Sodium ion soft package battery negative electrode slurry and preparation process thereof

Abstract

The invention relates to sodium ion soft package battery negative electrode slurry and a preparation process thereof, and belongs to the technical field of battery material preparation. The process comprises the following steps: mixing, dispersing and stirring sodium carboxymethyl cellulose (CMC) and water to form uniform slurry; adding a water-based carbon nanotube CNT into the slurry, and continuously dispersing and stirring; adding conductive carbon black SP and stirring; adding the main material hard carbon and stirring; and finally, adding a binder styrene butadiene rubber emulsion SBR, stirring, defoaming, and cooling to obtain the sodium ion soft package battery negative electrode slurry. Wherein the mass ratio of CMC to water is less than 0.6%, the mass ratio of CNT to water is less than 2.5%, the mass ratio of SP to water is less than 1.8%, the mass ratio of hard carbon to water is greater than 1.0, and the mass ratio of SBR to water is greater than 6%. The negative electrode slurry prepared by the invention can be used for preparing a sodium ion soft package battery negative electrode, and has the advantages of simple preparation process, low cost, stable performance and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and more particularly to a sodium ion soft-pack battery negative electrode slurry and a preparation process thereof. Background Art

[0002] With the increasing depletion of fossil fuels and the emergence of global environmental issues, renewable energy sources such as solar, tidal, wind, biomass, and geothermal energy have garnered increasing attention. To effectively utilize these intermittent energy sources, the development of excellent large-scale electrical energy storage devices is crucial. The development of clean and efficient energy storage systems has become a research hotspot. Sodium-ion batteries (SIBs) are considered an ideal alternative to lithium-ion batteries due to their abundant resources and low cost. In SIB systems, the selection and preparation of anode materials have a decisive influence on the overall battery performance. As a well-established electrochemical energy storage device, SIBs are widely used in portable electronic devices and electric vehicles due to their excellent energy and power performance. However, the intensive consumption of lithium resources inevitably increases their cost, hindering the practical application of SIBs in large-scale stationary applications. Thanks to the similar electrochemical properties of sodium and lithium and the abundance of sodium resources on Earth (2.36 wt%), SIBs have emerged as a viable alternative, rivaling LIBs in performance. In recent years, research has focused on developing high-performance cathode and anode materials for SIBs. In general, four categories of anode materials have been developed, including hard carbon materials, alloys, metal sulfides, and transition metal oxides. Among these materials, hard carbon has become the most attractive choice for sodium-ion pouch batteries (SIBs) due to its abundant resources, low sodium intercalation plateau, and good cycling stability.

[0003] However, as hard carbon materials composed of non-graphitizable structures, they generally have poor electrical conductivity, which hinders further improvement of their cycle and rate performance. Therefore, improving the conductivity of hard carbon materials is an effective strategy to improve their negative electrode performance. Since carbon nanotubes can form interconnected conductive networks and porous structures, the introduction of carbon nanotubes to connect hard carbon to form a composite negative electrode material with enhanced conductivity can better improve the cycle stability and rate performance, which is of great significance for the development of sodium-ion soft-pack batteries.

[0004] Currently, hard carbon materials have become one of the main choices for sodium-ion battery anode materials due to their high specific capacity, good cycle stability, and low cost. However, hard carbon materials inherently have poor electrical conductivity, which greatly limits the rate capability and cycle stability of sodium-ion batteries. To improve the electrochemical performance of hard carbon anode materials, it is usually necessary to add conductive agents and binders to the slurry and improve the conductive network structure of the electrode by optimizing the slurry preparation process.

[0005] In the prior art, CN116207257A discloses an aqueous negative electrode slurry for sodium-ion batteries. This slurry is prepared by mixing hard carbon, a spherical nano-scale conductive agent (Super-P), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a specified mass ratio using deionized water as a solvent, using a high-speed shear disperser. This method produces a uniformly dispersed negative electrode slurry with good cycle stability, but it does not provide a specific solution to the conductivity issues of the hard carbon material.

[0006] CN113161525A discloses a method for preparing negative electrode slurry for lithium-ion batteries. This method involves grading graphite into particle sizes and then adding a CMC aqueous gel and an SBR emulsion in stages to improve the dispersion and bonding properties of the slurry. However, this method primarily targets graphite negative electrode materials for lithium-ion batteries and does not consider the specific requirements of hard carbon negative electrodes for sodium-ion batteries.

[0007] CN111697194A proposes a method for preparing a silicon-carbon anode slurry. By selecting a carbon fiber composite (CMC) with a specific DS value and molecular weight, its hydrophobic groups effectively adsorb and coat the active material and conductive carbon black particles, forming a stable slurry. While this method improves the dispersion and adhesion of the electrode material, it still does not address the fundamental problem of poor conductivity of hard carbon materials.

[0008] CN118016846A discloses a rate-sensitive sodium-ion battery anode slurry and its preparation method. This method, by introducing CNT slurry and PAA glue, addresses the low viscosity and sieving difficulties of hard carbon slurry, thereby improving the battery's rate and cycle performance. However, this method is complex and lacks optimization of the CNT dispersion process, potentially resulting in inadequate conductive network construction.

[0009] CN116014135A describes a method for preparing negative electrode slurry for lithium-ion batteries. By adding CMC in two parts—one as a dry powder and the other as a gel solution—the dispersibility and stability of the slurry are improved. However, this method does not consider the effect of the conductive agent dispersion order on the formation of the electrode conductive network.

[0010] In summary, existing methods for preparing negative electrode slurries for sodium-ion batteries have the following shortcomings: First, they fail to effectively address the poor conductivity of hard carbon materials, limiting the battery's rate performance and cycling stability. Second, existing methods lack a rational sequence for the addition and dispersion of the conductive agent, making it difficult to form an ideal conductive network structure. Therefore, there is an urgent need to develop a process for preparing negative electrode slurries for sodium-ion soft-pack batteries that can effectively improve the conductivity of hard carbon materials and optimize the conductive network structure, thereby enhancing the overall performance of sodium-ion batteries. Summary of the Invention

[0011] In order to solve the technical problem that hard carbon materials have poor conductivity as negative electrode materials for sodium ion soft-pack batteries, which hinders further improvement of their cycle and rate performance, the purpose of the present invention is to propose a negative electrode slurry for sodium ion soft-pack batteries and a preparation process thereof. By introducing aqueous carbon nanotubes to construct a three-dimensional conductive network, the conductivity of the hard carbon negative electrode material is significantly improved to solve the problems raised in the above background technology.

[0012] To achieve the above objectives, the present invention is implemented through the following technical means: In a first aspect, the present invention discloses a process for preparing a negative electrode slurry for a sodium ion soft-pack battery, comprising the following steps: Step 1: mix sodium carboxymethyl cellulose (CMC) and water and disperse and stir to form a uniform slurry; Step 2: Add water-based carbon nanotubes (CNT) to the slurry and continue to disperse and stir for a period of time; Step 3: Add a certain amount of conductive carbon black SP to the slurry obtained in the previous step and stir for a period of time; Step 4: Add the main ingredient, hard carbon, to the slurry in step 3 and stir again; Step 5: Finally, add the binder styrene-butadiene rubber emulsion SBR, stir to remove bubbles, and cool to obtain the negative electrode slurry for the sodium ion soft-pack battery.

[0013] In some embodiments, the mass ratio of sodium carboxymethyl cellulose (CMC) to water in step 1 is less than 0.6%, and the dispersion stirring time of sodium carboxymethyl cellulose (CMC) and water in step 1 is not less than 1.5 h.

[0014] In some embodiments, the mass ratio of the aqueous carbon nanotubes (CNT) to water in step 2 is less than 2.5%, and the dispersion and stirring time in step 2 is not less than 0.5 h.

[0015] In some embodiments, the mass ratio of the conductive carbon black SP to water in step 3 is less than 1.8%, and the time for the dispersion and stirring in step 3 is not less than 1 hour.

[0016] In some embodiments, the mass ratio of the main ingredient hard carbon to water in step 4 is greater than 1.0, and the time for dispersing and stirring in step 4 is not less than 2 hours.

[0017] In some embodiments, the mass ratio of the binder styrene-butadiene rubber emulsion SBR to water in step 5 is greater than 6%, and the stirring and defoaming time in step 5 is not less than 1 hour.

[0018] In a second aspect, the present invention discloses a negative electrode slurry for a sodium ion soft-pack battery, which is prepared using the above-mentioned preparation process.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The present invention proposes a set of innovative solutions to the core problems faced in the industrialization process of sodium-ion batteries, such as low efficiency in constructing the electrode conductive network, significant polarization effect, and insufficient adaptability to large-scale production. This technology introduces an aqueous carbon nanotube (CNT) conductive system to construct a negative electrode slurry preparation process with multiple technical advantages. It can form a three-dimensional conductive network between active substances (such as hard carbon), significantly reduce the internal resistance of the electrode, and improve the efficiency of electron transfer. Compared with the traditional negative electrode slurry that only uses conductive carbon black, the negative electrode slurry of the present invention has lower electrode internal resistance and higher electron conduction efficiency; CNT can achieve the same or even better conductive effect with a lower addition amount (0.5%-2%), thereby reducing the amount of conductive carbon black added, thereby freeing up more space for active substances and improving energy density. Experiments have shown that the process of the present invention can produce The prepared negative electrode slurry can increase the battery energy density by 5%-10% under the same total amount of conductive additives; and the CNT network can shorten the Na+ diffusion path, reduce polarization, and improve rate performance. The sodium ion soft-pack battery prepared by this process can achieve a capacity retention rate of more than 1.5 times that of the traditional process at a 3C rate; the aqueous CNT slurry can be directly applied to existing coating equipment without modification, is suitable for large-scale production, reduces the cost and difficulty of process implementation, and has good industrial application prospects. Therefore, the present invention is a key step in promoting the industrialization process of sodium ion batteries and provides important technical support for building a green energy system. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is a diagram of the cycle performance of the negative electrode slurry of the sodium ion soft-pack battery prepared in Example 1.

[0020] Figure 2 This is a rate performance diagram of the negative electrode slurry for the sodium ion soft-pack battery prepared in Example 1. DETAILED DESCRIPTION The following detailed description of the embodiments of the technical solution of this application is provided in conjunction with the accompanying drawings. The following embodiments and drawings are intended only to more clearly illustrate the technical solution of this application and are therefore provided as examples only and are not intended to limit the scope of protection of this application. The accompanying drawings schematically illustrate only the parts relevant to the technical solution of this application and do not represent the actual structure of the product.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0022] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two), similarly, "multiple groups" refers to more than two (including two), and "multiple pieces" refers to more than two (including two).

[0023] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0024] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0025] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they should not be understood as limiting the embodiments of the present application.

[0026] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0027] In this embodiment, in a first aspect, the present invention discloses a process for preparing a negative electrode slurry for a sodium ion soft-pack battery, comprising the following steps: Step 1: mix sodium carboxymethyl cellulose (CMC) and water and disperse and stir to form a uniform slurry; Step 2: Add water-based carbon nanotubes (CNT) to the slurry and continue to disperse and stir for a period of time; Step 3: Add a certain amount of conductive carbon black SP to the slurry obtained in the previous step and stir for a period of time; Step 4: Add the main ingredient, hard carbon, to the slurry in step 3 and stir again; Step 5: Finally, add the binder styrene-butadiene rubber emulsion SBR, stir to remove bubbles, and cool to obtain the negative electrode slurry for the sodium ion soft-pack battery.

[0028] In some embodiments, the mass ratio of sodium carboxymethyl cellulose (CMC) to water in step 1 is less than 0.6%, and the dispersion stirring time of sodium carboxymethyl cellulose (CMC) and water in step 1 is not less than 1.5 h.

[0029] In some embodiments, the mass ratio of the aqueous carbon nanotubes (CNT) to water in step 2 is less than 2.5%, and the dispersion and stirring time in step 2 is not less than 0.5 h.

[0030] In some embodiments, the mass ratio of the conductive carbon black SP to water in step 3 is less than 1.8%, and the time for the dispersion and stirring in step 3 is not less than 1 hour.

[0031] In some embodiments, the mass ratio of the main ingredient hard carbon to water in step 4 is greater than 1.0, and the time for dispersing and stirring in step 4 is not less than 2 hours.

[0032] In some embodiments, the mass ratio of the binder styrene-butadiene rubber emulsion SBR to water in step 5 is greater than 6%, and the stirring and defoaming time in step 5 is not less than 1 hour.

[0033] In a second aspect, the present invention discloses a negative electrode slurry for a sodium ion soft-pack battery, which is prepared using the above-mentioned preparation process.

[0034] A process for preparing a negative electrode slurry for a sodium ion soft-pack battery comprises the following steps: Step 1: Mix sodium carboxymethyl cellulose (CMC) and water and disperse and stir to form a uniform slurry; at room temperature, use a stirring device to disperse and stir until the sodium carboxymethyl cellulose (CMC) is completely dissolved to form a uniform slurry; Step 2: Add water-based carbon nanotubes (CNT) to the slurry and continue to disperse and stir for a period of time; use a stirring device to disperse and stir to ensure that the water-based carbon nanotubes (CNT) are evenly dispersed in the slurry to form a stable suspension; Step 3: Add a certain amount of conductive carbon black SP to the slurry obtained in the previous step and stir for a period of time to ensure that the conductive carbon black SP is evenly dispersed in the slurry to form a stable suspension; Step 4: Add the main ingredient, hard carbon, to the slurry in step 3 and stir again; use a stirring device to disperse and stir at a certain speed to ensure that the main ingredient, hard carbon, is evenly dispersed in the slurry to form a stable suspension; Step 5: Finally, add the binder styrene-butadiene rubber latex (SBR), stir to remove bubbles, and cool to obtain the negative electrode slurry for the sodium ion soft-pack battery. In this step, use a stirring device to stir at a certain speed, then remove bubbles under vacuum conditions, and finally cool the slurry to 25°C to obtain the negative electrode slurry for the sodium ion soft-pack battery.

[0035] The present invention is further described below with reference to specific embodiments.

[0036] Example 1 (1) Mix 5.64 g of sodium carboxymethyl cellulose (CMC) with 1000 g of water and disperse at 500 rpm for 10 min, then at 1500 rpm for 2 h to form a uniform slurry; (2) Add 22.56 g of aqueous carbon nanotubes (CNT) to the above slurry and continue to disperse at a speed of 1500 rpm for 40 minutes; (3) Add 16.92 g of conductive carbon black SP to the slurry obtained in the previous step and stir at 1500 rpm for 1 h; (4) Add 1076.92 g of hard carbon as the main ingredient to the slurry in step 3 and disperse it again at a speed of 1500 rpm for 2 h.

[0037] (5) Finally, add 60.49 g of the binder styrene-butadiene rubber latex SBR, stir at 300 rpm for 1 h, and then defoam at a low speed of 60 rpm for 30 min.

[0038] Example 2 (1) Mix 5.64 g of sodium carboxymethyl cellulose (CMC) with 1000 g of water and disperse at 500 rpm for 10 min, then at 1500 rpm for 2 h to form a uniform slurry; (2) Add 16.92 g of conductive carbon black SP to the slurry obtained in the previous step and stir at 1500 rpm for 1 h; (3) Add 1076.92 g of hard carbon as the main ingredient to the slurry in step 2 and disperse it again at a speed of 1500 rpm for 2 h.

[0039] (4) Finally, add 60.49 g of the binder styrene-butadiene rubber latex SBR, stir at 300 rpm for 1 h, and then defoam at a low speed of 60 rpm for 30 min.

[0040] See also Figure 1 The sodium ion soft-pack battery prepared in Example 1 was subjected to a cycle performance test. As can be seen from the data in the figure, in the early stage (0-1000 cycles), the capacity retention rate dropped rapidly from nearly 100% to about 90%, and the decay slope was steep. It is speculated that this may be due to the initial decay caused by irreversible reactions such as SEI film formation and initial structural adjustment of active substances; in the middle stage (1000-3000 cycles), the decay slope slowed down significantly, and the capacity retention rate dropped from 90% to about 85%, indicating that the battery system gradually stabilized, irreversible reactions decreased, and cycle stability improved; in the late stage (3000-3690 cycles), the decay rate slowed down further, and the capacity retention rate finally remained above 80%, indicating that the battery still retained a high effective capacity after long-term cycling.

[0041] After 3690 cycles, the capacity retention rate still exceeded 80%, demonstrating excellent long-term cycling stability. The "fast at first, slow later" decay rate pattern is consistent with the general mechanism of battery cycling, namely, interface reconstruction in the initial stage and dynamic equilibrium in the later stage. The high capacity maintained at a high cycle number indicates that the sodium-ion soft-pack battery has a good structural design, interface compatibility, and material stability, which can support long-term cycling applications.

[0042] In summary, although the capacity of the sodium-ion soft-pack battery continues to decay during 3690 cycles, the decay rate gradually slows down, and it still retains a high capacity retention rate after long-term cycling, showing good cycle performance and long-life application potential.

[0043] See also Figure 2The sodium-ion soft-pack battery prepared in Example 1 was subjected to a cycle performance test. The slope was uniform throughout the entire process: from 100% at the beginning to -82% after 847 cycles, there was no stage-by-stage mutation in the decay process (such as fast in the early stage and a sudden drop in the later stage). This shows that at a 3C rate, the battery's attenuation mechanisms such as interface reaction (such as SEI film growth) and active material loss are continuous but stable, and there is no "cumulative structural damage" such as electrode pulverization and electrolyte depletion. The kinetic loss under high current does not amplify sharply with the cycle, and the system compatibility is good. In the early stage (0-200 cycles), the capacity dropped from 100% to 95%, and the decay was slightly faster due to the initial interface reconstruction and the initial formation of the SEI film; in the middle and late stages (200-847 cycles), the decay slope slowed down and remained stable, indicating that the interface has reached dynamic equilibrium and the decay has entered a "linear stage." After 847 3C cycles, the capacity retention rate is still over 80%, highlighting two major advantages. First, 3C is a "fast charging level" rate, with a charging and discharging time of about 20 minutes. Under this condition, the cycle life reaches 800+ cycles, indicating that the battery has high charging and discharging efficiency, small polarization, excellent dynamic performance, and high adaptability; second, it can support high-power scenarios such as power tools, fast charging energy storage, and high-frequency charging and discharging systems, reducing the life loss caused by the rate and expanding the scope of use.

[0044] In summary, the sodium-ion soft-pack battery exhibits "gentle decay and long-term stability" cycling characteristics at a high rate of 3C, which not only verifies the system's tolerance to large currents, but also provides performance support for fast charging and high-power applications, reflecting good rate cycle compatibility.

[0045] The specific embodiments disclosed in the present invention fall within the scope of protection of the claims of the present invention and are the specific lower implementation scope of the characteristic part of the present invention. The protection content of the specific embodiments is only an explanation of the protection scope of the claims of the present invention. The protection scope of the present invention is not limited to the protection content of the specific embodiments, and the protection content of the specific embodiments should not be understood as limiting the protection scope of the claims of the present invention. The product structure connection relationship that falls within the protection scope of the present invention falls within the protection content of the present invention; without departing from the protection essence of the present invention, conventional technical improvements to the structure of product components, such as improvements to the product structure in the specific embodiments of the present invention, will also fall within the protection essence of the present invention.

Claims

1. A process for preparing a negative electrode slurry for a sodium ion soft-pack battery, characterized in that: The following steps are involved: Step 1: mix sodium carboxymethyl cellulose (CMC) and water and disperse and stir to form a uniform slurry; Step 2: Add water-based carbon nanotubes (CNT) to the slurry and continue to disperse and stir for a period of time; Step 3: Add a certain amount of conductive carbon black SP to the slurry obtained in the previous step and stir for a period of time; Step 4: Add the main ingredient, hard carbon, to the slurry in step 3 and stir again; Step 5: Finally, add the binder styrene-butadiene rubber emulsion SBR, stir to remove bubbles, and cool to obtain the negative electrode slurry for the sodium ion soft-pack battery.

2. The process for preparing a negative electrode slurry for a sodium ion soft-pack battery according to claim 1, wherein: The mass ratio of sodium carboxymethyl cellulose (CMC) to water in step 1 is less than 0.6%, and the dispersion stirring time of sodium carboxymethyl cellulose (CMC) and water in step 1 is not less than 1.5 h.

3. The process for preparing a negative electrode slurry for a sodium ion soft-pack battery according to claim 1, wherein: In the step 2, the mass ratio of the aqueous carbon nanotubes CNT to water is less than 2.5%, and the time of the dispersion and stirring in the step 2 is not less than 0.5 h.

4. The process for preparing a negative electrode slurry for a sodium ion soft pack battery according to claim 1, wherein: In the step 3, the mass ratio of the conductive carbon black SP to water is less than 1.8%, and the time of the dispersion and stirring in the step 3 is not less than 1 h.

5. The process for preparing a negative electrode slurry for a sodium ion soft-pack battery according to claim 1, wherein: The mass ratio of the main material hard carbon to water in step 4 is greater than 1.0, and the time of dispersion and stirring in step 4 is not less than 2 hours.

6. The process for preparing a negative electrode slurry for a sodium ion soft-pack battery according to claim 1, wherein: The mass ratio of the binder styrene-butadiene rubber emulsion SBR to water in the step 5 is greater than 6%, and the stirring and defoaming time in the step 5 is not less than 1 h.

7. A sodium ion soft pack battery negative electrode slurry, characterized by: The invention is prepared by the preparation process according to any one of claims 1 to 6.

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