Sodium supplementing modification method of sodium battery without negative electrode and sodium battery without negative electrode

Abstract

The application discloses a sodium supplement modification method for a negative-electrode-free sodium battery and the negative-electrode-free sodium battery. A composite positive electrode sodium supplement agent is added in a positive electrode active material; the composite positive electrode sodium supplement agent is composed of a sodium-rich layered oxide of a sodium ion battery and sodium carbonate; the mass of the composite positive electrode sodium supplement agent is 0.5wt%-10wt% of the total mass of the positive electrode active material; meanwhile, an electrolyte sodium supplement agent is added in an electrolyte; the added amount of the electrolyte sodium supplement agent is 1wt%-4wt% of the total mass of the electrolyte; and the mass ratio of the added amount of the electrolyte sodium supplement agent to the added amount of the composite positive electrode sodium supplement agent is in the range of 0.2-2:1. Through the cooperation of the electrolyte sodium supplement and the positive electrode sodium supplement, the application realizes rapid sodium supplement, continuous sodium supplement and interface optimization, effectively compensates for the irreversible sodium loss in the first charge-discharge process of the negative-electrode-free sodium battery, significantly improves the first coulomb efficiency, the energy density and the cycle stability of the battery, and promotes the large-scale application of the negative-electrode-free sodium battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a sodium-addition modification method for a sodium-free negative electrode battery and a sodium-free negative electrode battery. Background Technology

[0002] Sodium-ion batteries without a negative electrode eliminate the need for traditional negative electrode active materials. During charging, sodium ions can be deposited in situ on the negative electrode current collector to form a sodium metal negative electrode. This characteristic not only significantly improves the battery's energy density but also simplifies the manufacturing process and reduces production costs, making it a research hotspot in the field of sodium-ion batteries. However, sodium-ion batteries without a negative electrode face significant technical bottlenecks during the first charge and discharge process: electrolyte decomposition forms a solid electrolyte interphase (SEI) film, and irreversible loss occurs when sodium metal is deposited on the current collector surface. These two phenomena together lead to a large loss of active sodium ions, thereby reducing the battery's initial coulombic efficiency, energy density, and cycle stability, severely restricting the large-scale application of sodium-ion batteries without a negative electrode.

[0003] Currently, sodium replenishment technologies for this problem mainly fall into two categories: one is electrolyte sodium replenishment, which directly replenishes active sodium ions by adding sodium replenishing agents such as sodium trimethylsilanolate to the electrolyte. However, this method suffers from low replenishment efficiency, easy side reactions between the sodium replenishing agent and the electrolyte, and rapid decay of the replenishment effect during long-term cycling. The other is cathode sodium replenishment, which adds sodium replenishing additives such as sodium carbonate and sodium oxalate to the cathode to release sodium ions during the first charge to compensate for losses. However, single cathode sodium replenishment suffers from slow replenishment rate, difficulty in controlling the amount of sodium replenished, and the tendency for sodium replenishing agents to leave inactive substances, affecting the conductivity of the cathode and the energy density of the battery. In existing technologies, electrolyte sodium replenishment and cathode sodium replenishment are mostly used separately, failing to form a synergistic effect. This makes it difficult to balance sodium replenishment efficiency, sodium replenishment stability, and overall battery performance, and to effectively solve the problems of initial efficiency and cycle degradation in cathode-less sodium batteries. Therefore, developing a composite sodium replenishment scheme that combines electrolyte sodium replenishment and cathode sodium replenishment for synergistic compensation is key to solving the above-mentioned technical problems. Summary of the Invention

[0004] The purpose of this invention is to provide a sodium-replenishing modification method for a negative electrode-free sodium battery and a negative electrode-free sodium battery, overcoming the shortcomings of existing negative electrode-free sodium batteries such as low efficiency and poor stability due to single sodium replenishment methods. By synergistic compensation of electrolyte sodium replenishment and positive electrode sodium replenishment, active sodium ions are efficiently replenished, improving the battery's initial coulombic efficiency, energy density and cycle life, and solving the sodium loss problem that restricts its large-scale application.

[0005] To achieve the above objectives, the technical solution provided by the present invention is as follows: The first aspect of this application provides a method for sodium-addition modification of a negative electrode-free sodium battery, the negative electrode-free sodium battery comprising a positive electrode, a negative electrode current collector, a separator, and an electrolyte, characterized in that: A composite positive electrode sodium supplement agent is added to the positive electrode active material; the composite positive electrode sodium supplement agent is composed of sodium-rich layered oxides from sodium-ion batteries and sodium carbonate; the mass of the composite positive electrode sodium supplement agent is 0.5wt% to 10wt% of the total mass of the positive electrode active material. Simultaneously, an electrolyte sodium supplement agent is added to the electrolyte, wherein the electrolyte sodium supplement agent is one or a mixture of two of sodium trimethylsilanolate and NaFSI; the amount of electrolyte sodium supplement agent added is 1wt% to 4wt% of the total mass of the electrolyte; Furthermore, the mass ratio of the amount of sodium supplement agent added to the electrolyte to the amount of sodium supplement agent added to the composite positive electrode is in the range of 0.2 to 2:1.

[0006] To optimize the above technical solution, the specific limitations also include: In the composite positive electrode sodium supplement, the mass ratio of sodium-rich layered oxide to sodium carbonate in the sodium-ion battery is 1:0.1 to 10.

[0007] Preferably, the sodium-rich layered oxide of the sodium-ion battery has the chemical formula Na. x TMO2, where 0.6≤x≤1.05, and TM is one or a combination of Mn, Fe, Ni, and Co.

[0008] Preferably, the composite positive electrode sodium supplement has a particle size of less than 5 μm and is prepared by mixing sodium-rich layered oxide of sodium-ion battery with sodium carbonate in a certain proportion, placing it in a sealed ball mill, adding milling beads, and milling at a speed of 200-700 rpm for 5-10 hours to obtain the composite positive electrode sodium supplement.

[0009] Furthermore, the electrolyte comprises a sodium salt, a solvent, and a functional additive; the sodium salt is one or a mixture of several of NaPF6 and NaClO4, with a concentration of 0.8–1.5 mol / L; the solvent is one or a mixture of several of ethylene carbonate, dimethyl carbonate, and diethylene glycol dimethyl ether; the functional additive is one or two of B / F rich additives and spatially confined anion additives, with an addition amount of 0.1 wt%–2 wt% of the total mass of the electrolyte.

[0010] Furthermore, the positive electrode active material is one or more of a polyanionic compound, Prussian blue, or a Prussian blue analogue; the polyanionic compound includes at least one of Na3V2(PO4)2F3, Na3V2(PO4)3, and Na4VMn(PO4)3.

[0011] Furthermore, the negative electrode current collector is a surface-modified aluminum foil, copper foil, or stainless steel foil, and its surface is provided with a sodium-loving coating or a porous structured coating.

[0012] A second aspect of this application provides a negative electrode-free sodium battery using the above-mentioned sodium-replenishing modification method, comprising a positive electrode, a negative electrode current collector, a separator, and an electrolyte, characterized in that: the positive electrode comprises a positive electrode current collector and a positive electrode slurry coated on the surface of the positive electrode current collector; the positive electrode slurry comprises a positive electrode active material with added composite positive electrode sodium replenishing agent, a conductive agent, and a binder; and the electrolyte contains an electrolyte sodium replenishing agent.

[0013] Preferably, in the positive electrode slurry, the conductive agent is one or more of Ketjen Black, single-walled / multi-walled carbon nanotubes, acetylene black, and Super P; and the binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, and sodium alginate.

[0014] Preferably, the membrane is a composite membrane with a thickness of 10–30 μm; the positive electrode side of the composite membrane is provided with a mixed coating of polymer matrix, MOF and solid electrolyte with a thickness of 2–8 μm; the negative electrode side of the composite membrane is provided with a sodium-loving coating with a thickness of 1–5 μm.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention effectively overcomes the current technical limitations of single sodium replenishment methods in non-negative electrode sodium batteries by synergistically compensating for sodium replenishment through electrolyte and positive electrode processes. This significantly improves the overall performance of the battery and demonstrates good potential for large-scale application. Compared to single sodium replenishment methods using only the positive electrode or electrolyte, this invention utilizes the rapid dissociation and release of sodium ions from electrolyte sodium replenishing agents (such as sodium trimethylsilanolate and NaFSI) to immediately compensate for the rapid sodium loss caused by SEI film formation during the initial charge-discharge cycle. Simultaneously, the slow decomposition and release of sodium ions from the composite positive electrode sodium replenishing agent continuously compensates for the long-term irreversible losses during sodium metal deposition. The synergistic effect of these two methods achieves comprehensive compensation effects including rapid sodium replenishment, continuous sodium replenishment, and interface optimization.

[0016] The optimized design of the composite positive electrode sodium replenisher in this invention not only eliminates the need for inactive carbon materials, thus improving the volumetric specific capacity of the sodium replenisher, but also promotes the decomposition of sodium carbonate, reduces its decomposition potential, and avoids the impact of residual inactive substances on battery performance. The electrolyte sodium replenisher and electrolyte functional additives work synergistically to optimize the composition and structure of the SEI film and inhibit sodium dendrite growth. The sodium-ion battery layered oxide in the composite positive electrode sodium replenisher can also improve the conductivity of the positive electrode. The combined effect of the two further optimizes battery performance. At the same time, the composite positive electrode sodium replenisher can be prepared by mechanical ball milling, and the electrolyte sodium replenisher can be directly added to the electrolyte without additional complex production processes. This makes it suitable for large-scale mass production, reduces production costs, and effectively solves the core problems of irreversible loss of active sodium ions and the difficulty in balancing sodium replenishment efficiency and stability in anode-less sodium batteries. It provides reliable technical support for the large-scale application of anode-less sodium batteries and has broad industrial application prospects. Detailed Implementation

[0017] The present invention will be further described in detail below through specific embodiments, but it should not be construed as limiting the scope of the present invention to the following embodiments. All technologies implemented based on the above content of the present invention fall within the scope of the present invention.

[0018] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the reagents, methods and equipment used are conventional reagents, methods and equipment in this technical field.

[0019] This invention provides a sodium-addition modification method for a negative electrode-free sodium battery. The negative electrode-free sodium battery includes a positive electrode, a negative electrode current collector, a separator, and an electrolyte. Its characteristics are: A composite positive electrode sodium supplement is added to the positive electrode active material; the composite positive electrode sodium supplement is composed of sodium-rich layered oxides from sodium-ion batteries and sodium carbonate; the mass of the composite positive electrode sodium supplement is 0.5wt% to 10wt% of the total mass of the positive electrode active material; Simultaneously, an electrolyte sodium supplement is added to the electrolyte. The electrolyte sodium supplement is one or a mixture of two of sodium trimethylsilanolate and NaFSI; the amount of electrolyte sodium supplement added is 1wt% to 4wt% of the total mass of the electrolyte. Furthermore, the mass ratio of the amount of sodium supplement added to the electrolyte to the amount of sodium supplement added to the composite positive electrode is in the range of 0.2 to 2:1.

[0020] This invention addresses the problem of irreversible loss of active sodium ions and the difficulty in balancing sodium replenishment efficiency and stability during the first charge and discharge of a sodium-free battery. It adopts a combined synergistic sodium replenishment mechanism involving electrolyte and cathode sodium replenishment, and by adjusting the ratio, amount, and process parameters of the sodium replenishing agent, a compensation system with rapid, continuous, and interface-optimized sodium replenishment is formed. This changes the single sodium replenishment method and significantly improves the battery's initial coulombic efficiency, energy density, and cycle life.

[0021] Among them, sodium trimethylsilanolate and NaFSI-type electrolyte sodium replenishing agents can rapidly dissociate and release sodium ions, immediately compensating for sodium loss in the initial SEI film formation during the first charge and discharge, thus solving the problem of slow sodium replenishment rate in a single sodium replenishment method; the composite cathode sodium replenishing agent composed of sodium-rich layered oxide and sodium carbonate in sodium-ion batteries can slowly decompose and release sodium ions, continuously compensating for the long-term irreversible loss of sodium metal deposition, thus filling the gap in the instability of a single sodium replenishment method; at the same time, the mass ratio range of 0.2 to 2:1 achieves the synergy of the two sodium replenishment methods, avoiding the low efficiency or performance degradation caused by the imbalance of sodium replenishing agent ratio, and maximizing the synergistic effect of the two, enabling the battery to achieve a leap in initial coulombic efficiency.

[0022] In some embodiments, the mass ratio of sodium-rich layered oxide to sodium carbonate in the composite positive electrode sodium supplement is 1:0.1 to 10.

[0023] Sodium-rich layered oxides in sodium-ion batteries can promote the decomposition of sodium carbonate, reduce its decomposition potential, improve the sodium replenishment efficiency of the positive electrode, and avoid the decrease in the conductivity of the positive electrode caused by sodium carbonate residue. The reasonable ratio takes into account both the amount and rate of sodium replenishment. The ratio of 0.1 to 10 covers different sodium replenishment needs, which not only ensures the volumetric specific capacity of the sodium replenishing agent, but also prevents side reactions caused by excessive sodium carbonate ratio or insufficient total sodium replenishment due to excessive layered oxide ratio.

[0024] The chemical formula of sodium-rich layered oxides in sodium-ion batteries is Na. x TMO2, where 0.6≤x≤1.05, and TM is one or a combination of Mn, Fe, Ni, and Co.

[0025] The sodium-rich characteristic of 0.6≤x≤1.05 ensures that the sodium replenishment agent has sufficient sodium ion release reserves to meet the sodium replenishment requirements of the first charge-discharge and long-term cycle of the negative electrode-less sodium battery. The combination selection of transition metals such as Mn, Fe, Ni, and Co can optimize the electronic conductivity and structural stability of the layered oxide. On the one hand, it can improve the overall conductivity of the positive electrode and avoid the impact of inactive material residues on battery performance. On the other hand, it can enhance the cycle stability of the sodium replenishment agent and reduce its structural collapse and performance degradation during repeated charge-discharge processes.

[0026] The composite positive electrode sodium supplement has a particle size of less than 5 μm. In some embodiments, its preparation method is as follows: sodium-rich layered oxide of sodium-ion battery is mixed with sodium carbonate in a certain proportion, placed in a sealed ball mill, and ball milling beads are added. The mixture is ball milled at a speed of 200-700 rpm for 5-10 hours to obtain the composite positive electrode sodium supplement.

[0027] The ultra-microstructure with a particle size of less than 5μm significantly increases the contact area between the sodium supplement and the positive electrode active material and electrolyte, accelerating the sodium ion release rate and improving the sodium supplement response speed. The sealed ball milling process is simple to operate and cost-controllable, and the sodium supplement can be prepared on a large scale without complex equipment, which is suitable for industrial mass production needs.

[0028] The electrolyte comprises a sodium salt, a solvent, and functional additives. In some embodiments, the sodium salt is one or a mixture of NaPF6 and NaClO4, with a concentration of 0.8–1.5 mol / L. The solvent is one or a mixture of ethylene carbonate, dimethyl carbonate, and diethylene glycol dimethyl ether. The functional additive is one or two of B / F-rich additives and spatially confined anion additives, with an addition amount of 0.1 wt%–2 wt% of the total mass of the electrolyte.

[0029] In some embodiments, the positive electrode active material is one or more of a polyanionic compound, Prussian blue, or a Prussian blue analogue; the polyanionic compound includes at least one of Na3V2(PO4)2F3, Na3V2(PO4)3, and Na4VMn(PO4)3.

[0030] In some embodiments, the negative electrode current collector is a surface-modified aluminum foil, copper foil, or stainless steel foil, the surface of which is provided with a sodium-loving coating or a porous structured coating.

[0031] The present invention also provides a negative electrode-free sodium battery using the above-mentioned sodium-replenishing modification method, comprising a positive electrode, a negative electrode current collector, a separator, and an electrolyte, characterized in that: the positive electrode comprises a positive electrode current collector and a positive electrode slurry coated on the surface of the positive electrode current collector; the positive electrode slurry comprises a positive electrode active material with added composite positive electrode sodium replenishing agent, a conductive agent, and a binder; and the electrolyte contains an electrolyte sodium replenishing agent.

[0032] This invention transforms the composite sodium replenishment mechanism into a practical improvement in battery performance. The positive electrode active material, incorporating a composite positive electrode sodium replenisher, is combined with a suitable ratio of conductive agent and binder to ensure the electrochemical and processing performance of the positive electrode. The electrolyte sodium replenisher, present in the electrolyte, synergistically compensates with the positive electrode sodium replenisher, achieving efficient and continuous sodium ion replenishment. This invention enables the battery to possess the core advantages of high initial coulombic efficiency, high energy density, and long cycle life.

[0033] In some embodiments, the conductive agent in the positive electrode slurry is one or more of Ketjen Black, single-walled / multi-walled carbon nanotubes, acetylene black, and Super P; the binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, and sodium alginate.

[0034] In some embodiments, the separator is a composite separator with a thickness of 10 to 30 μm; the positive electrode side of the composite separator is provided with a mixed coating of polymer matrix, MOF and solid electrolyte with a thickness of 2 to 8 μm; the negative electrode side of the composite separator is provided with a sodium-loving coating with a thickness of 1 to 5 μm.

[0035] The technical solution of the present invention will be further described in detail below with reference to specific embodiments: Example 1 Preparation of composite positive electrode sodium supplement: Select sodium-rich layered oxide Na 0.8 MnO2 (x=0.8) and sodium carbonate were uniformly mixed at a mass ratio of 1:1 and placed in a sealed ball mill. Zirconia grinding beads were added, and the mixture was ball-milled at 500 rpm for 8 hours to obtain a composite cathode sodium supplement with a particle size of approximately 4 μm. The amount of the composite cathode sodium supplement added was 5 wt% of the total mass of the cathode active material Na3V2(PO4)2F3. Electrolyte preparation: 1.0 mol / L NaPF6 was used as the sodium salt, and the solvent was EC:DMC=1:1 (volume ratio); sodium trimethylsilanolate was added as a sodium supplement agent, with an addition amount of 2 wt% of the total mass of the electrolyte; 1 wt% of B-rich additive was added, and the mixture was stirred evenly to obtain a sodium-supplemented electrolyte; the B-rich additive was potassium fluoroborate (KBF4) or a borate ester compound.

[0036] Positive electrode preparation: The positive electrode active material Na3V2(PO4)2F3, composite positive electrode sodium supplement, Ketjen black and polyvinylidene fluoride were mixed evenly according to the mass ratio of 90:5:3:2. NMP was added to make a positive electrode slurry, which was coated on an aluminum foil current collector and vacuum dried at 80°C for 12 hours. The positive electrode sheet was then sliced. Battery assembly: A 20μm thick composite separator is used, with a 5μm thick coating on the positive electrode side and a 3μm thick sodium-loving coating on the negative electrode side; the negative electrode current collector is a copper foil coated with sodium fluoroaluminate (sodium-loving coating); the positive electrode sheet, composite separator, and negative electrode current collector are stacked in sequence, the above electrolyte is injected, and the battery is sealed to obtain a sodium-free negative electrode battery.

[0037] In this embodiment, the mass ratio of electrolyte sodium replenisher to composite positive electrode sodium replenisher is 0.4:1.

[0038] Example 2 Compared with Example 1, the only difference is that the amount of sodium supplement added to the composite positive electrode is adjusted to 0.5 wt% of the total mass of the positive electrode active material in the preparation step of the composite positive electrode sodium supplement. All other steps, raw materials, and process parameters are exactly the same.

[0039] In this embodiment, the mass ratio of electrolyte sodium replenisher to composite positive electrode sodium replenisher is 2.0:1.

[0040] Example 3 Compared with Example 1, the only difference is that the amount of sodium supplement added to the composite positive electrode is adjusted to 10 wt% of the total mass of the positive electrode active material in the preparation step of the composite positive electrode sodium supplement. All other steps are exactly the same.

[0041] In this embodiment, the mass ratio of electrolyte sodium replenisher to composite positive electrode sodium replenisher is 0.2:1.

[0042] Example 4 Compared with Example 1, the only difference is that the amount of sodium trimethylsilanolate added as the electrolyte preparation step is adjusted to 1 wt%, and all other steps are exactly the same.

[0043] In this embodiment, the mass ratio of electrolyte sodium replenisher to composite positive electrode sodium replenisher is 0.2:1.

[0044] Example 5 Compared with Example 1, the only difference is that the amount of sodium trimethylsilanolate added as the electrolyte preparation step is adjusted to 4 wt%, and all other steps are exactly the same.

[0045] In this embodiment, the mass ratio of electrolyte sodium replenisher to composite positive electrode sodium replenisher is 0.8:1.

[0046] Example 6 Compared to Example 1, only in the preparation step of the composite cathode sodium supplement agent, the sodium-rich layered oxide was replaced with Na. 0.6 MnO2 (x=0.6), all other components are exactly the same.

[0047] In this embodiment, the mass ratio of electrolyte sodium replenisher to composite positive electrode sodium replenisher is 0.4:1.

[0048] Example 7 Compared to Example 1, only in the preparation step of the composite cathode sodium supplement agent, the sodium-rich layered oxide was replaced with Na. 1.05 MnO2 (x=1.05), all other components are exactly the same.

[0049] In this embodiment, the mass ratio of electrolyte sodium replenisher to composite positive electrode sodium replenisher is 0.4:1.

[0050] Example 8 Compared to Example 1, only the sodium supplementation step of the composite positive electrode was modified using Na. 0.6 Co 0.2 Mn 0.8 O2 and sodium carbonate were mixed at a mass ratio of 1:0.5 and ball-milled at 200 rpm for 10 hours.

[0051] In this embodiment, the mass ratio of electrolyte sodium replenisher to composite positive electrode sodium replenisher is 0.4:1.

[0052] Comparative Example 1 Compared with Example 1, the only difference is that the amount of sodium supplement added to the composite positive electrode is adjusted to 0.3 wt% in the preparation step of the composite positive electrode sodium supplement, and all other steps are the same.

[0053] In this comparative example, the mass ratio of electrolyte sodium replenisher to composite positive electrode sodium replenisher is 3.33:1.

[0054] Comparative Example 2 Compared with Example 1, the only difference is that the amount of sodium supplement added to the composite positive electrode is adjusted to 12wt% in the preparation step of the composite positive electrode sodium supplement, and all other steps are the same.

[0055] In this comparative example, the mass ratio of electrolyte sodium replenisher to composite positive electrode sodium replenisher is 0.17:1.

[0056] Comparative Example 3 Compared with Example 1, the only difference was that the amount of sodium supplement added to the electrolyte was adjusted to 6 wt% in the electrolyte preparation step, while all other steps remained the same.

[0057] In this comparative example, the mass ratio of electrolyte sodium replenisher to composite positive electrode sodium replenisher is 1.2:1.

[0058] Comparative Example 4 Compared with Example 1, the only difference was that the amount of sodium supplement added to the electrolyte was adjusted to 0.5 wt% in the electrolyte preparation step, while all other steps remained the same.

[0059] In this comparative example, the mass ratio of electrolyte sodium replenisher to composite positive electrode sodium replenisher is 0.1:1.

[0060] Comparative Example 5 Compared to Example 1, only the sodium supplementation step of the composite positive electrode was modified using Na. 0.5 MnO2 (x=0.5), all other parameters are the same.

[0061] In this comparative example, the mass ratio of electrolyte sodium replenisher to composite cathode sodium replenisher is 0.4:1.

[0062] Comparative Example 6 Compared to Example 1, only the sodium supplementation step of the composite positive electrode was modified using Na. 1.1 MnO2 (x=1.1), all other parameters are the same.

[0063] In this comparative example, the mass ratio of electrolyte sodium replenisher to composite cathode sodium replenisher is 0.4:1.

[0064] Comparative Example 7 Compared with Example 1, only the ratio of sodium replenishing agent was adjusted so that the mass ratio of electrolyte sodium replenishing agent to composite positive electrode sodium replenishing agent was 0.1:1, and all other aspects were the same.

[0065] Comparative Example 8 Compared with Example 1, only the ratio of sodium replenishing agent was adjusted so that the mass ratio of electrolyte sodium replenishing agent to composite positive electrode sodium replenishing agent was 2.4:1, and all other aspects remained the same.

[0066] Comparative Example 9 Compared to Example 1, the only difference is that no sodium supplementer is added in the electrolyte preparation step; all other steps are the same.

[0067] Comparative Example 10 Compared to Example 1, the only difference is that the composite positive electrode sodium supplement is not added in the positive electrode preparation step; all other steps are the same.

[0068] Table 1

[0069] Conclusion Analysis: This invention constructs a synergistic optimization scheme for sodium replenishment in the electrolyte and the cathode through examples. Examples 2 and 3 respectively verify the upper and lower limits of the amount of composite cathode sodium replenisher added. The results show that regardless of whether the amount is at the lower or upper limit, it can exert a synergistic sodium replenishment effect, with stable performance and no negative impact. Examples 4 and 5 conduct experiments on the upper and lower limits of the amount of electrolyte sodium replenisher added, verifying that this parameter range can adapt to different cost and performance requirements while ensuring the sodium replenishment effect.

[0070] Examples 6 and 7 verified the upper and lower limits of sodium content (x value) in sodium-rich layered oxides. The results showed that x values ​​within this range can ensure sodium ion release and reserve, promote improved sodium replenishment efficiency, and optimize cathode conductivity. Example 8 used multi-doped sodium-rich layered oxides to verify that the method of the present invention can be adapted to different types of sodium replenishment agents and exhibits excellent performance.

[0071] Comparative Examples 1 and 2 had their sodium-replenishing agent additions adjusted to the upper and lower limits outside the specified range. The results showed that insufficient addition could not achieve effective sodium replenishment, while excessive addition triggered side reactions, both leading to performance degradation. Comparative Examples 3 and 4 adjusted the electrolyte sodium-replenishing agent addition to outside the reasonable range. Excessive addition triggered side reactions in the electrolyte, damaging interfacial stability and weakening the continuous compensation effect of sodium replenishment from the positive electrode, resulting in significantly accelerated capacity decay during long-term battery cycling. Insufficient addition could not quickly compensate for initial sodium loss. Comparative Examples 5 and 6 used sodium-rich layered oxides with x values ​​outside the range. Too low an x ​​value resulted in insufficient sodium replenishment reserves, while too high an x ​​value affected structural stability, both reducing battery performance. Comparative Examples 9 and 10 used single positive electrode sodium replenishment and single electrolyte sodium replenishment methods, respectively. Neither could simultaneously achieve rapid and continuous sodium replenishment, weakening the synergistic effect and causing the overall battery performance to be significantly lower than the examples.

[0072] As shown in Comparative Examples 7 and 8, the study found that if the mass ratio of the electrolyte sodium replenisher to the composite cathode sodium replenisher is not suitable, the sodium replenishment system will become unbalanced, thus failing to achieve a truly effective synergistic sodium replenishment mechanism. Under some conditions, antagonistic phenomena may even occur, leading to a significant deterioration in the overall battery performance. When the ratio is too low, the rapid sodium loss caused by the formation of the SEI film in the early stage of the battery is difficult to be compensated in time, resulting in insufficient sodium replenishment response and directly leading to a low initial coulombic efficiency. When the ratio is too high, the excessive electrolyte sodium replenishment agent is prone to side reactions with the electrolyte and electrode interface, which damages the interface stability and weakens the continuous compensation effect of sodium replenishment at the positive electrode, causing the battery capacity to decay faster during long-term cycling.

[0073] Compared to existing single sodium replenishment methods, the composite sodium replenishment method of this invention achieves synergy between rapid sodium replenishment and continuous sodium replenishment, taking into account both sodium replenishment efficiency and stability, effectively optimizing battery interface performance, significantly improving overall battery performance, and breaking through existing technical bottlenecks.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for sodium-addition modification of a negative electrode-free sodium battery, the negative electrode-free sodium battery comprising a positive electrode, a negative electrode current collector, a separator, and an electrolyte, characterized in that: A composite positive electrode sodium supplement agent is added to the positive electrode active material; the composite positive electrode sodium supplement agent is composed of sodium-rich layered oxides from sodium-ion batteries and sodium carbonate; the mass of the composite positive electrode sodium supplement agent is 0.5wt% to 10wt% of the total mass of the positive electrode active material. Simultaneously, an electrolyte sodium supplement agent is added to the electrolyte, wherein the electrolyte sodium supplement agent is one or a mixture of two of sodium trimethylsilanolate and NaFSI; the amount of electrolyte sodium supplement agent added is 1wt% to 4wt% of the total mass of the electrolyte; Furthermore, the mass ratio of the amount of sodium supplement agent added to the electrolyte to the amount of sodium supplement agent added to the composite positive electrode is in the range of 0.2 to 2:

1.

2. The sodium-addition modification method for a sodium-free negative electrode battery according to claim 1, characterized in that: In the composite positive electrode sodium supplement, the mass ratio of sodium-rich layered oxide to sodium carbonate in the sodium-ion battery is 1:0.1 to 10.

3. The sodium-addition modification method for a sodium-free negative electrode battery according to claim 1, characterized in that: The sodium-ion battery has the chemical formula Na0 as its sodium-rich layered oxide. x TMO2, where 0.6≤x≤1.05, and TM is one or a combination of Mn, Fe, Ni, and Co.

4. The sodium-addition modification method for a sodium-free negative electrode battery according to claim 1, characterized in that: The composite positive electrode sodium supplement has a particle size of less than 5 μm. Its preparation method is as follows: sodium-rich layered oxide of sodium-ion battery is mixed with sodium carbonate in a certain proportion, and then placed in a sealed ball mill. Grinding balls are added, and the mixture is ball-milled at a speed of 200-700 rpm for 5-10 hours to obtain the composite positive electrode sodium supplement.

5. The sodium-addition modification method for a sodium-free negative electrode battery according to claim 1, characterized in that: The electrolyte comprises a sodium salt, a solvent, and a functional additive; the sodium salt is one or a mixture of NaPF6 and NaClO4, with a concentration of 0.8–1.5 mol / L; the solvent is one or a mixture of ethylene carbonate, dimethyl carbonate, and diethylene glycol dimethyl ether; the functional additive is one or two of B / F rich additives and spatially confined anion additives, with an addition amount of 0.1 wt%–2 wt% of the total mass of the electrolyte.

6. The sodium-addition modification method for a sodium-free negative electrode battery according to claim 1, characterized in that: The positive electrode active material is one or more of a polyanionic compound, Prussian blue, or a Prussian blue analogue; the polyanionic compound includes at least one of Na3V2(PO4)2F3, Na3V2(PO4)3, and Na4VMn(PO4)3.

7. The sodium-addition modification method for a sodium-free negative electrode battery according to claim 1, characterized in that: The negative electrode current collector is a surface-modified aluminum foil, copper foil, or stainless steel foil, and its surface is provided with a sodium-loving coating or a porous structured coating.

8. A negative electrode-free sodium battery employing the sodium-modification method as described in any one of claims 1 to 7, comprising a positive electrode, a negative electrode current collector, a separator, and an electrolyte, characterized in that: The positive electrode includes a positive electrode current collector and a positive electrode slurry coated on the surface of the positive electrode current collector; the positive electrode slurry includes a positive electrode active material with added composite positive electrode sodium supplement, a conductive agent and a binder; the electrolyte contains an electrolyte sodium supplement.

9. The sodium-ion battery without a negative electrode according to claim 8, characterized in that: In the positive electrode slurry, the conductive agent is one or more of Ketjen Black, single-walled / multi-walled carbon nanotubes, acetylene black, and Super P; the binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, and sodium alginate.

10. The sodium-ion battery without a negative electrode according to claim 8, characterized in that: The membrane is a composite membrane with a thickness of 10–30 μm; the positive electrode side of the composite membrane is provided with a mixed coating of polymer matrix, MOF and solid electrolyte with a thickness of 2–8 μm; the negative electrode side of the composite membrane is provided with a sodium-loving coating with a thickness of 1–5 μm.

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