Sodium supplementing method of sodium ion battery

Abstract

The invention provides a sodium supplementing method of a sodium ion battery. The sodium supplementing method comprises the following steps: preparing a sodium ion battery negative pole piece containing a water-soluble sodium supplementing agent; assembling the sodium-ion battery negative pole piece, a diaphragm, the sodium-ion battery positive pole piece and electrolyte into the sodium-ion battery, and performing reverse constant-current charging on the sodium-ion battery by taking the sodium-ion battery negative pole piece as an anode and the sodium-ion battery positive pole piece as a cathode to obtain the sodium-supplemented sodium-ion battery, according to the sodium supplementing method, the thermodynamic dilemma that the sodium supplementing agent needs to be oxidized and decomposed at the negative electrode and the negative electrode is in a cathode potential reduction environment during traditional first-time charging is fundamentally solved, efficient, uniform and controllable decomposition of the sodium supplementing agent is achieved, and the first-week coulombic efficiency and the overall electrochemical performance of the sodium ion battery are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology and relates to a method for replenishing sodium in sodium-ion batteries. Background Technology

[0002] During the initial charge and discharge cycle of sodium-ion batteries, a solid electrolyte interphase (SEI) film forms on the negative electrode surface, and structural rearrangement may occur in the positive electrode material. These processes irreversibly consume a large amount of sodium ions from the positive electrode, resulting in a significant decrease in the battery's initial coulombic efficiency (typically 70-85%) and reversible capacity. To compensate for this irreversible capacity loss and improve the battery's energy density and cycle life, "sodium replenishment" technology has become an indispensable key element in the industrialization of sodium-ion batteries.

[0003] Currently, the main sodium replenishment technologies proposed by domestic and international research institutions and enterprises include chemical pre-sodiuming, electrochemical pre-sodiuming, electrolyte additives, and cathode sacrificial salt additives. The method of adding sodium replenishing agents to the cathode is currently the most promising. This method uses sodium-rich materials as replenishing agents, mixing them with cathode active materials (such as layered oxides and polyanionic compounds) and coating them to form the cathode. During the first charge of the battery, the sodium-rich materials decompose under high voltage to release sodium ions to replenish the loss caused by SEI formation. However, many ideal sodium replenishing agents with high theoretical capacity (such as sodium oxalate and sodium carbonate) have extremely low electronic conductivity and excessively high thermodynamic decomposition potentials. In actual battery systems, they are difficult to form an effective continuous conductive network with the cathode material and conductive agent, resulting in slow, incomplete, and insufficient decomposition reaction kinetics, and the actual sodium replenishment efficiency is far lower than the theoretical value. To achieve the decomposition of sodium replenishment agents, it is often necessary to charge for a long time at extremely high voltages (usually >4.2V). This will violently catalyze the oxidative decomposition of the electrolyte, generate a large amount of gas and damage the structure of the positive electrode material, introducing serious safety hazards and cycle life degradation problems. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a sodium replenishment method for sodium-ion batteries. This method fundamentally solves the thermodynamic dilemma that the sodium replenishing agent needs to be oxidized and decomposed at the negative electrode, while the negative electrode is in a cathodic potential reduction environment during the first charge in traditional methods. It achieves efficient, uniform, and controllable decomposition of the sodium replenishing agent, thereby significantly improving the first-cycle coulombic efficiency and overall electrochemical performance of sodium-ion batteries.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] This invention provides a method for replenishing sodium in a sodium-ion battery, the method comprising the following steps:

[0007] S1. Preparation of negative electrode sheet: Preparation of a sodium-ion battery negative electrode sheet containing a water-soluble sodium supplement;

[0008] S2. Assemble the battery: Assemble the sodium-ion battery negative electrode, separator, sodium-ion battery positive electrode and electrolyte into a sodium-ion battery.

[0009] S3, First Reverse Polarity Charging to Replenish Sodium: Using the negative electrode of the sodium-ion battery as the anode, a high potential is applied from the outside; using the positive electrode of the sodium-ion battery as the cathode, a low potential is applied from the outside; the sodium-ion battery is charged in reverse constant current to obtain a sodium-replenished sodium-ion battery.

[0010] S4. Normal activation: After sodium replenishment is completed in step S3, the polarity of the positive and negative electrodes of the battery is restored to the traditional normal charge and discharge electrodes, and normal activation is performed.

[0011] In the method described in this invention, "a high potential is applied from the outside using the negative electrode of a sodium-ion battery as the anode and a low potential is applied from the outside using the positive electrode of a sodium-ion battery as the cathode," meaning that the potential applied at the anode is higher than the potential applied at the cathode, thereby forming a suitable current.

[0012] This invention pre-prepares a sodium-ion battery negative electrode sheet containing a water-soluble sodium supplement. After the sodium-ion battery is manufactured, the negative electrode sheet is used as the anode for reverse constant current charging. Electrons are forcibly drawn from the negative electrode, causing its potential to rise continuously, making it a true oxidation electrode. When its potential reaches the decomposition potential of the sodium supplement, the generated sodium ions immediately enter the electrolyte. Simultaneously, the positive electrode sheet of the sodium-ion battery acts as the cathode. A low potential is applied from outside the battery, and electrons flow into this electrode from the external circuit, causing its potential to drop continuously, making it a true reduction electrode. Sodium ions in the electrolyte migrate to the positive electrode and undergo an intercalation reaction, achieving pre-sodiumization of the positive electrode material.

[0013] The sodium replenishment method described in this invention temporarily reverses the electrode polarity during the first charge by controlling the external circuit, making the negative electrode containing the sodium replenishing agent the "anode." This creates the necessary oxidative decomposition environment for the sodium replenishing agent, fundamentally solving the thermodynamic dilemma that the sodium replenishing agent needs to be oxidized and decomposed at the negative electrode, while the negative electrode is in a cathodic potential reduction environment during the first charge in traditional methods. This method can be implemented within a standard battery structure without introducing a third electrode or changing the internal battery design. It can be achieved simply by adding an innovative sodium replenishment step to the traditional formation process, resulting in high system integration and ease of implementation.

[0014] Preferably, the water-soluble sodium supplement includes any one or a combination of at least two of the following: chain sodium carboxylate, cyclic sodium carboxylate, or nitrogen-based sodium carboxylate. Typical but non-limiting combinations include combinations of chain sodium carboxylate and nitrogen-based sodium carboxylate, combinations of cyclic sodium carboxylate and nitrogen-based sodium carboxylate, or combinations of chain sodium carboxylate and cyclic sodium carboxylate.

[0015] Preferably, the chain carboxylate sodium salt includes any one or a combination of at least two of sodium azide, sodium oxalate, sodium carbonate, sodium acetate, sodium formate, or sodium citrate. Typical but non-limiting combinations include combinations of sodium azide and sodium oxalate, combinations of sodium oxalate and sodium carbonate, or combinations of sodium acetate and sodium formate.

[0016] Preferably, the cyclic sodium salt includes any one or a combination of at least two of sodium crotonate, sodium rhodotin, or sodium squartzate. Typical but non-limiting combinations include combinations of sodium crotonate and sodium squartzate, combinations of sodium rhodotin and sodium squartzate, or combinations of sodium crotonate and sodium rhodotinate, etc.

[0017] Preferably, the sodium nitrogen-based carboxylic acid salt includes any one or a combination of at least two of disodium iminodiacetate, tetrasodium iminodisuccinate, tetrasodium ethylenediaminetetraacetate, sodium ethylenediamine-N,N'-diacetate, or disodium ethylenediamine-N,N'-diacetate. Typical but non-limiting combinations include combinations of disodium iminodiacetate and tetrasodium iminodisuccinate, combinations of sodium ethylenediamine-N,N'-diacetate and disodium ethylenediamine-N,N'-diacetate, or combinations thereof.

[0018] Preferably, the sodium-ion battery negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on one side surface of the negative electrode current collector.

[0019] Preferably, the negative electrode current collector comprises copper foil.

[0020] Preferably, the negative electrode active material layer includes a negative electrode material, a negative electrode conductive agent, a negative electrode binder, and a water-soluble sodium supplement.

[0021] Preferably, the negative electrode material includes any one or a combination of at least two of hard carbon, soft carbon, alloy negative electrode material or titanium-based negative electrode material. Typical but non-limiting combinations include combinations of hard carbon and soft carbon, combinations of alloy negative electrode material and titanium-based negative electrode material, or combinations of soft carbon and alloy negative electrode material, etc.

[0022] Preferably, the negative electrode conductive agent includes conductive carbon black and / or acetylene black.

[0023] Preferably, the negative electrode binder includes an aqueous binder.

[0024] Preferably, the sodium-ion battery negative electrode sheet is prepared by the following method: dissolving the negative electrode material, negative electrode conductive agent, negative electrode binder and water-soluble sodium supplement agent in water to obtain a negative electrode slurry, coating the negative electrode slurry on the surface of the negative electrode current collector, and drying to obtain the sodium-ion battery negative electrode sheet.

[0025] This invention uses an aqueous binder and water-soluble sodium supplementers in the negative electrode. During the preparation of the negative electrode slurry, the material is dissolved in water and uniformly precipitated during drying. The small particle size of the sacrificial salt and the high carbon content of the negative electrode significantly reduce the overpotential of the sacrificial salt, thereby reducing the decomposition voltage and achieving efficient utilization of the sacrificial salt. Utilizing the characteristics of the aqueous negative electrode slurry processing, water-soluble sodium supplementers are added simultaneously during homogenization, allowing them to dissolve and then uniformly precipitate during electrode drying, thus solving the problem of uneven dispersion caused by direct mixing of powders.

[0026] Preferably, the water-based adhesive is any one or a combination of at least two of sodium alginate, sodium carboxymethyl cellulose, polyacrylic acid, or styrene-butadiene rubber. Typical but non-limiting combinations include combinations of sodium alginate and sodium carboxymethyl cellulose, combinations of sodium carboxymethyl cellulose and polyacrylic acid, or combinations of polyacrylic acid and styrene-butadiene rubber.

[0027] Preferably, the mass ratio of the negative electrode material, the negative electrode conductive agent, and the negative electrode binder is 80:(10~20):(10~20), for example: 80:10:10, 80:12:15, 80:15:15, 80:20:10, or 80:20:20, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, based on the total mass of the negative electrode material, negative electrode conductive agent, and negative electrode binder as 100%, the mass of the water-soluble sodium supplement is 0.01% to 20%, for example: 0.01%, 0.05%, 1%, 5%, or 20%, etc., not limited to the listed values. Other unlisted values ​​within this range are also applicable. Preferably, it is 5% to 15%, for example: 5%, 8%, 10%, 12%, or 15%, etc., not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the diaphragm comprises a PE diaphragm.

[0030] Preferably, the sodium-ion battery positive electrode includes a positive current collector and a positive active material layer disposed on one side surface of the positive current collector.

[0031] Preferably, the positive current collector comprises aluminum foil.

[0032] Preferably, the positive electrode active material layer includes a positive electrode material, a positive electrode conductive agent, a positive electrode binder, and a water-soluble sodium supplement.

[0033] Preferably, the positive electrode material includes composite sodium iron phosphate, sodium vanadium phosphate, and Na. 0.44 MnO2, Na 0.67 MnO2, Na 0.67 Ni 0.33Mn 0.67 Any one or a combination of at least two of MnO2 or sodium vanadium fluorophosphate, typical but not limiting combinations include sodium iron phosphate and Na. 0.44 Combinations of MnO2, sodium vanadium phosphate and Na 0.44 The combination of MnO2 and Na 0.67 MnO2 and Na 0.67 Ni 0.33 Mn 0.67 A combination of MnO2 or Na 0.44 MnO2 and Na 0.67 Combinations of MnO2, etc.

[0034] Preferably, the positive electrode conductive agent includes conductive carbon black and / or acetylene black.

[0035] Preferably, the positive electrode binder comprises PVDF.

[0036] Preferably, the mass ratio of the positive electrode material, the positive electrode conductive agent, and the positive electrode binder is 70:(10~20):(10~20), for example: 70:10:10, 70:12:15, 70:15:15, 70:20:10, or 70:20:20, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Preferably, the electrolyte comprises a NaClO4 solution.

[0038] Preferably, the solvent of the electrolyte includes a mixed solvent of EC, PC and DMC.

[0039] Preferably, the current density of the reverse constant current charging is 5mA / g to 40mA / g, for example: 5mA / g, 10mA / g, 20mA / g, 30mA / g or 40mA / g, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the endpoint of the reverse constant current charging is calculated based on the amount of sodium supplement added to the negative electrode and the specific capacity of the sodium supplement, and the capacity or specific capacity is limited during the constant current charging process.

[0041] Preferably, the normal activation includes: after sodium replenishment is completed in step S3, the polarity of the positive and negative electrodes of the battery is restored to the traditional normal charge and discharge electrodes, that is, activation is performed with the negative electrode of the sodium-ion battery as the negative electrode and the positive electrode of the sodium-ion battery as the positive electrode.

[0042] Preferably, the activation current density is 10mA / g to 50mA / g, for example: 10mA / g, 20mA / g, 30mA / g, 40mA / g or 50mA / g, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The sodium replenishment method of the present invention controls the external circuit to temporarily reverse the electrode polarity during the first charge, so that the negative electrode containing the sodium replenishment agent becomes the "anode", creating the required oxidation decomposition environment for it. This fundamentally solves the thermodynamic dilemma that the sodium replenishment agent needs to be oxidized and decomposed at the negative electrode, while the negative electrode is in the cathode potential reduction environment during the first charge in the traditional method. This achieves efficient, uniform and controllable decomposition of the sodium replenishment agent, thereby significantly improving the first-cycle coulombic efficiency and overall electrochemical performance of sodium-ion batteries.

[0046] (2) This invention utilizes the characteristics of water-soluble sodium supplements dissolving in aqueous slurry and re-precipitating during the drying process to achieve molecular-level mixing and nanoscale uniform distribution of sodium supplements in the negative electrode, avoiding the agglomeration problem caused by dry mixing, ensuring the sufficiency and efficiency of the decomposition reaction, and the high carbon content of the negative electrode can significantly reduce the decomposition voltage of the sacrificial salt, thus achieving efficient utilization of the sacrificial salt.

[0047] (3) The present invention uses a sodium-ion battery negative electrode containing a water-soluble sodium supplement as the anode and a sodium-ion battery positive electrode as the cathode to perform reverse constant current charging on the sodium-ion battery to obtain a sodium-supplemented sodium-ion battery. During normal charging and discharging, the discharge specific capacity is significantly improved, which can basically realize the full utilization of the theoretical capacity of the positive electrode material and greatly improve the energy density of the battery. Detailed Implementation

[0048] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0049] The "range" disclosed in this invention can be defined in the form of 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 the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning 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 specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" 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" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0050] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0051] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0052] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0053] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can 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.

[0054] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0055] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0056] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0057] In this invention, "optional" means that something is optional, that is, it refers to any one of the two parallel solutions of "having" or "not having". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0058] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0059] The sodium-ion battery negative electrode sheets described in the embodiments and comparative examples of this invention are all prepared by the following method:

[0060] A negative electrode slurry is prepared by mixing negative electrode material, conductive carbon black SP, aqueous binder, and water-soluble sodium supplement with water at a mass ratio of 80:10:10:x (x is adjusted according to the examples and comparative examples). The amount of water-soluble sodium supplement added is x% of the total mass of negative electrode material, conductive agent, and aqueous binder. The negative electrode slurry is coated on the surface of copper foil (negative electrode current collector) and dried to form a sodium-ion battery negative electrode sheet. The dried sodium supplement is uniformly dispersed in the sodium-ion battery negative electrode sheet.

[0061] The sodium-ion battery positive electrode sheets described in the embodiments and comparative examples of this invention are all prepared by the following method:

[0062] The positive electrode material, acetylene black, and PVDF are mixed with water in a mass ratio of 80:10:10 to obtain a positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil (positive electrode current collector) and dried to obtain a sodium-ion battery positive electrode sheet.

[0063] Example 1

[0064] This embodiment provides a method for replenishing sodium in a sodium-ion battery, the method comprising the following steps:

[0065] S1. Use the above-mentioned sodium-ion battery negative electrode sheet containing sodium azide (the negative electrode material is hard carbon, the aqueous binder is polyacrylic acid, x=7.5, that is, the amount of sodium azide added is 7.5% of the total mass of hard carbon, conductive carbon black SP and polyacrylic acid).

[0066] S2. After assembling the sodium-ion battery negative electrode, PE separator, and sodium-ion battery positive electrode (the positive electrode material is sodium vanadium phosphate), inject 0.1 mol / L NaClO4 / EC:PC:DMC (volume ratio of 1:1:1) electrolyte to obtain a sodium-ion battery.

[0067] S3. Using the negative electrode of the sodium-ion battery as the anode, a high potential is applied from the outside, and using the positive electrode of the sodium-ion battery as the cathode, a low potential is applied from the outside. Then, a reverse constant current charging with a current density of 5mA / g is applied to the sodium-ion battery. The amount of sodium azide added is the active material mass, and the charging specific capacity is 412mAh / g as the cutoff specific capacity. At the same time, the cutoff voltage is set to 3V to reduce the side reactions on the electrode surface.

[0068] S4. After completing the sodium replenishment step, restore the normal properties of the electrodes. Using the sodium-ion battery negative electrode as the negative electrode and the sodium-ion battery positive electrode as the positive electrode, perform normal small current activation at 20mA / g.

[0069] After sodium replenishment and normal low-current activation, the sodium-ion battery underwent conventional charge-discharge testing (current density 20 mA / g). Its charge specific capacity was 147.2 mAh / g, and its discharge specific capacity was 114.8 mAh / g. This demonstrates that the present invention temporarily reverses the electrode polarity during the first charge, making the negative electrode containing the sodium replenishment agent the "anode," creating the necessary oxidative decomposition environment. This fundamentally solves the thermodynamic dilemma that the sodium replenishment agent needs to be oxidized and decomposed at the negative electrode, while the negative electrode is in a reducing environment during the traditional first charge.

[0070] Example 2

[0071] This embodiment provides a method for replenishing sodium in a sodium-ion battery, the method comprising the following steps:

[0072] S1. Use the above-mentioned sodium-ion battery negative electrode sheet containing disodium iminodiacetate (the negative electrode material is hard carbon, the aqueous binder is polyacrylic acid, x=10, that is, the amount of sodium carbonate added is 10% of the total mass of hard carbon, conductive carbon black SP, and polyacrylic acid).

[0073] S2, combine the sodium-ion battery negative electrode, PE separator, and sodium-ion battery positive electrode (positive electrode material is Na). 0.44 After assembling MnO2, a sodium-ion battery is obtained by injecting a 0.1 mol / L NaClO4 / EC:PC:DMC electrolyte (volume ratio 1:1:1).

[0074] S3. Using the negative electrode of the sodium-ion battery as the anode, a high potential is applied from the outside, and using the positive electrode of the sodium-ion battery as the cathode, a low potential is applied from the outside. Then, a reverse constant current charging with a current density of 10mA / g is applied to the sodium-ion battery. The amount of disodium iminodiacetate added is the active material mass, and the charging specific capacity is 302.7 mAh / g as the cutoff specific capacity. At the same time, the cutoff voltage is set to 3V to reduce the side reactions on the electrode surface.

[0075] S4. After completing the sodium replenishment step, restore the normal properties of the electrodes. Using the sodium-ion battery negative electrode as the negative electrode and the sodium-ion battery positive electrode as the positive electrode, perform normal small current activation at 10mA / g.

[0076] After sodium replenishment and normal low-current activation, the sodium-ion battery underwent conventional charge-discharge testing (current density 10 mA / g). Its charge specific capacity was 121.1 mAh / g, and its discharge specific capacity was 97.1 mAh / g. This demonstrates that the present invention temporarily reverses the electrode polarity during the first charge, making the negative electrode containing the sodium replenishment agent the "anode," creating the necessary oxidative decomposition environment. This fundamentally solves the thermodynamic dilemma that the sodium replenishment agent needs to be oxidized and decomposed at the negative electrode, while the negative electrode is in a reducing environment during the traditional first charge.

[0077] Example 3

[0078] This embodiment provides a method for replenishing sodium in a sodium-ion battery, the method comprising the following steps:

[0079] S1. Use the above-mentioned sodium-ion battery negative electrode sheet containing sodium squartz (the negative electrode material is hard carbon, the aqueous binder is sodium carboxymethyl cellulose, x=8, that is, the amount of sodium oxalate added is 8% of the total mass of hard carbon, conductive carbon black SP, and polyacrylic acid).

[0080] S2, combine the sodium-ion battery negative electrode, PE separator, and sodium-ion battery positive electrode (positive electrode material is Na). 0.44 After assembling MnO2, a sodium-ion battery is obtained by injecting a 0.1 mol / L NaClO4 / EC:PC:DMC electrolyte (volume ratio 1:1:1).

[0081] S3. Using the negative electrode of the sodium-ion battery as the anode, a high potential is applied from the outside, and using the positive electrode of the sodium-ion battery as the cathode, a low potential is applied from the outside. Then, a reverse constant current charging with a current density of 10mA / g is applied to the sodium-ion battery. The amount of sodium squartz added is the active material mass, and the charging specific capacity is 339 mAh / g as the cutoff specific capacity. At the same time, the cutoff voltage is set to 3V to reduce the side reactions on the electrode surface.

[0082] S4. After completing the sodium replenishment step, restore the normal properties of the electrodes. Using the sodium-ion battery negative electrode as the negative electrode and the sodium-ion battery positive electrode as the positive electrode, perform normal small current activation at 50mA / g.

[0083] After sodium replenishment and normal low-current activation, the sodium-ion battery underwent conventional charge-discharge testing (current density 50 mA / g). Its charge specific capacity was 124.2 mAh / g, and its discharge specific capacity was 98.1 mAh / g. This demonstrates that the present invention temporarily reverses the electrode polarity during the first charge, making the negative electrode containing the sodium replenishment agent the "anode," creating the necessary oxidative decomposition environment. This fundamentally solves the thermodynamic dilemma that the sodium replenishment agent needs to oxidize and decompose at the negative electrode, while the negative electrode is in a reducing environment during the traditional first charge.

[0084] Example 4

[0085] The only difference between this embodiment and Example 1 is that x=5, that is, the amount of sodium azide added is 5% of the total mass of hard carbon, conductive carbon black SP, and polyacrylic acid. All other conditions and parameters are exactly the same as in Example 1.

[0086] Example 5

[0087] The only difference between this embodiment and Embodiment 1 is that the current density of the reverse constant current charging is 20mA / g, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0088] Example 6

[0089] The only difference between this embodiment and Embodiment 1 is that the current density of the reverse constant current charging is 50mA / g, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0090] Comparative Example 1

[0091] This comparative example uses a conventional full cell composed of sodium vanadium phosphate and hard carbon, without sodium supplementation.

[0092] Comparative Example 2

[0093] This comparative example directly uses Na. 0.44 A conventional full cell consisting of MnO2 and hard carbon does not require sodium replenishment.

[0094] Comparative Example 3

[0095] The only difference between this comparative example and Example 1 is that sodium azide is not provided at the negative electrode. Instead, sodium azide is added to the sodium vanadium phosphate positive electrode (the amount added is 5% of the total mass of sodium vanadium phosphate, acetylene black, and PVDF) to supplement sodium. The electrode is not reversed during charging. All other conditions and parameters are exactly the same as in Example 1.

[0096] Comparative Example 4

[0097] The only difference between this comparative example and Example 2 is that disodium iminodiacetate is not used at the negative electrode; instead, disodium iminodiacetate is added to the Na... 0.44 In the MnO2 cathode (the amount of Na added is...) 0.44Sodium was added using MnO2, acetylene black, and 6% of the total mass of PVDF. The electrode was charged without reversing the polarity. All other conditions and parameters were exactly the same as in Example 1.

[0098] Comparative Example 5

[0099] The only difference between this comparative example and Example 3 is that sodium squartz is not placed at the negative electrode; instead, sodium squartz is added to the Na... 0.44 In the MnO2 cathode (the amount of Na added is...) 0.44 Sodium was added using MnO2, acetylene black, and 8% of the total mass of PVDF. The electrode was charged without reversing the polarity. All other conditions and parameters were exactly the same as in Example 1.

[0100] Comparative Example 6

[0101] The only difference between this comparative example and Example 1 is that the sodium replenishing agent for the negative electrode is coated onto the surface of the negative electrode after being homogenized with an organic binder, and the sodium-ion battery obtained is subjected to constant voltage discharge to replenish sodium. All other conditions and parameters are exactly the same as in Example 1.

[0102] Performance testing:

[0103] The sodium-ion batteries prepared in the examples and comparative examples were subjected to charge-discharge performance tests after sodium replenishment and activation. The test results of their charge and discharge specific capacities in the first week are shown in Table 1.

[0104] Table 1

[0105]

[0106] As shown in Table 1, and as demonstrated in Examples 1-6, this invention uses a sodium-ion battery negative electrode containing a water-soluble sodium supplement as the anode and a sodium-ion battery positive electrode as the cathode, and performs reverse constant current charging on the sodium-ion battery to obtain a sodium-supplemented sodium-ion battery. After normal low-current activation, the battery charge-discharge performance is tested, and the discharge specific capacity is significantly improved, essentially achieving full utilization of the theoretical capacity of the positive electrode material.

[0107] A comparison of Examples 1 and 4 shows that, in the sodium replenishment method of the present invention, the amount of water-soluble sodium replenishing agent added to the negative electrode sheet of the sodium-ion battery affects the sodium replenishment effect. Controlling the amount of water-soluble sodium replenishing agent added to 5%~15% of the total mass of the negative electrode material, negative electrode conductive agent, and negative electrode binder results in a better sodium replenishment effect. If the amount of water-soluble sodium replenishing agent added to the negative electrode sheet of the sodium-ion battery is too low, the sodium replenishment effect is poor and it is difficult to completely compensate for irreversible sodium loss; if the amount of water-soluble sodium replenishing agent added to the negative electrode sheet of the sodium-ion battery is too high, it is easy to cause excessive active sodium, which can lead to sodium precipitation at the negative electrode, posing a safety hazard. Therefore, the amount of sodium replenishing agent added should be based on the required replenishment capacity.

[0108] A comparison of Examples 1 and 5-6 shows that in the sodium replenishment method of the present invention, the current density of the reverse constant current charging affects the sodium replenishment effect. Controlling the current density of the reverse constant current charging between 5 mA / g and 40 mA / g results in a better sodium replenishment effect. If the current density of the reverse constant current charging is too low, the sodium replenishment rate is too low; if the current density of the reverse constant current charging is too high, the decomposition overpotential of the sodium replenishing agent is too large.

[0109] As can be seen from the comparison between Example 1 and Comparative Example 1, and Example 2 and Comparative Example 2, the sodium supplementation method of the present invention can significantly improve the discharge specific capacity during full battery cycling and greatly increase the energy density of the battery.

[0110] Comparisons between Example 1 and Comparative Example 3, Example 2 and Comparative Example 4, and Example 3 and Comparative Example 5 show that the water-soluble sodium supplement uniformly precipitates during drying at the negative electrode. Its smaller particle size and higher carbon content at the negative electrode significantly reduce the decomposition voltage of the sacrificial salt, achieving efficient utilization. This demonstrates that the present invention, by controlling the external circuit to temporarily reverse the electrode polarity during the first charge, makes the negative electrode containing the sodium supplement the "anode," creating the necessary oxidative decomposition environment. This fundamentally solves the thermodynamic dilemma that the sodium supplement needs oxidative decomposition at the negative electrode, while the negative electrode is in a reducing environment during the traditional first charge.

[0111] As can be seen from the comparison between Example 1 and Comparative Example 6, compared with coating the slurry on the negative electrode for direct discharge sodium replenishment, dissolving the soluble sodium replenishing additive in the slurry during the homogenization of the negative electrode, and then precipitating it out as drying, results in a more uniform distribution of the sodium replenishing additive in the negative electrode, smaller particles, and higher utilization rate of the sodium replenishing agent.

[0112] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for replenishing sodium in a sodium-ion battery, characterized in that, The sodium supplementation method includes the following steps: S1. Preparation of negative electrode sheet: Preparation of a sodium-ion battery negative electrode sheet containing a water-soluble sodium supplement; S2. Assemble the battery: Assemble the sodium-ion battery negative electrode, separator, sodium-ion battery positive electrode and electrolyte into a sodium-ion battery. S3, First Reverse Polarity Charging to Replenish Sodium: Using the negative electrode of the sodium-ion battery as the anode, a high potential is applied from the outside; using the positive electrode of the sodium-ion battery as the cathode, a low potential is applied from the outside; the sodium-ion battery is charged in reverse constant current to obtain a sodium-replenished sodium-ion battery. S4. Normal activation: After sodium replenishment is completed in step S3, the polarity of the positive and negative electrodes of the battery is restored to the traditional normal charge and discharge electrodes, and normal activation is performed.

2. The sodium supplementation method as described in claim 1, characterized in that, The water-soluble sodium supplement includes any one or a combination of at least two of the following: chain carboxylate sodium salt, cyclic sodium salt, or nitrogen-based carboxylate sodium salt; Preferably, the chain carboxylate sodium salt comprises any one or a combination of at least two of sodium azide, sodium oxalate, sodium carbonate, sodium acetate, sodium formate, or sodium citrate; Preferably, the cyclic sodium salt comprises any one or a combination of at least two of sodium crotonate, sodium roserite, or sodium squartzate; Preferably, the sodium nitrogen-based carboxylic acid salt includes any one or a combination of at least two of disodium iminodiacetate, tetrasodium iminodisuccinate, tetrasodium ethylenediaminetetraacetate, sodium ethylenediamine-N,N'-diacetate, or disodium ethylenediamine-N,N'-diacetate.

3. The sodium supplementation method as described in claim 1 or 2, characterized in that, The sodium-ion battery negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on one side surface of the negative electrode current collector; Preferably, the negative electrode active material layer includes a negative electrode material, a negative electrode conductive agent, a negative electrode binder, and a water-soluble sodium supplement; Preferably, the negative electrode material includes any one or a combination of at least two of hard carbon, soft carbon, alloy negative electrode materials or titanium-based negative electrode materials; Preferably, the negative electrode conductive agent includes conductive carbon black and / or acetylene black; Preferably, the negative electrode binder includes an aqueous binder; Preferably, the aqueous binder is any one or a combination of at least two of sodium alginate, sodium carboxymethyl cellulose, polyacrylic acid, or styrene-butadiene rubber; Preferably, the mass ratio of the negative electrode material, the negative electrode conductive agent, and the negative electrode binder is 80:(10~20):(10~20).

4. The sodium supplementation method as described in claim 3, characterized in that, Based on the total mass of the negative electrode material, negative electrode conductive agent and negative electrode binder as 100%, the mass of the water-soluble sodium supplement is 0.01% to 20%, preferably 5% to 15%.

5. The sodium supplementation method as described in claim 3 or 4, characterized in that, The sodium-ion battery negative electrode sheet is prepared by the following method: The negative electrode material, negative electrode conductive agent, negative electrode binder and water-soluble sodium supplement are dissolved in water to obtain a negative electrode slurry. The negative electrode slurry is coated on the surface of the negative electrode current collector and dried to obtain the negative electrode sheet of the sodium-ion battery.

6. The sodium supplementation method according to any one of claims 1-5, characterized in that, The sodium-ion battery positive electrode includes a positive current collector and a positive active material layer disposed on one side surface of the positive current collector; Preferably, the positive electrode active material layer includes a positive electrode material, a positive electrode conductive agent, a positive electrode binder, and a water-soluble sodium supplement; Preferably, the positive electrode material includes composite sodium iron phosphate, sodium vanadium phosphate, and Na. 0.44 MnO2, Na 0.67 MnO2, Na 0.67 Ni 0.33 Mn 0.67 Any one or a combination of at least two of MnO2 or sodium vanadium fluorophosphate; Preferably, the positive electrode conductive agent includes conductive carbon black and / or acetylene black; Preferably, the positive electrode binder comprises PVDF.

7. The sodium supplementation method as described in claim 6, characterized in that, The mass ratio of the positive electrode material, positive electrode conductive agent and positive electrode binder is 70:(10~20):(10~20).

8. The sodium supplementation method according to any one of claims 1-7, characterized in that, The current density of the reverse constant current charging is 5mA / g~40mA / g; Preferably, the endpoint of the reverse constant current charging is calculated based on the amount of sodium supplement added to the negative electrode and the specific capacity of the sodium supplement, and the capacity or specific capacity is limited during the constant current charging process.

9. The sodium supplementation method according to any one of claims 1-8, characterized in that, The normal activation includes: after sodium replenishment is completed in step S3, the polarity of the battery's positive and negative electrodes is restored to the traditional normal charge and discharge electrodes, and normal activation includes: Activation is performed using a sodium-ion battery negative electrode as the negative electrode and a sodium-ion battery positive electrode as the positive electrode.

10. The sodium supplementation method as described in claim 9, characterized in that, The activation current density is 10 mA / g to 50 mA / g.

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