Quick-charge sodium ion battery design method and sodium ion battery

Abstract

The invention provides a design method of a quick-charge sodium-ion battery and the sodium-ion battery, and the design method of the quick-charge sodium-ion battery comprises the following steps: S1, mixing a positive active material, a conductive agent, an adhesive and NMP to obtain positive slurry; s2, mixing a negative electrode active matter, a conductive agent, CMC, a binder and pure water to obtain negative electrode slurry; s3, coating two surfaces of an aluminum foil with the positive electrode slurry and the negative electrode slurry respectively for baking, and removing the NMP and the pure water to obtain a positive electrode plate and a negative electrode plate respectively; s4, laminating the positive pole piece and the negative pole piece to prepare a positive lamination body and a negative lamination body, and baking the positive lamination body and the negative lamination body to obtain a battery prefabricated product; and S5, performing electrolyte injection on the battery prefabricated product, and then performing formation and capacity grading to prepare the sodium ion battery. According to the design method of the quick-charge sodium-ion battery, the stability of the battery in a low-temperature environment is guaranteed.

Description

Fast-charging sodium-ion battery design method and sodium-ion battery Technical Field

[0001] This application belongs to the field of sodium-ion battery technology, specifically relating to a fast-charging sodium-ion battery design method and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries are a type of battery that is abundant in resources and low in cost. They have become a research hotspot in new energy and energy storage. In the fields of energy storage power stations, low-speed two-wheeled vehicles, and 12V vehicle start-stop power supplies, they have shown a trend of competing with or even replacing lithium-ion batteries. Moreover, their excellent low-temperature performance has been widely used in the field of low-temperature batteries.

[0003] However, in 12V start-stop battery applications, the battery needs to simultaneously possess low-temperature high-current starting capability and low-temperature charging performance without heating measures. While current sodium-ion batteries meet the discharge requirements, their fast charging, especially low-temperature charging cycles, have significant shortcomings. Existing technology can only meet the 0.1C charging cycle requirement at -10℃. Furthermore, 12V start-stop batteries are generally in a high SOC range in vehicles. In this range, the hard carbon electrode is in a low-potential plateau region, making it highly susceptible to sodium deposition during high-current or low-temperature charging. In severe cases, this can lead to internal short circuits and safety hazards, posing a significant risk to the application of sodium-ion batteries in automotive 12V starter batteries, especially in cold northern regions. Summary of the Invention

[0004] This application provides a fast-charging sodium-ion battery design method and sodium-ion battery, aiming to solve the problems in the prior art where sodium-ion batteries used in the field of 12V start-stop batteries have slow charging cycles at low temperatures and are prone to sodium precipitation leading to short circuits.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: Firstly, a fast-charging sodium-ion battery design method is provided, comprising the following steps: S1: mixing positive electrode active material, conductive agent, binder, and NMP to obtain a positive electrode slurry; S2: mixing negative electrode active material, conductive agent, CMC, binder, and pure water to obtain a negative electrode slurry; S3: coating the positive electrode slurry and the negative electrode slurry onto both sides of an aluminum foil and baking to remove NMP and pure water, thereby obtaining a positive electrode sheet and a negative electrode sheet respectively; S4: rolling and die-cutting the positive electrode sheet and the negative electrode sheet respectively, and then stacking them with a separator to form a positive electrode stack and a negative electrode stack, and baking the positive electrode stack and the negative electrode stack to obtain a battery preform; S5: injecting electrolyte into the battery preform, and then performing formation and capacity testing to produce a sodium-ion battery.

[0006] In combination with the first aspect, in a possible implementation, the positive electrode active material is at least one of layered metal oxides, polyanionic materials, and Prussian blue; the negative electrode active material is one or both of hard carbon and soft carbon.

[0007] In combination with the first aspect, in a possible implementation, when the positive electrode active material is a layered metal oxide, the metal element is selected from one of iron, nickel, manganese, and copper; the polyanionic material is sodium iron phosphate or sodium pyrophosphate iron.

[0008] In combination with the first aspect, in a possible implementation, the capacity of hard carbon per unit area of the negative electrode sheet is Q Sa , Sa , Sb , P , Sb , Sa , Hb , Ha , Ha , N , H , Hb , Ha , Sa , Ha , S , P , Ha , H , the capacity of soft carbon is Q S , the mass ratio of hard carbon is x, the mass ratio of soft carbon is y, then the total capacity per unit area of the negative electrode is Q N =x×Q H +y×Q S , where 0 < x < 1, 0 < y < 1, and x + y = 1; define the limiting potential of the negative electrode sheet after full charge in the battery as m V, and the value range of m is 0.1~0.5V; define the capacity with the negative electrode potential greater than m V as the available capacity Q a , the capacity with the negative electrode potential less than m V as the non-available capacity Q b , the total capacity of the negative electrode Q = Q a +Q b ; define the total capacity of the positive electrode potential as Q P , set the available capacity of the negative electrode Q a compared with the excess coefficient N of the positive electrode capacity Q P ; when the capacity per unit area of the positive electrode sheet is Q P , from Q P =(x×Q Ha +y×Q Sa ) / N, calculate the available capacity Q of hard carbon Ha and the available capacity Q of soft carbon Sa ; define the proportion of the capacity above m V in hard carbon as P H =Q Ha / (Q Ha +Q Hb ), the proportion of the capacity above m V in soft carbon is P <000002​​​​​​​​​​​​​​​​​Sa / P S .

[0009] In conjunction with the first aspect, in one possible implementation, when the positive electrode contains layered metal oxides, the capacity Q per unit area of ​​the positive electrode sheet... P = (95-95×R+110×w×R)×S, where R is the proportion of layered metal oxide in the positive electrode active material, 0≤R≤1; w is the capacity coefficient of layered metal oxide, 0.8≤w≤1.0; S is the positive electrode coefficient, which is related to the product of the positive electrode surface density and the proportion of positive electrode active material.

[0010] The fast-charging sodium-ion battery design method provided in this application, compared with existing technologies, uses NMP and pure water as solvents for the positive and negative electrode slurries, respectively, adapting to different binder characteristics to ensure uniform slurry dispersion and avoid excessive electrode polarization caused by uneven mixing, thus providing a foundation for fast-charging performance. After coating, baking removes the solvent, and rolling optimizes electrode density, reducing ion diffusion path length and improving ion transport efficiency under high current, enabling the battery to maintain a high capacity ratio at high rates from 2C to 5C. The baking process after stacking removes residual moisture from the electrodes and separator, preventing moisture from reacting with the electrolyte to generate harmful substances and ensuring battery stability at low temperatures. In the high SOC range, it reduces stress concentration on the negative electrode surface, lowering the risk of sodium precipitation during high-current or low-temperature charging and preventing internal short circuits.

[0011] In a second aspect, a sodium-ion battery is provided, manufactured based on a fast-charging sodium-ion battery design method as described in any of the possible implementations above, comprising: a casing having an internal separator that divides the interior of the casing into a first space and a second space, wherein the first space and the second space each contain an electrolyte; a positive electrode plate located in the first space; and a negative electrode plate located in the second space.

[0012] In conjunction with the second aspect, in one possible implementation, the material ratio of the positive electrode sheet is: 94%~95% positive active material, 2%~3% conductive agent, and 2%~3% binder; the material ratio of the negative electrode sheet is: 93%~94% negative active material, 2%~2.5% conductive agent, 1.5% CMC, and 2.5%~3% binder.

[0013] In conjunction with the second aspect, in one possible implementation, the areal density of the positive electrode sheet is 20~40 mg / cm², and the areal density of the negative electrode sheet is 10~30 mg / cm².

[0014] In conjunction with the second aspect, in one possible implementation, the charge / discharge voltage range of the sodium-ion battery is 2.0~3.9V.

[0015] The sodium-ion battery provided in this application, compared with existing technologies, uses NMP and pure water as solvents for the positive and negative electrode slurries, respectively, adapting to different binder characteristics to ensure uniform slurry dispersion and avoid excessive electrode polarization caused by uneven mixing, thus providing a foundation for fast-charging performance. Solvent removal through baking after coating and electrode density optimization through rolling reduce ion diffusion path length and improve ion transport efficiency under high current, enabling the battery to maintain a high capacity ratio at high rates from 2C to 5C. The baking process after stacking removes residual moisture from the electrodes and separator, preventing the reaction of moisture with the electrolyte to generate harmful substances and ensuring battery stability at low temperatures. Reducing stress concentration on the negative electrode surface in the high SOC range lowers the risk of sodium precipitation during high-current or low-temperature charging, preventing internal short circuits. Combined with precise material selection and parameter design, the separator's separating effect and negative electrode potential limitation work synergistically to further reduce the risk of short circuits. The positive and negative electrode sheets are made based on optimized material ratios and manufacturing processes, resulting in a dense and uniform electrode structure with a short ion diffusion path. This improves the reaction rate under high current, allowing the battery to maintain a high capacity ratio even during 2C~5C fast charging, thus addressing the shortcomings of existing fast charging technologies. The electrolyte exhibits good compatibility with the positive and negative electrode materials, maintaining good ion conductivity even at -20℃. Combined with the negative electrode potential limiting design, the battery can achieve efficient low-temperature charging without heating, overcoming the limitation of existing technologies that can only meet 0.1C charging at -10℃. Detailed Implementation

[0016] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0017] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is actually illustrative only and is in no way intended to limit this application or its application or use. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0019] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," and "above" are used here to describe the spatial positional relationship of a device or feature with other devices or features. Therefore, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways, and the spatial relative descriptions used herein will be interpreted accordingly.

[0020] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Additionally, "multiple" and "several" mean two or more, unless otherwise explicitly specified.

[0021] The design method for a fast-charging sodium-ion battery provided in this application is described below. The fast-charging sodium-ion battery design method includes the following steps: S1: Mixing positive electrode active material, conductive agent, binder and NMP to obtain positive electrode slurry; S2: Mixing negative electrode active material, conductive agent, CMC, binder and pure water to obtain negative electrode slurry; S3: Coating the positive electrode slurry and negative electrode slurry onto both sides of aluminum foil and baking to remove NMP and pure water, obtaining positive electrode sheet and negative electrode sheet respectively; S4: Rolling and die-cutting the positive electrode sheet and negative electrode sheet respectively, and then stacking them with a separator to form positive electrode stack and negative electrode stack, and baking the positive electrode stack and negative electrode stack to obtain battery preform; S5: Injecting electrolyte into the battery preform, and then performing formation and capacity testing to form a sodium-ion battery.

[0022] In specific implementation, this embodiment prepares the positive electrode slurry, negative electrode slurry, positive electrode sheet, and negative electrode sheet in steps, and then completes the sodium-ion battery preparation through stacking, baking, electrolyte injection, and capacity testing. First, the components of the positive and negative electrodes are mixed according to process requirements to ensure that the active material, conductive agent, and binder are uniformly dispersed, laying the foundation for the electron conduction and structural stability of the electrode. Then, the solvent is removed by coating and baking to form a dense and uniformly thick electrode sheet, reducing ion diffusion resistance. Subsequently, the physical properties of the electrode sheet are optimized by rolling and die cutting. After stacking, baking removes residual moisture and impurities to avoid affecting the stability of the electrolyte. Finally, electrolyte injection provides the ion conduction medium, the active sites of the electrode are activated by formation, and the product is screened for consistency to ensure that the overall performance of the battery meets the standards.

[0023] The fast-charging sodium-ion battery design method provided in this embodiment, compared with the prior art, uses NMP and pure water as solvents for the positive and negative electrode slurries, respectively, adapting to the characteristics of different binders to ensure uniform slurry dispersion and avoid excessive electrode polarization caused by uneven mixing, thus providing a foundation for fast-charging performance. After coating, baking removes the solvent, and rolling optimizes the electrode density, reducing the ion diffusion path length and improving ion transport efficiency under high current, enabling the battery to maintain a high capacity ratio at high rates from 2C to 5C. The baking process after stacking removes residual moisture from the electrodes and separator, preventing moisture from reacting with the electrolyte to generate harmful substances and ensuring battery stability at low temperatures. In the high SOC range, it reduces stress concentration on the negative electrode surface, lowering the risk of sodium precipitation during high-current or low-temperature charging and preventing internal short circuits.

[0024] In some embodiments, the positive electrode active material is at least one of layered metal oxides, polyanionic materials, and Prussian blue; the negative electrode active material is one or both of hard carbon and soft carbon.

[0025] In practice, this application removes NMP and water-soluble solvents by baking in an oven. The slurry is prepared using a dual planetary mixer. The positive and negative electrode slurries are then uniformly coated onto aluminum foil using a coating machine.

[0026] In practical implementation, low m values ​​can be designed for layered metal oxide systems, while high m values ​​can be designed for polyanionic material systems, forming a unified design standard. This allows batteries of different material systems to balance fast charging performance and low-temperature adaptability, overcoming the limitations of poor material system compatibility in existing technologies. It ensures that batteries can still achieve low-temperature charging without heating measures and maintain structural stability during high-current fast charging, further expanding the application scenarios of sodium-ion batteries in the field of 12V automotive start-stop power supplies.

[0027] In this embodiment, the positive electrode active material is selected from at least one of layered metal oxides, polyanionic materials, and Prussian blue. Among them, layered metal oxides have the advantage of high specific capacity, polyanionic materials have strong structural stability and long cycle life, and Prussian blue has excellent ion transport rate. Different materials can be flexibly combined according to actual needs to meet the high capacity and high stability requirements of 12V start-stop batteries. The negative electrode is selected from one or two of hard carbon and soft carbon. Hard carbon has the characteristics of low sodium intercalation potential and high specific capacity, while soft carbon has good conductivity and structural flexibility. The two can be used alone or in combination to achieve complementary performance.

[0028] In some embodiments, when the positive electrode active material is a layered metal oxide, the metal element is selected from iron, nickel, manganese, and copper; the polyanionic material is sodium iron phosphate or sodium iron pyrophosphate.

[0029] This embodiment improves the battery performance from the perspective of optimizing material properties. When the positive electrode active material is a layered metal oxide, metal elements such as iron, nickel, manganese, and copper are selected. These metal elements are rich in resources and low in cost, and the corresponding layered metal oxides (such as NaTMO2) have high ion insertion and extraction rates and specific capacities, providing a material basis for fast charging performance; the polyanion-based materials are limited to sodium iron phosphate or sodium pyrophosphate iron. Both have stable three-dimensional crystal structures and are not prone to structural distortion under high current charging and low temperature environments, effectively improving the cycle stability and low temperature adaptability of the battery.

[0030] Specifically, during implementation, the electronic conductivity of the iron, nickel, manganese, and copper-based layered oxides is better than that of other metal-based materials, which can reduce electrode polarization and improve the charging efficiency under high current, enabling the battery to maintain a high capacity at a rate of 3C to 5C; the ion diffusion coefficients of sodium iron phosphate and sodium pyrophosphate iron are high, and efficient ion transport can still be achieved in a low temperature environment of -20°C, solving the problem of poor low temperature charging performance in the prior art. At the same time, these materials have good compatibility with the negative electrode hard carbon and soft carbon, which is conducive to scale application, making the sodium ion battery more competitive in the 12V start-stop power supply field, and meeting the development needs of the new energy industry for resource conservation and cost control.

[0031] In some embodiments, the hard carbon capacity per unit area of the negative electrode sheet is Q H , the soft carbon capacity is Q S , the mass ratio of hard carbon is x, and the mass ratio of soft carbon is y. Then the total capacity per unit area of the negative electrode is Q N = xQ H + yQ S , where 0 < x < 1, 0 < y < 1, and x + y = 1; it is defined that the limiting potential of the negative electrode sheet after full charge in the battery is designed as m V, and the value range of m is 0.1 to 0.5V; the capacity with the negative electrode potential greater than m V is defined as the available capacity Q a , and the capacity with the negative electrode potential less than m V is defined as the non-available capacity Q b , and the total capacity of the negative electrode Q = Q a + Q b ; the total capacity of the positive electrode potential is defined as Q P , and the excess coefficient N of the available capacity Q a of the negative electrode compared to the positive electrode capacity Q P is defined, and the value range of N is 0.9 to 1.1; when the capacity per unit area of the positive electrode sheet is Q P , from Q P = (x × Q Ha + y × Q Sa ) / N, the available capacity Q Ha of hard carbon and the available capacity Q Sa of soft carbon are calculated; the proportion of the capacity above m V in hard carbon is defined as PH =Q Ha / (Q Ha +Q Hb In soft carbon, the proportion of capacity above mV is P. S =Q Sa / (Q Sa +Q Sb ), where Q Hb For hard carbon unusable capacity, Q Sb For soft carbon unusable capacity; calculate the design capacity Q per unit area of ​​the negative electrode. N =x×Q Ha / P H +y×Q Sa / P S .

[0032] This embodiment addresses the aforementioned issues by constructing a complete capacity design and potential control system, starting from the core parameter level. It defines a formula for the total capacity per unit area of ​​the negative electrode to adapt to single or mixed systems of hard carbon and soft carbon, achieving flexible combination and performance complementarity of negative electrode materials; and sets a negative electrode charging limit potential to restrict the usable capacity of the negative electrode to a potential greater than mV (Q). a This design avoids the negative electrode entering a low-potential plateau region during high SOC ranges, fundamentally reducing sodium deposition during high-current or low-temperature charging and significantly lowering the risk of internal short circuits. The excess capacity coefficient N of the negative electrode is limited to 0.9~1.1, breaking through the conventional design logic of an excess coefficient greater than 1.2 for sodium-ion batteries. This avoids the low-potential problem of the negative electrode caused by excess capacity while ensuring precise matching of positive and negative electrode capacities, improving ion utilization during fast charging. A series of calculation formulas enable quantitative design of the positive and negative electrode capacities, ensuring accurate parameter matching.

[0033] This embodiment limits the use of low-potential capacity of the negative electrode by limiting the m value, so that the negative electrode potential of the 12V battery is controlled within a safe range within the working voltage range, which is suitable for high SOC conditions. The optimization of the excess coefficient N improves the charging rate under high current, so that the battery can still maintain a high capacity ratio at 2C~5C rate. The design standards of hard carbon and soft carbon systems are unified, eliminating the need for separate design for different negative electrode materials and improving design efficiency.

[0034] In some embodiments, when the positive electrode active material is a layered metal oxide, the value of m ranges from 0.05 to 0.2V; when the positive electrode active material is a polyanionic material or Prussian blue, the value of m ranges from 0.1 to 0.3V.

[0035] In specific implementation, this embodiment refines the range of negative electrode charging limit potential m for different positive electrode material systems, precisely adapting to the fast charging, low-temperature charging, and safety requirements of 12V start-stop batteries in the background technology. When the positive electrode active material is a layered metal oxide, m is 0.05~0.2V. Because layered oxide system batteries are difficult to fully charge in the 12V operating voltage range, the sodium intercalation ratio of hard carbon is relatively low, and the negative electrode potential itself is relatively high at 3.65V. A lower m value can ensure usable capacity while preventing the negative electrode from entering the low potential region and reducing sodium precipitation. When the positive electrode active material is a polyanionic material or Prussian blue, m is 0.1~0.3V. Batteries of these material systems can be fully charged, and the sodium intercalation ratio of hard carbon is high. A higher m value can effectively limit the use of low potential capacity and prevent sodium precipitation in the high SOC range.

[0036] This embodiment achieves precise matching between different positive electrode material systems and negative electrode potential control, avoiding the problem of poor performance in some material systems caused by a fixed m-value design. In conjunction with the subsequent capacity calculation system, it further optimizes the synchronicity of positive and negative electrode ion insertion or extraction, improves reaction efficiency during high-current charging, and enables layered oxide system batteries to maintain high capacity at high rates, while polyanion-based material system batteries maintain safety and stability under full charge. This embodiment broadens the range of battery material selection, enabling different positive electrode material systems to meet the usage requirements of 12V start-stop batteries, thus improving the versatility of the technology.

[0037] In some embodiments, when the positive electrode contains layered metal oxides, the capacity Q per unit area of ​​the positive electrode sheet is... P = (95-95×R+110×w×R)×S, where R is the proportion of layered metal oxide in the positive electrode active material, 0≤R≤1; w is the capacity coefficient of layered metal oxide, 0.8≤w≤1.0; S is the positive electrode coefficient, which is related to the product of the positive electrode surface density and the proportion of positive electrode active material.

[0038] This embodiment provides the positive electrode plate's capacity per unit area Q. P The calculation formula enables accurate calculation of the positive electrode capacity under different proportions of layered metal oxides. Adjusting R adapts to different capacity requirements, w considers the actual capacity utilization efficiency of the layered metal oxides to avoid a disconnect between theoretical capacity and actual performance, and S correlates the positive electrode areal density and the active material ratio to ensure the matching of electrode structure and capacity. This embodiment achieves quantitative design of the positive electrode capacity, ensuring that the positive electrode capacity matches the usable negative electrode capacity Q. a By precisely matching the excess coefficient N, excessive or insufficient sodium intercalation in the negative electrode due to capacity mismatch is avoided, reducing sodium deposition at low potentials in the high SOC range and improving safety performance. When R is adjusted between 0 and 1, the capacity characteristics and structural stability of the positive electrode can be flexibly adjusted, balancing high capacity and high safety.

[0039] Based on the same inventive concept, this application also provides a sodium-ion battery, manufactured based on the fast-charging sodium-ion battery design method as described in any of the above embodiments. The sodium-ion battery includes a casing, a positive electrode, and a negative electrode. The casing has an internal separator that divides the interior of the casing into a first space and a second space, each containing an electrolyte. The positive electrode is located in the first space, and the negative electrode is located in the second space.

[0040] It should be noted that this embodiment achieves the insertion and extraction of sodium ions through electrode reactions, thereby completing the storage and release of electrical energy. During battery operation, the electrolyte acts as an ion-conducting medium, allowing sodium ions to migrate between the positive and negative electrode plates. During charging, the positive electrode active material undergoes an oxidation reaction, causing sodium ions to be extracted from the positive electrode and migrate through the electrolyte to the negative electrode, where they are inserted into the hard or soft carbon lattice structure. Simultaneously, electrons flow from the positive to the negative electrode through the external circuit. During discharging, sodium ions are extracted from the negative electrode, migrate back to the positive electrode, and are inserted into the positive electrode active material. Electrons form a current through the external circuit, supplying power to the 12V start / stop device.

[0041] In practice, the outer casing provides physical protection for the battery, and the separator separates the positive and negative electrode plates, preventing short circuits while allowing sodium ions to pass through, ensuring the battery structure is stable and ion conduction is smooth.

[0042] In practice, an external power source supplies power to the battery. Sodium ions are extracted from the positive electrode, pass through the electrolyte and the separator, and embed into the usable capacity region of the negative electrode. At this time, the negative electrode potential is limited to a safe range to prevent sodium deposition. During the discharge phase, the sodium ions embedded in the negative electrode are extracted and return to the positive electrode through the electrolyte. Electrons supply power to the load through the external circuit, realizing the output of electrical energy. Throughout the entire charge and discharge cycle, the separator continuously separates the positive and negative electrodes, the electrolyte ensures efficient ion transport, and the outer shell protects the internal structure from the influence of the external environment, ensuring stable battery operation.

[0043] The sodium-ion battery provided in this embodiment, compared with existing technologies, combines precise material selection and parameter design. The separator's role in separation and the negative electrode potential limitation work synergistically to further reduce the risk of short circuits. The positive and negative electrode sheets are made based on optimized material ratios and manufacturing processes, resulting in a dense and uniform electrode structure and a short ion diffusion path. This improves the reaction rate under high current, allowing the battery to maintain a high capacity ratio even during 2C~5C fast charging, thus addressing the fast charging shortcomings of existing technologies. The electrolyte exhibits good compatibility with the positive and negative electrode materials, maintaining good ion conductivity even at -20℃. Combined with the negative electrode potential limitation design, the battery can achieve efficient low-temperature charging without heating measures, overcoming the limitation of existing technologies that can only meet 0.1C charging at -10℃.

[0044] In some embodiments, the material ratio of the positive electrode sheet is: 94%~95% positive active material, 2%~3% conductive agent, and 2%~3% binder; the material ratio of the negative electrode sheet is: 93%~94% negative active material, 2%~2.5% conductive agent, 1.5% CMC, and 2.5%~3% binder.

[0045] In this embodiment, the positive electrode composition is 94%~95% positive active material, 2%~3% conductive agent, and 2%~3% binder. The high proportion of positive active material ensures the battery's high specific capacity, providing a foundation for fast charging and long cycle life. An appropriate amount of conductive agent constructs a continuous conductive network, reducing electron transport resistance and improving high-current charging efficiency. The binder ensures a strong bond between the active material and the aluminum foil, preventing the active material from detaching during charging and discharging, and improving electrode structure stability. The negative electrode composition is 93%~94% negative active material, 2%~2.5% conductive agent, 1.5% CMC, and 2.5%~3% binder. The high proportion of negative active material ensures sodium intercalation capacity, the conductive agent improves conductivity, and the CMC and SBR composite binder system combines dispersibility and adhesion, effectively improving the dispersion of hard carbon and / or soft carbon, enhancing electrode flexibility, and preventing electrode cracking during rolling and cycling.

[0046] This embodiment optimizes the proportion of conductive agent to reduce electrode polarization, enabling the battery to maintain more than 94% of its charging capacity at high rates of 3C to 5C, thus addressing the shortcomings of fast charging. Secondly, the optimization of the binder system improves the stability of the electrode structure. During low-temperature cycling and high-current charging in the high SOC range, the positive and negative electrode plates are less prone to structural damage, reducing the physical causes of sodium precipitation.

[0047] In some embodiments, the areal density of the positive electrode is 20-40 mg / cm², and the areal density of the negative electrode is 10-30 mg / cm². This range ensures the effective capacity of the battery while avoiding performance degradation caused by excessive areal density, allowing the battery to maintain a high capacity ratio during 2C-5C fast charging. A reasonable areal density results in a dense and uniform electrode structure after coating and rolling, allowing for more thorough contact between the active material, conductive agent, and binder, reducing internal contact resistance, improving electron and ion transport efficiency, and further optimizing fast charging performance. In low-temperature environments, a shorter ion diffusion path reduces the inhibitory effect of low temperature on ion transport, enabling the battery to achieve efficient charging without heating. A suitable areal density reduces internal stress in the electrode, making it less prone to cracking and detachment during cycling, thus improving the battery's cycle life.

[0048] In some embodiments, the charge / discharge voltage range of the sodium-ion battery is 2.0~3.9V. This voltage range is designed to meet the operating requirements of a 12V start-stop power supply. The upper limit voltage of 3.9V avoids excessive oxidation of the positive electrode material, preventing irreversible damage to its crystal structure and extending the life of the positive electrode. At the same time, it avoids excessive sodium insertion into the negative electrode due to excessive charging voltage, reducing sodium deposition at low potentials. The lower limit voltage of 2.0V avoids excessive reduction of the positive electrode material, preventing structural collapse and ensuring stable insertion and extraction of sodium ions during discharge, thus guaranteeing the effective capacity of the battery.

[0049] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A design method for a fast-charging sodium-ion battery, characterized in that, Includes the following steps: S1: Mix the positive electrode active material, conductive agent, binder, and NMP to obtain a positive electrode slurry; S2: Mix the negative electrode active material, conductive agent, CMC, binder, and pure water to obtain a negative electrode slurry; S3: Coat the positive electrode slurry and the negative electrode slurry onto both sides of an aluminum foil and bake to remove NMP and pure water, obtaining a positive electrode sheet and a negative electrode sheet respectively; S4: Roll and die-cut the positive electrode sheet and the negative electrode sheet respectively, and then stack them with a separator to form a positive electrode stack and a negative electrode stack, and bake the positive electrode stack and the negative electrode stack to obtain a battery preform; S5: Inject electrolyte into the battery preform, and then perform formation and capacity testing to produce a sodium-ion battery.

2. The fast-charging sodium-ion battery design method as described in claim 1, characterized in that, The positive electrode active material is at least one of layered metal oxides, polyanionic materials, and Prussian blue; the negative electrode active material is one or both of hard carbon and soft carbon.

3. The fast-charging sodium-ion battery design method as described in claim 2, characterized in that, When the positive electrode active material is a layered metal oxide, the metal element is selected from iron, nickel, manganese, and copper; the polyanionic material is sodium iron phosphate or sodium iron pyrophosphate.

4. The fast-charging sodium-ion battery design method as described in claim 2, characterized in that, The hard carbon capacity per unit area of the negative electrode sheet is Q H , and the soft carbon capacity is Q S . If the mass ratio of hard carbon is x and the mass ratio of soft carbon is y, then the total capacity per unit area of the negative electrode is Q N = x×Q H + y×Q S , where 0 < x < 1, 0 < y < 1, and x + y = 1; define the limiting potential of the negative electrode sheet after full charge in the battery as m V, and the value range of m is 0.1~0.5V; define the capacity with the negative electrode potential greater than m V as the available capacity Q a , and the capacity with the negative electrode potential less than m V as the non-available capacity Q b , and the total negative electrode capacity Q = Q a + Q b ; define the total capacity of the positive electrode potential as Q P . Set the excess coefficient N of the available capacity Q a of the negative electrode compared to the positive electrode capacity Q P , and the value range of N is 0.9~1.1; when the capacity per unit area of the positive electrode sheet is Q P , from Q P = (x×Q Ha + y×Q Sa ) / N, calculate the available capacity Q Ha of hard carbon and the available capacity Q Sa of soft carbon; define the proportion of the capacity above m V in hard carbon as P H = Q Ha / (Q Ha + Q Hb ), and the proportion of the capacity above m V in soft carbon as P S = Q Sa / (Q Sa + Q Sb ), where Q Hb is the non-available capacity of hard carbon, and Q Sb is the non-available capacity of soft carbon; calculate the designed capacity Q N per unit area of the negative electrode = x×Q Ha / P H + y×Q Sa / P S .

5. The fast-charging sodium-ion battery design method as described in claim 4, characterized in that, When the positive electrode active material is a layered metal oxide, the value of m ranges from 0.05 to 0.2V; when the positive electrode active material is a polyanionic material or Prussian blue, the value of m ranges from 0.1 to 0.3V.

6. The fast-charging sodium-ion battery design method as described in claim 4, characterized in that, When the positive electrode contains layered metal oxides, the capacity Q per unit area of ​​the positive electrode sheet P = (95-95×R+110×w×R)×S, where R is the proportion of layered metal oxide in the positive electrode active material, 0≤R≤1; w is the capacity coefficient of layered metal oxide, 0.8≤w≤1.0; S is the positive electrode coefficient, which is related to the product of the positive electrode surface density and the proportion of positive electrode active material.

7. A sodium-ion battery, manufactured based on the fast-charging sodium-ion battery design method according to any one of claims 1 to 6, characterized in that, include: The outer shell has an internal diaphragm that divides the interior of the outer shell into a first space and a second space, and the first space and the second space each contain an electrolyte. A positive electrode plate is located in the first space; and a negative electrode plate is located in the second space.

8. The sodium-ion battery as described in claim 7, characterized in that, The material composition of the positive electrode sheet is: 94%~95% positive active material, 2%~3% conductive agent, and 2%~3% binder; the material composition of the negative electrode sheet is: 93%~94% negative active material, 2%~2.5% conductive agent, 1.5% CMC, and 2.5%~3% binder.

9. The sodium-ion battery as described in claim 7, characterized in that, The positive electrode has a bifacial surface density of 20-40 mg / cm², and the negative electrode has a surface density of 10-30 mg / cm².

10. The sodium-ion battery as described in claim 7, characterized in that, The charge / discharge voltage range of the sodium-ion battery is 2.0~3.9V.