Sodium ion positive electrode based on particle size-conductive network adaptation relation, battery and electric device

Abstract

The invention provides a sodium ion positive electrode, which comprises two positive electrode active materials with different median particle sizes and two carbon nanotubes with different length-diameter ratios, and meets the following conditions: 1.2 < = D50B / D50A < = 5, 1.5 < = AR2 / AR1 < = 12, 2.1 < = phi < = 9.0, and the structural factor phi meets the formula I. According to the invention, the positive electrode formula design is constrained in a specific phi interval; under different particle size combinations, different CNT length-diameter ratio combinations and different CNT contents, a proper material design window is constructed, so that the synergistic improvement of the slurry and the electrochemical performance is successfully realized.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a sodium-ion cathode, battery, and power-consuming device based on the optimization of particle size-conductive network adaptation relationship. Background Technology

[0002] Optimization of the kinetic performance of sodium-ion battery cathode materials needs to be based on the synergistic control of particle size and conductive network. Due to the large radius of sodium ions, their diffusion resistance in cathode particles is more significant, amplifying the influence of the median particle size D50 of the cathode material on kinetics. When D50 increases (e.g., D50 of layered oxides exceeds 13 μm), the ion diffusion path is significantly lengthened, the contact area between particles is reduced, and the electron conduction efficiency drops sharply. Conversely, when D50 decreases to below 3 μm (e.g., in polyanionic materials), although the diffusion distance is shortened, the interfacial side reactions are intensified due to the sharp increase in specific surface area, thus forming a new kinetic bottleneck.

[0003] Carbon nanotubes (CNTs) possess unique advantages in constructing cross-particle conductive networks due to their high conductivity and high aspect ratio. However, their effectiveness is directly limited by the microstructural differences resulting from the D50 particle size of the cathode particles. For cathode particles with a larger D50, the interparticle gaps increase, requiring an increase in the CNT content to build cross-particle conductive bridges and ensure continuous electron transport between particles. For cathode particles with a smaller D50, due to the high risk of particle agglomeration, excessive CNTs can lead to uneven slurry dispersion, which in turn increases ion transport resistance.

[0004] Existing technologies also neglect the synergistic relationship between the aspect ratio of CNTs and the D50 of the cathode material. For large D50 cathode systems, using low aspect ratio CNTs results in low entanglement, which, while beneficial for dispersion, makes it difficult to form long-range conductive bridges across multiple large particles, leaving the conductive network incomplete. Conversely, for small D50 cathode systems, using high aspect ratio CNTs easily leads to entanglement and agglomeration due to strong van der Waals forces. This not only fails to conduct electricity effectively but also exacerbates the risk of slurry gelation, compromising processing stability. Therefore, simply controlling the CNT content without considering its morphology (aspect ratio) cannot achieve optimal conductive network construction. Currently, there is a lack of a precise control scheme that systematically links the three factors: cathode material D50, CNT content, and CNT aspect ratio.

[0005] Traditional solutions often rely solely on empirical adjustments to the total CNT content based on D50 size, or simply limit the range of CNT aspect ratios. They fail to provide a unified model and coordinated control of cathode particle size D50, CNT aspect ratio, and CNT content. This makes it difficult to precisely adapt the electron / ion transport network within the cathode, hindering the synergistic improvement of sodium-ion cathodes in terms of slurry processing stability, electron / ion kinetic balance, and electrical performance. This has become a significant bottleneck restricting the rate performance, low-temperature performance, and electrode process consistency of sodium-ion batteries.

[0006] Therefore, this application is submitted. Summary of the Invention

[0007] Given the background technology, this invention provides a sodium-ion cathode, battery, and power device based on particle size-conductive network adaptation relationship. It establishes a "dual particle size – dual aspect ratio – CNT content" linkage control mechanism for sodium-ion cathodes. By defining a "structural factor Φ", the effective particle size of the cathode active material, the effective aspect ratio of carbon nanotubes, and the total CNT content are uniformly characterized. The cathode formulation design is constrained within a specific Φ range, thereby universally achieving the following under different particle size combinations, different CNT aspect ratio combinations, and different CNT contents: (1) significant improvement in electron / ion dynamics in large particle size systems; (2) improved slurry stability and coating processability in small particle size systems; and (3) significant improvement in overall rate performance, low-temperature energy efficiency, and cycle performance.

[0008] To achieve the above objectives, the main technical solutions adopted by the present invention include: Firstly, this invention proposes a sodium ion positive electrode, comprising particles with a median particle size of D50. A The first positive electrode active material A has a median particle size of D50. B The second positive electrode active material B, the first carbon nanotube CNT1 with an aspect ratio of AR1, the second carbon nanotube CNT2 with an aspect ratio of AR2, other conductive agents, binders, additives and dispersants, and satisfying the following: 1.2≤D50 B / D50 A ≤5; 1.5≤AR2 / AR1≤12; 2.1≤Φ≤9.0; Wherein, the structural factor Φ satisfies equation I: , In formula I, w A w represents the mass percentage of the first positive electrode active material A in the total amount of positive electrode active materials. B C represents the mass percentage of the second positive electrode active material B in the total amount of positive electrode active material.tot denoted as , where is the mass percentage of carbon nanotubes in the total solid content of the cathode (total solid content of the cathode refers to the sum of solid and non-solid materials excluding solvents; non-solid materials include liquid dispersants, etc.), v1 is the mass percentage of the first carbon nanotube CNT1 in the total carbon nanotubes, v2 is the mass percentage of the first carbon nanotube CNT2 in the total carbon nanotubes, AR0 is the reference aspect ratio standard coefficient, taken as AR0=3000, and α is the exponential parameter coefficient, taken as α=0.5.

[0009] This invention constructs a hierarchical conductive network in a sodium-ion cathode by designing a two-stage cathode active material particle size and a two-stage carbon nanotube composite system. Based on extensive experimental and practical experience, the structure of this hierarchical conductive network is further optimized. By defining a structural factor Φ and coordinating the particle size and aspect ratio of the two-stage cathode active materials, the microstructure of the particle framework, pore filling, and network interpenetration in the cathode is comprehensively controlled. It was discovered that a sodium-ion cathode constructed according to the above rules can simultaneously achieve effective stabilization of the structural framework, reasonable filling of framework pores, improved particle contact, and elimination of conductive blind zones. This results in a synergistic effect of improving the slurry rheological properties and optimizing the electron / ion transport path, significantly improving the slurry stability and processability of the sodium-ion cathode, as well as its electrochemical performance at low temperatures, rate, and cycling.

[0010] It should be noted that in this invention, the value of "mass percentage" in the structure factor Φ is only the percentage value. For example, when the mass percentage of the first positive electrode active material A in the total positive electrode active material is 50wt%, the value of w in the structure factor Φ in Formula I is... A The value is 50. The structural factor Φ contains D50. A and D50 B Values ​​are taken in μm.

[0011] In some optimized designs, the sodium ion cathode further satisfies: 2≤D50 B / D50 A ≤4; 3≤AR2 / AR1≤6; 2.4≤Φ≤8.4.

[0012] In some optimized designs, the sodium ion cathode further satisfies: 2≤D50 B / D50 A ≤4; 3≤AR2 / AR1≤6; 5≤Φ≤8.4.

[0013] We found that within the further optimization design window, the sodium ion cathode achieved further optimization and improvement in at least one aspect, such as slurry stability, low temperature performance, rate capability, and cycle performance.

[0014] In satisfying the aforementioned design window, the parameters of the sodium-ion cathode of the present invention are generally within the range of commonly used material formulations in the art to meet general processing or electrochemical requirements. Within the commonly used material formulation range, parameters with advantageous formulation ranges can also be selected based on the design experience of those skilled in the art to obtain potential performance improvements in other aspects of the sodium-ion battery. As some optional parameter ranges, in some embodiments of the sodium-ion cathode of the present invention, the median particle size D50 of the first cathode active material A is... A 3μm~6μm (3μm≤D50) A ≤6μm), median particle size D50 of the second positive electrode active material B B 8μm~15μm (8μm≤D50) B The first carbon nanotube (CNT1) has an aspect ratio (AR1) of 1000-5000 (1000≤AR1≤5000), and the second carbon nanotube (CNT2) has an aspect ratio (AR2) of 8000-12000 (8000≤AR2≤12000). The mass percentage of carbon nanotubes in the total solid content of the cathode is 0.1 wt%~3 wt% (0.1≤C tot ≤3).

[0015] The composition ratio of the sodium-ion cathode of the present invention also satisfies the general composition ratio of sodium-ion cathodes. As some optional parameter ranges, in some embodiments of the sodium-ion cathode of the present invention, the mass percentage of the cathode active material in the total solid content of the cathode is 85 wt% to 95 wt%, the mass percentage of carbon nanotubes and other conductive agents in the total solid content of the cathode is 0.5 wt% to 3 wt%, the mass percentage of binder in the total solid content of the cathode is 0.1 wt% to 5 wt%, the mass percentage of additives in the total solid content of the cathode is 0 wt% to 3 wt%, and the mass percentage of dispersant in the total solid content of the cathode is 0 wt% to 3 wt%, and the sum of the above components is 100 wt% of the total solid content of the cathode.

[0016] The sodium-ion cathode of this invention can be prepared using a common material system and a coating method commonly used in the art. Those skilled in the art can also select high-performance materials based on known material selection experience to prepare the sodium-ion cathode of this invention.

[0017] In some designs, the positive electrode active material includes one or more of the following: sodium layered transition metal oxide positive electrode materials, polyanionic positive electrode materials, and Prussian blue positive electrode materials. Polyanionic positive electrode materials are preferred. The first positive electrode active material A and the second positive electrode active material B can be the same or different.

[0018] In some schemes, sodium layered transition metal oxide cathode materials have the general formula A1±δ M 1 V M 2 W M 3 X M 4 Y M 5 Z O 2-c Where A represents sodium as the main alkali metal and may also contain ≤10 at% potassium or lithium to increase interlayer spacing; M 1 A redox active metal in oxidation state +2, comprising at least one or more of nickel, copper, cobalt, and manganese, used to provide the main charge / discharge capacity; M 2 Selected from metals with an oxidation state greater than 0 and ≤ +4, typically Ti. 4+ Sn 4+ Zr 4+ Ru 4+ Or combinations thereof, used to stabilize lattice oxygen at high voltages; M 3 A metal with an oxidation state of +2, selected from Mg 2+ Zn 2+ Ca 2+ 、Sr 2+ At least one of them acts as a "pillar" to inhibit transition metal migration; M 4 Also selected from metals with an oxidation state greater than 0 and ≤ +4, preferably Al. 3+ Ga 3+ In 3+ 、Ge 4 + 、Nb 5+ One or more of these are used to adjust the bottleneck size of the sodium ion diffusion channel; M 5 Metals with an oxidation state of +3, selected from Fe 3+ Cr 3+ V 3+ Co 3+ At least one of them can provide additional electron transfer centers under high charge state; the values ​​of δ, V, W, X, Y, Z, and c satisfy 0≤δ≤1, V>0, W≥0, X≥0, Y≥0, Z≥0, at least one of W and Y>0, 0≤c<2, and all coefficients are calculated by charge balance to ensure overall electrochemical neutrality.

[0019] In some designs, polyanionic cathode materials include: phosphates, such as Na3V2(PO4)3, Na3Fe2(PO4)3, Na3MnTi(PO4)3, Na3V2(PO4)2F3, Na2FePO4F, etc.; pyrophosphates, such as Na2FeP2O7, Na2MnP2O7, Na4Fe3(PO4)2(P2O7), etc.; sulfates, such as NaFeSO4F, NaNiSO4F, etc.; and composite phosphates, such as phosphoric acid-silicic acid composite Na2FePO4SiO4 and phosphoric acid-boric acid composite Na3FePO4BO3, etc. Phosphoric acid-pyrophosphate is preferred.

[0020] In some designs, Prussian blue-based cathode materials include: low-sodium Prussian blue, such as Na... 0.74 Fe[Fe(CN)6] 0.96 ·3,2H₂O, Na 0.68 Mn[Fe(CN)6] 0.92 • 3.5H2O, etc.; high-sodium Prussian white, such as Na 1.76 Fe[Fe(CN)6]·2.1H2O, Na 1.92 Mn[Fe(CN)6] 0.98 ·1,8H₂O, Na 1.85 Ni[Fe(CN)6] 0.97 ·1.5H2O, etc.

[0021] In some schemes, other conductive agents may include carbon black, such as Super P, acetylene black, Ketjen black, etc.; two-dimensional carbon, such as graphene; three-dimensional graphitic carbon, such as micronized graphite, expanded graphite, etc.

[0022] In some solutions, the adhesive includes one or more of the conventional adhesives in the art, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, and epoxy resin.

[0023] In some formulations, the additive is selected from at least one of acidic additives, basic additives, reducing additives, oxidizing additives, complexing additives, and film-forming additives; among which, acidic additives are preferred, and the acidic additive is preferably at least one of oxalic acid, citric acid, acetic acid, and phosphoric acid; the basic additive is preferably at least one of trisodium borate, sodium dihydrogen phosphate, ammonium bicarbonate, and triethanolamine; the reducing additive is preferably at least one of ascorbic acid, ferrous oxalate, sodium sulfite, and hydrazine; the oxidizing additive is preferably at least one of benzoyl peroxide, TEMPO, and lithium nitrate; the complexing additive is preferably at least one of EDTA-2Na, trisodium citrate, sodium polyacrylate, and 15-crown-5; and the film-forming additive is preferably at least one of tris(trimethylsilane)phosphite (TMSPi), tetravinylsilane (TVS), LiPO2F2, and succinic anhydride.

[0024] In some formulations, the dispersant is selected from at least one of inorganic phosphate type, inorganic silicate type, organic anionic surfactant type, organic nonionic surfactant type, polymer homopolymer type, and polymer copolymer type; wherein the inorganic phosphate type is preferably at least one of trisodium phosphate, sodium hexametaphosphate, and sodium pyrophosphate; the inorganic silicate type is preferably at least one of sodium silicate, potassium silicate, and layered magnesium silicate; the organic anionic surfactant type is preferably at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and sodium α-olefin sulfonate; the organic nonionic surfactant type is preferably at least one of polyethylene glycol (PEG-4000), Tween-80, and octylphenol polyoxyethylene ether (OP-10); and the polymer homopolymer type is preferably polyacrylic acid (molecular weight 3×10⁻⁶). 3 The polymer is selected from at least one of polyvinylpyrrolidone (PVP-K30) and sodium polystyrene sulfonate (PSS), with the polymer copolymer type preferably selected from at least one of acrylic acid-maleic acid copolymer sodium salt, acrylic acid-acrylamide copolymer, and styrene-maleic anhydride copolymer sodium salt. In the phosphate-pyrophosphate cathode material system, inorganic phosphate type can be used as a preferred compound dispersant material.

[0025] The sodium-ion cathode of the present invention can be prepared using common preparation methods. For example, the above-mentioned materials can be dispersed in a solvent to form a cathode slurry, then coated onto a current collector, and subjected to necessary drying and rolling processes to obtain the cathode sheet.

[0026] Secondly, the present invention provides a sodium ion positive electrode sheet, comprising the aforementioned sodium ion positive electrode and a current collector. The choice of current collector is not limited, but aluminum foil is preferred.

[0027] Thirdly, the present invention provides a battery comprising the aforementioned sodium-ion positive electrode, and further comprising a negative electrode, a separator, and an electrolyte. The selection of the negative electrode, separator, and electrolyte is not limited, and can be chosen and applied from common materials used in sodium-ion batteries.

[0028] Fourth, the present invention provides an electrical device including the aforementioned battery. Exemplary examples include, but are not limited to, 3C digital devices (mobile phones, tablets, laptops, Bluetooth headsets, cameras, smartwatches), small household appliances (robot vacuum cleaners, projectors), power tools (electric drills, chainsaws, garden shears), personal transportation (electric bicycles, electric skateboards, balance bikes, electric motorcycles), low-speed vehicles (three-wheeled delivery vehicles, four-wheeled mobility scooters for the elderly, sightseeing vehicles), special-purpose vehicles (electric forklifts, AGVs, airport shuttle buses, electric ships), energy storage scenarios (home energy storage cabinets, industrial and commercial energy storage cabinets, communication base station UPS, data center backup power, wind-solar hybrid street light energy storage), grid-level applications (energy storage containers, peak-shaving and frequency-regulating power stations), and military and outdoor applications (drones, robots, portable power supplies, field energy storage boxes), etc.

[0029] Through the above technical solution, the present invention can achieve the following beneficial technical effects: (1) Particle size classification + CNT aspect ratio classification to construct a hierarchical conductive network: large-diameter particles serve as the framework, small-diameter particles fill the pores of the framework, and large and small particles work together to improve interfacial impedance and energy efficiency, while also improving particle adhesion and agglomeration. CNT2 with a large aspect ratio constructs a cross-particle and cross-pore conductive network, while CNT1 with a low aspect ratio fills the local conductive blind zone and improves the slurry rheology. A hierarchical network architecture is initially proposed, which provides a foundation for further synergistic optimization of electron / ion transport paths.

[0030] (2) Design structure factor Φ synergistic particle size classification + CNT aspect ratio classification to achieve unified design rules, and construct a suitable material design window by combining material particle size, CNT aspect ratio, classification content and ratio. When the formulation design meets the requirements of this design window (1.2≤D50) B / D50 A ≤5; 1.5≤AR2 / AR1≤12; 2.1≤Φ≤9.0), further achieving a significant improvement in the overall performance level of slurry stability, machinability, low temperature, rate performance and cycle performance.

[0031] (3) The present invention further optimizes the preferred range of the design window, and further improves the dynamic performance and slurry stability: by changing the value of the parameter within the selectable range, D50 is appropriately configured. B / D50 A By adjusting the AR2 / AR1 ratio and the value of Φ, the interfacial impedance can be significantly reduced, the 1C cycle capacity retention rate can be improved, the energy efficiency at 5℃ can be increased, and / or the slurry viscosity and kinetic stability can be improved. The initial viscosity of the slurry can be kept moderate, and the viscosity can not rise abnormally after standing for 10 hours, thus avoiding slurry gelation and improving coating stability and electrode consistency.

[0032] (4) Process-friendly and easy to scale up industrially: The structural factor Φ and all related parameters are designed to be selected from easily measurable parameters, which are suitable for real-time acquisition and calculation on the production line, and provide immediate feedback to guide the adjustment of each parameter and control range, ensuring the timeliness of electrode design and performance stability. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a comparison chart of the capacity retention rates at room temperature 1C / 1C cycles for Embodiment 1 and Comparative Example 1 of the present invention.

[0035] Figure 2 This is a comparison diagram of the state of the slurry prepared in Example 2 and Comparative Example 2 after settling for 10 hours. Detailed Implementation

[0036] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0037] All chemical raw materials used in the following examples and comparative examples were commercially available, and all apparatuses and operations involved were conventional in the art. All testing methods involved were conventional in the art.

[0038] Example 1: (1) The positive electrode formulation includes: First positive electrode active material A: Na4Fe3(PO4)2P2O7, small particle size product, D50 A = 4.0 μm, the first positive electrode active material A has a mass percentage of 40 wt% in the total positive electrode active material, w A Take 40.

[0039] Second positive electrode active material B: Na4Fe3(PO4)2P2O7, large particle size product, D50 B = 10.0 μm, the second positive electrode active material B has a mass percentage of 60 wt% in the total positive electrode active material, w B Take 60.

[0040] The mass percentage of the positive electrode active material in the total solid content of the positive electrode is 94.6 wt%.

[0041] First carbon nanotube CNT1: multi-walled CNT, AR1≈3000, the mass percentage of first carbon nanotube CNT1 in the total carbon nanotubes is 50 wt%, v1 is 50.

[0042] Second carbon nanotube CNT2: multi-walled CNT, AR2≈9000, the mass percentage of second carbon nanotube CNT2 in the total carbon nanotubes is 50 wt%, v2 is 50.

[0043] The mass percentage of CNTs in the total solid content of the cathode is 1.5 wt%, C tot Take 1.5.

[0044] Binder: PVDF, with a mass percentage of 2.5 wt% in the total solid content of the positive electrode.

[0045] Acidic additive: oxalic acid, with a mass percentage of 0.4 wt% in the total solid content of the positive electrode.

[0046] Dispersant: Polyvinylpyrrolidone, with a mass percentage of 0.6 wt% in the total solid content of the positive electrode.

[0047] Other conductive agent: Super P, with a mass percentage of 0.4 wt% in the total solid content of the positive electrode.

[0048] (2) Calculation of structural factor: .

[0049] (3) Preparation of the electrode: The above solid components were added to NMP and dispersed at high speed to obtain a positive electrode slurry with a solid content of about 55 wt%. The positive electrode slurry was coated on both sides of an aluminum foil with a thickness of 12 μm, dried at 100-120 ℃, and rolled to a compaction density of 1.8 g / cm³. 3 The coating thickness is approximately 160 μm, and the areal density is approximately 30 mg / cm³. 2 The positive electrode is obtained. The negative electrode is made of hard carbon, with the following formula: 95.5 wt% hard carbon, 1.5 wt% conductive carbon black, and 3.0 wt% PVDF.

[0050] (4) Cell preparation: The positive electrode, separator and negative electrode are wound into a core, and then the core is placed in an aluminum shell and then injected with electrolyte to make a sodium-ion battery.

[0051] Examples 2-10: Using the same method as in Example 1, the positive electrode formulation parameters were changed to obtain electrode sheets and cells with different parameter selections. The different parameter selections in each example are listed in Table 1.

[0052] Comparative Example 1: Compared with Example 1, only a single large-particle-size positive electrode active material, Na4Fe3(PO4)2P2O7, D50=12 μm, was used; a single CNT with an aspect ratio of approximately 4000, C tot Take 0.8. Other preparation methods are the same as in Example 1.

[0053] Comparative Example 2: Compared to Example 1, only a single small-particle-size positive electrode active material, Na4Fe3(PO4)2P2O7, with D50 = 2.8 μm, was used; a single CNT with an aspect ratio of approximately 8000, C tot Take 1.5. Other preparation methods are the same as in Example 1.

[0054] Comparative Examples 3-7: Using the same method as Example 1, the positive electrode formulation parameters were changed to obtain electrode sheets and cells with different parameter selections. The different parameter selections in each comparative example are listed in Table 1.

[0055] The slurries and battery cells prepared in the above embodiments and comparative examples were subjected to performance testing. The test results are listed in Table 2 and 3. Figure 1-2 middle.

[0056] The specific testing method is as follows: Particle size testing: A laser particle size analyzer and laser diffraction method were used for detection. Alcohol and the test substance were ultrasonicated together for 2 minutes at an ultrasonic intensity of 30%. The particle size distribution was obtained under the following conditions: refractive index 1.535, absorptivity 0.1, pump speed 2000 rpm / min, laser intensity greater than 70%, and occlusion 10-20%.

[0057] CNT aspect ratio test: In accordance with GB / T 33839-2021 standard, monodisperse CNT suspensions were prepared by ultrasonic dispersion. Microscopic morphology images of CNTs were obtained using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The length and diameter were measured using image analysis software, the aspect ratio was calculated, and statistical analysis was performed.

[0058] Viscosity Testing: The testing method was developed based on GB / T 2794-2013 and industry practice. First, samples were taken from three points (top, middle, and bottom) of the mixing tank and mixed, with a total sample volume ≥100 mL. The mixture was then vacuum-degassed at 25±1℃ for 10–15 min. Next, the slurry was poured into a test cup, with the rotor marking line submerged. After the rotor was immersed, it was allowed to stand for 1–2 min to allow the temperature to equalize. The test results were recorded after the readings stabilized. Measurements were taken three times at three different rotation speeds (12, 30, and 60 r / min), and the average value was taken. The viscosity test involved in this invention includes two tests: one is the initial viscosity obtained by testing the newly prepared slurry after the solid components of the positive electrode formulation have been fully dispersed in NMP; the other is the viscosity obtained after settling the newly prepared slurry for 10 hours.

[0059] Table 1

[0060] Table 2

[0061] As shown in Table 1-2: The sodium-ion batteries prepared in each embodiment exhibited excellent cycle performance, with significant improvements in cell cycle performance and energy efficiency at 5°C, as well as improved slurry stability. The energy efficiency at 5°C was greater than the national standard requirement of 83%.

[0062] Comparative Examples 1 and 2 both used ungraded carbon nanotubes with a single particle size and aspect ratio, making it difficult to construct a well-structured hierarchical conductive network in the cathode. The large-particle-size cathode material in Comparative Example 1 exhibited poor kinetics, with significant degradation in energy efficiency at both 1C cycling and 5℃. Figure 1 This demonstrates a significant difference in the 1C long-cycle capability of the batteries in Example 1 and Comparative Example 1 at room temperature. While the smaller particle size in Comparative Example 2 improved energy efficiency at 5°C, it still failed to effectively improve 1C cycle performance compared to Comparative Example 1, and as... Figure 2 As shown, the slurry prepared in Comparative Example 2 gelled after standing for 2 hours, exhibiting extremely poor coatability and making it difficult to adapt to industrial production.

[0063] Although comparative examples 3-7 were designed with particle size and CNT aspect ratio, the design window did not meet the requirements of this invention. The structure factor Φ was too large or too small, making it difficult to balance the 1C cycle, 5℃ energy efficiency and slurry coating performance.

[0064] As can be seen from Examples 1-6 compared to Examples 7-10, further optimization of the design window is achieved when 2 ≤ D50. B / D50 AWith values ​​of ≤4, 3≤AR2 / AR1≤6, and 2.4≤Φ≤8.4, the overall performance of the cathode can be further improved, increasing the capacity retention rate at 1C room temperature cycling to over 92%@1000, the energy efficiency at 5℃ to over 91%, and controlling the viscosity of the slurry to below 12000cp after 10 hours of settling.

[0065] As can be seen from Examples 1-4 compared to Examples 5-6, further optimization of the design window is achieved when 2 ≤ D50. B / D50 A With values ​​of ≤4, 3≤AR2 / AR1≤6, and 5≤Φ≤8.4, the overall performance of the cathode can be further improved, increasing the capacity retention rate at 1C room temperature cycling to over 93%@1000, the energy efficiency at 5℃ to over 91%, and controlling the viscosity of the slurry to below 9000cp after 10 hours of settling.

[0066] Based on the embodiments, comparative examples, and test results discussed above, the following conclusions can be drawn: This invention, based on a hierarchical conductive network structure, successfully achieves a step-by-step synergistic optimization and improvement of slurry stability, machinability, low-temperature performance, rate capability, and cycle performance by designing a structural factor Φ in conjunction with particle size classification and CNT aspect ratio to construct a suitable material design window.

[0067] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples.

Claims

1. A sodium ion positive electrode, comprising particles with a median particle size of D50. A The first positive electrode active material A has a median particle size of D50. B The second positive electrode active material B, the first carbon nanotube CNT1 with an aspect ratio of AR1, the second carbon nanotube CNT2 with an aspect ratio of AR2, other conductive agents, binders, additives and dispersants, and satisfying the following: 1.2≤D50 B / D50 A ≤5; 1.5≤AR2 / AR1≤12; 2.1≤Φ≤9.0; in, The structural factor Φ satisfies equation I: ， In formula I, w A w represents the mass percentage of the first positive electrode active material A in the total amount of positive electrode active materials. B C represents the mass percentage of the second positive electrode active material B in the total amount of positive electrode active material. tot denoted as , where is the mass percentage of carbon nanotubes in the total solid content of the cathode (total solid content of the cathode refers to the sum of solid and non-solid materials excluding solvents; non-solid materials include liquid dispersants, etc.), v1 is the mass percentage of the first carbon nanotube CNT1 in the total carbon nanotubes, v2 is the mass percentage of the first carbon nanotube CNT2 in the total carbon nanotubes, AR0 is the reference aspect ratio standard coefficient, taken as AR0=3000, and α is the exponential parameter coefficient, taken as α=0.

5.

2. The sodium ion positive electrode according to claim 1, characterized in that, Sodium ion cathode satisfies: 2≤D50 B / D50 A ≤4; 3≤AR2 / AR1≤6; 2.4≤Φ≤8.

4.

3. The sodium ion positive electrode according to claim 1, characterized in that, Sodium ion cathode satisfies: 2≤D50 B / D50 A ≤4; 3≤AR2 / AR1≤6; 5≤Φ≤8.

4.

4. The sodium ion positive electrode according to claim 1, characterized in that, The median particle size D50 of the first positive electrode active material A A The median particle size D50 of the second positive electrode active material B is 3μm~6μm. B The diameter of the carbon nanotubes ranges from 8 μm to 15 μm. The aspect ratio AR1 of the first carbon nanotube CNT1 is 1000-5000, and the aspect ratio AR2 of the second carbon nanotube CNT2 is 8000-12000. The mass percentage of carbon nanotubes in the total solid content of the cathode is 0.1 wt% to 3 wt%.

5. The sodium ion positive electrode according to claim 1, characterized in that, The positive electrode active material accounts for 85 wt% to 95 wt% of the total solid content of the positive electrode, the total amount of carbon nanotubes and other conductive agents accounts for 0.5 wt% to 3 wt% of the total solid content of the positive electrode, the binder accounts for 0.1 wt% to 5 wt% of the total solid content of the positive electrode, the additives account for 0 wt% to 3 wt% of the total solid content of the positive electrode, and the dispersant accounts for 0 wt% to 3 wt% of the total solid content of the positive electrode. The sum of the above components is 100 wt% of the total solid content of the positive electrode.

6. The sodium ion positive electrode according to claim 1, characterized in that, Positive electrode active materials include one or more of the following: sodium layered transition metal oxide positive electrode materials, polyanionic positive electrode materials, and Prussian blue positive electrode materials; Preferably, the sodium layered transition metal oxide cathode material has the general formula A 1±δ M 1 V M 2 W M 3 X M 4 Y M 5 Z O 2-c ,in, A indicates sodium as the main alkali metal and may also contain ≤10 at% potassium or lithium; M 1 Redox active metals with an oxidation state of +2, including any one or more of nickel, copper, cobalt, and manganese; M 2 Selected from metals with an oxidation state greater than 0 and ≤ +4, including Ti 4+ Sn 4+ Zr 4+ Ru 4+ Or a combination thereof; M 3 A metal with an oxidation state of +2, selected from Mg 2+ Zn 2+ Ca 2+ 、Sr 2+ At least one of them; M 4 Selected from metals with oxidation states greater than 0 and ≤ +4, including Al. 3+ Ga 3+ In 3+ 、Ge 4+ 、Nb 5+ One or more of the following; M 5 Metals with an oxidation state of +3, selected from Fe 3+ Cr 3+ V 3+ Co 3+ At least one of them; 0≤δ≤1, V>0, W≥0, X≥0, Y≥0, Z≥0, at least one of W and Y>0, 0≤c<2, and all coefficients make the general formula electrochemically neutral; Preferably, the polyanionic cathode material includes: phosphates, including one or more of Na3V2(PO4)3, Na3Fe2(PO4)3, Na3MnTi(PO4)3, Na3V2(PO4)2F3, and Na2FePO4F; pyrophosphates, including one or more of Na2FeP2O7, Na2MnP2O7, and Na4Fe3(PO4)2(P2O7); sulfates, including one or more of NaFeSO4F and NaNiSO4F; and composite phosphates, including one or more of phosphoric acid-silicic acid composite Na2FePO4SiO4 and phosphoric acid-boric acid composite Na3FePO4BO3. Preferably, Prussian blue-based cathode materials include: low-sodium Prussian blue, including Na... 0.74 Fe[Fe(CN)6] 0.96 ·3,2H₂O, Na 0.68 Mn[Fe(CN)6] 0.92 One or more of 3,5H₂O; high-sodium Prussian white, including Na 1.76 Fe[Fe(CN)6]·2.1H2O, Na 1.92 Mn[Fe(CN)6] 0.98 ·1,8H₂O, Na 1.85 Ni[Fe(CN)6] 0.97 One or more of 1,5H₂O; Preferably, other conductive agents include one or more of carbon black, two-dimensional carbon, and three-dimensional graphitic carbon; Preferably, the adhesive includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, and epoxy resin; Preferably, the additive is selected from at least one of acidic additives, basic additives, reducing additives, oxidizing additives, complexing additives, and film-forming additives; The acidic additive is preferably selected from at least one of oxalic acid, citric acid, acetic acid, and phosphoric acid; The alkaline additive is preferably selected from at least one of trisodium borate, sodium dihydrogen phosphate, ammonium bicarbonate, and triethanolamine; The reducing additive is preferably selected from at least one of ascorbic acid, ferrous oxalate, sodium sulfite, and hydrazine; The oxidizing additive is preferably selected from at least one of benzoyl peroxide, TEMPO, and lithium nitrate; The complexing additive is preferably selected from at least one of EDTA-2Na, trisodium citrate, sodium polyacrylate, and 15-crown-5; The film-forming additive is preferably selected from at least one of tris(trimethylsilane)phosphite (TMSPi), tetravinylsilane (TVS), LiPO2F2, and succinic anhydride; Preferably, the dispersant is selected from at least one of inorganic phosphate type, inorganic silicate type, organic anionic surfactant type, organic nonionic surfactant type, polymer homopolymer type and polymer copolymer type; The inorganic phosphate type is preferably selected from at least one of trisodium phosphate, sodium hexametaphosphate, and sodium pyrophosphate; the inorganic silicate type is preferably selected from at least one of sodium silicate, potassium silicate, and layered magnesium silicate; the organic anionic surfactant type is preferably selected from at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and sodium α-olefin sulfonate; the organic nonionic surfactant type is preferably selected from at least one of polyethylene glycol (PEG-4000), Tween-80, and octylphenol polyoxyethylene ether (OP-10); the polymer homopolymer type is preferably selected from at least one of polyacrylic acid, polyvinylpyrrolidone, and sodium polystyrene sulfonate; and the polymer copolymer type is preferably selected from at least one of sodium salt of acrylic acid-maleic acid copolymer, acrylic acid-acrylamide copolymer, and sodium salt of styrene-maleic anhydride copolymer.

7. A sodium ion positive electrode, comprising the sodium ion positive electrode as described in any one of claims 1-6.

8. A battery comprising the sodium-ion positive electrode as described in claim 7, and further comprising a negative electrode, a separator, and an electrolyte.

9. An electrical device comprising the battery of claim 8.

Images