Negative electrode slurry, negative electrode plate and preparation method

Abstract

The invention provides negative electrode slurry, a negative electrode plate and a preparation method, and belongs to the technical field of sodium ion batteries. Wherein the negative electrode slurry comprises a negative electrode active material, a first conductive agent, a second conductive agent, a dispersing agent and a binding agent; the negative active material is hard carbon; the first conductive agent is water-dispersed conductive slurry containing a nano conductive fiber carbon chain; the binder is styrene butadiene rubber emulsion; and in the negative electrode slurry, butadiene styrene rubber particles in the butadiene styrene rubber emulsion are filled in the three-dimensional frame structure of the nano conductive fiber carbon chain. The CNFC is added to be matched with the styrene-butadiene rubber, so that the styrene-butadiene rubber can be filled into a three-dimensional frame structure of the conductive nanofiber, and the high conductivity and good flexibility of the CNFC are utilized, so that the long-distance transmission of electrons among active substances of the pole piece is increased, and the conductivity is improved; and the butadiene styrene rubber is matched, so that long-distance connection and short-distance point connection among pole piece particles are effectively increased, and the conductivity and the processing performance of the hard carbon negative pole piece are comprehensively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a negative electrode slurry, a negative electrode sheet and a preparation method thereof. Background Art

[0002] In recent years, under the background of the global implementation of the "dual carbon" goal, electrochemical energy storage technology has developed rapidly and market demand has increased year by year. Electrochemical energy storage technology not only plays an important role in the utilization of renewable energy, the optimization of energy structure and environmental protection, but also has important significance for promoting energy transformation and reducing carbon emissions. Among many energy storage technologies, lithium-ion batteries (LIBs) dominate due to their high energy density and long cycle life. However, sodium-ion batteries (SIBs), as an emerging energy storage technology, have shown broad application prospects due to their unique advantages in raw material resource reserves, low cost, low temperature performance and safety performance, especially in the fields of large-scale energy storage and low-speed electric vehicles.

[0003] The core advantage of sodium-ion batteries lies in the selection of their electrode materials. Among them, hard carbon materials are widely considered to be the most likely negative electrode materials for sodium-ion batteries to be commercialized due to their low sodium storage potential, abundant carbon sources, low cost and mature technology. Although hard carbon negative electrode materials have many advantages in theory, they still face many challenges in practical applications. Due to the large specific surface area, high porosity, and surface defects and functional groups of hard carbon materials that are different from graphite, problems such as low peeling strength and severe powder floating on the surface of the pole pieces often occur during the preparation of the pole pieces. In addition, the intrinsic electronic conductivity of hard carbon materials is low, and it is difficult to fully infiltrate and disperse with the solvent during the pulping process, resulting in the conductive agent being unable to form a good conductive network, thereby affecting the overall performance of the battery.

[0004] In the prior art, some solutions have been proposed for the above-mentioned problems. For example, by adding PEDOT nanowires to the pole piece, the conductivity and flexibility of the negative electrode of the sodium ion battery are improved, thereby significantly improving its mechanical properties and cycle performance. However, the synthesis process of PEDOT nanowires is complicated and costly, which limits its application in large-scale production. In addition, conductive NCF / CB composite nanofibers were synthesized by electrostatic self-assembly and applied to the development of thick electrodes, achieving low cost, high flexibility and long-term stable cycle of the electrode. However, this technology has not conducted adaptability research based on the characteristics of different electrode materials. When applied to hard carbon materials, it may lead to a decrease in the compaction of the pole piece, thereby affecting the energy density of the battery cell.

[0005] Although the above-mentioned existing technologies have alleviated the application difficulties of hard carbon negative electrode materials to a certain extent, there are still many shortcomings. First, the materials and methods for improving conductivity and mechanical properties are often complex and costly, which is not conducive to large-scale production. Secondly, no adaptability research has been conducted on the unique characteristics of hard carbon materials, resulting in poor results of modified materials in practical applications. In addition, the solutions are mostly focused on improving a single performance indicator and fail to comprehensively improve the overall performance of sodium-ion batteries. For example, although conductivity and flexibility have been improved, in practical applications, it is often difficult to simultaneously meet the requirements of increasing the compaction of the electrode sheet, maintaining peel strength and flexibility, and solving the problem of powdering and material shedding of the negative electrode sheet, which seriously affects the cycle life and safety performance of the battery.

[0006] In summary, the main problems faced by existing sodium-ion battery negative electrode material technologies in practical applications include: the inability to solve the problem of easy powdering and material shedding of negative electrode sheets during processing while increasing the compaction of the electrode sheets and maintaining peeling strength and flexibility, resulting in difficulty in optimizing overall performance. Although existing technologies have made certain progress in improving the performance of hard carbon negative electrode materials, further research and optimization are still needed to solve various problems in practical applications and realize the widespread application of sodium-ion batteries in the field of energy storage. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a negative electrode slurry, comprising:

[0008] A negative electrode active material, a first conductive agent, a second conductive agent, a dispersant and a binder;

[0009] Wherein, the negative electrode active material is hard carbon; the first conductive agent is a water-dispersible conductive slurry containing nano-conductive fiber carbon chains; the binder is styrene-butadiene rubber latex;

[0010] In the negative electrode slurry, the styrene-butadiene rubber particles in the styrene-butadiene rubber emulsion are filled in the three-dimensional framework structure of the nano-conductive fiber carbon chain;

[0011] Preferably, the particle size of the styrene butadiene rubber particles in the styrene butadiene rubber emulsion is not greater than 200 nm;

[0012] Preferably, the solid content of the first conductive agent is 2wt% to 3wt%.

[0013] Preferably, the following components are included in parts by weight:

[0014] 90 to 95 parts of negative electrode active material;

[0015] 0.1 to 1 part of the first conductive agent;

[0016] 0.1 to 3 parts of the second conductive agent;

[0017] 1 to 2 parts of dispersant;

[0018] 1 to 3 parts of binder.

[0019] Preferably, the second conductive agent is selected from at least one of conductive carbon black, acetylene black and carbon nanotubes.

[0020] Preferably, the dispersant is sodium carboxymethyl cellulose powder.

[0021] Preferably, the solid content of the negative electrode slurry is 30wt% to 70wt%;

[0022] Preferably, the solid content of the negative electrode slurry is 43wt% to 55wt%.

[0023] Preferably, the viscosity of the negative electrode slurry is 800mPa.s to 10000mPa.s;

[0024] Preferably, the viscosity of the negative electrode slurry is 2000 mPa.s to 4000 mPa.s.

[0025] In addition, in order to solve the above problems, the present invention also provides a method for preparing the negative electrode slurry as described above, comprising:

[0026] Adding a dispersant into deionized water and dispersing the dispersant to obtain a dispersed colloid solution;

[0027] Adding a first conductive agent and a second conductive agent into the dispersed adhesive to obtain a conductive adhesive;

[0028] Adding the negative electrode active material to the conductive glue to knead it, and then adding a binder to mix to obtain a mixture;

[0029] Deionized water is added to the mixture to adjust the solid content and viscosity, and a vacuum defoaming treatment is performed to obtain the negative electrode slurry.

[0030] In addition, in order to solve the above problems, the present invention also provides a negative electrode sheet, comprising:

[0031] A negative electrode current collector, and a negative electrode active coating attached to the negative electrode current collector;

[0032] The negative electrode active coating is prepared from the negative electrode slurry as described above;

[0033] In the negative electrode active coating of the negative electrode plate, styrene-butadiene rubber particles as a binder are filled in the three-dimensional framework structure of nano-conductive fiber carbon chains as the first conductive agent.

[0034] Preferably, the negative electrode current collector comprises at least one of carbon-coated aluminum foil, double-glazed aluminum foil, carbon-coated copper foil, double-sided copper foil and etched aluminum foil.

[0035] In addition, in order to solve the above problems, the present invention also provides a method for preparing a negative electrode sheet, comprising:

[0036] Applying the negative electrode slurry as described above on the negative electrode current collector;

[0037] The negative electrode sheet is obtained by drying and rolling.

[0038] The present invention provides a negative electrode slurry, a negative electrode sheet and a preparation method. The negative electrode slurry comprises: a negative electrode active material, a first conductive agent, a second conductive agent, a dispersant and a binder; wherein the negative electrode active material is hard carbon; the first conductive agent is a water-dispersible conductive slurry containing nano-conductive fiber carbon chains; the binder is styrene-butadiene rubber latex; in the negative electrode slurry, styrene-butadiene rubber particles in the styrene-butadiene rubber latex are filled in the three-dimensional framework structure of the nano-conductive fiber carbon chains. The present invention adopts styrene-butadiene rubber particles and nano-conductive fiber carbon chains in the negative electrode slurry. On the one hand, the nano-conductive fiber carbon chain (CNFC) has a long chain structure and good charge transfer characteristics, can form a 3D network structure with high electron conduction, and can significantly improve the conductivity of the negative electrode plate of the sodium ion battery; on the other hand, since the chain CNFC rich in carboxyl groups has excellent hydrophilicity, it can promote the more uniform dispersion of active substances and conductive agent binders in the aqueous system; the styrene-butadiene rubber particles can be filled into the three-dimensional framework structure of the nano-conductive fiber carbon chain, which can increase the long-distance connection and short-distance point connection between the active substances, greatly increase the compaction, peeling strength and flexibility of the plate, and significantly improve the processing problem of powdering and falling of the hard carbon negative electrode plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a SEM image of the carbon nano-conductive fiber chain (CNFC) in the embodiment of the present application;

[0040] Figure 2 Schematic diagram of the process of preparing the negative electrode slurry in the embodiment of the present application;

[0041] Figure 3 This is a schematic diagram of the simulated structure of the negative electrode plate in the embodiment of the present application;

[0042] Figure 4 Schematic diagram of the process of preparing the negative electrode sheet in the embodiment of the present application.

[0043] Reference numerals:

[0044] 100, negative electrode plate; 1, negative electrode current collector; 2, negative electrode active coating; 21, styrene-butadiene rubber particles; 22, nano-conductive fiber carbon chain.

[0045] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0046] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] In the embodiment of the present application, the present invention provides a negative electrode slurry, comprising:

[0048] A negative electrode active material, a first conductive agent, a second conductive agent, a dispersant and a binder;

[0049] Wherein, the negative electrode active material is hard carbon; the first conductive agent is a water-dispersible conductive slurry containing nano-conductive fiber carbon chains; the binder is styrene-butadiene rubber latex;

[0050] In the negative electrode slurry, the styrene butadiene rubber particles in the styrene butadiene rubber emulsion are filled in the three-dimensional framework structure of the nano conductive fiber carbon chain.

[0051] The above-mentioned negative electrode slurry is used in the preparation of sodium ion batteries.

[0052] The components include negative electrode active material, a first conductive agent, a second conductive agent, a dispersant and a binder.

[0053] Specifically, the negative electrode active material can be hard carbon, the first conductive agent is a water-dispersible conductive slurry containing nano-conductive fiber carbon chain (CNFC), the binder is styrene-butadiene rubber emulsion (SBR), and the size of the particles in the styrene-butadiene rubber emulsion can be filled into the three-dimensional framework structure of the nano-conductive fiber carbon chain, so that in the negative electrode slurry, a composite structure or a composite form is formed in which the styrene-butadiene rubber particles in the styrene-butadiene rubber emulsion are filled in the three-dimensional framework structure of the nano-conductive fiber carbon chain, thereby further optimizing the performance of the electrode.

[0054] Among them, nano-conductive fiber carbon chain (CNFC) is a conductive material with a long chain structure. It is used in electrode materials due to its high electronic conductivity and mechanical flexibility.

[0055] CNFC not only has high electrochemical stability, but also has a rich surface carboxyl group and excellent hydrophilicity, which enables it to promote the uniform dispersion of active substances and conductive agents in aqueous systems and form an efficient 3D conductive network. This 3D network structure significantly improves the conductivity of the negative electrode of sodium ion batteries.

[0056] Specifically, refer to Figure 1 CNFC is a conductive fiber chain made by compounding nanocellulose and nanocarbon black through ultrasonic homogenization and other means. It has a high aspect ratio structure similar to carbon nanotubes, and has excellent electrochemical stability and mechanical flexibility. In addition, the nano conductive fiber carbon chain has abundant carboxyl groups and excellent hydrophilic processability.

[0057] Styrene butadiene rubber (SBR) is an elastomeric material, which is used in battery manufacturing in the present application embodiment because of its good mechanical properties and chemical stability. In the present application embodiment, the particle size of the rubber particles in the SBR emulsion is small, so that it can be filled into the three-dimensional framework structure of CNFC, increasing the peeling strength and flexibility of the pole piece. In addition, the combination of SBR and CNFC enables the pole piece to maintain a high mechanical strength during processing, preventing the problem of powdering and dropping.

[0058] In the negative electrode slurry, by adding CNFC and matching it with styrene butadiene rubber, the styrene butadiene rubber particles can be filled into the three-dimensional framework structure of the conductive nanofibers. The high conductivity and good flexibility of CNFC are used to increase the long-distance transmission of electrons between the active materials of the electrode piece to improve the conductivity. At the same time, the combination with styrene butadiene rubber effectively increases the long-distance connection and short-distance point connection between the electrode piece particles, comprehensively improving the conductivity and processing performance of the hard carbon negative electrode piece prepared further.

[0059] In summary, in the embodiment of the present application, styrene-butadiene rubber particles are used in combination with nano-conductive fiber carbon chains in the negative electrode slurry. On the one hand, the nano-conductive fiber carbon chain (CNFC) has a long chain structure and good charge transfer properties, and can form a 3D network structure with high electron conduction, which can significantly improve the conductivity of the negative electrode sheet of the sodium ion battery; on the other hand, due to the excellent hydrophilicity of the chain CNFC rich in carboxyl groups, the active substance and the conductive agent binder can be promoted to be more evenly dispersed in the aqueous system; the styrene-butadiene rubber particles are filled in the three-dimensional framework structure of the nano-conductive fiber carbon chain, which can increase the long-distance connection and short-distance point connection between the active substances, greatly increase the compaction, peeling strength and flexibility of the electrode sheet, and significantly improve the processing problem of powdering and falling off of the hard carbon negative electrode sheet.

[0060] Furthermore, the particle size of the styrene butadiene rubber particles in the styrene butadiene rubber emulsion is not greater than 200 nm;

[0061] As mentioned above, the particle size of the styrene butadiene rubber particles in the styrene butadiene rubber emulsion (SBR) used is not more than 200 nanometers, and the smaller particle size helps the styrene butadiene rubber particles to better penetrate and fill the three-dimensional network structure formed by the nano-conductive fiber carbon chain (CNFC). This filling effect can improve the bonding effect of the components in the slurry, enhance the contact between the active material and the current collector, and thus improve the structural stability and mechanical strength of the electrode.

[0062] Because the styrene-butadiene rubber particles can penetrate deep into the microstructure of CNFC, they are more evenly distributed in the electrode, which helps to form a more efficient electron conduction path. The small particle size of the binder can more accurately control the porosity and density in the electrode material, which is very important for the conductivity and electrochemical performance of the battery.

[0063] In the battery manufacturing process, the processing performance of electrode materials is an important consideration. Smaller particle size of styrene butadiene rubber particles can provide better rheology and coating properties, making it easier to evenly coat the slurry on the current collector and reducing defects that may occur during the manufacturing process, such as bubbles and uneven distribution.

[0064] Smaller styrene-butadiene rubber particles can provide denser bonding points at the microscopic scale, which helps improve the electrochemical stability and cycle life of the electrode. Such dense bonding points can effectively reduce the shedding of active materials during battery charging and discharging, especially under high-rate charging and discharging conditions.

[0065] Therefore, by optimizing the particle size of styrene-butadiene rubber particles to less than 200 nanometers, the battery performance can be improved while ensuring the stability and reliability of the battery under various conditions of use. This design is very critical in the research and development of high-performance battery materials and has a substantial driving effect on the realization of more efficient and stable sodium-ion batteries.

[0066] Furthermore, the solid content of the first conductive agent is 2 wt% to 3 wt%, for example, 2 wt%, 2.5 wt%, 3 wt%, etc.

[0067] Further, it includes the following components in parts by weight:

[0068] The negative electrode active material is 90 to 95 parts; for example, it can be 90 parts, 91 parts, 92 parts, 93 parts, 94 parts, 95 parts, etc.

[0069] The first conductive agent is 0.1 to 1 part; for example, it can be 0.1, 0.3, 0.5, 0.7, 0.9, 1, etc.

[0070] The second conductive agent is 0.1 to 3 parts; for example, it can be 0.1, 0.3, 0.5, 0.7, 0.9, 1, 2, 3, etc.

[0071] Dispersant 1 to 2 parts; for example, it can be 1 part, 2 parts, etc.

[0072] 1 to 3 parts of binder. For example, it can be 1 part, 2 parts, 3 parts, etc.

[0073] Furthermore, the second conductive agent is selected from at least one of conductive carbon black, acetylene black, and carbon nanotubes.

[0074] Furthermore, the dispersant is sodium carboxymethyl cellulose powder.

[0075] Furthermore, the solid content of the negative electrode slurry is 30 wt% to 70 wt%; for example, it can be 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt% and the like.

[0076] Furthermore, the solid content of the negative electrode slurry is 43 wt% to 55 wt%, for example, 43 wt%, 45 wt%, 50 wt%, 55 wt%, etc.

[0077] Furthermore, the viscosity of the negative electrode slurry is 800 mPa.s to 10000 mPa.s; for example, it may be 800 mPa.s, 1000 mPa.s, 1500 mPa.s, 2000 mPa.s, 3000 mPa.s, 5000 mPa.s, 7000 mPa.s, 9000 mPa.s, 1000 0 mPa.s, and the like.

[0078] Furthermore, the viscosity of the negative electrode slurry is 2000 mPa.s to 4000 mPa.s, for example, 2000 mPa.s, 3000 mPa.s, 4000 mPa.s, 5000 mPa.s, etc.

[0079] In addition, reference Figure 2 In an embodiment of the present application, a method for preparing the negative electrode slurry as described above is also provided, comprising:

[0080] Step S1, adding a dispersant into deionized water for dispersion to obtain a dispersed colloid solution;

[0081] Step S2, adding the first conductive agent and the second conductive agent into the dispersed adhesive to obtain a conductive adhesive;

[0082] Step S3, adding the negative electrode active material to the conductive glue for kneading, and then adding a binder and mixing to obtain a mixture;

[0083] As mentioned above, kneading treatment is a mixing process that physically mixes different components to ensure that each component is evenly distributed in the slurry.

[0084] By kneading, the first conductive agent (nano conductive fiber carbon chain) and the second conductive agent (such as conductive carbon black) can be evenly dispersed in the slurry to avoid local aggregation, thereby improving conductivity and mechanical properties.

[0085] During the kneading process, the binder (such as styrene-butadiene rubber) is fully mixed with the hard carbon and other components, which helps to enhance the bonding force of the pole piece and the stability of the overall structure.

[0086] Uniform mixing helps to improve the conductivity and mechanical strength of the electrode sheet, thereby improving the overall performance of the battery.

[0087] Step S4, adding deionized water to the mixture to adjust the solid content and viscosity, and performing vacuum defoaming treatment to obtain the negative electrode slurry.

[0088] As mentioned above, vacuum defoaming is a method of eliminating bubbles by reducing the gas content in the slurry.

[0089] During the slurry preparation process, mixing and stirring may introduce bubbles. The presence of bubbles will affect the uniformity and conductivity of the electrode, and may also cause defects in the electrode during the subsequent coating and drying process.

[0090] By vacuuming, the gas content in the slurry can be reduced, making it easier for the slurry to form high-density electrodes during coating and drying, thereby improving the energy density and cycle stability of the battery.

[0091] The presence of bubbles in the electrode may cause cracks or other defects in the electrode during subsequent battery assembly and use, affecting the safety and life of the battery.

[0092] In addition, reference Figure 3 In an embodiment of the present application, a negative electrode sheet is also provided, including:

[0093] A negative electrode current collector, and a negative electrode active coating attached to the negative electrode current collector;

[0094] The negative electrode active coating is prepared from the negative electrode slurry as described above;

[0095] In the negative electrode active coating of the negative electrode plate, styrene-butadiene rubber particles as a binder are filled in the three-dimensional framework structure of nano-conductive fiber carbon chains as the first conductive agent.

[0096] The negative electrode sheet includes two main parts: a negative electrode current collector and a negative electrode active coating. The negative electrode active coating is prepared from the negative electrode slurry, which contains styrene-butadiene rubber particles and nano-conductive fiber carbon chains. In the negative electrode active coating, the styrene-butadiene rubber particles as a binder are filled in the three-dimensional framework structure of the nano-conductive fiber carbon chain as the first conductive agent to form a three-dimensional spatial composite structure.

[0097] As mentioned above, nano-conductive fiber carbon chain (CNFC) has high conductivity and good flexibility, and can form a 3D network structure with high electron conduction. This structure helps to improve the overall conductivity of the negative electrode sheet, thereby improving the charge and discharge efficiency and rate performance of the battery.

[0098] As mentioned above, styrene-butadiene rubber is used as a binder to fill the three-dimensional framework structure of the nano-conductive fiber carbon chain, which helps to increase the long-distance connection and short-distance point connection between the active materials of the pole piece. This structure enhances the mechanical strength and flexibility of the pole piece and reduces the cracking and peeling of the pole piece during the battery charging and discharging process.

[0099] The combination of nano-conductive fiber carbon chain (CNFC) and styrene-butadiene rubber makes it easier to coat and roll the negative electrode during the preparation process, reduces the problem of powder shedding and material falling off the electrode, and improves the processing performance and production efficiency of the electrode.

[0100] By optimizing the use of conductive agents and binders, the internal resistance of the electrode can be reduced, the charging and discharging efficiency of the battery can be improved, and the cycle stability and life of the battery can be enhanced.

[0101] Styrene-butadiene rubber particles filled in the three-dimensional framework structure of CNFC help to form a more uniform and compact pole piece structure, reduce the porosity inside the pole piece, and thus improve the energy density and safety of the battery.

[0102] Compared with other conductive agents, such as PEDOT nanowires, the synthesis process of nano-conductive fiber carbon chain (CNFC) is relatively simple and low-cost, which helps to reduce the overall manufacturing cost of the battery.

[0103] The design of this negative electrode plate can adjust the ratio of conductive agent and binder according to different application requirements to meet different battery performance requirements, such as high rate, high energy density or long cycle life.

[0104] In summary, the design of this negative electrode sheet not only improves the electrochemical performance of the battery by optimizing the use of conductive agents and binders, but also enhances its mechanical properties and processing performance, and has broad application prospects.

[0105] Furthermore, the negative electrode current collector includes at least one of carbon-coated aluminum foil, double-glazed aluminum foil, carbon-coated copper foil, double-sided copper foil and etched aluminum foil.

[0106] In addition, reference Figure 4 The present application also provides a method for preparing a negative electrode sheet in an embodiment, comprising:

[0107] Step S5, coating the negative electrode slurry as described above on the negative electrode current collector;

[0108] Step S6, performing drying and rolling processing to obtain a negative electrode sheet.

[0109] In addition, in an embodiment of the present application, a battery is also provided, comprising the negative electrode plate in the aforementioned embodiment.

[0110] In addition, in an embodiment of the present application, an electrical device is also provided, including the battery in the aforementioned embodiment.

[0111] The present invention is further described below by means of specific examples, but it should be understood that these examples are only used for more detailed description and should not be construed as limiting the present invention in any form.

[0112] Embodiment 1:

[0113] This embodiment prepares negative electrode slurry and negative electrode sheet.

[0114] Experimental methods:

[0115] (1) Preparation of negative electrode slurry for sodium ion batteries:

[0116] The proportion of each solid component by weight is: 95.05 parts of negative electrode active material, 0.25 parts of first conductive agent, 1 part of second conductive agent, 1.2 parts of dispersant, and 2.5 parts of binder. The details are as follows:

[0117] In step S1, the 36 g dispersant is added to deionized water and uniformly dispersed to prepare a dispersed colloid solution with a certain solid content;

[0118] In step S2, 7.5 g of the first conductive agent nano-conductive fiber carbon chain and 30 g of the second conductive agent conductive carbon black are added to the dispersed adhesive solution of S1 and uniformly dispersed to obtain a conductive adhesive solution;

[0119] In step S3, 2851.5 g of hard carbon is added to the S2 conductive adhesive and kneaded, and then 187.5 g of a binder is added and stirred evenly at a low speed to obtain a mixture; wherein the binder is styrene-butadiene rubber emulsion; and the particle size of the styrene-butadiene rubber particles in the styrene-butadiene rubber emulsion is 170 to 180 nm;

[0120] In step S4, a proper amount of deionized water is added to adjust the viscosity to 2000-6000 mPa·s, and after vacuum defoaming, the negative electrode slurry is filtered using a 100-mesh sieve to obtain the negative electrode slurry.

[0121] (2) Preparation of negative electrode sheets for sodium ion batteries:

[0122] The negative electrode slurry was coated onto the copper foil, and the coating single surface density was controlled to 7 mg / cm 2 , dried at 60-120°C, cooled at room temperature, and rolled until the compaction density reaches 0.8-1.3 g / cc to obtain the negative electrode sheet.

[0123] Embodiment 2:

[0124] This embodiment prepares negative electrode slurry and negative electrode sheet.

[0125] Experimental methods:

[0126] It is basically the same as Example 1, except that:

[0127] The negative electrode active material was adjusted to 94.8 parts and the first conductive agent was adjusted to 0.5 parts.

[0128] (1) Preparation of negative electrode slurry:

[0129] The proportion of each solid component by weight is: 94.8 parts of negative electrode active material, 0.5 parts of first conductive agent, 1 part of second conductive agent, 1.2 parts of dispersant, and 2.5 parts of binder. The details are as follows:

[0130] In step S1, 36 g of the dispersant is added to deionized water and uniformly dispersed to prepare a dispersed colloid solution with a certain solid content;

[0131] In step S2, 15 g of the first conductive agent nano-conductive fiber carbon chain and 30 g of the second conductive agent conductive carbon black are added to the dispersed adhesive solution of S1, and uniformly dispersed to obtain a conductive adhesive solution;

[0132] In step S3, 2844 g of hard carbon is added to the S2 conductive adhesive for kneading, and then 187.5 g of a binder is added and stirred evenly at a low speed to obtain a mixture; wherein the binder is styrene-butadiene rubber emulsion; and the particle size of the styrene-butadiene rubber particles in the styrene-butadiene rubber emulsion is 180-190 nm;

[0133] Step S4 is the same as in Example 1.

[0134] (2) Preparation of negative electrode sheet: same as in Example 1.

[0135] Embodiment 3:

[0136] This embodiment prepares negative electrode slurry and negative electrode sheet.

[0137] Experimental methods:

[0138] It is basically the same as Example 1, except that:

[0139] The negative electrode active material was adjusted to 94.3 parts and the first conductive agent to 1 part.

[0140] (1) Preparation of negative electrode slurry:

[0141] The proportion of each solid component by weight is: 94.3 parts of negative electrode active material, 1 part of first conductive agent, 1 part of second conductive agent, 1.2 parts of dispersant, and 2.5 parts of binder. The details are as follows:

[0142] In step S1, 36 g of the dispersant is added to deionized water and uniformly dispersed to prepare a dispersed colloid solution with a certain solid content;

[0143] In step S2, 30 g of the first conductive agent nano-conductive fiber carbon chain and 30 g of the second conductive agent conductive carbon black are added to the dispersed adhesive solution of S1, and uniformly dispersed to obtain a conductive adhesive solution;

[0144] In step S3, 2829 g of hard carbon is added to the conductive adhesive solution S2 for kneading, and then 187.5 g of a binder is added and stirred evenly at a low speed to obtain a mixture; wherein the binder is styrene-butadiene rubber emulsion; and the particle size of the styrene-butadiene rubber particles in the styrene-butadiene rubber emulsion is 190 to 200 nm;

[0145] Step S4 is the same as in Example 1.

[0146] (2) Preparation of negative electrode sheet: same as in Example 1.

[0147] Embodiment 4:

[0148] This embodiment prepares negative electrode slurry and negative electrode sheet.

[0149] Experimental methods:

[0150] It is basically the same as Example 1, except that:

[0151] The negative electrode active material was adjusted to 93.3 parts and the first conductive agent to 2 parts.

[0152] (1) Preparation of negative electrode slurry:

[0153] The proportion of each solid component by weight is: 93.3 parts of negative electrode active material, 2 parts of first conductive agent, 1 part of second conductive agent, 1.2 parts of dispersant, and 2.5 parts of binder. The details are as follows:

[0154] In step S1, 36 g of the dispersant is added to deionized water and uniformly dispersed to prepare a dispersed colloid solution with a certain solid content;

[0155] In step S2, 60 g of the first conductive agent nano-conductive fiber carbon chain and 30 g of the second conductive agent conductive carbon black are added to the dispersed adhesive solution of S1, and uniformly dispersed to obtain a conductive adhesive solution;

[0156] In step S3, 2799 g of hard carbon is added to the conductive adhesive solution S2 for kneading, and then 187.5 g of a binder is added and stirred evenly at a low speed to obtain a mixture; wherein the binder is styrene-butadiene rubber emulsion; and the particle size of the styrene-butadiene rubber particles in the styrene-butadiene rubber emulsion is 140 to 150 nm;

[0157] Step S4 is the same as in Example 1.

[0158] (2) Preparation of negative electrode sheet: same as in Example 1.

[0159] Comparative Example 1:

[0160] In this comparative example, negative electrode slurry and negative electrode sheet were prepared.

[0161] Experimental methods:

[0162] It is basically the same as Example 1, except that:

[0163] In this comparative example, the first conductive agent nano conductive fiber carbon chain was not used.

[0164] (1) Preparation of negative electrode slurry:

[0165] The proportion of each solid component by weight is: 95.3 parts of negative electrode active material, 1 part of second conductive agent, 1.2 parts of dispersant, and 2.5 parts of binder. The details are as follows:

[0166] In step S1, 36 g of the dispersant is added to deionized water and uniformly dispersed to prepare a dispersed colloid solution with a certain solid content;

[0167] In step S2, 30 g of the second conductive agent, conductive carbon black, is added to the dispersed adhesive solution of S1 and uniformly dispersed to obtain a conductive adhesive solution;

[0168] In step S3, 2859 g of hard carbon is added to the S2 conductive adhesive solution for kneading, and then 187.5 g of a binder is added and stirred evenly at a low speed to obtain a mixture; wherein the binder is styrene-butadiene rubber emulsion; and the particle size of the styrene-butadiene rubber particles in the styrene-butadiene rubber emulsion is 140-150 nm;

[0169] Step S4 is the same as in Example 1.

[0170] (2) Preparation of negative electrode sheet: same as in Example 1.

[0171] Comparative Example 2:

[0172] In this comparative example, negative electrode slurry and negative electrode sheet were prepared.

[0173] Experimental methods:

[0174] It is basically the same as Example 1, except that:

[0175] In this comparative example, the first conductive agent nano conductive fiber carbon chain was not used.

[0176] (1) Preparation of negative electrode slurry:

[0177] The proportion of each solid component by weight is: 94.3 parts of negative electrode active material, 2 parts of second conductive agent, 1.2 parts of dispersant, and 2.5 parts of binder. The details are as follows:

[0178] In step S1, 36 g of the dispersant is added to deionized water and uniformly dispersed to prepare a dispersed colloid solution with a certain solid content;

[0179] In step S2, 60 g of the second conductive agent, conductive carbon black, is added to the dispersed adhesive solution of S1 and uniformly dispersed to obtain a conductive adhesive solution;

[0180] In step S3, 2829 g of hard carbon is added to the S2 conductive adhesive for kneading, and then 187.5 g of a binder is added and stirred evenly at a low speed to obtain a mixture; wherein the binder is styrene-butadiene rubber emulsion; and the particle size of the styrene-butadiene rubber particles in the styrene-butadiene rubber emulsion is 140-150 nm;

[0181] Step S4 is the same as in Example 1.

[0182] (2) Preparation of negative electrode sheet: same as in Example 1.

[0183] Comparative Example 3:

[0184] In this comparative example, negative electrode slurry and negative electrode sheet were prepared.

[0185] Experimental methods:

[0186] It is basically the same as Example 1, except that:

[0187] In this comparative example, conductive carbon black as the second conductive agent was not used.

[0188] (1) Preparation of negative electrode slurry:

[0189] The proportion of each solid component by weight is: 95.3 parts of negative electrode active material, 1 part of first conductive agent, 1.2 parts of dispersant, and 2.5 parts of binder. The details are as follows:

[0190] In step S1, 36 g of the dispersant is added to deionized water and uniformly dispersed to prepare a dispersed colloid solution with a certain solid content;

[0191] In step S2, 30 g of the first conductive agent nano-conductive fiber carbon chain is added to the dispersed adhesive solution of S1 and evenly dispersed to obtain a conductive adhesive solution;

[0192] In step S3, 2859 g of hard carbon is added to the S2 conductive adhesive solution for kneading, and then 187.5 g of a binder is added and stirred evenly at a low speed to obtain a mixture; wherein the binder is styrene-butadiene rubber emulsion; and the particle size of the styrene-butadiene rubber particles in the styrene-butadiene rubber emulsion is 140-150 nm;

[0193] Step S4 is the same as in Example 1.

[0194] (2) Preparation of negative electrode sheet: same as in Example 1.

[0195] Comparative Example 4:

[0196] In this comparative example, negative electrode slurry and negative electrode sheet were prepared.

[0197] Experimental methods:

[0198] It is basically the same as Example 1, except that:

[0199] In this comparative example, the first conductive agent nano conductive fiber carbon chain is not used to increase the binder content.

[0200] (1) Preparation of negative electrode slurry:

[0201] The proportion of each solid component by weight is: 94.8 parts of negative electrode active material, 1 part of second conductive agent, 1.2 parts of dispersant, and 3 parts of binder. The details are as follows:

[0202] In step S1, the 36 g dispersant is added to deionized water and uniformly dispersed to prepare a dispersed colloid solution with a certain solid content;

[0203] In step S2, 30 g of the second conductive agent, conductive carbon black, is added to the dispersed adhesive solution of S1 and uniformly dispersed to obtain a conductive adhesive solution;

[0204] In step S3, 2844 g of hard carbon is added to the conductive adhesive solution S2 for kneading, and then 225 g of a binder is added and stirred evenly at a low speed to obtain a mixture; wherein the binder is styrene-butadiene rubber emulsion; and the particle size of the styrene-butadiene rubber particles in the styrene-butadiene rubber emulsion is 140 to 150 nm;

[0205] Step S4 is the same as in Example 1.

[0206] Comparative Example 5:

[0207] In this comparative example, negative electrode slurry and negative electrode sheet were prepared.

[0208] Experimental methods:

[0209] It is basically the same as Example 1, except that:

[0210] The negative electrode active material was adjusted to 94.3 parts, the first conductive agent was adjusted to 1 part, and the styrene-butadiene rubber was adjusted to have a particle size of 500 nm.

[0211] (1) Preparation of negative electrode slurry:

[0212] The proportion of each solid component by weight is: 94.3 parts of negative electrode active material, 1 part of first conductive agent, 1 part of second conductive agent, 1.2 parts of dispersant, and 2.5 parts of binder. The details are as follows:

[0213] In step S1, the 36 g dispersant is added to deionized water and uniformly dispersed to prepare a dispersed colloid solution with a certain solid content;

[0214] In step S2, 30g of the first conductive agent nano-conductive fiber carbon chain and 30g of the second conductive agent conductive carbon black are added to the dispersed adhesive solution of S1 and uniformly dispersed to obtain a conductive adhesive solution;

[0215] In step S3, 2829 g of hard carbon is added to the S2 conductive adhesive and kneaded, and then 187.5 g of a binder is added and stirred evenly at a low speed to obtain a mixture; wherein the binder is styrene-butadiene rubber latex; and the particle size of the styrene-butadiene rubber particles in the styrene-butadiene rubber latex is 500-550 nm.

[0216] Step S4 is the same as in Example 1.

[0217] (2) Preparation of negative electrode sheet: same as in Example 1.

[0218] Horizontal comparison test:

[0219] Test method:

[0220] The dispersion state of the negative electrode slurry, the conductivity of the electrode sheet and the peeling force in the above Examples 1 to 4 and Comparative Examples 1 to 5 were tested respectively.

[0221] Test results and analysis:

[0222] Table 1. Test data of slurry fineness, electrode conductivity and peeling force in the examples and comparative examples

[0223] Instance Number Slurry fineness <![CDATA[Polar strip strength (N m -1 )]]> <![CDATA[Polar plate conductivity (S cm -1 )]]> <![CDATA[Electrode compaction (g / cm 3 )]]> Example 1 10 6.5 <![CDATA[5.2×10 -2 ]]> 0.95 Example 2 10 8.6 <![CDATA[5.8×10 -2 ]]> 0.95 Example 3 10 14.2 <![CDATA[6.5×10 -2 ]]> 0.95 Example 4 10 16 <![CDATA[5.5×10 -2 ]]> 0.93 Comparative Example 1 15 5.5 <![CDATA[4.5×10 -2 ]]> 0.95 Comparative Example 2 15 5.4 <![CDATA[5.1×10 -2 ]]> 0.95 Comparative Example 3 10 8 <![CDATA[4.8×10 -2 ]]> 0.95 Comparative Example 4 15 6.8 <![CDATA[4.3×10 -2 ]]> 0.95 Comparative Example 5 10 4.5 <![CDATA[5×10 -2 ]]> 0.9

[0224] (1) It can be seen from Table 1 that, compared with Comparative Example 1, the addition of nano-conductive fiber carbon chains to the negative electrode in Examples 1 and 3 can improve the conductivity of the electrode sheet, and the peel strength of the electrode sheet is significantly improved;

[0225] (2) It can be seen from Comparative Example 4 that when the addition amount of nano-conductive fiber chain is 2%, the peeling force is not significantly improved. Even when it is combined with small-particle styrene-butadiene rubber, the compaction density of the electrode is also reduced. This may be due to the influence of the three-dimensional framework structure of the conductive agent. The compaction of the electrode is reduced, the conductive agent and the active material cannot be in close contact, and the conductivity of the electrode is reduced.

[0226] (3) Comparative Examples 2 and 3 do not use the first conductive agent nano-conductive fiber carbon chain. Compared with Example 1, Example 1 uses nano-conductive fiber carbon chain, which has better conductivity. The first conductive agent nano-conductive fiber carbon chain and conductive carbon black are used in combination to reduce the amount of conductive carbon black used.

[0227] (4) Compared with Examples 1, 2, and 3 and Comparative Examples 1 and 4, adding nano-conductive fiber carbon chains to the negative electrode can improve the electrode peeling strength and appropriately reduce the content of the binder.

[0228] (5) In the embodiment, the adhesive is a styrene-butadiene rubber emulsion, which contains styrene-butadiene rubber particles, and the particle size of the styrene-butadiene rubber particles is not greater than 200 nm. The corresponding pole piece compaction value, the average value of embodiments 1 to 4 basically reaches 0.945 g / cm 3 In Comparative Example 5, since the particle size of the styrene-butadiene rubber particles is 500 nm, the electrode compaction is greatly reduced to 0.90 g / cm 3 ; It is explained that the pole pieces prepared in Examples 1 to 4 are due to the fact that the styrene butadiene rubber particles in the styrene butadiene rubber emulsion can be filled into the three-dimensional framework structure of the nano-conductive fiber carbon chain to form an embedded composite structure, resulting in a high degree of compaction, while in Comparative Example 5, since the styrene butadiene rubber particles exceed the particle size of 200nm and reach 500nm, such an embedded composite structure is not formed, resulting in the styrene butadiene rubber particles not being filled into the three-dimensional framework structure of the nano-conductive fiber carbon chain, but being outside the three-dimensional framework structure of the nano-conductive fiber carbon chain, resulting in a decrease in the compaction of the pole piece.

[0229] In summary, in the hard carbon negative electrode slurry, the nano conductive fiber carbon chain cooperates with the small particle size styrene butadiene rubber to significantly enhance the peeling strength of the electrode sheet while improving the conductivity of the electrode sheet.

[0230] The above are preferred implementation modes and corresponding embodiments of the present invention. It should be pointed out that, for those skilled in the art, without departing from the creative concept of the present invention, several modifications and improvements may be made, including but not limited to the adjustment of proportions, processes, dosages and reaction vessels, which all fall within the scope of protection of the present invention.

Claims

1. A negative electrode slurry, characterized in that: include: A negative electrode active material, a first conductive agent, a second conductive agent, a dispersant and a binder; Wherein, the negative electrode active material is hard carbon; the first conductive agent is a water-dispersible conductive slurry containing nano-conductive fiber carbon chains; the binder is styrene-butadiene rubber latex; In the negative electrode slurry, the styrene-butadiene rubber particles in the styrene-butadiene rubber emulsion are filled in the three-dimensional framework structure of the nano-conductive fiber carbon chain; Preferably, the particle size of the styrene butadiene rubber particles in the styrene butadiene rubber emulsion is not greater than 200 nm; Preferably, the solid content of the first conductive agent is 2wt% to 3wt%.

2. The negative electrode slurry according to claim 1, characterized in that: The negative electrode slurry includes the following components in parts by weight: 90 to 95 parts of negative electrode active material; 0.1 to 1 part of the first conductive agent; 0.1 to 3 parts of the second conductive agent; 1 to 2 parts of dispersant; 1 to 3 parts of binder.

3. The negative electrode slurry according to claim 1, characterized in that: The second conductive agent is selected from at least one of conductive carbon black, acetylene black and carbon nanotubes.

4. The negative electrode slurry according to claim 1, characterized in that: The dispersant is sodium carboxymethyl cellulose powder.

5. The negative electrode slurry according to claim 1, characterized in that: The solid content of the negative electrode slurry is 30wt% to 70wt%; Preferably, the solid content of the negative electrode slurry is 43wt% to 55wt%.

6. The negative electrode slurry according to claim 1, characterized in that: The viscosity of the negative electrode slurry is 800mPa.s to 10000mPa.s; Preferably, the viscosity of the negative electrode slurry is 2000 mPa.s to 4000 mPa.s.

7. A method for preparing the negative electrode slurry according to any one of claims 1 to 6, characterized in that: include: Adding a dispersant into deionized water and dispersing the dispersant to obtain a dispersed colloid solution; Adding a first conductive agent and a second conductive agent into the dispersed adhesive to obtain a conductive adhesive; Adding the negative electrode active material to the conductive glue to knead it, and then adding a binder to mix to obtain a mixture; Deionized water is added to the mixture to adjust the solid content and viscosity, and a vacuum defoaming treatment is performed to obtain the negative electrode slurry.

8. A negative electrode plate, characterized in that: include: A negative electrode current collector, and a negative electrode active coating attached to the negative electrode current collector; The negative electrode active coating is prepared from the negative electrode slurry according to any one of claims 1 to 6; In the negative electrode active coating of the negative electrode plate, styrene-butadiene rubber particles as a binder are filled in the three-dimensional framework structure of nano-conductive fiber carbon chains as the first conductive agent.

9. The negative electrode sheet according to claim 8, characterized in that: The negative electrode current collector comprises at least one of carbon-coated aluminum foil, double-glazed aluminum foil, carbon-coated copper foil, double-sided copper foil and etched aluminum foil.

10. A method for preparing a negative electrode sheet, characterized in that: include: Applying the negative electrode slurry according to any one of claims 1 to 6 on the negative electrode current collector; The negative electrode sheet is obtained by drying and rolling.

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