074] Among them, the positive electrode sodium supplement prepared using the embodiments of the present invention exhibits excellent performance, specifically meeting the following requirements: first-cycle charging specific capacity ≥144mAh / g, first-cycle discharging specific capacity ≥112mAh / g, first-cycle coulombic efficiency ≥76%, and capacity retention rate ≥85% after 200 cycles. Examples of these are provided, with the following preferred embodiments simultaneously meeting the requirements of first-cycle coulombic efficiency ≥79% and capacity retention rate ≥90% after 200 cycles. The remaining examples serve as comparative examples.

[0075] Please refer to Tables 1 to 3. Comparing Examples 1-13 and Comparative Example 1, it can be seen that the Na2MnO prepared using the present invention... 3-x When sodium supplementation is performed, the battery's first-week charging and discharging capacities are systematically improved, and its long-cycle performance is also somewhat improved, indicating that Na2MnO 3-x It has a significant sodium supplementation effect. This is due to Na2MnO 3-xThe process achieves efficient and complete electrochemical sodium removal during the initial charge, providing an additional sodium source to compensate for the irreversible consumption of sodium ions by the hard carbon anode during SEI film formation, thereby directly improving the reversible capacity of the entire battery. Secondly, this cathode sodium replenisher maintains a stable crystal structure during sodium removal without undergoing a phase transition. This "zero strain" or "low strain" characteristic results in a volume change far lower than traditional decomposition-type sodium replenishers, significantly reducing the mechanical impact on the integrity of the cathode microstructure and the electrode conductive network. Thus, efficient sodium replenishment is achieved without sacrificing battery cycle stability.

[0076] Please refer to Tables 1 to 3. Comparing Examples 1-13 and Comparative Example 4, it can be seen that when Na2MnO3 is selected as the sodium replenisher for the positive electrode, the charge-discharge performance and cycle performance deteriorate in the first week. This is because the sodium removal kinetics of Na2MnO3 are limited, making it difficult to effectively remove sodium within the normal operating voltage window of the battery. The introduction of this electrochemically inert component actually hinders the capacity utilization of the positive electrode.

[0077] Please refer to Tables 1 to 3. Comparing Examples 1-9 and Comparative Examples 2-3, it can be seen that the changes in the first-cycle charge specific capacity, first-cycle coulombic efficiency, and cycle capacity of sodium-ion batteries are affected by Na2MnO. 3-x The effect of oxygen vacancy content. This is due to the influence of Na₂MnO₂ content. 3-x When the oxygen vacancy content in the cathode sodium supplement is too low, the sodium removal kinetics are limited, affecting the cathode's capacity utilization and the battery's cycle performance. When the oxygen vacancy content is too high, the excessive oxygen vacancy content negatively impacts the battery's cycle performance. This may be because excessively high rotational speeds induce lattice oxygen escape, leading to excessive disorder and amorphization of the material, and the formation of electrochemically unstable phases (such as Na₂O). Although this sodium supplement exhibits the highest first-cycle charge specific capacity, it undergoes numerous irreversible side reactions with the electrolyte during sodium removal, consuming a large amount of active sodium source and disrupting the stability of the electrode / electrolyte interface, ultimately adversely affecting the battery's cycle life. Therefore, controlling the oxygen vacancy content in the cathode sodium supplement is crucial to ensuring effective sodium replenishment while improving battery cycle performance.

[0078] Please refer to Tables 2 and 3. Comparing Examples 5 and 10-13, it can be seen that when the specific surface area and median particle size of the positive electrode sodium supplement are too large or too small, it will affect the first-cycle coulombic efficiency and cycle capacity retention of the battery. This is because when the particle size of the positive electrode sodium supplement is too large and the specific surface area is too low, the contact interface between the positive electrode sodium supplement and the electrolyte is insufficient, and the ion / charge transfer kinetics are limited. This easily leads to a high sodium removal reaction initiation potential or incomplete reaction, manifested as a decrease in sodium supplementation efficiency, incomplete release of sodium source during the first charge, and deterioration of cycle stability. When the particle size of the positive electrode sodium supplement is too small and the specific surface area is too high, it easily aggravates the interfacial side reactions between the positive electrode sodium supplement and the electrolyte, leading to the consumption of effective sodium source, the formation of insulating byproducts on the surface, or the thickening of the interfacial film, thereby causing risks such as increased irreversible capacity, decreased first-cycle coulombic efficiency, and deterioration of cycle performance.

[0079] This invention also provides an electronic device comprising at least one of the aforementioned sodium-ion batteries, which provides electrical energy. The electronic device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, or power tool, etc. In one embodiment of this invention, the vehicle is, for example, a new energy vehicle, which can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the aforementioned sodium-ion battery, and therefore the advantages of including the aforementioned sodium-ion battery are not elaborated here.

[0080] In summary, this invention proposes a positive electrode sodium supplement agent, its preparation method, and its application. By introducing oxygen vacancies into the positive electrode sodium supplement agent, the average valence state of manganese is reduced, thereby lowering the sodium removal potential of the positive electrode sodium supplement agent and effectively exerting its sodium supplementation function. Controlling the oxygen vacancy content in the positive electrode sodium supplement agent allows for full utilization of its sodium supplementation function at a lower potential, reducing side reactions between the positive electrode sodium supplement agent and the electrolyte, and improving the cycle performance of sodium-ion batteries. It can improve the air stability of the positive electrode sodium supplement agent, reduce its sensitivity to water and carbon dioxide, and prevent deliquescence or carbonation. It can be stored, transported, and weighed and dispersed under normal dry conditions, and maintains the stability of sodium source release capacity during electrode preparation, thereby improving its operability and reliability in engineering applications. This solves the problems of strong alkaline sodium supplement agents such as sodium oxide readily reacting rapidly with moisture and carbon dioxide in the air, leading to the loss of effective sodium source, and introducing impurity phases, increasing the risk of slurry gelation, and interfacial side reactions during electrode preparation and battery assembly, thus improving the electrochemical consistency and safety of the battery. This technology ensures compatibility between the positive electrode sodium supplement and the positive electrode active material, matching its sodium removal potential with the charging potential platform of the positive electrode active material, significantly improving its compatibility and practicality as a sodium supplement. Simultaneously, the positive electrode sodium supplement fills the gaps between materials in the positive electrode sheet, constructing a good conductive network, reducing local overpotential, alleviating uneven current density distribution, and reducing the occurrence of side reactions in the positive electrode sheet, thereby improving battery cycle stability. It effectively avoids damage to the electrode structure caused by severe volume shrinkage of the positive electrode sodium supplement, thus ensuring the integrity of the electrode interface and improving the initial coulombic efficiency, cycle life, and safety performance of the full battery. By controlling the specific surface area and median particle size of the positive electrode sodium supplement, the contact interface between the positive electrode sodium supplement and the electrolyte, ion / charge transfer kinetics, etc., can be controlled, further improving battery capacity, initial coulombic efficiency reduction, and cycle performance.

[0081] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0082] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A positive electrode sodium supplement agent, characterized in that, The positive electrode sodium supplement is Na2MnO 3-x x is 0.1-0.

3.

2. The positive electrode sodium supplement agent according to claim 1, characterized in that, x represents the oxygen vacancy content.

3. The positive electrode sodium supplement agent according to claim 1, characterized in that, x is 0.17-0.

22.

4. The positive electrode sodium supplement agent according to claim 1, characterized in that, The specific surface area of ​​the positive electrode sodium supplement is 8m². 2 / g-10m 2 / g.

5. The positive electrode sodium supplement agent according to claim 1, characterized in that, The median particle size of the positive electrode sodium supplement is 4μm-5μm.

6. A method for preparing the positive electrode sodium supplement agent as described in any one of claims 1-5, characterized in that, include: The sodium and manganese sources are mixed and then calcined and cooled to obtain the precursor. The ball milling speed and time are set, and the precursor is ball milled in an inert atmosphere to obtain a positive electrode sodium supplement. The ball milling speed is 500rpm-700rpm, and the ball milling time is 24h-36h.

7. The method for preparing the positive electrode sodium supplement according to claim 6, characterized in that, The sodium source includes sodium carbonate, and the manganese source includes manganese hydroxide, wherein the specific surface area of ​​the manganese hydroxide is 7 m². 2 / g-11m 2 / g, wherein the median particle size of the manganese hydroxide is 3.5μm-5.5μm.

8. A sodium-ion battery, characterized in that, include: A positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material and a positive electrode sodium supplementer, wherein the positive electrode sodium supplementer is selected from the positive electrode sodium supplementer according to any one of claims 1-5 or the positive electrode sodium supplementer obtained by the preparation method according to any one of claims 6-7; Negative electrode sheet, including negative electrode active material; A diaphragm is disposed between the positive electrode and the negative electrode.

9. The sodium-ion battery according to claim 8, characterized in that, The positive electrode active material includes layered transition metal oxides, and / or the negative electrode active material includes hard carbon.

10. An electronic device, characterized in that, Including the sodium-ion battery according to any one of claims 8-9.

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