Sodium supplement, method for preparing sodium supplement, positive electrode sheet, method for preparing positive electrode sheet, and electrochemical device

Abstract

The application discloses a sodium supplement, a preparation method thereof, a positive plate, a preparation method thereof, and an electrochemical device. The sodium supplement comprises an inner core and a coating layer at least partially covering the inner core. The inner core comprises a sodium source material, and the material of the coating layer comprises a water-absorbing material. The inner core is at least partially covered in the coating layer, so that, in use, when the sodium supplement contacts moisture, the water-absorbing material of the coating layer contacts the moisture first, the moisture is fixed in the water-absorbing material, and the sodium source material of the inner core is covered by the water-absorbing material of the coating layer, thereby reducing the contact between the sodium source material and the moisture, reducing the formation of strong alkaline compounds on the surface of the positive electrode, and weakening the influence on the cycle stability of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a sodium supplement, a preparation method of the sodium supplement, a positive electrode sheet, a preparation method of the positive electrode sheet and an electrochemical device. BACKGROUND

[0002] The positive electrode sodium supplement technology usually introduces a sodium supplement into the positive electrode material, and the traditional sodium supplement is mainly sodium powder, sodium salt and organic sodium-containing solution. The high activity of metal sodium leads to high sensitivity to water, so that the positive electrode sodium supplement is sensitive to moisture. When the sodium supplement is mixed with the positive electrode material, water is easily adsorbed, strong alkaline compounds are formed on the surface of the positive electrode, and the cycle stability of the battery is affected. SUMMARY

[0003] The present application is carried out in view of the above-mentioned problems, and aims to provide a sodium supplement, which reduces the adsorption of water during the mixing of the sodium supplement and the positive electrode material, reduces the formation of strong alkaline compounds on the surface of the positive electrode, and weakens the influence on the cycle stability of the battery.

[0004] In order to achieve the above-mentioned purpose, the present application provides a sodium supplement, a preparation method of the sodium supplement, a positive electrode sheet, a preparation method of the positive electrode sheet and an electrochemical device.

[0005] In the first aspect, the present application provides a sodium supplement, which comprises a core and a coating layer at least partially covering the core, the core comprises a sodium source material, and the material of the coating layer comprises a water-absorbing material.

[0006] Therefore, in the technical scheme of the present application, the water-absorbing material is added to the sodium supplement, and the core is at least partially covered in the coating layer. When the sodium supplement contacts water, the water-absorbing material of the coating layer contacts water first, and the water is fixed in the water-absorbing material. The sodium source material of the core is covered by the water-absorbing material of the coating layer, so as to reduce the contact between the sodium source material and water, reduce the formation of strong alkaline compounds on the surface of the positive electrode, and weaken the influence on the cycle stability of the battery.

[0007] In any embodiment, the mass ratio of the sodium source material to the water-absorbing material is (1-5):1. Optionally, the mass ratio of the sodium source material to the water-absorbing material is (2-3):1. When the mass ratio of the sodium source material is higher than that of the water-absorbing material, sufficient sodium source can be used for irreversible sodium loss during the first discharge, improving the cycle stability of the battery. When the mass ratio of the sodium source material to the water-absorbing material is less than 1:1, the proportion of sodium source material is too small, the sodium replenishment effect is not obvious, sodium in the electrode needs to be consumed, reducing the battery capacity. At the same time, the proportion of water-absorbing material is too high, making the water-absorbing material coating on the outer layer of the sodium source material too thick, making it difficult for sodium ions to escape, resulting in poor sodium replenishment. When the mass ratio of the sodium source material to the water-absorbing material is greater than 5:1, the proportion of water-absorbing material is too small, which is not conducive to sufficient reaction with water. Some sodium source material will react with water that has not been absorbed by the water-absorbing material, producing strong alkaline substances, which will then corrode the electrode and reduce the electrode capacity.

[0008] In any embodiment, the coating layer further includes a conductive agent. Since the water-absorbing material is usually a material with weak conductivity, the sodium source material is coated in the water-absorbing material, and the migration rate of sodium ions slows down. Through the interpenetration of the conductive agent and the silica gel, the sodium source material coated in the water-absorbing material can migrate out quickly. The conductive agent introduced on the outer surface of the sodium supplement provides a channel for the migration of the sodium source material, thereby increasing the migration rate of the sodium source material in the sodium supplement.

[0009] In any embodiment, the mass of the sodium source material and the water-absorbing material is M1, and the mass of the conductive agent is M2, wherein M1:M2 is (1.5-8):1; optionally, M1:M2 is (2-5):1. The sum of the masses of the sodium source material and the water-absorbing material is greater than the mass of the conductive agent, which can improve sodium ion removal while reducing the residual conductive agent, reducing the amount of inert material, and reducing interference with the electrode. When M1:M2 is less than 1.5:1, the mass of the conductive agent is too large, resulting in a large amount of inert material remaining after sodium ion removal, affecting electrode performance. When M1:M2 is greater than 8:1, the mass of the conductive agent is too small, the sodium ion migration ability is insufficient, and the sodium ion removal efficiency is low.

[0010] In any embodiment, the conductive agent includes, but is not limited to, at least one of conductive carbon black, conductive graphite, acetylene black, and Ketjen black. Using the above conductive agents can increase the migration rate of sodium ions and improve the initial discharge capacity of the electrochemical device.

[0011] In any embodiment, the absorbent material includes, but is not limited to, at least one of silica gel, porous carbon, and activated alumina. Using these absorbent materials can adsorb moisture while coating the sodium source material, reducing the reaction between the sodium source material and water to form strongly alkaline substances.

[0012] In any embodiment, the sodium source material includes, but is not limited to, at least one of Na₂O, Na₂CO₃, NaF, and Na₂S. Using the above sodium source materials can effectively replenish the sodium source for the initial discharge of the electrode, compensating for irreversible sodium loss from the electrode.

[0013] In any embodiment, the particle size of the sodium supplement is 1–200 μm, optionally 100–150 μm. By controlling the particle size of the sodium supplement, water molecules can be adsorbed into the water-absorbing material, while providing a channel for the release of sodium ions. When the particle size of the sodium supplement is less than 1 μm, the particle size is too small, the specific surface area of ​​the sodium supplement increases, and it is prone to agglomeration, thus failing to function effectively. When the particle size of the sodium supplement is greater than 200 μm, the particle size is too large, affecting the release of sodium ions from the interior, which is not conducive to sodium supplementation.

[0014] Secondly, embodiments of this application provide a method for preparing a sodium supplement, which includes the following steps:

[0015] The core material is mixed with the molten coating material, solidified, and then granulated to obtain a sodium supplement.

[0016] By mixing the core material with the molten coating material, solidifying and granulating, a sodium supplement is obtained. This ensures that the core sodium source material is at least partially coated in the water-absorbing coating material, reducing the contact between the sodium source material and moisture, reducing the generation of strong alkaline substances, and reducing corrosion of the electrode.

[0017] In any embodiment, the steps of mixing the core material with the molten coating material, solidifying and granulating to obtain the sodium supplement include:

[0018] The sodium source material is mixed with the conductive agent to obtain the first mixture;

[0019] The water-absorbing material is melted and mixed with the first mixture to obtain the second mixture. The second mixture is then solidified and granulated to obtain the sodium supplement.

[0020] By first mixing the sodium source material with the conductive agent, the sodium source material and the conductive agent come into contact, thereby providing a channel for the release of sodium ions. At the same time, the sodium source material and the conductive agent are at least partially coated in the water-absorbing material to protect the sodium source material and reduce the generation of strongly alkaline substances when the sodium source material comes into contact with water.

[0021] In any embodiment, the step involves melting the absorbent material, mixing it with the first mixture to obtain a second mixture, and then solidifying and granulating the second mixture to obtain the sodium supplement.

[0022] After melting the absorbent material, the mixing speed with the first mixture is 1000–8000 r / min. Optionally, the mixing speed is 3000–6000 r / min. By controlling the mixing speed, the sodium-adding material and the conductive agent can be uniformly dispersed in the absorbent material, thereby improving the sodium-addition effect. When the mixing speed is less than 1000 r / min, the mixing uniformity is poor. When the mixing speed is greater than 8000 r / min, due to excessive shear force, adverse side reactions may occur, resulting in substances that are detrimental to sodium addition; and / or,

[0023] After melting the absorbent material, the mixing time with the first mixture is 10–60 minutes. Optionally, the mixing time is 20–40 minutes. By controlling the mixing time, the sodium-adding material and the conductive agent can be uniformly dispersed in the absorbent material, thereby improving the sodium-adding effect. When the mixing time is less than 10 minutes, the mixing uniformity is poor; when the mixing time is greater than 60 minutes, the mixing time is too long, affecting the production capacity. And / or,

[0024] Granulation after solidification of the second mixture includes stirring granulation, wherein the granulation speed is 1000–8000 r / min, optionally 3000–6000 r / min. By controlling the granulation speed, the particle size of the sodium supplement can be controlled, thus both adsorbing water into the water-absorbing material and providing migration channels for sodium ion removal. When the granulation speed is less than 1000 r / min, the sodium supplement particle size is easily too large, making sodium ion removal difficult and resulting in poor sodium supplementation effect. When the granulation speed is greater than 8000 r / min, the sodium supplement particle size is easily too small, causing water molecules to migrate in the sodium supplement and combine with the sodium supplement material to form a strongly alkaline substance, corroding the electrode. And / or,

[0025] The granulation process after solidification of the second mixture includes stirring granulation, wherein the granulation time is 3–10 min, optionally 4–6 min. By controlling the granulation time, the particle size of the sodium supplement can be controlled, thus both adsorbing moisture into the absorbent material and providing migration channels for sodium ion release. When the granulation time is greater than 10 min, the particle size of the sodium supplement is easily too small, causing water molecules to migrate within the sodium supplement and combine with the sodium supplement material to form a strongly alkaline substance that corrodes the electrode. When the granulation time is less than 3 min, the particle size of the sodium supplement is easily too large, making sodium ion release difficult and resulting in poor sodium supplementation effect.

[0026] In any embodiment, the step of mixing the sodium source material with the conductive agent to obtain a first mixture,

[0027] The sodium source material and the conductive agent can be mixed by grinding for 5–30 minutes, optionally 8–15 minutes. By controlling the mixing time, the sodium source material and the conductive agent can be thoroughly mixed, thus providing a channel for sodium ion release and facilitating sodium replenishment. When the mixing time is less than 5 minutes, the mixing is uneven, and the contact between the sodium source material and the conductive agent is insufficient. When the mixing time is greater than 30 minutes, side reactions may occur, which is not conducive to sodium replenishment.

[0028] In any embodiment, the melting temperature of the water-absorbing material is 200–300°C, optionally 240–260°C. By controlling the melting temperature of the water-absorbing material, the sodium-supplementing material can be at least partially coated within the molten water-absorbing material, reducing contact between the sodium-supplementing material and moisture, reducing the generation of strongly alkaline substances, and reducing corrosion of the electrode. When the melting temperature is below 200°C, the water-absorbing material cannot completely melt, resulting in poor coating properties. When the melting temperature is above 300°C, the water-absorbing material may undergo irreversible side reactions, generating substances that are detrimental to coating and reducing the protection of the sodium source material.

[0029] Thirdly, embodiments of this application provide a positive electrode sheet, including the sodium supplement agent and the positive electrode material of the first aspect of this application.

[0030] In any embodiment, the positive electrode material includes a positive electrode active material, a conductive material, and a binder.

[0031] In any embodiment, the mass ratio of the positive electrode active material, the conductive material, the binder, and the sodium replenishing agent is (70-90):(3-20):(3-20):(3-20). Optionally, the mass ratio of the positive electrode active material, the conductive material, the binder, and the sodium replenishing agent is (80-85):(5-10):(5-10):(5-10). By controlling the mass ratio of the positive electrode active material, the conductive material, the binder, and the sodium replenishing agent, a better sodium replenishment effect can be obtained. When there is too much sodium replenishing agent, after sodium replenishment is completed, the remaining water-absorbing material is an inert substance and no longer participates in charge transfer. A high proportion of sodium replenishing agent results in excessive residual inert material. The sodium in the sodium replenishing agent can only be extracted and cannot be embedded, occupying too much volume, which is not conducive to improving the electrode capacity and affects the electrode performance. When there is too little sodium replenishing agent, during the sodium replenishment process, the sodium source of the sodium replenishing agent is insufficient, requiring the consumption of sodium in the electrode, which also affects the electrode performance.

[0032] In any embodiment, the positive electrode active material includes, but is not limited to, at least one of sodium vanadium phosphate, sodium manganate, sodium manganese vanadium phosphate, sodium cobaltate, Prussian blue sodium, and sodium vanadium fluorophosphate. A highly active positive electrode can be obtained using the above-mentioned positive electrode active materials.

[0033] In any embodiment, the binder includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene copolymer, PVDF-tetrafluoroethylene copolymer, PVDF-hexafluoropropylene-tetrafluoroethylene copolymer, PVDF-pentafluoropropylene copolymer, PVDF-pentafluoropropylene-tetrafluoroethylene copolymer, PVDF-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, PVDF-chlorotrifluoroethylene copolymer, polytetrafluoroethylene, polychlorotrifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer. The above binders can bond the positive electrode active material, conductive agent, and sodium-supplementing material to the current collector, providing good electrode performance.

[0034] In any embodiment, the conductive material includes, but is not limited to, at least one of conductive carbon black, superconducting carbon black, conductive graphite, acetylene black, Ketjen black, graphene, and carbon nanotubes. Good conductivity can be achieved using the above-mentioned conductive materials, thereby improving the electrode capacity.

[0035] Fourthly, embodiments of this application provide a method for preparing a positive electrode sheet, which includes the following steps:

[0036] The sodium-supplementing material is mixed with the positive electrode material in a solvent, coated onto the surface of the positive electrode current collector, dried, cold-pressed, and cut to obtain the positive electrode sheet.

[0037] By mixing sodium-supplementing materials with positive electrode materials and then coating the mixture onto the surface of the positive electrode current collector, a positive electrode sheet containing sodium-supplementing agents can be obtained. This reduces irreversible sodium loss in the positive electrode sheet.

[0038] In any embodiment, the solvent comprises N-methylpyrrolidone. Using N-methylpyrrolidone allows for good mixing of the sodium-adding material with the positive electrode material, facilitating sodium replenishment.

[0039] Fifthly, embodiments of this application provide an electrochemical device including the positive electrode of the third aspect of this application.

[0040] In any embodiment, the electrochemical device includes a capacitor, a primary battery, or a secondary battery. Detailed Implementation

[0041] The following details the implementation of the sodium supplement, its preparation method, the solar power generation device, and the power consumption device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially the same structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand this application and is not intended to limit the subject matter of the claims.

[0042] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0045] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0046] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0047] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0048] When a sodium-ion battery discharges for the first time, a benign film called the positive electrode interface (CEI) is formed on the surface of the positive electrode, consuming some sodium ions. After these sodium ions form the CEI film, they can no longer be used for sodium ion extraction and insertion. For the positive electrode, this sodium ion loss is irreversible and will reduce the battery capacity, making the actual capacity of the battery lower than the theoretical capacity.

[0049] Therefore, numerous sodium replenishment technologies have emerged for the positive electrode. For example, one method for preparing a sodium replenishing agent primarily uses sodium powder, sodium salt, or organic sodium-containing solutions. However, the high reactivity of metallic sodium makes it highly sensitive to water, causing the sodium replenishing agent to be particularly sensitive to moisture. During mixing with the positive electrode material, the sodium replenishing agent easily adsorbs moisture, forming strongly alkaline compounds on the positive electrode surface, thus affecting the battery's cycle stability. Most methods for preparing sodium replenishing agents use aqueous solvents or mixtures, which cannot completely prevent moisture adsorption.

[0050] Surprisingly, by setting the sodium supplement as a sodium source material that is at least partially coated by the water-absorbing material, the sodium source material is encapsulated in the water-absorbing material, thereby reducing the contact between the sodium source material and water, reducing ultrasonically strong alkaline substances, and improving battery stability.

[0051] Based on this, this application provides a sodium supplement, a method for preparing the sodium supplement, a positive electrode, a method for preparing the positive electrode, and an electrochemical device.

[0052] In a first aspect, embodiments of this application propose a sodium supplement, comprising a core and a coating layer at least partially covering the core, the core comprising a sodium source material and the coating layer comprising a water-absorbing material.

[0053] Therefore, in the technical solution of this application embodiment, a water-absorbing material is added to the sodium replenisher, and the core is at least partially covered in the coating layer. When the sodium replenisher comes into contact with water during use, the water-absorbing material of the coating layer comes into contact with the water first, and the water is fixed in the water-absorbing material. Meanwhile, the sodium source material of the core is covered by the water-absorbing material of the coating layer, thereby reducing the contact between the sodium source material and water, reducing the formation of strong alkaline compounds on the positive electrode surface, and weakening the impact on the cycle stability of the battery.

[0054] In any embodiment, the mass ratio of the sodium source material to the water-absorbing material is (1-5):1. Optionally, the mass ratio of the sodium source material to the water-absorbing material is (2-3):1. When the mass ratio of the sodium source material is higher than that of the water-absorbing material, sufficient sodium source can be used for irreversible sodium loss during the first discharge, improving the cycle stability of the battery. When the mass ratio of the sodium source material to the water-absorbing material is less than 1:1, the proportion of sodium source material is too small, the sodium replenishment effect is not obvious, sodium in the electrode needs to be consumed, reducing the battery capacity. At the same time, the proportion of water-absorbing material is too high, making the water-absorbing material coating on the outer layer of the sodium source material too thick, making it difficult for sodium ions to escape, resulting in poor sodium replenishment. When the mass ratio of the sodium source material to the water-absorbing material is greater than 5:1, the proportion of water-absorbing material is too small, which is not conducive to sufficient reaction with water. Some sodium source material will react with water that has not been absorbed by the water-absorbing material, producing strong alkaline substances, which will then corrode the electrode and reduce the electrode capacity.

[0055] In any embodiment, the coating layer further includes a conductive agent. Since the water-absorbing material is usually a material with weak conductivity, the sodium source material is coated in the water-absorbing material, and the migration rate of sodium ions slows down. Through the interpenetration of the conductive agent and the silica gel, the sodium source material coated in the water-absorbing material can migrate out quickly. The conductive agent introduced on the outer surface of the sodium supplement provides a channel for the migration of the sodium source material, thereby increasing the migration rate of the sodium source material in the sodium supplement.

[0056] In any embodiment, the mass of the sodium source material and the water-absorbing material is M1, and the mass of the conductive agent is M2, wherein M1:M2 is (1.5-8):1; optionally, M1:M2 is (2-5):1. The sum of the masses of the sodium source material and the water-absorbing material is greater than the mass of the conductive agent, which can improve sodium ion removal while reducing the residual conductive agent, reducing the amount of inert material, and reducing interference with the electrode. When M1:M2 is less than 1.5:1, the mass of the conductive agent is too large, resulting in a large amount of inert material remaining after sodium ion removal, affecting electrode performance. When M1:M2 is greater than 8:1, the mass of the conductive agent is too small, the sodium ion migration ability is insufficient, and the sodium ion removal efficiency is low.

[0057] In any embodiment, the conductive agent includes, but is not limited to, at least one of conductive carbon black, conductive graphite, acetylene black, and Ketjen black. Using the above conductive agents can increase the migration rate of sodium ions and improve the initial discharge capacity of the electrochemical device.

[0058] In any embodiment, the absorbent material includes, but is not limited to, at least one of silica gel, porous carbon, and activated alumina. Using these absorbent materials can adsorb moisture while coating the sodium source material, reducing the reaction between the sodium source material and water to form strongly alkaline substances.

[0059] In any embodiment, the sodium source material includes, but is not limited to, at least one of Na₂O, Na₂CO₃, NaF, and Na₂S. Using the above sodium source materials can effectively replenish the sodium source for the initial discharge of the electrode, compensating for irreversible sodium loss from the electrode.

[0060] In any embodiment, the particle size of the sodium supplement is 1–200 μm, optionally 100–150 μm. By controlling the particle size of the sodium supplement, water molecules can be adsorbed into the water-absorbing material, while providing a channel for the release of sodium ions. When the particle size of the sodium supplement is less than 1 μm, the particle size is too small, the specific surface area of ​​the sodium supplement increases, and it is prone to agglomeration, thus failing to function effectively. When the particle size of the sodium supplement is greater than 200 μm, the particle size is too large, affecting the release of sodium ions from the interior, which is not conducive to sodium supplementation.

[0061] Secondly, embodiments of this application provide a method for preparing a sodium supplement, which includes the following steps:

[0062] The core material is mixed with the molten coating material, solidified, and then granulated to obtain a sodium supplement.

[0063] By mixing the core material with the molten coating material, solidifying and granulating, a sodium supplement is obtained. This ensures that the sodium source material is at least partially coated with the water-absorbing material, reducing the contact between the sodium source material and moisture, reducing the generation of strong alkaline substances, and reducing corrosion of the electrode.

[0064] In any embodiment, the steps of mixing the core material with the molten coating material, solidifying and granulating to obtain the sodium supplement include:

[0065] The sodium source material is mixed with the conductive agent to obtain the first mixture;

[0066] The water-absorbing material is melted and mixed with the first mixture to obtain the second mixture. The second mixture is then solidified and granulated to obtain the sodium supplement.

[0067] By first mixing the sodium source material with the conductive agent, the sodium source material and the conductive agent come into contact, thereby providing a channel for the release of sodium ions. At the same time, the sodium source material and the conductive agent are at least partially coated in the water-absorbing material to protect the sodium source material and reduce the generation of strongly alkaline substances when the sodium source material comes into contact with water.

[0068] In any embodiment, the step involves melting the absorbent material, mixing it with the first mixture to obtain a second mixture, and then solidifying and granulating the second mixture to obtain the sodium supplement.

[0069] After melting the absorbent material, the mixing speed with the first mixture is 1000–8000 r / min. Optionally, the mixing speed is 3000–6000 r / min. By controlling the mixing speed, the sodium-adding material and the conductive agent can be uniformly dispersed in the absorbent material, thereby improving the sodium-addition effect. When the mixing speed is less than 1000 r / min, the mixing uniformity is poor. When the mixing speed is greater than 8000 r / min, due to excessive shear force, adverse side reactions may occur, resulting in substances that are detrimental to sodium addition; and / or,

[0070] After melting the absorbent material, the mixing time with the first mixture is 10–60 minutes; alternatively, the mixing time is 20–40 minutes. By controlling the mixing time, the sodium-adding material and the conductive agent can be uniformly dispersed in the absorbent material, thereby improving the sodium-adding effect. When the mixing time is less than 10 minutes, the mixing uniformity is poor; when the mixing time is greater than 60 minutes, the mixing time is too long, affecting the production capacity; and / or,

[0071] Granulation after solidification of the second mixture includes stirring granulation, wherein the granulation speed is 1000–8000 r / min, optionally 3000–6000 r / min; by controlling the granulation speed, the particle size of the sodium supplement can be controlled, thereby both adsorbing water into the water-absorbing material and providing migration channels for sodium ion removal. When the granulation speed is less than 1000 r / min, the sodium supplement particle size is easily too large, making sodium ion removal difficult and resulting in poor sodium supplementation effect. When the granulation speed is greater than 8000 r / min, the sodium supplement particle size is easily too small, causing water molecules to migrate in the sodium supplement and combine with the sodium supplement material to form a strongly alkaline substance, corroding the electrode; and / or,

[0072] The granulation process after solidification of the second mixture includes stirring granulation, wherein the granulation time is 3–10 min, optionally 4–6 min. By controlling the granulation time, the particle size of the sodium supplement can be controlled, thus both adsorbing moisture into the absorbent material and providing migration channels for sodium ion release. When the granulation time is greater than 10 min, the particle size of the sodium supplement is easily too small, causing water molecules to migrate within the sodium supplement and combine with the sodium supplement material to form a strongly alkaline substance that corrodes the electrode. When the granulation time is less than 3 min, the particle size of the sodium supplement is easily too large, making sodium ion release difficult and resulting in poor sodium supplementation effect.

[0073] In any embodiment, the step of mixing the sodium source material with the conductive agent to obtain a first mixture,

[0074] The sodium source material and the conductive agent can be mixed by grinding for 5–30 minutes, optionally 8–15 minutes. By controlling the mixing time, the sodium source material and the conductive agent can be thoroughly mixed, thus providing a channel for sodium ion release and facilitating sodium replenishment. When the mixing time is less than 5 minutes, the mixing is uneven, and the contact between the sodium source material and the conductive agent is insufficient. When the mixing time is greater than 30 minutes, side reactions may occur, which is not conducive to sodium replenishment.

[0075] In any embodiment, the melting temperature of the water-absorbing material is 200–300°C, optionally 240–260°C. By controlling the melting temperature of the water-absorbing material, the sodium-supplementing material can be at least partially coated within the molten water-absorbing material, reducing contact between the sodium-supplementing material and moisture, reducing the generation of strongly alkaline substances, and reducing corrosion of the electrode. When the melting temperature is below 200°C, the water-absorbing material cannot completely melt, resulting in poor coating properties. When the melting temperature is above 300°C, the water-absorbing material may undergo irreversible side reactions, generating substances that are detrimental to coating and reducing the protection of the sodium source material.

[0076] Thirdly, embodiments of this application provide a positive electrode sheet, including the sodium supplement agent and the positive electrode material of the first aspect of this application.

[0077] In any embodiment, the positive electrode material includes a positive electrode active material, a conductive material, and a binder.

[0078] In any embodiment, the mass ratio of the positive electrode active material, the conductive material, the binder, and the sodium replenishing agent is (70-90):(3-20):(3-20):(3-20). Optionally, the mass ratio of the positive electrode active material, the conductive material, the binder, and the sodium replenishing agent is (80-85):(5-10):(5-10):(5-10). By controlling the mass ratio of the positive electrode active material, the conductive material, the binder, and the sodium replenishing agent, a better sodium replenishment effect can be obtained. When there is too much sodium replenishing agent, after sodium replenishment is completed, the remaining water-absorbing material is an inert substance and no longer participates in charge transfer. A high proportion of sodium replenishing agent results in excessive residual inert material. The sodium in the sodium replenishing agent can only be extracted and cannot be embedded, occupying too much volume, which is not conducive to improving the electrode capacity and affects the electrode performance. When there is too little sodium replenishing agent, during the sodium replenishment process, the sodium source of the sodium replenishing agent is insufficient, requiring the consumption of sodium in the electrode, which also affects the electrode performance.

[0079] In any embodiment, the positive electrode active material includes, but is not limited to, at least one of sodium vanadium phosphate, sodium manganate, sodium manganese vanadium phosphate, sodium cobaltate, Prussian blue sodium, and sodium vanadium fluorophosphate. A highly active positive electrode can be obtained using the above-mentioned positive electrode active materials.

[0080] In any embodiment, the binder includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene copolymer, PVDF-tetrafluoroethylene copolymer, PVDF-hexafluoropropylene-tetrafluoroethylene copolymer, PVDF-pentafluoropropylene copolymer, PVDF-pentafluoropropylene-tetrafluoroethylene copolymer, PVDF-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, PVDF-chlorotrifluoroethylene copolymer, polytetrafluoroethylene, polychlorotrifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer. The above binders can bond the positive electrode active material, conductive agent, and sodium-supplementing material to the current collector, providing good electrode performance.

[0081] In any embodiment, the conductive material includes, but is not limited to, at least one of conductive carbon black, superconducting carbon black, conductive graphite, acetylene black, Ketjen black, graphene, and carbon nanotubes. Good conductivity can be achieved using the above-mentioned conductive materials, thereby improving the electrode capacity.

[0082] Fourthly, embodiments of this application provide a method for preparing a positive electrode sheet, which includes the following steps:

[0083] The sodium-supplementing material is mixed with the positive electrode material in a solvent, coated onto the surface of the positive electrode current collector, dried, cold-pressed, and cut to obtain the positive electrode sheet.

[0084] By mixing sodium-supplementing materials with positive electrode materials and coating them onto the surface of the positive electrode current collector, a positive electrode sheet containing sodium-supplementing agents can be obtained, reducing irreversible sodium loss in the positive electrode sheet.

[0085] In any embodiment, the solvent comprises N-methylpyrrolidone. Using N-methylpyrrolidone allows for good mixing of the sodium-adding material with the positive electrode material, facilitating sodium replenishment.

[0086] Fifthly, embodiments of this application provide an electrochemical device including the positive electrode of the third aspect of this application.

[0087] In any embodiment, the electrochemical device includes, but is not limited to, a capacitor, a primary battery, or a secondary battery.

[0088] When the electrochemical device is a coin cell, it also includes an electrolyte and a negative electrode. The electrolyte includes, but is not limited to, NaClO4 solution.

[0089] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0090] The parameters of the sodium supplements in Examples 1 to 35 and Comparative Examples 1 to 3 of this application are as specified in Table 1.

[0091] Table 1. Sodium supplement parameters for Examples 1 to 35 and Comparative Examples 1 to 3

[0092]

[0093]

[0094]

[0095] Example 36

[0096] A method for preparing a sodium supplement includes the following steps:

[0097] The core material is mixed with the molten coating material, solidified, and then granulated to obtain a sodium supplement.

[0098] Example 37

[0099] A method for preparing a sodium supplement includes the following steps:

[0100] The sodium source material is mixed with the conductive agent to obtain the first mixture;

[0101] The water-absorbing material is melted and mixed with the first mixture to obtain the second mixture. The second mixture is then solidified and granulated to obtain the sodium supplement.

[0102] Example 38

[0103] The sodium source material and the conductive agent are ground and mixed to obtain the first mixture;

[0104] The water-absorbing material is melted and mixed with the first mixture to obtain the second mixture. The second mixture is then solidified and granulated to obtain the sodium supplement.

[0105] The preparation methods of the sodium supplements in Examples 39 to 75 of this application are the same as those in Example 38, except that they are prepared according to the parameters in Table 2.

[0106] Table 2. Preparation parameters of sodium supplements in Examples 36-75 and Comparative Examples 4-5

[0107]

[0108]

[0109] Comparative Example 4

[0110] A method for preparing a sodium supplement includes the following steps:

[0111] A sodium supplement is obtained by mixing an absorbent material with a sodium source material.

[0112] Comparative Example 5

[0113] A method for preparing a sodium supplement includes the following steps:

[0114] A sodium supplement is obtained by melting the water-absorbing material and mixing it with the sodium source material.

[0115] Example 76

[0116] A positive electrode sheet includes a sodium supplement and a positive electrode material.

[0117] Example 77

[0118] A positive electrode sheet includes a sodium supplement and a positive electrode material, wherein the positive electrode material includes a positive electrode active material, a conductive material, and a binder.

[0119] The cathode materials of Examples 78 to 88 of this application differ from those of Example 77 in that the parameters are as shown in Table 3.

[0120] Table 3 Parameters of the cathode materials in Examples 78 to 88

[0121]

[0122] The sodium supplements from Examples 1 to 35 and Comparative Examples 1 to 3 were used to prepare coin cells. The sodium supplements from Examples 36 to 75 and Comparative Examples 4 to 5 were used to prepare coin cells. The positive electrode sheets from Examples 76 to 88 were used to prepare coin cells. The following tests were performed:

[0123] Electrical performance testing

[0124] First-cycle efficiency: The battery was tested for the first time at 20mAg-1 in the voltage range of 2.5-4.4V (vs. Na+ / Na). First-cycle efficiency = first discharge capacity / first charge capacity.

[0125] Cyclic performance: Sodium-ion batteries were subjected to cyclic charge-discharge tests at a voltage range of 2.0 to 4.4V with a capacity of 20 mAg⁻¹ for 300 cycles. The initial charge-discharge capacity and the charge-discharge capacity after different number of cycles were obtained. Cyclic capacity retention rate = discharge capacity / charge capacity.

[0126] The results of the statistical experiment are shown in Table 4.

[0127] Table 4 Performance determination of sodium supplements in Examples 1 to 88 and Comparative Examples 1 to 5

[0128]

[0129]

[0130]

[0131]

[0132] As shown in Table 4, through Examples 1 to 4 and Comparative Examples 1 to 3, the addition of sodium source material and water-absorbing material to the sodium supplement, with the sodium source material at least partially coated in the water-absorbing material, significantly improves the battery's cycle performance and significantly reduces the difference between charging and discharging. Although the sodium source in Examples 1 to 3 easily combines with hydrogen ions to generate water or carbon dioxide gas during charging and discharging, affecting the material's cycle performance, and the water-absorbing material acrylic resin in Example 1 has weaker water absorption than silica gel, and the calcium silicate and calcium oxide in Examples 2 to 3 introduce additional metal ions, the electrical performance of Examples 1 to 3 is still superior to that of Comparative Examples 1 to 3.

[0133] As can be seen from Examples 4 to 10, a suitable mass ratio of sodium source material to water-absorbing material can improve the cycle performance of the battery.

[0134] As can be seen from Examples 11 to 15, different conductive agents and sodium source materials can all improve the cycle performance of the battery, with silica gel being the most effective when the water-absorbing material is used.

[0135] As shown in Examples 17 to 25, different M1:M2 ratios have a definite impact on the cycle performance of the battery. When the combined mass of the sodium source material and the absorbent material is greater than the mass of the conductive agent, it can improve sodium ion removal while reducing the residual conductive agent, decreasing the amount of inert material, and reducing interference with the electrode. When M1:M2 is less than 1.5:1, the mass of the conductive agent is excessive, resulting in a large amount of inert material remaining after sodium ion removal, affecting electrode performance. When M1:M2 is greater than 8:1, the mass of the conductive agent is too small, leading to insufficient sodium ion migration and lower sodium ion removal efficiency.

[0136] As shown in Examples 26 to 35, different sodium replenisher particle sizes have a certain impact on the cycle performance of the battery. By controlling the particle size of the sodium replenisher, water molecules can be adsorbed into the water-absorbing material, while providing a channel for the release of sodium ions. When the particle size of the sodium replenisher is less than 1 μm, the particle size is too small, the specific surface area of ​​the sodium replenisher increases, and it is prone to agglomeration, thus failing to function effectively. When the particle size of the sodium replenisher is greater than 200 μm, the particle size is too large, affecting the release of sodium ions from the interior, which is not conducive to sodium replenishment.

[0137] As can be seen from Examples 36 to 38 and Comparative Examples 4 to 5, the coating of sodium source material with water-absorbing material has a significant impact on improving the cycle performance of the battery. Compared with Comparative Example 4, Examples 36 to 38 can improve the cycle performance of the battery.

[0138] As shown in Examples 39 to 44, the mixing speed has a certain impact on the cycle performance of the battery. By controlling the mixing speed, the sodium-replenishing material and the conductive agent can be uniformly dispersed in the water-absorbing material, thereby improving the sodium replenishment effect. When the mixing speed is less than 1000 r / min, the mixing uniformity is poor. When the mixing speed is greater than 8000 r / min, due to excessive shear force, adverse side reactions will occur, resulting in substances that are detrimental to sodium replenishment.

[0139] As shown in Examples 45 to 50, the mixing time has a certain impact on the cycle performance of the battery. By controlling the mixing time, the sodium-replenishing material and the conductive agent can be uniformly dispersed in the water-absorbing material, thereby improving the sodium replenishment effect. When the mixing time is less than 10 minutes, the mixing uniformity is poor.

[0140] As can be seen from Examples 51 to 56, the granulation speed has a certain impact on the cycle performance of the battery.

[0141] As can be seen from Examples 57 to 62, the granulation time has a certain impact on the cycle performance of the battery.

[0142] As can be seen from Examples 63 to 68, the grinding and mixing time has a certain impact on the cycle performance of the battery.

[0143] As can be seen from Examples 69 to 75, the melting temperature has a certain impact on the cycle performance of the battery.

[0144] As shown in Examples 77 to 88, the ratio of positive electrode active material: conductive material: binder: sodium replenisher has a certain impact on the cycle performance of the battery. A better sodium replenishment effect can be obtained by controlling the mass ratio of positive electrode active material, conductive material, binder, and sodium replenisher. When there is too much sodium replenisher, the remaining absorbent material after sodium replenishment is inert and no longer participates in charge transfer. A high proportion of sodium replenisher results in excessive residual inert material, meaning the sodium in the replenisher can only be extracted and not embedded, occupying too much volume, which is detrimental to improving electrode capacity and affecting electrode performance. When there is too little sodium replenisher, the sodium source in the replenisher is insufficient during the replenishment process, requiring the consumption of sodium in the electrode, thus affecting electrode performance.

[0145] In summary, the sodium replenishing agent proposed in this application incorporates a water-absorbing material, at least partially coating the sodium source material within the water-absorbing material. This ensures that during use, when the sodium replenishing agent comes into contact with moisture, the water-absorbing material in the coating layer is the first to come into contact with the moisture, fixing the moisture within the water-absorbing material. Meanwhile, the core sodium source material remains encased in the water-absorbing material, thereby reducing contact between the sodium source material and moisture, minimizing the formation of strongly alkaline compounds on the positive electrode surface, and mitigating the impact on battery cycle stability.

[0146] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A sodium supplement, characterized in that, It includes a core and a coating layer that at least partially covers the core, the core comprising a sodium-source material and the coating layer comprising a water-absorbing material; The sodium supplement has a particle size of 1~200μm.

2. The sodium supplement as described in claim 1, characterized in that, The mass ratio of the sodium source material to the water-absorbing material is (1~5):

1.

3. The sodium supplement as described in claim 2, characterized in that, The mass ratio of the sodium source material to the water-absorbing material is (2~3):

1.

4. The sodium supplement as described in claim 1, characterized in that, The coating layer also includes a conductive agent.

5. The sodium supplement as described in claim 4, characterized in that, The mass of the sodium source material and the water-absorbing material is M1, and the mass of the conductive agent is M2, wherein: M1:M2 = (1.5~8):

1.

6. The sodium supplement as described in claim 5, characterized in that, M1:M2 is (2~5):

1.

7. The sodium supplement as described in claim 4, characterized in that, The conductive agent includes at least one of conductive carbon black, conductive graphite, acetylene black, and Ketjen black.

8. The sodium supplement as described in claim 1, characterized in that, The absorbent material includes at least one of silica gel, porous carbon, and activated alumina.

9. The sodium supplement as described in claim 1, characterized in that, The sodium source material includes at least one of Na2O, Na2CO3, NaF, and Na2S.

10. The sodium supplement as described in claim 1, characterized in that, The sodium supplement has a particle size of 100~150μm.

11. A method for preparing a sodium supplement as described in any one of claims 1 to 10, characterized in that, Includes the following steps: The core material is mixed with the molten coating material, solidified, and then granulated to obtain a sodium supplement.

12. The method for preparing the sodium supplement as described in claim 11, characterized in that, The steps of mixing the core material with the molten coating material, solidifying and granulating to obtain the sodium supplement include: The sodium source material is mixed with the conductive agent to obtain the first mixture; The water-absorbing material is melted and mixed with the first mixture to obtain the second mixture. The second mixture is then solidified and granulated to obtain the sodium supplement.

13. The method for preparing the sodium supplement as described in claim 12, characterized in that, The process involves melting the absorbent material, mixing it with the first mixture to obtain a second mixture, solidifying the second mixture, and then granulating it to obtain the sodium supplement. After the absorbent material is melted, it is mixed with the first mixture at a rotation speed of 1000~8000 r / min; and / or, After the absorbent material is melted, it is mixed with the first mixture for 10-60 minutes; and / or, Granulation of the solidified second mixture includes stirred granulation, wherein the granulation speed is 1000~8000 r / min; and / or, Granulation of the second mixture after solidification includes stirring granulation, wherein the granulation time is 3 to 10 minutes.

14. The method for preparing the sodium supplement as described in claim 13, characterized in that, The process involves melting the absorbent material, mixing it with the first mixture to obtain a second mixture, solidifying the second mixture, and then granulating it to obtain the sodium supplement. After the absorbent material is melted, it is mixed with the first mixture at a speed of 3000~6000 r / min; and / or, After the absorbent material is melted, it is mixed with the first mixture for 20-40 minutes; and / or, Granulation of the solidified second mixture includes stirred granulation, wherein the granulation speed is 3000~6000 r / min; and / or, Granulation of the second mixture after solidification includes stirring granulation, wherein the granulation time is 4-6 minutes.

15. The method for preparing the sodium supplement as described in claim 12, characterized in that, The first step involves mixing the sodium source material with a conductive agent to obtain a first mixture. The sodium source material and the conductive agent can be mixed by grinding, with a mixing time of 5 to 30 minutes.

16. The method for preparing the sodium supplement as described in claim 15, characterized in that, The sodium source material and the conductive agent can be mixed by grinding, with a mixing time of 8 to 15 minutes.

17. The method for preparing the sodium supplement as described in claim 12, characterized in that, The melting temperature of the water-absorbing material is 200~300℃.

18. The method for preparing the sodium supplement as described in claim 17, characterized in that, The melting temperature of the water-absorbing material is 240~260℃.

19. A positive electrode plate, characterized in that, Includes the sodium supplement as described in any one of claims 1 to 18 and the positive electrode material.

20. The positive electrode sheet as described in claim 19, characterized in that, The positive electrode material includes a positive electrode active material, a conductive material, and a binder.

21. The positive electrode sheet as described in claim 20, characterized in that, The mass ratio of the positive electrode active material, the conductive material, the binder and the sodium supplement is (70~90):(3~20):(3~20):(3~20).

22. The positive electrode sheet as described in claim 21, characterized in that, The mass ratio of the positive electrode active material, the conductive material, the binder and the sodium supplement is (80~85):(5~10):(5~10):(5~10).

23. The positive electrode sheet as described in claim 20, characterized in that, The positive electrode active material includes at least one of sodium vanadium phosphate, sodium manganate, sodium manganese vanadium phosphate, sodium cobaltate, Prussian blue sodium, and sodium vanadium fluorophosphate.

24. The positive electrode sheet as described in claim 20, characterized in that, The adhesive comprises at least one of polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene copolymer, PVDF-tetrafluoroethylene copolymer, PVDF-hexafluoropropylene-tetrafluoroethylene copolymer, PVDF-pentafluoropropylene copolymer, PVDF-pentafluoropropylene-tetrafluoroethylene copolymer, PVDF-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, PVDF-chlorotrifluoroethylene copolymer, polytetrafluoroethylene, polychlorotrifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

25. The positive electrode sheet as described in claim 20, characterized in that, The conductive material includes at least one of conductive carbon black, superconducting carbon black, conductive graphite, acetylene black, Ketjen black, graphene, and carbon nanotubes.

26. A method for preparing a positive electrode sheet as described in any one of claims 19 to 25, characterized in that, Includes the following steps: The sodium-supplementing material is mixed with the positive electrode material in a solvent, coated onto the surface of the positive electrode current collector, dried, cold-pressed, and cut to obtain the positive electrode sheet.

27. The method for preparing the positive electrode sheet as described in claim 26, characterized in that, The solvent includes N-methylpyrrolidone.

28. An electrochemical device, characterized in that, Includes the positive electrode as described in any one of claims 19 to 25.

29. The electrochemical device as claimed in claim 28, characterized in that, The electrochemical device includes a capacitor, a primary battery, or a secondary battery.

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