Composite conductive agent, negative electrode sheet, and sodium-ion battery thereof

Abstract

The application discloses a composite conductive agent, a negative plate and a sodium ion battery thereof, and the composite conductive agent comprises: first conductive carbon black and second conductive carbon black, which are mixed with each other, the BET specific surface area of the first conductive carbon black is smaller than that of the second conductive carbon black, the D50 average particle size of the particles of the first conductive carbon black is larger than that of the second conductive carbon black, the ratio M of the D50 average particle size of the first conductive carbon black to the D50 average particle size of the second conductive carbon black is 5-15, the BET specific surface area of the first conductive carbon black is 50 m2 / g-100 m2 / g, the BET specific surface area of the second conductive carbon black is 200 m2 / g-300 m2 / g, and the second conductive carbon black accounts for 5%-50% of the total amount of the composite conductive agent in terms of mass. Through the combination and synergy of the first conductive carbon black and the second conductive carbon black, a three-dimensional conductive network with high efficient electron permeability and excellent mechanical stability can be constructed under the premise of significantly reducing the total addition amount of the conductive carbon black.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a composite conductive agent, a negative electrode sheet, and a sodium-ion battery thereof. Background Technology

[0002] Sodium-ion battery hard carbon anodes typically suffer from numerous problems, including high porosity, poor conductivity, and significant volume changes due to sodium ion insertion / extraction, leading to electrode expansion. Given the porous nature and large volume variations of sodium-ion battery hard carbon anodes, single-component conductive carbon black is insufficient to balance the permeability, stability, and electrochemical stability of the conductive network at low addition levels. Using only large-particle conductive carbon black can result in poor localized conductive contact and insufficient inter-particle point contact; while using only small-particle conductive carbon black leads to low conductive network strength, making it prone to collapse during expansion and contraction, and the high specific surface area can trigger more side reactions, reducing capacity retention. Summary of the Invention

[0003] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, one object of the present invention is to propose a composite conductive agent, a negative electrode sheet and its sodium-ion battery, which can construct a three-dimensional conductive network with both high electronic permeability and excellent mechanical stability while significantly reducing the total amount of conductive carbon black added.

[0004] According to a first aspect of the present invention, the composite conductive agent comprises: a first conductive carbon black and a second conductive carbon black, wherein the first conductive carbon black and the second conductive carbon black are mixed together, the BET specific surface area of ​​the first conductive carbon black is smaller than that of the second conductive carbon black, the BET specific surface area of ​​the first conductive carbon black is 50 m² / g to 100 m² / g, and the BET specific surface area of ​​the second conductive carbon black is 200 m² / g to 300 m² / g; the D50 average particle size of the first conductive carbon black particles is larger than that of the second conductive carbon black particles, and the ratio M of the D50 average particle size of the first conductive carbon black particles and the D50 average particle size of the second conductive carbon black particles is 5 to 15; and the second conductive carbon black accounts for 5% to 50% of the total amount of the composite conductive agent by mass.

[0005] Optionally, the average D50 particle size of the first conductive carbon black is 50 nm to 200 nm, and the average D50 particle size of the second conductive carbon black is 10 nm to 50 nm.

[0006] Optionally, the second conductive carbon black accounts for 15% to 25% of the total amount of the composite conductive agent by mass.

[0007] According to a second aspect of the present invention, a negative electrode sheet includes: a current collector, the current collector being a plate-shaped component; and a coating layer disposed on the outside of the current collector, the coating layer being composed of a hard carbon base material, a composite conductive agent, and a binder, wherein the composite conductive agent is a composite conductive agent according to any one of the above descriptions.

[0008] Optionally, the coating layer is divided into a first coating layer and a second coating layer. The first coating layer is disposed on one side of the current collector in its thickness direction, and the second coating layer is disposed on the other side of the current collector in its thickness direction. The areal densities of the first coating layer and the second coating layer are different.

[0009] Optionally, the areal density of the first coating layer is 5.8 mg / cm³. 2 ~6.5mg / cm 2 The areal density of the second coating layer is 6.1 mg / cm³. 2 ~6.8 mg / cm 2 .

[0010] Optionally, the hard carbon main material has a BET specific surface area of ​​5m² / g to 12m² / g, a pH value of 7 to 11, a porosity of 20% to 40%, a particle size D10 of 0.5 to 2.5, a D50 of 4.5 to 6.5, and a D90 of 9 to 11.

[0011] Optionally, the adhesive is a mixture of SBR and CMC, with the ratio of SBR to CMC being 1.0 to 2.0:1 by mass.

[0012] Optionally, the ratio of the hard carbon, the binder, and the composite conductive agent by mass is 95:4.3:0.7.

[0013] According to a third aspect of the present invention, a sodium-ion battery includes any of the negative electrode sheets described above.

[0014] The composite conductive agent according to the embodiments of this application combines a first conductive carbon black and a second conductive carbon black. Through the combination and synergy of the first and second conductive carbon blacks, a three-dimensional conductive network with both high electronic permeability and excellent mechanical stability can be constructed in the hard carbon anode of sodium-ion batteries while significantly reducing the total amount of conductive carbon black added. The composite conductive agent for the hard carbon anode of sodium-ion batteries according to the embodiments of this application can effectively improve the initial coulombic efficiency, reversible capacity, rate performance, and long cycle life at low / high rates of sodium-ion batteries. Moreover, the preparation process is simple and suitable for mass production.

[0015] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a comparison diagram of the negative electrode film resistance of Example 1 and Comparative Example 1; Figure 2 This is a comparison graph of the 1C long cycle life of Example 1 and Comparative Example 1; Figure 3 This is a comparison chart of the 3C high-rate long cycle life of Example 1 and Comparative Example 1. Detailed Implementation

[0017] The composite conductive agent for a hard carbon negative electrode of a sodium-ion battery according to embodiments of the present invention will be described in detail below.

[0018] The composite conductive agent according to embodiments of this application includes: a first conductive carbon black and a second conductive carbon black. The composite conductive agent can be used in the hard carbon anode of sodium-ion batteries.

[0019] Specifically, a first conductive carbon black and a second conductive carbon black are mixed together. The BET specific surface area of ​​the first conductive carbon black is smaller than that of the second conductive carbon black. The BET specific surface area of ​​the first conductive carbon black is 50 m² / g to 100 m² / g, and that of the second conductive carbon black is 200 m² / g to 300 m² / g. The average D50 particle size of the first conductive carbon black particles is larger than that of the second conductive carbon black particles. The ratio M of the average D50 particle size of the first conductive carbon black particles to that of the second conductive carbon black particles is 5 to 15. By mass, the second conductive carbon black accounts for 5% to 50% of the total amount of the composite conductive agent.

[0020] In other words, the composite conductive agent for the hard carbon anode of sodium-ion batteries according to the embodiments of this application uses a combination of a first conductive carbon black and a second conductive carbon black. That is, the conductive agent of the hard carbon anode of this application is a composite conductive agent, which is formed by physical mixing of at least two kinds of conductive carbon black. The two kinds of conductive carbon black have differences in specific surface area and average particle size of primary particle D50.

[0021] Specifically, the BET specific surface area of ​​the first conductive carbon black is smaller than that of the second conductive carbon black. The BET specific surface area of ​​the first conductive carbon black is 50 m² / g to 100 m² / g, for example, 50 m² / g, 60 m² / g, 70 m² / g, 80 m² / g, 90 m² / g, or 100 m² / g, etc.; the BET specific surface area of ​​the second conductive carbon black is 200 m² / g to 300 m² / g, for example, 200 m² / g, 210 m² / g, 220 m² / g, 250 m² / g, 280 m² / g, or 300 m² / g, etc. If the BET specific surface area of ​​the first conductive carbon black or the second conductive carbon black is too high, it can easily lead to an increase in side reactions and a decrease in capacity retention.

[0022] Furthermore, the average D50 particle size of the first conductive carbon black particles is larger than that of the second conductive carbon black particles. Specifically, the ratio M of the average D50 particle size of the first conductive carbon black and the second conductive carbon black is between 5 and 15, for example, a ratio of 5:1, 8:1, 9:1, 10:1, 12:1, or 15:1. The larger particles of the first conductive carbon black form a framework that prevents the overall network from collapsing, while the smaller particles of the second conductive carbon black fill the gaps, ensuring localized conductivity without dead zones. In this embodiment, by limiting the ratio of the average D50 particle size of the first and second conductive carbon black particles, superior performance can be achieved in both physical filling and electrical contact.

[0023] Understandably, if the ratio M of the average D50 particle size of the first conductive carbon black and the average D50 particle size of the second conductive carbon black is less than 5, the particle size difference between the two conductive carbon blacks is too small. This results in a low effectiveness of the small particles of the second conductive carbon black embedding into the pores formed by the accumulation of large particles of the first conductive carbon black. The small particles of the second conductive carbon black act as a "filler," leading to higher porosity of the negative electrode, limited point contact between particles, and minimal improvement in the density and strength of the conductive network. Conversely, if the ratio M of the average D50 particle size of the first conductive carbon black and the average D50 particle size of the second conductive carbon black is greater than 15, the small particles of the second conductive carbon black are too small. Although they can enter the pores, their extremely high surface energy makes them prone to agglomeration, resulting in uneven dispersion and difficulty in improving conductivity. Furthermore, excessively small particles (ultra-high specific surface area) exacerbate side reactions in the electrolyte and hinder effective electron transport between large particles.

[0024] In this embodiment, by limiting the ratio M of the average D50 particle size of the first conductive carbon black to 5-15, the small particles can be precisely embedded in the most probable pore size formed by the accumulation of large particles, forming a "suspended dense" stacked structure. The most probable pore size is the diameter of the most numerous and predominant pores within the material. A ratio M of 5-15 not only increases the contact points between the conductive agents but also, to a certain extent, supports the electrode structure, preventing displacement of the conductive network when the hard carbon negative electrode of the sodium-ion battery expands.

[0025] It should be noted that if only large-particle single conductive carbon black is used, local contact is poor; if only small-particle single conductive carbon black is used, network strength is low and side reactions are high. In this embodiment, the first conductive carbon black and the second conductive carbon black are mixed together. The large-particle first conductive carbon black can transport electrons over long distances (low-resistance path), while the small-particle second conductive carbon black can collect charges and transfer at the interface. The division of labor between the first and second conductive carbon black can significantly improve the overall conductivity efficiency. Due to the efficient filling of the small-particle second conductive carbon black, there is no need to use excessive amounts of high specific surface area conductive carbon black. The composite conductive agent for the hard carbon anode of sodium-ion batteries in this embodiment can construct a highly stable conductive network for the hard carbon anode of sodium-ion batteries with high porosity and large volume expansion with a low amount of composite conductive carbon black.

[0026] In addition, by mass, the proportion of the second conductive carbon black in the total amount of the composite conductive agent is 5% to 50%, for example, the proportion of the second conductive carbon black in the total amount of the composite conductive agent is 5%, 10%, 15%, 20%, 30%, 40% or 50%, which is beneficial to the stability of the conductive network and the electrochemical stability.

[0027] Understandably, if the proportion of small particles (high specific surface area second conductive carbon black) is less than 5%, their quantity is insufficient to fill all the critical node pores in the skeleton of the large-particle first conductive carbon black. In local areas, electron transport still relies on long-distance jumps between large particles, resulting in high contact resistance. In high-rate discharge scenarios, this conductive network will rapidly deteriorate due to excessive local current density, which is detrimental to improving the rate performance of the cell. On the other hand, if the proportion of small particles is greater than 50%, on the one hand, the network skeleton is prone to disappearance, and the entire conductive network loses the mechanical support and main conductive path provided by the large particles; on the other hand, side reactions are prone to runaway. Small particles have a high specific surface area, and an excessively high proportion means a dramatic increase in the contact area between the electrode and the electrolyte, which will exacerbate the formation of the solid electrolyte interfacial film, consume more sodium ions, and lead to a further reduction in the initial coulombic efficiency, and the cycle life will also decrease accordingly.

[0028] In this embodiment, the first conductive carbon black has the characteristics of large particle size and low specific surface area, while the second conductive carbon black has the characteristics of small particle size and high specific surface area. It is evident that by using the large-particle-size, low-specific-surface-area first conductive carbon black as the structural framework, mechanical support and a long-range conductive path can be provided; simultaneously, the small-particle-size, high-specific-surface-area second conductive carbon black is used as a filler, penetrating deep into the pores and providing dense contact points. The synergistic effect of the first and second conductive carbon blacks reduces the total amount of slurry carbon black added to the hard carbon anode of sodium-ion batteries, improving the battery's initial efficiency and reversible capacity. Furthermore, the capacity retention rate is significantly improved after long cycles at low / high rates, far superior to single-component or conventional mixed solutions. This solves the inherent challenge of constructing a conductive network for hard carbon anodes, achieving an optimal balance between "improving initial efficiency" and "ensuring capacity." In other words, the composite conductive agent can construct a highly stable conductive network for the high-porosity, large-volume-expansion sodium-ion battery hard carbon anode with a low amount of composite conductive carbon black added.

[0029] The composite conductive agent for the hard carbon anode of sodium-ion batteries according to the embodiments of this application can construct a highly stable conductive network for the hard carbon anode of sodium-ion batteries with high porosity and large volume expansion with low addition amount of composite conductive carbon black. This can improve the initial efficiency and reversible capacity of sodium-ion batteries. Moreover, the capacity retention rate of sodium-ion batteries after long cycles at low / high rates is also significantly improved, which is far superior to single-component or conventional mixed solutions. This not only greatly reduces costs and increases capacity, but also solves the inherent problem of conductive network construction of hard carbon anodes, achieving a balance between "improving initial efficiency" and "ensuring capacity".

[0030] Therefore, the composite conductive agent for the hard carbon anode of sodium-ion batteries according to the embodiments of this application combines a first conductive carbon black and a second conductive carbon black. Through the combination and synergy of the first and second conductive carbon blacks, a three-dimensional conductive network with both high electronic permeability and excellent mechanical stability can be constructed in the hard carbon anode of sodium-ion batteries while significantly reducing the total amount of conductive carbon black added. The composite conductive agent for the hard carbon anode of sodium-ion batteries according to the embodiments of this application can effectively improve the initial coulombic efficiency, reversible capacity, rate performance, and long cycle life at low / high rates of sodium-ion batteries, and the preparation process is simple and suitable for mass production.

[0031] According to one embodiment of this application, the average D50 particle size of the first conductive carbon black is 50 nm to 200 nm, for example, the average D50 particle size of the first conductive carbon black is 50 nm, 60 nm, 70 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm or 200 nm, etc.; the average D50 particle size of the second conductive carbon black is 10 nm to 50 nm, for example, the average D50 particle size of the second conductive carbon black is 10 nm, 20 nm, 30 nm, 40 nm or 50 nm, etc.

[0032] Understandably, on the one hand, if only 50 nm to 200 nm first conductive carbon black is used without second conductive carbon black, there is a technical problem that the gaps between particles are large, and many areas on the surface of the active material cannot be covered. On the other hand, if only 10 nm to 50 nm second conductive carbon black is used without first conductive carbon black, there is a technical problem that although the coverage is high, it is prone to agglomeration and the "bridging" efficiency is low. Furthermore, by simultaneously satisfying that the average D50 particle size of the first conductive carbon black is 50 nm to 200 nm and the average D50 particle size of the second conductive carbon black is 10 nm to 50 nm, it is beneficial to achieve an average particle size of the second conductive carbon black that is an order of magnitude smaller than that of large particles (e.g., 1 / 5 to 1 / 2), which is beneficial to accurately fill the gaps between the particles with the second conductive carbon black, increase electron transport efficiency, and reduce resistance. In addition, the average D50 particle size of the first conductive carbon black is 50 nm to 200 nm. That is, the particle size of the first conductive carbon black is large enough to be stably "anchored" between hard carbon particles to act as a conductive network skeleton. With a small number of such particles, a long-range conductive framework covering the entire electrode can be built.

[0033] According to one embodiment of this application, the second conductive carbon black accounts for 15% to 25% of the total composite conductive agent by weight. It is understood that hard carbon itself has abundant pores, requiring small particles to penetrate these pores for "charge collection." If the content of the small-particle second conductive carbon black is less than 15%, the capacity deep within the hard carbon is difficult to release effectively; if the content of the small-particle second conductive carbon black is greater than 25%, although the surface conductivity is excellent, the micropores inside the hard carbon are easily blocked by excessive carbon black, hindering the diffusion of sodium ions. In this embodiment, by limiting the proportion of the second conductive carbon black to 15% to 25% of the total composite conductive agent, the large-particle first conductive carbon black can provide basic conductivity, and by controlling the amount of small-particle second conductive carbon black at 15% to 25%, a balance between performance and side reactions can be achieved.

[0034] This application also provides a negative electrode sheet, comprising: a current collector and a coating layer. The current collector is a plate-shaped component, and the coating layer is disposed on the outer side of the current collector. The coating layer is composed of a hard carbon base material, a composite conductive agent, and a binder. The composite conductive agent is a composite conductive agent according to any of the above embodiments. That is, the hard carbon base material, the composite conductive agent, and the binder can be prepared into a slurry, and the slurry can be coated onto the current collector to form a hard carbon negative electrode. Since the composite conductive agent is a composite conductive agent according to any of the above embodiments, a highly stable conductive network can be constructed for the hard carbon negative electrode of sodium-ion batteries with high porosity and large volume expansion with a low amount of composite conductive carbon black. The negative electrode sheet according to the embodiments of this application can be used as a hard carbon negative electrode for sodium-ion batteries.

[0035] According to the embodiments of this application, the hard carbon anode of the sodium-ion battery has advantages such as "structural adaptability, abundant resources, and comprehensive performance", which can meet the core requirements of sodium-ion batteries for anode materials that are "able to hold sodium, can be fast charged, have a long lifespan, and are low in cost".

[0036] According to one embodiment of this application, the coating layer is divided into a first coating layer and a second coating layer. The first coating layer is disposed on one side of the current collector in its thickness direction, and the second coating layer is disposed on the other side of the current collector in its thickness direction. The first and second coating layers are formed by coating with slurry, respectively, and the areal densities of the first and second coating layers are different. In this embodiment, by using a different areal density of the first and second coating layers, for example, the areal density of the first coating layer is less than that of the second coating layer, microscopic asymmetry can be created to compensate for the asymmetric stress during the manufacturing (drying) and use (charge and discharge expansion) processes of the battery, thereby achieving better wetting, lower cracking risk, and longer cycle life.

[0037] In some specific embodiments of this application, the areal density of the first coating layer is 5.8 mg / cm³. 2 ~6.5mg / cm 2 For example, the areal density of the first coating layer is 5.8 mg / cm³. 2 5.9 mg / cm 2 6.0 mg / cm 2 6.2 mg / cm 2 6.3 mg / cm 2 Or 6.5 mg / cm 2 The areal density of the second coating layer is 6.1 mg / cm³. 2 ~6.8 mg / cm 2 For example, the areal density of the second coating layer is 6.1 mg / cm³. 2 6.2 mg / cm 2 6.4 mg / cm 2 6.5 mg / cm2 6.6 mg / cm 2 Or 6.8 mg / cm 2 It is understandable that coating density affects the uniformity of active material distribution and the structural stability of the electrode. If the coating density is too low, the active material distribution will be uneven, easily leading to localized overheating or undercooling within the electrode, accelerating battery aging and performance degradation. Conversely, while a coating density that is too high can provide higher capacity, it also increases electrode stress, leading to electrode material detachment and structural damage, thus affecting the battery's cycle life. In this embodiment, a suitable areal density range of 5.8 mg / cm² is used. 2 ~6.8 mg / cm 2 It can provide optimal cycle performance and safety performance while ensuring battery capacity.

[0038] According to one embodiment of this application, the BET specific surface area of ​​the hard carbon base material is 5m² / g to 12m² / g, for example, the BET specific surface area of ​​the hard carbon base material is 5m² / g, 6m² / g, 8m² / g, 10m² / g or 12m² / g, etc.; the pH value is 7 to 11, for example, pH value is 7, 8, 9, 10 or 11, etc.; the porosity is 20% to 40%, for example, porosity is 20%, 22%, 25%, 30%, 35% or 40%, etc.; the particle size D10 is 0.5 to 2.5, for example, particle size D10 is 0.5, 1.0, 1.5, 2.0 or 2.5, etc.; the D50 is 4.5 to 6.5, for example, D50 is 4.5, 4.8, 5.0, 5.5, 6.0 or 6.5, etc.; the D90 is 9 to 11, for example, D90 is 9, 10 or 11, etc. After assembling the negative electrode of this embodiment into a battery, the battery was tested. The initial 0.1C charge capacity was 360~385mAh / g, and the initial coulombic efficiency was 85%~91%. In this embodiment, the BET specific surface area of ​​the hard carbon main material is 5m² / g~12m² / g, which is relatively low for hard carbon materials, resulting in advantages such as high initial coulombic efficiency, excellent processing performance, and long cycle life. The porosity is 20%~40%, meaning the BET is 5-12, while the porosity is as high as 20-40%, indicating that most of these pores are macropores or mesopores, rather than micropores that consume BET. In addition, the particle size D10 is 0.5~2.5, which can improve energy density, enhance electrode compaction and flexibility, and reduce resistance. Furthermore, the pH value is 7~11, which is weakly alkaline and compatible with CMC, reducing the risk of battery swelling. The initial charge capacity at 0.1C can reach 360mAh / g to 385mAh / g, and the initial coulombic efficiency can reach 85% to 91%, indicating excellent electrochemical performance and minimal energy density loss of the full battery.

[0039] In some specific embodiments of this application, the binder is a mixture of SBR and CMC, with the ratio of SBR to CMC by mass being 1.0 to 2.0:1. For example, the ratio of SBR to CMC by mass is 1:1, 1.2:1, 1.5:1, 1.8:1, or 2:1, etc. It is understood that, on the one hand, if SBR or CMC is used alone, that is, if either binder is used alone, it is easy to have shortcomings. For example, if only CMC is used, the electrode is prone to cracking and powdering during high-pressure compaction due to brittleness; while if only SBR is used, the lack of dispersion function will easily lead to a large degree of sedimentation of the slurry, making it difficult to coat. In this embodiment, by using SBR and CMC together, a synergistic system with stable dispersion, strong adhesion, and flexibility and crack resistance is formed.

[0040] In addition, using a mixture of SBR and CMC as a binder also has advantages for the composite conductive agent in the embodiments of this application. Specifically, when the electrode undergoes volume expansion and contraction during charging and discharging, the rigid CMC framework can maintain the basic configuration of the conductive network without collapsing, while the flexible SBR network can buffer stress, preventing electrode cracking and powder shedding, thereby protecting the fine conductive pathways constructed by conductive carbon black from being destroyed. These advantages enable excellent cycle stability, ultimately achieving a balance between high energy density and long cycle life.

[0041] According to one embodiment of this application, the ratio of hard carbon, binder, and composite conductive agent is 95:4.3:0.7. That is, the binder is a mixture of SBR and CMC, and the ratio of SBR to CMC is 1.0~2.0:1; the composite conductive agent is composite conductive carbon black; the three are dry-mixed in a ratio of 95:4.3:0.7 to form a slurry for coating.

[0042] In this embodiment, by adopting the above-mentioned formulation, it is beneficial to achieve high capacity and long cycle life. While ensuring electrode processing performance and structural stability, it maximizes the capacity and first-cycle efficiency of the hard carbon anode, while also considering rate performance. Specifically, 95% hard carbon ensures high energy density, 4.3% binder (especially utilizing the elasticity of SBR) provides strong structural support to cope with the volume expansion of hard carbon, and 0.7% ultra-low composite conductivity agent balances energy density and cost-effectiveness without sacrificing rate performance.

[0043] In addition, by adopting the above formula, the advantages of "high efficiency and low dosage" of "composite conductive agent conductive carbon black" can be fully utilized, demonstrating the advantages of low addition amount of composite conductive agent, extremely high conductivity and strong structural adaptability.

[0044] This application also provides a sodium-ion battery, including the hard carbon negative electrode of the sodium-ion battery of any of the above embodiments, which can improve the battery's initial coulombic efficiency and long cycle life at low / high rates.

[0045] The sodium-ion battery of this application will be described in detail below with reference to specific embodiments.

[0046] Example 1 In Example 1, a first conductive carbon black and a second conductive carbon black were mixed, with a mass ratio of first conductive carbon black to second conductive carbon black of 4:1. The specific surface area of ​​the first conductive carbon black was 65 m² / g, the specific surface area of ​​the second conductive carbon black was 235 m² / g, the average D50 particle size of the first conductive carbon black was 100 nm, the average D50 particle size of the second conductive carbon black was 15 nm, and M=6.67.

[0047] Hard carbon base material, binder, and composite conductive agent were dry-mixed in a ratio of 95:4.3:0.7 to prepare a slurry. The negative electrode slurry was then coated onto the current collector, and the areal density of the first coating layer was 6.2 mg / cm³. 2 The areal density of the second coating layer is 6.5 mg / cm³. 2 Hard carbon anodes are prepared and then assembled into the required sodium-ion batteries by combining them with appropriate cathodes, separators, electrolytes and other auxiliary materials.

[0048] Comparative Example 1 In Comparative Example 1, single conductive carbon black was selected as the conductive agent. The specific surface area of ​​the single conductive carbon black was 65 m² / g, and the average D50 particle size of the single conductive carbon black was 100 nm.

[0049] Hard carbon base material, binder, and single conductive carbon black were dry-mixed in a ratio of 94.3:4.3:1.4 to prepare a slurry. The negative electrode slurry was then coated onto the current collector. The areal density of the first coating layer was 6.2 mg / cm³. 2 The areal density of the second coating layer is 6.5 mg / cm³. 2 A hard carbon negative electrode was prepared and assembled into a sodium-ion battery corresponding to Comparative Example 1 by combining it with the same positive electrode, separator, electrolyte and other auxiliary materials as in Example 1.

[0050] The sodium-ion batteries of Example 1 and Comparative Example 1 were tested respectively, and the test results are as follows: Figures 1 to 3As shown, the composite conductive agent for the hard carbon anode of sodium-ion batteries according to the embodiments of this application can effectively reduce the film resistance of the hard carbon anode sheet of sodium-ion batteries, and improve the initial coulombic efficiency and long cycle life at low / high rates. Furthermore, compared to Example 1, the proportions of hard carbon main material, binder, and single conductive carbon black in Comparative Example 1 are different, which verifies the excellent performance achieved by adding half the amount of composite conductive agent in Example 1. Specifically, the amount of composite conductive agent added in Example 1 is 0.7%, while the amount of conductive carbon black added in Comparative Example 1 is 1.4%. Example 1 achieves excellent battery performance even with half the amount of conductive agent added.

[0051] In summary, the composite conductive agent for the hard carbon anode of sodium-ion batteries according to the embodiments of this application combines a first conductive carbon black and a second conductive carbon black. Adding this composite conductive agent to the hard carbon anode of the sodium-ion battery can significantly reduce the total amount of conductive carbon black by half (e.g., 0.5%~1%), while constructing a three-dimensional conductive network in the hard carbon anode of the sodium-ion battery that simultaneously possesses high electron permeability and excellent mechanical stability. The composite conductive agent for the hard carbon anode of sodium-ion batteries according to the embodiments of this application can effectively reduce the film resistance of the hard carbon anode sheet of the sodium-ion battery while reducing costs and increasing capacity, thereby improving the battery's initial coulombic efficiency and long cycle life at low / high rates. Furthermore, the preparation process is simple and suitable for mass production.

[0052] Other configurations and operations of the battery according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here.

[0053] In the description of this invention, it should be understood that the terms "center", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "inner", "outer", "circumferential", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0054] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0055] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0056] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A composite conductive agent, characterized in that, The composite conductive agent includes: A first conductive carbon black and a second conductive carbon black are mixed together. The BET specific surface area of ​​the first conductive carbon black is smaller than that of the second conductive carbon black. The BET specific surface area of ​​the first conductive carbon black is 50 m² / g to 100 m² / g, and the BET specific surface area of ​​the second conductive carbon black is 200 m² / g to 300 m² / g. The average D50 particle size of the first conductive carbon black particles is larger than that of the second conductive carbon black particles. The ratio M of the average D50 particle size of the first conductive carbon black particles and the average D50 particle size of the second conductive carbon black particles is 5 to 15. By mass, the second conductive carbon black accounts for 5% to 50% of the total amount of the composite conductive agent.

2. The composite conductive agent according to claim 1, characterized in that, The first conductive carbon black has an average D50 particle size of 50 nm to 200 nm, and the second conductive carbon black has an average D50 particle size of 10 nm to 50 nm.

3. The composite conductive agent according to claim 1, characterized in that, By mass, the second conductive carbon black accounts for 15% to 25% of the total amount of the composite conductive agent.

4. A negative electrode sheet, characterized in that, include: A current collector, wherein the current collector is a plate-shaped component; A coating layer is disposed on the outside of the current collector. The coating layer is composed of a hard carbon base material, a composite conductive agent, and a binder. The composite conductive agent is a composite conductive agent according to any one of claims 1-3.

5. The negative electrode sheet according to claim 4, characterized in that, The coating layer is divided into a first coating layer and a second coating layer. The first coating layer is disposed on one side of the current collector in its thickness direction, and the second coating layer is disposed on the other side of the current collector in its thickness direction. The areal densities of the first coating layer and the second coating layer are different.

6. The negative electrode sheet according to claim 5, characterized in that, The areal density of the first coating layer is 5.8 mg / cm³. 2 ~6.5mg / cm 2 The areal density of the second coating layer is 6.1 mg / cm³. 2 ~6.8 mg / cm 2 .

7. The negative electrode sheet according to claim 4, characterized in that, The hard carbon main material has a BET specific surface area of ​​5m² / g to 12m² / g, a pH value of 7 to 11, a porosity of 20% to 40%, a particle size of D10 of 0.5 to 2.5, D50 of 4.5 to 6.5, and D90 of 9 to 11.

8. The negative electrode sheet according to claim 4, characterized in that, The adhesive is a mixture of SBR and CMC, with the ratio of SBR to CMC being 1.0~2.0:1 by mass.

9. The negative electrode sheet according to claim 8, characterized in that, The ratio of the hard carbon, the binder, and the composite conductive agent by mass is 95:4.3:0.

7.

10. A sodium-ion battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 4-9.

Images